Comtech EF Data CDM-425, Installation And Operation Manual

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CDM-425 Advanced Satellite Modem
Revision 0
Appendix F F–1 MN-CDM-425
Appendix F. DOUBLE TALK
CARRIER-IN-CARRIER (CnC)
OPTION
WARNING! BEFORE ATTEMPTING TO COMMISSION A SATELLITE LINK USING
CARRIER-IN-CARRIER, YOU MUST ENSURE THAT THE LINK IS ROBUST
ENOUGH FOR NORMAL OPERATION. ONLY WHEN THIS HAS BEEN DONE – AND
ALL SYSTEM ISSUES (E.G., ANTENNA-POINTING, CABLING, TERRESTRIAL
INTERFERENCE, SATELLITE INTERFERENCE, ETC.) HAVE BEEN RESOLVED –
SHOULD YOU ATTEMPT THE USE OF CARRIER-IN-CARRIER.
F.1 Overview
Space segment costs are typically the most significant operating expense for any satellite-based
service, having a direct impact on the viability and profitability of the service. For a satellite
transponder that has finite resources in terms of bandwidth and power, the leasing costs are
determined by bandwidth and power used. Therefore, a satellite circuit should be designed for
optimal utilization to use a similar share of transponder bandwidth and power.
The traditional approach to balancing a satellite circuit – once the satellite and earth station
parameters are fixed – involves trade-off between modulation and coding. A lower order
modulation requires less transponder power while using more bandwidth; conversely, higher
order modulation reduces required bandwidth, albeit at a significant increase in power.
Comtech EF Data has added a new dimension to satellite communication optimization:
DoubleTalk Carrier-in-Carrier.
F.1.1 What is DoubleTalk Carrier-in-Carrier?
The CDM-425 Advanced Satellite Modem’s DoubleTalk Carrier-in-Carrier (CnC) option uses a
patented signal processing algorithm developed by Raytheon Applied Signal Technology that
allows both the forward and reverse carriers of a full duplex link to share the same segment of
transponder bandwidth, using patented “Adaptive Cancellation.” Raytheon Applied Signal