Commit e91611f4 authored by Manolis Surligas's avatar Manolis Surligas

Implement Golay (24, 12, 8) encoder/decoder

parent a84d80ad
Pipeline #38506470 (#43) passed with stage
in 10 minutes and 47 seconds
......@@ -74,5 +74,6 @@ install(FILES
lrpt_sync.h
lrpt_decoder.h
frame_acquisition.h
shift_reg.h DESTINATION include/satnogs
shift_reg.h
golay24.h DESTINATION include/satnogs
)
\ No newline at end of file
/* -*- c++ -*- */
/*
* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
*
* Copyright (C) 2016, 2017, 2018
* Libre Space Foundation <http://librespacefoundation.org/>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef INCLUDED_SATNOGS_GOLAY24_H
#define INCLUDED_SATNOGS_GOLAY24_H
#include <satnogs/api.h>
#include <cstdint>
#include <vector>
namespace gr
{
namespace satnogs
{
/*!
* \brief A binary Golay (24,12,8) encoder and decoder.
*
* A binary Golay (24,12,8) encoder and decoder. The implementation uses LUT
* based on the process described in the book:
*
* Morelos-Zaragoza, Robert H. The art of error correcting coding.
* John Wiley & Sons, 2006.
*
*/
class SATNOGS_API golay24
{
public:
golay24 ();
~golay24 ();
uint32_t
encode12(uint16_t in);
bool
decode24(uint16_t *out, uint32_t in);
private:
std::vector<uint32_t> d_H;
std::vector<uint32_t> d_X;
};
} // namespace satnogs
} // namespace gr
#endif /* INCLUDED_SATNOGS_GOLAY24_H */
......@@ -73,7 +73,8 @@ list(APPEND satnogs_sources
convolutional_deinterleaver.cc
lrpt_decoder_impl.cc
frame_acquisition_impl.cc
shift_reg.cc)
shift_reg.cc
golay24.cc)
if(${INCLUDE_DEBUG_BLOCKS})
list(APPEND satnogs_sources ${satnogs_debug_sources})
......
/* -*- c++ -*- */
/*
* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
*
* Copyright (C) 2016, 2017, 2018
* Libre Space Foundation <http://librespacefoundation.org/>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <gnuradio/io_signature.h>
#include <satnogs/golay24.h>
#include <satnogs/utils.h>
namespace gr
{
namespace satnogs
{
golay24::golay24 ()
{
d_H = { 0x7ff, 0xee2, 0xdc5, 0xb8b, 0xf16, 0xe2d, 0xc5b, 0x8b7, 0x96e, 0xadc,
0xdb8, 0xb71 };
d_X = {0x800, 0x400, 0x200, 0x100, 0x080, 0x040, 0x020, 0x010, 0x008, 0x004,
0x002, 0x001};
}
golay24::~golay24 ()
{
}
/**
* Encodes a 12-bit message
* @param in the input 12-bit message. The message should be placed at the
* 12 LS bits
* @return the coded 24-bit message. The message is placed at the 24 LS bits
*/
uint32_t
golay24::encode12 (uint16_t in)
{
uint32_t c[2] =
{ 0x0, 0x0 };
c[0] = in & 0xFFF;
for (size_t i = 0; i < 12; i++) {
uint32_t tmp = 0;
for (size_t j = 0; j < 12; j++) {
tmp ^= (((c[0] & d_H[i]) >> j) & 0x01);
}
c[1] = (c[1] << 1) ^ tmp;
}
return ((c[0] & 0xFFF) << 12) | (c[1] & 0xFFF);
}
static inline uint32_t
ham_dist(uint32_t x)
{
return bit_count(x & 0xFFF);
}
/**
* Decodes a single Golay (24, 12, 8) codeword
*
* @param out the 12-bit decoded message. The message is placed at the 12 LS bits
* @param in the coded 24 bit code word. The message should be placed at the
* 24 LS bits
* @return true if the decoding was successful, false in case the error correction
* could not be performed
*/
bool
golay24::decode24(uint16_t *out, const uint32_t in)
{
uint32_t e[2] = {0x0, 0x0};
uint32_t r[2] = {0x0, 0x0};
uint32_t c[2] = {0x0, 0x0};
uint32_t syndrome = 0x0;
bool found = false;
uint32_t col = 0;
uint32_t q = 0;
r[0] = (in >> 12) & 0xFFF;
r[1] = in & 0xFFF;
for(size_t j = 0; j < 12; j++) {
uint32_t tmp = 0x0;
for(size_t i = 0; i < 12; i++) {
tmp ^= (((d_X[j] & r[0]) >> i) & 0x1);
}
for(size_t i = 0; i < 12; i++) {
tmp ^= (((d_H[j] & r[1]) >> i) & 0x1);
}
syndrome = (syndrome << 1) ^ tmp;
}
if(ham_dist(syndrome) <= 3) {
e[0] = syndrome;
e[1] = 0x0;
}
else{
do {
if (ham_dist (syndrome ^ d_H[col]) <= 2) {
e[0] = syndrome ^ d_H[col];
e[1] = d_X[col];
found = 1;
}
col++;
}
while ((col < 12) && !found);
if ((col == 12) && !found) {
for (size_t j = 0; j < 12; j++) {
uint32_t tmp = 0x0;
for (size_t i = 0; i < 12; i++) {
tmp ^= (((d_H[j] & syndrome) >> i) & 0x1);
}
q = (q << 1) ^ tmp;
}
}
if (ham_dist (q) <= 3) {
e[0] = 0;
e[1] = q;
}
else {
col = 0;
found = 0;
do {
if (ham_dist (q ^ d_H[col]) <= 2) {
e[0] = d_X[col];
e[1] = q ^ d_H[col];
found = 1;
}
col++;
}
while ((col < 12) && !found);
if (col == 12 && !found) {
return false;
}
}
}
c[0] = r[0] ^ e[0];
c[1] = r[1] ^ e[1];
/* Return the message part only, not the parity */
*out = c[0];
return true;
}
} /* namespace satnogs */
} /* namespace gr */
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