Communication device, communication method, and program

Abstract

Provided is a communication system in which a moving user device communicates with a plurality of access points, wherein a communication device operating as the user device receives, from a first access point during data communication with the first access point via a first wireless link, guidance information for determining a roaming destination access point, and performs a handshake, via a second wireless link, with a second access point that is the roaming destination determined on the basis of the guidance information.

Description

Communication Apparatus, Communication Method, and Program

[0001] The present disclosure relates to wireless communication.

[0002] In a wireless LAN environment, there is a technique for performing roaming of a user terminal between a plurality of access points (for example, Patent Document 1).

[0003] Japanese Unexamined Patent Application Publication No. 2023-177768

[0004] IEEE 802.11r, [online], IEEE 802, [searched on February 6, 2025], Internet <URL: https: / / grouper.ieee.org / groups / 802 / 11 / Reports / tgr_update.htm>

[0005] An object of the present disclosure is to improve communication performance in a wireless communication system including a plurality of access points.

[0006] One aspect of the present disclosure is a communication apparatus that operates as the user apparatus in a communication system in which a moving user apparatus communicates with a plurality of access points, the communication apparatus comprising: a wireless interface capable of simultaneously establishing a first wireless link and a second wireless link; and a control unit, wherein the control unit is configured to: receive guidance information for determining a roaming destination access point from the first access point during data communication with the first access point via the first wireless link; and perform handshake with a second access point that is a roaming destination determined based on the guidance information via the second wireless link.

[0007] One aspect of the present disclosure is a communication apparatus that operates as the access point in a communication system in which a moving user apparatus communicates with a plurality of access points, the communication apparatus comprising a control unit configured to: acquire situation data reporting a status of a wireless communication environment from another access point included in the communication system; and transmit guidance information generated based on the situation information for determining a roaming destination access point to a first user apparatus during data communication with the first user apparatus.

[0008] One aspect of the present disclosure is a communication method performed by a communication device acting as a user device in a communication system in which a mobile user device communicates with a plurality of access points, the method comprising: receiving guidance information from a first access point for determining a roaming access point while communicating data with the first access point via a first radio link; and performing a handshake with a second access point, which is the roaming destination determined based on the guidance information, via a second radio link.

[0009] One aspect of the present disclosure is a communication method performed by a communication device acting as an access point in a communication system in which a mobile user device communicates with a plurality of access points, the method comprising: acquiring status data reporting the status of the wireless communication environment from other access points included in the communication system; and transmitting guidance information for determining a roaming access point, generated based on the status data, to the first user device during data communication with the first user device.

[0010] Other embodiments include a program for causing a computer to execute the above-mentioned communication method, or a computer-readable storage medium that non-temporarily stores said program.

[0011] According to this disclosure, communication performance can be improved in a wireless communication system that includes multiple access points.

[0012] A schematic diagram of the communication system according to the first embodiment. A hardware configuration diagram of the in-vehicle device according to the first embodiment. A hardware configuration diagram of the roadside device according to the first embodiment. A software configuration diagram of the in-vehicle device according to the first embodiment. A software configuration diagram of the roadside device according to the first embodiment. An example of status data and status master data generated and managed by the roadside device. A flowchart of the processing performed by the roadside device. A sequence diagram showing the data flow during handshake. A sequence diagram showing the data flow during roaming.

[0013] In wireless LAN environments such as Wi-Fi (registered trademark), there are systems that enable user terminal handover (hereinafter referred to as roaming) between multiple access points. In such systems, for example, the results of user terminal authentication and the status of data communication are shared among multiple access points. This makes it possible to reconnect and continue communication in a short time even if the user terminal moves and the connected access point changes.

[0014] Furthermore, there are efforts to apply Wi-Fi communication methods to high-speed moving vehicles. For example, by placing multiple access points along main roads and enabling roaming, low-cost mobile communication can be achieved.

[0015] However, a challenge with wireless LAN connections is that finding an access point itself takes time. Normally, when a terminal connects to an access point, it needs to scan for available access points, determine the access point to connect to based on the results, and perform a handshake. However, if this operation is performed while roaming, a period of interruption in data communication will occur. To solve this problem, it is necessary to continue the current data communication while preparing to connect to the next access point. The communication device according to this disclosure solves such problems.

