JP5336424B2 - Wireless communication terminal, wireless communication system, wireless communication control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To switch to a suitable next base station in a current location of a radio communication terminal before the radio communication terminal passes a base station between which radio communication is being established, in a radio communication system where a directional antenna of each of base stations has a directivity opposite to a moving direction of the radio communication terminal. <P>SOLUTION: In the radio communication terminal, candidate information determining one or more candidate base stations which are candidates for next radio communication establishment, is stored correspondingly to each base station while the radio communication is being established between the base station. An electric field strength in the radio communication between the base station, between which radio communication is being established currently, is measured (S1) and if the measured electric field strength reaches a preset upper limit threshold value or above (S5: Yes), candidate base stations corresponding to the base station, between which the radio communication is being established currently, are extracted from the candidate information (S8, 9). A base station connectable currently is selected from among the candidate base stations, and switch to the destination between which the radio communication is to be established is conducted (S10). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a wireless communication system in which a wireless communication terminal performs wireless communication with any one of a plurality of base stations, and more particularly to a base station to which wireless communication is established while the wireless communication terminal is moving. The present invention relates to a so-called handover processing technique for switching.

In general, in a wireless communication network such as a wireless LAN or a wireless MAN, a wireless communication terminal performs a so-called handover process in which one base station is selected from a plurality of base stations while moving and a wireless communication establishment destination is switched. It is known to do.
For example, the handover process described above selects a base station having the highest electric field strength (synonymous with radio signal strength) from a plurality of communicable base stations and establishes wireless communication with the base station. . A general wireless communication terminal is configured to have an interface that starts searching for the next base station when the electric field strength of the communication falls below a lower threshold while communicating with a base station that is moving. Here, consider a case where an omnidirectional antenna is used as the antenna of the wireless communication terminal and the base station. In this case, in the handover process, the base station is switched around the intermediate point between the two base stations. That is, the base station is switched in a state where the level difference between the electric field strengths of the two base stations is small. For this reason, switching between two base stations may be repeated multiple times due to fluctuations in electric field strength due to a temporary change in the radio wave propagation environment (hereinafter referred to as “switching phenomenon”).

On the other hand, Patent Document 1 discloses a wireless communication system using a directional antenna as an antenna of a wireless communication terminal and a base station in order to prevent the above switching phenomenon. This will be specifically described below. FIG. 16 quotes FIG. 3 of Patent Document 1.
As shown in FIG. 16, in the wireless communication system disclosed in Patent Document 1, the communication terminal 100 is arranged at the end of the train 300. Then, the communication terminal 100 transmits and receives radio waves in the range of the reception area 150 that is directed in the direction opposite to the moving direction of the train 300. That is, the communication terminal 100 has radio communication directivity in the direction opposite to the moving direction of the train 300.
On the other hand, the base stations 201 and 202 transmit and receive radio waves in the service areas 251 and 252 that are directed in the moving direction of the train 300. That is, the base stations 201 and 202 have radio communication directivity in the moving direction of the train 300.
In the wireless communication system configured as described above, the communication terminal 100 executes a handover process for performing wireless communication by selecting a base station having a higher electric field strength from the base stations 201 and 202. In this case, switching from the base station 201 to the base station 202 is performed at a position slightly beyond the base station 202. That is, switching from the base station 201 to the base station 202 is performed in a situation where the level difference between the electric field strengths of the base stations 201 and 202 is large. Therefore, it is possible to prevent the switching phenomenon that has occurred when the omnidirectional antenna is used.

In addition, handover processing that employs a method of constantly searching for a communicable base station and measuring electric field strength and switching to the base station with the highest electric field strength among the communicable base stations has been known. . A wireless communication terminal that employs this method may have a configuration in which an antenna for wireless communication and an antenna for handover processing are individually provided. However, it is not desirable to provide two antennas for the wireless communication terminal.
Therefore, there is a technique for performing wireless communication and handover processing using one antenna. In this case, when the wireless communication terminal searches for a base station that can always communicate and measures the electric field strength, the amount of data that can be transmitted by wireless communication (data communication capacity per unit time) decreases. For this reason, when the electric field strength of a base station with which wireless communication is currently established becomes equal to or lower than a preset threshold, selection of a base station with the highest electric field strength is started. In this way, by selecting a base station only when necessary, a wireless communication terminal can perform large-capacity data transmission with a base station with which wireless communication is currently established. is there.

JP 2006-319593 A

  By the way, in the wireless communication system disclosed in Patent Document 1, the communication terminal 100 is arranged at the tail end of the train 300. Therefore, for example, when video captured by a camera provided at the beginning of the train 300 is transmitted by wireless communication, from the beginning of the train 300 where the camera is installed to the end where the communication terminal 100 is installed. It becomes necessary to transmit video data by wired communication or wireless communication. Therefore, there arises a problem that the signal level of the video data photographed by the camera is attenuated before being transmitted to the communication terminal 100. On the other hand, it is conceivable to amplify the signal level of video data between the camera and the communication terminal 100. However, for this purpose, an amplification device for performing amplification is required, which causes a problem that the system configuration is complicated and expensive.

Therefore, a configuration in which the wireless communication terminal is arranged at the head of the vehicle is conceivable. FIG. 1 is a schematic diagram showing a schematic configuration of a radio communication system X according to an embodiment of the present invention to be described later. FIG. 17 is a diagram for explaining a case in which selection of the next base station is started when the electric field strength becomes equal to or lower than the lower threshold K1 in the wireless communication system X. 17 indicate the electric field strengths of the base stations W1 to W3.
In the wireless communication system X shown in FIG. 1, the wireless communication terminal Y has wireless communication directivity in the moving direction of the vehicle 10, and each of the base stations W <b> 1 to W <b> 3 has wireless communication directivity in the direction opposite to the moving direction of the vehicle 10. It has sex.
Here, in the wireless communication system X, when the electric field strength of the base station to which wireless communication is currently established becomes equal to or lower than a preset lower threshold K1, the next base station to establish wireless communication is selected. Consider a case where a handover process to be started is executed. FIG. 1 shows a state where the vehicle 10 is in a position where wireless communication is established between the wireless communication terminal Y and the base station W1. Hereinafter, a case where the vehicle 10 moves from the position illustrated in FIG. 1 toward the base station W2 will be described.

As shown in FIG. 17, when the movement of the wireless communication terminal Y is started and the wireless communication terminal Y approaches the base station W1 as time passes, the electric field strength of the base station W1 obtained by the wireless communication terminal Y gradually increases. Get higher. Thereafter, when the wireless communication terminal Y passes through the base station W1, the electric field strength of the base station W1 rapidly decreases and reaches the lower threshold K1 or less (time point T11). Thereby, the wireless communication terminal Y starts searching for the base station with the highest electric field strength. Thereafter, when the wireless communication terminal Y selects the base station W2 as the base station with the highest electric field strength, the wireless communication terminal Y switches from the base station W1 to the base station W2 (time point T12). The same applies when switching from the base station W2 to the base station W3 (time points T13 and T14).
As described above, in the configuration in which the wireless communication terminal Y has directivity in the moving direction, when the electric field strength of the base station W1 is equal to or lower than the lower limit threshold value K1, the electric field strength is rapidly reduced. In this state, the selection of the next base station W2 is started and the communication destination is switched. Therefore, when the switching is performed, the electric field strength of the base station W1 may be too low, and wireless communication may be interrupted.

Therefore, the field strength in wireless communication with a base station with which wireless communication is currently established is measured, and when the measured field strength reaches a preset upper threshold or higher, the next base station is selected. Thus, switching the establishment destination of wireless communication can be considered. In this case as well, the next base station can be selected based on the reception strength of the radio signal from each base station in the radio communication terminal.
As a result, the wireless communication terminal can select and switch to the next base station before passing through the base station with which wireless communication is currently established, that is, before the electric field strength in the wireless communication is sharply reduced. is there. Therefore, in such a wireless communication terminal, it is possible to prevent interruption of wireless communication when switching base stations. In addition, the above wireless communication terminal selects a base station to establish the next wireless communication only when the electric field strength is equal to or higher than the upper threshold, and thus realizes large-capacity data communication in normal wireless communication. can do.
However, when the wireless propagation environment is complex, for example, when the movement path of the wireless communication terminal is curved or when there are buildings such as buildings around and multiple reflections (multipath) occur, The propagation state of the radio signal varies greatly. For this reason, in a configuration in which switching to the next base station is performed based on the reception strength of the radio signal at the radio communication terminal before passing through the base station where radio communication is currently established, the next base station is appropriately There is a possibility that it cannot be selected, and there is a possibility that the subsequent stabilization of wireless communication may be hindered.

  Accordingly, the present invention has been made in view of the above circumstances, and the object of the present invention is to provide a wireless communication system in which the directional antenna of each base station has directivity in the direction opposite to the moving direction of the wireless communication terminal. Provided are a radio communication terminal, a radio communication system, and a radio communication control method capable of switching to an appropriate next base station at the current position of the radio communication terminal before the radio communication terminal passes through a base station in which radio communication is established There is.

In order to achieve the above object, the present invention is arranged at predetermined intervals along a predetermined movement route, and has directivity in a direction opposite to the movement direction of the wireless communication terminal moving along the movement route. The present invention is applied to a wireless communication terminal that performs wireless communication with any one of a plurality of base stations including a base station antenna, and includes the following (1) to (3): Configured as
(1) Electric field strength measuring means for measuring electric field strength in wireless communication with a base station where wireless communication is currently established.
(2) Corresponding to each base station, one or a plurality of candidate base stations and a plurality of candidate bases that are candidates for a destination of the next wireless communication when wireless communication with the base station is established Candidate information storage means for storing candidate information in which station priority is determined.
(3) When the wireless communication is currently established with any one of the base stations, and the electric field intensity measured by the electric field intensity measuring means reaches a preset upper limit threshold value or more, it is stored in the candidate information storage means The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information thus selected, and the base station that can be currently connected is selected from the candidate base stations according to the priority order. Base station switching means for switching the establishment destination.
And this invention is comprised by either of following (4)-(6).
(4) Corresponding to each base station, a connection destination in which whether or not to use the candidate information as a candidate for a next wireless communication establishment destination when wireless communication with the base station is established The base station switching means further includes a connection destination release flag storage means in which a release flag is stored, and the base station switching means does not use the candidate information for the connection destination release flag in the base station where wireless communication is currently established. If it is set, the base station is not selected based on the candidate information stored in the candidate information storage means, and an arbitrary base station that is currently connectable is selected to switch the establishment destination of wireless communication.
(5) Corresponding to each base station, a delay time memory in which delay time information in which a delay time until switching to the next base station is determined when wireless communication with the base station is established is stored The base station switching means extracts from the delay time information stored in the delay time storage means the delay time corresponding to the base station with which wireless communication is currently established, After the electric field intensity measured by the electric field intensity measuring means reaches a preset upper limit threshold or more, the establishment destination of the wireless communication is switched after the delay time elapses.
(6) A connection destination in which whether or not to use the candidate information as a candidate for an establishment destination of the next wireless communication when wireless communication with the base station is established corresponding to each base station Corresponding to each base station, the connection destination release flag storage means storing the release flag and the delay time until switching to the next base station when wireless communication with the base station is established is determined. A delay time storing means for storing the delay time information, wherein the base station switching means does not use the candidate information for the connection destination release flag in the base station where the wireless communication is currently established. If the field strength measured by the field strength measuring means reaches the upper limit threshold or higher, the base station is not selected based on the candidate information stored in the candidate information storage means. Currently connectable to Any desired base station is selected and the establishment destination of wireless communication is switched. Thereafter, the delay time corresponding to the base station with which wireless communication is currently established has elapsed, and then stored in the candidate information storage means. The base station is selected based on the candidate information and the establishment destination of the wireless communication is switched.
According to the present invention, since the next base station is selected from one or a plurality of candidate base stations set for each base station, the electric field strength measured by the electric field strength measuring means is If the wireless communication terminal is switched to the next base station before reaching the upper limit threshold set in advance and the wireless communication terminal passes through the base station that is currently establishing wireless communication, Switching to the base station can be prevented, and the subsequent wireless communication by the wireless communication terminal can be stabilized.
Further, the base station switching means, it is possible to select the currently connectable base station from among the candidate base station in accordance with the priority order. Therefore, it is possible to select a suitable base station that is set in advance as a base station to be connected next to the currently connected base station among the candidate base stations.

