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Difference Between kbps and ksps

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Ex Member
Ex Member

Aug 26th, 2013 at 12:21pm  
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

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« Last Edit: Nov 27th, 2013 at 12:58pm by Admin1 »  
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Ex Member
Ex Member

Reply #1 - Aug 26th, 2013 at 12:39pm  
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Eric Johnston
Senior Member

Posts: 2109
Reply #2 - 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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« Last Edit: Aug 30th, 2013 at 6:51am by Admin1 »  
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