Link

LinkBudgetOverview
Budget Overview
PreparedbyARABSATESC
p y
forDivona Engineers
26th 29th December 2014
Algiers-Divona
g HQ
Introduction

Linkanalysisistheprocessofcalculatingthecarrierpowerlevelstobe
transmittedfromtheEarthStationandtheSatelliteinordertoprovidethe
requiredoverallcarriertonoiseratioatthereceiveendofthelink.

Thepowerlevelswilldependonthetypeofservice,thecodingrate,the
EarthStationlocations,theSatellitescharacteristics.

Thedesignprocesswillalsobeconcernedwiththeallocationofsufficient
linkmargintoprovideanacceptablepropagationavailability.

TradeoffbetweenEarthStationcostsandSatelliteutilizationcostsmust
becarriedouttodefinetheminimumoverallsystemcost.

TheEarthStationpoweramplifiers,antennadiametersandlownoise
receivercharacteristicswillbeoptimizedtoarriveataminimumcost
solution
solution.

2
Therearethreemajorsetsofparameterswhichconstituteinput
Th th j t f t hi h tit t i t
valuestoconductlinkbudget.

Satellite

Earth
Carriers
Stations

3
 Earth
Stations

SiteLocationCoordinates.

AntennaSpecification[OperatingFrequencyRange,CPI,Gain,
G/T Diameter ]
G/T,Diameter].

, ,
HPA,SSPA,BUCSize.

LNA/LNBNoiseFigure(orNoiseTemp).

Feed,Waveguide,CableLosses

4
 Carriers

- Modulation scheme
scheme,
Modulation scheme BPSK QPSK 8PSK 16PSK
No. of phases
No.ofphases 2 4 8 16
Bitspersymbol 1 2 3 4

- Data Rate
- FEC Code rate
1/2,2/3,3/4,7/8,etc TPC, LDPC
- Roll-off
R ll ff factor
f t
20%, 25%,30%,35%
- BER , : 10E
10E-7
7, 10E
10E-8
8 etc & Corresponding Eb/No

5
Transponder throughput versus modulation scheme,

Transponder bw 36 Mhz
FEC 3/4
Roll-0ff factor 1.31
S b l rate
Symbol t 27 5 MSps
27.5

Modulation BPSK`
BPSK QPSK 8PSK 16PSK 32PSK
scheme
No. of phases 2 4 8 16` 32`

Bits per symbol 1 2 3 4 5

Through (MB/s) 20.62 41.25 61.87 82.5 103.12

put
Eb/No (dB) BER = 2.8 4.5 6.8 10.2 12.3
1E-7

6
BER:
Biterrorrate(orratio).
Theratioofbitsreceived
inerrortothetotal
number of bits
numberofbits
transmitted.BERisa
measureofthequality
ofadigitalsignal.

7
Satellite

Longitude
Frequencyband
SFD
EIRP
G/T
TransponderBW
Transponder BW
TransponderIBO/OBO
p /
TransponderC/IM
Uplink/DownlinkCrossPol IsolationPerformance

8
 LinkBudgetProcess:Insertinputstoobtainanoutput
(2) S/C
(1) ES
P
Parameters
t
I/P Values Parameters
(3) Carrier
Parameters

LB
ALBT
Analysis
Program

Database

Note : If any
two sets are
LB given, the
O/P Values
Results third set will
b determined
be d t i d

9
DigitalCarrierModulationParametersRelationships:
ConsiderthefollowingParameters: Modulat Noof Bits/
ModulationScheme=QPSK ion phases symbol
Numberofphases(M)=4
Bits
BitsperSymbol(m)
per Symbol (m) =2
2 BPSK 2 1
InformationRate[B/s]=IR
OverheadRate[B/s]=OH
DataRate[B/s](DR)=IR+OH QPSK 4 2
FECCodeRateFEC=3/4
d /
RSRate=188/204
CompositeRate =CR=(3/4)*(188/204) 8PSK 8 3
[ /]
TransmissionRate[B/s]=Tx R=DR/CR
/
Rollofffactor( )[%]=30% 16PSK 16 4
SymbolRate[S/s]=Tx R/m
NoiseBandwidth[Hz](Nbw)=Tx R/m
All t d B d idth [H ] (B ) (Nb )*(1+ )
AllocatedBandwidth[Hz](Ba)=(Nbw)*(1+)(A1) (A1)
LetEb/No=5.5(dB)atBERof1E6
ThenRequiredC/N=Eb/No+10LOG(DR/Nbw)(A2)
or C/N Rqd=5.5+10LOG(CR*m)(dB)..(A2)
orC/N = 5 5+10LOG(CR*m) (dB) (A2)