By the way, depending on the surrounding environment of the base station, for example, when the base station with which the wireless communication terminal currently establishes wireless communication exists in the building or in the vicinity of the building, In terms of position, the base station arranged at the next position of the base station is not necessarily the optimum one.
Therefore, according to the configuration of (4) above, when the wireless communication with the base station is established for each base station, the candidate information is used as a candidate for the next wireless communication establishment destination. A connection destination release flag storage means for storing a connection destination release flag for determining whether or not there is a connection destination, wherein the base station switching means is configured to release the connection destination at the base station where wireless communication is currently established. If the flag is set not to use the candidate information, the base station is not selected based on the candidate information stored in the candidate information storage means, and any currently connectable base station is selected and wirelessly selected. It is possible to switch the establishment destination of communication. If the connection destination release flag is set to use the candidate information in the base station where the wireless communication is currently established, the current wireless communication is established from the candidate information stored in the candidate information storage means. The candidate base station corresponding to the base station being operated is extracted, and a base station that can be currently connected is selected from the candidate base stations according to the priority order, and the establishment destination of wireless communication is switched.
As a result, a connection destination in which whether or not to use the candidate information as a candidate for a next wireless communication establishment destination when wireless communication with the base station is established corresponding to each base station is determined. Based on the release flag, if the connection destination release flag is set not to use the candidate information in the base station where wireless communication is currently established , the options of the next base station are limited to the candidate base station. Therefore, the wireless communication by the wireless communication terminal can be stabilized.

In addition, when the base station with which the wireless communication terminal currently establishes wireless communication exists, for example, in a building, a base station that is not necessarily positioned next to the base station immediately before the base station. Even if the station is not optimal, it is possible that it is known in advance that switching to the next base station is appropriate if the wireless communication terminal passes through the building.
Therefore, according to the configuration of (5) above, a delay with a predetermined delay time until switching to the next base station when wireless communication with the base station is established corresponding to each base station. time information is further provided with a delay time storage unit stored, the base station switching means, corresponding to the base station currently wireless communication from the delay time information stored in the delay time storage unit has been established The delay time is extracted and stored in the candidate information storage means after the delay time has elapsed after the electric field intensity measured by the electric field intensity measuring means reaches or exceeds a preset upper threshold value . The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information, and a currently connectable base station is selected from the candidate base stations according to the priority order . Where to establish Ri it is possible to replace.
Thus, for example, even if the base station arranged at the next position of the base station is not necessarily the most suitable position immediately before the base station, the delay time is such that the wireless communication terminal passes through the building. After the elapse of time, switching to the next base station can be performed.

Furthermore, according to the configuration of (6) above, when the wireless communication with the base station is established corresponding to each base station, the candidate information is used as a candidate for the establishment destination of the next wireless communication. A connection destination release flag storage means for storing a connection destination release flag for which a determination is made as to whether or not the next base station corresponds to each base station when wireless communication with the base station is established delay time information delay time is determined to switch to further comprise becomes by a delay time storage unit stored, the base station switching means, the connection destination in the current the base station wireless communication is established If the release flag is set not to use the candidate information , the candidate information stored in the candidate information storage means when the electric field intensity measured by the electric field intensity measuring means reaches the upper limit threshold or more. Based on The wireless communication establishment destination is switched by selecting an arbitrary base station that can be currently connected without performing selection, and then the delay time corresponding to the predetermined base station with which wireless communication is currently established has elapsed. Then, the candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information stored in the candidate information storage means, and the current candidate is selected from the candidate base stations according to the priority order. select the connectable base station is capable of switching the establishment target radio communications. If the connection destination release flag is set to use the candidate information in the base station where the wireless communication is currently established, the current wireless communication is established from the candidate information stored in the candidate information storage means. The candidate base station corresponding to the base station being operated is extracted, and a base station that can be currently connected is selected from the candidate base stations according to the priority order, and the establishment destination of wireless communication is switched.
Thus, for example, when the base station arranged at the next position of the base station is not necessarily the most suitable position immediately before the base station, the delay time is such that the wireless communication terminal passes through the building. Until the time elapses, a seamless wireless communication environment can be realized by performing wireless communication with an arbitrarily selected base station. After the delay time elapses, an appropriate next base station to be originally connected is established. Can be switched to.

Further, when the moving route includes a plurality of branch routes, and the plurality of base stations include a plurality of branch destination base stations arranged in the branch routes, the moving information is stored in the candidate information storage means. The candidate information includes the branch destination base station arranged in each of the branch paths as the candidate base station corresponding to the base station located before the branch point to each of the branch paths in the movement route. Whether or not the base station switching means is appropriate as the establishment destination of the wireless communication after the base station switching means establishes the wireless communication with the branch destination base station. If it is not appropriate, it is desirable to switch the establishment destination of wireless communication to the other branch destination base station.
As a result, if the base station after the wireless communication terminal of the wireless communication terminal is switched is the branch destination base station and the branch destination base station is not appropriate, the wireless communication establishment destination Is switched to the other branch destination base station, so that even if the wireless communication terminal is mistakenly connected to a branch destination base station arranged on a different route from the route on which it travels, It can be connected to obtain stable wireless communication.

More specifically, if the currently connected branch base station is suitable as a wireless communication establishment destination, the electric field strength in the wireless communication should show an increasing tendency, and the electric field strength tends to decrease. In this case, it is estimated that the currently connected branch base station is not appropriate as a wireless communication establishment destination.
Therefore, the base station switching means, when the wireless communication with the branch destination base station is established, when the field strength measured by the field strength measuring means tends to decrease, It may be determined that the communication establishment destination is not appropriate and the establishment destination of wireless communication is switched to the other branch destination base station.
However, the base station switching means is stored in the candidate information storage means when it is determined that wireless communication with the branch destination base station is not appropriate even after switching to all the branch destination base stations. In addition, it is desirable to select an arbitrary base station that can be currently connected without switching the base station based on the candidate information and switch the establishment destination of the wireless communication. As a result, even if wireless communication with all the branch base stations is not possible, if there is another base station capable of wireless communication, wireless communication with the base station can be continued. it can.

It is also conceivable to determine whether or not the currently connected branch base station is appropriate as a wireless communication establishment destination based on the position of the wireless communication terminal Y.
Specifically, it further comprises shortest distance acquisition means for acquiring the shortest distance from the wireless communication terminal to each of the branch paths, and the base station switching means establishes wireless communication with the branch destination base station. After that, when the difference between the two shortest distances from the shortest distance acquired by the shortest distance acquisition means reaches a predetermined threshold value or more, the shortest distance becomes the shortest branch path. If wireless communication is established with the separated path base station arranged, the wireless communication is continued, and wireless communication is established with the separated path base station arranged on the other branch path. In this case, it is conceivable that the wireless communication establishment destination is switched to the separation path base station arranged on the branch path having the shortest shortest distance.

By the way, the present invention may be understood as an invention of a wireless communication system including the wireless communication terminal or a wireless communication control method in the wireless communication system.
Specifically, the wireless communication terminal includes a wireless communication terminal that moves along a predetermined movement route and a plurality of base stations that are arranged at predetermined intervals along the movement route. A wireless communication system for establishing wireless communication with any one of the base stations, wherein each of the base stations has directivity in a direction opposite to the moving direction of the wireless communication terminal. it includes a, the wireless communication terminal, (1) the field intensity measuring means to (3), the candidate information storage means, Ri Na provided with the above-mentioned base station switching means (4) to (6 the Rukoto consists of either) may be regarded as an invention of a wireless communication system according to claim.
A wireless communication terminal that moves along a predetermined movement path; and a plurality of base stations that are arranged at predetermined intervals along the movement path, the wireless communication terminal and the plurality of base stations A wireless communication system for establishing wireless communication with any one base station, wherein each of the base stations includes a base station antenna having directivity in a direction opposite to a moving direction of the wireless communication terminal. The wireless communication terminal is configured to measure the electric field strength in the wireless communication with the base station with which the wireless communication is currently established, and the wireless communication with the base station corresponding to each base station. Candidate information storage means for storing candidate information in which one or a plurality of candidate base stations that are candidates for the establishment of the next wireless communication and the priority order of the plurality of candidate base stations are stored And one of the base stations When the wireless communication is currently established and the electric field strength measured by the electric field strength measuring means reaches a preset upper limit threshold or more, the current wireless communication is started from the candidate information stored in the candidate information storing means. Base station switching means for extracting the candidate base station corresponding to the base station with which the base station has been established, selecting a base station that is currently connectable from the candidate base stations according to the priority order, and switching a wireless communication establishment destination And the moving path includes a plurality of branch paths, and the plurality of base stations include a plurality of branch destination base stations arranged in the branch paths, respectively, and the candidate information The candidate information stored in the storage means is arranged in each of the branch paths as the candidate base station corresponding to the base station located before the branch point to each of the branch paths in the movement route. The base station switching means is determined to include the branch base station, and after the wireless communication with the branch base station is established, the branch base station is appropriately set as the establishment destination of the wireless communication. If it is not appropriate, the establishment destination of the wireless communication is switched to the other branch destination base station .
A wireless communication terminal that moves along a predetermined movement path; and a base station antenna that is arranged at predetermined intervals along the movement path and has directivity in a direction opposite to the movement direction of the wireless communication terminal. A wireless communication control method for establishing wireless communication with any one of a plurality of base stations provided, wherein wireless communication is established with any of the base stations, and wireless communication is currently established. When the electric field strength in the wireless communication with the base station is measured and the measured electric field strength reaches a predetermined upper limit threshold or more, the wireless communication with the base station is performed corresponding to each base station. Wireless communication is established from candidate information in which one or a plurality of candidate base stations that are candidates for the establishment of the next wireless communication and the priority order of the plurality of candidate base stations are determined. The above candidate corresponding to the base station Extracting Chikyoku, per the switched establishment target radio communication by selecting the currently connectable base station from among the candidate base station in the current said base station wireless communication is established, for each of the base station Correspondingly, when the wireless communication with the base station is established, the connection destination release flag that determines whether or not to use the candidate information as a candidate for the next wireless communication establishment destination uses the candidate information. If it is not set, the base station is not selected based on the candidate information, and an arbitrary base station that can be currently connected is selected and the wireless communication establishment destination is switched. The delay corresponding to the base station with which the current wireless communication is established from the delay time information in which the delay time until switching to the next base station is established when the wireless communication with the base station is established Extract time and measure After the delay time elapses after the electric field strength reaches a predetermined upper limit threshold or higher, or the base station where the wireless communication is currently established is switched at the base station where the wireless communication is established. Corresponding to each base station, when a wireless communication with the base station is established, a connection destination release flag that determines whether or not to use the candidate information as a candidate for a next wireless communication establishment destination is If it is set not to use candidate information, a delay with a predetermined delay time until switching to the next base station when wireless communication with the base station is established corresponding to each base station. When the delay time corresponding to the base station with which wireless communication is currently established is extracted from the time information, and the measured electric field strength reaches the upper limit threshold or higher, the base station is selected based on the candidate information. Connection is possible without doing A base station based on the candidate information after the delay time corresponding to the base station with which wireless communication is currently established has elapsed. This can be regarded as a wireless communication control method characterized by switching the establishment destination of wireless communication.
A wireless communication terminal that moves along a predetermined movement path; and a base station antenna that is arranged at predetermined intervals along the movement path and has directivity in a direction opposite to the movement direction of the wireless communication terminal. A wireless communication control method for establishing wireless communication with any one of a plurality of base stations provided, wherein wireless communication is established with any of the base stations, and wireless communication is currently established. When the electric field strength in the wireless communication with the base station is measured and the measured electric field strength reaches a predetermined upper limit threshold or more, the wireless communication with the base station is performed corresponding to each base station. Wireless communication is established from candidate information in which one or a plurality of candidate base stations that are candidates for the establishment of the next wireless communication and the priority order of the plurality of candidate base stations are determined. The above indication corresponding to the base station The base station extracts, upon switching the establishment target radio communication by selecting the currently connectable base station from among the candidate base station in accordance with the priorities, are those the movement path comprises a plurality of branch paths, The base station in which the plurality of base stations includes a plurality of branch destination base stations arranged in each of the branch paths, and the candidate information is located before a branch point to each of the branch paths in the movement path The candidate base stations corresponding to the stations are determined to include the branch destination base stations arranged in the branch paths, and after wireless communication with the branch destination base station is established, As a wireless communication control method characterized by determining whether or not a branch destination base station is appropriate as a wireless communication establishment destination, and switching to another branch destination base station when the wireless communication establishment destination is not appropriate Also catch It is possible.

