PHY: LtePhyEnb: broadcast beacons by default

Make enableBeacons default to true (was: default to enableHandover), so every
eNB/gNB broadcasts beacons regardless of handover -- as real base stations
always transmit reference signals. This makes the beacon-based radio link
monitoring / RLF detection path available out of the box, not only when
handover happens to be enabled.

Adds about 10s to fingerprint suite runtime (~238s -> ~248s).

Fingerprint impact (re-recorded): 105 of 132 simulations drift -- exactly the
handover-disabled ones, where beacons now flow. In every one of them ONLY tplx
and tilx move: the all-events fingerprints pick up the added beaconStarter
self-messages and beacon airframe send/receive events. ~tNl (network-level data
traffic) and sz (all scalar/statistic results) are byte-identical everywhere,
confirming beacons perturb neither the data plane nor the RNG stream -- the UE
beacon RX path early-outs before getSINR when handover is disabled, and beacon
TX draws no random numbers. The 27 handover-enabled simulations are unchanged
(beacons already flowed there). Both new error paths verified to fire.

Author: avarga

src/simu5g/stack/phy/LtePhyEnb.ned

@@ -25,18 +25,15 @@ simple LtePhyEnb extends LtePhyBase
         @class("LtePhyEnb");
 
         // Marks this eNB as a handover target: its beacons are used by UEs for handover
-        // feasibility assessment. Requires enableBeacons=true (the default when handover is
-        // on); the module errors out at initialization if beacons are disabled while
-        // handover is enabled.
+        // feasibility assessment. Requires enableBeacons=true (the default).
         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), decoupled from enableHandover so radio link
-        // monitoring can run without handover. Defaults to enableHandover (beacons flow
-        // exactly when handover is enabled). cellInfo.beaconInterval must be positive: a
-        // zero/negative interval is an error -- switch beacons off with enableBeacons=false.
-        bool enableBeacons = default(enableHandover);
+        // link failure (RLF) detection. On by default so radio link monitoring works out
+        // of the box; set to false to suppress beacons entirely. Must stay true when
+        // enableHandover=true. Requires cellInfo.beaconInterval > 0.
+        bool enableBeacons = default(true);
 
         double targetBler = default(0.001);
 }