Mirror/aicodix___modem
1
0
Fork 0
mirror of https://github.com/aicodix/modem.git synced 2026-04-27 14:30:34 +00:00
Code Issues Projects Releases Packages Wiki Activity
aicodix___modem/encode.cc
Ahmet Inan 513664a0e3 shuffle the code bits
2023-12-16 08:30:47 +01:00

373 lines
11 KiB
C++
Raw Blame History

/*
OFDM modem encoder
Copyright 2021 Ahmet Inan <inan@aicodix.de>
*/
#include <iostream>
#include <cassert>
#include <cmath>
#include "xorshift.hh"
#include "complex.hh"
#include "permute.hh"
#include "utils.hh"
#include "bitman.hh"
#include "decibel.hh"
#include "fft.hh"
#include "wav.hh"
#include "pcm.hh"
#include "mls.hh"
#include "crc.hh"
#include "psk.hh"
#include "qam.hh"
#include "polar_tables.hh"
#include "polar_helper.hh"
#include "polar_encoder.hh"
#include "bose_chaudhuri_hocquenghem_encoder.hh"
template <typename value, typename cmplx, int rate>
struct Encoder
{
typedef int8_t code_type;
static const int mod_bits = 4;
static const int code_order = 12;
static const int code_len = 1 << code_order;
static const int symbol_len = (1280 * rate) / 8000;
static const int guard_len = symbol_len / 8;
static const int max_bits = 2720 + 32;
static const int cons_cols = 256;
static const int cons_rows = 4;
static const int mls0_len = 127;
static const int mls0_poly = 0b10001001;
static const int mls1_len = 255;
static const int mls1_poly = 0b100101011;
static const int mls2_poly = 0b100101010001;
DSP::WritePCM<value> *pcm;
DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
DSP::FastFourierTransform<symbol_len, cmplx, 1> bwd;
CODE::CRC<uint16_t> crc0;
CODE::CRC<uint32_t> crc1;
CODE::BoseChaudhuriHocquenghemEncoder<255, 71> bchenc;
CODE::PolarSysEnc<code_type> polarenc;
CODE::FisherYatesShuffle<code_len> shuffle;
code_type code[code_len], mesg[max_bits];
cmplx fdom[symbol_len];
cmplx tdom[symbol_len];
cmplx temp[symbol_len];
cmplx kern[symbol_len];
cmplx guard[guard_len];
cmplx prev[cons_cols];
value papr_min, papr_max;
int code_off;
int mls0_off;
int mls1_off;
static int bin(int carrier)
{
return (carrier + symbol_len) % symbol_len;
}
static int nrz(bool bit)
{
return 1 - 2 * bit;
}
void clipping_and_filtering()
{
for (int i = 0; i < symbol_len; ++i) {
value pwr = norm(tdom[i]);
if (pwr > value(1))
tdom[i] /= sqrt(pwr);
}
fwd(temp, tdom);
for (int i = 0; i < symbol_len; ++i) {
if (norm(fdom[i])) {
temp[i] /= std::sqrt(value(symbol_len/4));
cmplx err = temp[i] - fdom[i];
value mag = abs(err);
value lim = 0.1;
if (mag > lim)
temp[i] -= ((mag - lim) / mag) * err;
} else {
temp[i] = 0;
}
}
bwd(tdom, temp);
for (int i = 0; i < symbol_len; ++i)
tdom[i] /= std::sqrt(value(symbol_len*4));
}
void tone_reservation()
{
for (int n = 0; n < 100; ++n) {
int peak = 0;
for (int i = 1; i < symbol_len; ++i)
if (norm(tdom[peak]) < norm(tdom[i]))
peak = i;
cmplx orig = tdom[peak];
if (norm(orig) <= value(1))
break;
for (int i = 0; i < symbol_len; ++i)
tdom[i] -= orig * kern[(symbol_len-peak+i)%symbol_len];
}
}
void symbol(bool papr_reduction = true)
{
bwd(tdom, fdom);
for (int i = 0; i < symbol_len; ++i)
tdom[i] /= std::sqrt(value(symbol_len*4));
if (papr_reduction) {
clipping_and_filtering();
tone_reservation();
}
for (int i = 0; i < guard_len; ++i) {
value x = value(i) / value(guard_len - 1);
value ratio(0.5);
x = std::min(x, ratio) / ratio;
x = value(0.5) * (value(1) - std::cos(DSP::Const<value>::Pi() * x));
guard[i] = DSP::lerp(guard[i], tdom[i+symbol_len-guard_len], x);
}
value peak = 0, mean = 0;
for (int i = 0; i < symbol_len; ++i) {
value power(norm(tdom[i]));
