I need to use approximate LLR algorithm for 16APSK demodulation. For that, I need to calculate noise variance which is given as

$Noise\;variance = \frac {Signal\;power\;\times\;Symbol\;time}{Sample\;time\;\times\;10^{\frac{Es/No}{10}}}$

I have the following informations SNR = 10, Signal Power = unity. Number of bits/symbol = 4, Code rate = 8/9

How can I know symbol time and sample time values? If I have to assume, what are the typical assumptions? And if Es/No = SNR? or it is dependent on symbol time and sample time? So far I have assumed Symbol time = Sample time. Though I can understand symbol time, I am unable to comprehend the meaning of sample time in this context.


1 Answer 1


This is to take into account the oversampling operation.

Symbol time = sample time implies no oversampling.

See AWGN model for more details about the conversion among EbN0, EsN0 and SNR.

For example, if a complex baseband signal is oversampled by a factor of 4, then EsNo exceeds the corresponding SNR by $10\log_{10}(4)$.


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