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#2162 APCO25 NID BCH decoder implementation. (#2163)

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Co-authored-by: Dennis Sheirer <dsheirer@github.com>
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Denny Sheirer
2025-02-27 08:09:46 -06:00
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parent 4e367bb5fe
commit 8718d04ef5
6 changed files with 1513 additions and 13 deletions
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src/test/java/io/github/dsheirer/edac/bch/BCH_63_16_23_P25_Test.java Normal file
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/*
* *****************************************************************************
* Copyright (C) 2014-2025 Dennis Sheirer
*
* 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/>
* ****************************************************************************
*/
package io.github.dsheirer.edac.bch;
import io.github.dsheirer.bits.CorrectedBinaryMessage;
import io.github.dsheirer.bits.IntField;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* Tests for the BCH decoder for APCO25 NID fragments protected by a BCH(63,16,23) code
*/
public class BCH_63_16_23_P25_Test
{
/**
* NAC: 1, DUID:0 (HDU), line 12 in the FDMA Table 19 NID Generator matrix.
*
* Octal: 00 0020 1430 2667 7236 1044
* Bin: 0 000 000 000 010 000 001 100 011 000 010 110 110 111 111 010 011 110 001 000 100 100
* Bin: 0000 0000 0001 0000 0011 0001 1000 0101 1011 0111 1110 1001 1110 0010 0010 0100
* Hex: 0 0 1 0 3 1 8 5 B 7 E 9 E 2 2 4
* Hex: 00103185B7E9E224
*/
private static final long[] P25_NID_BCH_63_16_GENERATOR_MATRIX = new long[16];
static
{
P25_NID_BCH_63_16_GENERATOR_MATRIX[0] = Long.parseLong("6331141367235452", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[1] = Long.parseLong("5265521614723276", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[2] = Long.parseLong("4603711461164164", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[3] = Long.parseLong("2301744630472072", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[4] = Long.parseLong("7271623073000466", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[5] = Long.parseLong("5605650752635660", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[6] = Long.parseLong("2702724365316730", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[7] = Long.parseLong("1341352172547354", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[8] = Long.parseLong("0560565075263566", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[9] = Long.parseLong("6141333751704220", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[10] = Long.parseLong("3060555764742110", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[11] = Long.parseLong("1430266772361044", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[12] = Long.parseLong("0614133375170422", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[13] = Long.parseLong("6037114611641642", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[14] = Long.parseLong("5326507063515373", 8);
P25_NID_BCH_63_16_GENERATOR_MATRIX[15] = Long.parseLong("4662302756473127", 8);
}
private static final IntField NAC_FIELD = IntField.length12(0);
private static final IntField DUID_FIELD = IntField.length4(12);
/**
* Creates a valid P25 NID 64-bit message containing the NAC and DUID values and calculated parity bits.
* @param nac
* @param duid
* @return
*/
public static CorrectedBinaryMessage create(int nac, int duid)
{
CorrectedBinaryMessage cbm = new CorrectedBinaryMessage(64);
cbm.setInt(nac, NAC_FIELD);
cbm.setInt(duid, DUID_FIELD);
long parity = 0;
for(int x = 0; x < 16; x++)
{
if(cbm.get(x))
{
parity ^= P25_NID_BCH_63_16_GENERATOR_MATRIX[x];
}
}
cbm.load(16, 48, parity);
return cbm;
}
/**
* Verify that the decoder can correct all 1-bit errors across the message bits 0-62. Note: this test ignores the
* unused parity bit at index 63.
* @param decoder that can correct one-bit errors.
* @param original that is fully formed across indices 0-62 with BCH parity bits
* @return true if the test is successful
*/
public static List<Integer> testOneBitErrors(BCH decoder, CorrectedBinaryMessage original, List<Integer> errors)
{
//Induce an additional 1 bit error and test across each bit position.
for(int error = 0; error < 63; error++)
{
if(!errors.contains(error))
{
CorrectedBinaryMessage localCopy = original.getSubMessage(0, 62);
for(int additionalError: errors)
{
localCopy.flip(additionalError);
}
localCopy.flip(error);
decoder.decode(localCopy);
localCopy.xor(original);
if(localCopy.cardinality() > 0)
{
errors.add(error);
return errors;
}
}
}
return Collections.emptyList();
}
public static List<Integer> testMultiBitErrors(BCH decoder, CorrectedBinaryMessage original, List<Integer> errors)
{
System.out.print("\rTesting: " + errors);
if(errors.size() + 2 >= decoder.getMaxErrorCorrection())
{
return Collections.emptyList();
}
for(int error = 0; error < 63; error++)
{
if(!errors.contains(error))
{
List<Integer> errorsCopy = new ArrayList<>(errors);
errorsCopy.add(error);
List<Integer> result = testOneBitErrors(decoder, original, errorsCopy);
if(!result.isEmpty())
{
return result;
}
errorsCopy = new ArrayList<>(errors);
errorsCopy.add(error);
result = testMultiBitErrors(decoder, original, errorsCopy);
if(!result.isEmpty())
{
return result;
}
}
}
return Collections.emptyList();
}
public static void main(String[] args)
{
System.out.println("Starting ....");
BCH decoder = new BCH_63_16_23_P25();
CorrectedBinaryMessage message = create(534, 2);
//Test correcting 1-11 bit errors
message.clear(63); //Clear the parity bit so that it doesn't interfere with the results validation
List<Integer> errors = new ArrayList<>();
List<Integer> results = testMultiBitErrors(decoder, message, errors);
System.out.println("Test Results: " + (results.isEmpty() ? "PASS" : "FAIL") + " Resulse: " + results);
//Test 11 bit errors.
CorrectedBinaryMessage errorMessage = message.getSubMessage(0, 63);
int[] errorArray = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
for(int error: errorArray)
{
errorMessage.flip(error);
}
decoder.decode(errorMessage);
System.out.println(" Original: " + message);
System.out.println("Corrected: " + errorMessage + " Corrected Bit Count: " + errorMessage.getCorrectedBitCount());
}
}