P25 - added Header Data Unit (HDU) error detection and correction with Golay(18,6,8) and ReedSolomon(36,20,17).

src/decode/p25/message/hdu/HDUMessage.java

@@ -1,15 +1,21 @@
 package decode.p25.message.hdu;
 
-import alias.Alias;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import alias.AliasList;
 import bits.BinaryMessage;
 import decode.p25.message.P25Message;
 import decode.p25.reference.DataUnitID;
 import decode.p25.reference.Encryption;
 import edac.CRC;
+import edac.Golay18;
+import edac.ReedSolomon_63_47_17;
 
 public class HDUMessage extends P25Message
 {
+	private final static Logger mLog = LoggerFactory.getLogger( HDUMessage.class );
+
 	public static final int[] MESSAGE_INDICATOR_A = { 64,65,66,67,68,69,82,83,
 		84,85,86,87,100,101,102,103,104,105,118,119,120,121,122,123,136,137,138,
 		139,140,141,154,155,156,157,158,159 };
@@ -22,6 +28,50 @@ public class HDUMessage extends P25Message
 		353,354,355,356,357,370,371	};
 	public static final int[] TALKGROUP_ID = { 372,373,374,375,388,389,390,391,
 		392,393,406,407,408,409,410,411 };
+
+	public static final int[] GOLAY_WORD_STARTS = { 64,82,100,118,136,154,172,
+		190,208,226,244,262,280,298,316,334,352,370,388,406,424,442,460,478,
+		496,514,532,550,568,586,604,622,640,658,676,694 };
+
+	public static final int[] LC_HEX_0 = { 64,65,66,67,68,69 };
+	public static final int[] LC_HEX_1 = { 82,83,84,85,86,87 };
+	public static final int[] LC_HEX_2 = { 100,101,102,103,104,105 };
+	public static final int[] LC_HEX_3 = { 118,119,120,121,122,123 };
+	public static final int[] LC_HEX_4 = { 136,137,138,139,140,141 };
+	public static final int[] LC_HEX_5 = { 154,155,156,157,158,159 };
+	public static final int[] LC_HEX_6 = { 172,173,174,175,176,177 };
+	public static final int[] LC_HEX_7 = { 190,191,192,193,194,195 };
+	public static final int[] LC_HEX_8 = { 208,209,210,211,212,213 };
+	public static final int[] LC_HEX_9 = { 226,227,228,229,230,231 };
+	public static final int[] LC_HEX_10 = { 244,245,246,247,248,249 };
+	public static final int[] LC_HEX_11 = { 262,263,264,265,266,267 };
+	public static final int[] LC_HEX_12 = { 280,281,282,283,284,285 };
+	public static final int[] LC_HEX_13 = { 298,299,300,301,302,303 };
+	public static final int[] LC_HEX_14 = { 316,317,318,319,320,321 };
+	public static final int[] LC_HEX_15 = { 334,335,336,337,338,339 };
+	public static final int[] LC_HEX_16 = { 352,353,354,355,356,357 };
+	public static final int[] LC_HEX_17 = { 370,371,372,373,374,375 };
+	public static final int[] LC_HEX_18 = { 388,389,390,391,392,393 };
+	public static final int[] LC_HEX_19 = { 406,407,408,409,410,411 };
+	public static final int[] RS_HEX_0 = { 424,425,426,427,428,429 };
+	public static final int[] RS_HEX_1 = { 442,443,444,445,446,447 };
+	public static final int[] RS_HEX_2 = { 460,461,462,463,464,465 };
+	public static final int[] RS_HEX_3 = { 478,479,480,481,482,483 };
+	public static final int[] RS_HEX_4 = { 496,497,498,499,500,501 };
+	public static final int[] RS_HEX_5 = { 514,515,516,517,518,519 };
+	public static final int[] RS_HEX_6 = { 532,533,534,535,536,537 };
+	public static final int[] RS_HEX_7 = { 550,551,552,553,554,555 };
+	public static final int[] RS_HEX_8 = { 568,569,570,571,572,573 };
+	public static final int[] RS_HEX_9 = { 586,587,588,589,590,591 };
+	public static final int[] RS_HEX_10 = { 604,605,606,607,608,609 };
+	public static final int[] RS_HEX_11 = { 622,623,624,625,626,627 };
+	public static final int[] RS_HEX_12 = { 640,641,642,643,644,645 };
+	public static final int[] RS_HEX_13 = { 658,659,660,661,662,663 };
+	public static final int[] RS_HEX_14 = { 676,677,678,679,680,681 };
+	public static final int[] RS_HEX_15 = { 694,695,696,697,698,699 };
+	
+	public static final ReedSolomon_63_47_17 mReedSolomonDecoder = 
+			new ReedSolomon_63_47_17();
 	
 	public HDUMessage( BinaryMessage message, DataUnitID duid,
             AliasList aliasList )
@@ -30,7 +80,7 @@ public class HDUMessage extends P25Message
 
