Wireless Communications I - Online-Offline Mobile and...

Compiled by OMAE OTERI ©2013 1

Wireless Communications I Purpose The aim of this course is to enable the student to;

1. understand the principles of satellite communications

2. understand the principles of Radar

3. understand how Wireless Local Area Networks (W-LAN) operate

Learning Outcomes At the end of this course, the student should be able to;

1. Describe how a satellite communication system works

2. Calculate satellite link budget

3. describe wireless communication channel access schemes

4. describe how W-LAN networks operate

Course Description Historical perspective; Satellite communication systems: orbits, station keeping, satellite altitude,

Satellite link design, the satellite system, saturation flux density, effective isotropic radiated power,

multiple access methods, INTELSAT, regional international Telecommunication satellites systems.

Terrestrial microwave communication systems. VSAT systems.

Multiple access schemes: FDMA, FDMA/FDD, TDMA, FAMA, DAMA, CDMA, Pure Aloha, Slotted

Aloha.

Radar communication systems: Principles of radar, pulsed and continuous wave radar, free space radar

range equation, radar transmitting systems and charging methods, rotary spark gap modulator, radar

receivers, automatic tracking radar, moving target indicator (MTI) and suppression of permanent

echoes, performance factors, the range pulse width, pulse reception frequency.

Short range wireless communication technologies: WIFI, Blue Tooth, Infra-red, WIMAX

Teaching Methodology 2 hour lectures and 1 hour tutorial per week and at least three 3- hour laboratory sessions per semester

organized on a rotational basis.

Mode of course assessment: Continuous assessment and written University examinations shall

contribute 30% and 70%, respectively of the total marks.

Instructional Materials/Equipment 1. Telecommunications laboratory

2. LCD projector

Course Textbooks 1. Roddy D. Coolen J, (2003), Electronic communications, Pearson Education, 4th Ed.

2. Gordon G. D. & Morgan W. L (1993), Principles of Communication Satellites, John Wiley &

Sons.

Course Journals

Reference Textbooks 1. Kennedy G & Davis B. (1999), Electronic Communication Systems, Tata McGraw Hill, 4th Ed.

2. Schiller J.H, (2007), Mobile Communications, Pearson Education

Reference Journals 1. IEEE Transactions on Wireless Communications

2. EURASIP Journal on Wireless Communications and Networking

3. Mobile Networks and Applications

http://journalseek.net/cgi-bin/journalseek/journalsearch.cgi?field=issn&query=1536-1276


http://journalseek.net/cgi-bin/journalseek/journalsearch.cgi?field=issn&query=1383-469X

WIRELESS COMMUNICATION 1

Compiled by OMAE M. OTERI ©2013 2

4. Communications Engineering and Design Magazine

5. IEEE Wireless Communications Magazine

WIRELESS COMMUNICATION I




COURSE BRIEF:

Introduction

History perspective

Satellite communication

Access methods

RADAR systems

WLANs: Bluetooth, Wi-Fi, WiMAX, ZigBee



INTRODUCTION

Communication- the process of transferring information from one location to another.

Telecommunication: tele- distance

Communicating over long distances.

In terms of media for transferring information there are 2 types: 1. Guided (wired)

2. Unguided (wireless)

Guided media

There is physical media applied in the transfer of information.

They include:

Unshielded twisted pair (UTP)

Shielded twisted pair (STP)

Coaxial cable

Fiber optic cable

Unguided media

It involves the use of unguided media to transfer information from one point to another

therefore leading to the concept of wireless communication. Different media signals include:

Light

Infrared

Microwaves

Radio waves

Sound waves

All the above signals use free space.

Applications:

1. Near field technology (NFC)- used in supermarkets and as a form of security

2. Wireless body networks

3. Phones- mobile phones using GSM and LTE

4. In hospitals- wireless body networks to give body parameters

5. Airports- to track airplanes

6. RADAR systems- used to detect cancer

7. Robots

8. SONAR systems

9. Remote communication

10. Bluetooth for data transmission

11. Monitoring systems/ surveillance

12. VSAT (very small aperture terminals) communication

13. Sensor (PIR)- emission of infrared triggers a signal

Fields

Communication and entertainment

Industrial

Medicine

Military

Astronomy

Biometric

Training



Advantages of wireless communication

Cable management is not required

Easy to maintain

Less susceptible to vandalism and destruction

Less expensive in the long run

Easy to control

Supports portable equipment

Occupies less space

Can be used in inaccessible locations

Has a higher capability to support more users

Disadvantages:

Security- can be tapped by any equipment at the same frequency

Easily affected by noise

High initial cost

High power is required

Health hazards

Some cannot be used over long distances e.g. Bluetooth

Electromagnetic spectrum

This gives the range of electromagnetic waves in existence.

It can start with the lowest wavelength/ highest frequency to the highest wavelength/ lowest

frequency.

