Roadside communication device, time synchronization method, and computer program

Abstract

To secure precision of a local time by time synchronization while suppressing delay of information processing other than the time synchronization.SOLUTION: A road side communication device to be used in a traffic control system includes: a high-order side transmission / reception section for executing signal processing based on a high-order side transmission system; a low-order side transmission / reception section for executing signal processing based on a low-order side transmission system; and a communication control section for repeating a downlink frame from the high-order side transmission / reception section to the low-order side transmission / reception section and repeating an uplink frame from the low-order side transmission / reception section to the high-order side transmission / reception section. The communication control section includes a CPU for performing time synchronization to correct a time of an internal clock with a reference pulse signal as an interruption signal with the highest priority on the basis of time information and the reference pulse signal generated by a satellite. The CPU executes priority cancellation processing to cancel setting to set the reference pulse signal to have the highest priority, only for a predetermined period.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a roadside communication device, a time synchronization method, and a computer program. [Background technology]

[0002] Patent Document 1 describes a signal control device that includes an internal clock, a signal generation unit, an acquisition unit, and a time management unit. The signal generation unit generates a control signal for a signal lamp based on the internal time. The acquisition unit acquires time information and a reference pulse signal (e.g., a 1PPS signal). When the time management unit acquires time information, it performs separate tasks: a time detection process that detects the reference time that is the starting point of the time information based on a reference pulse signal, and a time correction process that corrects the internal time (local time) based on the time information and the reference time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184103 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the time synchronization of Patent Document 1, if the reference pulse signal is detected as an interrupt signal, the accuracy of pulse detection is improved compared to the case of sampling processing, and the accuracy of the corrected local time can also be improved. However, since the reference pulse signal is a pulse signal with a period of, for example, one second, if interrupt processing is unconditionally executed at each rising edge of the pulse, the highest priority interrupt processing will intervene every second, which may cause other information processing to be delayed beyond the acceptable range.

[0005] An object of the present disclosure is to ensure the accuracy of local time achieved by time synchronization while suppressing delays in information processing other than time synchronization. [Means for solving the problem]

[0006] An apparatus according to one embodiment of the present disclosure is a roadside communication device used in a traffic control system, and comprises an upper-side transceiver unit that performs signal processing based on an upper-side transmission method, a lower-side transceiver unit that performs signal processing based on a lower-side transmission method, and a communication control unit that relays downlink frames from the upper-side transceiver unit to the lower-side transceiver unit and relays uplink frames from the lower-side transceiver unit to the upper-side transceiver unit, wherein the communication control unit has a CPU capable of performing time synchronization based on time information and a reference pulse signal generated by a satellite, using the reference pulse signal as a top priority interrupt signal to correct the time of an internal clock, and the CPU performs a priority release process that releases the setting that gives the reference pulse signal top priority for a predetermined period of time.

[0007] A method according to one aspect of the present disclosure is a time synchronization method executed by a CPU mounted on a roadside communication device, and includes a step of the CPU correcting the time of an internal clock based on time information generated by a satellite and a reference pulse signal, using the reference pulse signal as a top priority interrupt signal, and a step of the CPU canceling the setting that gives top priority to the reference pulse signal for a predetermined period of time.

[0008] A computer program according to one embodiment of the present disclosure is a computer program for causing a computer to function as a roadside communication device capable of time synchronization, and includes a step in which a CPU of the roadside communication device corrects the time of an internal clock based on time information and a reference pulse signal generated by a satellite, using the reference pulse signal as a top priority interrupt signal, and a step in which the CPU of the roadside communication device cancels the setting that gives top priority to the reference pulse signal for a predetermined period of time.

[0009] The present disclosure can be realized not only as a system and device having the above-mentioned characteristic configuration, but also as a program for causing a computer to execute such characteristic configuration. Furthermore, the present disclosure can be realized as a semiconductor integrated circuit that realizes part or all of the system and device. Effect of the Invention

[0010] According to the present disclosure, it is possible to ensure the accuracy of local time through time synchronization while suppressing delays in information processing other than time synchronization. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an example of the overall configuration of a traffic control system. [Diagram 2] FIG. 2 is a table showing upper side communication paths and lower side communication paths that can be adopted by roadside communication devices, sorted by type of roadside communication device. [Diagram 3] FIG. 3 is a block diagram showing an example of an internal configuration of the roadside communication device. [Figure 4] FIG. 4 is a block diagram illustrating an example of the internal configuration of the communication control unit. [Diagram 5] FIG. 5 is a sequence diagram illustrating an example of the operation of the communication control unit. [Figure 6] FIG. 6 is an explanatory diagram illustrating an example of the priority release process executed by the CPU. [Figure 7] FIG. 7 is an explanatory diagram showing another example of the priority release process executed by the CPU. [Figure 8] FIG. 8 is a table showing the priority order of information processing executed by the CPU for each type of roadside communication device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <Overview of the embodiment of the present disclosure> Below, an overview of the embodiments of the present disclosure will be listed and described. (1) The device of this embodiment is a roadside communication device used in a traffic control system, and comprises an upper-side transceiver unit that performs signal processing based on an upper-side transmission method, a lower-side transceiver unit that performs signal processing based on a lower-side transmission method, and a communication control unit that relays downlink frames from the upper-side transceiver unit to the lower-side transceiver unit and relays uplink frames from the lower-side transceiver unit to the upper-side transceiver unit, wherein the communication control unit has a CPU capable of performing time synchronization based on time information and a reference pulse signal generated by a satellite, thereby correcting the time of an internal clock using the reference pulse signal as a top priority interrupt signal, and the CPU performs a priority release process that releases the setting that gives the reference pulse signal top priority for a specified period of time.

