Margin Requirements; Carrier-In-Carrier Latency; Carrier-In-Carrier And Adaptive Coding And Modulation; Carrier-In-Carrier Link Design - Comtech EF Data SLM-5650A Installation And Operation Manual

SLM5650A_CDM625 Satellite Modem
DoubleTalk Carrier-in-Carrier Option
Unwanted interfering signal suppression of 30 dB or more has been achieved in commercial
products with minimal degradation of the demodulator performance.
15.4.2

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
BPSK
QPSK/OQPSK
8-PSK
8-QAM
16-QAM
15.4.3

Carrier-in-Carrier Latency

Carrier-in-Carrier has no measurable impact on circuit latency.
15.4.4

Carrier-in-Carrier and Adaptive Coding and Modulation

Carrier-in-Carrier is fully compatible with the VersaFEC Adaptive Coding and Modulation
(ACM) mode of operation in the SLM-5650A.
Carrier-in-Carrier combined with VersaFEC ACM can provide 100-200% increase in average
throughput.
15.4.5

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.
Nominal Margin*
0.3 dB
* Equal power and equal symbol rate for the
0.3 dB
interfering carrier and the desired carrier, i.e., 0 dB
PSD ratio. Measured at IF with AWGN, +10 dBc
0.5 dB
Adjacent Carriers, 1.3 spacing.
0.4 dB
0.6 dB
15–9
Revision 8
MN-SLM5650A