Comtech EF Data CDM-625 - Manual (Page 359)

CDM-625 Advanced Satellite Modem Revision 15
DoubleTalk Carrier-in-Carrier Option MN-CDM625
10–29
10.8 Carrier-in-Carrier Summary
Comtech EF Data’s DoubleTalk Carrier-in-Carrier can provide significant savings in operational
expenses. The following should be considered when evaluating DoubleTalk Carrier-in-Carrier:
• DoubleTalk Carrier-in-Carrier can only be used for full duplex links where the transmitting
earth station is able to receive itself.
• DoubleTalk Carrier-in-Carrier can be used in both bandwidth limited and power limited
situations.
• The maximum savings is generally achieved when the original link is symmetric in data rate.
10.9 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 3.3 = 1995.26 Watts
• Transponder Bandwidth = 36 MHz