9.2.8 Beam failure detection and recovery

For beam failure detection, the gNB configures the UE with beam failure detection reference signals (SSB or CSI-RS) and the UE declares beam failure when the number of beam failure instance indications from the physical layer reaches a configured threshold before a configured timer expires. For beam failure detection in multi-TRP operation, the gNB configures the UE with two sets of beam failure detection reference signals, and the UE declares beam failure for a TRP / BFD-RS set when the number of beam failure instance indications associated with the corresponding set of beam failure detection reference signals from the physical layer reaches a configured threshold before a configured timer expires.

SSB-based Beam Failure Detection is based on the CD-SSB associated to the initial DL BWP and can be configured for the initial DL BWPs, for DL BWPs containing the CD-SSB associated to the initial DL BWP, and, if supported, for DL BWPs not containing the CD-SSB associated to the initial DL BWP. Besides, SSB-based Beam Failure Detection can be also performed based on the non-cell defining SSB, if configured for the active DL BWP. Beam Failure Detection can be also performed based on CSI-RS, if configured for the active DL BWP.

After beam failure is detected on SpCell, the UE:

• triggers beam failure recovery by initiating a Random Access procedure on the SpCell;
• selects a suitable beam to perform beam failure recovery (if the gNB has provided dedicated Random Access resources for certain beams, those will be prioritized by the UE).
• includes an indication of a beam failure on SpCell in a BFR MAC CE if the Random Access procedure involves contention-based random access.

Upon completion of the Random Access procedure, beam failure recovery for SpCell is considered complete.

After beam failure is detected on an SCell, the UE:

• triggers beam failure recovery by initiating a transmission of a BFR MAC CE for this SCell;
• selects a suitable beam for this SCell (if available) and indicates it along with the information about the beam failure in the BFR MAC CE.

Upon reception of a PDCCH indicating an uplink grant for a new transmission for the HARQ process used for the transmission of the BFR MAC CE, beam failure recovery for this SCell is considered complete.

After beam failure is detected for a BFD-RS set of a Serving Cell, the UE:

• triggers beam failure recovery by initiating a transmission of a BFR MAC CE for this BFD-RS set;
• selects a suitable beam for this BFD-RS set (if available) and indicates whether the suitable (new) beam is found or not along with the information about the beam failure in the BFR MAC CE for this BFD-RS set.

Upon reception of a PDCCH indicating an uplink grant for a new transmission for the HARQ process used for the transmission of the BFR MAC CE for this BFD-RS set, beam failure recovery for this BFD-RS set is considered complete.

After beam failure is detected for both BFD-RS sets of SpCell concurrently, the UE:

• triggers beam failure recovery by initiating a Random Access procedure on the SpCell;
• selects a suitable beam for each failed BFD-RS set (if available) and indicates whether the suitable (new) beam is found or not along with the information about the beam failure in the BFR MAC CE for each failed BFD-RS set;
• upon completion of the Random Access procedure, beam failure recovery for both BFD-RS sets of SpCell is considered complete.