Fast SCell BFR

Technical Explanation

In carrier aggregation, beam failure on a secondary cell (SCell) previously triggered complex recovery signaling. Rel-18 standardizes Fast SCell BFR, where the UE immediately reports SCell beam failure and recommends a newly detected candidate beam using a compact MAC Control Element transmitted on the reliable primary cell (PCell), restoring high-capacity carrier aggregation in milliseconds.

Key Functions

• Reports beam failure on secondary carrier aggregation cells in under 5 milliseconds
• Transmits compact SCell BFR MAC CE signaling across the robust low-band PCell
• Identifies and activates candidate beams without initiating random access on SCells
• Prevents sudden carrier aggregation throughput collapses in multi-band mmWave setups