The assignee for this patent, patent number 8744448, is
Reporters obtained the following quote from the background information supplied by the inventors: "Up to now, when communication is conducted with radio connection in a multi-cell system (cellular system), a radio terminal communicates with a radio base station having a matched service set identifier (SSID). Then, when the radio terminal travels while calling the radio base station, electric waves become weaker with increasing distance from a center of a cell (wireless area), and a signal strength and a power level are changed. In this situation, when electric waves from another radio base station of an adjacent cell become more intense, call can be continued if the communication is switched to communication with this radio base station. This is called 'handover'.
"In order that the radio terminal accesses to a new radio base station, the radio terminal must search identifiers of a large number of radio base stations corresponding to connection candidates or having connection histories in order, and acquire a connectable radio base station. Further, radio base station cannot conduct communication through a network unless the radio base station registers information on itself and the subject radio terminal in a registration server of an IP network.
"FIG. 32 is an illustrative diagram illustrating a conventional handover of a radio terminal. An IP network (network communicatable in IP) is connected with a management device ME having the registration server therein. Also, the management device ME is connected with radio base stations (hereinafter referred to as 'radio cell stations') CS1, CS2, CS3, CS4, and CS5 under its control, which each radiate electric waves to form a cell, and form a communication area as a whole. Radio terminals (hereinafter referred to as 'radio personal stations') PSs include a PHS (personal handy-phone system) terminal, a DECT (digital enhanced cordless telecommunication) terminal, other cellular phones, and a radio LAN (local area network). Anyway, each of the personal stations conducts a digital radio communication with any radio cell station. A voice data communication between each of the radio personal stations and a partner terminal conforms to an IP call control protocol such as an SIP (session initiation protocol) or H.323, and is conducted with the use of RTP/RTCP.
"In order that the radio personal station PS connected to the radio cell station CS1 is connected to an IP terminal of an intended party through the IP network, the management server such as an SIP server needs to recognize which radio cell station CS is connected to the radio personal station PS at present. For that reason, the radio cell station CS1 transmits a REGISTER (position registration request) to the registration server of the SIP server, and registers identification information such as its own IP address and an identifier (telephone number) of the radio personal station PS in the registration server.
"Accordingly, when the radio personal station PS travels from a cell of the radio cell station CS1 to another cell (radio cell station CS3) during a call, the radio personal station PS cannot continue the call unless the radio connection is switched from CS1 to CS3. For that reason, handover is conducted, and in conducting the handover, the radio cell station CS3 transmits the REGISTER (position registration request) to the registration sever, and registers the position of a new radio cell station CS3. As a result, the radio cell station CS3 allows the registration server to recognize disconnection and reconnection. In this situation, unless smooth handover is conducted, the call is disconnected to deteriorate a call quality.
"Likewise, thereafter, every time the radio personal station PS travels from a cell of the radio cell station CS3 to a cell of the radio cell station CS4, from the cell of the radio cell station CS4 to a cell of the radio cell station CS5, and from the cell of the radio cell station CS 5 to the cell of the radio cell station CS2, the radio cell stations CS4, CS5, and CS2 transmit REGISTER, and repeat the position registration in the registration server. The call cannot be continued unless the position registration is conducted. However, it takes time to conduct the handover, and when reconnection fails, the radio personal station PS must again search the radio cell station CS for reconnection.
"Up to now, a technology has been proposed in which handover is conducted when a user travels from an area of one MGW (media gateway) currently connected to his cellular phone to an area of another MGW while calling by the cellular phone through an IMS (IP multimedia subsystem) (refer to JP-A 2009-177620).
"When a termination (TDM/1) of a first communication system is calling a termination (RTP/1) of a second communication system within one MGW 1, a mobile station travels to an area falling under the control of another MGW 2. In this state, a context of a termination (RTP/11) of the first communication system is added to a context of the MGW 1 that is a handover source. Further, a context for connecting a termination (TDM/2) of the first communication system and a termination (RTP/2) of the second communication system is added to a context within the MGW 2. It is assumed that the TDM/1 and the RTP/11 are one-way stream, and downstream with respect to the MGW 2.
"In a handover switching state, the RTP/1 and the TDM/1 are changed to one-way stream, and the RTP/1 and the RTP/11 are changed to two-way stream to conduct the switching of the streams of a source and a destination. Finally, in a handover completion state, only the termination (TDM/1) is released, and the termination (RTP/1) is continuously used as an anchor."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Problem to be Solved by the Invention
"Up to now, when the traveling radio terminal travels while repeating the handover, call is disconnected once and then reconnected. Therefore, there has been required a process for allowing the SIP and the other registration server to recognize disconnection and reconnection. Accordingly, every time the radio station travels from a cell of one radio base station to a cell of another base station, the call is not continued unless the position registration is conducted. It takes time to repeat the position registration during handover, and the call quality is largely deteriorated.
"In the technology of Patent document 1, when the handover occurs while communication is conducted between the first communication system such as the IP and the second communication system such as the radio communication through a certain MGW, a handover destination communicates by the first communication system through an handover source. Accordingly, one MGW is fixedly used, and a mobile communication exchange repetitively transmits and receives a request and a reply with respect to the source and the destination during the handover, and recognizes the position of the destination. However, Patent document 1 fails to disclose how the mobile communication exchange recognizes the switching of the MGW. Also, the repetition of handover requires much time, and the call quality is deteriorated by handover. However, those problems are not solved.
"Under the circumstances, the present invention aims at providing a radio base station device, a handover control system, and a handover control method, which can realize seamless handover while reducing the number of position registrations during a call, without making a management device and a partner terminal aware of handover.
"Means for Solving the Problems
"For the purpose of solving the above problems, according to the present invention, as a main feature, there is provided a radio base station device that relays a call connection of a radio terminal to a management device, comprising: a call connection control section for controlling the call connection of the radio terminal; and a position registration request section for requesting, of the management device, a position registration that associates identification information on the radio terminal with identification information on the radio base station device, wherein if the call connection control section receives a handover request from the radio terminal that conducts the call connection through another radio base station device, then the call connection control section controls the call connection of the radio terminal in such a manner that the radio base station device and the another radio base station device both relay the call connection of the radio terminal to the management device, and wherein while the radio base station device and the another radio base station device both relay the call connection of the radio terminal to the management device, the position registration request section does not request the position registration of the management device, and if the call connection relayed, to the management device, by both the radio base station device and the another radio base station device is ended, then the position registration request section requests the position registration of the management device.
"Advantageous Effects of the Invention
"According to the present invention, the radio base station device, the handover control system, and the handover control method can realize seamless handover while reducing the number of position registrations during a call, without making a management device and a partner terminal aware of handover."
For more information, see this patent: Takagi, Masaki; Shida, Tsuyoshi. Radio Base Station Device, Handover Control System, and Handover Control Method. U.S. Patent Number 8744448, filed
Keywords for this news article include: Technology,
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