make cell reselection periodic and with period of 20msec

srsue/hdr/stack/rrc/rrc.h

@@ -579,7 +579,6 @@ private:
   void leave_connected();
   void stop_timers();
   void start_con_restablishment(asn1::rrc::reest_cause_e cause);
-  void start_cell_reselection();
 
   void log_rr_config_common();
   void log_phy_config_dedicated();

srsue/hdr/stack/rrc/rrc_procedures.h

@@ -259,6 +259,7 @@ public:
   srslte::proc_outcome_t step();
   srslte::proc_outcome_t react(bool timeout);
   static const char*     name() { return "Go Idle"; }
+  void                   then(const srslte::proc_state_t& result);
 
 private:
   static const uint32_t rlc_flush_timeout_ms = 60; // TS 36.331 Sec 5.3.8.3
@@ -270,14 +271,18 @@ private:
 class rrc::cell_reselection_proc
 {
 public:
+  const static uint32_t cell_reselection_periodicity_ms = 20;
+
   cell_reselection_proc(rrc* rrc_);
   srslte::proc_outcome_t init();
   srslte::proc_outcome_t step();
   static const char*     name() { return "Cell Reselection"; }
+  void                   then(const srslte::proc_state_t& result);
 
 private:
   rrc* rrc_ptr;
 
+  srslte::timer_handler::unique_timer reselection_timer;
   srslte::proc_future_t<cs_result_t>  cell_selection_fut;
 };
 

srsue/src/stack/rrc/rrc.cc

@@ -253,16 +253,6 @@ void rrc::run_tti()
   // Run state machine
   switch (state) {
     case RRC_STATE_IDLE:
-
-      /* CAUTION: The execution of cell_search() and cell_selection() take more than 1 ms
-       * and will slow down MAC TTI ticks. This has no major effect at the moment because
-       * the UE is in IDLE but we could consider splitting MAC and RRC threads to avoid this
-       */
-
-      // If attached but not camping on the cell, perform cell reselection
-      if (nas->is_attached()) {
-        start_cell_reselection();
-      }
       break;
     case RRC_STATE_CONNECTED:
       measurements->run_tti();
@@ -1251,24 +1241,6 @@ void rrc::start_con_restablishment(reest_cause_e cause)
   callback_list.add_proc(connection_reest);
 }
 
-void rrc::start_cell_reselection()
-{
-  if (neighbour_cells.empty() and phy_sync_state == phy_in_sync and phy->cell_is_camping()) {
-    // don't bother with cell selection if there are no neighbours and we are already camping
-    return;
-  }
-
-  if (cell_reselector.is_busy()) {
-    // it is already running
-    return;
-  }
-
-  if (not cell_reselector.launch()) {
-    rrc_log->error("Failed to initiate a Cell Reselection procedure...\n");
-  }
-  callback_list.add_proc(cell_reselector);
-}
-
 void rrc::cell_search_completed(const phy_interface_rrc_lte::cell_search_ret_t& cs_ret,
                                 const phy_interface_rrc_lte::phy_cell_t&        found_cell)
 {

srsue/src/stack/rrc/rrc_procedures.cc

@@ -1101,14 +1101,44 @@ proc_outcome_t rrc::go_idle_proc::step()
   return proc_outcome_t::yield;
 }
 
+void rrc::go_idle_proc::then(const srslte::proc_state_t& result)
+{
+  if (not rrc_ptr->cell_reselector.launch()) {
+    rrc_ptr->rrc_log->error("Failed to initiate a Cell Reselection procedure...\n");
+    return;
+  }
+  rrc_ptr->callback_list.add_proc(rrc_ptr->cell_reselector);
+}
+
 /**************************************
  *    Cell Reselection procedure
  *************************************/
 
-rrc::cell_reselection_proc::cell_reselection_proc(srsue::rrc* rrc_) : rrc_ptr(rrc_) {}
+rrc::cell_reselection_proc::cell_reselection_proc(srsue::rrc* rrc_) : rrc_ptr(rrc_)
+{
+  // Timer for cell reselection procedure to self-relaunch periodically
+  reselection_timer = rrc_ptr->stack->get_unique_timer();
+  reselection_timer.set(cell_reselection_periodicity_ms, [this](uint32_t tid) {
+    if (not rrc_ptr->cell_reselector.launch()) {
+      rrc_ptr->rrc_log->error("Failed to initiate a Cell Reselection procedure...\n");
+      return;
+    }
+    rrc_ptr->callback_list.add_proc(rrc_ptr->cell_reselector);
+  });
+}
 
 proc_outcome_t rrc::cell_reselection_proc::init()
 {
+  if (not rrc_ptr->nas->is_attached() or rrc_ptr->is_connected()) {
+    // check if rrc is still idle
+    return proc_outcome_t::success;
+  }
+
+  if (rrc_ptr->neighbour_cells.empty() and rrc_ptr->phy_sync_state == phy_in_sync and rrc_ptr->phy->cell_is_camping()) {
+    // don't bother with cell selection if there are no neighbours and we are already camping
+    return proc_outcome_t::success;
+  }
+
   Info("Starting...\n");
   if (not rrc_ptr->cell_selector.launch(&cell_selection_fut)) {
     Error("Failed to initiate a Cell Selection procedure...\n");
@@ -1150,6 +1180,14 @@ proc_outcome_t rrc::cell_reselection_proc::step()
   return srslte::proc_outcome_t::success;
 }
 
+void rrc::cell_reselection_proc::then(const srslte::proc_state_t& result)
+{
+  // Schedule cell reselection periodically, while rrc is idle
+  if (not rrc_ptr->is_connected() and rrc_ptr->nas->is_attached()) {
+    reselection_timer.run();
+  }
+}
+
 /**************************************
  *    RRC Connection Re-establishment procedure
  *************************************/