Added option for Doppler frequency correction

lib/include/srslte/interfaces/ue_interfaces.h

@@ -474,7 +474,8 @@ typedef struct {
   int cqi_max; 
   int cqi_fixed; 
   float snr_ema_coeff; 
-  std::string snr_estim_alg; 
+  std::string snr_estim_alg;
+  bool cfo_is_doppler;
   bool cfo_integer_enabled; 
   float cfo_correct_tol_hz;
   float cfo_pss_ema;

srsue/hdr/phy/phch_recv.h

@@ -104,6 +104,8 @@ private:
   void   cell_search_inc();
   void   cell_reselect();
 
+  float  get_cfo();
+
   uint32_t new_earfcn;
   srslte_cell_t new_cell;
 

srsue/hdr/phy/phch_worker.h

@@ -73,7 +73,6 @@ public:
   float get_rsrp();
   float get_noise();
   float get_cfo();
-  float get_ul_cfo();
 
 private:
   /* Inherited from thread_pool::worker. Function called every subframe to run the DL/UL processing */

srsue/src/main.cc

@@ -203,6 +203,11 @@ void parse_args(all_args_t *args, int argc, char *argv[]) {
      bpo::value<string>(&args->expert.phy.equalizer_mode)->default_value("mmse"),
      "Equalizer mode")
 
+    ("expert.cfo_is_doppler",
+       bpo::value<bool>(&args->expert.phy.cfo_is_doppler)->default_value(false),
+       "Assume detected CFO is doppler and correct the UL in the same direction. If disabled, the CFO is assumed"
+        "to be caused by the local oscillator and the UL correction is in the opposite direction. Default assumes oscillator.")
+
     ("expert.cfo_integer_enabled",
      bpo::value<bool>(&args->expert.phy.cfo_integer_enabled)->default_value(false),
      "Enables integer CFO estimation and correction.")
@@ -215,12 +220,6 @@ void parse_args(all_args_t *args, int argc, char *argv[]) {
      bpo::value<float>(&args->expert.phy.cfo_pss_ema)->default_value(DEFAULT_CFO_EMA_TRACK),
      "CFO Exponential Moving Average coefficient for PSS estimation during TRACK.")
 
-    /* REF EMA is currently not used
-    ("expert.cfo_ref_ema",
-     bpo::value<float>(&args->expert.phy.cfo_ref_ema)->default_value(0.01),
-     "CFO Exponential Moving Average coefficient for RS estimation after PSS acquisition")
-    */
-
     ("expert.cfo_ref_mask",
      bpo::value<uint32_t>(&args->expert.phy.cfo_ref_mask)->default_value(1023),
      "Bitmask for subframes on which to run RS estimation (set to 0 to disable, default all sf)")

srsue/src/phy/phch_recv.cc

@@ -428,6 +428,25 @@ bool phch_recv::set_frequency()
   }
 }
 
+float phch_recv::get_cfo()
+{
+  float cfo = srslte_ue_sync_get_cfo(&ue_sync);
+
+  float ret = cfo*ul_dl_factor;
+
+  if (worker_com->args->cfo_is_doppler) {
+    ret *= -1;
+  }
+
+  if (radio_h->get_freq_offset() != 0.0f) {
+    /* Compensates the radio frequency offset applied equally to DL and UL */
+    const float offset_hz = (float) radio_h->get_freq_offset() * (1.0f - ul_dl_factor);
+    ret = cfo - offset_hz;
+  }
+
+  return ret/15000;
+}
+
 void phch_recv::set_sampling_rate()
 {
   current_srate = (float) srslte_sampling_freq_hz(cell.nof_prb);
@@ -633,7 +652,7 @@ void phch_recv::run_thread()
 
               metrics.sfo = srslte_ue_sync_get_sfo(&ue_sync);
               metrics.cfo = srslte_ue_sync_get_cfo(&ue_sync);
-              worker->set_cfo(ul_dl_factor * metrics.cfo / 15000);
+              worker->set_cfo(get_cfo());
               worker_com->set_sync_metrics(metrics);
 
               /* Compute TX time: Any transmission happens in TTI+4 thus advance 4 ms the reception time */
@@ -659,7 +678,7 @@ void phch_recv::run_thread()
               if (prach_buffer->is_ready_to_send(tti)) {
                 srslte_timestamp_copy(&tx_time_prach, &rx_time);
                 srslte_timestamp_add(&tx_time_prach, 0, prach::tx_advance_sf * 1e-3);
-                prach_buffer->send(radio_h, ul_dl_factor * metrics.cfo / 15000, worker_com->pathloss, tx_time_prach);
+                prach_buffer->send(radio_h, get_cfo(), worker_com->pathloss, tx_time_prach);
                 radio_h->tx_end();
                 worker_com->p0_preamble = prach_buffer->get_p0_preamble();
                 worker_com->cur_radio_power = SRSLTE_MIN(SRSLTE_PC_MAX, worker_com->pathloss+worker_com->p0_preamble);

srsue/src/phy/phch_worker.cc

@@ -223,20 +223,6 @@ float phch_worker::get_cfo()
   return cfo;
 }
 
-float phch_worker::get_ul_cfo() {
-  srslte::radio *radio = phy->get_radio();
-
-  if (radio->get_freq_offset() != 0.0f) {
-    /* Compensates the radio frequency offset applied equally to DL and UL */
-    const float ul_dl_ratio = (float) radio->get_tx_freq() / (float) radio->get_rx_freq();
-    const float offset_hz = (float) radio->get_freq_offset() * (1.0f - ul_dl_ratio);
-    return cfo - offset_hz / (15000);
-  } else {
-    return cfo;
-  }
-
-}
-
 void phch_worker::work_imp()
 {
   if (!cell_initiated) {
@@ -360,7 +346,7 @@ void phch_worker::work_imp()
   }
 
   /* Set UL CFO before transmission */  
-  srslte_ue_ul_set_cfo(&ue_ul, get_ul_cfo());
+  srslte_ue_ul_set_cfo(&ue_ul, cfo);
 
   /* Transmit PUSCH, PUCCH or SRS */
   bool signal_ready = false; 

srsue/ue.conf.example

@@ -172,6 +172,8 @@ enable = false
 # cfo_correct_tol_hz:   Tolerance (in Hz) for digial CFO compensation. Lower tolerance means that
 #                       a new table will be generated more often.
 #
+# cfo_is_doppler:        Assume detected CFO is doppler and correct the UL in the same direction. If disabled, the CFO is assumed
+#                        to be caused by the local oscillator and the UL correction is in the opposite direction. Default assumes oscillator.
 # cfo_pss_ema:           CFO Exponential Moving Average coefficient for PSS estimation during TRACK.
 # cfo_ref_ema:           CFO Exponential Moving Average coefficient for RS estimation after PSS acquisition
 # cfo_ref_mask:          Bitmask for subframes on which to run RS estimation (set to 0 to disable, default sf=[1, 5])
@@ -211,6 +213,7 @@ enable = false
 #pdsch_csi_enabled  = true     # Caution! Only TM1 supported!
 
 # CFO related values
+#cfo_is_doppler      = false
 #cfo_integer_enabled = false
 #cfo_correct_tol_hz  = 1.0
 #cfo_pss_ema         = 0.05