Beam Failure Recovery Sandbox

Simulate 3GPP MAC layer behavior for Beam Failure Detection (BFD) and Recovery (BFR). Interact with timers and signal drops.

RRC configuration

Max count (instance)

Detection timer (PBFD)actual: 40ms

Qout threshold

dBm

Measurements period

Signal environment

Signal drop start500ms

0ms2000ms

Drop duration400ms

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.