JP7444106B2 - wireless communication device - Google Patents

Description

The present invention relates to a wireless communication device that is mounted on a mobile object and performs wireless communication with any one of a plurality of access points.

An example of such a wireless communication device is disclosed in Japanese Unexamined Patent Publication No. 2014-192577 (Patent Document 1). Hereinafter, in the description of this background art, the reference numerals in Patent Document 1 will be cited in parentheses.

The wireless communication device of Patent Document 1 is installed in a mobile terminal (2) as a mobile object, and performs wireless communication with an access point (60). This wireless communication device includes a radio field strength detection unit (50) that detects the radio field strength (X1) in wireless communication with the connected access point (60), and the radio field strength (X1) is set to a roaming threshold (Xth). A determination is made at predetermined time intervals as to whether or not the value is less than . Then, when it is determined that the radio field strength (X1) is lower than the roaming threshold (Xth), roaming processing is performed to switch the access point (60) to be connected. In addition, this wireless communication device predicts the predicted position to which the mobile terminal (2) is expected to move every time a set time that is set shorter than the above-mentioned predetermined time elapses, and the predicted predicted position is connected to the mobile terminal (2). It is determined whether or not the access point (60) is within a range where wireless communication is possible. If it is determined that the predicted position of the mobile terminal (2) is not within the wireless communication range, roaming processing is performed.

Japanese Patent Application Publication No. 2014-192577

As described above, in the wireless communication device of Patent Document 1, in addition to the case where the reception strength from the connected access point is determined to be below the threshold, the predicted position where the mobile object is expected to move is connected. The device is also configured to perform roaming processing even if it is determined that the access point is not within the range where wireless communication is possible. By performing the roaming process also in this latter case, according to Patent Document 1, the roaming process can be performed at optimal timing even when the mobile object is moving at high speed.

By the way, according to the knowledge obtained by the present inventor, even when a mobile object is stopped and connected to the same access point, deterioration in communication quality such as poor communication may occur. Such deterioration in communication quality may be caused by, for example, ambient noise. In the wireless communication device of Patent Document 1, when the mobile body is stopped, roaming processing is not performed unless the reception strength from the access point to which it is connected falls below a threshold value. Therefore, even if the mobile unit is stopped and connected to the same access point, and the communication quality deteriorates due to factors other than a decline in reception strength from the access point, roaming processing will not be performed. There is a possibility that the quality of communication with the access point will remain degraded.

Therefore, it is necessary to realize a wireless communication device that can avoid the deterioration in communication quality that can occur when a mobile object is stopped and connected to the same access point, and can maintain appropriate communication quality with the access point. desired.

A first wireless communication device according to the present disclosure is a wireless communication device that is mounted on a mobile object and performs wireless communication with any of a plurality of access points, and includes a transmitting and receiving unit that transmits and receives electromagnetic waves to and from the access point. a reception strength determination unit that determines the reception strength of electromagnetic waves from each of the plurality of access points; and a roaming process that selects one of the plurality of access points and connects to the selected access point. and a roaming processing unit that performs the roaming process when the reception strength determination unit determines that the reception strength from the connected access point has become below a specified value. The roaming processing section executes both the first processing and the second processing of performing the roaming processing at a prescribed period regardless of the reception strength determined by the reception strength determination section, and the roaming processing section performs the roaming processing according to the roaming processing. Even if the selected access point is the same as the currently connected access point, processing is performed to temporarily disconnect from the access point and then reconnect.

A second wireless communication device according to the present disclosure is a wireless communication device that is mounted on a mobile body and performs wireless communication with any of a plurality of access points, and includes a transmitting and receiving unit that transmits and receives electromagnetic waves to and from the access point. a reception strength determination unit that determines the reception strength of electromagnetic waves from each of the plurality of access points; and a roaming process that selects one of the plurality of access points and connects to the selected access point. and a roaming processing unit that performs the roaming process when the reception strength determination unit determines that the reception strength from the connected access point has become below a specified value. The mobile body executes both the first process and the second process of performing the roaming process at a prescribed period regardless of the reception strength determined by the reception strength determination unit, and the mobile body The roaming processing unit further executes a third process of performing the roaming process when the moving object moves beyond a predetermined distance from a stop position, and the predetermined distance is determined when the moving object is at its maximum speed. The distance is set to be less than the distance traveled in one period of the specified period.

