Comtech EF Data CDM-750 - Manual (Page 259)

D–1
Appendix D. Doubletalk Carrier-in-
Carrier (CnC) OPTION
D.1 Introduction
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’s DoubleTalk
Carrier‐in‐Carrier option adds a new dimension to satellite
communication optimization.
D.1.1 What is DoubleTalk Carrier-in-Carrier?
The CDM‐750’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 Technology uses the term
DoubleTalk, and Comtech EF Data refers to it as DoubleTalk
Carrier‐in‐Carrier (CnC) 1 .
1
DoubleTalk
®
is licensed from Raytheon Applied Signal Technology.
DoubleTalk
®
is a registered trademark of Raytheon Applied Signal Technology.
Carrier‐in‐Carrier ® is a registered trademark of Comtech EF Data.
BEFORE ATTEMPTING TO COMMISSION A SATELLITE LINK USING CARRIER‐IN‐CARRIER (CnC),
THE USER
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
THE USER ATTEMPT THE USE OF CARRIER‐IN‐CARRIER.