Appendix J Revision 4
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
J–6
Table J-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.
J.4.1 DoubleTalk Carrier-in-Carrier Cancellation Process
The state-of-the-art signal processing technology employed via CnC continually estimates and
tracks all parametric differences between the local uplink signal and its image within the
downlink. Through advanced adaptive filtering and phase locked loop implementations, it
dynamically compensates for these differences by appropriately adjusting the delay, frequency,
phase and amplitude of the sampled uplink signal, resulting in excellent cancellation
performance.
When a conventional full duplex satellite connection is established between two sites, separate
satellite channels are allocated for each direction. If both directions transmitted on the same
channel, each side would normally find it impossible to extract the desired signal from the
aggregate due to interference originating from its local modulator. However since this
interference is produced locally, it is possible to estimate and remove its influence prior to
demodulation of the data transmitted from the remote location.
For the CnC cancellation, it is necessary to provide each demodulator with a copy of its local
modulator’s output.
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