A third wireless communication device according to the present disclosure is a wireless communication device that is mounted on a mobile object and performs wireless communication with any one of a plurality of access points, and includes a transmitting and receiving unit that transmits and receives electromagnetic waves to and from the access point. a reception strength determination unit that determines the reception strength of electromagnetic waves from each of the plurality of access points; and a roaming process that selects one of the plurality of access points and connects to the selected access point. and a roaming processing unit that performs the roaming process when the reception strength determination unit determines that the reception strength from the connected access point has become below a specified value. The roaming processing section executes both the first processing and the second processing of performing the roaming processing at a prescribed period regardless of the reception strength determined by the reception strength determination section, and the roaming processing section performs the roaming processing according to the roaming processing. If the selected access point is different from the currently connected access point, after the roaming process is completed, roaming notification data indicating that the connected access point has been changed is sent to the newly connected access point. Send multiple times to the access point.

According to the first to third wireless communication devices, the roaming processing unit executes the first process, so if the reception strength from the access point to which the mobile object is connected becomes less than the specified value due to movement of the mobile object, etc. can perform a roaming process and connect to the appropriate access point at that time. Furthermore, since the roaming processing unit executes the second process, the roaming process can be performed at regular intervals regardless of the strength of reception from the connected access point. Then, by performing the roaming process, it is possible to restore appropriate communication quality regardless of how good or bad the communication quality was before that. Therefore, it is possible to avoid deterioration in communication quality that may occur when a mobile object is stopped and connected to the same access point, and to maintain appropriate communication quality with the access point.

In addition, in order to avoid deterioration in communication quality due to a decrease in reception strength from the access point, it is possible to set the default value used in the first process high, but if the default value is set high, the frequency of execution of the roaming process will decrease. may become too high. In this regard, according to the first to third wireless communication devices, even if the reception strength from the connected access point does not fall below the specified value, roaming processing is performed at specified intervals to connect to an appropriate access point. can do. Therefore, by keeping the specified value to a value that prevents the roaming process from becoming too frequent, the deterioration in communication quality caused by continuing to connect to an inappropriate access point can be avoided by performing the roaming process at specified intervals. can do.

Further, according to the first wireless communication device, if the connection with the currently connected access point is maintained but the communication quality with the access point has deteriorated, the connection with the access point is temporarily disconnected. By reconnecting after doing so, it becomes easier to improve the quality of communication with the access point. In addition, even if the deterioration in communication quality as described above has not occurred, you can check the elapsed time since connecting to the access point by disconnecting from the access point and then reconnecting. This prevents the time from becoming too long and makes it easier to maintain good communication quality with the access point.

When a mobile object moves, there may be an access point more suitable than the currently connected access point even if the reception strength from the currently connected access point has not fallen below a specified value. According to the second wireless communication device, the roaming processing unit executes the third process, so in the above case, the roaming process can be performed without waiting until the roaming process by the second process is performed. Therefore, it becomes easier to quickly connect to an appropriate access point and ensure appropriate communication quality.

When multiple access points are connected to a communication partner of a mobile body (for example, a management device of a mobile body) via a switching hub, the switching hub collects identification information of the mobile body connected to the access point (for example, MAC address) is stored in the management table in association with the port to which the access point is connected. Then, the switching hub transmits the data received from the communication partner of the mobile unit from a port stored in association with the destination mobile unit of the data (hereinafter referred to as the “target mobile unit”). is transmitted to the target mobile unit via the access point to which the target mobile unit is connected. Therefore, in order to send data received from the mobile unit's communication partner to the target mobile unit, if the access point to which the target mobile unit is connected is changed due to roaming processing, the contents of the above management table must be adjusted accordingly. It is necessary to update it.

According to the third wireless communication device, when the access point to which the target mobile object is connected is changed due to roaming processing, roaming notification data is transmitted multiple times to the access point that has become the new connection destination. I can do it. Therefore, even if a communication error occurs, the probability that roaming notification data will not reach a new access point can be kept low. For example, when multiple access points are connected to a mobile communication partner via a switching hub as described above, the access point transmits the roaming notification data received from the wireless communication device to the switching hub. The contents of the above management table can be updated. According to the third wireless communication device, the roaming notification data can be reliably transmitted by the access point, so the contents of the management table can be updated more reliably.

Further characteristics and advantages of the wireless communication device will become clear from the following description of embodiments with reference to the drawings.

