JP2007318335A - Handover processing system, handover processing method and wireless base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly make a handover on the initiative of a base station to which a wireless communication terminal is connected. <P>SOLUTION: An IP telephone system is disclosed in which an IP telephone terminal is connected to one of a plurality of access points 1 through a wireless LAN and performs communication, wherein the connected access point is equipped with: an access point communication section 12 which acquires second reception levels detected by reception level detectors 13 at a plurality of peripheral access points when it is judged that a first reception level of a signal sent from the IP telephone terminal is equal to or below a threshold A; an access point specifying section 14 which specifies an access point being a handover destination based upon the plurality of second reception levels; and a signal communication section 11 which sends an execution instruction for a handover to the IP telephone terminal when it is judged that the difference between the second reception level by the access point being the handover destination and the first reception level, is not less than a threshold B. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a handover processing system, a handover processing method, and a radio base station that perform a handover process for switching an access point (base station) to which a radio communication terminal such as an IP telephone terminal is connected.

  Conventionally, among a plurality of access points, when a wireless communication terminal connected to one access point via a wireless LAN (Local Area Network) or the like has a low reception level of a signal transmitted from one access point, There is known a handover processing system that performs handover to an access point with a high reception level existing around the one access point.

In the above handover processing system, since a radio communication terminal generally has only one antenna for transmitting and receiving signals (communication unit), while communicating with one access point, Communication with a peripheral access point is not possible, and information on the peripheral access point cannot be obtained. For this reason, the wireless communication terminal recognizes that the connection is canceled because the signal from one connected access point stops reaching, and starts searching for nearby access points from that point. (For example, refer to Patent Document 1).
JP 2005-175932 A

However, as in the above-mentioned Patent Document 1 and the like, in a passive handover process in which a wireless communication terminal searches for a nearby access point from the point of time when it recognizes the disconnection with one access point, the wireless communication terminal is connected. It may take a predetermined time to be recognized as being released, and communication may be interrupted while searching for nearby access points.
In particular, in the case of an IP telephone system to which an IP telephone terminal is applied as a wireless communication terminal, it is necessary to instantaneously switch an access point in order to perform more stable communication, so that it is difficult to apply to the IP telephone system. There's a problem.

  Therefore, an object of the present invention is to provide a handover processing system, a handover processing method, and a radio base station that can appropriately perform a handover led by a base station to which a radio communication terminal is connected.

The invention described in claim 1
A plurality of base stations (for example, the access point 1 in FIG. 1) and a wireless communication terminal (for example, for example) connected to any of the plurality of base stations via a wireless communication line (for example, a wireless LAN) (for example, 1 and the like, and a handover processing system (for example, the IP telephone system of FIG. 1) for performing a handover process for switching a base station to which the wireless communication terminal is connected among the plurality of base stations. 100 etc.)
Among the plurality of base stations, a connected base station (for example, the first access point 1A in FIG. 1) connected to the wireless communication terminal via the wireless communication line is
First reception level acquisition means (for example, the signal communication unit 11 in FIG. 2) for acquiring a first reception level that is a reception level of a signal transmitted from the wireless communication terminal in the connection base station;
Reception level determination means (for example, the signal communication unit 11 in FIG. 2) for determining whether or not the first reception level acquired by the first reception level acquisition means is a predetermined value or less;
When the reception level determination means determines that the first reception level is less than or equal to a predetermined value, among the plurality of base stations, neighboring base stations existing around the connected base station (for example, FIG. 2nd reception level acquisition means (for example, FIG. 2) which acquires the 2nd reception level which is the reception level of the signal transmitted from the said radio | wireless communication terminal in 1 2nd and 3rd access points 1B, 1C, etc. Access point communication unit 12 etc.),
Based on the second reception level acquired by the second reception level acquisition means, base station specifying means for specifying a handover destination base station among the neighboring base stations (for example, the access point in FIG. 2) Specific part 14 etc.),
Information transmitting means (for example, the signal communication unit 11 in FIG. 2) for transmitting information used for connection to the base station specified by the base station specifying means to the wireless communication terminal is provided.

The invention according to claim 2 is the handover processing system according to claim 1,
The connecting base station is
When the reception level determination unit determines that the first reception level is equal to or lower than a predetermined value, a detection instruction transmission unit (for example, transmits a detection instruction of the second reception level to a neighboring base station) 2) including the access point communication unit 12 in FIG.
The surrounding base station is
A transmission / reception communication unit (for example, the signal communication unit 11 in FIG. 2) for transmitting / receiving a signal to / from the wireless communication terminal;
A reception level detection communication unit (for example, the reception level detection antenna 13a in FIG. 2) for detecting the second reception level;
Based on the reception of the detection instruction transmitted from the detection instruction transmission means, the reception level detection means (for example, the reception level detection section 13 in FIG. 2) detects the second reception level by the reception level detection communication section. Etc.)
Receiving level transmitting means (for example, the access point communication unit 12 in FIG. 2) for transmitting the second receiving level detected by the receiving level detecting means to the connected base station is provided.

