1. 1
6.6.
LINK BUDGETLINK BUDGET
PERFORMANCEPERFORMANCE
• characteristics of
– TX station
– RX station
• propagation
• noise, interference
• characteristics of satellite

2. 2
NOISENOISE
• noise voltage
• independent of frequency, “white” noise
kTBRun 4
2

k = 1.38 10-23 J/K, Boltzmann constant
B... noise bandwidth
R...resistance
T...absolute temperature
NOISENOISE
• at very high frequencies thermal noise
vanishes, only quantum noise remains
• Noise power
kTBBNN  0

3. 3
INVERSE SQUARE LAWINVERSE SQUARE LAW
• Carrier power
• Aeff... effective antenna aperture
• R...distance
• GT...transmit antenna gain
AG
R
PC effT
T
2
4

ANTENNA FORMULAANTENNA FORMULA
• effective aperture
A
G
Aeff 
4
2
2
222
2
4
4 DDG 

4. 4
CARRIER POWERCARRIER POWER







44
2
2
G
R
GP
C RTT
GPEIRP TT






R
Ls
4
2
free-space loss
CARRIER/NOISE RATIOCARRIER/NOISE RATIO
BTk
N
C
N
N
C
C s
  kBT
G
R
GP
N
C
s
RTT 1
/4
2 






  kT
G
R
GP
N
C
s
RTT
o
1
/4
2 







5. 5
FIGURE OF MERITFIGURE OF MERIT
• G/T
• important characteristic for
– satellite
– ground station
LINK BUDGETLINK BUDGET
CALCULATIONCALCULATION
• figures may vary widely
– EIRP high
– free-space loss very high
– receive carrier power very low
• logarithmic representation
advantageous

6. 6
LOGARITHMICLOGARITHMIC
REPRESENTATIONREPRESENTATION
• Signal-to-noise ratio [dB]
 
)log(10)log(10)log(10
)log(10/4log20)log(10)log(10
BkT
GRGP
N
C
s
RTT


  BkTGLEIRP dBHzKdBJKdBdBsdBW
N
C
][]/[]/[][][ / 
C/NC/Noo
• carrier power / noise density
  kTGLEIRP KdBJKdBdBsdBW
oN
C
]/[]/[][][ / 

7. 7
C/TC/T
• sometimes used in link budgets
• in [dBW/K]
• leaves out k = -228.6 dB(J/K)
• at the end of calculation B, k considered
 TGLEIRP KdBdBsdBW
T
C
/ ]/[][][

EEbb/N/Noo
• energy per bit / noise density
• r...rate of information rate (not
necessarily channel rate)
r
B
N
C
N
E
o
b


8. 8
SHANNON BOUNDSHANNON BOUND







N
C
BH 1log2
)/1(log/)/1(log
/
22 BNoCNoCBNoCH
CBNB o

eNCH o
B
log/lim 2


SHANNON BOUNDSHANNON BOUND
• limiting case: transmission rate = H:
e
N
HEH b
log2
0

dB
N
E
o
b
6.1

9. 9
EXAMPLEEXAMPLE
• EIRP
– f = 14.0 GHz
– antenna diameter: 2.4 m
– antenna efficiency: 60%
– transmit power: 16 W
dB
E
E
D
G 7.48
914
83
4.2
6.0log10log10 2
22
2
22




























EXAMPLE (2)EXAMPLE (2)
• corresponds to 1,174,897.5 W
dBWEIRP 7.607.48)16log(10 

10. 10
EXAMPLE (3)EXAMPLE (3)
• free-space loss
• f = 14 GHz












 





0214.0
6394
log20
4
log20log10
4
2
ERR
Ls
= 207.2 dB
EXAMPLE (4)EXAMPLE (4)
• free-space loss
• f = 11 GHz












 





0272.0
6394
log20
4
log20log10
4
2
ERR
Ls
= 205 dB

11. 11
EXAMPLE (5)EXAMPLE (5)
• free-space loss
• f = 30 GHz












 





01.0
6394
log20
4
log20log10
4
2
ERR
Ls
= 213.8 dB
ANTENNA GAINANTENNA GAIN
• 14 GHz: G = 48.7 dB
• 30 GHz: G = 55.3 dB
• difference: + 6.6 dB
• difference in free-space loss: - 6.6 dB !

