PowerPoint PresentationSatellite Systems and ServicesGeo-synchronous (GEO) Satellite SystemsSlide 4GEOs: IssuesLow Earth Orbiting (LEO) satellite systemsLEO’s issuesTranspondersBeamsOn-Board SwitchingPoint-to-Point LinkPoint-to-MultipointLEO SystemsIridiumIridium (cont’d)Slide 16Iridium: frequency reuseSlide 18TeledesicMilitary ApplicationsBattlespace ApplicationsBattlespaceCopyright 2002, S.D. Personick. All Rights Reserved. 1Telecommunications Networking IITopic 14Satellite Systems and ServicesDr. Stewart D. PersonickDrexel UniversityCopyright 2002, S.D. Personick. All Rights Reserved. 2Satellite Systems and Services•Geo-synchronous (GEO) Systems•Low Earth Orbiting (LEO) Systems•Transponders (vs. Regenerators)•Beams: Wide Area, Spot, Scanning•On-board switching•Long Haul Point-to-Point, Rural Areas and Developing Countries, GPS, VSAT, DBS, Iridium, TeledesicCopyright 2002, S.D. Personick. All Rights Reserved. 3Geo-synchronous (GEO) Satellite SystemsWe want the satellite to orbit the earth every 24 hours in an equatorial orbit: satellite appears to stay in a fixed position over the earth.What is h?EarthhLooking down from the north poleCopyright 2002, S.D. Personick. All Rights Reserved. 4Geo-synchronous (GEO) Satellite SystemsEarthDiameter of the Earth ~ 7927 milesRadius of GEO satellite ~26,261 miles = rF=mg [(3963/r)**2]=m(v**2)/r; r**3= g [(3963)**2] /[(v/r)**2] where m=mass of satelliteg=32.2ft/sec**2 =(32.2/5280) mi/sec**2v/r = 2pi/(24 x3600) rad/sec22,300 miCopyright 2002, S.D. Personick. All Rights Reserved. 5GEOs: Issues•Delay: 22,300 miles x 2 / (186,000 mi/sec) ~ 0.24 seconds (one way)•Signal loss due to long propagation paths•Limited number of equatorial slots (e.g. @2 degree spacing ~ 180 slots globally)•Does not cover very large latitudes: cos (*)~ 3963/26261 …. * ~81 degrees• However…no tracking is requiredCopyright 2002, S.D. Personick. All Rights Reserved. 6Low Earth Orbiting (LEO) satellite systemsEarth ~500 -1000miles above the earth (800-1600 km); orbit time < 2 hr22,300 mi(for reference)Copyright 2002, S.D. Personick. All Rights Reserved. 7LEO’s issues•Delay is ~20-40 times smaller than for GEOs•Very large number of possible orbits•Can cover all latitudes•Less propagation loss•But: tracking is required, and “handoffs” are requiredCopyright 2002, S.D. Personick. All Rights Reserved. 8TranspondersLNAFreq shiftBandwidth = BCopyright 2002, S.D. Personick. All Rights Reserved. 9BeamsEarthWide areaSpotScanningCopyright 2002, S.D. Personick. All Rights Reserved. 10On-Board SwitchingTransponder(s) orRegenerator(s)Switching matrixPacket or CircuitCopyright 2002, S.D. Personick. All Rights Reserved. 11Point-to-Point LinkTransponder-basedSpot beam(s) Transponder gain ~Up-link lossExamples:Satellite TV feedsVSATCopyright 2002, S.D. Personick. All Rights Reserved. 12Point-to-MultipointTransponder-basedE.g., DBS, GBS, rural telephone coverageCopyright 2002, S.D. Personick. All Rights Reserved. 13LEO SystemsOn-board Satellite processing (switching)Inter-satellite cross linksCopyright 2002, S.D. Personick. All Rights Reserved. 14Iridium•In service (re-purposed from its original market concept)•1610-1635 MHz; 1500lb satellites•66 active satellites: polar orbits6 polar planes, 11 satellites per plane, 48 spot beams/satellite•2.4 kbps: voice and data; ~277,000 simultaneous users /satellite (up to 52,000/beam)•600 mw handset power•~147 dB link loss budget with 16 dB of margin for voice….131 dB of prop. lossCopyright 2002, S.D. Personick. All Rights Reserved. 15Iridium (cont’d)•If we have a maximum number of users per beam of 52,000, and if we assume that the full bandwidth of 25 MHz is allocated to a single beam under this condition… then the bandwidth per user is [25,000,000/52,000] Hz = .48 kHz•Since each user is allocated 2.4 kbps, then (ignoring the issue of two-way communication), the bandwidth efficiency of the modulation must be: 2.4/0.48 = 5 bits per second/HzCopyright 2002, S.D. Personick. All Rights Reserved. 16Iridium (cont’d)•The 48 spot beams can be arranged in a 6x8 pattern on the ground (6 spots in the N-S direction of satellite motion x 8 spots E-W, perpendicular to the direction of satellite motion)•If we use 3 frequency sub-bands (out of the total of 25 MHz, I.e., 8.333 MHz per sub-band), and if each sub-band is used on 16 spot beams (1/3 of 48), then the frequency reuse is 16 •Each spot is approximately 525 miles in diameter(525 x 8 spots E-W x 6 planes = 25,200 miles at the equator)Copyright 2002, S.D. Personick. All Rights Reserved. 17Iridium: frequency reuse123123312123Single Spot BeamCopyright 2002, S.D. Personick. All Rights Reserved. 18Iridium (cont’d)•Satellites at ~480 mile altitude•“Make-before break” handoffs•RF cross links to 4 neighboring satellites@23GHz•No ground stations in the path from wireless end user to terrestrial gateway•Coverage anywhere in the worldCopyright 2002, S.D. Personick. All Rights Reserved. 19Teledesic•Non-polar orbits, initially > one hundred satellites, @ ~1500 km altitude (actuals: TBA) •Full service:~2004; Ka-band (~20/30 GHz)•Primarily service to fixed locations•~$4000.00 for two antennas + electronics (60 cm antenna diameter). Antennas in radomes•Multi-megabit per second data rates (up to: 51.84 Mbps up-link, 311.4 Mbps down-link)•Optical cross links ( 6-“lasercom”) @ 4.5Gbps •Covers -62 to +62 degrees latitude with > 25 degree look angle;+ 62 to 72 with >10 look angleCopyright 2002, S.D. Personick. All Rights Reserved. 20Military Applications•Strategic: links between senior command posts using: satellite, terrestrial, and ground to-airborne command post links. -Issues: encryption, vulnerability to attack•Tactical/battlespace: links to warfighters in the battlespace for command and control-Issues: LPI, LPD, no fixed base station infrastructureCopyright 2002, S.D. Personick. All Rights Reserved. 21Battlespace Applications•Examples:-GPS for position determination and reporting (situational awareness)-GBS to broadcast (push) information to the battlespace (e.g., situational information, maps, intelligence, command intent)-Battlefield wireless internet... with relaying + satellites for infrastructureCopyright 2002, S.D. Personick. All Rights Reserved. 22BattlespaceGBS RelayingMilstarIridiumPlatoonBrigade