The invention according to claim 3 is the handover processing system according to claim 1,
The connecting base station is
When the reception level determination means determines that the first reception level is less than or equal to a predetermined value, timing information defining the detection timing of the second reception level and communication with the wireless communication terminal A detection instruction transmission unit (for example, the access point communication unit 212 in FIG. 7) that transmits a detection instruction of the second reception level including frequency information that defines a frequency to a neighboring base station;
The surrounding base station is
A transmission / reception communication unit (for example, the signal communication unit 211 in FIG. 7) for performing transmission / reception of signals with the wireless communication terminal and detecting the second reception level;
Based on the detection instruction transmitted and received from the detection instruction transmission means, the second reception level is set for the transmission / reception at the frequency specified by the frequency information at the detection timing specified by the timing information. Reception level detection means (for example, the signal communication unit 211 in FIG. 7) detected by the communication unit,
Receiving level transmitting means (for example, the access point communication unit 212 in FIG. 7) for transmitting the second receiving level detected by the receiving level detecting means to the connected base station is provided.

According to a fourth aspect of the present invention, in the handover processing system according to the third aspect,
The surrounding base station is
After receiving the detection instruction transmitted from the detection instruction transmitting means, before transmitting the second reception level, control for transmitting a control signal for temporarily stopping transmission of a wireless communication terminal other than the wireless communication terminal A signal transmission unit (for example, the signal communication unit 211 in FIG. 7) is provided.

The invention described in claim 5
A plurality of base stations (for example, the access point 1 in FIG. 1) and a wireless communication terminal (for example, for example) connected to any of the plurality of base stations via a wireless communication line (for example, a wireless LAN) (for example, 1 is used to switch a base station to which the wireless communication terminal is connected among the plurality of base stations using a wireless communication system (for example, IP telephone system 100 of FIG. 1). A handover processing method for performing a handover process,
Among the plurality of base stations, a connected base station (for example, the first access point 1A in FIG. 1) connected to the wireless communication terminal via the wireless communication line is
A process of obtaining a first reception level that is a reception level of a signal transmitted from the wireless communication terminal in the connection base station;
A process of determining whether or not the acquired first reception level is a predetermined value or less;
When it is determined that the first reception level is equal to or lower than a predetermined value, among the plurality of base stations, neighboring base stations existing around the connected base station (for example, the second and second in FIG. 1) Processing to obtain a second reception level that is a reception level of a signal transmitted from the wireless communication terminal at the three access points 1B, 1C, etc .;
Based on the acquired second reception level, a process of specifying a handover destination base station from among the neighboring base stations,
When it is determined that the value is equal to or greater than the specific value, processing for transmitting information used for connection to the base station specified by the base station specifying means to the wireless communication terminal is performed.

The invention described in claim 6
A wireless base station (for example, the first access point 1A in FIG. 1) connected to a wireless communication terminal (for example, the IP telephone terminal 2 in FIG. 1) via a wireless communication line (for example, a wireless LAN). Because
First reception level acquisition means (for example, the signal communication unit 11 in FIG. 2) for acquiring a first reception level that is a reception level of a signal transmitted from the wireless communication terminal;
Reception level determination means (for example, the signal communication unit 11 in FIG. 2) for determining whether or not the first reception level acquired by the first reception level acquisition means is a predetermined value or less;
When the reception level determination means determines that the first reception level is equal to or lower than a predetermined value, neighboring base stations (for example, the second and third access points 1B and 1C in FIG. 1) exist in the vicinity. Etc.) second reception level acquisition means (for example, the access point communication unit 12 of FIG. 2) for acquiring a second reception level that is a reception level of a signal transmitted from the wireless communication terminal,
Based on the second reception level acquired by the second reception level acquisition means, base station specifying means for specifying a handover destination base station among the neighboring base stations (for example, the access point in FIG. 2) Specific part 14 etc.),
Information transmitting means (for example, the signal communication unit 11 in FIG. 2) for transmitting information used for connection to the base station specified by the base station specifying means to the wireless communication terminal is provided.

  ADVANTAGE OF THE INVENTION According to this invention, a hand-over can be appropriately performed by the said base station initiative, without interrupting the radio | wireless communication with the base station to which the said radio | wireless communication terminal and the said radio | wireless communication terminal are connected.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[Embodiment 1]
FIG. 1 is a diagram schematically showing a schematic configuration of an IP telephone system 100 exemplified as a preferred example of the handover processing system according to the first embodiment to which the present invention is applied.
In the IP telephone system (wireless communication system) 100 according to the first embodiment, for example, when the IP telephone terminal 2 is possessed by a user or the like and moves from a point A (POS-A) to a point C (POS-C), By performing a handover process for switching the access point 1 to which the IP telephone terminal 2 is connected at a predetermined timing, the call (communication) is performed without interruption.
Specifically, for example, as shown in FIG. 1, the IP telephone system 100 includes a plurality of (three in FIG. 1) access points (AP) 1,... (Institute of Electrical and Electronic Engineers) It is composed of an IP telephone terminal 2 connected via a wireless LAN such as the 802.11 standard, and a destination terminal 3 connected to the access point 1 via the Internet line N. Yes.

The plurality of access points (base stations) 1, for example, establish communication with the IP telephone terminal 2 at a predetermined frequency (CH) and communicate with the IP telephone terminal 2 via a predetermined gateway 4 and a wired LAN 5. They are connected so that they can communicate with each other. Specifically, the first access point 1A is connected to, for example, the first gateway 4A and performs wireless communication using “CH1” with the identifier “ESSID1”. The second access point 1B The third access point 1C is connected to the third gateway 4C and is connected to the second gateway 4B. The third access point 1C is connected to the third gateway 4C and has the identifier “ESSID3”. ”To perform wireless communication on“ CH3 ”.
Further, the plurality of access points 1,..., For example, have a communication capability range R with IP telephone terminals, and are arranged at predetermined intervals so that at least the communicable ranges R of adjacent access points 1 overlap. Has been.

