Apparatus and method for handover in a wireless communication system

Abstract

An apparatus and a method for handover in a wireless communication system are provided. The method is performed by a UE and includes receiving an RRC message from a source base station; and performing a handover procedure to handover from the source base station to a target base station in response to the RRC message, wherein: the RRC message comprises one of a first dedicated random access configuration associated with a CSI-RS of the target base station and a second dedicated random access configuration associated with a first SSB of the target base station, the CSI-RS is configured with a first dedicated random access resource by the first dedicated random access configuration, and the first SSB is configured with a second dedicated random access resource by the second dedicated random access configuration.

What is claimed is: 
     
         1 . A method performed by a User Equipment (UE) for handover, the method comprising:
 receiving a Radio Resource Control (RRC) message from a source base station; and   performing a handover procedure to handover from the source base station to a target base station in response to the RRC message, wherein:   the RRC message comprises one of a first dedicated random access configuration associated with a Channel State Information-Reference Signal (CSI-RS) of the target base station and a second dedicated random access configuration associated with a first Synchronization Signal Block (SSB) of the target base station,   the CSI-RS is configured with a first dedicated random access resource by the first dedicated random access configuration, and   the first SSB is configured with a second dedicated random access resource by the second dedicated random access configuration.   
     
     
         2 . The method of  claim 1 , further comprising:
 receiving a measurement configuration from the source base station;   performing a measurement according to the measurement configuration; and   transmitting a measurement report for the measurement to the source base station according to the measurement configuration,   wherein the measurement report comprises beam information.   
     
     
         3 . The method of  claim 2 , wherein the measurement configuration comprises an information element indicating to the UE to transmit the measurement report when a condition of beam information change is satisfied. 
     
     
         4 . The method of  claim 3 , wherein the condition of beam information change is satisfied when a beam identifier (ID) included in the measurement report is different from another beam ID included in a previous measurement report transmitted by the UE. 
     
     
         5 . The method of  claim 3 , wherein the condition of beam information change is satisfied when the beam information included in the measurement report is different from beam information included in a previous measurement report transmitted by the UE. 
     
     
         6 . The method of  claim 3 , wherein the condition of beam information change is satisfied when a beam set included in the measurement report is different from another beam set included in a previous measurement report transmitted by the UE. 
     
     
         7 . The method of  claim 1 , wherein the RRC message further comprises a configuration of a common random access resource. 
     
     
         8 . The method of  claim 7 , wherein the RRC message further comprises a parameter indicating a maximum number of random access attempts before the UE is allowed to use the common random access resource. 
     
     
         9 . The method of  claim 1 , further comprising:
 receiving the first dedicated random access resource from the source base station, the first dedicated random access resource being a contention-free random access resource associated with the CSI-RS;   determining whether a Channel State Information-Reference Signal Received Power (CSI-RSRP) of the CSI-RS is greater than a CSI-RS threshold; and   transmitting a random access preamble to the target base station by using the contention-free random access resource after determining that the CSI-RSRP is greater than the CSI-RS threshold.   
     
     
         10 . The method of  claim 9 , further comprising:
 determining that the CSI-RSRP is not greater than the CSI-RS threshold;   determining whether a Synchronization Signal (SS)-RSRP of a second SSB associated with a contention-based random access resource is greater than an SS-RSRP threshold; and   transmitting a random access preamble by using any SSB with a common random access resource after determining that the SS-RSRP is not greater than the SS-RSRP threshold.   
     
     
         11 . A User Equipment (UE) for handover, the UE comprising:
 a memory storing instructions; and   a processing circuitry coupled to the memory and configured to execute the stored instructions to:   receive a Radio Resource Control (RRC) message from a source base station; and   perform a handover procedure to handover from the source base station to a target base station in response to the RRC message, wherein:   the RRC message comprises one of a first dedicated random access configuration associated with a Channel State Information-Reference Signal (CSI-RS) of the target base station and a second dedicated random access configuration associated with a first Synchronization Signal Block (SSB) of the target base station,   the CSI-RS is configured with a first dedicated random access resource by the first dedicated random access configuration, and   the first SSB is configured with a second dedicated random access resource by the second dedicated random access configuration.   
     
     
         12 . The UE of  claim 11 , wherein the processing circuitry is further configured to execute the stored instructions to:
 receive a measurement configuration from the source base station;   perform a measurement according to the measurement configuration; and   transmit a measurement report for the measurement to the source base station according to the measurement configuration,   wherein the measurement report comprises beam information.   
     
     
         13 . The UE of  claim 12 , wherein the measurement configuration comprises an information element indicating to the UE to transmit the measurement report when a condition of beam information change is satisfied. 
     
     
         14 . The UE of  claim 13 , wherein the condition of beam information change is satisfied when a beam identifier (ID) included in the measurement report is different from another beam ID included in a previous measurement report transmitted by the UE. 
     
     
         15 . The UE of  claim 13 , wherein the condition of beam information change is satisfied when the beam information included in the measurement report is different from beam information included in a previous measurement report transmitted by the UE. 
     
     
         16 . The UE of  claim 13 , wherein the condition of beam information change is satisfied when a beam set included in the measurement report is different from another beam set included in a previous measurement report transmitted by the UE. 
     
     
         17 . The UE of  claim 11 , wherein the RRC message further comprises a configuration of a common random access resource. 
     
     
         18 . The UE of  claim 17 , wherein the RRC message further comprises a parameter indicating a maximum number of random access attempts before the UE is allowed to use the common random access resource. 
     
     
         19 . The UE of  claim 11 , wherein the processing circuitry is further configured to:
 receive the first dedicated random access resource from the source base station, the first dedicated random access resource being a contention-free random access resource associated with the CSI-RS;   determine whether a Channel State Information-Reference Signal Received Power (CSI-RSRP) of the CSI-RS is greater than a CSI-RS threshold; and   transmit a random access preamble to the target base station by using the contention-free random access resource after determining that the CSI-RSRP is greater than the CSI-RS threshold.   
     
     
         20 . The UE of  claim 19 , wherein the processing circuitry is further configured to:
 determining that the CSI-RSRP is not greater than the CSI-RS threshold;   determine whether a Synchronization Signal (SS)-RSRP of a second SSB associated with a contention-based random access resource is greater than an SS-RSRP threshold; and   transmit a random access preamble by using any SSB with a common random access resource after determining that the SS-RSRP is not greater than the SS-RSRP threshold.