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DATV: tighter bandwidth for SNR estimation (1.5 x nominal BW)

This commit is contained in:
f4exb 2021-03-13 18:15:24 +01:00
parent e79171c728
commit 6bf797ab6d
1 changed files with 32 additions and 8 deletions
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40
plugins/channelrx/demoddatv/leansdr/sdr.h
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@ -1808,10 +1808,15 @@ struct cnr_fft : runnable
out(_out),
fft(nfft),
avgpower(nullptr),
phase(0)
phase(0),
cslots_ratio(0.2),
nslots_shift_ratio(0.65),
nslots_ratio(0.1)
{
if (bandwidth > 0.25)
fail("CNR estimator requires Fsampling > 4x Fsignal");
fprintf(stderr, "cnr_fft::cnr_fft: bw: %f FFT: %d\n", bandwidth, fft.n);
if (bandwidth > 0.25) {
fail("cnr_fft::cnr_fft: CNR estimator requires Fsampling > 4x Fsignal");
}
}
~cnr_fft()
@ -1866,21 +1871,37 @@ struct cnr_fft : runnable
for (int i = 0; i < fft.n; ++i)
avgpower[i] = avgpower[i] * (1 - kavg) + power[i] * kavg;
#if 0
int bwslots = (bandwidth / 4) * fft.n;
if (!bwslots)
if (!bwslots) {
return;
}
// Measure carrier+noise in center band
float c2plusn2 = avgslots(icf-bwslots, icf+bwslots);
// Measure noise left and right of roll-off zones
float n2 = ( avgslots(icf-bwslots*4, icf-bwslots*3) +
avgslots(icf+bwslots*3, icf+bwslots*4) ) / 2;
#else
int cbwslots = bandwidth * cslots_ratio * fft.n;
int nstart = bandwidth * nslots_shift_ratio * fft.n;
int nstop = nstart + bandwidth * nslots_ratio * fft.n;
if (!cbwslots || !nstart || !nstop)
{
delete[] power;
delete[] data;
return;
}
// Measure carrier+noise in center band
float c2plusn2 = avgslots(icf - bwslots, icf + bwslots);
float c2plusn2 = avgslots(icf - cbwslots, icf + cbwslots);
// Measure noise left and right of roll-off zones
float n2 = (avgslots(icf - bwslots * 4, icf - bwslots * 3) + avgslots(icf + bwslots * 3, icf + bwslots * 4)) / 2;
float n2 = (avgslots(icf - nstop, icf - nstart) +
avgslots(icf + nstart, icf + nstop)) / 2;
#endif
float c2 = c2plusn2 - n2;
float cnr = (c2 > 0 && n2 > 0) ? 10 * logf(c2 / n2) / logf(10) : -50;
float cnr = (c2 > 0 && n2 > 0) ? 10 * log10f(c2 / n2) : -50;
out.write(cnr);
delete[] power;
delete[] data;
@ -1901,6 +1922,9 @@ struct cnr_fft : runnable
cfft_engine<T> fft;
T *avgpower;
int phase;
float cslots_ratio;
float nslots_shift_ratio;
float nslots_ratio;
};
// cnr_fft