[0016] A communication device according to one aspect of the present disclosure is a communication device that operates as a user device in a communication system in which a mobile user device communicates with a plurality of access points. Specifically, it has a wireless interface capable of simultaneously establishing a first wireless link and a second wireless link, and a control unit, wherein the control unit, while communicating data with the first access point via the first wireless link, receives guidance information from the first access point for determining the roaming access point, and performs a handshake with the second access point, which is the roaming destination determined based on the guidance information, via the second wireless link.

[0017] The communication device operates as a user device in the communication system and has a wireless interface capable of simultaneously establishing a first wireless link and a second wireless link.

[0018] Furthermore, the control unit of the communication device receives guidance information from the first access point during data communication via the first wireless link. Guidance information is information provided by the first access point for determining the roaming access point. The guidance information may specify the roaming access point, or it may be information provided for the user device to determine the roaming access point.

[0019] The control unit performs a handshake with the second access point, which is the roaming destination determined based on the guidance information, via the second wireless link. The handshake with the second access point via the second wireless link can be performed while data communication is taking place with the first access point via the first wireless link. This allows the handshake with the next access point to connect to to be performed before the connection destination switch occurs (i.e., during data communication). In other words, after data communication with the first access point ends, data communication with the second access point can begin immediately.

[0020] The guidance information may also include identifiers of candidate access points for roaming. In this case, the candidate roaming destination is specified by the first access point. The guidance information may also include the status of the wireless communication environment of other access points included in the communication system. The user device can determine the roaming destination access point based on this guidance information.

[0021] A communication device according to one aspect of this disclosure is a communication device that operates as an access point in a communication system in which a mobile user device communicates with a plurality of access points. Specifically, it performs the following: acquiring status data reporting the status of the wireless communication environment from other access points included in the communication system, and transmitting guidance information for determining a roaming access point, generated based on the status data, to the first user device during data communication with the first user device.

[0022] Communication devices operating as access points also have a wireless interface. The control unit acquires status data from other access points included in the communication system, reporting the status of the wireless communication environment. Status data is data used to estimate the quality of wireless communication and typically includes information such as channel availability, channel occupancy, and the number of connected terminals.

[0023] Furthermore, the control unit can generate guidance information based on the status data and transmit it to the user device.

[0024] Furthermore, when the control unit receives a roaming notification from the first user device, it may include the guidance information in the response corresponding to the roaming notification and transmit it to the first user device. A roaming notification is typically a notification that the destination access point will be switched. By including guidance information in the response to this notification, information for determining the destination access point can be efficiently transmitted to the first user device.

[0025] The control unit may determine an access point that is a candidate roaming destination for the first user device based on the acquired status data. In this case, the control unit may generate guidance information that includes the identifier of the determined access point. In this case, the guidance information will indicate or suggest the next access point to which the user device should connect.

[0026] The control unit may, based on the status data, provide the first user device with information to determine the roaming access point. In this case, the guidance information may, for example, notify the availability of wireless channels at multiple access points.

[0027] Furthermore, the control unit can perform a handshake with a second user device when a connection request is received from that second user device. This allows for a quicker completion of the connection with the new user device.

[0028] Furthermore, the control unit may generate status data reporting the availability of wireless channels in its own device, and transmit the generated status data to each of the other access points.

[0029] Thus, the first access point may, in addition to acquiring status data from other access points, also transmit status data from its own device. In this case, the control unit may transmit status data when the availability of its own wireless channel changes.

[0030] The following describes specific embodiments of this disclosure with reference to the drawings. Unless otherwise specified, the hardware configurations, module configurations, functional configurations, etc., described in each embodiment are not intended to limit the technical scope of the disclosure to those configurations alone.

[0031] (First Embodiment) [System Overview] An overview of the communication system according to the first embodiment will be described with reference to Figure 1. The communication system according to this embodiment consists of an on-board device 10 mounted on a vehicle and a plurality of roadside devices 20 installed along the road. The roadside devices 20 are an example of an "access point" in this disclosure. In the example in Figure 1, roadside devices 20A and 20B are shown as examples, but when there is no need to distinguish between them, they are collectively referred to as "roadside devices 20".

[0032] The communication system according to this embodiment is a system that performs wireless communication according to the communication procedure specified by IEEE 802.11. The roadside devices 20A and 20B each have a range (for example, a radius of about 100 meters) that enables data communication with the in-vehicle device 10. The in-vehicle device 10 can connect to either roadside device 20 and communicate while in motion. Furthermore, it can switch the connected roadside device 20 during communication (referred to as roaming).

