Add new parameter tx_amp_backoff_dB to L1 section of configuration file

Provides the backoff from full-scale output at the L1 entity
(frequency-domain samples). Default is, 36 dBFS, which is the correct
value when using the OAI RU entity. For O-RAN RU, this value should be
set according to the O-RU manufacturer requirements. For example 12
would corresponding to 14-bit input level (6 dB/bit).

Applies the TX amp backoff to PBCH, PDCCH and CSI

openair1/PHY/INIT/nr_init.c

@@ -554,7 +554,8 @@ int phy_init_nr_gNB(PHY_VARS_gNB *gNB)
   AssertFatal(pdcch_dmrs!=NULL, "NR init: pdcch_dmrs malloc failed\n");
 
   gNB->bad_pucch = 0;
-
+  if (gNB->TX_AMP == 0)
+    gNB->TX_AMP = AMP;
   // ceil(((NB_RB<<1)*3)/32) // 3 RE *2(QPSK)
   int pdcch_dmrs_init_length =  (((fp->N_RB_DL<<1)*3)>>5)+1;
 

openair1/PHY/NR_TRANSPORT/nr_dlsch.c

@@ -60,7 +60,7 @@ void nr_generate_pdsch(processingData_L1tx_t *msgTx,
   PHY_VARS_gNB *gNB = msgTx->gNB;
   NR_gNB_DLSCH_t *dlsch;
   c16_t** txdataF = gNB->common_vars.txdataF;
-  int16_t amp = AMP;
+  int16_t amp = gNB->TX_AMP;
   int xOverhead = 0;
   NR_DL_FRAME_PARMS *frame_parms = &gNB->frame_parms;
   time_stats_t *dlsch_encoding_stats=&gNB->dlsch_encoding_stats;

openair1/PHY/defs_gNB.h

@@ -644,6 +644,8 @@ typedef struct PHY_VARS_gNB_s {
   /// CSI variables
   nr_csi_info_t *nr_csi_info;
 
+  // reference amplitude for TX
+  int16_t TX_AMP;
   // PUCCH0 Look-up table for cyclic-shifts
   NR_gNB_PUCCH0_LUT_t pucch0_lut;
 

openair1/SCHED_NR/phy_procedures_nr_gNB.c

@@ -81,13 +81,23 @@ void nr_common_signal_procedures (PHY_VARS_gNB *gNB,int frame,int slot,nfapi_nr_
   LOG_D(PHY, "SSB first subcarrier %d (%d,%d)\n", fp->ssb_start_subcarrier, prb_offset, sc_offset);
 
   LOG_D(PHY,"SS TX: frame %d, slot %d, start_symbol %d\n",frame,slot, ssb_start_symbol);
-  nr_generate_pss(&txdataF[0][txdataF_offset], AMP, ssb_start_symbol, cfg, fp);
-  nr_generate_sss(&txdataF[0][txdataF_offset], AMP, ssb_start_symbol, cfg, fp);
+  nr_generate_pss(&txdataF[0][txdataF_offset], gNB->TX_AMP, ssb_start_symbol, cfg, fp);
+  nr_generate_sss(&txdataF[0][txdataF_offset], gNB->TX_AMP, ssb_start_symbol, cfg, fp);
 
   if (fp->Lmax == 4)
-    nr_generate_pbch_dmrs(gNB->nr_gold_pbch_dmrs[n_hf][ssb_index&7],&txdataF[0][txdataF_offset], AMP, ssb_start_symbol, cfg, fp);
+    nr_generate_pbch_dmrs(gNB->nr_gold_pbch_dmrs[n_hf][ssb_index & 7],
+                          &txdataF[0][txdataF_offset],
+                          gNB->TX_AMP,
+                          ssb_start_symbol,
+                          cfg,
+                          fp);
   else
-    nr_generate_pbch_dmrs(gNB->nr_gold_pbch_dmrs[0][ssb_index&7],&txdataF[0][txdataF_offset], AMP, ssb_start_symbol, cfg, fp);
+    nr_generate_pbch_dmrs(gNB->nr_gold_pbch_dmrs[0][ssb_index & 7],
+                          &txdataF[0][txdataF_offset],
+                          gNB->TX_AMP,
+                          ssb_start_symbol,
+                          cfg,
+                          fp);
 
   if (T_ACTIVE(T_GNB_PHY_MIB)) {
     unsigned char bch[3];
@@ -107,9 +117,12 @@ void nr_common_signal_procedures (PHY_VARS_gNB *gNB,int frame,int slot,nfapi_nr_
   nr_generate_pbch(&ssb_pdu,
                    gNB->nr_pbch_interleaver,
                    &txdataF[0][txdataF_offset],
-                   AMP,
+                   gNB->TX_AMP,
                    ssb_start_symbol,
-                   n_hf, frame, cfg, fp);
+                   n_hf,
+                   frame,
+                   cfg,
+                   fp);
 }
 
 
@@ -170,9 +183,7 @@ void phy_procedures_gNB_TX(processingData_L1tx_t *msgTx,
   
     VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME(VCD_SIGNAL_DUMPER_FUNCTIONS_PHY_gNB_PDCCH_TX,1);
 
