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CDM-625A Advanced Satellite Modem
Introduction
1.4.8
VersaFEC Adaptive Coding and Modulation (ACM)
1.4.8.1
VersaFEC ACM
System type
Symbol Rate Range
Interface
Remote SNR reporting
Max span of data rate
Switch point
(decreasing SNR)
Switch point hysteresis
Max fading rate
Max ModCod update rate
Configurable parameters
System latency
Monitored parameters
ModCod
Modulation
00
BPSK
01
QPSK
02
QPSK
03
QPSK
04
QPSK
05
8-QAM
06
8-QAM
07
8-QAM
08
16-QAM
09
16-QAM
10
16-QAM
11
16-QAM
Adaptive Coding and Modulation, using BPSK, QPSK, 8-QAM , 16-QAM and
VersaFEC short-block LDPC coding – a total of 12 ModCods
37 ksps to 4100 ksps
10/100 Base T Ethernet, with auto-negotiated Congestion Control
Automatically reported from remote modem – built in function at the physical
layer – requires no additional overhead
7:1 over range of adaptation
Corresponds to SNR (Eb/No) that gives BER = 5 x 10
0.3 dB
Approximately 1 dB/second (higher if Target Eb/No margin > 1 dB)
1 update every 2 seconds
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)
54 milliseconds maximum (for a system operating at 100 ksps, and assuming a WAN
buffer of 20 milliseconds, not including satellite path)
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
Spectral
Code Rate
efficiency,
bps/Hz
0.488
0.49
0.533
1.07
0.631
1.26
0.706
1.41
0.803
1.61
0.642
1.93
0.711
2.13
0.780
2.34
0.731
2.93
0.780
3.12
0.829
3.32
0.853
3.41
1–30
-8
Typical
Min. Data
Eb/No, for
Rate,
BER = 5 x 10
ACM Mode
-8
(dB)
(kbps)
2.4
18.1
2.2
39.6
2.7
46.7
3.4
52.2
3.8
59.6
4.6
71.5
5.2
78.8
5.6
86.6
6.5
108.5
7.1
115.5
7.7
122.8
8.1
126.2
MN-CDM625A
Revision 4
Max. Data
Rate,
ACM Mode
(Mbps)
2.00
4.38
5.16
5.78
6.60
7.91
8.73
9.59
12.01
12.79
13.61
14.00
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