Satellite communications

Satellite Communications

Sorin Adrian Barbulescu

PhD

Version 2.0

Copyright © 2014

Satellite Communications This e-book gives an introduction to the Satellite Communications field with pointers towards critical issues that should be considered in the design of a satellite system. It introduces the basic orbital parameters, the space environment, followed by a detailed presentation of the link budget and various satellite access schemes. The ground station architecture and requirements are formulated. Channel coding and joint source-channel coding are introduced. The building blocks of the satellite platform and the satellite payload are discussed, bent-pipe versus on-board processing architectures are compared. Satellite services, installation in orbit, limitations and solutions for TCP/IP traffic over satellite are covered. Network dimensioning and MAC layer issues will help you in the system optimisation. Examples of how to achieve privacy at no extra cost, protection from jamming and inter-satellite links are examined. A brief history of Australian contributions in this area with a focus on the latest developments in satellite communications equipment (e.g., the S-TECTM codec and the Satellite Network Access Point - SNAP) is also included. The author is Dr Sorin Adrian Barbulescu with more than 20 years experience in the field. He received his PhD from the University of South Australia in 1996 and the Graduate Certificate in Management in 1999. He has been working with the Institute for Telecommunications Research, University of South Australia, as a technical leader and project manager in projects applying the turbo coding technology in mobile and fixed satellite communications systems. This e-book is a general introduction to satellite communications in .ppt format. It is intended for those engineers and technicians working in the field who would like to get an overall understanding of the issues. Managers who need a sound understanding of the implications of the latest technology in improving the system efficiency and cutting costs will also benefit. It does not require a specific background although a basic knowledge of digital communications would be useful.

Disclaimer

YOU EXPRESSLY ACKNOWLEDGE AND AGREE THAT USING THE INFORMATION FROM THIS BOOK IS AT YOUR SOLE RISK AND THAT THE ENTIRE RISK AS TO SATISFACTORY QUALITY, PERFORMANCE, ACCURACY AND EFFORT IS WITH YOU. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DAMAGES WHATSOEVER, INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF PROFITS, LOSS OF DATA, BUSINESS INTERRUPTION OR ANY OTHER COMMERCIAL DAMAGES OR LOSSES, ARISING OUT OF OR RELATED TO YOUR USE OR INABILITY TO USE THE INFORMATION PROVIDED IN THIS BOOK. THE INFORMATION IS PROVIDED “AS IS”, WITHOUT ANY WARRANTY OF ANY KIND. YOU MAY MAKE ONLY ONE COPY OF THIS BOOK IN MACHINE-READABLE FORM FOR BACKUP PURPOSES ONLY. YOU MAY NOT REPRODUCE, RENT, LEASE, LEND OR SUBLICENSE PART OR WHOLE OF THE INFORMATION FROM THIS BOOK.

Table of contents

Introduction (Slide 1)

Bits of history – Concepts Bits of history – Technology References

Orbits (Slide 55)

Overview Kepler’s and Newton’s Laws Orbital Parameters Inclined Orbits Geostationary Orbit

Space Environment (Slide 133) Mechanical Effects Atmospheric Effects (Rain Attenuation) Polarisation Propagation & Channel Models

Source Coding (Slide 217) Channel capacity Huffman coding Arithmetic / Ziv-Lempel coding JPEG/MPEG

Channel Coding (Slide 247) Block Codes Convolutional Codes Turbo-like Codes (STEC Codec) Joint Source and Channel Coding Turbo source coding Packet Layer Coding Network Coding

Link Analysis (Slide 325)

Received Signal Power, EIRP Noise power The Uplink & Downlink Station-to-station link, Capacity curves

Satellite Access (Slide 379) FDMA TDMA CDMA OFDM Random Access

Earth Stations (Slide 451)

Standards Earth Stations Antennas Radio Frequency Subsystem Communication Subsystem

The Payload (Slide 505) Transparent Repeaters Multibeam Satellite Repeaters Regenerative Repeaters Generic Payloads Satellite Antenna Characteristics

The Platform (Slide 559) Attitude Control The Propulsion System The Power Supply Solar Power Satellites Solar Dish Engine, Laser Power Beaming Telemetry, Tracking and Command

Satellite Services (Slide 607)

Broadcasting Satellite Services (DBS, DVB-S2) Fixed Satellite Services (INTELSAT, VSAT) Navigational Satellite Services (NAVSTAR GPS) Earth Resource Satellite Services (Radarsat, NOAA) Mobile Satellite Services (IRIDIUM, INMARSAT) SCADA (Supervisory Control And Data Acquisition)

Satellite Installation (Slide 727)

Installation in Orbit Launch Vehicles Options Orbital Servicing Vehicles Reliability Issues Cost Issues Space Debris Mitigation

Satellite Internet (Slide 817)

TCP/IP over satellite issues Proposed Systems DVB: Multi-Protocol Encapsulation ATM connection handover in LEO networks

Satellite Network Design (Slide 901) Satellite Network Dimensioning Customer’s Requirements Traffic Data

Examples Cost of the Network “CONNECTS” – Australian satellite network

MAC layer optimisation (Slide 973) Cross-layer Issues Throughput Control Generic stream IP encapsulation Layer 2 Bridged Point-to-Multipoint

Specific issues (Slide 1009) Inter-satellite links (ISL) Privacy for each of us Protect your satellite link Global Broadcast System MIL-STD-3011 SAR Satellites Dish installation

New Trends (Slide 1087) Australian contribution: FedSat, Optus Broadband Satellite Links Australian Satellite Networks Key technology trends: space segment Key technology trends: ground segment Policies, regulatory and standard issues

SNAP (Slide 1201)

Definition of necessity Hidden assumptions Most important questions to ask Benefits of traffic aggregation Example of a Satellite-WiFi network

Appendices:

Digital Communications (Slide 1243) Time/Frequency representation of signals One single pulse A periodic signal Random signals Nyquist Theorems BPSK/QPSK modulation and BER Capacity

Digital Transmission (Slide 1303) Antenna Cancellation A/D & D/A Transmitter Linearisation Performance Degradation Phase Noise Effects

Tutorial Questions (Slide 1339) Link Budget Example (Slide 1381)

Glossary

SATELLITE COMMUNICATIONS © Copyright 2014Dr Sorin Adrian Barbulescu

Satellite Communications

Dr Sorin Adrian Barbulescu


The first reference to a geostationary satellites is by Arthur C Clarke (1917-2008) in a letter to the editor titled Peacetime Uses for V2 published in the 1945

February issue of Wireless World (page 58).Sir Arthur C Clarke: 90th Birthday Reflections

http://www.youtube.com/watch?v=3qLdeEjdbWE

http://lakdiva.org/clarke/1945ww/1945ww_feb.jpg

http://lakdiva.org/clarke/1945ww/1945ww_feb.jpg


The first man made satellite: Sputnik 04/10/1957

Sputnik.au


The geostationary orbit today


This “Satellite Communications” course is a synthesis of many specific topics e.g., orbits, link budgets, space propagation, which also draws from highly specialised fields e.g., source and channel coding, digital communications, traffic networking, RF and optical communications, all of them brought together from the perspective of communication techniques that can be achieved via satellites.


Application/Traffic

Digital Comms

Satellite orbits

channel & access

Satellite platform/payload


Satellite Communications is about moving data or information across large distances under some specific resource constraints: bandwidth power mass size speed

The system optimization depends on the application, but it always aims towards minimizing the use of resources in the space segment given the difficulty to replace those resources. While mass and size are simple to understand, power, bandwidth and speed can always be traded off in order to achieve the target bit error rate required by a particular application.


In satellite communications, bandwidth represents the range of frequencies that is occupied by an electromagnetic signal on a given transmission medium. It is the difference between the highest-frequency signal component and the lowest-frequency signal component. A typical voice signal has a bandwidth of approximately 3 kHz (one Hertz is one cycle of change per second). A high quality CD music can span a bandwidth of 20 kHz while an analogue television broadcast video signal has a bandwidth of 6 MHz. All communication signals are bandwidth limited. Every signal in time has an equivalent definition in terms of the occupied range of frequencies.


The symbol rate (baud rate) is the rate at which the signal state changes in the communications channel. Units of symbol rate are symbols/second (baud). The number of symbol states needed to uniquely represent any pattern of n bits is given by the expression M = 2n

symbol states.The information rate is defined as the speed at which binary information (bits) can be transferred from source to destination. Units of information rate are bits/second (bps). The bandwidth efficiency of a communications link is a measure of how well a particular modulation format and coding scheme is making use of the available bandwidth. Units for bandwidth efficiency of a digital communications link are bits/second/Hz.


Turbo Coded Modems

Orbits

Channel modelling

Satellite Design

Applications


http://www.stmi.com/index.php?option=com_docman&task=doc_download&gid=75&Itemid=274

If your business has a global reach in areas with no reliable or secure terrestrial communication infrastructure, you might need to consider a satellite based solution. The headquarters could be connected in a star architecture, via a hub, to all remote sites that would use very small aperture terminals (VSAT) links.


http://www.stmi.com/index.php?option=com_docman&task=doc_download&gid=75&Itemid=274

Depending of the type of business, a mesh architecture in which each remote site can communicate with any other remote site as shown here could be used. These satellite communications can be terrestrial, maritime or aeronautical. There is wide range of solutions for these type of satellite links which allow voice, video and data communications across the whole network.


http://www.comtechefdata.com/articles_papers/Optimizing%20Cellular%20Solutions.pdf

Providing GSM services via satellite GSM backhaul in the emerging markets, in geographically challenged areas, or areas in which conventional terrestrial transmission solutions are either not available or not appropriate could open new business opportunities.


Mobile Applications:- personal safety device- health monitoring which sends real time information back to doctors at health clinics (wearable technologies based on a permanent integration of clothing and technology).


For sat-talk go to:

http://www.satellite-links.co.uk

http://www.satmagazine.com

http://www.satellitetoday.com


Geocentric model of the solar system:

Aristotle (384 BC – 322 BC), Greek philosopher. In his work, Metaphysics, he describes the heavens composed of 55 concentric, crystalline spheres to which the celestial objects were attached and which rotated at different velocities, in an uniform circular motion, with the Earth at the centre.

Ptolemy (90 – 168), Roman citizen. In his Almagestastronomical treatise, planets moved on epicycles,

(circle with centre moving on concentric sphere)

It explained the retrograde movement of planets.

Later on the model evolved in epicycles on epicycles.

Bits of history - Concepts


Heliocentric model of the solar system:

Nicolai Copernicus (1473 - 1543), Polish astronomer. In his book On the Revolutions of the Heavenly Bodies, he proposed that the Sun is at the centre of the Solar System. This can explain the retrograde motion and also the variance in brightness of planets who are not always at the same distance from Earth. Aristarchus of Samos - island off the coast of Turkey, proposed the same sun-centerd system in 200 BC!

Tycho Brahe (1546 – 1601), Danish nobleman. He devised instruments that allowed precise measurements of the movements of planets, Mars in particular. This allowed Kepler, his assistant, to prove later on that the planet’s orbit is an ellipse, not a circle.




Johannes Kepler (1571 - 1630), German astronomer. He believed in the Copernican theory and in his Astronomia nova and Harmonices Mundi works he used Tycho Brahe’s measurements to formulate his three laws of planetary motion (1602, 1605, 1618):




Giordano Bruno (1548 - 1600), Italian philosopher. Catholic Encyclopedia (1908) asserts that "Bruno was not condemned for his defence of the Copernican system of astronomy, nor for his doctrine of the plurality of inhabited worlds, but for his theological errors, among which were the following: that Christ was not God but merely an unusually skilful magician....”

Galileo Galilei (1564 – 1642), Italian physicist, used the telescope to observe the movements of the planets and challenged the Church view in his Dialogue Concerning the Two Chief World Systems work published in 1632. His observations of the phases of Venus disproved the Ptolemaic version of geocentrism.




Isaac Newton (1642– 1727, Julian calendar ), English physicist. His Philosophia Naturalis Principia Mathematicawork described among other things, the three laws of motion (an object at rest tends to stay at rest and an object in uniform motion tends to stay in uniform motion, an applied force on an object equals the rate of change of its momentum with time, for every action there is an equal and opposite reaction) and the gravitational law which is a universal law that applies to objects on Earth as well to celestial bodies. This was confirmed by the slow down of Saturn upon passing Jupiter, the shape of the Earth being an oblate spheroidal, the correctly predicted return of Halley’s Comet and the explanation of tides and lunar motion.



The Earth moves around the sun:

James Bradley (1693 – 1762), English astronomer. In 1728, James Bradley, while searching for the elusive stellar parallax, detected the motion of the star Gamma Draconis over the course of the year caused by the yearly rotation of the Earth. This finding was the first direct evidence for the revolution of the Earth around the Sun. Aristarchus, Copernicus and Galileo were vindicated: “eppur si muove”... Friedrich Bessel (1784 – 1846), German scientist. In 1838 he was the first to use parallax in calculating the distance to a star (as you move, nearer objects will seem to move relative to more distant objects).



The Earth moves around its axis:

Leon Foucault (1819- 1868), French physicist. In 1851 he used long and heavy pendulum suspended from the ceiling of the Panthéon in Paris to demonstrate the spinning of the Earth. He also named the gyroscope in 1852.


http://upload.wikimedia.org/wikipedia/commons/a/ae/Pendule_de_Foucault.jpg

http://upload.wikimedia.org/wikipedia/commons/a/ae/Pendule_de_Foucault.jpg

http://en.wikipedia.org/wiki/File:3D_Gyroscope.png

http://en.wikipedia.org/wiki/File:3D_Gyroscope.png

http://upload.wikimedia.org/wikipedia/commons/3/35/Gyroscope_wheel-text.png

http://upload.wikimedia.org/wikipedia/commons/3/35/Gyroscope_wheel-text.png


Pierre Maurice Marie Duhem (1861 – 1916), French, and Willard Van Orman Quine (1908 – 2000), American, produced the Duhem-Quine thesis: empirical evidence cannot force the choice of a theory or its revision, or in other words, for any collection of empirical evidence, there would always be many theories able to account for it. In practice it is difficult to ever test a theory independently of other theories or assumptions. This means that when an experiment 'proves' a theory false it is really just proving the collection of theories and assumptions false, not necessarily the theory itself. Given that one cannot determine which theory is refuted by unexpected data, scientists must use judgements made according to the outcomes of the statistical hypothesis tests about which theories to accept or to reject.



Albert Einstein (1879 – 1955), German physicist. In 1916 he published the general theory of relativity. The source of gravity for Newton was mass. Einstein’s field equations show the source of gravity as the energy-momentum tensor which includes matter, radiation and other force fields. Gravity corresponds to changes in the properties of space and time, which in turn changes the straightest-possible paths that objects will naturally follow: “spacetime tells matter how to move;

matter tells spacetime how to curve”The orbit is akin to an ellipse that rotates on its focus; a binary system will emit gravitational waves, so it loses energy, the orbital period will decrease – too small effect for the solar system.


http://upload.wikimedia.org/wikipedia/commons/2/28/Relativistic_precession.svg

http://upload.wikimedia.org/wikipedia/commons/2/28/Relativistic_precession.svg


Some tests of general relativity theory:

the perihelion precession of Mercury: there is a 43 seconds of arc per century deviation from Newton’s theory which is explained by gravitation being mediated by the curvature of spacetime.

frame dragging - rotating bodies drag spacetime around themselves - was demonstrated by the launch in 2004 of the Gravity Probe B satellite, see also the 1997 LAGEOS satellite experiment.


http://upload.wikimedia.org/wikipedia/commons/8/8f/Geodetic_effekt.jpg

http://upload.wikimedia.org/wikipedia/commons/8/8f/Geodetic_effekt.jpg


About the Earth Orbit:Bits of history - Concepts

http://upload.wikimedia.org/wikipedia/commons/3/30/Galactic_longitude.JPG

The Earth moves through space at ~107,000 Km/h (30Km/s). Average distance between the Sun and Earth is ~150,000,000 Km. At the end of December, Earth is 5 million km closer to Sun than in June, getting 7% more energy. However the tilt away from the Sun of the Northern Hemisphere accounts for the loss of more than 50% of the energy so there is winter time! In the Northern Hemisphere, the land continues to cool until mid January whereas the ice is at its peak around March!Why the Southern hemisphere doesn’t fry in December when it is tilted towards the Sun at the closest point in its orbit? Because of the vast oceans surrounding the few bits of land!


About the Earth – Moon interaction:Bits of history - Concepts

“Beyond the Moon” – James Greig McCully

The Earth – Moon system rotates around an imaginary axis situated at around 3000 miles from the centre of the earth (that would be around 1000 miles inside the earth!) The main effect are the tides: two bulges of water, one towards the moon due to the lunar gravitation, the other away from the moon due to the centrifugal force. Thus there are two high and two low tides every day.Given the declination of lunar orbit relative to the equator, the two high tides can be of different height; furthermore, the declination changes in time, from 28.5˚N to 28.5˚S, so the pattern of tides will change too.


About the Earth – Moon interaction:Bits of history - Concepts

“Beyond the Moon” – James Greig McCully

The speed of the Moon is maximum at perigee and lowest at apogee; this makes the rate of change of tides nonlinear. The Moon orbits the Earth (once every 27.5 days) in the same direction as the west-to-east rotation of the Earth on its polar axis. Over 24 hours, the Moon moved on its orbit, so the high tide will happen on the same spot on Earth when the Earth catches up, that is 52 minutes later from one day to another; over one week, it just happens that the time for high tide becomes the time for low tide! During full or new moons, both solar and lunar gravitations are aligned causing higher tides! The maximum impact is only 18 inches of vertical water displacement, the rest is explained by other factors!


About the Solar System:Bits of history - Concepts

The inner planets (Mercury, Venus, Earth and Mars) are made of rock and metal whilst the outer planets (Jupiter, Saturn, Uranus and Neptune) are made of gases (hydrogen, helium, water, ammonia and methane). They move on almost circular orbits in the ecliptic plane. The inner and outer planets are separated by an asteroid belt. Neptune's orbit (~30AU) is surrounded by the Kuiper asteroid belt which is situated at the centre of the Oort Cloud (~ 1 light-year in diameter). “An astronomical unit (abbreviated as AU, au, a.u., or ua) is a unit of length now defined as 149,597,870,700 metres (92,955,807.273 mi) exactly, or roughly the mean Earth–Sun distance” (http://en.wikipedia.org/wiki/Astronomical_unit)A light-year (ly) is the distance that light travels in a vacuum in one Julian year (defined exactly as 365.25 days) and is equal to ≈ 63241.1 astronomical units.


About the Solar System:Bits of history - Concepts

http://upload.wikimedia.org/wikipedia/commons/c/c2/Solar_sys.jpghttp://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/Oort_cloud_Sedna_orbit.svg/1024px-Oort_cloud_Sedna_orbit.svg.png


About the Milky Way:Bits of history - Concepts

http://upload.wikimedia.org/wikipedia/commons/3/30/Galactic_longitude.JPG

The Milky Way is a spiral galaxy ~100,000 light-years (ly) in diameter and ~1,000 ly thick, with up to 400 billion stars. It is moving at a velocity of ~600 km per second. It is ~13.2 billion years old. It takes the Solar System ~250 million years to complete one orbit around the Galaxy. The orbital speed of the Solar System is ~220 Km/s. Proxima Centauri is the closest star to the Sun, at ~4.24 ly.


1749, American Benjamin Franklin invented the lightning rodwhich proved that lightning is a form of electricity which can move through air.

1819, Danish Hans Christian Oersted discovered that there is a relationship between electricity and magnetism ( a compass needle would move in the presence of an electric field).

1832, English Michael Faraday (& American Joseph Henry) invented the electromagnet based on the law of induction (a variable magnetic field produces an electromotive force).

1837, English Charles Wheatstone invented the telegraph in which a letter was literally pointed out by the current deflecting two of the needles towards it.

Bits of history - Technology


1843 American Samuel Morse built a telegraph line from Washington to Baltimore and sent the first dots and dashes over the line.

1864 Scottish James Maxwell showed in “A Dynamical Theory of the Electromagnetic Field” that “light is an electromagnetic disturbance” propagated through the field at a velocity of 310,740 m/s.

1873 Maxwell’s “A Treatise on Electricity and Magnetism” defines the four mathematical equations which describe the relationship between electricity and magnetism.

1876 American Alexander Graham Bell invented the telephone.



Bell’s claim is disputed by the Italian Antonio Meucci who in 1860 published in a New York’s Italian language newspaper his invention of a paired electro-magnetic transmitter and receiver, where the motion of a diaphragm modulated a signal in a coil by moving an electromagnet.

1887 German Heinrich Rudolf Hertz demonstrated the existence of electromagnetic waves can travel a distance.

1895, Italian Guglielmo Marconi invented the first radio transmitter which was demonstrated across the English Channel and in 1901 across the Atlantic Ocean. In 1943 the US Supreme Court overturned Marconi’s patents in favour of Serbian Nikola Tesla’s patents (1891), credited now with the invention of radio.



1900 Russian Constantin Perskyi introduces the word television at the World Fair in Paris.

1906 Russian Boris Rosing builds the first mechanical television combining a cathode ray tube with Paul Nipkow’sinvention which sends images over wires using a rotating metal disk calling it the electric telescope with 18 lines of resolution.

1927 American Philo Farnsworth, files for a patent on the first complete electronic television system, which he called the Image Dissector.

1929 Russian Vladimir Zvorykin shows the first practical electronic system for both the transmission and reception of images using his new kinescope tube.



1937 BBC begins high definition broadcasting.

4 Oct 1957 first artificial satellite launched: Sputnik 1 meaning “Travelling companion”, ~100 kg, T = 96 min, a radio beacon and a thermometer. Solved legal challenges with respect to crossing the air space of a sovereign country.

1957 Sputnik 2 carried a dog named Laika.

1958 Explorer 1, first US successful launch; NASA established

Apr. 1960, US launched the first weather satellite, Tiros I, it sent pictures of clouds to the Earth.

Aug. 1960, US launched Echo I, which reflected radio signals back to Earth.



Apr. 1961, Yuri Gagarin, the first man in space, for 1h48min.

Feb. 1962, John Glen circled the earth 3 times.

1962, Telstar, first LEO communication satellite.

1963, Syncom1 - Hughes, 240 telephone calls, first GEO communication satellite.

1964, Syncom 3, first live TV transmission (Olympic Games).

More than 100 satellites were placed in orbit every year.

July 1969, first man on the moon; there are around 600 satellites in Earth orbit and around 8,000 man-made objects.

1969 first TV broadcasting from the moon!



The Internet was originally developed by the DefenseAdvanced Research Projects Agency in US; Paul Baran of RAND was assigned the task of creating a decentralized communication network that could survive a nuclear attack. The concept was developed starting in 1964, and the first messages passed were between UCLA and the Stanford Research Institute in 1969 over a link built by Larry G. Roberts. (Leonard Kleinrock of MIT had published the first paper on packet switching theory in 1961.)

The transmission communications protocol, (TCP), was developed by Vint Cerf and Robert Kahn in 1972.

Robert Metcalfe is credited with Ethernet which is the basic communication standard in networked computers.



1979 IBM introduced a 'store and forward' network, now known as email.

1990 Tim Berners-Lee specified the linguistic construction of HTML while working at CERN, which meant that graphical websites started appearing and the world-wide-web became a reality. TCP/IP over satellite took off in early ‘00s.

February 10, 2009, the first ever satellite collision in space between the U.S. Iridium 33 satellite (560 kg) launched in 1997 collided with Russia's Cosmos 2251 satellite (960 kg), launched in 1993 and non-operational for a decade, at an altitude of ~800 km over Siberia, producing debris which flies at 7.8 km/s and will remain there for decades to come.



Mobile phones took off in late ‘80s and satellites are now used to provide backhaul connectivity for any location on earth.



According to the US Defense Department’s Cheyenne Mountain Operation Center, since the launch of Sputnik 1 by the Soviet Union in 1957, around 8000 satellites have made it to orbit.

There are over 2,500 satellites, ~1,000 operative, orbiting the Earth.

About 24,000 pieces of “significant” space junk are flying around, bigger than the size of a laptop. Another ~600,000 objects larger than 1 cm are hurtling round the earth at some 24,000 km/hour.

The definition of a satellite has changed: Surrey Satellite Technology Ltd (SSTL) is now building a prototype “palm-sat” –about the size of a Walkman – and is developing credit card size satellites. They will fly as a cloud, or swarm, talking to each other.




http://www.ucsusa.org/nuclear_weapons_and_global_security/space_weapons/technical_issues/ucs-satellite-database.html


1. G. Maral and M. Bousquet, “Satellite Communications Systems”, John Wiley & Sons, New York, 4th Edition, 2002.

2. P. Fortescue, “Spacecraft Systems Engineering”, 3rd Ed, 2002.3. M. J. Miller, B. Vucetic and L. Berry, (Eds.), “Satellite

communications: Mobile and Fixed Services”, Kluver Academic Publishers, Boston, 1993.

4. D. Roddy, “Satellite Communications”, McGraw-Hill TELECOM Engineering, 3rd Edition, 2001.

5. M. E. Long, “The Digital Satellite TV Handbook”, Newnes, 1999

6. Edited by P. A. Swan and C. L. Devieux, Jr, “Global mobile satellite systems : a systems overview”, Kluwer Academic Publishers, 2003.

References


7. T. Pratt, C. W. Bostian and J. Allnutt, “Satellite Communications”, [New York, NY] : Wiley, c2003.

8. S. Lin and D. Costello Jr, “Error Control Coding: fundamentals and applications”, Prentice-Hall, 1983/2005

9. D. C. Palter, “Satellites and the Internet”, SatNews Publishers, 2003.

10. F. G. Stremler, “Introduction to Communication Systems”, Reading, Mass. Addison-Wesley Pub. Co, 3rd Edition, 1990.

11. J. G. Proakis and M. Salehi, “Communication system engineering”, N.J. : Prentice Hall ; London : Pearson Education, c2002.

12. J. G. Proakis, “Digital Communications”, McGraw-Hill, Edition 2005.

References


13. International Telecommunication Union, “Handbook on Satellite Communications”, New York, NY : Wiley-Interscience ; Geneva , c2002.

14. M. R. Soleymani, Yingzi Gao and U. Vilaipornsawai, “Turbo coding for satellite and wireless communications”, KluwerPublishers, c2002.

15. R. E. Sheriff and Y. F. Hu, “Mobile satellite communication networks”, New York ; Chichester : Wiley, 2001.

16. J. R. Schott, “Remote Sensing”, Oxford University Press, 1997. 17. Ed. Keattisak Sripimanwat, “Turbo Code Applications: a

journey from a paper to realization“, Springer, 200518. Giovanni Giambene Editor, “Resource Management in Satellite

Networks – Optimization and Cross-Layer Design”, Springer 2007.

References


19. Giovanni Giambene Editor, “Resource Management in Satellite Networks – Optimization and Cross-Layer Design”, Springer 2007.

20. E. Del Re, M. Ruggieri Editors, “Satellite Communications and Navigation Systems”, Springer 2008

21. http://www.engnetbase.com/books/786/0967_fm.pdf22. http://www.engnetbase.com/books/1525/dke581 fm.pdf23. “Global Mobile Satellite Communications”

http://www.springerlink.com/content/u6142m/?p=720229987986473181848cf04ce0ebb7&pi=0

24. A. Nejat Ince Editor, “Digital Satellite Communications –Systems and Technologies – Military and Civil Applications” Kluwer Academic Publishers, 1992

25. IEEE Transactions on Wireless Communications

References


26. IEEE Communications Magazine27. IEEE Communications Surveys and Tutorials28. IEEE/ACM Transactions on Networking29. International Journal on Satellite Communications and

Networking30. http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-

Computer-Science/6-450Fall-2006/CourseHome/index.htm (Principles of Digital Communications 1 – Robert Gallager)

31. http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-451Spring-2005/CourseHome/index.htm (Principles of Digital Communications 2 – David Forney)

References


References32. https://directory.eoportal.org33. http://www.esa.int/ 34. http://www.intelsat.com/ 35. http://www.eutelsat.com/ 36. http://www.jpl.nasa.gov/basics 37. http://www.satellitetoday.com/viaonline/ 38. http://www.gilat.com 39. http://www.comtechefdata.com 40. http://www.hughespace.com/ 41. http://www.itu.int/ 42. http://www.allaboutsatellites.com


Orbits

Contents: Overview Kepler’s Laws Newton’s Law Orbital Parameters Inclined/GEO Orbits


Overview• International Telecommunication Union (ITU)

– Created in 1865 in Paris, is the UN agency responsible for information and telecommunication technologies (based in Geneva, Switzerland).

– The Radiocommunication sector (ITU-R), deals with the management of the radio-frequency spectrum and satellite orbit resource allocation.

– The Standardization sector (ITU-T) deals with standard definition.


Overview• Frequency planning is divided into 3 regions:

– Europe, Africa, formerly Soviet Union, Mongolia– Americas and Greenland– Asia, Australia and S-W Pacific

• Radio Regulations issued by ITU define– the allocation, coordination, notification and

mandatory specifications of different frequency bands to different radio services (WRC-12). The ITU-R list of recommendations can be found at http://www.itu.int/dms_pub/itu-r/opb/rec/R-REC-LS-2007-E02-PDF-E.pdf


OverviewSeries SubjectBO Satellite deliveryBR Recording for production, archival and play-out; film for televisionBS Broadcasting service (sound)BT Broadcasting service (television)F Fixed serviceM Mobile, radiodetermination, amateur and related satellite servicesP Radiowave propagationRA RadioastronomyRS Remote sensing systemsS Fixed-satellite serviceSA Space applications and meteorologySF Frequency sharing and coordination between fixed-satellite and fixed service systemsSM Spectrum managementSNG Satellite news gatheringTF Time signals and frequency standards emissionsV Vocabulary and related subjects


• L band (1-2 GHz)– not affected by weather– used for low data rates transmissions (~kbit/s)– require a low antenna directivity– relative low power requirements– used for mobile satellite systems (MSS) and

navigational systems

Overview


• C band (4-8 GHz)– small rain fade– medium data rates transmissions (~Mbit/s)– global/regional coverage for fixed satellite

services– satellite spacing of 2° requires parabolic

antennas larger than 2 m– medium power requirements

Overview


• X band (8-12 GHz)– significant rain fade– medium data rates transmissions (~10 Mbit/s)– global/regional coverage but also used for

terrestrial line of sight microwave links– military use– medium to very high power requirements

Overview


• Ku band (12-18 GHz)– significant rain fade, significant attenuation loss– high data rates transmissions (~100 Mbit/s)– global/regional/spot beam coverage for TV

broadcast– 1.2° spot beam can cover ~900 km– 0.6 m rx antenna, 1.2 m tx antenna

Overview


• Ka band (27-40 GHz)– very high rain fade and attenuation loss– high data rates transmissions (~100 Mbit/s)– spot beam coverage for civilian satellite

communications– highly directional antenna– better protection to interference– ideal for some applications e.g., satellite news

gathering which require smaller dishes.

Overview


• Ka band (27-40 GHz)– more bandwidth/capacity therefore more

flexibility for the satellite operator.– a Ka band communications system with antennas

and amplifiers similar to those used at X-band will theoretically yield a 5 to 6 dB increase in effective isotropic radiated power or a factor of 3 to 4 improvement in data rate all losses considered.

– it is more tolerant of solar corona effects than X-band.

Overview


• Extreme high frequency EHF (30-300 GHz)– achieve a high degree of survivability under both

electronic warfare and physical attack,– unlike systems dependent on lower frequencies,

EHF satellite communications recover quickly from the scintillation caused by a high-altitude nuclear detonation,

– reliable communications in a nuclear environment, minimal susceptibility to enemy jamming and eavesdropping, and the ability to achieve smaller secure beams with modest-sized antennas.

Overview


• Extreme high frequency EHF (40-78 GHz)– Three Advanced EHF geostationary satellites, 100

times more powerful than the 1990’s MILSTAR satellites will expand the MILSATCOM architecture of the US military to enable Transformational Communications and Network-Centric Warfare. AEHF protections include anti-jam capabilities using a phased-array antenna on the satellite that can minimize sensitivity in the direction of a jamming signal, Low Probability of Detection (LPD), a Low Probability of Intercept (LPI), and advanced encryption systems.

Overview


• Services:– Fixed satellite services (FSS)– Broadcasting satellite services (BSS)– Mobile satellite services (MSS)– Navigational satellite services– Meteorological satellite services

Overview


Earth's magnetic field traps fast-moving charged particles within an invisible magnetic prison. These form into inner and outer donut-shaped dynamic, rapidly changing clouds with the Earth at the centre. The inner cloud is composed mainly of protons, extends from ~1000 km to ~6,000 km. The outer cloud is composed mainly of high-energy, fast-moving electrons, extends from ~13,000 km to more than 40,000 km. Two satellites, the Van Allen Probes, were launched in 2012 to measure the particles, magnetic and electric fields, and waves that fill this geospace.

Overviewhttp://radbelts.gsfc.nasa.gov/outreach/

http://images.yourdictionary.com/images/science/ASvanall.jpg


Overviewhttp://www.nasa.gov/images/content/674608main_L14-MKviz1.jpg


• Low Earth Orbit (LEO):– Most popular are at altitudes from 200 to 1,000 Km,

circular orbit, just below the higher intensity levels of the inner Van Allen Belt

– near 90° inclination, the orbital period is ~1.5 h– operating frequency:1.0 to 2.5 GHz range– small path loss => lower transmit power– complex antenna tracking for < 20 min, interrupted

communication (radius of the footprint < 3000 km)– IRIDIUM, GLOBALSTAR, ELLIPSO, ECCO

Overview


• Medium Earth Orbit (MEO):– altitude around ~10,000 km, circular orbit,

between the inner and outer Van Allen belts– inclination about 50°, the orbital period is ~ 6 h– operating frequency:1.2 to 1.7 GHz range– NAVSTAR, ICO

Overview


• Geostationary Earth Orbit (GEO):– exact altitude of 35,786 km, circular orbit– the period is equal to that of the earth in the

same direction– appears as a fixed point in the sky– visibility of 43% of the earth’s surface– round-trip delay of ~250 ms– INTELSAT, EUTELSAT, PANAMSAT

Overview


Kepler's Laws

• These laws apply to any two bodies in space• The more massive body is the primary• The center of mass of the two body system

is the barycenter.• Kepler's First Law (1602)

The path followed by a satellite around the primary is an ellipse with the barycenter in one of the two focal points.


Kepler's Laws

Ellipse showing semi-major and semi-minor axes

semi-majorse

mi-m

inor

Fixed Foci


Kepler's Laws

• Kepler's Second Law (1605): For equal time intervals, a satellite will sweep out equal areas in its orbital plane, focused at the barycentre.

• A satellite will take longer to travel a given distance when it is further away from earth

• The velocity is less when the satellite is further away from earth.


Kepler's Laws

Ellipse showing semi-major and semi-minor axes

1T

2T

0T

3T 4T5T

6T7T

T is any unit of time (hour, day,..)


Kepler's Laws

• Kepler's Third Law (1618): The square of the orbital period is proportional to the cube of the mean distance between the two bodies (which is equal to the semi major axis).

• There is a fixed relationship between period and size.


Newton's Law

• Newton's Law (1667):Two bodies of mass m and M at distance r, attract each other with a force F = GMm/r2

• G = 6.672 x 10-11 m3kg-1s-2

• Mass of the Earth, ME = 5.974 x 1024 kg• µ = GM = 3.986 x 1014 m3s-2

• Radius of the earth RE = 6,378 km


Earth


http://en.wikipedia.org/wiki/File:EarthGravityPREM.jpg


Orbital parameters

• The orbits of communication satellites are in general ellipses defined by :

a = semi major axisb = semi minor axis

• e = eccentricity a2e2 = a2 - b2

• T = period T2 µ = 4π2a3

• V = velocity V2 = µ[(2/r) - (1/a)]


Orbital parameters

• Period T and velocity V for a circular orbit function of satellite altitude:

Altitude Radius P V(km) (km) (s) (m/s)200 6578 5309 7784800 7178 6052 745020000 26378 42636 388735786 42164 86164 3075


Orbital parameters

• Apogee: the farthest point from earthra = a(1 + e)

• Perigee: the closest point to earthrb = a(1 - e)

• Line of apsides: the line joining the apogee and the perigee through the centre of the

earth


Orbital parameters• Ascending node: the point where the orbit

crosses the equatorial plane going from south to north (Ω)

• Descending node: the point where the orbit crosses the equatorial plane going from north to south

• Line of nodes: the line joining the ascending and descending nodes through the centre of the earth.


Orbital parameters

• Inclination: the angle between the orbital plane and the earth’s equatorial plane

• Prograde orbit: an orbit in which a satellite moves in the same direction as earth’s rotation The inclination is between 0 and 90 degrees

• Retrograde orbit: an orbit in which a satellite moves in a direction counter to earth’s rotation The inclination is between 90 and 180 degrees


Orbital parameters

• Subsatellite point: the point on the earth vertically under the satellite

• Tropical year: the time required by the mean sun to complete one orbit (365.2422 days)

• Julian calendar: civil year = 365.25 days, leap year (extra day every four years in February)

• Gregorian calendar: years ending in two zeros are leap years if divisible by 400 (365.2425days)


Orbital parameters• Leap seconds: represent the difference between

the mean solar time in 1820 (determined by "Newcomb's Table of the Sun" which in 1954 was agreed to be 86,400 sec/day) and the caesium atomic clock which is 86,400.002 sec/day. The extra second was added at midnight, London time, on 31/12/2008, to match the two timescales. The earth has actually slowed with no more than ~2 msec since 1820.


Orbital parameters

• Sidereal day: one complete rotation of the earth relative to the fixed stars (23h56m4s); it is used to determine the height of the geostationary orbit

• Geocentric-equatorial coordinate system: enables coordination of satellite position with the earth station position

• Topocentric-horizon coordinate system: enables the calculation of look angles and range


Orbital parameters• Sun-synchronous orbit: the orientation remains

fixed relative to the sun ( requires a rate of rotation of 0.9856 °/day eastward)– a satellite crosses a given latitude at the same local solar time

and hence under approximately the same solar lighting conditions each day => used by weather and surveillance satellites (detect narcotics, foot trails through barren areas, identify telephone and electric poles, identify automobiles as sedan or station wagons).

– the direction of rotation of the orbital plane and the period (the rotation angle per day) are the same as the Earth's orbital period (the rotation angle per day).


Orbital parametersThe whole orbital plane of a satellite going around the Earth takes one year to complete one revolution, and the orbital plane of the satellite and the orientation of the Sun are always the same. This kind of orbit can only be a polar orbit with an inclination larger than 90°; this orbital inclination varies with the satellite's altitude. For example, Sarsat satellites at 860 km are inclined at 99°; at an altitude of 800 km, an orbital inclination of 98.4° is required. Looking at the Earth from a satellite in this orbit, the Sun's light would always be coming from the same angle, so the satellite would be appropriate for monitoring a site that must always be observed under the same conditions.


Tropic of Capricorn, north of Alice Springs, Australia. It marks the most southerly latitude at which the sun can appear

directly overhead at noon (the latitude is 23° 26′ 22″ south of Equator which equals the Earth's axial tilt).

Tropic of Cancer is the equivalent for the northern hemisphere.


Precession, the gradual shift in the orientation of the Earth's axis of rotation, which, like a wobbling top, traces out a conical shape in a

cycle of approximately 26,000 years(http://en.wikipedia.org/wiki/Precession_of_the_equinoxes)


A circle of latitude is not, with the sole exception of the Equator, the shortest distance between two points lying on the Earth. It is for this reason that an airplane travelling between an European and a North American city that share the same latitude will fly farther north, over Greenland for example.The main long-term cycle causes the axial tilt to fluctuate between about 22.5° and 24.5° with a 41,000 year periodicity. The average value of the tilt is now decreasing by about 0.47″ per year. This causes the Tropics of Cancer and Capricorn to drift towards the equator by about 15 metres per year, and the Arctic and Antarctic Circles to drift towards the Poles by the same amount.The Arctic/Antarctic Circles marks the southernmost/northernmost latitude (in the Northern/Southern Hemisphere) at which the sun can remain continuously above or below the horizon for 24 hours. The latitude of these circles plus the Earth's axial tilt is equal to 90°.


The nutation of a planet happens because the tidal forces - in the case of Earth, the principal sources of tidal force are the Sun and Moon - which cause the precession of the equinoxes vary over time so that the speed of precession is not constant. It was discovered in 1728 by the English astronomer James Bradley. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes. It has an amplitude of 9"21 (corresponding to almost 300 metres north and south).(http://en.wikipedia.org/wiki/Nutation)

Rotation (green), Precession (blue) and Nutation in obliquity

(red) of the Earth.


Inclined Orbits• Synchronous or sub-synchronous orbits: the rotation

period of a satellite is precisely equal to the length of the day, or to the length of a day divided by an integer.

• Due to the high number of satellites in geostationary orbits, sub-synchronous circular or elliptical orbits at a lower altitude are used.

• Stable orbits:– inclined circular geo-synchronous orbit– inclined elliptical geo-synchronous orbit– non-synchronous orbit: inclined circular/elliptical, equatorial


Inclined Orbits• MOLNYA:

– High altitude elliptical orbit (HEO) with a rotation period of 12 hours for a 63.4° inclined plane, the perigee is 500 km, the apogee is 40,000 km. The motion of the satellite at high altitude, at the apogee, is slow, whereas it is very fast at the perigee, in the vicinity of the South Pole. Three such satellites can give continuous coverage 24 hours a day. Doppler effect due to the velocity of satellite is significant (~16kHz).


Inclined OrbitsThe red thin line shows the unexpected loops and backtracks of the ground track using ECF (Earth-centered fixed) orbit trace rotating with the Earth while the thick blue line shows the elliptical ECI (Earth-centered inertial) orbit trace remaining fixed in space; those two orbit traces will always have an intersection point, which is where the spacecraft is located at that time.


Inclined OrbitsThe Flower Constellation (http://flowerconstellations.tamu.edu) shows the 5 petals of 2 satellites per HEO orbit arrangement.


Inclined OrbitsExample of a Flower Constellation for telemedicine designed such that achieves maximum dwelling time in the most populated areas (http://www.esa.int/gsp/ACT/doc/ARI/ARI%20Study%20Report/ACT-RPT-MAD-ARI-05-4108-FlowerConstellations-Rome.pdf)


Inclined OrbitsParameters of the Flower Constellation and relative ECF orbit.


Inclined Orbits

(Source: Encke, Infoterra-Global, 2006)


Geostationary Orbit

• The satellite must travel eastward at the same rotational speed as the earth

• The orbit must be circular• The inclination of the orbit must be zero=> There is only one geostationary orbit

Radius = 42,164 km, Altitude = 35,786 km


Geostationary Orbit

• Gravitational fields of the sun and the moon produce an inclination shift of 0.85 °/year

• Earth gravitational acceleration = 0.22 m/s2

(compared with 9.8 m/s2 on Earth)• The earth’s equatorial ellipticity and non

uniform density causes the satellite in a prograde orbit to drift eastward along the orbit.

=> station-keeping manoeuvres


Geostationary Orbit

• Station-keeping box: the maximum permitted values of the excursion of the satellite in longitude and latitude (except 105°W and 75°E)(±0.05° variation; ~ 75 km = 0.1°, 35 km deep)– N-S control budget: 43-48 m/s per year– E-W control budget: 1-5 m/s per year– ∆V5.4 m/s requires 2.3 kg propellant for 1000 kg

• Broadcast Service Satellites: (±0.1°)


Geostationary Orbit

• Look angles: azimuth & elevation– the earth station (ES) latitude: λES (S is negative)– the earth station longitude: φES (W is negative)– the longitude of the sub-satellite point: φSS

– the range from the ES to the satellite (S): d– the geostationary radius: RG = 42,164 km– the earth radius: RE = 6,378 km (65 m bulge at λ=0)– Maximum latitude: λES =cos-1(RE/RG) = 81.3º


Geostationary Orbit• Look angles (valid for latitudes λES < 81.3º)

– compute b = arccos[cos(φES - φSS)cos(λES)]– find azimuth angle A=arcsin[sin(| φES - φSS |)/ sin(b)]

λES φES - φSS Azimuth< 0 < 0 A< 0 > 0 360 - A> 0 < 0 180 - A> 0 > 0 180 + A

– find the range d2 = (RE)2 + (RG)2 - 2 RE RG cos(b)– the angle of elevation is: arccos[RG sin(b)/d]


Geostationary Orbit

• Limits of visibility:– at equator (λES = 0) and sea level, the ES can point

east or west at 90°, a maximum satellite longitude: φSS = φES ± arccos(RE / RG ) = φES ± 81.3°

– at a latitude λES ≠ 0 and altitude a above sea level:• define the lowest practical elevation: Elmin = 5°• calculate: S = arcsin[sin(90 + Elmin)(RE + a)/RG]• φSS = φES ± arccos[cos(90 - Elmin - S)/cos(λES)]


Geostationary Orbit

• Eclipses/Outage– equatorial plane is tilted at 23.4° to the ecliptic plane– during spring and autumnal equinoxes, when the sun

is crossing the equator, the satellite passes into the earth’s shadow => eclipses for 23 days before and after, from 10 to 72 minutes

– sun-transit outage, for 6 days around equinoxes, for maximum 10 minutes (when sun radiation comes within the beamwidth of the ES)


Geostationary Orbit• For orbital altitude lower than 200 km, satellites

can be directly injected into low-altitude orbits• For higher altitudes than 200 km, the satellite is

transferred from an initial low earth orbit to a Hohmann transfer elliptical orbit until it reaches the high earth orbit.

• The combined attractions of the Sun and the Moon cause an increase in the orbital inclination with ~1° /year.


Geostationary Orbit

• Crosstalk issues:– spatial selectivity of the space antennas of satellite

(multibeam antennas that have a specific radiation pattern)

– mutually orthogonally (circularly or linearly) polarized signals

– reverse use of frequency bands: frequencies for earth-to-space and space-to-earth are used in opposite directions.


Geostationary Orbit

• Crosstalk issues:– coordinating the frequency plans of neighbouring

satellite systems (e.g., adjacent satellites with the same low-power transmitters in the same part of the band)

– only 2° separation


Geostationary Orbit• Crosstalk issues:

– in the case of frequency modulation, an increase of the frequency modulation index increases the frequency band. However, the noise immunity of signal reception increases and the spectral density of the radiated signal decreases.

– Interference compensation methods: a special antenna receives the interfering signal and subtracts it from the signal in the main receiver path or a priori known differences from the useful signal.


Geostationary Orbit

• Advantages:– are almost stationary with respect to the ES– no interruptions in communications– large coverage area– negligible Doppler shift effects


Geostationary Orbit

• Disadvantages:– delay of 250 ms– due to the gravitational forces of the sun and the

moon, the position of the satellite is not stationary => need for propulsion devices

– the polar region requires small elevation angle that increases the receiver noise

– high transmit power and more sensitive receivers


Radar frequency bands:HF 3.0 - 30 MHzVHF 30 - 300 MHzUHF 300 - 1000 MHzL 1.0 - 2.0 GHzS 2.0 - 4.0 GHzC 4.0 - 8.0 GHzX 8.0 - 12.0 GHzKu 12.0 - 18.0 GHzK 18.0 - 26.5 GHzKa 26.5 - 40.0 GHzQ 30.0 - 50.0 GHzU 40.0 - 60.0 GHzV 50.0 - 75.0 GHzE 60.0 - 90.0 GHzF 90.0 - 140 GHzW 75.0 - 110 GHzD 110 - 170 GHzMn 110 - 300 GHz

Broadcast frequency bands:ULF 300 - 3000HzVLF 3 kHz - 30 kHzLF 30 kHz - 300 kHzMF 300kHz - 3 MHzHF 3.0 - 30 MHzVHF 30 - 300 MHzUHF 300 - 3000 MHzSHF 3 GHz - 30 GHzEHF 30 GHz - 300GHz


TV Broadcast in AustraliaAnalogue Digital

Channels Frequency (MHz) Channels Frequency (MHz)(0 – 5) (45 – 144) Not available (6 – 12) (174 – 235) (6 – 12) (174 – 230)(28 - 69) (526 – 820) (27 - 69) (519 – 820)==============================================

The Yagi digital TV antenna will be smaller: it will not need the 2609 mm (0-2) and the 1310 mm (3-5) elements; for VHF only the 743 mm (6-12); for UHF, the 272 mm (27-35), 249 mm (27-49), 214 mm (36-69) and the 194 mm (56-69).

==============================================(20 - 26) (470 – 512) for 2-way radio, CB.(70 – 80) (827 – 900) for mobile phones, W-CDMA


Terrestrial coordinatesA great circle is an imaginary circle on the surface of a sphere whose center is the center of the sphere. Great circles that pass through both the north and south poles are called meridians, or lines of longitude. In 1884, at the International Meridian Conference held in Washington DC, it was agreed that the civil day would start at midnight and the prime meridian, the starting point measuring the east-west locations of other meridians, will be the site of the old Royal Observatory in Greenwich, England. Longitude is expressed in degrees, minutes, and seconds of arc from 0 to 180 degrees eastward or westward from the prime meridian. For example, Adelaide, South Australia, is located at 138.6 degrees of arc east of the prime meridian: 138.6°E.


Terrestrial coordinatesUntil the 18th century, finding the exact longitude was one of the most difficult scientific problems due to the lack in the ability to measure it. Maps of the heavens in both hemispheres were not accurate enough. John Harrison, a clock maker found a mechanical solution, a clock that would keep the precise time at sea, regardless of temperature, humidity and moving of the ship. A forty-year struggle to build the perfect timekeeper, the chronometer.


Terrestrial coordinatesThe starting point for measuring north-south locations on Earth is the equator, a great circle which is everywhere equidistant from the poles.

Circles in parallel planes to the equator define north-south measurements called parallels, or lines of latitude. Latitude is expressed as an arc subtended on a meridian, between the equator and the parallel, as seen from the center of the Earth. Adelaide, South Australia, is located at 34.8 degrees south. One degree of latitude on the Earth's surface, changes from ~110.6 km at the Equator to ~111.7 km at the poles. (In 1671, Jean Richter noticed the pendulum has less momentum at the Equator vs in Paris, ~2.5 minutes lost. From this fact, Newton and Huyghens deduced the flatness of the globe at the poles.)

http://upload.wikimedia.org/wikipedia/commons/0/06/Two-types-of-latitude.png

http://upload.wikimedia.org/wikipedia/commons/0/06/Two-types-of-latitude.png


GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite launched in 2009 has three pairs of identical ultra-sensitive

accelerometers, mounted on three mutually orthogonal 'arms'. One of the arms is aligned with the satellite’s trajectory, one pointing towards the

centre of the Earth, and the third is perpendicular to the other two for the simultaneous measurement of six independent but complementary

components of the gravity field (www.esa.int)

There is a need of an accurate Digital Elevation Model (DEM) ofthe Earth, a digital representation of ground surface topography, asa reference for many applications, e.g., modeling water flow, massmovement, creation of relief maps, etc. Although the most accurateDEM is the ground surveying, optical and radar satellites havesignificant advantages.

WorldView-1 satellite, launched in 2007, is capable of providingelevation data with 0.50 meter ground sampling distance (GSD)resolution. The WorldView-2 satellite, launched in 2009, providesimages with 0.46 m GSD resolution, 8-band colour imagery and in-track colour stereo capabilities. The Worldview-3 scheduled for2014 will allow 0.31 GSD.

(http://www.digitalglobe.com)





components of the gravity field (www.esa.int)RECENT ADVANCES IN SATELLITE TECHNOLOGIES USING TO GENERATE

THE DIGITAL ELEVATION MODEL (DEM), 978-1-4244-3628-6/09/$25.00 ©2009 IEEE





components of the gravity field (www.esa.int)


1. Goce senses tiny variations in the pull of gravity over Earth 2. The data is used to construct an idealised surface, or geoid3. It traces gravity of equal 'potential'; balls won't roll on its 'slopes'4. It is the shape the oceans would take without winds and currents5. So, comparing sea level and geoid data reveals ocean behaviour6. Gravity changes can betray magma movements under volcanoes7. A precise geoid underpins a universal height system for the world8. Gravity data can also reveal how much mass is lost by ice sheets

(http://news.bbc.co.uk/2/hi/science/nature/8268942.stm)


The Soil Moisture and Ocean Salinity (SMOS) satellite was launched in 2009 to improve our understanding of the water cycle. Data from SMOS will be important for weather and climate modelling, water resource management, agriculture and also contribute to the forecasting of hazardous events such as floods.

(http://www.esa.int/SPECIALS/smos/SEMT0K6CTWF_0.html)


The SMOS mission measures microwave radiation emitted from Earth’s surface within the ‘L-band’, around a frequency of 1.4 GHz which provides the best sensitivity to variations of moisture in the soil and changes in the salinity of the ocean, coupled with minimal disturbance from weather, atmosphere and vegetation cover). The laws of physics mean that to take measurements in L-band, a huge antenna would have been required – too big for a satellite to carry. To overcome this challenge, a Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) was developed that replaced the huge antenna with 69 small antennas, distributed over the three arms (folded up for launch) and central hub of the instrument. The 69 antenna elements are antenna-receiver integrated units (each is 190 g, 165 mm in diameter and 19 mm high), each measures radiation emitted from Earth’s surface at L-band which is then added to synthesise the pinpointing of a much larger antenna.


This technique was used by astronomers for example, who combined27 radio telescopes, each 25 m in diameter, and deployed them on aY-shaped track extended up to 35 km, as shown in the figure above.SMOS borrowed these techniques – called ‘aperture synthesis’ or‘interferometry’– to mimic a much bigger antenna by placing 69small antennas along three arms that together form a Y-shape.The interferometric measurements will result in images from withina hexagon-like field of view about 1000 km across, enabling totalcoverage of Earth in under three days.


Space Environment

Contents:Mechanical Effects Atmospheric Effects Radiation, Ionospheric Effects, Rain Attenuation, Polarisation

Propagation Channel Models


Mechanical Effects

• atmospheric drag up to 400 km (due to atmospheric friction); the density depends on altitude, latitude, time, solar activity, etc

• the main effect: decrease in the semi-major axis, the breaking occurring at perigee reduces the altitude of the apogee

=> the orbit tends to become circular


Mechanical Effects• the Earth’s gravitational field varies with

altitude so parts of the satellite are attracted with different force resulting in a gravity gradient that does not pass through the center of mass of the satellite => a torque is created and is used to stabilise satellites in low orbit (~ 1E-7 Nm).

• meteorites and material particles (velocity ~km/s, mass 0.0001 ~ 0.1 g)


Mechanical Effects• launching vibrations• longitudinal and transverse accelerations• shocks during ignition• acoustic noise at lift off• reaction wheels: at a few rotations/second the

rotation speed can cause resonance and hence micro-vibrations which could negatively affect image quality in Earth observation satellites.


Mechanical Effects• A narrow beam high power communication

system can create a significant force in the radiating antenna.

• F = -EIRP/c, where EIRP is the effective isotropic radiated power and c is the speed of light.

• Ex: for an EIRP = 1 kW, F = 3E-6 N hence significant torque (the antenna axis should pass through the centre of mass of the satellite).


Federation Satellite (FedSat), Australia, 2002


Atmospheric Effects• Solar Radiation (torque ~ 5E-6 Nm)

– black body at 5,777°K, ~ 1370 W/m2, 8.73% of energy is in ultraviolet region (λ < 0.4 µm)38.15% is in the visible region (0.4 µm < λ < 0.7 µm)53.12% is in the infrared region (λ > 0.4 µm)

– the earth reflects one third of the sunlight that falls on it (this is known as earth’s elbedo or albedo).

– the lengths of days and nights change due to the inclination of earth’s axis of 23.5°


It takes 2 to 4 days after a solar flare for charged particles to impact the Earth’s magnetosphere (Courtesy of www.esa.int).


Atmospheric Effects• Earth Radiation

– black body at 250°K, total flux of 40 W/m2 for GEOs– radiation in the ultra-violet spectrum outside Earth’s

magnetosphere causes ionisation of materials:• increase in conductivity of insulators• decrease of 5%/year in efficiency of solar cells

– The atmosphere absorbs ultraviolet radiation -greenhouse effect- and far infrared radiation allowing only radiation in the region of 0.29 µm < λ < 2.3 µm


Atmospheric EffectsThe energy of electromagnetic radiation is related to its wavelength. The ultraviolet radiation, which is filtered by the ozone layer, at wavelengths smaller than 300 nm can break most of the carbon covalent bonds in the human tissue (an einstein is equal to one mol of photons, ~6E23; 1 cal = 4.184J).


Atmospheric Effects• Thermal effects

– the vacuum prevents heat exchanges by convection, heat transfer caused by movement of molecules from cool regions to warmer regions of lower density; movement of currents in a gas or a liquid.

– heat exchange occurs by conduction (transfer of energy through matter from particle to particle within a substance; e.g., a spoon in a cup of hot soup) and by radiation.

– power absorbed from the direct solar flux + the internal dissipated power = radiated power + stored (or returned) by exchanges during temperature variation.