Perspective view of moving body Control block diagram Conceptual diagram of wireless communication system control flow diagram Diagram showing an example of the execution status of roaming processing Diagram showing another example of the execution status of roaming processing

Embodiments of a wireless communication device will be described with reference to the drawings. The wireless communication device 30 is a device that is mounted on the mobile body 1 and performs wireless communication with any one of the plurality of access points 3. Here, the term "moving object" is a concept that includes any object that can move. As the moving body 1, an article conveyance vehicle (a conveyance vehicle that conveys articles 2) as shown in FIG. 1 can be exemplified. The article transport vehicle as the moving body 1 shown in FIG. 1 includes a traveling section 10 that travels along a moving route 40, and a main body section 20 that is connected to the traveling section 10 and holds the article 2. The moving path 40 is formed along the ceiling by running rails 41, and the running section 10 includes wheels 11 that roll on the running rails 41. That is, the article transport vehicle as the moving body 1 shown in FIG. 1 is an overhead transport vehicle. Note that the moving body 1 is an article carrier other than an overhead carrier, such as an article carrier that travels along a moving route 40 (including a virtually set route) formed along the floor. Good too. Furthermore, the mobile object 1 may be an object that moves passively, such as a mobile terminal that is carried by a worker and moves with the worker.

In this embodiment, the moving object 1 is an object that actively moves along a moving route 40, like the article carrier shown in FIG. As shown in FIG. 2, the moving body 1 includes a control unit 34 that controls the operation of the moving body 1. The functions of the control unit 34 and the functions of each functional unit included in the wireless communication device 30 are realized through cooperation between hardware such as an arithmetic processing unit and a program executed on the hardware. Note that the functional units of the wireless communication device 30 shown in FIG. 2 are at least logically distinct, and do not necessarily need to be physically distinct.

The control unit 34 controls the driving of a drive unit (not shown), such as an electric motor, to cause the moving body 1 to perform a movement operation of moving along the movement route 40. Although details will be omitted, the control unit 34 derives an estimated current position that is the current estimated position of the mobile body 1 and controls the moving operation of the mobile body 1. For example, the mobile body 1 is equipped with a reading device that reads address information of information holding bodies provided at a plurality of positions along the movement route 40 (information indicating the positions where the information holding bodies are provided), and and a measuring device that measures the moving distance, and the control unit 34 reads the address information read by the reading device and the moving distance of the moving object 1 measured by the measuring device (specifically, the reading device reads the address information). The estimated current position of the moving body 1 can be derived based on the distance traveled since the reading). For example, a one-dimensional code or a two-dimensional code can be used as the information carrier, and a one-dimensional code reader or a two-dimensional code reader can be used as the reading device. Furthermore, for example, a rotary encoder can be used as the measuring device. Note that the configuration is not limited to this, and for example, the mobile body 1 includes a GPS receiver that receives GPS signals from GPS (Global Positioning System) satellites, and the control unit 34 controls the mobile body 1 based on the GPS signals. It may also be configured to derive the estimated current position.

As shown in a conceptual diagram of a wireless communication system in FIG. 3, a plurality of access points 3 are arranged so that their respective communication areas A (areas where wireless communication is possible) partially overlap. Each of the access points 3 is connected to a wired communication network N. Each of the access points 3 is installed so that its position with respect to the movement path 40 is fixed.

The access point 3 is a device that relays communication between the mobile body 1 (specifically, the wireless communication device 30 mounted on the mobile body 1) and a communication partner of the mobile body 1. In this embodiment, the communication partner of the mobile body 1 is the management device 5 that manages the mobile body 1, and the control unit 34 controls the operation of the mobile body 1 in accordance with commands from the management device 5. For example, the control unit 34 controls the movement operation of the mobile body 1 and the transfer operation of the article 2 between the mobile body 1 and the transfer target location in response to a transport command for the article 2 from the management device 5. Control.

In the example shown in FIG. 3, a plurality of access points 3 are connected to a management device 5 via a relay device 4 (here, a switching hub). The relay device 4 includes a plurality of ports to which the access points 3 are connected, and stores the identification information of the mobile unit 1 connected to the access point 3 in a management table by associating it with the port to which the access point 3 is connected. I remember it. The identification information of the mobile body 1 is, for example, the MAC (Media Access Control) address of the wireless communication device 30 installed in the mobile body 1. Then, the relay device 4 transmits the data received from the management device 5 from the port stored in association with the mobile unit 1 that is the destination of the data (hereinafter referred to as “target mobile unit”). is transmitted to the target mobile body via the access point 3 to which the target mobile body is connected.