12. 12
C/NC/N
• f = 14.0 GHz
• GT= 48.7 dB
• P = 16 W = 12 dBW
• R = 39,000,000 m
• G/T = 4.2 dB/K
• B = 1 MHz
  BkTGLEIRP dBHzKdBJKdBdBsdBW
N
C
][]/[]/[][][ / 
dB
N
C
3.260.60)6.228(2.42.2077.60
0

C/NC/Noo
• normalized to 1 Hz noise bandwidth
dBHz
N
C
3.86)6.228(2.42.2077.60
0


13. 13
C/TC/T
• without k
KdBW
T
C
/3.1422.42.2077.60 
BACK-OFFBACK-OFF
• usually the max. EIRP of ground station
is given
• back-off in dB from max. EIRP
• EIRP = EIRPmax - BO
• max. EIRP may drive HPA into
saturation
– not possible for multi-carrier operation
– also degradation depending on modulation
scheme

14. 14
ADDITIONAL LOSSESADDITIONAL LOSSES
OUTPUT LOSSESOUTPUT LOSSES
• HPA connected to feed via waveguide
• resulting in additional loss
• design should be such that output
losses are minimum
• Lout

15. 15
POINTING LOSSPOINTING LOSS
• antennas not totally aligned
• movement of satellite
• pointing loss,
• 0.2...1 dB
• Lpu
CONTOUR LOSSCONTOUR LOSS
• satellite antenna gain reduces at outer
zones with respect to beam center
G/T = 4.2 dB/K
G/T = 0.2 dB/K

16. 16
ATMOSPHERICATMOSPHERIC
ATTENUATIONATTENUATION
• gaseous absorption in atmosphere
• attenuation by hydrometeors
• depending on rain rate, drop size,
frequency
• Latu
C/T at TRANSPONDERC/T at TRANSPONDER
 TGLLLLLBOEIRP
T
C
atucupuout su / 

17. 17
EXAMPLEEXAMPLE
• f = 14.0 GHz
• GT= 48.7 dB
• P = 16 W = 12 dBW
• Output back-off: 2 dB
• R = 39,000,000 m
• G/T = 4.2 dB/K
EXAMPLEEXAMPLE
• Lout = 0.7 dB
• Latu = 0.6 dB
• Lcu = 3 dB
• Lpu = 0.4 dB

18. 18
RESULTRESULT
 TGLLLLLBOEIRP
T
C
atucupuout su / 
KdBW
T
C
/3.1482.46.034.02.20727.60 
POWER FLUX DENSITYPOWER FLUX DENSITY
• At transponder input
r
EIRP
A
EIRP effeff
2
4

LLLL
GP
EIRP
atucuout pu
Tout
eff 
LLLLGPEIRP atupucuoutTouteff 
in dB

19. 19
SPREADING LOSSSPREADING LOSS
)4log(10 2
rLspr  in dBm 2
mdBLspr
22
8.162)390000004log(10 
INPUT FLUX DENSITYINPUT FLUX DENSITY
• in dBW/m2
LLLLLGP spratupucuoutTout 

20. 20
TRANSPONDER FLUXTRANSPONDER FLUX
DENSITYDENSITY
• parameter of transponder
• IPFD… input power flux density for
saturation
• can be set by telemetry to adjust the
sensitivity of transponder
• e.g. sat = - 98 dBW/m2
INPUT BACK-OFFINPUT BACK-OFF
• Difference of actual received flux
density and IPFD
• Bin = sat - 

21. 21
POWER TRANSFER CURVEPOWER TRANSFER CURVE
Input back-off
Output
back-off
sat
Bin
Bout
EXAMPLEEXAMPLE
• Pout = 16 W = 12 dBW
• GT = 46.3 dB
• Output loss: 0.7 dB
• Distance R = 39,000 km (24,375 mi)
• Pointing loss: 0.3 dB
• Contour: 1 dB
• Atmospheric attenuation: 1.5 dB

22. 22
EXAMPLE (EXAMPLE (contcont.).)
mdBLspr
22
8.162)390000004log(10 
LLLLLGP spratupucuoutTout 
8.1625.13.017.03.4812 
mdBW 2
/106
EXAMPLE (EXAMPLE (contcont.).)
sat = -98 dBW/m2
• Bin = sat - dB

23. 23
Input back-off
Output
back-off
sat
Bin= 8 dB
Bout= 3.5 dB
in linear region: Bout = Bin - 4.5 dB typically
SATELLITE EIRPSATELLITE EIRP
• Maximum EIRP of transponder:
specified EIRPsat
• EIRP due to drive level:
EIRP = EIRPsat - Bout
• Example:
• EIRPsat = 49 dBW
EIRP = 49 - 3.5 = 45.5 dBW