Atmospheric Effects• Radiation

– for a perfectly conducting passive sphere, the equilibrium temperature T depends only on the thermo-optical properties of the exterior surface, that is essentially its colour: Surface T(° C) absorptivity emissivitywhite paint -75 0.2 0.8black paint +11 0.97 0.9bright gold +155 0.25 0.045


Atmospheric Effects

• The Van Allen belts– charged solar wind particles trapped by the

terrestrial magnetic field:• the inner electrons belt: max 1.5 ~ 2 RE

• the high energy protons belt: max 1.5 ~ 2, up to 4 RE

• the outer electrons belt: max 3.0 ~ 6, up to 7 RE

– the geostationary satellite is at ~6 RE


Atmospheric Effects

• The Van Allen belts– solar flares affect the minority carriers in

semiconductors due to excitation of the electron levels of atoms

– other effects: the optical transmission of glasses, plastics are ionised, degradation of performance of the solar cells

– radiation hardness: increased shield thickness


Atmospheric Effects• SOHO (Solar and Heliospheric Observatory) is a satellite in orbit

around the Lagrange point L1 since 1996, between the Earth and the Sun, at about 150,703,456 kilometers (92 million miles) from the Sun and only about 1,528,483 kilometers (1 million miles) from the Earth (almost four times farther than the moon which is at ~384,000 km - http://sohowww.nascom.nasa.gov/).

• The Herschel Space Observatory became the largest ever infrared space observatory when it was launched in May 2009. Equipped with a 3.5 metre diameter reflecting telescope and instruments cooled to close to absolute zero, after a four-month journey from Earth, Herschel and his little brother Plank will spend a nominal mission lifetime of 3 years in orbit around the Lagrange point L2.


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Atmospheric Effects• Herschel, named after Sir William Herschel who demonstrated in

1800 the existence of infrared light, will be in a 800 000 km Lissajous orbit. His companion, Planck, named after the German scientist Max Plank, the founder of quantum theory, will be in a 300 000 km Lissajous orbit around L2. While Herschel will take the first census of star-forming galaxies throughout the Universe, Plank will study the relic radiation from the Big Bang.

• In 2018 the James Webb Space Telescope will orbit around Lagrange point L2. Main tasks for investigations: cosmology and the structure of the Universe, origin and evolution of galaxies, history of the Milky Way and its neighbours, birth and formation of stars, origin and evolution of planetary systems.


Atmospheric Effects

http://en.wikipedia.org/wiki/File:Lissajous_orbit_l2.jpg

http://upload.wikimedia.org/wikipedia/commons/e/e6/Lissajous_orbit_l2.jpg

http://upload.wikimedia.org/wikipedia/commons/e/e6/Lissajous_orbit_l2.jpg


Atmospheric Effects• The next 9 to 14 year cycle of solar storms will most likely peak in

2013 (use a pencil to mark it on your calendar, it might change!)• The active solar period is characterized by more often violent

eruptions and solar flares on the Sun which shoot energetic photons and highly charged matter toward Earth.

• This activity impacts the Earth’s ionosphere and geomagnetic field, with a potential impact on satellites, GPS availability, ISS activities and even airline communications.

• More auroras, sheets of red and green lights, will be observed.• The increased solar magnetic activity will be reflected in a larger

number of sunspots – dark blotches on the Sun.


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Atmospheric Effects• Atmospheric layers

– troposphere: up to 8 km above the poles & up to 16 km above the equator, has weather, waves: it’s quicker to fly from US to Europe than the other way around!

– stratosphere: up to 50 km, contains the ozone layer which absorbs the Sun’s harmful ultraviolet light

– mesosphere: up to 80 km, protects us from meteorites– thermosphere: up to 500 km, temperature rises to high

values due to absorption of ultraviolet radiation (90-400 km region is also known as the ionosphere)


Atmospheric Effects• Atmospheric layers:

– exosphere: higher than 500 km, merges into the vacuum of space; it is extremely rarefied and is composed mainly of hydrogen and helium.

– effects: • absorption, • scintillation, • polarisation rotation, • dispersion, scattering• frequency change


Atmospheric Effects

Westerlies between 30ºN and 60ºN

Westerlies between 30ºS and 60ºS

Easterlies between 30ºN and 30ºS

The number of Hadley Cells depends on the

speed of rotation

The Sun heats the equator more strongly than the poles. Hot air rises at the equator and flows at higher altitude towards the poles, cold air

flows at low altitude from the poles to the equator. The east-west pattern of winds is due to the rotation of the Earth and the law of

conservation of angular momentum.


Atmospheric Effects• Ground wave propagation: f < 30 MHz, e.g., AM,

propagate along the earth’s curvature and have a direct component and a ground reflected component.

• Ionospheric waves: 30 < f < 300 MHz, e.g., FM, VHF TV, short wave radio, are reflected by the ionosphere and travel much further.

• Tropospheric scattering: 300 MHz < f < 3GHz, the signals are scattered by the troposphere.

• Line of sight: ~3 GHz < f, used in satellite comms, the earth’s atmosphere offers very little resistance.


Atmospheric Effects• Absorption

– as a result of energy absorption by the atmospheric gases. For vertical incidence (90º), pressure = 1 atm, 20º C, the total zenith attenuation at ground level is:

• 22.3 GHz due to resonance absorption in water vapour (1 dB attenuation)

• 60.0 GHz due to resonance absorption in oxygen (around 200 dB attenuation)

– depends on the angle of elevation, temperature and relative humidity


Atmospheric Effects

• Absorption– One favourable window of communications from

28 GHz to 42 GHz where the attenuation is on the order of 0.13 dB/km

– A second favourable window is from 75 GHz to 95 GHz where the attenuation is on the order of 0.4 dB/km


(Courtesy of http://www.ausairpower.net/AC-0500.html)


Atmospheric Effects• Rain attenuation

– the rain rate Rp is defined as the minimum rainfall value [mm/h] that will occur for p% of the time in the region of interest (p = 0.001 => 5.3 min)

– specific attenuation: γ = a(Rp)b [dB/km]– path attenuation: A = γ Lr c– path length: Lr = 4 for 0 < |λES| < 36°

(km) Lr = 4 - 0.075(|λES|-36) for |λES| > 36°


Atmospheric Effects• Rain attenuation

– tables are used for the a,b and c coefficients and for the rain rate Rp,

– Example: Darwin (λES = -12d26m), 12.5 GHza = 0.02, b = 1.383, c = 0.356, R0.01 = 97.4 mm/h

=> γ = 0.02(97.4)1.383 = 11.25 dB/kmLr = 4 kmA = γ Lr c = (11.25)(4)(0.356) = 16 dB


Atmospheric Effects• Scintillation

– is a fading phenomenon with a period from three seconds to several tens of seconds for a time period up to about one and a half hour,

– it is caused by differences in the atmospheric refractive index: appears as an instability in both the phase and amplitude of the signal,

– early afternoon on hot humid days, at low elevation angle and high frequencies (7-14 GHz).


Polarisation• Electromagnetic wave

– E is the magnitude of the electric field– H is the magnitude of the magnetic field– E = HZ0, Z0 = 120πohms

H

EDirection of propagation


Polarisation• Linear polarisation

– the direction of the line traced out by the tip of the vector E determines the polarisation of the wave.

– vertical polarisation = vector E perpendicular to the Earth’s surface. For an arbitrary angle:

E = Ex + Ey

Ex = Ex sin(ωt)

Ey = Eysin(ωt)

The resultant is at an angle α:α = arctan(Ey/Ex)

E is still linearly polarised


Polarisation• Circular polarisation

– the tip of vector E traces out a circle. – this happens when the two components of the

vector E are equal in magnitude but have a constant phase shift of 90°

E = Ex + Ey

Ex = E cos(ωt)

Ey = E sin(ωt)

The resultant is at an angle α:α = ωt

which is not constant in time


Polarisation• Antenna polarisation

– is defined by the polarisation of the wave it transmits

– for maximum transfer power, the polarisation of the receiving antenna has to be aligned to that of the wave it receives

E V = Vmax V = 0E


Polarisation• Antenna polarisation

– an antenna designed to receive a given sense of polarisation will receive no energy from a wave with the orthogonal polarisation

– depolarisation: an orthogonal component from the transmitted polarisation is generated

• ionospheric depolarisation: Faraday rotation (< 10 GHz)• rain depolarisation: differential attenuation

differential phase shift• ice depolarisation (2~5 dB)


Polarisation• Dispersion

– The propagation delay of a radio wave through the ionosphere is a function of frequency. Dispersion is the difference in the time delay between the lower and upper frequencies of the spectrum of the transmitted signal. The delay decreases with increasing transmitted frequency and increasing pulse width, as shown in the following graph for a pulse of width τ[μs] transmitted through the ionosphere with a total electronic content of 5E17el/m2.


Polarisation


Propagation• Scattering

– It occurs when the propagation medium consists of a large number of objects with dimensions that are small compared to the wavelength.

– If the maximum depth of protuberances of the surface is less than a threshold:

hc = λ/8/sin(θ) the surface is considered smooth otherwise is rough (λ is the wavelength, θ is the angle of incidence).


Propagation• Scattering

– Depending on the characteristics and location of scatterers with respect to the receiver, a rough surface can be a source of:– narrowband fading – small path differences, a

few λs, between rays coming from scatterers near the receiver causing phase differences but arriving at essentially the same time - or

– wideband fading – time delays comparable to the symbol period of the transmission.


Propagation• Line of Sight

– The optical line of sight can be expressed as:d = 3.57 sqrt(Kh)

where d is the distance between the antenna and the horizon in kilometers, h is the antenna height in meters and K is a factor that accounts for refraction (~4/3).

– For two antennas:d = 3.57 [sqrt(Kh1) + sqrt(Kh2)]


Propagation• Fresnel Zone:

– Any small element of space in the path of an electromagnetic wave may be considered the source of a secondary wavelet and can have constructive and destructive effects on communications

RS

DSatellite

Receiver


Propagation• Fresnel Zone:

– The attenuation due to obstruction is negligible if there is no obstruction within 0.6 times the radius of the first Fresnel zone at any point between the tx/rx.

R = 17.3sqrt[SD/f/(S+D)] with R in meters, S and D in kilometers and f in GHz.

– Ex.: for a satellite, SD/(S+D) ≈ 1; at 4 GHz, the R is 17.3/2 ≈ 8.7 m => ≈ 5 m clearance from the nearest building or tree (important for small satellite dishes)


Propagation• Free space loss

– it is due to spherical dispersion of the radio wave– d is the distance between the transmitting and

receiving antennas and λ is the signal wavelength

Lp = (4πd/ λ)2

Lp(dB) = 92.4 + 20log10f(GHz) + 20log10d(km)(f = 6 GHz, d = 36000km, Lp = 199.2 dB)


Propagation• Doppler shift:

– Occurs when a single carrier wave is received by a mobile receiver (moving with speed v, at an angle θ) or when a Low Earth Orbit satellite signal is received by a fixed/mobile receiver.

– The received frequency, fR, is the transmitted frequency, fT, changed by an amount called Doppler shift, fD.

fD = (v/c) fT cosθ, where c is 3E8 m/s


Propagation• Doppler shift:

– When the distance between the transmitter and receiver decreases:

fR = fT + fD

– When the distance between the transmitter and receiver increases:

fR = fT – fD

– The receiver must be capable to acquire and track the signal in the above range of frequencies


PropagationAltitude Period Doppler Area(km) (ppm) (radius,km)

200 1h28m 24.8 8081000 1h45m 20.9 234910000 5h47m 6.5 536135768 23h56m4s 0 6027

Q: what is the maximum Doppler shift for Molnya at C band?


Propagation• AWGN:

– The simplest channel model is the additive white Gaussian noise (AWGN) channel. In this channel the desired signal is degraded by thermal noise associated with the physical channel itself as well as electronics at the transmitter and receiver.

– This model is good for fixed space communications and some wire transmissions, such as coaxial cable.

– It is not good for terrestrial wireless transmission or mobile satellite communications.


Propagation• Shadowing:

– Occurs due to obstruction of the signal by trees, buildings which considerably attenuate the direct line-of-sight wave

– It depends on the elevation angle from the mobile terminal to the satellite, the type of vertical or horizontal polarization, frequency and on the type and density of surrounding vegetation or buildings

– The amplitude of the direct wave is approximated by a log-normal distribution


Propagation• Shadowing:

– Typical shadow margin values, in dB, for 35% and 85% tree density function of elevation angle are:

Frequency (MHz) 30º 45º 60º1000 5/9 4/7 3/51500 6/11 5/9 4/73000 9/16 8/11 6/10

– At frequencies lower than 300 MHz, vertical polarized signals are attenuated more than horizontal polarized.


Propagation• Multipath propagation:

– Occurs when the signal is scattered by surrounding structures or waves

– Specular wave is produced by signal reflection from the ground in the direction of the satellite

– Diffuse waves result from various reflections from the surrounding terrain

– Representative types of environment: urban areas, open areas, suburban and rural areas


Propagation• Signal fading:

– the received signal consists of reflected waves of the same frequency with random amplitudes and phases => the signal envelope is a Rayleigh random variable

– the received signal includes also the direct signal => the signal envelope has a Rice distribution

– the received signal consists of a direct and a reflected wave which has a propagation delay, τ, => frequency selective fading with “notches” spaced 1/ τ Hz apart


Propagation• Markov Model:

– A simple channel model is the On-Off model. The two states of the model characterize the channel as being in a good state (non-fade) or in a bad state (fade)

– The bit error rate (BER) is assumed to go to 0 during the good state and to 0.5 during the bad state.

– The model can be extended to four or more states to get a more accurate representation of error patterns measured on specific satellite channels.



good good

bad bad

pq

1 - p

1 - q

p is the transition probability from the good state to the bad state

q is the transition probability from the bad state to the good state

At each time slot there is a single transition



– The probabilities p and q can be derived from the estimation of the mean time spent by the channel in either of the two states:

• E[Tgood] = 0p+1(1-p)p+2(1-p)2p+3(1-p)3p+…= (1-p)/p• E[Tbad] = 0q+1(1-q)q+2(1-q)2q+3(1-q)3q+…= (1-q)/q

where E[Tgood] and E[Tbad] represent mean time and are expressed in terms of the number of time slots.



– The average fading duration, FD, and the average fading rate, FR, can be used to compute the E[Tgood] and E[Tbad] for a given signalling frame period, P, as shown below:

• E[Tbad] = FD / P (time slots)• E[Tgood] = 1 / (FR * P) – FD / P (time slots)

– From the above equations, the p and q probabilities can be calculated and used in the Markov model.



– G is the probability to be in a good state– B is the probability to be in a bad state– Under stationary conditions:

• p * G = q * B• G + B = 1

– From the above equations, • G = q / (p + q) and • B = p / (p + q)


Propagation• A more complicated model for a fading channel:


PropagationAccurate estimates for specific link losses can be made by simulations. The main losses to be considered are:– Multipath Fading Loss – this is the loss due to fading on the

Land, Maritime or Aeronautical channels of the uncodedmodulation used relative to an AWGN channel.

– HPA Nonlinearity Loss – this is the degradation in the BER due to HPA nonlinearity of uncoded modulation

– Adjacent Channel Interference – this is the loss due to both the power spillage from the adjacent channel and spectral regrowth when an adjacent channel passes through the HPA.

– Co–Channel Interference – this is the loss due to receiving an attenuated carrier at the same frequency as the wanted channel.


Model Frequency range Terrain dependence Antenna height above ground

Free space No frequency limitation No terrain dependence. Gives the same transmission loss in all directions.

The model assumes no ground influence.

Longley-Rice 20 MHz to 40 GHz No terrain dependence. Terrain influence is given as a terrain roughness parameter to the model, entered by the operator. Gives the same transmission loss in all directions.

0.5 – 3000 m. The 3000 m above ground level antenna height limitation does not significantly reduce accuracy for higher antenna heights.

ITU-R P.370-7 30 – 1000 MHz Terrain information is taken from the ITU Digitized World Map to determine the path lengths over land and over sea. Gives the same transmission loss in all directions, if the path is wholly over land or sea.

One antenna in the interval 1.5 –40 m and the other antenna 37.5 – 1200 m above ground.

Okumura-Hata/COST-231-Hata

150 – 2000 MHz (no hard limit at 2000 MHz –can be used for 2 GHz cellular applications)

No terrain dependence. The operator can enter a type of environment (urban, suburban, rural etc.). Gives the same transmission loss in all directions. The distance is limited to 1 – 20 km.

One antenna in the interval 30 –200 m and the other antenna 1 – 10 m above ground.

COST-231 – Walfish-Ikegami

800 – 2000 MHz (no hard limit at 2000 MHz –can be used for 2 GHz cellular applications)

No terrain dependence. The operator can enter the type of environment and parameters describing the buildings and streets. Gives the same transmission loss in all directions. The distance is limited to 0.02 – 5 km.

One antenna in the interval 4 – 50 m and the other antenna 1 – 3 m above ground.



ITU-R P.526-6 From about 500 MHz to above 100 GHz. For situations where one or both of the antennas are high above ground (such as in ground-to-air and air-to-air links) it can be used from 100 MHz.

Terrain information taken from the height and terrain classification databases. Gives fully terrain dependent transmission loss, however neglecting the electrical characteristics of the ground and ground reflections.

Valid for all antenna heights.

Detvag-90/FOI 10 kHz to above 100 GHz. Ionosphere propagation is not considered.

Terrain information taken from the height and terrain classification databases. Gives fully terrain dependent transmission loss.

The fast methods (non-GR ground wave) have limitations on the maximum antenna height:Frequency Height30 MHz 300 m100 125300 591000 263000 13Note that for most practical cases the influence of the ground (apart from diffraction) can be neglected above 1 GHz even at low antenna heights.



CRC 30 MHz to above 100 GHz

Terrain information taken from the height and terrain classification databases. Gives fully terrain dependent transmission loss.

Valid for all antenna heights.

ITU-R P.452-9 0.7 GHz to above 100 GHz

Diffraction calculations are performed using the P.526 method, giving terrain dependence. Rain scatter parameters are read from the ITU Digitized World Map. Otherwise the model is not terrain dependent.

The model is intended for stations on the surface of the earth. Antenna heights should be less than a few hundred metres.

ITU-R P.619-1 From about 300 MHz to above 20 GHz. The lower limit is due to neglecting of ionospheric scintillation. The upper limit is due to the modelling of tropospheric scintillation.

No terrain dependence, apart from consideration to shadowing by the earth considered as a sphere.

The model is applicable for earth-space paths, with the space station being at non-geostationary orbit height or above and the earth station being on the surface of the earth, with antenna height less than a few hundred metres.

ITU-R P.676-2 and P.618-6

1 – 350 GHz. P.618-6 for space paths does not include the oxygen gap consideration at 60 GHz.

Not applicable. The transmission loss calculated by the atmospheric attenuation models is added to the loss calculated by the selected propagation model.

No antenna height dependence is included (apart from the satellite height for the space path model). This limits the applicability to heights up to a few thousand metres for terrestrial paths.


Application Frequency Recommended propagation model

Ground-to-ground

<30 MHz, ground wave

Detvag-90/FOI. Quick/Low if terrain data is not available; otherwise Quick/High.

>30 MHz Terrain data available:Detvag-90/FOI, Quick/Low if antenna height conditions are fulfilled. Otherwise Detvag-90/FOI, Advanced, GTD. CRC (if available) is applicable irrespective of antenna heights.No terrain data available:Longley-Rice.For specific services:Broadcast: ITU-R P.370Cellular: Okumura-Hata/COST-231-Hata or COST-231 – Walfish-Ikegami

Ground-to-air <30 MHz, ground wave

Detvag-90/FOI. Quick/High.

30 – 100 MHz Terrain data available: Detvag-90/FOI, Advanced, GTD. CRC (if available) is applicable irrespective of antenna heights.No terrain data available:Longley-Rice

>100 MHz Terrain data available:ITU-R P.526 is the first choice due to its fast calculation speed.Detvag-90/FOI, Advanced, GTD. CRC (if available) is applicable irrespective of antenna heights. No terrain data available:Longley-Rice

Air-to-air >30 MHz Longley-Rice as an overall method at heights where terrain obstructions are not importantITU-R P.526 for cases where the terrain influence due to obstructions are of interest

Earth-to-space >50 MHz ITU-R P.619.

Space-to-space All frequencies Free space.


Large scale fading, m(t), and small scale fading, r(t)


PropagationA small-scale fading model is used for channels in which significant changes in signal amplitude and phase occur as a result of small changes (as small as a λ/2) in the spatial separation between a receiver and transmitter. It manifests through:– time-spreading of the signal (or signal dispersion): the

fading degradation can be frequency-selective or frequency-nonselective also called flat fading,

– time-variant behavior of the channel due to motion: the fading degradation can be fast or slow-fading.


PropagationFor a single transmitted impulse, the time Tm, between the first and last received component represents the maximum excess delay during which the multipath signal power falls to some threshold level below that of the strongest component (~10 dB less). A channel is said to exhibit frequency-selective fading or channel-induced ISI if Tm > Ts. This condition occurs whenever the received multipath components of a symbol extend beyond the symbol’s time duration, similar to the effects of a filter block. Otherwise we have flat fading, there is no interference with the neighbouring received symbols.


PropagationThe coherence bandwidth, f0 ~ 1/Tm, defines the range of frequencies over which the channel passes all spectral components with approximately equal gain and linear phase. Frequency selective channel can thus be defined also by the condition f0 < 1/Ts ~ W, the signal bandwidth.


Propagation

Scintillation effects due toatmospheric disturbances in asatellite link.

Example from the Rayleigh FadingChannels modelling (Chapter 70),“Telecommunications Handbook” .


PropagationThe coherence time, T0, is a measure of the expected time duration over which the channel’s response is essentially invariant. The frequency equivalent is spectral broadening or Doppler spread, denoted by fd ~ 1/T0 also called the fading bandwidth or fading rate of the channel. A fast fading channel is characterised by T0 < Ts, (fd > W) where Ts is the duration of a transmitted symbol. The channel changes a few times during the symbol propagation therefore leading to distortion of the baseband pulse. This can cause a loss in synchronization, filter mismatch and in the end a loss of SNR.


PropagationIn practice, to mitigate the effects of fast fading, instead of fd < W, a stronger condition is used: fd << W.Otherwise, random frequency modulation occurs which translates in an irreducible error rate that cannot be overcome by simply increasing Eb /N0. For voice-grade applications (targeting BER ~ 10−3), the Doppler shift should be fd < 0.01 × W. Therefore, to avoid fast-fading distortion and the Doppler-induced irreducible error rate, the signalling rate should exceed the fading rate by a factor of 100 to 200.


Propagation

Rician Fading Channel Model

Parameters:τ = multipath delay

C/M = carrier to multipath ratio

Bf = fading bandwidth


Propagation

Rayleigh Fading Channels (Chapter 70), “Telecommunications Handbook”


The ozone hole is defined as area of the region with total ozone below 220 Dobson units (describe the thickness of the ozone layer in a column directly above the location being measured). The hole began to form in mid August, and by mid September had reached an area of around 25 million square kilometres, larger than the average for the last decade and remained near this size into early October. It had shrunk to around 20 million square kilometres by mid October and remained a similar size till mid November, when its size dropped rapidly but remained at a few million square kilometres until mid December. It filled by the summer solstice.

September 2011, NASA image courtesy Ozone Hole Watch


http://en.wikipedia.org/wiki/File:Ozone_altitude_UV_graph.svg

The figure shows how far into the atmosphere each of the three types of UV radiation penetrates. UV-c (red, 280-100 nm) is entirely screened out by ozone around 35 km altitude, while UV-a (blue, 400-315 nm) reaches the surface, but it is not genetically damaging.

It is the UV-b (green, 315-280 nm) radiation that can cause sunburn and that can also cause genetic damage, resulting in things like skin cancer, if exposure to it is prolonged.


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Source Coding

Before transmitting images, we compress them, using source coding which requires capacity….Contents:

Channel capacity Huffman coding Arithmetic / Ziv-Lempel coding JPEG/MPEG coding


Channel capacityMessages with a higher probability of occurrence convey relatively little information. Information is proportional to the uncertainty of an outcome and information contained in independent outcomes should add. For a discrete memoryless source (DMS) S, which generates symbols xi with probability Pi, the information content of a symbol, I(xi), is defined as - log2P(xi). The average information produced per symbol is the entropy of the source S defined as:

H(S) = - Σ[P(xi) * log2P(xi)] over all symbols.


Channel capacityThe source entropy H(S) satisfies the following relation: 0 ≤ H(S) ≤ log2m where m is the size of the source alphabet (number of symbols). For a binary source that generates independent symbols 0 and 1 with equal probability the entropy is -½log2½-½log2½ = 1 bit/symbol. A discrete memoryless channel (DMC) is a statistical model with an input X and an output Y. During each signaling interval, the channel accepts an input symbol from X and in response it generates an output symbol from Y.


“discrete” means finite alphabets X, Y; “memoryless” means that the current outputs depends on only the current input and not on any of the previous inputs.x1 y1

x2 DMC with y2

… m inputs and n outputs …xi yj

xm yn

Channel capacity

P(yj|xi)


Channel capacityP(yj|xi) is the channel transition probability, conditional probability of obtaining output yj given the input is xi. A lossless channel is described by a channel matrix with only one nonzero element in each column.The conditional entropy H(X|Y) is a measure of the average uncertainty remaining about the channel input after the channel output has been observed:

H(X|Y) = - Σ Σ [P(xi, yj) * log2 P(xi | yj)]Mutual information is I(X; Y) = H(X) - H(X|Y) bit/sym


Channel capacityThe channel capacity per symbol for a DMC is defined as Cs = max I(X; Y) bit/sym where the maximization is over all possible input probability distributions P(xi)on X. For an Additive band-limited White Gaussian Noise (AWGN) channel with zero mean and the variance σ2 the capacity is:

Cs = max I(X; Y) = ½ log2(1 + S/N) bit/samplewhere S/N is the signal-to-noise ratio at the channel output. For fixed bandwidth B and 2B samples/second:

C = B log2(1 + S/N) bit/second


Channel capacityExample of a lossless channel:


Channel capacityExample of a binary symmetric channel:


Huffman CodingConsider a DMS and a binary code word of ni bits assigned to each symbol xi. The average code word length L per source symbol is ΣP(xi)ni bits per source symbol. The source coding theorem states that for a DMS with entropy H(X), the average code word length L is bounded by the entropy: L ≥ H(X). The code efficiency, η, can be written as: η = H(X)/L. One can design fixed/variable length codes, prefix-free codes, uniquely decodable codes, etc. If Σ2^^(-ni) ≤ 1 an instantaneous binary code exists (Kraft inequality).


Huffman CodingDeveloped in 1952, Huffman coding sorts the elements of the alphabet in order of decreasing probability; it then combines the two lowest probability symbols into a new symbol in a recursive fashion until only two symbols are left. These are assigned the binary bits 0 and 1. The reverse process follows with a new bit added at each step. The rate of the Huffman code, RH, satisfies:

H(S) ≤ RH ≤ H(S) + pmax + 0.086 where pmax is the probability of the most probable symbol. The lower bound is achieved when the pi are powers of two.


Huffman CodingIf k symbols are encoded together, a tighter bound can be achieved:

H(S) ≤ RH ≤ H(S) + (pmax,k + 0.086)/kIn this way, one can get coding rates arbitrarily close to the entropy. The drawback is that, in order to achieve this, the size of the source alphabet has an exponential growth. It also needs to know the source statistics in advance. There is also an adaptive Huffman coding when these statistics are not known but has increased complexity and vulnerability to channel errors.


Huffman Coding


Arithmetic CodingArithmetic coding is based on the fact that the value of the cumulative density function (cdf) FX(x) of a sequence x is distinct from the value of the cdf for any other sequence of symbols. By simply ordering the sequences such that xi < xj if i < j, then any element in the set defined as [FX(xi-1), FX(xi)] can be used as a unique tag for the sequence xi. For a sequence of length k the bounds are: H(S) ≤ RA ≤ H(S) + 2/kIt has an advantage when long sequences are encoded or there is a substantial imbalance in source probabilities.


Universal CodesWhen the source statistics are not known or are variable universal coding schemes are required. An example is the Ziv-Lempel codes which are dictionary-based codes that encode strings of symbols by sending information about their location in a dictionary. The dictionary is seeded with the letters of the source alphabet and new patterns of longer and longer strings are added during coding. It is used by the UNIX compress command or in the .gif image compressed file format (http://web.mit.edu/c_hill/www/Lempel-Ziv.pdf)


Universal Codes“The basic idea is to parse a sequence into distinct phrases, and then establish codewords for each of these phrases. We start with the shortest distinct phrase at the beginning of the sequence of data, and then continue by taking each subsequent phrase that is unique from those before it. To encode these phrases, we place them in a dictionary, and the next time we need to use a phrase, we just send its number, as opposed to the entire phrase.Consider the sequence:

ABBABBABBBAABBBABABBB


Universal CodesUsing the process described above, our first distinct phrase at the beginning of the sequence is clearly the single letter A.

A|BBABBABBBAABBBABABBBNow we take the next shortest distinct phrase that we have not already seen. Here this is the single letter B.

A|B|BABBABBBAABBBABABBBContinuing in this manner, we get the following:

A|B|BA|BB|AB|BBA|ABB|BAB|ABBB|


Universal CodesNow, to encode this parsing, we simply place the phrases into a dictionary as described above, and then refer to them each subsequent time by their number:1 2 3 4 5 6 7 8 9A B BA BB AB BBA ABB BAB ABBB 0A 0B 2A 2B 1B 4A 5B 3B 7BIn this arrangement, the first row gives the dictionary number of each phrase, the second row gives each phrase, and the third row gives the codeword of each phrase.”


b c c a c b c c c c c c c c c c c a c c c aA = a,b,c

Address Entry

b

0 0, null1 0, a2 0, b3 0, c4 2, c [b

c]c transmit 2 create 4: 2,c

5 3, c [c c]

c transmit 3 create 5: 3,c6 3, a [c

a]a transmit 3 create 6: 3,a

7 1, c [a c]

c transmit 1 create 7: 1,c8 3, b [c

b]b transmit 3 create 8: 3,b

9 4, c [b c c] c c transmit 4 create 9: 4,c10 5, c [c c c]c c transmit 5 create 10: 5,c11 10, c [c c c

c]c c c transmit 10 create 11: 10,cc c c c transmit 11 create 12: 11,c 12 11, c [c c c c c]a c transmit 6 create 13: 6,c 13 6, c [c a c]c c a transmit 10 create 14: 10,a 14 10, a [c c c a]

transmit 1

Courtesy of www.sis.pitt.edu/~pmunro/is2140/LZexample.ppt


JPEG encoding

JPEG baseline decoder block diagram

8×8 blocks

FDCT Quantizer Entropy Encoder

Table Specifications


Source Image Data

Compressed Image Data

IDCTDequantizer



Compressed Image Data

Entropy Decoder

JPEG baseline encoder block diagram

Reconstructed Image Data


• 2D 8×8 DCT (FDCT)

64 pixels in space domain 64 DCT coefficients in frequency domain

∑∑= =

++=

7

0

7

0 16)12(cos

16)12(cos),()()(

41),(

x y

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JPEG encoding


MPEG-2

DCT QuantizerDigitizer

MPEG-2 encoder

Buffer

Rate controller

Inverse

Quantizer

Inverse

DCT

Motion Compensator

Variable Length Coding

Predicted image

Difference image

Motion Estimator

Reconstructed image

R, G, B conversion to luminance, two chrominance components and sync


Defines coding of all types of multimedia information: new video compression techniques new audio & voice encoding techniques allows more interaction by the user it is scalable it is object based, allows scenes to be composed of

natural and synthetic objects

MPEG-4


Objects: a scene is composed of audio-visual objects (AVO) natural objects (images, video, voice) or synthetic

objects (text, animation, video) objects are given positions in 3-D space can be encoded/decoded separately to achieve

better compression rate and different quality can be dynamically moved, changed and created.

MPEG-4


Objects: there is a specific new language used for scene

description, binary format for scenes (BIFS) it is used in real-time streaming in its own stream

with pointers to AVO streams objects descriptors (OD) are used to identify objects

placed in Elementary Streams (ES) ODs contain Elementary Stream Descriptors (ESD)

to identify necessary decoders.

MPEG-4


MPEG-4ISO MPEG-4 Part 10 (AVC) or ITU-T H.264

Video Encoder (source: www.vcodex.com)


MPEG-4“The input frame Fn is processed in units of a macroblock (corresponding to 16x16 pixels in the original image). Each macroblock is encoded in intra or inter mode. In either case, a prediction macroblock P is formed based on a reconstructed frame. In Intra mode, P is formed from samples in the current frame n that have previously encoded, decoded and reconstructed (note that the unfiltered samples are used to form P). In Inter mode, P is formed by motion-compensated prediction from one or more reference frame(s). In the Figures, the reference frame is shown as the previous encoded frame F’n-1 ; however, the predicton for each macroblock may be formed from one or two past or future frames (in time order) that have already been encoded and reconstructed. The prediction P is subtracted from the current macroblock to produce a residual or difference macroblock Dn. This is transformed (using a block transform) and quantized to give X, a set of quantized transform coefficients. These coefficients are re-ordered and entropy encoded. The entropy-encoded coefficients, together with side information required to decode the macroblock (such as the macroblock prediction mode, quantizer step size, motion vector information describing how the macroblock was motion compensated,etc) form the compressed bitstream.” (source: www.vcodex.com)


MPEG-4ISO MPEG-4 Part 10 (AVC) or ITU-T H.264

Video Decoder (source: www.vcodex.com)


MPEG-4“The decoder receives a compressed bitstream from the network abstraction layer (NAL). The data elements are entropy decoded and reordered to produce a set of quantized coefficients X. These are rescaled and inverse transformed to give Dn’ (this identical to the Dn’ shown in the Encoder). Using the header information decoded from the bitstream, the decoder creates a prediction macroblock P, identical to the original prediction P formed in the encoder. P is added to Dn’ to produce uF’n which this is filtered to create the decoded macroblock F’n.

It should be clear from the Figures and from the discussion above that the purpose of the reconstruction path in the encoder is to ensure that both encoder and decoder use identical reference frames to create the prediction P. If this is not the case, then the predictions P in encoder and decoder will not be identical, leading to an increasing error or “drift” between the encoder and decoder.” (source: www.vcodex.com)


Channel CodingContents: Block Codes Convolutional Codes Turbo-like Codes, (STEC Codec) Joint Source and Channel Coding Turbo source coding Packet Layer Coding Network Coding


Channel CodingSource Source

Encoder

Channel Encoder Modulator

Channel

Sink SourceDecoder

Channel Decoder Demodulator

Signal propagation + noise => errors; to reduce or eliminate the errors we either increase the

transmitted power or introduce some protection!


Why should one use channel coding?

A BPSK/QPSK uncoded signal requires a signal to noise ratio (Eb/N0) of 10 dB to achieve a bit error rate BER less than 1E-5.

If convolutional codes are used, the Eb/N0 is ~5 dB.

If turbo-like codes are used, the Eb/N0 is ~1.0 dB.

(Remember that 3 dB saving is equivalent to reducing to half the transmitted power!)

Channel Coding


“This page contains several computer programs, written in C/C++ language (and some Matlab scripts), that implement encoding and decoding routines of popular error correcting codes (ECC), such as Reed-Solomon codes, BCH codes, the binary Golay code, a binary Goppa code, a Viterbi decoder and more.”

http://www.eccpage.com/

Channel Coding


Channel CodingError Control Coding• One way: forward error control coding

– Block codes – Convolutional codes – Viterbi decoding– Turbo-like codes – MAP/SISO decoding– Joint source and channel coding– Packet and Network Layer layer coding

• Two way: automatic repeat request (ARQ), requires a second satellite channel for feedback– Stop and wait, Go back N, Selective repeat


Channel Coding• For memoryless channels, the capacity doesn’t

change if feedback is available because the capacity is calculated for infinite block lengths.

• For finite block lengths, there is a gap from capacity to the maximum achievable bound which increases with the shortening of the block size.

• For finite block lengths, feedback, variable length coding and trellis termination can significantly impact the performance.


Channel Coding• Example: same efficiency and probability of

error can be achieved by the following block lengths:– BL = 3100 bits when no feedback is available– BL = 200 bits, when decision feedback and variable

length coding is available– BL = 20 bits, when decision feedback, variable

length coding and trellis termination is available.• There is a significant difference in the delay

associated with the three cases described above!


Channel CodingCoding gain in AWGN channel is a function of the minimum Euclidian distance of the code, that is the minimum distance in the signal space between any two codewords. When operating at rates below the channel capacity, the probability of error can go to zero. The larger the minimum Euclidian distance is, the better the code performs in AWGN channels.It is possible for codes designed for high-SNR channels to have a negative coding gain at low SNRs: the spreading of the information bit energy over the larger number of coded bits can not be compensated by the extra redundancy provided by the code.


Channel CodingIn fading channels, one can combine a good AWGN channel code with interleaving in order to increase the time diversity. This allows similar performance as to the maximum ratio combining diversity when the diversity order equals the minimum Hamming distance of the code (Hamming distance of two codewords is the number of coded symbols that differ between the two codewords).Maximizing the Hamming distance and interleaver size improves the performance of a code in fading channels.A Rayleigh, Rician or just a simple ON/OFF Markov model can be used to characterize a fading channel (e.g., heavy rain, shadowing, blocking or scintillation).


Block Codesk

n

information bits coded bits

Singelton bound: the minimum distance of an (n, k) block code is upper bounded by:

dmin ≤ n – k + 1The minimum distance of a block code, dmin, is the smallest Hamming distance between any two codewords.


A code allows to correct up to t errors and to detect emore errors if 2t + e < dmin. A packet error occurs if the received block has more than t errors. Maximum distance separable codes, e.g., Reed-Solomon (n, k, t) code, reach the Singleton bound: dmin = n – k + 1. RS codes operate on symbols of m bits; the maximum length of a RS code is n = 2m - 1 sym.For a Gaussian channel or a binary symmetric channel with bit error probability pb, the error probability of a code symbol is ps = 1 – (1 - pb)m where m is the number of bits per code symbol.

Block Codes


Assuming independent symbol errors, the packet error distribution is:

P(i, n) = (n i)(ps)i(1 – ps)n-i

Therefore, the packet error probability is:Pp = 1 - Σ P(i, n) for i = 0 to t

Ex: RS codes are used in CDs, space communications.Calculate the packet error rate for the RS(255,223,16), using 8-bit symbols, for BPSK at Eb/N0 = 5 dB. Use pb = Q(sqrt(2*k/n*Eb/N0)) where Q(x) is defined as 1/sqrt(2π)*integralx to ∞ (exp(-z2/2)dz).

Block Codes


A code C(n, k, d) is set to be a perfect code if it can correct exactly t errors or less and not a single codeword with more than t errors, d = 2t + 1. It has also to satisfy the condition: |C|Σ (n i) = 2n with i from 0 to t, where (n i) = n!/(i!(n-i)!) and |C| = 2k for a binary code.

Ex: C(23, 12, 7) binary Golay code has dmin = 7, so t = 3.

Ex: C(n, 1, n) repetition code for odd n is a perfect code that can correct (n-1)/2 errors.

Block Codes


Ex: (7, 4) Hamming code has n = 2m – 1, k = 2m – m – 1, so n – k = m = 3 redundant bits. The minimum distance of all Hamming codes is dmin = 3, so only t = 1 error in a codeword of n = 2m – 1 symbols can be corrected. For C(7, 4, 3), the Hamming bound is also reached:

24Σ (7 i) for i = 0 to 1 = 24 (1+7) = 27= 2n

The exact probability of error is given by:Pe = Σ (n i)(pb)i(1 – pb)n-i with i from t + 1 to n,where (n i) = n!/(i!(n-i)!)The bit error probability, Pb, can be estimated as:

Pb ~ Pe * dmin / n

Block Codes


The free distance of a convolutional code, df, is the smallest number of different code bits occurring in any two different paths. For BPSK modulation in a Gaussian channel and soft decision decoding, the error probability of two sequences differing in j positions is given by the formula: Pj = 0.5erfc[sqrt(jEs/N0)] = Q[sqrt(2jEs/N0)]

An upper bound of the bit error probability can be found: Pe < (1/k)ΣwjPj where j is from d to ∞, wj is the number of paths having distances j, while k is the number of information bits encoded at a time to produce n coded bits.

Convolutional Codes


The asymptotic coding gain of a binary convolutionalcode, G, can be defined as:

G = df *(k/n). where k/n is the code rate of the binary code. If N is the number of paths which are separated by df, as with block codes, the probability of decoding error is:

Pe ~ N*df *Q[sqrt(2*G*Eb/N0)]

Please note that in order to find df, one has to find out the wj distribution, which means that similar work is required to calculate either the Pe or the bound.

Convolutional Codes


Convolutional Codesht

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Convolutional Codes

g(1) = 5O = (1 0 1); g(2) = 7O = (1 1 1)

D1di

pi

D0

qi

x

y

s

S X=0 X=1

Y=0 0 1

Y=1 1 0

Modulo 2 addition

D is a one bit delay element


Convolutional CodesState at time i State at time i+1

00

01

10

11

d=0 =>q=0, p=0

d=1 =>q=0, p=1

00

01

10

11

D1D0 D1D0

State 0:

State 1:

State 2:

State 3:


Convolutional Codes

g(1)1 = (1 1);g(1)

2 = (0 1)

g(2)1 = (0 1);g(2)

2= (1 0)

g(3)1 = (1 1);g(3)

2 = (1 0)


In a noiseless system the transmitted “path” through the trellis isreceived without any errors. When noise is present, some codedbits can be reversed, fact that leads to a broken “path”: somecombinations of coded bits are impossible to be connected on acontinuous “path”.

The best the receiver can do is to find the most likely “path” inthe trellis that is the closest to the received sequence of bits. Inthis way the coded bits affected by noise are corrected by takinginto account the history embedded in the “path”. The tool toachieve this is the Viterbi decoder.

The higher the number of states, the better the performance is!

Convolutional Codes


Convolutional Codes

00

01

10

11

i i+1 i+2 i+3 i+4


The operation of a turbo-like codec relies on the followingideas: the use of uncorrelated inputs, the divide and conquerprinciple and the iterative processing of information.

The information bits to be transmitted are stored in a memory inorder to be scrambled (interleaved) to produce two“uncorrelated” sequences that are then encoded and transmitted.

This concept is the key to the exceptional performance of turbocodes. The type of interleaver and its size plays a significant rolein the performance that can be achieved.

Turbo-like Codes


Given that the interleaver used is large, the actual encoders can be kept simple and still have a very large number of states associated with the trellis of the turbo code. Therefore, the turbo decoder can be implemented using two simple state machines that operate on each sequence.

The information produced by the decoders contains not only the decoded message but also the degree of confidence in the decision (soft output). Binary hard outputs are replaced by real number soft outputs: a high positive number indicates a higher confidence in decoding a ‘1’, whereas a high negative number indicates a higher confidence in decoding a ‘0’.

Turbo-like Codes


If the 2 memory cell shift register is replaced with a 1000 memory cell shift register, the Viterbi decoder would be required to investigate a huge number of possible states (21000

states, which is a one followed by 301 zeros).

In a turbo encoder of 1000 memory cells, 996 represent the memory used for interleaving, the two component encoders using 2 cells each. Thus the number of possible states to be searched by each elementary decoder is kept small, only 22 = 4 states, but with a significant increase in performance.

Turbo-like Codes


Turbo-like Codes

D D D D

INT

D D D D

di

pi

qi

di

Parallel Turbo Encoder

Mul

tiple

xer


Turbo-like Codes

Hybrid Turbo Encoder

Encoder1 Encoder2INT

INT Encoder3

Serial Turbo Encoder


Bit-interleaved coded modulation is a technique in which the encoder output is interleaved before being sent to the modulator or constellation mapper. If this technique is applied to high order modulations using Gray mapping, the properties of the code are preserved regardless of the modulation used. Serial concatenated codes have very low error floor. Their best design is achieved when the lowest possible rate code is used for the outer encoder in order to maximise the interleaver gain (this gain increases exponentially with the outer code free distance). Therefore the inner encoder should be a simple rate 1 recursive encoder; this feature is useful when high data rates are required.

Turbo-like Codes


Turbo-like Codes

Turbo Encoder PuncturingMapper

andModulator

Channel

DemodulatorLLRBit

EstimatorTurbo Decoder

d dpq

I, Q

I*, Q*d*p*q*

d’

Coded Communication System


Turbo-like Codes

Interleaver De-Interleaver

De-Interleaver

Output

extrinsic information

extrinsic information

DEC1 DEC2dk*

pk*

di* qi*

Generic Turbo Decoder


Decoder DEC1 provides a soft output that is a measure of the reliability of each decoded bit. From this reliability information, the extrinsic information is produced, which does not depend on the current input to the decoder. This extrinsic information, after interleaving, is passed on to DEC2 that uses this information to decode the interleaved bit sequence.

The performance of a turbo coding scheme improves as the number of decoder iterations is increased. However, the coding gain from one iteration to another, decreases with the number of iterations. As each iteration involves two decoding stages, the overall complexity depends on how efficiently the decoding algorithm is implemented.

Turbo-like Codes


Turbo-like Codes


Turbo-like CodesIP

N P

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t 42-

151

Turbo Codes can achieve capacity for large block

sizes !


Turbo-like CodesIP

N P

rogr

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t 42-

151


Bounds for the AWGN channel, SNR = 0 dB, Probability of block error of 10-3

“Channel Coding Rate in the Finite Blocklength Regime” Yury Polyanskiy, H. Vincent Poor and Sergio Verdú,

IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 56, NO. 5, MAY 2010


Normalized rates for various practical codes over AWGN, Probability of block error of 10-4

“Channel Coding Rate in the Finite Blocklength Regime” Yury Polyanskiy, H. Vincent Poor and Sergio Verdú,

IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 56, NO. 5, MAY 2010


The Quadratic Permutation Polynomial (QPP) interleaver is used in 3GPP LTE. For an information block size N, the x-th interleaved output position is given by П(x) = (f2x2+f1x) mod N; 0< x,f1,f2< N.This can be computed recursively as П(x + 1) = ((f2x2 + f1x) + (2f2x + f1 + f2)) mod N = (П(x) + Г(x)) mod N where Г(x) = (2f2x + f1 + f2) mod N, and it can also be computed recursively as: Г(x + 1) = (Г(x) + g) mod N, where g = 2f2.

Turbo-like Codes

“Configurable and Scalable High Throughput Turbo Decoder Architecture for Multiple 4G Wireless Standards”


The QPP interleaver is a maximum contention free and vectorizableinterleaver that allows various parallelism factors M for the decoder implementation – see table below. In this case M can be any factor of the block size N. This means that M parallel decoders can store and fetch data from M memories without contention. A similar performance can be achieved by the Almost Regular Permutation (ARP) interleaver which is used in the WiMAX standard.

Turbo-like Codes

“Configurable and Scalable High Throughput Turbo Decoder Architecture for Multiple 4G Wireless Standards”


“Field Experiments on MIMO Multiplexing with Peak Frequency Efficiency of 50 Bit/Second/Hz Using MLD Based Signal Detection for OFDM High-Speed Packet Access, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 26, NO. 6, AUGUST 2008”

In the field experiments conducted in the Yokosuka ResearchPark (YRP) district of Yokosuka city, Japan, a top of 4.92 Gbps in a 100-MHz channel bandwidth was achieved in a downlink OFDM radio link, centre carrier frequency of 4.635 GHz, at an SNR<30 dB. The bandwidth efficiency was ~50 bit/second/Hz. A12-by-12 MIMO multiplexing was used, 64QAM data modulation, and turbo coding with the coding rate of R = 8/9 at the average speed of 10 km/h under non-line-of-sight (NLOS) conditions.

A similar throughput of 4.92 Gbps at the speed of 30 km/h was achieved at an SNR only ~0.5 dB higher.

Turbo-like Codes


Turbo-like CodesUnequal Error Protection (UEP)

DC bits AC bits

DC AC DC AC DC AC …...

Header

HeaderOriginal JPEG codestream

Data partitioned JPEG codestream

[1] W. Xiang, S. A. Barbulescu and S. S. Pietrobon, “Unequal error protection applied to JPEG image transmission using Turbo codes”, in Proc. IEEE Information Theory Workshop (ITW’2001), Cairns, Australia, pp. 64-66, Sept. 2001.


Turbo-like Codes

Turbo Diversity Scheme (TDS)

[2] W. Xiang and S. A. Barbulescu, “Turbo diversity scheme applied to JPEG image transmission”, Proceedings using Turbo codes”, in Proc. IEEE Information Theory Workshop (ITW’2001), Cairns, Australia, pp. 64-66, Sept. 2001.


STEC codec


STEC codecPrivate links

Interleaver Table

(RAM)

Load Designed and

controlled by the user and not by the

codec supplier

It is not specific to the S-TECTM codec; the user has 100%

control of the interleaver


STEC codec


Joint source-channel codingWhy should one consider joint source-channel coding?

• independent source and channel coding can be optimum based on the Shannon Separation Principle on the assumption that the information sequence length goes to infinity

• This implies:• infinite delay and,• infinite complexity.

• In practical systems, the above assumption is not true.


Joint source-channel codingShannon’s “Joint Source-Channel Coding Theorem with Fidelity Criterion” states the following:

“For a given memoryless source and a given memorylesschannel with capacity C, for sufficiently large source block lengths, the source can be transmitted via a source-channel code over the channel at transmission rate of r = Rc/Rssource symbols/channel symbols (Rc = channel coding rate, Rs = source coding rate) and reproduced at the receiver end within an end-to-end distortion given by D if

r * R(D) < C, where R(D) is the rate-distortion function.”


Joint source-channel codingIn the case of discrete binary non-uniform independent and identically distributed source with distribution p0, we have D = Pe (BER). So R(D) = R(Pe) is defined as:

hb(p0) – hb(Pe) if 0 ≤ Pe ≤ minp0, 1-p0or

0 if Pe > minp0, 1-p0

where hb(.) is the binary entropy functionhb(x) = -x*log2x – (1-x)*log2(1-x)


RVLC = reversible variable-length codes, free distance = 2

JPEG/MPEG Encoder

Turbo Encoder

JPEG/MPEG Decoder

Turbo Decoder

WirelessChannel

Modulator

Demodulator

(using RVLC)

iterative decoding

Iterative source-channel decoding


Iterative source-channel decoding• State Transition Probabilities (STP) algorithm

– The message bits out of a source encoder have normally non-uniform probability density function (p.d.f)

– Entropy coding like VLCs can be used to exploit this redundancy and hence achieve the rate as close as to the entropy of the source

– A-priori information “hidden” in variable-length codes can be utilized by the iterative source-channel codec using the STP algorithm


Bit-trellis for VLCsIterative source-channel decoding


• Generic formula to derive STPs from tree presentation of VLCs

• STPs can be naturally embedded into MAP decoding algorithm because the algorithm only needs a small modification to incorporate STPs. As shown below, the last term in Branch Metrics is the STPs. ',, mmi

kδ

∑∑

∈

∈+

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)(

),(1

1)|,(

k

k

Sg

iSfkkk P

PmSidnSP

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,, '

mSidmSPirL kkkrkckmmi

k ==== +χδ



Iterative source-channel decoder



Turbo Source CodingWhy should one consider turbo source coding?

• The source encoder eliminates redundancy in the information stream in order to minimise the amount of data required to be transmitted. The channel encoder increases redundancy which is used to recover the data from the noise. • Until now, the source encoding was done at the application layer, using different software packages e.g., compress, gzip, bzip2, etc, based on Lempel-Ziv algorithm, Huffman algorithm.• Much faster compression/decompression, requires no extra software at the application layer, can be performed on applications which are not usually compressed, could be extended to image compression.


Turbo Source CodingHow does it work?

• The source of length ‘n’ and entropy H(U) can be perfectly reconstructed from a binary sequence of length ‘k’ and entropy n * H(U) for sufficiently large ‘n’ (very large blocks!) • This means that lossless data compression can be achieved by using a turbo encoder followed by puncturing 1- H(U)/2 percentage of the coded bits• When noise is present in the channel, less bits are punctured to allow extra redundancy which is used in the decoding process to recover the data.


Turbo Source Coding


Packet Layer CodingThe rationale behind the Packet Layer Coding (PLC) technique, also known as Upper Layers Forward Error Correction (UL-FEC):

• The physical layer channel coding can handle small-scale fading using interleaver based techniques.

• PLC uses large codewords which span over multiple data packets so it can offer better protection against long fading events.

(Globecom 2009, “Packet Coding Performance with Correlated Fading and Shadowing”, Marco Papaleo et al)


Packet Layer CodingThe PLCs used are simple block codes which encode kinput packets into n > k coded packets, each packet having also a cyclic redundancy check (CRC).The packet layer decoder operates only on those packets that pass the CRC check, therefore the channel model is equivalent to a Binary Erasure Channel. The most popular codes used as PLCs are Reed Solomon, LDPC and Fountain codes. The RS code are the best, being MDS codes, they can decode successfully if at least k correct input packets are received over a set of n packets.


Packet Layer CodingPLCs are used in the DVB-RCS+M, the return link, an extension of the DVB-RCS standard for mobiles.(ETSI EN 301 790 V1.5.1 “Digital Video Broadcasting (DVB): Interaction channel for satellite distribution systems,” May 2009).

DVB-RCS+M implements the support of the delivery of broadband mobile satellite services (MSS) to collective terminals mounted on mobile platforms such as airplanes, ships, trains, busses, and vehicles. The DVB-S2 waveform in the forward link can now be spread. The return link uses the multi-frequency time division multiple access (MF-TDMA) and a new SCPC as the forward link.


Packet Layer Coding


Packet Layer Coding

Satellite Interactive Network


Packet Layer CodingThe spectrum spreading of the DVB-S2 is an option in the forward link that can be used to mitigate interference to and from adjacent systems, and countermeasures for mobile propagation characteristics.

The Return Channel Satellite Terminal (RCST) uses a turbo (double binary Circular Recursive Systematic Convolutional) and a concatenated scheme of CC (rate ½ K=7) and RS (255, 239, 8) codes, each with a by-passable CRC-16 code for error detection.


Packet Layer CodingThe RCST has an additional forward error correction option that can be implemented in the link layer (Link Layer FEC) with specific packet encapsulation schemes.

LL-FEC is introduced to support reception in situations of high Packet Loss Ratio (PLR) at the Multiple Protocol Encapsulation level, for mobile channels when the speed is too high and/or the signal-to-noise ratio is too low. It may also occur due to obstruction, blockage, or other situations in which the line of sight is interrupted.


Packet Layer CodingThe LL-FEC frame is composed from the Application Data Table (ADT) made of Layer 3 datagrams, e.g., IP packets, plus possible padding, and the FEC Data Table, the parity data of the code.

The LL-FEC can use a Raptor code (version of Fountain codes) for LL-FEC frame ADT sizes up to 12 Mbytes or the MPE-FEC Reed-Solomon code for LL-FEC frame ADT sizes up to 191 Kbytes. The chosen code is identified in the forward link signalling.


Packet Layer CodingExample: We assume a terminal moving at a speed of ν km/h, transmitting with a carrier frequency f0. The resulting maximum Doppler shift fd is given by: fd = f0 * ν / cwhere c is the speed of light. We assume that one physical layer codeword, TCW, is mapped into one packet layer symbol of duration Ts. The simulations shown here use a constant Ts = 0.001s. The channel coherence time is defined as: Tc ~ 0.5/ fd.


Packet Layer CodingExample (cont): We assume that the small scale fluctuations of the channel are slow with respect to TCW, the performance of physical layer can be computed considering only the first order fading statistics (quasi-stationary condition): Tc » TCW

Codeword error rate (CER) in a Rayleigh fading channel for different values of fdTs for MDS codes are shown in the following graph. Analytical results are in solid lines and numerical results are in dashed lines. There is a ~3 dB improvement for a Rice channel (line of sight present).


Packet Layer CodingExample (cont):


Network CodingNetwork coding field started in 2000 with a key paper thatproved it can increase the network capacity comparedwith using routing alone. It is known that for point-to-point communication, source separation coding, whereeach source is treated independently, is optimal.In a satellite network which relays data between multipletransmitters and multiple receivers, a satellite may encodea number of received packets, possibly from more thanone transmitter. Similarly, a receiver may decode packetstransmitted by possibly more than one satellite.(R. Ahlswede, N. Cai, S.-Y. R. Li, and R. W. Yeung, “Network information flow,”IEEE Trans. Inf. Theory, vol. 46, no. 4, pp. 1204–1216, Jul. 2000)


Network CodingNetwork coding can also improve the efficiency of abroadcasting station (BS) to user equipment (UE) ascompared to traditional ARQ schemes. At higher layers, apacket is either error free or it is discarded and aretransmission is requested. The BS collects all therequests from all UEs and before retransmission, itdivides the set of erased blocks into subsets such that nomore than one erased block is in the subset. Theadvantage comes from the fact that the erased blocks in asubset are encoded combined using modulo-2 addition (orother network code) into a single block for transmission.


Network Coding

Lars Rasmussen et al, “Efficient Network Coding for Wireless Broadcasting”, WCNC 2010


Network CodingFor example, assume that in a conventional ARQ systemwith 2 users, from a sequence of 6 packets blocks I1, I2, I3,I4, and I6 are received in error and are requested forretransmission, making a total of five retransmittedblocks. This particular error matrix for the 2 users is:

E1 = 1 0 0 1 0 1 and E2 = 0 1 1 0 0 1Network coding reduces the number of blocks we need toretransmit to only three (encoded) blocks I1 ⊕ I2, I3 ⊕ I4and I6. Assuming the retransmissions are receivedcorrectly, both UEs can retrieve the respective erasedblocks through simple modulo-2 addition.


