Simulate 3GPP MAC layer behavior for Beam Failure Detection (BFD) and Recovery (BFR). Interact with timers and signal drops.
RRC configuration
actual: 40ms
dBm
Signal environment
500ms
0ms2000ms
400ms
50ms1000ms
Simulation analysis
StatusIdle
MAC layer trace
No events generated. Signal is good.
Technical reference
Key definitions
Qout (Out-of-Sync)
The physical layer threshold where the radio link is considered unreliable (usually 10% BLER on PDCCH). When PHY detects this, it sends a standardized "BFI" to MAC.
BFI (Beam Failure Instance)
An indication sent from Layer 1 (PHY) to Layer 2 (MAC) when the radio link quality of all serving control beams drops below Qout.
The recovery process
1
Detection
PHY measures reference signals (SSB/CSI-RS) periodically and checks against Qout.
2
Accumulation
MAC counts BFI indications. Uses 3GPP specific timers (pbfd) for hysteresis.
3
Trigger
If BFI_COUNTER ≥ MaxCount, UE declared Beam Failure and starts restoration.