As shown in FIG. 2, the wireless communication device 30 includes a transmitting/receiving section 31, a reception strength determining section 32, and a roaming processing section 33. The wireless communication device 30 is configured to be able to exchange information with the control unit 34. Further, the plurality of functional units included in the wireless communication device 30 are configured to be able to exchange information with each other.

The transmitting/receiving unit 31 is a functional unit that transmits and receives electromagnetic waves to and from the access point 3. The transmitting/receiving unit 31 is a communication interface that performs wireless communication with the access point 3. In this embodiment, the electromagnetic waves used for communication between the transmitter/receiver 31 and the access point 3 are radio waves, and the transmitter/receiver 31 transmits and receives radio waves to and from the access point 3 . Note that the electromagnetic waves used for communication between the transmitter/receiver 31 and the access point 3 may be electromagnetic waves other than radio waves.

The reception strength determining unit 32 is a functional unit that determines the reception strength of electromagnetic waves (radio waves in this embodiment) from each of the plurality of access points 3. The reception strength determination unit 32 determines the reception strength from each of the plurality of access points 3, for example, based on the reception strength of beacon signals periodically transmitted from the access points 3.

The roaming processing unit 33 is a functional unit that performs roaming processing. The roaming process is a process of selecting one of a plurality of access points 3 and connecting to the selected access point 3. The roaming processing unit 33 selects one access point 3 based on the determination result by the reception strength determining unit 32 in the roaming process. For example, in roaming processing, the roaming processing unit 33 selects the access point 3 with the highest reception strength. If the access point 3 selected by the roaming process is different from the currently connected access point 3, the roaming processing unit 33 disconnects from the currently connected access point 3 and connects to the selected access point 3. Perform processing. Note that if the connection with the access point 3 that was connected before the roaming process was executed has already been disconnected, the roaming processing unit 33 only performs the process of connecting to the selected access point 3.

In this embodiment, if the access point 3 selected by the roaming process is different from the access point 3 to which the connection is currently being made, the roaming processing unit 33 indicates that the access point 3 to which the connection is made has been changed after the completion of the roaming process. The roaming notification data D (see FIG. 3) is configured to be transmitted multiple times to the newly connected access point 3. The newly connected access point 3 transmits the received roaming notification data D to the relay device 4, thereby updating the contents of the above-mentioned management table in the relay device 4. Specifically, the relay device 4 transfers the identification information of the mobile unit 1 that is the transmission source of the roaming notification data D to the access point 3 that transmitted the roaming notification data D to the relay device 4 (i.e., the new mobile unit 1 of the mobile unit 1). The content of the management table is changed so that it is associated with the port to which the access point 3) is connected.

In this embodiment, even if the access point 3 selected by the roaming process is the same as the currently connected access point 3, the roaming processing unit 33 temporarily disconnects from the access point 3 and then reconnects to the access point 3. configured to perform processing. As described below, the roaming processing unit 33 is configured to execute both the first process and the second process. At least in the second process, or in both the first process and the second process, the roaming processing unit 33 performs a process of once disconnecting from the currently connected access point 3 and then reconnecting as described above. I do.

The roaming processing unit 33 executes both the first process and the second process. The first process is a process in which roaming processing is performed when the reception strength determination unit 32 determines that the reception strength from the connected access point 3 has become equal to or less than the specified value V. In the first roaming process, an access point 3 different from the currently connected access point 3 is basically selected. Further, the second process is a process of performing roaming processing at a prescribed period P regardless of the reception strength determined by the reception strength determination unit 32. The start time of the prescribed period P can be, for example, the start time or end time of the previous roaming process.

The reception strength determination unit 32 determines whether the reception strength from the currently connected access point 3 has become equal to or less than the prescribed value V at a cycle shorter than the prescribed cycle P. Therefore, the roaming processing unit 33 performs roaming processing according to the control flow shown in FIG. 4. Specifically, the roaming processing unit 33 determines whether the reception strength from the connected access point 3 has become equal to or less than the specified value V until the specified period P has elapsed (step #02: No). is repeated (step #01). Then, when it is determined that the reception strength from the connected access point 3 has become equal to or lower than the specified value V (step #01: Yes), the roaming processing unit 33 performs roaming processing (specifically, roaming processing by the first processing). processing) (step #03). Further, when the specified period P has elapsed without the reception strength from the connected access point 3 falling below the specified value V (step #01: No, step #02: Yes), the roaming processing unit 33 performs roaming processing (specific Specifically, roaming processing (second processing) is performed (step #03).

