Margin Requirements; Carrier-In-Carrier Latency; Carrier-In-Carrier And Adaptive Coding And Modulation; Carrier-In-Carrier Link Design - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem

3.14.6 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 Radyne DMD50, the additional margin requirements are as follows:
Modulation
BPSK
QPSK/OQPSK
8-PSK
8-QAM
16-QAM

3.14.7 Carrier-in-Carrier Latency

Carrier-in-Carrier has no measurable impact on circuit latency.

3.14.8 Carrier-in-Carrier and Adaptive Coding and Modulation

Carrier-in-Carrier is fully compatible with VersaFEC Adaptive Coding and Modulation (ACM)
mode of operation in the Radyne DMD50.
Carrier-in-Carrier combined with VersaFEC ACM can provide 100 – 200% increase in average
throughput.

3.14.9 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.
MN-DMD50– Revision 3
Nominal Margin*
* Equal power and equal symbol rate
for the interfering carrier and the
0.3 dB
desired carrier, i.e., 0 dB PSD ratio.
0.3 dB
Measured at IF with AWGN, +10 dBc
0.5 dB
Adjacent Carriers, 1.3 spacing.
0.4 dB
0.6 dB
Theory of Operation
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