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aicodix___modem/decode.cc
Ahmet Inan c0fedcbc57 added support for QAM4096
2025-07-18 12:52:01 +02:00

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/*
OFDM modem decoder
Copyright 2021 Ahmet Inan <inan@aicodix.de>
*/
#include <iomanip>
#include <iostream>
#include <cstdint>
#include <cassert>
#include <cmath>
namespace DSP { using std::abs; using std::min; using std::cos; using std::sin; }
#include "common.hh"
#include "schmidl_cox.hh"
#include "bip_buffer.hh"
#include "theil_sen.hh"
#include "xorshift.hh"
#include "complex.hh"
#include "decibel.hh"
#include "blockdc.hh"
#include "hilbert.hh"
#include "phasor.hh"
#include "bitman.hh"
#include "delay.hh"
#include "wav.hh"
#include "pcm.hh"
#include "fft.hh"
#include "mls.hh"
#include "psk.hh"
#include "qam.hh"
#include "polar_list_decoder.hh"
#include "hadamard_decoder.hh"
template <typename value, typename cmplx, int rate>
struct Decoder : Common
{
typedef int16_t code_type;
typedef SIMD<code_type, 32> mesg_type;
typedef DSP::Const<value> Const;
static const int guard_len = rate / 300;
static const int symbol_len = guard_len * 40;
static const int filter_len = 129;
static const int extended_len = symbol_len + guard_len;
static const int buffer_len = 5 * extended_len;
static const int search_pos = extended_len;
static const int tone_off = - tone_count / 2;
DSP::ReadPCM<value> *pcm;
DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
DSP::BlockDC<value, value> blockdc;
DSP::Hilbert<cmplx, filter_len> hilbert;
DSP::BipBuffer<cmplx, buffer_len> input_hist;
DSP::TheilSenEstimator<value, tone_count> tse;
SchmidlCox<value, cmplx, search_pos, symbol_len, guard_len> correlator;
CODE::HadamardDecoder<6> hadamard_decoder;
CODE::PolarListDecoder<mesg_type, code_max> polar_decoder;
mesg_type mesg[bits_max];
code_type code[bits_max], perm[bits_max];
cmplx demod[tone_count], chan[tone_count], tone[tone_count];
cmplx fdom[symbol_len], tdom[symbol_len];
value index[tone_count], phase[tone_count];
value snr[symbols_max];
value cfo_rad, sfo_rad;
int symbol_pos;
int crc_bits;
static int bin(int carrier)
{
return (carrier + symbol_len) % symbol_len;
}
static value nrz(bool bit)
{
return 1 - 2 * bit;
}
static cmplx demod_or_erase(cmplx curr, cmplx prev)
{
if (norm(prev) > 0) {
cmplx demod = curr / prev;
if (norm(demod) < 4)
return demod;
}
return 0;
}
const cmplx *mls0_seq()
{
CODE::MLS seq0(mls0_poly, mls0_seed);
value cur = 0, prv = 0;
for (int i = 0; i < tone_count; ++i, prv = cur)
fdom[bin(i+tone_off)] = prv * (cur = nrz(seq0()));
return fdom;
}
cmplx map_bits(code_type *b, int bits)
{
switch (bits) {
case 1:
return PhaseShiftKeying<2, cmplx, code_type>::map(b);
case 2:
return PhaseShiftKeying<4, cmplx, code_type>::map(b);
case 3:
return PhaseShiftKeying<8, cmplx, code_type>::map(b);
case 4:
return QuadratureAmplitudeModulation<16, cmplx, code_type>::map(b);
case 6:
return QuadratureAmplitudeModulation<64, cmplx, code_type>::map(b);
case 8:
return QuadratureAmplitudeModulation<256, cmplx, code_type>::map(b);
case 10:
return QuadratureAmplitudeModulation<1024, cmplx, code_type>::map(b);
case 12:
return QuadratureAmplitudeModulation<4096, cmplx, code_type>::map(b);
}
return 0;
}
void demap_soft(code_type *b, cmplx c, value precision, int bits)
{
switch (bits) {
case 1:
return PhaseShiftKeying<2, cmplx, code_type>::soft(b, c, precision);
case 2:
return PhaseShiftKeying<4, cmplx, code_type>::soft(b, c, precision);
case 3:
return PhaseShiftKeying<8, cmplx, code_type>::soft(b, c, precision);
case 4:
return QuadratureAmplitudeModulation<16, cmplx, code_type>::soft(b, c, precision);
case 6:
return QuadratureAmplitudeModulation<64, cmplx, code_type>::soft(b, c, precision);
case 8:
return QuadratureAmplitudeModulation<256, cmplx, code_type>::soft(b, c, precision);
case 10:
return QuadratureAmplitudeModulation<1024, cmplx, code_type>::soft(b, c, precision);
case 12:
return QuadratureAmplitudeModulation<4096, cmplx, code_type>::soft(b, c, precision);
}
}
void demap_hard(code_type *b, cmplx c, int bits)
{
switch (bits) {
case 1:
return PhaseShiftKeying<2, cmplx, code_type>::hard(b, c);
case 2:
return PhaseShiftKeying<4, cmplx, code_type>::hard(b, c);
case 3:
return PhaseShiftKeying<8, cmplx, code_type>::hard(b, c);
case 4:
return QuadratureAmplitudeModulation<16, cmplx, code_type>::hard(b, c);
case 6:
return QuadratureAmplitudeModulation<64, cmplx, code_type>::hard(b, c);
case 8:
return QuadratureAmplitudeModulation<256, cmplx, code_type>::hard(b, c);
case 10:
return QuadratureAmplitudeModulation<1024, cmplx, code_type>::hard(b, c);
case 12:
return QuadratureAmplitudeModulation<4096, cmplx, code_type>::hard(b, c);
}
}
void shuffle(code_type *dest, const code_type *src, int order)
{
if (order == 8) {
CODE::XorShiftMask<int, 8, 1, 1, 2, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 256; ++i)
dest[seq()] = src[i];
} else if (order == 11) {
CODE::XorShiftMask<int, 11, 1, 3, 4, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 2048; ++i)
dest[seq()] = src[i];
} else if (order == 12) {
CODE::XorShiftMask<int, 12, 1, 1, 4, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 4096; ++i)
dest[seq()] = src[i];
} else if (order == 13) {
CODE::XorShiftMask<int, 13, 1, 1, 9, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 8192; ++i)
dest[seq()] = src[i];
} else if (order == 14) {
CODE::XorShiftMask<int, 14, 1, 5, 10, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 16384; ++i)
dest[seq()] = src[i];
} else if (order == 15) {
CODE::XorShiftMask<int, 15, 1, 1, 3, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 32768; ++i)
dest[seq()] = src[i];
} else if (order == 16) {
CODE::XorShiftMask<int, 16, 1, 1, 14, 1> seq;
dest[0] = src[0];
for (int i = 1; i < 65536; ++i)
dest[seq()] = src[i];
}
}
const cmplx *next_sample()
{
cmplx tmp;
pcm->read(reinterpret_cast<value *>(&tmp), 1);
if (pcm->channels() == 1)
tmp = hilbert(blockdc(tmp.real()));
return input_hist(tmp);
}
int64_t meta_data()
{
shuffle(code, perm, 8);
polar_decoder(nullptr, mesg, code, frozen_256_71, 8);
int best = -1;
for (int k = 0; k < mesg_type::SIZE; ++k) {
crc0.reset();
for (int i = 0; i < 71; ++i)
crc0(mesg[i].v[k] < 0);
if (crc0() == 0) {
best = k;
break;
}
}
if (best < 0)
return -1;
uint64_t md = 0;
for (int i = 0; i < 55; ++i)
md |= uint64_t(mesg[i].v[best] < 0) << i;
return md;
}
Decoder(DSP::ReadPCM<value> *pcm, const char *const *output_names, int output_count) : pcm(pcm), correlator(mls0_seq())
{
blockdc.samples(filter_len);
DSP::Phasor<cmplx> osc;
const cmplx *buf;
int output_index = 0;
int sample_count = 0;
while (output_index < output_count) {
do {
if (!pcm->good())
return;
buf = next_sample();
++sample_count;
} while (!correlator(buf));
symbol_pos = correlator.symbol_pos;
cfo_rad = correlator.cfo_rad;
std::cerr << "symbol pos: " << sample_count - buffer_len + symbol_pos << std::endl;
std::cerr << "coarse cfo: " << cfo_rad * (rate / Const::TwoPi()) << " Hz " << std::endl;
osc.omega(-cfo_rad);
for (int i = 0; i < symbol_len; ++i)
tdom[i] = buf[i+symbol_pos] * osc();
fwd(fdom, tdom);
for (int i = 0; i < tone_count; ++i)
tone[i] = fdom[bin(i+tone_off)];
for (int i = 0; i < symbol_len; ++i)
tdom[i] = buf[i+symbol_pos+symbol_len] * osc();
for (int i = 0; i < guard_len; ++i)
osc();
fwd(fdom, tdom);
for (int i = 0; i < tone_count; ++i)