FIG. 5 schematically shows an example of the execution status of roaming processing, and FIG. 6 schematically shows another example of the execution status of roaming processing. In FIG. 5, since the mobile unit 1 is stopped until the time between time T3 and time T4, the reception strength from the access point 3 to which it is connected is maintained constant, and after that, when the mobile unit 1 moves, A situation is assumed in which the reception strength from the connected access point 3 decreases accordingly, and the reception strength from the connected access point 3 decreases to the specified value V at time T5, which is after time T4. In such a situation, time T1, time T2 when one period of prescribed period P has elapsed from time T1, time T3 when one period of prescribed period P has elapsed from time T2, and time T3 from time T3. At each time T4 when one period of the prescribed period P has elapsed, roaming processing according to the second processing is performed, and the mobile body 1 is reconnected to the access point 3 to which it is currently connected. Then, at time T5, when one period of the specified period P has not elapsed since time T4, the roaming process according to the first process is performed, and the mobile unit 1 has a reception strength lower than that of the access point 3 to which it is connected. Connected to high access point 3.

In FIG. 6, as the mobile unit 1 continues to move until time T14, the reception strength from the connected access point 3 decreases to the specified value V before the specified period P has elapsed, and after time T14, the mobile unit 1 continues to move. It is assumed that by stopping the access point 3, the reception strength from the connected access point 3 is maintained constant. In such a situation, a time T12 at which one period of the specified period P has not elapsed since time T11, a time T13 where one period of the specified period P has not elapsed from time T12, and a specified period from time T13. At each time T14 when one cycle of the cycle P has not yet elapsed, the roaming process according to the first process is performed, and the mobile unit 1 selects an access point 3 whose reception strength is higher than that of the access point 3 to which it is connected. connected to. Then, at time T15 when one period of the prescribed period P has elapsed from time T14, roaming processing according to the second processing is performed, and the mobile body 1 is reconnected to the access point 3 to which it is currently connected.

Note that the technical features of the wireless communication device 30 disclosed in this specification can also be applied to a control method for the wireless communication device 30, and the control method for the wireless communication device 30 is also disclosed in this specification. This control method includes a step in which the transmitting/receiving section 31 transmits and receives electromagnetic waves to and from the access point 3, a step in which the reception strength determining section 32 determines the reception strength of the electromagnetic waves from each of the plurality of access points 3, The roaming processing unit 33 selects one of the plurality of access points 3 and performs roaming processing to connect to the selected access point 3. In this embodiment, this control method further includes a step in which the roaming processing unit 33 transmits the roaming notification data D to the newly connected access point 3 multiple times.

[Other embodiments]
Next, other embodiments of the wireless communication device will be described.

(1) In the above embodiment, the configuration in which the roaming processing unit 33 executes both the first process and the second process has been described as an example. However, the present disclosure is not limited to such a configuration, and may also be configured such that the roaming processing unit 33 further executes the third process. The third process is a process of performing a roaming process when the moving body 1 moves for a predetermined distance or more from the stop position, and the predetermined distance is the period during which the movable body 1 moves at the maximum speed for one cycle of the predetermined period P. set to less than the distance. In this case, if the mobile object 1 moves more than a specified distance from the stop position before the specified period P elapses while the reception strength from the connected access point 3 does not fall below the specified value V, the third Roaming processing is performed. Note that the roaming processing unit 33, for example, acquires information on the moving distance of the moving body 1 from the control unit 34, and determines whether the moving body 1 has moved a predetermined distance or more from the stop position.

(2) In the above embodiment, even if the access point 3 selected by the roaming process is the same as the currently connected access point 3, the roaming processing unit 33 temporarily disconnects the access point 3. The explanation has been given using an example of a configuration in which the process of reconnecting from the server is performed. However, the present disclosure is not limited to such a configuration, and if the access point 3 selected by the roaming process is the same as the access point 3 currently connected, the roaming processing unit 33 terminates the connection with the access point 3. It is also possible to have a continuous configuration.