[0013] According to the roadside communication device of this embodiment, the CPU executes a priority cancellation process that cancels the setting that gives the reference pulse signal the highest priority for a specified period of time, thereby ensuring the accuracy of local time achieved by time synchronization while suppressing delays in information processing other than time synchronization.

[0014] (2) In the roadside communication device of this embodiment, the priority release process is preferably a process of masking a maskable interrupt port to which the reference pulse signal is input for the predetermined period of time. In this case, the rising edge of the reference pulse signal is not input to the interrupt port during the predetermined period, so the frequency of time synchronization is reduced to approximately every predetermined period. This ensures the accuracy of the local time obtained by time synchronization while suppressing delays in information processing other than time synchronization.

[0015] (3) In the roadside communication device of this embodiment, the priority canceling process may be a process of lowering the priority of the reference pulse signal that is currently set as the highest priority for the predetermined period of time. In this case, since the reference pulse signal is no longer the highest priority during the predetermined period, information processing other than time synchronization is executed with priority during the predetermined period. Therefore, it is possible to ensure the accuracy of the local time by time synchronization while suppressing delays in information processing other than time synchronization.

[0016] (4) In the roadside communication device of this embodiment, the roadside communication device is preferably a traffic signal controller used for controlling power to a signal lamp at an intersection. In this case, a traffic signal controller that exhibits the above-mentioned operational effects can be obtained as a roadside communication device used in a traffic control system.

[0017] (5) When the roadside communication device of this embodiment is a traffic signal controller, it is preferable that, among the information processing performed by the CPU, receiving from a central device has the second highest priority, and transmitting to the central device has the third highest priority. The reason is that, considering the inherent functions of a traffic signal controller, the priority of information processing related to signal control, such as signal control commands and signal operation status information, should be raised.

[0018] (6) In the roadside communication device of the present embodiment, the roadside communication device is preferably a wireless communication device used for at least one of providing information to vehicles and collecting information from vehicles. In this case, among roadside communication devices used in a traffic control system, a wireless communication device (for example, an optical beacon and an ITS wireless roadside unit) that provides the above-mentioned operational effects can be obtained.

[0019] (7) In the roadside communication device of this embodiment, the wireless communication device is preferably an optical beacon that uses near-infrared light as a wireless medium. In this case, among the roadside communication devices used in the traffic control system, an optical beacon having the above-mentioned operational effects can be obtained.

[0020] (8) When the roadside communication device of this embodiment is an optical beacon, it is preferable that, among the information processing executed by the CPU, reception from the vehicle-mounted unit has the second highest priority, and transmission to the vehicle-mounted unit has the third highest priority. The reason is that in order to ensure reliable optical communication with the vehicle-mounted device in the limited communication area on the road, the priority of information processing related to communication with the vehicle-mounted device should be raised. Also, the reason for giving the priority to reception from the vehicle-mounted device higher than the priority of transmission to the vehicle-mounted device is that with optical beacons, the transmission information is switched when reception from the vehicle-mounted device is triggered.

[0021] (9) In the roadside communication device of the present embodiment, the wireless communication device is preferably an ITS wireless roadside unit that uses radio waves in a predetermined frequency band as a wireless medium. In this case, an ITS wireless roadside unit that provides the above-mentioned operational effects can be obtained among the roadside communication devices used in a traffic control system.

[0022] (10) When the roadside communication device of this embodiment is an ITS wireless roadside unit, it is preferable that, among the information processing executed by the CPU, transmission to an in-vehicle unit has the second highest priority, and reception from a sensor has the third highest priority. The reason is that, considering that ITS wireless roadside units provide vehicle-oriented information with high freshness, such as vehicle detection information, the priority of information processing related to transmission to in-vehicle units should be raised.Also, considering that information with high frequency of updates, such as sensor information generated by ITS-compatible sensors, is collected, the priority of information processing related to reception from sensors should be raised.

