What Is Doubletalk Carrier-In-Carrier; Application Requirements - Comtech EF Data DMD-2050E Installation And Operation Manual

DMD2050E Universal Satellite Modem
3.11.1

What is DoubleTalk Carrier-in-Carrier?

The DMD2050E DoubleTalk Carrier-in-Carrier option utilizes 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).
CnC was first introduced in Comtech EF Data products in the CDM-Qx Satellite Modem and,
more recently, in the CLO-10 Link Optimizer.
The implementation of DoubleTalk Carrier-in-Carrier in the DMD2050E has been further refined,
and some of the limitations that existed in the CDM-Qx implementation have been overcome.
This innovative technology provides a significant improvement in bandwidth and power utilization,
beyond what is possible with FEC and modulation alone, allowing users to achieve
unprecedented savings. When combined with advanced modulation and FEC, it allows for multi-
dimensional optimization:
Reduced operating expense (OPEX) – e.g., Occupied Bandwidth & Transponder Power;
Reduced capital expenditure (CAPEX) – e.g., Block Up Converter/High-Power Amplifier
(BUC/HPA) size and/or antenna size;
Increased throughput without using additional transponder resources;
Increased link availability (margin) without using additional transponder resources;
A combination of any of the above to meet different objectives.
: When carriers share common bandwidth, up to 50% savings in transponder utilization
Summary
is possible.
3.11.2

Application Requirements

The following conditions are necessary in order to operate DoubleTalk Carrier-in-Carrier:
Link must be full duplex.
A DMD2050E must be used at the end of the link where the cancellation needs to take
place.
The transponder is operated as Loopback. That is, each end of the link must be able to see a
copy of its own signal in the return (downlink) path from the satellite. The looped back signal
is then subtracted which leaves the signal from the distant end of the link. DoubleTalk
Carrier-in-Carrier cannot be used in spot beam systems.
MN-DMD2050E Revision 2
Theory of Operation
3–27