Limit uplink signal normalization to avoid clipping

lib/include/srslte/phy/ue/ue_ul.h

@@ -100,6 +100,8 @@ typedef struct SRSLTE_API {
   cf_t *srs_signal; 
   cf_t *sf_symbols;
 
+  float last_amplitude;
+
   uint16_t current_rnti;  
   bool signals_pregenerated;
 }srslte_ue_ul_t;
@@ -128,6 +130,8 @@ SRSLTE_API void srslte_ue_ul_set_cfo_enable(srslte_ue_ul_t *q,
 SRSLTE_API void srslte_ue_ul_set_normalization(srslte_ue_ul_t *q, 
                                                bool enabled);
 
+SRSLTE_API float srslte_ue_ul_get_last_amplitude(srslte_ue_ul_t *q);
+
 SRSLTE_API void srslte_ue_ul_set_cfg(srslte_ue_ul_t *q, 
                                      srslte_refsignal_dmrs_pusch_cfg_t *dmrs_cfg, 
                                      srslte_refsignal_srs_cfg_t        *srs_cfg,

lib/include/srslte/phy/utils/vector.h

@@ -138,6 +138,7 @@ SRSLTE_API float srslte_vec_corr_ccc(const cf_t *x, cf_t *y, const uint32_t len)
 
 /* return the index of the maximum value in the vector */
 SRSLTE_API uint32_t srslte_vec_max_fi(const float *x, const uint32_t len);
+SRSLTE_API uint32_t srslte_vec_max_abs_fi(const float *x, const uint32_t len);
 SRSLTE_API uint32_t srslte_vec_max_abs_ci(const cf_t *x, const uint32_t len);
 
 /* quantify vector of floats or int16 and convert to uint8_t */

lib/src/phy/ue/ue_ul.c

@@ -294,6 +294,25 @@ void pucch_encode_bits(srslte_uci_data_t *uci_data, srslte_pucch_format_t format
   }
 }
 
+static float limit_norm_factor(srslte_ue_ul_t *q, float norm_factor, cf_t *output_signal)
+{
+  uint32_t p = srslte_vec_max_abs_fi((float*) output_signal, 2*SRSLTE_SF_LEN_PRB(q->cell.nof_prb));
+  float amp = fabsf(*((float*) output_signal + p));
+
+  if (amp*norm_factor > 0.95) {
+    norm_factor = 0.95/amp;
+  }
+  if (amp*norm_factor < 0.1) {
+    norm_factor = 0.1/amp;
+  }
+  q->last_amplitude = norm_factor*amp;
+  return norm_factor;
+}
+
+float srslte_ue_ul_get_last_amplitude(srslte_ue_ul_t *q) {
+  return q->last_amplitude;
+}
+
 /* Choose PUCCH format as in Sec 10.1 of 36.213 and generate PUCCH signal 
  */
 int srslte_ue_ul_pucch_encode(srslte_ue_ul_t *q, srslte_uci_data_t uci_data,
@@ -353,7 +372,10 @@ int srslte_ue_ul_pucch_encode(srslte_ue_ul_t *q, srslte_uci_data_t uci_data,
     }
     
     if (q->normalize_en) {
-      float norm_factor = (float) q->cell.nof_prb/15/10;
+      float norm_factor = (float) q->cell.nof_prb/15/40;
+
+      norm_factor = limit_norm_factor(q, norm_factor, output_signal);
+
       srslte_vec_sc_prod_cfc(output_signal, norm_factor, output_signal, SRSLTE_SF_LEN_PRB(q->cell.nof_prb));
     }
     ret = SRSLTE_SUCCESS; 
@@ -424,6 +446,9 @@ int srslte_ue_ul_srs_encode(srslte_ue_ul_t *q, uint32_t tti, cf_t *output_signal
     
     if (q->normalize_en) {
       float norm_factor = (float) q->cell.nof_prb/15/sqrtf(srslte_refsignal_srs_M_sc(&q->signals));
+
+      norm_factor = limit_norm_factor(q, norm_factor, output_signal);
+
       srslte_vec_sc_prod_cfc(output_signal, norm_factor, output_signal, SRSLTE_SF_LEN_PRB(q->cell.nof_prb));
     }
     
