rfsimulator: add delay and Doppler simulation for circular orbit and add according channel models SAT_LEO_TRANS and SAT_LEO_REGEN

Delay and Doppler computation is done as in Matlab function dopplerShiftCircularOrbit: https://de.mathworks.com/help/satcom/ref/dopplershiftcircularorbit.html
2024-08-20 16:46:25 +02:00
parent 68b07d542c
commit 6a8edaf317
4 changed files with 149 additions and 14 deletions
@@ -28,7 +28,7 @@
 #include <unistd.h>
 #include <stdbool.h>
 #include <errno.h>
-
+#include <complex.h>

 #include <common/utils/assertions.h>
 #include <common/utils/LOG/log.h>
@@ -52,14 +52,85 @@
  either we regenerate the channel (call again random_channel(desc,0)), or we keep it over subframes
  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,
-                 int rxAnt,
-                 channel_desc_t *channelDesc,
-                 int nbSamples,
-                 uint64_t TS,
-                 uint32_t CirSize
-               ) {
+void rxAddInput(const c16_t *input_sig,
+                c16_t *after_channel_sig,
+                int rxAnt,
+                channel_desc_t *channelDesc,
+                int nbSamples,
+                uint64_t TS,
+                uint32_t CirSize)
+{
+  if ((channelDesc->sat_height > 0) && (channelDesc->enable_dynamic_delay || channelDesc->enable_dynamic_Doppler)) { // model for transparent satellite on circular orbit
+    /* assumptions:
+       - The Earth is spherical, the ground station is static, and that the Earth does not rotate.
+       - An access or link is possible from the satellite to the ground station at all times.
+       - The ground station is located at the North Pole (positive Zaxis), and the satellite starts from the initial elevation angle 0° in the second quadrant of the YZplane.
+       - Satellite moves in the clockwise direction in its circular orbit.
+    */
+    const double radius_earth = 6371e3; // m
+    const double radius_sat = radius_earth + channelDesc->sat_height;
+    const double GM_earth = 3.986e14; // m^3/s^2
+    const double w_sat = sqrt(GM_earth / (radius_sat * radius_sat * radius_sat)); // rad/s
+
+    // start_time and end_time are when the pos_sat_z == pos_gnb_z (elevation angle == 0 and 180 degree)
+    const double start_phase = -acos(radius_earth / radius_sat); // SAT is just rising above the horizon
+    const double end_phase = -start_phase; // SAT is just falling behind the horizon
+    const double start_time = start_phase / w_sat; // in seconds
+    const double end_time = end_phase / w_sat; // in seconds
+    const uint64_t duration_samples = (end_time - start_time) * channelDesc->sampling_rate;
+    const double t = start_time + ((TS - channelDesc->start_TS) % duration_samples) / channelDesc->sampling_rate;
+
+    const double pos_sat_x = 0;
+    const double pos_sat_y = radius_sat * sin(w_sat * t);
+    const double pos_sat_z = radius_sat * cos(w_sat * t);
+
+    const double vel_sat_x = 0;
+    const double vel_sat_y =  w_sat * radius_sat * cos(w_sat * t);
+    const double vel_sat_z = -w_sat * radius_sat * sin(w_sat * t);
+
+    const double pos_ue_x = 0;
+    const double pos_ue_y = 0;
+    const double pos_ue_z = radius_earth;
+
+    const double dir_sat_ue_x = pos_ue_x - pos_sat_x;
+    const double dir_sat_ue_y = pos_ue_y - pos_sat_y;
+    const double dir_sat_ue_z = pos_ue_z - pos_sat_z;
+
+    const double dist_sat_ue = sqrt(dir_sat_ue_x * dir_sat_ue_x + dir_sat_ue_y * dir_sat_ue_y + dir_sat_ue_z * dir_sat_ue_z);
+    const double vel_sat_ue = (vel_sat_x * dir_sat_ue_x + vel_sat_y * dir_sat_ue_y + vel_sat_z * dir_sat_ue_z) / dist_sat_ue;
+
+    double dist_gnb_sat = 0;
+    double vel_gnb_sat = 0;
+    if (channelDesc->modelid == SAT_LEO_TRANS) {
+      const double pos_gnb_x = 0;
+      const double pos_gnb_y = 0;
+      const double pos_gnb_z = radius_earth;
+
+      const double dir_gnb_sat_x = pos_sat_x - pos_gnb_x;
+      const double dir_gnb_sat_y = pos_sat_y - pos_gnb_y;
+      const double dir_gnb_sat_z = pos_sat_z - pos_gnb_z;
+
+      dist_gnb_sat = sqrt(dir_gnb_sat_x * dir_gnb_sat_x + dir_gnb_sat_y * dir_gnb_sat_y + dir_gnb_sat_z * dir_gnb_sat_z);
+      vel_gnb_sat = (vel_sat_x * dir_gnb_sat_x + vel_sat_y * dir_gnb_sat_y + vel_sat_z * dir_gnb_sat_z) / dist_gnb_sat;
+    }
+
+    const double c = 299792458; // m/s
+    const double prop_delay = (dist_gnb_sat + dist_sat_ue) / c;
+    if (channelDesc->enable_dynamic_delay)
+      channelDesc->channel_offset = prop_delay * channelDesc->sampling_rate;
+
+    const double f_Doppler_shift_sat_ue = (vel_sat_ue / (c - vel_sat_ue)) * channelDesc->center_freq;
+    const double f_Doppler_shift_gnb_sat = (-vel_gnb_sat / c) * channelDesc->center_freq;
+    if (channelDesc->enable_dynamic_Doppler)
+      channelDesc->Doppler_phase_inc = 2 * M_PI * (f_Doppler_shift_gnb_sat + f_Doppler_shift_sat_ue) / channelDesc->sampling_rate;
+
+    static uint64_t last_TS = 0;
+    if(TS - last_TS >= channelDesc->sampling_rate) {
+      last_TS = TS;
+      LOG_I(HW, "Satellite orbit: time %f s, Doppler: gNB->SAT %f kHz, SAT->UE %f kHz, Delay %f ms\n", t, f_Doppler_shift_gnb_sat / 1000, f_Doppler_shift_sat_ue / 1000, prop_delay * 1000);
+    }
+  }
+
  // channelDesc->path_loss_dB should contain the total path gain
  // so, in actual RF: tx gain + path loss + rx gain (+antenna gain, ...)
  // UE and NB gain control to be added
@@ -94,9 +165,16 @@ void rxAddInput( const c16_t *input_sig,
      } //l
    }

