Training Sat Comm Part 2

Andrea Bucciarelli 1 - 25

LINK BUDGET

POWER LINK BUDGET

NOISE LINK BUDGET

LINK PERFORMANCE: C/No RATIO


Introduction to Satellite Communications and VSAT Networks

Part 2 - LINK BUDGETLINK BUDGET ANTENNA GAIN 4TRANSMITTED POWER IN A GIVEN DIRECTION 6EFFECTIVE ISOTROPICALLY RADIATED POWER (EIRP) 7ONE LINK ONLY RECEIVED POWER 8FREE SPACE LOSS VERSUS FREQUENCY AND DISTANCE 9ATTENUATION BY ATMOSPHERIC GASES ATTENUATION DUE TO PRECIPITATION AND CLOUDSNOMOGRAM FOR DETERMINATION OF SPECIFIC ATTENUATIONTYPICAL VALUES OF RAIN ATTENUATION 11DETERMINATION OF ARAIN MAPS OF RAINFALL CONTOURS 12MAPS OF RAIN ALL CONTOURS ONE LINK ONLY RECEIVED POWER 13ORIGIN OF NOISE 14NOISE CHARACTERIZATION 15NOISE CHARACTERIZATION 16NOISE CONTRIBUTION OF AN ATTENUATOR 17CASCADE SYSTEMS 18NOISE LINK BUDGET SATELLITE ANTENNA NOISE TEMPERATURE 19NOISE LINK BUDGETEARTH STATION ANTENNA NOISE TEMPERATURE 20CLEAR SKY NOISE TEMPERATURE 21EARTH STATION ANTENNA NOISE TEMPERATURE CARRIER TO NOISE RATIO (CNR) AT RECEIVER INPUT 23PROBLEM LINK PERFORMANCE UPLINK C/NO : (C/NO)U 24DOWNLINK C/NO : (C/NO)D 25CHARACTERISTICS OF INTERMODULATION PRODUCTSINTERMODULATION NOISE POWER AMPLIFIER NON LINERATIES POWER AMPLIFIER NON LINERATIES TOTAL LINK OPERATION TOTAL LINK BUDGET LINEAR OPERATION EXERCISE TOTAL LINK ( C / NO)T TOTAL LINK BUDGET LINEAR OPERATION


TOTAL LINK BUDGET NON LINEAR OPERATION TOTAL LINK BUDGET NON LINEAR OPERATION TOTAL LINK BUDGET NON LINEAR OPERATION WITH INTERFERENCE TOTAL LINK BUDGET NON LINEAR OPERATION WITH INTERFERENCE EXERCISE PERFORMANCE MEASUREMENT AT USERS END TYPES OF OBJECTIVES AVAILABILITY


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The antenna gain is defined as the ratio of the power per unit solid anglereceived/radiated by the antenna in a given direction to the power per unitsolid angle received/radiated by an isotropic antenna supplied with thesame power

The gain is maximum at boresight and is given by:

G Aeffmax =4

2pi

where = radiofrequency wavelength ( = cf )

Aeff = effective aperture area of the antenna

Reflector antenna

The aperture is a disc of diameter D with area A

A D= pi 2 4/ A Aeff =

where is the aperture efficiency (a tipical value for is 0.6-0.7)

G Dmax =

pi

2


Antenna radiation patternAntenna radiation pattern = gain variations as a function of the angle .relative to boresight

Half power beamwidth 3dB = full angular width between two directionswhere the gain is 3 dB below maximum

3 70dB D= (degrees)For small off-axis angle : ( ) ( )G GdB dB dB = max, /12 3 2where: Gmax,dB = 10 log Gmax

= 10 log (piD/)2

D

=3dB/2

=1

3dB

major lobeside lobes

3 dB down

G max

G max, dB

30 dBtyp -3 dB

3dB

1


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ISOTROPIC ANTENNA

ACTUAL ANTENNA

PRT

4 2pi FRIIS EQUATION

= =P G RT T / 4 2pi POWER Flux density at distance R (W/m2)

GT =1

Isotropic antenna

Power radiated perunit solid anglePT / 4pi

PT

Isotropic antenna

Power radiated perunit solid angle

PT / 4pi

Actual antenna

Power radiated per unit solid angle( )

G TPT / 4pi

Power received on area A:= ( )PT / 4pi G (A / R ) T 2

( )[ ]= AP G RT T / 4 2pi= A

xGT

distance R Area A

Solid angle = A/R 2PT

GT


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PR = EIRPsat + GR - LFS (dBW) theoretical situationPR = EIRPsat + GR - L (dBW) real situationL = LFS + LFTx + LFRx + LAG + LRAIN + LR/T + LPOL (dB)