10
SatelliteLINK

11
UplinkEIRP

HavingaTXESwithanAntennasizeDiameterandHPA/BUC
size we can start defining our uplink EIRP by
sizewecanstartdefiningouruplinkEIRPby

EIRP=HPA OBO WGLoss+AntennaGain

Assuming0dBOBOand0dBwaveguidelossesthecomputed
p p
uplinkEIRPofastationwithHPApowerof20dBW and
AntennaGainof50dBi

12
 FluxEquationandFluxDensity

Thepowerpersquaremeterthatarrivesatthereceive
sideofthetransponder

The flux density, or power per unit area at a distance d from an

isotropic radiator is:

PT
dBW/
4 d 2 m2

Th
Theareaexpandswiththesquareofthedistance
d ith th f th di t
1
YouwillnotethattheisarepresentationofFreeSpacePathLoss
4 d 2
(FSPL)

13
 FluxEquationandFluxDensity

NowforFluxdensityreceivedatsatelliteinputreference.The
actualPowersourceistheTXESHPApower(P)andwithAntenna
GainAmplificationtheUplinkEIRPcomputed.ThusFluxDensity
willbeupdatedas

PT G T
dBW/
4 d 2 m2

Flux=EIRP FSPL
AddingsomefurtherAtmosphericandrainloss(Lr )dB

Flux=EIRPFSPLLr
Flux = EIRP FSPL Lr

14
 SatelliteSFD

TheSFD(saturatedfluxdensity)isthepowerper
squaremeterthatisneededattheinputtosaturatethe
transponder(maximumoutputpowerofthe
transponderamplifier)

Typicalvalue: 80~90dBW/m

SinceSatelliteSFDreferenceusedforanormalized1m2areasurfacearea,
thecomparisonbetweenSFDandCarrieruplinkFluxshallbeconsideredas:

4
FluxDelta=SFD(sat) (EIRPFSPLLr )+
2

ThisFluxDeltawillbeamajorinputforthecalculationasCarrierInputBackOff

15
OperationIBO/OBO

EachTransponderwillhavearecommendedIBO/OBOvaluesfrom
theoperatorforthefullloadingofthetransponderbasedonmode
ofoperation.

Thisrecommendedoperationismainlytoguaranteethesignal
Thi d d ti i i l t t th i l
amplificationtomaintainwithinalinearrange.

16
OperationIBO/OBO

BelowaresponseIBO/OBOplotshowingthreemainmodesof
loading(SingleCarrier,TwoCarrier,MultiCarriers)
0
Single-Carrier OBO (dB)

-2 Two-Carrier OBO (dB)

M ulti-Carrier OBO (dB)
-4

-6
ut Backoff (dB)

-8

-10
Outpu

-12

-14

-16

-18
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0
Input Backoff (dB)

17
OperationIBO/OBO

BelowtableshowingtherecommendedIBO/OBOhighestvaluesto
maintainlinearperformanceperoperationmode.

ThosevalueswillbeusedforcomputingcarriersBackoffandEIRP
thatbeenamplified.

Single Carrier Input Single Carrier Output Two Carrier Input Two Carrier Output Multi Carrier Input Multi Carrier Output
Backoff Backoff Backoff Backoff Backoff Backoff
(IBO) (OBO) (IBO) (OBO) (IBO) (OBO)

0.0 dB 0.0 dB -3.7 dB -2.3 dB -4.3 dB -3.1 dB

ADeltafactor(F)willbepresentedasF=OBOIBO.
ThisValuewillusedforCarriersPowerComputation
p

18
CarrierIBO/OBO

ItshallbeNotedthatSFDvaluetobeconsideredovertheuplink
locationstation.

