JP2011035566A - Terminal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of controlling an increase and decrease of traffic and maintaining an optimal traffic when control information from a base station device is transferred. <P>SOLUTION: Each of a plurality of sub-frames forming a frame includes a first period and a second period. The first periods included in each of the sub-frames forming the frame are used for different base station devices. A control information extracting unit 66 extracts from a received signal control information whose source is the base station device and which indicates the first period used by the base station device. A measuring unit 114 measures the amount of the received signal. A transfer amount determining unit 116 and a transfer information determining unit 118 change the amount of control information to be transferred among the extracted control information according to the amount of the measured signal, and determine the control information to be transferred. An instructing unit 92 transmits a signal storing the determined control information, in a predetermined second period. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a communication technique, and more particularly to a terminal device that transmits and receives 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, due to the distance between terminal devices and the influence of obstacles that attenuate radio waves, a situation occurs in which radio signals do not reach each other, that is, a situation where carrier sense does not function. When carrier sense does not function, packet signals transmitted from a plurality of terminal devices collide.

  On the other hand, when a wireless LAN is applied to vehicle-to-vehicle communication, it is necessary to transmit information to an unspecified number of terminal devices, so it is desirable that the signal be transmitted by broadcast. However, at an intersection or the like, an increase in the number of vehicles, that is, an increase in the number of terminal devices increases traffic, and therefore, an increase in packet signal collision is assumed. As a result, data included in the packet signal is not transmitted to other terminal devices. If such a situation occurs in vehicle-to-vehicle communication, the objective of preventing a collision accident at the intersection encounter will not be achieved. Furthermore, if the road-to-vehicle communication is executed in addition to the vehicle-to-vehicle communication, the communication forms are various. In that case, reduction of the mutual influence between vehicle-to-vehicle communication and road-to-vehicle communication is requested | required.

  In order to reduce the mutual influence, for example, each base station apparatus secures a period to be used for road-to-vehicle communication, and broadcasts control information including information on the period. The terminal device recognizes a period to be used for road-to-vehicle communication based on the control information, and performs vehicle-to-vehicle communication in other periods. In order to reduce the mutual influence, it is preferable that control information is received by as many terminal devices as possible. On the other hand, the area where control information is transmitted from the base station apparatus is limited to a predetermined range. In such an environment, in order to expand the area where the control information is transmitted, it is effective that the terminal device transfers the control information. However, since the traffic increases due to the transfer of the control information, suppression of the traffic increase is desired.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for controlling an increase / decrease in traffic and maintaining an optimum traffic amount when transferring control information from a base station apparatus. It is in.

  In order to solve the above-described problem, a terminal device according to an aspect of the present invention includes a plurality of subframes in which each of a plurality of subframes forming a frame includes a first period and a second period, and forms a frame. The first period included in each is used for different base station apparatuses, receives signals from the base station apparatus in each first period, and communicates with other terminal apparatuses in each second period. A communication unit that transmits / receives a signal and a control information that indicates that the base station device is an information source from the signal received by the communication unit and that indicates the first period that the base station device uses An extraction unit for extracting information, a measurement unit for measuring the amount of signal received by the communication unit, and control information to be transferred among the control information extracted by the extraction unit according to the amount of signal measured by the measurement unit Do not change the amount of Comprising al, a determination unit that determines control information to be transferred, a signal determined control information is stored in the determination unit so as to transmit the predetermined second time period, and an instruction unit for instructing the communication unit. The extraction unit extracts at least one of control information transmitted directly from the base station apparatus and control information transferred by another terminal apparatus.

  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.

  ADVANTAGE OF THE INVENTION According to this invention, when transferring the control information from a base station apparatus, the increase / decrease in traffic can be controlled and the optimal traffic amount can be maintained.

