Comtech EF Data Vipersat SLM-5650A, Installation And Operation Manual

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SLM-5650A Satellite Modem
Revision 10
Appendix H G–10 MN-SLM-5650A
G.3.2 Margin Requirements
Typical interfering signal cancellation is 28 to 35 dB (depending on the product). The residual
interfering signal appears as noise causing a slight degradation of the Eb/No. To compensate for
the residual noise, a small amount of additional link margin is required to maintain the BER.
Margin requirements depend on the product, modulation and power ratios:
For the SLM-5650A, the additional margin requirements are as follows:
Modulation Nominal Margin*
* Equal power and equal symbol rate for the
interfering carrier and the desired carrier, i.e., 0 dB
PSD ratio. Measured at IF with AWGN, +10 dBc
Adjacent Carriers, 1.3 spacing.
BPSK 0.3 dB
QPSK/OQPSK 0.3 dB
8-PSK 0.5 dB
8-QAM 0.4 dB
16-QAM 0.6 dB
G.3.3 Carrier-in-Carrier Latency
Carrier-in-Carrier has no measurable impact on circuit latency.
G.3.4 Carrier-in-Carrier Link Design
Carrier-in-Carrier link design involves finding the FEC and modulation combination that provides
optimal bandwidth utilization. Just like conventional link design, it is an iterative process that
involves trying different FEC and modulation combinations with Carrier-in-Carrier until an optimal
combination is found.
For optimal Carrier-in-Carrier performance, it is recommended that the two carriers have similar
symbol rate and power. This can be achieved by selecting appropriate MODCODs as shown in
following sections.