According to the present invention, since the next base station is selected from one or a plurality of candidate base stations set for each base station, the electric field strength measured by the electric field strength measuring means is If the wireless communication terminal is switched to the next base station before reaching the upper limit threshold set in advance and the wireless communication terminal passes through the base station that is currently establishing wireless communication, Switching to the base station can be prevented, and the subsequent wireless communication by the wireless communication terminal can be stabilized.
In addition, when the base station after the wireless communication establishment destination of the wireless communication terminal is switched is the branch destination base station, it is determined whether or not the branch destination base station is appropriate. In some cases, even if the wireless communication terminal is erroneously connected to a branch destination base station arranged on a different route from the route traveled by switching the establishment destination of the wireless communication to another branch destination base station, Stable wireless communication can be obtained by connecting to an appropriate branch destination base station.

The schematic diagram which shows schematic structure of the radio | wireless communications system X which concerns on embodiment of this invention. The block diagram which shows schematic structure of the radio | wireless communication terminal Y which concerns on embodiment of this invention. The figure which shows an example of candidate table T1 memorize | stored in the radio | wireless communication terminal Y which concerns on embodiment of this invention. The figure which shows an example of the communication setting table T2 memorize | stored in the radio | wireless communication terminal Y concerning embodiment of this invention. The flowchart for demonstrating an example of the procedure of the hand-over process which the radio | wireless communication terminal Y which concerns on embodiment of this invention performs. The figure for demonstrating the result of a handover process. The figure for demonstrating the result of a handover process. The figure for demonstrating the result of a handover process. The schematic diagram which shows schematic structure of the radio | wireless communications system X1 which concerns on Example 2 of this invention. The figure which shows an example of the transition of the electric field strength in the radio | wireless communications system X1 which concerns on Example 2 of this invention. The figure which shows an example of candidate table T1 'memorize | stored in the radio | wireless communication terminal Y concerning Example 2 of this invention. The figure which shows an example of the communication setting table T2 'memorize | stored in the radio | wireless communication terminal Y which concerns on Example 2 of this invention. The flowchart for demonstrating an example of the procedure of the hand-over process which the radio | wireless communication terminal Y which concerns on Example 2 of this invention performs. The schematic diagram which shows schematic structure of the radio | wireless communications system X2 which concerns on Example 3 of this invention. The flowchart for demonstrating an example of the procedure of the hand-over process which the radio | wireless communication terminal Y which concerns on Example 3 of this invention performs. The figure which quoted FIG. 3 of patent document 1. FIG. The figure for demonstrating the case where selection of the next base station is started when the electric field strength becomes below the lower threshold K1 in the radio communication system X.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
As shown in FIG. 1, a radio communication system X according to the present embodiment includes a radio communication terminal Y and a plurality of base stations W1 to W3. In the following, an unspecified base station among the base stations W1 to W3 is referred to as a base station W.
In the wireless communication system X, wireless communication is established between the wireless communication terminal Y and any one of the base stations W1 to W3, and wireless signals are transmitted and received. At this time, between the wireless communication terminal Y and the base station W, wireless communication conforming to a wireless LAN communication standard (for example, IEEE802.11a, b, g, n) is executed according to a communication protocol such as TCP / IP. Is done.
The wireless communication terminal Y is mounted on the head of a vehicle 10 (train, car, etc.) that travels (moves) along a predetermined track L (movement route) such as a track or road. Move along L. Here, the right direction in FIG. 1 is the traveling direction of the vehicle 10 and is in front of the vehicle 10. In the present embodiment, the case where the wireless communication terminal Y is mounted on the vehicle 10 will be described as an example, but the present invention is not limited to this. For example, the wireless communication terminal Y may be mounted on a moving object that moves on a belt conveyor (an example of a movement path) in a production factory or the like.

The base stations W1 to W3 are arranged at predetermined intervals along the trajectory L along which the wireless communication terminal Y moves. In FIG. 1, base stations W1 to W3 are illustrated as base stations arranged along the trajectory L. However, the same applies to the preceding stage of the base station W1 and the subsequent stage of the base station W3 at predetermined intervals. Base stations are arranged. Of course, a plurality of vehicles on which the wireless communication terminal Y is mounted run on the track L in the same manner as the vehicle 10.
Further, in the wireless communication system X, another track is provided in parallel with the track L, and wireless communication is performed with a vehicle traveling in the opposite direction to the vehicle 10 along the track. A base station W11 and the like are arranged on the trajectory. At this time, the base station W11 has radio communication directivity in a direction opposite to the traveling direction of the vehicle.

Here, a schematic configuration of the base stations W1 to W3 will be described with reference to FIG.
Each of the base stations W1 to W3 is common in that it includes antenna units 21 and 22 (hereinafter abbreviated as “antennas 21 and 22”) and wireless communication units 23 and 24.
On the other hand, the base station W1 is connected to the base stations W2 and W3 in that a management unit 30 is wired to the wireless communication unit 23 and can perform wired communication with the management unit 30. Different. The management unit 30 is an information processing apparatus such as a personal computer provided with a monitor (not shown) for displaying an image taken by the vehicle 10. The base station W1 may perform wireless communication with the management unit 30. Further, each of the base stations W1 to W3 may be connected to the management unit 30 by wire.

The antenna 21 (an example of an antenna for a base station) has two antenna elements having directivity in one direction, and diversity that preferentially uses the one having the better radio wave condition among the two antenna elements. It is an antenna. Of course, the antenna 21 may have only one antenna element.
In the base station W, the two antenna elements of the antenna 21 are oriented so that the directing direction is opposite to the moving direction of the vehicle 10 (left direction in FIG. 1). That is, the antenna 21 has radio communication directivity in a direction opposite to the moving direction of the radio communication terminal Y mounted on the vehicle 10 moving along the track L.
On the other hand, the antenna 22 is a diversity antenna including, for example, two antenna elements having directivity in both left and right directions. The two antenna elements of the antenna 22 are oriented so that the directing direction is bidirectional in both the moving direction of the vehicle 10 and the direction opposite to the moving direction (left and right bidirectional in FIG. 1). That is, the antenna 22 has radio communication directivity in the moving direction of the vehicle 10 and in the direction opposite to the moving direction.

The wireless communication units 23 and 24 include control devices such as arithmetic devices such as CPUs and various storage devices. The wireless communication units 23 and 24 execute wireless communication processing using the antennas 21 and 22 by executing processing according to the control program stored in the storage device. Note that the wireless communication units 23 and 24 are wired and can perform wired communication between each other.
Specifically, the wireless communication unit 23 performs wireless communication processing for transmitting and receiving wireless signals to and from the wireless communication terminal Y using the antenna 21. In addition, the wireless communication unit 23 uses a predetermined frame set as a beacon signal including a MAC address (or an IP address or the like) as identification information of the base stations W1 to W3 on which the wireless communication unit 23 is mounted. Transmission is performed from the antenna 21 intermittently every time. For example, the beacon signal is transmitted at intervals of 10 ms to 100 ms. As a result, the wireless communication terminal Y receives the beacon signal transmitted from the wireless communication unit 23 every predetermined time. Here, the case where the MAC address is included in the beacon signal will be described as an example. However, when the communication channel of the communication frequency is different for each of the base stations W1 to W3, the beacon signal varies depending on the communication channel. It is also possible to identify the base station W of the signal transmission source.
On the other hand, the wireless communication unit 24 performs wireless communication processing for transmitting and receiving wireless signals to and from adjacent base stations using the antenna 22. For example, the radio communication unit 24 of the base station W1 includes the base station W2 arranged on the right side of the base station W1 in FIG. 1 or a base station (not shown) arranged on the left side of the base station W1 in FIG. Wireless communication with In the wireless communication system X, base stations other than the base station W1 connected to the management unit 30 are directly connected to the base station W1 by the wireless communication unit 24 or indirectly through a base station therebetween. Thus, communication is performed with the management unit 30 by performing wireless communication. For example, when the base station W2 receives a radio signal transmitted from the radio communication terminal Y, the base station W2 transmits the radio signal to the management unit 30 via the base station W1.

Next, a schematic configuration of the wireless communication terminal Y will be described with reference to FIG.
As shown in FIG. 2, the wireless communication terminal Y includes an antenna unit 11 (hereinafter abbreviated as “antenna 11”), a camera 12, and a wireless communication control device 13.
The antenna 11 has two antenna elements 11a and 11b having directivity in one direction, and is a diversity antenna that preferentially uses the better one of the two antenna elements 11a and 11b. is there. Of course, the antenna 11 may have only one antenna element.
In the wireless communication terminal Y, the two antenna elements 11a and 11b of the antenna 11 are oriented such that the pointing direction thereof is the moving direction of the vehicle 10 (the right direction in FIG. 1). That is, the antenna 11 has directivity of wireless communication in the moving direction of the wireless communication terminal Y mounted on the vehicle 10 moving along the track L. The antenna 11 only needs to be able to transmit and receive radio waves in the moving direction of the wireless communication terminal Y, and may be capable of transmitting and receiving radio waves in the direction opposite to the moving direction.
The camera 12 is disposed at the top of the vehicle 10 and captures an image that can be seen in front of the vehicle 10. For example, the camera 12 is an analog video camera, a digital video camera, or the like. In the wireless communication terminal Y, video data captured by the camera 12 is encoded into IP packet data or the like by the wireless communication control device 13 and transmitted by wireless communication.

As shown in FIG. 2, the wireless communication control apparatus 13 includes a wireless LAN module 131, a handover control unit 132, an information storage unit 133, and the like.
The wireless LAN module 131 performs wireless communication with the base station W by transmitting and receiving wireless signals via the antenna 11. As described above, the wireless LAN module 131 is compliant with a general wireless LAN communication standard (for example, IEEE802.11a, b, g, n).
In addition, the wireless LAN module 131 acquires a MAC address corresponding to each of the base stations W1 to W3 from beacon signals individually transmitted from the base stations W1 to W3. As described above, since the beacon signal includes identification information such as the MAC address of the local station, by acquiring the MAC address included in the beacon signal, the beacon signal transmission source The base station W can be specified.
Further, the wireless LAN module 131 has an electric field strength measurement function for measuring electric field strength (RSSI) which is the strength of the wireless signal received by the antenna 11. Specifically, the wireless LAN module 131 measures electric field strength by measuring power induced in the antenna 11 by the wireless signal. For example, the wireless LAN module 131 individually measures the electric field strength in wireless communication with each of the base stations W1 to W3 based on the beacon signals individually transmitted from the base stations W1 to W3.
In the wireless LAN module 131, the measurement of the electric field strength by the electric field strength measurement function and the wireless communication between the wireless communication terminal Y and the base station W are performed in parallel by a time division process using the antenna 11. It is processed. Of course, it is conceivable to have separate antennas for each function.

The handover control unit 132 includes an arithmetic unit such as an MPU and a control device such as a RAM and a ROM, and executes various processes according to a predetermined control program. Of course, the wireless LAN module 131 and the handover control unit 132 may be configured as an integrated control device or electric circuit.
Specifically, the handover control unit 132 is configured to determine the field strength of wireless communication with each of the base stations W measured by the wireless LAN module 131 and a later-described candidate table stored in the information storage unit 133. Based on T1 and the communication setting table T2, a handover process (see the flowchart in FIG. 5) described later is performed to sequentially switch base stations that are wireless communication establishment destinations (communication partners) of the wireless communication terminal Y.
Thereby, in the wireless communication system X, video data captured by the camera 12 of the wireless communication terminal Y is transmitted to any of the base stations W1 to W3, and the video data is transmitted to the management unit 30. The The handover process executed by the handover control unit 132 will be described in detail later.

