TLMN645 CLASS 11FALL 2002

Low Earth (LEO)

Medium Earth (OEO)

Satellite Systems

FedEx Data Network

• Created its own Digital Data Network in the 1980’s using a private land mobile wide area system called Digital Assisted Dispatch System (DADS)

• System is based on an 802.11 messaging standard on a 800 MHz network providing digital messaging to trucks 40,000 mobile voice units and 2,500 hand-held. 760 base stations

FedEx FUTURE WIRELESS NETWORK

• Fedex’s intention is to move to the public network. “We're going to move to a public network structure because the coverage has gotten very robust, the cost has come down and the speed has gone up. We've hit a crossover point where going to the public network just makes a whole lot of sense. We will be looking at 2.5G and 3G networks as they get

• deployed.

FedEx Use of ATT Wireless Data

• Ken Pasley, FedEx's director of wireless systems development, said the AT&T Wireless General Packet Radio Service (GPRS) network "gives us significantly more bandwidth" than the company's private network and will allow FedEx to expand the types of applications used on tracking devices. The throughput of the GPRS network is approximately 20K to 40K bit/sec., compared with the 19.2K bit/sec. FedEx gets on its private nationwide network. This will allow couriers to send "fat" files such as digital signatures and could also support voice recognition technology,

Satellite-Related Terms

• Earth Stations – antenna systems on or near earth• Uplink – transmission from an earth station to a

satellite• Downlink – transmission from a satellite to an

earth station• Transponder – electronics in the satellite that

convert uplink signals to downlink signals

Ways to CategorizeCommunications Satellites

• Coverage area– Global, regional, national

• Service type– Fixed service satellite (FSS)– Broadcast service satellite (BSS)– Mobile service satellite (MSS)

• General usage– Commercial, military, amateur, experimental

Classification of Satellite Orbits

• Circular or elliptical orbit– Circular with center at earth’s center – Elliptical with one foci at earth’s center

• Orbit around earth in different planes– Equatorial orbit above earth’s equator– Polar orbit passes over both poles– Other orbits referred to as inclined orbits

• Altitude of satellites– Geostationary orbit (GEO)– Medium earth orbit (MEO)– Low earth orbit (LEO)

Satellite Orbits

Geometry Terms

• Elevation angle - the angle from the horizontal to the point on the center of the main beam of the antenna when the antenna is pointed directly at the satellite

• Minimum elevation angle

• Coverage angle - the measure of the portion of the earth's surface visible to the satellite

Minimum Elevation Angle

• Reasons affecting minimum elevation angle of earth station’s antenna (>0o)– Buildings, trees, and other terrestrial objects

block the line of sight– Atmospheric attenuation is greater at low

elevation angles– Electrical noise generated by the earth's heat

near its surface adversely affects reception

Overview:GEO Orbit

• Advantages of the the GEO orbit – No problem with frequency changes– Tracking of the satellite is simplified– High coverage area

• Disadvantages of the GEO orbit– Weak signal after traveling over 35,000 km– Polar regions are poorly served– Signal sending delay is substantial

Satellite GEO vs LEO

LEO

GEO

Overview:LEO Satellite Characteristics

• Circular/slightly elliptical orbit under 2000 km• Orbit period ranges from 1.5 to 2 hours• Diameter of coverage is about 8000 km• Round-trip signal propagation delay less than 20

ms• Maximum satellite visible time up to 20 min• System must cope with large Doppler shifts• Atmospheric drag results in orbital deterioration

LEO SATELLITES

Source: Globalstar?

Overview: MEO Satellite Characteristics

• Circular orbit at an altitude in the range of 5000 to 12,000 km

• Orbit period of 6 hours• Diameter of coverage is 10,000 to 15,000 km• Round trip signal propagation delay less than 50

ms• Maximum satellite visible time is a few hours

Satellite MEOMedium Earth Orbit (10,000

Km)

LEO

GEO

MEO

GPS System

Orbit (Delay)Geostationary22,000 miles36,000 Km

Low Earth (LEO)400 miles800 Km

Roundtrip delayGEO 1/4 sec.Or 250 ms

LEOdelay 10 to 50 ms .

MEOdelay> 66 ms

MEOOrbit 10,000 Km Acceptable delay

for voice- 100 to 200 ms.

