Added NR symbol offset helper function

lib/include/srsran/phy/common/phy_common_nr.h

@@ -533,6 +533,15 @@ SRSRAN_API srsran_mcs_table_t srsran_mcs_table_from_str(const char* str);
  */
 SRSRAN_API uint32_t srsran_min_symbol_sz_rb(uint32_t nof_prb);
 
+/**
+ * @brief Computes the time in seconds between the beginning of the slot and the given symbol
+ * @remark All symbol size reference and values are taken from TS 38.211 section 5.3 OFDM baseband signal generation
+ * @param l Given symbol index
+ * @param scs Subcarrier spacing
+ * @return Returns the symbol time offset in seconds
+ */
+SRSRAN_API float srsran_symbol_offset_s(uint32_t l, srsran_subcarrier_spacing_t scs);
+
 /**
  * @brief Computes the time in seconds between two symbols in a slot
  * @note l0 is expected to be smaller than l1

lib/src/phy/common/phy_common_nr.c

@@ -152,34 +152,40 @@ uint32_t srsran_min_symbol_sz_rb(uint32_t nof_prb)
   return 0;
 }
 
-float srsran_symbol_distance_s(uint32_t l0, uint32_t l1, srsran_subcarrier_spacing_t scs)
+float srsran_symbol_offset_s(uint32_t l, srsran_subcarrier_spacing_t scs)
 {
-  // l0 must be smaller than l1
-  if (l0 >= l1) {
-    return 0.0f;
-  }
-
-  // Count number of symbols in between
-  uint32_t count = l1 - l0;
-
   // Compute at what symbol there is a longer CP
   uint32_t cp_boundary = 7U << (uint32_t)scs;
 
-  // Select whether extra CP shall be added
+  // First symbol CP
-  uint32_t extra_cp = 0;
+  uint32_t N = 160;
-  if (l0 < cp_boundary && l1 >= cp_boundary) {
-    extra_cp = 16;
-  }
 
-  // Compute reference FFT size
+  // Symbols in between the first and l
-  uint32_t N = (2048 + 144) * count + extra_cp;
+  N += (2048 + 144) * l;
+
+  // Add extra samples at the longer CP boundary
+  if (l >= cp_boundary) {
+    N += 16;
+  }
 
+  // Compute time using reference sampling rate
   float TS = SRSRAN_LTE_TS / (float)(1U << (uint32_t)scs);
 
-  // Return symbol distance in microseconds
+  // Return symbol offset in seconds
   return (float)N * TS;
 }
 
+float srsran_symbol_distance_s(uint32_t l0, uint32_t l1, srsran_subcarrier_spacing_t scs)
+{
+  // l0 must be smaller than l1
+  if (l0 >= l1) {
+    return 0.0f;
+  }
+
+  // Return symbol distance in seconds
+  return srsran_symbol_offset_s(l1, scs) - srsran_symbol_offset_s(l0, scs);
+}
+
 bool srsran_tdd_nr_is_dl(const srsran_tdd_config_nr_t* cfg, uint32_t numerology, uint32_t slot_idx)
 {
   // Protect NULL pointer access