WIXLIB

CS 294-7: Mobile Satellite SystemsProf. Randy H. KatzCS DivisionUniversity of California, BerkeleyBerkeley, CA 94720-1776 19961

Mobile Satellite Systems Like cellular systems, except that the basestations (i.e., satellites) move as will asmobile devices Satellite coverage attractive for areas of worldnot well served by existing terrestialinfrastructure: ocean areas, developingcountries2

Mobile Satellite Systems Interesting aspects of the satellite link:– 270 ms propagation delay (geosync)– Transmission cost independent of distance– Very high bit rates are possible; can avoid bandwidthlimitations of terrestrial links– An inherently broadcast medium– Dynamic assignment of channels between geographicallydispersed users– A transmitting station can receive its own transmission;can be exploited for transmission control3

Mobile Satellite Systems Assigned Frequencies–––––––––––P Band: 0.225-0.39 GHzJ Band: 0.35-0.53 GHzL Band: 0.39-1.55 GHzS Band: 1.55-5.2 GHzC Band: 3.9-6.2 GHzX Band: 5.2-10.9 GHzK Band: 10.9-36.0 GHzKu Band: 15.35-17.25 GHzQ Band: 36-46 GHzV Band: 46-56 GHzW Band: 56-100 GHzEarlier satellites, interferencewith terrestrial microwave links(4/6 GHz)Newer generation satellitesystems (14/16 GHz)Also interest in 20/30 GHzsystems (Ka Band, NASA ACTS) Antenna gain proportional to ƒ2, free space loss to 1/ƒ2 Counterbalanced by noise and absorption issues4

Equivalent Isotropic RadiatedPower (EIRP) Maximum power flux density at distance rfrom a transmitting antenna of gain G:– ΨΜ (G Ps) / (4 π r2)– An isotropic (omnidirectional) radiator would generatethis flux density EIRP is defined as G Ps– When expressed as dBW, Ps in W, G in dB:EIRP Ps G– e.g., transmit power of 6 W and antenna gain of 48.2 dB:EIRP 10 log 6 48.2 56 dBWEIRP InLossy LinkReceived PowerFree Space Loss: PR EIRP GR - 10 log (4 π r / λ)2 (dBW)5

Receiver Power EquationΨm EIRP/4πr2Effective Aperature of Receiver AntennaPR Ψm Aeffsurface areaof the sphere 4 π r2Aeff is proportionalityconstantIsotropicTransmitterGain measuresdirectionality ofreceiver antennaReceiver ΨmG Max Flux DenΨiIsotropic Flux DenAeff G λ2 / 4 π (antenna efficiency x aperature area)PR EIRP GR λ2 : EIRP GR - 10 log (4 π r / λ)2 in dB“Free Space Loss”4 π r2 4 π6

Free Space Loss FSL 10 log (4 π r / λ)2– in dBW , FSL 32.4 20 log r 20 log ƒ– e.g., ES to satellite is 42,000 km, ƒ is 6 GHz, what is FSL?» FSL 32.4 20 log 42000 20 log 6000 200.4 dB» Very large loss!!– e.g., EIRP 56 dBW, receive antenna gain 50 dB» PR 56 50 - 200.4 -94.4 dBW 355 pW Other sources of losses––––Feeder lossesAntenna misalignment lossesFixed atmospheric and ionospheric lossesEffects of rain PR EIRP GR - Losses, in dBW7

Noise Sources System Noise– Received power is very small, in picowatts– Thermal noise from random motion of electrons– Antenna noise: antenna losses sky noise (backgroundmicrowave radiation)– Amplifier noise temperature: energy absorptionmanifests itself as heat, thus generating thermal noise Carrier-to-Noise Ratio– C/N PR - PN in dB– PN k TN BN– C/N EIRP GR - LOSSES - k -TS - BNwhere k is Boltzman’s constant, TS is system noisetemperature, TN is equivalent noise temperature, BN isthe equivalent noise bandwidth– Carrier to noise power density (noise power per unit b/w):C/N0 EIRP G/T - Losses - k8

NoiseShannon’s Law: B BN log2 (PR / PN 1)Where B information-carrying capacity of the link (bits/unit bandwidth)BN usable bandwidth (hertz)PR/PN must not get too small!Noise power usually quoted in terms of noise temperature: PN k TN BNThe noise temperature of a noise source is that temperature that producesthe same noise power over the same frequency range: TN PN / k BNNoise density (noise per hertz of b/w): N0 PN / BN k TNCarrier-to-Noise: C/N0 PR / N0 PR / k TN : EIRP G/T - k - Losses in dBReceiver antenna figure of merit: increaseswith antenna diameter and frequency;More powerful xmit implies cheaper receiverSun, Moon, Earth, GalacticNoise, Cosmic Noise, SkyNoise, Atmospheric Noise,Man-made Noise9

