A target base station for a handover by a user equipment from one component carrier served by a source base station to one component carrier served by the target base station, the target base station comprising: means configured to receive a handover request message from the source base station that have served multiple component carriers, including the one component carrier, used for carrier aggregation by the user equipment, wherein the handover request message includes information for indicating the number of multiple component carriers which were used for the carrier aggregation with the source base station; means configured to send, to the source base station, a handover request confirm message in response to the received handover request message, after waiting until sufficient communication resources are available, the sufficient communication resources enabling an allocation of the same number of component carriers as the number of the multiple component carriers which were used for the carrier aggregation with the source base station; means configured to perform a random access procedure with the user equipment in the one component carrier served by the target base station after sending the handover request confirm message; means configured to increase the number of component carriers for the user equipment from the one component carrier to multiple component carriers for the carrier aggregation with the target base station, so that the number of multiple component carriers for the carrier aggregation with the target base station is same as the number of multiple component carriers that were used for the carrier aggregation with the source base station; and means configured to perform carrier aggregation with the user terminal, using the increased multiple component carriers. means configured to receive a handover request message from the source base station that have served multiple component carriers, including the one component carrier, used for carrier aggregation by the user equipment, wherein the handover request message includes information for indicating the number of multiple component carriers which were used for the carrier aggregation with the source base station; means configured to send, to the source base station, a handover request confirm message in response to the received handover request message, after waiting until sufficient communication resources are available, the sufficient communication resources enabling an allocation of the same number of component carriers as the number of the multiple component carriers which were used for the carrier aggregation with the source base station; means configured to perform a random access procedure with the user equipment in the one component carrier served by the target base station after sending the handover request confirm message; means configured to increase the number of component carriers for the user equipment from the one component carrier to multiple component carriers for the carrier aggregation with the target base station, so that the number of multiple component carriers for the carrier aggregation with the target base station is same as the number of multiple component carriers that were used for the carrier aggregation with the source base station; and means configured to perform carrier aggregation with the user terminal, using the increased multiple component carriers. <EOS>