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 another 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 of FIG. 1 and FIG. FIGS. 4A to 4D are diagrams showing frame formats defined in the communication system of FIGS. FIGS. 5A and 5B are diagrams showing another format of the frame defined in the communication system of FIGS. 1 and 2. FIGS. 6A to 6C are diagrams illustrating the format of a frame generated by each base station apparatus in the communication system of FIG. FIGS. 7A and 7B are diagrams showing a format of a MAC frame stored in a packet signal defined in the communication system of FIGS. 1 and 2. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. 1 and FIG. It is a figure which shows the process outline | summary in the measurement part of FIG. FIGS. 10A and 10B are diagrams showing another processing outline in the measurement unit of FIG. FIG. 9 is a diagram illustrating a data structure of a correspondence table stored in a transfer information determination unit in FIG. 8. It is a figure which shows the operation | movement outline | summary of the communication system of FIG. 1 and FIG. 4 is a flowchart showing a procedure for notifying an empty slot in the base station apparatus of FIG. 3. It is a flowchart which shows the notification procedure of the collision slot in the base station apparatus of FIG. It is a flowchart which shows the determination procedure of the transmission process in the terminal device of FIG. It is a flowchart which shows the transmission procedure of the data in the terminal device of FIG. It is a flowchart which shows the transfer procedure of the control information in the terminal device of FIG.

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a communication system that performs data communication between terminal devices mounted on a vehicle. The terminal device broadcasts a packet signal that stores 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. In such inter-vehicle communication, when the number of terminal devices increases at an intersection or the like, the generation probability of a packet signal increases. In addition, coexistence of road-to-vehicle communication is also required. In order to cope with this, the communication system according to the present embodiment executes the following processing.

  The communication system according to the present embodiment includes a plurality of base station devices in addition to a plurality of terminal devices, and each base station device is installed at each intersection, for example. The base station apparatus repeatedly defines a frame including a plurality of subframes. Further, the subframe is divided into a plurality of slots. Of the plurality of slots included in each subframe, some are secured as control slots and road and vehicle slots, and the rest are secured as vehicle slots and vehicle periods. Here, the control slot is a slot for the base station apparatus to broadcast-transmit a packet signal storing control information (hereinafter also referred to as “control information”). The road and vehicle slot is a slot for the base station device to transmit data to the terminal device, and the vehicle and vehicle slot is a slot for broadcasting data between the terminal devices. The vehicle period is a period during which data is broadcast by CSMA between terminal devices.

  One base station apparatus broadcasts control information in any of a plurality of subframes, and does not broadcast control information in the remaining subframes. When each base station apparatus broadcasts control information in a different subframe, the transmission timing of the control information is different from each other, and the terminal apparatus is caused to receive the control information accurately. Here, the control information includes information indicating the period allocated to the control slot and the road and vehicle slot. By receiving the control information, the terminal device generates a frame corresponding to the control information and specifies the period of the control slot and the road and vehicle slot included in each subframe. The terminal device executes the road-to-vehicle communication in these periods by specifying the periods of the control slot and the road and vehicle slots, and executes the vehicle-to-vehicle communication in the remaining periods. Therefore, when the terminal device recognizes the content of the control information, interference between road-vehicle communication and vehicle-to-vehicle communication is reduced.

  The communication area formed by the base station device is limited to a predetermined range. In order to expand the range in which the interference between road-vehicle communication and vehicle-to-vehicle communication is reduced, control information should be received in a wide range by the terminal device. In order to cope with this, for example, the terminal device may transfer the control information by inter-vehicle communication. However, if the control information transferred increases, the traffic increases. In order to suppress an increase in traffic, the terminal device executes the following process. The control information includes information on the number of transfers by the terminal device. The terminal device gives priority to the control information so that the priority becomes higher as the number of transfers is smaller for each base station device serving as an information source. On the other hand, the terminal device measures the traffic volume of inter-vehicle communication in a predetermined period, and determines the amount of control information to be transferred according to the traffic volume. For example, the amount of control information is reduced as the traffic amount increases. Furthermore, the terminal device executes the transfer in order from the control information with the highest priority according to the amount of control information to be transferred.

  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 a 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, and a seventh vehicle 12g, collectively referred to as a vehicle 12. , The eighth vehicle 12h, and the network 202. Each vehicle 12 is equipped with a terminal device (not shown). An area 200 is formed by the base station apparatus 10.

  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 central portion. 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 terminal device mounted on each vehicle 12 acquires data and broadcasts a packet signal in which the data is stored. The data includes, for example, information related to the location. Here, before explaining the embodiment of the present invention, the operation when the terminal device corresponds to a known wireless LAN, that is, the case corresponding to CSMA / CA will be described. Each terminal device broadcasts and transmits data when it is determined that transmission is possible by executing carrier sense. Therefore, data from a plurality of terminal devices may collide. Moreover, the probability of occurrence of a collision increases as the number of terminal devices increases. In particular, in a place such as an intersection, although a collision of the vehicle 12 is likely to occur, a data collision is also likely to occur, and data is not used in a place where data is required.

