Comtech EF Data CDM-570A - Manual (Page 524)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix G Revision 2
G–6
Figure G-3. Same Link Using CDM-570A with DoubleTalk Carrier-in-Carrier
Figure G-4. Duplex Link Optimization
The CDM-570A/AL CnC module operates on the near-zero signal before the demodulator, and is
waveform agnostic. This means that no prior knowledge of the underlying modulation, FEC, or
any other waveform specific parameter is required in order to perform the signal suppression
operation. The only caveat to this is that the waveform must be sufficiently random.
Because acquiring the delay and frequency offset of the interfering carrier is fundamentally a
correlation operation, anything deterministic in the interfering carrier (within the correlation
window of the algorithm) will potentially produce false correlation peaks and result in incorrect
delays and/or frequency. Normally, this is not a problem, since energy dispersal techniques are
utilized in the vast majority of commercial and military modems. However, it is something that
must be kept in mind when troubleshooting a system that utilizes the DoubleTalk Carrier-in-
Carrier technique for signal suppression.