MATLAB: Does changing the Symbol Period for an AWGN Channel Block cause the Bit Error Rate (BER) to change

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I have an AWGN Channel Block in my model and changing the Symbol Period of this block to a value greater than the minimum required causes my bit error rates to change. I expect that variations in the Symbol Period value have no effect on the real-world channel model.

Best Answer

The Symbol Period in the AWGN Channel block affects the amount of noise added per sample. Therefore, it must be in conformance with the system parameters. Changing the symbol period while keeping all other parameters of the block and model the same amounts to changing the variance of the noise added to the signal. This would thus cause a change in the final error rate.
NoiseVariance = (SignalPower * SymbolPeriod) / (SampleTime * 10^(EsNodB/10))
If SampleTime and SymbolPeriod are the same, you receive a trivial relation. Otherwise, there will be a scaling factor.
In general, a good rule of thumb for selecting the Symbol Period value is to set it to be what you model as the symbol period in the model (perhaps the data source rate if it matches). A symbol could have 3 bits and be oversampled by 4, but it depends on how it was generated. Thus, the value would depend upon what constitutes a symbol and what the oversampling applied to it is.
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