Comtech EF Data CDM-425, Installation And Operation Manual

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CDM-425 Advanced Satellite Modem
Revision 0
Appendix F F–3 MN-CDM-425
Figure F-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. CnC 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-425 Advanced Satellite Modem itself. CnC 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.
CnC 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 differences resulting from antenna size/gain variations between the two ends of
the link. An example of the latter would be transient power differences due to different
levels of atmospheric fading in the uplinks. CnC compensates for the asymmetries, up to
a certain extent.