From 885562539e1ede623f4695b667b31347a0b50f59 Mon Sep 17 00:00:00 2001
From: juribeparada <juribeparada@gmail.com>
Date: Thu, 1 Feb 2018 11:56:18 -0300
Subject: [PATCH] Changing metric calculation for Viterbi decoder NXDN

---
 NXDNConvolution.cpp | 17 ++++-------------
 NXDNFACCH1.cpp      |  4 ++--
 NXDNSACCH.cpp       |  4 ++--
 NXDNUDCH.cpp        |  4 ++--
 4 files changed, 10 insertions(+), 19 deletions(-)

diff --git a/NXDNConvolution.cpp b/NXDNConvolution.cpp
index 049bdb6..8db6a05 100755
--- a/NXDNConvolution.cpp
+++ b/NXDNConvolution.cpp
@@ -27,12 +27,12 @@ const unsigned char BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U
 #define WRITE_BIT1(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
 #define READ_BIT1(p,i)    (p[(i)>>3] & BIT_MASK_TABLE[(i)&7])
 
-const uint8_t BRANCH_TABLE1[] = {0U, 0U, 0U, 0U, 1U, 1U, 1U, 1U};
-const uint8_t BRANCH_TABLE2[] = {0U, 1U, 1U, 0U, 0U, 1U, 1U, 0U};
+const uint8_t BRANCH_TABLE1[] = {0U, 0U, 0U, 0U, 2U, 2U, 2U, 2U};
+const uint8_t BRANCH_TABLE2[] = {0U, 2U, 2U, 0U, 0U, 2U, 2U, 0U};
 
 const unsigned int NUM_OF_STATES_D2 = 8U;
 const unsigned int NUM_OF_STATES = 16U;
-const uint32_t     M = 2U;
+const uint32_t     M = 4U;
 const unsigned int K = 5U;
 
 CNXDNConvolution::CNXDNConvolution() :
@@ -72,16 +72,7 @@ void CNXDNConvolution::decode(uint8_t s0, uint8_t s1)
   for (uint8_t i = 0U; i < NUM_OF_STATES_D2; i++) {
     uint8_t j = i * 2U;
 
-    uint16_t metric0 = 0;
-    uint16_t metric1 = 0;
-    
-	if (s0 != 99U)
-    	metric0 = (BRANCH_TABLE1[i] ^ s0);
-    	
-	if (s1 != 99U)
-    	metric1 = (BRANCH_TABLE2[i] ^ s1);
-    	
-    uint16_t metric = metric0 + metric1;
+    uint16_t metric = abs(BRANCH_TABLE1[i] - s0) + abs(BRANCH_TABLE2[i] - s1);
 
     uint16_t m0 = m_oldMetrics[i] + metric;
     uint16_t m1 = m_oldMetrics[i + NUM_OF_STATES_D2] + (M - metric);
diff --git a/NXDNFACCH1.cpp b/NXDNFACCH1.cpp
index 48f4639..63a3377 100644
--- a/NXDNFACCH1.cpp
+++ b/NXDNFACCH1.cpp
@@ -89,12 +89,12 @@ bool CNXDNFACCH1::decode(const unsigned char* data, unsigned int offset)
 	unsigned int index = 0U;
 	for (unsigned int i = 0U; i < NXDN_FACCH1_LENGTH_BITS; i++) {
 		if (n == PUNCTURE_LIST[index]) {
-			temp2[n++] = 99U;
+			temp2[n++] = 1U;
 			index++;
 		}
 
 		bool b = READ_BIT1(temp1, i);
-		temp2[n++] = b ? 1U : 0U;
+		temp2[n++] = b ? 2U : 0U;
 	}
 
 	CNXDNConvolution conv;
diff --git a/NXDNSACCH.cpp b/NXDNSACCH.cpp
index 304b20d..e4ec9e5 100755
--- a/NXDNSACCH.cpp
+++ b/NXDNSACCH.cpp
@@ -83,12 +83,12 @@ bool CNXDNSACCH::decode(const unsigned char* data)
 	unsigned int index = 0U;
 	for (unsigned int i = 0U; i < NXDN_SACCH_LENGTH_BITS; i++) {
 		if (n == PUNCTURE_LIST[index]) {
-			temp2[n++] = 99U;
+			temp2[n++] = 1U;
 			index++;
 		}
 
 		bool b = READ_BIT1(temp1, i);
-		temp2[n++] = b ? 1U : 0U;
+		temp2[n++] = b ? 2U : 0U;
 	}
 
 	CNXDNConvolution conv;
diff --git a/NXDNUDCH.cpp b/NXDNUDCH.cpp
index e58460e..eabcca7 100644
--- a/NXDNUDCH.cpp
+++ b/NXDNUDCH.cpp
@@ -110,12 +110,12 @@ bool CNXDNUDCH::decode(const unsigned char* data)
 	unsigned int index = 0U;
 	for (unsigned int i = 0U; i < NXDN_FACCH2_LENGTH_BITS; i++) {
 		if (n == PUNCTURE_LIST[index]) {
-			temp2[n++] = 99U;
+			temp2[n++] = 1U;
 			index++;
 		}
 
 		bool b = READ_BIT1(temp1, i);
-		temp2[n++] = b ? 1U : 0U;
+		temp2[n++] = b ? 2U : 0U;
 	}
 
 	CNXDNConvolution conv;