The most common form of the spectrum:

Waves Frequency

Gamma rays 1019Hz

X-rays 1017Hz

Ultraviolet-40nm 1015Hz

Light(visible)-violet 450nm

-red 750nm

Infrared EHF

SHF

UHF

VHF

HF

MF

LF

VLF

ULF

SLF

ELF

Millimeter

Microwave

Radio wave

Radio waves

Have the longest λ and the lowest frequency.

Start from the low frequency up to ultrahigh frequency (UHF).

Commonly used in radio and TV communication with AM, SW and FM.



Microwaves

Follows the radio waves in terms of λ and frequency.

Commonly used in cellular communications and radar systems.

Usually divided into several bands Ku, K, Ka, X, C, S, L, and P.

Used in the 2nd world war.

They can penetrate some obstacles.

Affected by reflection, refraction, scattering and dispersion.

Free frequency ranges

These are frequency bands that do not require one to acquire a license to be able to use them.

They include the following bands:

902-928 MHz (cordless phones)

2.4-2.4835 GHz (Wi-Fi and Bluetooth)

5.725-5.850 GHz (Wi-Fi)

It came with the standard IEEE 802.11

These frequency bands are commonly used for research.

This helps with coming up with new technologies for instance the WLANs IEEE 802.11



HISTORICAL PERSPECTIVE

Before 1800s

The earliest forms of wireless communication included the use of smoke, fire, drums and horns.

There are several people who contributed to the current state of wireless communication more

so its electronic form. These people include:

Isaac Newton- existed in around 1600 and contributed so much to the laws of gravity being

used in satellite communication.

Ampere, Faraday and Henry- did the first experiment on electricity and magnetism.

Gauss was also there. They came up with Maxwell’s Equations

Volta- electricity generation

Ohm and Kirchhoff- electric circuit analysis.

1830s: Invention of the telegraph (tele- distance,graph- writing)

1867: Maxwell predicted the existence of electromagnetic waves. He combined the different

expressions being used today in electromagnetism which were earlier developed by people like

Ampere and Gauss.

1887:

Hertz confirmed the existence of electromagnetic waves.

Alexander Graham Bell invented the telephone.

Marconi developed a communication in the 1890s.

1901: 1st transoceanic communication as a result of Marconi’s system

In the 1st world war there were many developments in radio communication from a simple

radio system to a heterodyne radio system by 1920.

Mobile radios were developed and fitted in cars.

AM and SW were developed in this time.

1923-1935: development of TV systems

1935: FM systems developed

1937: PCM developed

2nd world war led to the development of microwave systems.

RADAR systems were developed

1st computer (ENIAC) was developed

1947: transistor developed

1946: mobile phone developed

1950: Shannon developed information theory

1950: AI was developed

1960s: development of ICs which made electronic systems smaller in size

1970s; microprocessors developed

1979: the 1st cellular system developed in Japan

1983: mobile telephony advanced with the development of AMPs (advanced mobile phone

system- 1st generation)

1989:Groupe System (Speciale) mobile (GSM) developed in Europe

1991: introduction of digital systems

1992: introduction of 1st GSM mobile phone SMS system introduced

1993: introduction of CDMA technology

1994: introduction of GSM in the US

Wireless LAN

Commonly using Wi-Fi (wireless fidelity).

Made possible by the standard introduced by IEEE in 1990. The standard was referred to as

IEEE 802.11.



In 1997 the 1st form of this wireless communication was introduced transmitting a few Mbps

(up to 2Mbps).

In 1999 two of the standards 802.11a and b were introduced,

802.11b came 1st with 1-11Mbps and using 2.4GHz frequency for transmission.

802.11a was also introduced this time with 1.54Mbps and operating at a frequency of 5GHz.

In 2003 802.11g was introduced operating at 2.4GHz.

In 2009 802.11n standard was introduced at a frequency of 2.4GHz and 5GHz.

Bluetooth

It was introduced in 1998 by Ericsson to be used for short range communication between

different mobile devices. Operating at a frequency of 2.4GHz.

WiMAX

Worldwide interoperability for microwave access.

Introduced in 2003 to be used in 4G networks.

Used as a licensed frequency.

Uses IEEE 802.16e standard.

Wireless Communication Standards

Standards- rules and procedures laid down by telecommunication bodies to be followed by

consumers and companies producing different communication products.

Importance:

1. They create interoperability for different equipment.

2. They protect local markets

3. They protect consumers

4. They ensure quality products are produced

5. To enable specialization therefore companies producing communication products are

able to improve on them and make them better.

Bodies enforcing standards

IEEE Institute of Electrical and Electronics Engineers

ITU International Telecommunication Union

FCC Federal Communication Commission

Intel Sat International Telecommunication Satellite

ISO International Organization of Standards

ANSI American National Standards Institute

TIA/EIA (for cabling standards)

TIA -Telecommunication Industry Association

EIA -Electronic Industry Association

CCK Communications Commission of Kenya

KEBS Kenya Bureau of Standards

EBK Engineering Board of Kenya

Mobile Phone Generations

There are 4 generations: 1st, 2nd, 3rd and 4th generation

1st generation

Dealing with voice in analogue form in the early 1990s.

