JP5830259B2 - Wireless device - Google Patents

Description

  The present invention relates to communication technology, and more particularly to a radio apparatus that transmits a signal including predetermined information.

  Road-to-vehicle communication is being studied to prevent collisions at intersections. In the road-to-vehicle communication, information on the situation of the intersection is communicated between the roadside device and the vehicle-mounted device. Road-to-vehicle communication requires the installation of roadside equipment, which increases labor and cost. On the other hand, if it is the form which communicates information between vehicle-to-vehicle communication, ie, onboard equipment, installation of a roadside machine will become unnecessary. In that case, for example, the current position information is detected in real time by GPS (Global Positioning System), etc., and the position information is exchanged between the vehicle-mounted devices so that the own vehicle and the other vehicle enter the intersection respectively. (See, for example, Patent Document 1).

JP 2005-202913 A

  In a wireless LAN (Local Area Network) compliant with a standard such as IEEE 802.11, an access control function called CSMA / CA (Carrier Sense Multiple Access Collision Aviation) is used. Therefore, in the wireless LAN, the same wireless channel is shared by a plurality of terminal devices. In such CSMA / CA, a packet signal is transmitted after confirming that no other packet signal is transmitted by carrier sense. When applying a wireless LAN to inter-vehicle communication such as ITS (Intelligent Transport Systems), it is necessary to transmit information to terminal devices mounted on each of an unspecified number of vehicles. It is desirable that

  As a result, the terminal device detects the approach of another vehicle by receiving the broadcast signal, and notifies the driver of the approach by notifying the driver of the approach to the driver. To arouse. Apart from such broadcast communication in ITS, one-to-one unicast communication may be required. However, when the communication function for unicast communication is mounted on the terminal device separately from the communication function for ITS, the circuit scale of the terminal device increases. On the other hand, when the communication function for ITS and the communication function for unicast communication are made common, interference occurs between them.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for performing broadcast communication and unicast communication while suppressing an increase in circuit scale and an increase in interference amount. .

In order to solve the above problems, a radio apparatus according to an aspect of the present invention includes a first mode of broadcast communication that broadcasts a packet signal with a first power by performing carrier sense in a partial period in a frame, and a frame. A communication unit that executes one of the second modes of unicast communication that transmits a packet signal to other wireless devices by using the second power by performing carrier sense regardless of the operation mode of the communication unit, A control unit for instructing switching between the first mode and the second mode. Second power in a communication unit is less than the first power, the control unit, if the communication unit has transitioned a packet signal corresponding to the second mode of reception from a non-receiving state status, area of the broadcast communication Even when the first mode is switched to the second mode and the communication unit transitions from a reception state to a non-reception state of a packet signal corresponding to the second mode of the unicast communication, the unicast communication The second mode is switched to the first mode of the broadcast communication .

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, broadcast communication and unicast communication can be executed while suppressing an increase in circuit scale and an increase in interference amount.

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the base station apparatus for ITS of FIG. FIGS. 3A to 3D are diagrams showing frame formats defined in the communication system of FIG. FIGS. 4A to 4B are diagrams illustrating the configuration of the subframes of FIGS. 3A to 3D. FIGS. 5A and 5B are diagrams showing a format of a MAC frame stored in a packet signal defined in the communication system of FIG. It is a figure which shows another structure of the communication system of FIG. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. It is a flowchart which shows the selection procedure of the communication mode in the terminal device of FIG.

  Before describing the present invention in detail, an outline will be described. Embodiments of the present invention relate to a communication system that performs vehicle-to-vehicle communication between terminal devices mounted on a vehicle, and also executes road-to-vehicle communication from a base station device installed at an intersection or the like to a terminal device. As inter-vehicle communication, the terminal device broadcasts and transmits a packet signal storing information such as the speed and position of the vehicle (hereinafter referred to as “data”). Further, the other terminal device receives the packet signal and recognizes the approach of the vehicle based on the data. The driver is alerted by notifying the driver of the approach of the vehicle. In order to reduce interference between vehicle-to-vehicle communication and road-to-vehicle communication, the base station apparatus repeatedly defines a frame including a plurality of subframes.

