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use a horizontally modulated simplex code for the preamble

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This commit is contained in:
Ahmet Inan 2023-05-11 13:06:45 +02:00
commit 0698e22d57
2 changed files with 18 additions and 26 deletions
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29
decode.cc
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@ -27,7 +27,7 @@ namespace DSP { using std::abs; using std::min; using std::cos; using std::sin;
#include "mls.hh"
#include "crc.hh"
#include "psk.hh"
#include "hadamard_decoder.hh"
#include "simplex_decoder.hh"
#include "polar_tables.hh"
#include "polar_helper.hh"
#include "polar_encoder.hh"
@ -171,7 +171,7 @@ struct Decoder
static const int code_order = 12;
static const int mod_bits = 2;
static const int code_len = 1 << code_order;
static const int meta_len = 128;
static const int meta_len = 63;
static const int symbol_len = 256;
static const int filter_len = 33;
static const int guard_len = symbol_len / 8;
@ -190,7 +190,7 @@ struct Decoder
DSP::BipBuffer<cmplx, buffer_len> input_hist;
SchmidlCox<value, cmplx, search_pos, symbol_len, guard_len> correlator;
CODE::CRC<uint32_t> crc;
CODE::HadamardDecoder<8> hadamard;
CODE::SimplexDecoder<6> simplex;
CODE::PolarEncoder<mesg_type> polarenc;
CODE::PolarListDecoder<mesg_type, code_order> polardec;
CODE::ReverseFisherYatesShuffle<code_len> shuffle;
@ -275,16 +275,9 @@ struct Decoder
std::cerr << "symbol pos: " << symbol_pos << std::endl;
std::cerr << "coarse cfo: " << cfo_rad * (sample_rate / Const::TwoPi()) << " Hz " << std::endl;
osc.omega(-cfo_rad);
for (int i = 0; i < symbol_pos; ++i)
buf = next_sample();
for (int i = 0; i < symbol_len; ++i)
tdom[i] = buf[i] * osc();
for (int i = 0; i < guard_len; ++i)
osc();
fwd(fdom, tdom);
for (int i = 0; i < subcarrier_count; ++i)
prev[i] = fdom[bin(i)];
next_sample();
osc.omega(-cfo_rad);
for (int i = 0; i < symbol_len+guard_len; ++i)
buf = next_sample();
for (int i = 0; i < symbol_len; ++i)
@ -292,16 +285,16 @@ struct Decoder
for (int i = 0; i < guard_len; ++i)
osc();
fwd(fdom, tdom);
for (int i = 0; i < subcarrier_count; ++i)
cons[i] = demod_or_erase(fdom[bin(i)], prev[i]);
for (int i = 0; i < meta_len; ++i)
cons[i] = demod_or_erase(fdom[bin(i+1)], fdom[bin(i)]);
for (int i = 0; i < subcarrier_count; ++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);
for (int i = 0; i < meta_len; ++i)
code[i] = DSP::clamp<value>(16 * cons[i].real(), -127, 127);
CODE::MLS seq(0b1000011);
for (int i = 0; i < meta_len; ++i)
code[i] *= nrz(seq());
int oper_mode = hadamard(code);
int oper_mode = simplex(code);
if (oper_mode != 1) {
std::cerr << "operation mode " << oper_mode << " unsupported." << std::endl;
continue;