NR_UE: improve NFAPI_NR_DMRS_TYPE1_linear_interp()

The DL filter was shifted relative to the contributing DM-RS pilots.
This is fixed by using the UL filter from gNB.

openair1/PHY/NR_UE_ESTIMATION/filt16a_32.h

@@ -252,12 +252,7 @@ static const short filt8_rep4[8] = {16384, 16384, 16384, 16384, 0, 0, 0, 0};
 
 // DL
 // DMRS_Type1
-static const short filt16_dl_first[16] = {12228, 12228, 12228, 12228, 8192, 8192, 8192, 8192, 4096, 4096, 4096, 4096, 0, 0, 0, 0};
-
-static const short filt16_dl_middle[16] =
-    {2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048};
-
-static const short filt16_dl_last[16] = {4096, 4096, 4096, 4096, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+// using UL filter
 
 // DMRS_Type2
 static const short filt16_dl_first_type2[16] = {16384, 16384, 16384, 8192, 8192, 8192, 8192, 8192, 8192, 0, 0, 0, 0, 0, 0};

openair1/PHY/NR_UE_ESTIMATION/nr_dl_channel_estimation.c

@@ -1300,13 +1300,15 @@ void NFAPI_NR_DMRS_TYPE1_linear_interp(NR_DL_FRAME_PARMS *frame_parms,
 #endif
 
     if (pilot_cnt == 0) { // Treat first pilot
-      c16multaddVectRealComplex(filt16_dl_first, &ch, dl_ch, 16);
+      c16multaddVectRealComplex(filt16_ul_p0, &ch, dl_ch, 16);
+    } else if (pilot_cnt == 1 || pilot_cnt == 2) {
+      c16multaddVectRealComplex(filt16_ul_p1p2, &ch, dl_ch, 16);
     } else if (pilot_cnt == 6 * nb_rb_pdsch - 1) { // Treat last pilot
-      c16multaddVectRealComplex(filt16_dl_last, &ch, dl_ch, 16);
+      c16multaddVectRealComplex(filt16_ul_last, &ch, dl_ch, 16);
     } else { // Treat middle pilots
-      c16multaddVectRealComplex(filt16_dl_middle, &ch, dl_ch, 16);
+      c16multaddVectRealComplex(filt16_ul_middle, &ch, dl_ch, 16);
       if (pilot_cnt % 2 == 0) {
-      dl_ch += 4;
+        dl_ch += 4;
       }
     }
   }