[0033] Roaming can be performed by multiple roadside devices 20 sharing information about the in-vehicle device 10. For example, roadside device 20B shares information about the in-vehicle device 10 (e.g., authentication information) with roadside device 20A. If the destination of the in-vehicle device 10 changes from roadside device 20A to roadside device 20B during data communication, roadside device 20B accepts the connection from the in-vehicle device 10 based on the shared information and continues communication.

[0034] On the other hand, in wireless LAN systems, when user devices move at high speeds, roaming processing can take time, potentially preventing sufficient communication time from being secured. In recent years, high frequency bands, mainly millimeter waves, are sometimes used to achieve high-speed communication. However, as the frequency band increases, the communication range for each access point narrows, leading to frequent roaming. If the time required for roaming is not reduced, the communication time that can be secured at each access point will decrease.

[0035] To solve this problem, this embodiment utilizes an MLD (Multi-Link Device) as the in-vehicle device. An MLD is a communication device that can establish multiple wireless links simultaneously. In this embodiment, the in-vehicle device 10 is capable of simultaneously establishing two wireless links, link 1 and link 2.

[0036] Here, we assume that the in-vehicle device 10 is communicating data with the roadside device 20A using link 1 while the vehicle is in motion. The in-vehicle device 10 identifies the roadside device 20B, which is the next access point to connect to, and performs a handshake with the roadside device 20B using link 2 while communicating data via link 1. In this embodiment, the user device can perform roaming at high speed by using multiple links to communicate.

[0037] [Hardware Configuration] Next, the hardware configuration of each device that makes up the system will be described. Figure 2 is a schematic diagram showing an example of the hardware configuration of an in-vehicle device 10 that can be mounted on a vehicle.

[0038] The in-vehicle device 10 can be configured as a computer having a processor (CPU, GPU, etc.), main memory (RAM, ROM, etc.), and auxiliary storage (EPROM, hard disk drive, removable media, etc.). The auxiliary storage contains an operating system (OS), various programs, various tables, etc., and by executing the programs stored therein, various functions (software modules) that match a predetermined purpose, as described later, can be realized. However, some or all of the functions may be realized as hardware modules by hardware circuits such as ASICs and FPGAs.

[0039] The in-vehicle device 10 is comprised of a control unit 101, a storage unit 102, a communication unit 103, a location information acquisition unit 104, and an input / output unit 105.

[0040] The control unit 101 is a computing unit that realizes various functions of the in-vehicle device 10 by executing a predetermined program. The control unit 101 can be implemented by a hardware processor such as a CPU. The control unit 101 may also be configured to include RAM, ROM (Read Only Memory), cache memory, etc.

[0041] The storage unit 102 is means for storing information, and is configured of a storage medium such as a RAM, a magnetic disk, or a flash memory. The storage unit 102 stores programs executed by the control unit 101, data used by the programs, and the like.

[0042] The communication unit 103 is a wireless communication interface for transmitting and receiving wireless signals. The communication unit 103 is configured to be capable of transmitting and receiving wireless signals conforming to standards such as wireless LAN, for example. For example, when the control unit 101 requests a network connection, a wireless connection with the roadside device 20 is established via the communication unit 103. In the present embodiment, the communication unit 103 is configured to be capable of establishing a plurality of links simultaneously. This enables the control unit 101 to, for example, communicate with another access point using link 2 while communicating with an arbitrary access point using link 1.

[0043] The position information acquisition unit 104 acquires position information of the host vehicle. The position information acquisition unit 104 includes a GPS antenna and a positioning module for positioning position information. The GPS antenna is an antenna that receives positioning signals transmitted from positioning satellites (also referred to as GNSS satellites). The positioning module is a module that calculates position information based on signals received by the GPS antenna. Note that the position information acquisition unit 104 may determine the traveling direction of the host vehicle based on changes in position information.

[0044] The input / output unit 105 is a unit that receives input from an occupant of the vehicle and presents information to the occupant. Specifically, the input / output unit 105 includes a touch panel and control means therefor, and a liquid crystal display and control means therefor. In the present embodiment, the touch panel and the liquid crystal display are configured as a single touch panel display.

[0045] Next, the hardware configuration of the roadside device 20 will be described. FIG. 3 is a diagram schematically illustrating an example of the hardware configuration of the roadside device 20.

[0046] Similarly to the on-vehicle device 10, the roadside device 20 can be configured as a computer including a processor (CPU, GPU, etc.), a main storage device (RAM, ROM, etc.), and an auxiliary storage device (EPROM, hard disk drive, removable media, etc.).

[0047] The roadside device 20 is configured to include a control unit 201, a storage unit 202, and a communication unit 203.

