Resolves #269 - creates a generic Viterbi decoder and a Digital Mobile Radio (DMR) 3/4 Rate Viterbi decoder implementation for decoding Trellis Coded Modulation (TCM) encoded DMR Data packets.

src/edac/trellis/ViterbiDecoder_3_4_DMR.java

@@ -0,0 +1,159 @@
+/*******************************************************************************
+ * sdrtrunk
+ * Copyright (C) 2014-2017 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 edac.trellis;
+
+import bits.BinaryMessage;
+import bits.CorrectedBinaryMessage;
+
+import java.util.List;
+
+public class ViterbiDecoder_3_4_DMR extends ViterbiDecoder
+{
+    /**
+     * Viterbi decoder for Digital Mobile Radio (DMR) 3/4 rate Trellis Coded Modulation (TCM) encoded messages.
+     */
+    public ViterbiDecoder_3_4_DMR()
+    {
+        super(3,4);
+    }
+
+    /**
+     * Decodes a 3/4 rate trellis coded modulation (TCM) encoded DMR binary message containing 196 bits that have
+     * already been deinterleaved.
+     *
+     * @param encodedMessage to decode that has already been deinterleaved.
+     * @return decoded message
+     */
+    public BinaryMessage decode(BinaryMessage encodedMessage)
+    {
+        int[] symbols = getSymbols(encodedMessage);
+
+        Path mostLikelyPath = decode(symbols);
+
+        return getMessage(mostLikelyPath);
+    }
+
+    /**
+     * Extracts the decoded/corrected message from the surviving path argument.
+     *
+     * @param path to extract a message from
+     * @return corrected binary message.
+     */
+    private static CorrectedBinaryMessage getMessage(Path path)
+    {
+        List<Node> mNodes = path.getNodes();
+
+        //Each node contains an input value excluding the starting(0) and final flushing(0) nodes.
+        CorrectedBinaryMessage message = new CorrectedBinaryMessage((mNodes.size() - 2) * 3);
+
+        if(mNodes.size() > 2)
+        {
+            for(int x = 1; x < mNodes.size() - 1; x++)
+            {
+                int inputValue = mNodes.get(x).getInputValue();
+
+                int messageOffset = 3 * (x - 1);
+
+                if((inputValue & 4) == 4)
+                {
+                    message.set(messageOffset);
+                }
+
+                if((inputValue & 2) == 2)
+                {
+                    message.set(messageOffset + 1);
+                }
+
+                if((inputValue & 1) == 1)
+                {
+                    message.set(messageOffset + 2);
+                }
+            }
+        }
+
+        //Transfer the corrected error count to the message
+        message.setCorrectedBitCount(path.getError());
+
+        return message;
+    }
+
+    /**
+     * Extracts (49) four-bit symbols (196 bits / 4) from the deinterleaved DMR binary message
+     *
+     * @param encodedMessage that deinterleaved and contains 196-bits of 3/4 TCM encoding
+     * @return symbols
+     */
+    public int[] getSymbols(BinaryMessage encodedMessage)
+    {
+        //Ensure we have an integral number of transmitted symbols (nibbles) in the message
+        if(encodedMessage.size() % getOutputBitLength() != 0)
+        {
+            throw new  IllegalArgumentException("Encoded message must contain an integral number of 4-bit symbols -" +
+                " message size: " + encodedMessage.size());
+        }
+
+        int[] symbols = new int[encodedMessage.size() / getOutputBitLength()];
+
+        int index = 0;
+        int pointer = 0;
+
+        while(index < encodedMessage.size())
+        {
+            int symbol = encodedMessage.getInt(index, index + (getOutputBitLength() - 1));
+            symbols[pointer++] = symbol;
+            index += getOutputBitLength();
+        }
+
+        return symbols;
+    }
+
+    /**
+     * Creates a DMR node
+     * @param inputValue for the specific trellis node
+     * @param transmittedOutputValue the actual transmitted output value
+     * @return created node
+     */
+    @Override
+    protected Node createNode(int inputValue, int transmittedOutputValue)
+    {
+        return new DMRNode(inputValue, transmittedOutputValue);
+    }
+
+    /**
+     * Creates a DMR flushing node.  DMR uses an input value of zero to flush the final output value out of the
+     * encoder.
+     *
+     * @param transmittedOutputValue the actual transmitted output value
+     * @return
+     */
+    @Override
+    protected Node createFlushingNode(int transmittedOutputValue)
+    {
+        return new DMRNode(0, transmittedOutputValue);
+    }
+
+    /**
+     * Creates a DMR starting node.  DMR uses a starting input value of zero for the initial node.
+     */
+    @Override
+    protected Node createStartingNode()
+    {
+        return new DMRNode(0,0);
+    }
+}