Add option to use global noise power for all RX channels in RFSimulator

Added new command line option to channelmod: noise_power_dBFS. This options
allows the user to configure noise power in dBFS added instead of the per-channel
value.

This makes it so noise is not accumulated per channel reaching higher than expected
values.

The dBFS unit allows easy configuration. The gNB by default uses -36 dBFS setting.
To reach 3dB SNR one should set the noise_power_dBFS value to -39.

To configure using command line use --channelmod.noise_power_dBFS -50. Using this
setting the gNB and nrUE connect without issue.

radio/rfsimulator/apply_channelmod.c

@@ -42,12 +42,13 @@
   legacy: we regenerate each sub frame in UL, and each frame only in DL
 */
 void rxAddInput(const c16_t *input_sig,
-                c16_t *after_channel_sig,
+                cf_t *after_channel_sig,
                 int rxAnt,
                 channel_desc_t *channelDesc,
                 int nbSamples,
                 uint64_t TS,
-                uint32_t CirSize)
+                uint32_t CirSize,
+                bool add_noise)
 {
   if ((channelDesc->sat_height > 0) && (channelDesc->enable_dynamic_delay || channelDesc->enable_dynamic_Doppler)) { // model for transparent satellite on circular orbit
     /* assumptions:
@@ -127,12 +128,12 @@ void rxAddInput(const c16_t *input_sig,
   const double pathLossLinear = pow(10,channelDesc->path_loss_dB/20.0);
   // Energy in one sample to calibrate input noise
   // the normalized OAI value seems to be 256 as average amplitude (numerical amplification = 1)
-  const double noise_per_sample = pow(10,channelDesc->noise_power_dB/10.0) * 256;
+  const double noise_per_sample = add_noise ? pow(10,channelDesc->noise_power_dB/10.0) * 256 : 0;
   const uint64_t dd = channelDesc->channel_offset;
   const int nbTx=channelDesc->nb_tx;
 
   for (int i=0; i<nbSamples; i++) {
-    struct complex16 *out_ptr=after_channel_sig+i;
+    cf_t *out_ptr = after_channel_sig + i;
     struct complexd rx_tmp= {0};
 
     for (int txAnt=0; txAnt < nbTx; txAnt++) {
@@ -166,8 +167,8 @@ void rxAddInput(const c16_t *input_sig,
       channelDesc->Doppler_phase_cur[rxAnt] += channelDesc->Doppler_phase_inc;
     }
 
-    out_ptr->r = lround(rx_tmp.r*pathLossLinear + noise_per_sample*gaussZiggurat(0.0,1.0));
-    out_ptr->i = lround(rx_tmp.i*pathLossLinear + noise_per_sample*gaussZiggurat(0.0,1.0));
+    out_ptr->r += rx_tmp.r * pathLossLinear + noise_per_sample * gaussZiggurat(0.0, 1.0);
+    out_ptr->i += rx_tmp.i * pathLossLinear + noise_per_sample * gaussZiggurat(0.0, 1.0);
     out_ptr++;
   }
 

radio/rfsimulator/rfsimulator.h

@@ -23,13 +23,15 @@
 
 #ifndef __RFSIMULATOR_H
 #define  __RFSIMULATOR_H
+#include <stdbool.h>
 void rxAddInput( const c16_t *input_sig,
-                 c16_t *after_channel_sig,
+                 cf_t *after_channel_sig,
                  int rxAnt,
                  channel_desc_t *channelDesc,
                  int nbSamples,
                  uint64_t TS,
-                 uint32_t CirSize
+                 uint32_t CirSize,
+                 bool apply_noise
                );
 
 #endif

radio/rfsimulator/simulator.c

@@ -1006,7 +1006,9 @@ static int rfsimulator_read(openair0_device *device, openair0_timestamp *ptimest
   // Clear the output buffer
   for (int a=0; a<nbAnt; a++)
     memset(samplesVoid[a],0,sampleToByte(nsamps,1));
-
+  cf_t temp_array[nbAnt][nsamps];
+  bool apply_noise_per_channel = get_noise_power_dBFS() == INVALID_DBFS_VALUE;
+  int num_chanmod_channels = 0;
   // Add all input nodes signal in the output buffer
   for (int sock = 0; sock < MAX_FD_RFSIMU; sock++) {
     buffer_t *ptr=&t->buf[sock];
@@ -1024,12 +1026,18 @@ static int rfsimulator_read(openair0_device *device, openair0_timestamp *ptimest
 
       for (int a=0; a<nbAnt; a++) {//loop over number of Rx antennas
         if ( ptr->channel_model != NULL ) { // apply a channel model
-          rxAddInput(ptr->circularBuf, (c16_t *) samplesVoid[a],
+          if (num_chanmod_channels == 0) {
+            memset(temp_array, 0, sizeof(temp_array));
+          }
+          num_chanmod_channels++;
+          rxAddInput(ptr->circularBuf,
+                     temp_array[a],
                      a,
                      ptr->channel_model,
                      nsamps,
                      t->nextRxTstamp,
-                     CirSize);
+                     CirSize,
+                     apply_noise_per_channel);
         }
         else { // no channel modeling
           int nbAnt_tx = ptr->th.nbAnt; // number of Tx antennas
@@ -1063,6 +1071,26 @@ static int rfsimulator_read(openair0_device *device, openair0_timestamp *ptimest
       } // end for a (number of rx antennas)
     }
   }
+  if (apply_noise_per_channel && num_chanmod_channels > 0) {
+    // Noise is already applied through the channel model
+    for (int a = 0; a < nbAnt; a++) {
+      sample_t *out = (sample_t *)samplesVoid[a];
+      for (int i = 0; i < nsamps; i++) {
+        out[i].r += lroundf(temp_array[a][i].r);
+        out[i].i += lroundf(temp_array[a][i].i);
+      }
+    }
+  } else if (num_chanmod_channels > 0) {
+    // Apply noise from global setting
+    int16_t noise_power = (int16_t)(32767.0 / powf(10.0, .05 * -get_noise_power_dBFS()));
+    for (int a = 0; a < nbAnt; a++) {
+      sample_t *out = (sample_t *)samplesVoid[a];
+      for (int i = 0; i < nsamps; i++) {
+        out[i].r += lroundf(temp_array[a][i].r + noise_power * gaussZiggurat(0.0, 1.0));
+        out[i].i += lroundf(temp_array[a][i].i + noise_power * gaussZiggurat(0.0, 1.0));
+      }
+    }
+  }
 
   *ptimestamp = t->nextRxTstamp; // return the time of the first sample
   t->nextRxTstamp+=nsamps;