Features:

1. Slow



2. Low bandwidth

3. High power consumption and dissipation

4. Very expensive

2nd generation

Using AMPs and GSM technology from the 1980s.

Dealing with voice and text (SMS). Data is also included.

Features:

1. Faster

2. Had more bandwidth than 1st generation

3. Less power consumption and dissipation

4. Uses TDMA and FDMA

3rd generation

Using GSM and HSPDA from the 1990s.

Features:

1. Higher bandwidth

2. Faster

3. Less power consumption per given section

4. Currently being used by most countries

5. Internet was enabled.

4G networks (2000s)

Used in most wireless technologies e.g. WiMAX and IP.

More advanced.

High bandwidth

Faster

Less power consumption and dissipation

Voice data and video

Uses LTE (Long Term Evolution) technology



SATELLITE COMMUNICATION

Satellite- a body revolving around another body.

Types: 1. Natural

2. Artificial

Natural satellites

They are smaller natural bodies orbiting/ revolving around larger natural bodies.

E.g. moon is a satellite of the earth

Earth is a satellite of the sun

Sun is a satellite of galactic center.

Galactic center is a satellite of the black hole

The 1st satellite communication was done using the moon.

The US and UK were communicating using the same.

This inspired the intervention of artificial satellites being used to date.

Artificial satellites

This is a manmade object in space revolving/ orbiting round the earth.

The 1st artificial satellite was sent to space by Russia (USSR in 1957) called sputnik.

Followed by USA in 1958.

In Africa, Egypt was the 1st country followed by South Africa, Nigeria, Algeria, Mauritius

and Morocco.

Countries with the capability to send satellites to space

There were around 10 countries with the capability of sending satellites to space as of 2011.

They include:

Soviet Union (Russia and Ukraine)

USA

France

UK

Japan

China

India

North Korea

South Korea

Iran

Israel

These countries use equipment like rockets to send satellites to space.

Types of satellites

These types depend on their applications. They include:

Military

Weather

Earth observation

Astronomy

Research

Communications

Bio satellites

Space ships

Space stations



Satellite orbits

Orbit- this is a path followed by objects revolving around other bigger bodies.

Satellite orbit- path followed by a satellite in space.

There are several classifications:

Centric

Altitude

Inclination

Eccentric

Synchronous

Semi- synchronous

Geo- synchronous

Areo- synchronous

Helio- synchronous

Special classifications

1. Centric

There are 3 types: Geocentric

Heliocentric

Areocentric

These classifications are given in terms of the body being orbited.

Geocentric-they orbit the earth and in total are approximately over 2000 satellites.

Heliocentric-satellites that go round the sun. Are very few in number.

Areocentric-they orbit planet mars

2. Altitude

They are stationed according to the distance from the earth.

There are 3main categories: low earth orbiting (LEO)

Medium earth orbiting (MEO)

High earth orbiting (HEO)

Low earth orbiting- these orbit at a distance of less than 2000km.

Medium earth orbiting- they orbit at a distance between 2000km and slightly less than

35000km.

High earth orbiting- orbit at a distance above 35000km.

3. Inclination

Satellites orbiting an object at an angle of more than 0 degrees.

Classified according to the angle of inclination.

The main one being at an angle of 90 degrees which pass over the poles-polar satellites.

4. Eccentricity

This is in terms of the shape of the orbit (orbit trace). There are two main categories:

Circular

Elliptic

Circular-they make a circular trace as they orbit the object



satellite

h

earth

R

R=earth’s radius

h=satellite distance

Elliptic- they make an elliptic trace.

earth

Major axisMinor

axis

5. Synchronous

These are satellites that orbit at the same speed as that of the body they are orbiting.

They take the same time to cover a circular distance e.g. for the earth they take 24hours.

6. Semi- synchronous

They take half the total time taken by the body they are orbiting. For the earth they take 12

hours. They move at a higher speed.

7. Geo-synchronous

They orbit around the earth which means they take 24 hours just like the earth.

There are several which include:

a) Geostationary-to the earth observer they appear to be at the same point. The earth

stations have their antennae facing the same direction.

b) Super synchronous- they are slightly above the geo stationery distance.

c) Sub synchronous- slightly below the geo stationery distance.



d) Graveyard- this is an orbit where are satellites are supposed to be sent to after they fail/

after being through with their missions.

Also slightly above the geo stationery distance by a few 100kilometres.

Recommendations have been made by the bodies governing satellites to send the failed

satellites to the graveyard orbit.

8. Areo synchronous

Synchronous satellites orbiting mars thus take slightly more than 24 hours.

9. Helio synchronous

They take the same time as the sun.

10. Special classifications

They include:

a) Sun synchronous-they move as the sun moves which means they pass through a given

location at the same time. Commonly used to take images of the earth.

b) Moon orbit- they are at the same height as that of the moon.

c) Pro grade- moves in the direction of the bodies they are orbiting.

d) Retrograde- moves in the opposite direction of the bodies they are orbiting.