(3) In the above embodiment, if the access point 3 selected by the roaming process is different from the currently connected access point 3, after the roaming process is completed, the roaming processing unit 33 selects the newly connected access point. The configuration in which the roaming notification data D is transmitted multiple times to the mobile station No. 3 has been described as an example. However, the present disclosure is not limited to such a configuration, and may include a configuration in which the roaming processing unit 33 transmits the roaming notification data D only once to the newly connected access point 3 after completing the roaming process. It is also possible to do this.

(4) Note that the configurations disclosed in each of the embodiments described above may be applied in combination with configurations disclosed in other embodiments unless there is a conflict. combinations) are also possible. Regarding other configurations, the embodiments disclosed herein are merely illustrative in all respects. Therefore, various modifications can be made as appropriate without departing from the spirit of the present disclosure.

[Summary of the above embodiment]
An overview of the wireless communication device described above will be described below.

A wireless communication device that is mounted on a mobile object and performs wireless communication with any of a plurality of access points, the device comprising a transmitter/receiver unit that transmits and receives electromagnetic waves to and from the access point, and electromagnetic waves from each of the plurality of access points. and a roaming processing unit that selects one of the plurality of access points and performs roaming processing to connect to the selected access point, The processing unit includes a first process of performing the roaming process when the reception strength determination unit determines that the reception strength from the access point to which the connection is being made has become equal to or less than a predetermined value; and a second process of performing the roaming process at regular intervals regardless of the received reception strength.

According to this configuration, the roaming processing unit executes the first process, so if the reception strength from the access point to which the mobile object is connected falls below the specified value due to movement of the mobile object, etc., the roaming process is performed. and connect to the appropriate access point at that point. Furthermore, since the roaming processing unit executes the second process, the roaming process can be performed at regular intervals regardless of the strength of reception from the connected access point. Then, by performing the roaming process, it is possible to restore appropriate communication quality regardless of how good or bad the communication quality was before that. Therefore, it is possible to avoid deterioration in communication quality that may occur when a mobile object is stopped and connected to the same access point, and to maintain appropriate communication quality with the access point.

In addition, in order to avoid deterioration in communication quality due to a decrease in reception strength from the access point, it is possible to set the default value used in the first process high, but if the default value is set high, the frequency of execution of the roaming process will decrease. may become too high. In this regard, according to the present configuration, even if the reception strength from the currently connected access point does not fall below a specified value, it is possible to perform roaming processing at specified intervals and connect to an appropriate access point. Therefore, by keeping the specified value to a value that prevents the roaming process from becoming too frequent, the deterioration in communication quality caused by continuing to connect to an inappropriate access point can be avoided by performing the roaming process at specified intervals. can do.

Here, even if the access point selected by the roaming process is the same as the currently connected access point, the roaming processing unit performs a process of temporarily disconnecting from the access point and then reconnecting. It is preferable to do so.

According to this configuration, if the connection with the currently connected access point is maintained but the communication quality with the access point has deteriorated, the connection with the access point is temporarily disconnected and then reconnected. This makes it easier to improve the quality of communication with the access point. In addition, even if the deterioration in communication quality as described above has not occurred, you can check the elapsed time since connecting to the access point by disconnecting from the access point and then reconnecting. This prevents the time from becoming too long and makes it easier to maintain good communication quality with the access point.

Further, the roaming processing unit further executes a third process of performing the roaming process when the mobile body moves beyond a predetermined distance from a stop position, and the predetermined distance is such that the mobile body moves at a maximum speed of the predetermined distance. It is preferable that the distance is set to less than the distance traveled in one cycle.

When a mobile object moves, there may be an access point more suitable than the currently connected access point even if the reception strength from the currently connected access point has not fallen below a specified value. According to this configuration, since the roaming processing unit executes the third process, in the above case, the roaming process can be performed without waiting until the roaming process by the second process is performed. Therefore, it becomes easier to quickly connect to an appropriate access point and ensure appropriate communication quality.

In addition, when the access point selected by the roaming process is different from the access point to which the roaming process is being connected, the roaming processing unit may perform a roaming process that indicates that the access point to which the connection destination is changed after the roaming process is completed. It is preferable to send the notification data multiple times to the newly connected access point.

