updated lerp channel estimation

nulled estimates at DC

openair1/PHY/NR_UE_ESTIMATION/nr_dl_channel_estimation.c

@@ -749,16 +749,23 @@ int nr_pdsch_channel_estimation(PHY_VARS_NR_UE *ue,
 
       for (uint8_t idxPil=0; idxPil<10; idxPil+=2 ) {
         rxF   = (int16_t *)&rxdataF[aarx][(symbol_offset+nushift+re_offset)];
-        ch[idxPil]   = (int16_t)(((int32_t)pil[idx8Sym*8+idxPil]*rxF[0] - (int32_t)pil[idx8Sym*idxPil+1]*rxF[1])>>15);
-        ch[idxPil+1] = (int16_t)(((int32_t)pil[idx8Sym*8+idxPil]*rxF[1] + (int32_t)pil[idx8Sym*idxPil+1]*rxF[0])>>15);
+        ch[idxPil]   = (int16_t)(((int32_t)pil[idx8Sym*8+idxPil]*rxF[0] - (int32_t)pil[idx8Sym*8+idxPil+1]*rxF[1])>>15);
+        ch[idxPil+1] = (int16_t)(((int32_t)pil[idx8Sym*8+idxPil]*rxF[1] + (int32_t)pil[idx8Sym*8+idxPil+1]*rxF[0])>>15);
+        // Nulling estimates at DC
+        if (re_offset == 0) {
+          ch[idxPil] = 0;
+          ch[idxPil+1] = 0;
+        }
         re_offset = (re_offset+2)&(ue->frame_parms.ofdm_symbol_size-1);
       }
       
       simple_lerp(ch, dl_ch);
+#ifdef DEBUG_PDSCH
       for(uint8_t i=0; i<16; i++) {
         printf("%d\t",dl_ch[i]);
       }
       printf("\n");
+#endif
       dl_ch += 16;
       re_offset = (re_offset-2)&(ue->frame_parms.ofdm_symbol_size-1);
     }
@@ -770,6 +777,11 @@ int nr_pdsch_channel_estimation(PHY_VARS_NR_UE *ue,
         rxF   = (int16_t *)&rxdataF[aarx][(symbol_offset+nushift+re_offset)];
         ch[idxPil]   = (int16_t)(((int32_t)pil[used_pils+idxPil]*rxF[0] - (int32_t)pil[used_pils*idxPil+1]*rxF[1])>>15);
         ch[idxPil+1] = (int16_t)(((int32_t)pil[used_pils+idxPil]*rxF[1] + (int32_t)pil[used_pils*idxPil+1]*rxF[0])>>15);
+        // Nulling estimates at DC
+        if (re_offset == 0) {
+          ch[idxPil] = 0;
+          ch[idxPil+1] = 0;
+        }
         re_offset = (re_offset+2)&(ue->frame_parms.ofdm_symbol_size-1);
       }
 
@@ -788,16 +800,14 @@ int nr_pdsch_channel_estimation(PHY_VARS_NR_UE *ue,
 
 void simple_lerp(int16_t *in, int16_t *out)
 {
-  __m128i est, sum, sign;
+  __m128i est, sign;
   __m128i *x0 = (__m128i*)in;
   __m128i *x1 = (__m128i*)(in+2);
   __m128i *y = (__m128i*)out;
 
   est  = _mm_add_epi16 (*x0, *x1);
-  //sum  = _mm_and_si128(est, _mm_set1_epi16(0x7FFF));
   sign = _mm_and_si128(est, _mm_set1_epi16(0x8000));
   est  = _mm_or_si128(_mm_srli_epi16(est, 1), sign);
   y[0] = _mm_unpacklo_epi32(*x0, est);
   y[1] = _mm_unpackhi_epi32(*x0, est);
 }
-