[0023] (11) In the roadside communication device of the present embodiment, it is preferable that the roadside communication device is a roadside repeater that relays communication between a central unit and another roadside communication device. In this case, among the roadside communication devices used in the traffic control system, a roadside repeater device that exhibits the above-mentioned operational effects can be obtained.

[0024] (12) The method according to this embodiment is a time synchronization method executed by the CPU of the roadside communication device described above in (1) to (11). Therefore, the time synchronization method according to this embodiment has the same effects as those of the roadside communication device described above in (1) to (11).

[0025] (13) The program according to the present embodiment is a computer program for causing a computer to function as the roadside communication device according to any one of (1) to (11) above. Therefore, the program according to the present embodiment has the same effects as those of the roadside communication device according to any one of (1) to (11) above.

[0026] <Details of the embodiment of the present disclosure> Hereinafter, the details of the embodiments of the present disclosure will be described with reference to the drawings. Note that at least some of the embodiments described below may be combined in any combination.

[0027] [Overall system configuration] FIG. 1 is a block diagram showing an example of the overall configuration of a traffic control system 10. As shown in FIG. As shown in FIG. 1, a traffic control system 10 of this embodiment includes a central device 1 and a plurality of roadside communication devices (hereinafter also referred to as “communication devices”) 2 which are roadside communication nodes that communicate with the central device 1.

[0028] The roadside communication devices 2 constituting the traffic control system 10 include a roadside repeater 2A, a traffic signal controller 2B, an optical beacon 2C, and an ITS (Intelligent Transport Systems) wireless roadside device 2D. The central device 1 is installed in a traffic control center or the like. The roadside relay device 2A is installed at an intersection or a road relatively far from the central device 1. The other roadside communication devices 2B to 2D are installed at intersections or roads relatively close to the roadside relay device 2A.

[0029] In this embodiment, information contained in the downstream transmission signal from the central device 1 to the roadside communication device 2 is referred to as "downlink information DL", and information contained in the upstream transmission signal from the roadside communication device 2 to the central device 1 is referred to as "uplink information UL".

[0030] In addition, when focusing on one communication device 2, the communication carried out on the central device 1 side (left side in Figure 1) from the perspective of that device is called "upper side communication", and the communication path and transmission method adopted for the upper side communication are called the "upper side communication path" and the "upper side transmission method", respectively. Similarly, when focusing on one communication device 2, communication carried out on the opposite side of the central device 1 from the perspective of the device itself (the right side in Figure 1) is referred to as "lower-side communication," and the communication path and transmission method adopted for lower-side communication are referred to as the "lower-side communication path" and "lower-side transmission method," respectively.

[0031] The central device 1 is, for example, a PC (Personal Computer) server, and has a communication device (not shown) capable of communication based on a predetermined downstream transmission method. The roadside repeater 2A is a communication device having a relay function for communication between the central device 1 and other communication devices 2B to 2D. The upstream communication path of the roadside repeater 2A includes a wireless medium (mobile line) 3 conforming to standards such as LTE (Long Term Evolution) or the fifth generation mobile communication system (5G). However, the upstream communication path of the roadside repeater 2A may be a wired medium such as a dedicated line.

[0032] The communication path for downstream communication of the roadside repeater 2A is formed of a wired medium (communication cable) 4 such as a dedicated line or a private line. One or a plurality of communication devices 2B to 2D are connected to the roadside repeater 2A via the wired medium 4.

[0033] The traffic signal controller 2B is a control device that controls the power supply to the traffic signal lamps of the traffic signal. The optical beacon 2C is a communication device that uses a wired medium (communication cable) 4 for the upper communication path and near-infrared light (wireless medium) for the lower communication path. The ITS wireless roadside unit 2D is a communication device that employs a wired medium (communication cable) 4 for an upper communication path and employs radio waves (wireless medium) in the 700 MHz band for a lower communication path.

[0034] As shown by the wavy line in FIG. 1, an optical beacon 2C or an ITS wireless roadside unit 2D may be connected via a wired medium 5 to the downstream side of the traffic signal controller 2B. In this case, the traffic signal controller 2B serves as a communication device having a relay function for communication between the roadside repeater 2 and other communication devices 2C and 2D. Note that the roadside repeater 2A and the traffic signal controller 2B may be connected to traffic control devices other than those shown in the figure, such as a vehicle detector and a traffic information board.

[0035] 1, the central device 1 transmits a transmission signal including downlink information DL for the communication devices 2B to 2D to be controlled to the wireless base station 6. The wireless base station 6 transfers the received transmission signal to the roadside relay device 2A. The roadside repeater 2A extracts the downlink information DL from the transmission signal of the upper side transmission method, and generates a transmission signal based on the lower side transmission method including the extracted downlink information DL. The roadside repeater 2A transmits the generated transmission signal to the communication devices 2B to 2C of the predetermined destination.