[0048] The control unit 201 is an arithmetic unit that implements various functions of the roadside device 20 by executing a predetermined program. The control unit 201 can be implemented by, for example, a hardware processor such as a CPU. Further, the control unit 201 may be configured to include RAM, ROM (Read Only Memory), cache memory, and the like.

[0049] The storage unit 202 is a means for storing information, and is configured by a storage medium such as RAM, a magnetic disk, or a flash memory. The storage unit 202 stores programs executed by the control unit 201, data used by the programs, and the like.

[0050] The communication unit 203 is a wireless communication interface for transmitting and receiving wireless signals to and from the on-vehicle device 10. The communication unit 203 is configured to be capable of transmitting and receiving wireless signals conforming to standards such as wireless LAN, for example.

[0051] [Software Configuration] Next, the software configuration of each device configuring the system will be described. FIG. 4 is a diagram schematically showing the software configuration of the on-vehicle device 10 according to the present embodiment. The hardware configuration of the on-vehicle device 10 is as shown in FIG. 2.

[0052] In the present embodiment, the control unit 101 included in the on-vehicle device 10 is configured to include a communication control unit 1011 as a software module. These software modules may be implemented by executing a program stored in the storage unit 102 by the control unit 101 (such as a CPU). Note that information processing executed by a software module is synonymous with information processing executed by the control unit 101 (such as a CPU).

[0053] The communication control unit 1011 establishes a connection with one of the multiple roadside devices 20 and performs data transmission and reception (including roaming).

[0054] The communication control unit 1011 first requests a connection from the roadside equipment 20 included in the communication system. The communication control unit 1011 sends, for example, a probe request to an access point belonging to a predetermined group, and initiates a connection sequence with the roadside equipment 20 that responds to it. Alternatively, the communication control unit 1011 may receive a beacon frame transmitted from the roadside equipment 20 and initiate a connection sequence in response.

[0055] Furthermore, the communication control unit 1011 performs switching of the connection destination (roaming) between other roadside devices 20 as needed.

[0056] Here, the features of roaming in this embodiment will be described. During data communication with the roadside device 20A, the communication control unit 1011 receives information (guidance information) from the roadside device 20A to guide the next roadside device 20B to be connected. As will be described later, the guidance information is information generated by the roadside device 20 to guide the roaming destination roadside device. In this example, it is assumed that the communication control unit 1011 receives guidance information from the roadside device 20A while communicating with the roadside device 20A using link 1. Furthermore, it is assumed that the guidance information specifies roadside device 20B as the roaming destination roadside device.

[0057] The communication control unit 1011 uses link 2 to detect when it has entered the communication range of the roadside device 20B, and uses link 2 to initiate a connection sequence (handshake) with the roadside device 20B. Once data communication with the roadside device 20A is complete, the communication control unit 1011 can immediately begin data communication with the roadside device 20B, with which the handshake has been completed.

[0058] Next, the software configuration of the roadside device 20 will be described. Figure 5 is a schematic diagram showing the software configuration of the roadside device 20 according to this embodiment. The hardware configuration of the roadside device 20 is as shown in Figure 3.

[0059] In this embodiment, the control unit 201 of the roadside device 20 is configured to have three software modules: a communication control unit 2011, an authentication unit 2012, and a shared unit 2013. These software modules may be implemented by the control unit 201 (CPU, etc.) executing programs stored in the storage unit 202. The information processing performed by the software modules is synonymous with the information processing performed by the control unit 201 (CPU, etc.).

[0060] The communication control unit 2011 performs data communication with the in-vehicle device 10. Specifically, the communication control unit 2011 performs the following processes.

[0061] (1) The communication control unit 2011 performs a handshake with the in-vehicle device 10. In response to a probe request sent from the in-vehicle device 10, the communication control unit 2011 starts a handshake that includes authentication processing. The authentication processing is performed by the authentication unit 2012, which will be described later. If the authentication result for the target in-vehicle device 10 has already been received from another roadside device 20, the authentication processing is omitted (described later). The above description is an example for active scanning, but when performing passive scanning, the communication control unit 2011 may periodically broadcast a beacon frame to notify the presence of its own device.

[0062] (2) Processing to perform data communication with the in-vehicle device 10 Once the handshake with the in-vehicle device 10 is complete, the communication control unit 2011 starts data communication with the in-vehicle device 10. Data communication may be performed, for example, by repeatedly sending multiple data blocks and receiving block Ack.