Hereinafter, the access point 1 will be described in detail with reference to FIG. 2 and FIG.
FIG. 2 is a block diagram of the access point 1. FIG. 3 is a diagram for explaining the execution timing of the handover in the IP telephone system 100.
In the following description, a plurality of access points 1,... That have established a wireless link with the IP telephone terminal 2 are referred to as “connection access points”, and access points 1 existing in the vicinity thereof are referred to as “connection access points”. Let's say “peripheral access points”.

  As shown in FIG. 2, the access point 1 includes a signal communication unit 11 that transmits and receives signals to and from the IP telephone terminal 2 with which a wireless link is established (wireless connection), and access point communication that communicates with other access points 1. Unit 12, a reception level detection unit 13 that detects a reception level of a signal from an IP telephone terminal that has not established a radio link, an access point specification unit 14 that specifies a handover destination access point 1, a handover A timing determination unit 15 that determines the timing, a control unit 16 that controls these units, and the like are provided.

The signal communication unit (transmission / reception communication unit) 11 establishes a wireless link with the IP telephone terminal 2 and performs communication, for example, and a transmission / reception antenna for transmitting / receiving signals to / from the IP telephone terminal 2 11a.
That is, for example, when establishing a radio link, the signal communication unit 11 receives a probe request transmitted from the IP telephone terminal 2 at a predetermined frequency by the transmission / reception antenna 11a, and the ESSID information included in the probe request and the When the ESSID of the access point 1 matches, a wireless link is established with the IP telephone terminal 2.
When a plurality of access points 1 are present around the IP telephone terminal 2, the one with the highest signal reception level selected by the IP telephone terminal 2 is selected as the connection access point from among those whose ESSIDs match each other. It has come to be.

In addition, the signal communication unit 11 serves as a first reception level acquisition unit, for example, when transmitting / receiving a signal to / from the IP telephone terminal 2 with which the wireless link is established, and is transmitted from the IP telephone terminal 2 by the transmission / reception antenna 11a. The first reception level of the received signal is acquired at a predetermined timing.
Furthermore, the signal communication unit 11 determines, as the reception level determination means, for example, whether or not the acquired first reception level is equal to or lower than a predetermined value (for example, threshold A; see FIG. 3). Yes.
Here, the threshold value A is defined in consideration of, for example, the communicable range R of the plurality of access points 1... And the signal reception level. Specifically, the threshold value A is determined between adjacent access points 1. It is defined such that a predetermined reception level can be maintained without interruption of communication with the IP telephone terminal 2 in a region where the communicable range R overlaps.

The signal communication unit 11 also receives, for example, a first reception level by the access point 1 connected to the IP telephone terminal 2 and a second reception of a signal from the IP telephone terminal 2 by the access point 1 that is the handover destination. When it is determined that the difference from the level is equal to or greater than a specific value (for example, threshold B) (described later), an association cancellation signal with the connection access point is transmitted to the IP telephone terminal 2.
That is, for example, the signal communication unit 11 determines the timing of the handover when the timing determination unit 15 determines that the difference between the first reception level and the second reception level is equal to or greater than the threshold value B. When this is done (details will be described later), an association cancellation signal is transmitted to the IP telephone terminal 2. As a result, the IP telephone terminal 2 is notified that the connected access point side is about to release the radio link, and is instructed to execute handover for the peripheral access point that is the handover destination.
Here, the signal communication unit 11 functions as an execution instruction information transmitting unit that transmits a handover execution instruction to the IP telephone terminal 2.
Further, the signal communication unit 11 transmits (notifies) the identifier “ESSID”, the frequency “CH”, and the MAC (Media Access Control) address of the second access point 1B to be handed over to the IP telephone terminal 2. At this time, the signal communication unit 11 functions as information transmission means for transmitting information used for connection to the handover destination to the wireless communication terminal.

  The access point communication unit 12 is connected to, for example, a wired LAN 5 and transmits / receives various information between the plurality of access points 1 connected to the wired LAN 5.

  That is, the access point communication unit 12 of the connection access point, for example, as a detection instruction transmission unit, when the signal communication unit 11 determines that the first reception level is a predetermined value or less, Among the points 1,..., A measurement request signal (detection instruction) of a second reception level that is a reception level of a signal transmitted from the IP telephone terminal 2 by the peripheral access point is transmitted to the peripheral access point. .

In addition, the access point communication unit 12 of the peripheral access point transmits, for example, a second reception level (described later) detected by the reception level detection unit 13 to the connection access point as a reception level transmission unit. .
Thereby, the access point communication unit 12 of the connection access point acquires the second reception level which is the reception level of the signal transmitted from the IP telephone terminal 2 by the peripheral access point as the second reception level acquisition unit. Can be done.

  The reception level detection unit (reception level detection means) 13 includes, for example, a reception level detection antenna 13a, and detects a second reception level of a signal transmitted from the IP telephone terminal 2 with which no wireless link is established. belongs to.