  Therefore, the communication system 100 arranges the base station device 10 at the intersection. Base station apparatus 10 repeatedly generates a subframe frame including a plurality of slots based on a signal received from a GPS satellite (not shown), and further repeatedly generates a frame including a plurality of subframes. Here, some of the plurality of slots correspond to control slots and road and vehicle slots. Further, the remaining period includes a vehicle slot and a vehicle period. Further, the base station apparatus 10 specifies a vehicle slot (hereinafter referred to as “empty slot”) that is not used for communication between a plurality of terminal devices by measuring the received power in each vehicle slot. The base station device 10 also estimates the possibility that packet signals transmitted from a plurality of terminal devices are colliding with each other in each vehicle slot, whereby a vehicle slot (hereinafter referred to as a “collision slot”) in which a collision has occurred. ”). The base station apparatus 10 includes information on the identified empty slot and collision slot in the control information. The base station apparatus 10 broadcasts control information in the control slot.

  The plurality of terminal apparatuses receive the control information broadcast by the base station apparatus 10 and generate a frame based on the control information. As a result, the frame generated in each of the plurality of terminal devices is synchronized with the frame generated in the base station device 10. In addition, when a plurality of terminal devices exist in the vicinity of the base station device 10, one of the empty slots is selected based on the control information. The terminal device notifies the data at the selected vehicle slot. Here, the terminal device reports data in a vehicle slot corresponding to the selected vehicle slot over a plurality of frames.

  For example, when the 10th slot from the beginning of the frame is selected, the 10th slot from the beginning of the frame is used in the next frame. If the control information indicates that the used vehicle slot is a collision slot, the terminal device further selects another empty slot. The terminal device repeatedly executes the above process over a period that exists in the vicinity of the base station device 10. When the plurality of terminal devices do not exist in the vicinity of the base station device 10, data is transmitted by executing CSMA / CA during the vehicle period. Further, the plurality of terminal devices receive data from the base station device 10 in the road and vehicle slot.

  FIG. 2 shows another configuration of the communication system 100 according to the embodiment of the present invention. FIG. 2 corresponds to the case where a plurality of intersections in FIG. 1 are shown. The communication system 100 includes a first base station device 10a, a second base station device 10b, a third base station device 10c, which are collectively referred to as a base station device 10, and a first vehicle 12a, a second vehicle 12b, which are collectively referred to as a vehicle 12, A third vehicle 12c is included. FIG. 2 is shown in the same manner as FIG. 1, in which the first vehicle 12a travels in the east direction, the second vehicle 12b travels in the west direction, and the third vehicle 12c travels in the south direction. Yes. The first vehicle 12a travels in the vicinity of the second base station device 10b, and the terminal device mounted on the first vehicle 12a receives control information from the second base station device 10b. Here, even if a terminal device mounted on a vehicle (not shown) running behind the first vehicle 12a cannot directly receive control information from the second base station device 10b, the second base station device I want to receive control information from 10b. Therefore, the terminal device mounted on the first vehicle 12a should transfer control information from the second base station device 10b.

  The second vehicle 12b travels in the vicinity of the third base station device 10c, and the terminal device mounted on the second vehicle 12b receives control information from the third base station device 10c. Here, the vehicle 12 coming from the front of the second vehicle 12b toward the second vehicle 12b, for example, the terminal device mounted on the first vehicle 12a receives control information from the third base station device 10c. I hope. Therefore, the terminal device mounted on the second vehicle 12b should transfer control information from the third base station device 10c. The third vehicle 12c travels in the vicinity of the first base station device 10a, and the terminal device mounted on the third vehicle 12c receives control information from the first base station device 10a. Here, a terminal device mounted on a vehicle (not shown) traveling behind the third vehicle 12c desires to receive control information from the first base station device 10a. Therefore, the terminal device mounted on the third vehicle 12c should transfer control information from the first base station device 10a. That is, when the control information from the base station apparatus 10 is directly received, the terminal apparatus should preferentially transfer the control information.