Geostationary satellite orbital time and distance

This is calculated based on some assumptions and some laws of mechanics. The laws include

those of Newton and Kepler.

The circular distance:

satellite

h

earth

R

The satellite requires two forces for it to stay in orbit: centripetal and centrifugal forces.



Gravitational pull

If the 2 forces are balanced then the satellites will keep the same distance from the earth i.e the

force pulling the earth and the force applied to it such that it can fly in space.

The gravitational force is given by:

𝐹𝑔 = 𝑚𝑔′

m= mass

g’= gravitational pull

𝑔′ = 𝑔 (𝑅

𝑅 + ℎ)

2

The force applied on the satellite:

𝐹𝑐 =𝑚𝑣2

𝑅 + ℎ

v= velocity

The two forces should balance and therefore be equal for the satellite

𝐹𝑔 = 𝐹𝑐

𝑚𝑣2

𝑅 + ℎ= 𝑚𝑔 (

𝑅

𝑅 + ℎ)

2

𝑣2 = 𝑔 (𝑅

𝑅 + ℎ)

2

⋅ 𝑅 + ℎ

𝑣2 = 𝑔𝑅2

𝑅 + ℎ

𝑣 = 𝑅√𝑔

𝑅 + ℎ

Orbital time taken is given by;

𝑇 =𝐷

𝑣

𝑇 = 2𝜋(𝑅 + ℎ)

𝑣

Substituting v in the above equation

𝑇 =2𝜋 (𝑅 + ℎ)

𝑅 √𝑔

𝑅+ℎ

Squaring both sides:

𝑇2 =(2𝜋)2 (𝑅 + ℎ)3

𝑅2𝑔

To obtain the distance we make h the subject of the equation. Therefore

ℎ =(𝑇𝑅)

2

3 𝑔1

3

(2𝜋)2

3

− 𝑅

𝑔 = 9.81𝑚/𝑠2



𝑇 = 24 ℎ𝑜𝑢𝑟𝑠

𝑅 = 6371𝑘𝑚

ℎ =(24 × 6371)

2

3 (9.81 × 10−3 × 604)1

3

(2𝜋)2

3

− 6371

= 35855𝑘𝑚

Satellite sub systems

These are subsections of a satellite that facilitate the operation of a satellite.

They are divided into two: Service sub systems

Communication sub systems

1. Service sub systems

These sections support the satellite in space as it performs its functions. They include:

i. Structural sub systems

ii. Power sub systems

iii. Thermal sub systems

iv. Telemetry sub systems

v. Inclination sub systems

a) Structural

These are the sections that support the satellite equipment.

They protect the satellite against small meteor attacks.

They provide physical strength to the satellite.

They are constructed from small material but which are light.

b) Power

Provides power to the different sections of the satellite.

The commonly used source is solar energy.

The solar panels are placed on wings which are folded until the satellite is in orbit when they

open. The power provided by solar is around 1400Watts per square meter. The efficiency is

from 10% to 14%. Research is done to increase the same.

The wings/ panels are usually rotated to make sure that they face the sun continually.

The source of energy when the earth’s shadow is present is batteries. Other sources could be

radioactive sources of energy.

The power requirements should be minimal since the sources in space are quite expensive.

Most communication equipment will require voltage of up to 12volts. But other devices like

motors will require more e.g. apogee motors used to change the orbit from elliptic to circular.

c) Thermal

These systems protect the satellite from extreme temperatures in space. These can be in terms

of very high or very low temperatures.

Cooling systems will be used for high temperatures, also the design should incorporate sections

that can control the temperature variations.

d) Telemetry

Used to monitor the operation of the satellite equipment. If there is a problem, it is

communicated to an earth station used to control the satellite operation. The operators can be

able to rectify the situation.



There will be regular communication between these sections and the earth station. The section

is also designed together with the satellite equipment.

e) Inclination and orbit

Used to control the satellite height and hence its orbit. The commonly used devices are motors-

apogee motors. In case of any changes they are communicated and acted on.

2. Communication sub systems

These are sections which together are used to transmit and receive signals. It has the transmitter

and receiver.

antennaChannel filter

High

frequency

amp

High

frequency

amp

Output

filter multiplexerantenna

Oscillator/frequency

convertor

Fig: Communication equipment



The antenna receives the transmitted signal from an earth station.

This signal is then filtered to remove unwanted frequency signals e.g. noise.

The filtered signal is then amplified by the high frequency amplifier.

NOTE: The uplink frequency is usually higher than the downlink frequency. This is because

it is possible to transmit at high frequency from the ground. Since it is possible to provide high

power as opposed to space where power sources are limited.

The lower frequency for downlink has lower power requirements.

After frequency conversion the signal passes through another high frequency amplifier for

amplification. This one has a lower frequency than the first amplifier.

The output filter will remove any noise and separate the signal required from the others ready

for downlink transmission.

