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center subcarriers at DC for decoding

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This commit is contained in:
Ahmet Inan 2023-03-08 08:24:47 +01:00
commit c844a3a181
1 changed files with 12 additions and 8 deletions
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20
decode.cc
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@ -178,7 +178,7 @@ struct Decoder
static const int mesg_bits = data_bits + 32;
static const int subcarrier_count = 64;
static const int payload_symbols = 32;
static const int first_subcarrier = 16;
static const int first_subcarrier = -subcarrier_count / 2;
static const int cons_total = payload_symbols * subcarrier_count;
static const int buffer_len = 2 * symbol_len + guard_len;
static const int search_pos = symbol_len;
@ -200,6 +200,10 @@ struct Decoder
const uint32_t *frozen_bits;
int symbol_pos;
static int bin(int carrier)
{
return (carrier + first_subcarrier + symbol_len) % symbol_len;
}
static int nrz(bool bit)
{
return 1 - 2 * bit;
@ -218,8 +222,8 @@ struct Decoder
CODE::MLS seq(0b1100111);
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
for (int i = first_subcarrier + 1; i < first_subcarrier + subcarrier_count; ++i)
fdom[i] = nrz(seq());
for (int i = 1; i < subcarrier_count; ++i)
fdom[bin(i)] = nrz(seq());
return fdom;
}
void systematic()
@ -278,7 +282,7 @@ struct Decoder
osc();
fwd(fdom, tdom);
for (int i = 0; i < subcarrier_count; ++i)
prev[i] = fdom[first_subcarrier+i];
prev[i] = fdom[bin(i)];
for (int i = 0; i < symbol_len+guard_len; ++i)
buf = next_sample();
for (int i = 0; i < symbol_len; ++i)
@ -287,9 +291,9 @@ struct Decoder
osc();
fwd(fdom, tdom);
for (int i = 0; i < subcarrier_count; ++i)
cons[i] = demod_or_erase(fdom[first_subcarrier+i], prev[i]);
cons[i] = demod_or_erase(fdom[bin(i)], prev[i]);
for (int i = 0; i < subcarrier_count; ++i)
prev[i] = fdom[first_subcarrier+i];
prev[i] = fdom[bin(i)];
for (int i = 0; i < subcarrier_count; ++i)
mod_soft(code+mod_bits*i, cons[i], 8);
CODE::MLS seq(0b10000011);
@ -317,9 +321,9 @@ struct Decoder
osc();
fwd(fdom, tdom);
for (int i = 0; i < subcarrier_count; ++i)
cons[subcarrier_count*j+i] = demod_or_erase(fdom[first_subcarrier+i], prev[i]);
cons[subcarrier_count*j+i] = demod_or_erase(fdom[bin(i)], prev[i]);
for (int i = 0; i < subcarrier_count; ++i)
prev[i] = fdom[first_subcarrier+i];
prev[i] = fdom[bin(i)];
std::cerr << ".";
}
std::cerr << " done" << std::endl;