  The base station apparatus selects any of a plurality of subframes for road-to-vehicle communication, and broadcasts a packet signal in which control information and the like are stored during the period of the head portion of the selected subframe. The control information includes information related to a period for the base station apparatus to broadcast the packet signal (hereinafter referred to as “road vehicle transmission period”). The terminal device specifies a road and vehicle transmission period based on the control information, and broadcasts a packet signal in a period other than the road and vehicle transmission period. Thus, since the road-to-vehicle communication and the vehicle-to-vehicle communication are time-division multiplexed, the collision probability of packet signals between them is reduced. The inter-vehicle communication is performed by the CSMA method in a period for performing inter-vehicle communication other than the road-vehicle transmission period (hereinafter referred to as “vehicle transmission period”).

  The above communication corresponds to ITS based on broadcast communication. In broadcast communication, since many terminal devices are given transmission opportunities, the amount of data transmitted from each terminal device is regulated. On the other hand, in addition to such broadcast communication, execution of unicast communication is desired. For example, in unicast communication, a large amount of data is transmitted to a specific destination device. In order to reduce the circuit scale of the terminal device, it is better that the standards for broadcast communication and unicast communication have many common parts. However, when there are many common parts, there is a high possibility that broadcast communication and unicast communication interfere with each other. In order to cope with this, the communication system according to the present embodiment executes the following processing.

  As the communication mode, the terminal device can execute a first mode for executing broadcast communication and a second mode for executing unicast communication. Broadcast communication is as described above, and unicast communication is common with broadcast communication in terms of frequency band, modulation scheme, and CSMA scheme. On the other hand, in unicast communication, a frame configuration like broadcast communication is not defined in order to increase the amount of data that can be communicated. Furthermore, in order to reduce interference from unicast communication to broadcast communication, transmission power in unicast communication is defined to be smaller than transmission power in broadcast communication. For this reason, the area that can be covered by one unicast communication base station apparatus (hereinafter referred to as “unicast base station apparatus”) is smaller than the area that can be covered by the ITS base station apparatus. The terminal device normally performs broadcast communication by selecting the first mode. When receiving a packet signal from the unicast base station device, the terminal device performs unicast communication by selecting the second mode. .

  Here, ITS by broadcast communication will be described first. FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. This corresponds to a case where one intersection is viewed from above. The communication system 100 includes an ITS base station device 10, a first vehicle 12a, a second vehicle 12b, a third vehicle 12c, a fourth vehicle 12d, a fifth vehicle 12e, a sixth vehicle 12f, a seventh vehicle, and a seventh vehicle. The vehicle 12g, the 8th vehicle 12h, the 1st pedestrian 16a and the 2nd pedestrian 16b named generically as the pedestrian 16 are included. Each vehicle 12 is provided with a terminal device (not shown). The area 212 is formed around the ITS base station apparatus 10, and the outside area 214 is formed outside the area 212.

  As shown in the drawing, the road that goes in the horizontal direction of the drawing, that is, the left and right direction, intersects the vertical direction of the drawing, that is, the road that goes in the up and down direction, at the center. Here, the upper side of the drawing corresponds to the direction “north”, the left side corresponds to the direction “west”, the lower side corresponds to the direction “south”, and the right side corresponds to the direction “east”. The intersection of the two roads is an “intersection”. The first vehicle 12a and the second vehicle 12b are traveling from left to right, and the third vehicle 12c and the fourth vehicle 12d are traveling from right to left. Further, the fifth vehicle 12e and the sixth vehicle 12f are traveling from the top to the bottom, and the seventh vehicle 12g and the eighth vehicle 12h are traveling from the bottom to the top.

  The ITS base station device 10 controls communication between terminal devices. The ITS base station apparatus 10 repeats a frame including a plurality of subframes based on a signal received from a GPS satellite (not shown) or a frame formed by another ITS base station apparatus 10 (not shown). Generate. Here, the road vehicle transmission period can be set at the head of each subframe. The ITS base station apparatus 10 selects a subframe in which the road and vehicle transmission period is not set by another ITS base station apparatus 10 from among the plurality of subframes. The ITS base station apparatus 10 sets a road and vehicle transmission period at the beginning of the selected subframe. The ITS base station apparatus 10 broadcasts a packet signal in the set road-vehicle transmission period.

  The vehicle 12 is driven by an engine and is equipped with a terminal device. When the first mode is selected, the terminal device generates a frame based on the control information included in the received packet signal. As a result, the frame generated in each of the plurality of terminal apparatuses is synchronized with the frame generated in the ITS base station apparatus 10. Moreover, a terminal device alert | reports a packet signal by performing CSMA / CA in a vehicle transmission period. For example, the terminal device stores information on the location in the packet signal. The terminal device also stores control information in the packet signal. That is, the control information transmitted from the ITS base station device 10 is transferred by the terminal device.

