Patent ID: 8160587
Filing Date: 2012-04-17
Classification: H04W

Abstract:
1. A handoff control method in a radio communication system having a plurality of radio terminals, a plurality of base stations which perform radio communications with the radio terminals, and a base station controller which controls the base stations, wherein, in a cover range of a first base station among the radio terminals, a plurality of second base stations each having a cover range smaller than the cover range of the first base station exist and, radio frequencies with which the base stations communicate with the radio terminals are allowed to differ in the radio communication system, wherein: each of the plurality of radio terminals, which has a positional information detection unit, transmits positional information which includes longitude and latitude of own radio terminal detected by the positional information detection unit, to the base station controller through a base station communicating with the own radio terminal by a first route update message; a table is prepared beforehand in the base station controller, the table stores therein positional information items of the plurality of base stations connected to own base station controller, information items of frequencies used for transmissions/receptions between the plurality of radio terminals and the plurality of base stations, and decision conditions in handoff operations set for the respective base stations, the decision conditions including threshold values of distances between the radio terminals and the respective base stations, and threshold values of power values of radio signals received by the radio terminals from the respective base stations; and the base station controller, when receiving the positional information from one radio terminal among the plurality of radio terminals by the first route update message through the radio base station communicating with the radio terminal, refers to the table to obtain distances between the radio terminal and the respective base stations based on the positional information received from the radio terminal and the positional information items of the respective base stations stored in the table, and compares obtained distances with the threshold values of distances set for the respective base stations; the base station controller, when finding the obtained distance which is equal to or less than threshold value of distance for a corresponding base station, sets the corresponding base station as the base station of the handoff candidate, and commands the radio terminal to alter a frequency thereof to the frequency of the base station of the handoff candidate by transmitting a handoff request message; the radio terminal having received the handoff request message, alters the frequency in compliance with command, and measures a power value of a radio signal from the base station of the handoff candidate and notifies the base station controller of the power value, by transmitting a second route update message including the power value through the base station communicating with the radio terminal; and the base station controller refers to the table and, in a case where notified power value is equal to or more than the threshold value of the power value for the handoff candidate stored in the table, the base station controller controls the radio terminal to handoff to the base station of the handoff candidate.