Add BCH decoding of network ID (NAC/DUID)
git-svn-id: http://op25.osmocom.org/svn/trunk@89 65a5c917-d112-43f1-993d-58c26a4786be
This commit is contained in:
stevie
parent
5ea83dbf72
commit
504a4f8b54
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@ -10,8 +10,8 @@ unlimited permission to copy, distribute and modify it.
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Basic Installation
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==================
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The commands `./bootstrap; ./configure; make; make install' should
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configure, build, and install this package. The following
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Briefly, the shell commands `./configure; make; make install' should
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configure, build, and install this package. The following
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more-detailed instructions are generic; see the `README' file for
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instructions specific to this package.
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@ -60,6 +60,7 @@ ourlib_LTLIBRARIES = _op25.la
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# These are the source files that go into the shared library
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_op25_la_SOURCES = \
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abstract_data_unit.cc \
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bch.cc \
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data_unit.cc \
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header.cc \
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ldu1.cc \
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@ -0,0 +1,213 @@
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/* -*- C++ -*- */
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/*
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* Copyright 2008 Steve Glass
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*
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* This file is part of OP25.
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*
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* OP25 is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* OP25 is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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* License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with OP25; see the file COPYING. If not, write to the Free
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* Software Foundation, Inc., 51 Franklin Street, Boston, MA
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* 02110-1301, USA.
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*/
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#include <bch.h>
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/*
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* APCO P25 BCH(64,16,23) encoder.
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*/
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uint64_t
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bch_64_encode(uint16_t val)
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{
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static const uint64_t encoding_matrix[] = {
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0x8000cd930bdd3b2aLL,
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0x4000ab5a8e33a6beLL,
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0x2000983e4cc4e874LL,
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0x10004c1f2662743aLL,
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0x0800eb9c98ec0136LL,
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0x0400b85d47ab3bb0LL,
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0x02005c2ea3d59dd8LL,
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0x01002e1751eaceecLL,
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0x0080170ba8f56776LL,
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0x0040c616dfa78890LL,
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0x0020630b6fd3c448LL,
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0x00103185b7e9e224LL,
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0x000818c2dbf4f112LL,
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0x0004c1f2662743a2LL,
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0x0002ad6a38ce9afbLL,
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0x00019b2617ba7657LL
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};
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uint64_t cw = 0LL;
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for(uint8_t i=0; i < 16; ++i) {
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if(val & (1 << (15 - i))) {
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cw ^= encoding_matrix[i];
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}
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}
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return cw;
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}
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/*
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* APCO P25 BCH(64,16,23) decoder.
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*/
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bool
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bch_64_decode(uint64_t& cw)
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{
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int elp[24][22], s[23];
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int d[23], L[24], uLu[24];
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int locn[11], reg[12];
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int i, j, u, q, n;
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bool syndrome_error = false;
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bool decoded = true;
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static const int BCH_GF_EXP[64] = {
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1, 2, 4, 8, 16, 32, 3, 6, 12, 24, 48, 35, 5, 10, 20, 40,
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19, 38, 15, 30, 60, 59, 53, 41, 17, 34, 7, 14, 28, 56, 51, 37,
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9, 18, 36, 11, 22, 44, 27, 54, 47, 29, 58, 55, 45, 25, 50, 39,
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13, 26, 52, 43, 21, 42, 23, 46, 31, 62, 63, 61, 57, 49, 33, 0,
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};
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static const int BCH_GF_LOG[64] = {
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-1, 0, 1, 6, 2, 12, 7, 26, 3, 32, 13, 35, 8, 48, 27, 18,
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4, 24, 33, 16, 14, 52, 36, 54, 9, 45, 49, 38, 28, 41, 19, 56,
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5, 62, 25, 11, 34, 31, 17, 47, 15, 23, 53, 51, 37, 44, 55, 40,
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10, 61, 46, 30, 50, 22, 39, 43, 29, 60, 42, 21, 20, 59, 57, 58,
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};
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// first form the syndromes
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for(i = 1; i <= 22; i++) {
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s[i] = 0;
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for(j = 0; j <= 62; j++) {
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if(cw & (1LL << j)) {
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s[i] ^= BCH_GF_EXP[(i * j) % 63];
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}
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}
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if(s[i]) {
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syndrome_error = true;
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}
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s[i] = BCH_GF_LOG[s[i]];
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}
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// if there are errors, compute elp and try to correct them