Required Power

• GEO (INMARSAT-A)-40 watt transmitter into 1.2 m dish

• MEO (ICO) 5000 watts satellite power

• LEO (Sat. GS 1000 w. IR 1400 w.)– Iridium .57 watts average– Globalstar 400 mw. (to gateway)

Technology:LEO-UPSIDE DOWN CELLULAR SYSTEM

Iridium System

• 48 satellites in 8 planes

• TDMA (slots), voice 2.4/4.8 kb/s, data 2.4 kb/s

• Operates around 1610 MHz, Inter-sat 22-23 GHz .Users can go direct to satellite, return through gateways

• end to end delay 100-210 ms. Below the 400 ms required for voice.

Iridium Handsets (when first available)

Iridium Gateways

Why Iridium Failed?

• 1,

• 2.

• 3.

• 4.

Iridium Status• The Department of Defense, through its Defense

Information Systems Agency (2000), awarded• Iridium Satellite LLC $72 million contract for 24

months of satellite communications services. This contract would provide unlimited airtime for 20,000 government users over the Iridium satellite network.

• The contract includes options which, if exercised, would bring the cumulative value of this contract to $252 million and extend the period of performance to December 2007.

Globalstar

• 48 satellites with CDMA access

• voice up to 9 kb/s in 1.25 MHz channels

• No intersatellite links, “bent pipe”

• Access by gateways-would take 200 to cover whole earth- deployment will be less than that. Service within 1000 miles of a gateway. Service area size of Alaska

Globalstar Orbits 48 satellites

Globalstar

Phone Gateway

Globalstar Satellite

Globalstar Telephones

PREVIOUS 2002

Globalstar Status

Teledesic - Broadband Internet in the sky

• 24 active SATs.s in 12 planes. 1350 km alt.

• Broadband fixed and mobile Ka operation (18-31 GHz)

• low bit error rates 10-10

• Latency 20-75 ms. Roundtrip < than 100 ms

• Packet mode(512 bits), TDMA access

• Operates from gateways( e.g.ISPs) with bit rates155 Mb/s to 1.244 Gb/s

Teledesic Orbits

Multimedia-TeledesicOn 1 October 2002, it was reported that Teledesic was

officially suspending its satellite construction work.

MEO

Orbit (Delay)Geostationary22,000 miles36,000 Km

Low Earth (LEO)400 miles800 Km

Roundtrip delayGEO 1/4 sec.Or 250 ms

LEOdelay 10 to 50 ms .

MEOdelay> 66 ms

MEOOrbit 10,000 Km Acceptable delay

for voice- 100 to 200 ms.

ICO

• 10 satellites at 10,000 Km.• First Satellite Launched June 2001• two and sometimes three in view• each satellite covers 30% earth’s surface• Two communication systems

– S band spot beams (163 users) direct to mobiles– C band to Satellite Access Notes (SANs)– The air interface is expected to operate through ICO

satellites at data rates of up to 144 kbps.

ICO Architecture

• ICO's satellites use a bent-pipe architecture, In a bent-pipe system the satellite is used to relay communication between the end-user equipment and a ground station that is part of the terrestrial infrastructure. The terrestrial infrastructure, provides the connection to the destination network or end-user.

ICO Satellites

ICO Ground SegmentC band

ICO Orbits

ICO Projected Markets

• Maritime

• Transportation

• Government

• Oil, Gas, Construction

• Individuals and small businesses

• Rural and underserved in US and around the world

ICO Status

• 2001 First satellite successfully launched.

• 2002 Company signs an agreement to acquire Constellation Communications Holdings, Inc. and is awaiting FCC approval and the satisfaction of certain other closing conditions to close these transactions

Example:LEO Status: SkybridgePlanned: 80 LEO satellites using frequency in

Ku-band (12GHz to 15GHz), orbiting at an altitude of 1469km.Total capacity will be over 200Gbps. Data rate: from 16kbit/s to 2Mbit/s uplink and 16kbit/s to 20Mbit/s downlink.

Status:The LEO constellation projected 64 to 80 satellites and was originally expected to enter service in 2002. However, development of the LEO component is now on hold, and the brand will be used to offer service over leased GEO capacity.