Table D-2. Versafec Implementation Of Acm - 100 Ksymbols/Sec Example Case - Comtec CDM-840 Installation And Operation Manual

CDM-840 Remote Router
Appendix D
VersaFEC ACM Latency
D.2.1
Examining the data in Table D-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 D-2. VersaFEC Implementation of ACM – 100 ksymbols/sec Example Case
ModCod Modulation
00
01
02
03
04
05
06
07
08 16-QAM
09 16-QAM
10 16-QAM
11 16-QAM
Figure D-1. VersaFEC Codes vs. Constrained Capacity
Code Rate
BPSK 0.488
QPSK 0.533
QPSK 0.631
QPSK 0.706
QPSK 0.803
8-QAM 0.642
8-QAM 0.711
8-QAM 0.780
0.731
0.780
0.829
0.853
OVERALL SYSTEM LATENCY = Worst-case ModCod (ModCod0)
Latency = 34 milliseconds, NOT INCLUDING WAN BUFFER OR SATELLITE PATH
Spectral efficiency,
Bit rate (throughput)
bps/Hz
0.49
1.07
1.26
1.41
1.61
1.93
2.13
2.34
2.93
3.12
3.32
3.41
D–4
MN-CDM840
Minimum Latency,
In milliseconds
49 kbps 34
107 kbps 32
126 kbps 30
141 kbps 28
161 kbps 26
193 kbps 30
213 kbps 28
234 kbps 27
293 kbps 27
312 kbps 26
332 kbps 25
341 kbps 25
Revision 3