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if(syndrome_error) {
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L[0] = 0; uLu[0] = -1; d[0] = 0; elp[0][0] = 0;
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L[1] = 0; uLu[1] = 0; d[1] = s[1]; elp[1][0] = 1;
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for(i = 1; i <= 21; i++) {
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elp[0][i] = -1;
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elp[1][i] = 0;
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}
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u = 0;
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do {
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++u;
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if(-1 == d[u]) {
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L[u + 1] = L[u];
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for(i = 0; i <= L[u]; i++) {
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elp[u + 1][i] = elp[u][i];
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elp[u][i] = BCH_GF_LOG[elp[u][i]];
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}
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} else {
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// search for words with greatest uLu(q) for which d(q) != 0
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q = u - 1;
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while((-1 == d[q]) && (q > 0)) {
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--q;
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}
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// have found first non-zero d(q)
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if(q > 0) {
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j = q;
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do {
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--j;
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if((d[j] != -1) && (uLu[q] < uLu[j]) ) {
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q = j;
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}
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} while(j > 0);
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}
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// store degree of new elp polynomial
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if(L[u] > L[q] + u - q) {
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L[u + 1] = L[u];
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} else {
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L[u + 1] = L[q] + u - q;
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}
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// form new elp(x)
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for(i = 0; i <= 21; i++) {
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elp[u + 1][i] = 0;
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}
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for(i = 0; i <= L[q]; i++) {
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if(elp[q][i] != -1) {
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elp[u + 1][i + u - q] = BCH_GF_EXP[(d[u] + 63 - d[q] + elp[q][i]) % 63];
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}
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}
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for(i = 0; i <= L[u]; i++) {
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elp[u + 1][i] ^= elp[u][i];
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elp[u][i] = BCH_GF_LOG[elp[u][i]];
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}
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}
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uLu[u + 1] = u - L[u + 1];
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// form (u+1)th discrepancy
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if(u < 22) {
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// no discrepancy computed on last iteration
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if(s[u + 1] != -1) {
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d[u + 1] = BCH_GF_EXP[s[u + 1]];
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} else {
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d[u + 1] = 0;
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}
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for(i = 1; i <= L[u + 1]; i++) {
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if((s[u + 1 - i] != -1) && (elp[u + 1][i] != 0)) {
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d[u + 1] ^= BCH_GF_EXP[(s[u + 1 - i] + BCH_GF_LOG[elp[u + 1][i]]) % 63];
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}
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}
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// put d(u+1) into index form
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d[u + 1] = BCH_GF_LOG[d[u + 1]];
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}
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} while((u < 22) && (L[u + 1] <= 11));
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++u;
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if(L[u] <= 11) { // Can correct errors
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// put elp into index form
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for(i = 0; i <= L[u]; i++) {
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elp[u][i] = BCH_GF_LOG[elp[u][i]];
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}
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// Chien search: find roots of the error locator polynomial
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for(i = 1; i <= L[u]; i++) {
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reg[i] = elp[u][i];
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}
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n = 0;
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for(i = 1; i <= 63; i++) {
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q = 1;
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for(j = 1; j <= L[u]; j++) {
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if(reg[j] != -1) {
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reg[j] = (reg[j] + j) % 63;
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q ^= BCH_GF_EXP[reg[j]];
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}
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}
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if(0 == q) {
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locn[n++] = 63 - i; // store root and error location number indices
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}
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}
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if(n == L[u]) {
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// no. roots = degree of elp hence <= t errors
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for(i = 0; i < L[u]; i++) {
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cw ^= 1LL << (locn[i]);
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}
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} else {
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// elp has degree > t hence cannot solve
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decoded = false;
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}
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} else {
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decoded = false;
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}
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}
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return decoded;
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}
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@ -0,0 +1,39 @@
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/* -*- C++ -*- */
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/*
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* Copyright 2008 Steve Glass
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*
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* This file is part of OP25.