Link Analysis

Content: Equivalent Isotropic Radiated Power (EIRP) Received Signal Power Noise Power at the receiver input The Uplink The Downlink Station-to-station link


Logarithmic Units: decibels• A power ratio of P1/P2 expressed in bels is

log10(P1/P2) bels

• The same power ratio of P1/P2 expressed in decibels is10log10(P1/P2) dB

• A power expressed in decibels relative to 1 W is shown as dBW. For example, 50 W expressed in decibels relative to 1 W would be equivalent to:

10 log10(50/1) ≈ 17 dBW

• A power expressed in decibels relative to 1 mW is shown as dBm. For example, 50 W expressed in decibels relative to 1 mW would be equivalent to:

10 log10(50/0.001) ≈ 47 dBm


Logarithmic Units: decibels

• The ratio of two voltages V1/V2 expressed in decibels is20 log10(V1/V2)

because power is proportional to voltage squared• A voltage of 0.5 V expressed in decibels relative to 1V is

20 log10(0.5/1) ≈ -6 dBV

• A voltage of 0.5 V expressed in decibels relative to 1µV is20 log10(0.5/10-6) ≈ 114 dB µ V

• Only voltage and current have the factor of 20 in front of the logarithm


Logarithmic Units: decilogs• The ratio of any two like quantities can be expressed in

logarithmic units called decilogs. For example, the ratio of two temperatures T1 and T2 can be expressed as:

10 log10(T1/T2) decilogs

However the name decilog is seldom used and it is common practice to call the decibel equivalent.

• For example a temperature of 290 K would be given as:10 log10(290/1) ≈ 24.6 dBK

• A bandwidth of 36 MHz is equivalent to:10 log10(36 x 106 /1) ≈ 75.6 dBHz

• Boltzmann’s constant, k = 1.38 x 10-23 J/K10 log10k = -228.6 dB (or dBJ/K)


EIRP

• isotropic antenna: has the same radiated power in any direction

• antenna gain, G(θ), is the ratio of power radiated (or received) per unit

solid angle by the antenna in a given direction θ to the power radiated (or received) per unit solid angle by an isotropic antenna fed with the same power.


EIRP• the maximum gain is in the direction of

maximum radiation, the electromagnetic axis of the antenna called boresight:

Gmax = (4π / λ2)Aeff = (4π / λ2) η A = η(π D / λ)2

Gmax, dBi = 10 log[η(π D / λ)2]

λ = c/f, c is the velocity of light, 3E8 m/s, f is the frequency of the wave, D is diameter of an antenna with a circular aperture, A = π D2 / 4, and η is the antenna efficiency


EIRP

• angular beamwidth is the angle defined by the directions corresponding to a given fallout with respect to the maximum value

• the 3 dB beamwidth: θ3 dB = 70(λ/D) (degrees) (as defined on the next slides)Gmax = η(70π / θ3 dB )2 = 29000/ (θ3 dB )2, for η =0.6

θ3 dB (deg): 0.1 1 10 Gmax (dB): 65 45 25


EIRP

“Satellite Communications Systems” Maral & Bousquet

θ3 dB = 70(λ/D)


EIRP

“Satellite Systems for Personal and Broadband Communications” Lutz, Werner & Jahn

2θ3 dB = 70(λ/D)


EIRP

• power radiated per unit solid angle by an isotropic antenna fed from a radiofrequency source of power PT is: PT / 4π

• for an actual antenna: (PT / 4π)GT

• power received at distance R by an area A is:PR = (PT / 4π)GT (A/R2) = (PTGT / 4πR2)A= ΦA

• PTGT = EIRP • Φ = PTGT / 4πR2 = power flux density


Received signal powerPR = (PTGT / 4πR2)AAReff = GR/(4π/ λ2)=> PR = (PTGT / 4πR2) GR/(4π/ λ2) =

= (PTGT ) (λ / 4πR)2 GR == (PTGT ) (1 / LFS)GR

where LFS = (4πR / λ)2 is called free space lossPR = EIRP - LFS + GR (dBW)


Received signal power

• a geostationary satellite, φSS , R0 = 35,786 km• earth station latitude λES , longitude: φES • LFS = (4πR0 / λ)2 (R/R0)2

where (R/R0)2 = 1 + 0.42[1 - cos(λES )cos(Δφ)] and Δφ = φES - φSS.

The (R/R0)2 is between 1 and 1.356 (0 to 1.3 dB)

Frequency (GHz) 1 5 10 20LFS(R0) (dB) 183 197 203 209



• attenuation in the atmosphere: L = LFS LA

• losses in transmitter feeder: PTX = PT LFTX

• losses in receiver feeder: PRX = PR/LFRX

• de-pointing losses (dB): LT = 12(θT/ θ3dB)2

LR = 12(θR/ θ3dB)2

• polarisation miss match losses: LPOL



PRX = [(PTXGTmax) / (LT LFTX)] [1 / (LFS LA)] [GRmax / (LR LFRX LPOL)]which can be expressed in dB as:

PRX = EIRP - L + GR

EIRP characterises the transmitting equipment; it takes into account the losses between transmitter amplifier, LFTX, and the antenna and the reduction in antenna gain due to misalignment, LT

L characterises the transmission medium and accounts for the free space loss, LFS, plus the attenuation in the atmosphere, LA

GR characterises the receiving equipment; it takes into account the losses between the antenna and the receiver, LFRX , the loss due to misalignment, LR , and polarisation mismatch, LPOL


Noise power at the receiver input

• white noise is noise with constant power spectral density, N0, in the frequency band B:

N0 = kT (W/Hz) where k is Boltzmann’s constant, 1.38E-23 in Joule/Kelvin, and T is the temperature of a resistance given in Kelvin degrees (= 273º + Celsius degrees).

• noise power, N, captured by a receiver with equivalent noise bandwidth BN is:

N = N0BN = kTBN (W)T is the receiver noise temperature

• noise figure: F = 1 + T/T0



• noise power at radio frequencies is generated by the thermal noise caused by the thermal motion of electrons in the devices of the receiver. For frequencies higher than 21*T [GHz] the dominant component of noise will be the quantum noise rather than the thermal noise.

• For example, a system with an equivalent noise temperature of 100ºK can use the thermal noise formula up to frequencies of 2,100 GHz.

• Quantum noise is caused by the uncertainty of some physical quantity, e.g., photons and electrons and is critical in optical communications.


Noise power at the receiver input• the system noise temperature, TS, at any one point is

obtained by summing all noise temperatures corresponding to noise generated upstream, Tu, and all noise temperatures equivalent to the noise generated downstream of the point considered, Td. Therefore, Ts = Tu + Td

feeder

Receiver front end

LNA IF

Tu Td

MIXERantenna



• Tu = TA / Lf + (1 – 1/Lf)Tf where Lf is the loss in the feeder, Tf is the

physical temperature of the feeder (~290 K) and TA is the antenna temperature

• Ex: TA = 50 K, TF = 290 K, Lf = 1 dBTu = 50/100.1 + 290(1 – 1/100.1)

= 39.7 + 59.6 = 99.3 K


Noise power at the receiver input• The feeder loss reduces the antenna noise but it

makes its own contribution to the noise that causes an increase in the system noise temperature

• every 0.1 dB of upstream attenuation makes a contribution of 290(1 – 1/100.01) = 6.6 K to the system noise temperature



• To estimate Td, consider that the receiver blocks are a low noise amplifier (LNA), a mixer (M) and an IF amplifier

• Td = TLNA + TM/GLNA + TIF/GLNAGM

• Ex: TLNA = 150 K, GLNA = 50 dBTM = 850 K, GM = -10 dB,TIF = 400 K, GIF = 30 dBTd = 150 + 850/105 + 400/10510-1 = 150 K


Noise power at the receiver input• Carrier to noise ratio at the receiver input

C = PRX

PRX = [(PTXGTmax) / (LT LFTX)] [1 / (LFS LA)] [GRmax / (LR LFRX LPOL)]

N0 = kTC/N0 = [(PTXGTmax) / (LT LFTX)] x

[1 / (LFS LA)] x[(GRmax /T)/ (LR LFRX LPOL)] x (1/k)

Figure of merit = G/T = (GRmax /T)/ (LR LFRX LPOL)

C/N0 = EIRP – L + G/T – k (dB)


Uplink

(C/N0)U = (EIRP)ES(1/LU) (G/T)S(1/k)

GTGR

PRX

feeder

Earth Station (ES)

Satellite (S)


Uplink• Frequency fU = 14 GHz• Earth Station:

Transmitting amplifier power, PTX = 100 WLoss between amplifier and antenna, LFTX = 0.5 dBAntenna diameter, D = 4 mAntenna efficiency, η = 0.6Maximum pointing error, θT = 0.1°It is on the edge of the 3 dB coverage area

• Earth station – satellite, R = 40,000 km• Atmospheric attenuation, LA = 0.3 dB


Uplink

• Satellite parameters:Receiving beam half power angular width, θ3dB = 2°Antenna efficiency, η = 0.55Receiver noise figure, F = 3 dBLoss between antenna and receiver, LFRX = 1 dBThermodynamic temperature of the connection, Tf = 290 KAntenna noise temperature, TA = 290 K


Uplink

• (EIRP)ES = PTXGTmax /(LTLFTX)GTmax = η(π DES / λ)2 = η(π DES fU / c)2 =

= 0.6 [π x 4 x 14 x 109 / (3 x 108)]2

= 206340 => 53.1 dBiLT = 12(θT/θ3dB)2 and θ3dB = 70(λ/DES) = 70(c/DESfU)

= 12(θT DESfU / 70c)2 => 0.9 dBLFTX = 0.5 dB

• (EIRP)ES = 20dBW + 53.1dBi – 0.9dB – 0.5 dB = 71.7 dBW


Uplink

• Attenuation on the upward path:LU = LFSLA

LFS = (4πR / λ)2 = (4πR fU / c)2 = = 5.51020 => 207.4 dB

LA = 0.3 dB

LU = 207.7 dB


Uplink• Figure of merit, (G/T)S, of the satellite:

(G/T)S = (GRmax /T)/ (LR LFRX LPOL)T = Tu + Td = TA / LFRX + (1 – 1/LFRX)Tf + Td

where Td is the temperature at the input of the receiver which can be extracted from the receiver noise figure definition: F = 1 + Td/T0

Td = (F – 1) T0 = (100.3 – 1)290 = 290 KT = 290/100.1 + (1 – 1 / 100.1)290 + Td = 230 + 59 + Td = 578K => 10 log 578 = 27.6 dBKNote: the Tu is the limiting factor in calculating the (G/T)S. From T ≈ 290 + Td results that it is needlessly costly to install a receiver with a very low noise figure on board a satellite: say F => 0 then Td = > 0, so T remains close to 290 => 24.6 dB


Uplink

• Figure of merit, (G/T)S, of the satellite:(G/T)S = (GRmax /T)/ (LR LFRX LPOL)

GRmax = η(π DS / λ)2 and θ3dB = 70(λ/DS)= 0.55(π 70 / 2)2 = 6650 => 38.2 dBi

LR = 12(θR/ θ3dB)2 = 12[(θ3dB / 2)/ θ3dB]2 = 3 dBLFRX = 1 dBLPOL = 0 dB

(G/T)S = 38.2 – 27.6 – 3 – 1 – 0 = 6.6 dBK-1


Uplink

(C/N0)U = (EIRP)ES(1/LU) (G/T)S(1/k)=> 71.7 – 207.7 + 6.6 + 228.6 = 99.2 dBHz

One last check: make sure that you don’t saturate the satellite, that is, the power flux density received by the satellite (defined on slide 11 minus other losses EXCEPT the free space loss) is less than the saturation value defined for that satellite.


Downlink

• Satellite parameters:Transmitting beam half power angular width, θ3dB = 2°Antenna efficiency, η = 0.55Transmitter amplifier power, PTX = 10 WLoss between amplifier and antenna, LFTX = 1 dB

• Frequency fD = 12 GHz• Earth station – satellite distance, R = 40,000 km• Atmospheric attenuation, LA = 0.3 dB


Downlink

• Earth Station on the edge of the 3 dB coverage area:

Receiver noise figure, F = 1 dBLoss between antenna and receiver, LFRX = 0.5 dBAntenna diameter, D = 4 mAntenna efficiency, η = 0.6Maximum pointing error, θR = 0.1°Ground noise temperature, TGROUND = 45 KSky noise temperature, TSKY = 20 KThermodynamic temperature of the feeder, Tf = 290 K


Downlink

• (EIRP)S = PTXGTmax /(LTLFTX)GTmax = η(π DS / λ)2 = η(π 70 / θ3dB)2 =

= 0.55 [π 70 / 2]2

= 6650 => 38.2 dBiLT = 3 dBLFTX = 1 dB

• (EIRP)S = 10 dBW + 38.2 dBi – 3 dB – 1 dB = 44.2 dBW


Downlink

• Attenuation on the downlink path:LD = LFSLA

LFS = (4πR / λ)2 = (4πR fD / c)2 = = 4.04 x 1020 => 206.1 dB

LA = 0.3 dB

LD = 206.4 dB


Downlink

• Figure of merit, (G/T)ES, of the earth station:(G/T)ES = (GRmax /T)/ (LR LFRX LPOL)

T = Tu + Td = TA / LFRX + (1 – 1/LFRX)Tf + Tdwhere Td is the temperature at the input of the receiver which can be extracted from the receiver noise figure definition: F = 1 + Td/T0

Td = (F – 1) T0 = (100.1 – 1)290 = 75 KTA = TSKY + TGROUND = 20 + 45 = 65 K

T = 65/100.05 + (1 – 1 / 100.05)290 + 75 = 164.5 K => 22.2 dBK(Note that in the particular case of pointing to the sun, TSUN is

10,000K => T becomes ~ 40 dBK)


Downlink• Figure of merit, (G/T)ES, of the earth station:

(G/T)ES = (GRmax /T)/ (LR LFRX LPOL)GRmax = η(π DES / λ)2 = η(π DfD / c)2 =

= 0.6(π x 4 x 12 x 109 / 3 x 108)2 = 151597 => 51.8 dBiLR = 12(θR/ θ3dB)2 = 12(θRDfD/70c)2 = 0.6 dBLFRX = 0.5 dBLPOL = 0 dB

• (G/T)ES = 51.8 – 22.2 – 0.6 – 0.5 – 0 = 28.5 dBK-1

• (C/N0)D = (EIRP)S(1/LD) (G/T)ES(1/k)=> 44.2 – 206.4 + 28.5 + 228.6 = 94.9 dBHz


Station-to-station link

GTGRPRXfeeder

Earth Station (ES)

Satellite (S)

(C/No)U

feeder

(C/No)D

Earth Station (ES)

(C/No)T

PTX



[(C/N0)T]-1 = [(C/N0)U]-1 + [(C/N0)D]-1

Ex: (C/N0)U = 99.2 dB = 109.92

(C/N0)D = 94.9 dB = 109.49

(C/N0)T = 10log[(109.92 109.49)/(109.92 + 109.49)] = 93.5 dB



• Repeater model: amplifies the power of the received signal and changes the frequency– Input back-off: IBO = Pi / Pi,sat

– Output back-off: OBO = Po / Po,sat

– Saturation gain: Gsat = Po,sat / Pi,sat

– Satellite power gain: GS = (OBO/IBO) Gsat

(C/N0)U = IBO (C/N0)U,sat (C/N0)D = OBO (C/N0)D,sat



• Satellite input back-off in the uplink– required to move the operating point in the linear

portion of the transfer characteristic of the satellite TWTA (IBO = Pi / Pi,sat)

– (C/N0)U = IBO (C/N0)U,sat

– (C/N0)U = (EIRP)ES,sat - IBOS+ (1/LU) + (G/T)S + (1/k)=> the earth station is required to reduce the EIRP that

would saturate the transponder by a certain amount(EIRP)ES = (EIRP)ES,sat - IBOS



• Satellite output back-off in the downlink– required to move the operating point in the linear

portion of the transfer characteristic of the satellite TWTA (OBO = Po / Po,sat)

– (C/N0)D = OBO (C/N0)D,sat

– (C/N0)D = (EIRP)S,sat - OBOS+ (1/LU) + (G/T)ES + (1/k)=> the satellite outputs a reduced EIRP

(EIRP)S = (EIRP)S,sat - OBOS


Station-to-station link• Percent of time performance specification

– Statistically based performance: P = average annual time percentage outage, PW = average annual worst month time percentage outage, PW = 2.84 P0.87

(ITU-R P.841-4 recommendation)Outage P [%] Reliability 100- P [5] Outage time10 90 876 hr0.1 99.9 8.76 hr0.05 99.95 4.38 hr0.01 99.99 53 min0 100 0 hr


• From the link budget calculation:C/N0 = EIRP – L + G/T – k (dB)

• The C/N0 can also be expressed as:C/N0 = Eb/N0 + 10 log10 Rb

where Eb/N0 is the energy per information bit to noise power density ratio and Rb is the information bit rate.

• Therefore, for a given link, there is a pair of Eb/N0and Rb that can be achieved.

• For a certain Eb/N0 and modulation type there is a certain BER that can be achieved in a given channel



Steps to design a link:1. Identify the target bit error rate (BER) for the link.2. Search for a satellite modem that can achieve the

target BER at the lowest Eb/N0.3. Add 2 to 3 dB link margin (see link availability).4. Compute the C/N0 for the station-to-station link.5. Design the up-link and the down-link such that each

link is above the targeted station-to-station C/N0.6. Repeat from step 2 for various modulations and

coding rates combinations to reduce the bandwidth.



Steps to minimize the link cost:1. Find out the total Power Equivalent Bandwidth

(PEB) which is the total satellite power used by the carriers represented as a bandwidth equivalent.

2. The charge for the satellite use is for the larger of either total BW or total PEB.

3. Minimize total BW and/or total PEB and try to get them as close as possible.



http://www.comtechefdata.com/articles_papers/SM%20May10%20ComtechEF.pdf

The following two slides show two graphs of availability vs. link margin. A change in guaranteed annual availability from 99.8% to 99.6% equates to 17.5 hours per year (365 Day*24hours/day*0.002 = 17.5 Hours). It can be seen that these 17.5 hours/year demand or save 2.5/0.35dB of link margin for a Ku/C band link. This means that if 99.8% availability is required instead of 99.6% we need an additional 2.5/0.35dB of link margin. Conversely, having only 99.6% availability would save 2.5/0.35dB.




http://www.comtechefdata.com/articles_papers/SM%20May10%20ComtechEF.pdf


http://www.comtechefdata.com/articles_papers/WP-CDM625_ACM_White_Paper.pdf


Satellite Access

Contents: FDMA TDMA CDMA OFDM Random Access


Satellite Access• Consider a network of N stations

– One carrier per station-to-station link (requires N(N-1) carriers of low capacity)

– One carrier per transmitting station(requires only N carriers of higher capacity)

• For a satellite based network, it is more efficient to send fewer carriers of high capacity


FDMA(Frequency Division Multiple Access)

• The repeater channel is divided into sub-bands, each assigned to one carrier

• Guard intervals are provided between each band to avoid interference as a result of imperfections of oscillators and filters

• The downlink receiver selects the required carrier in accordance with the appropriate frequency


FDMA• FDM/FM/FDMA

– The analogue baseband signals of the earth station are combined to form a frequency division multiplex (FDM) signal.

– It contains the total traffic from the transmitting earth station to all other stations.

– This multiplex signal modulates a carrier (FM) which accesses the satellite repeater channel on a particular frequency.


FDMA• FM

– In theory, the spectrum of a frequency-modulated carrier extends to infinity.

– In a satellite system, the bandwidth of the transmitted FM signal is limited by the intermediate-frequency amplifiers, BIF. The required bandwidth is estimated by Carson’s rule as:

2(∆F + FM) < BIF < 2(∆F + 2FM)where ∆F is the peak carrier deviation produced by the modulating baseband signal, and FM is the highest frequency component in the baseband signal.


FDMA• FM

– The deviation ratio, D = ∆F / FM– Ex1: For commercial FM sound broadcasting in North

America, ∆F = 75 kHz and FM = 15 kHz– Ex2: a video signal of bandwidth 4.2 MHz is used to

frequency modulate a carrier, the deviation ratio being 2.56. The peak deviation is ∆F = 2.56 x 4.2 = 10.752 MHz. The signal bandwidth is

BIF > 2(10.75 + 4.2) = 29.9 MHzBIF < 2(10.75 + 8.4) = 38.3 MHz.

In practice, a 36 MHz satellite transponder is required for this signal.


FDMA• TDM/PSK/FDMA

– The digital baseband signals are combined to form a time division multiplex (TDM) signal.

– It contains the total traffic from the transmitting earth station to all other stations.

– This signal then modulates a carrier by phase-shift keying (PSK) which accesses the satellite repeater channel on a particular frequency.


FDMA• SCPC/FDMA

– The baseband signals at the earth station each modulate a carrier directly.

– Each carrier accesses the satellite repeater channel on a particular frequency.

– One carrier per station-to-station link principle


FDMA• Intermodulation

– a satellite repeater channel has a non-linear transfer characteristic; it simultaneously amplifies several carriers at different frequencies

– when N sinusoidal signals at frequencies f1, f2, ..fNpass through a non-linear amplifier, the output contains not only the N signals at the original frequencies but also undesirable signals called intermodulation products:fIM = m1f1 + m2f2 + … mNfN (Hz)


FDMA

• Intermodulation– mi are positive or negative integers– order of modulation, X = |m1| + |m2| + … |mN|– in practice, only product of order 3 and 5 are

significant– the transfer characteristic of a non-linear amplifier

is changing from single to multicarrier operation mode (higher input back-off required).


FDMA

• Intermodulation– If there are two or more carriers of different

powers, the IM products will be higher next to the carrier of higher amplitude.

– By increasing the number of carriers for the same input power relative to saturation, the (C/No)IMwill decrease due to the increased level of IM products.

– For many carriers per transponder, e.g. 64, the IM behaves as significantly increased noise floor.


FDMA• Intermodulation noise:

[(C/N0)IM]-1 = [(C/N0)IM,U]-1 + [(C/N0)IM,D]-1

(carrier power-to-intermodulation noise power)

• Interference noise:[(C/N0)I]-1 = [(C/N0)I,U]-1 + [(C/N0)I,D]-1

• Overall station-to-station link:[(C/N0)T]-1 = [(C/N0)U]-1 + [(C/N0)D]-1

+ [(C/N0)IM]-1 + [(C/N0)I]-1


FDMAC

arri

er p

ower

–to

-noi

se p

ower

spec

tral

den

sity

Input power relative to saturation

(C/No)U(C/No)IM

(C/No)D

(C/No)T

0 dBsaturation

Input back-off


FDMA

• the total power of the output channel is less than that which would exist in the absence of back-off

• the useful power per carrier is reduced by allocation of part of the total power to intermodulation products

• For 4 carriers (accesses) the throughput drops to 60% (for 8 – 50%; for 14 – 40%)


FDMA• uses low cost hardware technology, simple to

build / deploy, common for analogue systems.• there is no need for network timing, ISI is low,

little or no equalisation is needed; continuous tx• requires guard bands and RF filtering to

minimize adjacent channel interference (ACI).• the maximum bit rate per channel is fixed and

usually small, inhibiting the flexibility in bit rate capability therefore the amount of traffic.


FDMA• The total capacity decreases as the number of

carriers increases due to the reduction in (C/N0)T for each carrier (the back-off is larger when the number of carriers is higher).

• Needs power control of each transmitter in order to avoid the capture effect (carriers of high power have a higher power gain).

• Lacks flexibility (due to a fixed frequency plan)• Higher cell site system costs than TDMA.


TDMA(Time Division Multiple Access)

• only one carrier at any one time => no more intermodulation products => TWT can be operated at saturation

• burst mode is suited only to digital signals• burst acquisition and synchronisation is

required by each station• network synchronisation


TDMA• Burst structure

– header or preamble• carrier and bit recovery field:

– to synchronise the local oscillator in a receiving station to the carrier frequency (the bit sequence provides a constant carrier phase for rapid carrier recovery)

– to synchronise the bit decision clock to the symbol rate (a bit sequence providing alternating opposite phases)

• unique word field:– to identify the start of a burst; resolves carrier ambiguity

• telephone/telex/service channel fields


TDMA

• Burst structure– traffic field

• multiple of N symbols depending on the capacity of each station (e.g., N = 64 symbols)

– guard time between each burst to allow for synchronisation imperfections (e.g. 64 symbols)

– reference bursts / traffic bursts


TDMA

• Unique Word– the miss probability is the probability the correlator

failed to detect the UW even though it is present in the bit stream

• Let E = maximum number of errors allowed, I = actual number of errors detected in UW and N = UW length

• If I ≤ E, the detected sequence is declared to be a UW• If I > E, the detected sequence is declared not to be a

UW, that is a UW is missed


TDMA

• Unique Word– the probability of receiving a sequence of N bits

containing I errors in any particular arrangement is:• pI = pI(1 - p)N-I where p is the bit error probability

– all possible combinations of N taken I at a time is:• NCI = N!/[I!(N - I)!]

– the probability of receiving any sequence of N bits containing I errors is:

• PI = NCI x pI


TDMA

• Unique Word– the condition for a miss occurring is that I > E :

• Pmiss = PE+1 + PE+2 + … PN

Therefore the formula written in full is:Pmiss = Σ pI(1 - p)(N-I) N!/[I!(N - I)!] with I = E+1,…N

– the acquisition time, assuming one UW per frame:Tack = (1 - Pmiss) x Tframe/2 + (1 - Pmiss) x Pmiss x 2Tframe/2 + …

≈ Tframe/2 if Pmiss = is small


TDMA• Unique Word

– the false detection probability is the probability that a sequence which is not the UW could be interpreted as the UW if it differs in up to E bit positionsPfalse detection = (0.5)N Σ N!/[I!(N - I)!]

with I = 0, 1, ...E


TDMA• Pre-assigned TDMA

– Ex: the common signalling channel (CSC) for INTELSAT’s Spade network

– each station has allocated a time slot in which it can send a burst to request the allocation of a transmit frequency

– a 50 ms frame with one reference burst and 49 data bursts => up to 49 earth stations


TDMA• Demand-assigned TDMA (DAMA)

– the burst length assigned to a station may be varied as the traffic demands or,

– the number of bursts per frame used by a given station may be varied

– used in speech transmission: digital speech interpolation (DSI) allows N terrestrial channels to be carried by M satellite channels, where M < N (e.g., M = 127, N = 240)


TDMA

• DAMA example of traffic matrix from “Handbook on Satellite Communications”. Consider the network traffic needs below:

Total traffic for these 5 Earth stations is 15 Erlangs

Station To/from stationsA B C D E

A 3.5 2 1.5 1B 1.5 1 1C 1.5 1.5D 0.5


TDMA• Using a blocking factor of 2%, the total number of

half-circuits calculated by the Erlang B table is 98.Required number of pre-assigned carriers

Station To/from stationsA B C D E TOTAL

A 8 6 5 4 23B 8 5 4 4 21C 6 5 5 5 21D 5 4 5 3 17E 4 4 5 3 16


TDMA

• The previous table showed a need for 49 two-directional pre-assigned SCPC channels. From the Erlang Table, we find that the traffic capacity for this number of channels is 39.3 Erlangs compared with the current pre-assigned SCPC network traffic of 15 Erlangs

• Advantages of a DAMA system:– Increase the traffic capacity by more than 150%– Give full flexibility to the distribution of traffic


TDMA• Throughput (η)

– it is defined as the ratio of the satellite repeater channel capacity in single carrier operation (only one access only) and the capacity of the same channel for the multiple access case

– if Σti is the sum of the times not devoted to transmission of traffic in a frame TF, then:

η = 1 - Σti / TF


TDMA• Throughput (η)

– assume the transfer capacity is R in a single carrier operation

– assume r be the signalling rate associated with one telephone channel

– the number n of telephone channels in the frame is given by:

n = η R / r– for 50 accesses in the INTELSAT/EUTELSAT

TDMA system the throughput is 85.2 %


TDMA vs FDMA• Uplink power requirements

– usually the TDMA earth stations have to transmit at a higher bit rate than FDMA, therefore a higher EIRP is required.

– assume same Eb/N0 requirements, same losses and the same satellite G/T, an increase in the data rate, requires a corresponding increase in the C/N0which can be achieved only through an increase in the earth station EIRP.


TDMA vs FDMA

• Uplink power requirements– 14 GHz, LU = 212 dB, satellite G/T = 10 dB/K– Required Eb/N0 is 12 dB– earth station antenna gain = 46 dB– T1 uplink in FDMA (1.544 Mbit/s = 62 dBb/s)1) Calculate the transmit power for the earth station2) Calculate the increase in EIRP if the downlink is

TDMA at a transmission rate of 74 dBb/s


TDMA vs FDMA

• Uplink power requirementsC/N0 = Eb/N0 + R = 12 +62 = 74 dBHz(C/N0)U = (EIRP)ES(1/LU) (G/T)S(1/k)(EIRP)ES = (C/N0)U + (LU) - (G/T)S + (k) =

= 74 + 212 - 10 - 228.6 = 47.4 dBWEIRP = PTGT

PT = EIRP - GT = 47.4 - 46 = 1.4 dBW => 1.38 W


TDMA vs FDMA

• Uplink power requirementsthe rate increase in TDMA mode is:

74 - 62 = 12 dBb/s, therefore the earth station EIRP must be increasedwith the same amount:

PT = 1.4 + 12 = 13.4 dBW => 21.9 W


TDMA vs FDMA

• Uplink power requirements– FDMA requires a small transmit earth station– TDMA permits more efficient use of the satellite

transponder by eliminating the need for back-off=> hybrid system in which the uplink FDMA signals

are converted to a time-division-multiplex format in the transponder before being amplified by the TWTA which can be operated in saturation


TDMA• on-board signal processing: “decouples” the

uplink from the downlink• satellite-switched TDMA uses antenna spot

beams (space-division multiplexing)• more costly equipment• better utilisation of the space segment due to

higher throughput


TDMA• Digital modulation is required.• Allows flexible bit rate; low battery consumption

given that data transmission is not continuous.• No precise expensive narrowband filters are

required, no frequency guard bands are required.• Allows the utilisation of digital techniques e.g.,

digital speech interpolation.• Easier for mobiles or base stations.• Can easily implement demand assignment.


TDMA• Can be used in networks with multiple carriers

which operate in TDMA mode.• Allows operation close to the saturation point.• Requires network-wide timing synchronisation.• Requires digital signal processing for matched

filtering, correlation detection, etc.• Demands high peak power in the transmit or

broadcast mode, adaptive equalisation, channel estimation, high synchronisation overhead.


CDMA(Code Division Multiple Access)

• code division multiple access: transmission at the same time in the same bandwidth

• each transmitter is identified by a “code” which– must be easily distinguishable from a replica of

itself shifted in time– must be easily distinguishable regardless of other

codes used on the network


CDMA• Direct Sequence

– the binary message m(t) = ±1, at a bit rate Rb, is multiplied by a binary sequence p(t), called chip, at the chip rate Rc which is 1E2 to 1E6 times greater than Rb

– the composite signal m(t)p(t) then modulates a carrier by phase-shift keying whose frequency is common to all stations.

c(t) = m(t) p(t) cos (ωt)


CDMA

• Direct Sequence– c(t) has a wide spectrum; Rc/Rb = spreading ratio– at the receiver: r(t) = c(t) + Σci(t) which is

multiplied by the chip sequence p(t)x(t) = r(t) p(t) = [c(t) + Σci(t)] p(t) =

= [m(t)p(t) + Σmi(t)pi(t)]p(t) == m(t)p2(t) + Σmi(t)pi(t)p(t) ≈ m(t)

– despreading before demodulation => better SNR


CDMA• Frequency Hopping

– the binary message m(t) = ±1, at a bit rate Rb, modulates a carrier whose frequency is generated by a frequency synthesiser controlled by a binary sequence (code) generator.

– the generator delivers chips with a bit rate Rc

c(t) = m(t) cos [ωc(t)t]– there are N possible frequencies => log2N chips– the hop rate is RH = Rc/ log2N


CDMA• Frequency Hopping

– at the receiver the carrier is multiplied by a carrier generated under the same conditions as at the transmitter to get:x(t) = m(t) cos [ωc(t)t] cos [ωc(t)t] =

= m(t) + m(t) cos [2ωc(t)t] = m(t) after low pass filtering

– three types: RH = Rb, RH >> Rb, and RH << Rb


CDMA• Throughput (η)

– maximum number of accesses Nmax is function of Rb, Rc, and Eb/N0

– the throughput is lower than for TDMA– 36 MHz, 64 kbit/s channels, BPSK (Ref. 1, p317) BER Eb/N0 Nmax Mbit/s η1E-4 8.4 dB 82 5.3 15%1E-5 9.6 dB 62 4 11%1E-6 10.5 dB 51 3.3 9%


TDMA vs FDMA vs CDMAM deLaChapelle, C. McLain, “Optimum Waveforms for Broadband Mobile Satellite

Communications”, Ka and Broadband Communication Conference, 2006

Only one terminal accesses the resource at any frequency and time. It must transmit with an EIRP that just reaches the off-axis power spectral density (PSD) limit and the maximum information rate that can be supported by that EIRP.




The Root Mean Square (1 σ) value of errors in knowledge of the transmit PSD due to power control and pointing error may be up to 1 dB (26%) of the PSD. Regulators may require a high probability of meeting the PSD limits, often up to 99.99% (3.7 σ).

This margin required to meet the PSD limits is a percentage of the PSD of each individual access, but for CDMA, it applies to the aggregate of all terminals sharing the same bandwidth. The errors of each terminal sharing a bandwidth are independent and so they do not add linearly. The CDMA system will require a smaller margin than for a MF-TDMA by a factor of 1/N2.




For a 99.99% probability of meeting the off-axis PSD limit an MF-TDMA system must hold a 2.9 dB margin. On the other hand, for a CDMA system with 100 terminals the required margin falls to 0.4 dB, which is a 2.5 dB advantage in PSD utilization efficiency.


Dual Polarization per Beam“Capacity Potential of Mobile Satellite Broadcasting Systems

Employing Dual Polarization per Beam”, 5th Advanced Satellite Multimedia Systems Conference and the 11th Signal Processing for

Space Communications Workshop, 2010.

Dual polarization per beam requires twice the number of waveguides for the antenna feeds. However, this architecture simplifies handling the high power challenges due to the use of low power beam-forming and multi-matrices power amplifiers. The figure shows a dual polarization/beam S-band feed prototype.


Example of a forward link frequency plan of a single polarization per beam employing six beams. Each beam is separated in three frequency bands each of width B, and co-channel beams are isolated in polarization (frequency reuse 2) providing an overall useful band of 6B. With dual polarization the capacity becomes 12B.


The cumulative distribution function of the MIMO and SISO capacities over the LMS and the ideal spatial i.i.d. Rayleigh fading channels. Even if under Rayleigh fading the decorrelation renders the capacity distribution of the SISO scheme much worse than MIMO, the high correlation in dual LMS channel renders the capacity performance almost equal to that of MIMO.


OFDMThe use in the physical layer of a satellite system of Orthogonal Frequency Division Multiplexing (OFDM) was ignored until recently due to the rather high peak-to-average power ratio (PAPR), which renders it particularly sensitive to non-linear distortion as that introduced by the on-board high power amplifier. However, recent work has shown that it can be used, in conjunction with turbo codes with sufficient channel interleaving, and suitable pre-distortion techniques.


OFDMIn OFDM all the carrier signals are orthogonal to each other, allowing high spectral efficiency, rate adaptability, eliminating cross-talk between sub-channels and the need for guard bands.• The sub-carrier spacing is Δf = k/TS where TS is

the symbol duration and k is a positive integer, typically equal to 1.

• With N sub-carriers, the total pass-band bandwidth will be B ≈ N·Δf (Hz).


OFDM

http://upload.wikimedia.org/wikipedia/commons/4/4e/OFDM_transmitter_ideal.png


OFDM

http://upload.wikimedia.org/wikipedia/commons/9/90/OFDM_receiver_ideal.png


OFDM• Data predistorters: act on the mapping of

constellation points, prior to signal shaping, and have to compensate the non-linear system with memory constituted by the cascade of the transmit filters and the on-board HPA.

• Waveform predistorters: are placed after the pulse shaping filter thus having to compensate only for the HPA memoryless non-linearity.

(S Cioni et al, “On the use of OFDM radio interface for satellite digital multimedia broadcasting systems”, Int. J. Satell. Commun. Network. 2006)


OFDMThe waveform predistorter is located after the pulse shaping transmit filter, and can correct the average positions of the individual clusters and reduce their variance, bounding the effects of ISI.


Random Access• totally asynchronous protocols

– Pure ALOHA random multiple access protocol– the selective reject (SREJ) ALOHA protocol

• protocols with synchronisation– the Slotted ALOHA protocol

• protocols with assignment on demand (DAMA)– R-ALOHA, R-TDMA– contention based priority oriented demand

assignment


Random Access• Consider a system made of a satellite channel

and M earth stations with bursty traffic, each having λ/M packet generation rate

• All packets are of equal duration τ (s)• The probability of a new packet to be generated

is given by S = λτ per packet.• The satellite carries both new and retransmitted

packets. Consider G as the probability of a packet to arrive at the satellite channel input.


Random Access• Assuming that the packet emission follows a

Poisson distribution, the probability that kpackets arrive at the satellite channel during any interval of t packets duration is:

Prob[k, t] = (Gt)kexp(-Gt)/(k!)• For random transmissions the probability of no

collision is Prob[k = 0, t = 2].• For synchronised transmissions the probability

of no collision is Prob[k = 0, t = 1].


Random Access


Random Access

All the users compete for access on the same Physical Random Access Channel (PRACH) which is mapped one-to-one to the Random Access Channel (RACH) at the transport layer. In 3GPP, the user terminal sends one or several preamble bursts, listens on the acquisition indicator channel that it was successfully detected, then transmits the message part, as described in the diagram. The same scenario can be applied to a GEO bent-pipe satellite where the propagation delay of ~560 ms has to be taken into account (preamble+message sent together).


ASC = Access Service Class

RACH = Random Access Channel

AI = Acquisition Indicator

PRC = Power Ramping Control

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Packet Reservation Multiple Access

PRMA is a MAC layer protocol based on S-ALOHA. It starts with a silent state. When an access request arrives, it moves to a contending state where an attempt to reserve resources is made. It could result in a failed request if no resources, e.g., no free slots are available, or it could go into an active state if the request is successful. After the transmission is finished, e.g., a talkspurt ends, the allocated slot is released and the protocol returns to the silent state again. PRMA is suitable for S-UMTS and LEO systems (delay < 30 ms).


The performance of PRMA is affected by the scheduling technique that is used.– First in First out: serves packets according to their arrival– Weighted round robin: gives weighted access to the available

bandwidth to each class of service; each class is served in proportion to its associated weight

– Class-based queuing: aims to guarantee the bandwidth portion of each class

– Early deadline first: each packet is given the priority based on its deadline



In the case of a variable satellite channel due to shadowing and/or multipath fading, the throughput can be improved by cross layer design, where channel state information (CSI) is passed to the scheduler. In this scenario the scheduler will check the estimated Eb/N0for each user or class of users (spot beams). For each slot, where more packets compete for priority, the scheduler will allocate the packet for which the Eb/N0 is above a certain threshold, in order to improve the total goodput (throughput at the receiver end) of the network.



Conclusions• FDMA should be used when there are only a few

carriers with a large volume of traffic per carrier.• For small volumes of traffic per carrier and large

number of accesses TDMA and CDMA should be used; CDMA is cheaper and can cope with inter-system interference but has lower throughput. TDMA is more expensive but can offer demand assignment.

• Random access should be used for short messages, randomly generated with long dead times between them.


Earth Stations

Contents: Standards Earth Stations Antennas Radio Frequency Subsystem Communication Subsystem Network Interface Subsystem


Standards - FSSINTELSAT F G/T EIRP Diameter ServiceStandards (GHz) (dB/K) (dBW) (M)A (IESS 201) 6/4 >40 70-90 30 TV, FDMA, TDMAA revised >35 16B (IESS 202) 6/4 >32 60-85 11-14 TV, FDMA, TDMAC (IESS 203) 14/11 >39 72-87 14-18 TV, FDMA, TDMAC revised >37 11-13D1 6/4 >23 53-57 5 SCPC/FME1 (IBS/IDR) 14/11 >25 57-86 3.5 400 channels @ 64 kbit/sE2 (IBS/IDR) 14/11 >29 55-83 5.5 700 channels @ 64 kbit/sE3 (IBS/IDR) 14/11 >34 49-77 7.7 1000 channels @ 64 kbit/s


Standards - FSSFrequency Antenna Size StandardKu 1.2 - 1.8 KKu 2.4 - 4.5 E1Ku 4.5 – 7 E2C 3.7 - 4.5 F1C 5.5 - 7.5 F2C 7.3 – 9.0 F3C 1.8 - 3.7 HC/Ku Up to 4.5 G


Standards - MSSINMARSAT F G/T EIRP Diameter ServiceStandards (GHz) (dB/K) (dBW) (M)A 1.6/1.5 >-4 37 0.9 SCPC/FM, (parabolic antenna) SCPC/BPSK/TDMAB 1.6/1.5 >-4 33 0.9 SCPC/OQPSK @ 16 kbit/s(parabolic antenna)C 1.6/1.5 >-23 14 text messaging @1.2 kbit/s(omnidirectional)M 1.6/1.5 >-12 19-25 0.5 briefcase, @ 128 kbit/s

Figure of merit = G/T (Noise figure = F = 1 + T/T0)


Standards - LRITSince the beginning of 2009, the new Long-Range Identification Tracking system (LRIT) adopted by the International Maritime Organization (IMO) is compulsory for all ships from Members States of the IMO. They have to report their position up to four times per day using a new satellite-based service coordinated by the International Mobile Satellite Organization (IMSO); the system is compulsory for thousands of sea-going vessels over 300 gross tonnage (GRT).

The increased level of danger at sea lead to the adoption of more satellite voice and mostly data equipment onboard ships. This would also allow monitoring ports and ships in transit near and within domestic waters with reliable communications means.


Standards - LRITLRIT data can be provided now, using Inmarsat C, mini-C or D+. The Inmarsat terminal on the vessel has a built-in global positioning system (GPS) receiver, which provides the vessel's position. The Inmarsat terminal also has a built-in unique identity, or ID. Remote control is already possible today with Inmarsat C, mini-C and D+.


Earth Stations Antennas

• Characteristics required– high directivity along the axis of the antenna– low directivity in all other directions– high antenna efficiency– high isolation between orthogonal polarisations– low antenna noise temperature– continuous pointing in the direction of the

satellite regardless of wind, temperature, etc.


Earth Stations Antennas“ACMA: Guidelines on the assessment of installations against electromagnetic

radiation (EMR) exposure limits (Edition September 2000)”The fundamental limits in the ACMA AS/NZS 2772.1 (Int):1998 standard arebased on a quantity known as Specific Absorption Rate (SAR). The SAR is ameasure of the rate at which energy is absorbed from an electromagnetic field intobiological tissue. The SAR measure must be used when the transmitter is operatedin close proximity to the human body. The measurements of electromagnetic fieldshave to be averaged over a period of any six minutes with the average not toexceed the limit for continuous exposure, that is 0.2 mW/cm2.

The U.S. Environmental Protection Agency (EPA) has developed models forpredicting ground-level field strength and power density for FM radio andtelevision broadcast antennas. The EPA model suggests a realistic approximationfor ground reflection is obtained by assuming a maximum 1.6-fold increase infield strength leading to an increase in power density of 2.56 (1.6 × 1.6).



For example, if a facility is transmitting at a frequency of100 MHz with a total nominal EIRP (including allpolarisations) of 10 kW (10,000 W) from a tower-mountedantenna, and the height above ground level to the centre ofthe antenna is 50 m, the following formula will predict themaximum power density that could be expected at a point2 m above ground (approximate head level) and at adistance of 20 m from the base of the tower:

2 m20 m

50 mR = 52 m

2/075.075.064.0 cmmWmW/ )m (52

W) (10,000 = S 22 ≈≈

π

REIRP 0.64 =

R4EIRP 2.56 = S

22 ππ


Earth Stations AntennasIn the previous example, it can be shown fromtrigonometry that the angle below horizontal ofthe line between the antenna and the observationpoint 2 m above ground level at a distance of 20 mfrom the antenna, is about 68°. Assume that theantenna in this example has its main beam(boresight) pointed approximately toward thehorizon and that at an angle of 68°, the field Frelative to the main beam (relative gain) is –6 dB(a factor of 0.5 in terms of field strength and 0.25in terms of power density). The previouscalculation then becomes:

22 /019.0/19.025.06.06.0 cmmWmW )m (52

W) (10,000 )( 4 = R

EIRPF 4 = S 22 ≈≈×

ππ

Note: ACMA has determined that the offaxis relative linear gain at any anglegreater than 45º from the main beammay be conservatively approximated bya 10 fold reduction from main beamgain i.e., F=0.1. For angles less than45º from the main beam direction,relative linear gain is assumed to be 1.0.


Earth Stations AntennasRECOMMENDATION ITU-R S.728-1: Maximum permissible level of off-axis EIRP density from VSATs operating with geostationary satellites in the 14 GHz frequency band used by the FSS at any angle φ specified below, (off the main-lobe axis of an earth-station antenna, in any direction within 3° of the geostationary satellite orbit) should not exceed the following values:

Angle off-axis Maximum EIRP in any 40 kHz band2° ≤ φ ≤ 7° 33 – 25 logφ dBW7° < φ ≤ 9.2° 12 dBW9.2° < φ ≤ 48° 36 – 25 logφ dBWφ > 48° – 6 dBW

In addition, the cross-polarized component in any direction φ degrees from the antenna main-lobe axis should not exceed the following limits:

Angle off-axis Maximum EIRP in any 40 kHz band2° ≤ φ ≤ 7° 23 – 25 logφ dBW7° < φ ≤ 9.2° 2 dBW



• Types– the horn antenna

• high figure of merit• expensive, bulky, no longer in use

– the phased array antenna • used when the beam is in constant movement as in

the case of stations mounted on mobiles• expensive

– the parabolic antenna



Horn Antenna at Bell Telephone Laboratories, New Jersey, 1959

http://en.wikipedia.org/wiki/Image:Bell_Labs_Horn_Antenna_Crawford_Hill_NJ.jpg

http://en.wikipedia.org/wiki/Image:Bell_Labs_Horn_Antenna_Crawford_Hill_NJ.jpg


Earth Stations AntennasA 184-element phased array from EMS Technologies, electronically steerable in elevation and mechanically steerable in azimuth, and is 29.5 inches in diameter, 13 inches deep, and weighs 119 pounds.

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Earth Stations Antennas• ITR – SPOTx antenna:

– type: Gregorian– diameter: 8 m– polarisation: circular– efficiency: 75%– frequency: 8.4 GHz (X) 14.25 GHz (Ku)– gain: 54.3 dB 58.4 dB– beamwidth (-3 dB): 0.4° 0.19 °– antenna noise temperature: 50K



• Types of parabolic antenna mounting– the symmetrical or axisymmetrical mounting

• the feed support and the feed itself partially block the incoming flux => reduced antenna efficiency

• captures the radiation emitted by the ground which increases the antenna noise temperature to > 100 K

• to achieve low noise temperature, a directional primary feed and a long focal length are required.

• cumbersome


Earth Stations Antennas• ITR - FedSat TT&C antenna specifications:

– type: parabolic, 3 m diameter– data rates: 4 kbps/15Mbps (Up/Down) – polarisation: circular (LHC/RHC)– frequency: 2 GHz (S)– gain: 34.5 dB– beamwidth (-3 dB): 3°– System G/T: Tx/Rx: 9.3dB @ 5º

Rx only: 12 dB @ 5º


Earth Stations Antennas• In 2008, 2011 and 2012 the same antenna was used for

the TT&C links with the Ariane5 rocket which carries Europe's Automated Transfer Vehicle (ATV).

• Every 12 months or so, the ATV lifts ~20 tonnes of cargo from its Kourou launch site in French Guiana to the ISS and also boosts the Station's altitude. An on board high precision navigation system guides the ATV on a rendezvous trajectory towards ISS. The ATV remains there for up to six months then it re-enters the Earth's atmosphere to dispose of up to 6.5 tonnes of Station’s waste.


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Earth Stations Antennas• In December 2010, ITR tracked the US’s SpaceX

Dragon Spacecraft and received telemetry data, suchas its temperature, the direction it is pointing in andwhether all the systems are working correctly. TheDragon is being developed by the Californian spacetransportation company SpaceX under NASA’sCommercial Orbital Transformation Services programto develop commercial supply services to the ISS andencourage the growth of the commercial space industry.

(http://www.spacex.com/dragon.php)



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Dragon Highlights:• Fully autonomous rendezvous and docking with manual override capability• 6,000 kg payload up-mass to LEO; 3,000 kg payload down-mass• Payload Volume: 10 pressurized, 14 m3 unpressurized• Supports up to 7 passengers in Crew configuration• Two-fault tolerant avionics system with extensive heritage• Reaction control system with 18 MMH/NTOthrusters designed and built in-house; •1290 kg of propellant supports a mission fromsub-orbital insertion to ISS to re-entry• Designed for water landing under parachutefor ocean recovery• Lifting re-entry for landing precision & low-g’s• Ablative, high-performance heat shield andsidewall thermal protection



• Types of parabolic antenna mounting– the offset mounting

• enables microwave circuits to be located immediately behind the primary feed without masking effects

• it is used for small diameter antennas (1 to 4 m)• as for the symmetrical antennas, the spillover remains

oriented towards the ground and the antenna temperature remains high



By courtesy of CSIRO



• Types of parabolic antenna mounting– the reflector mounting

• the phase centre of the primary feed is located at the first focus S of an auxiliary hyperbolic (Cassegrain) or parabolic (Gregorian) reflector

• the other focus R of the auxiliary reflector coincides with the focus of the main parabolic reflector

• low noise temperature• microwave circuits can be located behind the primary

feed but masking effect of the auxiliary feed remain.



• Multibeam antennas– developed for direct-to-home(DTH) reception of

TV carriers from broadcasting geostationary satellites located at separate orbital positions

– multiple-beam torus antenna (MBTA) developed by COMSAT Laboratories is equivalent for each beam, to an antenna of 9.8 m aperture and has a gain of 50 dB at 4-6 GHz with a noise temperature of 30 K for an elevation angle of 20°


Earth Stations Antennas• Types of tracking

– tracking consists of maintaining the axis of the antenna beam in the direction of the satellite

– fixed antenna without tracking– programmed tracking: the azimuth and elevation

angles are calculated in advance– closed-loop tracking:

• tracking information does not come from the ground• high accuracy (tracking error less than 0.005°)


Earth Stations Antennas• Closed-loop automatic tracking

– sequential amplitude detection• the variation in received signal level enable to determine the

direction of maximum gain which corresponds to the highest received signal level

• conical scanning: for small antennas, complex mechanics• step-by-step tracking in each dimension: limited dynamic

response, the step size must be small enough• electronic tracking: successive displacement of the beam in

the four cardinal directions by varying the impedance of four microwave devices coupled at the source waveguide


Earth Stations Antennas• Closed-loop automatic tracking

– mode extraction monopulse• the fundamental transverse electric TE11 mode propagates

if the incident wave arrives along the axis of the guide• if there is a deviation, the TM01and TE21 modes are

generated; they are odd functions of depointing and are orthogonal => permits depointing measurement

• tracking error of the order of 0.02 θ3dB.• used in 30 m diameter earth stations


Earth Stations Antennas• Sub Reflector Tracking (SRT)

– At Ka-band frequencies, due to the narrow antenna beam widths, conventional antenna mount structures have limitations: movement screw backlash, axis bearing wobble, structure windup, and mount wind deflection.

– SRT beam steering replaces the conventional beam steering via movement of the main reflector. There are significant cost advantages due to reduction in the complexity of the mount and elimination of the tracking servo system and also significant performance improvements due to more accurate tracking.ht

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Radio Frequency Subsystem• On the transmitting side:

– modulation from baseband to IF (e.g. 70 MHz)– filtering and equalisation– up-conversion from IF to RF (e.g. 6 GHz)

• On the receiving side:– down-conversion from RF (GHz) to IF (MHz)– filtering and equalisation of group propagation

delay– carrier demodulation from IF to baseband


Radio Frequency Subsystem

Serial – to –Parallel

Converter

LPF

cos(ωct)

LPF

BPFΣ-90°

Binary data in

Baseband QPSK/QAM

output

Block diagram of a QPSK/QAM modulator

(LPF = low pass filter; BPF = band pass filter)


Radio Frequency Subsystem• Modulator (baseband to IF)

MAPPERTX FILT

TX FILT

INT

INT

DAC×

exp(-jnπ/2)

LPF #1

LPF #2

LPF #3

SAW #1

SAW #2

SAW #3

×

DDS

Low-IFBinary data in

This particular scheme assumes that the sampling rate is always four times the IF: fs = Nrs = 4fIF where rs is the symbol rate and N

is the oversampling factor. The complex multiplication can be replaced by a multiplexer/inverter (+In, +Qn+1, -In+3, -Qn+4)

IF



• Transmission Equipment– power amplifiers:

• klystrons: cheaper, up to 5 kW • travelling wave tube amplifiers (TWTA): largest

bandwidth, better efficiency, higher gain, up to 3 kW• transistor amplifiers: up to 0.1 kW, large bandwidth,

worst efficiency, non-linear behaviour, gain variation in time


Radio Frequency Subsystem• Transmission Equipment

Technology F P Eff BW Gain(GHz) (kW) (%) (MHz) (dB)

Klystron 6 1-5 50 60 4014 0.5-3 35 90 4018 1.5 35 120 4030 0.5 30 150 40

TWTA 6 0.1-3 40 600 15014 0.1-2.5 50 700 5018 0.5 50 1000 5030 0.05-0.15 50 3000 50

FET 6 <0.1 30 600 3014 <0.05 20 500 30



• Receiving Equipment– system noise temperature, T:

T = Tu + Td

Tu = TA / LFRX + (1 – 1/LFRX)Tf +where TA is the antenna temperature, LFRX is the feeder loss and Tf is the feeder temperature

Td = To(F - 1) = TLNA + TM/GLNA + TIF/GLNAGM

– the LNA is the critical module that determines the system noise temperature


Radio Frequency Subsystem• Receiving Equipment

– gallium arsenide technology (GaAs) used for LNA– high electron mobility transistors (HEMT)

Frequency band Noise temperature Noise figure(GHz) of the LNA (K) (dB)

4 30 0.4312 65 0.8820 130 1.640 200 2.3


Radio Frequency Subsystem• Single frequency conversion from RF to IF

– The RF signal captured by the dish is amplified by the LNA then filtered by a band pass filter centeredon the carrier frequency fc.

– The signal is then mixed with a variable local carrier adjusted to produce the same intermediate frequency, IF, usually at 70 or 140 MHz.

– After filtering with a sharp band pass filter, the signal is fed to the demodulator block.


Parallel– to Serial

Converter

Integrator

cos(ωct)

-90°

Binary data out

QPSK/QAM input

Block diagram of a QPSK/QAM demodulator

Integrator t = T

t = T

Communication Subsystem


• Demodulator (IF to baseband)

IF

Binary data outRX FILT

RX FILT

DEC

ADC×

exp(jnπ/2)

LPF #1

LPF #2

LPF #3

SAW #1

SAW #2

SAW #3

×

DDS

STRCPR

DEC

AMB.REM.

FREQ. EST.

FRAME SYNC.

CHAN. EST.

UWPROC.

FREQ. ADJ.

BURST DETECTAGC

This particular scheme assumes that the sampling rate is always four times the IF: fs = Nrs = 4fIF where rs is the symbol rate and N

is the oversampling factor. The complex multiplication can be replaced by a multiplexer/inverter (+In, +Qn+1, -In+3, -Qn+4)

Low-IF



Uncoded modulation• BER function of Eb/N0 and modulation type for an

additive white noise Gaussian (AWGN) channel.

http://en.wikipedia.org/wiki/File:PSK_BER_curves.svg


Channel Coding Advantages

• The channel capacity theorem states that in order to transmit with a bandwidth efficiency of 1 bit/s/Hz using QPSK modulation, at an arbitrary low BER (Rb < C), the minimum Eb/N0 is 0.2 dB.

• For QPSK modulation, a BER < 10-10 requires an Eb/N0greater than 13 dB.

• Channel coding is used to reduce the 13 dB gap.


Channel Coding Advantages

• Capacity bounds:

Bandwidth Shannon QPSK 8PSK 16QAMEfficiency bound bound bound bound[bit/s/Hz] [dB] [dB] [dB] [dB]

1.0 0.0 0.2 0.2 0.01.5 0.9 1.5 1.3 1.12.0 1.7 ∞ 2.9 2.12.5 2.8 - 4.8 3.3


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Courtesy of Prof Alex Grant


2 ACI + CCI + TWT

Channel Model


The Payload

Contents: Transparent RepeatersMultibeam Satellite Repeaters Regenerative Repeaters Generic Payloads Satellite Antenna Characteristic


The Payload

• Captures the carriers transmitted by the earth station with as little interference as possible

• Amplifies the received carriers while limiting noise and distortion

• Changes carrier frequency (down-conversion)• Amplifies the transmitting carriers• Radiates the carriers in a given frequency band,

polarisation to their destination


The Payload

• The uplink is characterised by the figure of merit (G/T)• The downlink is characterised by the effective isotropic

radiated power (EIRP)• They are related by the station-to-station link:

[(C/N0)T]-1 = [(C/N0)U]-1 + [(C/N0)D]-1

• For a fixed (C/N0)T it can be rewritten as:C = A[(G/T]-1 + B[EIRP]-1

where A, B and C are constants


Transparent Repeaters

• Non-linearities:– power gain: ratio of output power to input power– 1 dB compression point: the point where the output

power deviates with 1 dB from the extension of the linear part. It is used to define the part of the input output characteristic considered to be linear. It is also used to characterise the power of a transistor amplifier

– the AM/AM and AM/PM is usually given in a tabular form for each power amplifier



• Non-linearities:– The non-linearity due to the satellite amplifier is

memoryless; however, when considering the input and output multiplexers, the satellite channel behaves like a a nonlinear channel with memory!

