CDM-570A/570AL Satellite Modem with Optional Packet Processor
Revision 5
DoubleTalk Carrier-in-Carrier Option G–10 MN-CDM570A
G.4.3 Carrier-in-Carrier Latency
Carrier-in-Carrier has no measurable impact on circuit latency.
G.4.4 Carrier-in-Carrier and Adaptive Coding and Modulation
Carrier-in-Carrier will be fully compatible with the VersaFEC Adaptive Coding and Modulation
(ACM) mode of operation that will be available in future releases of the CDM-570A/AL.
Carrier-in-Carrier combined with VersaFEC ACM can provide a 100-200% increase in average
throughput compared to to a traditional side-by-side link without ACM.
G.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.
G.4.5.1 Symmetric Data Rate Link
NOTE: CnC operation with symmetrical links requires the Symbol Rate to be offset by 0.1% or
higher on one of the links when the IP Data Interface is selected.
Consider the following example:
Satellite & Transponder IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1 Africa – 4.5 m
Earth Station 2 Africa – 3.0 m
Data Rate 1.0 Mbps / 1.0 Mbps
The traditional link was based on QPSK TPC 7/8, and required 1.6 MHz of leased bandwidth
(BW).
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