TheEarlyDefinedFluxDeltaisourCarrierIBO.
4
(CarrierIBO)FluxDelta=SFD(sat) (EIRPFSPLLr )+
2

NowtoknowtheCarrierAmplifiedEIRPbytheSatellitewewill
simply
simply

CarrierOBO=CarrierIBO+F

CarrierEIRPDownlink=EIRP(sat) {CarrierOBO}

19
CarrierIBO/OBO

Whensaturatingthetransponder,thesatellitetransmitswith
When saturating the transponder the satellite transmits with
theEIRPindicatedintheEIRPfootprints

20
CarrierIBO/OBO

TopreventnonlineareffectsduetosaturationoftheTWTA,
To prevent non linear effects due to saturation of the TWTA
someinputbackoff istaken,whichresultsinoutputbackoff

21
CarrierIBO/OBO

Thesatelliteinputandoutputbackoff percarrierchangeaccordingly

22
CarrierIBOandPEB!
TheCarrierUplinkTowardasatellitetransponderwouldhaveaflux
Th C i U li k T d t llit t d ld h fl
projectionthatbeenhighlightedasCarrierIBO.

IfMulticarrieroperatedoverthesametransponderthetotalflux
valuesshallnotexceedthetransponderSFDdesignatedvalueandits
recommendedOperatingpoint(IBO)ofthetransponder!

ToAllowusunderstandingtheuplinkCarrierEIRPlimitintothe
transponderwedefinePowerEquivalentBW(PEB)whichisa
functionofCarrierIBOtoTransponderIBOanditsBWashereunder:

CarrierPEB
10 * log
l CarrierIBO
C i IBO Transponde
T d r . IBO
Transponde r . BW

23
CarrierIBOandPEB!

CarrierPEB
10 * log CarrierIBO Transponde r . IBO
Transponde r . BW

Case A B C D
TransponderBW 36 36 72 72
TransponderIBO 4 4 4 6
CarrierIBO 12 9 12 9
CxrIBO TPIBO 8 5 8 3
LinearValue 0.2 0.3 0.2 0.5
PEB( Mhz ) 5.7 11.4 11.4 36.1

From here
F h comes th
the statement
t t t off P
Power lilimited
it d When
Wh PEB comes
higher than Carrier Allocated BW ! The limit coming from excess
Power Consumed on Transponder level

24
UplinkC/No&C/NDerivation

As we have seen in a previous section, the product of transmit

power and antenna gain is called the "Equivalent Isotropically
Radiated Power" and is a figure
g of merit of the transmitting
g station.
We can therefore write:

EIRP
dBW/m2
4 d 2

The received carrier power collected by the receiving antenna

having an effective aperture area Ae is given by:

EIRP
C * Ae * Ae dBW
4 d 2

25
 UplinkC/No&C/NDerivation
Recall that the receive antenna gain is given in terms of its effective
aperture by:

GR 4 Ae
2
Therefore we can write the received power as:

2 2 2
EIRP GR 4 d EIRP
C EIRP RG EIRP G GR
4 d 2 4 4 d R FSL
2
4 d
Where FSL stands for the Free Space Loss,

FSL, is the path free space loss in Decibels = -20 log (4 d/ ) dB

In more easier form ,,FSL= 32.4+20 log

g d + 20 log
gf
Where d is distance in Km ,
While f is Frequency in Mhz 26
UplinkC/No&C/NDerivation

Note once again that this FSL term is a function of frequency and
is not just the inverse square law energy spreading loss. This form
is very convenient for use in link analysis. Since the total path is
not in free space, but passes through the atmosphere, a loss term
for atmospheric absorption must be added. The equation now
becomes:

C EIRP GR
dBW
FSL L

The actual level of the carrier received is not critical since the
receiver has gain to restore the signal to a workable level.

27
 UplinkC/No&C/NDerivation

RecallingtheThermalNoisePower causedbyrandommotionofelectrons.
relatedtoTemperature.