 	    /* NID CRC is checked in the message framer, thus a constructed message
 	     * means it passed the CRC */
-	    mCRC = new CRC[ 2 ];
+	    mCRC = new CRC[ 3 ];
 	    mCRC[ 0 ] = CRC.PASSED;
 	    
 	    checkCRC();
@@ -38,8 +88,103 @@ public class HDUMessage extends P25Message
 	
 	private void checkCRC()
 	{
-		/* Do Golay(18,6,8) check here */
+		/* Golay( 18,6,18 ) error detection and correction */
-		/* Do RS(36,20,17) check here */
+		for( int index: GOLAY_WORD_STARTS )
+		{
+			Golay18.checkAndCorrect( mMessage, index );
+		}
+		
+    	mCRC[ 1 ] = CRC.PASSED;
+
+		/* Reed-Solomon( 36,20,17 ) error detection and correction
+		 * Check the Reed-Solomon parity bits. The RS decoder expects the link 
+		 * control data and reed solomon parity hex codewords in reverse order.  
+		 * The RS(24,12,13) code used by P25 removes the left-hand 47 data hex 
+		 * words, so we replace them with zeros. */
+        int[] input = new int [63];
+        int[] output = new int [63];
+        
+        input[  0 ] = mMessage.getInt( RS_HEX_15 );
+        input[  1 ] = mMessage.getInt( RS_HEX_14 );
+        input[  2 ] = mMessage.getInt( RS_HEX_13 );
+        input[  3 ] = mMessage.getInt( RS_HEX_12 );
+        input[  4 ] = mMessage.getInt( RS_HEX_11 );
+        input[  5 ] = mMessage.getInt( RS_HEX_10 );
+        input[  6 ] = mMessage.getInt( RS_HEX_9 );
+        input[  7 ] = mMessage.getInt( RS_HEX_8 );
+        input[  8 ] = mMessage.getInt( RS_HEX_7 );
+        input[  9 ] = mMessage.getInt( RS_HEX_6 );
+        input[ 10 ] = mMessage.getInt( RS_HEX_5 );
+        input[ 11 ] = mMessage.getInt( RS_HEX_4 );
+        input[ 12 ] = mMessage.getInt( RS_HEX_3 );
+        input[ 13 ] = mMessage.getInt( RS_HEX_2 );
+        input[ 14 ] = mMessage.getInt( RS_HEX_1 );
+        input[ 15 ] = mMessage.getInt( RS_HEX_0 );
+        
+        input[ 16 ] = mMessage.getInt( LC_HEX_19 );
+        input[ 17 ] = mMessage.getInt( LC_HEX_18 );
+        input[ 18 ] = mMessage.getInt( LC_HEX_17 );
+        input[ 19 ] = mMessage.getInt( LC_HEX_16 );
+        input[ 20 ] = mMessage.getInt( LC_HEX_15 );
+        input[ 21 ] = mMessage.getInt( LC_HEX_14 );
+        input[ 22 ] = mMessage.getInt( LC_HEX_13 );
+        input[ 23 ] = mMessage.getInt( LC_HEX_12 );
+        input[ 24 ] = mMessage.getInt( LC_HEX_11 );
+        input[ 25 ] = mMessage.getInt( LC_HEX_10 );
+        input[ 26 ] = mMessage.getInt( LC_HEX_9 );
+        input[ 27 ] = mMessage.getInt( LC_HEX_8 );
+        input[ 28 ] = mMessage.getInt( LC_HEX_7 );
+        input[ 29 ] = mMessage.getInt( LC_HEX_6 );
+        input[ 30 ] = mMessage.getInt( LC_HEX_5 );
+        input[ 31 ] = mMessage.getInt( LC_HEX_4 );
+        input[ 32 ] = mMessage.getInt( LC_HEX_3 );
+        input[ 33 ] = mMessage.getInt( LC_HEX_2 );
+        input[ 34 ] = mMessage.getInt( LC_HEX_1 );
+        input[ 35 ] = mMessage.getInt( LC_HEX_0 );
+        /* indexes 36 - 62 are defaulted to zero */
+
+        boolean irrecoverableErrors = mReedSolomonDecoder.decode( input, output );
+
+        if( irrecoverableErrors )
+        {
+        	mCRC[ 2 ] = CRC.FAILED_CRC;
+        }
+        else
+        {
+        	mCRC[ 2 ] = CRC.PASSED;
+        	
+        	/* Only fix the codeword data hex codewords */
+        	repairHexCodeword( input, output, 16, LC_HEX_19 );
+        	repairHexCodeword( input, output, 17, LC_HEX_18 );
+        	repairHexCodeword( input, output, 18, LC_HEX_17 );
+        	repairHexCodeword( input, output, 19, LC_HEX_16 );
+        	repairHexCodeword( input, output, 20, LC_HEX_15 );
+        	repairHexCodeword( input, output, 21, LC_HEX_14 );
+        	repairHexCodeword( input, output, 22, LC_HEX_13 );
+        	repairHexCodeword( input, output, 23, LC_HEX_12 );
+        	repairHexCodeword( input, output, 24, LC_HEX_11 );
+        	repairHexCodeword( input, output, 25, LC_HEX_10 );
+        	repairHexCodeword( input, output, 26, LC_HEX_9 );
+        	repairHexCodeword( input, output, 27, LC_HEX_8 );
+        	repairHexCodeword( input, output, 28, LC_HEX_7 );
+        	repairHexCodeword( input, output, 29, LC_HEX_6 );
+        	repairHexCodeword( input, output, 30, LC_HEX_5 );
+        	repairHexCodeword( input, output, 31, LC_HEX_4 );
+        	repairHexCodeword( input, output, 32, LC_HEX_3 );
+        	repairHexCodeword( input, output, 33, LC_HEX_2 );
+        	repairHexCodeword( input, output, 34, LC_HEX_1 );
+        	repairHexCodeword( input, output, 35, LC_HEX_0 );
+        }
+	}
+	
+	private void repairHexCodeword( int[] input, int[] output, int index, int[] indexSet )
+	{
+		if( input[ index ] != output[ index ] )
+		{
+			mLog.debug( "Fixing index: " + index );
+			mMessage.load( indexSet[ 0 ], 6, output[ index ] );
+			mCRC[ 2 ] = CRC.CORRECTED;
+		}
 	}
 	