The multiplexer will select the required signal for downlink transmission which will pass

through the antenna.

All these processes can result to the introduction of noise to the signal which needs to be

removed by the filters.

Examples of noise include:

Electromagnetic interference

Thermal noise

Shot noise

Gaussian noise

Flicker noise

Partition noise

The commonly used antenna are parabolic dishes because of their high directivity. Their

performance is in terms of gain and the solid angle. θ

Main lobe

Radiation pattern

θ

Satellite link equation

This is the equation that describes the signal transmitted and received by the satellite and the

earth stations.



𝑃𝑇 − 𝑝𝑜𝑤𝑒𝑟 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑

𝑃𝑅 − 𝑝𝑜𝑤𝑒𝑟 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑑 𝑅𝑋 − 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑟

𝑇𝑋 − 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑟 𝐺𝑇 − 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑟 𝑔𝑎𝑖𝑛

𝐺𝑅 − 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑔𝑎𝑖𝑛 The power density is given by:

𝑃𝐷𝑖 =𝑃𝑇

4𝜋𝑑2

This is affected by the gain as follows:

𝑃𝐷𝑖 𝐺 =𝑃𝑇𝐺𝑇

4𝜋𝑑2

The received power is given by:

𝑃𝑅 = 𝑃𝐷𝑖𝐺 . 𝐴𝑒𝑓𝑓

𝐴𝑒𝑓𝑓 =𝐺𝑅𝜆2

4𝜋

𝑃𝑅 = 𝑃𝑇𝐺𝑇𝐺𝑅 . ( 𝜆

4𝜋𝑑)2

𝑃𝑅 =𝑃𝑇𝐺𝑇𝐺𝑅

(4𝜋𝑑

𝜆)2

𝑙𝑜𝑠𝑠𝑒𝑠 = (4𝜋𝑓𝑑

𝑐)2

In terms of dB:

𝐹𝑆𝐿 = 20 log(4𝜋𝑓𝑑

𝑐)

Where f is in terms of megahertz (MHz) and d in terms of kilometers (km).

= 20 log(4𝜋𝑓𝑑 × 103 × 106

3 × 108)

= 32.44 + 20 log 𝑓 + 20 log 𝑑

𝑃𝑅𝑑𝐵 = 𝑃𝑇𝑑𝐵 + 𝐺𝑇𝑑𝐵 + 𝐺𝑅𝑑𝐵 − 𝐹𝑆𝐿𝑑𝐵 The above is known as the link equation.



Additional losses

Apart from the free space losses there are additional losses which result from the following:

Atmospheric losses.

Antenna misalignment

Polarization mismatch

The sum of all the above losses is assumed to be 5dB.

Example:

i. Determine the free space losses given the satellite distance to be 42,000km for a signal

of 6 GHz.

𝐹𝑆𝐿 = 32.44 + 20 log 𝑑 + 20 log 𝑓

= 32.44 + 20 log 6000 + 20 log 42000

= 200.46𝑑𝐵

ii. Determine the received signal power if the transmitted signal power is 200W. The

antenna gain GT=40dB and GR=20dB

𝑃𝑅𝑑𝐵 = 𝑃𝑇𝑑𝐵 + 𝐺𝑇𝑑𝐵 + 𝐺𝑅𝑑𝐵 − 𝐹𝑆𝐿𝑑𝐵

23.01 + 40 + 20 − 200.46

−117.45𝑑𝐵

𝑃𝑅 = 1.79𝑝𝑊

Effective isotropic radiated power (EIRP)

This is the product of the power transmitted and the gain of the transmitter antenna.

𝐸𝐼𝑅𝑃 = 𝑃𝑇𝐺𝑇

𝐸𝐼𝑅𝑃𝑑𝐵 = 𝑃𝑇𝑑𝐵 + 𝐺𝑇𝑑𝐵 In terms of the link equation

𝑃𝑅𝑑𝐵 = 𝐸𝐼𝑅𝑃𝑑𝐵 + 𝐺𝑅𝑑𝐵 − 𝐹𝑆𝐿𝑑𝐵 It is the radiated power in all directions just like the case of an omnidirectional antenna.

The above equation can be given in terms of uplink and downlink form.

Uplink

This is the equation that is represented in uplink parameters.

Uplink from the earth’s station to the satellite.

The equation is given by:

𝑃𝑅𝑑𝐵 = 𝑃𝑇𝑑𝐵𝑈 + 𝐺𝑇𝑑𝐵𝑈 + 𝐺𝑅𝑑𝐵𝑈 − 𝐹𝑆𝐿𝑑𝐵

Sometimes it is given in terms of power density:

∅ = 𝑃𝐷 =𝑃𝑇

4𝜋𝑑2

With gain:

=𝑃𝑇𝐺𝑇

4𝜋𝑑2=

𝐸𝐼𝑅𝑃

4𝜋𝑑2

Exercise:

Obtain the uplink equation in terms of Φ.