  On the other hand, a terminal device that cannot receive a packet signal from the ITS base station device 10, that is, a terminal device that exists outside the area 214 broadcasts the packet signal by executing CSMA / CA regardless of the frame configuration. . Furthermore, the terminal device notifies the driver of the approach of the vehicle on which the other terminal device is mounted by receiving a packet signal from the other terminal device.

  FIG. 2 shows a configuration of the ITS base station apparatus 10. The ITS base station apparatus 10 includes an antenna 20, an RF unit 22, a modem unit 24, a processing unit 26, a network communication unit 28, and a control unit 30. The processing unit 26 includes a frame definition unit 32, a selection unit 34, and a generation unit 36.

  The RF unit 22 receives a packet signal from a terminal device (not shown) or another ITS base station device 10 by the antenna 20 as a reception process. The RF unit 22 performs frequency conversion on the received radio frequency packet signal to generate a baseband packet signal. Further, the RF unit 22 outputs a baseband packet signal to the modem unit 24. In general, baseband packet signals are formed by in-phase and quadrature components, so two signal lines should be shown, but here only one signal line is shown for clarity. Shall be shown. The RF unit 22 includes an LNA (Low Noise Amplifier), a mixer, an AGC, and an A / D conversion unit.

  As a transmission process, the RF unit 22 performs frequency conversion on the baseband packet signal input from the modem unit 24 to generate a radio frequency packet signal. Further, the RF unit 22 transmits a radio frequency packet signal from the antenna 20 during the road-vehicle transmission period. The RF unit 22 also includes a PA (Power Amplifier), a mixer, and a D / A conversion unit.

  The modem unit 24 demodulates the baseband packet signal from the RF unit 22 as a reception process. Further, the modem unit 24 outputs the demodulated result to the processing unit 26. The modem unit 24 also modulates the data from the processing unit 26 as a transmission process. Further, the modem unit 24 outputs the modulated result to the RF unit 22 as a baseband packet signal. Here, since the communication system 100 corresponds to an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, the modem unit 24 also performs FFT (Fast Fourier Transform) as reception processing and IFFT (Inverse Fast Forward) as transmission processing. Also execute.

  The frame defining unit 32 receives a signal from a GPS satellite (not shown), and acquires time information based on the received signal. In addition, since a well-known technique should just be used for acquisition of the information of time, description is abbreviate | omitted here. The frame defining unit 32 generates a plurality of frames based on the time information. For example, the frame defining unit 32 generates ten “100 msec” frames by dividing the “1 sec” period into ten on the basis of the timing indicated by the time information. By repeating such processing, the frame is defined to be repeated.

  The frame defining unit 32 may detect control information from the demodulation result and generate a frame based on the detected control information. Such processing corresponds to generating a frame synchronized with the timing of the frame formed by the other ITS base station apparatus 10. 3A to 3D show frame formats defined in the communication system 100. FIG. FIG. 3A shows the structure of the frame. The frame is formed of N subframes indicated as the first subframe to the Nth subframe. For example, when the frame length is 100 msec and N is 8, a subframe having a length of 12.5 msec is defined. The description of FIGS. 3B to 3D will be described later and returns to FIG.

  The selection part 34 selects the sub-frame which should set a road and vehicle transmission period among several sub-frames contained in the flame | frame. More specifically, the selection unit 34 receives a frame defined by the frame defining unit 32. The selection unit 34 inputs a demodulation result from another ITS base station device 10 or a terminal device (not shown) via the RF unit 22 and the modem unit 24. The selection unit 34 extracts a demodulation result from another ITS base station device 10 from the input demodulation results. The selection unit 34 specifies the subframe that has not received the demodulation result by specifying the subframe that has received the demodulation result. This corresponds to specifying a subframe in which the road and vehicle transmission period is not set by another ITS base station apparatus 10, that is, an unused subframe. When there are a plurality of unused subframes, the selection unit 34 selects one subframe at random. When there are no unused subframes, that is, when each of a plurality of subframes is used, the selection unit 34 acquires reception power corresponding to the demodulation result, and gives priority to subframes with low reception power. Select

  FIG. 3B shows a configuration of a frame generated by the first ITS base station apparatus 10a. The first ITS base station device 10a sets a road and vehicle transmission period at the beginning of the first subframe. In addition, the first ITS base station device 10a sets the vehicle transmission period following the road and vehicle transmission period in the first subframe. The vehicle transmission period is a period during which the terminal device can notify the packet signal. That is, the first ITS base station apparatus 10a can notify the packet signal in the road and vehicle transmission period which is the head period of the first subframe, and the terminal apparatus in the vehicle and vehicle transmission period other than the road and vehicle transmission period in the frame. Is defined such that the packet signal can be broadcast. Furthermore, the first ITS base station apparatus 10a sets only the vehicle transmission period from the second subframe to the Nth subframe.

