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aicodix___modem/decode.cc
Ahmet Inan e27c8e1e06 added extended length constant
2023-12-14 08:21:34 +01:00

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/*
OFDM modem decoder
Copyright 2021 Ahmet Inan <inan@aicodix.de>
*/
#include <algorithm>
#include <iostream>
#include <cassert>
#include <cmath>
namespace DSP { using std::abs; using std::min; using std::cos; using std::sin; }
#include "bip_buffer.hh"
#include "theil_sen.hh"
#include "xorshift.hh"
#include "trigger.hh"
#include "complex.hh"
#include "decibel.hh"
#include "blockdc.hh"
#include "hilbert.hh"
#include "phasor.hh"
#include "bitman.hh"
#include "delay.hh"
#include "sma.hh"
#include "wav.hh"
#include "pcm.hh"
#include "fft.hh"
#include "mls.hh"
#include "crc.hh"
#include "osd.hh"
#include "psk.hh"
#include "polar_tables.hh"
#include "polar_helper.hh"
#include "polar_encoder.hh"
#include "polar_list_decoder.hh"
template <typename value, typename cmplx, int search_pos, int symbol_len, int guard_len>
struct SchmidlCox
{
typedef DSP::Const<value> Const;
static const int match_len = guard_len | 1;
static const int match_del = (match_len - 1) / 2;
DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
DSP::FastFourierTransform<symbol_len, cmplx, 1> bwd;
DSP::SMA4<cmplx, value, symbol_len, false> cor;
DSP::SMA4<value, value, 2*symbol_len, false> pwr;
DSP::SMA4<value, value, match_len, false> match;
DSP::Delay<value, match_del> delay;
DSP::SchmittTrigger<value> threshold;
DSP::FallingEdgeTrigger falling;
cmplx tmp0[symbol_len], tmp1[symbol_len];
cmplx kern[symbol_len];
cmplx cmplx_shift = 0;
value timing_max = 0;
value phase_max = 0;
int index_max = 0;
static int bin(int carrier)
{
return (carrier + symbol_len) % symbol_len;
}
static cmplx demod_or_erase(cmplx curr, cmplx prev, value pwr)
{
if (!(norm(curr) > pwr))
return 0;
if (!(norm(prev) > pwr))
return 0;
cmplx cons = curr / prev;
if (!(norm(cons) <= 4))
return 0;
return cons;
}
public:
int symbol_pos = 0;
value cfo_rad = 0;
value frac_cfo = 0;
SchmidlCox(const cmplx *sequence) : threshold(value(0.17*match_len), value(0.19*match_len))
{
fwd(kern, sequence);
for (int i = 0; i < symbol_len; ++i)
kern[i] = conj(kern[i]) / value(symbol_len);
}
bool operator()(const cmplx *samples)
{
cmplx P = cor(samples[search_pos+symbol_len] * conj(samples[search_pos+2*symbol_len]));
value R = value(0.5) * pwr(norm(samples[search_pos+2*symbol_len]));
value min_R = 0.00001 * symbol_len;
R = std::max(R, min_R);
value timing = match(norm(P) / (R * R));
value phase = delay(arg(P));
bool collect = threshold(timing);
bool process = falling(collect);
if (!collect && !process)
return false;
if (timing_max < timing) {
timing_max = timing;
phase_max = phase;
index_max = match_del;
} else if (index_max < symbol_len + guard_len + match_del) {
++index_max;
}
if (!process)
return false;
frac_cfo = phase_max / value(symbol_len);
DSP::Phasor<cmplx> osc;
osc.omega(frac_cfo);
symbol_pos = search_pos - index_max;
index_max = 0;
timing_max = 0;
for (int i = 0; i < symbol_len; ++i)
tmp1[i] = samples[i+symbol_pos+symbol_len] * osc();
fwd(tmp0, tmp1);
value min_pwr = 0;
for (int i = 0; i < symbol_len; ++i)
min_pwr += norm(tmp0[i]);
min_pwr /= symbol_len;
for (int i = 0; i < symbol_len; ++i)
tmp1[i] = demod_or_erase(tmp0[i], tmp0[bin(i-1)], min_pwr);
fwd(tmp0, tmp1);
for (int i = 0; i < symbol_len; ++i)
tmp0[i] *= kern[i];
bwd(tmp1, tmp0);
int shift = 0;
value peak = 0;