  FIG. 3 shows the configuration of the base station apparatus 10. The base station apparatus 10 includes an antenna 20, an RF unit 22, a modem unit 24, a processing unit 26, a GPS positioning unit 28, a control unit 30, and a network communication unit 80. The processing unit 26 includes a detection unit 32, a frame definition unit 34, and a generation unit 36. The detection unit 32 includes a power measurement unit 38, a quality measurement unit 40, an empty slot identification unit 42, and a collision slot identification unit 44. .

  The GPS positioning unit 28 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 GPS positioning unit 28 outputs time information to the frame defining unit 34. The frame defining unit 34 acquires time information from the GPS positioning unit 28. The frame defining unit 34 generates a plurality of frames based on the time information. For example, the frame defining unit 34 generates 10 frames of “100 msec” by dividing the period of “1 sec” into 10 with reference to the timing of “0 msec”. By repeating such processing, the frame is defined to be repeated.

  Here, each frame includes a priority period formed by a plurality of slots and a general vehicle period having a predetermined length. The plurality of slots included in the priority period are classified into at least one control slot, at least one road vehicle slot, and a plurality of priority vehicle slots. The priority vehicle slot corresponds to the aforementioned vehicle slot, and the general vehicle period corresponds to the aforementioned vehicle period. The leading slot among the plurality of slots included in the priority period is set as a “control slot”. As described above, the control slot is a slot used for the base station apparatus 10 to broadcast control information. The road car slot is arranged in a plurality of slots following the control slot. The priority vehicle slot is arranged in the remaining slots following the road vehicle slot. In the control slot and the road and vehicle slot, transmission of packet signals to the terminal device is prohibited. Therefore, the control information includes information on the control slot and the road and vehicle slot, and the terminal device executes only reception of the packet signal in the control slot and the road and vehicle slot based on the information.

  The priority vehicle slot is used by a terminal device existing within a certain range from the base station device 10, and the general vehicle period is within the area 200 and outside the certain range from the base station device 10. Let the terminal device use it. Whether to use the priority vehicle slot or the general vehicle period is determined by the terminal device. Processing for determination will be described later. Further, in a plurality of priority vehicle slots, the terminal device is caused to control the transmission timing so as to follow the control information notified in the control slot. That is, the terminal device 14 selects one of the priority vehicle slots based on the information on the empty slot and the collision slot included in the control information. On the other hand, in the general vehicle period, the transmission timing is controlled autonomously by the terminal device. That is, the terminal apparatus determines transmission timing based on CSMA.

  Since the communication system 100 employs an Orthogonal Division Multiplexing (OFDM) modulation scheme, each slot is defined to be composed of a plurality of OFDM symbols. The OFDM symbol is composed of a guard interval (GI) and a valid symbol. A guard time may be provided in the front part or the rear part of each slot. Here, a group of a plurality of OFDM symbols included in the slot corresponds to the aforementioned packet signal.

  4A to 4D show frame formats defined in the communication system 100. FIG. FIG. 4A shows a frame configuration. As shown in the figure, it is defined that a plurality of frames are repeated such as the i-th frame to the (i + 2) -th frame. The period of each frame is “100 msec”, for example. FIG. 4B shows the configuration of one frame. As shown in the drawing, a priority period is arranged in front of one frame, and a general vehicle period is arranged behind the priority period. The priority period is composed of M slots. The first slot arranged at the beginning of the frame corresponds to the control slot, and the five slots from the second slot to the sixth slot following the control slot correspond to the road and vehicle slots. The number of road and vehicle slots may not be “5”. Further, M-6 slots from the seventh slot to the Mth slot following the road vehicle slot correspond to the priority vehicle slot.

  FIG. 4C shows the configuration of one slot. As shown in the figure, guard times are provided at the front portion and the rear portion of the slot. The remaining period of the slot is composed of N OFDM symbols. Note that the packet signal transmitted in the general vehicle period is also composed of a plurality of OFDM symbols. FIG. 4D shows the configuration of one OFDM symbol. As shown in the figure, one OFDM symbol is composed of a GI and an effective symbol. Returning to FIG.