  FIG. 3C shows a configuration of a frame generated by the second ITS base station device 10b. The second ITS base station apparatus 10b sets a road and vehicle transmission period at the beginning of the second subframe. Also, the second ITS base station apparatus 10b sets the vehicle transmission period from the first subframe and the third subframe to the Nth subframe after the road and vehicle transmission period in the second subframe. FIG. 3D shows a configuration of a frame generated by the third ITS base station device 10c. The third ITS base station apparatus 10c sets a road and vehicle transmission period at the beginning of the third subframe. Also, the third ITS base station apparatus 10c sets the vehicle transmission period from the first subframe, the second subframe, and the fourth subframe to the Nth subframe after the road and vehicle transmission period in the third subframe. . In this way, the plurality of ITS base station devices 10 select different subframes, and set the road and vehicle transmission period at the head of the selected subframe. Returning to FIG. The selection unit 34 outputs the selected subframe number to the generation unit 36.

  The generation unit 36 sets a road and vehicle transmission period in the subframe of the subframe number received from the selection unit 34, and generates an RSU packet signal to be notified in the road and vehicle transmission period. In the following description, the RSU packet signal and the packet signal are used without distinction. FIGS. 4A to 4B show subframe configurations. FIG. 4A shows a subframe in which a road and vehicle transmission period is set. As illustrated, one subframe is configured in the order of a road and vehicle transmission period and a vehicle and vehicle transmission period. FIG. 4B shows the arrangement of packet signals during the road and vehicle transmission period. As illustrated, a plurality of RSU packet signals are arranged in the road and vehicle transmission period. Here, the front and rear packet signals are separated by SIFS (Short Interframe Space).

  Here, the configuration of the RSU packet signal will be described. FIGS. 5A and 5B show the formats of MAC frames stored in packet signals defined in the communication system 100. FIG. FIG. 5A shows the format of the MAC frame. In the MAC frame, “MAC header”, “LLC header”, “message header”, “data payload”, and “FCS” are arranged in order from the top. Information included in the data payload will be described later. FIG. 5B is a diagram illustrating a configuration of a message header generated by the generation unit 36. The message header includes a basic part.

  The basic part includes “protocol version”, “transmission node type”, “number of reuses”, “TSF timer”, and “RSU transmission period length”. The protocol version indicates the version of the corresponding protocol. The transmission node type indicates the transmission source of the packet signal including the MAC frame. For example, “0” indicates a terminal device, and “1” indicates the ITS base station device 10. When the selection unit 34 extracts a demodulation result from another ITS base station device 10 from among the input demodulation results, the selection unit 34 uses the value of the transmission node type. The reuse count indicates an index of validity when the message header is transferred by the terminal device, and the TSF timer indicates the transmission time. The RSU transmission period length indicates the length of the road and vehicle transmission period, and can be said to be information relating to the road and vehicle transmission period. Returning to FIG.

  The network communication unit 28 is connected to a network 202 (not shown). The network communication unit 28 receives traffic jam information from the network 202. The generation unit 36 acquires the traffic jam information from the network communication unit 28 and stores it in the data payload, thereby generating the RSU packet signal described above. The control unit 30 controls processing of the entire ITS base station apparatus 10.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it can be realized by a program loaded in the memory, but here it is realized by their cooperation. Draw functional blocks. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 6 shows another configuration of the communication system 100. The communication system 100 includes an ITS base station device 10, a terminal device 14, and a unicast base station device 18. The combination of the ITS base station device 10 and the terminal device 14 in the communication system 100 is the same as in FIG. 1 and corresponds to ITS by broadcast communication. The unicast base station device 18 is a base station device for executing unicast communication with the terminal device 14, and is connected to a network (not shown). The unicast base station apparatus 18 is different from the ITS base station apparatus 10 in that it does not define a frame configuration. The transmission power of the unicast base station apparatus 18 is defined to be lower than the transmission power of the ITS base station apparatus 10. For example, the former is defined to be less than half of the latter, or the former transmission power is defined to be 10 mW or less and the latter transmission power is defined to be 100 mW or less.