value next = 0;
for (int i = 0; i < symbol_len; ++i) {
value power = norm(tmp1[i]);
if (power > peak) {
next = peak;
peak = power;
shift = i;
} else if (power > next) {
next = power;
}
}
if (peak <= next * 4)
return false;
int pos_err = std::nearbyint(arg(tmp1[shift]) * symbol_len / Const::TwoPi());
if (abs(pos_err) > guard_len / 2)
return false;
symbol_pos -= pos_err;
cfo_rad = shift * (Const::TwoPi() / symbol_len) - frac_cfo;
if (cfo_rad >= Const::Pi())
cfo_rad -= Const::TwoPi();
return true;
}
};
void base37_decoder(char *str, long long int val, int len)
{
for (int i = len-1; i >= 0; --i, val /= 37)
str[i] = " 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"[val%37];
}
template <typename value, typename cmplx, int rate>
struct Decoder
{
typedef int8_t code_type;
#ifdef __AVX2__
typedef SIMD<code_type, 32 / sizeof(code_type)> mesg_type;
#else
typedef SIMD<code_type, 16 / sizeof(code_type)> mesg_type;
#endif
typedef DSP::Const<value> Const;
static const int code_order = 11;
static const int mod_bits = 2;
static const int code_len = 1 << code_order;
static const int symbol_len = (1280 * rate) / 8000;
static const int filter_len = (((21 * rate) / 8000) & ~3) | 1;
static const int guard_len = symbol_len / 8;
static const int extended_len = symbol_len + guard_len;
static const int max_bits = 1360 + 32;
static const int cons_cols = 256;
static const int cons_rows = 4;
static const int cons_total = cons_rows * cons_cols;
static const int code_off = - cons_cols / 2;
static const int mls0_len = 127;
static const int mls0_off = - mls0_len + 1;
static const int mls0_poly = 0b10001001;
static const int mls1_len = 255;
static const int mls1_off = - mls1_len / 2;
static const int mls1_poly = 0b100101011;
static const int buffer_len = 6 * extended_len;
static const int search_pos = buffer_len - 4 * extended_len;
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, cons_cols> tse;
SchmidlCox<value, cmplx, search_pos, symbol_len/2, guard_len> correlator;
CODE::CRC<uint16_t> crc0;
CODE::CRC<uint32_t> crc1;
CODE::OrderedStatisticsDecoder<255, 71, 4> osddec;
CODE::PolarEncoder<mesg_type> polarenc;
CODE::PolarListDecoder<mesg_type, code_order> polardec;
int8_t genmat[255*71];
mesg_type mesg[max_bits], mess[code_len];
code_type code[code_len];
cmplx cons[cons_total], prev[cons_cols];
cmplx fdom[symbol_len], tdom[symbol_len];
value index[cons_cols], phase[cons_cols];
value cfo_rad, sfo_rad;
const uint32_t *frozen_bits;
int symbol_pos;
int oper_mode;
int crc_bits;
static int bin(int carrier)
{
return (carrier + symbol_len) % symbol_len;
}
static int nrz(bool bit)
{
return 1 - 2 * bit;
}
static cmplx demod_or_erase(cmplx curr, cmplx prev)
{
if (!(norm(prev) > 0))
return 0;
cmplx cons = curr / prev;
if (!(norm(cons) <= 4))
return 0;
return cons;
}
const cmplx *mls0_seq()
{
CODE::MLS seq0(mls0_poly);
for (int i = 0; i < symbol_len/2; ++i)
fdom[i] = 0;
for (int i = 0; i < mls0_len; ++i)
fdom[(i+mls0_off/2+symbol_len/2)%(symbol_len/2)] = nrz(seq0());
return fdom;
}
void systematic()
{
polarenc(mess, mesg, frozen_bits, code_order);
int code_bits = 1 << code_order;
for (int i = 0, j = 0; i < code_bits && j < crc_bits; ++i)
if (!((frozen_bits[i/32] >> (i%32)) & 1))
mesg[j++] = mess[i];
}
cmplx mod_map(code_type *b)
{
return PhaseShiftKeying<4, cmplx, code_type>::map(b);
}
void mod_hard(code_type *b, cmplx c)
{
PhaseShiftKeying<4, cmplx, code_type>::hard(b, c);
}
void mod_soft(code_type *b, cmplx c, value precision)
{
