Glossary - Comtech EF Data SLM-5650A Installation And Operation Manual

SLM5650A_CDM625 Satellite Modem
DoubleTalk Carrier-in-Carrier Option

15.8 Glossary

Bandwidth, Allocated or Occupied
Bandwidth or Allocated Bandwidth or Occupied Bandwidth is the frequency space required by a
carrier on a transponder.
For example: A Duplex 10 Mbps Circuit with 8PSK Modulation, FEC Rate 3/4 and 1.4 Spacing
requires:
• Allocated BW = (DR / SE) * CSF [(Data Rate / Spectral Efficiency) * Carrier Spacing
Factor]
• Allocated BW = 6.222 MHz = (10 / 2.25) * 1.4
For a 36 MHz transponder, 6.222 MHz corresponds to 17.3% Bandwidth Utilization.
Bandwidth, Leased (LBW)
Almost all satellite operators charge for the Leased Bandwidth (LBW). Leased Bandwidth or
Leased Resource is the greater of the Allocated Bandwidth and Power Equivalent Bandwidth.
For example: If a carrier requires 3 MHz of Allocated BW and 4.5 MHz of PEB, the Leased
Bandwidth is 4.5 MHz
Bandwidth, Power Equivalent (PEB)
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
• Transponder Bandwidth = 36 MHz
• Power Available / MHz = 1995.26 / 36 = 55.424 W
• If a carrier uses 24 dBW, its PEB = 10
This corresponds to 12.59% of available transponder power.
CnC Ratio
Ratio of Interfering Carrier Power to Desired Carrier Power (unit in dB).
The Interfering Carrier is the Tx Carrier from local modulator; the Desired Carrier is the carrier
from the distant end received by the local demodulator.
At the station transmitting C1: CnC Ratio (in dB) = PowerC1 (in dBm) – PowerC2 (in dBm)
3.3
= 1995.26 Watts
2.4
/ 55.424 = 4.532 MHz
15–21
Revision 8
MN-SLM5650A