  On the other hand, the unicast base station apparatus 18 is the same as the ITS base station apparatus 10 in other respects, for example, in the frequency band, modulation scheme, CSMA scheme, and the like. For example, the unicast base station apparatus 18 executes processing similar to the IEEE802.11a and g standards and the IEEE802.11p standard. Therefore, although the description of the configuration of the unicast base station apparatus 18 is omitted here, the unicast base station apparatus 18 periodically notifies the beacon signal in order to inform the surroundings of its existence.

  The unicast base station device 18 is disposed in a limited place such as a drive-through or a parking lot. Further, the area formed by the unicast base station apparatus 18 is narrower than the area 212 formed by the ITS base station apparatus 10. Therefore, the terminal device 14 normally selects the first mode and executes broadcast communication according to the frame defined by the ITS base station device 10. On the other hand, when the terminal apparatus 14 enters the area formed by the unicast base station apparatus 18, the terminal apparatus 14 switches the first mode to the second mode. The terminal device 14 performs unicast communication with the unicast base station device 18. Further, when the terminal device 14 leaves the area formed by the unicast base station device 18, the terminal device 14 returns the second mode to the first mode.

  FIG. 7 shows a configuration of the terminal device 14 mounted on the vehicle 12. The terminal device 14 includes an antenna 40, an RF unit 42, a modem unit 44, a processing unit 46, and a control unit 48. The processing unit 46 includes a switching control unit 70, a first communication unit 72, and a second communication unit 74. The first communication unit 72 includes a timing specifying unit 50, a transfer determining unit 56, an acquiring unit 58, a notification unit 60, and a generating unit 62. The timing specifying unit 50 includes an extracting unit 52 and a carrier sense unit 54. The second communication unit 74 includes a carrier sense unit 64, a generation unit 66, and a reception processing unit 68. The antenna 40, the RF unit 42, and the modem unit 44 perform the same processing as the antenna 20, the RF unit 22, and the modem unit 24 in FIG. Therefore, here, the difference will be mainly described.

  On the other hand, the modem unit 44 and the processing unit 46 receive packet signals from other terminal devices 14 and the ITS base station device 10 (not shown) in the first mode. As described above, the modem unit 44 and the processing unit 46 receive the packet signal from the ITS base station apparatus 10 in the road and vehicle transmission period. As described above, the modem unit 44 and the processing unit 46 receive packet signals from other terminal devices 14 during the vehicle transmission period. Further, the modem unit 44 and the processing unit 46 may receive a packet signal from the unicast base station apparatus 18 (not shown) even in the first mode. The modem unit 44 and the processing unit 46 receive a packet signal from a unicast base station device 18 (not shown) in the second mode.

  The switching control unit 70 instructs switching between the first mode and the second mode as the operation mode of the terminal device 14. Here, the operation in the first mode corresponds to the operation of the first communication unit 72, and the operation in the second mode corresponds to the operation of the second communication unit 74. More specifically, the switching control unit 70 operates the first communication unit 72 unless the modem unit 44 and the RF unit 42 have received a beacon signal from the unicast base station device 18 for a predetermined period. Select. In addition, the switching control unit 70 selects the first communication unit 72 when the modem unit 44 and the RF unit 42 transition from the non-reception state to the reception state of the beacon signal from the unicast base station device 18. To the selection of the second communication unit 74. Further, the switching control unit 70 selects the second communication unit 74 when the modulation / demodulation unit 44 and the RF unit 42 transition from the reception state to the non-reception state of the beacon signal from the unicast base station device 18. To the selection of the first communication unit 72. The non-reception state indicates that no reception has been performed for a predetermined period. Of the first communication unit 72 and the second communication unit 74, only the one selected by the switching control unit 70 operates.

  When the first communication unit 72 is selected by the switching control unit 70, the first communication unit 72 notifies the packet signal by performing carrier sense during the vehicle transmission period in the frame. When the demodulation result from the modem unit 44 is a packet signal from the ITS base station device 10 (not shown), the extraction unit 52 specifies the timing of the subframe in which the road-vehicle transmission period is arranged. In that case, the extraction part 52 estimates that it exists in the area 212 of FIG. The extraction unit 52 generates a frame based on the timing of the subframe and the content of the message header of the packet signal, specifically, the content of the RSU transmission period length. Note that the generation of the frame only needs to be performed in the same manner as the frame defining unit 32 described above, and thus the description thereof is omitted here. As a result, the extraction unit 52 generates a frame synchronized with the frame formed in the ITS base station device 10.