It can also be given in terms of carrier to noise ratio. 𝐶

𝑁𝑑𝐵= 𝑃𝑇𝑑𝐵 + 𝐺𝑇𝑑𝐵 + 𝐺𝑅𝑑𝐵 − 𝐹𝑆𝐿𝑑𝐵 − 𝑁𝑑𝐵



𝑁 = 𝑘𝑇

𝑘 − 𝐵𝑜𝑙𝑡𝑧𝑚𝑎𝑛𝑛 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 = 1.38 × 10−23 𝐽/𝐾

𝑇 − 𝐴𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 (300𝑜𝐾 𝑟𝑜𝑜𝑚 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒)

𝐶

𝑁𝑑𝐵= 𝑃𝑇𝑑𝐵 + 𝐺𝑇𝑑𝐵 + (

𝐺𝑅

𝑇)𝑑𝐵 − 𝐿𝑑𝐵 − 𝐾𝑑𝐵

(𝐺𝑅

𝑇)𝑑𝐵 − 𝑓𝑖𝑔𝑢𝑟𝑒 𝑜𝑓 𝑚𝑒𝑟𝑖𝑡

Downlink equation

This is represented in terms of the downlink parameters. It is used from the satellite to the earth

stations. Similar to the uplink equation only that U is replaced by D. in some cases the

bandwidth is also considered since noise is a function of bandwidth. When it is applied then it

is subtracted from the above equation since 𝑁 = 𝑘𝑇𝐵

VSATs

Very small aperture terminals

They are systems used to communicate two way. They are used together with satellites to

receive and transmit data. Characterized by small dishes up to 3m in diameter but most

commonly from 75cm to 2m.

They are networked to share resources. They use the star and mesh topologies and can also use

a combination of the two.

They are applied in: a) communication-telephony

-internet

b) Industrial-SCADA (support control and data acquisition)



MULTIPLE ACCESS METHODS

These are techniques used in accessing communication systems or media.it is necessary since

several systems would require to access a medium or a communication system.

They use communication protocols for media access control (MAC) in layer 2 of the OSI and

layer 4 of the TCP/IP models.

These models can be applied in satellite communication systems. These techniques include:

Frequency division multiple access (FDMA)

Time division multiple access (TDMA)

Code division multiple access (CDMA)

Demand assigned multiple access (DAMA)

Fixed/permanent assigned multiple access (FAMA)

ALOHA



1. FDMA

The whole frequency spectrum is divided into several bands which are then assigned to the

several communicating devices.

Commonly used in satellite and most wireless technologies.

The whole time range can be used in fiber optic communication but in terms of Wave Division

Multiple Access (WDMA).

2. TDMA

This is where time is divided into small slots which can then be used by communicating

devices. The whole frequency spectrum is used by each device. The whole bandwidth is

available for use by any communicating device.

The time slots can be of the same or different sizes depending on the communicating device. It

can be fixed or dynamic.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

frequ

en

cy

FDMA

time

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

time

TDMA



3. CDMA

This is characterized by communicating devices being given a unique code to communicate.

The whole frequency and time spectrum are available for communication. It is also known as

the spread spectrum.

The advantage is that according to Shannon’s channel capacity principle the whole bandwidth

is available and more bits can be sent without being affected by noise.

𝐶 = 𝐵 log2(1 +𝑆

𝑁)

𝐶 − 𝐶ℎ𝑎𝑛𝑛𝑒𝑙 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝐵 − 𝑏𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ

𝑆

𝑁− 𝑆𝑖𝑔𝑛𝑎𝑙 𝑡𝑜 𝑛𝑜𝑖𝑠𝑒 𝑟𝑎𝑡𝑖𝑜

The higher the bandwidth the higher the channel capacity. It is most commonly used in the 3G

mobile communication networks.

4. DAMA

A communicating device is given a slot according to its requirements.

It is assigned a time or frequency slot which is available and when it is through it releases it for

use by any other device.

It is more efficient since there is no idle time. Several devices can use a limited number of

channels e.g. 10 devices can use 5 channels at different times.

5. FAMA

Communicating devices are assigned slots permanently even if they are not using the slots.

This is less efficient since the slots are idle when the devices are not using them e.g. only 5

devices can use 5 channels.

6. ALOHA

It was developed for computers to communicate using wireless technology. It was first used in

the Hawaiian Islands. It used the UHF range to communicate.

There are two types: -pure ALOHA

-Slotted ALOHA

It used probability to determine how possibly the devices would be able to communicate.

Specifically the Poisson distribution.

Poisson distribution:

𝑃(𝑥) =𝑒−𝜇𝜇𝑥

𝑥!

𝜇 − 𝑚𝑒𝑎𝑛

𝑥 − 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑢𝑐𝑐𝑒𝑠𝑠𝑒𝑠 𝑖𝑛 𝑎𝑛 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 Pure ALOHA

It is such that when a communicating device needs to send information it will end it. If there is

a collision it will retransmit the information.