 	@Override
@@ -114,10 +259,8 @@ public class HDUMessage extends P25Message
 		return getTalkgroupID();
 	}
 	
-	/* Temporary override */
 	public boolean isValid()
 	{
-		return true;
+		return mCRC[ 2 ] != null && mCRC[ 2 ] != CRC.FAILED_CRC;
 	}
-
 }

src/decode/p25/message/tdu/lc/TDULinkControlMessage.java

@@ -13,7 +13,7 @@ import decode.p25.reference.Vendor;
 import decode.p25.reference.VendorLinkControlOpcode;
 import edac.CRC;
 import edac.Golay24;
-import edac.ReedSolomon_24_12_13;
+import edac.ReedSolomon_63_47_17;
 
 public class TDULinkControlMessage extends P25Message
 {
@@ -49,8 +49,8 @@ public class TDULinkControlMessage extends P25Message
 	public static final int[] OPCODE = { 66,67,68,69,70,71 };
 	public static final int[] VENDOR = { 72,73,74,75,88,89,90,91 };
 	
-	public static final ReedSolomon_24_12_13 mReedSolomonDecoder = 
+	public static final ReedSolomon_63_47_17 mReedSolomonDecoder = 
-						new ReedSolomon_24_12_13();
+						new ReedSolomon_63_47_17();
 	
 	public TDULinkControlMessage( BinaryMessage message, DataUnitID duid,
             AliasList aliasList )

src/edac/Golay18.java

@@ -0,0 +1,54 @@
+package edac;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import bits.BinaryMessage;
+
+/*******************************************************************************
+ *     SDR Trunk 
+ *     Copyright (C) 2014 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/>
+ *     -----------------------------------------------------------------------
+ *     Galois24 decoder based on Hank Wallace's tutorial/algorithm located at:
+ *     http://www.aqdi.com/golay.htm
+ ******************************************************************************/
+
+/**
+ * Golay 18/6/8 decoder.  Uses the Golay24 edac class to perform edac on Golay
+ * 18 messages by treating the Golay 18 message as a Golay 24 message with the 
+ * left-most 6 bits set to zero.
+ */
+public class Golay18
+{
+	private final static Logger mLog = LoggerFactory.getLogger( Golay18.class );
+
+	/**
+	 * Performs error detection and correction.
+	 */
+	public static void checkAndCorrect( BinaryMessage message, int startIndex )
+	{
+		int value = message.getInt( startIndex, startIndex + 17 );
+
+		BinaryMessage temp = new BinaryMessage( 24 );
+		temp.load( 6, 18, value );
+
+		BinaryMessage corrected = Golay24.checkAndCorrect( temp, 0 );
+
+		int correctedValue = corrected.getInt( 6, 23 );
+		
+		message.load( startIndex, 18, correctedValue );
+	}
+}

src/edac/Golay23.java

@@ -14,7 +14,7 @@ public class Golay23
 	};
 
 	/**
-	 * Implements Golay(23,11,7) error detection and correction.  Returns the
+	 * Implements Golay(23,12,7) error detection and correction.  Returns the
 	 * number of detected errors.  If the error count is less than or equal to
 	 * the max correctable errors (3), then the error bits are corrected.  
 	 * Otherwise the message is left intact and an error count greater than 3

src/edac/ReedSolomon_63_47_17.java

@@ -18,12 +18,12 @@ package edac;
  *     along with this program.  If not, see <http://www.gnu.org/licenses/>
  ******************************************************************************/
 
-public class ReedSolomon_24_12_13 extends BerlekempMassey_63
+public class ReedSolomon_63_47_17 extends BerlekempMassey_63
 {
 	/**
 	 * Reed-Solomon RS(24,12,13) decoder
 	 */
-	public ReedSolomon_24_12_13()
+	public ReedSolomon_63_47_17()
     {
 		/* TT = 6 = maximum correctable bit errors */
 	    super( 6 );