Comtech EF Data DMD-2050E - Manual (Page 91)

DMD2050E Universal Satellite Modem Theory of Operation
MN-DMD2050E Revision 2 3–49
3.11.14 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.
3.11.15 Glossary
Allocated Bandwidth
Bandwidth or Allocated Bandwidth or Occupied Bandwidth is the frequency space required by a
carrier on a transponder.
For example, a Duplex E1 (2.048 Mbps) Circuit with 8-PSK Modulation, FEC Rate 3/4 and 1.4
Spacing requires:
2.548 MHz = 2.048 / (3 * 0.75) * 1.4 * 2
For a 36 MHz transponder, 2.548 MHz corresponds to 7.078% Bandwidth Utilization.
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 = 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.