Method and apparatus for performing beam failure recovery in a wireless communication

1. A method for performing, by a user equipment (UE), a beam failure recovery (BFR) in a wireless communication system, the method comprising:

receiving, from a base station, configuration information about a candidate beam reference signal (RS) set,

wherein the candidate beam RS set is comprised of only channel state information-reference signals (CSI-RSs);

selecting a beam RS among the CSI-RSs of the candidate beam RS set based on a predetermined condition,

wherein the selecting comprises:

selecting the beam among the CSI-RSs of the candidate beam RS set having a RS received power (RSRP) value that exceeds a threshold;

selecting the beam RS among specific synchronization signal blocks (SSBs) having a RSRP value that exceeds the threshold, based on RSRP values based on none of the CSI-RSs within the candidate beam RS exceeding the threshold,

wherein SSBs which are connected to a physical random access channel (PRACH) include the specific SSBs;

selecting the beam RS among i) the SSBs and ii) the CSI-RSs, based on RSRP values for all of the CSI-RSs and RSRP values for all of the SSBs not exceeding the threshold,

wherein, based on the CSI-RSs including at least one CSI-RS indirectly connected to the PRACH, the beam RS selected based on RSRP values for all of the CSI-RSs and RSRP values for all of the SSBs not exceeding the threshold is a beam RS among i) the SSBs and ii) specific CSI-RSs directly connected to the PRACH within the CSI-RSs, and

wherein, based on at least one of the specific CSI-RSs being quasi-co-located with one of the SSBs with respect to a spatial reception parameter, the beam RS selected based on RSRP values for all of the CSI-RSs and RSRP values for all of the SSBs not exceeding the threshold is a beam RS among i) the SSBs and ii) CSI-RSs which are not quasi-co-located with any of the SSBs with respect to a corresponding spatial reception parameter within the specific CSI-RSs; and

transmitting a PRACH preamble to the base station via a PRACH resource connected to the selected beam RS.

2. The method of claim 1 , wherein all the SSBs are SSBs within a serving cell, within a serving carrier, or within an active bandwidth part (BWP).

3. A user equipment (UE) for performing a beam failure recovery (BFR) in a wireless communication system, the UE comprising:

a transmitter configured to transmit a radio signal;

a receiver configured to receive the radio signal; and

a processor configured to control the transmitter and the receiver,

wherein the processor is configured to:

receive, from a base station, configuration information about a candidate beam reference signal (RS) set,

wherein the candidate beam RS set is comprised of only channel state information-reference signals (CSI-RSs);

select a beam RS among the CSI-RSs of the candidate beam RS set based on a predetermined condition,

wherein the selecting comprises:

select the beam among the CSI-RSs of the candidate beam RS set having a RS received power (RSRP) value that exceeds a threshold;

select the beam RS among specific synchronization signal blocks (SSBs) having a RSRP value that exceeds the threshold, based on RSRP values based on none of the CSI-RSs within the candidate beam RS exceeding the threshold,

wherein SSBs which are connected to a physical random access channel (PRACH) include the specific SSBs;

select the beam RS among i) the SSBs and ii) the CSI-RSs, based on RSRP values for all of the CSI-RSs and RSRP values for all of the SSBs not exceeding the threshold,

wherein, based on the CSI-RSs including at least one CSI-RS indirectly connected to the PRACH, the beam RS selected based on RSRP values for all of the CSI-RSs and RSRP values for all of the SSBs not exceeding the threshold is a beam RS among i) the SSBs and ii) specific CSI-RSs directly connected to the PRACH within the CSI-RSs, and

wherein, based on at least one of the specific CSI-RSs being quasi-co-located with one of the SSBs with respect to a spatial reception parameter, the beam RS selected based on RSRP values for all of the CSI-RSs and RSRP values for all of the SSBs not exceeding the threshold is a beam RS among i) the SSBs and ii) CSI-RSs which are not quasi-co-located with any of the SSBs with respect to a corresponding spatial reception parameter within the specific CSI-RSs; and

transmit a PRACH preamble to the base station via a PRACH resource connected to the selected beam RS.

4. The UE of claim 3 , wherein all the SSBs are SSBs within a serving cell, within a serving carrier, or within an active bandwidth part (BWP).