  That is, for example, the reception level detection unit 13 of the peripheral access point uses the reception level detection antenna 13a based on the reception of the measurement request signal (reception level acquisition request) transmitted from the access point communication unit 12 of the connection access point. The second reception level is detected. Specifically, for example, when the IP telephone terminal 2 and the first access point 1A establish a wireless link, the reception levels of the second and third access points 1B and 1C existing in the vicinity thereof The detection unit 13 receives a signal transmitted from the IP telephone terminal 2 at a predetermined frequency by the reception level detection antenna 13a and detects the reception level.

The access point specifying unit 14 is for specifying the handover destination access point 1 from among the plurality of access points 1.
That is, the access point specifying unit 14 of the connected access point is, for example, a plurality of base points that are detected by the reception level detecting unit 13 of the peripheral access point and acquired by the access point communication unit 12 via the wired LAN 5 as a base station specifying unit. Based on the second reception level, the peripheral access point having the highest reception level is specified as the handover destination access point 1.

Based on the difference between the second reception level by the peripheral access point of the handover destination specified by the access point specification unit 14 and the first reception level by the connection access point, the connection access point timing determination unit 15 It determines the timing of handover.
That is, the connection access point timing determination unit 15 acquires the second reception level of the handover destination peripheral access point at a predetermined timing, and the difference from the first reception level of the connection access point is a specific value. (For example, threshold B; see FIG. 3). Then, the timing determination unit 15 determines a time point when it is determined that the difference between the reception levels is equal to or greater than the threshold value B as the handover execution timing.

  For example, although not shown, the control unit 16 is configured by a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like, and comprehensively controls each unit.

Next, the IP telephone terminal 2 will be described in detail with reference to FIG. FIG. 4 is a block diagram of the IP telephone terminal 2.
As shown in FIG. 4, the IP telephone terminal 2 includes, for example, a wireless communication processing unit 21 that performs wireless communication with the access point 1 via a wireless LAN, a handover execution processing unit 22 that performs handover, and each of these units. The control part 23 etc. which control are provided.

The wireless communication processing unit 21 includes, for example, a transmission / reception antenna 21a for transmitting / receiving a signal to / from the access point 1, and uses a predetermined identifier “ESSID” corresponding to the access point 1 from the transmission / reception antenna 21a. Signals are transmitted and received at the frequency “CH”.
That is, for example, when establishing a wireless link with the first access point 1A and performing communication, the wireless communication processing unit 21 transmits and receives a signal with the frequency “CH1” with the identifier “ESSID1”, and the second When communicating with the access point 1B by establishing a radio link, transmitting and receiving a signal at the frequency “CH2” with the identifier “ESSID2”, and establishing a radio link with the third access point 1C to perform communication In this case, the identifier is “ESSID3” and the signal is transmitted and received at the frequency “CH3”.

  Further, the wireless communication processing unit 21 specifies the identifier “ESSID” of the handover destination peripheral access point transmitted from the signal communication unit 11 of the connection access point after specifying the handover destination peripheral access point by the connection access point. A frequency “CH” and a MAC (Media Access Control) address are received.

  For example, the handover execution processing unit 22 releases the radio link with the connection access point and becomes a handover destination based on the association release signal transmitted from the connection access point and received by the wireless communication processing unit 21. The execution of a handover to a peripheral access point is processed.

  For example, although not shown, the control unit 23 includes a CPU, a RAM, a ROM, and the like, and controls the respective units in an integrated manner.

  Although the detailed description of the destination terminal 3 is omitted, any terminal that can communicate with the IP telephone terminal 2 may be used. For example, an IP telephone terminal, a general telephone terminal, a mobile phone terminal, etc. Can be mentioned.

Next, handover processing by the IP telephone system 100 will be described with reference to FIG.
Here, FIG. 5 is a diagram illustrating an example of an operation related to the handover process. In FIG. 5, wireless communication between the access point 1 and the IP telephone terminal 2 is represented by “wavy line”, and wired communication between the access points 1 and between the access point 1 and the called terminal 3 is represented by “solid line”. It shall represent.

When making a call with the called terminal 3, as shown in FIG. 5, first, the IP telephone terminal 2 searches for the access point 1 capable of establishing a wireless link with all identifiers “ESSID” and frequency “CH”. Perform (step S1). Specifically, the wireless communication processing unit 21 of the IP telephone terminal 2 transmits a probe request with a predetermined identifier “ESSID” from the transmission / reception antenna 21a at a predetermined frequency “CH”.
When the probe request is received by the transmission / reception antenna 11a of the signal communication unit 11 in the plurality of access points 1, the access of the identifier that matches the identifier (for example, “ESSID1”) included in the probe request. The point (for example, the first access point 1A with the identifier “ESSID1”) returns a probe response to the probe request.

In the IP telephone terminal 2, when the probe response is received by the transmission / reception antenna 21a, the wireless communication processing unit 21 detects the reception level of the probe response and connects the access point 1 having the highest reception level to the connection destination access. It is specified as a point (for example, the first access point 1A etc.). Then, the wireless communication processing unit 21 transmits an association request from the transmission / reception antenna 21a in order to establish a wireless link with the identified access point 1.
Then, the first access point 1A as the connection destination returns an association response to the association request received by the transmission / reception antenna 11a of the signal communication unit 11, so that the access point 1 and the IP telephone terminal 2 A wireless link is established between them (step S2).
Subsequently, the IP telephone terminal 2 starts a call (communication) with a call destination terminal 3 connected via a SIP server (not shown), and communicates with the call destination terminal 3 via the first access point 1A. Data is transmitted and received (steps S3 and S4).

