Comtech EF Data SLM-5650A - Manual (Page 299)

15–1
Chapter 15. DoubleTalk
Carrier-in-Carrier OPTION
Before attempting to commission a satellite link using Carrier-in-Carrier, 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.
15.1 Introduction
Space segment costs are typically the most significant operating expense for any satellite-based
service. Such costs have 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. A satellite circuit should therefore be designed for
optimal utilization to use a similar share of transponder bandwidth and power.
The traditional approach towards 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 serves to resolve this issue.
15.2 What is DoubleTalk Carrier-in-Carrier?
The SLM-5650A’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 and is a registered trademark of Raytheon Applied Signal
Technology. Carrier-in-Carrier is a registered trademark of Comtech EF Data.