By the way, as described above, in the wireless communication system X, the wireless communication terminal Y has directivity in the moving direction, and the base stations W1 to W3 are in a direction opposite to the moving direction of the wireless communication terminal Y. This configuration has directivity.
Therefore, for example, when the wireless communication terminal Y has established wireless communication with the base station W1, a wireless signal received from the base station W1 as the wireless communication terminal Y approaches the base station W1. Becomes higher (see FIG. 17).
However, when the wireless communication terminal Y passes through the base station W1, the wireless communication terminal Y suddenly deviates from the wireless communication directing range of the base station W1. Therefore, when the wireless communication terminal Y passes through the base station W1, the electric field strength from the base station W1 obtained by the wireless communication terminal Y is predetermined as the wireless communication terminal Y approaches the base station W1. It reaches the maximum value at, and then decreases rapidly.

Therefore, in the wireless communication terminal Y, the electric field strength in the wireless communication with the base station W where the wireless communication is currently established is measured, and the measured electric field strength has reached the preset upper limit handover threshold or more. In this case, it is conceivable to select the next base station and switch the wireless communication establishment destination. The next base station selected at this time is generally the one having the highest electric field strength, for example, based on the electric field strength of the radio signal from each of the base stations W in the radio communication terminal Y. Conceivable.
As a result, the wireless communication terminal Y selects and switches the next base station W before passing through the base station W where the wireless communication is currently established, that is, before the electric field strength in the wireless communication is sharply reduced. Therefore, it is possible to prevent the wireless communication from being interrupted when the base station W is switched. In this regard, in the conventional system, as shown in FIG. 17, switching is performed after the electric field strength of the base station in communication suddenly decreases, so there is a possibility that wireless communication may be interrupted during the switching. It was. In addition, since the wireless communication terminal Y selects a base station to establish the next wireless communication only when the electric field strength is equal to or higher than the handover threshold, a large amount of data is required in normal wireless communication. Communication can be realized.

  However, in such a configuration, before the wireless communication terminal Y suddenly decreases the electric field strength in wireless communication with the base station W with which wireless communication is currently established, that is, the wireless communication terminal Y performs wireless communication. At the time before passing through the established base station, the next base station W is selected and switched. Therefore, at that time, the electric field strength of wireless communication with the base station W that should be connected next is not necessarily sufficiently high. Therefore, for example, when the base station W having the highest electric field strength is selected as the base station W to be connected next based only on the electric field strength obtained at that time, the base station that is different from the base station to be connected next is originally selected. And subsequent wireless communication may become unstable.

On the other hand, in the wireless communication terminal Y, a candidate table T1 (an example of candidate information) and a communication setting table T2 (delay time) used in a handover process (see the flowchart of FIG. 5) described later are stored in the information storage unit 133. Specific correspondence information including an example of information) is stored in advance. The information storage unit 133 is a storage unit such as a nonvolatile memory, and is an example of a candidate information storage unit and a delay time storage unit. Then, the handover control unit 132 executes a handover process based on the unique correspondence information.
As a result, the wireless communication connection destination can be switched to an appropriate base station as much as possible even before passing through the base station W where the wireless communication is currently established, and the stability of the wireless communication is ensured. be able to. Of course, the candidate table T1 and the communication setting table T2 may be stored in the information storage unit 133 as integral table information.

Hereinafter, an example of the candidate table T1 and the communication setting table T2 will be described with reference to FIGS. 3 and 4, and then a handover process executed by the handover control unit 132 will be described with reference to FIG.
First, as shown in FIG. 3, the candidate table T1 corresponds to each of the base stations W1 to W3, and when the wireless communication with the base stations W1 to W3 is established, the next wireless communication is established. Candidate base stations 1 to 3 that are the previous candidates are predetermined. The candidate table T1 may define one candidate base station corresponding to each of the base stations W1 to W3.
When the wireless communication terminal Y moves along the predetermined track L, in principle, the wireless communication terminal Y performs wireless communication with any of the base stations W1 to W3. The base station W suitable for the next wireless communication establishment destination is known. Therefore, the candidate table T1 predetermines a suitable base station W as the next base station according to the position of the wireless communication terminal Y.
Specifically, in the candidate table T1 shown in FIG. 3, when wireless communication with the base station W1 is established, the base stations are set as candidate base stations 1, 2, and 3 that are candidates for the next wireless communication establishment destination. Stations W2, W3 and W4 are defined. In the candidate table T1, the base station W is identified by the MAC address. Here, the MAC addresses of the base stations W1 to W3 are (0000.0000.0001 to 0000.0000.0003), and thereafter, similarly, the base stations W4, W5,. The MAC address is (0000.0000.0004, 0000.0000.0005, ...). Similarly, for the base stations W2, W3..., When the wireless communication is established with each of the base stations W, the candidate base stations 1 to 3 that are candidates for the establishment destination of the next wireless communication are individually set. It has been established.
The numbers “1 to 3” of the candidate base stations 1 to 3 indicate the priority of selection. In the handover process (S9) described later, the base station is selected according to the priority. Become.

On the other hand, the communication setting table T2 shown in FIG. 4 is used in a handover process executed when wireless communication with the base stations W1 to W3 is established for each of the base stations W1 to W3. As various parameters, “handover threshold”, “delay time”, and “connection destination release flag” are determined in advance.
On the trajectory L, the radio propagation environment in radio communication with the radio communication terminal Y is different for each of the base stations W1 to W3, but when the radio communication terminal Y moves along the trajectory L, The contents of the radio propagation environment in the radio communication with the next connected base station W depending on which of the base stations W1 to W3 the radio communication terminal Y is performing radio communication with. Is known. Therefore, the communication setting table T2 stores “handover threshold”, “delay time”, and “connection open flag” suitable as various parameters used in the handover process in advance according to the position of the wireless communication terminal Y. It is determined.

Here, the “handover threshold” means that the electric field strength has reached the maximum value for each base station W as the wireless communication terminal Y approaches the base station W in which communication is established, that is, in the handover process. It is an upper limit threshold set as an index for determining the timing of switching to the next base station. Specifically, when the maximum value of the electric field strength of wireless communication between the wireless communication terminal Y and each of the base stations W is (K + α), the “handover threshold” corresponding to each of the base stations W is It is set to a value lower by a predetermined value α than the maximum value (K + α) of the electric field strength for each base station W. For example, in the example shown in FIG. 4, the “handover threshold” of the base station W1 is “−65 dBm”, the “handover threshold” of the base station W2 is “−70 dBm”, and the “handover threshold” of the base station W3. "Is set to" -68 dBm ".
The “delay time” is the time from when the timing for switching the wireless communication establishment destination to the next base station arrives until when switching is actually performed. This time is determined by the movement of the wireless communication terminal Y until the “delay time” elapses for each base station W when wireless communication is established with the base station W. , The time until the wireless communication with the base station to be connected next to the base station W in which the wireless communication is established is set in advance. For example, if a building such as a station building existing between two base stations is in the way and wireless communication cannot be performed with the next base station, avoid that building and connect to the next base station. This is the time required for the wireless communication terminal Y to move to a position where wireless communication can be performed. It is also possible to set “delay distance” instead of “delay time”.
Furthermore, the “connection destination release flag” indicates whether or not to use the candidate table T1 when selecting the next base station in the handover process, that is, whether or not to limit the connection destination candidates. . For example, when there is a building such as a station building between two base stations, it is difficult to perform wireless communication with the next base station while avoiding the building. "Is set to ON.

Hereinafter, an example of a procedure of the handover process executed by the handover control unit 132 in the wireless communication terminal Y will be described according to the flowchart of FIG. 5, S1, S2,... Represent processing procedure (step) numbers. Note that the present invention can also be understood as a wireless communication control method for executing each step of the handover process.
The handover process is executed by the handover control unit 132 in a state where wireless communication is established between the wireless communication terminal Y and any of the base stations W1 to W3. The base station that first establishes wireless communication is, for example, the base station with the highest electric field strength at that time. Thereafter, in the wireless communication terminal Y, the handover process is executed, so that the base station to which wireless communication is established is sequentially switched to the base stations W1 to W3 as the vehicle 10 moves. Thereby, in the wireless communication system X, video data captured by the camera 12 of the wireless communication terminal Y is transmitted to any of the base stations W1 to W3, and the video data is transmitted to the management unit 30. The

(Steps S1 and S2)
First, the handover control unit 132 determines the electric field of the wireless communication with the base station that is currently establishing wireless communication, which is measured continuously or every predetermined time by the electric field strength measurement function of the wireless LAN module 131. The strength is acquired from the wireless LAN module 131 (step S1). At this time, the wireless LAN module 131 for measuring the electric field strength of the wireless communication with the base station currently establishing the wireless communication corresponds to the electric field strength measuring means. The electric field strength measured here may be an average value for each predetermined period.
Next, in step S2, the handover control unit 132 determines whether wireless communication with the base station W is currently established. For example, when the electric field strength measured by the wireless LAN module 131 is equal to or lower than a preset lower limit value, it is determined that wireless communication has not been established.
Here, if it is determined that wireless communication is not currently established (No in S2), the process proceeds to step S21. If it is determined that wireless communication is currently established (Yes in S2). Side), the process proceeds to step S3.

(Steps S21 to S22)
In step S21, the handover control unit 132 searches for an arbitrary base station W capable of wireless communication at the current position, and establishes wireless communication with the searched base station W. At this time, the base station W that is a candidate for the connection destination is not limited to the candidate base stations 1 to 3 defined in the candidate table T1. Accordingly, even if wireless communication cannot be established with any of the candidate base stations 1 to 3, wireless communication by the wireless communication terminal Y can be performed by arbitrarily selecting a base station existing in the vicinity. Can continue.
In step S22, the handover control unit 132 stores the base station W after the regular switching in step S10 described later or the base station W when the delay timer is activated in step S71 described later in the internal memory. To remember. Thereby, for example, the base station W connected immediately before switching the connection destination in step S21 is stored. Thereafter, the process proceeds to step S3.

(Steps S3 to S4)
Thereafter, in step S3, the handover control unit 132 reads the candidate table T1 and the communication setting table T2 stored in the information storage unit 133, and selects “candidate bases corresponding to the base station currently establishing the wireless communication”. Various types of information such as “stations 1 to 3”, “handover threshold”, “delay time”, and “connection open flag” are extracted. However, when a base station is stored in advance in step S22 or step S62 described later, “candidate base stations 1 to 3”, “handover threshold”, “delay time”, “ Various types of information such as “connection destination release flag” are extracted. Therefore, for example, when the base station W2 is switched to the base station W3 in step S21 or step S61, information corresponding to the base station W3 after the switching is not extracted in step S3. By extracting the information corresponding to the previously connected base station W2, the adverse effect of being connected to the base station W4 that should be connected next to the base station W3 is prevented.
In step S4, it is determined whether or not a delay timer started in step S71 described later is in operation. Here, when the delay timer is operating (Yes side of S4), the process proceeds to step S41, and when not operating (No side of S4), the process proceeds to step S5. Steps S41 and S71 will be described later.

(Step S5)
Next, in step S5, the handover control unit 132 determines that the electric field strength measured by the wireless LAN module 131 is equal to or greater than a handover threshold determined corresponding to the base station with which wireless communication is currently established. Judge whether there is.
Here, if it is determined that the electric field intensity measured in step S1 is equal to or higher than the handover threshold (Yes side of S5), it is determined that the wireless communication terminal Y has approached the base station in communication. Then, the process proceeds to step S6. In step S5, while it is determined that the electric field strength measured in step S1 is not equal to or higher than the handover threshold (No side in S5), the process returns to step S1.
As described above, in the wireless communication system X, the electric field of the base station excluding the base station until the electric field strength in the wireless communication with the base station with which wireless communication is currently established becomes equal to or higher than the handover threshold. Strength measurement is not performed. Therefore, in normal wireless communication of the wireless communication terminal Y, it is possible to realize large-capacity data transmission such as video data captured by the camera 12 using only the antenna 11.