Then, the signal communication unit 11 of the first access point 1A receives the reception level (first level) of the signal transmitted from the IP telephone terminal 2 and received by the transmission / reception antenna 11a in a state where the wireless link with the IP telephone terminal 2 is established. 1 reception level) is detected at a predetermined timing, and it is determined whether or not the first reception level is equal to or less than a threshold value A (see FIG. 3).
Here, when the user who owns the IP telephone terminal 2 moves from the point A to the point B, the reception level of the signal from the IP telephone terminal 2 detected by the signal communication unit 11 gradually decreases (FIG. 3). reference).
When the signal communication unit 11 determines that the first reception level is equal to or lower than the threshold A (step S5), the access point communication unit 12 determines that the peripheral access point (for example, the second and third access points). 1B, 1C), a measurement request signal (detection instruction) for the reception level (second reception level) of the signal transmitted from IP telephone terminal 2 is transmitted via wired LAN 5 (step S6).

In the second and third access points 1 </ b> B and 1 </ b> C, the reception level detection unit 13 receives a predetermined request from the IP telephone terminal 2 based on the second reception level measurement request signal received by the access point communication unit 12. Is received by the reception level detection antenna 13a and the reception level (second reception level) is detected (step S7).
Thereafter, the access point communication unit 12 returns the second reception level detected by the reception level detection unit 13 to the first access point 1A by a reception level acquisition response signal (step S8).

In the first access point 1A, upon receiving the second reception levels transmitted from the second and third access points 1B and 1C by the access point communication unit 12, the access point specifying unit 14 The access point with the highest reception level (for example, the second access point 1B) is identified as the handover destination access point 1 (step S9).
Then, the signal communication unit 11 transmits (notifies) the identifier “ESSID”, the frequency “CH”, and the MAC (Media Access Control) address of the second access point 1B that is the handover destination to the IP telephone terminal 2 ( Step S10).

Thereafter, the timing determination unit 15 of the first access point 1A acquires the second reception level of the second access point 1B that is the handover destination at a predetermined timing, and the first access point 1A of the first access point 1A It is determined whether the difference from the reception level is equal to or greater than the threshold value B.
That is, the signal communication unit 11 of the first access point 1A detects the first reception level of the signal from the IP telephone terminal 2 at a predetermined timing, and the access point communication unit 12 receives the second access point 1B. In response to this, an acquisition request for the second reception level of the signal from the IP telephone terminal 2 is transmitted (step S11).
Then, in the second access point 1B, the access point communication unit 12 sends the second reception level detected by the reception level detection unit 13 to the first access point 1A by the reception level acquisition response signal. A reply is made (step S12).
When it is determined that the difference between the first reception level and the second reception level is greater than or equal to the threshold B and the handover timing is determined (step S13), the signal communication unit 11 Then, the association cancellation signal is transmitted from the transmission / reception antenna 11a (step S14).

In the IP telephone terminal 2, when the association cancellation signal is received by the transmission / reception antenna 21a, the wireless communication processing unit 21 cancels the wireless link with the first access point 1A, and subsequently searches for peripheral access points. The second access point is based on various information (identifier “ESSID”, frequency “CH”, MAC (Media Access Control) address) of the second access point 1B acquired in advance from the access point 1A. In order to establish a wireless link with 1B, an association request is transmitted from the transmitting / receiving antenna 21a.
Then, the second access point 1B as the handover destination returns an association response to the association request received by the transmission / reception antenna 11a of the signal communication unit 11, so that the second access point 1B and the IP telephone A wireless link is established with the terminal 2 (step S15).
Thereby, the handover to the second access point 1B is completed.

  Thereafter, the IP telephone terminal 2 transmits / receives data to / from the call destination terminal 3 via the second access point 1B (Steps S16 and S17). The call (communication) with the callee terminal 3 is disconnected through this.

  As described above, according to the IP telephone system 100 of the first embodiment, the connection access point performs peripheral access of signals transmitted from the IP telephone terminal 2 in a state where a wireless link with the IP telephone terminal 2 is established. It is possible to specify the handover destination by acquiring the reception level by the point. That is, each access point 1 includes a reception level detection unit 13 including a reception level detection antenna 13a in addition to a transmission / reception antenna 11a for communication with the IP telephone terminal 2. Even during communication, it is possible to properly detect the reception level of signals from other IP telephone terminals. Further, at the moment when the difference between the second reception level of the peripheral access point and the first reception level of the connected access point becomes equal to or greater than the threshold B, handover is performed to the IP telephone terminal 2 by issuing an association release signal. As a result, the access point is switched in a short time, and the handover between the IP phone terminal 2 and the call destination terminal 3 is performed without interruption of the call with the access point 1. Can be performed at an appropriate position in a short time.

  In the first embodiment, at the time of handover to the second access point 1B, the IP telephone terminal 2 establishes a radio link with the second access point 1B by an association release signal from the first access point 1A. However, the present invention is not limited to this, but requests the IP telephone terminal 2 to establish a wireless link with the second access point 1B by issuing a unique access point switching signal instead of the association cancellation signal. You may make it do.

