Add helper functions for abs freq point a.

lib/include/srsran/common/band_helper.h

@@ -105,6 +105,15 @@ public:
    */
   double get_ul_center_freq(const srsran_carrier_nr_t& carrier);
 
+  /**
+   * @brief Compute the absolute frequency point A for a arfcn
+   *
+   * @param nof_prb Number of PRBs.
+   * @param arfcn Given ARFCN.
+   * @return frequency point A in arfcn notation.
+   */
+  uint32_t get_abs_freq_point_a_arfcn(uint32_t nof_prb, uint32_t arfcn);
+
   class sync_raster_t
   {
   protected:
@@ -139,6 +148,8 @@ private:
   // internal helper
   double get_center_freq_from_abs_freq_point_a(uint32_t nof_prb, uint32_t freq_point_a_arfcn);
 
+  double get_abs_freq_point_a_from_center_freq(uint32_t nof_prb, double center_freq);
+
   // Elements of TS 38.101-1 Table 5.2-1: NR operating bands in FR1
   struct nr_operating_band {
     uint16_t             band;
@@ -292,8 +303,8 @@ private:
   }};
 
   static const uint32_t nof_nr_bands_fr2                                   = 8;
-  static constexpr std::array<nr_band, nof_nr_bands_fr2> nr_band_table_fr2 = {{
-    {257, KHZ_60, 2054166, 1, 2104165, 2054166, 1, 2104165},
+  static constexpr std::array<nr_band, nof_nr_bands_fr2> nr_band_table_fr2 = {
+      {{257, KHZ_60, 2054166, 1, 2104165, 2054166, 1, 2104165},
        {257, KHZ_120, 2054167, 2, 2104165, 2054167, 20, 2104165},
 
        {258, KHZ_60, 2016667, 1, 2070832, 2016667, 1, 2070832},
@@ -303,8 +314,7 @@ private:
        {260, KHZ_120, 2229167, 2, 2279165, 2229167, 2, 2279165},
 
        {261, KHZ_60, 2070833, 1, 2084999, 2070833, 1, 2084999},
-    {261, KHZ_120, 2070833, 2, 2084999, 2070833, 2, 2084999}
-  }};
+       {261, KHZ_120, 2070833, 2, 2084999, 2070833, 2, 2084999}}};
 
   // Elements of TS 38.101-1 Table 5.4.3.3-1 : Applicable SS raster entries per operating band
   struct nr_band_ss_raster {

lib/src/common/band_helper.cc

@@ -129,6 +129,20 @@ double srsran_band_helper::get_center_freq_from_abs_freq_point_a(uint32_t nof_pr
           SRSRAN_NRE);
 }
 
+uint32_t srsran_band_helper::get_abs_freq_point_a_arfcn(uint32_t nof_prb, uint32_t arfcn)
+{
+  return freq_to_nr_arfcn(get_abs_freq_point_a_from_center_freq(nof_prb, nr_arfcn_to_freq(arfcn)));
+}
+
+double srsran_band_helper::get_abs_freq_point_a_from_center_freq(uint32_t nof_prb, double center_freq)
+{
+  // for FR1 unit of resources blocks for freq calc is always 180kHz regardless for actual SCS of carrier
+  // TODO: add offset_to_carrier
+  return center_freq -
+         (nof_prb / 2 * SRSRAN_SUBC_SPACING_NR(srsran_subcarrier_spacing_t::srsran_subcarrier_spacing_15kHz) *
+          SRSRAN_NRE);
+}
+
 srsran_ssb_patern_t srsran_band_helper::get_ssb_pattern(uint16_t band, srsran_subcarrier_spacing_t scs) const
 {
   // Look for the given band and SCS