Comtech EF Data CDM-570 - Manual (Page 344)

CDM-570/570L Satellite Modem with Optional IP Module Revision 12
Appendix B MN/CDM570L.IOM
B–2
Example: In the above diagram, the (Co+No)/No measured is 4.6 dB. If Rate 1/2 QPSK is being
used, this would correspond to an E
b
/N
0
of approximately 2.6 dB.
The exact relationship used to derive the table values is as follows:
E
b
/N
0
= 10 log
10
(10
(Co+No/No )/10)
-1) - 10 log
10
(FEC Code Rate) - 10 log
10
(bits/symbol)
Where:
• E
b
/N
0
and (Co+No)/No are expressed in dB
• Bits/symbol = 1 for BPSK
• Bits/symbol = 2 for QPSK
• Bits/symbol = 3 for 8-PSK/8-QAM
• Bits/symbol = 4 for 16-QAM
• Code Rate for ‘uncoded’ = 1
Note: Pay close attention to the sign of the middle term