LFTx Tx feeder lossLFRx Rx feeder loss coaxial cables, waveguides, duplexer, filtersLAG Attenuation by atmospheric gas - depending on antenna elevationLRAIN Attenuation due to precipitation and cloudsLR/T Attenuation due to Rx/Tx antennas misalignmentLPOL Attenuation due to polarization mismatch between Tx and Rx

coverage problems pointing errors misalignment between the antenna geometrical axes and

electrical axes no perfect satellite stabilization

LINEAR RHCP LHCPLINEAR 20 log cos 3 dB 3 dBRHCP 3 dB 0 LHCP 3dB 0

angle between the two directions of polarization

LOGARITHMS:

A dB[dimension] = 10 Log10 a [dimension]Log (a x b) = Log a + Log bLog (a / b) = Log a - Log b

Log ax = x Log a


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Contours of RAINFALL RATE R0.01 (mm/h) exceeded for 0.01% of ANAVERAGE YEAR:


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NOISE consist of all unwanted contributions of energy at the receiverinput which tend to corrupt the desired signal

Noise finds its origin in:

radiation from radiating bodies located within the field of view of theantenna, i.e. : satellite antenna : earth earth station antenna : galactic and cosmic sources, atmospheric

gases, rain, ground (at small elevation angles)

noise generated within the electronics of the receiver

interference from other transmitters

It should be noted that any attenuation process which involves energyabsorption is inevitably associated with thermal noise generation from themedium


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NOISE POWER SPECTRAL DENSITY N 0 (W/Hz):

N0 (f) = amount of noise power per unit of bandwidthIf N 0 (f) constant = N 0 white noiseGiven N = NOISE POWER (W) measured in bandwidth B:

N0 = N / B(W / Hz) (W) (Hz)

NOISE TEMPERATURE of noise source: T (K)

T = temperature of a passive system (resister for instance) which wouldgenerate the SAME amount of noise than the considered source of noise

T = N / KB = No / Kk = Boltzmanns constant = 1.379 x 1023 W/K . Hz.

NO(f)

NO

(W/Hz)

B frequency ( Hz)

(physical temperaturemay not be T)

SOURCE OF NOISE

physicaltemperature

T

availablepower (W) :

N = KTB

V2 = 4 KTBR (noise voltage)R


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EFFECTIVE INPUT NOISE TEMPERATURE of a system : Te (K)

Te = noise temperature of a source at the input of the system (considerednoise free) that produces the same contribution to the system output noiseas the internal noise of the actual system itself

NOISE FIGURE F:

ratio of the total system output noise power to that part of the systemoutput noise power engendered by an input source at the referencetemperature T0 = 290 K

F = S NS NIN IN

OUT OUT

//

NOUT = K T0 GB + KTe GB

F = 1 + TTe

0 F (dB) = 10 log F

actual(noisy)system

noisefree

system

no input noiseT = 0

physicaltemperature

T = Te

sameavailable

noise power:N = kTe G B

G = Power gain of the system

GIN OUT


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An ATTENUATOR is a system composed entirely of passive elementsassumed to be in thermal equilibrium at ROOM TEMPERATURE T(This is a good approximation for lossy transmission line and waveguide)

EFFECTIVE INPUT NOISE TEMPERATURE :

Te = (L - 1 ) Twhere L is the ATTENUATOR power loss.

Note that the above relation indicates that the noise figure of an attenuatoris F = L IF ROOM TEMPERATURE EQUALS T0 =290 K

L = 10L dB( ) /10

ATTENUATORPower loss = LTemperature T


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TA = averaged contribution of earth noise temperature (about 290 k ) andsurrounding background (galactic) noise temperature (about 5 k)With spot beam antenna Earth is viewed within the entire antenna patternand TA is about 290 K

Noise temperature T at receiver input:

T = TA /LFRX + TF(1 - 1/LFRX) + TRWith TA = 290 K assuming TF 290 K (ambient) :

T TF + TR = 290 + TR

It is useless to install onboard the satellite a receiver with a very loweffective input noise temperature TR

RECEIVERFEEDER

TA = 290 K

TF TR LFRX

T

EARTH = BLACK BODY AT 290 KSATELLITE


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CLEAR SKY:

TA = TSKY + TGROUND

where:TSKY = clear sky contribution to antenna noise temperature (K)TGROUND = ground contribution to antenna noise temperature (K)RAIN:

TA = T SKY/ARAIN + Tm (1 - 1/ARAIN) + TGROUNDwhere:A RAIN= attenuation due to rain, clouds and atmospheric gases along themain beam axisTm = effective medium temperature (K) due to rain, clouds andgases = 1.12 TAMB (K) - 50 , where TAMB is the ambient temperature at theearth station location

SKY TSKY

TGROUND

GROUND

TGROUND

GROUND

SKY

TSKY/ARAIN

RAIN = attenuator Tm/ARAINA

ARAIN Tm(1-1/ARAIN)


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EXERCISEGiven the receiving equipment of an earth station :

Operating frequency = 12 GHz Elevation angle E = 45

FEEDER: TF = 290 K, L FRX = 0.5 dBLNA : TLNA = 50 K , G LNA = 50 dBMIXER : TMX = 500 K, G MX = -10 dB (L MX 10 dB)IF AMP : TIF = 1000 K, G IF = 30 dB

Calculate: antenna noise temperature T A (consider both clear sky conditions and

rain with attenuation A RAIN 3 dB , assume T GROUND = 50 K) system noise temperature T

TA

Feeder

Antenna

T

LNA X IFAMP

LO

TMX GMXTIF GIF

Down Converter

Mixer

TFLFRX

TLNA GLNA


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One link only

C = carrier power at receiver input (W) = PRX = ( PT GT ) G/Lwhere G = GRMAX / LFRX LR (LR = antenna off axis gain fall-out)N0 = effective noise power spectral density (W/Hz) = kTwhere T = system noise temperature (K)

BIF = receiver noise bandwidth (Hz)The FIGURE OF MERIT G/T (K-1) characterizes the effectiveness of thereceiving end

J = Ws = WHz C

NO

= ( ) W K

KJ

1

Hz

CN EIRP L

GT KdBHZ dBW dB dBK dBWK Hz0

1 11 1 1

= +

+

+

( )

CN

CN BdB dBHz dBHz

=

+

0

11

C/N0 = (PTGT) (1 / L) (G / T ) (1 / k)

C/N = C / NOBIF

Figure of merit of receiver (K-1)

EIRP(W) PathLoss

1.38 x 10-23

J/K- 228.6 dBWK-1

Hz-1

Tx LFTX LFRX

RxPTx PT

GT GR

L= LFS LA PR PRX

Tdistance R

C / N0

(Hz)


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(C/N0)U = (EIRP)ES (1/L)U (G/T)SL (1/k)

EIRPES = (PT GT )ES =(PTX / LFTX )ES (GTmax / LT )ESLT = 12 (T/3dB )2T = Earth Station depointing angle (depends on type of tracking, if any)

(G/T)SL = (GRmax /LR )SL (1/LFRX )SL (1/T)SLLR = usually 3 dB for Earth Station located at edge of coverageT = satellite system noise temperature = 290 + TR (K)

(G/T )SL depends on earth station line of sight directionExpressing POWER FLUX DENSITY (W / m2):

= EIRPES / 4piR2

C = PRX = AReff (1/LFRX) = (GR 2 / 4pi) (1 / LFRX ) = (GRmax / LR )SL (1/LFRX)SL (2 / 4pi)

LFRX RX

PR

(C/NO)0

SATELLITE (SL)

GTmax

EARTHSTATION (ES)

R

GT

GRmaxantennaboresight

GR

PRX

edge of coverage:-n dB (typ. -3 dB) contour

LFRX RX PR

(C/NO)U

PRX

T


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(C/N0)D = (EIRP)SL (1/L)D (G/T)LS (1/k)

(C / NO)D computation assumes that a noiseless signal is generated by thesatellite

EIRPSL = (PT GT )SL = (PTX /LFTX )SL (GTmax /LT )SLLT = usually 3 dB for Earth Station located at edge of coverage

(G/T)ES = (GRmax / LR )ES (1/ LFRX )ES (1/ T)ESLR = 12 (R /3dB )2

R = Earth Station depointing angle (depends on type of tracking, if any)T = Earth Station system noise temperature, includes antenna noise TAwhich varies with elevation angle E and amount of rain

edge of coverage:-n dB (typ. -3 dB) contour

R

GT

antennaboresight

(C/N0)D

LFRX RX PR PRX

LFTXTxPTX

T

SATELLITE (SL)

carrier

PT

GR

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Training Sat Comm Part 2