RADIO ACCESS TERMINAL, BASE STATION CONTROLLER, AND HANDOFF CONTROL METHOD IN RADIO COMMUNICATION SYSTEM

• US 20090264134A1
• Filed: 04/14/2009
• Published: 10/22/2009
• Est. Priority Date: 04/14/2008
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Mazawa, Shiro, Xu, Dan, Uchida, Tsutomu, Katsu, Yuichiro
• Granted Patent: US 8,160,587 B2
• Time in Patent Office: Days
• US Class Current: 455/437
• 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 radio frequencies with which the radio base stations communicate with the radio terminals are allowed to differ in the radio communication system, wherein:

the radio terminal, which has positional information detection means, transmits positional information detected by the positional information detection means, to the base station controller through the radio base station communicating with the radio terminal;

a table is prepared beforehand in the base station controller, the table stores therein positional information items of the base stations, information items of frequencies used for transmissions/receptions to/from the radio terminals and decision conditions in handoff operations, as to the respective base stations connected to the base station controller itself; and

the base station controller selects, when the positional information is received from the radio terminal, the base station being a handoff candidate on the basis of the positional information of the radio terminal, the positional information items of the respective base stations and the decision condition in the handoff operation, with reference to the table, and transmits a handoff request message in which the information of the frequency of the base station being the handoff candidate is contained, to the radio terminal through the base station communicating with the radio terminal.

2. The handoff control method as defined in claim 1, wherein:

threshold values of distances between the radio terminal and the respective base stations, and threshold values of power values of radio signals from the respective base stations at the radio terminal are set for the respective base stations as the handoff decision conditions stored in the table;

the base station controller obtains distances between the radio terminal and the respective base stations from 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 the distances set for the respective base stations;

in a case where any of the obtained distances is equal to or less than the threshold value of the distance of corresponding base station, the base station controller 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 the 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 through the base station communicating with the radio terminal; and

the base station controller refers to the table and, in a case where the notified power value is equal to or more than the threshold value of the power value of the base station of the handoff candidate stored in the table, the base station controller controls the radio terminal to hand off to the base station of the handoff candidate.

3. A radio terminal in a radio communication system having a plurality of base stations which perform radio communications with the radio terminal, and a base station controller which controls the base stations, wherein radio frequencies with which the radio base stations communicate with the radio terminal are allowed to differ in the radio communication system, the radio terminal comprises:

positional information detection means; and

means for altering a frequency for communication set at hardware within the radio terminal,

wherein the radio terminal;

cyclically transmits positional information detected by said positional information detection means to the base station controller through the radio base station communicating with the radio terminal; and

alters, when the radio terminal receives a handoff request message in which information of the frequency of the base station of a handoff candidate is contained from the base station controller, the frequency for communication set at the hardware within the radio terminal by the means for altering, and receives a radio signal from the base station of the handoff candidate.

4. The radio terminal as defined in claim 3, wherein the radio terminal:

alters the frequency for communication set at the hardware within radio terminal itself in compliance with the handoff request message from the base station controller, 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 through the base station communicating with the radio terminal; and

the radio terminal thereafter hands off to the base station of the handoff candidate, in compliance with a handoff command which is for handing off to the base station of the handoff candidate and is received from the base station controller.

5. A base station controller 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 the base station controller which controls the base stations, wherein radio frequencies with which the radio base stations communicate with the radio terminals are allowed to differ in the radio communication system, the base station controller comprises:

a table storing therein positional information items of the base stations, information items of frequencies used for transmissions/receptions to/from the radio terminals and decision conditions in handoff operations, as to the respective base stations connected to the base station controller itself,

wherein

when the base station controller receives the positional information cyclically transmitted 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 items of the respective base stations and the decision condition in the handoff operation, with reference to the table, and transmits a handoff request message in which the information of the frequency of the base station being the handoff candidate is contained, to the radio terminal through the base station communicating with the radio terminal.

6. The base station controller as defined in claim 5, wherein:

threshold values of distances between the radio terminal and the respective base stations, and threshold values of power values of radio signals from the respective base stations at the radio terminal are set for the respective base stations as the handoff decision conditions stored in the table;

the base station controller obtains distances between the radio terminal and the respective base stations from 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 the distances set for the respective base stations;

in a case where any of the obtained distances is equal to or less than the threshold value of the distance of corresponding base station, the base station controller 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 the handoff request message;

the base station controller receives power value information of the base station of the handoff candidate which is measured by the radio terminal, refers to the table and, in a case where the power value is equal to or more than the threshold value of the power value of the base station of the handoff candidate stored in the table, controls the radio terminal to hand off to the base station of the handoff candidate.