• Transponder bandwidth is usually the most
expensive resource in a satellite communications
• For maximum efficiency, a satellite link should
be engineered to balance bandwidth and power.
• Traditionally, it involved playing with
modulation and coding to get the right balance for
fixed satellite and earth station parameters.
Traditionally, you could reduce Bandwidth or Power,
but not both without significantly increasing the
Reduce Occupied Bandwidth :
Use Higher Order Modulation
• Increases Transponder Power Utilization
• Increases HPA Size and/or Antenna Size.
Reduce Transponder Power Utilization :
Use Lower Order Modulation or more powerful FEC
• Increases Occupied Bandwidth
• Reduces HPA Size and/or Antenna Size
Without Using Lower Order Modulation
• Increase Antenna Size antenna size
Reduce bandwidth by 50%.
Increase data throughput by a factor of 2.
Reduce antenna size by 30%.
Reduce transmitter power by a factor of 2.
Provide 3dB more link margin.
Allocated BW PEB
Portion of transponder BW actually used. Fraction of transponder power required to
Linear function of modulation and FEC. Complicated function of hub antenna,
remote antenna and satellite specifics
along with required Eb/No.
Decreases with higher order modulation. Increases with powerful FEC.
“Bandwidth Limited” links have greater
allocated than PEB.
“Power Limited” links have greater PEB
Allocated Bandwidth :
Bandwidth, Allocated Bandwidth or Occupied Bandwidth is
the frequency space required by a carrier on a transponder.
E.g. : a duplex E1 (2.048 Mbps) circuit with 8-PSK modulation,
FEC rate 3/4 and 1.4 spacing requires:
2.048 / (3 * 0.75) * 1.4 * 2 = 2.548 MHz
For a 36 MHz transponder, 2.548 MHz corresponds to 7.078%
Power Equivalent Bandwidth :
Power Equivalent Bandwidth (PEB) is the transponder power
used by a carrier, represented as bandwidth equivalent.
PEB calculation example:
•Transponder EIRP = 37 dBW
•Output Backoff (OBO) = 4 dB
•Available EIRP = 37 – 4 = 33 dBW = 10^3.3= 1995.26 Watts
•Transponder Bandwidth = 36 MHz
•Power Available / MHz = 1955.26 / 36 = 55.424 W
•If a carrier uses 24 dBW, then
PEB = Power used by your carrier/transponder saturated
PEB = 10^2.4/ 55.424 = 4.532 MHz
This corresponds to 12.59% of available transponder power.
• Antenna Gain
• Power of Amplifier
• Path Loss
• Rain Attenuation
Receiving Earth Station
• Antenna Gain
• LNA /LNB Noise Temperature
• Other Equipment
Is the effective radiated power from the
transmitting side and is the product of the
antenna gain and the transmitting power,
EIRP = Gt + Pt –Lf [dB]
Lf is the Feed Losses
Signal Power (Pr) :
Pr = EIRP – Path Loss + Gr (sat) [dB]
Path Loss = (4ΠD / λ) 2
D is the Slant Range (m)