I uses the acknowledgement and retransmit principle. If the sending node does not receive an

acknowledgement then it retransmits the information. The probability and throughput are given

in terms of Poisson distribution.

𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦𝑝𝑢𝑟𝑒 = 𝜇𝑒−2𝜇

𝑡ℎ𝑟𝑜𝑢𝑔ℎ𝑝𝑢𝑡 = 𝑒−2𝜇



Slotted ALOHA

This is an improved form of the pure ALOHA where the probability and throughput are given

as:

𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦𝑠𝑙𝑜𝑡𝑡𝑒𝑑 = 𝜇𝑒−𝜇

𝑡ℎ𝑟𝑜𝑢𝑔ℎ𝑝𝑢𝑡 = 𝑒−𝜇 Example:

Given the number of successes = 4 μ = 2 determine the probability using Poisson.

𝑥 = 4

𝜇 = 2

= Probability =𝑒−224

4!

P(4) = 0.09



RADAR

Radio detection and ranging.

This is a device that uses radio waves to detect objects at a distance.

transmitter

receiver

diplexer object

antenna

Consists of a transmitter, receiver, diplexer and antenna.

The pulsed radar uses a single antenna since it uses different times to transmit and receive.

Operation

The radar system is activated by a moving target. It ends a high power signal from its

transmitter through the diplexer and the antenna to the target.

The antenna in this case is connected to the transmitter.

After the signal strike the target it is reflected back to the radar where it is received through the

antenna to the receiver.

The antenna in this case is connected to the receiver. The receiver can amplify it so that it can

be usable. The diplexer coordinates the transmitter and receiver as they use the antenna.

The antenna is parabolic because of its properties e.g. directive gain.

Radar performance indicators/parameters

These are parameters determine the performance of a radar. They are obtained using the radar

range equation.

target

PT GT

antenna

AoS

𝑃𝑇 − 𝑝𝑜𝑤𝑒𝑟 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑

𝑃𝑅 − 𝑝𝑜𝑤𝑒𝑟 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑑

𝐴𝑜 − 𝑐𝑎𝑝𝑡𝑢𝑟𝑒 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑛𝑡𝑒𝑛𝑛𝑎

𝑠 − 𝑡𝑎𝑟𝑔𝑒𝑡 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎 Power density



𝑃𝐷𝑖 =𝑃𝑇

4𝜋𝑟2

Introducing the gain:

𝑃𝐷𝑖 𝐺 =𝑃𝑇𝐺𝑇

4𝜋𝑟2

When this power strikes the target the resulting power density will be multiplied by the surface

area.

𝑃𝐷𝑖 𝑇 =𝑃𝑇𝐺𝑇𝑆

4𝜋𝑟2

After reflection the power received by the antenna is given by:

𝑃𝑅 =𝑃𝑇𝐺𝑇𝐴𝑜 𝑆

(4𝜋𝑟2)2

𝑟 − 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑓𝑟𝑜𝑚 𝑟𝑎𝑑𝑎𝑟 𝑡𝑜 𝑡𝑎𝑟𝑔𝑒𝑡

𝐺𝑇 =4𝜋 𝐴𝑜

𝜆2

𝜆 − 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ

𝑃𝑅 =𝑃𝑇 𝑆 𝐴𝑜2

4𝜋𝑟4𝜆2

Distance is obtained as:

𝑟𝑚𝑎𝑥 = {𝑃𝑇𝐴𝑜2 𝑆

4𝜋𝑃𝑅𝜆2}0.25

This is the radar range equation.

Factors affecting received power

An increase in the power transmitted (PT) results in an increase in the power received.

An increase in the capture area (Ao) results in an increase in the power received.

An increase in the target area (S) results in an increase in the power received.

An increase in the distance (r) results in a decrease in the power received.

An increase in the wavelength (λ) results in a decrease in the power received.

Effects of noise

Noise also affects the received power. The more the noise the less the received power. This

affects the efficiency of the radar system. The received power is usually taken to be:

𝑃𝑅 = 𝑁𝑅 = 𝑘𝑇𝑆𝐵𝑆

𝑁

𝑘 − 𝑏𝑜𝑙𝑡𝑧𝑚𝑎𝑛 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑇𝑆 − 𝑛𝑜𝑖𝑠𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒

𝐵 − 𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ 𝑆

𝑁− 𝑠𝑖𝑔𝑛𝑎𝑙 𝑡𝑜 𝑛𝑜𝑖𝑠𝑒 𝑟𝑎𝑡𝑖𝑜

If 𝑆

𝑁= 1

Then 𝑃𝑅 = 𝑁𝑅 = 𝑘𝑇𝑆𝐵

Substituting in the radar range equation:


4𝜋 𝑘𝑇𝐵 𝜆2}0.25



Additional parameters affecting the range equation

1. Temperature

2. Bandwidth

Example:

Given a radar transmitting power of 200W to detect a target of 1m2. Determine the maximum

distance if the minimum power received is2 × 10−10. Take GT = 20dB Ao = 0.5m2 f = 6GHz.