– For input level p, the output level and phase can be modelled analytically as follows:

• Amplitude(p) = ap/(1+bp2)• Phase(p) = cp2/(1+dp2)


Transparent Repeaters• Non-linearities:

– Constellation warping is more significant for higher order modulations that have a large difference between the instantaneous energy and the average energy, e.g. 16QAM schemes or higher.

– Some constellation points are compressed, some are rotated, depending of how close to saturation the current operating point (defined by the average energy) is.

– In general this distortion is invertible but would lead to noise amplification. Constellation prewarping could also be used.

– The best solution is the centroid averaging method that can be used as a reference for the metric calculation in the decoder.


16QAM Modulation


Performance of 16QAM Modulation


Required Eb/N0 for BER = 10-6

IBO [dB] 0 2 3 4 5 6 10

OBO [dB] 0 0.77 1 1.36 1.75 2.2 4.4

Eb/N0 for same average

energy[dB]- 7.4 5.9 5.24 4.9 4.5 4.05

Final budget [dB] - 8.17 6.9 6.6 6.65 6.7 8.45

Performance of 16QAM Modulation



– Spectral Spreading is caused by passing an input signal through a nonlinearity.

– One effect of the spreading is the reduced power of the signal in the useful bandwidth of operation => decrease in the energy per transmitted symbol. For example:

IBO [dB] Signal energy lost [dB]10 0.156 0.293 0.450 0.64

– A second effect is the interference with the adjacent channels



– Intersymbol interference (ISI) is caused by the combined effects of the nonlinearity plus filter memory

– The effect is that the received symbols are scattered within a cluster centered around the received warped constellation points.

– Decision feedback equalization, Volterra equalization are used in uncoded systems

– Turbo equalization can be used efficiently to combat the ISI.


ISI for 16QAM Modulation



• Multicarrier operation:– intermodulation products: components that appear at

linear combinations of the carrier frequencies– only odd intermodulation products (IM) occur in the

vicinity of the input frequencies– the most common are the third order products:

2fi - fj and fi + fj - fk

– the maximum power is shared with the unwanted intermodulation products



• Multicarrier operation:– the input stage has a wide band (hundreds of MHz)– tens of carriers will give rise to a large number of IM

products => channelisation (sub-bands with reduced number of carriers)

• limited increase of intermodulation noise• increased total power of the repeater


Transparent Repeaters• The output high power amplifier:

– a small back-off has the benefit of high power but also high IM noise due to the non-linear region

– a large back-off reduces intermodulation but also reduces the available output power

– the optimum back-off point is that for which the overall link is maximised (C/N0)T

– efficiency: the ratio of radio-frequency output power to the direct current electric power consumed


Non equiprobable constellations16QAM


Transparent Repeaters• TWTA vs SSPA

Parameter TWTA SSPAOperating band: C, Ku, Ka C, KuSaturated output power (W): 20-200 20-40Gain at saturation (dB) 55 70-90Third order IM (dB) 10-12 14-18DC to RF efficiency(%) 50-65 30-45Mass (Kg) 1.5-2.2 0.8-1.5


Multibeam Satellite Repeaters

• Have several rx/tx antennas• Provide coverage to different service zones

– fixed interconnection (transponder hopping)– reconfigurable interconnection (on-board switching)

• reconfigure the payload by changing the connection between the channel output and the transmitting antennas

• the capacity of the satellite is adapted to the changing in the traffic demand

• power splitters and combiners or cross-bar couplers


Multibeam Satellite Repeaters

(http://ieeexplore.ieee.org/iel1/35/401/00007656.pdf)


Regenerative Repeaters• Perform carrier demodulation and remodulation• Applications:

– interconnection of networks with different data rates– reduced EIRP for the mobile stations and operate the

satellite close to saturation– ATM networks with better throughput

• Examples:– ITALSAT– Advanced Communications Technology Satellite


Regenerative Repeaters



Regenerative Repeaters• Digital component technology:

– radiation resistant• CMOS sensitive to latch-up phenomena caused by heavy

ions => hardened can withstand cumulative doses < 100krad• Bipolar and gallium arsenide (GaAs) are not affected by the

latch-up but by single upset errors– high speed (GaAs have delays < 0.1 ns per gate)– low power consumption (CMOS but consumption

increases with frequency)– high integration density (CMOS - 1E7 gates per chip)


Regenerative Repeaters• AMERHIS: interactive broadband DVB_RCS/S

On-Board Processor Communication System– Combines DVB-S (downlink) and DVB-RCS (uplink)

standards into a regenerative multi-spot system.– On-board multiplexing of DVB-RCS channels into

one or more DVB-S data streams cross-connecting and broadcasting uplink and downlink channels coming from separate coverage areas.

– 4 transponders of 33 MHz each (64 ch @0.5 Mbit/s)– On-Board budget: 210W, 216 Mbps, 30 Kg


Generic PayloadsTo cope with the rapid changes in technology, the best satellite system architecture should be that of a relay, bent pipe satellite. However, to improve the link budget, the QoS, and delay transmissions, regenerative payloads are preferred (the signal is demodulated and packet switching/routing can be performed at the satellite level). The main drawback is the lack of flexibility and adaptability to new technologies, as all digital hardware is based on ASICs. The use of FPGAs would allow the software radio concept to be applied to satellite payloads.


Generic PayloadsThe reconfiguration process can be detailed as follows:– upload of the binary file representing the new functionality to

be implemented in the FPGA from the ground station to the satellite’s on-board memory,

– switch off the FPGA to be reconfigured (in the near future it will be possible to reprogram specific slices of the FPGA while the rest of the FPGA is able to function as programmed),

– load the new configuration on the FPGA through a specific interface (e.g., JTAG)

– send back telemetry to confirm the new configuration was loaded correctly (e.g., CRC of the binary code of the FPGA)

– switch on the FPGA and the new services.


Generic PayloadsSatellites operate in a high radiation environment caused by the protons and electrons belts of high energy generated by Earth’s magnetic field. Cosmic radiation and solar flares can modify a memory state or induce a non-desired circuit behaviour in high integrated circuit technology, even leading to latch-up or burnout.Total Ionizing Dose (TID) is defined by the aggregation of interactions of a large number of protons and electrons within a part of the FPGA device. This interaction induces electrons/holes in gates or MOS structures.


Generic PayloadsThe effects of ionization on electrons or holes can be seen in changing some characteristics of the components (the threshold voltage of the gate or the mobility level) on a permanent or semipermanent level. Single-Event Effects (SEE): a short time charge can be sufficient to induce state changes introducing random errors (single-event upsets - SEU) in logical circuits and/or memories. Devices are more sensitive to SEE as they are reduced in size because a switching state requires less energy. Thus new devices are sensitive to protons as well as heavy ions, increasing the SEE rate.


Generic PayloadsCommon techniques for SEU detection and/or correction:– Tripling the function: a majority vote over three repetitions of

the operation is used. – Doubling the logical circuit: using a XOR operation between

two identical implementation of a logical function.– Comparing the current configuration of a logic block with the

initial file, at regular intervals.– Calculating a CRC for each cell and comparing CRC values– Reprogrammed regularly the logic block using the partial

configuration function (SEU scrubbing), at regular interval function of the sensitivity of the application.

(SEU for GEO is in the order of 1E-7 error/bit/day)


Satellite Antenna Characteristics• Issues to be considered:

– Polar orbit satellites suffer from frequent temperature change from +90° when the reflector is radiated by the sun to -90° when the satellite goes into the shadow of the globe. This has an impact on the antenna shape and the antenna gain if it works at millimeter band.

– For GEOs using multibeam arrays, if the beams that are separated in frequency serve the same coverage, the Inter Modulation beams could be identical to the signal beams, a worst-case IM interference scenario.


Satellite Antenna Characteristics• Types of antenna beam:

– circular beam– elliptical beam– shaped beam (e.g. combining the radiation of several

elementary beams generated by different radiating elements located at the focus of an antenna reflector)

• Adaptive antennas, multiple beam and/or phased array antennas are designed to service separate geographic regions (allows frequency reuse)


Satellite Antenna Characteristics• Adaptive antennas

– First used as radar antennas with sidelobe cancelingcharacteristics

– Resolution is defined as the minimum tolerable angular separation between desired and interfering signals; an antenna with N degrees-of-freedom (ports) can suppress more than N-1 interfering sources.

– Basic configuration is: N ports, N complex weights, a signal summing network and a weight determining algorithm


Satellite Antenna Characteristics

• Multibeam antennas– Any antenna with more than one input (or output) port

if different radiation patterns are obtained when signals are injected at these different ports (N > 5 usually)

– The larger the aperture, the greater the resolving power that can be obtained, the quicker the change of the radiation pattern.

– Types: lenses, reflectors and phased arrays



• Multibeam lens antennas• Multiple beams in space can be created by focusing the

energy of a primary array of feed horns through a microwave lens. The axial symmetry of such configuration allows low aberration for scanned beams, thus resulting in low sidelobes and cross-polarization components

• Two types: refractive lenses using solid dielectric lens and constraint lenses which is a form of space-fed array where the ray path through the lens is constrained to follow an RF transmission line in order to reach the reradiating elements



• Multibeam reflector antennas• Design simplicity, ease of construction, inherent bandwidth,

light weight and low cost• Large multibeam feed structures must be offset-fed types to

avoid excessive blockage and high sidelobe levels• Each feed element separately illuminates the reflector to

generate a component beam. By properly exciting feed elements and thus summing individual component beams, a desired shaped beam may be achieved to serve specific ground coverage area.



• Phased array antennas• The reflector type antenna has a feed of N elements plus a

refractor (lens) or reflector which focuses the feed patterns into a number of narrow beams

• The phased arrays type consists of an array of antenna elements each of which has a wide earth coverage beam pattern; the pattern is controlled by the amplitude and phase excitation of each element => increased flexibility that allows the radiation pattern to be adjusted function of the traffic fluctuations and simultaneously placing jammers in antenna nulls.


Satellite Antenna Characteristics• Multibeam (MBA) vs phased array antennas

• phased array antennas are focused at a design frequency fo to receive signals from a given direction by adjusting an array of phase shifters. The signal suppression varies approximately as |f –fo|2, where f is the operating frequency.

• Multibeam antennas focus received signals by introducing differential path delays and translating a feed located in the focal region of the lens or paraboid. Therefore, the system remains focused over a very wide frequency band. An MBA with the aperture D = 120λ can suppress interfering signals more than 20 dB for |f –fo|, < 0.05f.


Satellite Antenna Characteristics• Miura-ori a method of folding up antennas

• It is similar to a classic origami flower where by pulling on opposite corners, the antenna is unfolded in space. This is based on a simple origami-inspired folding and it is less prone to failure.

• The technique was developed at Tokyo University's lnstituteof Space and Aeronautical Science in 1970 by Professor Koryo Miura. Similar work is done at Kyoto University by Professor Hagiwara Ichiro. Links:

– http://www.youtube.com/watch?v=67rJhgPjJvY&feature=related– http://www.youtube.com/watch?v=_9AqFovcl2A&feature=related


Satellite Antenna Characteristics• Miura-ori (http://www.miura-ori.com/English/e-usage.htm)

– It facilitates simultaneous extension or contraction in two directions perpendicular on each other

– Folds flat items for carrying and storing– Allows consecutive folding movement of the entire surface– Can be folded and unfolded just by pulling (shoving)– Can be supplied to sheet of large area due to the consecutive

movement– Easy and natural folding and unfolding operation– Creases open up to 180 degrees– No damages and tears when creases are reversed


The Platform

Content: Attitude Control The Propulsion System The Power Supply Solar Power Satellites Solar Dish Engine, Laser Beaming Telemetry, Tracking and Command


The Platform• The platform design depends on:

– the requirements of the communication payload– the orbit (orbit control, type of materials)– the launch (vibrations, folded panels)

• The main characteristics of the subsystems:– the maximum mass– spacecraft power– reliability


The Platform

• The interfaces between subsystems:– mechanical (vibration, shocks)– thermal (temperature, heat flux)– electric (voltage, current, power)– magnetic (fields, momentum)– electromagnetic (couplings)– information (rate, formats)


Attitude Control

• Determines the motion of the body of the satellite about its centre of mass– the yaw axis: points in the direction of the centre of

the earth– the roll axis: is in the plane of the orbit, perpendicular

to the yaw axis and in the direction of the velocity– the pitch axis: is perpendicular on the yaw and roll

axis in the south direction for a geostationary satellite


Attitude Control


Attitude Control• Attitude sensors

– measure the orientation of the satellite axes with respect to external references• earth: 0.05° accuracy, based on infra-red radiation of the

earth which appears as a black body of 255K against the background temperature of 4K

• sun: 0.005° accuracy, using photo-voltaic elements • stars: 10-4 degree accuracy, compares an image of a given

portion of the sky against a reference map (complex)

– measure the change in position with time (gyrometers)


Attitude Control


Attitude Control• Actuators: modify the attitude by generating a

torque (T = Fd) which in turn change the velocity or angular acceleration about an axis– angular momentum devices use the conservation of

angular momentum(reaction wheels, gyroscopes)– thrusters which produce reaction forces on the

satellite by expelling propellant– magnetic coils which exploit the earth magnetic field– solar sails which exploit the solar radiation pressure


Attitude Control


Attitude Control• Gyroscopic stabilisation

– kinetic energy: 2K = mv2 = m(rω)2 = (mr2)ω 2 = I ω2

where ω is the angular velocity and I is the moment of inertia

– the conservation of the angular momentum, L = Iω, implies that the orientation of L remains fixed in the inertial space

– by choosing an L aligned with the pitch axis, the pitch axis remains fixed in spite of the movement of the satellite, with limited movements on roll/yaw axes


Attitude Control• Spin stabilisation

– the satellite is given a rotation movement (spin) about one of the principal axes of inertia

– rotating antenna with low gain or– contra-rotation of the antenna – for a geostationary satellite the axis of rotation is

parallel with the poles (the pitch axis)– tens of revolutions per minute


Attitude Control• “Three-axis” stabilisation

– the body of the satellite maintains a fixed orientation with respect to the local coordinate system, therefore with respect to the earth

– unfolding solar panels aligned with the pitch axis and rotating about this axis in order to follow the sun

– flywheels (inertia wheels) mounted on board the satellite in a vacuum chamber and suspended on magnetic bearings to reduce friction(5 to 10 kg, 5,000 to 20,000 rotations/min)


Attitude Control


The Propulsion System• Generates reaction forces resulting from the

expulsion of material– low power thruster for attitude and orbit control, from

mN to a few Newtons (RCS - reaction control system)– medium to high power thrusters, hundreds of Newtons

to tens of hundreds of Newtons (AKM - apogee kick motor, PKM - perigee kick motor)

– the specific impulse, Isp, is the impulse (force x time) communicated during a time dt by unit weight of propellant consumed during this time interval


The Propulsion System

Type of propellant Isp (s) Thrust (N)Cold gas (nitrogen) 70 lowHydrazine 220-300 0.5-20Bi-propellant 290-310 500-12000Electric ions 1,000 to 10,000 < 0.1Solid 290 10-300,000

(Isp = Fdt/gdM where g = 9.807 m/s2)


The Propulsion System• Chemical propulsion:

– generates gases by chemical combustion of solid/liquid propellants

– used for high trust• Electric propulsion:

– involves the use of an electrostatic or electromagnetic field to accelerate and eject ionised material

– reduction in the mass of propellants– large amount of electric power (25 to 50 W/mN)


The Power Supply• Components:

– a primary source of energy, e.g. solar generator– a secondary source of energy that is used when the

primary source doesn’t work, e.g. in an eclipse period or during the first minutes following injection into the transfer orbit phase

– regulation, distribution and protection circuits. • After an eclipse the voltage delivered by solar cells is

around 2.5 times the nominal value• The battery voltage can vary from 15% to 30% between the

start and the end of an eclipse


The Power Supply• Primary energy sources:

– solar cells operate accordingly to the principle of the voltaic effect: a voltage appears at the connections to a p-n junction subjected to a photon flux

– the incident solar flux, assumed to be normal to the surface is estimated at 1,370 W/m2

– a typical 2 cm by 2 cm silicon cell can produce a voltage of 400 mV and a current of 140 mA.

– The conversion efficiency: 15% down to 10% in 10 years for a geostationary satellite


The Power Supply

• Primary energy sources: technologies• Cell type efficiency efficiency weight cost

BOL EOL% KW/m2 % KW/m2 Kg/m2 1000$/m2

Silicon 15 0.20 9 0.12 0.15 40GaAs 19 0.25 14 0.19 0.72 160Multijunction 25 0.34 19 0.25 0.72 200Thin film 13 0.17 9 0.13 0.10 20


The Power Supply

• Primary energy sources: solar panels– the cells are connected in series and parallel in order

to deliver the required voltage (e.g., 42 V) and current of several tens of amps.

– groups of cells are connected in parallel to avoid the loss of a whole branch if an open circuit breakdown of a cell occurs

– a short circuit cell leads to unbalanced current distribution => diodes in series with each branch


The Power SupplyIn July 2008 MIT announced the development of a solar concentrator made from a mixture of dyes that is applied to the surface of the glass to allow light to travel a much longer distance. The dye molecules coated on the glass absorb sunlight and re-emits it at different wavelengths. The light is trapped within the glass and transported to solar cells along the edge, creating electricity and allowing light into the room as well. The focused light increases the electrical power obtained from each solar cell by a factor of over 40. (http://web.mit.edu/newsoffice/2008/solarcells-0710.html)


The Power Supply

• Primary energy sources: solar panels– flexible panels rolled up during launching– rigid panels, folded for launching and deployed in

orbit by means of springs, cables and pulleys– the performance is in the order of:

• Silicon: 130 W/m2 50 W/Kg• GaAs: 160 W/m2 60 W/Kg


The Power Supply• Secondary energy sources: battery cells

– eclipses occur 90 days per year for as long as 70 min– capacity C (A h): characteristic of the product of the

current drawn and the time of use– specific energy (Wh/kg): the energy stored per unit

mass– mean discharge voltage– depth of discharge– charge efficiency


The Power Supply

• Secondary energy sources: technology– nickel-cadmium cells (30 Wh/kg)– nickel-hydrogen cells: higher specific energy and

greater lifetime (80 Wh/kg)– silver-hydrogen: high specific energy but limited

lifetime => used for LEOs (100 Wh/kg)– silver-zinc (130 Wh/kg)– lithium ion (160 Wh/kg)


Solar Power Satellites• Solar-power satellites (SPS) and wireless power

transmission (WPT) represent the possibility of gathering solar energy and use microwave transmission to send it to earth (1968). A power receiving antenna (rectenna) would convert the transmitted microwave energy in electrical energy

• A solar panel = 10 Km2, a tx antenna = 2 km diameter and a rectenna = 4 km diameter, can deliver 1 GW of electric power. A point-to-point WPT of 30 kW of microwaves was transmitted over one mile. A 800W microwave beam from a rocket to a free flying satellite.


Solar Power Satellites• 1979 Reference System Concept for SPS (USA): placing

a constellation of 60 SPS (5 x 10 x 0.5 km deep) in geostationary Earth orbit, each would provide 5 GW of power using a 2.45 GHz microwave beam.

• 1 km diameter for the transmitting antenna • The power receiving rectenna: 10 km x 10 km• 1999 NASA: the Space Solar Power Exploratory

Research and Technology (SERT) project: power density limited to 100-200 W/m2 corresponding to 15% of the intensity of normal noontime summer sunlight


Solar Power Satellites• 1994-1995 Yamasaki: Japan developed and tested a

rectenna 3.2m x 3.6m composed of 256 arrays, each with 9 elements; microwave frequency of 2.45 GHz, 3 m diameter parabolic transmitter of 5 kW; a peak RF-DC conversion efficiency of 64%

• By 2040, Japan will operate a giant SPS that will send microwaves with a lower power than cellular phones

• It will generate 1 GW/s, equivalent to a nuclear plant.• Huge solar panels: 3 km x 1 km with a 1 km diameter

power-transmission antenna


Solar Power SatellitesEADS Astrium, Europe'sbiggest space company,announced in January 2010that is seeking partners to flya demonstration solar powermission in orbit by 2015.

The Japanese Institute forUnmanned Space ExperimentFree Flyer which includesMitsubishi Electric, NEC,Fujitsu and Sharp aims tocommercialize SPS by 2030.


Solar Power Satellites• ANSI/IEEE standard for maximum permissible human

exposure to microwave radiation is 82 W/m2 averaged over six minutes (some countries use 10 W/m2).

• Efficiency (URSI white paper on SPS – Sep.2006):• Solar power to DC 13% (outside Earth’s magnetosphere)• DC power to RF power 78%• RF collection efficiency 87%• RF power to DC (rectenna) 80%

Total efficiency: 7%Therefore to generate 1 GW at the ground level one needs to collect about 14GW in space !


Solar Power Satellites• If the launch costs can be in the order of US$150/Kg,

the estimated power-generation cost of an SPS system can be around US$0.2/kWh.

• Today launch costs: US$10,000 for LEO (*6 for GEO).– By 2025: estimated at US$100– By 2040: estimated at US$10

• 5 kW/m2/day terrestrial solar cell * 0.17 solar cell efficiency = 0.85 kW/m2/day

• 1.37 kW/m2 solar power flux in space * 24 hours*0.07 efficiency = 2.3 kW/m2/day => 2.7 times better!


Solar Power SatellitesIn August 2011, the International Academy of Astronautics published the Space Solar Power assessment report regarding the latest in technologies and opportunities.

• Type I “Microwave Classic” SPS• Type II “Modular Electric Laser” SPS• Type III “Modular Sandwich Microwave” SPS


Solar Dish Engine

http://www.infiniacorp.com/main.php


Solar Dish EngineAn innovation in solarconcentrator design is the use ofstretched-membranes in which athin reflective membrane isstretched across a rim or hoop.A second membrane is used toclose off the space behind. Apartial vacuum is drawn in thisspace, bringing the reflectivemembrane into a sphericalshape.

http://www.infiniacorp.com/main.php


Sun-Powered Laser BeamingThe main problem with the use of a microwave beamer forefficient space-to-Earth power transfer is the diffractive beamspreading. This spreading is proportional to the ratio of(wavelength)/(transmitter aperture) thus requiring big spaceantennas (~ 1 km) and bigger surface rectennas (~10 km).Currently this can be implemented only through expensivemultiple launches and in-space assembly of such largeantennas.

These limitations can be overcome using a laser-based systemwith 100,000 times smaller than microwave wavelengths andnegligible spreading.


Sun-Powered Laser Beaming

http://www.f1.fhtw-berlin.de/studiengang/ut/publis/2004/SPS04.pdf

“One SPS unit 110.7 km² of PVcells is placed in GEO with anadditionally concentrator generatingnearly 53 GW of the incoming 275GW of direct sunlight. The energyis transmitted to ground via laserbeam at a receiver of PV cells of68.9 km² which finally insert 7.9GW of electricity (plus additionalterrestrial irradiation) into the grid.Together with the terrestrialirradiation this unit delivers 10 GWof constant power.”


Earth-Powered Laser Beaming

http://lasermotive.com/wp-content/uploads/2010/04/Wireless-Power-for-UAVs-March2010.pdf


Telemetry, Tracking and ControlThe main international body that recommends space communications protocols is the Consultative Committee for Space Data Systems (CCSDS) www.ccsds.org. The first protocols developed in the 80s, Packet Telemetry (TM), Telecommand (TC) and Advanced Orbiting Systems (AOS) were later restructured as Space Packet Protocol, Data Link, Synchronization and Channel Coding. Currently they are organised based on the five layers of the ISO model, as described here.


Telemetry, Tracking and ControlSCPS – Space Communications Protocol SpecificationsSCPS-NP – SCPS Network ProtocolSCPS-SP – SCPS Security ProtocolSCPS-TP – SCPS Transport ProtocolSCPS-FP – SCPS File ProtocolCFDP – CCSDS File Delivery ProtocolLossless Data Compression standardImage Data Compression standardProximity-1 Space Link Protocol


Telemetry, Tracking and Control• Telemetry links:

– provided by a separate carrier with data rates from tens of bits/s to a few kbit/s,

– it is used to transmit analogue quantities, sampled, quantised and encoded or binary system states,

– allows automatic remote measurement, monitoring and record keeping of data from scientific, housekeeping and engineering sensors on-board a spacecraft.


Telemetry, Tracking and Control• Tracking links:

– provided by a separate carrier with data rates from tens of bits/s to a few kbit/s,

– is used to measure the distance (range) from the Earth station to the satellite using the phase shift between the transmitted and received tones (∆φ = 2πf(2R)/c),

– it also measures the radial velocity (range rate) based on the Doppler effect (requires operation of the transponder in a coherent mode).


Telemetry, Tracking and Control• Control links (Telecommand):

– provided by a separate carrier with data rates from hundreds of bit/s to a few kbit/s,

– used to adjust a parameter on board the satellite or to load registers in a computer memory,

– security is very important => encryption, repetition with verification (deferred execution, sent back to the ground, its authenticity verified, then executed),

– the link must be insensitive to interference or jamming and survive even the attitude is perturbed.


Satellite ServicesContents:Broadcasting Satellite Services (DBS, DVB-S2,

Integrated Services Digital Broadcasting – Satellite)Fixed Satellite Services (INTELSAT, INMARSAT)Navigational Satellite Services (NAVSTAR GPS)Earth Resource Satellite Services (Radarsat, NOAA)Mobile Satellite Services (Iridium, THURAYA, ACeS)SCADA (Supervisory Control And Data Acquisition)


Satellite ServicesThe Alice Springs School of the Air provides an educational service for about 120 children living on properties or settlements covering over 1.3 million square kilometers of Central Australia using Interactive Distance Learning via satellite.


Satellite ServicesThere are 15 other Schools of the Air: 1 in NT, 5 in WA, 1 in SA, 3 in NSW and 5 in QLD. All started out by using the Royal Flying Doctor facilities (http://www.flyingdoctor.net/).


Satellite ServicesIntegrated Marine Observing System (IMOS), created in 2007, is designed to be a fully-integrated, national system which contributes to research in ocean change, climate variability, major boundary currents, continental shelf processes and biological responses.

(http://www.imos.org.au)


Satellite ServicesTerrestrial Ecosystem Research Network (TERN), was created in 2009 in order to provide infrastructure and procedures through which a wide array of ecosystem research data and knowledge can be stored, accessed and analysed.

(http://www.tern.org.au)


Satellite ServicesThe ARGOS system was launched in 1978 by CNES and NASA. The platform flies aboard POES and MetOp satellites. The ARGOS messages sent on a 401.65 MHz frequency at 400 bps are stored onboard and retransmitted to one of the three main receiving stations in Virginia, Alaska and Norway. There are also nearly 60 other L-band receiving stations which retransmit received data to processing centres in Washington, USA, and Toulouse, France.

(http://www.argos-system.org)


(http://www.argos-system.org)


Satellite Services“The Argos system calculates locations by measuring the Doppler Effect on transmission frequency. The Doppler Effect is the change in frequency of a sound wave or electromagnetic wave that occurs when the source of vibration and observer are moving relative to each other.” It can also extract the GPS position from the 128 bit message, if available. Argos-3 provides two way communications at up to 4.8kbps uplink. (http://www.argos-system.org)


MPEG-4• MPEG-4

– In MPEG-2, all sources (video, graphics, text) are combined into a plane of pixels.

– MPEG-4 is object based, different objects organised in a hierarchical fashion are being encoded and transmitted separately in Elementary Streams; the final composition of individual multimedia objects, including timing, spatial placing, event-driven behaviour, is described in Binary Format of Scenes (BIFS) language => optimum use of best codecs!


MPEG-4• ISO MPEG-4 Part 10 (AVC) or ITU-T H.264

– Average rate savings of 50% relative to MPEG-2– Enhanced motion estimation with variable block size– Integer block transform (4x4) with reduced losses– Improved in-loop deblocking filter– Enhanced entropy coding (context based adaptive

binary arithmetic coding - CABAC)– Each frame is processed in macroblocks (16x16)

encoded in intra or inter mode.


MPEG-4• MPEG-4 Animation Framework eXtensions

– Defines a collection of tools for interactive animated contents: geometric models define object appearance with linear or nonlinear deformations (muscle movement), physical and biomechanical models that add engineering or environment conditioned behaviour (inertia, gravity, collision, deformation), behaviour and cognitive models (respond to stimuli from the environment and learn => facial and bone animation)


MPEG-7• Describes multimedia content for indexing,

cataloguing, advanced search tools, program selection and intelligent content description.– Defines syntax and semantics of multimedia

descriptors– MPEG-4 has built in MPEG-7 data type that allows

for example a Personal Video Recorder to autonomously choose programs based on user preference and the descriptors in the MPEG-7 stream.


MPEG-21• MPEG-21: Users that interact with Digital Items.

– “The goal of MPEG-21: defining the technology needed to support Users to exchange, access, consume, trade and otherwise manipulate Digital Items in an efficient, transparent and interoperable way.”

– “MPEG-21 identifies and defines the mechanisms and elements needed to support the multimedia delivery chain as well as the relationships between and the operations supported by them.”


Direct Broadcast Systems• Analogue FM/ PAL:

– analogue receiver bandwidth of 36 MHz for FM/TV transmission with 25 MHz/V frequency deviation

– requires a C/N > 13 dB for acceptable picture quality• Digital TV:

– MPEG-2 compression to 8.5 Mbit/s, – a rate 3/4 QPSK, DSNG signal requires a C/N > 0 dB

to operate with PAL quality in the same 36 MHz=> significant savings in both bandwidth and C/N


Direct Broadcast Systems• DBS in United States

– high power satellites spaced at 0.1°– EIRP of 51 to 60 dBW at 17/12 GHz– Lowest resolution: 640x480x24x16 = 118 Mbit/s – High-definition TV: 1920x1080x30x16 = 995 Mbit/s– MPEG-2 compression:

• 4 Mbit/s for a movie channel• 5 Mbit/s for a variety channel• 6 Mbit/s for sports channel


Direct Broadcast Systems

• Link budget:– Satellite EIRP 51 dBW– antenna noise temperature 35 K– LNB noise figure 1.1 dB– losses of 4 dB– a receiving antenna size of 60 cm would allow the

use of 41.6 Mbit/s (25.8 Mbaud) for FEC rate of 7/8 in a transponder bandwidth (at -3 dB) of 33 MHz.


Direct Broadcast Systems• Direct-to-home (DTH) future directions

– 16QAM, 32QAM and 64QAM to allow transport of typical satellite channels on 8 MHz channels used by cable networks (CATV)

• Digital satellite news gathering (DSNG)– four QPSK rate 3/4 signals at 8 Mbit/s may be

placed in a 36 MHz transponder in frequency division multiplex using 0.9 m tx antennas.


Direct Broadcast Systems• DVB-S1

– QPSK modulation, CC-RS: rate ½ (4.5), rate 2/3 (5.0), rate ¾ (5.5), rate 5/6 (6.0), rate 7/8 (6.4)

• DVB-DSNG (digital satellite news gathering)– As above plus 8PSK: rate 2/3 (6.9), rate 5/6 (8.9) rate

8/9 (9.4)– Optional 16QAM: rate ¾ (9.0), rate 7/8 (10.7)

• DVB-S2– LDPC codes, BCH codes, Serial Concatenated Codes



– Modulations: QPSK, 8PSK, 4-12APSK, 4-12-16APSK – Roll-offs: 0.2, 0.25, 0.35– Coding rates: 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6,

8/9, 9/10– BCH outer code, LDPC inner code– 64800(16200) bits block– Capacity increase over DVB-S: ~30%



– Transponder cost (36 MHz): 1.3 Meuro/y • 8,500 users for DVB-S• 22,000 users for DVB-S2

– Combining DVB-S2 and latest audio/video codecs, the number of channels in a 36 MHz transponder is:

• 20-25 SDTV• 5-6 HDTV

– Multi-spot Ka band satellites further reduce the satellite capacity cost.


DVB-RCS2The Next Generation DVB-RCS system will include specifications for a significantly more powerful “RCS2” physical layer (a 16-state turboΦ code and a 3D turbo code, support for adaptive coding and modulation, support for continuous phase modulation, both continuous carrier and MF-TDMA, random access - not required to request capacity in advance), IP packet return link encapsulation as well as for the management (Higher Layer Satellite – HLS).The Mobile version of DVB-RCS, RCS+M, will be adapted to the Next Generation RCS. The DVB-RCS is a NATO standard for satellite communications.


Integrated Services Digital Broadcasting (Japan)

• Can handle multiple MPEG2-TS (transport streams) in which audio, video and data are multiplexed

• The system employs hierarchical modulation with a maximum information bit rate of 52 Mbit/s, sufficient to transmit two HDTV programs, in 34.5 MHz using TC8PSK– HDTV (1080) requires 22 Mbit/s– SDTV (480) requires 6 or 8 Mbit/s


Header

Transport Stream Cell 188 bytes

Header Payload

4 bytes

Sync bytetransport_priority

Payload_unit_start_indicator

Transport_packet_error_indicator

13-bit PID

Continuity_counter – 4 bits

Adaption_field_control– 2 bits

Transport_scrambling_control – 2 bits



• Multi-protocol encapsulation (MPE) provides a mechanism for transporting data network protocols over MPEG-2 Transport Streams in DVB networks, optimised for IP with a 48-bit MAC address space

• Datagram sections: maximum length 4080 bytes, fragmenting allowed

• Header can be scrambled, divided into 6 bytes



• MPE is not very efficient or elegant but it seems to be generally accepted, for the time being, and is supported by commercial products

• Packetised Elementary Streams (PES) is used for asynchronous/synchronous data streams; allows IP packets of up to 64 kbytes and it is supported by commercial products

• Most efficient is to use a private adaptation layer that defines its own segmentation/reassembly



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Direct Broadcast Systems• DVB-RCS vs DOCSIS (data over cable service

interface specifications)– DOCSIS defines interface standards for cable

modems and supporting equipment; currently being modified to be used over satellites and take advantage of the available infrastructure on the ground.

– HDTV and web enabled set-top boxes for regular TV use DOCSIS

– Downstream data rates 27 to 36Mbit/s, upstream up to 10Mbit/s


Direct Broadcast Systems• Hughes Networks Systems

– DirecTV: 18" diameter antenna or 18"x24" elliptical antenna for receiving 3 satellites simultaneously

– In early ’00s, DirecTV combined TV reception with Broadband IP capabilities using SpaceWay 2 Ka-band satellite (on-board traffic switching/routing).

– DirecTV and Microsoft will integrate DirecTV's programming with PCs running Windows Media Center edition, the Xbox 360, and some portable devices. HTPCs will function as DirecTV receivers.


Direct Broadcast Systems• Digital video broadcasting (DVB)-Europe, ETSI

standard EN300421: Direct-to-home (DTH)• to consumer integrated receiver decoders (IRD)• to satellite master antenna TV (SMATV)• MPEG-2 main profile at main level (MP@ML):

– similar to PAL quality can be achieved at 4-6 Mbit/s– studio quality requires 8-9 Mbit/s

• transport packets of 188 bytes• RS - CC (k =7, 1/2-2/3-3/4-5/6-7/8 with QPSK • Required Eb/N0: 4.5 dB to 6.5 dB


• Operating since 1964• US$1.1 billion in annual revenue• the widest distribution network

communications company• 29 satellites in operation• in 1965 launched of Early Bird, world’s first

commercial communications satellite• in 1969 transmitted Apollo XI lunar landing

INTELSAT.com


INTELSAT.com• In 1974 created the world’s first international

digital voice communications service• Enabled White House - Kremlin “hot line” • In the 80’s enabled broadcasters to use small

transportable earth stations to broadcast major news events

• In the 90’s focused on Internet applications and multimedia, “pay-as-you-go” services, etc


INTELSAT Services• International and domestic telephony and data• Internet services

– backbone connections at speeds up to 155 Mbit/s– Internet trunking for regional ISP– Direct-to-Home services using DVB/IP– Internet access

• Corporate Networks• Broadcast Services


INTELSAT 90x Satellites• C-Band:

– Number of transponders: 32 x 72 MHz and 12 x 36 MHz– Frequency: 5850 to 6425 MHz and 3625 to 4200 MHz– EIRP: Hemi/Zone Beam 43 to 37 dBW,

Global Beam 34 to 31 dBW

• Ku-Band:– Number of transponders: 8 x 72 MHz and up to 8 x 36 MHz– Frequency band: 14 to 14.5 GHz and 10.95 to 11.20 and

11.45 to 11.70 GHz– EIRP: Spot 52 to 47 dBW


IP Multicast Video Streaming• IP multicast video streaming enables many

clients to be connected by a single stream and achieving significant efficiencies in satellite and terrestrial bandwidth (e.g., 4 Mbit/s outbound from a hub in US and 128 kbit/s return satellite channels).=> satellites can achieve efficiencies by transmitting multicast streams to multicast-enabled terrestrial networks


• Launched in 2004 with Lufthansa Airline, Connexionby Boeing was adopted by many other airlines, Singapore Airlines offering live TV since 2005 (US$10/hour). It used Ethernet or 802.11 (WiFi) through a Ku-band Loral Skynet satellite network.

• The US$320 million revenue was less than $5 billion per year as initial estimated at a US$500k/aircraft cost. After 1 billion losses (less than 5 minutes of usage per aircraft per day on average) it closed at the end of 2006. The technology could be used by UAVs/military.

In-flight Entertainment


• Rockwell Collins formed in 2000 the In Flight Network joint venture with News Corp that used the Globalstar LEO satellite system but closed by 2001 similar to other companies, e.g., Inflightonline and AirTV.

• Today 2nd generation technology weighing ~75 kg (not 500 kg as for the Connexion equipment) aims at less than US$100k/aircraft installation costs, lower operating costs, quick installation - over night - and cheaper service fees targeted at ~US$10 per flight.



• Aircell offers today its Gogo in-flight internet service for the North American market based on its air-to-ground network developed since 1990s.

• Panasonic Avionics plans to launch its eXConnectbroadband service in 2010 based on Intelsat’s Ku band satellite network, delivering WiFi connectivity for email and internet ; it will also support mobile telephony through AeroMobile which uses the Inmarsat network.

• The Row44 system is based on the Hughes Network Systems’ Ku band satellite network and can offer datalinkspeed averages of more than 30 Mbps.



• In December 2007, Air France – KLM was the first operator to allow passengers to text messages high in the sky using OnAir, a joint venture of Airbus-SITA. Today they offer GSM/GPRS/WiFi internet based on the Inmarsat’s SwiftBroadband service, up to 24 voice calls and 432 kbps per data channel.

• Tiny base stations installed on the plane block out land-based signals and allow cell phones in the plane to connect with the onboard base station. This will keep the mobile phone power level to a minimum. Data and phone calls are routed via a satellite to the ground.



Very Small Aperture Terminal (VSAT)

A VSAT network has three components:

• A virtually unlimited number of VSAT earth stations with small dish antenna (1-2 m in diameter). The indoor part is a small desktop or PC that contains the receiver and transmitter.

• A network of geostationary satellites.

• A central hub (earth station) with a very large antenna (5-12m in diameter) which monitors and controls all the network components.


Why use VSATs?A VSAT network has significant advantages over a terrestrial network (lease lines, X.25, ISDN, Frame Relay, ATM, Internet):

• Low price: 1/2 to 1/3 the price of an equivalent Frame Relay

• Reliability: 99.9% network availability per year

• Coverage: can go where land lines are either not available, are expensive, are of poor quality or are not secure.

• Expendability/flexibility: easy to add, move, delete nodes

• Unmatched Speed and Broadcast Capability


VSAT - COMSYS• Star data terminals (64 kbit/s to 128 kbit/s)

– SkyBlaster (Gilat), DT7000/2000 (Hughes) at < US$1500– ArcLight (ViaSat former Scientific Atlanta) at ~ US$1000– WildBlue => ~ US$500

• DVB-RCS systems, initially at 384 kbit/s but finally up to 2 Mbit/s are selling at ~US$1500. DAMA terminals– Advantage (Gilat) at < US$1000– DialAw@y IP (Gilat) at < US$2000

• Hubs and Master Control Stations ~ US$500,000• Network Management Systems ~US$200,000


NAVSTAR GPS• the NAVigation Satellite Timing And Ranging

Global Positioning System launched in 1978• positioning accuracies range from 100 m (95%

of the time), to 5 to 10 m, to relative accuracies at the sub-meter, and sub-centimetre level

• the day-to-day running of the GPS program and operation of the system rests with the US Department of Defence (DoD), the management being performed by the US Air Force.


NAVSTAR GPS• 27 satellites - plans for 32- (~ 930 kg, 4 km/s)

with a minimum of 21 active 98% of the time• 6 Orbital planes at 55° inclination • 20,200 km above the Earth's surface • 11 hours 58 minute orbital period (12 sidereal

hours) • visible for approximately 5 hours above the

horizon


NAVSTAR GPS• Standard Positioning Service:

– transmits a coarse acquisition (C/A) code based on Gold codes, 1023 chips at 1.023 Mchip/s, and a navigation message at 50 bit/s on the L1 signal (1575.42 MHz)

• Precise Positioning Service– transmits the P code at 10.23 Mchip/s which would

repeat every 38 weeks (recently shortened to 1 week) on the L2 signal (1227.60 MHz)


NAVSTAR GPS

90°

L1 carrier

C/A code

Navigation dataP code

ΣL1 signal


NAVSTAR GPS• real-time navigation:

– uses a minimum of four pseudorange measurements to four satellites which are used to solve for the three-dimensional coordinates of the receiver and the clock offset between the receiver oscillator and GPS system time.

– differential GPS (DGPS) uses the pseudorangeobservable for positioning, but also incorporates real-time corrections for the errors inherent in the measurements.


NAVSTAR GPS

http://www.aero.org/education/primers/gps/howgpsworks.html


NAVSTAR GPS

http://www.nytimes.com/2009/05/03/automobiles/03DASHTOP.html?_r=1


NAVSTAR GPS

“Just like previous TomTom GPS units, but with a $10/month subscription for Weather, Traffic, Google Search, & Fuel Prices” (http://gpsmagazine.com/)

http://www.gpsmagazine.com/2009/05/tomtom_go_740_live_connected_g.php

http://www.gpsmagazine.com/2009/05/tomtom_go_740_live_connected_g.php


NAVSTAR GPS

“LiveViewGPS's PT-8200 can work inside a parking garage, an elevator, movie theater, basement. Relying on GPS, A-GPS, and nearby cell towers, the PT8200 can automatically switch into triangulation mode, combining last known GPS

location data with cell tower position fixes to triangulate its location on the map.” (http://gpsmagazine.com/)

http://www.gpsmagazine.com/2009/04/liveviewgps_covert_gps_tracker.php

http://www.gpsmagazine.com/2009/04/liveviewgps_covert_gps_tracker.php


NAVSTAR GPS• Error Source Stand-alone Differential

Satellite clock 15.0 m 0.1 mEphemeris 40.0 m 1.0 mOrbit 5.0 m 0.13 mIonosphere 12.0 m 1.0 mTroposphere 3.0 0.5 Total root sum squared

44.8 m 3.3 m


NAVSTAR GPS• high precision carrier phase positioning:

– uses the much more precise carrier phase observations to measure the whole number of complete wavelengths between the satellite and receiver.

– the two carriers have short wavelengths (19 cm for L1 and 24 cm for L2)

– uses linear combinations of the two frequencies and differencing techniques => errors < 1 cm


NAVSTAR GPS• Selective Availability

– Dither is an intentional manipulation of the satellite clock frequency resulting in the generation of the carrier waves and the codes with varying wavelengths. Therefore, the distance between each C/A code chip will be variable, and no longer the designed 293 m =>pseudorange errors of +/-100 m

– Epsilon refers to errors imposed within the description of the satellite orbit in the ephemeris data sent in the broadcast message.


NAVSTAR GPS• More to consider:

– The GPS satellites move on MEOs, where Earth's gravity is weaker (spacetime is less warped by Earth's mass the further away you go).

– The atomic clocks in the satellites run 45 micro seconds faster per day than clocks on the ground, deep in the Earth's gravitational well.

– If this effect isn't taken into account when the satellite signals are synced, the GPS coordinates would be out by more than 10 kilometres.


• Global coverage, independent of GPS but fully interoperable with it and with GLONASS.

• 27+3 MEO satellites (23,616 km and inclined at 56°) plus three GEO satellites (Inmarsat’s AOR-E & IOR-F5 and ESA’s Artemis) to become operational by 2014-15.

• open service (OS): OS signals will be broadcast in two bands, at 1164–1214 MHz and at 1563–1591 MHz, < 4m accuracy, 95% of the time once every second

• commercial service (CS): 0.01 to 1 m accuracy.

Galileo (EU)


Galileo (EU)• Worldwide annual turnover from products and services directly associated with satellite radio navigation was estimated at around € 130 billion in 2010 and is expected to reach € 240 billion in 2020. • It is estimated that, already, 6-7% of GDP in Western countries, i.e., € 800 billion in the European Union, is dependent on satellite radio navigation.• The EU contribution to the Galileo and EGNOS programmes for 2007-2013 amounts to ~€ 3.4 billion (development phase ~€ 600 million, deployment phase ~€ 2.4 billion, operation of EGNOS ~€ 400 million).


GLONASS• Global Navigation Satellite Service (Russian Federation)• designed for 24 satellites, three orbital planes whose ascending

nodes are 120 degrees apart, 8 satellites equally spaced in each plane with argument of latitude displacement of 45 degrees.

• the full system will be completed by 2012.• 19,100 km circular (MEO), 64.8 deg inclination, 8 day repeat

track. Russian company KB Navis claims it has created the world's first chipset smaller than a penny for a new generation of multi-signal navigation devices that can receive the signals of four systems at the same time: Glonass, GPS, Galileo and the Chinese Compass


BeiDou Navigation System• The current BeiDou 1 Chinese satellite navigation system has 4

geostationary satellites that service an area from 70°E to 140°E, and from 5°N to 55°N. The remote terminal sends a signal that is received by each satellite at different times; this info is sent to a ground station that computes the position of the terminal.

• China launched its second GEO satellite in spring 2009 for its Compass Navigation Satellite System (CNSS) - BeiDou 2. China intends to provide first a regional capability for Compass/Beidou, followed by completion of its full 30-MEO, 5-GEO constellation after 2015 and before 2020.

• positioning accuracy within 10 m, velocity accuracy with 0.2m/s, and timing accuracy within 50 nanoseconds.


Earth Resource SatellitesAccording to a 2010 report from Northern Sky Research, the use of commercial Earth resource satellites can be divided in three phases:

• Phase 1: started in 1972 with the U.S. Landsat series launch, operating in multispectral bands.• Phase 2: from 1978 to 1998 new systems from Russia, France, Japan, India and Canada entered the market.• Phase 3: Since 1998 there are more than 25 Earth resource satellites in-orbit today; they are capable of high resolution data and some satellite imagery is free. • The new Phase 4 will see the beginning of the use of Earth resource satellites as a commodity.


Spot High Resolution Telescope

SPOT (France) Optical: Pan(10m) and Multi(3) Band (20m)

50 Mbit/s QPSK

LandSat (USA) Optical: Pan(15m) and Multi(7) Band (30m)

150 Mbit/s(AQPSK)

Radarsat(Canada)

SyntheticAperture Radar(SAR)

105 Mbit/s(QPSK)

Terra (Nasa) Modis DirectBroadcast

13.125 Mbit/s(UOQPSK)

Typical Remote-Sensing Satellites

Earth Resource Satellites


Multispectral Mode

Imaging is performed in three spectral bands. The bands used are band XS1 covering 0.50 to 0.59 µm (green), band XS2 covering 0.61 to 0.68 µ m (red) and band XS3 covering 0.79 to 0.89 µm (near infrared). By combining the data recorded in these channels, colour composite images can be produced with a pixel size of 20 meters.

SPOT imaging


Useful spectral bands


Effect of disease on vegetation reflectance


Assume: 40km swath and 2m pixels = 20,000 pixels per scan line

12 bits per pixel, for 3 bands

Number of scan lines/sec 400

Rate = 20,000 x 12 x 3 x 400

= 288 Mbit/sec

Typical data rates in current systems are from 10 to 360 Mbit/s


Orbiting Carbon ObservatoryThirty billion tons of carbon dioxide, CO2, are producedfrom the burning of fossil fuels each year. About halfstays in the air, the other half disappears, nobody quiteknows where. In some years, all of the excess CO2disappears, in other years, all of it stays in the air.Humans account for 2% of the world’s CO2 emissions,natural sources, like the decay of dead plants, account forthe rest of 98%.Two centuries ago, CO2 levels were at about 280 ppm.Today’s level is 387 ppm and rising.


Orbiting Carbon ObservatoryA satellite in a ~700 km polar orbit could measure levelsof CO2 by using an instrument with three spectrometersto analyse light reflected off Earth. CO2 absorbs certainwavelengths of light in the near infrared; by measuringhow dim those parts of the spectrum are, the observatorycan determine how many CO2 molecules the light haspassed through. The spacecraft would be able to pick outemissions from a power plant or along highways. It willfly in a loose formation with the other Earth-observingsatellites of NASA's Afternoon Constellation, "A-Train":Aura, Glory, Parasol, Calipso, CloudSat and Aqua.


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http://www.bbc.co.uk/news/world-europe-18978483Greenland's ice sheet: the thawed ice area jumped from 40% of the ice sheet to 97% in just four days from 8/7/12.


Radarsat• The RADARSAT-1 satellite

– near-polar (i = 98.6°), sun-synchronous orbit at ~800 km, period ~100 min, repeat cycle of 24 days

– SAR antenna• 5.3 GHz, C-band wavelength (5.6 cm)• steerable antenna with multi-mode imaging capabilities• transmits microwave energy pulse towards Earth and

measures the amount of energy returned to the satellite

– data is either transmitted directly at 105 Mbit/s or stored on an board tape recorder.


Radarsat• Applications:

– images from 50 km x 50 km to 500 km x 500 km per scene and resolution from 8 m to 100 m.

– incidence angles from 10° to 59°.– data used in conjunction with other optical satellites

(LANDSAT, SPOT, IRS, etc)– agriculture, defence surveillance, forestry, floods,

disaster management, fires, geology, hydrology, ice, marine, mapping, etc


Radarsat• The Australia mosaic: a compilation of 165 images

captured from mid-November 2000 to mid-February 2001 by RADARSAT-1 using synthetic aperture radar (SAR).

• Radarsat-2 was launched in Dec. 2007 has a 3 m resolution imaging employing a state-of-the-art phased array antenna composed of an array of hundreds of miniature transmit-receive modules.


NOAA• 1970 National Oceanic and Atmospheric

Administration (NOAA): to observe, predict and protect the environment, weather/climate assessments. – geostationary operational environmental satellites

(GOES) for short-range warning– polar-orbiting environmental satellites (POES) for

longer term forecasting• 1994 merger between the US’s Defense Meteorological

Satellites and POES => National Environmental Satellite, Data, and Information Service (NESDIS).


• GOES • satisfies National Weather Service (NWS) requirements for

24-hour observation of weather and Earth’s environment to support storm-scale weather forecasting

• To meet requirements, GOES continuously maintains operational satellites at two locations (75 degrees West and 135 degrees West), with an on-orbit spare ready

• POES

• provides a continuous flow of global environmental information in support of NWS operational requirements

• Requires two satellites on-orbit, Sun-synchronous, orbit period 101 minutes, altitude 870km

• Scan width 2700 km, circles the Earth 14 times a day


International Space Station• ISS has 450-tonne and 1200 cubic metres of pressurized space - enough room for seven crew and a vast array of scientific experiments. The ISS moves around the planet at 17,500 mph, completing one orbit every 90 minutes. Its altitude ranges from 208 to 285 miles at an inclination of 51.6°.

• More than four times as large as the Russian Mir space station, 356 feet across and 290 feet long, with almost an acre of solar panels to provide electrical power to six state-of-the-art laboratories.


International Space Station• Microgravity research will focus on biotechnology (more effective medicines with fewer side effects, and to better understand tissue growth in the body), physics, combustion and materials science.

• Life science research will seek improvements in the treatment of diseases of the heart, and maladies such as anemia, cancer, diabetes and osteoporosis; improve plant growth systems and soil, water and energy conservation.

• Space science capabilities include study of the Sun, planets, comets, asteroids, and the galaxies beyond the Milky Way. Studies of the Sun will provide better understanding of its affect on Earth's weather and environment, and greater solar forecasting accuracy.


International Space Station• Earth sciences studies will be made of food production alter natives, ocean and fresh water issues, regional and global climate, geology, land use, and the Earth's environmental response to natural and human-induced variables.

• Engineering Research and Technology efforts will be devoted to several specific areas, including advanced robotics, sensors and energy storage, communication systems and electromagnetic propulsion.

• Commercial Product Development will be furthered by industry participation in space research designed to create new processes, products and services that provide competitive economic advantages, new jobs and better lives.


Tiangong 1 - "Heavenly Palace”• Since 2003, China became the third country to independently senda man in space, using the Shenzhou capsule system.

• In September 2011 the Tiangong-1 space lab was deployed as part of the Chinese efforts to build a 60 tonne space station.

• In November 2011, the unmanned Shenzhou-8 craft docked at an altitude of 340km. The vehicles used radar and optical sensors to compute their proximity to each other and guide their final approach and contact. A video feed from orbit showed the final moments of the vehicles coming together.

• A bigger and powerful Long March 5 rocket will be capable of putting more than 20 tonnes in a low-Earth orbit.


Tiangong 1 - "Heavenly Palace”• In June 2012, Shenzhou-9 craft with 2 men & one women docked with the Tiangong-1 space lab, the fourth Chinese manned mission.

• Only two members of the crew entered the lab at any one time. The third individual remained in the Shenzhou craft in case of emergency.

• During the flight, a range of scientific experiments were done, including a number of medical tests geared towards understanding the effects of weightlessness on the human body.


In 1992, the U.S. FCC allocated a spectrum in the "S" band (2.3 GHz) for nationwide broadcasting of satellite-based Digital Audio Radio Service (DARS). In 1997:CD Radio, renamed Sirius Satellite Radio, and American Mobile Radio, renamed XM Satellite Radio, paid more than US$80 million each to use space in the S-band for digital satellite transmission.XM car radios using chipsets designed by STMicroelectronics are used by General Motors, Honda, Toyota, Lexus, Nissan, Saab, Volkswagen, Porsche, Subaru, Suzuki, Cadillac, Buick, Chevrolet. Sirius services are used by Audi, BMW, DaimlerChrysler, Ford, Jaguar, Jeep, Mazda, Mercedes-Benz, Volvo, Mini. XM and Sirius merged in July 2008, Sirius XM.

Satellite Radio


Players: XM Radio Sirius WorldSpaceTotal debt: ~ US$ 1.6 billionTotal subscribers: ~ 14,000,000Total revenue: ~ US$ 1 billion

Satellites: 2 GEOs 3 elliptical 2 GEOs(“Rock” 85°W & “Roll” 115°W) geosynchronousMarket: USA USA nonUSAMonthly fee: US$10 US$13 US$5Radio cost: ~US$80Programs: ~100 commercial free channels, CD sound quality

Satellite Radio


Satellite RadioWi-Fi networks might interfere with satellite radio broadcasts: Sirius: 2320.0 2332.5 MHzXM Radio: 2332.5 2345.0 MHz Wi-Fi signals for 802.11: 2400.0 2483.0 MHz

RELY project in Europe demonstrated and validated the provision of added-value Live Digital Radio, Enhanced Navigation Services, Juke Box and Webcasting services in a vehicular environment. An S-band payload on Eutelsat W2A launched in 2009 is used as a proof-of concept for the new DVB-SH (satellite to handhelds) standard.


Satellite Radio“The XM chipset consists of two custom circuits able to process XM's digital signal transmitted either by XM's satellites or the XM's terrestrial repeater network. Called STA400 and STA450, the chipset designed by ST, has been fabricated using CMOS and proprietary high speed bipolar technology.

The STA400 Channel Decoder integrates all of the functions needed to demodulate the phase modulated signal: analog-to-digital converter, QPSK demodulator, signal power estimator, automatic gain control, TDM demultiplexor, Viterbi and Reed-Solomon decoders, deinterleaver and decryption circuits. The STA450 Source Decoder, performs the E-PAC decompression plus the volume and tone control for the decompressed audio signal.” (source: www.st.com)


The I2 generation of 4 satellites launched in early ’90s is expected to be in commercial operation until 2014 while the I3 generation of 5 satellites launched in 1996-1998 would be in commercial operation until 2018. They can provide one global beam and up to 7 spot beams. The I4 generation – 3 satellites - built by Astrium in 2005-2008 is a veritable powerhouse compared with the I3 spacecraft, offering Xpress Link Ku-band and L-band services: – Greater call capacity than all five I-3s put together – 60 times more power than any one of its predecessors – 12 times greater efficiency in its use of radio spectrum – 16 times the capacity and 25 times the receiver sensitivity– One global beam, 19 wide spot beams for mini-M and other

high-end maritime services, 228 narrow spot-beams.

Inmarsat


By 2013 a new generation of satellite, the Alphasat I-XL, will be launched using the Alphabus that will be able to supply approximately five times the communications capacity of a single I4 satellite across 41 MHz of L-band. It will have a 12 m aperture antenna reflector, an electrical power of 12 kW and a design lifetime of 15 years. It will be launched by the Ariane 5 ECA.

The Alphabus model, will support missions that have a launch mass of more than eight tones and 18 kW payload power. These can use novel systems such as ion engines, which are more efficient than chemical thrusters in maintaining the orbit or a spacecraft over extended periods. The satellite cost is estimated at USD350 million and will provide redundancy to the I4 network.