(Step S6)
Subsequently, in step S6, the handover control unit 132 sets the “connection destination release flag” corresponding to the base station with which wireless communication is currently established to ON (= “1”) based on the communication setting table T2. ) Or not.
If it is determined that the “connection destination release flag” is ON (= “1”) (Yes in S6), the process proceeds to step S61, and the “connection destination release flag” is OFF ( = "0") (No in S6), the process proceeds to step S7.

(Steps S61 to S62)
In step S61, the handover control unit 132 searches for an arbitrary base station W capable of wireless communication at the current position, establishes wireless communication with the searched base station W, and performs processing in step S7. To migrate. At this time, the base station W that is a candidate for the connection destination is not limited to the candidate base stations 1 to 3 defined in the candidate table T1.
Thus, when the wireless communication with the predetermined base station whose connection destination release flag is set to ON in advance is established, the electric field strength measured in step S1 has reached the handover threshold or more. At the time, any base station that can be currently connected without selecting a base station based on the candidate table T1 is selected, and the establishment destination of wireless communication is switched. Thereby, it is possible to continue wireless communication between the wireless communication terminal Y and the base station W.
In step S62, the handover control unit 132 stores the base station W after the regular switching in step S10 described later or the base station W when the delay timer is activated in step S71 described later in the internal memory. To remember. Thereby, for example, the base station W connected immediately before switching the connection destination in step S61 is stored. As described above, when the base station W is stored here, in the step S3, the handover control unit 132 displays information corresponding to the stored base station in the candidate table T1 and the communication setting. It will be extracted from the table T2.

(Step S7)
Next, in step S7, the handover control unit 132 determines whether or not the “delay time” corresponding to the base station currently establishing the wireless communication is set based on the communication setting table T2 (ie, 0 second). It is determined whether or not it is larger.
At this time, if it is determined that “delay time” is not set (No side of S7), the process proceeds to step S8, and if it is determined that “delay time” is set ( (Yes side of S7), the process proceeds to step S71.

(Steps S71 and S41)
In step S71, the handover control unit 132 activates a delay timer for measuring time for determining whether the “delay time” has elapsed. Thereby, after the electric field intensity acquired in step S1 reaches the handover threshold or more (Yes side of S5), until the “delay time” elapses (No side of S41), the step S4 It is determined that the delay timer is operating (Yes in S4), and step S41 is executed.
In step S41, until the delay timer times out, that is, until the “delay time” elapses (No side of S41), the process returns to step S1, and the “delay time” has elapsed and the delay timer has elapsed. Is timed out (Yes in S41), the process proceeds to step S8.

(Step S8)
Thereafter, when it is determined that the delay time is not set (“delay time” is 0 second) (No side of S7), or when the delay time has elapsed and the delay timer has timed out in step S41. In the subsequent step S8, the handover control unit 132 extracts the base station W that is currently capable of wireless communication with the wireless communication terminal Y.
Specifically, the field strength of the beacon signal from each of the base stations W measured by the handover controller 132 by the field strength measurement function of the wireless LAN module 131 is equal to or greater than a preset reference value. It is determined whether or not wireless communication with each base station W is possible. Further, a communicable base station may be determined by frequency scanning.
At this time, the handover control unit 132 may determine whether or not wireless communication is currently possible for only the candidate base stations 1 to 3 corresponding to the base station with which wireless communication is currently established. Conceivable. As a result, it is not necessary to determine whether or not wireless communication with all the base stations existing in the vicinity is possible, and the processing load is reduced.

(Steps S9 to S10)
Thereafter, in step S9, the handover control unit 132 selects the base stations extracted as base stations capable of wireless communication from among the candidate base stations 1 to 3 corresponding to the base stations with which wireless communication is currently established. The base station having the highest priority among the stations is selected as the next base station.
That is, in the step S9, a base station belonging to only one of the base station extracted in the step S8 and the candidate base stations 1 to 3 is not selected. In step S9, the base station having the highest electric field strength is selected from the base stations belonging to both the base station extracted in step S8 and the candidate base stations 1 to 3 without being limited to the priority order. May be.
In step S10, the handover control unit 132 executes processing for switching the communication destination from the base station in which wireless communication is currently established to the base station selected in step S9. Here, the handover control unit 132 when executing the processes of steps S8 to S10 corresponds to the base station switching means.
As a result, wireless communication is established between the wireless communication terminal Y and the base station W selected in step S9. After step S10, the process returns to step S1, and the handover process is repeatedly executed. At this time, the base station stored in step S22 or step S62 is reset.

As described above, in the wireless communication system X, in steps S8 to S10, the next base station is selected from the candidate base stations 1 to 3 set for each base station W. For this reason, the field strength measured in step S1 reaches the handover threshold value set in advance, and the wireless communication terminal Y establishes the next wireless communication destination before passing through the base station that is currently establishing wireless communication. Can be prevented from being switched to a base station other than the candidate base stations 1 to 3, and the subsequent wireless communication by the wireless communication terminal Y can be stabilized.
Further, if the base station arranged at the next position of the base station is not necessarily the most suitable position immediately before the base station currently performing wireless communication, the wireless communication terminal Y moves until the delay time described above. During wireless communication, a seamless wireless communication environment can be realized by performing wireless communication with an arbitrarily selected base station, and after the delay time has elapsed, switching to the appropriate next base station to be originally connected It can be performed.

Hereinafter, when the vehicle 10 travels on the track L from the state where the wireless communication between the wireless communication terminal Y and the base station W1 is established using FIG. 1 and FIGS. An example of a result of executing the handover process will be described.
Here, in FIG. 1 and FIG. 6 to FIG. 8, the position where the electric field intensity from the base station W1 obtained by the wireless communication terminal Y is the maximum is the position where the electric field intensity from the base station W2 is the maximum. Is P2. Further, a station building (building) exists between the base station W2 and the base station W3, and the base station W2 is provided immediately before the station building. Therefore, at the position P2, it is assumed that the station building is in the way and wireless communication cannot be performed between the wireless communication terminal Y and the base station W3. The same problem arises when the communication propagation environment is complicated for other reasons, such as when the track L is curved, not limited to buildings.
Further, a position where wireless communication with the base station W11 is possible after the wireless communication terminal Y passes through the base station W2 is P3. Furthermore, after the wireless communication terminal Y passes through the base station W2, a position where wireless communication with the base station W3 is possible is defined as P4. At this time, the time required for the vehicle 1 to move from the position P2 to the position P4 is “3 seconds”.

First, when the vehicle 10 starts running from the state shown in FIG. 1 and the vehicle 10 reaches the position P1, the electric field strength of wireless communication between the wireless communication terminal Y and the base station W1 is It reaches or exceeds the handover threshold (−65 dBm) defined in the communication setting table T2 (Yes side in S5). At this time, as shown in FIG. 4, the “connection open flag” corresponding to the base station W1 is OFF (No side of S6), and the “delay time” is not set (No side of S7). Shifts to step S8.
At this time, since there is no building such as a station building between the position P1 and the base station W2, the wireless communication terminal Y can perform wireless communication with the base station W2. Therefore, in the subsequent steps S8 to S10, the base station W2 which is the base station having the highest priority order to be connected next while establishing wireless communication with the base station W1 and currently capable of wireless communication is selected. Thus, the establishment destination of the wireless communication of the wireless communication terminal Y is switched.

Next, as shown in FIG. 6, when the vehicle 10 reaches the position P2, the electric field strength in wireless communication with the base station W2 reaches a handover threshold (−70 dBm) or more (Yes side of S5).
Here, as shown in FIG. 4, in the communication setting table T2, the “connection destination open flag” corresponding to the state where the wireless communication between the wireless communication terminal Y and the base station W2 is established is ON (= 1) (Yes side of S6). Therefore, the process proceeds to step S61, and wireless communication is started with an arbitrary base station. At this time, since the electric field strength of the wireless communication with the base station W2 is the highest, the wireless communication with the base station W2 is continued.
At this time, as shown in FIG. 4, the “delay time” corresponding to the state where the wireless communication between the wireless communication terminal Y and the base station W2 is established is set to “3 seconds” (S7). Yes side), the process proceeds to step S71, and the delay timer is activated.

Then, as shown in FIG. 7, when the vehicle 10 reaches the position P3 and wireless communication cannot be performed between the wireless communication terminal Y and the base station W2 (No side of S2), The establishment destination of wireless communication is switched to the base station W11 capable of wireless communication at that time (S21). At this time, in step S22, it is stored that the base station with which wireless communication was previously established is the base station W2.
Thereafter, as shown in FIG. 8, when “3 seconds” as the “delay time” elapses and the delay timer times out (Yes in S41), the process proceeds to step S8. At this time, the vehicle 10 has reached the position P4.
In Steps S8 to S10, the handover control unit 132 sets the corresponding candidate base stations 1 to 3 when wireless communication with the base station W2 is established based on the candidate table T1. The base station W3 which is the base station having the highest priority and is currently capable of wireless communication is selected, and the wireless communication terminal Y establishes the wireless communication destination from the base station W11 to the base station W3. .
As described above, when the base station W3 arranged at the next position of the base station W2 is not optimal at the position immediately before the base station W2 currently establishing the wireless communication due to the presence of the station building, the wireless communication is performed. A seamless wireless communication environment can be realized by performing wireless communication with the arbitrarily selected base station W11 during the delay time until the terminal Y passes the station building, and after the delay time has elapsed, Switching to an appropriate next base station W3 to be originally connected can be performed.

By the way, in the above embodiment, when the “delay time” is set and the wireless communication is established with the base station in which the “connection destination open flag” is set to ON in advance, When the electric field strength measured in step S1 reaches or exceeds a preset handover threshold (Yes side of S5), switching to an arbitrary base station until the delay time elapses (S61), Although the case where the wireless communication establishment destination is switched based on the candidate table T1 when the delay time has elapsed (S8 to S10) has been described, the present invention is not limited to this.
For example, by omitting the steps S6, S61 to S62, until the delay time elapses after the electric field strength measured in the step S1 reaches or exceeds a preset handover threshold, Except when the wireless communication is interrupted (No in S2), the wireless communication with the base station currently establishing the wireless communication is continued, and the establishment destination of the wireless communication is switched after the delay time has elapsed. Conceivable. As a result, for example, when there is a building such as a station building immediately after the base station that is currently establishing wireless communication, at least the wireless communication is blocked by electromagnetic waves from the building, and wireless communication is performed at an appropriate timing. The establishment destination can be switched.
In addition, when wireless communication is established with a predetermined base station in which the “connection open flag” is set to ON in advance (Yes in S6), even after the “delay time” has elapsed, Establish wireless communication by selecting any currently connectable base station from the base stations including the base stations other than the candidate base stations 1 to 3 without selecting the base station based on the candidate table T1. It is also possible to perform processing so as to switch the destination. As a result, a gap in a communicable range is generated between two consecutive base stations on a certain track L, and the gap is interpolated by a communicable range of a base station different from the two base stations. However, when it is known that the boundary of the communicable range of each of these base stations cannot be clearly defined, wireless communication with any base station is possible without limiting the connection order or candidate base stations. By establishing communication, wireless communication by the wireless communication terminal Y can be continued. When wireless communication is established with other base stations excluding the predetermined base station, the base station selection based on the candidate table T1 may be executed.