[0036] The communication devices 2B to 2D under the control of the roadside repeater 2A transmit transmission signals, including uplink information UL for the central device 1, based on the upper side transmission method to the roadside repeater 2A. The roadside repeater 2A extracts the uplink information UL from the received transmission signal, and generates a transmission signal based on the upper side transmission method including the extracted uplink information UL. The roadside repeater 2A transmits the generated transmission signal to the wireless base station 6. The wireless base station 6 transfers the received transmission signal to the central device 1.

[0037] The downlink information DL addressed to the traffic signal controller 2B includes, for example, a "signal control command." The signal control command is control information including a cycle length, a split, an offset, and the like to be executed by the traffic signal controller 2B in the next cycle. The uplink information UL transmitted from the traffic signal controller 2B includes, for example, "signal control execution information" and "signal operation status information." The signal control execution information is information that indicates the control content executed by the traffic signal controller 2B in the previous cycle. The signal operation status information is information that indicates the operation status of the traffic signal controller 2B in the current cycle.

[0038] The downlink information DL addressed to the optical beacon 2C includes, for example, “traffic congestion information” and “current location information.” The uplink information UL transmitted from the optical beacon 2C includes, for example, “probe data” (vehicle travel trajectory information) received from a vehicle. The downlink information DL addressed to the ITS wireless roadside device 2D includes, for example, “signal information” and “road linear information.” The uplink information UL transmitted from the ITS wireless roadside device 2D includes, for example, “vehicle-to-vehicle communication information” received from a vehicle.

[0039] FIG. 2 is a table showing upper side communication paths and lower side communication paths that can be adopted by the roadside communication device 2, sorted by type of the roadside communication device 2. In FIG. In Figure 2, "UD type" means a transmission method that conforms to the "UD type interface standard" established by the Universal Transportation Management System Association (UTMS Association). The UD type transmission method is a transmission method that enables IP (Internet Protocol) communication.

[0040] "U-type" refers to a transmission method that conforms to the "U-type interface standard" established by the UTMS Society. The U-type transmission method is a serial communication method that does not support IP communication. "M-type" refers to a transmission method that conforms to the "M-type interface standard" established by the UTMS Society. The M-type transmission method is a serial communication transmission method that does not support IP communication.

[0041] [Internal configuration of roadside communication device] FIG. 3 is a block diagram showing an example of the internal configuration of the roadside communication device 2. As shown in FIG. 3, the roadside communication device 2 includes a housing 20 and a plurality of electronic devices housed in the housing 20. The plurality of electronic devices include an upper-side transceiver unit 21, a lower-side transceiver unit 22, a communication control unit 23, a storage unit 24, and a GNSS (Global Navigation Satellite System) receiver unit 25. The GNSS receiver unit 25 may be disposed outside the housing 20.

[0042] The upper transceiver 21, the lower transceiver 22, the storage unit 24 and the GNSS receiver 25 are each electrically connected to the communication control unit 23. In addition, in the case of a communication device 2 having multiple communication ports for lower-side communication, such as a roadside relay device 2A and a traffic signal controller 2B, multiple lower-side transceivers 22 are provided, as shown by the wavy lines in Figure 3.

[0043] The upper-side transmitting / receiving unit 21 is a communication interface that executes predetermined signal processing (such as modulation / demodulation, photoelectric conversion, and AD / DA conversion) based on an upper-side transmission method. The downstream side transmitting / receiving unit 22 is a communication interface that executes predetermined signal processing (such as modulation / demodulation, optical / electrical conversion, and AD / DA conversion) based on a downstream side transmission method.

[0044] The upper side transmitting / receiving unit 21 demodulates or converts the transmission signal (carrier signal) input from the upper side communication path into an electrical signal to regenerate a downstream frame. The upper side transmitting / receiving unit 21 outputs the regenerated downstream frame to the communication control unit 23. The upper-side transmitting / receiving unit 21 modulates the upstream frame input from the communication control unit 23 into a transmission signal of a predetermined frequency or converts it into an optical signal. The upper-side transmitting / receiving unit 21 outputs the modulated or converted transmission signal to the upper-side communication path.

[0045] The lower-side transmitting / receiving unit 22 demodulates or converts the transmission signal (carrier signal) input from the lower-side communication path into an electrical signal to reproduce an upstream frame. The lower-side transmitting / receiving unit 22 outputs the reproduced upstream frame to the communication control unit 23. The lower-side transceiver 22 modulates the downstream frame input from the communication control unit 23 into a transmission signal of a predetermined frequency or converts it into an optical signal. The lower-side transceiver 22 outputs the modulated or converted transmission signal to the lower-side communication path.

