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estimate SFO by cross-correlating S&C symbols

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This commit is contained in:
Ahmet Inan 2021-09-07 00:19:06 +02:00
commit 96ea292b0c
1 changed files with 26 additions and 2 deletions
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28
decode.cc
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@ -188,6 +188,8 @@ struct Decoder
static const int search_pos = buffer_len - 4 * (symbol_len + guard_len);
DSP::ReadPCM<value> *pcm;
DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
DSP::FastFourierTransform<symbol_len/2, cmplx, -1> fwd2;
DSP::FastFourierTransform<symbol_len/2, cmplx, 1> bwd2;
DSP::BlockDC<value, value> blockdc;
DSP::Hilbert<cmplx, filter_len> hilbert;
DSP::BipBuffer<cmplx, buffer_len> input_hist;
@ -203,6 +205,7 @@ struct Decoder
code_type code[65536];
cmplx cons[cons_max], prev[cols_max];
cmplx fdom[symbol_len], tdom[symbol_len];
cmplx head[symbol_len/2], tail[symbol_len/2];
value index[cols_max], phase[cols_max];
value cfo_rad, sfo_rad;
const uint32_t *frozen_bits;
@ -241,6 +244,19 @@ struct Decoder
fdom[(i+mls0_off/2+symbol_len/2)%(symbol_len/2)] = nrz(seq0());
return fdom;
}
int displacement()
{
for (int i = 0; i < symbol_len/2; ++i)
head[i] *= conj(tail[i]);
bwd2(tail, head);
int idx = 0;
for (int i = 0; i < symbol_len/2; ++i)
if (norm(tail[i]) > norm(tail[idx]))
idx = i;
if (idx > symbol_len/4)
idx -= symbol_len/2;
return -idx;
}
void lengthen()
{
int code_bits = 1 << code_order;
@ -463,6 +479,9 @@ struct Decoder
int cons_rows = cons_cnt / cons_cols;
int code_off = - cons_cols / 2;
// get middle half of S&C symbol for coarse SFO estimation
fwd2(head, buf + symbol_pos + symbol_len / 4);
for (int i = 0; i < symbol_pos+2*(symbol_len+guard_len); ++i)
buf = next_sample();
for (int i = 0; i < symbol_len; ++i)
@ -486,6 +505,11 @@ struct Decoder
std::cerr << ".";
}
std::cerr << " done" << std::endl;
fwd2(tail, buf + symbol_len + guard_len + symbol_len / 4);
value dis_sfo_rad = (displacement() * Const::TwoPi()) / ((cons_rows+2)*(symbol_len+guard_len));
std::cerr << "dis sfo: " << 1000000 * dis_sfo_rad / Const::TwoPi() << " ppm" << std::endl;
if (1) {
value sum_slope = 0, sum_yint = 0;
for (int j = 0; j < cons_rows; ++j) {
@ -509,8 +533,8 @@ struct Decoder
// cons[i] *= DSP::polar<value>(1, -(avg_yint+avg_slope*((i%cons_cols)+code_off)));
sfo_rad -= avg_slope * symbol_len / value(symbol_len+guard_len);
cfo_rad += avg_yint / (symbol_len+guard_len);
std::cerr << "coarse sfo: " << 1000000 * sfo_rad / Const::TwoPi() << " ppm" << std::endl;
std::cerr << "finer cfo: " << cfo_rad * (rate / Const::TwoPi()) << " Hz " << std::endl;
std::cerr << "avg sfo: " << 1000000 * sfo_rad / Const::TwoPi() << " ppm" << std::endl;
std::cerr << "avg cfo: " << cfo_rad * (rate / Const::TwoPi()) << " Hz " << std::endl;
}
value precision = 16;
if (1) {