CDM-625A Advanced Satellite Modem MN-CDM625A
Appendix F Revision 4
F–6
Figure F-3. Same Link Using CDM-625A and DoubleTalk
Carrier-in-Carrier
Figure F-4. Duplex Link Optimization
CnC 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.
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