Forum: GNU Radio PSK Demodulator performance

F762b223a87f868db769f9a297fe976c?d=identicon&s=25 Mike W. (mike_w)
on 2014-05-03 09:36
(Received via mailing list)
Does anyone have any information on the performance - specifically the
implementation loss of the Gnuradio PSK demodulator block? I am trying
to
work out a link budget. Typically this would be 1dB or so from ideal.



Mike
B4ffbc711addde4c649b1ed526df6157?d=identicon&s=25 Martin Braun (Guest)
on 2014-05-03 11:27
(Received via mailing list)
On 05/03/2014 09:35 AM, Mike Willis wrote:
> Does anyone have any information on the performance  specifically the
> implementation loss of the Gnuradio PSK demodulator block? I am trying
> to work out a link budget. Typically this would be 1dB or so from ideal.

By ideal, you mean the theoretical BER values for a given Eb/N0? If so,
that would be easy to determine -- have a look at berawgn.py, replace
the slicer with the PSK demod and allow for some initialization time.

Cheers,
Martin
D17685d174fee4ca258c75cce7bc2202?d=identicon&s=25 Marcus Müller (Guest)
on 2014-05-04 06:21
(Received via mailing list)
Hi Mike!

Well, from a purely algorithmic point of view, there is no approximate
magic happening inside the PSK demapper
(from constellation.cc):
    unsigned int
    constellation_psk::get_sector(const gr_complex *sample)
    {
      float phase = arg(*sample);
      float width = M_TWOPI / n_sectors;
      int sector = floor(phase/width + 0.5);
      if(sector < 0)
        sector += n_sectors;
      return sector;
    }

This is "perfect" up to the degree that arg() works well enough, which
is
mainly a matter of float accuracy, I guess, and should therefore be well
below any significance.

The other thing is the finite-length root-raised cosine matched
filtering;
I think you can derive losses for that, but I think Martin's approach of
measuring things might be faster and more accurate in the end.

Greetings,
Marcus
B4ffbc711addde4c649b1ed526df6157?d=identicon&s=25 Martin Braun (Guest)
on 2014-05-05 13:19
(Received via mailing list)
On 03.05.2014 13:16, Marcus Mller wrote:
> Hi Mike!
>
> Well, from a purely algorithmic point of view, there is no approximate
> magic happening inside the PSK demapper

Oh, I assumed Mike was talking about the entire demod chain
(sync/eq/demap), which would have its own inherent loss. Maybe Mike can
clarify.

If I'm correct, there's the question of the correct metric, since Eb/N0
alone might not be the only factor affecting BER.

M
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