Difference Between kbps and ksps

What is the difference between bits per second and symbols per second? Can anyone explain how these terms are used for defining data rate of VSAT terminal.

Thanks & Regards
Martin

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