Comtech EF Data CDM-700 - Manual (Page 129)

CDM-700 High Speed Satellite Modem Revision 5
Forward Error Correction Options MN/CDM700.IOM
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
Eb/No at
BER = 10
-5
Guaranteed
(Typical in
parentheses)
Eb/No at
BER = 10
-8
Guaranteed
(Typical in
parentheses)
Spectral
Efficiency
(bps / Hz)
Symbol Rate
Occupied *
Bandwidth
for 50 Mbps
Composite
Data Rate
(25% Rolloff)
QPSK
Rate 3/4 Turbo 3.9 dB
(3.4 dB)
4.2 dB
(3.7 dB)
1.46 bps/Hz 0.68 x bit rate 39.292 MHz
QPSK
Rate 7/8 Turbo 4.4 dB
(3.9 dB)
4.6 dB
(4.1 dB)
1.70 bps/Hz 0.59 x bit rate 33.889 MHz
8-PSK
Rate 3/4 Turbo 6.7 dB
(6.2 dB)
7.0 dB
(6.5 dB)
2.20 bps/Hz 0.46 x bit rate 26.194 MHz
8-PSK
Rate 7/8 Turbo 7.3 dB
(6.8 dB)
7.6 dB
(7.1 dB)
2.55 bps/Hz 0.39 x bit rate 22.593 MHz
16-QAM
Rate 3/4 Turbo 7.7 dB
(7.2 dB)
8.0 dB
(7.5 dB)
2.93 bps/Hz 0.34 x bit rate 19.646 MHz
16-QAM
Rate 7/8 Turbo 8.3 dB
(7.8 dB)
8.5dB
(8.0 dB)
3.39 bps/Hz 0.29 x bit rate 16.945 MHz
64-QAM
Rate 3/4 Turbo 12.0 dB
(11.5 dB)
12.3 dB
(11.8 dB)
4.39 bps/Hz 0.23 x bit rate 13.097 MHz
64-QAM
Rate 7/8 Turbo 12.6 dB
(12.1 dB)
12.9 dB
(12.4 dB)
5.09 bps/Hz 0.20 x bit rate 11.296 MHz
* 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.
7–3