chan[i] = fdom[bin(i+tone_off)];
for (int i = 0; i < tone_count; ++i) {
index[i] = tone_off + i;
phase[i] = arg(demod_or_erase(chan[i], tone[i]));
}
tse.compute(index, phase, tone_count);
std::cerr << "coarse sfo: " << -1000000 * tse.slope() / Const::TwoPi() << " ppm" << std::endl;
std::cerr << "residual cfo: " << 1000 * tse.yint() * rate / (Const::TwoPi() * symbol_len) << " mHz" << std::endl;
for (int i = 0; i < tone_count; ++i)
tone[i] *= DSP::polar<value>(1, tse(i+tone_off));
for (int i = 0; i < tone_count; ++i)
chan[i] = DSP::lerp(chan[i], tone[i], value(0.5));
CODE::MLS seq0(mls0_poly, mls0_seed);
for (int i = 0; i < tone_count; ++i)
chan[i] *= nrz(seq0());
for (int i = 0; i < symbol_len; ++i)
tdom[i] = buf[i+symbol_pos+symbol_len+extended_len] * osc();
for (int i = 0; i < guard_len; ++i)
osc();
fwd(fdom, tdom);
CODE::MLS seq1(mls1_poly);
auto clamp = [](int v){ return v < -127 ? -127 : v > 127 ? 127 : v; };
mod_bits = 1;
oper_mode = -1;
symbol_count = 0;
for (int j = 0, k = 0; j < symbol_count + 1; ++j) {
head_off = (block_skew * j + first_head) % block_length;
tail_off = (block_skew * j + first_tail) % block_length;
if (j) {
for (int i = 0; i < extended_len; ++i)
correlator(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 < tone_count; ++i)
tone[i] = fdom[bin(i+tone_off)];
for (int i = 0; i < tone_count; ++i)
if (i % block_length == head_off || i % block_length == tail_off)
tone[i] *= nrz(seq1());
for (int i = 0; i < tone_count; ++i)
demod[i] = demod_or_erase(tone[i], chan[i]);
for (int i = 0; i < head_tones; ++i)
head[i] = clamp(std::nearbyint(127 * demod[i*block_length+head_off].real()));
int head_data = hadamard_decoder(head);
if (head_data < 0) {
std::cerr << "head data damaged" << std::endl;
head_data = 0;
}
hadamard_encoder(head, head_data);
for (int i = 0; i < head_tones; ++i) {
tone[block_length*i+head_off] *= head[i];
demod[block_length*i+head_off] *= head[i];
}
for (int i = 0; i < head_tones; ++i) {
index[i] = tone_off + block_length * i + head_off;
phase[i] = arg(demod[block_length*i+head_off]);
}
for (int i = 0; i < tail_tones; ++i)
tail[i] = clamp(std::nearbyint(127 * demod[i*block_length+tail_off].real()));
int tail_data = hadamard_decoder(tail);
if (tail_data < 0) {
std::cerr << "tail data damaged" << std::endl;
tail_data = 0;
}
hadamard_encoder(tail, tail_data);
for (int i = 0; i < tail_tones; ++i) {
tone[block_length*i+tail_off] *= tail[i];
demod[block_length*i+tail_off] *= tail[i];
}
for (int i = 0; i < tail_tones; ++i) {
index[i+head_tones] = tone_off + block_length * i + tail_off;
phase[i+head_tones] = arg(demod[block_length*i+tail_off]);
}
tse.compute(index, phase, head_tones + tail_tones);
//std::cerr << "Theil-Sen slope = " << tse.slope() << std::endl;
//std::cerr << "Theil-Sen yint = " << tse.yint() << std::endl;
for (int i = 0; i < tone_count; ++i)
demod[i] *= DSP::polar<value>(1, -tse(i+tone_off));
for (int i = 0; i < tone_count; ++i)
chan[i] *= DSP::polar<value>(1, tse(i+tone_off));
CODE::XorShiftMask<int, 14, 1, 5, 10, 1> combination;
int trial = (head_data << 6) | tail_data;
int comb = 0;
for (int i = 0; i <= trial; ++i)
comb = combination();
int poly_index = comb & 15;
int seed_value = comb >> 4;
if (seed_value == 0)
std::cerr << "reserved seed value detected" << std::endl;
CODE::MLS seq(slm_poly[poly_index], seed_value);
for (int i = 0; i < tone_count; ++i)
if (i % block_length != head_off && i % block_length != tail_off)
demod[i] *= nrz(seq());
value sp = 0, np = 0;
for (int i = 0, l = k; i < tone_count; ++i) {
cmplx hard(1, 0);
if (i % block_length != head_off && i % block_length != tail_off) {
int bits = mod_bits;
if (mod_bits == 3 && l % 32 == 30)
