Comtech EF Data CDD-880, Installation And Operation Manual

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CDD-880 Multi Receiver
Router
MN-CDD880
Appendix H Revision 2
H–4
Figure H-1. VersaFEC Codes vs. Constrained Capacity
H.3.1
VersaFEC ACM Latency
Examining the data in Table H-2 , latency for each MODCOD is shown for the example of
VersaFEC ACM at a fixed 100 ksymbols/second rate. Of particular note is that even though the
MODCODs span a 7:1 variation in throughput, the latency is only varying between 25 and 34
milliseconds. In the example shown the worst-case latency for this ACM scheme is 34
milliseconds.
Table H-2. Example Case – VersaFEC Implementation of ACM (100 ksymbols/sec)
Modulation
(MODCOD No.)
Code Rate
Spectral Efficiency
(bps/Hz)
Bit Rate (Throughput)
(in kbps)
Minimum Latency
(in milliseconds)
BPSK (00) 0.488 0.49 49 34
QPSK (01) 0.533 1.07 107 32
QPSK (02) 0.631 1.26 126 30
QPSK (03) 0.706 1.41 141 28
QPSK (04) 0.803 1.61 161 26
8-QAM (05) 0.642 1.93 193 30
8-QAM (06) 0.711 2.13 213 28
8-QAM (07) 0.780 2.34 234 27
16-QAM (08) 0.731 2.93 293 27
16-QAM (09) 0.780 3.12 312 26
16-QAM (10) 0.829 3.32 332 25
16-QAM (11) 0.853 3.41 341 25
OVERALL SYSTEM LATENCY = Worst-case MODCOD (MODCOD 00)
Latency = 34 milliseconds, NOT INCLUDING WAN BUFFER OR SATELLITE PATH