  For example, the frame defining unit 34 may receive the number of base station apparatuses 10 to be multiplexed from an administrator, and divide each frame into subframes corresponding to the number of base station apparatuses 10 to be multiplexed. As a result, the frame is formed of a plurality of subframes. FIG. 4B corresponds to the case where the number of subframes included in one frame is “1”. In addition, the frame period is constant regardless of the number of subframes included in the frame. In the frame defining section 34, each subframe is defined so as to include a priority period formed by a plurality of slots and a general vehicle period having a predetermined length, as in the conventional frame configuration. Is done. In addition, the plurality of slots in the priority period are classified into at least one control slot, at least one road vehicle slot, and a plurality of priority vehicle slots.

  Here, among the plurality of subframes, the control slot and the road and vehicle slot in one subframe are preferentially used by the base station apparatus 10. In each subframe other than the subframe including the control slot used by the base station apparatus 10, the control slot and the road and vehicle slot are used for another base station apparatus 10 (not shown). That is, each base station apparatus 10 uses a control slot and a road and vehicle slot in mutually different subframes. For example, the frame defining unit 34 receives an instruction from the manager, and determines a control slot and a road and vehicle slot to be used by itself according to the instruction. Further, the frame defining unit 34 outputs information on the determined control slot and road and vehicle slot to the generating unit 36.

  FIGS. 5A and 5B show another format of the frame defined in the communication system 100. FIG. FIG. 5A corresponds to one frame in FIG. FIG. 5B shows a detailed configuration of the frame of FIG. Here, the number of subframes is “N”. As illustrated, a first subframe, a second subframe, and an Nth subframe are arranged in order from the top of the frame. In the first subframe, a first control slot, a first road vehicle slot, a first priority vehicle slot, and a first general vehicle period are arranged, which are the control slots in FIG. Corresponding to road vehicle slot, priority vehicle slot, and general vehicle period. For this reason, the first control slot, the first road vehicle slot, and the first priority vehicle slot constitute a priority period.

  Also, the second subframe and the Nth subframe are configured in the same manner as the first subframe. The first control slot to the Nth control slot are collectively referred to as a control slot, the first road car slot to the Nth road car slot are collectively referred to as a road car slot, and the first priority car slot to the Nth priority car. The vehicle slot is collectively referred to as a priority vehicle slot, and the first general vehicle period to the Nth general vehicle period are collectively referred to as a general vehicle period. Here, the base station apparatus 10 uses, for example, a first control slot and a first road car slot. Other base station devices 10 multiplexed with the base station device 10 do not use the first control slot and the first road vehicle slot. Instead, the other base station apparatus 10 uses the second control slot, the second road vehicle slot, and the like, and the base station apparatus 10 does not use these. In the communication system 100 shown in FIG. 2, for example, the first base station apparatus 10a uses the first control slot and the first road car slot, and the second base station apparatus 10b uses the second control slot and the second road slot. Use car slots. The priority vehicle slot and the general vehicle period of each subframe are used in common by the plurality of terminal devices 14. Returning to FIG.

  Note that the frame defining unit 34 may define the priority period so that all priority periods are used in the priority vehicle slots in subframes that do not use control slots or the like. FIGS. 6A to 6C show the format of a frame generated by each base station apparatus 10 in the communication system 100. FIG. FIG. 6A shows the format of a frame generated by the first base station apparatus 10a, for example. The first base station apparatus 10a uses the first control slot and the first road vehicle slot in the first subframe. On the other hand, the first base station apparatus 10a uses the priority period as the priority vehicle slot in the second to Nth subframes. For example, the priority period of the second subframe is used as a second priority vehicle slot. The same applies to the remaining subframes.

  FIG. 6B shows a format of a frame generated by the second base station apparatus 10b, for example. The second base station apparatus 10b uses the second control slot and the second road vehicle slot in the second subframe. On the other hand, the second base station apparatus 10b uses the priority period as the priority vehicle slot in the first subframe, the third subframe to the Nth subframe. For example, the priority period of the first subframe is used as the first priority vehicle slot. The same applies to the remaining subframes. FIG. 6C shows a format of a frame generated by the Nth base station apparatus 10n, for example. The Nth base station apparatus 10n uses the Nth control slot and the Nth road car slot in the Nth subframe. On the other hand, the Nth base station apparatus 10n uses the priority period as the priority vehicle slot in the first to N−1th subframes. For example, the priority period of the first subframe is used as the first priority vehicle slot. The same applies to the remaining subframes. Returning to FIG.

