Communication methods and communication devices

Abstract

To improve communication performance in wireless communication systems that include multiple access points. [Solution] A communication method performed by a first access point included in a plurality of access points in a communication system in which a mobile user device communicates with a plurality of access points. The first access point transmits a first control signal in a first frequency band to control communication with the user device, performs data communication with the user device in the first frequency band, and transmits a second control signal in a second frequency band during data communication with the user device, which is a signal requesting the other access points to stop transmitting the first control signal.

Description

Technical Field

[0001] The present disclosure relates to wireless communication.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0006] One aspect of the present disclosure is In a communication system in which a mobile user device communicates with multiple access points, a first access point among the multiple access points performs a communication method comprising: transmitting a first control signal in a first frequency band to control communication with the user device; performing data communication with the user device in the first frequency band; and transmitting a second control signal in a second frequency band during data communication with the user device, which is a signal requesting other access points to stop transmitting the first control signal.

[0007] One aspect of this disclosure is, In a communication system in which a mobile user device communicates with multiple access points, the communication device functions as a first access point and has a control unit that performs the following: transmitting a first control signal in a first frequency band for controlling communication with the user device; performing data communication with the user device in the first frequency band; and transmitting a second control signal in a second frequency band, which is a signal requesting other access points to stop transmitting the first control signal, during data communication with the user device.

[0008] Other embodiments include an apparatus for performing the above method, a program for causing a computer to perform the method, or a computer-readable storage medium that non-temporarily stores the program. [Effects of the Invention]

[0009] According to this disclosure, communication performance can be improved in a wireless communication system that includes multiple access points. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram illustrating the communication system according to the embodiment. [Figure 2] Hardware configuration diagram of the in-vehicle device according to the embodiment. [Figure 3] Hardware configuration diagram of the roadside device according to this embodiment. [Figure 4] A software configuration diagram of an in-vehicle device according to an embodiment. [Figure 5] A software configuration diagram of the roadside device according to this embodiment. [Figure 6] A flowchart illustrating the phases performed by each device. [Figure 7] A sequence diagram showing the data flow during the connection phase and the transmission / reception phase. [Figure 8] A sequence diagram showing the data flow during the handover phase. [Modes for carrying out the invention]

[0011] In wireless LAN environments such as Wi-Fi (registered trademark), there are systems that enable the handover of user terminals between multiple access points. In such systems, for example, the authentication results of the user terminal are shared among multiple access points. This makes it possible to reconnect quickly, even if the user terminal moves and the destination access point changes, by skipping the authentication phase.

[0012] Furthermore, there are efforts to apply Wi-Fi communication methods to fast-moving vehicles. For example, by placing multiple access points along main roads and enabling handover, mobile communication can be achieved at a low cost.

[0013] Wi-Fi access points generally transmit two types of frames: control frames to manage communication with user devices, and data transmission frames. However, when multiple Wi-Fi access points are placed at short intervals, data communication frames transmitted by one access point and control frames transmitted by an adjacent access point may interfere with each other, potentially leading to problems such as an increased error rate or a decrease in data communication speed. The communication method described herein solves the aforementioned problems.

[0014] A communication method according to one aspect of the present disclosure is a communication method executed by a first access point included in the plurality of access points in a communication system in which a moving user device communicates with the plurality of access points, the method including: transmitting a first control signal for controlling communication with the user device in a first frequency band; performing data communication with the user device in the first frequency band; and transmitting, in a second frequency band, a second control signal, which is a signal for requesting other access points to stop transmitting the first control signal, during the data communication with the user device.

[0015] The first access point is one of the plurality of access points capable of communicating with a moving user device. The plurality of access points may be, for example, a plurality of roadside devices installed at predetermined intervals along a road.

[0016] The first access point transmits and receives both a control frame (first control signal) for controlling communication with the user device and a data frame in the first frequency band. On the other hand, when the plurality of access points are arranged in proximity to each other, problems such as interference between the control frame and the data frame may occur. For example, during data communication between the first access point and the user device, interference may occur due to a control frame (first control signal) transmitted from an adjacent second access point.

[0017] To solve this problem, the first access point transmits, during data communication with the user device, a second control signal, which is a signal for requesting other access points to stop transmitting the first control signal, in a second frequency band. The first access point may continuously transmit the second control signal during data communication with the user device. Other access points stop transmitting the first control signal during the period in which they receive the second control signal.

