Compute noise variance to be used in MMSE

openair1/PHY/NR_ESTIMATION/nr_ul_channel_estimation.c

@@ -120,7 +120,8 @@ int nr_pusch_channel_estimation(PHY_VARS_gNB *gNB,
                                 int ul_id,
                                 unsigned short bwp_start_subcarrier,
                                 nfapi_nr_pusch_pdu_t *pusch_pdu,
-                                int *max_ch) {
+                                int *max_ch,
+                                uint32_t *nvar) {
 
   c16_t pilot[3280] __attribute__((aligned(32)));
   const int chest_freq = gNB->chest_freq;
@@ -186,6 +187,8 @@ int nr_pusch_channel_estimation(PHY_VARS_gNB *gNB,
 
 #endif
 
+  int nest_count = 0;
+  uint64_t noise_amp2 = 0;
   c16_t ul_ls_est[symbolSize] __attribute__((aligned(32)));
   memset(ul_ls_est, 0, sizeof(c16_t) * symbolSize);
   NR_ULSCH_delay_t *delay = &gNB->ulsch[ul_id].delay;
@@ -284,12 +287,16 @@ int nr_pusch_channel_estimation(PHY_VARS_gNB *gNB,
           int k = pilot_cnt << 1;
           ul_ch[k] = c16mulShift(ul_ch[k], ul_inv_delay_table[k], 8);
           ul_ch[k + 1] = c16mulShift(ul_ch[k + 1], ul_inv_delay_table[k + 1], 8);
+          noise_amp2 += c16amp2(c16sub(ul_ls_est[k], ul_ch[k]));
+          noise_amp2 += c16amp2(c16sub(ul_ls_est[k + 1], ul_ch[k + 1]));
+
 #ifdef DEBUG_PUSCH
           re_offset = (k0 + (n << 2) + (k_line << 1)) % symbolSize;
           c16_t *rxF = &rxdataF[soffset + re_offset];
           printf("ch -> (%4d,%4d), ch_inter -> (%4d,%4d)\n", ul_ls_est[k].r, ul_ls_est[k].i, ul_ch[k].r, ul_ch[k].i);
 #endif
           pilot_cnt++;
+          nest_count += 2;
         }
       }
 
@@ -307,6 +314,8 @@ int nr_pusch_channel_estimation(PHY_VARS_gNB *gNB,
         multadd_real_four_symbols_vector_complex_scalar(filt8_rep4, &ch, &ul_ls_est[n]);
         ul_ls_est[n + 4] = ch;
         ul_ls_est[n + 5] = ch;
+        noise_amp2 += c16amp2(c16sub(ch0, ch));
+        nest_count++;
       }
 
       // Delay compensation
@@ -501,7 +510,12 @@ int nr_pusch_channel_estimation(PHY_VARS_gNB *gNB,
 #ifdef DEBUG_CH
   fclose(debug_ch_est);
 #endif
-  return(0);
+
+  if (nvar && nest_count > 0) {
+    *nvar = (uint32_t)(noise_amp2 / nest_count);
+  }
+
+  return 0;
 }
 
 

openair1/PHY/NR_ESTIMATION/nr_ul_estimation.h

@@ -47,7 +47,8 @@ int nr_pusch_channel_estimation(PHY_VARS_gNB *gNB,
                                 int ul_id,
                                 unsigned short bwp_start_subcarrier,
                                 nfapi_nr_pusch_pdu_t *pusch_pdu,
-                                int *max_ch);
+                                int *max_ch,
+                                uint32_t *nvar);
 
 void dump_nr_I0_stats(FILE *fd,PHY_VARS_gNB *gNB);
 