[0046] The communication control unit 23 is made up of an arithmetic processing device including a central processing unit (CPU), a random access memory (RAM), and a field-programmable gate array (FPGA). The storage unit 24 is made up of an auxiliary storage device including at least one non-volatile memory of a hard disk drive (HDD) and a solid state drive (SDD). The storage unit 24 may include a flash read only memory (ROM), a universal serial bus (USB) memory, an SD card, or the like. The communication control unit 23 reads out the computer program stored in the storage unit 24 into a main memory (RAM) and performs various information processing operations in accordance with the program.

[0047] The communication control unit 23 is capable of performing relay processing involving format conversion on communication frames in both the upstream and downstream directions input from the transmission / reception units 21 and 22 . Specifically, the communication control unit 23 converts the downstream frame of the upper side transmission method input from the upper side transmitting / receiving unit 21 into a format of the lower side transmission method. The communication control unit 23 outputs the converted downstream frame of the lower side transmission method to the lower side transmitting / receiving unit 22.

[0048] Conversely, the communication control unit 23 converts the upstream frame of the lower-side transmission method input from the lower-side transmitting / receiving unit 22 into a format of the upper-side transmission method. The communication control unit 23 outputs the converted upstream frame of the upper-side transmission method to the upper-side transmitting / receiving unit 21. However, when the upper side transmission method and the lower side transmission method are the same (for example, when both are UD type transmission methods), the communication control unit 23 does not perform the above format conversion, and routing is performed based on MAC addresses, IP addresses, etc.

[0049] The communication control unit 23 determines the timing of transmitting a communication frame and the like in accordance with the local time kept by the internal clock 34 (see FIG. 4) of the communication device 2. The communication control unit 23 can execute time synchronization to correct the time of the internal clock 34 by using a satellite system.

[0050] The GNSS receiver 25 is composed of a communication device such as a GPS (Global Positioning System) receiver. The GPS receiver can output a message in a predetermined format, a 1 PPS (1 Pulse Per Second) signal, and a clock signal of a predetermined frequency (10 MHz). The GNSS receiver 25 does not necessarily need to be able to output a clock signal. In this embodiment, the GNSS receiving unit 25 outputs to the communication control unit 23 a message in a National Marine Electronics Association (NMEA) format including time information, and a 1PPS signal, which is a type of reference pulse signal.

[0051] The NMEA message contains time information at the time of positioning (specifically, Coordinated Universal Time). The rising edge of the 1PPS signal indicates the realization point of the time information contained in the NMEA message that the GNSS receiver 25 received immediately before. The communication control unit 23 corrects the local time of the internal clock 34 at the rising edge of the 1PPS signal so that the local time of the internal clock 34 coincides with the time information of the NMEA message (time synchronization).

[0052] [Internal configuration of the communication control unit] FIG. 4 is a block diagram showing an example of the internal configuration of the communication control unit 23. As shown in FIG. 4 shows an example of the configuration of the communication control unit 23 when the communication device 2 is an optical beacon 2C. Therefore, the "vehicle-mounted device" in the figure means a vehicle-mounted device capable of optical communication using near-infrared light. 4, the communication control unit 23 includes an FPGA 31, a buffer memory 32, and a CPU 33. The CPU 33 includes an internal clock 34 and an internal clock 35.

[0053] When upstream data (upstream frame) A received from an in-vehicle device is input from the lower transceiver unit 22, the FPGA 31 outputs the input upstream data A to the buffer memory 32 and outputs a read request for the upstream data A to the CPU 33 via the interrupt port A. The CPU 33 reads the upstream data A from the buffer memory 32, and generates upstream data (upstream frame) A to be transmitted to the central device 1. The generated upstream data A is output to the buffer memory 32 via the FPGA 31. The FPGA 31 retrieves the upstream data A output by the CPU 33 from the buffer memory 32 , and outputs the retrieved upstream data A to the upper transmission / reception unit 21 to transmit it to the central device 1 .

[0054] When downstream data (downstream frame) B received from the central equipment 1 is input from the upper transmission / reception unit 21, the FPGA 31 outputs the input downstream data B to the buffer memory 32. The CPU 33 reads out the downstream data B from the buffer memory 32, and generates downstream data (downstream frame) B to be transmitted to the vehicle-mounted device. The generated downstream data B is output to the buffer memory 32 via the FPGA 31. The FPGA 31 retrieves the downstream data B output by the CPU 33 from the buffer memory 32, and outputs the retrieved downstream data B to the downstream transmitting / receiving unit 22 for transmission to the vehicle-mounted device.

[0055] The FPGA 31 has an input port for the 1PPS signal output by the GNSS receiving unit 25, and outputs the input 1PPS signal to an interrupt port C of the CPU 33, which will be described later. The CPU 33 has a serial communication port to which time information is input from the GNSS receiver 25, and is connected to the FPGA 31 and the buffer memory 32 via a communication bus. The CPU 33 is a CPU capable of hardware interrupts, and has multiple interrupt ports A to C (three in the example).