[0018] The second frequency band is, for example, a frequency band used for information sharing between multiple access points belonging to the same group, and is a sub-frequency band different from the frequency band (first frequency band) used for primary data communication with user devices. Typically, the first frequency band is a lower frequency band than the second frequency band. For example, if the second frequency band is in the gigahertz range, the first frequency band can be in the megahertz range. The transmission of the second control signal is stopped, for example, when the first access point terminates communication with the user device.

[0019] This configuration makes it possible to reduce radio interference between adjacent access points. In particular, since the first control signal is instructed to stop transmission using a frequency band different from the frequency band used for data communication, interference reduction can be achieved without affecting the main data communication.

[0020] Furthermore, the second frequency band may be a frequency band with a wider communication range than the first frequency band. The second frequency band is used for sharing information between multiple access points, and therefore, it is preferable that it has a wider communication range than the first frequency band. For example, the second frequency band may be a frequency band below 5 GHz, and the first frequency band may be a frequency band of 5 GHz or higher.

[0021] The second control signal may be transmitted as an unmodulated signal, provided that it can request the cessation of transmission of the first control signal.

[0022] The second frequency band may be a frequency band on which a third control signal is transmitted for sharing information about the user device with other access points. The third control signal can be, for example, a signal for sharing the authentication results of a user device between access points, or a signal for sharing information about the target user device among multiple access points when performing a handover.

[0023] 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 described therein.

[0024] (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 "access points". In the example in Figure 1, roadside devices 20A, 20B, and 20C are shown as examples, but when there is no need to distinguish between them, they are collectively referred to as "roadside device 20".

[0025] The communication system according to this embodiment is a system that performs wireless communication according to the communication procedure defined by IEEE 802.11. Multiple roadside devices 20 identify a group The group has a common group address and a unique local address for each device. The group is part of the Mobility domain in the IEEE 802.11 standard. It can also be a corresponding item. Multiple roadside devices 20 may belong to a common BSS (Basic Service Set). The on-board device 10, which is a network device, can access any of the roadside devices 20 using a common identifier such as a group address or BSSID, and receive authentication. The authentication result is shared among multiple roadside devices 20, allowing the on-board device 10 to change the connected roadside device 20 without having to perform the authentication procedure again. Each of the roadside devices 20A, 20B, and 20C has a range within which data communication with the on-board device 10 is possible (for example, a radius of about 100 meters; shown by the dotted line in Figure 1). The in-vehicle device 10 can connect to any of the roadside devices 20 and communicate while in motion. Furthermore, it can switch the connected roadside device 20 during communication.

[0026] In a Wi-Fi communication system, an access point (roadside device 20) periodically transmits a beacon frame (an example of the "first control signal" in this disclosure) to discover a user device (in-vehicle device 10). Upon receiving this, the user device (in-vehicle device 10) identifies a candidate access point (roadside device 20) to connect to. However, if beacon frames are transmitted in the same frequency band (first frequency band) as those used for data communication, interference may occur between multiple access points. For example, when the in-vehicle device 10 is communicating data with the roadside device 20A, a beacon frame transmitted by the roadside device 20B may reach the in-vehicle device 10. If both communication channels are the same, interference may occur, potentially leading to problems such as an increased error rate or a decrease in data communication speed.

[0027] Therefore, in this embodiment, each roadside device 20 transmits a signal (the "second control signal" in this disclosure; hereinafter referred to as the stop request signal) to surrounding roadside devices 20 requesting them to stop transmitting beacon frames while performing data communication with the in-vehicle device 10. A roadside device 20 that receives the signal stops the periodic transmission of beacon frames while receiving the signal. The transmission of the stop request signal ends when the source roadside device 20 terminates data communication.

[0028] Furthermore, in the communication system according to this embodiment, each roadside device 20 is configured to communicate with the in-vehicle device 10 in two frequency bands, a first frequency band and a second frequency band, and the stop request signal is transmitted in the second frequency band.

