Bugifx simultaneous RACH with multiple UEs

- replaced taus with a random seed + random number generation
- this fixes the bug with multiple UEs starting RA in the same time frame and slot
  and selecting the same preamble index

openair2/LAYER2/NR_MAC_UE/nr_ra_procedures.c

@@ -30,9 +30,6 @@
  * \warning
  */
 
-/* Tools */
-#include "SIMULATION/TOOLS/sim.h"	// for taus
-
 /* RRC */
 #include "NR_RACH-ConfigCommon.h"
 #include "RRC/NR_UE/rrc_proto.h"
@@ -280,6 +277,10 @@ void ra_preambles_config(NR_PRACH_RESOURCES_t *prach_resources, NR_UE_MAC_INST_t
   int PLThreshold = 0;
   long deltaPreamble_Msg3 = 0;
   uint8_t noGroupB = 0;
+  // Random seed generation
+  long long tmp = rdtsc_oai();
+  unsigned short int *seed = (unsigned short int*)&tmp;
+
   RA_config_t *ra = &mac->ra;
   NR_RACH_ConfigCommon_t *setup;
   if (mac->scc) setup = mac->scc->uplinkConfigCommon->initialUplinkBWP->rach_ConfigCommon->choice.setup;
@@ -378,28 +379,28 @@ void ra_preambles_config(NR_PRACH_RESOURCES_t *prach_resources, NR_UE_MAC_INST_t
     if(ra->ra_PreambleIndex < 0 || ra->ra_PreambleIndex > 63) {
       if (noGroupB) {
         // use Group A preamble
-        ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % ra->cb_preambles_per_ssb);
+        ra->ra_PreambleIndex = ra->starting_preamble_nb + (nrand48(seed) % 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
-        ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % sizeOfRA_PreamblesGroupA);
+        ra->ra_PreambleIndex = ra->starting_preamble_nb + (nrand48(seed) % 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
-        ra->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 + (nrand48(seed) % (ra->cb_preambles_per_ssb - sizeOfRA_PreamblesGroupA));
         ra->RA_usedGroupA = 0;
       }
     }
   } else { // Msg3 is being retransmitted
     if (ra->RA_usedGroupA && noGroupB) {
-      ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % ra->cb_preambles_per_ssb);
+      ra->ra_PreambleIndex = ra->starting_preamble_nb + (nrand48(seed) % ra->cb_preambles_per_ssb);
     } else if (ra->RA_usedGroupA && !noGroupB){
-      ra->ra_PreambleIndex = ra->starting_preamble_nb + ((taus()) % sizeOfRA_PreamblesGroupA);
+      ra->ra_PreambleIndex = ra->starting_preamble_nb + (nrand48(seed) % sizeOfRA_PreamblesGroupA);
     } else {
-      ra->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 + (nrand48(seed) % (ra->cb_preambles_per_ssb - sizeOfRA_PreamblesGroupA));
     }
   }
   prach_resources->ra_PreambleIndex = ra->ra_PreambleIndex;
@@ -837,6 +838,9 @@ void nr_ra_failed(uint8_t mod_id, uint8_t CC_id, NR_PRACH_RESOURCES_t *prach_res
 
   NR_UE_MAC_INST_t *mac = get_mac_inst(mod_id);
   RA_config_t *ra = &mac->ra;
+  // Random seed generation
+  long long tmp = rdtsc_oai();
+  unsigned short int *seed = (unsigned short int*)&tmp;
 
   ra->first_Msg3 = 1;
   ra->ra_PreambleIndex = -1;
@@ -850,7 +854,7 @@ void nr_ra_failed(uint8_t mod_id, uint8_t CC_id, NR_PRACH_RESOURCES_t *prach_res
     LOG_D(MAC, "In %s: [UE %d][%d.%d] Maximum number of RACH attempts (%d) reached, selecting backoff time...\n",
           __FUNCTION__, mod_id, frame, slot, ra->preambleTransMax);
 
-    ra->RA_backoff_cnt = rand() % (prach_resources->RA_PREAMBLE_BACKOFF + 1);
+    ra->RA_backoff_cnt = nrand48(seed) % (prach_resources->RA_PREAMBLE_BACKOFF + 1);
     prach_resources->RA_PREAMBLE_TRANSMISSION_COUNTER = 1;
     prach_resources->RA_PREAMBLE_POWER_RAMPING_STEP += 2; // 2 dB increment
     prach_resources->ra_PREAMBLE_RECEIVED_TARGET_POWER = nr_get_Po_NOMINAL_PUSCH(prach_resources, mod_id, CC_id);