[0063] (3) Roaming Processing The communication control unit 2011 also has a function to control roaming between multiple roadside devices 20. For example, based on the communication result with the in-vehicle device 10, the communication control unit 2011 decides to switch the connection destination of the in-vehicle device 10 to another roadside device 20 (roaming). When roaming is performed, the communication control unit 2011 can transmit information (guidance information) about the other roadside device 20 that will be the new connection destination of the in-vehicle device 10 to the in-vehicle device 10. This guidance information includes information about the roadside device 20 that are candidates for roaming destinations. The in-vehicle device 10 can use this information to switch the roadside device 20 to which it is connected. The communication control unit 2011 can also transmit information about the in-vehicle device 10 (such as the identifier of the in-vehicle device 10 and the sequence number in data transmission) to the other roadside device 20 that are candidates for roaming destinations.

[0064] The authentication unit 2012 authenticates the in-vehicle device 10 based on a request from the communication control unit 2011. Authentication can be performed based on authentication information received from the in-vehicle device 10. Authentication information includes, for example, an identifier for uniquely identifying the in-vehicle device 10, a key used when connecting the in-vehicle device 10 to the communication system, or an electronic certificate. The authentication information stored in the in-vehicle device 10 and the authentication information transmitted to the roadside device 20 may be different. For example, if a private key is stored in the in-vehicle device 10, a hash generated based on that private key may be transmitted to the roadside device 20. The authentication unit 2012 may also perform authentication using, for example, PSK (Pre-Shared Key). In this case, the authentication information will be a key generated based on a passphrase. The authentication unit 2012 may also perform, for example, IEEE 802.1x authentication. In this case, the authentication information will be a combination of username and password, or an electronic certificate.

[0065] Furthermore, if the authentication of the in-vehicle device 10 is successful, the authentication unit 2012 transmits the authentication result to other roadside devices 20 belonging to the same communication system. This allows the other roadside devices 20 to continue communication without having to perform authentication again when roaming occurs.

[0066] The shared unit 2013 exchanges and shares data with other roadside devices 20 included in the communication system to report the status of the wireless communication environment. In this embodiment, the status of the wireless communication environment includes the usage status of multiple wireless channels provided by each roadside device 20.

[0067] In this embodiment, the shared unit 2013 generates data representing the usage status of wireless channels in its own device (hereinafter referred to as status data) and transmits it to other roadside devices 20. The status data may include information such as, for example, "According to the standard, 20 channels are available, and 10 of them are currently in use." Figure 6(A) shows an example of status data. The status data includes the identifier of the device, the location information of the device, the communication standard, the frequency band, the authentication method, a list of wireless channels available according to the standard, and a list of wireless channels currently in use. The status data may be stored in the storage unit 202 (status data 202A in Figure 5).

[0068] Furthermore, the shared unit 2013 receives status data from other roadside devices 20 and performs the process of registering it in a database (hereinafter referred to as status master data). The status master data is a database that manages the status of the wireless communication environment in multiple roadside devices 20. Figure 6(B) shows an example of status master data. The status master data is updated each time status data is received from other roadside devices 20. The status master data may also be stored in the storage unit 202 (status master data 202B in Figure 5).

[0069] As the shared unit 2013 performs the operations described above, the multiple roadside devices 20 included in the communication system will be able to grasp the availability of each other's wireless channels in real time.

[0070] The status data may be broadcast, but if the communication system has a wide range, adjacent roadside devices 20 may relay the status data to each other so that it is delivered to all roadside devices 20. Alternatively, the status data may be transmitted to other roadside devices 20 via a wired backbone line or server equipment.

[0071] [Processing Flowchart] Next, we will explain the processing flow in communication. In this example, we will explain assuming that a vehicle equipped with an on-board device 10 is traveling on a road where multiple roadside devices 20 are located. Figure 7 is a flowchart of the process by which a roadside device 20 exchanges status data with other roadside devices 20. This process is performed periodically by each of the multiple roadside devices 20.

[0072] First, in step S11, the shared unit 2013 generates data (status data) representing the usage status of wireless channels in its own device and transmits it to other roadside devices 20. The status data may include the roadside device identifier, location information, coverage information, communication standard, frequency band, authentication method, a list of wireless channels available according to the standard, and a list of wireless channels currently in use.

[0073] Next, in step S12, the shared unit 2013 receives status data from other roadside devices 20 and registers it in the status master data 202B. If a record corresponding to the same roadside device 20 already exists, the contents of that record are updated. By having multiple roadside devices 20 repeatedly perform the process shown in Figure 7, the roadside devices 20 included in the communication system can grasp the availability of wireless channels of other roadside devices 20 in real time.

