Method for performing handover, user equipment, base station, and radio communication system

Abstract

Provided is a method for performing a handover from a first base station to a second base station by a user equipment that is performing a radio communication over a communication channel formed by aggregating a plurality of component carriers. The method includes a step of transmitting a handover command for a component carrier for which a handover has been approved by the second base station among the plurality of component carriers from the first base station to the user equipment and a step of trying to make an access from the user equipment to the second base station for each component carrier in response to the handover command.

1 . A method for a User Equipment (UE) comprising:
 performing carrier aggregation by aggregating three component carriers served by a source base station;   receiving a handover command from the source base station, the handover command including first and second indexes respectively corresponding to first and second component carriers among the three component carriers; and   performing a handover from the source base station to a target base station with the first and second component carriers,   wherein the method further comprises:
 receiving, from target base station, control information for using a third component carrier among the three component carriers after the handover, the control information including a third index corresponding to the third component carrier; and 
 performing, with the target base station, carrier aggregation by aggregating the first and second component carriers respectively indicated by the first and second indexes received from the source base station and the third component carrier indicated by the third index received from the target base station. 
   
     
     
         2 . A User Equipment (UE) comprising:
 a radio transceiver; and   a hardware processor configured to:
 perform carrier aggregation by aggregating three component carriers served by a source base station; 
 receive, via the radio transceiver, a handover command from the source base station, the handover command including first and second indexes respectively corresponding to first and second component carriers among the three component carriers; and 
 perform a handover from the source base station to a target base station with the first and second component carriers, 
   wherein the hardware processor is further configured to:
 receive, from target base station via the radio transceiver, control information for using a third component carrier among the three component carriers after the handover, the control information including a third index corresponding to the third component carrier; and 
 perform, with the target base station, carrier aggregation by aggregating the first and second component carriers respectively indicated by the first and second indexes received from the source base station and the third component carrier indicated by the third index received from the target base station. 
   
     
     
         3 . A method for a target base station, the method comprising:
 transmitting, to a User Equipment (UE), control information for using a third component carrier among three component carriers that were used by the UE for carrier aggregation with a source base station, after a handover by the UE from the source base station to the target base station with a first component carrier and a second component carrier among the three component carriers, the control information including a third index corresponding to the third component carrier, wherein both of a first index corresponding to the first component carrier and a second index corresponding to the second component carrier are included in a handover command that was sent from the source base station to the UE; and   providing, to the UE, the three component carriers including:
 the first and second component carriers respectively indicated by the first and second indexes received from the source base station, and 
 the third component carrier indicated by the third index received from the target base station, 
   wherein the three component carriers are used by the UE for the carrier aggregation with the target base station.   
     
     
         4 . A target base station comprising:
 a radio transceiver; and   a hardware processor configured to:
 transmit, to a User Equipment (UE), control information for using a third component carrier among three component carriers that were used by the UE for carrier aggregation with a source base station, after a handover by the UE from the source base station to the target base station with a first component carrier and a second component carrier among the three component carriers, the control information including a third index corresponding to the third component carrier, wherein both of a first index corresponding to the first component carrier and a second index corresponding to the second component carrier are included in a handover command that was sent from the source base station to the UE; and 
 provide, to the UE, the three component carriers including:
 the first and second component carriers respectively indicated by the first and second indexes received from the source base station, and 
 the third component carrier indicated by the third index received from the target base station, 
 
   wherein the three component carriers are used by the UE for the carrier aggregation with the target base station.