Comtech EF Data CDM-750 - Manual (Page 279)

CDM-750 Advanced High-Speed Trunking Modem Revision 2
Appendix D MN-CDM750
D–21
D.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 = (Data Rate) / (Spectral Efficiency) x (Carrier Spacing Factor)
Allocated BW = 6.43 MHz = (10 / 2.177/) * 1.4
For a 36 MHz transponder, 2.548 MHz corresponds to 17.9% 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 3.3
= 1955.26 Watts
• Transponder Bandwidth = 36 MHz
• Power Available / MHz = 1955.26 / 36 = 54.424 W
• If a carrier uses 24 dBW, its PEB = 10 2.4 / 54.424
= 4.532 MHz
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 and the Desired Carrier is the carrier
from the distant end received by the local demodulator.