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estimate SNR using corrected symbols

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Ahmet Inan 2021-06-11 08:38:17 +02:00
commit 30f39ce41b
1 changed files with 27 additions and 1 deletions
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28
decode.cc
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@ -357,7 +357,7 @@ struct Decoder
}
}
value snr = DSP::decibel(sp / np);
std::cerr << "Es / N0: " << snr << " dB" << std::endl;
std::cerr << "init 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));
@ -375,6 +375,32 @@ struct Decoder
int count = ldpcdec(code, code+data_bits+32+12*16);
if (count < 0)
std::cerr << "payload LDPC decoding did not converge." << std::endl;
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];
for (int k = 0; k < Mod::BITS; ++k)
tmp[k] = 1 - 2 * (code[Mod::BITS*(code_cols*j+i)+k] < 0);
cmplx symbol = fdom[bin(i+code_off)] / head[bin(i+code_off)];
cmplx hard = Mod::map(tmp);
cmplx error = symbol - hard;
sp += norm(hard);
np += norm(error);
}
}
value snr = DSP::decibel(sp / np);
std::cerr << "corr 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);
}
for (int i = 0; i < data_bits+32+12*16; ++i)
CODE::set_le_bit(out, i, code[i] < 0);
int ret = bchdec1(out, out+(data_bits+32)/8, 0, 0, data_bits+32);