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*
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* OP25 is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* OP25 is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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* License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with OP25; see the file COPYING. If not, write to the Free
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* Software Foundation, Inc., 51 Franklin Street, Boston, MA
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* 02110-1301, USA.
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*/
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#ifndef INCLUDED_BCH_H
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#define INCLUDED_BCH_H
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#include <stdint.h>
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/*
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* BCH encode val and return the result.
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*/
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extern uint64_t bch_64_encode(uint16_t val);
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/*
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* BCH decode codeword cw and correct errors. If successful, the cw is
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* error-corrected and true is returned; otherwise returns false.
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*/
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extern bool bch_64_decode(uint64_t& cw);
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#endif /* INCLUDED_BCH_H */
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@ -20,6 +20,7 @@
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* 02110-1301, USA.
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*/
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#include <bch.h>
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#include <data_unit.h>
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#include <header.h>
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#include <ldu1.h>
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#include <packet.h>
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#include <terminator.h>
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/*
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* Construct a data unit given the initial frame_sync and network ID.
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*/
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data_unit_sptr
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data_unit::make_data_unit(uint64_t frame_sync, uint64_t network_ID)
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{
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data_unit_sptr d;
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uint8_t type = (network_ID >> 48) & 0xf;
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switch(type) {
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case 0x0:
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d = data_unit_sptr(new header(frame_sync, network_ID));
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break;
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case 0x3:
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d = data_unit_sptr(new terminator(frame_sync, network_ID, false));
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break;
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case 0x5:
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d = data_unit_sptr(new ldu1(frame_sync, network_ID));
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break;
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case 0xa:
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d = data_unit_sptr(new ldu2(frame_sync, network_ID));
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break;
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case 0x9: // VSELP "voice packet"
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case 0xc:
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d = data_unit_sptr(new packet(frame_sync, network_ID));
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break;
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case 0xf:
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d = data_unit_sptr(new terminator(frame_sync, network_ID, true));
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break;
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};
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if(bch_64_decode(network_ID)) {
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uint8_t type = (network_ID >> 48) & 0xf;
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switch(type) {
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case 0x0:
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d = data_unit_sptr(new header(frame_sync, network_ID));
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break;
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case 0x3:
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d = data_unit_sptr(new terminator(frame_sync, network_ID, false));
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break;
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case 0x5:
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d = data_unit_sptr(new ldu1(frame_sync, network_ID));
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break;
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case 0xa:
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d = data_unit_sptr(new ldu2(frame_sync, network_ID));
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break;
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case 0x9: // VSELP "voice packet"
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case 0xc:
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d = data_unit_sptr(new packet(frame_sync, network_ID));
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break;
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case 0xf:
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d = data_unit_sptr(new terminator(frame_sync, network_ID, true));
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break;
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};
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}
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return d;
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}
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@ -46,7 +46,7 @@ op25_decoder_f::~op25_decoder_f()
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}
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/*
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* Take an incoming float value, convert to a symbol and process.
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* Take an incoming float value, convert to a dibit symbol and process.
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*/
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int
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op25_decoder_f::work(int nof_output_items, gr_vector_const_void_star& input_items, gr_vector_void_star& output_items)
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@ -125,7 +125,6 @@ op25_decoder_f::identifies(dibit d)
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d_network_ID |= d;
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const size_t LAST_NETWORK_ID_SYMBOL = 56;
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if(LAST_NETWORK_ID_SYMBOL == d_symbol) {
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// ToDo: BCH (64,16,23) decoding
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identified = true;
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}
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return identified;
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@ -181,7 +180,7 @@ op25_decoder_f::sync_receive_symbol(dibit d)
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if(d_data_unit->complete(d)) {
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gr_message_sptr msg(d_data_unit->decode());
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if(msg) {
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// ToDo: prefix frame with status symbols + other header stuff
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// ToDo: prefix frame with status symbols
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d_msgq->insert_tail(msg);
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}
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++d_data_units;
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