-    nr_generate_dci_top(msgTx, slot,
-			(int32_t *)&gNB->common_vars.txdataF[0][txdataF_offset],
-			AMP, fp);
+    nr_generate_dci_top(msgTx, slot, (int32_t *)&gNB->common_vars.txdataF[0][txdataF_offset], gNB->TX_AMP, fp);
 
     VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME(VCD_SIGNAL_DUMPER_FUNCTIONS_PHY_gNB_PDCCH_TX,0);
   }
@@ -189,7 +200,20 @@ void phy_procedures_gNB_TX(processingData_L1tx_t *msgTx,
     if (csirs->active == 1) {
       LOG_D(PHY, "CSI-RS generation started in frame %d.%d\n",frame,slot);
       nfapi_nr_dl_tti_csi_rs_pdu_rel15_t *csi_params = &csirs->csirs_pdu.csi_rs_pdu_rel15;
-      nr_generate_csi_rs(&gNB->frame_parms, (int32_t **)gNB->common_vars.txdataF, AMP, gNB->nr_csi_info, csi_params, slot, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
+      nr_generate_csi_rs(&gNB->frame_parms,
+                         (int32_t **)gNB->common_vars.txdataF,
+                         gNB->TX_AMP,
+                         gNB->nr_csi_info,
+                         csi_params,
+                         slot,
+                         NULL,
+                         NULL,
+                         NULL,
+                         NULL,
+                         NULL,
+                         NULL,
+                         NULL,
+                         NULL);
       csirs->active = 0;
     }
   }

openair2/GNB_APP/L1_nr_paramdef.h

@@ -56,6 +56,7 @@
 #define CONFIG_STRING_L1_RX_THREAD_CORE                    "L1_rx_thread_core"
 #define CONFIG_STRING_L1_TX_THREAD_CORE                    "L1_tx_thread_core"
 #define HLP_TP_SIZ "thread_pool_size paramter removed, please use --thread-pool"
+#define CONFIG_STRING_L1_TX_AMP_BACKOFF_dB                 "tx_amp_backoff_dB"
 /*----------------------------------------------------------------------------------------------------------------------------------------------------*/
 /*                                            L1 configuration parameters                                                                             */
 /*   optname                                         helpstr   paramflags    XXXptr              defXXXval                  type           numelt     */
@@ -80,6 +81,7 @@
   {CONFIG_STRING_L1_MAX_LDPC_ITERATIONS,               NULL,       0,         .uptr=NULL,           .defintval=5,               TYPE_UINT,     0},         \
   {CONFIG_STRING_L1_RX_THREAD_CORE,                    NULL,       0,         .uptr=NULL,           .defintval=-1,              TYPE_UINT,     0},          \
   {CONFIG_STRING_L1_TX_THREAD_CORE,                    NULL,       0,         .uptr=NULL,           .defintval=-1,              TYPE_UINT,     0},          \
+  {CONFIG_STRING_L1_TX_AMP_BACKOFF_dB,                 NULL,       0,         .uptr=NULL,           .defintval=36,              TYPE_UINT,     0},         \
 }
 // clang-format on
 #define L1_CC_IDX                                          0
@@ -100,6 +102,7 @@
 #define L1_MAX_LDPC_ITERATIONS                             15
 #define L1_RX_THREAD_CORE                                  16
 #define L1_TX_THREAD_CORE                                  17
+#define L1_TX_AMP_BACKOFF_dB                               18
 
 /*----------------------------------------------------------------------------------------------------------------------------------------------------*/
 #endif

openair2/GNB_APP/gnb_config.c

@@ -773,6 +773,9 @@ void RCconfig_NR_L1(void)
       RC.gNB[j]->L1_rx_thread_core = *(L1_ParamList.paramarray[j][L1_RX_THREAD_CORE].iptr);
       RC.gNB[j]->L1_tx_thread_core = *(L1_ParamList.paramarray[j][L1_TX_THREAD_CORE].iptr);
       LOG_I(PHY,"L1_RX_THREAD_CORE %d (%d)\n",*(L1_ParamList.paramarray[j][L1_RX_THREAD_CORE].iptr),L1_RX_THREAD_CORE);
+      RC.gNB[j]->TX_AMP = (int16_t)(32767.0 / pow(10.0, .05 * (double)(*L1_ParamList.paramarray[j][L1_TX_AMP_BACKOFF_dB].uptr)));
+      LOG_I(PHY, "TX_AMP = %d (-%d dBFS)\n", RC.gNB[j]->TX_AMP, *L1_ParamList.paramarray[j][L1_TX_AMP_BACKOFF_dB].uptr);
+      AssertFatal(RC.gNB[j]->TX_AMP > 300, "TX_AMP is too small, must be larger than 300 (is %d)\n", RC.gNB[j]->TX_AMP);
       if (strcmp(*(L1_ParamList.paramarray[j][L1_TRANSPORT_N_PREFERENCE_IDX].strptr), "local_mac") == 0) {
         // sf_ahead = 2; // Need 4 subframe gap between RX and TX
       } else if (strcmp(*(L1_ParamList.paramarray[j][L1_TRANSPORT_N_PREFERENCE_IDX].strptr), "nfapi") == 0) {