4𝜋𝑃𝑅𝜆2}0.25

= {200 × 0.52 × 1

4𝜋 × (2 × 10−10) × 0.052}0.25

= 1.679𝑘𝑚

Radar Bands

These are different ranges of frequencies hat a radar operates in. They were developed

during/before the Second World War. They include UHF, L, S, C, X, Ku, K, and Ka.

Types of radar systems.

They include:

Pulse

Continuous wave/Doppler

Frequency modulated continuous wave.

1. Pulse

It is the one discussed earlier which send signals in terms of pulses.

2. Continuous Wave/Doppler

Uses a non-pulsed signal in its operation. It also uses the Doppler Effect where targets moving

closer will have a frequency of 𝑓𝑜 + 𝑓𝐷 and those moving away have 𝑓𝑜 − 𝑓𝐷

𝑓𝑜 − 𝑑𝑜𝑝𝑝𝑙𝑒𝑟 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦

Moving Target Indicator

It facilitates the process of detecting moving targets where noise from stationary targets is

filtered out leaving only the signal from the moving target therefore identifying it.

3. Frequency modulated continuous wave

This I used to detect objects that are used to detect objects that are very close to the radar

system. It uses frequency modulation which operates over small distances.

Other radar systems:

Tracking and surveillance

Remote sensing

Medical- cancer detection

Astronomy



WIRELESS COMUNICATION TECHNOLOGIES- WLAN These are short distance low bandwidth communication networks.

They include:

1. Bluetooth

2. ZigBee

3. Wi-Fi

4. WiMAX

They are classified according to the following characteristics:

Frequency of operation

Power consumption

Distance covered

Power dissipation

Bandwidth

modulation technology

protocols

architecture

licensed or not

General description of electrical and electronic stuff

definition

logo

construction

features

operation

application

security

1. Bluetooth 802.15.1

This is a low power, low distance technology developed in 1994 by Ericsson.

Currently being managed by the special interest group.

Features:

Operates at a frequency of 2.4-2.4835GHz

Distance 1-100m

Low power consumption

Low power dissipation up to 100mW

Bandwidth up to 54Mbps

Modulation – FHSS (frequency hop spread spectrum)

Unlicensed frequency

Construction

It has 4layers i.e. application, middleware, link layer and physical layer.

Developed to replace the short distance wired networks (R 232)

Implemented in embedded form and USB dongle.

It has two man architecture forms i.e. Picconet and scatter net

Picconet- a master and slave implementation i.e. 1 master 7 slaves



master

slave slave

Scatter net- more than one master i.e. more than one Picconet

master

slave slave

master

slaveslave

Protocols

This includes:

Link management protocol

Logical link control

Adaptation protocol

Radio frequency communication

Operation

Uses FHSS where each device can hop up to 1600 times a second. There are several bands

within the frequency range of 2.4-2.4835GHz.

These bands are in 2MHz range starting from 2.402-2.48GHz.

Applications

Data transfer

Small networks

Mobile phones

Laptops

Printers



Security

Advantages

No cables required over short distances

Low power consumption

Portable

Low power dissipation

Disadvantages

Interference

Security level not that high

Distance is limited/ range of communication is low.

2. ZigBee 802.15.4

It is equivalent to Bluetooth but with lower power applications.

Features:

Frequency of operation 2.4GHz, 915MHz, 858MHz

Distance up to 100m

Power consumption and dissipation very low

Bandwidth up to 250Kbps

Modulation technique – DSSS (direct sequence spread spectrum)

Construction

Based on media access control and physical layer.

Can be implemented in embedded form.

Applications

Monitoring systems

Wireless sensor networks

MEMS and NEMS

3. Wi-Fi 802.11

Wireless fidelity

A higher power bandwidth communication technique used to develop wireless LANs.

Developed and managed under the IEEE 802.11 standard.

The generations for Wi-Fi include 802.11, 802.11a, 802.11b up to 802.11g except L, M and Z.

They were developed into 4generations:

802.11

802.11a/b

802.11g

802.11n

Features

Frequency of operation 2.4GHz to 5GHz unlicensed.

Distance up to 100m but can be extended to 100km

Power dissipation and consumption is higher

Bandwidth up to 600Mbps

Modulation techniques-DSSS



Construction

Embedded commonly with mobile devices.

Implemented in the MAC and physical layer

The network implementation is -ad-hoc

- Mesh

- Infrastructure

Security

Done using WEP- wired equivalent privacy

WAP- Wi-Fi protected access

CSMA/CA and CD (carrier sense multiple access/ collision avoidance and detection)

Applications

Wireless LANs

WAN

PAN

Last mile

Limitations

Man in the middle

4. WiMAX 802.16

Worldwide interoperability for microwave access

High power long distance technology to implement last mile networks.

Features

Frequency 2-11GHZ, 3.5GHZ, 5.85GHz

Some are licensed

Distance up to 10km

Power high

Bandwidth 50Mbps

MAN

Applications

Mobile phones 4G networks

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