Table 8-1. Spectral Efficiency Using Doubletalk Carrier-In-Carrier - Comtech EF Data CDM-750 Installation And Operation Manual

CDM-750 High Speed Trunking Modem
DoubleTalk Carrier-in-Carrier Option
for example, if the delay is known to be around 240ms, set the minimum search delay to 230ms
and the maximum search delay to 250ms.
As advances in modem technologies – including advanced modulation and FEC techniques –
approach their theoretical limits of power and bandwidth efficiencies, CnC allows satellite users to
achieve spectral efficiencies (bps/Hz) that cannot be achieved with modulation and FEC alone.
Table 8-1 illustrates how QPSK, when used with CnC, approaches the bandwidth efficiency of
16APSK.

Table 8-1. Spectral Efficiency using DoubleTalk Carrier-in-Carrier

As shown here, CnC allows equivalent spectral efficiency using a lower order modulation and/or
FEC Code Rate; CAPEX is therefore reduced by allowing the use of a smaller BUC/HPA and/or
antenna. And, as CnC can be used to save transponder bandwidth and/or transponder power, it
can be successfully deployed in bandwidth-limited as well as power-limited scenarios.
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