Inmarsat


The I5 generation of 3 satellites is scheduled to be launched in 2013-2014 will provide Ka-band services and are referred as Global Xpress with expected commercial life beyond 2028. The 702HP spacecraft has 89 spot beams and can produce 15 Kw using ultra triple-junction gallium arsenide solar cells.The service will offer seamless global coverage at speeds of up to 50 Mbps to antennas of 60 cm diameter or 10 Mbps to an iPad (20 cm) and will combine the services offered at Ka-band by the I5 geostationary satellites, with the existing L-band services. The I5 satellites are built by Boeing Space and Intelligence Systems. The ground segment is provided by iDirect while SeaTelInc. and Thrane & Thrane are contracted for the manufacture of satellite terminals.

Inmarsat


The Broadband Global Area Network (BGAN) service launched in 2005 provides a fast, efficient connection, allowing you to download 50 K files, e-mail or attachments in about 10 seconds.

Advanced spot-beam technology allows Inmarsat to maintain a footprint stretching across most countries in the world; with the launch of Inmarsat 4 generation of satellites it achieved world coverage by 2009, except for the extreme polar regions.

The maximum bandwidth within each spot-beam is 496 kbit/s. But because BGAN is a packet data network, the average bandwidth available is shared among several connected users if they transmit data at the same time.

BGAN


Since August 2008, Inmarsat’s BGAN is used by a European Union-backed emergency response initiative to set up temporary GSM networks in disaster zones. The BGAN terminals are connected to a GSM picocell base station designed for deployment during the first days of an emergency and provides a 300-meter radius for communication between GSM devices.


The Institute for Telecommunications Research (ITR) at the University of South Australia was involved in the study and development phases of the technology used today in BGAN.– Following a successful bid, ITR developed in 1996 the first

commercial application of turbo codes that used 16QAM. The objective of the project was to reduce the bandwidth occupied by the High Speed Data Rate Inmarsat service

– Engineering prototypes, “Gold bricks”, were developed that implemented a turbo code in both FPGA and Shark DSPs.

– Follow up projects with Inmarsat involved the development of even higher data rates that can be used for maritime, landline and aeronautical services.

BGAN


A constellation of ~40 bent-pipe satellites, each using 16 beams and thirteen 1.25 MHz CDMA sub-bands at an altitude of 1414 km and inclination of 52°. The satellites need to connect the user’s call to a gateway on the ground, otherwise the call is lost. Many Globalstar satellites are experiencing degraded performance of the amplifiers for the S-band satellite communications antenna.

GLOBALSTAR

The cause: the South Atlantic Anomaly, the region where Earth’s inner van Allen radiation belt is closer to Earth, thus, for a given altitude, the radiation intensity is greater within this region than elsewhere.


Iridium's constellation consists of 66 LEOs, in a near-polar orbit at an altitude of 780 km and inclination 86.4°. The satellites are cross-linked operating as a fully meshed network and supported by multiple in-orbit spares. More than 250,000 subscribers in 2008.

The constellation is made of six orbital planes, evenly spaced around the Earth, each with 11 satellites equally spaced apart from each other in that orbital plane. The cellular lookdown antenna has 48 spot beams arranged as 16 beams in three sectors. The four intersatellite cross links (one ahead and one behind on the same orbit, and two others on adjacent orbits) operate at 10 Mbit/s in Ka-band. Ka-band feeder links connect with the ground gateways.

IRIDIUM


A single satellite completely circles the Earth once every 100 minutes, traveling at a rate of ~27,000 Km/h, and traveling from horizon to horizon across the sky in about ten minutes.

Main services are voice and low data rates transmission (Iridium's 9601 short burst data transceiver provides packet data, two-way connection, QPSK modulation, TDMA/FDMA.

Iridium NEXT generation satellite constellation, will be fully operational by 2016: 66 new satellites, end-to-end IP technology, low resolution images, launch additional payloads into space, utilizing Iridium's cross-links to deliver sensor and other data from anywhere on the globe to any other point.

IRIDIUM


Bottom view of the satellite showing well the Main Mission Antennas arrangement placed at 120 degrees apart. The four bronze dishes are the Gateway Antennas used to send the signals to the ground processing stations (http://www.obsat.com/irimage_e.html)


Sky Connect INDOORS is an Iridium voice, SMS and data terminal for land, mobile, and ship locations that can provide standard telephone service via Iridium. A computer may be attached for e-mail and Internal access. (http://www.iridium.com/products/product.php?linx=0046)

The 9505A, using L-band spectrum between 1616 and 1626.5 MHz, offers up to 30 hours of standby time and up to 3.2 hours of talk time. It is water, shock & dust resistant. Cost: USD3-USD15(http://www.iridium.com/products/product.php?linx=0001)


FROST & SULLIVAN’S FEBRUARY 2008 LEOSATELLITE TELEPHONE QUALITY OF SERVICE

COMPARISON (http://www.frost.com)

“… calls through the Iridium system are nearly three and half times more likely to be successfully connected and completed, without being dropped, than calls placed through the Globalstarnetwork. In Southern Florida, Iridium’s call success rate was measured to be 93.0%, compared to Globalstar’s 26.7%. While on the Texas Gulf Coast Iridium’s call success rate was measured to be 97.2 percent, compared to Globalstar’s 29.8 percent. Call success was defined, as it was last year, as a call connection on first attempt and the connection being maintained for a period of three minutes.”


GSM GPRS EDGE UMTSBands (MHz) 900/1800 900 / 1800 900 / 1800 2000 / 2500

Regulation Telecom Telecom, Telecom, Telecom,Licensed Licensed Licensed Licensed

Max. Data (kbps) 14.4 115.2 384 144 – 2000Typical (kbps) 14.4 30 50 – 80 30 – 300Transfer mode Circuit Packet Packet Circuit/packetApplications Voice Data Data Voice and DataMobility support High High High Low to highCoverage Wide Wide Wide Local to wideDeployment costsHigh Incremental Incremental High

UMTS - Europe


S-UMTS - Europe

• S-UMTS specific issues:– Time-varying multipath fading– Variable delay (variable satellite elevation)– Power control– Diversity techniques: temporal, polarization, spatial– Spot beams– Narrow-band multiuser detection


S-UMTS: Geostationary Satellite Payload Design

• modular architecture• large reflector antenna, 10 m or more, a large number of feed

elements (80-120) forming 160 high-performance beams• high performance mobile mission: G/T >10 dB/K, EIRP > 68 dBW

• transparent (digital or analogue), evolutionary capability, 320 x 5 MHz spectrum blocks

• re-configurable resource allocation in-orbit– RF power & spectral capacity

• on-board pilot tone test system• payload mass & power: 900 kg , 10 kW


S-UMTS: Geostationary Satellite Payload Design

Ka-BandRx/Tx

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THURAYA satellite/tri-band 900/1800/1900 MHz GSM/phone/GPS /camera/Micro browser (HTML, WAP 1.0, WAP 2.0) provides connectivity to networks in Asia, Africa, Australia, Europe and in North America. Weight of 170g, 138.5 x 52 x 18.8 mm (h x w x d)


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• Successful launch of GARUDA-1 satellite by Proton rocket from Baikonur / 4,500kg• One of the most powerful telecommunications

satellites ever launched (14 kilowatts of solar power)

• Largest commercial satellite ever built by Lockheed Martin / 12 year operational life / 144 spot beams• Acquired by Inmarsat in 2006 part of the world wide

BGAN service

Asia Cellular Satellite (ACeS)


• Enables affordable communication from anywhere in the region via satellite and GSM global roaming

• Group 3 Fax, 2.4 kbps in ACeS, 9.6 kbps in GSM900

• Seamless roaming between the ACeS satellite and GSM networks (dual mode ACeS/GSM at GSM comparable call charges)

• One telephone number/one bill, world’s smallest satellite phone!

• G-wave by ACeS: an IP based ultraportable satellite transceiver; WiFi, Ethernet up to 230 kbps.

Asia Cellular Satellite (ACeS)


Solaris Mobile, a joint venture company between SES Astra and Eutelsat, was established in early 2008. Solaris Mobile S-band payload was launched on April 3, 2009 on board of the W2A satellite located at 10ºE.Main business:

• multimedia services (Mobile TV and radio, Interactive broadcast, Content delivery)• vehicular applications (entertainment, location based services, remote vehicule diagnostic and software download

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The Quantum Car Receiver allows for two way datacommunications with the satellite using antennasembedded within vehicles. It can receive mobile realtime TV and internet radio with up to 10 TV channelsand 50 -100 radio stations at digital quality.


SCADASCADA (Supervisory Control And Data Acquisition) is a resource management system for remote areas. It includes the process of collecting data and performing actions on it remotely. The transmission media can be a terrestrial or a satellite network.

SCADA applications can be in the areas of oil & gas exploration, fleet monitoring, well monitoring, remote (hydro) power generation, pipeline operations, power transmission and distribution, metering operations, inventory management of tank storage facilities, flood warning and flood control, irrigation, waste water treatment, environmental monitoring.


SCADASCADA Telemetry Data Modems:(http://www.networkinv.com/index.php?id=413)

• Globalstar Axonn AXTracker• Globalstar GSP-1620 Data Modem• Hughes HNS 9201 BGAN Terminal• Iridium 9522A satellite data modem• Iridium 9601-DGS• Orbcomm Communicators• Skywave DMR-200 (IsatData Pro service)• Thrane Explorer 500 BGAN Terminal (M2M service)• Thrane TT-3026LM EasyTrack• ViaSat LinkStar VSAT System


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SCADASpecifications:

- Data rates: 2,400 to 64,000 kbps- Network Topology: SCPC (point-to-point) and

Star (point-to-multipoint)- Modulatation: BPSK, QPSK and OQPSK- Access methods:

Outbound TDM, Inbound TDMA, Enhanced Slotted Aloha

- Interfaces: DB9 RS-232, RJ45 Ethernet

Advantages: reliability, security, low recurring comms costs, low cost private HUB, effective utilisation of space segment, system scalability.


Global Satellite NetworkLarge terminal numbers

Low cost terminalsLow capital cost - Microsatellite One and two way service types

Flexible Operation – SDRGlobally Distributed – Global Data Sets

A combination not previously possible developed by the Institute for Telecommunications Research

www.itr.unisa.edu.au


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Terrestrial sensor networks gather data

Data collection from space enables the monitoring of data virtually anywhere, including remote

locations

Mission Concept


Communications System

Reception of more than 100,000 user messages in the satellite field of view within 25KHz channel


Satellite Installation

Contents: Installation in Orbit Launch Vehicles Options Orbital Servicing Vehicles Reliability Issues Cost Issues Space Debris Mitigation


Installation in OrbitTake the space elevator!

“The Space Elevator is based on a thinvertical tether stretched from the groundto a mass far out in space, and electricclimbers that drive up and down thetether. The rotation of the Earth and ofthe mass around it keeps the tether tautand capable of supporting the climbers.The climbers move as fast trains, andcarry no fuel on board - they arepowered by a combination of sunlightand laser light projected from theground” (http://www.isec.info/welcome). ht

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Installation in OrbitTake the space elevator!• Yuri Artsutanov proposed the Space Elevator in 1960• Launch satellites into orbit around the Earth• Inject payloads into planetary transfer orbits thus able to

launch payloads to Mars or other planets• Power beaming competition

(http://www.spaceward.org/elevator2010-pb)• Tether Strength Challenge: develop a material that is

sufficiently light and strong enough to bear its own weight against the force of Earth's gravity.(http://www.spaceward.org/elevator2010-ts)


Installation in OrbitTake the space elevator!

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• The trip to GEO will take a few days withno high accelerations and sudden zero-genvironment of a rocket launch.• The transition to zero-g will be smooth, theweight of the Space Elevator passengers willdrop smoothly therefore will be gentler onthe human body.• The current risky atmospheric re-entry willbe replaced by a smooth descent with a 360degrees panoramic view of the Earth, theseas, the cities, down to the ground station.


Installation in OrbitTake the space elevator!• Super-strong carbon nanotube ribbon would have to

stretch at least 22,000 miles and it would have to supportan elevator car that might weigh 7 metric tons, plus a 13-ton payload.

• It costs $10,000 per kilogram to send a load into spaceusing Delta and Atlas rockets. A space elevator couldtransport loads at a cost of $3,000 per kg initially,dropping to $300 per kg later on.

• It will cost $1.5 billion in research and development and$18 billion to actually build.

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Installation in Orbit– stage I: from the launching site on the surface of the

earth, the satellite is positioned in a low earth orbit (circular, 200 km, VLEO = 7,784 m/s)

– stage II: the satellite is injected into a transfer orbit (Hohmann transfer orbit, elliptical) via a first velocity increment that occurs at the perigee which corresponds to the low earth orbit (Vp = 10,239 m/s)

– stage III: the satellite is injected into a circular orbit via a second velocity increment that occurs at the apogee (Va = 1,597 m/s) corresponding to the final geosynchronous orbit (35,786 km, Vs = 3,075 m/s)


Installation in OrbitOrbit velocity:

V2 = 2µ/r - µ /a where:

a is the semi-major axis of the ellipse a = [(hP + hA)/2] + RE = [(200 + 35,786)/2] + 6,378 = 24,371 kmµ is the earth gravitational constant =3.986E14 m3/s2

r is the distance from the centre of the earth to the point concerned on the ellipse which moves with velocity V

• at the perigee, rP = 6,578 km => VP = 10,239 m/s• at the apogee, rA = 42,166 km => VA = 1,597 m/s


Installation in OrbitVelocity increment function of the latitude of the launch site


Installation in OrbitIn orbit mass reduction function of the latitude of the launch site


Installation in Orbit• For geostationary satellites the best launching site is at

the equator and towards East• For an inclined orbit, i, the desired inclination is obtained

by choosing the launch azimuth, A, as a function of the latitude of the launch site λES using:

cos(i) = sin(A) cos(λES)• The take-off velocity, due to the rotation of the earth is:

Vλ = VE sin(A) cos(λES)with VE = 2π6,378,000/86,164= 465 m/s (at the equator)


Installation in Orbit• Launch window:

– to permit determination of the attitude which is related to the angles of the sun and earth with respect to the satellite axes

– to ensure an electric power supply– to be within radio visibility of the control station

during the critical phases– to guarantee thermal control– to avoid saturating the sensors or disappearance of

references during critical manoeuvres.


FedSat Launch


Launch Vehicles

Solid-fuel rocket engines have three important advantages: •Simplicity•Low cost•Safety

They also have two disadvantages: •Thrust cannot be controlled.•Once ignited, the engine cannot be stopped or restarted.

The disadvantages mean that solid-fuel rockets are useful for short-lifetime tasks (like missiles), or for booster systems. When you need to be able to control the engine, you must use a liquid propellant system (www.hobbyspace.com/Links/RLVCountdown.html).


Launch VehiclesIn 1926, Robert Goddard tested the first liquid-propellant rocketengine based on gasoline and liquid oxygen. He also worked on and solved a number of fundamental problems in rocket engine design, including pumping mechanisms, cooling strategies and steering arrangements. These problems are what make liquid-propellant rockets so complicated. The basic idea is simple. In most liquid-propellant rocket engines, a fuel and an oxidizer (for example, gasoline and liquid oxygen) are pumped into a combustion chamber. There they burn to create a high-pressure and high-velocity stream of hot gases. These gases flow through a nozzle that accelerates them further (5,000 to 10,000 mph exit velocities being typical), and then they leave the engine.


Launch VehiclesMost launchers have three stages, each stage dropping away once it has fulfilled its purpose, thus launchers become progressively lighter and require less fuel. (Ex. Ariane-5 rocket launches)– 30-m boosters are attached to increase the thrust at liftoff– each booster contains approximately 230 tonnes of propellant

used in only 2 to 3 minutes– the main Vulcain engine under the main stage is ignited and

some seven seconds later the boosters ignite to enable liftoff– vertically lift off and after approximately five seconds it turns

progressively towards the east for a geostationary orbit – after 2 minutes it reached a height of around 60 km, at which

point the boosters separate and fall into the sea.


Launch Vehicles– the main stage burns for about 12 minutes during its ascent in

preparation for the horizontal trajectory which is handled by the upper stage engine

– once above the Earth’s atmosphere (>150 km) the fairing, which protected the satellites, is no longer needed and is jettisoned.

– the launcher reaches its highest velocity of around 8 km/s. – the launcher’s upper stage engine is cut and the computer on

board the launcher commands the satellite to spin on their axis to put them into the correct position to continue by themselves their journey into space.

– the upper stage is sent into what is called “cemetery orbit” to avoid any damage to other satellites and launchers.


European Space AgencyAnnual budget of 2.9 billion euros, about a quarter of NASA’s.15 member nations contribute in proportion to their gross national product to its mandatory programs (scientific exploration, space exploration and science probes). Other programs are Earth observation, telecommunications and launches. Current projects:– Rossetta probe launched in 2004 to meet comet Wirtanen– Mars Express, called Beagle, a remote observation spacecraft– Huygens probe, part of Saturn-bound Cassini, to land on Titan– Crew Return Vehicle for the International Space Station– BepiColombo probe to explore Mercury– Galileo, the European version of GPS


European Space AgencyAriane 4 was known as the “workhorse” of the Ariane family. • first flight on 15 June 1988 => over 100 successful launches.• versatile launcher: the first stage can hold two or four strap-on

boosters, or none at all. This means that it can lift into orbit satellites weighing from 2,000 to nearly 4,800 kg, nearly three times as much as the Ariane-3 launcher.

• Its role was gradually being taken over by the Ariane-5 launcher and the last Ariane-4 flight took place in 2003.

• Ariane 4 captured 50% of the market in launching commercial satellites (104 successful launches and only 3 failures).


European Space AgencySome of the Ariane 4 family statistics:

Type: 42 44LP 44LHeight: <58.72 m <58.72 <58.72Diameter1: 3.8 m 3.8 m 3.8 mLiftoff mass: 362 t 420 t 470 t Max. payload mass2: 3.48 t 4.22 t 4.73 t

1 With fairing 2 Includes mass of spacecraft, dual launch system


European Space AgencyThe Ariane 5 family:• Ariane 5G (Generic) has a payload capability to GTO is 6,200 kg.• The Ariane 5G+ had an improved second stage, with a GTO

capacity of 6,950 kg.• The Ariane 5 ECA has a GTO launch capacity of 10,000 kg for

dual payloads or 10,500 kg for a single payload. • Ariane 5 ES ATV has been designed for launching the Automated

Transfer Vehicle for up to 21,000 kg in LEO. • Ariane 5 ECB was planned to have a capacity of 12,000 kg, but

ECB was put on hold due to budget cuts.


European Space AgencyThe Ariane 5 family:• Ariane-5’s first test flight in 1996 was a failure due to a data

conversion from 64- bit floating point to a 16-bit signed integer. This was followed by other failures until March 2002 when the 8,111 kg Envisat environmental satellite was put in a 800 km orbit.

• The first successful launch of the Ariane-5 ECA took place on February 2005 when it launched the XTAR-EUR military communications satellite, a 'SLOSHSAT' small scientific satellite and a MaqSat B2 payload simulator.


European Space AgencyThe number of ground stations used to track the launcher depends on the type of launcher and the mission itself.– the French Guyana ground station tracks the first five minutes– a tracking station in Natal, on the coast of Brazil takes over for

the next 3 minutes during which the main stage separates and the second stage ignites

– the ground station on Ascension Island, in the middle of the Atlantic Ocean tracks the launcher for approximately 9 minutes until the satellites are injected into geostationary transfer orbit.

– transportable tracking stations


Lockheed-Martin• Athena, Proton, Titan, Atlas. • The Atlas launch vehicle families:

– the Atlas II (IIA and IIAS) is capable of lifting payloads ranging in mass from 2,812 kg to 3,719 kg to geosynchronous transfer orbit (GTO).

– the Atlas III (IIIA and IIIB) family is capable of lifting payloads up to 4,500 kg to GTO

– Atlas V (400 and 500 series) family is capable of lifting payloads up to 8,670 kg to GTO.

– delivered more than 50 satellites in the past 8 years.


Boeing• the first Delta II flew some 40 years ago.• Delta II launched the entire Global Positioning System

constellation for the U.S. Air Force• It can lift payloads of 900 kg to 2,000 kg to GTO and

2,800 to 5,800 kg to LEO. • Five versions of the Delta IV with payload capability

from 4,200 kg to 13,000 kg. First launch was in 2002.• Since December 2006, Boeing and Lockheed-Martin got

the approval to merge launch vehicle operations and become United Launch Alliance supplier.


Orbital Science Corporation• Taurus: four stage rocket

– 1,500 kg in LEO– 400 kg in GEO– > 50 launches in the last

decade with 100% success rate

– New Taurus XL rocket: 2 failures out of 8 launchings, last one the Orbiting Carbon Observatory (Feb. 2009)


Orbital Science Corporation

• Pegasus: three-stage, delta-wing rocket for satellites weighing up to 500 kg– It is carried aloft by a “Stargazer” L-1011 aircraft

to an altitude of 13,000 m– free-fall for 5 s before ignition– places satellites into LEO in about 10 minutes– first mission in 1990; 40 missions conducted– flawless record since 1996


Orbital Science Corporation


Sea Launch• Sea Launch is a sea-based launch system made of the

Sea Launch Commander ship where the launcher (Zenit 3SL roket) and its payload are assembled and the self-propelled platform Ocean Odyssey used as launch pad. It allows the rockets to be fired from the optimum position on Earth's surface thus increasing payload capacity and reducing costs.

• See a spectacular launch failure in January 2007• Created in 1995 by Boeing (owns 40%), it filed for

bankruptcy in June 2009. Emerged from bankruptcy in 2010 with a Russian corporation as a majority owner.


Sea Launch


NASA• The Space Shuttles began operations on 12 April 81 and

ended on 21 July 2011, after 135 launches at USD1.5billion each (6 built, 5 flew, Challenger disintegrated in 1986 at launch, Columbia broke apart during re-entry in 2003).

• the payload assist module (PAM) is designed as a higher altitude booster of satellites deployed in near Earth orbit but operationally destined for higher altitudes.– the PAM is used to boost various satellites to GTO or

other higher energy orbits after deployment from the space shuttle vehicle.


NASA

http://en.wikipedia.org/wiki/Space_shuttle


NASA

– The PAM-D is capable of launching satellites weighing up to 1,500 kg.

– The PAM-DII is for satellites weighing up to 2,200 kg. – The PAM-A is for satellites weighing up to 2,400 kg.– The PAM's deployable stage consists of a spin-

stabilized, solid-fuelled rocket motor and a payload attach fitting to mate with the unmanned spacecraft


NASAThe Orbiter weighs 165,000 pounds empty. The external tank weighs 78,100 pounds empty. The two solid rocket boosters (SRB) weigh 185,000 pounds empty each.

Each SRB holds 1.1 million pounds of fuel. The external tank holds 143,000 gallons of liquid oxygen (1,359,000 pounds) and 383,000 gallons of liquid hydrogen (226,000 pounds). The whole vehicle --shuttle, external tank, solid rocket booster casings and all the fuel --has a total weight of 4.4 million pounds at launch. 4.4 million pounds to get 165,000 pounds in orbit! The orbiter can carry a 65,000 pound payload (up to 15 x 60 feet in size).

The fuel weighs almost 20 times more than the Orbiter.


NASA1.T minus 31 s - the on-board computers take over the launch.2.T minus 16 s – the platform is drenched with water to protect the orbiter from damage by acoustical energy and rocket exhaust3.T minus 6.6 s - the three space shuttle main engines (SSMEs) are ignited one at a time (0.12 s apart). The engines build up to more than 90 percent of their maximum thrust. 4.T minus 3 s – SSMEs are in lift-off position. 5.T minus 0 s - the Solid Rocket Boosters (SRBs) are ignited and the shuttle lifts off the pad. 6.T plus 20 s - the shuttle rolls right (180º roll, 78º pitch) so that the orbiter is below the external tank (ET) to prevent a "top heavy" attitude, to reduce the stress on the wings and tail at mach one speed and to allow the astronauts to see the horizon.7.T plus 60 s - shuttle engines are at maximum throttle.


NASA8. T plus 2 min - SRBs separate from the orbiter and fuel tank at

an altitude of 45 km. Main engines continue firing. Parachutes deploy from the SRBs. SRBs will land in the ocean (about 225 km) off the coast of Florida. Ships will recover the SRBs and tow them back to Cape Canaveral for processing and re-use.

9. T plus 7.7 min - main engines throttled down to keep acceleration below 3g's so the shuttle does not break apart.

10. T plus 8.5 min – the orbiter rolls back, the engines shut down. 11. T plus 9 min – the ET separates from the orbiter and will burn

up upon re-entry. 12. T plus 10.5 min – Orbital Maneuvering System (OMS) engines

fire to move in low orbit. 13. T plus 45 min - OMS engines fire again to place you in a

higher, circular orbit (about 400 km).


Launch Vehicles• Russia:

– Series A (Soyuz Launcher)• 5000 kg into a 350 km circular orbit• 2500 kg into a 1400 km circular orbit

– Series B for 250 to 500 kg in low orbit– Series C (Cosmos) used for the SS-5 missile

• 1110 kg into a 1000 km circular 51° inclined orbit– Series D (Proton)

• 52 m high, can place 17 to 27 tonnes in low orbit• mass at take-off of 700 tonnes


Launch Vehicles

• China:– Long March launchers – number of stages: 2 to 3– length (m): 30 to 50– diameter (m): 3.35– mass (tonne): 190 to 460– lift-off thrust (MN): 3 to 6– payload mass (tonne): up to 5


Launch Vehicles• Tourism in space:

– October 2004: first privately funded manned spacecraft, SpaceShipOne rocket plane, reached an altitude of 112 km and Mach 3 speed ( = 3 x 340 m/s -speed of sound) claiming the US$10M Ansari X price.

– Space tourism bookings for US$200k for 5 minutes in space are available from www.outbackencounter.com

– To encourage the commercial space industry, the US Congress approved the no-liability regime for tourism ventures in case of accidents or failures.


Other Launch Options

Courtesy of www.tethers.com


Other Launch Options“In a momentum-exchange tether system, a long, thin, high-strength cable is deployed in orbit and set into rotation around a central body. If the tether facility is placed in an elliptical orbit and its rotation is timed so that the tether is oriented vertically below the central body and swinging backwards when the facility reaches perigee, then a grapple assembly located at the tether tip can rendezvous with and capture a payload moving in a lower orbit. Half a rotation later, the tether can release the payload, tossing it into a higher energy orbit. This concept is termed a momentum-exchange tether because when the tether picks up and tosses the payload, it transfers some of its orbital energy and momentum to the payload, resulting in a drop in the tether facility’s apogee.”(sourced from www.tethers.com)


Other Launch Options“In order for the tether facility to boost multiple payloads, it must have the capability to restore its orbital energy and momentum after each payload transfer operation. If the tether facility has a power supply, and a portion of the tether contains conducting wire, then the power supply can drive current along the tether so as to generate thrust through electro-dynamic interactions with the Earth's magnetic field. By properly controlling the tether current during an orbit, the tether facility can reboost itself to its original orbit. The tether facility essentially serves as a large "orbital energy battery," allowing solar energy to be converted to orbital energy gradually over a long period of time and then rapidly transferred to the payload.”(sourced from www.tethers.com)


Other Launch Options“Momentum-Exchange/Electrodynamic-Reboost (MXER) Tether Boost Facilities can reduce the cost of not only in-space propulsion, but also Earth-to-Orbit launch. For in-space propulsion applications, the MXER tether can serve as a fully reusable upper stage. By eliminating the need for each payload to have a dedicated upper stage vehicle, payloads can be launched on much smaller and less expensive rockets. As an example, a MXER tether designed to boost a 5 metric ton satellite from LEO to GTO could reduce the launch vehicle required for that satellite from a $45M Delta-II down to a $13M Dnepr 1 rocket, a roughly four-fold reduction in launch costs.”(sourced from www.tethers.com)


Other Launch Options“Design of an Electromagnetic Launcher for Earth-to-Orbit (ETO) Microsatellite Systems”, International Conference on Recent Advances in Space Technologies, Istanbul, Turkey, 2009.The paper proposes a vertical takeoff Electromagnetic Launcher (EML) for Earth-To-Orbit microsatellite systems. Design specifications are 6 km/s muzzle velocity and 20000 Gee’s acceleration for a 100 kg payload.


Orbital DetectionSpace Fence, also known as the US Air Force Space Surveillance System, is an array of dispersed radars that track satellites above 33º latitude as well as monitoring over-the-horizon threats from sea and air forces. It can see objects from a current minimum of 12 inches in size down to two inches in size. It has three transmitters and six receiver stations spread across US at around 33º latitude. Lake Kickapoo station in Texas is the largest continuous wave (CW) transmitter in the world with an average radiated power of 766.8 KW and operates at a frequency of 216.98 MHz. It produces a "fence" of electromagnetic energy that can detect objects out to an effective range of 15,000 nautical miles.Australia signed an agreement in late 2010 to cooperate with US in expanding the tracking capabilities from 20,000 to 200,000 objects.


Orbital DetectionThe Space Situational Awareness, an ESA Programme that had an initial three-year period to 2011 preparatory phase with operational services to be implemented in 2012-19.

• Survey and tracking of objects in Earth orbit – comprising satellites, discarded launch stages and debris that orbit the Earth,• Monitoring space weather -comprising particles and radiation coming from the Sun,• Watching for near-Earth objects -comprising natural objects that can potentially impact Earth.(http://www.esa.int/esaMI/SSA/)


Orbital DetectionSpace-Based Surveillance System (SBSS): will be a constellation of five satellites in LEO to look at satellites and other objects in GEO. It uses the missile defense experiment launched in 1996 that looked for ballistic missiles using a visible and an infrared sensor. The first satellite was launched in September 2010 in a sun synchronous orbit at 650 km altitude. It has a visible sensor which can find and track objects in space -- even new spacecraft launches and maneuvers -- with significantly greater speed, capacity and sensitivity than previous space sensors. The satellite also has an onboard image-processing payload and software that is reprogrammable to enhance mission flexibility and upgrades.

(http://www.boeing.com/defense-space/space/satellite/sbss.html)


Orbital DetectionRapid Attack Identification Detection and Reporting System(RAIDRS) is a terrestrial hybrid architecture of sensors, communication links, and data processing systems used by the United States Air Force (USAF) intended to analyze the data from satellites and determine if they are being affected by some external force. It’s a data situational awareness system that analyzes the data received at satellite downlinks. RAIDRS detects electromagnetic interference on satellites and identifies the source of potential jamming. Expected to be fully operational by 2011 it will have the capability for data fusion and to analyze radio frequency energy across many bands.


Orbital Servicing VehicleProgress is an unmanned Russian ship used to supply up to 2.5 tonnes of cargo to ISS, 3 to 4 times a year.http://en.wikipedia.org/wiki/Progress_spacecraft


Orbital Servicing VehicleKounotori or HTV, is an unmanned Japanese ship used to resupply the ISS with up to 5.3 tonnes of cargo. It was grabbed by the Space Station Remote Manipulator System (Canadarm2).http://en.wikipedia.org/wiki/File:HTV-2_Kounotori_2_grappled_by_Canadarm2.jpg


Orbital Servicing Vehicle• Modular On-orbit Servicing (MOS) concept from

Air Force Research Lab, USA. Benefits:– Enhancing operational availability (fix a wrong orbit)– Mission flexibility (replacing satellite components)– Scalability (on-orbit assembly, fuelling)– Extending satellite life by decontaminating optics,

reapplying coatings, filling cracks, lubricating joints.– Cleaning space debris– Reduce life cycle cost of satellites


Orbital Servicing Vehicle• Modular On-orbit Servicing (MOS) concept from

Air Force Research Lab, USA. • XSS-10 experiment (2003): a single micro-satellite to

demonstrate the ability to provide imagery for diagnosis, pointing of the imager and proximity flying

• XSS-11 experiment (2005): a single micro-satellite to demonstrate docking, the ability to understand the geometry of a novel/damaged in rotation satellite

• XSS-12 experiment: a single micro-satellite to demonstrate servicing (docking to a disfigured, dead, tumbling micro-satellite, bringing it back to life, and towing it to its proper orbit)


Orbital Servicing Vehicle• Agile Orbital Servicing Vehicle, Hyper-OSV from

National Space Development Agency, Japan– Long term in-orbit surviving functions, e.g. solar

panel, communication antenna, are provided by the “mother ship” (NSDA-Japan)

– Reconfigurable function for various servicing missions– Cooperative operation by multiple robots, HOSVs– Mobility by walking and free-flying; it has a

reconfigurable manipulator made of two arms of 60+30 cm length (local motion synchronised capture)


Orbital Servicing Vehicle


Orbital Servicing Vehicle• Modular On-orbit Serviceable Satellite arch. for

Defense Advanced Research Projects Agency, US– The satellite’s attitude must remain stable enough to

allow rendezvous with a servicing vehicle after failure– The satellite must support the capability to physically

receive new hardware– The satellite must be able to integrate the new

replacement h/w into its existing architecture– The satellite must be able to detect and isolate

anomalies, relaying health data to a ground center



Defense Advanced Research Projects Agency, US– “Remove and Replace” architecture

+ Clean, modular system+ May be performed indefinitely+ Demonstrated man-in-loop technology– Access to all serviceable hardware– Failed on-orbit replaceable unit removal adds complexity– Failed/replaced module should be de-orbited– Non-standard satellite packaging is required



Defense Advanced Research Projects Agency, US– “Plug and Stay” architecture

+ Traditional satellite design and packaging can be maintained+ Additional h/w can be added to a port+ New h/w can be brought on-line while the existing one is on+ De-orbit of failed h/w is not required, just powered down+ Low risk– Interference/blockage with physical structures– Mass properties update to attitude control s/w might be done– Limited by the number of available ports



Defense Advanced Research Projects Agency, US• “Plug and Stay” architecture• Provide module-to-module power based on a mechanical

connection rather inductively coupled connection• Utilize an electrically based, dedicated data bus, instead of

fiber optic or wireless data interfaces• Self-contained module thermal control• Major modular addition with self-contained propulsion• Baseline redundant (GHz+ rates) IEEE-1394 data busses for

satellite-to-module or inter-module communications.


Orbital Servicing VehicleAutonomous Nanosatellite Guardian for Evaluating Local Space (ANGELS) is a program that targets the launch of a small satellite in 2013-14 into GEO that would “escort” a larger satellite in order to monitor the space around the host satellite, watching for intruders and threats. ANGELS builds on experience from XSS-10 and XSS-11, that explore rendezvous, proximity, and station-keeping techniques with very small satellites. The XSS-10 was recently used to get 30m close to a Delta II booster, sending pictures and TV images.

(http://www.afa.org/magazine/june2006/0606space.asp)


Orbital Servicing VehicleSatmagazine, April 2007: “Orbiter Express is the first Atlas mission the United Launch Alliance (ULA) company conducted for the U.S. Air Force since ULA was established in December 2006 by merging the government launch services operations of Lockheed Martin and Boeing. Orbital Express is an in-space refueling demonstration mission consisting of the Autonomous Space Transfer and Robotic Orbiter, or Astro, prototype servicing satellite and the NextSat serviceable spacecraft. The mission tests the ability of robotic refueling and servicing satellites in space. Such a capability could extend the lives of government and commercial spacecraft.” http://www.boeing.com/companyoffices/gallery/images/orbital_express/index-gallery04.html


Orbital Servicing VehicleAn X-37 Orbital Test Vehicle, was launched in April 2010 using Atlas V rocket and returned in December 2010. A second one flew between March and June 2012.

“As part of its mission goals, the X-37 was designed to rendezvous with friendly satellites to refuel them, or to replace failed solar arrays using a robotic arm. Its payload could also support Space Control (Defensive Counter-Space, Offensive Counter-Space), Force Enhancement and Force Application systems.” http://en.wikipedia.org/wiki/File:Boeing_X-

37B_inside_payload_fairing_before_launch.jpg


Orbital Servicing VehicleThe Swedish Space Corporation in collaboration with the German Space Agency (DLR) launched on 15 June 2010 two satellites, Mango and Tango, initially mated together. After successful separation, they orbited Earth following closely linked paths, moving further apart and closer together. This project tested processes in autonomous formation flight and satellite rendezvous. DLR is also developing a demonstration mission called DEOS, planned for 2015, where two satellites will act as the “servicer” and the “client” spacecraft in need of capture and “repair”. The purpose is to understand how best to approach and grab other objects.

http://www.sscspace.com/products-services/satellite-systems/satellite-missions/prisma-1


Orbital Servicing VehicleIn March 2011, Intelsat signed a contract with MacDonald, Dettwiler and Associates Ltd. to deliver the Space Infrastructure Servicing (“SIS”) vehicle into near geosynchronous orbit, where it will service commercial and government satellites in need of additional fuel, re-positioning or other maintenance.

The SIS vehicle’s robotic arm will be used in refuelling and to perform critical maintenance and repair tasks, such as releasing jammed deployable arrays and stabilizing or towing smaller space objects or debris. http://www.mdacorporation.com/corporate/news/pr/pr2011031501.cfm


Reliability issues• The failure rate, λ(t), is the limit, as the time

interval ∆t tends to zero, of the number of pieces of equipment which fail during ∆t to the number of pieces of equipment in a correct operating state.– infant mortality phase– useful life (constant λ)– wear-out phase– it is measured in Fit, number of failures in 109 hours


Reliability issues

• The reliability, R(t), or the probability of survival, is defined as:

R(t) = exp[-∑λ(u)∆(u)]which for a constant failure rate, λ, becomes:

R(t) = exp[-λt]• The mean time to failure (MTTF) is the mean

time T of the occurrence of the first failure after entering service (For constant λ, T = 1/λ)


Reliability issues

• The mean satellite lifetime, τ, of designed maximum lifetime U, and MTTF, T = 1/λ, is :

τ = T[1 - exp(-U/T)]Ex.: MTTF = 10 years, U = 5 years => τ = 3.9 years

U = 10 years => τ = 6.2 yearsU = 20 years => τ = 8.6 years

– components prone to wear-out (e.g., thrusters, vacuum tube cathodes) have failures at end of life whose probability density can be modelled by a normal distribution


Reliability issues• Serial reliability: as the number of series

components increases, the reliability decreasesRs = R1* R2 * R3 * …

• Parallel reliability: a parallel system is not considered failed unless all parallel branch subsystems have failed.

Rp = 1 – (1 – R1) * (1 – R2) * (1 – R3) * …


Reliability issues• Component reliability (expressed in Fit):

resistors 5 to 10potentiometers: 200capacitors: 3 to 20diodes: 4 to 50transistors: 10 to 50integrated circuits: 10 to 500TWT: 150transformers: 200quartz crystals: 80relays: 400


Cost issues• US$100-200 million for a capacity of the order of

4000 kg at take-off (2,200 kg in geo orbit)• For the same capacity placed in orbit, the cost

depends on:– inclination of the transfer orbit– accuracy with which the orbit is obtained– thermal, static and dynamic mechanical constraints

• Total cost of ownership (TCO): satellite and launch vehicle (75%), operation, insurance (10%)


Cost issues• The Aerospace Corporation developed a Small Satellite

Cost Model using cost estimating relationships for developing and producing a spacecraft system with the following subsystems: Attitude Determination and Control Subsystem, Propulsion , Power, Telemetry, Tracking, & Command, Command & Data Handling, Structure, Thermal, Integration, Assembly and Test, Program Management and Systems Engineering, Launch and Orbital Operations Support.

• http://www.aero.org/capabilities/sscm/index.html


Cost issues• “Contemporary launch vehicles have launch costs of

$10,000 to $20,000 per kilogram of net payload to low Earth orbit (LEO) and $60,000 to $120,000 per kilogram of net payload to geosynchronous Earth orbit (GEO). NASA has initiated two activities aimed at identifying technologies and systems capable of producing dramatic reductions in launch costs. The Highly Reusable Space Transportation Systems (HRST) study goal is $200-400/kg to LEO (a factor of 50 reduction from current systems); the Affordable In-Space Transportation (AIST) study goal is $2,000-4,000/kg to GEO (a factor of 30 reduction)” – 2004 JPL report on www.astroexpo.com


Cost issues• The CubeSat concept was developed by California

Polytechnic State University and Stanford University and refers to small LEOs: 10 x 10 x 10 cm, 1.3W, <1kgo Project definition costs: US$5,000o Spacecraft construction: frame €2,300, attitude control € 2,000,

communications € 8,500, antenna €3,000, solar cells €2,000, other. Total of US$30,000

o Launch preparation cost: US$16,000o Launch cost: US$4,000

Total cost of placing an educational CubeSat in orbit is estimated at: US$55,000


Space Debris MitigationThe international forum for the coordination of activities related to the issues of man-made and natural debris in space is the Inter-Agency Space Debris Coordination Committee . The goal is to exchange information on space debris research activities between member space agencies, to facilitate opportunities for co-operation in space debris research, to review the progress of ongoing co-operative activities and to identify debris mitigation options. Space debris are all man made objects including fragments / elements thereof, in Earth orbit or re-entering the atmosphere, that are non functional.


Space Debris MitigationThe guidelines provided describe existing practices for limiting the generation of space debris in the environment with a focus on the following:

• Limitation of debris released during normal operations• Minimisation of the potential for on-orbit break-ups• Post-mission disposal (removing spacecraft and orbital stages that have reached the end of their mission operations from the useful densely populated orbit regions• Prevention of on-orbit collisions.


Space Debris MitigationRegions A and B should be protected regions with regard to the generation of space debris.


Space Debris MitigationSpacecraft that have terminated their mission should be manoeuvred away from GEO. The recommended minimum increase in perigee altitude at the end of re-orbiting, taking into account all orbital perturbations, is:

235 km + (1000·CR·A/m) whereCR: the solar radiation pressure coefficient (1 < CR < 2),A/m: aspect area to dry mass ratio [m2/kg]235 km: sum of the upper altitude of the GEO protected region (200 km) and the maximum descent of are-orbited space system due to lunar-solar and geopotential perturbations (35 km).


Space Debris MitigationSpace systems that are terminating their operational phases in orbits that pass through the LEO region, should be de-orbited (direct re-entry is preferred) or where appropriate manoeuvred into an orbit with a reduced lifetime. Retrieval is also a disposal option. A space system should be left in an orbit in which, using an accepted nominal projection for solar activity, atmospheric drag will limit the orbital lifetime (< 25 years) after the completion of operations. Surviving debris should be confined to uninhabited regions, such as broad ocean areas; environmental pollutants should also be minimised.


Space Debris MitigationPassivation ⎯ the elimination of all stored energy on a space system to reduce the chance of break-up.

• Residual propellants and other fluids, should be depleted either by depletion burns or venting.• Batteries should be adequately designed and manufactured, to prevent breakups. Charging lines should be de-activated. • High-pressure vessels should be vented to a level guaranteeing that no break-ups can occur. Heat pipes may be left pressurised if the probability of rupture can be demonstrated to be very low. • Self-destruct systems should be designed not to cause unintentional destruction due to interference.• Power to flywheels and momentum wheels should be terminated during the disposal phase.


Space Debris MitigationEstimation of penalty for re-orbiting at end-of-life. Required propellant for lifetime reduction within 25 years.

For orbits above 1400 km, less energy is required to re-orbit above 2000 km than to manoeuvre into a disposal orbit with a lifetime of 25 years or less.


The knowledge on all known objects in space is maintained and kept up-to-date through the DISCOS database (Database and Information System Characterising Objects in Space)

(Credits: European Space Agency)


In December 2004 there were 1,124 known objects in the vicinity of the geostationary ring: 31% were controlled satellites, 37% drifted around the earth and 13% oscillated around the stable equilibrium points. There were 153 uncontrolled objects of which no orbit data were available and 60 unidentified objects.



There are more than 22,000 objects actively being tracked, 500,000 particles ranging in size between 1-10cm across, and perhaps tens of millions of other particles smaller than 1cm, all travelling at several kilometres per second - sufficient velocity for even the smallest to damage the International Space Station.

Two incidents produced hundreds of thousands of new fragments. The first was China's deliberate destruction of a decommissioned weather satellite using a missile in 2007. The second was the accidental collision in 2009 of the Cosmos 2251 and Iridium 33 satellites.


This image shows the results of a lab test impact between a small sphere of aluminium (Al) travelling at approximately 6.8 km/second and a block 18 cm thick of Al.

• Al sphere diameter: 1.2cm• Al sphere mass: about 1.7 g• Impact crater diameter: 9.0 cm• Impact crater depth: 5.3 cm

In such an impact, the pressure and temperature can exceed those found at the centre of the Earth, e.g. greater than 365 GPa and more than 6000 K. (Credits: European Space Agency)


A picture of the damage caused by a micrometeoroid or small piece of space debris on the solar array of the Hubble space telescope. The arrays, which were built in Europe, were returned to ESA for analysis of in-orbit degradation. The crater is about 4 mm in diameter and was probably made by a particle of 0.5 mm diameter.



http://actu.epfl.ch/news/cleaning-up-earth-s-orbit-a-swiss-satellite-to-tac/

The Swiss Space Center at EcolePolytechniqueFederale de Lausanne has started in 2012 the CleanSpace One project that will deliver a family of satellites specially designed to clean up space debris.


http://www.eos-aus.com/

“Satellite Laser Ranging (SLR) is used to track objects in space. It involves the firing of laser pulses through a telescope at passing satellites and measuring the time taken for the pulses to return to

earth - EOS SLR facilities at Mount Stromlo in Canberra and the Moblas facilities in Western Australia.

Ablation is “the process of generating forces on objects by means of surface interactions with energy projected from a distant point”. Laser beams, directed from earth to intersect with objects in space, generate significant forces if the interaction is carefully controlled. This technology will allow pieces of space debris and other objects in space to be physically maneuvered into a different orbit using long range high power plasma beam (ablation).


Satellite Internet

Contents: TCP/IP over satellite Proposed Systems:

StarBand, HughesNet, Spaceway, ViaSat, SkyEdge, SkyBridge, Teledesic, Eutelsat

DVB: Multi-Protocol Encapsulation ATM connection handover in LEO networks


Open Systems Interconnectionsand TCP/IP

– Data Link / Physical Layer: defines the connection of the actual media used & the format of frames

– Network Layer: the IP protocol, a connectionless mode of operation that forwards and switches packets via any network route without guarantee of delivery

– Transport Layer: TCP, a connection oriented which provides guaranteed delivery (or UDP- connectionless)

– Application Layer: FTP protocol for file transfer, Simple Mail Transfer Protocol (SMTP) for email, or Hypertext Transport Protocol (HTTP) for browsing


TCP/IPInformationFlow

Physical medium

DL Layer Protocol

Network Layer

Protocol

Transport Layer Protocol

Application Layer Protocol

Physical

Data Link

Network

Transport

Application

Physical

Data Link

Physical

Data Link

Network

Physical

Data Link

Network

Transport

Application

Network Layer

Protocol

DL Layer Protocol

Physical medium

Router

Client Server


TCP/IP– TCP provides a reliable byte streaming, full duplex

connection oriented protocol– The TCP ensures that data is received in the correct

order by using a sliding window in which each segment is identified by a sequence number

– In the case of receiving an out-of-order segment, a duplicate acknowledgment is sent to the transmitter

– A TCP sender uses acknowledgments (ACK) transmitted by the receiver to determine its sending rate and to ensure reliable data delivery


TCP/IP– It uses window-based flow control mechanism to

prevent buffer overruns in the receiver and through the network

– It was designed initially for low bit error rates and low round trip time (RTT)

– On an error-free link, the minimum window size to keep the bandwidth full is the Bandwidth-Delay (RTT) product. For example, a 10 Mbit/s satellite link with a 500 ms delay requires a window size of 5 Mbit or 625 kbytes. A double satellite hop requires 1.25 Mbytes.


TCP/IP– A fixed window size creates an upper bound on the

throughput of a TCP connection:Maximum Throughput = Window size / Delay

– With a typical 32 kbyte window on Windows XP, the fastest that a TPC connection can transmit data over a satellite link with a 500 ms delay is 32/0.5 = 64 kbyte/s = 512 kbit/s. For the same window size:

LAN WAN SatelliteRTT (ms) 5 100 500Max Thr (Mbit/s) 51.2 2.56 0.512


Main issues

– Long / Variable Feedback Delay affects rate adjustment, congestion avoidance and error recovery

– Large Bandwidth-Delay Products means that the sender and receiver must be able to handle large amounts of data in a single window

– Asymmetric use requires different bandwidths– Higher Transmission Errors lead to packets not

acknowledged => the sender interprets this as congestion avoidance => reduced throughput


Previous solutionsRFC 1323 TCP Extensions for High Performance, 1992 (http://www.ietf.org/rfc/rfc1323.txt)• the sequence number space used to identify

segments is 16 bit long yielding a maximal delay-bandwidth product of 512 kbit/s; for a RTT of 520 ms, a maximum data rate for a single TCP connection is about 1 Mbit/s

• a set of window scaling options in excess of 1 Gbit/s is proposed; a window size of 146 kbytes can deliver 1.8 Mbit/s; timestamps for RTTM & PAWS


RFC 2001 TCP Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery Algorithms• a larger initial window of three or four segments

will allow more segments to flow into the network, decreasing the time it takes to complete the slow-start process.

• “fast restart” allows for retransmissions of a packet in advance of a timer expiration; it halves the TCP window size instead of reducing it to one when a packet is lost.

Previous solutions


TCP/IPTCP implements two controllers:

– Flow control: allows data exchange based on a sliding window protocol between two TCP nodes

– Congestion control: scheme based on two algorithms:• Slow start (SS) using the cwnd variable• Congestion Avoidance (CA) using the ssthresh (slow start threshold)

variable

The source sends first one TCP segment and waits for an ACK. Then, for each received ACK, it doubles the amount of data until cwnd reaches the ssthresh value; then the increase is linear, one extra segment per RTT.


TCP/IPIf the Retransmission TimeOut (RTO) at the source expires before a segment is acknowledged, TCP re-enters the SS phase, resets the cwnd (reduces throughput!) and re-transmits the first unacknowledged segment in the sequence.

While this behaviour in a terrestrial network is suitable in the case of network overloading, in a satellite link, a lost acknowledgement doesn’t necessarily mean traffic congestion! It could be simply caused by errors in the propagation channel with no need to reduce throughput!


• TCP Congestion Control– TCP CC needs to create losses to probe for

bandwidth– TCP CC would need to know the bandwidth

delay product for optimal performance

Con

gest

ion

win

dow Receiver window

Slow start threshold (should be bw delay product)

Packet loss

RTT

Packet loss

Network capacity

Previous solutions


• Vegas Congestion Control– Uses throughput as indication of congestion– Tunes itself to the bandwidth delay product of

the connection

Con

gest

ion

win

dow Receiver window

Bandwidth delay product

RTT

Network capacity

Previous solutions


tSlow Start = RTT*[1+log2(B*RTT/L)] where:RTT is the round trip timeB is the bit rateL is the average packet length in bits

For L = 1KB:Type RTT 1Mbit/s 10Mbit/s 155Mb/sLEO 50ms 0.18s 0.35s 0.55sMEO 250ms 1.49s 2.32s 3.31sGEO 550ms 3.91s 5.73s 7.91s

Previous solutions


RFC 2018 TCP Selective Acknowledgment Options• if a packet is lost, the enhanced TCP allows for the

retransmission of the single lost packet, rather than retransmitting that packet and all packets that have been subsequently transmitted (TCP SACK)

• the forward ACK (FACK) introduces new variables to more accurately track the amount of outstanding data in the network and maintain TCP self-clocking with multiple losses; decouples the congestion control from data recovery

Previous solutions


• Multiple losses per RTT– Basic TCP acknowledgment can only indicate

the highest in order packet received

Pks

Acks

1 2 3 4 5 6 7 8

1 2 2 2 2 2

Previous solutions


• Selective Negative Acknowledgments (SNACK)– Enables the signalling of missing packets above the

highest in order one

Pks

Acks

1 2 3 4 5 6 7 8

1 2 2 2 2 2

3 3 3 3

5 5 5Snacks

Previous solutions


– RFC 2488 Enhancing TCP over Satellite Channels Using Standard Mechanisms, 1999• outlines several IETF standardised mechanisms that

enable TCP to more effectively utilise the available capacity of the network path

– RFC 2760 TCP Research Related to Satellites, 2000• outlines algorithms and mechanisms not mature

enough to be recommended by the IETF with the goal to educate researchers

Previous solutions


– RFC 4614 A Roadmap for Transmission Control Protocol (TCP) Specification Documents – 2006• This roadmap provides a brief summary of the

documents defining TCP and various TCP extensions that have accumulated in the RFC series. This serves as a guide for TCP implementers and other parties who desire information contained in several IETF standardised mechanisms that enable TCP to more effectively utilise the available capacity of the network path (http://tools.ietf.org/html/rfc4614)

Previous solutions


TCP performance function of PERThe maximum throughput on an unlimited bandwidth channel using the Maximum Segment Size (MSS) is:

for p < 1%: Throughput = k*MSS/RTT/sqrt(p)

where k is 1.31 in the case of random segment losses without delayed ACKs and p is packet error rate (PER)

When timeouts are considered:

for p > 1%: Throughput = MSS/(RTT*sqrt(0.66*b*p) +RTO*min(1, 3*sqrt(0.375*b*p))*p*(1+32*p*p))where b is the number of segments acknowledged by each ACK


Simulation ResultsMaximum

Transmission

Unit

(the largest payload supported by the underlying physical network)

802.3 Ethernet: 1500 bytes

X.25:

576 bytes


Simulation Results


End-user performance expectations – conversational services

(reference [19], p71)


End-user performance expectations – interactive services



End-user performance expectations – streaming services



Typically TCP sends one 40 byte ACK for every two 1500 byte data packets, the return bandwidth is only 1.3% of the throughput in the forward direction (optimistic scenario). Test results:

Large file transfer 2.7%HTTP 6-12%

Tests have shown that for a return channel of 128 kbit/s the throughput in the forward direction reaches an equilibrium of about 4.7 Mbit/s. Forward web traffic of 45 Mbit/s generates 2.7 Mbit/s return traffic.

TCP is an asymmetric two-way link


Performance Enhancing Proxies (PEP)

What are PEPs ?• Given the limitations of the TCP/IP over satellite, are there

any other ways to increase the throughput?• Yes, if one is prepared to modify or replace completely the

TCP/IP protocols with some specific protocol optimised for the satellite channel. These devices are called PEPs and they usually sit at each end of the satellite link, on the ground, as the first interface from the satellite to the terrestrial networks.

Are they the optimum solution?• No, if one needs both speed and security at the same time


Performance Enhancing ProxiesOther options:• different Transport Layer Protocols:

– the Satellite Transport Protocol developed at Berkeley– the Space Communications Protocol Standard– the Xpress Transport Protocol

• different Link Layer Protocols:– the Lincoln Laboratory Link Layer developed at MIT – TCP-Aware Link Layers that look at the TCP header to

increase transmission speed and delete duplicate ACKs, thus preventing the TCP from reducing its congestion window


Other options:• TCP Spoofing:

– a technique by which TCP ACK information is manipulated to overcome problems caused by high latency

– a gateway looks at the TCP header and sends ACKs to the source while taking responsibility for delivering the data

– once ACKs are received from destination, they are removed– it doesn’t solve the window size limitations but it can

overcome the effects of the slow start algorithm– can cause broken connections, overrides TCP’s congestion

control mechanisms on terrestrial network => network failure

Performance Enhancing Proxies


Other options:• TCP Splitting:

– a technique by which a gateway converts the TCP traffic into an intermediate protocol that is well suited for transmission over a satellite channel.

– at the other end, the protocol is converted back to TCP– it requires access to the TCP header; it will not work with

encryption techniques that encrypt the transport header.– SatBooster from Flash Networks, Wireless IP Suite

Enhancer (WISE) from MIT Lincoln Laboratory, SkyXGateway XR10/45 from Mentat, etc



Other options:• TCP Splitting:

– reduces return channel bandwidth requirements by 75%– reduces the amount of FEC usage needed, therefore better

bandwidth utilisation– reduces bandwidth consumption by isolating

transmissions: avoids wasting satellite bandwidth retransmitting any packets lost on the terrestrial network

– can’t provide any enhancement for IPSec encrypted packets

– it is not efficient for low speed links (less than 100 kbit/s)



Other options:• Compression:

– By compressing the data before handing it to TCP, the effective throughput rate can be a multiple of the limited transmission rate (VoIP as low as 4.8 kbit/s)

– Compression ratios vary (1.5 to 3.5), more efficient techniques require longer compression/decompression times (1 to 13 seconds)

– Example of savings assuming US$2,000,000/year for a 45 Mbit/s transponder using a US$3000 compression device at each end with an average compression ratio of 2:1.



Bandwidth: 8-2 Mbit/s 64-64 kbit/s 1Mbit/s – 128 kbit/sConnection: forward/return symmetric VSAT with 10 nodesTotal BW: 10Mbit/s 128 kbit/s 2.280 Mbit/sCost of BW: $444,444/y $5688/y $101,333/yNr. compression 2 2 11devicesCost of devices: $6,000 $6,000 $33,000BW savings: $222,222/y $2844/y $50,666/yPayback 10 days 2.1 years 8 months

(very efficient investment)



Multiple TCP connections, in aggregate, are able to use more of the available bandwidth. Applications designed for satellite links could open multiple simultaneous TCP connections, send part of a file over each connection and reassemble it at the receiver end. Large scale use of this technique can be detrimental to network stability, one user grabbing bandwidth from the other users.- Caching (browser caching and shared caching: Squid), rule of thumb: 50% hit ratio and 33% bandwidth savings)- Pre-fetching (downloading the embedded objects on a HTML page and send them => reduce downloading time)



Security issues for PEPsIt is not always convenient to provide encryption at the application or transport layers using VPN, secure Web browsing using SSL or secure email using PGP or S/MIME. Encrypted email can not be virus checked at gateways, SSL protection can not be applied to UDP, or there could be other issues with the firewall protection.Encryption at link layer protects all data but does not protect intermediate points such as routers.

