Modifying comments in soft_algs.c.

lte/phy/lib/modem/src/soft_algs.c

@@ -50,7 +50,6 @@
  * \param S Soft demapping auxiliary matrix
  * \param sigma2 Noise vatiance
  */
-/* Note: Optimized implementation of approximate LLR algorithm, July 2014*/
 void llr_approx(const _Complex float *in, float *out, int N, int M, int B,
     _Complex float *symbols, uint32_t (*S)[6][32], float sigma2) {
   int i, s, b;
@@ -59,7 +58,7 @@ void llr_approx(const _Complex float *in, float *out, int N, int M, int B,
   float x, y, d[64];
 
   for (s=0; s<N; s++) {  	/* recevied symbols */
-	  /* Compute exp{·} of the distances between received symbol and all constallation symbols */
+	  /* Compute the distances squared d[i] between the received symbol and all constellation points */
 	  for (i=0; i<M; i++) {
 		x = __real__ in[s] - __real__ symbols[i];
 		y = __imag__ in[s] - __imag__ symbols[i];
@@ -71,8 +70,9 @@ void llr_approx(const _Complex float *in, float *out, int N, int M, int B,
 		num = d[S[0][b][0]];
 		den = d[S[1][b][0]];
 
-		/* half the constellation symbols have '1'|'0' at any bit pos. */
-	        for (i=1; i<M/2; i++) {
+		/* Minimum distance squared search between recevied symbol and a constellation point with a
+		 '1' and a '0' for each bit position */
+	        for (i=1; i<M/2; i++) { /* half the constellation points have '1'|'0' at any given bit position */
 	        	if (d[S[0][b][i]] < num) {
 	        		num = d[S[0][b][i]];
 	        	}
@@ -106,7 +106,6 @@ void llr_approx(const _Complex float *in, float *out, int N, int M, int B,
  * \param S Soft demapping auxiliary matrix
  * \param sigma2 Noise vatiance
  */
-/* Note: Optimized implementation of exact LLR algorithm, July 2014*/
 void llr_exact(const _Complex float *in, float *out, int N, int M, int B,
     _Complex float *symbols, uint32_t (*S)[6][32], float sigma2) {
   int i, s, b;
@@ -115,19 +114,20 @@ void llr_exact(const _Complex float *in, float *out, int N, int M, int B,
   float x, y, d[64];
 
   for (s=0; s<N; s++) {  	/* recevied symbols */
-    	/* Compute exp{·} of the distances between received symbol and all constallation symbols */
+    	/* Compute exp{·} of the distances squared d[i] between the received symbol and all constellation points */
     	for (i=0; i<M; i++) {
     		x = __real__ in[s] - __real__ symbols[i];
     		y = __imag__ in[s] - __imag__ symbols[i];
     		d[i] = exp(-1*(x*x + y*y)/sigma2);
     	}
 
+	/* Sum up the corresponding d[i]'s for each bit position */
     	for (b=0; b<B; b++) {/* bits per symbol*/
     		/* initiate num[b] and den[b] */
     		num = 0;
     		den = 0;
-    	        /* half the constellation symbols have '1'|'0' at any bit pos. */
-    	        for (i=0; i<M/2; i++) {
+    	    	
+    	        for (i=0; i<M/2; i++) { /* half the constellation points have '1'|'0' at any given bit position */
     	        	num += d[S[0][b][i]];
     	        	den += d[S[1][b][i]];
     	        }