In the radio communication system X according to the above embodiment, the case where the vehicle 10 moves along one track L has been described as an example. Hereinafter, a case where a plurality of branch routes are included in the moving route of the vehicle 10 will be described.
FIG. 9 is a diagram illustrating a schematic configuration of the wireless communication system X1 according to the second embodiment. In addition, the same code | symbol is attached | subjected about the structure similar to the said wireless communication system X, and the description is abbreviate | omitted.
As shown in FIG. 9, in the wireless communication system X1, the track L, which is the moving path of the vehicle 10, is branched in a different direction from a branch point P10 located downstream in the traveling direction from the base station W1. Branches to paths L1 and L2. A branch destination base station W21 and a branch destination base station W31 are arranged along the branch paths L1 and L2. Further, a base station W22 is arranged on the branch path L1 after the branch destination base station W21, and a base station W32 is arranged on the branch path L2 after the branch destination base station W31.
The branch destination base stations W21 and W31 and the base stations W22 and W32 include the antennas 21 and 22, the wireless communication units 23 and 24, and the like, similarly to the base stations W2 and W3. Hereinafter, the base station W1, the branch destination base stations W21 and W31, the base stations W22 and W32, etc. are collectively referred to as a base station, and when any of the branch destination base stations W21 and W31 is indicated. It is called a branch destination base station.
In the wireless communication system X1 configured as described above, the movement route of the wireless communication terminal Y mounted on the vehicle 10 differs depending on which of the branch routes L1 and L2 the vehicle 10 moves. The base station to be connected next to the base station W1 as the establishment destination of the wireless communication of the wireless communication terminal Y is the branch destination base station when the wireless communication terminal Y moves along the branch path L1. When the wireless communication terminal Y moves along the branch path L2, it is the branch destination base station W31.

Here, FIG. 10 shows that in the wireless communication system X1, when the vehicle 10 moves along one of the branch paths L1 and L2, the wireless communication terminal Y establishes the wireless communication that is moving. As shown, the transition of the field strength of the wireless communication in each of the case of being connected to the correct base station (solid line) and the case of being connected to the wrong base station (broken line) is shown. The correct base station is the branch destination base station W21 when moving along the branch path L1, and the branch destination base station W31 when moving along the branch path L2. The erroneous base station is the branch destination base station W31 when moving along the branch path L1, and the branch destination base station W21 when moving along the branch path L2.
Points P11 to P13 shown in FIG. 10 are travel positions of the wireless communication terminal Y and correspond to the points P11 to P13 shown in FIG. Here, the point P11 is after the wireless communication terminal Y has established the wireless communication destination from the base station W1 to any one of the separation destination base stations W21 and W31, and from the branch point P10. Is the front (upstream) position. Further, the point P12 is a position where the wireless communication terminal Y has moved away from the other branch path by a predetermined amount after starting to move along the branch path L1, L2 from the branch point P10. The point P13 is a position where the electric field strength of the wireless communication is expected to reach the handover threshold or higher when the wireless communication terminal Y establishes wireless communication with the correct base station. It is.

As shown in FIG. 10, there is no difference in electric field strength between the points P11 to P12 between the case where the wireless communication terminal Y establishes the wireless communication is correct and the case where it is incorrect.
On the other hand, between the point P12 and the point P13, the separation distance between the branch paths L1 and L2 is somewhat large, and if the branch destination base station to which the wireless communication terminal Y is established is correct, The wireless communication terminal Y approaches the branch destination base station. However, if the branch destination base station to which the wireless communication is established is incorrect, the wireless communication terminal Y moves away from the branch destination base station. Therefore, as shown in FIG. 10, when the wireless communication establishment destination of the wireless communication terminal Y is correct, the electric field strength tends to increase gradually, but the wireless communication establishment destination is incorrect. There is a tendency for the electric field strength to decrease gradually.
When the branch base station to which the wireless communication is established is correct, the wireless communication terminal Y gradually approaches the branch base station and the electric field strength increases, and the electric field strength at the point P13 is the handover. The threshold is exceeded. However, if the branch destination base station to which the wireless communication is established is incorrect, the radio communication terminal Y gradually moves away from the branch destination base station and the electric field strength decreases, and the electric field strength is reduced by the handover. Never exceed the threshold.
Therefore, in the wireless communication system X1, the handover control unit 132 of the wireless communication terminal Y executes a handover process (see the flowchart in FIG. 13) described later, whereby the wireless communication establishment destination is the branch destination base station. After switching to, it is determined whether or not the branch destination base station is appropriate as a wireless communication establishment destination. If not, the wireless communication establishment destination is switched to another branch destination base station.

11 and 12 show examples of the candidate table T1 ′ and the communication setting table T2 ′ stored in the information storage unit 133 of the wireless communication terminal Y in the wireless communication system X1.
As shown in FIG. 11, in the candidate table T1 ′, a maximum of three candidate base stations 1 to 3 are set in advance as candidates for the next wireless communication establishment destination corresponding to each base station.
In particular, candidate base stations 1 to 3 corresponding to the base station W1 include at least the branch destination base stations W21 and W31 arranged on the branch paths L1 and L2, respectively. If there are more branch paths from the track L, each of the branch destination base stations arranged on all the branch paths should be registered in advance as a candidate base station corresponding to the base station W1. That's fine.

As shown in FIG. 12, the communication setting table T2 ′ stores a MAC address corresponding to each base station and various parameters used in handover processing (see FIG. 13) described later. The various parameters include “handover threshold”, “branch flag”, and “connected flag”.
Here, the “handover threshold” is set in advance for each base station, and the electric field strength reaches the maximum value when the wireless communication terminal Y approaches the base station where the communication is established. That is, it is an index value for determining the switching timing to the next base station in the handover process.
The “branch flag” indicates whether or not the base station is a branch destination base station arranged on the branch path. Specifically, in the wireless communication system X1, the “branch flag” corresponding to the base stations W1, W22, W32 is set in advance to “0” indicating that it is not a branch destination base station, and the branch destination base stations W21, W31 The “branch flag” corresponding to is preset to “1” indicating that it is a branch destination base station.
Further, the “connected flag” indicates whether or not the wireless communication terminal Y is already connected to a branch destination base station. The handover control unit 132 sets “1” for a connected branch destination base station and “0” for a branch destination base station that is not yet connected in a handover process described later.

Hereinafter, an example of the procedure of the handover process executed by the handover control unit 132 of the wireless communication terminal Y in the wireless communication system X1 according to the second embodiment will be described according to the flowchart of FIG. Here, S111, S112,... In FIG. 13 represent processing procedure (step) numbers. Note that the present invention can also be understood as a wireless communication control method for executing each step of the handover process.
Also in the handover process, similarly to the handover process (see FIG. 5) described in the above embodiment, a process based on the delay time and the connection destination release flag may be executed.

(Steps S111 to S112, S121)
First, the handover controller 132 executes steps S111 to S112 similar to steps S1 to S2 (see FIG. 5).
Specifically, the handover control unit 132 is currently establishing wireless communication that is measured continuously or every predetermined time (for example, about 1 second) set by the field strength measurement function of the wireless LAN module 131. The field strength of wireless communication with the base station is acquired from the wireless LAN module 131 (step S111).
In step S112, the handover control unit 132 determines whether radio communication is currently established with any base station.
Here, if it is determined that wireless communication is not currently established (No side of S112), the process proceeds to step S121. In step S121, the handover control unit 132 searches for an arbitrary base station capable of wireless communication at the current position, and establishes wireless communication with the searched base station.
On the other hand, when it is determined that wireless communication is currently established (Yes in S112), the process proceeds to step S113.

(Steps S113 to S114)
In step S113, the handover control unit 132 determines, from the candidate table T1 ′ and the communication setting table T2 ′ stored in the information storage unit 133, the “candidate base station corresponding to the base station that is currently establishing wireless communication. Various information such as “1 to 3”, “handover threshold”, “branch flag”, and “connected flag” are extracted.
In step S114, the handover control unit 132 determines whether or not the “branch flag” corresponding to the base station currently establishing the wireless communication is “1”, that is, whether or not the branch base station. to decide. If it is determined that the “branch flag” is “0” (No in S114), the process proceeds to step S115, and if it is determined that the “branch flag” is “1” (S114). Yes side), the process proceeds to step S122.

(Step S115)
If the base station where the current wireless communication is established is not a branch destination base station, in the subsequent step S115, the handover control unit 132 determines that the electric field strength measured by the wireless LAN module 131 is the current wireless communication established. It is determined whether or not the threshold value is equal to or higher than a handover threshold determined in accordance with the base station that is present.
Here, when it is determined that the electric field strength measured in step S111 is equal to or higher than the handover threshold (Yes in S115), it is determined that the wireless communication terminal Y has approached the base station in communication. Then, the process proceeds to step S116. In step S115, while it is determined that the electric field strength measured in step S111 is not equal to or higher than the handover threshold (No in S115), the process returns to step S111.

(Step S116)
In step S116, the handover control unit 132 executes a process for extracting a base station that is currently capable of wireless communication.
Specifically, whether the field strength of the beacon signal from each base station measured by the handover controller 132 by the field strength measurement function of the wireless LAN module 131 is equal to or greater than a preset reference value. Therefore, it is determined whether or not wireless communication with each of the base stations is possible. Further, a communicable base station may be determined by frequency scanning.
At this time, the handover control unit 132 may determine whether or not wireless communication is currently possible for only the candidate base stations 1 to 3 corresponding to the base station with which wireless communication is currently established. Conceivable. As a result, it is not necessary to determine whether or not wireless communication with all the base stations existing in the vicinity is possible, and the processing load is reduced.

(Steps S117 to S118)
After that, in step S117, the handover control unit 132 extracts the base stations extracted as base stations capable of wireless communication from among the candidate base stations 1 to 3 corresponding to the base stations with which wireless communication is currently established. The base station having the highest priority among the stations is selected as the next base station. In step S117, the base station having the highest electric field strength is selected from the base stations belonging to both the base station extracted in step S116 and the candidate base stations 1 to 3 without being limited to the priority order. May be.
In step S118, the handover control unit 132 executes processing for switching the communication destination from the base station in which wireless communication is currently established to the base station selected in step S117. Thereby, wireless communication is established between the wireless communication terminal Y and the base station selected in step S117. After step S118, the process returns to step S111, and the handover process is repeatedly executed.

(Steps S122 to S123)
On the other hand, if it is determined in step S114 that the “branch flag” is “1”, that is, if the base station currently establishing wireless communication is one of the branch destination base stations W21 and W31, step S122 follows. In S126, the handover control unit 132 determines whether or not the branch destination base station that is currently establishing the wireless communication is appropriate as the wireless communication establishment destination, and the wireless communication establishment destination is determined according to the determination result. To control.
Specifically, first, in step S122, the handover control unit 132 sets the “connected flag” corresponding to the branch destination base station currently established in the information storage unit 133 to “1”. To do.
In step S123, the handover control unit 132 determines whether or not the electric field strength in the wireless communication with the branch base station that is currently establishing the wireless communication tends to decrease. For example, the handover control unit 132 determines whether or not the electric field strength tends to decrease by calculating the slope of the change in the electric field strength based on the predetermined number of times of the electric field strength measured in step S111. To do. Note that the method for determining whether or not the electric field strength is decreasing is not limited to this. For example, whether or not the electric field strength tends to decrease is determined based on the calculation result of the moving average over a certain period or the calculation result obtained by smoothing the measured electric field strength by a predetermined filtering process. It is possible to do.
If it is determined in step S123 that the electric field strength tends to decrease (Yes in S123), the branch base station that is currently establishing wireless communication is not appropriate as the wireless communication establishment destination, and the process proceeds to step S124. To do. On the other hand, if it is determined that the electric field strength is increasing or leveling and is not decreasing (No in S123), the branch base station that is currently establishing the wireless communication is appropriate. The process proceeds to step S115, and the wireless communication with the branch base station currently establishing the wireless communication is continued.
By the way, depending on the shape of the branch paths L1 and L2, the field strength may be increased even after the branch destination base station is appropriate after switching the wireless communication connection destination of the wireless communication terminal Y to the branch destination base station. On the other hand, the electric field strength may increase when the branch base station is not appropriate. Therefore, until the predetermined delay time elapses after the connection is switched to the branch destination base station, the determination process in step S123 is retained (not executed), and after the predetermined delay time elapses, the process proceeds to step S123. It is conceivable to execute a determination process. Thereby, the influence by the shape of the branch paths L1 and L2 can be eliminated. The predetermined delay time may be stored in advance in the communication setting table T2 ′ corresponding to each base station.