  During the period in which the first control slot and the first road vehicle slot are arranged, the priority vehicle slot is also arranged by the second base station apparatus 10b and the like. However, since the second base station apparatus 10b and the like do not detect as an empty slot if the first control slot and the first road and vehicle slot are used, data communication between the terminal apparatuses 14 is not performed. Therefore, occurrence of a collision with control information and data in road-to-vehicle communication is suppressed. On the other hand, when there is a slot that is not used as the first road vehicle slot, data communication between the terminal devices 14 is performed, so that the frame utilization efficiency is improved. Returning to FIG. In this embodiment, it is assumed that the frame defining portion 34 forms the frame shown in any of FIGS. 5B and 6A to 6C.

  As reception processing, the RF unit 22 receives a packet signal transmitted in communication between other terminal devices (not shown) by the antenna 20 in each priority vehicle slot. Here, when the frames as shown in FIG. 5B and FIGS. 6A to 6C are repeated, the data of the frame is stored in the slot selected from the plurality of priority vehicle slots. It is broadcast at intervals. Further, the data includes the identification number of the terminal device that is the notification source. Therefore, the RF unit 22 receives data from the terminal device at a frame period. The RF unit 22 also receives data during the general vehicle period.

  The RF unit 22 performs frequency conversion on a radio frequency packet signal received via the antenna 20 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 in a control slot and a road and vehicle slot included in one subframe, and transmits a radio frequency packet signal. Is generated. Further, the RF unit 22 transmits a radio frequency packet signal from the antenna 20. 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 the OFDM modulation scheme, the modem unit 24 also executes FFT (Fast Fourier Transform) as reception processing and also executes IFFT (Inverse Fast Fourier Transform) as transmission processing.

  The power measuring unit 38 receives the received signal from the RF unit 22 or the modem unit 24 in the priority vehicle slot and measures the received power. Here, the received power is measured in slot units. Therefore, the power measuring unit 38 measures the received power for each of the plurality of priority vehicle slots. The power measuring unit 38 outputs the received power in slot units to the empty slot specifying unit 42 and the collision slot specifying unit 44. The quality measuring unit 40 receives the demodulation result from the modem unit 24 in the priority vehicle slot and measures the signal quality. Here, the error rate is measured as the signal quality. In addition, since a well-known technique should just be used for the measurement of an error rate, description is abbreviate | omitted here. Further, as the signal quality, instead of the error rate, EVM (Error Vector Magnet) or the like may be measured. The quality measuring unit 40 outputs an error rate for each of the plurality of priority vehicle slots to the collision slot specifying unit 44.

  The empty slot identifying unit 42 receives the received power in slot units from the power measuring unit 38. The empty slot specifying unit 42 compares each received power with a threshold value (hereinafter referred to as “empty slot threshold value”), and determines a priority vehicle slot whose received power is smaller than the empty slot threshold value. Identify. That is, the empty slot specifying unit 42 detects, as an empty slot, a priority vehicle slot that can be used for communication between a plurality of terminal devices from among a plurality of priority vehicle slots. Here, when there are a plurality of empty slots, the empty slot specifying unit 42 specifies them. The empty slot specifying unit 42 outputs information regarding the specified empty slot to the generating unit 36.

  The collision slot specifying unit 44 receives the received power for each slot from the power measuring unit 38 and receives the error rate for each slot from the quality measuring unit 40. The collision slot specifying unit 44 associates the received power with the error rate for each slot. The collision slot identifying unit 44 compares the received power with the first threshold value and compares the error rate with the second threshold value for each slot. The collision slot specifying unit 44 specifies a priority vehicle slot whose received power is larger than the first threshold value and whose error rate is worse than the second threshold value as a collision slot. That is, the collision slot identifying unit 44 recognizes a priority vehicle slot whose communication power is deteriorated although reception power is large as a collision slot. As described above, the collision slot specifying unit 44 detects, as a collision slot, a priority vehicle slot in which a collision has occurred due to a plurality of terminal apparatuses transmitting signals in duplicate. The collision slot identification unit 44 outputs information regarding the identified collision slot to the generation unit 36.