[Embodiment 2]
The IP telephone system 200 according to the second embodiment will be described below with reference to FIGS.
Here, FIG. 6 is a diagram schematically showing a schematic configuration of the IP telephone system 200 according to the second embodiment to which the present invention is applied. FIG. 7 is a block diagram of the access point 201, and FIG. 8 is a diagram schematically showing the data structure of the CTS signal transmitted from the access point 201.
The IP telephone system 200 of the second embodiment is substantially the same as that of the first embodiment except for the configuration of the access point 201. Therefore, the same components are denoted by the same reference numerals and the description thereof is omitted.

  As shown in FIGS. 6 and 7, the access point 201 of the IP telephone system 200 according to the second embodiment is transmitted from the connection access point without including the reception level detection unit 13 according to the access point 1 according to the first embodiment. The signal reception unit 211 detects the second reception level according to the timing information and frequency information of the measurement request signal.

Hereinafter, the access point 201 will be described in detail with reference to FIGS.
First, the access point communication unit 212 of the connection access point, as the detection instruction transmission unit, for example, when it is determined that the first reception level of the signal received by the transmission / reception antenna 11a is equal to or lower than the threshold A, A measurement request signal including timing information defining the detection timing of the second reception level of the signal from the IP telephone terminal 2 and frequency information defining the frequency “CH” of wireless communication with the IP telephone terminal 2 is used as a peripheral access point. It is supposed to send.
Here, the measurement request signal includes, for example, the identifier “ESSID”, the frequency “CH”, the MAC address, etc. of the IP telephone terminal 2 that has established a wireless link with the access point 1A in addition to the timing information. Yes.
The timing information specifically refers to, for example, an interval of data transmission / reception (for example, 20 [ms]) between the access point 1A and the IP telephone terminal 2, and each access point 201 has another IP address. When a radio link is established with the telephone terminal 2, any timing after transmission of the measurement request signal in consideration of the duration time of a CTS (Clear To Send) signal (described later) to the other IP telephone terminal 2 Defines whether the second reception level should be detected.

For example, the signal communication unit (transmission / reception communication unit) 211 establishes a wireless link with the IP telephone terminal 2 to perform communication, and transmits a signal transmitted from the IP telephone terminal 2 with which the wireless link is not established. The reception level (second reception level) is detected.
That is, the signal communication unit 211 of the peripheral access point (for example, the access point 1C), for example, as a reception level detection unit, at a detection timing specified in the timing information of the measurement request signal received by the access point communication unit 212. The reception level of the signal from the IP telephone terminal 2A is detected by the frequency “CH” of the radio link between the connection access point and the IP telephone terminal (hereinafter referred to as “IP telephone terminal 2A”). Specifically, the signal communication unit 211 of the peripheral access point, for example, once in the state where the radio link is established with a predetermined IP telephone terminal (hereinafter referred to as “IP telephone terminal 2C”). “CH3” is switched to the frequency “CH1” of the wireless link between the access point 1A and the IP telephone terminal 2A included in the measurement request signal, and the signal transmitted from the IP telephone terminal 2A is received by the transmitting / receiving antenna 11a. It is like that.

At this time, the signal communication unit 211 transmits, for example, a CTS signal (control signal) that stops transmission of a signal from the IP telephone terminal 2C to the IP telephone terminal 2C for a predetermined time as a control signal transmission unit. It has become.
For example, as shown in FIG. 8, the CTS signal (frame) is used for frame control that defines the type of frame, duration that specifies a data transmission prohibition time, MAC address of a wireless terminal that is not prohibited from data transmission, and frame error inspection. It consists of data such as FCS (Frame Check Sequence).
Thus, by defining the MAC address of the IP telephone terminal 2A as the MAC address, when the IP telephone terminal 2C receives the CTS signal, the signal transmission is prohibited for the duration time. Even if the CTS signal is received, the signal transmission is not prohibited. Then, while signal transmission from the IP telephone terminal 2C is prohibited, the access point 1C is connected between the IP telephone terminal 2A and the access point 1A so as to match the timing at which the signal is transmitted from the IP telephone terminal 2A. A second reception level is detected by receiving a signal at the frequency “CH” of the radio link.

Next, handover processing by the IP telephone system 200 will be described with reference to FIG.
Here, FIG. 9 is a timing chart showing an operation related to the handover process. The handover process of the IP telephone system 200 according to the second embodiment is the same as that according to the first embodiment except for the points described below, so that the description thereof will be omitted. Further, it is assumed that the access point 1A and the IP telephone terminal 2A are wirelessly connected with the frequency “CH1”, and the access point 1C and the IP telephone terminal 2C are wirelessly connected with the frequency “CH3”.
Further, in FIG. 9, wireless communication between the access point 201 and the IP telephone terminal 2 is represented by “one-dot chain line”, and wired communication between the access points 201 is represented by “solid line”.

  As shown in FIG. 9, when the access point 1A determines that the first reception level is equal to or lower than the threshold A in a state where the IP telephone terminal 2A has established a wireless link, Step S5; see FIG. 5), a request for measuring the reception level (second reception level) of the signal transmitted from the IP telephone terminal 2A to the peripheral access point (for example, the access point 1C) at the predetermined time t1. A signal (detection instruction) is transmitted via the wired LAN 5.

In the access point 1C, when the measurement request signal is received by the access point communication unit 212, the signal communication unit 211 allows the signal transmission from the IP telephone terminal 2A and the IP telephone terminal at a predetermined time t2. A CTS signal for stopping signal transmission from 2C is transmitted from the transmission / reception antenna 11a at the frequency “CH3”.
As a result, the IP telephone terminal 2C that has received the CTS signal by the transmitting / receiving antenna 11a stops signal transmission from the wireless communication processing unit 21 for the time specified by the duration of the CTS signal.

