Mobile communication system, base station apparatus and mobile station apparatus

A method for random access to a first base station at a time of handover, the first base station being configured with a first signature group and a second signature group, the method comprising:

• determining, by the first base station, a reference used for random access, wherein the reference indicates a signature within the first signature group or the second signature group;
• sending, by the first base station, a message including at least a portion of the reference to a mobile station via a second base station;
• receiving, by the first base station, a random access preamble including the signature indicated by the reference from the mobile station in instances where the reference indicates a signature within the first signature group;
• and
• receiving, by the first base station, a random access preamble including the signature within the second signature group from the mobile station in instances where the reference indicates a signature within the first signature group.

A mobile station for random access to a first base station at a time of handover, the first base station being configured with a first signature group and a second signature group, the mobile station comprising:

• a receiver, configured to receive a message including a reference used for random access from a second base station;
• a scheduling section, configured to determine whether the reference indicates a signature within the first signature group or the second signature group;
• and
• a transmitter, configured to send a random access preamble including the signature indicated by the reference to the first base station in instances where the number indicates a signature within the first signature group, and to perform a contention resolution processing in instances where the reference indicates a signature within the second signature group.

A base station for random access at a time of handover, the base station being configured with a first signature group and a second signature group, the base station comprising:

• a signature managing section, configured to determine a number used for random access, wherein the number indicates a signature within the first signature group or the second signature group;
• a transmitter, configured to send a message including the number to a mobile station via another base station;
• and
• a receiver, configured to receive a random access preamble including the signature indicated by the number from the mobile station in instances where the number indicates a signature within the first signature group, and to receive a random access preamble including the signature within the second signature group from the mobile station in instances where the number indicates a signature within the first signature group.