PHY: LtePhyEnb: decouple beacon emission from enableHandover (add enableBeacons)

Beacons are the measurement signal UEs use both for handover feasibility
assessment and for radio link monitoring (RLF detection). Gating their
emission on enableHandover meant radio link monitoring could not run without
handover, and would silently not exist otherwise.

Add a separate enableBeacons parameter that controls beacon broadcasting.
It defaults to enableHandover, so existing configurations are unaffected
(beacons flow exactly when they did before). enableHandover=true now requires
beacons to actually flow (enableBeacons=true and beaconInterval>0); otherwise
the eNB errors out at initialization instead of silently disabling handover.

Fingerprint-neutral: full suite 132/132 OK (default enableBeacons==enableHandover
reproduces prior behavior in every baseline config).

Author: avarga

src/simu5g/stack/phy/LtePhyEnb.cc

@@ -71,7 +71,17 @@ void LtePhyEnb::initialize(int stage)
         }
 
         beaconInterval_ = cellInfo_->par("beaconInterval");
-        if (beaconInterval_ != 0 && par("enableHandover").boolValue()) {
+        bool enableHandover = par("enableHandover");
+        bool enableBeacons = par("enableBeacons");
+        bool beaconsWillFlow = enableBeacons && beaconInterval_ != 0;
+        // Handover feasibility assessment (and radio link monitoring) in the UEs is driven by
+        // these beacons, so handover cannot silently work without them.
+        if (enableHandover && !beaconsWillFlow)
+            throw cRuntimeError("enableHandover=true requires the eNB to broadcast beacons, but "
+                    "they are disabled (enableBeacons=%s, cellInfo.beaconInterval=%gs); set "
+                    "enableBeacons=true and beaconInterval>0, or set enableHandover=false",
+                    enableBeacons ? "true" : "false", beaconInterval_);
+        if (beaconsWillFlow) {
             beaconStarter_ = new cMessage("beaconStarter");
             scheduleAt(NOW, beaconStarter_);
         }

src/simu5g/stack/phy/LtePhyEnb.ned

@@ -24,9 +24,18 @@ simple LtePhyEnb extends LtePhyBase
     parameters:
         @class("LtePhyEnb");
 
-        // Enables broadcasting beacons which are used for handover feasibility assessment in UEs
+        // Marks this eNB as a handover target: its beacons are used by UEs for handover
+        // feasibility assessment. Requires enableBeacons (beacons are the input to that
+        // assessment); the module errors out at initialization if beacons are disabled.
         bool enableHandover = default(false);
 
+        // Enables broadcasting periodic beacons (at cellInfo.beaconInterval). Beacons are the
+        // measurement signal UEs use both for handover feasibility assessment and for radio
+        // link monitoring (RLF detection), so they are decoupled from enableHandover to allow
+        // radio link monitoring without handover. Defaults to enableHandover for backward
+        // compatibility. Broadcasting also requires cellInfo.beaconInterval > 0.
+        bool enableBeacons = default(enableHandover);
+
         double targetBler = default(0.001);
 }