Re: [Discuss-gnuradio] Question on Samples/Symbols (sps) in "PSK Demodulation" tutorial.

[Cinaed Simson]

Hi Ashish - the short of it is:

  (samples/sec)/(symbols/sec) = samples/symbol

If the bandwidth is complex, then samples/sec = sampling rate in MHz,
and symbols/sec is the baud rate.

There are lot of reasons why you would get into trouble by just by
changing samples/symbol.

You need to post the grc file, or the flowgraph for the problem.

-- Cinaed


On 12/27/18 9:00 AM, Ashish S wrote:
> Hello everyone, 
>  I have some confusion on samples/symbols concept in GNU Radio and it's
> driving me crazy when I start to overthink on this. 
> 
> *How I did PSK modulation during my studies was : *
>        Generate random bits, group them according to modulation type
> (here considering QPSK) and then pass it through some channel and then
> demodulate it. 
> this whole thing runs in a loop for different values of SNR and I used
> to plot BER vs SNR. Here is the quick snapshot 
> 
> image.png
> 
> 
> *Running through the PSK modulation(example provided on GNU radio
> tutorials)*
> flowgraph : mpsk_stage1.grc 
>    We have a  random source which outputs 10k samples in the range of
> [0,255] as a byte stream and constellation modulator outputs complex
> baseband signal (based on constellation object mapping provided)
> This constellation modulator has *samples/symbols *as an input which
> needs to be >=2 .
> 
> why is this >=2  and since random source repeats its 10k samples every
> period , can't it just group two  bits and map as a symbol. ? 
> When I tend to increase the SPS from 2 to 64 keeping everything the same
> , the constellation starts to mess up and the fft plot goes narrower.
> Can anyone of you give an insight into this, please ?
> 
> 
> *When SPS is 4*
> image.png
> *
> *
> *When SPS is 2*
> 
> image.png
>  
> *When SPS is 16* 
> image.png
> 
> *When SPS is 64*
> *
> *
> image.png
> 
> 
> Ashsih
> 
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