Carrier-to-Noise RatioExample Calculation Example:– 12 GHz frequency,free space loss 206 dB,antenna pointing loss 1 dB,atmospheric absorption 2 dB– Receiver G/T 19.5 dB/K,receiver feeder loss 1 dB– EIRP 48 dBW Calculation:– C/N0 -206 - 1 - 2 19.5 - 1 48 228.6 86.1(Note that Boltzmann’s constant k 1.38 x 10-23 J/K -228.6 dB)– Bottom-line: while the received signal is very small, thebackground noise sources are even smaller (but many othereffects increase the noise temperature, like rain absorption)10

Simplified Link Equation 10 log (C/N0) PS GS - FS L GR - TR - k - L dB where––––––––C/N0: ratio of signal pwr to noise pwr after being received (Hz)PS: RF pwr delivered to transmitting antenna (dBW)GS: Gain of the transmitting antenna relative to isotropic rad (dBi)FSL: Free space loss (dB)GR: Gain of the receiving antenna (dBi)TR: Composite noise temperature of the receiver (dBK)k: Boltzmann’s constant (-288.6 dBW/K-Hz)L: Composite of propagation loss (dB) G 10 log (η π2 D2/λ2) dBi– η: antenna efficiency, D: diameter FSL 10 log [(4 π r)2/λ2] dBPath loss and antennagain increase with squareof radio frequency– r is distance11

Frequency vs. Losses vs. BER Higher transmission frequency has the advantage ofrequiring a smaller receiver antenna BUT suffers from higher attenuation losses throughatmosphere To achieve the same C/N0 performance, which isrelated to BER, actually needs a LARGER antennathan same transmission power at a lower frequency But still frequency allocation advantages for highfrequencies Solution is to use higher transmitter power at thesatellite and earth station for the higher frequencytransmissions12

Atmospheric Attenuation50Decreasing angle of elevation% of signalpower lossloss in3.0dBAbsorption byHeavy Rain2.54-6 GHz402.0Absorption byThick Fog1.5301.02010AtmosphericAbsorption5 10 20 30 40 Elevation of Satellite0.550 13

Atmospheric Attenuation99.9Decreasing angle of elevation% of signalpower lossloss in30dBAbsorption byHeavy Rain12-14 GHz9920Absorption byThick Fog1590302510AtmosphericAbsorption5 10 20 30 40 Elevation of Satellite550 14

Atmospheric Absorption Contributing Factors:–––––Molecular oxygenUncondensed water vaporRainFog and cloudsSnow and hailConstantDepend onweather Effects are frequency dependent– Molecular oxygen absorption peaks at 60 GHz– Water molecules peak at 21 GHz Decreasing elevation angle will also increaseabsorption loss15

Atmospheric AbsorptionLocationSat Ant PointingLoss, dBRain Attenuation, dB Atmos Absorp 1/4 Canada 1/2 Canada0.1% dB, Summer0.5%1%Coverage 20.30.41% of the time, rain attenuation exceeds 0.3 dB(99% of the time, it is less than or equal to 0.3 dB)0.5% of the time, it exceeds 0.5 dB0.1% of the time, it exceeds 1.9 dB16

Antenna Temperature1000Galaxy Noise100Galactic NoiseRegionTemp (K)Low NoiseRegionTropospheric NoiseRegion5 deg elev10Rain addsnoise as wellas attenuation90 deg elev10.11.0Freq (GHz)10.0100.017

Rain and Signal Losses Rain Effect– Rainfall introduces attenuation by absorption and scattering ofsignal energy– Absorptive attenuation introduces noise» A dB rain attenuation yields power loss ratio of 10A/10» Effective noise temperature of rain TRain TA (1 - 1/A)» TA is a measured quantity between 270 and 290 K– Suppose “clear sky” C/N is 20 dB, effective noise temperature is400 K, apparent absorber temperature is 280 K, rain attenuationexceeds 1.9 dB 0.1% of time, how does this effect C/N?» 1.9 dB 1.55:1 power loss (i.e., 101.9/10 1.55)» Train 280(1-1/1.55) 99.2 K» 400 99.2 499.2 Kchange in noise power is 499.2 - 400 0.96 dB( 10 log (499.2/400))» C/N 20 - 1.9 - 0.96 17.14 dB18