Noise
NoisePower
Power
No =kTB
T=NoiseTemperature
(
k=TheBoltzmannconstant(1.38x1023 J/K))

B=ReceiverBandwidth

kcanhaveunitsdBJ/KordBW/Hz/K

26Jan15 Sat.TelecomOverveiw 28
UplinkC/No&C/NDerivation

C EIRP G R 1
NO FSL L K T SYS

C 10Log EIRP 1 10Log GR 10Log K

NO FSL L T
SYS

C EIRP FSPL L G / T 228.6 dB.Hz

NO
Where 228.6 is the Boltzmanns Constant in Decibel

C C
10 log(NoiseBW ) dB
N No

29
 UplinkC/No&C/NDerivation

C EIRP FSPL L G / T 228.6 10Log ( Nbw) dB

N
P ti FSPL = 32.4+20
Presenting 32 4+20 log
l d + 20 log
l f

C
EIRP 32.4 20Log (d ) 20 log( f ) L G / T 228.6 10Log ( Nbw)
N

Approximate
pp FSPL p
per band to GEO can be used as :
C-Band (200 dB)
Ku-Band (207 dB)
Ka Band (214 dB).
Ka-Band dB)

30
 DownlinkC/No&C/NDerivation
The Downlink C/N will be using same derivation as
uplink C/N with EIRP considered the carrier
downlink EIRP and G/T value of the Earth
Station Reception side

C
EIRP 32.4 20Log (d ) 20 log( f ) L G / T 228.6 10Log ( Nbw)
N

31
 DownlinkC/No&C/NDerivation
The Downlink C/N will be using same derivation as
uplink C/N with EIRP considered the carrier
downlink EIRP and G/T value of the Earth
Station Reception side

C
EIRP 32.4 20Log (d ) 20 log( f ) L G / T 228.6 10Log ( Nbw)
N

Obtaining G and T, then, G/T = G - Tsys (dB/K)

We will need to compute the reception system Thermal Noise as
following slide

32
 SystemNoiseTemperature
ConsiderNcascadedandimpedancematchedsystemseachwiththesame
bandwidthbutwithitsownpowergainGi (orlossGi=1/Li)andnoisefigureFi

Overallnoisefigureofthesystem

Effectiveinputnoisetemperature

33
 SystemNoiseTemperature
ThusNoiseTemperatureandNoiseFigurearerelatedasbelowequation
Th N i T t d N i Fi l t d b l ti
state

34
SystemNoiseTemperature
LNA
LOSS GLNA=60dB
LNA = 60 dB RECEIVER
L F

L=0.5dB Noise Figure F= 1 35 dB

NoiseFigureF=1.35dB
350K
Ta=35 400K
TLNA=40
MajorNoiseContribution

Using the input of the Low Noise Amplifier (LNA) as a reference point, the
totall system noise
i temperature iis calculated
l l d as ffollows:
ll
a 0 ( L 1) 0 ( f 1)
sysy 1
L L GLNA

TSYS
35
290
1.122 1 40 290 1.35 1
31.2 31.5 40 0.00001
1.122 1.122 105

=102.7K

35
SystemNoiseTemperature

36
TotalC/No

37
 TotalC/No(DownlinkDominant)

Theaboveexampleofadominantdownlink(duesmallG/T)thateven
The above example of a dominant downlink ( due small G/T ) that even
increasinguplinkpowerby3dBaveryminor0.2dBimprovedinthetotal
C/No

38
 TotalC/No(DownlinkDominant)

Butforthesamelink,increasingreceptiongainby3dBwillhaveadirect
impactonthetotalC/No

39
 TotalC/No(UplinkDominant)

HavingabigreceptionAntennawithbigG/T,ifweincreaseitsgainby3dB,
theimpactwillbeverylowontotalC/No

40
 TotalC/No(UplinkDominant)

However,the3dBincreaseontheuplinkEIRPwillhaveanoticedimpacton
theoverallC/No.