  On the other hand, when the extraction unit 52 has not received the RSU packet signal, the extraction unit 52 estimates that the extraction unit 52 exists outside the area 214 in FIG. When it is estimated that the extraction unit 52 exists in the area 212, the extraction unit 52 selects a vehicle transmission period. When it is estimated that the extraction unit 52 exists outside the area 214, the extraction unit 52 selects a timing unrelated to the frame configuration. When the vehicle transmission period is selected, the extraction unit 52 outputs information on the frame and subframe timing and the vehicle transmission period to the carrier sense unit 54. When the extraction unit 52 selects a timing unrelated to the frame configuration, the extraction unit 52 instructs the carrier sense unit 54 to execute carrier sense.

  The carrier sense unit 54 receives information regarding the timing of the frames and subframes and the vehicle transmission period from the extraction unit 52. The carrier sense unit 54 measures the interference power by executing carrier sense during the vehicle transmission period. Moreover, the carrier sense part 54 determines the transmission timing in a vehicle transmission period based on interference power. More specifically, the carrier sense unit 54 stores a predetermined threshold value in advance, and compares the interference power with the threshold value. If the interference power is smaller than the threshold value, the carrier sense unit 54 determines the transmission timing. When the carrier sense unit 54 is instructed by the extraction unit 52 to execute carrier sense, the carrier sense unit 54 determines the transmission timing by executing CSMA without considering the frame configuration. The carrier sense unit 54 notifies the generation unit 62 of the determined transmission timing.

  The acquisition unit 58 includes a GPS receiver, a gyro sensor, a vehicle speed sensor, and the like (not shown). Based on data supplied from the GPS receiver, the acquisition position 58, the traveling position, the moving speed, and the like of the terminal device 14 (hereinafter referred to as “position information”). Are collectively called). The existence position is indicated by latitude and longitude. Since a known technique may be used for these acquisitions, description thereof is omitted here. The acquisition unit 58 outputs the position information to the generation unit 62.

  The transfer determination unit 56 controls the transfer of the message header. The transfer determination unit 56 extracts a message header from the packet signal. When the packet signal is directly transmitted from the ITS base station apparatus 10, the number of reuses is set to “0”, but when the packet signal is transmitted from another terminal apparatus 14, The number of reuses is set to a value of “1 or more”. The transfer determination unit 56 selects a message header to be transferred from the extracted message header. Here, for example, the message header with the smallest number of reuses is selected. In addition, the transfer determination unit 56 may generate a new message header by combining the contents included in the plurality of message headers. The transfer determination unit 56 outputs the message header to be selected to the generation unit 62. At that time, the transfer determination unit 56 increases the reuse count by “1”.

  The generation unit 62 receives position information from the acquisition unit 58 and receives a message header from the transfer determination unit 56. The generation unit 62 stores the position information in the data payload using the MAC frame shown in FIGS. The generation unit 62 generates a packet signal including a MAC frame, and broadcasts the generated packet signal via the modem unit 44, the RF unit 42, and the antenna 40 at the transmission timing determined by the carrier sense unit 54. Send. This corresponds to inter-vehicle communication. The transmission timing is included in the vehicle transmission period.

  The notification unit 60 acquires the packet signal from the ITS base station device 10 (not shown) and the packet signal from the other terminal device 14 (not shown) via the extraction unit 52. As a process for the acquired packet signal, the notification unit 60 notifies the driver of the approach of another vehicle 12 (not shown) or the like via a monitor or a speaker according to the content of the data stored in the packet signal. Furthermore, the notification unit 60 notifies the driver of traffic jam information and the like via a monitor and a speaker.

  When the second communication unit 74 is selected by the switching control unit 70, the second communication unit 74 transmits a packet signal to the unicast base station apparatus 18 by performing carrier sense regardless of the frame. At that time, the transmission power set in the RF unit 42 is smaller than the transmission power set in the RF unit 42 when the first communication unit 72 is operating. The carrier sense unit 64 determines the transmission timing by executing CSMA without considering the frame configuration, similarly to the case where the carrier sense unit 54 instructs the execution of carrier sense from the extraction unit 52. The generation unit 66 generates a packet signal to be transmitted at the transmission timing determined by the carrier sense unit 64. The packet signal includes data destined for a predetermined communication device to communicate via the unicast base station device 18. The reception processing unit 68 receives a packet signal received from a predetermined communication device via the unicast base station device 18. The destination of the packet signal is the terminal device 14. In addition, the reception processing unit 68 extracts data from the packet signal and executes processing according to the data.

