Conditional handover management

Abstract

A source base station receives, from a candidate base station while a user device is operating in a source cell of the source base station, a first message that indicates a conditional handover configuration providing information for user device operation within a candidate target cell of the candidate base station, but does not indicate a corresponding condition for handing over to the candidate target cell. The source base station generates the corresponding condition for handing over to the candidate target cell, and sends, to the user device, a second message that indicates the conditional handover configuration and the corresponding condition.

1 . A method, in a source base station, comprising:
 receiving, from a candidate base station while a user device is operating in a source cell of the source base station, a first message that indicates a conditional handover configuration providing information for user device operation within a candidate target cell of the candidate base station, but does not indicate a corresponding condition for handing over to the candidate target cell;   generating, by processing hardware of the source base station, the corresponding condition for handing over to the candidate target cell;   sending, to the user device, a second message that indicates the conditional handover configuration and the corresponding condition; and   causing, by the processing hardware and prior to the user device determining that the corresponding condition is satisfied, the user device to release the conditional handover configuration and perform an immediate handover to a target cell of a base station other than the candidate base station.   
     
     
         2 . The method of  claim 1 , further comprising:
 sending a handover request to the candidate base station,   wherein receiving the first message includes receiving, from the candidate base station in response to the handover request, a handover request acknowledgment message that indicates the conditional handover configuration but not the corresponding condition.   
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . The method of  claim 1 , wherein causing the user device to release the conditional handover configuration and perform the immediate handover includes sending to the user device a handover command message for immediate handover to the target cell. 
     
     
         6 . The method of  claim 5 , wherein:
 the handover command message includes an indication to release the conditional handover configuration; and   causing the user device to release the conditional handover configuration includes causing the user device to release the conditional handover configuration in response to the indication included in the handover command message.   
     
     
         7 . The method of  claim 1 , wherein causing the user device to perform the immediate handover includes causing the user device to perform a random access procedure with the base station other than the candidate base station, and wherein causing the user device to release the conditional handover configuration includes causing the user device to release the conditional handover configuration after the user device performs the random access procedure. 
     
     
         8 . The method of  claim 1 , wherein:
 the conditional handover configuration is a first conditional handover configuration, the corresponding condition is a first corresponding condition, the candidate target cell is a first candidate target cell, and the candidate base station is a first candidate base station; and   the method further comprises:
 receiving, from a second candidate base station while the user device is operating in the source cell of the source base station, a third message that indicates a second conditional handover configuration providing information for user device operation within a second candidate target cell of the second candidate base station, and 
 sending, to the user device, a fourth message that indicates the second conditional handover configuration and a second corresponding condition for handing over to the second candidate target cell. 
   
     
     
         9 . The method of  claim 8 , further comprising:
 causing, by the processing hardware, the user device to determine that the second conditional handover configuration is no longer valid.   
     
     
         10 . The method of  claim 8 , wherein:
 causing the user device to release the first conditional handover configuration and perform the immediate handover to the target cell includes causing the user device to release the first conditional handover configuration and perform the immediate handover to the target cell after the user device determines that the second corresponding condition is satisfied.   
     
     
         11 . The method of  claim 5 , wherein:
 causing the user device to perform the immediate handover to the target cell includes causing the user device to perform a handover to the second candidate target cell; and   causing the user device to release the first conditional handover configuration further comprises causing the user device to release all unused conditional handover configurations.   
     
     
         12 . The method of  claim 1 , wherein sending the second message includes sending a radio resource control, RRC, container message that includes (i) an RRC reconfiguration message that includes the conditional handover configuration and (ii) the corresponding condition. 
     
     
         13 . (canceled) 
     
     
         14 . (canceled) 
     
     
         15 . A source base station comprising processing hardware configured to:
 receive, from a candidate base station while a user device is operating in a source cell of the source base station, a first message that indicates a conditional handover configuration providing information for user device operation within a candidate target cell of the candidate base station, but does not indicate a corresponding condition for handing over to the candidate target cell;   generate the corresponding condition for handing over to the candidate target cell;   send, to the user device, a second message that indicates the conditional handover configuration and the corresponding condition; and   prior to the user device determining that the corresponding condition is satisfied, cause the user device to release the conditional handover configuration and perform an immediate handover to a target cell of a base station other than the candidate base station.   
     
     
         16 . The source base station of  claim 15 , wherein the processing hardware is further configured to:
 send a handover request to the candidate base station,   wherein the processing hardware is configured to receive the first message by receiving, from the candidate base station in response to the handover request, a handover request acknowledgment message that indicates the conditional handover configuration but not the corresponding condition.   
     
     
         17 . The source base station of  claim 15 , wherein the processing hardware is configured to cause the user device to release the conditional handover configuration and perform the immediate handover by sending to the user device a handover command message for immediate handover to the target cell. 
     
     
         18 . The source base station of  claim 17 , wherein:
 the handover command message includes an indication to release the conditional handover configuration; and   the processing hardware is configured to cause the user device to release the conditional handover configuration by causing the user device to release the conditional handover configuration in response to the indication included in the handover command message.   
     
     
         19 . The source base station of  claim 15 , wherein the processing hardware is configured to:
 cause the user device to perform the immediate handover by causing the user device to perform a random access procedure with the base station other than the candidate base station; and   cause the user device to release the conditional handover configuration by causing the user device to release the conditional handover configuration after the user device performs the random access procedure.   
     
     
         20 . The source base station of  claim 15 , wherein:
 the conditional handover configuration is a first conditional handover configuration, the corresponding condition is a first corresponding condition, the candidate target cell is a first candidate target cell, and the candidate base station is a first candidate base station; and   the processing hardware is further configured to:
 receive, from a second candidate base station while the user device is operating in the source cell of the source base station, a third message that indicates a second conditional handover configuration providing information for user device operation within a second candidate target cell of the second candidate base station, and 
 send, to the user device, a fourth message that indicates the second conditional handover configuration and a second corresponding condition for handing over to the second candidate target cell. 
   
     
     
         21 . The source base station of  claim 20 , wherein the processing hardware is further configured to cause the user device to determine that the second conditional handover configuration is no longer valid. 
     
     
         22 . The source base station of  claim 20 , wherein the processing hardware is configured to cause the user device to release the first conditional handover configuration and perform the immediate handover to the target cell by causing the user device to release the first conditional handover configuration and perform the immediate handover to the target cell after the user device determines that the second corresponding condition is satisfied. 
     
     
         23 . The source base station of  claim 17 , wherein the processing hardware is configured to:
 cause the user device to perform the immediate handover to the target cell by causing the user device to perform a handover to the second candidate target cell; and   cause the user device to release the first conditional handover configuration by causing the user device to release all unused conditional handover configurations.   
     
     
         24 . The source base station of  claim 15 , wherein the processing hardware is configured to send the second message by sending a radio resource control, RRC, container message that includes (i) an RRC reconfiguration message that includes the conditional handover configuration and (ii) the corresponding condition.