In addition, after the transmission of the CTS signal, in the access point 1C, the signal communication unit 211 matches the transmission timing of the signal from the IP telephone terminal 2A based on the detection timing defined in the measurement request signal. A process of switching the wireless communication frequency “CH3” to the wireless communication frequency “CH1” of the IP telephone terminal 2A is performed. In FIG. 9, the wireless communication frequency of the access point 1C is switched to the frequency “CH1” at a predetermined time t3.
Then, the signal communication unit 211 receives a signal transmitted from the IP telephone terminal 2A at the frequency “CH1” by the transmission / reception antenna 11a and detects the reception level (second reception level).

Thereafter, the signal communication unit 211 performs a process of switching the wireless communication frequency “CH1” to the wireless communication frequency “CH3” of the IP telephone terminal 2C at a predetermined time t4.
After switching the frequency, at a predetermined time t5, the access point communication unit 212 returns the second reception level detected by the signal communication unit 211 to the first access point 1A using a measurement response signal.

In the access point 1A, although not shown, the reception levels of peripheral access points other than the access point 1C are obtained in the same manner as described above, and the access point specifying unit 14 accesses the access point 1 having the highest reception level. Is specified as the handover destination access point 1 (step S9; see FIG. 5).
Thereafter, the process proceeds to step S10, and the subsequent processing is executed.

  As described above, according to the IP telephone system 200 of the second embodiment, the peripheral access point is detected based on the measurement request signal transmitted from the connection access point and is defined by the timing information included in the measurement request signal. At the timing, the second reception level can be detected using the signal communication unit 11 at the frequency “CH” of the wireless link between the connection access point and the IP telephone terminal 2. That is, even when the peripheral access point has established a wireless link with another IP telephone terminal 2 by the signal communication unit 211, the frequency of the signal communication unit 211 is switched to the wireless communication frequency of the connection access point at a predetermined timing. Accordingly, the second reception level can be appropriately detected using the signal communication unit 211 without providing an antenna dedicated to detection of the reception level.

  In addition, since the access point 1C transmits a CTS signal to the IP telephone terminal 2C and prohibits transmission of the signal from the IP telephone terminal 2C, the IP telephone terminal 2C receives the IP telephone terminal 2A. A period during which communication with the access point 1C due to the level measurement is impossible can be known in advance, and inadvertent data loss can be prevented.

The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.
For example, the connection access point specifies the handover destination access points 1 and 201 based on the detection result of one time at a predetermined timing of the reception level of the peripheral access point. , 201 is not limited to this.
Hereinafter, the IP telephone system of Modification 1 will be described with reference to FIG.

FIG. 10 is a diagram schematically showing an access point specifying method in the handover process by the IP telephone system of the first modification.
In FIG. 10, the reception levels of the access points 1B and 1C are represented by solid lines, the predicted reception level of the access point 1B is represented by a one-dot chain line, and the predicted reception levels of the access point 1C are represented by a two-dot chain line. To do.

  As shown in FIG. 10, in the IP telephone system of the first modification, the access point specifying unit 14 sets the second reception level of each of a plurality of peripheral access points (for example, access points 1B and 1C) to a predetermined value. A handover destination may be specified by measuring a plurality of times in the time, more preferably constantly, and predicting a future reception level based on the transition of the reception level. For example, in FIG. 10, although the current reception levels of the access points 1B and 1C are substantially the same, the reception level of the access point 1C gradually decreases from the transition so far. The reception level of the access point 1B is predicted to increase. In this case, it is considered preferable that the handover destination is the access point 1B.

  As described above, in the IP telephone system of the first modification, the access point 1 that is predicted to have a higher reception level in the future based on the transition of the reception level of the peripheral access point is changed to the access point 1 that is the handover destination. Can be specified as In this way, a more appropriate access point 1 can be specified as the handover destination access point 1, and the handover can be appropriately performed.

  In the first modification, for example, the peripheral access point may notify the connection access point every time the second reception level is detected, or an average value is taken every predetermined time. You may make it notify a thing.

  In the above embodiment, the wireless LAN is exemplified as the wireless communication line. However, the present invention is not limited to this, and for example, a Bluetooth (registered trademark) standard communication line may be used.

  Furthermore, in the above-described embodiment, the IP telephone systems 100 and 200 are exemplified as the handover processing system. However, the present invention is not limited to this. For example, the wireless communication terminal acquires and reproduces image and sound information by streaming. In this case, the present invention may be applied to a system for performing handover for reproducing information without interruption.

It is the figure which showed typically schematic structure of the IP telephone system illustrated as a suitable example of the handover processing system of Embodiment 1 to which this invention was applied. It is a block diagram of the access point which comprises the IP telephone system of FIG. It is a figure explaining the execution timing of the hand-over by the IP telephone system of FIG. FIG. 2 is a block diagram of an IP telephone terminal constituting the handover processing system of FIG. It is a figure which shows an example of the operation | movement which concerns on the handover process by the IP telephone system of FIG. It is the figure which showed typically schematic structure of the IP telephone system illustrated as a suitable example of the handover processing system of Embodiment 2 to which this invention was applied. It is a block diagram of the access point which comprises the IP telephone system of FIG. It is the figure which showed typically the data structure of the CTS signal transmitted from the access point of FIG. 7 is a timing chart showing an operation related to a handover process by the IP telephone system of FIG. 6. It is the figure which showed typically the access point identification method in the handover process by the IP telephone system of the modification 1.