The most common solution is IPSec which applies protection at the network layer.


Security issues for PEPsWhy is IPSec an issue for PEPs? It hides the TCP header information required by PEPs in order to optimise the satellite link. What are the solutions?

1. Use secure sockets layer (SSL): good only for TCP because encrypts the TCP payload but leaves the TCP header in clear. UDP does not need to be accelerated so it can use IPSec.

2. Terminate the IPSec tunnel at the PEP: the PEPs can now become attractive points of attack and are not transparent for the end users; might need costly protection.

3. Make TCP headers visible: traffic analysis based on the TCP headers can be used by attackers reducing thus security.


Security issues for PEPs4. Multi-layer IPSec protocol: the payload of the IP packet is

encrypted with a different key than the TCP header and it is provided only to the end points. The key used to protect the TCP header is provided to the PEPs and the end points. Highly complex and difficult to implement.

5. Move the PEPs before the IPSec encryptors: increases the complexity of the system, there is a need to differentiate between flows which will go over a satellite link and flows which will go to a terrestrial end point, auto tuning of the buffer size for flows with various bandwidth-delay product, differentiation between packet loss due to network congestion or due to noise, etc.


TCP/IP over satelliteQoS approaches (“The Communications Handbook”, Jerry D. Gibson)

• Integrated Services (IntServ): based on resource reservation for each flow of traffic for the whole end-to-end path; made in advance and upon request using resource reservation protocols (e.g., RSVP). Offers guaranteed services (GS) - maximum queuing and delivery time - and controlled load services (CLS) function of delay and loss probabilities.

• Differentiated services (DiffServ): manages traffic at the aggregate level, differentiated per hop behaviors (PHB) based on the DiffServ Codepoint in the IP packet header, scales well to large networks.


TCP/IP over satellite


TCP/IP over satellite“The network includes the satellite with OBP capability, traffic and resource management functions, a gateway station, interconnecting satellite and terrestrial segments, satellite terminals of various types and a Master Control Station that is responsible for the Call Admission Control. The satellite network can be seen as an underlying network, aimed at interfacing Overlying Networks (OLNs) based on different protocols, such as IP, ATM, X.25, Frame Relay, N-ISDN, and MPEG based. The transparency of the satellite network is guaranteed by the use of one interworking function (IWF) for each protocol.”


TCP/IP over satellite


TCP/IP over satellitehttp://www.cs.cornell.edu/skeshav/real/index.html“REAL is a network simulator originally intended for studying the dynamic behaviour of flow and congestion control schemes in packet-switched data networks. It takes as input a scenario, which is a description of network topology, protocols, workload and control parameters. It produces as output statistics such as the number of packets sent by each source of data, the queueing delay at each queueing point, and the number of dropped and retransmitted packets. REAL is written in C, and will run on Digital Unix/ SunOS/ Solaris/ IRIX/ BSD4.3/Ultrix /UMIPS systems on VAX, SUN, SPARC, MIPS, Alpha, SGI or DECstation hardware.”


StarBand• StarBand was founded in 2000, the first company to

offer internet over satellite. It filled for bankruptcy in 2001 and since 2005 is a service brand of Spacenet Inc. (which is owned by Gilat Satellite Networks) It is a two-way, always-on, high-speed satellite Internet service available throughout North America, and several Caribbean and Central American countries.

• Uses the Gilat SkyEdge VSAT platform, US$299.• NOVA 500: 512 kbps / 100 kbps @ US$50/month• NOVA 1500: 1.5 Mbps / 256 kbps @US$100/month


HughesNet

• Previously known as DirecPC then DirecWay, HughesNet is a high speed satellite Internet system operating at Ku band with 1W, 2W or 4W transmitters.

• Download speeds (Mbit/s): 2.0, 1.5 1.0• Upload speeds (kbit/s): 300, 250, 200• Price (US$): 90, 60, 40• It can allow VPN clients but at 50 to 75% speed.• Requires a different dish than for the DIRECTV dish.• Over 400,000 customers.


Spaceway• Hughes Network Systems will deploy 16 HS 702

geostationary satellites and another 20 satellites in medium earth orbit at 10,352 km, at Ka band, 10Gbit/s/sat

• uplink: 512 kbit/s to 16 Mbit/s; downlink up to 30 Mbit/s• 66 cm antenna, IP/ATM protocols, available since 2007• onboard digital processing, packet switching and spot-

beam technology (tx with 1500 element phased array, 2m diameter, forming multiple hopping spot beams).

• combined digital video, audio and data streams with global coverage for the next generation of HughesNet.


WildBlue• WildBlue uses the DOCSIS 3.0 format for broadband

Internet access, the same technique used by cable operators to provide higher speeds.

• More than 400,000 rural U.S. customers.• WildBlue Communications started in 2009 to offer a 18

Mbps service, which is about 12 times faster than earlier services. Remember that the trade-off is “speed” for “number of subscribers”, so any fixed satellite transponder capacity can be used for a smaller number of users who get higher bandwidth, or for o a larger number of subscribers who receive less bandwidth.


WildBlue• In October 2009 ViaSat signed a definitive agreement to

acquire WildBlue Communications in a cash and stock transaction valued at $568 million (www.satellitetoday.com)

• WildBlue’s Ka-band broadband service is powered by the ViaSat SurfBeam networking system and will use the 140 Gbps capacity on the ViaSat-1 satellite, launched in 2011.

• WildBlue was geared towards personal use and is priced to fit a personal budget, HughesNet aims more at heavy users and businesses in rural areas.


ViaSat - SurfBeam• It is a very cost effective two-way system based on an

open standard, DOCSYS, used with cable modems. This allows a drop in monthly costs down to USD39 on existing satellites and USD20 on future spot beam satellites. The terminal cost, including the dish, the 2-watt SSPA and LNB, and the Ka/Ku ODU is under USD500.

• Receives up to 108 Mbps, transmits up to 1 Mbps, ideal for Internet access, Voice over IP, MPEG video over IP, multicast, etc.


ViaSat – SurfBeam(source: viasat.com)


ViaSat - ArcLight“ArcLight incorporate two ViaSat-exclusive technologies: Code

Reuse Multiple Access (CRMA) and Asymmetric Paired Carrier Multiple Access (A-PCMA).

PCMA enables data transmissions coming back to the hub from remote sites to be combined within the same bandwidth as the outbound channel.

Rather than requiring additional bandwidth for return channels, ArcLight needs only the space segment required by the outbound broadcast to support two-way satellite services.” (source: viasat.com)


ViaSat - LinkStar• LinkStar is a two-way BOD system based on the DVB-

RCS standard, up to 60 Mbps using DVB-MPE forward channel, 1.67 to 3.33 Mbps for the return channel

• QPSK modulation, MF-TDMA for the return channel, L-band Tx/Rx, 1 to 2 watt Ku band, 4 to 5 watt C band.

• Up to 10,000 sites for each regional node supporting Multi-protocol Label Switching (MPLS)-based IP Virtual Private Networks (VPNs)

• A customised Ka band version is used for the reception of Eutelsat SkyPlex multimedia satellite network.


ViaSat - LinkWayS2

• LinkWayS2 is a MF-TDMA modem used in USA Army’s Warfighter Information Network-Tactical (WIN-T) and Marine’s Support Wide Area Network (SWAN) program.

• Completely independent fast-hopping transmit and receive paths supporting Wideband Global Satellite (WGS), IF ranges of 950 – 2050 MHz with 20 dB MF-TDMA receive power burst-to-burst dynamic range.

• integrated DVB-S2 receiver/decoder, advanced turbo coding, 8PSK/QPSK/BPSK, 16-queue IP QoS scheme using Class-Based Weighted Fair Queuing (CBWFQ).


Skystar Advantage• A Gilat product, a private VSAT network for data,

multimedia over IP and voice applications• can simultaneously support SDLC, X.25, TCP/IP

including IP routing, voice, MPEG1, MPEG2, etc• low power consumption ~25 W• remote terminal information bit rates: 50 bit/s to

128 kbit/s• antenna size: 0.55 m to 1.8 m


SkyEdgeIt is a Gilat product offering two-way Mesh, Star, and Multi-star topology with the following features:– Data, Interactive, On-Demand – Full Telephony Capabilities – Embedded Accelerated VPN, IP & HTTP, and acceleration – Enhanced DVB-RCS Support – Mesh VOIP – Satellite Diversity/Multiple Outbounds– End-to-End QoS– Ultra Low Power Consumption


SkyEdge• Outbound Carrier: Standard: DVB-S

– Carrier bit rate: 340 Kbps – 66 Mbps – Modulation: QPSK or 8PSK (optional) – Coding: Viterbi & Reed Solomon or Turbo (optional) – FEC Rate: 1/2, 2/3, 3/4, 5/6, 7/8

• Inbound Carrier: Access Scheme: Combined TDMA, FDMA & DAMA, standard DVB-RCS – Bit rate: 40 Kbps – 2 Mbps – Modulation: GMSK & MSK – Coding: Turbo coding FEC ~3/4, ~7/8


SkyBridge• 80 LEO satellite system in the Ku band orbiting at an

altitude of 1,469 km, 53° => 30 ms propagation time• 140 gateway stations for worldwide coverage, each

gateway covers a circular area with a radius of 350 km• gateway stations will interface with the terrestrial

network through an ATM switch (“bent-pipe” satellites)• GEO-based access services for the corporate users• forward 20/100 Mbit/s, return 2/10 Mbit/s• Put on hold in 2002 due to lack of funding – Alcatel.


Teledesic• “Internet in the sky” proposal• 800/288/30 LEOs at an altitude of 1375 km, at Ka band• intersatellite links at 60 GHz, with full onboard

processing and onboard switching• uplink speed up to 2 Mbit/s• downlink speed up to 64 Mbit/s• the satellite constellation would ensure that the

elevation angle for any user is higher than 40°• Merged with ICO Global Communications


iPSTARiPSTAR (www.ipstar.com) is a spot-beam 14 kW, 112 transponders, satellite placed at 120 degree East longitude designed to provide two-way Internet service over satellite, with information capacity up to 40 Gbps, to customers in India, China, East Asia, South East Asia, Australia and New Zealand.

The physical layer uses higher order modulation and turbo product codes (TPC) in a Dynamic Link Assignment (DLA) system designed by Shin Satellite Public Company (Shin Sat).


iPSTARThe DLA is able to control both the type of modulation and coding rate function of channel condition, from a maximum of 3.52 bits per symbol using 16QAM modulation with a 0.879 rate TPC to a minimum of 0.65 bits per symbol using QPSK with a 0.325 rate TPC. The iPSTAR satellite provides transponders of 65, 90, 120 and 150 Watts allowing each user a forward link of up to 12 Mbps and a return link of up to 4.1 Mbps. The access for the return link uses Aloha to gain entry to the system, Slotted Aloha for non-real time applications and Multiple Frequency TDMA for high data rate services.


Digital Video BroadcastingMulti-Protocol Encapsulation

• The MPEG2 (1993) standard enabled the compression and synchronization of video, audio and data elementary streams to set top boxes using 188 byte packets

• The DVB standards body defined a standard to be used along with MPEG2 that enables the synchronized demultiplexing of separate elementary streamsassociated with the same service, the authorization of end users and the encryption of all MPEG2 transport streams (DVB-S allows over 8,000 virtual channels in a single Multi Channel Per Carrier, MCPC, signal)



• The MPE is a data link layer protocol defined by DVB as part of the EN 301 192 standard: it provides means to carry IP packets over the MPEG transport stream. The ransport stream format uses a Program Map Table (PMT) with unique PIDs; the elementary streams associated with that program have PIDs listed in the PMT. A receiver can decode a particular "channel" by decoding only the payloads of each PID associated with its program.

• SES Broadband is an example of service for Europe that allows Internet access and SCADA communications.



• Access types:– Unicast: point-to-point transmission protocol– Broadcast: point-to-multipoint transmission protocol in a

unidirectional sense. It essentially means propagating the same message to all nodes in a network in an effort to reach all receivers.

– Multicast: point-to-multipoint transmission protocol that starts with the receivers and works backwards to the sender so that optimal paths through the network are established. Subsequently, point-to-multipoint protocols deliver the message from the sender over these paths to the receivers.



• The IP Multicast standard:– new multicast routing, addressing and group management

protocols– Multicast Backbone (MBone) created to enable applications

such as the broadcasting of live video and audio to multiple users concurrently

– Multicast IP addresses are tunnelled across a network of Multicast routers to all hosts that have joined particular Multicast sessions

– Applications: Netshow, Whiteboard, etc



• The DVB Multi-Protocol Encapsulation standard:– Unicast and Multicast IP packets can be encapsulated under an

MPEG2 transport stream– allows broadcasters to use their current DVB MPEG2

broadcasting equipment for the transmission of digital video and Internet data concurrently

– the end user can receive Internet data at more than 100 times the speed of the fastest modem

– it is compliant with well known reliability techniques– only authorized end users can receive it



• Multicast issues:– IP Multicast: is UDP based (best effort service) and must be

enabled on the entire network between the originator and the receivers; blocked by ISPs

– UDP (no ACK required) instead of TCP, avoids ACK implosion– Reliable multicast protocols: XTP, PGM (must be enabled)– Multicast Fan-Out for satellites: allows the originator and client

to communicate using standard TCP-based applications over any type of network, while transparently taking advantage of multicast over satellite links



• Multicast Fan-Out advantages: transfer a 25 Mbyte file to ten recipients over a 750 kbit/s satellite link– For a single receiver, the transfer takes 730 seconds.– Using a protocol gateway, the transfer time reduces to 280 s.– Using integrated data compression in the protocol gateway,

the transfer time can be reduced to 61 s.– Using Multicast Fan-Out, the delivery of the same file to ten

recipients is reduced from 7300 s to 66 s.


Eutelsat• Transmits Internet Protocol over satellite using the

DVB European standard for digital TV• Pull Services: high speed web browsing where a single

user requests a specific item• Push or multicast services: a file or stream is

transmitted to many users at the same time• DVB PC Card => Satellite Interactive Terminal (SIT),

or DVB set-top-boxes, plus 45 to 84 cm dish• Hub to SIT at up to 4 Mbit/s, return link at 16 kbit/s


Eutelsat• SKYPLEX is the on board processor specified by

EUTELSAT and ESA that allows multiplexing to be performed on the satellite.

• the HOT BIRD™ 6, 7 & 8 use DVB-RCS at Ku and Ka

• Downward-compatible solutions based on hierarchical modulations, with conventional DVB-S and DVB-DSNG kept for the high-priority stream, could use turbo coding for low-priority streams or for non real time services such as the DVB Multimedia Home Platform.


Skyplex

For information for a Skyplex terminal go to:http://www.viasat.com/_files/skyplex_v003_print.pdf


EADS Astrium delivered in 2010 its first satellite operating exclusively in Ka-band frequencies called KA-SAT at 9°E covering the European market. This was followed in 2011 by ViaSat-1, a high-capacity Ka-band broadband satellite ordered by ViaSat to serve the North American market.

Both satellites will use ViaSat’s Ka-band SurfBeam® networking system. The ViaSat SurfBeam® DOCSIS® technology is currently used by ~300,000 Internet subscribers to WildBlue and Telesatlaunched in 2005. The business case for this technology is built on the compatibility with tens of millions of cable customers using DOCSIS, together with powerful new Ka-band multi-spot satellites that can facilitate important economies of scale to enable satellite-based consumer Internet services to achieve costs and bandwidth comparable to ADSL.


In March 2008 Eutelsat and SpeedCast announced a new global maritime broadband communications service. The service combines Internet access, VoIP, Video-on-Demand, IPTV services and secure VPN capabilities with guaranteed bandwidth for mission critical corporate applications addressing the commercial shipping sector. The system will use a small one metre Ku-band stabilised satellite antenna, able to switch automatically from one satellite coverage beam to another.

The service will compete directly with Inmarsat maritime services. The current FB500 terminal offers Standard IP up to 432 kbps and Streaming IP up to 256 kbps. Antenna is 50 cm in diameter. It also support voice, fax and SMS and the satellite network has global coverage.


• Constellation of near polar low earth orbiting satellites (e.g. Iridium, Teledesic).

• Each satellite is equipped with:– full signaling ATM switch.– Inter Satellite Links (ISL) to neighbouring satellites

(geodesic network topology)

ATM Connection Handover in LEO Satellite Networks


• Handover is caused by satellite orbital migration.– Spot beam ground speed ≈ 24,000 km/h

• Handover always occurs between adjacent satellites.

• Handover always occurs in the direction of an approaching satellite.



• Terminal and Satellite:– around 3 milliseconds (900 km).– one order of magnitude larger than terrestrial cellular.

• Satellite and Satellite:– around 14 milliseconds (4000 km - Iridium).– two orders of magnitude larger than terrestrial cellular.

• Increases time to establish new ATM connections.



Satellite

Mobile Terminal

Link to old access point

Link to new access point

Intra-satellite Handover


Inter-satellite Handover

Satellite

Mobile Terminal

Link to old access point

Link to new access point


ATM Forum Handover Weaknesses

• Cell loss:– Uncoordinated path switching (downstream).– Old path segment release.– Uncoordinated terminal release.– Out-of-order delivery of signaling.– Uncoordinated path switching (upstream).

• Cell mis-sequencing• Increased cell transfer delay / variance.


Routing in LEO constellation

• Fixed Virtual Nodes (VNs): when the satellites move in the sky, the VNs remain unchanged in their positions, thus the virtual topology remains fixed because VNs are just embodied by different satellites.

• discrete-time dynamic virtual topology routing (DT-DVTR) bases its behaviour on the assumption that in some intervals of time the topology of the satellite network does not change, and that during these intervals the cost associated with each link connecting two LEO satellites is assumed to remain unchanged.


Routing in LEO constellation• IP tunnels can be created for satellite-terrestrial segment

isolation purposes across the satellites links between pairs of single IP hosts scattered across the terrestrial backbones. The main advantages are:– Adapt the tunnelling network layer and routing protocols inside

the constellation network to its specific needs and constraints.– Separate routing updates and addressing in the constellation

network from routing updates and addressing in the Internet.– Makes the asymmetry transparent to the routing algorithms,

which assume the presence of symmetric two-way links with similar properties (a “virtual” bi-directional IP link).


Satellite Network Design

Contents:• Satellite Network Dimensioning • Customer’s Requirements• Traffic Data• Examples• Cost of the Network• “CONNECTS” - Australian satellite network


Satellite Network Dimensioning

Link Design

- Modulation- Coding- Access

- Filtering

System Dimensioning- Carrier&Frame

organisation- Beam design

- Cluster design

Market Prediction

Definition of Service Profiles Traffic Modeling

Estimation of Capacity Req. (Info bit rate)

System Bandwidth Requirements (Frequency)

Iterative system design dimensioning

Limitations & constraints:- technological- regulatory- economical- predefined system parameters

User traffic demand

Satellite system implementation


Satellite Network Dimensioning• Market prediction

– Identification of the market segment, e.g. land services for private/business users in remote areas.

– Service profile: mobile/portable e.g. emergency services using handheld or laptop type terminal or fixed access points, e.g. a school or Internet café.

– Assessment of the population concentration threshold below which the implementation of satellite service becomes profitable compared to a terrestrial solution.

– Assessment of the local infrastructure required.


Satellite Network Dimensioning• Market prediction

– Assessment of the gross potential market (GPM) as the group of potential users outside the terrestrial coverage (local business, local government, mining/exploration)

– From this pool, estimate the service penetration, i.e., the percentage of GPM people subscribing to the service, based on the affordability (ratio between the GDP per capita and tariff rates) and the predicted take-up rate of the market.

– Estimate the potential number of subscribers for each type of economic region.


Satellite Network Dimensioning• Generic Multiservice Source Traffic Model

– Create a “linear” model based on Poisson arrival process and negative exponent distributed holding time to all services and traffic types.

– Estimate a constant bit rate per user per service defined by application frequency, mean call holding time, burstiness, busy hour factor, etc.

– Source uplink traffic has to be correlated with the destination downlink traffic with a potentially different capacity demand, depending on the asymmetry of the service.


Satellite Network Dimensioning• Generic Multiservice Source Traffic Model

– Assess the total contribution of on-demand services from individual and group terminals. Add the contribution of broadcast services.

– This will produce a first estimate of the beam capacity requirements.

– Consider now the hard blocking issue with the assumption that blocked calls are lost = > Erlang-B formula gives the blocking probability, pB. For an acceptable pB and a number of available channels => traffic efficiency => capacity requirements.


Satellite Network Dimensioning• Link Design

– Modulation– Coding– Filtering– Link budget

• Design and implementation of the hub and the VSAT terminals

• One off costs: network installation• On going costs: operation and maintenance


Satellite Network Dimensioning• Satellite Bandwidth Requirements

– The key cost that will have the greatest impact on the business success is the operating cost part of which a significant proportion is the satellite bandwidth cost.

– The operating cost divided by the number of users has to be lower than any other alternative available to the end users.

– If this is not the case, the whole process needs to be iterated considering other services, markets, technologies, etc.


Customer’s requirements

The main reasons for using VSAT services are:– Cost savings (91%)– Flexibility (84%)– Reliability (80%)– Data rates supported (65%)– No other services meet needs (41%)

(J.T. Johnson, “Users rate VSAT networks”, Data Communications Magazine, 1992)



• Interface to end equipment: the customer is reluctant to reconfigure or change the existing user’s terminal therefore it is important that all physical interfaces be software defined and downloadable from the Network Management System (NMS).

• Set-up time: the time to set up a network (90 days for a 100-node network) or the time to expand by additional new sites (days).



• Performance of the network, flexibility: the quality of service delivered to the customer depends on the amount of traffic. The system can be optimised for a target capacity. However, one should allow for spare capacity for 20% more traffic and 20% more VSATs than initially expected. Growth beyond the original capacity or reduction in capacity should be allowed in the system design.



• Failure and disaster recovery: there is a perception that satellite communications are risky given their dependency on an object too far away to be repaired in case of failure. Different levels of redundancy must be built into the system at the hub, VSAT, satellite and terrestrial backup connections. Diagnostic tests, sensing of link failure and automatic recovery increase the service availability and the cost.


Customer’s requirements• Blocking probability, availability: there is a

trade-off between the system capacity and the probability that the total traffic demand might exceed the capacity of the network. If there is no spare capacity, all new calls are blocked. For VSAT networks the typical blocking probability is 0.1%. Network availability refers at the ratio of the time a VSAT is functioning properly to the total available time for usage. It depends on tx, space segment, link and rx availability.


Customer’s requirements• The customer must specify the performance

objectives:– The main type of traffic: stream or bursty– The main type of data rates required– The main type of applications (data, voice, broadcast)– Average delay for interactive applications– Model parameters:

• The rate at which the messages are generated• The time between messages (inter-arrival time)• The duration (in seconds) or length (in bits) of the message


Traffic data• The Poisson model makes the following

assumptions:– The probability of one message being generated in a

small time interval ∆t (∆t0) is proportional to that interval, therefore equal to λ∆t, where λ is a constant

– ∆t is considered small enough, so there cannot be more than one arrival in ∆t, and the probability of no message being generated in ∆t is equal to 1- λ∆t

• The probability of K messages being generated in an interval T is P(K) = (λT)K(e-λT)/K!


Traffic data

• The average number of messages being generated in T seconds is <K> = λT

• The time τ between messages is a continuous distributed exponential random variable with the probability density function f(τ) = λe-λτ

• The average inter-arrival time, IAT, is 1/ λ• The average message length can follow either an

exponential or a geometric distribution.


Traffic data

• Queuing systems (a queuing system has customers, servers and waiting rooms)– Arrival behaviour is the probability distribution of

customer arrival (how often a customer would arrive to the system); memoryless, when the arrival of one customer is independent of other customers.

– Serving behaviour is the probability distribution of service (the distribution of the serving time for each customer); memoryless, when the serving time for one customer is independent of all other customers.


Traffic data• The simplest model is M/M/1/∞: memoryless arrival

distribution, memoryless serving distribution, only one server in the system and there is infinite number of waiting rooms to all customers.

• Assumptions: unlimited supply of customers, once served they would not come back immediately, all customers are waiting, first-come-first-serve.

• Probability for this system to have k customers, Pk, is (1 - ρ)ρk, where ρ = λµ is the total traffic in Erlangs, λis the total arrival rate and µ is the mean serving time.


Traffic data• The model used for wireless telephony systems is

M/M/n/n: memoryless arrival distribution, memorylessserving distribution, with n servers in the system. There are no spare waiting rooms, when all servers are busy, customers would be lost.

• Real traffic will be slightly higher because there is not infinite supply of customers, once blocked, customers would come back immediately.

• Probability for this system to have k customers, Pk, is ρk/k!/sum(ρi/i!) over all n servers, where ρ is the offered traffic or offered load.


Traffic data• When all n servers are busy, a new customer coming to

the system would be blocked. The blocking probability, Pblocking = ρn/n!/sum(ρi/i!) over all n servers (Erlang-B)

• Quality of Service (QoS) is equivalent to Pblocking

• Trade off between QoS, offered traffic and channels.• If an average user would make a phone call every half

an hour that would last 1.5 minutes, the traffic generated would be ρ = 2/60 x 1.5 = 50mEr. An area with 20,000 customers would generate a total traffic of 20,000 x 0.05 = 1,000Er. Find the number of channels required for QoS of 2%.


VSAT network dimensioning• Example from “VSAT networks” - Gerard Maral


VSAT network dimensioning• System Dimensioning for a VSAT network

– Traffic type: enquiry-response application.– Consider a star architecture in which every VSAT has

a number of cluster control units (CCU) connected to it via the local terrestrial links. RCV is the bit rate.

– Assume slotted ALOHA transponder inbound access protocol (used usually for low and bursty traffic).

– The bit rates for the inbound / outbound are Rvh / Rhv.– First an error-free link is assumed and retransmissions

take place due to collisions in the random access.



– Enquiry message: 20 bytes– Response message: 256 bytes– Addressing: 6 bytes– The generation of enquiry messages at the CCU is a

Poisson process– Number of CCUs per VSAT: M– Number of VSATs: N– Average message generation rate at every CCU: λ

(messages per hour)



– CCU-VSAT link: Rcv = M λ(26+256)*8/3600 bit/s– Hub-FEP link: Rhf = M λN(26+256)*8/3600 bit/s– VSAT-hub link conveys enquiry messages only with a

length of 32 bytes (26 for CCU + 6 for addressing) VSAT-hub link: Rvh = M λN(32)*8/3600 bit/s

– Hub-VSAT outbound link conveys response messages only with a length of 262 bytes (256 for CCU + 6 for addressing) hub-VSAT link: Rhv = M λN(262)*8/3600 bit/s


VSAT network dimensioning


VSAT network dimensioning• System Dimensioning for a VSAT network:

– Acceptable response time should be in the order of a few seconds.

– Curve1 shows the strong influence of the CCU-VSAT link bit rate on the overall response time.

– Curve2 shows the negligible effect the VSAT-hub link bit rate has once it exceeds four times the offered traffic in this link (we used small fixed length messages).

– System sensitivity to N, M, λ has to be investigated.


Network dimensioning• Satellite Network Sizing for Internet Access

(white paper presented by James R. Luecke, CTO, STM Wireless Inc, February 2001)

• Analysis of providing Internet service over conventional C and Ku-band satellites using a DVB-based forward link that can support access data rates as high as 48 Mbit/s.

• The Poisson model is used for human-initiated processes, such as telephone calls but not for WAN/LAN traffic.

• Internet traffic is dominated by Hypertext Transfer Protocol (HTTP) => request-response protocol.

• Instead of a Poisson arrival, an ON-OFF process results.


Network dimensioning• The ON-OFF process is characterized by multiple

requests during the ON period followed by an inactive period, or OFF period, that is significantly longer than the inter-arrival time during the ON period.

• When the asymptotic shape of the distribution is hyperbolic, e.g., the Pareto distribution, the process tends to exhibit self-similarity: has observable bursts at all time scales (Ethernet, WAN and Internet traffic).

• Self-similarity results in larger buffer sizes, higher packet loss rates and fewer simultaneous flows.


Network dimensioning• The effective bandwidth, C, required for a self-similar

traffic source (large number of users) is:C= µ+(HH(1-H)(1-H)sqrt(-2ln(ε))1/H a1/(2H)B-(1-H)/H µ1/(2H)

where:µ - the mean bit rate of the traffic stream (bit/s)H - the Hurst parameter (0.5 for Brownian noise

process, 0.9 for Internet traffic)ε - target cell or packet loss ratio (CLR)a – the variance coefficient of the traffic stream (bit-s)B – buffer or queue size (bit)


Network dimensioning


Network dimensioning• The capacity required for N sources with the same target

loss is:CN= Nµ + (C1 - µ)N1/(2H)

where C1 is the capacity required for a single source and it is viewed as a grade of service.

• It can be seen that there is a multiplexing gain, GN, for self-similar traffic:

GN = C1 x N / CN

Ex: 250 active self-similar sources require only 1/10th the bandwidth as compared to fixed access per user approach.


Network dimensioning• The utilization of a resource can be defined as ρ = Nµ/CN

Ex: for H = 0.9, utilization falls below 40%, 60% of the available capacity must be allocated to deal with the inherent burstiness of the traffic.


Network dimensioning• The Hurst parameter for TCP/IP networks varies between

0.85 and 0.95 (0.9 used here).• The variance coefficient, a, can range from 6 kbit-s for

wireline modem, 300 kbit-s for LAN to 1 Mbit-s for WAN, (1.3 Mbit-s used here).

• The mean traffic per user, µ, is from 6 kbit/s to 12 kbit/s as recommended by ETSI for browser (WWW) traffic.

• User activity, λ, is 5 hours of access per week per user during the cumulative busy period from 5p.m. to 10p.m. (35 hours) (that gives λ = 0.14).



The total number of subscribers is NTOT = Nmax/ λ = 1765/0.14 = 12600 users with GOS = 360 kbit/s for 1 user


Network dimensioning• The total number of subscribers is 12600, the allocated

per user traffic level of 24.5 kbit/s well less than the grade of service (3.4 kbit/s if DVB bandwidth is equally shared)

• Satellite transponder cost: US$350,000/month.• US$28/month/subscriber just for the cost of the DVB

channel; add the return link access cost, the equipment cost => around US$100/month, higher than DSL or cable access.

• Starband advertised 150 kbit/s “guaranteed” for each of the 19,000 subscribers => more likely 2.3 kbit/s guaranteed per user.


Network dimensioningFebruary 2008: “Radyne’s SkyWire Gateway can replace 2 SCPC carriers with a single TDMA carrier allowing for an immediate pooling of bandwidth. SkyWire is a hubless TDMA system without an expensive M&C system and has no annual software licensing or maintenance fees which keeps your capital investment at a minimum while improving your overall network performance. Networks can be as small as point to point links (only 2 sites just like a basic SCPC link) and can be expanded easily as your network grows or requirements change. Because traffic in virtually all Ethernet networks in any direction is self-similar, there are substantial benefits to be gained by sharing both TIME and BANDWIDTH resources on such links over the satellite.”

(http://www.radyne.net/uploads/tech_docs/1691WP024%20Rev%201-0%20Radyne's%20SkyWire%20SCPC%20Whitepaper.pdf)


Network dimensioning“Although SCPC circuits are very efficient with regard to the transmission of synchronous data, packed based data and more importantly, self-similar data is inherently inefficient and inappropriate for SCPC transmission. With less than 70% typical data circuit utilization there is significant potential to reduce operational cost and improve network performance through data circuit sharing techniques such as Radyne’s SkyWire Gateway TDMA products. By combining 2 traditional SCPC circuits into one (1) TDMA circuit users will realize a 20 - 45% reduction in total satellite bandwidth required for the same overall application performance.”



Network dimensioningRadyne’s TDMA replacement for two SCPC links:



Cost issues• To become competitive with xDSL services, the DVB

system would need to support more than 30,000 subscribers.

• Due to the burstiness of the traffic from independent users, more than 50% of the bandwidth has to be reserved to cope with the burstiness.

• If a number of businesses are aggregated together and traffic shaping or smoothing can be achieved, the variance coefficient can be reduced and the number of users increased (a reduction to half of the variance coefficient is equivalent to a 25% increase in the number of users).


Cost issues• Ways to shape the traffic:

– Channel coding => reduce user CLR– Storage area network– Network performance management – On board processing => increased available bandwidth

• Satellite Network Access Point (SNAP):– Community based satellite earth stations– Aggregation of traffic within each community– Traffic bandwidth shaping and management– Very low error (< 1E-10) transmission over satellite channels

using turbo coding technology


Cost issues (30 VSAT network)cost per unit no. Total = 1,833,000

VSATequipment 10,000 30 units 300,000installation 1,000 30 units 30,000spare parts 1,000 30 units 30,000maintenance 1,000 30 x 5 150,000

Hublease cost per year 40,000 5 years 200,000connection cost 20,000 5 years 100,000

Satellitebandwidth (1.25 MHz) 200,000 5 years 1,000,000

Licenceone-time fee 8,000 1 8,000per VSAT per year 100 30 x 5 15,000


Cost issues• VSAT terminal cost to drop below US$1,000• Hubless VSAT network using onboard

processing satellite as a hub in the sky– Lower delay– Onboard demodulation, processing of data,

remodulation• Use of non-geostationary satellites• Use of Ka band• New services


Example #1• There is an ISP in Sydney who has opened a small office

on Hamilton Island to provide 250 islanders access to the internet. The company has a phone link between Sydney and Hamilton which is used as the islander’s back channel. The downlink is provided via satellite at 400 kbit/s. Nielsen NetRatings showed that the average Australian internet user spends over 13 hours on line a month. If all users are online at the same time we would need 400 x 250 kbit/s = 100,000 Kbit/s = 100 Mbit/s. This would cost a fortune! What we will do instead is provide an acceptable Grade of Service to the users.


Example #1• We slightly over dimension to allow room for growth. We

say that the average user offers 15 hours of traffic a month. And that each user will log on once a day. Using these assumptions this means that on average :

• Call frequency λ = 1 call per day = 1/24 = 0.042 calls per hour, duration H = 0.5 hours per call. This means that the offered traffic per user is: Au= λ x H = 0.042 x 0.5 = 0.021 Erlangs

• The Traffic intensity for the cluster is therefore the number of users U multiplied by the traffic intensity per user: ATot= U x Au = 250 x 0.021 = 5.25 Erlangs.


Example #1• To allow for peak times (i.e, people will more likely use

the internet at 7 pm than 4 am) we will over dimension by a factor of 2 => the traffic intensity is 10.5 Erlangs.

• We assume that a GOS of 0.5% is adequate (Your attempt to connect will be blocked 1 in 200 times on average). From an Erlang B traffic table we find that to achieve a 0.5% GOS with traffic intensity of 10.5 Erlangs we need 20 lines. This means that we need to be able to support a capacity of 400 Kbps x 20 = 8 Mbps.

• For QPSK modulation using rate ½ coding and roll off 20% due to the filters =>1.2 x 8/(2 x ½) = 9.6 MHz.


Example #2• There is a need to provide Internet access at 256 kbit/s

download, 64 kbit/s upload for 5000 users in a relative high density suburb. If we were to try to offer 5000 internet users each a connection that meets the specific performance baseline 100% of the time, we would require a 1280 Mbit/s internet pipe. The proposed solution to the problem is to install 5 Very Small Aperture Terminals (VSATs), which can aggregate the traffic of 1000 users each to achieve a multiplexing gain. This multiplexing gain is generated by the fact that internet traffic tends to be very bursty.


Example #2The following parameters are used:• Hurst parameter H = 0.9 ;• Packet loss ratio ε = 0.000001;• Variance coefficient a = 1.3×106 bits/sec (WAN)• Buffer size B = 1×105 bits.• Mean bit rate per user, μ1 = 1.2 ×104 bits/sec


Example #2• Assuming λ = 0.14, the number of simultaneous active

users is 140 for every VSAT cluster. We introduce a 20% increase to the capacity of this to set a baseline based on 170 simultaneous users per VSAT.

• So we aggregate the required capacity over 170 simultaneous connections:

If a 1.5 factor due to compression techniques is used, the total capacity required for each VSAT is 12.1 MBit/s.


Example #2

We will also assume 250 users/Km2. Thus, we get a total network coverage required of 20 Km2. We consider using a Mesh system of 802.11g transmitters to support each VSAT. For a high powered outdoor mesh WAP, we expect to get +24 dBm transmit power. Typical receive sensitivity required to achieve 11 Mbps on an 802.11g network for a users network adapter is -90 dBm. We assume that we can have line of sight. We use the PCSExtension to the Hata model to determine how much coverage we get from each Mesh point.


Example #2

So, each node on the mesh can provide detection out to 800m, meaning that it can provide 2.01 Km2 of coverage. Thus, in order to cover the area, we need 10 wireless access points.


Example #2


Example #3• System Dimensioning for an aeronautical service

using a LEO satellite constellation network


Australian satellite network• Following the Australian National Broadband Strategy

plan released in 2004, the CONNECTS project, part of the International Space University program in July 2004, identified several critical applications to rural and remote communities which would benefit from broadband access, including health, education, business, and entertainment.

• The proposed solution includes the design of two satellites, named IPOz1 and IPOz2, to provide flexible broadband coverage of Australia, New Zealand and South-East Asia.


Australian satellite network


Cost (Millions USD)



Revenue (Millions USD)



• The Australian, 04/10/2007: “AUSTRALIA will spend $927 million to join the US's military satellite communications program. Defence Minister Brendan Nelson confirmed that Defence would fund one satellite as part of a global constellation of six satellites designed to provide secure wide-band military communications to US and Australian forces deployed around the globe. He also said Australia would acquire its own dedicated UHF satellite in about 2009.”



“Known as the Wideband Global Satellite system, the first satellite will be operational early next year with the complete constellation running by 2013. Four of the six satellites will be focused in Australia's area of broad strategic interest, including the Indian and Pacific oceans. The WGS satellites will eventually replace Defence'sleased transponders on the Singtel-Optus C1 satellite.”



(http://www.defenseindustrydaily.com/americas-wideband-gapfiller-satellite-program-02733/)

“Each satellite can route 2.4 to 3.6 Gbps of data –providing more than 10 times the communications capacity of the predecessor DSCS III satellite. Indeed, one WGS satellite will provide more throughput than the entire Defense Service Communications Satellite (DSCS) constellation currently on station. Using reconfigurable antennas and a digital channelizer, WGS also offers added flexibility to tailor its coverage areas, and to connect X-band and Ka-band users anywhere within the satellite's field of view.”



• The Australian, 04/10/2007: “The Australian Academy of Science's National Committee for Space Science (NCSS) has called on the federal Government to provide $100 million over 10 years to help launch an Australian space program. Spearheading the Australian push into space would be Sundiver, a mission to send the first spacecraft crashing into the Sun, beating NASA and the European Space Agency to what has been described as the "holy grail" of space physics.”



MAC Layer Optimisation

Contents: Cross-layer issues Throughput control Generic Stream IP encapsulation Layer 2 Bridged Point-to-Multipoint


Why strict layered approach doesn’t work: the specific user parameters depend on the application and are

defined at the top level while the OSI system is designed from the bottom up there is no direct communication from the bottom layer to the

top layer, therefore information is lost one fixed configuration is not suitable for unreliable

dynamically varying channels (due to fade, rain, etc) the necessity of efficiently managing bandwidth and power diversity of QoS requirements for multimedia traffic classes the need to integrate heterogeneous networks global optimisation is more efficient than local optimisation

Cross-layer issues


The main objective is to maintain the end to end quality of service (QoS) for the customer. If the satellite link changes, e.g., due to rain fade, the latest satellite modem technology can use adaptive coding and modulation (ACM).

Example 1: a 7 Mbit/s data stream processed by a rate 7/8 encoder and 16QAM modulator would occupy a 2 MHz (with ideal filtering). During adverse conditions, the data rate could be dropped to 2 Mbit/s and processed by a rate 1/2 encoder and QPSK modulator and would occupy the same bandwidth but would allow an increase of the link margin by 5 dB.

Cross-layer issues


Cross-layer issues


Example 2:


Cross-layer issues


“The WAN FIFO produces two control signals that enable and disable the sending of Ethernet Pause Frames. A Pause Frame is an Ethernet frame designed to implement flow control at the MAC layer. A switch supporting 802.3x can send a Pause Frame (with Pause time set to 0xFFFF) to force the link partner to stop sending data. Devices use the Auto-Negotiation protocol to discover the Pause Frame capabilities of the device at the other end of the link. When the WAN FIFO reaches a fill state of 87%, it signals the Ethernet Switch to send Pause frames back to the LAN to inhibit the sending of further data. The Pause Frames continue to be sent until the FIFO fill state has reduced to 75%. At this point, normal operation in resumed by sending a Pause Frame with Pause time set to 0x0000.”


If the physical layer and MAC layer could be optimised together, it was shown that minimum energy is consumed for an optimum transmission power which is proportional to the packet length.

Around 50% improvement in goodput and 20% improvement in transmission rate can be achieved by using the Maximum Transfer Unit (MTU) for a particular BER.

Increasing the frame length could improve the throughput depending on the channel.

Cross-layer issues


The ACM is able to maintain the link at a reduced data rate. However, there are other upper layers that could use this information for more efficient management:Call Admission Control (CAC) deals with limiting the number of connections to the network. Although due to statistical multiplexing there can be more registered calls than channels, there is a non-zero probability that more users than the available number of channels will transmit at once causing some connections to drop packets. In case of a sudden reduction in the bandwidth availability, the CAC needs to be informed in order to avoid total network breakdown.

Cross-layer issues


CAC and Dynamic Bandwidth Allocation (DBA) engines are responsible for the efficient use of radio resources in the satellite network. They are usually implemented in the Network Control Center (NCC) situated in the hub or sometimes on board of regenerative satellites. CAC schemes can be divided into two classes: Deterministic QoS guarantees: a new connection is accepted

provided the worst case scenario’s conditions are met. Statistical QoS guarantees: assumes that is a very low

probability that all connections will transmit at their peak rate at the same time, therefore losses will occur but a high channel utilisation is achieved.

Cross-layer issues


CAC and DBA techniques depend on the type of satellite network: LEOs vs GEOs, on board processing vs bent pipe architecture, CDMA vs TDMA or MF-TDMA, on board cross-connectivity between any pair of beams and so on.

The satellite admission control has to be coordinated with the terrestrial admission control. The satellite network could use the IP Integrated Services (IntServ) – focused on individual packet flows in order to admit or reject the requests of flows) while the terrestrial network could use IP Differentiated Services (DiffServ) – scalable service differentiation, focused on the aggregate of flows.

Cross-layer issues


IntServ model uses explicit signaling of QoS requirements to reserve resources (bandwidth, buffers) a priori for a given traffic flow. Resource Reservation Protocol (RSVP) performs this signaling function. RSVP can also be used to set up MPLS explicit label switched paths with QoSrequirements for aggregated flows. There are two services: guaranteed service provides a deterministic end-to-end packet

delay for a flow by controlling the queuing delay on each node controlled-load service used for adaptive applications sensitive

to traffic overload but tolerant to some delay; provides the same service as best-effort service in a lightly loaded network

IntServ is not easily scalable to large public IP networks.

Cross-layer issues


DiffServ model was designed to be scalable. When a packet enters a DiffServ domain via an ingress router, the DiffServ field in the IPv4 header (TOS octet) is set to a particular class of service as defined by the Per-Hop Behaviour (PHB) class policy: Expedited Forwarding (EF): low loss, low delay, low jitter Assured Forwarding (AF): 4 sets of buffer & bandwidth Best Effort (BE)

The resources are allocated on a per-class basis defined by PHB and the amount of state information which needs to be stored in each router within the domain does not increase with the number of flows as with IntServ.

Cross-layer issues


Policing deals with limiting the traffic contribution by connections already active to ensure that some user’s data does not unfairly reduce the QoS to other users.

Resource Queuing and Scheduling refers to fairness between similar traffic sources and different treatment for different traffic sources

Increased Queuing due to bandwidth bottleneck results in bursty traffic which leads to erratic performance when multiple independent TCP sources are competing for bandwidth.

Cross-layer issues


Active Queue Management could also adapt its policy function of the amount of satellite resource available e.g., by switching between “random early detection” (random dropping packets before the queue is full) and “tail drop queue” (drop packets which arrive at the queue after the queue is full) algorithms.

Joint source-channel coding was shown to achieve better performance than separate source and channel coding.

Turbo source coding combines a source encoder and a channel encoder to produce a coded stream that can be decoded by a single MAP engine.

Cross-layer issues


Increasing MAC level retransmissions, in order to avoid TCP retransmissions decreases the power consumption. This is an example of joint optimisation to save resources.

A better performance for TCP connections can be achieved by jointly choosing the bit error rate, modulation, FEC and the information bit rate of a satellite link that maximisesthe goodput of a single TCP connection.

When the request of resources in a DVB-RCS synchronises with the TCP transmission window, queuing delay and congestion with timeout expiration are reduced!

Cross-layer issues


Goodput of a single TCP Reno connection for various C/N0(reference [19], p297)

Cross-layer issues


ETSI TC-SES/BSM (Satellite Earth Stations / Broadband Satellite Multimedia) working group has defined a protocol stack architecture based on: Satellite-Dependent (SD) layer which include the lower layers:

Satellite Physical (SPHY) Satellite Medium Access (SMAC) Satellite Link Control (SLC)

Satellite-Independent (SI) layer made mainly of IPV4/IPV6These two blocks are interfaced to each other through SI-SAP

(Satellite Independent – Service Access Point) layer External Layers:

UDP/TCP/OtherApplications

Cross-layer issues


The SI-SAP layer provides the following services: data transfer: send/receive data for unicast/multicast modes address resolution: associates a broadcast satellite multimedia

identifier (BSM_ID) address to the IPv4 packet. The BSM_ID is used to identify a BSM network point of attachment and allows IP layer address resolution protocols to be used over the BSM.

resource reservation: used to open, modify and close SD layer queues when sending data. It assigns queuing identifier (QID) and defines or modifies the queue properties.

flow control: allows activation of the SD layers to provide SI-SAP flow control for a specific QID

group receive/sent: used to configure SD for multicasting

Cross-layer issues


A few examples :

BNC connectors for NRZ signals, G703, etc. Simple HDLC protocol (bit stuffing) Delaying the ACK packets (ACK pacing) Traffic shaping (dynamically limits the

bandwidth allocation per process or per user) TCP splitting (False ACKs) Satellite Network Interface Processor (SnIP)

Evolution of satellite modem interfaces


BNC, HDLC, or SnIP interfaces as used in the satellite modem provided by http://www.datumsystems.com • HDLC: bursty IP traffic is converted in a continuous

bit stream over the satellite link using a simple Ethernet bridge interface. A simple medium access control (MAC) layer as part of the satellite modem.

• SnIP: open source bootloader and Linux operating system 10/100 Base-T interface plus a new USB interface. Sophisticated routing and bridging applications available.

Evolution of satellite modem interfaces


Throughput Control Delaying the ACK packets (ACK pacing) uses

the fact that the source transmit rate (window growth) is based on the return rate of the ACK packets.

By appropriately delaying returning ACKs, the sources will adjust their traffic accordingly thus reducing the buffer sizes at the gateway.

This engine could be directly implemented in the medium access layer (MAC) of the satellite modem and use the information from the physical layer about the change in bandwidth availability.


IP packetsData buffer

To the satellite

ACK control From the satellite

ACK packets

Data packets

ACK buffer(s)ACK packets

Transmit control

Throughput Control


– Achieves buffer size reduction for bulk TCP transfers compared with other schemes which require buffering the order of round trip time (RTT) delays.

– It is shown that for an access buffer size of only 10% of the bandwidth delay product, the average link utilization is 95% versus 65% with TCP Reno.

– It can also improve fairness between competing TCP transfers if buffering is used per-flow (or per class).

– It needs to be implemented at only one side of the connection, the sender side, with no changes to the TCP protocol stacks.

Throughput Control


Traffic Shaping which doesn’t touch TCP window sizesbut includes real-time network monitoring, real-time policy enforcement and control, compiled policies, dynamic bandwidth management, guaranteed maximum packet latencies, etc.If feedback regarding the satellite bandwidth availability is present, the bandwidth allocation can be dynamically changed for the new traffic conditions.The main advantage is that low delay ACKs can be sent to the existing applications from the terrestrial gateway, thus avoiding the long RTT delay of the GEO satellite.

Throughput Control


Throughput Control


TCP splitting by using the XTP protocol deals with breaking the TCP connection and sending false ACKs to the source. Its own congestion control mechanism can detect the change in satellite bandwidth availability and adjust the source transmission rate.

Throughput Control


Courtesy of www.packeteer.com


SkyX Congestion ControlSkyX can be configured to use XTP congestion control to effect the necessary variable transmission rate when the available bandwidth of the link is constantly changing.It meters out packets at the rate at which acknowledgments are received, increasing throughput until packet loss occurs, which results in a slowing down.Quick recovery from loss is performed by use of XTP fast negative acknowledgments and its ability to selectively retransmit when data is lost.This is correlated with the amount of memory available. No new TCP connections are allowed when free memory falls below 25%, while when less than 10%, no new data for existing connections is accepted.


SkyX PerformanceCourtesy of www.packeteer.com


Generic stream IP encapsulation

Assuming that the satellite gateway implements a DiffServ architecture (or similar for ATM traffic), the IP packets are marked in their TOS field for the particular class of service they belong to. Therefore the satellite modem needs to treat differently the delay sensitive packets from the non-real time packets. The MAC layer in your modem can then simply create two (or more) queues:

1. Q_MG (Maximum Gain) for non-real time data traffic sensitive to loss but not to delay. All default (DE) packets for best effort service are put in this queue. It is similar to ATM ABR/UBR - adaptation layer AAL3/4 or VBDC & FCA in DVB-RCS.



2. Q_mD (minimum Delay) for low-loss, low-latency and low-jitter services. All expedited forwarding (EF) and assured forwarding (AF) type of packets are buffered in this queue. It is equivalent to constant bit rate (CBR) mode for applications like G711 speech codecs (similar to ATM adaptation layer AAL1) or CRA & RBDC in DVB-RCS. It provides a minimum guaranteed amount of forwarding resources (buffer space and bandwidth), delay sensitive or real-time applications e.g., voice over IP (VoIP) and video.



The Q_mD has to be kept almost empty all the time. The packets in the Q_mD can be encoded by a rate 1/2 code in short blocks, say 188 bytes as the MPEG2 option in DVB-RCS, to achieve minimum delay (5 to 10 ms). The packets in the Q_MG can be encoded by a rate 3/4 code, in longer blocks up to tens of thousands of bits, in order to achieve maximum gain and also save satellite bandwidth. Both type of packets operate at similar Eb/No of ~3dB using QPSK modulation or ~7dB using 16QAM, at 70 MHz. The decoder is able to automatically identify the type of packets and use the correct decoder rate.



This is a simple solution that is possible to implement using the S-Tec™ codec which can handle various block sizes and data rates up to 10 Mbit/s. It matches the QoS, improves on the performance of the DVB-RCS standard and operates at BER < 1E-10. This flexibility is not available to satellite modems based on LDPCs of TPCs codecs.


Layer 2Bridged Point-to-Multipoint

(see Comtechefdata 2011 whitepaper)

In many secure IP-networks data traffic is encrypted prior to arriving at the satellite gateway. This requires operation at “Layer 2” in the OSI model. Standard Layer 2 Ethernet switches or other networking products operating at Layer 2 do not support hub-spoke networks. Comtech EF Data provides a solution that enables Layer 2 bridged connectivity in a point-to-multipoint network; the satellite network appears as a bridged LAN from the perspective of the secure networks.


Layer 2Bridged Point-to-Multipoint

(see Comtechefdata 2011 whitepaper)

Key advantages:• Broadcast (Multicast) Traffic: packets destined to

all remotes are transmitted only once in the shared forward link (FL).

• Statistical Multiplexing: Shared FL capacity is utilized by the remote terminals that are active at a given time (i.e. capacity is not dedicated to idle terminals, nor is excess capacity dedicated to low data rate terminals) providing both higher peak throughput and higher average throughputs.


Specific issuesContents: Inter-satellite links (ISL) Privacy for each of us Protect your satellite link Global Broadcast SystemMIL-STD-3011 SAR satellites Dish installation


ISLRadio-frequency (RF) links• Allocated bands:

– 22.55 to 23.55 GHz– 32.0 to 33.0 GHz– 54.23 to 58.2 GHz– 59 to 64 GHz– 120 GHz

• These frequencies correspond to strong absorption by the atmosphere

• RF links are used for low throughputs while optical links are used for tens of Mbit/s and higher


ISLAdvantages of RF-ISL

– Propagation loss is reduced to free space losses– Wide antenna beamwidth (0.2º at 60 GHz for a 2m

antenna)– Antenna pointing error can be a tenth of the

beamwidth which leads to a pointing error loss of less than 0.5 dB

– Antenna temperature in the case of a GEO-GEO link is of the order of 10K

– At 60 GHz, the receiver figure of merit G/T is 25 to 29 dBK-1, and transmitter EIRP 72 to 78 dBW


ISLOptical links• Allocated bands:

– 0.8 to 0.9 µm (AlGaAs laser diode)– 1.06 µm (Nd:YAG laser diode)– 0.532 µm (Nd:YAG laser diode)– 10.6 µm (CO2 laser)

• More efficient high capacity links due to the greater antenna gain. A 240 Mbit/s ISL over a 60º angular arc separation requires 500 W of RF power (1000 W d.c.) for a 2 m antenna using RF-ISL, while optical-ISL using 30 cm antenna (lens) requires 40 mW.


ISLAdvantages of optical-ISL links• Antenna gain is proportional to (D/λ)2 where D is

the diameter and λ is the wavelength. The wavelength of a 30 GHz signal is 1E-2 m while for a laser it is < 1E-6 m. Accounting for an order of magnitude difference in antenna size, the optical antenna gain is 1E+6 times the RF antenna gain.

• On-off key (OOK) amplitude modulation is used which requires on-board demodulation

• The optical power required is typically under 1 W, most of it required by the tracking subsystem.


ISLAdvantages of optical-ISL links• Doesn’t require government frequency assignment• Smaller and lighter equipment size• Narrower beamwidth and larger directivity than RF

(a circular area of ~800m diameter from a GEO beam using one micron wavelength and 10 cm diameter of the optical aperture of the transmitting telescope).

• Higher bandwidth: a 30 ps pulse width has > 30 GHz bandwidth; 1000 channels 30 GHz wide require 3E13 Hz which is 10% of a laser frequency of 3E14 Hz (for a wavelength λ of 1μm).


1 GHz 1 THz(1 000 GHz)

1 PHz (1 000 000 GHz)

1 mm 1 µm(1 000 nm)

100 mm(10 cm)

1 TeraHerz = 1 000 GigaHerz

1 PetaHerz = 1 000 000 GigaHerz


ISLLight Amplification by Stimulated Emission of Radiation (LASER)– The electrons in the atoms of a laser medium are energized, to an

excited state by an energy source. External photons are used to bombard the atoms to emit the stored energy in the form of photons in a stimulated emission in a coherent fashion. The emitted photons have the same frequency characteristic as the atoms of the laser medium and in turn act on other excited atoms to release more photons. This process results in amplification of light due to the back and forth movement between two parallel mirrors. One of the mirrors, which is only partially silvered allows the laser light to escape through.


ENERGY SOURCE

RESONATORLaser Material

Basic components of a laser


ISL– Solid lasers offer the highest power output and are usually

operated in a pulsed manner to generate a burst of light over a short time (ruby crystals and Neodymium-doped glasses)

– Semiconductor lasers such as Gallium Arsenide can be excited by the direct application of electrical current across the junction and they can be operated in the CW mode with > 50% efficiency. Commonly used in CD players and laser printers.

– Gas lasers like the helium-neon laser are known for high frequency stability, colour purity, and minimal beam spread. Carbon dioxide lasers are very efficient, and consequently they are the most powerful continuous wave (CW) lasers.


Visible / IR Light : 400 - 1000 nm = 750 - 300 THz (1012 Hz)AlGaAs 800nm : 375 THz,

Nd:YAG 1064nm : 281 THz, AlGaAs 1550nm: 193 THz(Erbium 1550nm)

Wavelength

UV IR

300 nm 400 nm 500 nm 700 nm600 nm

Nd:YAG 532 nm

Ar 514 nm

HeCd 441 nm

InGaN 399 nm

Rh6G 597 nm

Ruby 694 nm

HeNe 632.8 nmAr 488 nm

Gas

Solid

Liquid


ISLIn an optical link budget, the signal in watts/bit, is replaced by the number of photons/bit, therefore we have the ratio of signal photons to noise photons per bit.

hν is the energy per photon, h is Plank’s constant, 6.625E-34 watt-second (joule) per photon per Hz and ν is the laser frequency.

The received optical power is P = nhνf with n the number of photons per bit and f the signal data rate in bits per second.

BER is a function of the number of photoelectrons per bit and the modulation type.


ISL

The formula for BER is given by:

Pe = Q1(a,b) – 0.5exp[-(aa+bb)/2]I0(ab)

with a=sqrt[SNR*(1-cosθ)] and b=sqrt[SNR*(1+cosθ)]

where Q1 is Marcum Q function and I0 is the first kind modified Bessel function of order zero, θ is the phase error (assuming a uniform distribution of the phase error).