[0074] In the explanation of Figure 7, steps S11 and S12 are shown together for convenience, but the two steps do not necessarily have to be executed together. Also, the execution order of each step does not have to be as shown in the figure. Furthermore, the processing of step S11 may be triggered when the availability of the wireless channel of the device changes. In other words, if there is no change in the availability of the wireless channel of the device, the execution of step S11 may be skipped.

[0075] Next, we will specifically describe the processes performed by each device while the vehicle equipped with the on-board device 10 is in motion. Figure 8 is a sequence diagram of data transmitted and received between the on-board device 10 and the roadside device 20 when the on-board device 10 connects to the roadside device 20 included in the communication system. In this example, the access point to which the on-board device 10 first connects is the roadside device 20A, and the access point to which the on-board device 10 next connects (i.e., the roaming destination) is the roadside device 20B. Furthermore, the on-board device 10 communicates with the roadside device 20A via link 1.

[0076] First, the in-vehicle device 10 sends a probe request to find the roadside device. Here, we have given an example where an active scan is performed based on a probe request sent from the in-vehicle device 10, but the connection sequence may also start with a beacon frame sent from the roadside device 20A. A beacon frame is data broadcast by the roadside device 20 to announce the presence of its own device. In this case, when the in-vehicle device 10 receives a beacon frame from the roadside device 20A, the in-vehicle device 10 starts the sequence to connect to the roadside device 20A.

[0077] Upon receiving a probe request addressed to itself, the roadside device 20A sends a probe response containing its network information to the in-vehicle device 10. Upon receiving the probe response, the in-vehicle device 10 sends an authentication request to the roadside device 20A requesting authentication. The authentication request may include authentication information (such as key information) held by the in-vehicle device 10.

[0078] When the roadside device 20A receives an authentication request, it performs a step (step S21) to authenticate the in-vehicle device 10. In step S21, the roadside device 20A (authentication unit 2012) authenticates the in-vehicle device 10 based on the authentication information received from the in-vehicle device 10. Authentication may be performed, for example, by PSK (Pre-Shared Key) or IEEE 802.1x authentication.

[0079] Once authentication of the in-vehicle device 10 is complete, the roadside device 20A performs a process to share the authentication result with other roadside devices 20 included in the communication system (step S22). For example, the roadside device 20A (authentication unit 2012) transmits the authentication result performed in step S21 to a roadside device 20B belonging to the same communication system (or the same group) (for example, a roadside device 20B having the same group address as roadside device 20A). Sharing of the authentication result may be performed via a server device or the like that manages multiple roadside devices 20 included in the communication system. This eliminates the need for each roadside device 20 to individually authenticate the in-vehicle device 10.

[0080] If the authentication unit 2012 has already received authentication results from other roadside devices 20 for the target in-vehicle device 10, steps S21 and S22 are skipped.

[0081] Once the authentication process is complete, the roadside device 20A sends a notification (authentication completion notification) to the in-vehicle device 10 indicating that the authentication has been completed.

[0082] Once authentication is complete, the in-vehicle device 10 sends an association request (connection request) to the roadside device 20A. In response, the roadside device 20A sends an association response to the in-vehicle device 10. The handshake between the in-vehicle device 10 and the roadside device 20A is completed through the process described above.

[0083] Once the handshake between the in-vehicle device 10 and the roadside device 20A is complete, data communication begins. Data communication may, for example, involve the in-vehicle device 10 transmitting data collected in the vehicle to the roadside device 20A. Data communication may also be performed by repeatedly transmitting multiple data blocks and receiving block Ack.

[0084] Figure 9 is a sequence diagram of data transmitted and received between the in-vehicle device 10 and the roadside device 20 when roaming is performed. The illustrated process starts when the in-vehicle device 10 decides to perform roaming from roadside device 20A to roadside device 20B. The timing of roaming can be determined, for example, based on the location information of the in-vehicle device 10, the field strength of the wireless signal, the communication error rate, etc.

[0085] First, the in-vehicle device 10 sends a request (roaming request) to the roadside device 20A requesting it to perform roaming. In step S31, the communication control unit 2011 determines, based on the status master data, the candidate roadside device 20 to which the in-vehicle device 10 will connect next (i.e., the roaming destination). For example, the communication control unit 2011 determines a roadside device that includes the in-vehicle device 10, which is in motion, in its coverage and has an available radio channel as a candidate roaming destination. The communication control unit 2011 also generates information (guidance information) to guide the user to the candidate roadside device for roaming. The guidance information includes the identifier of the roadside device for roaming. If there are two or more candidate access points for roaming, the guidance information may include two or more identifiers.

