Comtech EF Data CDM-Qx Dokumentacja Pobierz pdf (Strona 188)

CDM-Qx/QxL Multi-Channel Satellite Modem with DoubleTalk™ Carrier-in-Carrier® Revision 7

DoubleTalk™ Carrier-in-Carrier® (CnC) MN/CDMQX.IOM

9–2

9.3 System Functionality

Figure 9-1 illustrates a conventional FDMA system, where two carriers are placed in non-

overlapping channels.

Figure 9-2 shows the same link using the CDM-Qx/QxL equipped with the DoubleTalk

Carrier-

in-Carrier option. Note that now only 50% of the bandwidth is being used, as now both carriers

are occupying the same bandwidth.

The transponder downlinks the composite signal containing both carriers on the same band to the

CDM-Qx/QxL, which then translates the signal to near baseband where it can be filtered

(decimated) and then processed as a complex envelope signal. The CDM-Qx/QxL then

suppresses the version of the near end carrier on the downlink side and then passes the desired

carrier to the demodulator for normal processing.

Figure 9-1. Traditional FDMA System (without CnC)

Figure 9-2. Same System Using CDM-Qx/QxL and DoubleTalk

Carrier-in-Carrier

It is recommended that the user start with the traditional FDMA configuration as shown in Figure

9-1. Th

is allows the user to establish the links, make sure the modems and RF equipment are all

functioning correctly, and that a reasonable Eb/No has been set in each direction for the modulation

and code rate selected.

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Comtech EF Data CDM-Qx Dokumentacja Strona 188