ISLModulation types:– Pulse-gated binary modulation– Pulse-polarization binary modulation– Pulse-position modulation– On-off keying

Noise sources:– Solar background radiation– Platform vibrations (mechanical, inherent orbital motion and

electro-optic tracker)– Pointing loss factors– Higher spread due to atmospheric scatter in uplink than in

downlink (which has little spread except for the last ~30 km from Earth). Shower curtain analogy.


Antenna PropertiesRF

LASER


ISL link budget LEO - LEO

Extrapolate to LEO - LEO linkValue Units dBw

Transmitted power 25 mW -16.02Transmitter Optics loss 76% -1.16Transmitter pointing loss 4.1 microrad -2.40Transmitter Strehl loss lam/9.5 -1.88Transmitter diameter 2.5 inchesTransmitter divergence 16.54 microradTransmitter Gain 21.54 microrad 108.39Range Loss 6500 km -279.91Receiver Gain 2.50 inches 107.67Receiver optics loss 55.3 % -2.57Received signal 106.00 nW -87.89Required Signal 523 pW -92.81LINK MARGIN 4.92

Assumptions:Wavelength 825 nmRequired BER 1.00E+06

Bit Rate 5000 kbit/sec 5 Mbit/secR=1/2, K=7 convolution code, Viterbi decoding > 10.5 Mbit/secRequired SNR 3.1


http://www.eurekalert.org/pub_releases/2006-12/esa-awf121806.php

“Artemis, the European Space Agency Advanced Relay and Technology Mission Satellite, successfully relayed optical laser links from an aircraft in early December 2006. These airborne laser links, established over a distance of 40 000 km during two flights at altitudes of 6000 and 10 000 metres, represent a world first.

The relay was set up through six two-way optical links between a Mystère 20 equipped with the airborne laser optical link LOLA (Liaison Optique Laser Aéroportée) and the SILEX laser link payload on board ARTEMIS in its geostationary orbital position at 36 000 kilometres altitude: a feat equivalent to targeting a golf ball over the distance between Paris and Brussels.”


“These tests were made by Astrium SAS (France), the prime constructor for both LOLA and SILEX, as part of the airborne laser optical link programme conducted by the DGA (French MoD procurement agency) from its Flight Test Centre at Istres, in the south of France.

Since November 2005, Artemis has been relaying optical signals from KIRARI, the Japanese Optical IntersatelliteCommunications Engineering Test Satellite – OICETS (two-way optical communication).”

In November 2001, Artemis made a world premiere by establishing a laser link with the French Earth Observation satellite SPOT-4 (LEO): imaging data was sent by SPOT-4 using a laser beam as signal carrier to Artemis and from there by radio waves to the ground.


• AlGaAs diodes - 60 mW transmit power (800 / 860 nm)• 2 / 50 Mbps optical link (LEO - GEO)• BER ~ 10-8, Availability 95 % (stopped working in Jan 2008)

Payload:• 150kg (70kg movable)• Power 130W• Telescope Diam. 25cm

ISL:• < 45,000 km• Pointing < 2 µrad• Delay ~ 0.25 sec• Telescope Diam. 25cm

PASTEL optical terminal (SPOT-4 satellite)


• Optical LEO ISL: KIRARI - ARTEMIS


ISS - JEM

• Japanese Experiment Module (JEM)– space - earth experiment with

International Space Station (ISS)

• Optical antenna, 15cm aperture• 2.5 Gbps modulator• Tests of space affects on electronics• Demonstration experiment:

36 GB in 2 mins (!)


HAP-LEO/GEO links

• High Altitude Platforms (HAP) at ~20 km altitude could allow to have an RF link to the ground and an optical link to a LEO or even a GEO satellite.

• In the case of a HAP-LEO link, a laser with a larger wavelength, e.g., Erbium (1550 nm), could be used to generate a wider optical spot (but lower gain) that would simplify the pointing procedure.

• For GEOs, higher diameter lenses would guarantee a higher gain.• The HAP could have a huge memory to store the data

downloaded from LEOs at ~10 Gbit/s which later on can be sent to the ground via reduced bandwidth RF links.


Iridium Flare


www.heavens-above.com


Public key cryptography


Rx

Geostationary Satellite

Tx

3. Rx uses its private key to decrypt the new mode setup.

1. Tx and Rx power on in the same default mode.2. Tx uses the Rx public key to encrypt the new mode setup

for the Rx and sends it using the same default mode.

5. Tx can change the setup mode pseudo-randomly.4. Tx switches to the new mode setup.


S-TECTM enabled Satellite Modem

Outer

EncoderInterleaver

Inner

Encoder

The interleaver is a very large memory, typically 45 kbitand can go up to 1 million bit.

The data is written sequentially into the interleaver and it is read in a pseudo-random order which can be programmed.

This pseudo-random order (106!) used to read data from the interleaver is the critical factor for achieving privacy.


The particular parameters that need to beestablished before communication can startbetween two turbo-like systems are as follows:

– Interleaver generator seed– S, the separation threshold for the interleaver– Interleaver size N– Initial turbo encoder states– Puncturing pattern– Bit to symbol mapping– Unique Words, UWs, are used to differentiate between

normal communication mode and secret key exchangemode.

– Error vector to be added at the encoder output


Secret Key Exchange The secret key could contain all the system parameters for a sequence of different seeds that can be used on a block by block basis. The secret key exchange is based on Diffie-Hellman algorithm and contains the following steps:

1. Both the transmitter and receiver are configured in an identical default mode. This mode is identified by the use of a specific unique word called UW_C.

2. The transmitter uses a secret number, b, to calculate the secret key, s, that needs to be exchanged with the receiver. This secret key is calculated using the public y of the receiver:

s = yb mod p = (ga )b mod p = gab mod p


Secret Key Exchange (cont)3. Once the transmitter decides that s is a good seed,

it sends z = gb mod p. All this communication takes place in a default mode, in an “open” channel, but using the specific UW identifier for the secret key exchange mode called UW_K.

4. After normal demodulation and decoding of z, the receiver calculates the value:

za mod p = (gb)a mod p = s5. Both transmitter and receiver reinitialise

themselves using the same secret key s and the communication resumes using the UW_C identifiers.


Secret Key Exchange (cont) This secret key exchange process is a one way

process therefore it doesn’t require a two-way satellite link.

Can be done on the fly, with minimum overheads The process can be repeated in a pseudo random

fashion, that is new keys can be exchanged as often as desired.

In case there is a communication breakdown, both rx and tx can be reset to a well defined default state.


1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0.6 0.8 1 1.2 1.4 1.6 1.8

Eb/No [dB]

BER

100%

99.90%

99%

90%

BER sensitivity function of interleaver mismatch


1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0.6 0.8 1 1.2 1.4 1.6

Eb/No [dB]

BER

64k

48k

32k

16k

BER sensitivity function of the interleaver size


Benefits The proposed scheme does not increase the cost by

using additional encryption/decryption blocks. The secret key exchange can occur over one-way

satellite links and doesn’t increase the delay. The same satellite modem can operate at less than

1dB from the channel capacity. Can be used with any PEPs to increase throughput.

Your business will have a competitive advantage by using the best satellite modem technology and at the same time unique security advantages.


Benefits Can be extended to multi-user detection (MUD)

schemes where more users transmitting within the same bandwidth need to be decoded at the same time.


Protect your satellite linkWashington Times: “Saddam's government obtained special electronic jamming equipment from Russia that was set up around several sites in Iraq. The jammers attempted to disrupt the signals sent by U.S. GPS satellites that are used to guide joint direct attack munitions, the military's premier satellite-guided bombs.

The encounter with the GPS jammers in March 2003 showed that the Air Force needed "stronger signals" on the constellation of 24 navigation satellites to defeat jamming equipment, said Gen. Lord, who is in charge of U.S. nuclear missiles and satellite communications networks for the military. The ground-based jammer uses electromagnetic radio frequency energy to knock out transmissions.”


Protect your satellite link


Protect your satellite linkWashington Times: “…"Dazzling" is defined as temporary interference with a satellite's optical sensors, as opposed to permanent damage of a satellite's components. David Wright and Laura Grego of the Union of Concerned Scientists said that existing U.S. ground lasers … already could accomplish some dazzling, if not damaging, missions. Wright and Grego co-authored the study, "The Physics of Space Security," with UCS colleague Lisbeth Gronlund.”

China also has a low-energy laser that can "blind" low-orbiting satellites, the report said. The Pentagon also is investigating China's capability of killing satellites with a "microsatellite" — a very small spacecraft, the report said.”


Protect your satellite linkIn August 2006, President Bush laid out a new US national space policy which said Washington would "preserve its rights, capabilities and freedom of action in space" and "dissuade or deter others from either impeding those rights or developing capabilities intended to do so". It also threatened to "deny, if necessary, adversaries the use of space capabilities hostile to US national interests.” The US has also been carrying out research on lasers that could knock out enemy satellites and the Bush administration has repeatedly ruled out the idea of a global treaty banning putting weapons in space.

In January 2007 a Chinese Feng Yun 1C polar orbit weather satellite (865km) was destroyed by an anti-satellite system launched from or near China's Xichang Space Centre.


Protect your satellite link(Courtesy of Jeff McCarthy, DSTO)

e.g TCP/IP

crypto

ATM

Error control

Jammer

Noise


Error control+interleaving+spread spectrum

Example solution: Block interleaver 20*6Say over multiple hops (20 symbols/hop)

20

6

in

out(1 error in 6)

Error burst (19 consecutive symbols)e.g. jammed hop



Spread Spectrum

Jammer

On board processing

TCP/IP

Crypto

ATM

Error control



Jammer

Desired uplink signal

(Adaptive) nulling- Phased array- Multiple beams

JammerDesired signal

Spot Beam discrimination- Steerable Dish- Phased array

Additional AJ countermeasures:



Jammer

Adaptive beam nullingSatellite spot beam

TCP/IP

Crypto

ATM

Error control

Spread Spectrum

On board processing



For an uncoded BPSK waveform, the probability of error is:pe = Q[sqrt(2 (Eb/N0))]

For a coded system with code rate Rc and minimum distance 2t+1, the probability of error is:

pe ≈ Q[sqrt(2 (Eb/N0)Rc(2t+1))]

For a coded system in which the waveform is spread to bandwidth Wwith processing gain W/R, R being the data rate, the signal power is defined as S = EbR, while the jammer power is J = J0W. The probability of error is:

pe ≈ Q[sqrt(2 (S/J)(W/R)Rc(2t+1))]

One should use a turbo code that operates at low Eb/N0 and then spread the spectrum of the coded waveform function of how much bandwidth is available. For small amounts of extra bandwidth, coding is always better than processing gain.


However, one should remember that before measuring BER, the modem needs to lock and acquire the signal, both frequency and timing, for which the processing gain – from de-spreading – is essential.

From information theory it is well known that white Gaussian noise is the most difficult channel, that is, for a given power level, the achievable bit rate is least. So the ideal jamming, when the waveform is not known, is AWGN.

Frequency-hopping spread spectrum moves the waveform from one carrier to another in a pseudo-random pattern, every channel symbol(s). For N carrier frequencies, there is a processing gain of N. However, although it sounds impressive, it is vulnerable to partial-band jamming. By jamming one frequency only, the BER can be limited to ~1/N. The way to improve its performance is to send multiple copies of each bit on randomly selected frequencies, achieving a diversity order of 2 or higher.


Symmetric differential PSK (SDPSK) and Gaussian minimum shift keying (GMSK) modulations are usually used in tactical fast frequency hopping (FFH) FDMA for on-board processing (OBP) satellite communication system against jamming.

In GMSK the digital data stream is first shaped with a Gaussian filter before being applied to a frequency modulator. This reduces sideband power, which in turn yields excellent performance in the presence of ACI ; however, the Gaussian filter increases the modulation memory in the system and causes ISI.

SDPSK encodes information bits using the phase difference, Δφ, between successive symbols, with a value in the set -π/2, π/2. The limited phase shift of SDPSK minimizes its sensitivity towards spectral spreading from nonlinear amplification and ISI and achieves better BER than conventional DPSK in the presence of ISI/ACI. FFH/SDPSK is robust and performs better than FFH/GMSK.


The Responsibilities of Space Faring Nations by Michael Kreponand Michael Katz-Hyman: “The more we learn about space and the more we benefit from space, the more our options for space warfare are constrained. The central dilemma of US space policy: the essential and vulnerable nature of satellites used for national and economic security. The more we seek to protect our satellites by the use of force in space, the more vulnerable our satellites will become if our own practices are emulated by others. The vulnerability of satellites to hostile acts is too great to be “solved,” and that vulnerability will only be accentuated by the use of force to “protect” satellites. Deterrence based on vulnerability in space is an inescapable fact of life. When space warriors pursue the flight testing and deployment of dedicated ASAT capabilities, they paradoxically reinforce deterrence while accentuating the satellite vulnerability they seek to escape.”


Global Broadcast SystemGBS is a high bandwidth data broadcast system designed to carry heavy multimedia files to users worldwide, freeing up local networks from bandwidth intensive files. Raytheon started the development of GBS for USA’s DoD in 1996 part of the conflict in Bosnia. It operates over Ka-band transponders and leased Ku-band transponders on commercial satellites. In one-way broadcast mode, it can transfer data at rates of 96 Mbps via a satellite channel, or it can broadcast video content, including commercial channels such as CNN, to deployed locations.

In June 2006, the GBS incorporated a commercial, two-way satellite TV standard, DVB-RCS that allowed commanders in Iraq to uplink video from unmanned aerial vehicles operating over battlefields in Iraq to anywhere in the world. (http://www.fcw.com/online/news/94953-1.html)


Global Broadcast SystemGBS is an extension of the USA’s Defense Information Systems Network (DISN) and a part of the overall USA’s DoD MILSATCOM (MILitary SATellite COMmunications) system.

It uses a form of “push and store” to distribute high-bandwidth information for local relay, thereby saving critical two-way military satellite communications systems from having to handle every field request.

It can provide high-volume data directly into 18-inch antennas, allowing streaming to and storage in mobile field devices thus expediting the process and share of mission critical information. It can provide classified and unclassified data in a secure manner, vital to in-theater commanders.


MIL-STD-3011Interoperability standard for the

Joint Range Extension Application Protocol (JREAP)(http://assist.daps.dla.mil)

JREAP enables tactical data to be transmitted over digital media and networks not originally designed for tactical data exchange. JREAP extends the range of Tactical Digital Information Links (TADIL) by permitting tactical data messages to be transmitted over long-distance networks, e.g., satellite links.

TADILs are standardized radio communication data links used by the US armed forces. Formatted tactical digital messages are embedded inside of JREAP messages as data fields within available commercial and Government protocols, such as those used over satellites and terrestrial links.


MIL-STD-3011The main capabilities of JREAP are:

• extending the range-limited tactical networks to beyond LOS while reducing their dependence upon relay platforms;

• reducing the loading on stressed networks;• providing backup communications in the event of the loss of the

normal link, and • providing a connection to a platform that may not be equipped

with the specialized communications equipment for that TADIL.

JREAP provides network and transport layer functionality. JREAP software can be integrated into a host system or into a stand-alone processor. The appropriate interface terminals are required at each end of any JREAP alternate media link.


MIL-STD-3011• MIL-STD-3011 is divided into the following sections:

– Applicable Documents, – Definitions of Terms and Acronyms, – General Requirements for the design of the generic JREAP

applicable to all media, – Detailed Requirements pertaining to important design

considerations and implementation recommendations, and – Notes.

• The appendices address the implementation specifics for underlying media protocols: – Half-Duplex Announced Token Passing Protocol, – Full-Duplex Synchronous or Asynchronous Point-to-Point

Connection, and – Encapsulation over Internet Protocol (IP).


MIL-STD-3011(http://www.fas.org/irp/program/disseminate/tadil.htm)

Tactical Digital Information Link (TADIL) A/B (called Link-11) employs netted communication techniques and a standard message format for exchanging digital information among airborne (TADIL A) as well as land-based and shipboard (TADIL B) tactical data systems. – Link-11 data communications must be capable of operation in

either the high-frequency (HF) or ultra-high-frequency (UHF) bands. Link-11 provides encrypted 2.4 kbps computer-to-computer digital radio communications in the high frequency (HF) and ultra-high frequency (UHF) bands among Tactical Data System (TDS) equipped ships, aircraft and shore sites.



TADIL C (called Link-4) is a non-secure data link used for providing vector commands to fighters. It is a netted, time division link operating in the UHF band at 5 kbps.– Link-4A is in operation in the United States Armed Services

and forces of the North Atlantic Treaty Organization (NATO). Link-4A provides digital surface-to-air, air-to-surface, and air-to-air tactical communications. This link was designed to replace voice communications for the control of tactical aircraft and now includes digital data communication between surface and airborne platforms. Link-4A is reliable but not secure, nor jam-resistant.

– Link-4C is a fighter-to-fighter data link fitted to the F-14 only.



TADIL J (called Link-16) is a tactical data link employed by the US Navy, the Joint Services, some nations of NATO and Japan. Uses the Joint Tactical Information Distribution System (JTIDS) which is the communications component of Link-16. It is a UHF, frequency hopping, 51 frequencies, in the 960 - 1215 MHz band.– Link-16 provides jam resistance, improved security, increased

throughput, increased amounts / granularity of information exchange, reduced data terminal size, digitized, jam-resistant, secure voice capability, relative navigation, precise participant location and identification and increased numbers of participants. It uses a Time Demand Multiple Access (TMDA) architecture and the MIL-STD-6016 J message format standard.



The TADIL J Range Extension (JRE) program for US Air Force addresses the requirement to pass secure/anti-jam data and voice via a common means in a timely manner beyond line-of-sight (BLOS) without the use of a dedicated airborne relay.

One way to extend the range of a JTIDS network BLOS is to employ airborne assets as relays between zones. This allows deployment over a very large area an integrated JTIDS network that provides interconnectivity between all the elements in a theater. The concept envisions JRE, which operates in Ku/SHF, as a gateway between existing JTIDS and satellite terminals.



The JTIDS terminal would be linked to the JRE gateway for transmitting and receiving TADIL J messages from a particular JTIDS zone. Linked at the other end of the gateway will be the satellite terminal whose function is to transmit and receive messages via satellite using both Ku and SHF bands.

A COTS workstation with the appropriate hooks to allow it to interact with a JTIDS terminal and a satellite terminal can be used. The main gateway software will perform message forwarding, buffering, prioritization, protocols, etc, that would allow the gateway to perform the JRE functions.


MIL-STD-3011Satellite TADIL-J (STADIL-J) has been developed by US Navy and it is not compatible with JRE. It uses geosynchronous satellites to give surface ranges up to 9600 nautical miles from the satellite sub-point.

It represents a family of standards using UHF half duplex DAMA channels at 2.4/4.8 kbps or 9.6 kbps for non-DAMA. It has been declared requirement for US Navy surface platforms, it best suits only one-way “broadcast” mode. To be migrated to EHF bands.

Latency (satellite propagation time of ~250 ms) impacts on the ability to operate in a two-way link mode.


MIL-STD-3011Satellite Tactical Data Link (STDL) has been developed by UK Royal Navy and it is not compatible with either JRE or STADIL-J. It will be used for exchange of Surveillance and Mission Management Data.

It can be operated in a broadcast or network mode. It uses DAMA protocols with 2 channels (1 channel Tx in each direction) to achieve Full Duplex. Includes Priority Interrupt slots, similar to Link-22.

Specific platform will perform data forwarding between STDL and Link-16, Link-11 or Link-22.


SAR SatellitesSynthetic Aperture Radar (SAR) started in mid 20th century based on new signal processing techniques which allowed resolution improvements beyond the limitation of physical antenna aperture. From the first airborne SAR systems, e.g., AIRSAR system built by NASA Jet Propulsion Laboratory operating at P, L and C band, the efficiency was significantly increased with the launch of the first SAR satellite, SEASAT, in 1978. A few of the most significant civilian SAR missions at the end of the 20th century are below:• The Shuttle Imaging Radar missions: SIR-A in 1981, SIR-B in

1982,SIR-C/X in 1994• European Remote Sensing : ERS-1 in 1991, ERS-2 in 1995• Japanese joint optical/radar mission J-ERS-1 in 1992• Canadian RADARSAT-1 in 1995• Shuttle Radar Topography Mission in 2000


SAR SatellitesTerraSAR-X operates in X-band for multiple scientific applications in such fields as: hydrology, geology, climatology, oceanography, environmental and disaster monitoring, and cartography. Since becoming operational in 2008, it conducted the first LEO-LEO optical inter-satellite link at 5.625 Gbps, the first bistatic X-band experiment and first demonstration of TOPSAR SAR operation mode, an improvement over the conventional ScanSAR mode.

TanDEM-X launched in 2010, was designed to fly in close formation with TerraSAR-X to achieve the desired interferometricbaselines in a highly reconfigurable constellation. Operating each SAR in mono-static mode, allows along-track InSAR processing for large areas giving velocity measures of ocean currents, sea ice and moving objects.


SAR SatellitesThe short baseline provided by the split aperture antenna is ideal for InSAR detection of fast moving targets such as vehicles; the long baseline aperture, as illustrated opposite for the split system, is ideal for the detection of slow moving objects such as sea ice. The use of intertwined helical orbits gives variable horizontal and vertical baselines.


SAR SatellitesIn the bistatic mode, as illustrated, the SAR instruments of the two spacecraft look into a common footprint thus providing very slightly different views of the observed target area. One satellite serves as a transmitter and both satellites record the scattered signal simultaneously. This mode avoids errors from temporal decorrelation and atmospheric disturbances.

The scientific use of the data can be divided into 3 areas: new quality Digital Elevation Models (e.g., for hydrology), along-track interferometry (e.g., measurement of ocean currents) and new bi-static applications (e.g., polarimetric SAR interferometry).


SAR SatellitesLacrosse: Operated by the US National Reconnaissance Office Lacrosse is a constellation of spy satellites that have been referred to as Onyx, Vega, Indigo and other code names. Apparently three are currently in operational use. Spatial resolution is quoted at 1m in push-broom (stripmap) mode and ~12-25 cm in spotlight mode. Each of these huge sky-high night watchers weighs 15 tons and is as big as a school bus”.

They orbit 400 miles above Earth's surface. Each satellite has a huge wire-mesh radar antenna and 150-ft solar panels to generate the kilowatts of electricity required by its powerful radar transmitter.


SAR SatellitesAstroSAR-Lite is a UK low cost mini-satellite focused to provide coverage with high resolution radar able to image through typical tropical 80% cloud cover, dust storms and heat haze for the regional user in the tropics and sub-tropics. It is optimised to maritime, environmental, security and disaster monitoring applications and orbits at 500km in sun synchronous mode; operating at X-band with both H and V polarisations it provides spotlight, stripmap and scanSAR resolutions of 1m, 3m and 20-30m spatial resolution with swath widths of 10 x 10, 20 x 1000 and 200 x 1000 sq kmsrespectively. Mechanical steering of the whole satellite provides major beam pointing of ±45°, enabling access to both left and right sides, augmenting and simplifying the electronic beam steering thus minimising cost of the expensive TR modules that are typical of other active phased array systems.


SAR SatellitesCOSMO-SkyMed is an Italian constellation composed of four satellites with an X-band SAR. The four satellites are phased at 90°. The altitude is 619.6 km (period = 97 mins) and the revisit time is a few hours. It is dual use with spotlight, stripmap and scanSARmodes having spatial resolutions of <1m, 15m and 30m respectively and in future will have access to L-band data from Argentinian satellites for emergency responses.

Ground segments are in Sweden, Argentina and Italy.

The COSMO-SkyMed system architecture is a good example for Multi-Mission/Multi-Sensor (MM/MS) capabilities as can be seen in next slide, allowing tasking of up to 5 civilian and up to 5 defence partners to participate.


SAR Satellites


SAR SatellitesThe Defence White Paper, May 2009, recommends that Australia obtains a satellite based synthetic aperture radar (SAR) system primarily for defence applications:

“9.80 As a significant new measure, the Government places a high priority on assured access to high-quality space-based imagery to meet Defence's needs for mapping, charting, navigation and targeting data. It has decided to improve Australia's intelligence collection capabilities by acquiring a satellite with a remote sensing capability, most likely to be based on a high-resolution, cloud-penetrating, synthetic aperture radar. This important capability will add to Australia's standing as a contributing partner within our alliance framework with the United States, which will be given access to the imagery collected by this system.”


SAR Satellites“9.78 We need comprehensive levels of situational awareness in the ADF's primary operational environment, including a capacity for continuous wide area surveillance of our northern approaches. In other contingencies, we need very high levels of situational awareness in the specific area of ADF operations.”

” 9.101 The Government has placed a priority on space situational awareness and has requested that Defence explore means by which to strengthen our space situational awareness and mission assurance capability. This will include the ADF developing a career stream for space specialists.”


Dish installation• True north (Geographic north): The location of the earth's

axis of rotation and is the basis for lines of latitude and longitude. (90° N, where all meridians of longitude intersect.)

• Magnetic north: The north direction shown on a compass determined by the earth's internal magnetic field. The true north pole and the magnetic north pole are currently about 1500 km apart.

• Declination: The error caused by the earth's magnetic field. For a magnetic compass, the needle will point towards magnetic north rather than true north. Depending on where you are on the earth's surface this difference may be as much as 30°. Adelaide has 8°9' E declination.


Dish installation

http://www.ngdc.noaa.gov/seg/geomag/declination.shtml


Dish installation• The segment of the geostationary arc that is visible from any

one location on the Earth's surface depends on the latitude of the site. Sites relatively close to the Earth's equator will be able to access a wider section of the geostationary arc than those located at the higher latitudes. For example, Adelaide, located at 34.8° south latitude, can potentially receive any geostationary satellite located at 34.8° ± 73.5° longitude.

• The calculated antenna elevation angles assume the use of a prime focus antenna. For an offset dish antenna, subtract the offset angle that the manufacturer lists in the specifications from the calculated elevation angle.

• The LNB should be hand rotated while monitoring the signal level until peak performance is obtained from one sense of polarization.


Dish installation• Lighting protection: the satellite antenna must have a proper

electrical ground to prevent lightning strikes from damaging the outdoor electronics or gaining entry into the home. A No. 10 AWG or larger solid copper ground wire should be used to connect the antenna mount to ground.

• Feedhorn to be centered over the dish and placed at the correct focal length of the dish

• Waterproof the feeder-LNB-cable connections to avoid losses due to moisture.

• Cable connection: 75-ohm coaxial cable are typical. RG-59U coax can be used to span distances of up to 30m. If longer lengths are needed, lower loss RG-6 or even better RG-11 should be used. Avoid any splitting or unnecessary connectors.


Dish installation• Measuring G/T: the most important parameter of the ground

station is the figure of merit, the G/T. Although it can be calculated as described in the “Link Budget” section, it is often more reliable to measure it because it gives a more accurate value (usually smaller) including losses that can not be estimated easily, e.g., connector losses due to humidity or mechanical faults.

• After a new dish/LNA/cable is installed, the following steps should be used to measure the actual G/T:1. Calculate the beamsize correction factor L = 1 + 0.38 (θs / θa)2 where

θs is the diameter of the radio sun in degrees at the operating frequency and θa is the antenna 3 dB beamwidth at the operating frequency. The θs is frequency dependent, one can use 0.5º for operating frequencies above 3000 MHz, 0.6º for 1420 MHz, and 0.7ºfor 400 MHz. For small dishes with a beamwidth > 2º, just use L = 1.


Dish installation2. Measure the noise power, Psun, when the dish points to the sun.3. Measure the noise power, Pcold sky , when the dish points towards a

cold sky.4. Calculate the value Y = Psun / Pcold sky.5. Find the solar flux density, F, at the operating frequency, using the

USAF Space Commands measurements made at 245, 410, 610, 1415, 2695, 4995, 8800, and 15400 MHz. (use interpolation if your operating frequency is different). Go to the following website: http://www.swpc.noaa.gov/ftpdir/lists/radio/45day_rad.txt

6. Calculate G/T = ((Y-1)*8*π*k*L)/(F*λ2) where:k is the Boltzmann's constant =1.38 *10-23 joules/deg K

andλ is the wavelength in meters at the operating frequency

7. There can be a decrease of 0.5 to 1 dB in the G/T measurements made at low elevation, e.g., 5º, relative to measurements made at elevations higher than 30º due to the increase in noise from the ground.


New Trends

Contents: Australian contribution: FedSat, Optus C/D Broadband satellite links Australian Satellite Networks, NBN Co Key technology trends: space segment Key technology trends: ground segment Policies, regulatory and standards issues


2009 - 2013The Government provided $48.6 million over 4 years to support theestablishment of the Australian Space Science Program.

$40.0 million for the establishment of the Australian SpaceResearch Program to support space research, innovation andskills development.

$8.6 million to establish a Space Policy Unit in theDepartment of Innovation, Industry, Science and Research tocoordinate Australia's national and international civil spaceactivities, including partnerships with international spaceagencies.


Successful projects:

• Scramjet-based Access-to-space Systems – taking Australia’s world-leading scramjet technology one step closer to possible future use in a fuel-efficient hybrid launch vehicle for transporting payloads into space.• Antarctic Broadband – developing satellite-based broadband communications technology for use by the Antarctic community to transfer data; the project will also build expertise in small satellite communications systems in Australia. • Platform Technologies for Space, Atmosphere and Climate –developing technologies for space research, including tracking and navigation, weather and climate monitoring, and atmospheric modelling.


Successful projects (cont):

• GRACE Follow-on Mission – h/w for a laser ranging system suitable to be flown on NASA’s GRACE mission in 2016. It will provide the ability to understand and predict the water balance across Australian catchments.• Automatic Laser Tracking of Space Debris – to improve space situational awareness thereby reducing the risk of collisions between satellites and space debris; develop a space surveillance industry built upon indigenous Australian technology.• SAR Formation Flying – to investigate SAR satellites flying in small formations to enhance real-time environmental monitoring. It will identify optimum orbits for monitoring over Australia and the region.


Successful projects (cont):

• Unlocking the LANDSAT Archive for Future Challenges –will result in international standard infrastructure for delivering Australia’s Earth observation data and the delivery of satellite imagery based environment data in a form usable by researchers, policy makers and private sector.• Space-based National Wireless Sensor Network - will develop and demonstrate a space-ready communications payload and complete ground system for use in marine monitoring, defence sensor monitoring and industrial automation scenarios. The project will build significant, persistent Australian space capability, generating intellectual property and enabling technologies in satellite communications and sensor networks.


A bit of historyAll postal and telecommunications services in Australia have been controlled by the Postmaster-General's Department (PMG), created in 1901, at Federation. In 1946 the Overseas Telecommunications Commission (OTC ) government body was established.In 1975 PMG was split into Australia Post and Telecom Australia (as a trading name for Australian Telecommunications Commission which in 1989 was reconstituted as Australian Telecommunications Corporation ATC). In 1992 the government merged Telecom Australia and OTC into AOTC which in 1995 changed its name to Telstra.


A bit of history

Aussat Pty Ltd was established in 1981 as a public enterprise to build, own and operate the Australian communications satellite system. In early 1990s the government decided to sell Aussat Pty Ltd together with and a telecommunications licence to Optus Communications consortium. Since 2001 the company became SingTel Optus Pty Ltd. Since 1985, there were launched four generations (3As, 3Bs, 1C and 3Ds) of satellites.


The Aussat A1 satellite made by Hughes (11 of 12 W transponders and 4 of 30 W transponders) launched from the payload bay of space shuttle Discovery on August 27, 1985, to become the first Australian owned and operated communications satellite.

A 13m dish was used for distribution of Seven Network programs to remote Australia.

(http://spaceinfo.com.au/2010/08/31/aussie-satellite-anniversary/)


A bit of history• 1 Apr. 1947 Long Range Weapons Establishment formed• 24 Apr. 1947 The name “Woomera” selected • 22 Mar. 1949 First missile launched from Woomera• 13 Feb. 1957 First Skylark rocket launched• 7 Sep. 1958 First Black Knight launched• 5 June 1964 First Europa launched• 5 June 1964 Modified Blue Streak launched• 24 May 1966 First Europa launched with satellite• 29 Nov. 1967 WRESAT 1 satellite launched on Redstone• 12 Jun. 1970 Last Europa launch.• 28 Oct. 1971 Prospero satellite launched on Black Arrow


WRESATHeight: 1.59 m

Base: 0.76 m

Mass: 45 Kg

Length with 3rd stage motor: 2.17 m

Mass with 3rd stage motor: 72.6 Kg

Launched: 29/11/1967

(Australia was the 4th country to launch its own satellite from its own territory after USSR, USA and France)

Re-entered orbit: 10/01/1968


Launch options from Australia


Launch options from Australia

• NASA announced in August 2006 that Woomera ( 127,000 square kilometres, ~ area of England) was selected as the launch site for rockets to service the International Space Station (ISS) with cargo such food and fuel, starting in 2008, as often as every two weeks.

• RocketPlane Kistler and Space-X are the two American companies selected to launch rockets ($207M for Stage 1).

• Work on a $100M launch site at Woomera to start in 2007…• “Woomera was chosen because it can be used for polar and

equatorial launches and because of its clean land area.”


Federation Satellite (FedSat)• The Cooperative Research Centre for Satellite

Systems was established in 1998 to deliver sustainable advantage for Australian industries, universities and government agencies involved in services based on the applications of small satellites.

• UniSA, Codan, DSTO, CSIRO, Auspace, Vipac, QUT, La Trobe, U-Newcastle, UTS

• http://www.crcss.csiro.au


Federation Satellite (FedSat)• FedSat was an Australian scientific microsatellite

launched in Dec. 2002 by Japan’s National Space Development Agency on a HII-A rocket.

• Objectives:– to establish Australian capability in microsatellites– to develop expertise for sustaining those industries– to test and develop Australian intellectual property– to provide a research platform for Australian space-

science, communications and GPS studies


Federation Satellite (FedSat)– 58 cm cube, ~50 kg, – ~800 km circular orbit (LEO) at inclination 98.7°– GPS Receiver Payload provided by NASA for

timing data and accurate measurements of the satellite’s position

– NewMag Payload built by CRCSS and University of California, Los Angeles, measures the earth’s magnetic field and study magnetospheric wave-propagation


Federation Satellite (FedSat)

– High Performance Computing Payload supplied by Johns Hopkins University for testing reconfigurable computing technology in space

– Ka-band Transponder Payload built by CRCSS handles the new experimental high-frequency and high-capacity Ka part of the radio spectrum

– UHF-band Transponder Payload built by CRCSS handles two way communications and TT&C backup (UHF on the uplink and Ka on the downlink)


Federation Satellite (FedSat)– Baseband Processor Payload supplied by CRCSS

provides on-board computer processing of the Ka-and UHF-band payloads. Flexible burst demodulator.

• Reconfigurable FPGA• IF signal synthesis and sampling• TDMA scheme, ALOHA-style request slot, 1 to 5 users• Uplink up to 4 ksym/s, stored on FedSat until it is

downlinked to the TT&C station• Downlink up to 256 ksym/s• Turbo coding on the up-link and ARQ


Federation Satellite (FedSat)BAND FREQUENCY

• UHF• UPLINK 312-315 MHz 313.55 MHz• DOWNLINK 400.15 -401.00MHz 400.4 MHz

• S Band• UPLINK 2025 - 2075 MHz ~2030.4375 MHz• DOWNLINK 2200 - 2290 MHz ~2205.0000 MHz

• Ka Band• UPLINK 29.9 - 30.0 GHz 29.93 GHz• DOWNLINK 20.1 - 20.2 GHz 20.13 GHz


Federation Satellite (FedSat)• The Platform

– Six honeycomb outer panels, and an interior double shelf dividing the platform equipment from the payloads; two S-band patch antennae and the communications payload antennae (UHF quarter-wave whip, and Ka-band isoflux)

• Communications System• Data Handling System• Attitude Control System• Power Sub-System


Federation Satellite (FedSat)• Communications System

– The platform communications link provides down-link data rates of up to 1 Mbit/s and an output power of 2 W (suppressed carrier, BPSK modulation).

– The on-board receiver accepts telecommand data BPSK modulated, with up-link rates of between 8 bit/s and 4 kbit/s. Redundancy is provided through the experimental communications payload, with a UHF up-link at 4 kbit/s, and a Ka-band down-link with 125 kbits or 250 kbit/s capability.


Federation Satellite (FedSat)• Communications System

– Communications are secured using two separate S-band receive and transmit antennae on the top and bottom of the spacecraft.

– These antennae communicate with the central Data Handling System (DHS) via the Packet TelecommandDecoder (PTD) and the Telemetry Processor Unit (TPU)


Federation Satellite (FedSat)• Attitude Control System

– attitude knowledge, accurate to ± 2°– sun-sensors made of an array of 256 photodiodes

illuminated via an orthogonal slit => a numerical correlator compares the magnitude of the outputs of each detector element around the current location with an expected pattern to improve accuracy.

– the sun sensor has a 120° field of view with an illuminated area has a width of at least 2 pixels, resulting in a resolution of at least 0.5°.


Federation Satellite (FedSat)• Attitude Control System

– a 3-axis fluxgate magnetometer is used to provide attitude knowledge during eclipse.

– 3 precision reaction wheels mounted on orthogonal axes, designed by the Canadian company Dynacon, provide initial attitude acquisition during LEOP, and maintain attitude during normal operations. These provide enough torque to counter the general perturbation torques and the disturbance torques caused by the boom and associated equipment.


Federation Satellite (FedSat)• The Power Sub-System

– a redundant Power Conditioning System (PCS) with a fully regulated +28 V ± 2% power bus that supplies all of the payload and platform units

– sixteen Nickel Cadmium Batteries cells • 28 V, with a capacity of 6 Ah, depth of discharge is 25%• cells failure => the regulators are able to draw all necessary

power from the remaining cells with double the charge rate, and a maximum depth of discharge of 40% rather than the normal 25%.


Federation Satellite (FedSat)• The Power Sub-System

– Solar Array• FedSat has body mounted solar panels on four of its sides,

one panel with four strings, and three panels with five strings.

• flat panel Gallium Arsenide cell types, with Germanium substrates, and a minimum efficiency of 19.8%.

• slow degradation rate to last the three year nominal lifetime of FedSat and still provide adequate power.

• a maximum power of around 60 W.


Federation Satellite (FedSat)• In addition to the scientific instruments, FedSat

carries a CD with Paul Kelly singing From little things, big things grow, as well as messages recorded in 2000 from “the average Aussie”.

• The CD was conceived as a time capsule, a record of what Australians hoped at the turn of the millennium. It is assumed that at an altitude of ~800km it will remain in orbit another 100 years before aerodynamic drag causes re-entry.


Federation Satellite (FedSat)• There is a trend to recognize the cultural and

historical significance of some space objects, e.g. the Vanguard I satellite launched in 1958, now the oldest manufactured object in space! Or Syncom 3 launched in 1963, the first geostationary satellite!

• It is also important from the point of view of understanding the effects on materials exposed to the space environment for more than 50 years!


The last signal received from FedSat was on 07/07/07.


Optus C1 Satellite• Launched 12 June 2003• Geostationary orbit at 156º E, 9 KW solar array• 2000 kg + 2800 kg fuel for 416 Kg payload• +15 years life• Bent-pipe architecture• Commercial use at Ku band (24 transponders)• Defence use at UHF, X and Ka bands• Costs higher than AU$300 million


Optus C1 Satellite• UHF band

– Uplink: 290-320 MHz, Downlink: 240-270 MHz– Single dual helix tx/rx antenna Earth Coverage– One 25 kHz @ 400 W plus five 5 kHz @ 100 W

• X band– Uplink: 7.9-8.4 GHz, Downlink: 7.25-7.75 GHz– 31 dBW Earth Coverage, 37 dBW Regional

Coverage, 44 dBW Steerable Spot (2000 km)– Four 60 MHz transponders, 50 W TWTA


Optus C1 Satellite• Ka band

– Uplink: 30.0-31.0 GHz, Downlink: 20.2-221.2 GHz– 34 dBW Earth Coverage, 41 dBW Littoral Coverage,

47 dBW Steerable Spot (1800 km)– Four 33 MHz transponders, 120 W TWTA each

• Integration with other US based platforms– “Global Information Grid”– “Network Centric Warfare”


Optus D1 Satellite• Launched on Friday 13 October 2006 from

French Guyana aboard an Ariane 5 rocket• Geostationary orbit at 160º E, 3.9 m height, 2300

kg, 3-axis stabilization, 17 m solar array• +15 years life (replaced Optus B1)• Bent-pipe architecture, Ku-band, BW = 54 MHz• 16 @ 150 W and 8 @ 44 W transponders• Solar array power = 4800 W


Optus D2 Satellite• Launched on Saturday 6 October 2007 to replace Optus

B3 satellite which has been operating since 1994.• Geostationary orbit at 156º E, 3.9 m height, 3-axis

stabilization, 21.4 m solar array, 2393/1160 kg, • +15 years life, broadcasting, FSS• Ku-band, BW = 54 MHz (Australia)• 16 @ 125 W and 8 @ 44 W transponders• Solar array power = 6440 W• EIRP: 44-52 dBW, G/T = 0 to 5 dB/K


Optus D3 Satellite• In August 2009 Optus launched D3 satellite, co-located

with C1, following continued demand for access, especially for television broadcast services, with companies such as FOXTEL to deliver new services to customers on a direct-to-home satellite platform including high definition content.

• Ku-band, BW = 36 MHz (BSS) 54 MHz (FSS)• 24 @ 125 W (BSS) and 8 @ 44 W transponders (FSS)• Solar array power = 6440 W• EIRP: 44-52 dBW, G/T = -5 to +8 dB/K.


Deep Space Communications The Island Lagoon site at Woomera, established in 1960, was the

first deep space station outside the United States. Honeysuckle Creek, ACT, 26 m @ 2.2 GHz antenna, was built

for the Apollo manned missions to the Moon. It provided the first pictures of man walking on the Moon, on the 21/07/1969, part of Apollo11 mission. Honeysuckle Creek had voice and telemetry contact with the lunar module. It’s been replaced by the Tracking and Data Relay Satellite (TDRS) system. (http://www.honeysucklecreek.net/)

Tidbinbilla ACT, is the only NASA tracking station still operational in Australia today. (http://www.cdscc.nasa.gov/Pages/pg01_overview.html)


JP2008The JP2008 is an ongoing project for the Australian Defence Force (ADF) regarding SATCOM capabilities.

– Phase 1 (1994) investigated requirements for OPTUS B L-band payload and prepared activities for Phase 2.

– Phase 2A concerned the Defence Mobile Communications Network. Phase 2B (UHF payload) and 2C (acquisition of three C/Ku band offshore terminals) addressed ADF’s aircraft and offshore SATCOM capability.

– Phases 3A and 3B were studies into Military Ground and Space segment. In 1998, Phase 3C was a Theatre and Broadcast System (TBS) capability/technology demonstrator.


The Australian Theatre Broadcast System

Optus C1Continental

Australia Beam

UplinkTerminal

1,800km DiameterSteerable

Spot Beam


JP2008– The TBS uses commercial satellite technology to deliver data,

audio and video. It uses modified commercial-off-the-shelf hardware and a software architecture custom-designed to meet the ADF's requirements. In 2003, TBS also included e-mail, web browsing, situational awareness, database replication, information dissemination and streaming video.

– Phase 3E is the Advanced SATCOM Terrestrial Infrastructure System (ASTIS) that used the Defence payload on the Optus C1 satellite. It provided satellite comms to complement the space segment being procured by Phase 3D and extended the strategic level Defence Information Environment (DIE) to the operational and tactical environments. BAE Systems Australia was the main supplier of equipment.


JP2008– Phase 3F - ADF SATCOM Capability Terrestrial Upgrade

request for tender was issued in October 2007 regarding:1. Delivery of a new Satellite Ground Station near Geraldton in

Western Australia (SGS-W), fitted with two X-band a single Ka-band and an optional Ku-band Earth Terminals (ETs);

2. upgrade elements within the Satellite Ground Station located at HMAS HARMAN (SGS-E) to meet the performance potential of the new SGS-W;

3. upgrade the Ground Segment Operations Centre (GSOC)4. deliver a performance-based, through-life support

arrangement for the ADSCC Ground Segment.– Phase 4 will focus on Military Space & Ground equipment.


Wideband Global Satcom (WGS)WGS is a constellation of six satellites that will provide service in both the X and Ka-band frequency spectrums. WGS will supplant X-band communications now provided by the US Defense Satellite Communications System (DSCS) and will provide a new two-way Ka-band service. WGS is a multi-service program that leverages commercial methods and technological advances in the satellite industry to design, build, launch and support a constellation of military communications satellites. When Australia wanted to be included in the network, it agreed to fund a sixth US$300-million Block 2 satellite as a price of admission. The full contract is valued at US$1.84 billion, including training, ground support and other services. The first WGS Space Vehicle was launched in Oct 2007 and provides more capacity than the entire DSCS constellation.


Wideband Global Satcom (WGS)WGS is based on Boeing’s 702 commercial satellite which allows the detection of jamming but do not offer the encrypted capabilities of the hardened Milstar satellites. The video broadcast capabilities of WGS mimics what has already been developed for the direct-to-home satellite broadcast industry, except that WGS provides encryption for real-time imagery of enemy locations. It also sends live feeds of NFL football games, secure Internet and video teleconferencing capabilities with senior civilian officials while flying to and from theaters of operation. The second WGS iteration will include transmissions to unmanned airborne intelligence, surveillance and reconnaissance aircraft. Potential upgrades include laser communications and extending a UAV data-link capability to robotic tanks and other ground-based weapon systems.


UHF payload on Intelsat 22Under a contract valued at approximately US$167 million, Intelsat was responsible for the construction, integration and operation of a UHF payload with its Intelsat 22 satellite, 72ºE, for the Australian Defence Force (ADF). The satellite was built by Boeing Space and Intelligence Systems, based on a Boeing 702B bus and has 48 C-band and 24 Ku-band 36 MHz equivalent transponders, plus a UHF payload with eighteen 25 kHz channels. The ADF is purchasing part of the UHF payload and has an option to purchase the remainder. The satellite was launched in March 2012.

The UHF payload is compliant with U.S. Department of Defence Mil-Std-188-181 and Volna Treaty (Russian) requirements for interoperability (www.satnews.com).


Space Situational Awareness“The Australian Defence Satellite Communications Ground Station is located at Kojarena, 30 km east of Geraldton in Western Australia. It is operated by the ADF Defence Signals Division [DSD]. As of November 2005, the base housed five radomes and eight satellite antennas. This is a major Australian DSD signals interception facility, and is part of a worldwide system of satellite communications keyword monitoring known as Echelon operating within the wider UK-USA signals intelligence system. Since 2007 Geraldton facility is used in the WGS system. Three 19‐metre antennas and two smaller antennas are used in a joint US-Australian ground station for the US Department of Defense Mobile User Objective System, a narrow-band networked satellite constellation for Ultra‐High‐Frequency satellite communications enabling secure all‐weather and all‐terrain 3‐G mobile telecommunications.”http://nautilus.wpengine.netdna-cdn.com/wp-content/uploads/2011/12/After-Obama-Back-to-the-Bases-footnoted-version-18-April-1500.pdf


Space Situational AwarenessThrough a new Space Situational Awareness (SSA) Partnership signed in 2010 the US intends to establish a powerful space surveillance sensor in Western Australia, preferably at North West Cape part of the US global Space Surveillance Network (SSN). The Space Surveillance Network consists of a world‐wide network of optical and radar sensors supporting the Joint Space Operations Center (JSpOC). It has two principal functions:• to provide a global public good through detection and location of

the large volume of space debris orbiting the earth from 5 cm to 1m in size, up to 36,000 km, and threatening to damage the satellites.

• to detect objects in space for offensive and defensive aspects of war‐fighting in space.

http://nautilus.wpengine.netdna-cdn.com/wp-content/uploads/2011/12/After-Obama-Back-to-the-Bases-footnoted-version-18-April-1500.pdf


Other Facilities• Pine Gap is a Defence facility outside Alice Springs jointly run

by the Australian and United States Governments. The facility is an essential part of Australia’s national defence and alliance with the United States. Pine Gap provides intelligence and early warning that would be unavailable from any other means and is unique in the region, e.g., the 40 metre radome built in 2011.

• a large US phased array space radar facility to be built within the Harold E. Holt Naval Communications Station at North West Cape on the Exmouth Gulf, playing an important role for US Space Command – locating, identifying and tracking adversary satellites to be neutralised in space war.

• Pine Gap and North West Cape facilities function in concert with the huge American investment in military and intelligence satellite and communications systems.


Broadcasting Satellites• Reception of free television programs (DVB) from

satellites: Panamsat 2 & 8, Asiasat 2 & 3S, Insat 2E, Palapa C2, Optus B1 & B3, Thaicom 3, Intelsat 701 & 702, Apstar 2R

• Programs: news, sports, music, regional channels, ABC• Costs of dish + LNA + receiver: ~$300• More info:

– http://www.kansat.com.au– http://www.lyngsat.com


Satellite plan speed vs other technologies


Broadband Internet via SatellitesSome providers of internet via satellite in Australia:

– http://www.aussiebroadband.com.au/– http://www.activ8me.net.au/– http://www.elderscommunications.com.au/– http://www.harboursat.com.au/– http://www.optus.com.au/sbsatellite– http://www.reachnet.com.au/– http://www.skymesh.net.au/– http://www.bigpond.com/homepage/– http://www.westnet.com.au/– http://www.orionsat.com.au/


Australian Satellite Network• Australian Communications and Media Authority

(ACMA) (http://www.acma.gov.au)• The Radiocommunications Act 1992 (the Act) regulates how

these systems can communicate and gives the ACMA a number of powers in relation to space objects; namely, any objects (artificial or natural) that are beyond, intended to go beyond, or have been beyond, the major portion of the Earth's atmosphere. Satellites and launch vehicles are examples of these.

• A space system consists of one or more Earth stations and a space station, which can transmit and receive information to and from Earth stations or other space stations using radiocommunications.


Australian Satellite Network• One satellite can be made up of a number of satellite networks

providing a combination of services, such as FSS, BSS, or MSS, in a number of different frequency ranges.

• Providing any of these services involves use of the radiofrequency spectrum. The frequency bandwidths employed can vary from 75 kHz for use in telecommand and telemetry to around 65 MHz for use in high capacity communication circuits.– feeder links: the transmission path for channels between gateway Earth

stations and satellites that carry trunk or network traffic – service links: the transmission path for channels between end-users and

satellites that carry traffic intended for end-users such as direct-to-home radio, television and Internet services or satellite mobile telephony.


NBN Co• Two 30 Gbps forward 10 Gbps return multi spot beam Ka-band satellites. Typical Ku-band satellite could only offer a maximum of 500 MHz per satellite.• Capacity provides a CIR of 300 Kbps per user.• The NBN Co third generation satellite will provide more than 30 times the capacity of any current broadcast satellite over Australia. The CPE performance will enable download speeds of 12 Mbps and return of 2 Mbps. • Improved latency performance through performance enhancing proxy (PEP). Adaptive Coding Modulation (ACM) extends availability in high rainfall areas.• The beam/gateway design will be optimised by the satellite vendor to provide 100% coverage of the Australian landmass.


NBN Co


NBN Co• The forward link (gateway to end user) is DVB-S2 using an Advanced Coding and Modulation Scheme, which provides up to15 dB of uplink margin in case of rain fade. The modulation schemes run from QPSK ¼ @ 0.49 bits / Hz to 32APSK 9/10 @ 4.45 bits / Hz.

• The return link is DBV-RCS with Multi Frequency Time Division Multiplexing targeting at least 8PSK and over 2 bits / Hz. A typical CPE uses a 0.8 to1.2 meter antenna with a 2 watt BUC.

• There will be more than 1.5 GHz of spectrum allocated to this service based on a four frequency reuse scheme using around 10 gateways across Australia.


NBN Co


European projects• TWISTER (http://www.twiater-project.net) Terrestrial

Wireless Infrastructure integrated with Satellite Telecommunications for E-Rural applications

• MAESTRO (http://ist-maestro.dyndns.org/MAESTRO) Mobile Applications & Services based on Satellite & Terrestrial Interworking

• SatNEx (http://www.satnex.org) Satellite Network of Excellence has the goal to achieve a long-lasting integration of European research in satellite comms.

• NEWCOM (http://newcom.ismb.it/public/index.jsp) Network of Excellence in Wireless Communications


Key technology trends: space segment

Disruptive Market Forces and Technologies:• high power Ka-Band satellites. • Ka-Band satellites will alleviate the use of Ku-

Band for DVB and DBS, as well as consumer satellite Internet access.

• Ka-Band equipment will become more available for enterprise and government applications & will help satellite compete with DSL.So

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• The new powerful satellites that will replace retiring satellites will triple the number of transponders in orbit but the number of satellites in orbit will only increase slightly over the forecast period of 2012 to 2017.

• There are currently 292 satellites that host 12,014 transponders (equivalents of 36MHz) in C, Ku, and Ka-Bands.

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Total VSAT market revenue along with unit shipments



Total VSAT market share



VSAT equipment manufacturers



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• Globally, there are over 1 billion personal computers in service, 4 billion wireless phones and over 1 billion wireline phones. Yet there are only a couple hundred million dedicated M2M devices in service.

• Twenty years from now these number should be reversed, perhaps 10 billion phones and computers in service with 25 to 50 billion M2M devices.



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Iridium Short Burst Data Transceivers:Generation 2: 9602 Generation 1: 9601

• The 9601 device is 10.6cm by 5.6cm and had a price point of $250 to $300.

• The 9602 is 3 times smaller and has a 50% lower price point of $150 to $200. This is a good example of how m2m devices are shrinking in size and cost.



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In general, satellite hardware and airtime are substantially more expensive than theirterrestrial-based counterparts. Average Revenue Per User (ARPU) among cellular operators are in the range of $6-$7 per month, where as satellite companies are in the$24 per month range. In addition, hardware prices for satellite M2M equipment rangefrom $74 - $3,200.



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• Large GEO satellites with power systems 20 kW => 55 cm satellite antennas (low cost equipment)

• rocket fairing of 4 m in diameter• solar cells

• increased efficiency: 26% for GaAs/Ge, towards 35%• more resistant to damage caused by high energy particles

from the sun, reduced cumulative radiation damage• parabolic reflectors that gathers 8 times more light• flywheel storage of energy as a substitute for batteries



• The Lockheed Martin ACeS has 2 twelve-metre antennas with 140 beams per satellite

• Phase array antennas can route traffic dynamically => increased efficiencies– photonic techniques to power and control the active

elements in phased arrays– hybrid optoelectronic signal processors that can steer

beams as fast as onboard traffic routing requires



• On-board processing– route signals from an uplink beam to a different

downlink antenna beam (at RF or IF)– phased array antenna beam forming and pointing– demodulate & decode signals– read headers or addresses and route signals function

of precedence and priority– place signals in queues– allocate the instantaneous required bandwidth



• On-board processing– link qualities approaching fiber with BER < 10-10

– Satellite Switched TDMA (SSTDMA) to at least 100x100 crossbar configuration

– Sub-channelization of transponders • COMDEV, Canada => 30 % increase in their capacity by

using BEAM*LINKTM processors (167 SAW filters, surface acoustic wave technology)

• adjustment of transponder gain for earth terminal classes => increasing the power to disadvantaged users



• TWTAs– only a few manufacturers of space qualified TWTs:

• Thomson in Europe, Hughes EDD in USA and NEC/Toshiba in Japan

– the electronic power conditioner efficiency > 94%– 3D electromagnetic modelling of TWT

• efficiency > 75%• reduced mass < 700 g• increased power > 250 W



• Wide Bandwidth Transponder– The Advanced Communications Technology Satellite

(ACTS) - USA had a 900 MHz Ka-band transponder that could carry both 622 Mbit/s (STM-4 or OC-12) and 155 Mbit/s (STM-1 or OC-3c) information rates.

– Wideband internetworking engineering test and demonstration (WINDS) – Japan satellite targets 1.2 Gbit/s information rates with bent-pipe architecture through a 1.1 GHz transponder



• Optical communications and inter-satellite links– telescope aperture equivalent to that of the antenna of

a radio frequency system could provide tens of dBsof link efficiency improvement

– a much narrower beamwidth– unregulated optical spectrum– optical intersatellite links can run at Gbit/s– high power lasers and high speed laser switching for

wavelength technology (0.8, 0.86, 1.06, 1.55 µm)



• Internet in the sky:– Integration of satellite with high-altitude platform

systems (HAPS) at 20 km altitude using optical communications

– By 2010: 1G-internet satellite 5-50 Gbit/s– By 2020: 2G-internet satellite 50-500 Gbit/s– By 2030: 3G-internet satellite 0.5-50 Tbit/s– Space Information Super Corridor on Equatorial

Orbit (6 satellites at 15,500 km, 0°inclination orbit)



• The Cisco Internet Router in Space (IRIS) is a radiation-tolerant router that implements network services directly onboard a satellite, part of Next-Generation Global Services. IRIS is hosted on Intelsat 14 and was created at the request of the U.S. Department of Defense to document the benefits and risk reduction of routing and other network services directly onboard a satellite as part of a Joint Capabilities Technology Demonstration.

SATELLITE COMMUNICATIONS © Copyright 2014Dr Sorin Adrian Barbulescuht

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• Advantages of Cisco NGGS network with its space-based IP router:

o Single-hop communications: it can route traffic between bands (Ku and C) and across transponders to interconnect small, geographically dispersed sites in a single hop, eliminating delays in excess of 500 milliseconds (ms) and double-bandwidth utilization. o Efficient bandwidth usage: multiple service levels with billing based on actual usage, not on static bandwidth subscriptions, information rates up to 512 Kbps and burst rates as high as 5.2 Mbps—that feature bandwidth on demand.