[0086] Once a roadside device that is a candidate for roaming destination is determined, the communication control unit 2011 of the roadside device 20A transmits a roaming response to the in-vehicle device 10. The roaming response is a notification accepting roaming, and in this embodiment, it includes guidance information.

[0087] Upon receiving the roaming response, the in-vehicle device 10 determines the roadside device 20B to roam to based on the guidance information included in the roaming response (step S32), and sends a probe request to the roadside device 20B using link 2. In the following description, the handshake with the roadside device 20B is performed using link 2. At this time, communication with the roadside device 20A using link 1 is still ongoing. The sequence of connections is as described with reference to Figure 8. If the authentication result of the in-vehicle device 10 has been shared in advance, the authentication process is omitted.

[0088] Once the handshake between the in-vehicle device 10 and the roadside device 20B is complete, the in-vehicle device 10 switches to the roadside device 20, which is the data communication partner (step S33). In this step, for example, the in-vehicle device 10 sends a request to the roadside device 20A to terminate data communication on link 1. In response, the roadside device 20A terminates data communication with the in-vehicle device 10.

[0089] Furthermore, at this time, the roadside device 20A transmits information (context information) regarding the target in-vehicle device 10 to the communication control unit 2011 of the roadside device 20B. The context information may include the identifier of the target in-vehicle device 10, its movement status, and the status of data transmission and reception (sequence number). The transmission of context information may be performed via a server device or the like that manages multiple roadside devices 20 included in the communication system. The in-vehicle device 10 also requests the roadside device 20B to start data communication using link 2.

[0090] In the example shown in Figure 9, roaming is initiated by the on-board device 10, but roaming may also be initiated by the roadside device 20A. In this case, the roadside device 20A notifies the on-board device 10 of the occurrence of roaming. Guidance information may also be transmitted from the roadside device 20A to the on-board device 10 at this time. The on-board device 10 responds to the notification and starts the roaming procedure. It is also possible to perform roaming in this manner.

[0091] As described above, the roadside device 20 according to the first embodiment generates status data that reports the status of its wireless communication environment and shares this data among multiple roadside devices. The roadside device 20A also provides the in-vehicle device 10 with information to guide it to a roadside device that is a candidate for roaming, based on the shared status data. The in-vehicle device 10 communicates with the roadside device 20A via link 1 and, based on the guidance information received from the roadside device 20A, uses link 2 to perform a handshake with the roadside device 20B that is the roaming destination.

[0092] With this configuration, the in-vehicle device 10 can identify the next roadside device to connect to before roaming occurs. Furthermore, because the in-vehicle device 10 uses different wireless links to simultaneously perform handshakes with the roadside devices at the roaming destination, roaming can be performed at high speed.

[0093] (Modification of the First Embodiment) In the first embodiment, the roadside device 20A determines a candidate roadside device 20B for roaming based on the status master data and guides it to the on-board device 10. On the other hand, the roadside device for roaming may be determined by the on-board device 10. For example, the roadside device 20A may transmit part or all of the status master data, or information generated based thereon, to the on-board device 10 as guidance information. The on-board device 10 may determine a roadside device suitable as a roaming destination based on the guidance information.

[0094] (Modifications) The embodiments described above are merely examples, and this disclosure may be modified as appropriate without departing from its essence. For example, the processes and means described in this disclosure can be freely combined and implemented as long as no technical inconsistencies arise.

[0095] Furthermore, in the first embodiment, data representing the usage status of the wireless channel in the roadside device 20 was given as an example of status data, but other information may be included in the status data as long as it is possible to estimate the quality of wireless communication. For example, a numerical value representing the number of terminals currently connected to the device may be included in the status data.

[0096] Furthermore, in this embodiment, each roadside device 20 performs authentication of the in-vehicle device 10, but the authentication of the in-vehicle device 10 may be performed by an external authentication server. In this case, the authentication server and each roadside device 20 may communicate wirelessly or via a wired connection. Even in this case, the authentication result of the in-vehicle device 10 is shared among all roadside devices 20 included in the communication system.

[0097] Furthermore, a process described as being performed by a single device may be divided and executed by multiple devices. Conversely, a process described as being performed by different devices may be executed by a single device. In a computer system, the hardware configuration (server configuration) by which each function is implemented can be flexibly changed.