peak = std::max(peak, power);
mean += power;
}
mean /= symbol_len;
if (mean > 0) {
value papr(peak / mean);
papr_min = std::min(papr_min, papr);
papr_max = std::max(papr_max, papr);
}
pcm->write(reinterpret_cast<value *>(guard), guard_len, 2);
pcm->write(reinterpret_cast<value *>(tdom), symbol_len, 2);
for (int i = 0; i < guard_len; ++i)
guard[i] = tdom[i];
}
void pilot_block()
{
CODE::MLS seq2(mls2_poly);
value code_fac = std::sqrt(value(symbol_len) / value(cons_cols));
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
for (int i = code_off; i < code_off + cons_cols; ++i)
fdom[bin(i)] = code_fac * nrz(seq2());
symbol();
}
void schmidl_cox()
{
CODE::MLS seq0(mls0_poly);
value mls0_fac = std::sqrt(value(2 * symbol_len) / value(mls0_len));
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
fdom[bin(mls0_off-2)] = mls0_fac;
for (int i = 0; i < mls0_len; ++i)
fdom[bin(2*i+mls0_off)] = nrz(seq0());
for (int i = 0; i < mls0_len; ++i)
fdom[bin(2*i+mls0_off)] *= fdom[bin(2*(i-1)+mls0_off)];
symbol(false);
}
void meta_data(uint64_t md)
{
uint8_t data[9] = { 0 }, parity[23] = { 0 };
for (int i = 0; i < 55; ++i)
CODE::set_be_bit(data, i, (md>>i)&1);
crc0.reset();
uint16_t cs = crc0(md << 9);
for (int i = 0; i < 16; ++i)
CODE::set_be_bit(data, i+55, (cs>>i)&1);
bchenc(data, parity);
CODE::MLS seq1(mls1_poly);
value mls1_fac = std::sqrt(value(symbol_len) / value(mls1_len));
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
fdom[bin(mls1_off-1)] = mls1_fac;
for (int i = 0; i < 71; ++i)
fdom[bin(i+mls1_off)] = nrz(CODE::get_be_bit(data, i));
for (int i = 71; i < mls1_len; ++i)
fdom[bin(i+mls1_off)] = nrz(CODE::get_be_bit(parity, i-71));
for (int i = 0; i < mls1_len; ++i)
fdom[bin(i+mls1_off)] *= fdom[bin(i-1+mls1_off)];
for (int i = 0; i < mls1_len; ++i)
fdom[bin(i+mls1_off)] *= nrz(seq1());
symbol();
}
cmplx mod_map(code_type *b)
{
return QuadratureAmplitudeModulation<16, cmplx, code_type>::map(b);
}
Encoder(DSP::WritePCM<value> *pcm, const uint8_t *inp, int freq_off, uint64_t call_sign, int oper_mode, int reserved_tones) :
pcm(pcm), crc0(0xA8F4), crc1(0x8F6E37A0), bchenc({
0b100011101, 0b101110111, 0b111110011, 0b101101001,
0b110111101, 0b111100111, 0b100101011, 0b111010111,
0b000010011, 0b101100101, 0b110001011, 0b101100011,
0b100011011, 0b100111111, 0b110001101, 0b100101101,
0b101011111, 0b111111001, 0b111000011, 0b100111001,
0b110101001, 0b000011111, 0b110000111, 0b110110001})
{
int offset = (freq_off * symbol_len) / rate;
code_off = offset - cons_cols / 2;
mls0_off = offset - mls0_len + 1;
mls1_off = offset - mls1_len / 2;
value kern_fac = 1 / value(10 * reserved_tones);
for (int i = 0; i < reserved_tones / 2; ++i) {
fdom[bin(code_off-1-i)] = kern_fac;
fdom[bin(code_off+cons_cols+i)] = kern_fac;
}
bwd(kern, fdom);
papr_min = 1000, papr_max = -1000;
pilot_block();
schmidl_cox();
meta_data((call_sign << 8) | oper_mode);
if (oper_mode > 0) {
const uint32_t *frozen_bits = nullptr;
int data_bits = 0;
switch (oper_mode) {
case 17:
data_bits = 2720;
frozen_bits = frozen_4096_2752;
break;
case 18:
data_bits = 2048;
frozen_bits = frozen_4096_2080;
break;
case 19:
data_bits = 1360;
frozen_bits = frozen_4096_1392;
break;
default:
return;
}
for (int i = 0; i < data_bits; ++i)
mesg[i] = nrz(CODE::get_le_bit(inp, i));
crc1.reset();
for (int i = 0; i < data_bits / 8; ++i)
crc1(inp[i]);
for (int i = 0; i < 32; ++i)
mesg[i+data_bits] = nrz((crc1()>>i)&1);
polarenc(code, mesg, frozen_bits, code_order);
shuffle(code);
for (int i = 0; i < cons_cols; ++i)
prev[i] = fdom[bin(i+code_off)];
