LS channel estimation based on SRS at gNB

openair1/PHY/INIT/nr_init.c

@@ -198,9 +198,14 @@ int phy_init_nr_gNB(PHY_VARS_gNB *gNB,
   for (int id=0; id<NUMBER_OF_NR_SRS_MAX; id++) {
     gNB->nr_srs_info[id] = (nr_srs_info_t *)malloc16_clear(sizeof(nr_srs_info_t));
     gNB->nr_srs_info[id]->srs_generated_signal = (int32_t*)malloc16_clear(fp->samples_per_frame*sizeof(int32_t));
+    gNB->nr_srs_info[id]->noise_power = (double*)malloc16_clear(sizeof(double));
     gNB->nr_srs_info[id]->srs_received_signal = (int32_t **)malloc16(Prx*sizeof(int32_t*));
+    gNB->nr_srs_info[id]->srs_ls_estimated_channel = (int32_t **)malloc16(Prx*sizeof(int32_t*));
+    gNB->nr_srs_info[id]->srs_estimated_channel = (int32_t **)malloc16(Prx*sizeof(int32_t*));
     for (i=0;i<Prx;i++){
       gNB->nr_srs_info[id]->srs_received_signal[i] = (int32_t*)malloc16_clear(fp->samples_per_frame*sizeof(int32_t));
+      gNB->nr_srs_info[id]->srs_ls_estimated_channel[i] = (int32_t*)malloc16_clear(fp->samples_per_frame*sizeof(int32_t));
+      gNB->nr_srs_info[id]->srs_estimated_channel[i] = (int32_t*)malloc16_clear(fp->samples_per_frame*sizeof(int32_t));
     }
   }
 

openair1/PHY/INIT/nr_init_ue.c

@@ -325,9 +325,14 @@ int init_nr_ue_signal(PHY_VARS_NR_UE *ue,
     srs_vars[gNB_id]->active = false;
     ue->nr_srs_info = (nr_srs_info_t *)malloc16_clear(sizeof(nr_srs_info_t));
     ue->nr_srs_info->srs_generated_signal = (int32_t *) malloc16_clear( (2*(fp->samples_per_frame)+2048)*sizeof(int32_t) );
+    ue->nr_srs_info->noise_power = (double*)malloc16_clear(sizeof(double));
     ue->nr_srs_info->srs_received_signal = (int32_t **)malloc16( fp->nb_antennas_rx*sizeof(int32_t *) );
+    ue->nr_srs_info->srs_ls_estimated_channel = (int32_t **)malloc16( fp->nb_antennas_rx*sizeof(int32_t *) );
+    ue->nr_srs_info->srs_estimated_channel = (int32_t **)malloc16( fp->nb_antennas_rx*sizeof(int32_t *) );
     for (i=0; i<fp->nb_antennas_rx; i++) {
       ue->nr_srs_info->srs_received_signal[i] = (int32_t *) malloc16_clear( (2*(fp->samples_per_frame)+2048)*sizeof(int32_t) );
+      ue->nr_srs_info->srs_ls_estimated_channel[i] = (int32_t *) malloc16_clear( (2*(fp->samples_per_frame)+2048)*sizeof(int32_t) );
+      ue->nr_srs_info->srs_estimated_channel[i] = (int32_t *) malloc16_clear( (2*(fp->samples_per_frame)+2048)*sizeof(int32_t) );
     }
 