(Steps S124 to S126)
In step S124, the handover control unit 132 refers to the candidate table T1 ′ and determines whether or not there is a branch destination base station whose “connected flag” is “0”. In other words, there are branch destination base stations that are located on a different branch route from the branch route on which the branch base station that is currently establishing wireless communication is located, and that have not yet been attempted for communication connection. It is determined whether or not.
Here, when there is no branch destination base station whose “connected flag” is “0”, that is, after switching to all branch destination base stations, wireless communication with the branch destination base station is not appropriate. (No side of S124), the process proceeds to step S126.
When the process proceeds to step S126, the “connected flag” corresponding to all branch destination base stations is reset by the handover control unit 132, and the process returns to step S121. Thereby, in step S121, the establishment destination of the wireless communication is switched to an arbitrary base station that can communicate at the present time.
On the other hand, if it is determined that there is a branch base station whose “connected flag” is “0” (Yes in S124), the process proceeds to step S125.

On the other hand, in step S125, the handover controller 132 determines from the branch destination base station that is currently establishing wireless communication that another branch destination whose “connected flag” has been confirmed to be present in step S124 is “0”. The establishment destination of wireless communication is switched to the base station. Thereafter, the process returns to step S111, and the same process as described above is repeatedly executed. Thereby, even when the wireless communication terminal Y establishes the wireless communication destination not the branch destination base station arranged along the movement path of the wireless communication terminal Y, the wireless communication terminal Y subsequently moves along the movement path of the wireless communication terminal Y. It will be connected to the arranged branch destination base station.
For example, when the vehicle 10 moves from the branch point P10 to the branch path L1, the branch destination base station in which the wireless communication terminal Y is established on the branch path L1. In the case of W21, wireless communication with the branch destination base station W21 is continued as it is, and thereafter, the base station is sequentially switched to the base stations after the base station W22.
On the other hand, when the vehicle 10 moves from the branch point P10 to the branch path L1, the wireless communication terminal Y establishes the wireless communication destination on the other branch destination path L2 instead of the branch path L1. When the branch destination base station W31 is arranged, the wireless communication establishment destination is switched from the branch destination base station W21 to the branch destination base station W31, and then sequentially to the base stations after the base station W32. It will be switched.

As described above, in the wireless communication system X1, when the base station after switching is the branch destination base station (here, the branch destination base stations W21 and W31), the suitability of the branch destination base station is determined by wireless communication. If it is not appropriate, the wireless communication establishment destination is switched to another branch destination base station.
Therefore, even when the wireless communication terminal Y is mistakenly connected to a branch destination base station disposed on a route different from the route on which the wireless communication terminal Y moves, the wireless communication terminal Y can subsequently connect to an appropriate branch destination base station to obtain stable wireless communication. Can do.

In the second embodiment, the case where the suitability of the connection-destination branch-destination base station is determined based on the electric field strength in the radio communication with the branch-destination base station that is currently establishing wireless communication has been described.
In the third embodiment, as another method for determining the suitability of the branch destination base station of the connection destination, a method of determining based on the position of the wireless communication terminal Y mounted on the vehicle 10 will be described.
FIG. 14 is a diagram illustrating a schematic configuration of the wireless communication system X2 according to the third embodiment. In addition, the same code | symbol is attached | subjected about the structure similar to the said radio | wireless communications system X, X1, and the description is abbreviate | omitted.
In the wireless communication system X2 according to the third embodiment, the wireless communication terminal Y has a GPS receiver and the like, and has a latitude coordinate acquisition function for acquiring the latitude coordinates of its current location by the GPS receiver. Yes. In addition, if the position coordinate of the said wireless communication terminal Y can be acquired, it will not be restricted to what uses GPS.

In the wireless communication system X2, the information storage unit 133 of the wireless communication terminal Y stores at least the background coordinates R1 (x1, y1) of the base station W1 and the background coordinates R2 (x10, y10) of the branch point P10, Background coordinates R3 (x11, y11), R4 (x12, y12) of each of the bending points P21, P22 in each of the branch paths L1, L2, and background coordinates R5 (x21, y21), R6 of each of the branch destination base stations W21, W31 (X31, y31) is stored. The background coordinates R1 to R6 are an orthogonal coordinate system when the vehicle 10 is viewed from above, and are merely an example of information indicating the position coordinates of each point.
Further, the information storage unit 133 of the wireless communication terminal Y passes through the vehicle 10 from the base station W1 to the branch destination base stations W21 and W31 corresponding to the branch paths L1 and L2, respectively. The background coordinates R1 to R6 are stored as information for specifying each straight line route. Specifically, the route information corresponding to the branch route L1 is the latitude coordinates R1, R2, R3, R5, and the route information corresponding to the branch route L2 is the latitude coordinates R1, R2, R4, R6. is there.

Hereinafter, an example of the procedure of the handover process executed by the handover control unit 132 of the wireless communication terminal Y in the wireless communication system X2 according to the third embodiment will be described according to the flowchart of FIG. Here, S131, S132,... In FIG. 15 represent processing procedure (step) numbers. Note that the present invention can also be understood as a wireless communication control method for executing each step of the handover process.
Here, the same processing steps (S111 to S118, S121) as the handover processing described in the second embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the handover process according to the third embodiment, steps S131 to S134 are executed by the handover control unit 132 instead of steps S122 to S126 in the handover process according to the second embodiment (see FIG. 13).

(Steps S131 to S132)
First, when the base station that is currently establishing wireless communication is the branch base station (Yes in S114), in the subsequent step S131, the handover control unit 132 uses the GPS or the like with the background coordinate acquisition function to The background coordinates of the wireless communication terminal Y are acquired. Here, it is assumed that the latitude coordinates R20 (x20, y20) of the position P20 shown in FIG. 14 are obtained as the latitude coordinates of the wireless communication terminal Y.
Next, in step S132, the handover control unit 132 acquires the shortest distance from the wireless communication terminal Y to each of the travel routes L1 and L2 as the separation distance. Here, the handover control unit 132 when executing the processing corresponds to the shortest distance acquisition unit.
Specifically, as shown in FIG. 14, the handover control unit 132 draws a perpendicular to each of the branch routes L1 and L2 from the position P20 of the wireless communication terminal Y. The shortest distance to the point that intersects L2 is calculated. At this time, the handover control unit 132 acquires the background coordinates R1 to R6 stored in the information storage unit 133, the route information corresponding to each of the branch routes L1 and L2, and the step S131. The separation distance can be calculated based on the background coordinates of the wireless communication terminal Y. Of course, the lengths of the separation distances d1 and d2 may be acquired by image processing.
For example, if the distance between the position P20 and the branch path L1 is d1, the distance d1 can be calculated based on the following equations (1) to (5). Here, Lx1 and Ly1 are intersection coordinates of a perpendicular line from the position P20 to the branch path L1 and the branch path L1. The distance d2 between the position P20 and the branch path L2 may be calculated similarly.
Ls = (x20-x10) * (x11-x10) + (y20-y10) * (y11-y10) (1)
Lb = (x11-x10) ^ 2 + (y11-y10) ^ 2 (2)
Lx1 = x10 + (x11-x10) * Ls / Lb (3)
Ly1 = y10 + (y11-y10) * Ls / Lb (4)

(Step S133)
In step S133, the handover control unit 132 determines that the difference in the separation distance between the two branch paths from the shortest separation distance from the position P20 of the wireless communication terminal Y calculated in step S132 is the same. It is determined whether or not a predetermined threshold value is set in advance.
Specifically, in the wireless communication system X2, since there are two branch paths, the branch paths L1 and L2, the separation distance between the position P20 of the wireless communication terminal Y and the branch path L1 calculated in step S132. It is determined whether or not the difference (| d1-d2 |) between d1 and the position P20 of the wireless communication terminal Y and the separation distance d2 of the branch path L2 is equal to or greater than the predetermined threshold value.
Here, the predetermined threshold value is set to a distance longer than a distance predicted as an error occurring in the background coordinates acquired using the GPS by the handover control unit 132. For example, when the distance between the branch paths L1 and L2 is 30 m at the maximum and a measurement error of the current position of the wireless communication terminal Y is predicted to occur at a maximum of 10 m, it is slightly larger than the measurement error. 15m may be set as the predetermined threshold value. Thereby, the influence of the measurement error by GPS can be eliminated.
If it is determined in step S133 that the difference in the separation distance is not equal to or greater than the predetermined threshold (No side in S133), the process proceeds to step S115.
On the other hand, if it is determined that the difference in the separation distance is equal to or greater than the predetermined threshold (Yes in S133), the process proceeds to step S134.

(Step S134)
In step S134, the handover control unit 132 identifies the branch path with the shortest separation distance calculated in step S132, and uses the branch destination base station arranged on the branch path as the establishment destination of wireless communication. Set. Specifically, if the base station that is currently establishing wireless communication is a branch destination base station arranged on the branch path with the shortest separation distance calculated in step S132, the establishment of wireless communication continues. Is done. On the other hand, if the base station that is currently establishing wireless communication is not the branch destination base station arranged on the branch path with the shortest separation distance calculated in step S132, the wireless communication establishment destination is the above-described step S132. Is switched to the branch destination base station arranged on the branch path with the shortest separation distance calculated in (1).
For example, as shown in FIG. 14, the position P20 obtained as the background coordinates of the wireless communication terminal Y is the distance d1 of the branch path L1 from the wireless communication terminal Y and the branch path L2 from the wireless communication terminal Y. Let us consider a case where the difference between the distance L2 and the separation distance d2 reaches a predetermined threshold value or more, and the separation distance d1 of the branch path L1 is shorter than the separation distance d2 of the branch path L2. In this case, when the wireless communication terminal Y establishes wireless communication with the branch destination base station W21 arranged on the branch path L1, the wireless communication is continued as it is. On the other hand, when the wireless communication terminal Y has established wireless communication with the branch destination base station W31 arranged on the branch path L2, the establishment destination of the wireless communication is the branch destination base station. It is switched to W21.
As described above, in the wireless communication system X2, when the base station after switching is the branch destination base station (here, the branch destination base stations W21, W31), the suitability of the branch destination base station is determined. Judging from the position information of the communication terminal Y, if it is not appropriate, the wireless communication establishment destination is switched to another branch destination base station.
Therefore, even when the wireless communication terminal Y is erroneously connected to a base station disposed on a route different from the route on which the wireless communication terminal Y moves, the wireless communication terminal Y can subsequently connect to an appropriate branch destination base station to obtain stable wireless communication. .

  By the way, as another method for determining the suitability of the branch destination base station of the connection destination, it is conceivable to use the two different methods described in the second and third embodiments in combination. For example, when the vehicle 10 is traveling outdoors, the handover control unit 132 performs determination based on position information (see Example 3), and the vehicle 10 is traveling indoors such as underground. In some cases, it is conceivable to switch the determination method in time so that the determination based on the electric field strength (see Example 2) is performed. The handover control unit 132 preferentially performs the determination based on the position information of the wireless communication terminal Y (see Example 3), and the electric field can be obtained on the condition that the position information cannot be acquired. It is also conceivable to switch the determination method so that the determination based on the intensity (see Example 2) is performed.