PhaseShiftKeying<4, cmplx, code_type>::soft(b, c, precision);
}
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);
}
Decoder(uint8_t *out, int *len, DSP::ReadPCM<value> *pcm, int skip_count) :
pcm(pcm), correlator(mls0_seq()), crc0(0xA8F4), crc1(0x8F6E37A0)
{
CODE::BoseChaudhuriHocquenghemGenerator<255, 71>::matrix(genmat, true, {
0b100011101, 0b101110111, 0b111110011, 0b101101001,
0b110111101, 0b111100111, 0b100101011, 0b111010111,
0b000010011, 0b101100101, 0b110001011, 0b101100011,
0b100011011, 0b100111111, 0b110001101, 0b100101101,
0b101011111, 0b111111001, 0b111000011, 0b100111001,
0b110101001, 0b000011111, 0b110000111, 0b110110001});
blockdc.samples(2*extended_len);
DSP::Phasor<cmplx> osc;
const cmplx *buf;
bool okay;
do {
okay = false;
do {
if (!pcm->good())
return;
buf = next_sample();
} while (!correlator(buf));
symbol_pos = correlator.symbol_pos;
cfo_rad = correlator.cfo_rad;
std::cerr << "symbol pos: " << 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+extended_len] * osc();
fwd(fdom, tdom);
CODE::MLS seq1(mls1_poly);
for (int i = 0; i < mls1_len; ++i)
fdom[bin(i+mls1_off)] *= nrz(seq1());
int8_t soft[mls1_len];
uint8_t data[(mls1_len+7)/8];
for (int i = 0; i < mls1_len; ++i)
soft[i] = std::min<value>(std::max<value>(
std::nearbyint(127 * demod_or_erase(
fdom[bin(i+mls1_off)], fdom[bin(i-1+mls1_off)]).real()),
-127), 127);
bool unique = osddec(data, soft, genmat);
if (!unique) {
std::cerr << "OSD error." << std::endl;
continue;
}
uint64_t md = 0;
for (int i = 0; i < 55; ++i)
md |= (uint64_t)CODE::get_be_bit(data, i) << i;
uint16_t cs = 0;
for (int i = 0; i < 16; ++i)
cs |= (uint16_t)CODE::get_be_bit(data, i+55) << i;
crc0.reset();
if (crc0(md<<9) != cs) {
std::cerr << "header CRC error." << std::endl;
continue;
}
oper_mode = md & 255;
if (oper_mode && (oper_mode < 14 || oper_mode > 16)) {
std::cerr << "operation mode " << oper_mode << " unsupported." << std::endl;
continue;
}
std::cerr << "oper mode: " << oper_mode << std::endl;
if ((md>>8) == 0 || (md>>8) >= 129961739795077L) {
std::cerr << "call sign unsupported." << std::endl;
continue;
}
char call_sign[10];
base37_decoder(call_sign, md>>8, 9);
call_sign[9] = 0;
std::cerr << "call sign: " << call_sign << std::endl;
okay = true;
} while (skip_count--);
*len = 0;
if (!okay || !oper_mode)
return;
for (int i = 0; i < symbol_pos+extended_len; ++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 < cons_cols; ++i)
prev[i] = fdom[bin(i+code_off)];
std::cerr << "demod ";
for (int j = 0; j < cons_rows; ++j) {
for (int i = 0; i < extended_len; ++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 < cons_cols; ++i)
cons[cons_cols*j+i] = demod_or_erase(fdom[bin(i+code_off)], prev[i]);
for (int i = 0; i < cons_cols; ++i)
prev[i] = fdom[bin(i+code_off)];
std::cerr << ".";
}
std::cerr << " done" << std::endl;
if (1) {
value sum_slope = 0, sum_yint = 0;
for (int j = 0; j < cons_rows; ++j) {
for (int i = 0; i < cons_cols; ++i) {
code_type tmp[mod_bits];
mod_hard(tmp, cons[cons_cols*j+i]);
index[i] = i + code_off;
phase[i] = arg(cons[cons_cols*j+i] * conj(mod_map(tmp)));
}
tse.compute(index, phase, cons_cols);
//std::cerr << "Theil-Sen slope = " << tse.slope() << std::endl;
//std::cerr << "Theil-Sen yint = " << tse.yint() << std::endl;
sum_slope += tse.slope();
sum_yint += tse.yint();
for (int i = 0; i < cons_cols; ++i)
cons[cons_cols*j+i] *= DSP::polar<value>(1, -tse(i+code_off));
}
value avg_slope = sum_slope / cons_rows;
value avg_yint = sum_yint / cons_rows;