[0029] The first frequency band is the primary frequency band used for data communication, and is typically a frequency band of 5 GHz or higher, such as 5 GHz and 60 GHz. While this frequency band allows for high-speed data communication, it is characterized by a relatively short communication range of several tens to a hundred meters. The second frequency band is a frequency band used for secondary data communication, and is typically a sub-5GHz frequency band such as 2.4GHz. In the sub-5GHz band, the data communication speed is inferior to frequency bands above 5GHz (e.g., the 60GHz band), but it has the characteristic of having a communication range several times that of the above frequency band (e.g., several hundred meters). In the example in Figure 1, the dotted line indicates the communication range of the first frequency band. The communication range of the second frequency band is wider than the range shown by the dotted line.

[0030] In this embodiment, the roadside device 20 has a function to perform data communication with the in-vehicle device 10 in the first frequency band. Furthermore, the roadside device 20 has a function to share information with other roadside devices 20 using the second frequency band. The signals transmitted and received in the second frequency band (in this disclosure) The third control signal can be, for example, a signal for sharing the authentication result of the in-vehicle device 10 among roadside devices, or a signal for sharing information about the in-vehicle device 10 performing a handover among multiple roadside devices 20. By using the second frequency band, which has a wider communication range than the first frequency band, to transmit a stop request signal, it is possible to request that more roadside devices 20 stop transmitting beacon frames.

[0031] [Hardware configuration] Next, we will describe the hardware configuration of each device that makes up the system. 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The memory unit 102 is a means for storing information and is composed of storage media such as RAM, magnetic disks, and flash memory. The memory unit 102 stores programs executed by the control unit 101, data used by those programs, and so on.

[0036] The communication unit 103 is a wireless communication interface for sending and receiving wireless signals. The communication unit 103 is configured to send and receive wireless signals that conform to standards such as wireless LAN. Furthermore, the communication unit 103 can send and receive these wireless signals in two different frequency bands. In this embodiment, the communication unit 103 can send and receive wireless signals in two frequency bands: a frequency band of 5 GHz or higher (first frequency band) and a frequency band of less than 5 GHz (second frequency band).

[0037] The location information acquisition unit 104 acquires the location information of vehicle 1. The location information acquisition unit 104 includes a GPS antenna and a positioning module for determining the location information. The GPS antenna is an antenna that receives positioning signals transmitted from positioning satellites (also called GNSS satellites). The positioning module is a module that calculates location information based on the signals received by the GPS antenna. The location information acquisition unit 104 may also determine the direction of travel of vehicle 1 based on the change in location information.

[0038] The input / output unit 105 is a unit that receives input from the vehicle occupants and presents information to the occupants. Specifically, the input / output unit 105 consists of a touch panel and its control means, and a liquid crystal display and its control means. The touch panel and liquid crystal display are as described in this implementation. In terms of form, it consists of a single touch panel display.

[0039] Next, the hardware configuration of the roadside device 20 will be described. Figure 3 is a schematic diagram showing an example of the hardware configuration of the roadside device 20.

[0040] The roadside device 20 can be configured as a computer having a processor (CPU, GPU, etc.), main memory (RAM, ROM, etc.), and auxiliary memory (EPROM, hard disk drive, removable media, etc.), similar to the in-vehicle device 10.

[0041] The roadside device 20 is comprised of a control unit 201, a storage unit 202, and a communication unit 203.

[0042] The control unit 201 is a computing unit that realizes various functions of the roadside device 20 by executing a predetermined program. The control unit 201 can be implemented by a hardware processor such as a CPU. The control unit 201 may also be configured to include RAM, ROM (Read Only Memory), cache memory, etc.

[0043] The memory unit 202 is a means for storing information and is composed of storage media such as RAM, magnetic disks, and flash memory. The memory unit 202 stores programs executed by the control unit 201, data used by those programs, and so on.

[0044] The communication unit 203 is a wireless communication interface for sending and receiving wireless signals to and from the in-vehicle device 10. The communication unit 203 is configured to send and receive wireless signals conforming to standards such as wireless LAN. Similar to the communication unit 103, the communication unit 203 can send and receive these wireless signals in two different frequency bands.

[0045] [Software Configuration] Next, the software configuration of each device constituting the system will be described. Figure 4 is a schematic diagram showing the software configuration of the in-vehicle device 10 according to this embodiment. The hardware configuration of the in-vehicle device 10 is as shown in Figure 2.