for (int j = 0; j < cons_rows; ++j) {
for (int i = 0; i < cons_cols; ++i)
fdom[bin(i+code_off)] = prev[i] *
mod_map(code+mod_bits*(cons_cols*j+i));
symbol();
}
}
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
symbol();
std::cerr << "PAPR: " << DSP::decibel(papr_min) << " .. " << DSP::decibel(papr_max) << " dB" << std::endl;
}
};
long long int base37_encoder(const char *str)
{
long long int acc = 0;
for (char c = *str++; c; c = *str++) {
acc *= 37;
if (c >= '0' && c <= '9')
acc += c - '0' + 1;
else if (c >= 'a' && c <= 'z')
acc += c - 'a' + 11;
else if (c >= 'A' && c <= 'Z')
acc += c - 'A' + 11;
else if (c != ' ')
return -1;
}
return acc;
}
int main(int argc, char **argv)
{
if (argc < 6 || argc > 8) {
std::cerr << "usage: " << argv[0] << " OUTPUT RATE BITS CHANNELS INPUT [OFFSET] [CALLSIGN]" << std::endl;
return 1;
}
const char *output_name = argv[1];
if (output_name[0] == '-' && output_name[1] == 0)
output_name = "/dev/stdout";
int output_rate = std::atoi(argv[2]);
int output_bits = std::atoi(argv[3]);
int output_chan = std::atoi(argv[4]);
const char *input_name = argv[5];
if (input_name[0] == '-' && input_name[1] == 0)
input_name = "/dev/stdin";
int freq_off = output_chan == 1 ? 1500 : 0;
if (argc >= 7)
freq_off = std::atoi(argv[6]);
long long int call_sign = base37_encoder("ANONYMOUS");
if (argc >= 8)
call_sign = base37_encoder(argv[7]);
if (call_sign <= 0 || call_sign >= 129961739795077L) {
std::cerr << "Unsupported call sign." << std::endl;
return 1;
}
const int reserved_tones = 8;
const int band_width = 1600 + (25 * reserved_tones) / 4;
if ((output_chan == 1 && freq_off < band_width / 2) || freq_off < band_width / 2 - output_rate / 2 || freq_off > output_rate / 2 - band_width / 2) {
std::cerr << "Unsupported frequency offset." << std::endl;
return 1;
}
if (freq_off % 50) {
std::cerr << "Frequency offset must be divisible by 50." << std::endl;
return 1;
}
typedef float value;
typedef DSP::Complex<value> cmplx;
std::ifstream input_file(input_name, std::ios::binary);
if (input_file.bad()) {
std::cerr << "Couldn't open file \"" << input_name << "\" for reading." << std::endl;
return 1;
}
const int data_len = 340;
uint8_t *input_data = new uint8_t[data_len];
for (int i = 0; i < data_len; ++i)
input_data[i] = std::max(input_file.get(), 0);
int oper_mode = 0;
for (int i = 256; i < 340; ++i)
if (!oper_mode && input_data[i])
oper_mode = 17;
for (int i = 170; i < 256; ++i)
if (!oper_mode && input_data[i])
oper_mode = 18;
for (int i = 0; i < 170; ++i)
if (!oper_mode && input_data[i])
oper_mode = 19;
CODE::Xorshift32 scrambler;
for (int i = 0; i < data_len; ++i)
input_data[i] ^= scrambler();
DSP::WriteWAV<value> output_file(output_name, output_rate, output_bits, output_chan);
output_file.silence(output_rate);
switch (output_rate) {
case 8000:
delete new Encoder<value, cmplx, 8000>(&output_file, input_data, freq_off, call_sign, oper_mode, reserved_tones);
break;
case 16000:
delete new Encoder<value, cmplx, 16000>(&output_file, input_data, freq_off, call_sign, oper_mode, reserved_tones);
break;
case 44100:
delete new Encoder<value, cmplx, 44100>(&output_file, input_data, freq_off, call_sign, oper_mode, reserved_tones);
break;
case 48000:
delete new Encoder<value, cmplx, 48000>(&output_file, input_data, freq_off, call_sign, oper_mode, reserved_tones);
break;
default:
std::cerr << "Unsupported sample rate." << std::endl;
return 1;
}
output_file.silence(output_rate);
delete []input_data;
return 0;
}
Reference in a new issue View git blame Copy permalink