Method and apparatus for supporting RACH-less mobility with pre-allocated beams in wireless communication system

1. A method performed by a user equipment (UE) operating in a wireless communication system, the method comprising:

receiving, from a source base station, a measurement configuration;

reporting, to the source base station, measurement results according to the measurement configuration;

receiving, from the source base station, a mobility control information message generated by a target base station,

wherein the mobility control information message includes a rach-Skip field informing the UE that a random access procedure is to be skipped,

wherein the mobility control information message includes a pre-allocated uplink (UL) grant configuration including i) information on one or more pre-allocated beams and ii) information on a quality threshold, and

wherein the one or more pre-allocated beams are associated with one or more synchronization signal (SS) blocks or one or more channel state information (CSI) reference signals (RSs) transmitted by the target base station;

synchronizing to a target cell served by the target base station based on the mobility control information message;

based on a quality of at least one of the one or more pre-allocated beams meeting the quality threshold, performing an UL transmission to the target base station via the at least one pre-allocated beam based on the pre-allocated UL grant configuration, without performing the random access procedure with the target base station based on the rach-Skip field informing the UE that the random access procedure is to be skipped; and

based on none of the one or more pre-allocated beams meeting the quality threshold, performing the random access procedure with the target base station.

2. The method of claim 1 , wherein the UL transmission includes a mobility complete message in response to the reception of the mobility control information message.

3. The method of claim 1 , wherein the method further comprises:

retransmitting the UL transmission to the target base station based on the pre-allocated UL grant configuration until an acknowledgement is received from the target base station or a maximum number of retransmissions is reached.

4. The method of claim 3 , wherein the retransmission is performed via beams other than the at least one beam meeting the threshold.

5. The method of claim 1 , wherein the method further comprises:

considering mobility to the target cell successfully completed based on a reception of an acknowledgement from the target base station.

6. The method of claim 5 , wherein a successful reception of a physical downlink control channel (PDCCH) transmission addressed to a UE-specific radio network temporary identity (RNTI) is considered as the reception of the acknowledgement.

7. The method of claim 1 , wherein the method further comprises:

considering mobility to the target cell unsuccessfully completed based on an acknowledgement not being received from the target base station before a timer expires or a maximum number of retransmissions is reached.

8. The method of claim 7 , wherein the method further comprises:

releasing the pre-allocated UL grant configuration; and

triggering a radio resource control (RRC) connection reestablishment procedure.

9. The method of claim 1 , wherein the mobility control information message includes a pre-allocated sounding reference signal (SRS) configuration including information on the one or more pre-allocated beams, and

wherein the UL transmission includes an SRS transmission.

10. The method of claim 9 , wherein the SRS transmission is performed until a PDCCH addressed to a UE-specific RNTI is successfully received.

11. The method of claim 10 , wherein the method further comprises:

transmitting a mobility complete message to the target base station based on successful reception of the PDCCH addressed to the UE-specific RNTI.

12. The method of claim 10 , wherein the method further comprises:

performing the random access procedure with the target base station based on the PDCCH addressed to the UE-specific RNTI not being successfully received before a timer expires or a maximum number of SRS transmissions is reached.

13. The method of claim 1 , wherein the UE is in communication with at least one of a mobile device, a network, and/or autonomous vehicles other than the UE.

14. A user equipment (UE) configured for operating in a wireless communication system, the UE comprising:

at least one transceiver;

at least one processor; and

at least one memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:

receiving, from a source base station using the at least one transceiver, a measurement configuration;

reporting, to the source base station using the at least one transceiver, measurement results according to the measurement configuration;

receiving, from the source base station using the at least one transceiver, a mobility control information message generated by a target base station,

wherein the mobility control information message includes a rach-Skip field informing the processor that a random access procedure is to be skipped,

wherein the mobility control information message includes a pre-allocated uplink (UL) grant configuration including i) information on one or more pre-allocated beams and ii) information on a quality threshold, and

wherein the one or more pre-allocated beams are associated with one or more synchronization signal (SS) blocks or one or more channel state information (CSI) reference signals (RSs) transmitted by the target base station;

synchronizing to a target cell served by the target base station based on the mobility control information message;

based on a quality of at least one of the one or more pre-allocated beams meeting the quality threshold, performing, using the at least one transceiver, an UL transmission to the target base station via the at least one pre-allocated beams based on the pre-allocated UL grant configuration, without performing the random access procedure with the target base station based on the rach-Skip field informing the processor that the random access procedure is to be skipped; and

based on none of the one or more pre-allocated beams meeting the quality threshold, performing, using the at least one transceiver, the random access procedure with the target base station.

15. A processing apparatus configured to operate a wireless device in a wireless communication system, the processing apparatus comprising:

at least one processor; and

at least one memory operably connectable to the at least one processor, wherein the at least one processor is configured to perform operations comprising:

obtaining a measurement configuration;

generating measurement results according to the measurement configuration;

obtaining a mobility control information message generated by a target base station,

wherein the mobility control information message includes a rach-Skip field informing the processor that a random access procedure is to be skipped,

wherein the mobility control information message includes a pre-allocated uplink (UL) grant configuration including i) information on one or more pre-allocated beams and ii) information on a quality threshold, and

wherein the one or more pre-allocated beams are associated with one or more synchronization signal (SS) blocks or one or more channel state information (CSI) reference signals (RSs) transmitted by the target base station;

synchronizing to a target cell served by the target base station based on the mobility control information message;

based on a quality of at least one of the one or more pre-allocated beams meeting the quality threshold, controlling the wireless device to perform an UL transmission to the target base station via the at least one pre-allocated beam based on the pre-allocated UL grant configuration, without performing the random access procedure with the target base station based on the rach-Skip field informing the processor that the random access procedure is to be skipped; and

based on none of the one or more pre-allocated beams meeting the quality threshold, controlling the wireless device to perform the random access procedure with the target base station.