openair1/PHY/NR_TRANSPORT/nr_ulsch_demodulation.c

@@ -1482,7 +1482,7 @@ uint8_t nr_ulsch_mmse_2layers(NR_DL_FRAME_PARMS *frame_parms,
                               int shift,
                               unsigned char symbol,
                               int length,
-                              int noise_var)
+                              uint32_t noise_var)
 {
   int *ch00, *ch01, *ch10, *ch11;
   int *ch20, *ch30, *ch21, *ch31;
@@ -1881,6 +1881,7 @@ void nr_rx_pusch(PHY_VARS_gNB *gNB,
   //----------------------------------------------------------
   start_meas(&gNB->ulsch_channel_estimation_stats);
   int max_ch = 0;
+  uint32_t nvar = 0;
   for(uint8_t symbol = rel15_ul->start_symbol_index; symbol < (rel15_ul->start_symbol_index + rel15_ul->nr_of_symbols); symbol++) {
     uint8_t dmrs_symbol_flag = (rel15_ul->ul_dmrs_symb_pos >> symbol) & 0x01;
     LOG_D(PHY, "symbol %d, dmrs_symbol_flag :%d\n", symbol, dmrs_symbol_flag);
@@ -1890,7 +1891,7 @@ void nr_rx_pusch(PHY_VARS_gNB *gNB,
         pusch_vars->dmrs_symbol = symbol;
 
       for (int nl=0; nl<rel15_ul->nrOfLayers; nl++) {
-        
+        uint32_t nvar_tmp = 0;
         nr_pusch_channel_estimation(gNB,
                                     slot,
                                     get_dmrs_port(nl,rel15_ul->dmrs_ports),
@@ -1898,7 +1899,9 @@ void nr_rx_pusch(PHY_VARS_gNB *gNB,
                                     ulsch_id,
                                     bwp_start_subcarrier,
                                     rel15_ul,
-                                    &max_ch);
+                                    &max_ch,
+                                    &nvar_tmp);
+        nvar += nvar_tmp;
       }
 
       nr_gnb_measurements(gNB, ulsch, pusch_vars, symbol, rel15_ul->nrOfLayers);
@@ -1929,6 +1932,8 @@ void nr_rx_pusch(PHY_VARS_gNB *gNB,
     }
   }
 
+  nvar /= (rel15_ul->nr_of_symbols * rel15_ul->nrOfLayers * frame_parms->nb_antennas_rx);
+
   if (gNB->chest_time == 1) { // averaging time domain channel estimates
     nr_chest_time_domain_avg(frame_parms,
                              pusch_vars->ul_ch_estimates,
@@ -2055,7 +2060,6 @@ void nr_rx_pusch(PHY_VARS_gNB *gNB,
 
       // Apply MMSE for 2 Tx layers
       if (rel15_ul->nrOfLayers == 2) {
-        int noise_var = 100; // TODO: Get noise variance
         nr_ulsch_mmse_2layers(frame_parms,
                               pusch_vars->rxdataF_comp,
                               pusch_vars->ul_ch_mag0,
@@ -2067,7 +2071,7 @@ void nr_rx_pusch(PHY_VARS_gNB *gNB,
                               pusch_vars->log2_maxh,
                               symbol,
                               nb_re_pusch,
-                              noise_var);
+                              nvar);
       }
 
       stop_meas(&gNB->ulsch_mrc_stats);

openair1/PHY/TOOLS/tools_defs.h

@@ -97,6 +97,17 @@ extern "C" {
 #define squaredMod(a) ((a).r*(a).r + (a).i*(a).i)
 #define csum(res, i1, i2) (res).r = (i1).r + (i2).r ; (res).i = (i1).i + (i2).i
 
+  __attribute__((always_inline)) inline uint32_t c16amp2(const c16_t a) {
+    return a.r * a.r + a.i * a.i;
+  }
+
+  __attribute__((always_inline)) inline c16_t c16sub(const c16_t a, const c16_t b) {
+    return (c16_t) {
+        .r = (int16_t) (a.r - b.r),
+        .i = (int16_t) (a.i - b.i)
+    };
+  }
+
   __attribute__((always_inline)) inline c16_t c16Shift(const c16_t a, const int Shift) {
     return (c16_t) {
         .r = (int16_t)(a.r >> Shift),