Comtech EF Data CDM-625A - Manual (Page 74)

CDM-625A Advanced Satellite Modem MN-CDM625A
Introduction Revision 3
1–30
1.4.8 VersaFEC Adaptive Coding and Modulation (ACM)
1.4.8.1 VersaFEC ACM
System type
Adaptive Coding and Modulation, using BPSK, QPSK, 8-QAM , 16-QAM and
VersaFEC short-block LDPC coding – a total of 12 ModCods
Symbol Rate Range 37 ksps to 4100 ksps
Interface 10/100 Base T Ethernet, with auto-negotiated Congestion Control
Remote SNR reporting
Automatically reported from remote modem – built in function at the physical
layer – requires no additional overhead
Max span of data rate 7:1 over range of adaptation
Switch point
(decreasing SNR)
Corresponds to SNR (Eb/No) that gives BER = 5 x 10 -8
Switch point hysteresis 0.3 dB
Max fading rate Approximately 1 dB/second (higher if Target Eb/No margin > 1 dB)
Max ModCod update rate 1 update every 2 seconds
Configurable parameters
Minimum and Maximum ModCod (ModCods 00-11)
Remote Demod Unlock Action: Maintain current ModCod
Go to minimum ModCod
Target Eb/No margin (0 to 4.5 dB, 0.5 dB steps)
System latency
54 milliseconds maximum (for a system operating at 100 ksps, and assuming a WAN
buffer of 20 milliseconds, not including satellite path)
Monitored parameters
Tx and Rx ModCods
Local and Remote SNR
(-3.0 dB to +22.0dB, 0.1dB resolution, +/- 0.5 dB accuracy)
Config and monitor menus displaying data rate, modulation and code rate update
dynamically with ModCod
ModCod Modulation Code Rate
Spectral
efficiency,
bps/Hz
Typical
Eb/No, for
BER = 5 x 10 -8
(dB)
Min. Data
Rate,
ACM Mode
(kbps)
Max. Data
Rate,
ACM Mode
(Mbps)
00 BPSK 0.488 0.49 2.4 18.1 2.00
01 QPSK 0.533 1.07 2.2 39.6 4.38
02 QPSK 0.631 1.26 2.7 46.7 5.16
03 QPSK 0.706 1.41 3.4 52.2 5.78
04 QPSK 0.803 1.61 3.8 59.6 6.60
05 8-QAM 0.642 1.93 4.6 71.5 7.91
06 8-QAM 0.711 2.13 5.2 78.8 8.73
07 8-QAM 0.780 2.34 5.6 86.6 9.59
08 16-QAM 0.731 2.93 6.5 108.5 12.01
09 16-QAM 0.780 3.12 7.1 115.5 12.79
10 16-QAM 0.829 3.32 7.7 122.8 13.61
11 16-QAM 0.853 3.41 8.1 126.2 14.00