Radio access terminal, base station controller, and handoff control method in radio communication system

• US 8,160,587 B2
• Filed: 04/14/2009
• Issued: 04/17/2012
• Est. Priority Date: 04/14/2008
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Xu, Dan, Katsu, Yuichiro, Uchida, Tsutomu, Mazawa, Shiro
• Primary Examiner(s): Gelin, Jean
• Application Number:
  US12/423,049
• Publication Number:
  US 20090264134A1
• Time in Patent Office: 1,099 Days
• Field of Search: 455/438, 455/439, 455/432.1, 455/432.3, 455/433, 455/435.2, 455/435.3, 455/436, 455/437, 455/440
• US Class Current: 455/436
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 36/32 by location or mobility data, e.g. speed data
• CPC Class Codes: H04W 84/045 using private Base Stations, e.g. femto Base Stations, home Node B

Abstract

In a radio communication system wherein radio frequencies for communicating with a radio terminal are different in radio base stations, a table in which positional information, information on the frequency used for transmission/reception to/from the terminal, and a decision condition in a handoff operation are stored as to each base station is prepared in a base station controller beforehand. When the positional information is received from the radio terminal, the base station controller selects the base station being a handoff candidate, on the basis of the positional information of the radio terminal, the positional information of each base station and the decision condition of the handoff operation with reference to the table, and it transmits a handoff request message which contains the information on the frequency of the base station being the handoff candidate, to the radio terminal through the base station communicating with the radio terminal.

Claims

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.