Fixed UE measurements timing issue (when reportInterval > 200 ms, or when time-to-trigger < 200 ms)

src/lte/model/lte-ue-rrc.cc

@@ -45,7 +45,6 @@ NS_LOG_COMPONENT_DEFINE ("LteUeRrc");
 namespace ns3 {
 
 
-
 /////////////////////////////
 // CMAC SAP forwarder
 /////////////////////////////
@@ -1885,7 +1884,10 @@ LteUeRrc::VarMeasReportListAdd (uint8_t measId, ConcernedCells_t enteringCells)
 
   NS_ASSERT (!measReportIt->second.cellsTriggeredList.empty ());
   measReportIt->second.numberOfReportsSent = 0;
-  SendMeasurementReport (measId);
+  measReportIt->second.periodicReportTimer
+    = Simulator::Schedule (UE_MEASUREMENTS_DELAY,
+                           &LteUeRrc::SendMeasurementReport,
+                           this, measId);
 
   std::map<uint8_t, std::list<PendingTrigger_t> >::iterator
     enteringTriggerIt = m_enteringTriggerQueue.find (measId);
@@ -1943,6 +1945,8 @@ LteUeRrc::VarMeasReportListErase (uint8_t measId, ConcernedCells_t leavingCells,
 
   if (reportOnLeave)
     {
+      // TODO: this might fail because the VarMeasReportList entry might have been deleted already
+      // TODO: this might produce unexpectedly repeating measurement report
       SendMeasurementReport (measId);
     }
 

src/lte/model/lte-ue-rrc.h

@@ -35,6 +35,26 @@
 
 namespace ns3 {
 
+
+/**
+ * \brief Artificial delay of UE measurements procedure
+ *
+ * i.e. the period between the time layer-1-filtered measurements from PHY
+ * layer is received and the earliest time the actual measurement report
+ * submission to the serving cell is invoked.
+ *
+ * This delay exists because of racing condition between several UE measurements
+ * functions which happen to be scheduled at the same time. The delay ensures
+ * that:
+ *  - measurements (e.g. layer-3-filtering) is always performed before
+ *    reporting, thus the latter always uses the newest layer-1-filtered
+ *    measurements from PHY; and
+ *  - time-to-trigger is always performed just before the reporting, so there
+ *    would still be chance to cancel the reporting if necessary.
+ */
+static const Time UE_MEASUREMENTS_DELAY = MicroSeconds (1);
+
+
 class LteRlc;
 class LteMacSapProvider;
 class LteUeCmacSapUser;
@@ -287,7 +307,7 @@ private:
 
   LteMacSapProvider* m_macSapProvider;
   LtePdcpSapUser* m_drbPdcpSapUser;
-  
+
   LteAsSapProvider* m_asSapProvider;
   LteAsSapUser* m_asSapUser;