1 petabyte is 1 million gigabytes



• Eutelsat’s KA-SAT launched in Dec. 2010 is a 70 Gbps capacity Ka-band spot beam satellite with planned coverage over Europe, the Middle East, and Northern Africa.

• ViaSat-1 was launched in 2011, a Ka band Internet satellite with capacity of over 140 Gbpsto cover North America.

• Both satellites use ViaSat's next generation SurfBeam networking system (DOCSIS based).



Software Defined Radio (SDR) platforms• SDR is a key technology for regenerative satellites in

which some or all physical layer functions are software defined, e.g., digital frequency conversion, sampling, filtering, equalization, linearization, modulation, coding, routing, etc.

• Faster and cheaper re-configurable missions.• Easy bug fixes, functional enhancement.• Various air interfaces.



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• Pico and nano class satellites:– As large as a softball they can be built and launched

for as little as $100,000 to $500,000 ,“swarms” of small satellites, 10 or 20 per launch vehicle, could take multiple, distributed measurements or observations of weather phenomena, or the Earth’s magnetic fields, providing a more comprehensive assessment than is possible with a single satellite. (University of Florida http://www.ufl.edu)



• http://cubesat.calpoly.edu/: The CubeSat Project was developed by California Polytechnic State University, San Luis Obispo and Stanford University's Space Systems Development Lab. It provides a standard physical layout and design guidelines, a flight proven deployment system, coordination of required documents and export licenses, integration and acceptance testing facilities with formalized schedules, shipment of flight hw to the launch site and integration to LV, confirmation of successful deployment and telemetry information.



• http://swisscube.epfl.ch/: The size of SwissCube is 10x10x10 cm and weights less than 1 Kg. Launched in September 2009, the SwissCube has less than a few watt power it carries the sub-systems, e.g., structure, on-board computer, comms, attitude control, antennas, that exist on larger satellites.



The BeeSat is a pico satellite project of the Technical University of Berlin. The main objective is the on orbit verification of newly developed coin size micro reaction wheels for picosatellite applications. (UHF, 0.5W, Tx/Rx 9600/4800bps)

http://www.raumfahrttechnik.tu-berlin.de/menue/forschung/projekte/beesat/v-menue2/about_beesat



On 11 Feb 2014, the first four of 131 cubesats were launched from the ISS. The cubesats were Earth imaging spacecraft built by San Francisco-based Planet Labs to give a comprehensive snapshot of Earth almost daily, with pictures sent back for analysis within hours.

http://www.planet.com/story/



Skybox satellites are capable of taking imagery at < 1 meter resolution & also video and providing power, attitude control, comms, thermal management, and imaging support in a box at about the size of a phone book that consumes less power than a 100w light bulb.

http://www.skyboximaging.com//



• GEO Platform Swarm of Pico-Satellites:– As many as 100,000 pico-satellites, 23 g each, that

appear to “orbit” a point in GEO or rotate like a disk, and can occupy an area up to 25 km by 50 km.

– They frequency shift, delay and retransmit signals independently using wire antennas to a feed structure that would be tethered passively » “pencil” beams.

– Electromagnetic recollection of the swarm for upgrade, retrofit or avoid attack by terrorists.



– Swarm intelligence studies a system composed of many locally acting individuals which displays a meaningful global behaviour, make use of self-organising, decentralised control mechanisms, have: collective robustness – the failure of individual

components does not significantly hinder the performance of the swarm;

individual simplicity – agents act following simple rules; scalability – the performance of the swarm is not

dependent on the number of agents in the swarm



• The Japanese Aerospace Exploration Agency (JAXA) tested a Furoshiki spacecraft in January 2006. Assisted by ESA's Advanced Concepts Team, it has chosen the robotics institute of the Vienna University of Technology to develop the small robots.

Once in space, the mother satellite deployed three 'daughters'. These pulled out a woven net into a triangle, leaving the mother satellite at the centre. Once the net is deployed, palm-sized robots 'crawled' along the net into prearranged positions.

• http://www.youtube.com/watch?v=1vnHF_ayKQM


http://www.isas.jaxa.jp/e/forefront/2006/nakasuka/index.shtml



Recent studies have identified the advantages of centrifugal forces to deploy large structures in space:

• Testing can be performed on existing spinning satellites.• The centrifugal force is always in the plane of rotation of the

spinning satellite. Therefore, as long as the rotational forces are dominating, the out-of-plane motion will be negligible.

• The control of the centrifugal deployment is relatively simple.• The control forces can be applied to the centre hub using both fast

and slow deployment velocities.http://www.esa.int/gsp/ACT/doc/MAD/pub/ACT-RPR-MAD-2007-DesignConsiderationsAndDeploymentSimulationsSpaceWebs.pdf

http:// www.esa.int/gsp/ACT/doc/MAD/pub/ACT-RPT-MAD-ARI-05-4109a-SpaceWebs-KTH.pdf http://dave.joanddave.co.uk/thesis/David_McKenzie_PhD.pdf



The SUAINEADH (pronounced 'shin-aid' after the Gaelic word for 'twisting net' ) experiment: to deploy a space-web using centrifugal forces and to stabilise the web once full deployment has been achieved. The payload consists of a central hub section, a 2x2 m square web and four corners masses (daughters) attached to the web. An onboard reaction wheel is used to spin the system to the required angular velocity for the deployment sequence to begin. After the constraints attaching the daughter sections to the mother are released and they begin to deploy due to the centrifugal forces acting on the system.(http://www.rexusbexus.net/)


Key technology trends: ground segment

By courtesy of CSIRO



In April 2007 CSIRO Australia has signed a deal with Patriot Antenna Systems USA for CSIRO’s MultiBeamAntenna technology. The CSIRO’s MultiBeamtechnology will allow Patriot to expand its current product range and further deployments in the US, India and Asia are expected. Patriot Antenna Systems manufactures a complete line of antenna sizes from 60 cm to 18 m. These antennas are utilised in industries including Broadcast, Cable, DTH, VSAT, Military and Large Aperture Earth Stations and Radio Telescopy.



• More efficient ground stations– A few hundred watts in Ku/Ka band– Low noise amplifier for receivers: noise figure (NF)

of 3 dB or less over 2 GHz bandwidth– Flatness of amplitude and phase characteristics in

frequency up-converters and down-converters.– Multibit/Hz modulation schemes– Very high speed coding hardware, e.g., turbo code

chip set for more than 1 Gbit/s data rates.



• More efficient compression techniques– http://www.xiplink.com/ announced compression

algorithms that can boast bandwidth gains of 200% or more for most data types.



• Very Small Aperture Terminals (VSAT)– more than 1,000,000 two way VSATs worldwide– price to consumer of less than US$500– business terminal < US$2,000

• 46 cm antenna• 45 Mbit/s downlink• 2 Mbit/s uplink, 1 to 5 W transmitter • currently C and Ku band users with planned systems to

operate at Ka band



• Direct-to-Home and DBS services– digital compression has allowed the delivery of good

quality pictures at a bit rate of 2 Mbit/s allowing up to 20 TV channels to be transmitted simultaneously by a single high-power Ku-band transponder

– mass-production of chip sets– digital audio broadcasting– Internet access through the DVB-S2 service


Key technology trends: Policies, regulatory and standards

http://media.theaustralian.com.au/audio/scienceonair/071009-space.mp3

• Deregulation and privatization of the telecom services industry forced the manufacturing industry to become far more business-focused.

• The impact of the Internet led to all major manufacturers to acquire data communications companies to integrate the IP-based developments in their systems

• Outsourcing manufacturing to specialist companies• Vertical integration: manufacturers to network operators


Key technology trends: Policies, regulatory and standards

• World Trade Organization (WTO): accords with respect to trade in telephone services

• major constraints in international satellite trade in terms of landing rights agreements, annual licensing fees for terminals, non-tariff barriers, etc.

• concerns about allocation of frequencies and orbital slots (“paper satellites”)

• security and privacy of information being relayed on satellite systems


Satellite Network Access Point (SNAP)

Contents: Definition of necessity Hidden assumptionsMost important questions to ask Benefits of traffic aggregation Example of a Satellite-WiFi network


“Necessity, who is the mother of invention.” Plato, 427-347 BCE

“School of Athens”Raphael, Vatican


What is necessity? The best technical solution depends on how the answer to this question is formulated.

Example: I want to be able to watch the latest movie release.


Historical perspective:

‘80s: a single analogue TV channel occupied one satellite transponder (36 MHz).

(36 MHz per SDTV)

‘90s: six digital MPEG2 channels transmitted using DVB-S per satellite transponder (36 MHz).

(6 MHz per SDTV)

‘00s: twenty digital MPEG4 channels transmitted using DVB-S2 per satellite transponder (36 MHz).

(1.8 MHz per SDTV)


Assumptions: US$3,000/month/MHz for satellite bandwidthMPEG4 and DVB-S2 an average of 2 MHz bandwidth per video channel.

Necessity #1:“I need access to as many movies I want, at any time I want.”

satellite time used = 24 hours/day

US$6,000/month


Necessity #2:“I need to watch a movie a day, any time I want.”

satellite time used = 2 hours/day assuming that one can make a request and receive the movie say, in the next half hour, any time of the day

US$500/month


satellite time used = 2 hours/day but, chances are that another 50 people want to watch the

same new release as you. The movie will be downloaded over satellite once and then distributed for free to all 50

users over a WiFi or WiMax network

Necessity #3:“I need to watch a movie a day, any time I want, but I am prepared to order it well in advance.”

US$10/month


Have you considered that your individual needs combined with your community needs may define

the optimum satellite based technical solution ?

Telehealth

Internet Education

Local

Government

Local

Business Telehealth

Internet Education

LocalBusiness

LocalGovernment

Think

aggregation

of

services !


Are you an informed user when trying to find out the truth about satellite communications solutions?

Q#1: What is the latest available satellite modem technology ?

Q#2: Is the service optimized for my type of traffic?

Q#4: How can the cost of satellite time be reduced ?

Q#5: How does an individual-based solution compare with a community-based solution ?

Most important questions for the optimum solution:

Q#3: How can the amount of satellite traffic be reduced ?


Q#1: What is the latest available satellite modem technology ?

Non-equiprobable constellations for non-linear satellite channels


Centroid estimation for non-linear satellite channels


Internet traffic is an ON-OFF process, Self-Similar traffic.

It has a Pareto distribution, not a Poisson distribution.

Q#2: Is the service optimized for my type of traffic?


Video transmission over a VSAT link at an average of 256 kbit/s and maximum bandwidth limitation of 512 kbit/s.


Video transmission over a SNAP link at an average of 256 kbit/s with bursts of up to 2,048 kbit/s for the same cost.


Compression techniques: ratios vary (1.5 to 3.5), more efficient techniques require longer compression and decompression times (1 to 13 seconds)

Example of savings assuming US$2,000,000/year for a 45 Mbit/s transponder using a US$3,000 compression device at each end with an average compression ratio of 2:1.

Ex:http://www.expand.com/solutions/Satellite.htmlhttp://www.juniper.net/products/appaccel/

Q#3: How can the amount of satellite traffic be reduced ?


Compression Advantages

Bandwidth: 8-2 Mbit/s 64-64 kbit/sConnection: forward/return symmetricTotal bandwidth: 10Mbit/s 128 kbit/sCost of BW: $444,444/y $5688/yNr. compression devices 2 2Cost of compression devices: $6,000 $6,000

Bandwidth savings: $222,222/y $2,844/y

Payback 10 days 2.1 years


(www.cisco.com/en/US/products/ps6587)

Compression Ratios


Caching/Pre-fetching

Caching (browser caching and shared caching: Squid, CISCO) is widely used in all terrestrial networks. As a rule of thumb: 50% hit ratio and 33% bandwidth savings.

Pre-fetching (downloading the embedded objects on a HTML page and send them => reduces downloading time)

Multiple TCP connections, in aggregate, are able to use more of the available bandwidth. Applications designed for satellite links could open multiple simultaneous TCP connections, send part of a file over each connection and reassemble it at the receiver end.


The system requirements depend on the peak rates needed:

• video: average rate = 75 kb/s, but peak rate of 384 kb/s

Scenario 1: 10 individual VSAT channels need: average rate = 750 kb/s, but peak rate of 3840 kb/s

Statistical Multiplexing Gain (SMG)

As peaks occur at different moments in time (statistical multiplexing), there is a need of only a small increase of the average rate, say 400 kb/s, to allow enough margin for any user to reach peak rates, the system therefore needs only 750+400 =1150 kb/s instead of 3840 kb/s.

Scenario 2: 1 aggregated channel for 10 users needs: average rate = 750 kb/s, but peak rate of 1150 kb/s due to statistical multiplexing


Statistical Multiplexing Gain (SMG)

SMG = peak bit rate / beam capacity

Traffic scenario for a satellite link of 8,192 kb/s [1]:

• data: non-real-time 64 kb/s with activity factor 1%,

• video: peak rate of 384 kb/s and peak-to-average ratio 5,

• voice: 64 kb/s, activity factor 40%.

[1] T.Le-Ngoc, “Switching for IP-Based Multimedia Satellite Communications”, IEEE Journal on Selected Areas in Communications, VOL.22, NO. 3, pp.462-471, April 2004.


Satellite Network Access Point – traffic shaping


Telehealth

Internet Education

Local Government

Local Business

Turbo Coding

Aggregation of applications and services using the latest satellitetechnologies provides the optimum mechanism to service thecommunication needs of a community rather than individual users.

Satellite modems

Wireless LANBandwidthManagement

Q#4: How can the cost of satellite time be reduced ?


Satellite Network Access Point - antenna


Satellite Network Access Point – indoors unit


The 100BASE-TX Ethernet connection between ITR and the outside world was replaced by a 2 Mbit/s Satellite

connection.

Equivalent to an SMG of 50 !!!


Parameters VSAT SNAPSatellite BW reduction factor (1 / coding rate / modulation)

1(4/3/2=0.67)

½ to ¼ (8/7/8 = 0.14)

Compression, caching NO YES

Traffic Burstiness Capability NO YES

Optimised Satellite Protocol NO (TCP) YES (XTP)

Traffic Management (statistical multiplexing, congestion control)

NO YES

Operating point (Eb/No) for bit error rates less than 1E-10

3 to 5 dB 1.5 dB

Scalability NO 1 to 20 Mbit/s

End users Individuals Community

Q#5: How does an individual-based solution compare with a community-based solution ?


“When combining GQoS with DVB-S2/ACM it allows network operators to

increase DVB-S2 efficiency gains by combining multiple small networks into a single, larger carrier. It also allows

the network operator to maintain distinct QoS settings by remotes,

bandwidth groups and applications. By tightly integrating ACM and GQoS, service providers can create more

flexible service offerings and improve customer satisfaction in geographies

commonly impacted by adverse weather conditions.”

http://www.idirect.net/Products/iDirect-IntelligentPlatform/Group-QoS.aspx


Satellite communication is EXPENSIVE!

Cost of a GEO satellite: USD500 millionCapacity: 100 GbpsCost per Gbps: USD5,000,000

Cost of a fiber optic cable: USD300 million(US- Japan, 10,000 km long)Capacity: 8 TbpsCost per Gbps: USD37,500


O3B Networks (Sep. 2008) (http://www.o3bnetworks.com/) O3b Networks, funded by Google Inc., Liberty Global, Inc.

and HSBC Principal Investments, will deploy the world’s first ultra-low-latency, Medium Earth Orbit (MEO), Ka-band, fiber-speed satellite network designed to improve Internet access for millions of consumers and businesses in emerging markets like Africa. Service activation and ground equipment is scheduled for 2012.

The new Gilat MEO VSAT equipment will enable automatic tracking of the satellites and seamless handoff between satellites. Specific terminals target 3G Cellular/WiMAXbackhaul, IP trunking, and broadband connectivity for SMEs and ISP backhaul.


1.0B

8% are internet users

1.4B

8% are internet

users400M

18% are internet users370M

36% are internet users

177M

21% are internet

users

202M

28% are

internet users

Source: Australian Space Development Conference, July 2010“Connecting the Other 3 Billion”, Brian Holz, O3b Networks


• 8 Satellites operational in FY2012 Each Satellite has 12 Fixed Feed 2-Axis Steerable

Antennas Each Satellite has >10 Gbps throughput

• 20 Satellites operational by 2015• Equatorial Medium Earth Orbit (MEO) ~8100 km circular altitude, <0.01º inclination Equal phasing between satellites 288 minute orbital period 360 minute ground repeat Round trip latency of < 130 ms

Source: Australian Space Development Conference, July 2010“Connecting the Other 3 Billion”, Brian Holz, O3b Networks


SNAP is a turn key solution for all the communication needs in a remote area: provides terrestrial wireless interconnectivity

enables remote monitoring and supervision

reduces costs through aggregation of traffic

enhances safety through vehicle-to-vehicle communications

improves the quality of life for people working in remote areas through access to Internet


SNAP network architecture: SNAP-H: is the hub of the network which provides the link to the headquarters.

SNAP-G: is the gateway for each project site that handles all the communications for the remote area:

operations related traffic

monitoring, supervision, data back-up

internet browsing

video and audio teleconferencing


Project Site architecture: SNAP-G is the gateway that aggregates and prioritizes the traffic based on specified QoS. The statistical multiplexing gain reduces the required satellite bandwidth, therefore the on-going costs.

WiMax / Spread Spectrum backhaul links of up to 50 / 100 Km can be used to interconnect various camp sites. All these links are connected via a bridge to SNAP-G.

WiFi links from PDAs and mobile phones can also be integrated and extended up to 15 km.


Camp Site architecture: Each camp site is connected via a bridge to the main camp site.

The local connectivity over a radius of ~1 Km can be handled by a WiFi network made of:

802.11p equipment for vehicle to vehicle communications

WiFi enabled mobile phones

IP Wireless camera

WiFi enabled laptops with external antenna


Link example: 1024 kbit/s downlink, 256 kbit/s uplink

• coding rate 8/9,16QAM, roll-off 1.4

• satellite bandwidth ~ $4000/MHz/month

• bandwidth = 1280 * 9 / 8 / 4 * 1.4 = 504 KHz

• total data = 1280000 * 60 * 60 * 24 / 8 ~ 13 GB/day

• total cost = $4000 * 0.504 ~ $2000/month

Data traffic is ~ 414 GB/month, less than $5/GB with no contention or oversubscription ratio.

Aggregation of traffic achieves significant statistical multiplexing gains which would allow servicing more than 100 users at a cost of less than $20/month.


The satellite bandwidth could be shared in time and frequency between many project sites as follows:

• on a regular basis in timePS1 PS2 PS3 PS1 PS2 PS3 PS1 PS2 PS3

• on a traffic demand basis in timePS1 PS2 PS3 PS1 PS2

• on a traffic demand basis in frequencyPS1 to hub

Hub to PS1 PS2 to hub Hub to PS2

satellite bandwidth satellite bandwidth

time

time


Equipment Unit cost No Total cost

Antenna (Ku) 2,000 1 2,000

RF transceiver 7,000 1 7,000

Modem 3,000 1 3,000

Point-to-point Wireless Bridge

5,000/pair(62 km range)

2 camp sites active any time

10,000

WiFi access point (Cohda)

4,000/camp (2 km range)

2 camp sites active any time

8,000

Wireless VoIP Phone

300 10 3,000

Wireless Camera 500 4 2,000

TOTAL CAPEX 35,000

Project Site capital expense (CAPEX) costs

Hub

CA

PEX


Digital Communications

Contents: Time/Frequency representation of signals One single pulse A periodic signal Random signals Nyquist Theorems BPSK/QPSK modulation and BER Capacity


Time Frequency


Time Frequency

τ/2-τ/2

V

time

g(t)

g(t) = Vτ/T + Σ(2Vτ /T)[sin(nπτ/T)/(nπτ/T)]cos(2πnt/T)

T 2T-T-2T

1/τ 2/τ 3/τ

frequency

n = 1, 2, 3,…

1/T 2/T 3/T 9/T

Fourier Series


Time Frequency

τ/2-τ/2

V

time t

g(t)

G(f) = ∫ g(t) exp(-2πjft) dt

G(f) = Fourier Transform

G(f) = V τ [sin(π τ f)]/(π τ f)

+∞

-∞


G(f) = V τ [sin(π τ f)]/(π τ f)

~ (f)-1

G(f) = V τ [sin(π τ f)]2/(π τ f) 2

~ (f)-2

G(f) ~ (f)-3


Time Frequency


Time Frequency

• A single finite pulse in time has an infinite spectrum with a continuous distribution in frequency

• The shorter the pulse, the broader the spectrum• Sudden changes in a pulse shape imply high

frequencies in the spectrum• Sudden changes in the spectrum imply

oscillatory behaviour in the time domain


Time Frequency

Parceval’s theorem for energy signals: (the energy delivered to a 1-ohm resistor)

Energy = ∫ |g(t)|2 dt = (2π)-1 ∫ |G(ω)|2 dω+∞

-∞

+∞

-∞

The quantity |G(ω)|2 is called energy spectral density, it represents the energy per unit of frequency normalized to a resistance of 1 ohm.


Time Frequency

The signal power in a 1-ohm resistor is:

The quantity Sg(ω) is called power spectral density, it describes the distribution of power versus frequency normalized to a resistance of one ohm.

Power = lim (1/T) ∫ |g(t)|2 dt = (2π)-1 ∫ Sg(ω) dω+T/2

T→∞

+∞

-T/2 -∞

Sg(ω) = lim (1/T) |GT(ω)|2T→∞


Time Frequency

• Autocorrelation function rg(τ) for a signal g(t) of finite energy is defined as:

rg(τ) = lim (1/T)∫ g*(t) g(t + τ) dt+T/2

-T/2

Frg(τ) = Sg(ω)

• The power spectral density is the Fourier transform of the autocorrelation function for finite-energy signals.

T→∞


Time Frequency

• Random Binary Waveform – each pulse is of duration Tb, – two possible pulse levels –A and +A equally likely– Statistically independent

rg(τ) = A2(1- τ/Tb) for τ < Tb

rg(τ) = 0 for τ > Tb

S(ω) = A2Tb[sin(ωTb/2)/(ωTb/2)] 2


Time Frequency


Time Frequency

• Nonreturn-to-Zero (NRZ): 94.8%, 90%, 77%

-π/Tb π/Tb

-π/2Tb π/2Tb


Time Frequency

• Return-to-Zero (RZ): continuous + discrete at odd multiples of the bit rate


Time Frequency

• Split-Phase (Manchester Code): no DC components


Time Frequency

• Bipolar Return-to-Zero (BRZ)


Time Frequency

• Delay Modulation (Miller Code): magnetic recording


Nyquist Theorems

• The behaviour of a system can be characterised by the impulse response of the system defined as h(t) = Tδ(t), where δ(t) is the unit impulse function

• The output of a linear time-invariant system, given an input f(t), can be expressed as a convolution in the time domain, or as a multiplication in the frequency domain:

F f(t) * h(t) = F(ω)H(ω)


Nyquist Theorems

• When sending rectangular pulses in a bandwidth limited channel, the pulses will spread in time, and the pulse from one symbol will smear into the time interval of succeeding symbols.

• This is called intersymbol interference (ISI) and leads to increased probability of the receiver making an error in detecting a symbol.


Nyquist Theorems


Nyquist Theorems

Minimum-Bandwidth TheoremIf synchronous impulses, having a transmission rate of fs symbols per second, are applied to an ideal, linear-phase brick-wall low-pass channel having a cut-off frequency fN = fs/2, then the responses to these impulses can be observed independently, that is, without intersymbol interference


Nyquist Theorems


Nyquist Theorems

The brick-wall filter is not realizable– The infinite attenuation slope would require an

infinite number of filter sections– The decay in the lobes of the time-domain response

is very slow– The smallest symbol timing imperfections would

cause a very large ISI degradationThe solution is the vestigial symmetry theorem


Nyquist Theorems

Vestigial Symmetry TheoremThe addition of a skew-symmetrical, real-valued transmittance function Y(ω) to the transmittance of the ideal low-pass filter maintains the zero-axis crossing of the impulse response. The zero-axis crossings provide the necessary condition for ISI-free transmission.Y(ωN – x) = - Y(ωN + x) where 0< x < ωN= 2πfN


Nyquist Theorems


Nyquist Theorems

Root Raised Cosine Filter• Filtering is required in the transmission unit and

in the receiving unit• The impulse response of the optimum receiver

filter is the mirror image of the desired input signal, the matched filter

=> Split the overall raised cosine response into two root raised cosine filters for tx and rx


Nyquist Theorems

ISI-Free and Jitter-Free TheoremFor ISI-free transmission, the null points of the ideal brick-wall low-pass filter impulse response have to be maintained. To avoid data transition jitter, additional null points located halfway between adjacent null points are required. These simultaneous zero crossing conditions are satisfied by a raised-cosine filter with roll-off 1.


Nyquist Theorems

H(ω) = ½[1 + cos(πω/2ωN)] where 0< ω < ωN= 2πfN

Jitter-Free is too expensive:having a bandwidth twice the minimum channel bandwidth is more expensive than to compensate for some peak-to-peak data transition jitter of 20 to 30%


Nyquist Theorems

Pulses not impulses !- for an impulse, the amplitude of the Fourier

transform is constant over all frequencies- for a single pulse the spectrum profile is sin(x)/x - an [πfTs/sin(πfTs)] shaped amplitude equalizer

has to be added to the ideal brick-wall channel transfer function.


Nyquist Theorems


BPSK/QPSK Modulations

-A +A -A +A

-A

+A

+/-Acos(2πfct) +/-Acos(2πfct) +/-Asin(2πfct)


BPSK Modulation

BPSK

Modulator

Raised cosine

filter

+A, -A

+/-Acos(2πfct)fs

fsfs /2

Bandwidth = (1 + α)fs/2


BPSK ModulationNo filtering

2fs

fc + fs

1.5fs


8PSK Modulation

-A +A

-A

+A

I

Q


16QAM Modulation

-A +A

-A

+A

+3A

+3A

-3A

-3A I

Q


APSK Modulation


APSK Modulation

ρ1 = r2/r1ρ2 = r3/r1


APSK Modulation

There is no capacity dependency on the relative phase shift between different rings due to the fact that the distance between the rings is

larger than the distance between the points on each ring.


APSK Modulation


APSK Modulation

The histogram of the transmitted signal envelope power shows that 4+12-APSK envelope is more concentrated around the outer ring

amplitude than 16QAM similar to 16PSK.


Sampling of bandwidth limited signals

• The bandpass sampling theorem states that if a bandpass signal m(t) has a spectrum of bandwidth ωB (= 2πfB) and an upper frequency limit ωu (= 2πfu), then m(t) can be recovered from ms(t) by bandpass filtering if fs = 2fu/k, where k is the largest integer not exceeding fu/fB.

• All higher sampling rates are not necessary usable unless they exceed 2fu.


Modulation of an analogue signal


Demodulation of an analogue signal


Sampling and quantisation

• Voice signal < 4 kHz• Sampling theorem requires fs > 8 kHz• Quantisation of each sample on 8 bits results

in a 64 kbit/s data rate (e.g. ISDN service)• Bandwidth (no filtering or rolloff 1):

– BPSK modulation: 1bit/symbol => 128 kHz– 4AM or QPSK: 2 bit/symbol => 64 kHz– 16AM or 16QAM: 4 bit/symbol => 32 kHz


Sampling and quantisation

• Bandwidth (brick-wall filter at fs/2 or rolloff 0):– BPSK modulation: 1bit/symbol => 64 kHz– 4AM or QPSK: 2 bit/symbol => 32 kHz– 16AM or 16QAM: 4 bit/symbol => 16 kHz

• The more bits per symbol the more sensitive to noise therefore an increase in SNR is required to achieve the same probability of error

• Attenuation of the signal increases with distance


Capacity

• Channel capacity C = B*log2[1 + SNR] bps• Ex.1: SNR = 20 dB, RF bandwidth = 30 kHz

C = 30000*log2 [1+100] = 199.75 kbpsThe US Digital Cellular Standard data rate is 48.6 kbps, about one fourth of the theoretical limit.

• Ex2: RF bandwidth = 200 kHzSNR = 30, C = 200000*log2 [1+1000] = 1.99 Mbps SNR = 10, C = 200000*log2 [1+10] = 691 kbpsThe GSM data rate is 270.833 kbps


Capacity

• Channel capacity C = B*log2[1 + SNR] bps• For zero-mean noise with power N we get level

spacings of sqrt(N). Using the rms value of the observed signal plus noise, we can find the number of discernible levels M in one dimension:

sqrt[(S+N)/N] = sqrt(1+S/N) = sqrt(1+SNR)• C = B*log2[1 + SNR] = B*log2[M2] = 2B*log2M

This is the maximum limit that can be achieved for a specific modulation


Capacity

• Unfortunately the same C is also used for carrier power in a link budget

• SNR = Es/N0 = k * Eb/N0

where k is the number of information bits per two dimensional symbol

• C/N0 = (Es/N0 ) * Rs = (Eb/N0 ) * Rb

• Translated in dB:C/N0 = Es/N0 + 10 log10 Rs = Eb/N0 + 10 log10 Rb


Earth Stations

Given the available uplink of C/N0 = 77 dB, QPSK modulation, uncoded, and a target BER = 10-10, what is the maximum information data rate that can be transmitted ?

C/N0 = Eb/N0 + 10 log10 RbQPSK modulation requires Eb/N0 = 13 dB to achieve the target BER; the maximum data rate is 77 - 13 = 64 dB, that is 106.4 bit/s = 2.5 Mbit/s


Digital Transmission

Content: Antenna Cancellation A/D & D/A (Prof Brian L. Evans)Transmitter Linearisation Performance Degradation Phase Noise Effects


Antenna Cancellation(“Achieving Single Channel, Full Duplex Wireless Communication”

by Jung Il Choiy, Mayank Jainy, Kannan Srinivasany, Philip Levis, Sachin Katti, MobiCom’10, September 20–24, 2010, Chicago, Illinois, USA)

“The transmission signal from a node is split among two transmit antennas. A separate receive antenna is placed such that its distance from the two transmit antennas differs by an odd multiple of half the wavelength of the center frequency of transmission. The antenna cancellation performance depends on the signal bandwidth: 60.7 dB is the best possible for a 5 MHz signal in the 2.4 GHz band; Similarly, a reduction of 46.9 dB for 20 MHz and 34.3 dB for 85 MHz signal bandwidths.”


A/D (Brian L. Evans)

[ ] ( )sTkfkf =

• By sampling a continuous-time signal at isolated, equally-spaced points in time, we obtain a sequence of numbers

k ∈ …, -2, -1, 0, 1, 2,…Ts is the sampling period.

Sampled analog waveform( ) ( )∑

∞

−∞=

−=k

ssampled Tkttftf )( δf(t)

t

Ts

Ts

( )tfsampled


• Sampling replicates spectrum of continuous-time signal at integer multiples of sampling frequency (ωs = 2 π fs)

( ) ( ) ) (2cos2 ) (cos2 1 1 )( ...+++=−= ∑∞

−∞=

ttT

Tktt sssk

sTsωωδδ

( ) ) (2cos)(2 ) (cos)(2 )( 1 )( )()( ...+++== ttfttftfT

ttftg sss

Tsωωδ

ω

G(ω)

ωs 2ωs−2ωs −ωs

ω

F(ω)

2πfmax-2πfmax

maxmaxmax 2222 ifonly and if gap fffff ss >⇔−< πππ

Modulationby cos(2 ωs t)

Modulationby cos(ωs t)

A/D (Brian L. Evans)


D/A (Brian L. Evans)• Oversampling eases analog filter design and

creates spectrum to put noise at inaudible frequencies

• Add dither (noise) at quantizer input to break up harmonics caused by quantization

• Shape quantization noise into high frequencies • State-of-the-art in 20/24-bit audio converters

Oversampling 64x 256x 512xQuantization 8 bits 6 bits 5 bitsDynamic range 110 dB 120 dB 120 dB


D/A (Brian L. Evans)

• Upsampling by 4: for each input sample, output the input sample followed by three zeros. Four times the samples on output as input increases sampling rate by factor of 4

• FIR filter performs interpolation

Digital 4x Oversampling Filter

16 bits44.1 kHz

28 bits176.4 kHz4 FIR Filter16 bits

176.4 kHz

1 2

Input to Upsampler by 4

Output of Upsampler by 4

1 2 3 4 5 6 7 8

1 2

Output of FIR Filter

3 4 5 6 7 8


Texas Inst. www.ti.com/sc/docs/dsps/dsphome.htm 45

Agere Systems www.lucent.com/micro/dsp/ 25

Moto-rola www.mot.com/SPS/DSP/ 10

Analog Devices www.analog.com/SHARC_2154 8

DSP manufacturers and their market sharehttp://www.bdti.com/Resources/PocketGuide


Transmitter LinearisationThe requirement for the linear power transmitter comes from a consideration of the modulation scheme, the required bit rate, and the required Adjacent Channel Power (ACP) specifications for a given system. Linear Class A amplifiers are rarely used in practice for power outputs above a few watts for reasons of cost, complexity and low power efficiency. Linearisation techniques may be applied to non linear Class AB, and Class C RF amplifiers. A few of the most popular techniques are presented here.


Transmitter Linearisation

Class A amplifier output

(linear, no dead zone but low power efficiency - ~25%)


Transmitter LinearisationClass B amplifier output (has a dead zone but has a higher power efficiency ~78.5%)

Class AB amplifier (no dead zone) Class C amplifier


Transmitter LinearisationCartesian Feedback

In this technique a baseband modulator produces quadrature signals which are then up converted to the transmit carrier frequency and passed through the power amplifier. A sample of the power amplifier output is then down converted using the same local oscillator to provide a quadrature baseband version of the amplifier output , which is then used to provide negative feedback to the baseband input. This principle is illustrated in the following diagram.


Transmitter LinearisationFeedforward Linearisation

An error signal is derived at RF by subtracting the input of the amplifier from the output using suitable attenuation and phase shift. The error signal is then amplified, phase shifted and summed with the output.This technique has been proposed for multiple carrier base stations because of its broadband performance. The performance is degraded by the effects of temperature drifts and ageing. The use of two amplifiers makes this option very expensive.


Transmitter LinearisationAdaptive Predistortion

A transfer function is applied to the signal prior to amplification such that the product of this with amplifier transfer function is a linear transfer function. A look up table is used to apply the predistortion and this is constantly updated to account for temperature drifts using a quadrature feedback signal. It may be too slow for TDMA systems but it offers better performance than the previous techniques; it also requires a greater use of DSP processing.


Analogue implementations of Quadrature hybrid circuits are imperfect and contribute to distortion of the transmitted signal. The main sources of distortion are:

Quadrature Phase ErrorThe phase shift introduced in real quadrature frequency converters is not always exactly 90° due to:– The phase difference between the LO signals that are used to

multiply the I and Q channels may not be 90°. – Differences in the phase responses of the I and Q channel

transmit and receive filters.

Performance Degradation


– The impedance mismatch between the mixers and the 90°phase shift circuit and the amount of isolation between the two output ports on the phase shift circuit.

– There is always some phase difference introduced by the RF paths taken through signal splitters and combiners between the I and Q channels.

The last three sources of error are frequency dependent and become worse for high data rate systems. Due to the wide bandwidths involved this may result in frequency dependent errors occurring across the band.



Amplitude Imbalance between I and QAmplitude imbalance between the I and Q channels has two main sources. The first is from the amplitude imbalances between the input and output ports of RF splitters and combiners and differences in conversion loss between the output ports of I and Q channel mixers. The second is from amplifier and filter gain differences in the I and Q channels before the mixer in up converters and after the mixer in down converters. Amplitude imbalance causes distortion of the constellation.



Carrier LeakthroughReal mixers produce many spurious products that arise from intermodulation terms and leakthrough of the LO and RF signals out of the IF output port of the mixer. The leakthrough of the LO signal lies in the middle of the wanted pass band of the modulated signal and cannot be removed by filtering. The LO radiated power could be comparable or greater than the actual modulated power. DC components are created out of the down converter mixer from both self mixing of the receiver LO and the transmitter LO mixing with the receiver LO.



Case ‘b’ has parameters which are probably better than that which may be achieved with the best possible analogue design. Case ‘a’ is the same as ‘b’ but without ideal, or infinite carrier suppression. Case ‘c’ has parameters which are achievable from a good design and case ‘d’ would be typical of an average design.




BER for 8–PSK with Combined Errors



BER for 16–QAM with Combined Errors



BER for 64–QAM with Combined Errors


Phase Noise EffectsBER degradation can also be caused by phase noise for a number of M–QAM/PSK schemes. The phase noise performance of LO sources within the system is critical. The Carrier Recovery Loop (CRL) is a scheme able to remove phase jitter within the loop bandwidth assuming the bandwidth is small compared to the data rate so that phase estimates derived by the CRL are constant over the symbol period. Phase noise is related to the broader term of frequency stability, which is the degree to which a signal source produces the same frequency value throughout a specified interval of time.


Phase Noise EffectsFrequency stability can be qualified as long term or short term. Long term stability is caused by frequency fluctuations that occur over intervals of greater than a few seconds, also referred to as frequency drift and can be related to the aging of components used in the oscillator design. Short term stability may have both deterministic and random components. These are frequency fluctuations occurring over intervals of less than a second. They can be power supply fluctuations or mechanical vibration identified by deterministic frequency components in the spectrum or random.


Phase Noise Effects

Ideal and Nonideal Oscillator Spectral Densities


Phase Noise EffectsIn a coherent communications system demodulation is performed by correlating the phase of the received signal with the phase of a reference signal which is adjusted under feedback by the CRL. The phase noise of the LO signals is transferred to the modulated signal by the frequency conversion process. This, combined with AWGN, causes the phase estimate of the CRL to change. There is a finite amount of error between the phase of the received signal and the CRL phase estimate in the form of phase jitter. The amount of phase error is quantified by taking the variance of the phase estimate error.


Phase Noise EffectsAs the amount of phase noise and AWGN increases, so too does the phase error variance. The effect on the demodulation process can be seen using the received signal constellation. The random phase jitter causes each point in the signal constellation to have a radial component of movement. The random phase jitter can move the symbols close to or over the decision threshold and add to the BER caused by AWGN alone. The exact value of phase variance can often vary depending on CRL bandwidth, CRL topology, type of modulation, and SNR operating point.


Implementation Loss vs Phase Jitter Variance for BPSK and QPSK


1. Determine the maximum distance from a geostationary satellite to an earth station located on the equator considering a minimum elevation angle of 10 degrees.

Questions


2. What is the round trip propagation ?


3. Determine the speed at the perigee and apogee for Molnya (P = 500km, A = 40,000km).


4. Which are the advantages of an elliptical orbit ?


5. Determine the maximum latitude of an earth station seen by a GEO satellite considering a minimum elevation angle of 15 degrees.


6. Determine the change in speed at apogee and perigee if the semi-major axis of the satellite orbit is doubled.


7. Find the longitude of the ascending and descending nodes for a satellite in a polar orbit which is seen at the same distance from a geostationary satellite situated at 100° E.


8. Calculate the azimuth and elevation angles for an earth station located at λES = 20.8°S and φES = 138.6°E that needs to receive a geostationary satellite located at φSS= 170°E.


9. The period of a satellite in an elliptical orbit is 100 minutes. What is the period of the satellite if the semi-major axis is doubled?


10. Find the minimum number of satellites placed on the same circular polar orbit at an altitude of 800km such that a satellite can see one satellite ahead and another one behind?


11. An elliptical orbit has the perigee at 200 km and the apogee at 40,000 km altitude and zero degrees inclination. A receiver ground station is situated on the equator. What would be the maximum distance between the receiver and the satellite?


12. The iPSTAR geostationary satellite is located at longitude φSS= 120°E.Which are the positions of the furthest geostationary satellites that could be connected with iPSTAR through inter-satellite links?


13. A polar satellite (inclination of 90°) placed at an altitude of 800 km needs to establish inter-satellite links with a geostationary satellite. What is the maximum distance expected at the moment when the plan defined by the orbit of the polar satellite contains the geostationary satellite?


14. Describe the solar system models held by Aristotle and Ptolemy.

15. Who launched the first artificial satellite, what was called and what legal problem solved?


16. Based on intelligence regarding a new terrorist attack on Mumbai, you are required to decide which project(s) should be funded:

• To launch a satellite in an orbit describing a circle of diameter 100 km, at 10km altitude, hovering above Mumbay to monitor the local phone communications or

• To launch a satellite in an orbit describing a circle of diameter 1000 km at 100 km altitude, hovering above India that could also extend the surveillance across other cities.


17. Would a ground station situated on the Equator at longitude 0° be able to see more of the geostationary orbit compared with a ground station situated also on the Equator but at 90°E longitude?

18. What would be the required altitude of a ground station placed at the North Pole to see a geostationary satellite?


19. A source produces random symbols with the following probabilities: p1 = 0.35, p2 = 0.3, p3 = 0.09, p4 = 0.25, p5 = 0.01. List the Huffman codewords and calculate the average length and its efficiency. The symbols are generated at a rate of 1 Msym/s. Find a code and a modulation that would allow you to transmit these symbols in a 1 MHz bandwidth (α = 0.2) at less than 1E-6 bit error rate at Eb/N0 = 5 dB.


20. Assume the source transmits at a rate of 1Msymbol/sec. The six symbols, u1, u2, u3, u4, u5 and u6, have the following probabilities: p1 = 0.3, p2 = 0.23, p3 = 0.17, p4 = 0.15, p5 = 0.10 and p6 = 0.05.

– Find the Huffman code for this source.– Calculate the entropy of the source and

the average length of the code.– If a rate ¾ channel encoder is used, what

is the coded rate at the output of the encoder?


21. Draw the encoder and trellis for the following convolutional code (one input, two outputs):

g(1) = (1 1 0 1) and g(2) = (1 0 1 1).

Label each branch in the trellis with the information/coded bits.


22.Which are the generator polynomials? Draw the trellis and label each branch in the trellis with the information/coded bits.


23. Calculate the probability of error for a Golay code at S/N = 5 dB.


24. Draw the encoder for the following code: g1 = 133o, g2 = 171o, g3 = 156oand find the outputs generated from state 3.


25. In a satellite modem, every data bit is repeated five times, and at the receiver, a majority vote decides the value of each data bit. If the uncoded bit error probability p is 0.01, calculate the coded bit error probability when using this best-of-five code.

(Hint: probability that all 5 bits are flipped is p5; probability that 4 bits are flipped is (5, 4)p4(1-p) and so on.)


26. Which code would be better: a concatenation of the previous code with a similar one or a new repeat code which repeats every data bit twenty five times? Justify your answer.


27. What is Hamming distance? What is the minimum distance for a block code? What is the maximum nr. of errors that can be corrected by a block code with n = k+6 ?

28. What is the Hamming distance between the following two codewords:

- (1, 1, 1, 1, 0, 0, 0, 1) and- (0, 0, 0, 0, 1, 1, 1, 0)


29. What is the Euclidian distance? Why is it important?

30. What is the Euclidian distance between the following two codewordsin a QPSK system [ S1(-a, -a), S2(-a, a), S3(a, -a), S4(a, a)]:

- (S1, S2, S1, S1, S4, S1, S2, S1 )- (S4, S3, S1, S2, S4, S3, S4, S1)


31. In a station-to-station link budget, should I increase more the C/N0 in the uplink or in the downlink direction?


32. Which of the C-band or Ku-band allows lower power margin for increasing the availability of a link with the same percentage?


33. What is the maximum bandwidth efficiency for 16QAM uncoded? How does it change if the uncoded signal is replaced with a rate ½ coded signal and the same 16QAM is used?


34. How does the noise figure change with the increase in frequency?


35. What is the free space loss at 1 GHz and 20 GHz?.


36. How does antenna gain change function of diameter? How does antenna gain change function of frequency?


37. Which are the steps to design a satellite link? Which are the steps to minimize the link cost?


38. What is the 3dB angular beamwidth?


39. Given the available uplink of C/N0 = 77 dB and a target BER < 10-7, what is the maximum information data rate that can be transmitted using a rate ½ turbo coded scheme and 16QAM? (use the included figure on the next slide)


40. Find the total (C/N0)T for a station-to-station link given the saturation uplink (C/N0)U,sat is 74 dB and the saturation downlink (C/N0)D,sat is 76 dB? How would (C/N0)T change if the output back off, OBOsat, is increased from 0 dB to 3 dB?


41. A geostationary satellite transmits 155 Mbit/s on a frequency of 10 GHz with an EIRP is 40 dBW. The figure of merit, (G/T)ES, of the earth station is 28.8 dBK-1. Which is the available Eb/N0 for the receiver?


42. The available uplink is C/N0 = 70 dB.A satellite modem using rate 4/5 turbo coded 16QAM modulation sends an information data rate of 2 Mbit/s. What is the expected BER? What is the expected BER if the coding rate is changed to 5/6? In the case of coding rate 5/6, with how many dBs should the link margin increase in order to maintain the same BER as in the case of coding rate 4/5?


43. Determine the maximum distance between two LEO satellites on an orbit of 1000 km altitude that allows them to communicate with each other.


44. A polar satellite at an altitude of 800 km passes on top of Adelaide (longitude ~139° E) at 12 noon. After this pass, around what time will be the satellite visible from Adelaide again? Argue your answer.


45. Draw the encoder for the convolutional code defined by the generating polynomials g1 = 151o, g2

= 105o and g3 = 121o. Which are the values of the three encoder outputs x, y and z, for the input sequence values: 1,1,0,0,1,1? Encoder starts in state zero.

P3 Link budget

SATELITE: PAS-2 @ 166 EastLINK TYPE: 2 way, Adelaide - Adelaide

UPLINK THERMALAntenna Diammeter 1.80 m designer's choiceAntenna Efficiency 0.50 Antenna specificationAntenna TX gain 45.56 dBWSatellite transponder bandwidth: 36.00 MHz Satellite specificationMaximum SFD at the satellite for the whole transponder: -98.80 dBW/m^2 Satellite specificationPercentage of transponder bandwith used: 0.04Maximum EIRP: 49.63 remaining SFD plus 10log(4PI^2range^2)HPA power 4.00 dBW designer's choice: adjust this after the Maximum EIRP is calculated, for a given antennaGround Earth Station EIRP 49.56 dBW Should be less than the maximum EIRP due to satellite SFD and occupied bandwidthSatellite Input back-off (IBO) 8.20 dB Satellite Operator specificationOperating Ground Earth Station EIRP 49.24 dBCarrier frequency 14.2360 GHz Satellite Operator specificationSlant range 37774 kmFree space loss 207.05 dBAtmospheric loss 0.50 dB Site specific parameterUplink rain attenuation 0.00 dB Site specific parameterConversion to flux density 44.52 dB/m^2Contribution to saturated flux density at satellite antenna -113.79 dBW/m^2 -112.90 if IBO is ignored similar formula: -113.79Power received at satellite antenna -158.31 dBWSatellite G/T -0.40 dB/K Satellite specificationUplink thermal C/No 69.89 dBHzC/N 8.43

DOWNLINK THERMALNominal satellite EIRP 51.80 dBW Satellite specificationSatellite Output back-off (OBO) 12.00 dB Satellite Operator specificationAvailable EIRP as percentage of transponder used 25.70Carrier frequency 12.4860 GHz Satellite Operator specificationSlant range 37774 kmFree space loss 205.91 dBAtmospheric loss 0.00 dB Site specific parameterDownlink rain attenuation 0.00 dB Site specific parameterConversion to flux density 43.38 dB/m^2Flux density at earth station antenna 69.08 dBW/m^2Earth Station (E-3) G/T 5.00 dB/K designer's choiceDownlink thermal C/No 67.49 dBHz

AVAILABLE CARRIER TO NOISE DENSITY RATIOAvailability 100.00 % estimateInter and intra system interference loss 1.00 dB estimateModem losses (synchronization, phase noise) 1.00 dB estimateTotal C/Io 95.00 dBHz estimateAvailable C/No 63.51 dBHz

LINK MARGINModulation (e.g., 2 for QPSK, 4 for 16QAM) 2.00 bit/sym designer's choiceCoding rate 0.50 designer's choiceBit rate 1000.00 kbits/s Application specificationRolloff 0.40 Satellite modem specification for the target BER and for the selected coding & modulatioRequired Bandwidth 1.40 MHzMiscellaneous Losses 1.00 dB estimateAvailable Eb/No 2.51 dBRequired Eb/No 2.00 dB Satellite modem specification for the target BER and for the selected coding & modulatioLink margin 0.51 dB Should be positive, ~1dB

Calculation of azimuth and elevationAdelaide latitude: -34.90 Site specific parameter

longitude: 138.60 Site specific parameterPas-8 longitude: 166.00 East Satellite specification

longitude difference: -0.48b: 0.76Azimuth: 42.18 No correction is required for the calculated valueRange: 37773.72Elevation: 40.09

Link Analysis Page 1

Glossary

16QAM 16 Quadrature Amplitude Modulation 8PSK 8 Phase Shift Keying ACeS Asia Cellular Satellite ACK Acknowledgement ACM Adaptive Coding and Modulation ACMA Australian Communications and Media Authority ACTS Advanced Communications Technology Satellite AF Assured Forwarding AM Amplitude Modulation ANGELS Autonomous Nanosatellite Guardian for Evaluating Local Space ANSI American National Standards Institute A-PCMA Asymmetric Paired Carrier Multiple Access APK Apogee Kick Motor APSK Amplitude and Phase Shift Keying ARQ Automatic Repeat Request ASAT Anti Satellite ASIC Application Specific Integrated Circuit ATM Asynchronous Transport Mode ATV Automatic Transfer Vehicle AVC Audio Video Coding AWGN additive white Gaussian noise BCH Bose-Chaudhuri-Hocquenheim BE Best Effort BER Bit Error Rate BGAN Broadband Global Area Network BNC bayonet Neill-Concelman BOD Bandwidth On Demand BOL Beginning Of Life BPSK Binary Phase Shift Keying BSS Broadcasting Satellite Services CA Congestion Avoidance C/A Coarse Acquisition CABAC Context Based Adaptive Binary Arithmetic Coding CAC Call Admission Control CATV Cable TV CBR Constant Bit Rate CC Congestion Control CCSDS Consultative Committee for Space Data Systems CCU Cluster Control Units CD Compact Disk

CDMA Code Division Multiple Access CEV Crew Exploration Vehicle CLR Cell Loss Ratio CMOS Complementary metal–oxide–semiconductor CRA Channel Rate Adaption CRC Cyclic Redundancy Check CRCSS Cooperative Research Centre for Satellite Systems CRMA Code Reuse Multiple Access CSC Common Signalling Channel CSI Channel State Information CSIRO Commonwealth Scientific and Industrial Research Organisation CW Continuous Wave DAMA Demand-assigned TDMA DBA Dynamic Bandwidth Allocation DBS Digital Broadcast Systems DC Direct Current DCT Discrete Cosine Transform DGPS Differential GPS DHS Data Handling System DiffServ Differentiated Services DLA Dynamic Link Assignment DOCSIS Data Over Cable Service Interface Specifications DoD Department of Defence DS-CDMA Direct Sequence CDMA DSI Digital Speech Interpolation DSNG Digital Satellite News Gathering DT-DVTR Discrete Time – Dynamic Virtual Topology Routing DTH Direct-to-Home DVB Digital Video Broadcasting DVB-C Digital Video Broadcasting – Cable DVB-RCS Digital Video Broadcasting – Return Channel Satellite DVB-S Digital Video Broadcasting – Satellite DVB-T Digital Video Broadcasting – Terrestrial ECC Error Correcting Codes EDGE Enhanced Data rates for GSM Evolution EF Expedited Forwarding EGPRS Enhanced GPRS EIRP Equivalent Isotropic Radiated Power EOL End Of Life ESA European Space Agency ET External Tank F Noise figure FACK Forward Acknowledgement FDCT Forward DCT FDMA Frequency Division Multiple Access

FEC Forward Error Control FH-CDMA Frequency Hopping CDMA FIT Failures in 1E9 hours FM Frequency Modulation FPGA Field Programmable Gate Array FSS Fixed Satellite Services FTP File Transfer Protocol G/T Figure of merit GA Gallium Arsenide GDP Gross Domestic Product GEO Geostationary Earth Orbit GLONAS Global Navigation Satellite Service GMSK Gaussian MSK GOES Geostationary Operational Environmental Satellites GPM Gross Potential Market GPRS General Packet Radio Service GPS Global Positioning System GSM Global System for Mobile GTO Geostationary Transfer Orbit HDLC High-level Data Link Control HDTV High Definition TV HEMT High Electron Mobility Transistors HRST Highly Reusable Space Transportation Systems HTTP Hyper Text Transport Protocol IAT Inter Arrival Time IBO Input back-off IDCT Inverse DCT IEEE Institute of Electrical and Electronics Engineers IETF Internet Engineering Task Force IF Intermediate Frequency IM Inter Modulation IntServ Integrated Services IP Internet Protocol IPSec IP Security ISDB Integrated Services Digital Broadcasting ISDN Integrated Services Digital Network ISI Inter Symbol Interference ISL Inter Satellite Links ISO International Standards Organization ISS International Space Station ITR Institute for Telecommunications Research ITU International Telecommunications Union IWF Inter Working Function JPL Jet Propulsion Laboratory JTAG Join Test Action Group (the name for the IEEE 1149.1 standard)

LASER Light Amplification by Stimulated Emission of Radiation LDPC Low Density Parity Check Codes LEO Low Earth Orbit LNA Low Noise Amplifier LNB Low Noise Block MAC Medium Access Control MAP Maximum A Posteriori MBA Multi Beam Antenna Mbone Multicast Backbone MBTA Multiple Beam Torus Antenna MCPC Multi Channels Per Carrier MEO Medium Earth Orbit MF Multiple Frequency MIME Multipurpose Internet Mail Extensions MIT Massachusetts Institute of Technology MOS Modular On-orbit Servicing MPE Multi Protocol Encapsulation MPEG Motion Picture Expert Group MPLS Multi-Protocol Label Switching MSK Minimum Shift Keying MSL Maximum Segment Life MSS Mobile Satellite Systems; Maximum Segment Size MTTF Mean Time To Failure MTU Maximum Transmission Unit NASA National Aeronautics and Space Administration NESDIS National Environmental Satellite, Data, and Information Service NMS Network Management System NOAA National Oceanic and Atmospheric Administration NRZ Non Return to Zero NSDA National Space Development Agency NWS National Weather Service OBO Output back-off OBP On Board Processing ODU Outdoors Unit OLN Overlying Networks OOK On-Off Key OS Operating System OSI Open System Interconnections OSV Orbital Servicing Vehicle PAL Phase Alternating Lines PAM Payload Assist Module PCS Power Conditioning System PEP Performance Enhancing Proxies PER Packet Error Rate PES Packetised Elementary Streams

PGP Pretty Good Privacy PHB Per-Hop Behaviour PKM Perigee Kick Motor PM Phase Modulation POES Polar Orbiting Environmental Satellites POWS Protect Against Wrapped Sequence numbers ppm parts per million PRACH Physical Random Access Channel PRMA Packet Reservation Multiple Access PTD Packet Telecommand Decoder QID Queuing Identifier QoS Quality of Service QPSK Quadrature Phase Shift Keying QUT Queensland University of Technology RACH Random Access Channel RAIDRS Rapid Attack Identification Detection and Reporting System RBDC Rate Based Dynamic Capacity RF Radio Frequency RFC Request For Comment RTO Retransmission TimeOut RTT Round Trip Time RTTM Round Trip Time Measurement RVLC Reversible Variable Length Codes RX Receiver S/MIME Secure/Multipurpose Internet Mail Extensions SACK Selective Acknowledgement SAR Synthetic Aperture Radar SBSS Space-Based Surveillance System SCPC Single Channel Per Carrier SCPS Space Communications Protocol Specifications SDLC Synchronous Data Link Communication SDTV Standard Definition TV SERT Space Solar Power Exploratory Research and Technology SEE Single Event effect SEU Single Event Upset SIT Satellite Interactive Terminal SMATV Satellite Master Antenna TV SMTP Simple Mail Transfer Protocol SNACK Selective Negative Acknowledgments SNAP Satellite Network Access Point SnIP Satellite Network Interface Processor SNR Signal to Noise Ratio SOHO Solar and Heliospheric Observatory SPS Solar Power Satellites SRB Solid Rocket Booster

SREJ Selective Reject ALOHA SS Slow Start SSL Secure Sockets Layer SSPA Solid State Power Amplifier SSTDMA Satellite Switched TDMA STK Satellite Tool Kit STP State Transition Probabilities S-UMTS Satellite UMTS TC Turbo Codes TCO Total Cost of Ownership TCP Transmission Control Protocol TDM Time Division Multiplex TDMA Time Division Multiple Access TID Total Ionizing Dose TOS Type of Service TPC Turbo Product Code TPU Telemetry Processor Unit TS Transport Stream TT&C Telemetry Tracking and Command TTL Time-to-live field TWTA Traveling Wave Tube Amplifier TX Transmitter UAV Unmanned Aerial Vehicles UDP User Datagram Protocol UHF Ultra High Frequency UMTS Universal Mobile Telecommunications System UniSA University of South Australia UTS University of Technology Sydney URSI International Union of Radio Sciences – in French UW Unique Word VLC Variable Length Codes VN Virtual Nodes VoIP Voice over IP VPN Virtual Private Network VSAT Very Small Aperture Terminal WAN Wide Area Network WiFi Wireless Fidelity WINDS Wideband internetworking engineering test and demonstration WPT Wireless Power Transmission WTO World Trade Organization WWW World Wide Web xDSL X Digital Subscriber Line (of any type) XTP Xpress Transport Protocol

Satellite communications

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Transcript of Satellite communications