Added volk'ed version of llr_approx

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

@@ -34,6 +34,54 @@
 
 #include "soft_algs.h"
 
+#define LLR_APPROX_USE_VOLK
+
+
+#ifdef LLR_APPROX_USE_VOLK
+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;
+  float num, den;
+  int change_sign = -1;
+  float x, y, d[64];
+
+  for (s = 0; s < N; s++) {     /* recevied 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];
+      d[i] = x * x + y * y;
+    }
+
+    for (b = 0; b < B; b++) {   /* bits per symbol */
+      /* initiate num[b] and den[b] */
+      num = d[S[0][b][0]];
+      den = d[S[1][b][0]];
+
+      /* 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]];
+        }
+        if (d[S[1][b][i]] < den) {
+          den = d[S[1][b][i]];
+        }
+      }
+      /* Theoretical LLR and approximate LLR values are positive if
+       * symbol(s) with '0' is/are closer and negative if symbol(s)
+       * with '1' are closer.
+       * Change sign if mapping negative to '0' and positive to '1' */
+      out[s * B + b] = change_sign * (den - num) / sigma2;
+    }
+  }
+
+}
+
+#else 
+
 /**
  * @ingroup Soft Modulation Demapping based on the approximate
  * log-likelihood algorithm
@@ -92,6 +140,8 @@ llr_approx(const _Complex float *in, float *out, int N, int M, int B,
 
 }
 
+#endif
+
 /**
  * @ingroup Soft Modulation Demapping based on the approximate
  * log-likelihood ratio algorithm
@@ -108,8 +158,7 @@ llr_approx(const _Complex float *in, float *out, int N, int M, int B,
  * \param S Soft demapping auxiliary matrix
  * \param sigma2 Noise vatiance
  */
-void
-llr_exact(const _Complex float *in, float *out, int N, int M, int B,
+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;