//for (int i = 0; i < cons_cnt; ++i)
// cons[i] *= DSP::polar<value>(1, -(avg_yint+avg_slope*((i%cons_cols)+code_off)));
sfo_rad -= avg_slope * symbol_len / value(extended_len);
cfo_rad += avg_yint / extended_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;
}
if (1) {
std::cerr << "Es/N0 (dB):";
value sp = 0, np = 0;
for (int j = 0; j < cons_rows; ++j) {
for (int i = 0; i < cons_cols; ++i) {
code_type tmp[mod_bits];
mod_hard(tmp, cons[cons_cols*j+i]);
cmplx hard = mod_map(tmp);
cmplx error = cons[cons_cols*j+i] - hard;
sp += norm(hard);
np += norm(error);
}
value precision = sp / np;
value snr = DSP::decibel(precision);
std::cerr << " " << snr;
for (int i = 0; i < cons_cols; ++i)
mod_soft(code+2*(cons_cols*j+i), cons[cons_cols*j+i], precision);
}
std::cerr << std::endl;
} else {
value precision = 8;
for (int i = 0; i < cons_total; ++i)
mod_soft(code+mod_bits*i, cons[i], precision);
}
int data_bits = 0;
switch (oper_mode) {
case 14:
data_bits = 1360;
frozen_bits = frozen_2048_1392;
break;
case 15:
data_bits = 1024;
frozen_bits = frozen_2048_1056;
break;
case 16:
data_bits = 680;
frozen_bits = frozen_2048_712;
break;
default:
return;
}
*len = data_bits / 8;
crc_bits = data_bits + 32;
CODE::PolarHelper<mesg_type>::PATH metric[mesg_type::SIZE];
polardec(metric, mesg, code, frozen_bits, code_order);
systematic();
int order[mesg_type::SIZE];
for (int k = 0; k < mesg_type::SIZE; ++k)
order[k] = k;
std::sort(order, order+mesg_type::SIZE, [metric](int a, int b){ return metric[a] < metric[b]; });
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[order[k]] < 0);
if (crc1() == 0) {
best = order[k];
break;
}
}
if (best < 0) {
std::cerr << "payload decoding error." << std::endl;
*len = 0;
return;
}
int flips = 0;
for (int i = 0, j = 0; i < data_bits; ++i, ++j) {
while ((frozen_bits[j / 32] >> (j % 32)) & 1)
++j;
bool received = code[j] < 0;
bool decoded = mesg[i].v[best] < 0;
flips += received != decoded;
CODE::set_le_bit(out, i, decoded);
}
std::cerr << "bit flips: " << flips << std::endl;
}
};
int main(int argc, char **argv)
{
if (argc < 3 || argc > 4) {
std::cerr << "usage: " << argv[0] << " OUTPUT INPUT [SKIP]" << std::endl;
return 1;
}
typedef float value;
typedef DSP::Complex<value> cmplx;
const char *output_name = argv[1];
if (output_name[0] == '-' && output_name[1] == 0)
output_name = "/dev/stdout";
const char *input_name = argv[2];
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;
}
int skip_count = 0;
if (argc > 3)
skip_count = std::atoi(argv[3]);
const int data_max = 1360 / 8;
uint8_t *output_data = new uint8_t[data_max];
int data_len = 0;
switch (input_file.rate()) {
case 8000:
delete new Decoder<value, cmplx, 8000>(output_data, &data_len, &input_file, skip_count);
break;
case 16000:
delete new Decoder<value, cmplx, 16000>(output_data, &data_len, &input_file, skip_count);
break;
case 44100:
delete new Decoder<value, cmplx, 44100>(output_data, &data_len, &input_file, skip_count);
break;
case 48000:
delete new Decoder<value, cmplx, 48000>(output_data, &data_len, &input_file, skip_count);
break;
default:
std::cerr << "Unsupported sample rate." << std::endl;
return 1;
}
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;
return 1;
}
CODE::Xorshift32 scrambler;
for (int i = 0; i < data_len; ++i)
output_data[i] ^= scrambler();
for (int i = 0; i < data_len; ++i)
output_file.put(output_data[i]);
delete []output_data;
return 0;
}
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