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

A base station in a wireless communication network, the base station comprising:

• a radio communication interface configured to communicate with a mobile station via a communication channel formed by aggregating a plurality of component carriers;
• processing circuitry configured to control a handover of the mobile station from another base station,
• wherein, the processing circuitry is configured to allocate two or more component carriers, and notify a timing adjustment value to the mobile station, the timing adjustment value being decided based on another timing adjustment value for a component carrier on which the mobile station carries out random access, and
• wherein the radio communication interface is configured to receive information transmitted from the mobile station on a transmission timing adjusted by the mobile station using the timing adjustment value notified for the component carrier for which the random access has been skipped.

A wireless communication system comprising:

• a mobile station;
• a first base station;
• and
• a second base station,
• wherein the mobile station includes:
• a first radio communication interface configured to communicate with the second base station via a communication channel formed by aggregating a plurality of component carriers;
• and
• first processing circuitry configured to
• control a handover from the first base station to the second base station by the first radio communication interface,
• carry out a random access, to the second base station, on at least one of two or more component carriers,
• skip the random access, to the second base station, for at least another of the two or more component carriers, and
• set a timing adjustment value for the at least one of the two or more component carriers on which the random access is carried out,
• wherein the first processing circuitry is configured to adjust transmission timing on the at least another of the two or more component carriers for which the random access has been skipped by using the timing adjustment value, and
• the second base station includes:
• a second radio communication interface configured to communicate with the mobile station via the communication channel;
• second processing circuitry configured to control the handover of the mobile station from the first base station,
• wherein, the second processing circuitry is configured to allocate the two or more component carrier, and notify the timing adjustment value to the mobile station for the at least one of the two or more component carriers on which the mobile station carries out the random access, and
• wherein the second radio communication interface is configured to receive information, about the at least another of the two or more component carriers for which the random access has been skipped, transmitted from the mobile station on a transmission timing adjusted by the mobile station using the timing adjustment value for the at least one of the two or more component carriers on which the mobile station carries out the random access.

A method executed by a mobile station in a wireless communication network, the method comprising:

• communicating with a base station via a communication channel formed by aggregating a plurality of component carriers;
• controlling, using processing circuitry, a plurality of handovers from a first base station to a second base station, the plurality of handovers including at least a first handover and a second handover;
• for the first handover, carrying out a random access, to the second base station, on at least a first component carrier and a second component carrier of two or more component carriers;
• for the second handover, carrying out the random access, to the second base station, on at least the first component carrier, and skipping the random access, to the second base station, for at least the second component carrier;
• for the second handover, setting a timing adjustment value for the first component carrier on which the random access is carried out;
• and
• adjusting transmission timing to the second base station for the second component carrier for which the random access has been skipped by using the timing adjustment value.

A method executed by a base station in a wireless communication network, the method comprising:

• communicating with a mobile station via a communication channel formed by aggregating a plurality of component carriers;
• controlling a handover of the mobile station from another base station;
• allocating two or more component carrier, and notify timing adjustment value to the mobile station, the timing adjustment value being decided based on another timing adjustment value for a component carrier on which the mobile station carries out random access;
• and
• receiving information transmitted from the mobile station on a transmission timing adjusted by the mobile station using the timing adjustment value for the component for which the random access has been skipped.