41
TransponderC/IM IntermodulationProducts

Case(1):SingleCleanCarrier
O/P
I/P

Case (2) : Two Clean Carriers

Case(2):TwoCleanCarriers

I/P O/P

fA fB
2fA fB fA fB 2fB fA
42
TransponderC/IM
IntermodProducts:ThreeCleanCarriers
d d h Cl C i

I/P

fA fB fC

0/P

fA +fB fC fA fB fC
fC +fA fB

fB +fC fA
43
TransponderC/IM

IntermodProducts:MultiCleanCarriers

I/P

fA fN

O/P

44
TransponderC/IM

45
TransponderC/IM

TWTATransferCharacteristics(Tabularformfora36MhzTP)

Input Output Saturated Carrier to Saturated Carrier to

Intermodulation Intermodulation
Back-off Back-off Nosie Noise
(dB) (dB) Density (dB-Hz) C/IM (dB)
14 8.1
8 1 102 26.4
26 4
13 7.2 100.5 24.9
12 6.5 99 23.4
11 5.8 97.5 21.9
10 5.1 96 20.4
9 4.5 94.5 18.9
8 3.9 93 17.4
7 34
3.4 91 5
91.5 15 9
15.9
6 2.9 90 14.4
5 2.5 89 13.4
4 2.3 88 12.4
3 2.1 86.5 10.9
46
TransponderC/IM

Aloadedtransponderwithmultiplecarriersshowingthe3rd IM
impactoneachpartofthetransponderspectrum
p p p p

47
OtherImpairments
BesidecomputedUplink/DownlinkCarriertoThermalnoisethe
B id d U li k /D li k C i Th l i h
totalCarriertoNoisewillneedtoincludeotherimpairmentsas:

Crosspolarization
p
Adjacentcarrier
Adjacentsatellite

AllthoseimpairmentsareexpressedasaC/Ivalueandsimilarto
aC/Nofthewantedsignal.

MathematicallyweusuallyPutallthosevaluesinparallelto
obtainthefinalC/N

48
OtherImpairments

49
CrossPolarization

s/cRXxpol=30dB s/cTXxpol=30dB

E/STXxpol=30dB E/S RX x pol =30dB

E/SRXxpol = 30dB

50
CrossPolarization

s/cRXxpol=30dB s/cTXxpol=30dB

E/STXxpol=24dB E/SRXxpol =17dB

51
BW&PowerLimited!
Carrier Allocated Bandwidth given by: [Ballocated =symbol rateX(1+) ]
Required C/N given by: [C/Nrequied =Eb/No + 10log(data rate/noise bw) ]

According to the given E/S parameters & S/C parameters, the Link Budget
lt determines
result d t i h
how much h power and
db d idth are consumed
bandwidth d iin
terms of:

Carrier Allocated Bandwidth [Ballctd]

Carrier Power Equivalent BW [PEB]
Carrier power [C/Nresulting]

Bandwidth viewpoint p :
i- PEBrslt = Ballctd : Optimal operation
ii- PEBrslt Ballctd : Power limited operation
Iii- PEBrslt Ballctd : Bandwidth limited operation

Power viewpoint :
i- C/Nrslt = C/Nrqd : Link optimal operation
ii- C/Nrslt C/Nrqd : Link realized. Excess TX Power.
Iii C/Nrslt C/Nrqd : Link Not realized.
Iii- realized Insufficient TX Power
Power.

52
OptimizationofSatelliteOperatingPoint

For multicarrier RF channel operation (FDMA) the satellite

operating point must be selected before the link design
can be finalized. This is determined byy the composite
p
input power to the satellite amplifier, or the total input
backoff, IBO.
y
If the individual IBOi for each carrier is reduced by
increasing the uplink EIRP, then the uplink C/No will be
increased proportionally. This will also decrease the
output OBOi and increase the downlink EIRP which
increases the downlink C/No
C/No.
The decreases in IBOi also decrease the overall IBO and
OBO. As this occurs, the intermodulation noise increases,
or the saturated C/Io decreases and each individual carrier
C/Io decreases.

53
OptimizationofSatelliteOperatingPoint

Therefore,, as the carrier levels are increased and the

transponder operating point changes, the carrier to noise
ratios increase. However, the carrier to intermodulation
noise decreases and a tradeoff occurs.
Therefore, there is an optimum selection of IBO that will
maximize the overall C/No.

54
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