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CDM-700 High Speed Satellite Modem
Forward Error Correction Options
Table 7-1 provides the Eb/No, spectral efficiency and occupied bandwidth for the CDM-700
70/140 MHz; L-Band CDM700 will satisfy the 100 MHz composite data rate column.
Table 7-1. Eb/No, Spectral Efficiency and Occupied Bandwidth
Mode
QPSK
Rate 3/4 Turbo
QPSK
Rate 7/8 Turbo
8-PSK
Rate 3/4 Turbo
8-PSK
Rate 7/8 Turbo
16-QAM
Rate 3/4 Turbo
16-QAM
Rate 7/8 Turbo
64-QAM
Rate 3/4 Turbo
64-QAM
Rate 7/8 Turbo
* The occupied bandwidth is defined at the width of the transmitted spectrum taken at the -10 dB
points on the plot of power spectral density. This equates to 1.15 x symbol rate for the CDM-700
transmit filtering.
7.3
End-to-End Processing Delay (Latency)
In many cases, FEC methods that provide increased coding gain do so at the expense of increased
processing delay. However, with TPC this increase in delay is very modest. Also, the effects of
delay are more problematic at low data rates, and generally negligible at higher data rates.
Delay for the Gigabit Ethernet and HSSI interface are shown in Figure 7-1 and Figure 7-2 with
the Rx Buffer (HSSI) at minimum. In packet networks, minimum Rx Buffer is the normal setting.
Expected performance for the G.703 interface is similar to HSSI.
Eb/No at
Eb/No at
-5
BER = 10
BER = 10
Guaranteed
Guaranteed
(Typical in
(Typical in
parentheses)
parentheses)
3.9 dB
4.2 dB
(3.4 dB)
(3.7 dB)
4.4 dB
4.6 dB
(3.9 dB)
(4.1 dB)
6.7 dB
7.0 dB
(6.2 dB)
(6.5 dB)
7.3 dB
7.6 dB
(6.8 dB)
(7.1 dB)
7.7 dB
8.0 dB
(7.2 dB)
(7.5 dB)
8.3 dB
8.5dB
(7.8 dB)
(8.0 dB)
12.0 dB
12.3 dB
(11.5 dB)
(11.8 dB)
12.6 dB
12.9 dB
(12.1 dB)
(12.4 dB)
-8
Spectral
Efficiency
(bps / Hz)
1.46 bps/Hz
1.70 bps/Hz
2.20 bps/Hz
2.55 bps/Hz
2.93 bps/Hz
3.39 bps/Hz
4.39 bps/Hz
5.09 bps/Hz
7–3
Revision 5
MN/CDM700.IOM
Occupied *
Bandwidth
for 50 Mbps
Symbol Rate
Composite
Data Rate
(25% Rolloff)
0.68 x bit rate
39.292 MHz
0.59 x bit rate
33.889 MHz
0.46 x bit rate
26.194 MHz
0.39 x bit rate
22.593 MHz
0.34 x bit rate
19.646 MHz
0.29 x bit rate
16.945 MHz
0.23 x bit rate
13.097 MHz
0.20 x bit rate
11.296 MHz
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