@@ -491,7 +516,10 @@ int srslte_ue_ul_pusch_encode_rnti_softbuffer(srslte_ue_ul_t *q,
     }
     
     if (q->normalize_en) {
-      float norm_factor = (float) q->cell.nof_prb/15/sqrtf(q->pusch_cfg.grant.L_prb);
+      float norm_factor = (float) q->cell.nof_prb/15/sqrtf(q->pusch_cfg.grant.L_prb)/2;
+
+      norm_factor = limit_norm_factor(q, norm_factor, output_signal);
+
       srslte_vec_sc_prod_cfc(output_signal, norm_factor, output_signal, SRSLTE_SF_LEN_PRB(q->cell.nof_prb));
     }
     

lib/src/phy/utils/vector.c

@@ -368,6 +368,10 @@ uint32_t srslte_vec_max_fi(const float *x, const uint32_t len) {
   return srslte_vec_max_fi_simd(x, len);
 }
 
+uint32_t srslte_vec_max_abs_fi(const float *x, const uint32_t len) {
+  return srslte_vec_max_fi_simd(x, len);
+}
+
 // CP autocorr
 uint32_t srslte_vec_max_abs_ci(const cf_t *x, const uint32_t len) {
   return srslte_vec_max_ci_simd(x, len);

srsue/src/phy/phch_worker.cc

@@ -1296,8 +1296,8 @@ void phch_worker::encode_pusch(srslte_ra_ul_grant_t *grant, uint8_t *payload, ui
 
   uint8_t dummy[2] = {0,0};
   log_h->info_hex(payload, grant->mcs.tbs/8,
-              "PUSCH: tti_tx=%d, alloc=(%d,%d), tbs=%d, mcs=%d, rv=%d%s%s%s, cfo=%.1f KHz%s%s\n",
+              "PUSCH: tti_tx=%d, amp=%.2f, alloc=(%d,%d), tbs=%d, mcs=%d, rv=%d%s%s%s, cfo=%.1f KHz%s%s\n",
-              (tti + HARQ_DELAY_MS) % 10240,
+              (tti + HARQ_DELAY_MS) % 10240, srslte_ue_ul_get_last_amplitude(&ue_ul),
               grant->n_prb[0], grant->n_prb[0] + grant->L_prb,
               grant->mcs.tbs / 8, grant->mcs.idx, rv,
               uci_data.uci_ack_len > 0 ? (uci_data.uci_ack ? ", ack=1" : ", ack=0") : "",
@@ -1350,8 +1350,8 @@ void phch_worker::encode_pucch()
       srslte_cqi_value_tostring(&cqi_report, cqi_str, SRSLTE_CQI_STR_MAX_CHAR);
     }
 
-    Info("PUCCH: tti_tx=%d, n_pucch=%d, n_prb=%d, ack=%s%s%s%s, sr=%s, cfo=%.1f KHz%s\n",
+    Info("PUCCH: tti_tx=%d, amp=%.2f, n_pucch=%d, n_prb=%d, ack=%s%s%s%s, sr=%s, cfo=%.1f KHz%s\n",
-         (tti + 4) % 10240,
+         (tti + 4) % 10240, srslte_ue_ul_get_last_amplitude(&ue_ul),
          ue_ul.pucch.last_n_pucch, ue_ul.pucch.last_n_prb,
          uci_data.uci_ack_len > 0 ? (uci_data.uci_ack ? "1" : "0") : "no",
          uci_data.uci_ack_len > 1 ? (uci_data.uci_ack_2 ? "1" : "0") : "",
@@ -1384,7 +1384,8 @@ void phch_worker::encode_srs()
   
   float tx_power = srslte_ue_ul_srs_power(&ue_ul, phy->pathloss);  
   float gain = set_power(tx_power);
-  Info("SRS:   power=%.2f dBm, tti_tx=%d%s\n", tx_power, TTI_TX(tti), timestr);
+
+  Info("SRS:   power=%.2f dBm, amp=%.2f, tti_tx=%d%s\n", tx_power, srslte_ue_ul_get_last_amplitude(&ue_ul), TTI_TX(tti), timestr);
 }
 
 void phch_worker::enable_pregen_signals(bool enabled)