  The operation of the communication system 100 configured as above will be described. FIG. 8 is a flowchart illustrating a communication mode selection procedure in the terminal device 14. If the beacon signal is received from the unicast base station apparatus 18 (Y in S10), the switching control unit 70 selects execution of the second mode (S12). On the other hand, if the beacon signal is not received from the unicast base station apparatus 18 (N of S10), the switching control unit 70 selects the execution of the first mode (S14).

  According to the embodiment of the present invention, the second mode is selected when the beacon signal is received from the unicast base station apparatus, and the first mode is selected in other cases. Therefore, priority is given to unicast communication. Can be selected. In addition, while the unicast communication is preferentially selected and the transmission power in the second mode is made smaller than the transmission power in the first mode, the amount of interference with broadcast communication can be reduced. In addition, since there is no frame definition in unicast communication, the amount of data that can be transmitted can be increased. In addition, since there are many common parts in unicast communication and broadcast communication, the circuit scale can be reduced. Further, since the first mode and the second mode are automatically switched depending on whether or not a beacon signal is received from the unicast base station apparatus, the operability for the driver can be improved.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  In the embodiment of the present invention, the switching control unit 70 receives the second signal when the modem unit 44 and the RF unit 42 transition from the receiving state to the non-receiving state of the beacon signal from the unicast base station device 18. The selection of the communication unit 74 is switched to the selection of the first communication unit 72. However, not limited to this, for example, the switching control unit 70 may switch the selection of the second communication unit 74 to the selection of the first communication unit 72 based on another criterion. Specifically, the switching control unit 70 is connected to the speed sensor of the vehicle 12, and when the data from the speed sensor transits from the stop of the vehicle 12 to the operation, the switching control unit 70 selects the second communication unit 74 for the first selection. Switch to the selection of the communication unit 72. According to this modification, unicast communication can be restricted while the vehicle 12 is stopped. Further, the switching control unit 70 may switch the selection of the second communication unit 74 to the selection of the first communication unit 72 based on the driver's operation. According to this modification, switching according to the driver's intention can be realized.

  10 ITS base station device, 12 vehicle, 14 terminal device, 16 pedestrian, 18 unicast base station device, 20 antenna, 22 RF unit, 24 modulation / demodulation unit, 26 processing unit, 28 network communication unit, 30 control unit, 32 frame definition unit, 34 selection unit, 36 generation unit, 40 antenna, 42 RF unit, 44 modulation / demodulation unit, 46 processing unit, 48 control unit, 50 timing identification unit, 52 extraction unit, 54 carrier sense unit, 56 transfer determination unit 58 acquisition unit, 60 notification unit, 62 generation unit, 64 carrier sense unit, 66 generation unit, 68 reception processing unit, 70 switching control unit, 72 first communication unit, 74 second communication unit, 100 communication system.

Claims (2)

The first mode of broadcast communication that broadcasts the packet signal with the first power by executing carrier sense in a partial period in the frame, and the packet signal to other wireless devices by executing carrier sense regardless of the frame A communication unit that performs any one of the second modes of unicast communication that transmits at a second power;
As an operation mode of the communication unit, a control unit that instructs switching between the first mode and the second mode,
The second power in the communication unit is smaller than the first power,
Wherein, prior Symbol communication unit the unicast communication in the second mode to the corresponding packet signal non-receiving state if the transition to the state of reception from, even within the broadcast coverage area, the When the first mode of broadcast communication is switched to the second mode of unicast communication, and the communication unit transitions from a receiving state to a non-receiving state of a packet signal corresponding to the second mode of unicast communication, A wireless device , wherein the second mode of unicast communication is switched to the first mode of broadcast communication . In the broadcast communication area performed by the control unit, when the communication unit transitions from a non-reception state to a reception state of a packet signal corresponding to the second mode of the unicast communication, the broadcast communication 2. The wireless device according to claim 1, wherein switching from the first mode to the second mode of the unicast communication is further restricted while a vehicle including the wireless device is stopped.

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