Beam selection in unlicensed operation
The invention includes a method performed by a user equipment, UE, for selecting a directional beam for a random access procedure in a wireless network comprising: performing a plurality of directional listen-before-talk, LBT, procedures in a respective plurality of different directions associated with a respective plurality of beams, determining respective first metrics based on received power of respective reference signals associated with the respective beams, determining respective second metrics based on channel occupancy, CO, or LBT failures in the respective beams and selecting one of the beams to be used for the random access procedure based on the first metrics and the second metrics. The invention further includes a complementary method performed by a network node, as well as a UE and a network node configured to perform operations corresponding to such methods.
1. A method by a user equipment (UE) for performing a random access procedure in a wireless network, the method comprising:
performing a plurality of directional listen-before-talk (LBT) procedures in a respective plurality of different directions associated with a respective plurality of beams;
determining respective first metrics based on received power of respective reference signals associated with the respective beams;
determining respective second metrics based on channel occupancy (CO) or LBT failures in the respective beams; and
selecting one of the beams to be used for the random access procedure based on the first metrics and the second metrics.
2. The method of claim 1 , wherein the respective reference signals include one or more of the following: SSB/PBCH Block (SSB), and channel state information reference signals (CSI-RS).
3. The method of claim 1 , wherein determining the respective first metrics comprises measuring reference signal received power (RSRP) of the respective reference signals.
4. The method of claim 1 , wherein determining the respective second metrics comprises one of the following for each second metric:
determining the second metric based on success or failure of the LBT procedure on the corresponding beam; or
receiving the second metric from a network node in the wireless network.
5. The method of claim 1 , wherein selecting one of the beams comprises:
selecting a first set of the beams having respective first metrics greater than a first threshold; and
when the first set is not empty, selecting from the first set a beam having the lowest second metric.
6. The method of claim 5 , wherein selecting one of the beams further comprises, when the first set is empty, selecting a beam having the lowest second metric.
7. The method of claim 1 , wherein selecting one of the directional beams comprises:
selecting a first set of the beams having respective first metrics greater than a first threshold and respective second metrics less than a second threshold;
when the first set is not empty, selecting a beam from the first set based on one of the following criteria: randomly, a highest first metric of the first set, or a lowest second metric of the first set.
8. The method of claim 7 , wherein selecting one of the beams further comprises, when the first set is empty:
selecting a second set of beams having respective second metrics less than the second threshold; and
when the second set is not empty, selecting a beam from the second set based on one of the following criteria: randomly, or a lowest second metric of the second set.
9. The method of claim 8 , wherein selecting one of the beams further comprises, when the first set and the second set are empty, selecting one of the directional beams based on one of the following criteria: randomly, or a beam with the lowest second metric.
10. The method of claim 1 , wherein:
the UE is served by a first beam; and
selecting one of the beams, other than the first beam, is in response to one of the following:
a count of consecutive LBT failures, on the first beam, has exceeded a maximum amount; or
expiration of a timer without a successful LBT procedure on the first beam while the timer was running.
11. The method of claim 1 , wherein:
the directional LBT procedures are performed in unlicensed frequency spectrum; and
the wireless network is one of the following:
an NG-RAN configured to support NR unlicensed (NR-U) operation; or
an E-UTRAN configured to support LTE licensed assisted access (LAA) operation.
12. The method of claim 1 , wherein the selected beam fulfills the following conditions:
a received power value of the associated reference signal is above a first pre-defined threshold associated with the first metrics; and
either a channel occupancy (CO) value of the associated reference signal is below a second pre-defined threshold associated with the second metrics, or an LBT failure value is below a second pre-defined threshold associated with the second metrics.
13. A user equipment (UE) configured to perform a random access procedure in a wireless network, the UE comprising:
radio transceiver circuitry configured to communicate with a network node in the wireless network; and
processing circuitry operatively coupled to the radio transceiver circuitry, whereby the processing circuitry and the radio transceiver circuitry are configured to:
perform a plurality of directional listen-before-talk (LBT) procedures in a respective plurality of different directions associated with a respective plurality of beams;
determine respective first metrics based on received power of respective reference signals associated with the respective beams;
determine respective second metrics based on channel occupancy (CO) or LBT failures in the respective beams; and
select one of the beams to be used for the random access procedure based on the first metrics and the second metrics.
14. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform a random access procedure in a wireless network, configure the UE to perform operations corresponding to the method of claim 1 .