Comtech EF Data CDM-710G, Installation And Operation Manual

Page: 162 / 246

CDM-710G High-Speed Satellite Modem Revision 1
Forward Error Correction Options MN-CDM710G
11–2
11.2.1 Range of Data Rates
For a detailed Data Rate Range refer to Sect. 1.6 SUMMARY OF SPECIFICATIONS .
11.2.2 Eb/No, Es/No Spectral Efficiency and Occupied Bandwidth
Depending upon the operating mode DVB standard uses different modes of specifying
performance with a modem in IF Loop and Additive White Gaussian Noise (AWGN):
•
DVB-S2 (QPSK, 8PSK, 16APSK and 32APSK with LDPC and BCH): PER (packet
error rate) = 10-7 after LDPC and BCH at the specified Es/No. This is a theoretical value
with perfect carrier recovery and symbol synchronization, and no modem oscillator phase
noise. The manufacturer decides the implementation margin and specifies performance.
The other difference is the use of PER (packet error rate) based upon a 188 or 204 byte MPEG
frame size instead of BER (bit error rate).
Note: The CDM-710G uses only a 188 byte MPEG frame size.
Also, note the use of Es/No instead of Eb/No. When links operate at constant symbol rate so this
is good method for comparing the performance of different modulation types and code rates.
The relation between the two quantities is given by:
Eb/No = Es/No - 10xLog(Spectral Efficiency)
The tables that follow provide the spectral efficiency DVB-S2 schemes. Another useful parameter
is the occupied bandwidth is the bandwidth between -10 dB points of the power spectral density,
which are approximately:
Occupied Bandwidth = 1.19
x
Symbol Rate, for 35% Rolloff
= 1.15
x
Symbol Rate, for 25% Rolloff
= 1.12 x Symbol Rate, for 20% Rolloff
Figure 11-1 through Figure 11-4 illustrate the error performance characteristics.