[0056] The interrupt port A is asserted by the FPGA 31 when an event occurs of "reception from the vehicle-mounted device" (buffering of uplink data A is completed). The interrupt port B is asserted by the FPGA 31 when an event occurs of "reception from the central device 1" (completion of buffering of downstream data B). The interrupt port C is asserted by the FPGA 31 when an event occurs such as the rising edge of the "1PPS signal."

[0057] In this embodiment, it is assumed that the priority order of the interrupt ports A to C with respect to the CPU 33 is set as follows: interrupt port C (first place), interrupt port A (second place), and interrupt port B (third place). The interrupt port C of the CPU 33 is, for example, a maskable interrupt terminal that allows interrupt processing to be enabled / disabled.

[0058] When the interrupt port A is asserted, the CPU 33 reserves the timer mask including the polling process and the interrupt process B with a lower priority, and executes the interrupt process A. The interrupt process A is information processing on the uplink data A received from the vehicle-mounted device. The information processing on the uplink data A includes, for example, a process of determining a data storage location according to the destination of the uplink data A, and a format conversion of the uplink data A.

[0059] When the interrupt port B is asserted, the CPU 33 suspends the timer mask including the polling process and executes the interrupt process B. The interrupt process B is information processing related to the downstream data B received from the central device 1. The information processing related to the downstream data B includes, for example, a process of determining a data storage position according to the destination of the downstream data B, and a format conversion of the downstream data B.

[0060] When the interrupt port C is asserted, the CPU 33 suspends the timer mask including the polling process and the lower priority interrupt processes A and B, and executes the interrupt process C. The interrupt process C is time synchronization using time information and a 1PPS signal. As described above, time synchronization is a process of correcting the local time of the internal clock 34 so that the local time of the internal clock 34 coincides with the time information of the NMEA message at the rising edge of the 1PPS signal.

[0061] The internal clock 35 is made up of a PLL (Phase Locked Loop) circuit including a voltage controlled oscillator, and outputs a clock signal of a predetermined frequency generated by the oscillator to the internal clock 34 . The internal clock 34 keeps track of local time with an accuracy of less than a millisecond, based on a clock signal supplied from the internal clock 35. Note that the internal clock 34 is not limited to a built-in clock of the CPU 34, and may be a clock provided outside the CPU 33, such as a real-time clock (RTC) mounted on a circuit board of the roadside communication device 2.

[0062] 4, the CPU 33 of the present embodiment can also execute a "priority release process" that releases the setting that gives the highest priority to the time synchronization process based on the 1PPS signal for a predetermined period of time. The details of the priority release process will be described later.

[0063] [Operation of the communication control unit] FIG. 5 is a sequence diagram showing an example of the operation of communication control unit 23. As shown in FIG. 5, when the FPGA 31 detects the completion of reception from the central device (completion of reception of downstream data B), it asserts the interrupt port B (priority 3) of the CPU 33 (step S1). As a result, the CPU 33 suspends the timer mask including the polling process (not shown) and starts the interrupt process B.

[0064] Next, when the FPGA 31 detects the completion of reception from the vehicle-mounted device (completion of reception of uplink data A), it asserts the interrupt port A (priority 2) of the CPU 33 (step S2). As a result, the CPU 33 suspends timer masking including polling processing (not shown) and interrupt processing B, and starts interrupt processing A.

[0065] Next, when the FPGA 31 detects the rising edge of the 1PPS signal, it asserts the interrupt port C (priority 1) of the CPU 33 (step S3). As a result, the CPU 33 suspends the timer mask including the polling process (not shown), the interrupt process A, and the interrupt process B, and starts the interrupt process C (time synchronization using time information and the 1PPS signal).

[0066] [Problems with giving top priority to time synchronization based on 1PPS signals] As described above, according to the roadside communication device 2 of this embodiment, the 1PPS signal is input to the highest priority interrupt port C of the CPU 33 capable of hardware interrupts, so that the interrupt processing C (time synchronization) can be started more quickly than in the case where the rising edge of the 1PPS signal is sampled at a predetermined polling interval.

[0067] However, because the 1PPS signal is a pulse signal with a one-second period, if interrupt process C were to be executed unconditionally every time the 1PPS signal rises, interrupt process C, which has the highest priority, would intervene every second, which could cause other information processing such as interrupt processes A and B to be delayed beyond the acceptable range. Furthermore, once time synchronization is performed, the roadside communication device 2 can keep the correct local time within the accuracy range of the internal clock 34 (such as the internal clock of the CPU 33 and a real-time clock) for a while.

