[linux-dvb] symbol rate and signal level

Andy Walls awalls at radix.net
Wed Jun 11 13:03:28 CEST 2008


On Tue, 2008-06-10 at 23:24 -0700, alireza ghahremanian wrote:
> Dear friends 
> 
> What is the relation between symbol rate and signal level, why when decrease the symbol rate the signal level increase ?
> 

S/N = Es/No * Rs/B

S = Received signal power (Watts)
N = Noise power (Watts)

Es = Average energy per symbol (Joules/symbol)
No = Noise density (Watts/Hz)

Rs = Symbol rate (Symbols/second)
B  = Bandwidth (Hz)


For a particular BER, the receiver will require a certain Es/No.  If S
goes down, then Rs must go down (or B must go up) as well to maintain
the same Es/No and hence the same BER.


So in the case of lowering Rs and holding S/N the same, you are
operating at a higher Es/No which means a lower BER.


-Andy




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