-    // Fixme: lround(), rount(), ... is detected by valgrind as error, not found why
-    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));
+    if (channelDesc->Doppler_phase_inc != 0.0) {
+      double complex in = CMPLX(rx_tmp.r, rx_tmp.i);
+      double complex out = in * cexp(channelDesc->Doppler_phase_cur[rxAnt] * I);
+      rx_tmp.r = creal(out);
+      rx_tmp.i = cimag(out);
+      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++;
  }

@@ -709,6 +709,10 @@ static bool flushInput(rfsimulator_state_t *t, int timeout, int nsamps_for_initi
        samplesVoid[i]=(void *)&v;

      rfsimulator_write_internal(t, t->lastWroteTS > 1 ? t->lastWroteTS - 1 : 0, samplesVoid, 1, t->tx_num_channels, 1, false);
+
+      buffer_t *b = &t->buf[conn_sock];
+      if (b->channel_model)
+        b->channel_model->start_TS = t->lastWroteTS;
    } else {
      if ( events[nbEv].events & (EPOLLHUP | EPOLLERR | EPOLLRDHUP) ) {
        socketError(t,fd);
@@ -761,6 +765,8 @@ static bool flushInput(rfsimulator_state_t *t, int timeout, int nsamps_for_initi
                            nsamps_for_initial;
          LOG_D(HW, "UE got first timestamp: starting at %lu\n", t->nextRxTstamp);
          b->trashingPacket=true;
+          if (b->channel_model)
+            b->channel_model->start_TS = t->nextRxTstamp;
        } else if (b->lastReceivedTS < b->th.timestamp) {
          int nbAnt= b->th.nbAnt;