Explanation of symbols

100, 200 IP telephone system (handover processing system)
1,201 access point (base station)
11, 211 Signal communication unit (first reception level acquisition unit, transmission / reception communication unit, reception level determination unit, information transmission unit)
11a Transmission / reception antenna 12, 212 Access point communication unit (second reception level acquisition means, detection instruction transmission means, reception level transmission means)
13 Reception level detector (Reception level detection means)
13a Reception level detection antenna (reception level detection communication unit)
14 Access point identification unit (base station identification means)
15 Timing determining unit 2 IP telephone terminal (wireless communication terminal)
3 Call terminal

Claims (6)

A base station comprising a plurality of base stations and a wireless communication terminal that communicates with any of the plurality of base stations via a wireless communication line, and the base station to which the wireless communication terminal is connected among the plurality of base stations A handover processing system for performing a handover process for switching between,
Among the plurality of base stations, a connection base station connected to the wireless communication terminal via the wireless communication line is:
First reception level acquisition means for acquiring a first reception level that is a reception level of a signal transmitted from the wireless communication terminal in the connection base station;
A reception level determination unit that determines whether or not the first reception level acquired by the first reception level acquisition unit is a predetermined value or less;
When the reception level determination means determines that the first reception level is equal to or lower than a predetermined value, the wireless communication in a peripheral base station existing around the connection base station among the plurality of base stations Second reception level acquisition means for acquiring a second reception level that is a reception level of a signal transmitted from the terminal;
Based on the second reception level acquired by the second reception level acquisition means, base station specifying means for specifying a handover destination base station from among the neighboring base stations,
A handover processing system comprising: information transmission means for transmitting information used for connection to the base station identified by the base station identification means to the wireless communication terminal. The connecting base station is
When it is determined by the reception level determination means that the first reception level is a predetermined value or less, a detection instruction transmission means for transmitting a detection instruction of the second reception level to a neighboring base station,
The surrounding base station is
A transmission / reception communication unit for transmitting / receiving signals to / from the wireless communication terminal;
A reception level detection communication unit for detecting the second reception level;
A reception level detection means for detecting the second reception level by the reception level detection communication unit based on the reception of the detection instruction transmitted from the detection instruction transmission means;
The handover processing system according to claim 1, further comprising: a reception level transmission unit that transmits the second reception level detected by the reception level detection unit to the connected base station. The connecting base station is
When the reception level determination means determines that the first reception level is less than or equal to a predetermined value, timing information defining the detection timing of the second reception level and communication with the wireless communication terminal A detection instruction transmitting means for transmitting a detection instruction of the second reception level including frequency information defining a frequency to a neighboring base station;
The surrounding base station is
While performing transmission and reception of signals with the wireless communication terminal, a communication unit for transmission and reception for detecting the second reception level,
Based on the detection instruction transmitted and received from the detection instruction transmission means, the second reception level is set for the transmission / reception at the frequency specified by the frequency information at the detection timing specified by the timing information. A reception level detecting means for detecting by the communication unit;
The handover processing system according to claim 1, further comprising: a reception level transmission unit that transmits the second reception level detected by the reception level detection unit to the connected base station. The surrounding base station is
After receiving the detection instruction transmitted from the detection instruction transmitting means, before transmitting the second reception level, control for transmitting a control signal for temporarily stopping transmission of a wireless communication terminal other than the wireless communication terminal 4. The handover processing system according to claim 3, further comprising a signal transmission unit. The wireless communication among the plurality of base stations using a wireless communication system comprising a plurality of base stations and a wireless communication terminal connected to any of the plurality of base stations via a wireless communication line for communication A handover processing method for performing a handover process for switching a base station to which a terminal is connected,
Among the plurality of base stations, a connection base station connected to the wireless communication terminal via the wireless communication line is:
A process of obtaining a first reception level that is a reception level of a signal transmitted from the wireless communication terminal in the connection base station;
A process of determining whether or not the acquired first reception level is a predetermined value or less;
When it is determined that the first reception level is equal to or lower than a predetermined value, a signal transmitted from the wireless communication terminal in a peripheral base station existing around the connected base station among the plurality of base stations A process of obtaining a second reception level that is a reception level of
Based on the acquired second reception level, a process of specifying a handover destination base station from among the neighboring base stations,
A hand that performs processing for transmitting information used for connection to the base station specified by the base station specifying means to the wireless communication terminal when it is determined that the value is equal to or greater than the specific value. Over processing method. A wireless base station connected to a wireless communication terminal via a wireless communication line,
First reception level acquisition means for acquiring a first reception level that is a reception level of a signal transmitted from the wireless communication terminal;
A reception level determination unit that determines whether or not the first reception level acquired by the first reception level acquisition unit is a predetermined value or less;
A second reception level of a signal transmitted from the wireless communication terminal in a peripheral base station in the vicinity when the first reception level is determined to be equal to or less than a predetermined value by the reception level determination unit; Second reception level acquisition means for acquiring the reception level of
Based on the second reception level acquired by the second reception level acquisition means, base station specifying means for specifying a handover destination base station from among the neighboring base stations,
An information transmitting means for transmitting information used for connection to the base station specified by the base station specifying means to the wireless communication terminal.

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