[0068] For this reason, it is considered that there is little need to perform the interrupt process C (time synchronization) using the 1PPS signal as an interrupt signal every second, and it is sufficient to perform it every predetermined period To. Therefore, the CPU 33 of this embodiment executes a "priority release process" that releases the setting that gives the 1PPS signal the highest priority for a predetermined period To. If the accuracy of the internal clock 34 is ±50 ppm, the time deviation after, for example, three minutes is a maximum of 50×10 -6 ×180sec=9msec.

[0069] Therefore, assuming that the communication device 2 operates with a time accuracy of 100 msec or less, a maximum time difference of 9 msec is within the acceptable range. For this reason, the predetermined period To for performing the priority release process may be set to, for example, about 3 minutes. The predetermined period To can be timed by the internal clock 34, or may be timed by counting the number of interrupts of the 1PPS signal.

[0070] [Example 1 of priority cancellation processing] FIG. 6 is an explanatory diagram showing an example of the priority release process executed by the CPU 33. As shown in FIG. The priority release process shown in FIG. 6 is a process for masking a maskable interrupt port C for a predetermined period To (hereinafter, referred to as "mask process").

[0071] Specifically, after executing time synchronization once, the CPU 33 outputs a mask command Sm of the 1PPS signal to the FPGA 31. Furthermore, the CPU 33 releases the mask command Sm after a predetermined period To has elapsed. In this case, as shown in FIG. 6, the rising edge of the 1PPS signal is not input to the interrupt port C during the predetermined period To, so that the frequency of time synchronization is reduced to approximately every predetermined period To (for example, every 3 minutes).

[0072] Therefore, by executing the masking process in FIG. 6, it is possible to ensure the accuracy of the local time based on the time synchronization while suppressing delays in information processing other than the time synchronization. In the example of FIG. 6, the mask command Sm is output to the FPGA 31, but the mask process for the interrupt port C may be executed within the CPU 33.

[0073] [Example 2 of priority cancellation processing] FIG. 7 is an explanatory diagram showing another example of the priority canceling process executed by the CPU 33. In FIG. The priority canceling process shown in FIG. 7 is a process for lowering the priority of the 1PPS signal that is set as the highest priority for a predetermined period To (hereinafter, referred to as a "priority changing process").

[0074] Specifically, after executing time synchronization once, the CPU 33 outputs an assignment change command Sc for the interrupt ports A to C to the FPGA 31. After a predetermined period To has elapsed, the CPU 33 negates the assignment change command Sc or outputs a restoration command Sr to the FPGA 31 to restore the assignment to the original state. In the example of Figure 7, the allocation change command Sc is a command to change reception from the vehicle-mounted unit to interrupt port C (priority 1), reception from the central device to interrupt port B (priority 2), and 1PPS signal to interrupt port B (priority 3).

[0075] In this case, since the 1PPS signal is input to the interrupt port B, which does not have the highest priority, during the predetermined period To, information processing other than time synchronization is given priority during the predetermined period (for example, 3 minutes) To. Therefore, by executing the order change process in FIG. 7, it is possible to ensure the accuracy of the local time based on the time synchronization while suppressing delays in information processing other than the time synchronization.

[0076] In the example of FIG. 7, the allocation change command Sc and the restoration command Sr are output to the FPGA 31. However, the CPU 33 may internally execute the priority change process for the interrupt ports A to C. Furthermore, the priority of the 1PPS signal does not necessarily have to be changed to the lowest priority, but may be changed to the second priority or lower.

[0077] [Variations in priority order] Fig. 8 is a table summarizing the priority of information processing executed by the CPU 33 for each type of roadside communication device 2. Specifically, Fig. 8 is a table summarizing preferred priorities of information processing for the traffic signal controller 2B, the optical beacon 2C, and the ITS wireless roadside device 2D. As shown in FIG. 8, for all the roadside communication devices 2B to 2D, the priority of the 1PPS signal is set to "1" (highest priority) so that time synchronization is set as the highest priority.

[0078] In the case of the traffic signal controller 2B, it is preferable to set the priority of "receiving from the central unit" to "2" and the priority of "transmitting to the central unit" to "3." The reason is that, considering the function of the traffic signal controller 2B (power control of signal lamps), the priority of information processing related to signal control, such as signal control commands and signal operation status information, should be raised.The reason why the priority of "transmission to ITS wireless roadside units" is relatively high at "4" is because the priority of transmission to in-vehicle units is "2" in the ITS wireless roadside units described below.

[0079] In the case of the optical beacon 2C, it is preferable to set the priority of "receiving from the vehicle-mounted unit" to "2" and the priority of "transmitting to the vehicle-mounted unit" to "3." The reason is that in order to ensure reliable optical communication with the onboard unit in the limited communication area on the road (approximately 6 m in the direction of vehicle travel), the priority of information processing related to communication with the onboard unit should be raised. Also, since road-to-vehicle communication between the optical beacon 2C and the onboard unit is initiated upon reception of uplink light, reception from the onboard unit should be given as high a priority as possible.