[0046] In this embodiment, the control unit 101 of the in-vehicle device 10 is configured to include a communication control unit 1011 as a software module. This software module may be implemented by the control unit 101 (CPU, etc.) executing a program stored in the storage unit 102. The information processing performed by the software module is synonymous with the information processing performed by the control unit 101 (CPU, etc.).

[0047] The communication control unit 1011 establishes a connection with one of the multiple roadside devices 20 and performs data transmission and reception (including handover processing).

[0048] First, the communication control unit 1011 detects the presence of a roadside device 20 included in the communication system and performs the step of requesting a connection to the communication system. In this step, the communication control unit 1011 receives a beacon frame transmitted from the roadside device 20 and, in response, performs an authentication procedure using pre-stored authentication information. 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 a communication system, or an electronic certificate. Note that 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. This establishes a connection between the in-vehicle device 10 and the communication system.

[0049] Secondly, the communication control unit 1011 performs data transmission and reception between the in-vehicle device 10 and the roadside device 20, and, if necessary, performs switching of the connection destination (handover) between other roadside devices 20. Specific control methods will be discussed later.

[0050] 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.

[0051] In this embodiment, the control unit 201 of the roadside device 20 is configured to have two software modules: a communication control unit 2011 and an authentication unit 2012. Each software module may be implemented by the control unit 201 (CPU, etc.) executing a program 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.).

[0052] The communication control unit 2011 performs data communication with the in-vehicle device 10. Specifically, the communication control unit 2011 performs the following processing.

[0053] (1) A process that broadcasts a signal to discover the in-vehicle device 10 and performs authentication based on a request from the in-vehicle device 10. The communication control unit 2011 periodically broadcasts beacon frames to discover the in-vehicle device 10. When a response is received from the in-vehicle device 10, the communication control unit 2011 performs a handshake with the in-vehicle device 10, which includes authentication processing. The authentication process is performed by the authentication unit 2012, which will be described later. Furthermore, if the authentication result for the target in-vehicle device 10 has already been received, the authentication process is omitted (see below). The transmission of beacon frames and authentication processing are performed using the first frequency band.

[0054] (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. The data communication is performed in the first frequency band. Data communication may be performed, for example, by repeatedly sending multiple data blocks and receiving block acknowledgments.

[0055] Furthermore, the communication control unit 2011 has a function to control handovers between multiple roadside devices 20. For example, based on the communication status 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 (handover). For example, the communication control unit 2011 determines another roadside device 20 that will be the new connection destination of the in-vehicle device 10 and transmits information about that roadside device 20 to the in-vehicle device 10. This information includes information about candidate roadside devices 20 for connection destinations. This information is transmitted using the first frequency band. The in-vehicle device 10 can use this information to switch the connection destination roadside device 20. Furthermore, the communication control unit 2011 transmits information about the on-board device 10 to other roadside devices 20 that are candidates for handover. This information is transmitted using the second frequency band.

[0056] Furthermore, the communication control unit 2011 continuously transmits stop request signals using the second frequency band during data communication with the in-vehicle device 10. The stop request signals are broadcast. It may also be transmitted via unicast to other roadside devices 20 that may cause interference. The communication control unit 2011 terminates the transmission of the stop request signal when data communication between itself and the in-vehicle device 10 ends.

[0057] Furthermore, the communication control unit 2011 stops transmitting the aforementioned beacon frames during the period when it receives a stop request signal from another roadside device 20.

[0058] The authentication unit 2012 authenticates the in-vehicle device 10 based on a request from the communication control unit 2011. The authentication unit 2012 may, for example, perform authentication using PSK (Pre-Shared Key). In this case, the authentication information will be a key generated based on a passphrase. Alternatively, the authentication unit 2012 may, for example, perform IEEE802.1x authentication. In this case, the authentication information will be a combination of username and password, or an electronic certificate.

[0059] 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 information is transmitted using the second frequency band. As a result, other roadside devices 20 can continue communication without having to perform authentication again if a handover occurs.

[0060] [Processing flowchart] Next, the processing flow in communication will be explained. Figure 6 is a diagram illustrating the processing phases performed by the in-vehicle device 10 and the roadside device 20 according to this embodiment. In this example, the explanation will be based on the assumption that a vehicle equipped with the in-vehicle device 10 is traveling on a road where multiple roadside devices 20 are arranged.

