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Aug 26th, 2013 at 1:24pm
Assume 27.5 Msps (mega symbols per second) for typical large outlink download carrier.
If BPSK modulation then 1 bit/symbol ( 27.5 Mbit/s)
If QPSK modulation then 2 bit/symbol ( 55 Mbit/s)
If 8PSK modulation then 3 bit/symbol ( 82.5 Mbit/s)
If 16QAM modulation then 4 bit/symbol ( 110 Mbit/s)
Above bits are transmission rate bits.
If using 7/8 FEC the information rate is less, by factor of 7/8
Information rate is what matters to the end user, less overheads due to IP headers etc.
What is information rate for 27.5 Msps, 8PSK, 3/4 rate FEC ?
Higher order modulation a need higher C/N
7/8 FEC has less effect than 1/2 FEC
In heavy rain or small dish use BPSK and 1/2 rate FEC
In clear sky, very big dish, use 16QAM, 7/8 FEC
Hope that helps
Best regards, Eric
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