Comtech EF Data CDM-625 - Manual (Page 333)

CDM-625 Advanced Satellite Modem Revision 15
DoubleTalk Carrier-in-Carrier Option MN-CDM625
10–3
Figure 10-1. Conceptual Block Diagram
This performance is achieved through advanced signal processing algorithms that provide
superior cancellation while tracking and compensating for the following common link
impairments:
1. Time varying delay: In addition to the static delays of the electronics and the round-trip
delay associated with propagation to the satellite and back, there is a time-varying
component due to movement of the satellite. The CnC module tracks and compensates for
this variation.
2. Frequency offset and drift: Common sources are satellite Doppler shift, up and down
converter frequency uncertainties, and other drift associated with the electronics in the
CDM-625 itself. The CnC module tracks and compensates for this frequency offset and drift.
3. Atmospheric effects: Fading and scintillation can affect amplitude, phase, and spectral
composition of the signal and the degree to which it correlates with the original signal. The
CnC module tracks and compensates for these atmospheric related impairments.
4. Link Asymmetries: Various asymmetries in the forward and return link can produce
differences in the relative power of the two received signal components. These can be both
deterministic (static) or random (and time varying). An example of the former would be the