[0061] The first phase (P1) is the phase in which the in-vehicle device 10 recognizes the presence of the roadside device 20 and performs a handshake with the communication system (connection phase). In the connection phase, the in-vehicle device 10 receives a beacon frame transmitted from the roadside device 20 and, in response, requests a handshake from the communication system. The handshake is performed through the transmission of a probe request, an authentication request, an association request, etc. These data are transmitted in the first frequency band. When a roadside device 20 receives a handshake request from an in-vehicle device 10, it establishes a connection with the in-vehicle device 10 and then performs authentication of the in-vehicle device 10. The authentication result is shared with multiple other roadside devices 20 included in the communication system via the second frequency band. Each of the roadside devices 20 can recognize that the in-vehicle device 10 has been authenticated by the communication system, based on the acquired authentication result.

[0062] The next phase (P2) is the phase in which the in-vehicle device 10 and the roadside device 20 transmit and receive data (transmission / reception phase). Once the connection between the in-vehicle device 10 and the roadside device 20 is established and authentication of the in-vehicle device 10 is completed, data communication between the in-vehicle device 10 and the roadside device 20 begins. In the transmission / reception phase, for example, the transmission of multiple data blocks and the reception of block acknowledgments may be repeated.

[0063] During the transmission / reception phase, if predetermined conditions are met, the system proceeds to the phase for determining whether a handover is necessary. These predetermined conditions may include, for example, the communication quality between the in-vehicle device 10 and the roadside device 20 falling below a predetermined value.

[0064] In the handover determination phase (P3), the roadside device 20 that is communicating with the in-vehicle device 10 determines that there is another roadside device 20 that can perform the handover. If a handover is possible, the roadside device 20 transmits information to the on-board device 10 about other roadside devices 20 that are candidates for the handover destination, and the on-board device 10 switches the connection destination. If there are no roadside devices 20 that can be used for the handover, communication is terminated.

[0065] Next, we will specifically explain the processes that each device performs in each of the aforementioned phases. Figure 7 is a sequence diagram of data transmitted and received between the in-vehicle device 10 and the roadside device 20 during the connection phase and the transmission / reception phase. In this example, the access point with which the in-vehicle device 10 first communicates is designated as roadside device 20A, and the access point to which the handover takes place is designated as roadside device 20B.

[0066] First, roadside devices 20A and 20B begin the periodic transmission of beacon frames. A beacon frame is data broadcast in the first frequency band by roadside device 20 to announce the presence of its own device. When the in-vehicle device 10 receives a beacon frame from the roadside device 20, the in-vehicle device 10 initiates the procedure to connect to the roadside device 20.

[0067] The beacon frame contains the identifier of the roadside device 20, and the in-vehicle device 10 sends a probe request to the roadside device 20 containing the identifier of the roadside device 20 that it wishes to connect with. If beacon frames are received from multiple roadside devices 20, the in-vehicle device 10 may select the roadside device 20 with the strongest signal strength. In this case, the in-vehicle device 10 selects roadside device 20A as the connection destination and sends a probe request to roadside device 20A.

[0068] When the roadside device 20A receives a probe request addressed to itself, the roadside device 20A stops transmitting beacon frames (step S12) and sends a probe response containing its own network information, etc., to the in-vehicle device 10. Upon receiving a 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.

[0069] When the roadside device 20A receives an authentication request, it proceeds to the step of performing authentication of the in-vehicle device 10 (step S13). In step S13, 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 IEEE802.1x authentication.

[0070] Once the 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 S14). For example, the roadside device 20A (authentication unit 2012) transmits the authentication result performed in step S13 to a roadside device 20B belonging to the same communication system (for example, a roadside device 20B having the same group address as roadside device 20A). This eliminates the need for each roadside device 20 to individually authenticate the in-vehicle device 10.

[0071] Furthermore, if the authentication unit 2012 has already received authentication results from other roadside devices 20 for the target in-vehicle device 10, the authentication process will be skipped.

[0072] Then, the roadside device 20A starts broadcasting a signal requesting the cessation of beacon frame transmission (stop request signal) (step S15). The stop request signal is transmitted continuously until the stop timing arrives. The stop request signal is an unmodulated signal (for example, This may also be a pulse signal with a fixed pulse width. Upon receiving a stop request signal, the roadside device 20B stops the periodic transmission of beacon frames until the continuously transmitted stop request signals are interrupted (step S16).