Transmission Losses Up-Link (Geosync)– Up-link ƒ 6.175 GHz, D 36,000 km– Path loss is a function of frequency and distance minustransmitter and receiver antenna gain– Loss 132.7 - 20 log dt - 20 log drdt transmitter antenna: 30 mdr satellite receiver antenna: 1.5 m– Loss 132.7 - 29.5 - 3.5 94.7 dBTransmitted pwr/received pwr 2.95 x 109 Down-Link– Down-link ƒ 3.95 GHz– Footprint of antenna affects its gain; wide area footprintyields a lower gain, narrow footprint a higher gain– Loss 136.6 - 20 log dt - 20 log drLoss 136.6 - 3.5 - 29.5 103.6 dB19

Downlink Footprintπ x 39622 square miles (full earth coverage)G 4π 240002 147 22 dBπ 39622π x 15002 square miles (CONUS coverage)G 4π 240002 1024 30 dBπ 15002Greater directionality implies antenna larger size or increased frequency4 x antenna covering area 1/4 of size yields gain 16 x as great (12 dB)20

Downlink Footprint36 MHz transponder:One color TV channel OR1200 voice channels OR50 Mbps data rateAntenna is beam formed toprovide specific coverage areasSpot beams: high power, narrow beamStrong signal to supportsmaller antennas vs. worse weatherWeaker signal requires larger antennas21

Typical LossesFrontend Gain: 14 dBAntenna GainSpot: 29 dBGlobal: 17 dBTransponder output: 8 dBWAntenna GainSpot: 26 dBGlobal: 14 dBEIRPSpot: 34 dBWGlobal: 22 dBWFree space loss:200 dBAttenuation in rain& cloud: 2 dB6 GHzFree space loss:196 dBEIRP: 105 dBWAntenna Gain: 62 dBXmit output: 43 dBWAntenna Gain: 59 dBReceived SignalSpot: -103 dBWGlobal: -115 dBW4 GHz4-6 GHz system22

-1610-18Atmos LossLoss due to bad rainstorm(worse losses at 20/30 GHz)Output SignalPower AmpLow Noise AmpSat Ant GainSat AmplificationES Rcv Ant GainSat-Earth Path LossAtmos LossSat Ant GainEarth-Sat Path LossXmit LossES Xmit Ant GainES AmplifiersInput SignalTypical Losses (4/6 0-18023

Satellite Link Summary: Up-Link4/6 GHz 12/14 GHz 20/30 GHz 12/14 GHz35252020Transmitter power, dBw-1-1-1-1Transmitter system loss, dB55467662Transmitter antenna gain, dB0-0.5-2-0.5Atmospheric loss, dB-200-208-214-208Free space loss, dB20465360Receiver antenna gain, dB-1-1-1-1Receiver system loss, dB-92-93.5-69-68.5Received power, dBw1000100010001000Noise temperature, K363635036Received b/w, MHz-128-128-118-128Noise, dBw3634.54959.5Received SNR, dB2102510Loss in bad storm, dB3424.52449.5Received SNR in bad storm, dBDBS, receive-only ES1.8 m, 9 m satellite antenna24

Satellite Link Summary: Down-Link4/6 GHz 12/14 GHz 20/30 GHz 12/14 GHz1820810Transmitter power, dBw-1-1-1-1Transmitter system loss, dB16444958Transmitter antenna gain, dB-197-206-210-206Atmospheric loss, dB0-0.6-2-0.6Free space loss, dB51447244Receiver antenna gain, dB-1-1-1-1Receiver system loss, dB-114-100.6-85-96.6Received power, dBw25010002501000Noise temperature, K363635036Received b/w, MHz-131-128-121-128Noise, dBw1727.43631.4Received SNR, dB2102510Loss in bad storm, dB1517.41121.4Received SNR in bad storm, dBDBS, receive-only ES1.8 m, 9 m satellite antenna25

Satellite Path Diversity forImproved Service Availability Two alternatives:– Single path, “medium power”(16-17 dB link margin)» Still mostly line of sightservice» Handoff will improveservice availability but onlyif more satellites in view– Multiple path, “low power” (7-8dB link margin)» Substantial improvementsin service availability» Handoff further improvesservice availability» Works with any orbit26

DBS SystemsBandDownlink freq alloc, GHzUplink freq alloc, GHzPrimary UseSecondary UseTerrestrial InterferenceSatellite SpacingDetermined bySatellite InterferenceSatellite EIRP, dBWHigh PowerKu12.2-12.717.3-17.8DBSPt-to-PtNo9 degITUNo51-60Medium PowerKu11.7-12.214-14.5Pt-to-PtDBSNo2 degFCCYes40-48Low PowerC3.7-4.25.925-6.425Pt-to-PtDBSYes2-3 degFCCYes33-37Ku band: less utilized; not used in land-based microwave systems,60 cm dishes (vs. 3 m C-band dishes)27