L ... Tracks L1, L2 ... Branch routes W1-W3, W21, W32 ... Base stations W21, W31 ... Branch destination base stations X, X1, X2 ... Wireless communication system Y ... Wireless communication terminal 10 ... Vehicles 11, 21, 22 ... Antenna unit 11a, 11b ... Antenna element 12 ... Camera 13 ... Wireless communication control device 131 ... Wireless LAN module 132 ... Handover control unit 133 ... Information storage unit 23, 24 ... Wireless communication unit 30 ... Management unit

Claims (9)

A plurality of base stations having base station antennas arranged at predetermined intervals along a predetermined movement path and having directivity in a direction opposite to the movement direction of the wireless communication terminal moving along the movement path. A wireless communication terminal that performs wireless communication with any one of the base stations,
Electric field strength measuring means for measuring electric field strength in wireless communication with a base station where wireless communication is currently established;
Corresponding to each base station, priority is given to one or a plurality of candidate base stations and a plurality of candidate base stations that are candidates for a next wireless communication establishment destination when wireless communication with the base station is established. Candidate information storage means for storing candidate information for which ranking is determined;
When the wireless communication is currently established with any one of the base stations and the electric field strength measured by the electric field strength measuring means reaches a preset upper limit threshold or more, the above-mentioned information stored in the candidate information storage means The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information, and a base station that is currently connectable is selected from the candidate base stations according to the priority order. Base station switching means for switching between,
Ri name with a,
Corresponding to each base station, when a wireless communication with the base station is established, a connection destination release flag that determines whether or not to use the candidate information as a candidate for a next wireless communication establishment destination is And further comprising a stored connection destination release flag storage means, wherein the base station switching means is set so that the connection destination release flag does not use the candidate information in the base station where wireless communication is currently established. Then, without selecting a base station based on the candidate information stored in the candidate information storage means, select any currently connectable base station and switch the establishment destination of wireless communication, or
Corresponding to each base station, a delay time storage means for storing delay time information in which a delay time until switching to the next base station when wireless communication with the base station is established is further stored The base station switching means extracts the delay time corresponding to the base station with which wireless communication is currently established from the delay time information stored in the delay time storage means, and measures the electric field strength. After the delay time has elapsed after the electric field intensity measured by the means reaches a preset upper threshold or more, the establishment of wireless communication is switched, or
Corresponding to each base station, when a wireless communication with the base station is established, a connection destination release flag that determines whether or not to use the candidate information as a candidate for a next wireless communication establishment destination is Corresponding to the stored connection destination release flag storage means and each of the base stations, a delay time determined until switching to the next base station when wireless communication with the base station is established Delay time storage means for storing information, wherein the base station switching means is set so that the connection destination release flag does not use the candidate information in the base station where wireless communication is currently established. If the electric field intensity measured by the electric field intensity measuring means reaches the upper limit threshold or more, the current connection is made without selecting the base station based on the candidate information stored in the candidate information storing means. Possible assignment The base station is selected and the establishment destination of the wireless communication is switched, and then the delay time corresponding to the base station with which the wireless communication is currently established has elapsed, and then the above-mentioned stored in the candidate information storage means wireless communication terminal, wherein Rukoto switched establishment target radio communication by performing the selection of the base station based on the candidate information. A plurality of base stations having base station antennas arranged at predetermined intervals along a predetermined movement path and having directivity in a direction opposite to the movement direction of the wireless communication terminal moving along the movement path. A wireless communication terminal that performs wireless communication with any one of the base stations,
Electric field strength measuring means for measuring electric field strength in wireless communication with a base station where wireless communication is currently established;
Corresponding to each base station, priority is given to one or a plurality of candidate base stations and a plurality of candidate base stations that are candidates for a next wireless communication establishment destination when wireless communication with the base station is established. Candidate information storage means for storing candidate information for which ranking is determined;
When the wireless communication is currently established with any one of the base stations and the electric field strength measured by the electric field strength measuring means reaches a preset upper limit threshold or more, the above-mentioned information stored in the candidate information storage means The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information, and a base station that is currently connectable is selected from the candidate base stations according to the priority order. Base station switching means for switching between,
Ri name with a,
The movement path includes a plurality of branch paths, and the plurality of base stations include a plurality of branch destination base stations arranged in the branch paths,
The candidate information stored in the candidate information storage means is arranged in each branch path as the candidate base station corresponding to the base station located before the branch point to each branch path in the movement path It is determined to include the above branch destination base station,
After the base station switching means establishes wireless communication with the branch destination base station, it determines whether the branch destination base station is appropriate as an establishment destination of wireless communication. wireless communication terminal, wherein Rukoto switched established destination to another of the branch destination base station. After the base station switching means establishes wireless communication with the branch destination base station, when the field strength measured by the field strength measuring means tends to decrease, the branch destination base station The wireless communication terminal according to claim 2 , wherein the wireless communication terminal determines that the establishment destination is not appropriate and switches the establishment destination of wireless communication to the other branch destination base station. The candidate stored in the candidate information storage means when the base station switching means determines that wireless communication with the branch destination base station is not appropriate even after switching to all the branch destination base stations. 3. The wireless communication terminal according to claim 2 , wherein the base station is not selected based on the information, but an arbitrary base station that is currently connectable is selected and a wireless communication establishment destination is switched. Further comprising shortest distance acquisition means for acquiring the shortest distance from the wireless communication terminal to each of the branch paths;
After the base station switching means establishes wireless communication with the branch base station, a difference between two shortest distances from the shorter one of the shortest distances acquired by the shortest distance acquisition means is set in advance. When the wireless communication is established with the separated path base station arranged on the branch path having the shortest shortest distance when the threshold value is reached, the wireless communication is continued, When wireless communication is established with the separated path base station arranged on the branch path, the wireless communication establishment destination is switched to the separated path base station arranged on the branched path with the shortest shortest distance. The wireless communication terminal according to claim 2 , wherein the wireless communication terminal is a wireless communication terminal. A wireless communication terminal that moves along a predetermined movement path; and a plurality of base stations that are arranged at predetermined intervals along the movement path, wherein one of the wireless communication terminal and the plurality of base stations A wireless communication system for establishing wireless communication with one base station,
Each of the base stations includes a base station antenna having directivity in a direction opposite to the moving direction of the wireless communication terminal,
The wireless communication terminal establishes wireless communication with the base station corresponding to each base station and electric field strength measuring means for measuring the electric field strength in wireless communication with the base station with which wireless communication is currently established. Candidate information storage means for storing candidate information in which one or a plurality of candidate base stations that are candidates for the establishment of the next wireless communication and the priority order of the plurality of candidate base stations are stored, When the wireless communication is currently established with any one of the base stations and the electric field strength measured by the electric field strength measuring means reaches a preset upper limit threshold or more, the above-mentioned information stored in the candidate information storage means The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information, and a base station that is currently connectable is selected from the candidate base stations according to the priority order. Switching base station Ri name and a conversion means,
Corresponding to each base station, when a wireless communication with the base station is established, a connection destination release flag that determines whether or not to use the candidate information as a candidate for a next wireless communication establishment destination is And further comprising a stored connection destination release flag storage means, wherein the base station switching means is set so that the connection destination release flag does not use the candidate information in the base station where wireless communication is currently established. Then, without selecting a base station based on the candidate information stored in the candidate information storage means, select any currently connectable base station and switch the establishment destination of wireless communication, or
Corresponding to each base station, a delay time storage means for storing delay time information in which a delay time until switching to the next base station when wireless communication with the base station is established is further stored The base station switching means extracts the delay time corresponding to the base station with which wireless communication is currently established from the delay time information stored in the delay time storage means, and measures the electric field strength. After the delay time has elapsed after the electric field intensity measured by the means reaches a preset upper threshold or more, the establishment of wireless communication is switched, or
Corresponding to each base station, when a wireless communication with the base station is established, a connection destination release flag that determines whether or not to use the candidate information as a candidate for a next wireless communication establishment destination is Corresponding to the stored connection destination release flag storage means and each of the base stations, a delay time determined until switching to the next base station when wireless communication with the base station is established Delay time storage means for storing information, wherein the base station switching means is set so that the connection destination release flag does not use the candidate information in the base station where wireless communication is currently established. If the electric field intensity measured by the electric field intensity measuring means reaches the upper limit threshold or more, the current connection is made without selecting the base station based on the candidate information stored in the candidate information storing means. Possible assignment The base station is selected and the establishment destination of the wireless communication is switched, and then the delay time corresponding to the base station with which the wireless communication is currently established has elapsed, and then the above-mentioned stored in the candidate information storage means wireless communication system according to claim Rukoto switched establishment target radio communication by performing the selection of the base station based on the candidate information. A wireless communication terminal that moves along a predetermined movement path; and a plurality of base stations that are arranged at predetermined intervals along the movement path, wherein one of the wireless communication terminal and the plurality of base stations A wireless communication system for establishing wireless communication with one base station,
Each of the base stations includes a base station antenna having directivity in a direction opposite to the moving direction of the wireless communication terminal,
The wireless communication terminal establishes wireless communication with the base station corresponding to each base station and electric field strength measuring means for measuring the electric field strength in wireless communication with the base station with which wireless communication is currently established. Candidate information storage means for storing candidate information in which one or a plurality of candidate base stations that are candidates for the establishment of the next wireless communication and the priority order of the plurality of candidate base stations are stored, When the wireless communication is currently established with any one of the base stations and the electric field strength measured by the electric field strength measuring means reaches a preset upper limit threshold or more, the above-mentioned information stored in the candidate information storage means The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information, and a base station that is currently connectable is selected from the candidate base stations according to the priority order. Switching base station Will and a conversion means,
The movement path includes a plurality of branch paths, and the plurality of base stations include a plurality of branch destination base stations arranged in the branch paths,
The candidate information stored in the candidate information storage means is arranged in each branch path as the candidate base station corresponding to the base station located before the branch point to each branch path in the movement path It is determined to include the above branch destination base station,
After the base station switching means establishes wireless communication with the branch destination base station, it determines whether the branch destination base station is appropriate as an establishment destination of wireless communication. A radio communication system characterized in that the establishment destination is switched to another branch destination base station. A plurality of wireless communication terminals that move along a predetermined movement path, and a base station antenna that is arranged at predetermined intervals along the movement path and has directivity in a direction opposite to the movement direction of the wireless communication terminal A wireless communication control method for establishing wireless communication with any one of the base stations,
The wireless communication with any base station is currently established, and the electric field strength in the wireless communication with the base station with which the wireless communication is currently established is measured, and the measured electric field strength is equal to or greater than a preset upper threshold. When wireless communication with the base station is established corresponding to each base station, the one or more candidate base stations that are candidates for the establishment destination of the next wireless communication and the plurality of base stations The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information in which the priority order of the candidate base station is determined, and the currently connectable base station is selected from the candidate base stations When switching the establishment of wireless communication ,
In the base station where the wireless communication is currently established, the candidate information is set as a candidate for the next wireless communication establishment destination when the wireless communication with the base station is established for each base station. If the connection destination release flag that determines whether or not to use is set not to use the candidate information, the base station is not selected based on the candidate information, and any currently connectable base station is selected. Switch the establishment destination of wireless communication, or
Corresponding to each base station, when wireless communication with the base station is established, the wireless communication is currently established from delay time information in which the delay time until switching to the next base station is determined Extracting the delay time corresponding to the base station and switching the establishment destination of the wireless communication after the delay time has elapsed after the measured electric field intensity reaches or exceeds a preset upper threshold, or
In the base station where the wireless communication is currently established, the candidate information is set as a candidate for the next wireless communication establishment destination when the wireless communication with the base station is established for each base station. If the connection destination release flag for which use is determined is set not to use the candidate information, the following is performed when wireless communication with the base station is established for each base station. The delay time corresponding to the base station with which wireless communication is currently established is extracted from the delay time information in which the delay time until switching to the base station is determined, and the measured electric field strength exceeds the upper threshold At that time, without selecting a base station based on the candidate information, an arbitrary base station that is currently connectable is selected and the wireless communication establishment destination is switched. At the above delay corresponding to the station From There has elapsed, the radio communication control method characterized by switching the establishment target radio communication by performing the selection of the base station based on the candidate information. A plurality of wireless communication terminals that move along a predetermined movement path, and a base station antenna that is arranged at predetermined intervals along the movement path and has directivity in a direction opposite to the movement direction of the wireless communication terminal A wireless communication control method for establishing wireless communication with any one of the base stations,
The wireless communication with any base station is currently established, and the electric field strength in the wireless communication with the base station with which the wireless communication is currently established is measured, and the measured electric field strength is equal to or greater than a preset upper threshold. When wireless communication with the base station is established corresponding to each base station, the one or more candidate base stations that are candidates for the establishment destination of the next wireless communication and the plurality of base stations The candidate base station corresponding to the base station with which wireless communication is currently established is extracted from the candidate information in which the priority order of the candidate base station is determined, and currently connectable from the candidate base stations according to the priority order When selecting the base station and switching the establishment destination of wireless communication,
The movement path includes a plurality of branch paths, and the plurality of base stations include a plurality of branch destination base stations arranged in the branch paths,
The candidate information includes the branch destination base station arranged in each of the branch paths as the candidate base station corresponding to the base station located before the branch point to each of the branch paths in the movement route. It is stipulated in
After wireless communication with the branch destination base station is established, it is determined whether or not the branch destination base station is appropriate as a wireless communication establishment destination. A wireless communication control method characterized by switching to a destination base station.