[0073] The aforementioned authentication results and stop request signals are transmitted via the second frequency band. The second frequency band is a lower frequency band than the primary frequency band (first frequency band) used for data communication. Generally, as the frequency of radio waves decreases, the communication range widens due to diffraction attenuation characteristics. Therefore, the roadside device 20A can stop transmitting beacon frames to the roadside device 20B at a time before the in-vehicle device 10 enters the communication range of the roadside device 20B's first frequency band.

[0074] Once the aforementioned process is complete, the roadside device 20A sends a notification (authentication completion notification) to the on-board device 10 indicating that authentication has been completed.

[0075] Once authentication is complete, the in-vehicle device 10 sends an association request to the roadside device 20A, and the roadside device 20A sends an association response to the in-vehicle device 10. Additionally, procedures for encrypted communication may be performed. The above process completes the handshake between the in-vehicle device 10 and the communication system.

[0076] Once the handshake between the in-vehicle device 10 and the communication system is complete, data communication is initiated in step S17. The data communication may, for example, involve the in-vehicle device 10 transmitting data collected in the vehicle to the roadside device 20A. The data communication may also be performed by repeatedly transmitting multiple data blocks and receiving block acknowledgments.

[0077] Note that the order of some of the processes shown in Figure 7 may be changed. For example, the process in step S15 (the process of initiating the transmission of the stop request signal) may be performed at any time before the process in step S17 is executed.

[0078] Figure 8 is a sequence diagram of data transmitted and received between the in-vehicle device 10 and the roadside device 20 during the handover phase. The illustrated process begins when the roadside device 20A decides to hand over the communication from the in-vehicle device 10 to another roadside device 20B. Whether or not to perform a handover can be determined based on, for example, the location information of the in-vehicle device 10, the radio wave field strength, the communication error rate, etc.

[0079] First, in step S21, the communication control unit 2011 starts the handover process. In this step, based on information such as the movement of the in-vehicle device 10, the location information of the in-vehicle device 10, and the location information of other roadside devices 20, a candidate roadside device (in this example, roadside device 20B) is determined as the next access point (handover destination) to which the in-vehicle device 10 will connect. Note that there may be multiple candidate roadside devices.

[0080] Once a candidate roadside device for the handover destination is determined, the communication control unit 2011 of roadside device 20A terminates the transmission of the stop request signal, which it had been continuing since step S15 (step S22). Detecting this, roadside device 20B resumes transmitting the beacon frame (step S23). Furthermore, the communication control unit 2011 of the roadside device 20A transmits information regarding the target in-vehicle device 10 to the communication control unit 2011 of the roadside device 20B in the second frequency band. This information may include the identifier and movement status of the in-vehicle device 10. Furthermore, the communication control unit 2011 of the roadside device 20A transmits information to the in-vehicle device 10 regarding the roadside device that is a candidate for the handover destination. This allows the in-vehicle device 10 to recognize the roadside device 20 to which it should connect next.

[0081] If the identifier of roadside device 20B is notified to the on-board device 10 as the roadside device to which the handover will occur, the on-board device 10 will respond to the beacon frame transmitted from roadside device 20B and initiate a connection with roadside device 20B. If there are multiple candidates for roadside devices to which the handover will occur, the on-board device 10 may decide which roadside device 20 to connect to next based on radio wave conditions, etc. The series of connection procedures, starting with the reception of the beacon frame, are as described with reference to Figure 7. If the authentication result of the in-vehicle device 10 has been shared in advance, the authentication process is omitted and communication begins immediately.

[0082] As described above, in the first embodiment, the roadside device 20, while communicating with the in-vehicle device 10 using the first frequency band, uses the second frequency band to request a nearby roadside device 20 to stop transmitting beacon frames. With this configuration, interference between data communication frames and control frames between adjacent roadside devices can be avoided, enabling faster and more reliable data communication.

[0083] (modified version) 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.

[0084] Furthermore, in the embodiment, an example was given in which the authentication results of the in-vehicle device 10 and information for handover are shared among multiple roadside devices using the second frequency band. However, other information related to the in-vehicle device 10 may also be shared using the second frequency band. Examples of such information include location information, attribute information, speed, and direction of movement information of the in-vehicle device 10.

