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estimate SNR using hard decision

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This commit is contained in:
Ahmet Inan 2021-06-10 21:06:53 +02:00
commit 7e362ae224
1 changed files with 26 additions and 1 deletions
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27
decode.cc
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@ -13,6 +13,7 @@ namespace DSP { using std::abs; using std::min; using std::cos; using std::sin;
#include "resampler.hh"
#include "trigger.hh"
#include "complex.hh"
#include "decibel.hh"
#include "blockdc.hh"
#include "hilbert.hh"
#include "phasor.hh"
@ -337,7 +338,31 @@ struct Decoder
tdom[i] = resam[i] * osc();
value precision = 16;
if (1) {
cmplx *cur = tdom + symbol_pos - (code_rows + 1) * (symbol_len + guard_len);
fwd(fdom, cur);
value sp = 0, np = 0;
for (int j = 0; j < code_rows; ++j) {
for (int i = 0; i < code_cols; ++i)
head[bin(i+code_off)] = fdom[bin(i+code_off)];
fwd(fdom, cur += symbol_len+guard_len);
for (int i = 0; i < code_cols; ++i) {
int8_t tmp[Mod::BITS];
cmplx symbol = fdom[bin(i+code_off)] / head[bin(i+code_off)];
Mod::hard(tmp, symbol);
cmplx hard = Mod::map(tmp);
cmplx error = symbol - hard;
sp += norm(hard);
np += norm(error);
}
}
value snr = DSP::decibel(sp / np);
std::cerr << "Es / N0: " << snr << " dB" << std::endl;
// $LLR=log(\frac{p(x=+1|y)}{p(x=-1|y)})$
// $p(x|\mu,\sigma)=\frac{1}{\sqrt{2\pi}\sigma}}e^{-\frac{(x-\mu)^2}{2\sigma^2}}$
value sigma = std::sqrt(np / (2 * sp));
precision = 1 / (sigma * sigma);
}
cmplx *cur = tdom + symbol_pos - (code_rows + 1) * (symbol_len + guard_len);
fwd(fdom, cur);
for (int j = 0; j < code_rows; ++j) {