When multiple access points are connected to a communication partner of a mobile body (for example, a management device of a mobile body) via a switching hub, the switching hub collects identification information of the mobile body connected to the access point (for example, MAC address) is stored in the management table in association with the port to which the access point is connected. Then, the switching hub transmits the data received from the communication partner of the mobile unit from a port stored in association with the destination mobile unit of the data (hereinafter referred to as the “target mobile unit”). is transmitted to the target mobile unit via the access point to which the target mobile unit is connected. Therefore, in order to send data received from the mobile unit's communication partner to the target mobile unit, if the access point to which the target mobile unit is connected is changed due to roaming processing, the contents of the above management table must be adjusted accordingly. It is necessary to update it.

According to this configuration, when the access point to which the target mobile object is connected is changed due to roaming processing, roaming notification data can be transmitted multiple times to the access point that has become the new connection destination. Therefore, even if a communication error occurs, the probability that roaming notification data will not reach a new access point can be kept low. For example, when multiple access points are connected to a mobile communication partner via a switching hub as described above, the access point transmits the roaming notification data received from the wireless communication device to the switching hub. The contents of the above management table can be updated. According to this configuration, the roaming notification data can be reliably transmitted by the access point, so the contents of the management table can be updated more reliably.

Further, it is preferable that the start time of the prescribed cycle is the start time or end time of the previous roaming process.

According to this configuration, the start time of the prescribed cycle can be appropriately set so as to avoid unnecessarily performing the roaming process according to the second process immediately after the roaming process according to the first process is performed. .

The wireless communication device according to the present disclosure only needs to be able to achieve at least one of the above-mentioned effects.

1: Mobile body 3: Access point 30: Wireless communication device 31: Transmission/reception section 32: Reception strength determination section 33: Roaming processing section D: Roaming notification data P: Specified period V: Specified value

Claims (3)

A wireless communication device that is mounted on a mobile object and performs wireless communication with any of a plurality of access points,
a transmitter/receiver unit that transmits and receives electromagnetic waves to and from the access point;
a reception strength determination unit that determines the reception strength of electromagnetic waves from each of the plurality of access points;
a roaming processing unit that selects one of the plurality of access points and performs roaming processing to connect to the selected access point,
The roaming processing unit performs a first process of performing the roaming process when the reception strength determination unit determines that the reception strength from the access point to which it is connected has become equal to or less than a specified value, and the reception strength determination unit and a second process of performing the roaming process at a prescribed cycle regardless of the reception strength determined by;
The roaming processing unit is configured to perform a process of temporarily disconnecting and then reconnecting to the access point, even if the access point selected by the roaming process is the same as the currently connected access point. Communication device. A wireless communication device that is mounted on a mobile object and performs wireless communication with any of a plurality of access points,
a transmitter/receiver unit that transmits and receives electromagnetic waves to and from the access point;
a reception strength determination unit that determines the reception strength of electromagnetic waves from each of the plurality of access points;
a roaming processing unit that selects one of the plurality of access points and performs roaming processing to connect to the selected access point,
The roaming processing unit performs a first process of performing the roaming process when the reception strength determination unit determines that the reception strength from the access point to which it is connected has become equal to or less than a specified value, and the reception strength determination unit and a second process of performing the roaming process at a prescribed cycle regardless of the reception strength determined by;
The moving body is a transport vehicle that transports articles,
The roaming processing unit further executes a third process of performing the roaming process when the mobile body moves beyond a predetermined distance from the stop position,
In the wireless communication device, the specified distance is set to be less than a distance that the mobile object moves at a maximum speed during one period of the specified period. A wireless communication device that is mounted on a mobile object and performs wireless communication with any of a plurality of access points,
a transmitter/receiver unit that transmits and receives electromagnetic waves to and from the access point;
a reception strength determination unit that determines the reception strength of electromagnetic waves from each of the plurality of access points;
a roaming processing unit that selects one of the plurality of access points and performs roaming processing to connect to the selected access point,
The roaming processing unit performs a first process of performing the roaming process when the reception strength determination unit determines that the reception strength from the access point to which it is connected has become equal to or less than a specified value, and the reception strength determination unit and a second process of performing the roaming process at a prescribed cycle regardless of the reception strength determined by;
If the access point selected by the roaming process is different from the currently connected access point, the roaming processing unit generates roaming notification data indicating that the access point to which the connection is made has been changed after the roaming process is completed. A wireless communication device that transmits a plurality of times to the access point that has become a new connection destination.

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