bits = 2;
if (mod_bits == 6 && l % 64 == 60)
bits = 4;
if (mod_bits == 10 && l % 128 == 120)
bits = 8;
if (mod_bits == 12 && l % 128 == 120)
bits = 8;
demap_hard(perm+l, demod[i], bits);
hard = map_bits(perm+l, bits);
l += bits;
}
cmplx error = demod[i] - hard;
sp += norm(hard);
np += norm(error);
}
value precision = sp / np;
snr[j] = precision;
precision = std::min(precision, value(127));
for (int i = 0; i < tone_count; ++i) {
if (i % block_length != head_off && i % block_length != tail_off) {
int bits = mod_bits;
if (mod_bits == 3 && k % 32 == 30)
bits = 2;
if (mod_bits == 6 && k % 64 == 60)
bits = 4;
if (mod_bits == 10 && k % 128 == 120)
bits = 8;
if (mod_bits == 12 && k % 128 == 120)
bits = 8;
demap_soft(perm+k, demod[i], precision, bits);
k += bits;
}
}
if (!j) {
int64_t meta_info = meta_data();
if (meta_info < 0) {
std::cerr << "preamble decoding error." << std::endl;
break;
}
if (meta_info > 255) {
std::cerr << "unsupported operation mode: " << meta_info << std::endl;
break;
}
if (!setup(meta_info))
break;
k = 0;
for (int i = 0; i < symbol_pos+symbol_len+extended_len; ++i)
correlator(buf = next_sample());
std::cerr << "oper mode: " << oper_mode << std::endl;
}
if (differential) {
for (int i = 0; i < tone_count; ++i)
chan[i] = fdom[bin(i+tone_off)];
} else {
for (int i = head_off; i < tone_count; i += block_length)
chan[i] = DSP::lerp(chan[i], tone[i], value(0.5));
for (int i = tail_off; i < tone_count; i += block_length)
chan[i] = DSP::lerp(chan[i], tone[i], value(0.5));
}
}
if (oper_mode < 0)
continue;
DSP::quick_sort(snr, symbol_count + 1);
std::cerr << "Es/N0 (dB): " << DSP::decibel(snr[0]) << " .. " << DSP::decibel(snr[symbol_count/2]) << " .. " << DSP::decibel(snr[symbol_count]) << std::endl;
crc_bits = data_bits + 32;
shuffle(code, perm, code_order);
polar_decoder(nullptr, mesg, code, frozen_bits, code_order);
int best = -1;
for (int k = 0; k < mesg_type::SIZE; ++k) {
crc1.reset();
for (int i = 0; i < crc_bits; ++i)
crc1(mesg[i].v[k] < 0);
if (crc1() == 0) {
best = k;
break;
}
}
if (best < 0) {
std::cerr << "payload decoding error." << std::endl;
continue;
}
for (int i = 0; i < data_bits; ++i)
CODE::set_le_bit(data, i, mesg[i].v[best] < 0);
const char *output_name = output_names[output_index++];
if (output_count == 1 && output_name[0] == '-' && output_name[1] == 0)
output_name = "/dev/stdout";
std::ofstream output_file(output_name, std::ios::binary | std::ios::trunc);
if (output_file.bad()) {
std::cerr << "Couldn't open file \"" << output_name << "\" for writing." << std::endl;
continue;
}
CODE::Xorshift32 scrambler;
for (int i = 0; i < data_bytes; ++i)
data[i] ^= scrambler();
for (int i = 0; i < data_bytes; ++i)
output_file.put(data[i]);
}
}
};
int main(int argc, char **argv)
{
if (argc < 3) {
std::cerr << "usage: " << argv[0] << " INPUT OUTPUT.." << std::endl;
return 1;
}
typedef float value;
typedef DSP::Complex<value> cmplx;
const char *input_name = argv[1];
if (input_name[0] == '-' && input_name[1] == 0)
input_name = "/dev/stdin";
DSP::ReadWAV<value> input_file(input_name);
if (input_file.channels() < 1 || input_file.channels() > 2) {
std::cerr << "Only real or analytic signal (one or two channels) supported." << std::endl;
return 1;
}
std::cerr << std::fixed << std::setprecision(1);
int output_count = argc - 2;
switch (input_file.rate()) {
case 44100:
delete new Decoder<value, cmplx, 44100>(&input_file, argv+2, output_count);
break;
case 48000:
delete new Decoder<value, cmplx, 48000>(&input_file, argv+2, output_count);
break;
default:
std::cerr << "Unsupported sample rate." << std::endl;
return 1;
}
return 0;
}
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