Apply Doppler Effect

openair1/SIMULATION/TOOLS/multipath_channel.c

@@ -29,6 +29,7 @@
 #include "sim.h"
 
 //#define DEBUG_CH
+//#define DOPPLER_DEBUG
 
 uint8_t multipath_channel_nosigconv(channel_desc_t *desc)
 {
@@ -201,11 +202,16 @@ void __attribute__ ((no_sanitize_address)) multipath_channel(channel_desc_t *des
   }
 #endif
 
+  struct complexd cexp_doppler[length];
+  if (desc->max_Doppler != 0.0) {
+    get_cexp_doppler(cexp_doppler, desc, length);
+  }
+
   for (int i=0; i<((int)length-dd); i++) {
     for (int ii=0; ii<desc->nb_rx; ii++) {
       struct complexd rx_tmp={0};
       for (int j=0; j<desc->nb_tx; j++) {
-        struct complexd *chan=desc->ch[ii+(j*desc->nb_rx)];        
+        struct complexd *chan=desc->ch[ii+(j*desc->nb_rx)];
         for (int l = 0; l<(int)desc->channel_length; l++) {
           if ((i>=0) && (i-l)>=0) {
             struct complexd tx;
@@ -215,14 +221,23 @@ void __attribute__ ((no_sanitize_address)) multipath_channel(channel_desc_t *des
             rx_tmp.i += (tx.i * chan[l].r) + (tx.r * chan[l].i);
           }
           if (i==0 && log_channel == 1) {
-	           printf("channel[%d][%d][%d] = %f dB \t(%e, %e)\n",
-                    ii, j, l, 10*log10(pow(chan[l].r,2.0)+pow(chan[l].i,2.0)),
-		         chan[l].r,
-		         chan[l].i);
+            printf("channel[%d][%d][%d] = %f dB \t(%e, %e)\n",
+                   ii, j, l, 10 * log10(pow(chan[l].r, 2.0) + pow(chan[l].i, 2.0)), chan[l].r, chan[l].i);
 	        }
         } //l
       }  // j
 
+      if (desc->max_Doppler != 0.0)
+        rx_tmp = cdMul(rx_tmp, cexp_doppler[i]);
+
+#ifdef DOPPLER_DEBUG
+      printf("[k %2i] cexp_doppler = (%7.4f, %7.4f), abs(cexp_doppler) = %.4f\n",
+                   i,
+                   cexp_doppler[i].r,
+                   cexp_doppler[i].i,
+                   sqrt(cexp_doppler[i].r * cexp_doppler[i].r + cexp_doppler[i].i * cexp_doppler[i].i));
+#endif
+
       rx_sig_re[ii][i+dd] = rx_tmp.r*path_loss;
       rx_sig_im[ii][i+dd] = rx_tmp.i*path_loss;
 #ifdef DEBUG_CH

openair1/SIMULATION/TOOLS/random_channel.c

@@ -453,7 +453,7 @@ void tdlModel(int  tdl_paths, double *tdl_delays, double *tdl_amps_dB, double DS
   }
 }
 
-void get_cexp_doppler(struct complexd *cexp_doppler, channel_desc_t *chan_desc)
+void get_cexp_doppler(struct complexd *cexp_doppler, channel_desc_t *chan_desc, const uint32_t length)
 {
   // TS 38.104 - Table G.3-1
   uint16_t Dmin = 2;
@@ -466,9 +466,10 @@ void get_cexp_doppler(struct complexd *cexp_doppler, channel_desc_t *chan_desc)
 #endif
 
   double phase0 = 2 * M_PI * uniformrandom();
-  double cos_theta[chan_desc->channel_length];
-  double fs[chan_desc->channel_length];
-  for (int t_idx = 0; t_idx < chan_desc->channel_length; t_idx++) {
+  double cos_theta[length];
+  double fs[length];
+
+  for (uint32_t t_idx = 0; t_idx < length; t_idx++) {
     double t = t_idx / (chan_desc->sampling_rate * 1e6);
     if (t >= 0 && t <= Ds / v) {
       cos_theta[t_idx] = (Ds / 2 - v * t) / sqrt(Dmin * Dmin + (Ds / 2 - v * t) * (Ds / 2 - v * t));
@@ -1898,6 +1899,7 @@ int random_channel(channel_desc_t *desc, uint8_t abstraction_flag) {
 #ifdef DEBUG_CH
             printf("(%d,%d,%d)->(%e,%e)\n",k,aarx,aatx,desc->ch[aarx+(aatx*desc->nb_rx)][k].r,desc->ch[aarx+(aatx*desc->nb_rx)][k].i);
 #endif
+
           } //channel_length
 #ifdef DEBUG_CH_POWER
           ch_power_count++;

openair1/SIMULATION/TOOLS/sim.h

@@ -348,6 +348,15 @@ void set_channeldesc_owner(channel_desc_t *cdesc, channelmod_moduleid_t module_i
 \param module_name is the C string to use as model name for the channel pointed by cdesc
 */
 void set_channeldesc_name(channel_desc_t *cdesc,char *modelname);
+
+/** \fn void get_cexp_doppler(struct complexd *cexp_doppler, channel_desc_t *chan_desc, const uint32_t length)
+\brief This routine generates the complex exponential to apply the Doppler shift
+\param cexp_doppler Output with the complex exponential of Doppler shift
+\param desc Pointer to the channel descriptor
+\param length Size of complex exponential of Doppler shift
+*/
+void get_cexp_doppler(struct complexd *cexp_doppler, channel_desc_t *chan_desc, const uint32_t length);
+
 /** \fn void random_channel(channel_desc_t *desc)
 \brief This routine generates a random channel response (time domain) according to a tapped delay line model.
 \param desc Pointer to the channel descriptor