[0085] Furthermore, while the embodiment shows an example of transmitting (uploading) data from the in-vehicle device 10 to the communication system, the direction of communication is not limited to this. It is also possible to transmit data from the communication system to the in-vehicle device 10, and data may be freely sent and received within the communication period.

[0086] Furthermore, in this embodiment, the second frequency band is set to a frequency band of less than 5 GHz and the first frequency band is set to a frequency band of 5 GHz or higher, but other frequency bands may also be used.

[0087] Furthermore, in the embodiment, an example was given in which a beacon frame (first control signal) is transmitted in the first frequency band and a stop request signal (second control signal) is transmitted in the second frequency band. However, as long as the frequencies are different, the frequency bands (for example, megahertz band and gigahertz band, 2.4GHz band and 5GHz band, etc.) do not necessarily have to be different. For example, they may be different channels in a wireless LAN. Furthermore, the modulation scheme and bitrate of the signals transmitted in the first frequency band and the signals transmitted in the second frequency band may differ. The modulation scheme and bitrate can also be set so that the signal transmitted in the second frequency band has a wider range than the signal transmitted in the first frequency band.

[0088] Furthermore, although the embodiment shows an example where the authentication result of the in-vehicle device 10 is transmitted from roadside device 20A to roadside device 20B, three or more roadside devices may relay the received information to each other. This makes it possible for all roadside devices 20 included in the communication system to share information about the in-vehicle device 10.

[0089] 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.

[0090] 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.

[0091] 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. [Explanation of symbols]

[0092] 10...In-vehicle equipment 20...Roadside equipment 101,201...Control Unit 102,202...Storage section 103,203... Communications Department 104...Location information acquisition unit 105...Input / output section

Claims

1. In a communication system in which a mobile user device communicates with multiple access points, a communication method performed by a first access point included in the multiple access points, Transmitting a first control signal in a first frequency band to control communication with the user device, Data communication with the user device is performed in the first frequency band. During data communication with the user device, a second control signal is transmitted in the second frequency band, which is a signal requesting other access points to stop transmitting the first control signal. A communication method for executing this.

2. During data communication with the user device, the second control signal is continuously transmitted. The communication method according to claim 1.

3. The first control signal includes a signal that is transmitted periodically to discover the user device. If the second control signal transmitted from another access point is being received, the transmission of the first control signal is stopped. The communication method according to claim 1.

4. The second frequency band is a frequency band with a wider communication range than the first frequency band. The communication method according to claim 1.

5. The second control signal is an unmodulated signal. The communication method according to claim 1.

6. The aforementioned communication system is a communication system capable of handover, The aforementioned second frequency band is a frequency band for sharing information about the user device to be handed over with other access points belonging to the same group. The communication method according to claim 1.

7. The aforementioned communication system is a communication system capable of handover, A third control signal, which is a signal for sharing information about the user device to be handed over with other access points, is transmitted in the second frequency band. The communication method according to claim 1.

8. In a communication system in which a mobile user device communicates with multiple access points, a communication device that functions as a first access point, Transmitting a first control signal in a first frequency band to control communication with the user device, Data communication with the user device is performed in the first frequency band. During data communication with the user device, a second control signal is transmitted in the second frequency band, which is a signal requesting other access points to stop transmitting the first control signal. A communication device having a control unit that performs the following.

9. The control unit continuously transmits the second control signal during data communication with the user device. The communication device according to claim 8.

10. The first control signal includes a signal that is transmitted periodically to discover the user device. The control unit stops transmitting the first control signal when it is receiving the second control signal transmitted from another access point. The communication device according to claim 8.

11. The second frequency band is a frequency band with a wider communication range than the first frequency band. The communication device according to claim 8.

12. The second control signal is an unmodulated signal. The communication device according to claim 8.

13. The aforementioned communication system is a communication system capable of handover, The aforementioned second frequency band is a frequency band for sharing information about the user device to be handed over with other access points belonging to the same group. The communication device according to claim 8.

14. The aforementioned communication system is a communication system capable of handover, The control unit transmits a third control signal in the second frequency band, which is a signal for sharing information about the user device to be handed over with other access points. The communication device according to claim 8.

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