Comtech EF Data CDM-625 - Manual (Page 411)

CDM-625 Advanced Satellite Modem Revision 15
Adaptive Coding and Modulation (ACM) MN-CDM625
17–15
17.12 VersaFEC ACM – Summary of Specifications
System type
Adaptive Coding and Modulation, using BPSK, QPSK, 8-QAM , 16-QAM and
VersaFEC short-block LDPC coding – total of 12 ModCods
Symbol Rate Range 37-4100 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 One update every two seconds (no restriction on distance between ModCods)
Configurable parameters
• Minimum and Maximum ModCod (ModCod0 through ModCod11)
• Remote Demod Unlock Action: Maintain current ModCod
Go to minimum ModCod
• Target Eb/No margin (0-4.5 dB, 0.5 dB steps)
System latency
54 ms max. (for a system operating at 100 ksps, and assuming a WAN
buffer of 20 ms, not including satellite path)
Monitored parameters
• Tx and Rx ModCods
• Local and Remote SNR
(-3.0 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
Modulation Code Rate
Spectral Efficiency,
bps/Hz
Typical
Eb/No, for
BER = 5 x 10 -8
Min. Data Rate,
ACM mode
Max. Data Rate,
ACM mode
BPSK 0.488 0.49 2.4 dB 18.1 kbps 2.00 Mbps
QPSK 0.533 1.07 2.2 dB 39.6 kbps 4.38 Mbps
QPSK 0.631 1.26 2.7 dB 46.7 kbps 5.16 Mbps
QPSK 0.706 1.41 3.4 dB 52.2 kbps 5.78 Mbps
QPSK 0.803 1.61 3.8 dB 59.6 kbps 6.60 Mbps
8-QAM 0.642 1.93 4.6 dB 71.5 kbps 7.91 Mbps
8-QAM 0.711 2.13 5.2 dB 78.8 kbps 8.73 Mbps
8-QAM 0.780 2.34 5.6 dB 86.6 kbps 9.59 Mbps
16-QAM 0.731 2.93 6.3 dB 108.5 kbps 12.01 Mbps
16-QAM 0.780 3.12 7.0 dB 115.5 kbps 12.79 Mbps
16-QAM 0.829 3.32 7.5 dB 122.8 kbps 13.61 Mbps
16-QAM 0.853 3.41 8.0 dB 126.2 kbps 14.00 Mbps