     if (abstraction_flag == 0) {

openair1/PHY/NR_ESTIMATION/nr_ul_channel_estimation.c

@@ -36,6 +36,7 @@
 
 //#define DEBUG_CH
 //#define DEBUG_PUSCH
+//#define SRS_DEBUG
 
 #define NO_INTERP 1
 #define dBc(x,y) (dB_fixed(((int32_t)(x))*(x) + ((int32_t)(y))*(y)))
@@ -1091,3 +1092,62 @@ void nr_pusch_ptrs_processing(PHY_VARS_gNB *gNB,
     }// last symbol check
   }//Antenna loop
 }
+
+int nr_srs_channel_estimation(PHY_VARS_gNB *gNB,
+                              int frame,
+                              int slot,
+                              nfapi_nr_srs_pdu_t *srs_pdu,
+                              nr_srs_info_t *nr_srs_info,
+                              int32_t *srs_generated_signal,
+                              int32_t **srs_received_signal,
+                              int32_t **srs_estimated_channel,
+                              double *noise_power) {
+
+  if(nr_srs_info->n_symbs==0) {
+    LOG_E(NR_PHY, "(%d.%d) nr_srs_info was not generated yet!\n", frame, slot);
+    return -1;
+  }
+
+  NR_DL_FRAME_PARMS *frame_parms = &gNB->frame_parms;
+  int32_t **srs_ls_estimated_channel = nr_srs_info->srs_ls_estimated_channel;
+  uint64_t subcarrier_offset = frame_parms->first_carrier_offset + srs_pdu->bwp_start*12;
+
+  for (int ant = 0; ant < frame_parms->nb_antennas_rx; ant++) {
+
+    memset(srs_ls_estimated_channel[ant], 0, frame_parms->samples_per_frame*sizeof(int32_t));
+    memset(srs_estimated_channel[ant], 0, frame_parms->samples_per_frame*sizeof(int32_t));
+
+    for(int sc_idx = 0; sc_idx < nr_srs_info->n_symbs; sc_idx++) {
+
+      int16_t generated_real = srs_generated_signal[nr_srs_info->subcarrier_idx[sc_idx] + subcarrier_offset]&0xFFFF;
+      int16_t generated_imag = (srs_generated_signal[nr_srs_info->subcarrier_idx[sc_idx] + subcarrier_offset]>>16)&0xFFFF;
+
+      int16_t received_real = srs_received_signal[ant][nr_srs_info->subcarrier_idx[sc_idx] + subcarrier_offset]&0xFFFF;
+      int16_t received_imag = (srs_received_signal[ant][nr_srs_info->subcarrier_idx[sc_idx] + subcarrier_offset]>>16)&0xFFFF;
+
+      // We know that nr_srs_info->srs_generated_signal_bits bits are enough to represent the generated_real and generated_imag.
+      // So we only need a nr_srs_info->srs_generated_signal_bits shift to ensure that the result fits into 16 bits.
+      int16_t ls_estimated_real = (int16_t)(((int32_t)generated_real*received_real + (int32_t)generated_imag*received_imag)>>nr_srs_info->srs_generated_signal_bits);
+      int16_t ls_estimated_imag = (int16_t)(((int32_t)generated_real*received_imag - (int32_t)generated_imag*received_real)>>nr_srs_info->srs_generated_signal_bits);
+
+      srs_ls_estimated_channel[ant][nr_srs_info->subcarrier_idx[sc_idx] + subcarrier_offset] = ls_estimated_real + (((int32_t)ls_estimated_imag<<16)&0xFFFF0000);
+
+#ifdef SRS_DEBUG
+      if(sc_idx == 0) {
+        LOG_I(NR_PHY,"______________________________ Rx antenna %i _______________________________\n", ant);
+      }
+      if(nr_srs_info->subcarrier_idx[sc_idx]%12 == 0) {
+        LOG_I(NR_PHY,":::::::::::::::::::::::::::::::::::: %i ::::::::::::::::::::::::::::::::::::\n", nr_srs_info->subcarrier_idx[sc_idx]/12);
+        LOG_I(NR_PHY,"\t  __genRe________genIm__|____rxRe_________rxIm__|____lsRe________lsIm_\n");
+      }
+      LOG_I(NR_PHY,"(%4i) %6i\t%6i  |  %6i\t%6i  |  %6i\t%6i\n",
+            nr_srs_info->subcarrier_idx[sc_idx],
+            generated_real, generated_imag,
+            received_real, received_imag,
+            ls_estimated_real, ls_estimated_imag);
+#endif
+    }
+  }
+
+  return 0;
+}
\ No newline at end of file

openair1/PHY/NR_ESTIMATION/nr_ul_estimation.h

@@ -62,4 +62,14 @@ void nr_pusch_ptrs_processing(PHY_VARS_gNB *gNB,
                               uint8_t nr_tti_rx,
                               unsigned char symbol,
                               uint32_t nb_re_pusch);
+
+int nr_srs_channel_estimation(PHY_VARS_gNB *gNB,
+                              int frame,
+                              int slot,
+                              nfapi_nr_srs_pdu_t *srs_pdu,
+                              nr_srs_info_t *nr_srs_info,
+                              int32_t *srs_generated_signal,
+                              int32_t **srs_received_signal,
+                              int32_t **srs_estimated_channel,
+                              double *noise_power);
 #endif

openair1/PHY/NR_UE_TRANSPORT/srs_modulation_nr.c

@@ -120,6 +120,7 @@ int generate_srs_nr(nfapi_nr_srs_pdu_t *srs_config_pdu,
 
   if(nr_srs_info) {
     nr_srs_info->n_symbs = 0;
+    nr_srs_info->srs_generated_signal_bits = log2_approx(amp);
   }
 
 #ifdef SRS_DEBUG

openair1/PHY/defs_nr_common.h

@@ -243,8 +243,12 @@ typedef struct {
 typedef struct {
   uint16_t n_symbs;
   uint16_t subcarrier_idx[6*NR_MAX_NB_RB];
+  uint8_t srs_generated_signal_bits;
   int32_t *srs_generated_signal;
   int32_t **srs_received_signal;
+  int32_t **srs_ls_estimated_channel;
+  int32_t **srs_estimated_channel;
+  double *noise_power;
 } nr_srs_info_t;
 
 typedef struct NR_DL_FRAME_PARMS NR_DL_FRAME_PARMS;

openair1/SCHED_NR/phy_procedures_nr_gNB.c

@@ -804,6 +804,14 @@ int phy_procedures_gNB_uespec_RX(PHY_VARS_gNB *gNB, int frame_rx, int slot_rx) {
         }
 
         nr_get_srs_signal(gNB,frame_rx,slot_rx,srs_pdu, gNB->nr_srs_info[i], gNB->nr_srs_info[i]->srs_received_signal);
+
+        nr_srs_channel_estimation(gNB,frame_rx,slot_rx,srs_pdu,
+                                  gNB->nr_srs_info[i],
+                                  gNB->nr_srs_info[i]->srs_generated_signal,
+                                  gNB->nr_srs_info[i]->srs_received_signal,
+                                  gNB->nr_srs_info[i]->srs_estimated_channel,
+                                  gNB->nr_srs_info[i]->noise_power);
+
         srs->active = 0;
       }
     }