[0098] The present disclosure can also be realized by supplying a computer program implementing the functions described in the embodiments above to a computer, and having one or more processors in the computer read and execute the program. Such a computer program may be provided to the computer by a non-temporary computer-readable storage medium that can be connected to the computer's system bus, or it may be provided to the computer via a network. Non-temporary computer-readable storage mediums include, for example, any type of disk such as magnetic disks (floppy disks, hard disk drives (HDDs), etc.), optical disks (CD-ROMs, DVDs, Blu-ray discs, etc.), read-only memory (ROM), random access memory (RAM), EPROM, EEPROM, magnetic cards, flash memory, optical cards, and any type of medium suitable for storing electronic instructions.

[0099] 10...In-vehicle device 20...Roadside device 101, 201...Control unit 102, 202...Storage unit 103, 203...Communication unit 104...Location information acquisition unit 105...Input / output unit

Claims

1. In a communication system in which a mobile user device communicates with multiple access points, a communication device operating as the user device comprises a wireless interface capable of simultaneously establishing a first wireless link and a second wireless link, and a control unit, wherein the control unit performs the following actions: receiving guidance information from the first access point for determining a roaming access point while communicating data with the first access point via the first wireless link; and performing a handshake with the second access point, which is the roaming destination determined based on the guidance information, via the second wireless link.

2. The communication device according to claim 1, wherein the control unit performs a handshake with the second access point via the second wireless link during data communication with the first access point via the first wireless link.

3. The communication device according to claim 1, wherein the guidance information includes an identifier of an access point that is a candidate for roaming destination.

4. The communication device according to claim 1, wherein the guidance information includes the status of the wireless communication environment of other access points included in the communication system.

5. The communication device according to claim 4, wherein the control unit determines the access point to be the roaming destination based on the guidance information.

6. A communication device operating as an access point in a communication system in which a mobile user device communicates with multiple access points, the communication device having a control unit that performs the following: acquiring status data reporting the status of the wireless communication environment from other access points included in the communication system; and transmitting guidance information for determining a roaming access point, generated based on the status data, to the first user device during data communication with the first user device.

7. The communication device according to claim 6, wherein when the control unit receives a roaming notification from the first user device, it includes the guidance information in the response corresponding to the roaming notification and transmits it to the first user device.

8. The communication device according to claim 6, wherein the control unit determines an access point that is a candidate roaming destination for the first user device based on the acquired plurality of status data, and generates the guidance information including the identifier of the determined access point.

9. The communication device according to claim 6, wherein the guidance information includes the availability status of wireless channels of multiple access points.

10. The communication device according to claim 6, wherein the control unit generates status data reporting the availability of wireless channels in its own device, and transmits the generated status data to each of the other access points.

11. The communication device according to claim 10, wherein the control unit transmits the status data when the availability of the wireless channel of the device changes.

12. A communication method performed by a communication device acting as a user device in a communication system in which a mobile user device communicates with multiple access points, the method comprising: receiving guidance information from a first access point for determining a roaming access point while communicating data with the first access point via a first radio link; and performing a handshake with a second access point, which is the roaming destination determined based on the guidance information, via a second radio link.

13. The communication method according to claim 12, wherein a handshake with the second access point via the second wireless link is performed during data communication with the first access point via the first wireless link.

14. The communication method according to claim 12, wherein the guidance information includes an identifier of a candidate access point for roaming, or the status of the wireless communication environment of other access points included in the communication system.

15. A communication method performed by a communication device acting as an access point in a communication system in which a mobile user device communicates with multiple access points, the method comprising: acquiring status data reporting the status of the wireless communication environment from other access points included in the communication system; and transmitting guidance information for determining a roaming access point, generated based on the status data, to the first user device during data communication with the first user device.

16. The communication method according to claim 15, wherein when a roaming notification is received from the first user device, the response corresponding to the roaming notification includes the guidance information and is transmitted to the first user device.

17. The communication method according to claim 15, which determines an access point that is a candidate roaming destination for the first user device based on the multiple status data acquired, and generates the guidance information including the identifier of the determined access point.

18. The communication method according to claim 15, comprising generating status data that reports the availability of wireless channels in the device itself, and transmitting the generated status data to each of the other access points.

19. The communication method according to claim 18, wherein the status data is transmitted when the availability of the wireless channel of the device changes.

20. A program for causing a computer to execute the communication method described in any one of claims 12 to 19.

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