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added BCH forward error correction

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This commit is contained in:
Ahmet Inan 2021-06-10 11:05:39 +02:00
commit 0e9f46efd1
3 changed files with 29 additions and 11 deletions
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4
README.md
View file

@ -3,10 +3,10 @@
Quick start:
Create file ```uncoded.dat``` with ```64768``` bits of random data:
Create file ```uncoded.dat``` with ```64576``` bits of random data:
```
dd if=/dev/urandom of=uncoded.dat bs=1 count=8096
dd if=/dev/urandom of=uncoded.dat bs=1 count=8072
```
Encode file ```uncoded.dat``` to ```encoded.wav``` [WAV](https://en.wikipedia.org/wiki/WAV) audio file with 8000 Hz sample rate, 16 bits and only 1 (real) channel:

18
decode.cc
View file

@ -25,6 +25,8 @@ namespace DSP { using std::abs; using std::min; using std::cos; using std::sin;
#include "crc.hh"
#include "osd.hh"
#include "psk.hh"
#include "galois_field.hh"
#include "bose_chaudhuri_hocquenghem_decoder.hh"
template <typename value, typename cmplx, int search_pos, int symbol_len, int guard_len>
struct SchmidlCox
@ -155,7 +157,7 @@ struct Decoder
static const int filter_len = (((21 * rate) / 8000) & ~3) | 1;
static const int guard_len = symbol_len / 8;
static const int code_bits = 64800;
static const int data_bits = code_bits - 32;
static const int data_bits = code_bits - 32 - 12 * 16;
static const int code_cols = 432;
static const int code_rows = code_bits / code_cols / Mod::BITS;
static const int code_off = -216;
@ -177,6 +179,9 @@ struct Decoder
SchmidlCox<value, cmplx, search_pos, symbol_len/2, guard_len> correlator;
CODE::CRC<uint16_t> crc0;
CODE::CRC<uint32_t> crc1;
typedef CODE::GaloisField<16, 0b10000000000101101, uint16_t> GF;
GF gf;
CODE::BoseChaudhuriHocquenghemDecoder<24, 1, 65343, GF> bchdec1;
CODE::OrderedStatisticsDecoder<255, 71, 4> osddec;
int8_t genmat[255*71];
cmplx head[symbol_len], tail[symbol_len];
@ -341,8 +346,15 @@ struct Decoder
}
}
}
int ret = bchdec1(out, out+(data_bits+32)/8, 0, 0, data_bits+32);
if (ret < 0) {
std::cerr << "payload BCH error." << std::endl;
return;
}
if (ret)
std::cerr << "payload BCH corrected " << ret << " errors." << std::endl;
crc1.reset();
for (int i = 0; i < code_bits / 8; ++i)
for (int i = 0; i < (data_bits+32)/8; ++i)
crc1(out[i]);
if (crc1())
std::cerr << "payload CRC error." << std::endl;
@ -399,7 +411,7 @@ int main(int argc, char **argv)
std::cerr << "Couldn't open file \"" << output_name << "\" for writing." << std::endl;
return 1;
}
const int data_len = code_len - 32 / 8;
const int data_len = code_len - (32 + 12 * 16) / 8;
for (int i = 0; i < data_len; ++i)
output_file.put(output_data[i]);
delete []output_data;

18
encode.cc
View file

@ -27,7 +27,7 @@ struct Encoder
static const int symbol_len = (1280 * rate) / 8000;
static const int guard_len = symbol_len / 8;
static const int code_bits = 64800;
static const int data_bits = code_bits - 32;
static const int data_bits = code_bits - 32 - 12 * 16;
static const int code_cols = 432;
static const int code_rows = code_bits / code_cols / Mod::BITS;
static const int mls0_len = 127;
@ -39,7 +39,8 @@ struct Encoder
DSP::FastFourierTransform<symbol_len, cmplx, 1> bwd;
CODE::CRC<uint16_t> crc0;
CODE::CRC<uint32_t> crc1;
CODE::BoseChaudhuriHocquenghemEncoder<255, 71> bchenc;
CODE::BoseChaudhuriHocquenghemEncoder<255, 71> bchenc0;
CODE::BoseChaudhuriHocquenghemEncoder<65535, 65343> bchenc1;
cmplx fdom[symbol_len];
cmplx tdom[symbol_len];
cmplx guard[guard_len];
@ -115,7 +116,7 @@ struct Encoder
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);
bchenc0(data, parity);
CODE::MLS seq4(mls1_poly);
value mls1_fac = sqrt(value(symbol_len) / value(mls1_len));
for (int i = 0; i < symbol_len; ++i)
@ -132,13 +133,17 @@ struct Encoder
symbol();
}
Encoder(DSP::WritePCM<value> *pcm, uint8_t *inp, int freq_off, uint64_t call_sign) :
pcm(pcm), crc0(0xA8F4), crc1(0xD419CC15), bchenc({
pcm(pcm), crc0(0xA8F4), crc1(0xD419CC15), bchenc0({
0b100011101, 0b101110111, 0b111110011, 0b101101001,
0b110111101, 0b111100111, 0b100101011, 0b111010111,
0b000010011, 0b101100101, 0b110001011, 0b101100011,
0b100011011, 0b100111111, 0b110001101, 0b100101101,
0b101011111, 0b111111001, 0b111000011, 0b100111001,
0b110101001, 0b000011111, 0b110000111, 0b110110001})
0b110101001, 0b000011111, 0b110000111, 0b110110001}), bchenc1({
0b10000000000101101, 0b10000000101110011, 0b10000111110111101,
0b10101101001010101, 0b10001111100101111, 0b11111011110110101,
0b11010111101100101, 0b10111001101100111, 0b10000111010100001,
0b10111010110100111, 0b10011101000101101, 0b10001101011100011})
{
code_off = (freq_off * symbol_len) / rate - code_cols / 2;
mls0_off = code_off + 90;
@ -153,6 +158,7 @@ struct Encoder
crc1(inp[i]);
for (int i = 0; i < 4; ++i)
inp[data_bits/8+i] = (crc1() >> (8*i)) & 255;
bchenc1(inp, inp+(data_bits+32)/8, data_bits+32);
for (int j = 0; j < code_rows; ++j) {
for (int i = 0; i < code_cols; ++i) {
value tmp[Mod::BITS];
@ -233,7 +239,7 @@ int main(int argc, char **argv)
return 1;
}
const int code_len = 64800 / 8;
const int data_len = code_len - 32 / 8;
const int data_len = code_len - (32 + 12 * 16) / 8;
uint8_t *input_data = new uint8_t[code_len];
for (int i = 0; i < data_len; ++i)
input_data[i] = input_file.get();