[0080] In the case of the ITS wireless roadside unit 2D, it is preferable to set the priority of "transmission to vehicle-mounted unit" to "2" and the priority of "reception from sensor" to "3." The reason is that, considering that the ITS wireless roadside unit 2D provides vehicle-oriented information with high freshness, such as vehicle detection information, the priority of information processing related to transmission to the in-vehicle unit should be raised.Also, considering that information with high update frequency, such as sensor information generated by ITS-compatible sensors, is collected, the priority of information processing related to reception from the sensor should be raised.

[0081] [Other Modifications] The embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of the equivalents of the configurations described in the claims.

[0082] In the above embodiment, the reference pulse signal is a 1PPS signal, but the period and the number of pulses of the reference pulse signal are not particularly limited. Specifically, the reference pulse signal may be a signal in which one pulse occurs every several seconds (e.g., a PP2S (Pulse Per 2 Seconds) signal), or a signal in which a pulse occurs multiple times per second (e.g., a 5PPS (5 Pluses Per Seconds) signal in which five pulses occur per second). [Explanation of symbols]

[0083] 1 central unit 2 Roadside communication device (communication device) 2A Roadside repeater 2B Traffic signal controller 2C Light Beacon 2D ITS wireless roadside machine 3 Wireless medium 4. Wired media (communication cables) 5. Wired media (communication cables) 20. Cabinet 21 Upper side transmitter / receiver 22 Lower side transmitter / receiver 23 Communication control section 24 Memory section 25 GNSS receiver 31 FPGA 32 Buffer Memory 33 CPU 34 Internal Clock 35 Internal Clock A interrupt port (priority 2) B Interrupt port (priority 3) C Interrupt port (priority 1) UL Uplink Information DL Downlink Information

Claims

1. A roadside communication device for use in a traffic control system, an upper-side transceiver unit that performs signal processing based on an upper-side transmission method; a lower-side transmitting / receiving unit that performs signal processing based on a lower-side transmission method; a communication control unit that relays downstream frames from the upper side transceiver unit to the lower side transceiver unit and relays upstream frames from the lower side transceiver unit to the upper side transceiver unit, The communication control unit a CPU capable of executing time synchronization for correcting the time of an internal clock based on time information and a reference pulse signal generated by a satellite, said reference pulse signal being used as an interrupt signal with the highest priority; The CPU includes: A roadside communication device that executes a priority cancellation process that cancels the setting of the reference pulse signal as having the highest priority for a predetermined period of time by lowering the priority level of the reference pulse signal that is currently set as having the highest priority for the predetermined period of time.

2. The roadside communication device includes:

2. The roadside communication device according to claim 1, which is a traffic signal controller used for controlling power to signal lamps at an intersection.

3. 3. The roadside communication device according to claim 2, wherein, among the information processes executed by said CPU, reception from a central unit has the second highest priority, and transmission to said central unit has the third highest priority.

4. The roadside communication device includes:

2. The roadside communication device according to claim 1, which is a wireless communication device used for at least one of providing information to vehicles and collecting information from vehicles.

5. The wireless communication device includes:

5. The roadside communication device according to claim 4, which is an optical beacon using near-infrared light as a wireless medium.

6. 6. The roadside communication device according to claim 5, wherein, among the information processes executed by said CPU, reception from the vehicle-mounted device has the second highest priority, and transmission to the vehicle-mounted device has the third highest priority.

7. The wireless communication device includes:

5. The roadside communication device according to claim 4, which is an ITS wireless roadside unit that uses radio waves in a predetermined frequency band as a wireless medium.

8. 8. The roadside communication device according to claim 7, wherein, among the information processes executed by the CPU, transmission to an in-vehicle device has the second highest priority, and reception from a sensor has the third highest priority.

9. The roadside communication device includes:

2. The roadside communication device according to claim 1, which is a roadside repeater device for repeating communication between the central device and another roadside communication device.

10. A time synchronization method executed by a CPU mounted on a roadside communication device, comprising: a step of the CPU correcting the time of the internal clock based on time information and a reference pulse signal generated by a satellite, the reference pulse signal being used as an interrupt signal with the highest priority; The time synchronization method includes a step in which the CPU cancels the setting of the reference pulse signal as the highest priority for a predetermined period by lowering the priority level of the reference pulse signal that is currently set as the highest priority for the predetermined period.

11. A computer program for causing a computer to function as a roadside communication device capable of time synchronization, a step in which a CPU of the roadside communication device corrects the time of an internal clock based on time information and a reference pulse signal generated by a satellite, using the reference pulse signal as an interrupt signal with the highest priority; A computer program comprising: a step in which a CPU of the roadside communication device cancels the setting of the reference pulse signal as the highest priority for a predetermined period by lowering the priority of the reference pulse signal that is currently set as the highest priority for the predetermined period.

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