7.2 FH: auto-compute FFT size

doc/ORAN_FHI7.2_Tutorial.md

@@ -791,7 +791,6 @@ Edit the sample OAI gNB configuration file and check following parameters:
         compression
       * `iq_width_prach`: Width of PRACH IQ samples: if 16, no compression, if <16, applies
         compression
-      * `fft_size`: size of FFT performed by RU, set to 12 by default
     * `prach_config`: PRACH-specific configuration
       * `eAxC_offset`:  PRACH antenna offset
       * `kbar`: the PRACH guard interval, provided in RU

executables/nr-ru.c

@@ -912,7 +912,7 @@ static void fill_rf_config(RU_t *ru, char *rf_config_file)
   }
 }
 
-static void fill_split7_2_config(split7_config_t *split7, const nfapi_nr_config_request_scf_t *config, int slots_per_frame)
+static void fill_split7_2_config(split7_config_t *split7, const nfapi_nr_config_request_scf_t *config, int slots_per_frame, uint16_t ofdm_symbol_size)
 {
   const nfapi_nr_prach_config_t *prach_config = &config->prach_config;
   const nfapi_nr_tdd_table_t *tdd_table = &config->tdd_table;
@@ -934,6 +934,8 @@ static void fill_split7_2_config(split7_config_t *split7, const nfapi_nr_config_
       }
     }
   }
+
+  split7->fftSize = log2(ofdm_symbol_size);
 }
 
 /* this function maps the RU tx and rx buffers to the available rf chains.
@@ -1157,7 +1159,7 @@ void *ru_thread( void *param ) {
   nr_dump_frame_parms(fp);
   nr_phy_init_RU(ru);
   fill_rf_config(ru, ru->rf_config_file);
-  fill_split7_2_config(&ru->openair0_cfg.split7, &ru->config, fp->slots_per_frame);
+  fill_split7_2_config(&ru->openair0_cfg.split7, &ru->config, fp->slots_per_frame, fp->ofdm_symbol_size);
 
   if(!emulate_rf) {
     // Start IF device if any

radio/COMMON/common_lib.h

@@ -195,6 +195,8 @@ typedef struct split7_config {
   struct {
     symbol_direction_t sym_dir[14];
   } slot_dirs[160];
+  /*! this is the exponent in 2^X for the FFT size */
+  uint16_t fftSize;
 } split7_config_t;
 
 /*! \brief RF frontend parameters set by application */

radio/fhi_72/oran-config.c

@@ -729,7 +729,7 @@ static bool set_fh_frame_config(const openair0_config_t *oai0, struct xran_frame
   return true;
 }
 
-static bool set_fh_ru_config(const paramdef_t *rup, int nru, struct xran_ru_config *ru_config)
+static bool set_fh_ru_config(const paramdef_t *rup, uint16_t fftSize, int nru, struct xran_ru_config *ru_config)
 {
   ru_config->xranTech = XRAN_RAN_5GNR;
   ru_config->xranCat = XRAN_CATEGORY_A;
@@ -740,7 +740,8 @@ static bool set_fh_ru_config(const paramdef_t *rup, int nru, struct xran_ru_conf
   ru_config->iqWidth_PRACH = *gpd(rup, nru, ORAN_RU_CONFIG_IQWIDTH_PRACH)->uptr;
   AssertFatal(ru_config->iqWidth_PRACH <= 16, "IQ Width for PRACH cannot be > 16!\n");
   ru_config->compMeth_PRACH = ru_config->iqWidth_PRACH < 16 ? XRAN_COMPMETHOD_BLKFLOAT : XRAN_COMPMETHOD_NONE;
-  ru_config->fftSize = *gpd(rup, nru, ORAN_RU_CONFIG_FFT_SIZE)->uptr;
+  AssertFatal(fftSize > 0, "FFT size cannot be 0\n");
+  ru_config->fftSize = fftSize;
   ru_config->byteOrder = XRAN_NE_BE_BYTE_ORDER;
   ru_config->iqOrder = XRAN_I_Q_ORDER;
   ru_config->xran_max_frame = 0;
@@ -779,6 +780,7 @@ bool set_fh_config(int ru_idx, int num_rus, const openair0_config_t *oai0, struc
     DevAssert(oai0->rx_freq[0] == oai0->rx_freq[i]);
   DevAssert(oai0->nr_band > 0);
   DevAssert(oai0->nr_scs_for_raster > 0);
+  AssertFatal(oai0->threequarter_fs == 0, "cannot use three-quarter sampling with O-RAN 7.2 split\n");
 
   // we simply assume that the loading process provides function to_nrarfcn()
   // to calculate the ARFCN numbers from frequency. That is not clean, but the
@@ -869,7 +871,7 @@ bool set_fh_config(int ru_idx, int num_rus, const openair0_config_t *oai0, struc
     return false;
   if (!set_fh_frame_config(oai0, &fh_config->frame_conf))
     return false;
-  if (!set_fh_ru_config(rup, nru, &fh_config->ru_conf))
+  if (!set_fh_ru_config(rup, oai0->split7.fftSize, nru, &fh_config->ru_conf))
     return false;
 
   fh_config->bbdev_enc = NULL;

radio/fhi_72/oran-params.h

@@ -91,13 +91,11 @@
 
 #define ORAN_RU_CONFIG_IQWIDTH "iq_width"
 #define ORAN_RU_CONFIG_IQWIDTH_PRACH "iq_width_prach"
-#define ORAN_RU_CONFIG_FFT_SIZE "fft_size"
 
 // clang-format off
 #define ORAN_RU_DESC {\
   {ORAN_RU_CONFIG_IQWIDTH,       "sample IQ width (16=uncompressed)\n",       PARAMFLAG_MANDATORY, .u8ptr=NULL, .defuintval=16, TYPE_UINT8, 0}, \
   {ORAN_RU_CONFIG_IQWIDTH_PRACH, "PRACH sample IQ width (16=uncompressed)\n", PARAMFLAG_MANDATORY, .u8ptr=NULL, .defuintval=16, TYPE_UINT8, 0}, \
-  {ORAN_RU_CONFIG_FFT_SIZE,      "Size of FFT at RU\n",                       PARAMFLAG_MANDATORY, .u8ptr=NULL, .defuintval=12, TYPE_UINT8, 0}, \
 }
 // clang-format on
 

targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band77.273prb.fhi72.4x4-vvdn.conf

@@ -295,7 +295,6 @@ fhi_72 = {
     ru_config = {
       iq_width = 9;
       iq_width_prach = 9;
-      fft_size = 12;
     };
     prach_config = {
       eAxC_offset = 4;

targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.273prb.fhi72.4x4-benetel550.conf

@@ -288,7 +288,6 @@ fhi_72 = {
     ru_config = {
       iq_width = 9;
       iq_width_prach = 9;
-      fft_size = 12;
     };
     prach_config = {
       eAxC_offset = 4;

targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.273prb.fhi72.4x4-benetel650.conf

@@ -288,7 +288,6 @@ fhi_72 = {
     ru_config = {
       iq_width = 9;
       iq_width_prach = 9;
-      fft_size = 12;
     };
     prach_config = {
       eAxC_offset = 4;

targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.273prb.fhi72.4x4-liteon.conf

@@ -286,7 +286,6 @@ fhi_72 = {
     ru_config = {
       iq_width = 9;
       iq_width_prach = 9;
-      fft_size = 12;
     };
     prach_config = {
       eAxC_offset = 4;