Contents

Mobile Satellite systems types

Mobile Satellite Systems (Types)

• Geostationary Systems:   --INMARSAT ($15,000 telephone, $5.50/min)

                                           --MSAT ($2000 telephone, $1.45/min)

• Big “LEO” Systems:       --ARIES                              --ELLIPSO                

                                           --IRIDIUM                         -- ODYSSEY

• Little “LEO” Systems:    --Orbcomm                          --LEOSAT

                                           --STARNET                        --VITASAT                                     

IRIDIUM

• Motorola

• Voice (4.8 kbps), Data (2.4 kbps), Fax, Location Services

• 66 satellites in 6 polar orbits (780 km)

• 48 spot beams per satellite forming “cells”, 230 simultaneous duplex conversations

• Satellite-to-satellite links as well as to ground (Ka band@20 GHz to gateways & cross links,

   L band at 1.5GHz to handhelds)

• FDMA uplink, TDM downlink

• Supports satellite handoff during calls

ICO Global Communications

• Funded by Inmarsat, Hughes to build the satellites

• ICO = Intermediate Circular Orbit (8-10,000 km)

– 6-20 satellites to cover earth, vs. 40-70 for LEO and 3-6 for GEO

– 200 ms propagation delay

– High average elevation angle from user to satellite (>40 degrees)

– High probability of visibility from more than one satellite, yields  path diversity (70% of

   each footprint overlaps with another  satellite)

– Relatively slow moving satellites (1 degree per minute)

– Minimum requirements for establishing a connection:

» User can see satellite 10 degrees above horizon

ODYSSEY

• TRW

• Voice, Data (9.6 kbps), Fax, Location Services

• 12 satellites, 4 in each of 3 orbital planes, 3000 voice circuits per satellite

• CDMA access techniques

• No handover between satellites, because of  long satellite visibility from ground

 

• Steering antenna scheme also eliminates  need for spot beam handovers

Teledesic

• Major Investors: Bill Gates. Craig McCaw

• 21 orbital planes, 40 satellites per plane, 840  satellites total

• 700 km, circular orbits, high elevations

• 20 Ghz Ka band, large number of satellites creates rain attenuation problems

• Hand held communicators can see two satellites at all times: soft handoff, load sharing

• Voice/Data up to 2 Mbps

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