Fix preamble shift at gNB for RA works with all preambles

openair1/PHY/NR_TRANSPORT/nr_prach.c

@@ -678,19 +678,10 @@ void rx_nr_prach(PHY_VARS_gNB *gNB,
       }
       
       else {
+        preamble_shift  -= NCS;
 
-        // FIXME: It is working, but we need to differentiate between odd and even preamble index
-        //  Check why preamble_shift does not match with UE
-        //  TS 38.211 Section 6.3.3.1 Sequence generation
-        if(preamble_index%2==0) {
-          preamble_shift  = (NCS==0)? 0 : (preamble_index % (N_ZC/NCS));
-          preamble_shift *= NCS;
-        } else {
-          preamble_shift  -= 2*NCS;
         if (preamble_shift < 0)
-            preamble_shift+=N_ZC;
-        }
-
+          preamble_shift+=((N_ZC/NCS)*NCS);
       }
     } else { // This is the high-speed case
       new_dft = 0;

openair2/LAYER2/NR_MAC_UE/mac_defs.h

@@ -257,6 +257,8 @@ typedef struct {
   uint8_t RA_attempt_number;
   /// Random-access procedure flag
   uint8_t RA_active;
+  /// Random-access preamble index
+  int ra_PreambleIndex;
   /// Flag for the Msg1 generation: enabled at every occurrence of nr prach slot
   uint8_t generate_nr_prach;
 

openair2/LAYER2/NR_MAC_UE/nr_ra_procedures.c

@@ -64,6 +64,8 @@ void init_RA(module_id_t mod_id,
 
   RA_config_t *ra          = &mac->ra;
   ra->RA_active            = 1;
+  ra->ra_PreambleIndex     = -1;
+  ra->RA_usedGroupA        = 1;
   ra->RA_RAPID_found       = 0;
   ra->preambleTransMax     = 0;
   ra->first_Msg3           = 1;
@@ -251,7 +253,7 @@ void ra_preambles_config(NR_PRACH_RESOURCES_t *prach_resources, NR_UE_MAC_INST_t
   int messageSizeGroupA = 0;
   int sizeOfRA_PreamblesGroupA = 0;
   int messagePowerOffsetGroupB = 0;
-  int PLThreshold;
+  int PLThreshold = 0;
   long deltaPreamble_Msg3 = 0;
   uint8_t noGroupB = 0;
   RA_config_t *ra = &mac->ra;
@@ -354,37 +356,34 @@ void ra_preambles_config(NR_PRACH_RESOURCES_t *prach_resources, NR_UE_MAC_INST_t
   }
   /* Msg3 has not been transmitted yet */
   if (ra->first_Msg3) {
+    if(ra->ra_PreambleIndex < 0 || ra->ra_PreambleIndex > 63) {
       if (noGroupB) {
         // use Group A preamble
-      prach_resources->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % ra->cb_preambles_per_ssb);
+        ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % ra->cb_preambles_per_ssb);
         ra->RA_usedGroupA = 1;
       } else if ((ra->Msg3_size < messageSizeGroupA) && (dl_pathloss > PLThreshold)) {
         // Group B is configured and RA preamble Group A is used
         // - todo add condition on CCCH_sdu_size for initiation by CCCH
-      prach_resources->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % sizeOfRA_PreamblesGroupA);
+        ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % sizeOfRA_PreamblesGroupA);
         ra->RA_usedGroupA = 1;
       } else {
         // Group B preamble is configured and used
         // the first sizeOfRA_PreamblesGroupA RA preambles belong to RA Preambles Group A
         // the remaining belong to RA Preambles Group B
-      prach_resources->ra_PreambleIndex = ra->starting_preamble_nb + sizeOfRA_PreamblesGroupA + ((taus()) % (ra->cb_preambles_per_ssb - sizeOfRA_PreamblesGroupA));
+        ra->ra_PreambleIndex = ra->starting_preamble_nb + sizeOfRA_PreamblesGroupA + ((taus()) % (ra->cb_preambles_per_ssb - sizeOfRA_PreamblesGroupA));
         ra->RA_usedGroupA = 0;
       }
-
-    // TODO: Remove to generate random ra_PreambleIndex
-    printf("prach_resources->ra_PreambleIndex = %i\n", prach_resources->ra_PreambleIndex);
-    prach_resources->ra_PreambleIndex = 21;
-    ra->RA_usedGroupA = 1;
-
+    }
   } else { // Msg3 is being retransmitted
     if (ra->RA_usedGroupA && noGroupB) {
-      prach_resources->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % ra->cb_preambles_per_ssb);
+      ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % ra->cb_preambles_per_ssb);
     } else if (ra->RA_usedGroupA && !noGroupB){
-      prach_resources->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % sizeOfRA_PreamblesGroupA);
+      ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % sizeOfRA_PreamblesGroupA);
     } else {
-      prach_resources->ra_PreambleIndex = ra->starting_preamble_nb + sizeOfRA_PreamblesGroupA + ((taus()) % (ra->cb_preambles_per_ssb - sizeOfRA_PreamblesGroupA));
+      ra->ra_PreambleIndex = ra->starting_preamble_nb + sizeOfRA_PreamblesGroupA + ((taus()) % (ra->cb_preambles_per_ssb - sizeOfRA_PreamblesGroupA));
     }
   }
+  prach_resources->ra_PreambleIndex = ra->ra_PreambleIndex;
 }
 
 // RA-RNTI computation (associated to PRACH occasion in which the RA Preamble is transmitted)