  The empty slot specifying unit 42 and the collision slot specifying unit 44 set the first priority vehicle slot to the Nth priority vehicle slot as detection targets as priority vehicle slots. That is, regardless of the number of subframes included in the frame, all priority vehicle slots included in the frame are targeted for detection. In addition, when the frame format corresponds to FIGS. 6A to 6C, the empty slot specifying unit 42 and the collision slot specifying unit 44 each other than the subframe including the control slot used by itself. In the subframe, the control slot and the road vehicle slot are added to the detection target as priority vehicle slots.

  The generation unit 36 receives information related to the empty slot from the empty slot specifying unit 42 and receives information related to the collision slot from the collision slot specifying unit 44. The generation unit 36 generates control information while including information regarding empty slots and information regarding collision slots. Here, each of the plurality of subframes included in the frame is assigned a number (hereinafter referred to as “subframe number”) that is “1” and “2” in order from the front. In addition, each of the plurality of slots included in the priority period is assigned a number (hereinafter referred to as “slot number”) that is “1” and “2” in order from the front for each subframe. Yes. The generation unit 36 includes, as control information, the slot number and subframe number of the empty slot included in the previous priority period in the control information. Similar processing is performed for the collision slot.

  The generation unit 36 receives information on frames and slots from the frame definition unit 34. In particular, the generation unit 36 specifies the control slot and the road and vehicle slot used by itself from the information regarding the control slot and the road and vehicle slot. This corresponds to a control slot and a road and vehicle slot in one of a plurality of subframes constituting the frame. The production | generation part 36 includes the information regarding the control slot and road vehicle slot which self uses. FIGS. 7A and 7B show the format of a MAC frame stored in a packet signal defined in the communication system 100. FIG. FIG. 7A shows the format of the MAC frame. In the MAC frame, “MAC header”, “extended MAC header”, “MSDU”, and “FCS” are arranged in order from the top. The MSDU stores data, where the MSDU includes information about empty slots and information about collision slots.

  FIG. 7B shows the format of the extended MAC header. The extended MAC header includes, in order from the top, “number of transfers”, “subframe number”, “frame period”, “slot length”, “number of subframes”, “number of priority vehicle slots”, “number of road and vehicle slots”. , “Transmission processing decision threshold” is arranged. Note that the configuration of the extended MAC header is not limited to that in FIG. 7B, and some elements may be excluded, or other elements may be included. The number of transfers indicates the number of times that the control information transmitted from the base station apparatus 10, in particular, the contents of the extended MAC header is transferred by a terminal apparatus (not shown). The generation unit 36 sets the number of transfers to “0”. The subframe number is a number of a subframe in which the base station apparatus 10 uses a control slot and a road and vehicle slot.

  The frame period indicates the period of the frame, and is set to, for example, “100 msec” as described above. The slot length indicates a slot period. The number of subframes indicates the number of subframes forming one frame. The number of priority vehicle slots indicates the number of priority vehicle slots in a subframe in which the base station apparatus 10 uses control slots and road and vehicle slots. The number of road and vehicle slots indicates the number of road and vehicle slots in the subframe in which the base station apparatus 10 uses the control slot and the road and vehicle slot. The threshold value for determining transmission processing is a threshold value used by a terminal device (not shown). Details of the threshold value for determining transmission processing will be described later. Returning to FIG.

  The generation unit 36 periodically assigns control information to control slots to be used. The generation unit 36 outputs control information to the modem unit 24 in the assigned control slot. In addition, when the generation unit 36 acquires information to be transmitted to the terminal device, the generation unit 36 stores the acquired information in a packet signal (hereinafter, such a packet signal is also referred to as “data”). At that time, the MAC frame shown in FIGS. 7A to 7B is used. Information acquisition is performed via the network communication unit 80. The network communication unit 80 is connected to a network 202 (not shown). The generation unit 36 assigns data to road and vehicle slots. The generation unit 36 outputs data to the modem unit 24 at the allocated road and vehicle slot.

  The modem unit 24 and the RF unit 22 broadcast the control information and data generated by the generating unit 36 from the antenna 20 in the assigned control slot and road and vehicle slot. Note that the data may be transmitted to a specific terminal device without being broadcast. Among the terminal devices that have received the control information, the terminal devices that exist within a predetermined range from the base station device 10 recognize the timing of each slot, and among the priority vehicle slots reserved for communication between the terminal devices. Use at least one of Further, when reporting data over a plurality of frames, the terminal device uses priority vehicle slots having the same relative timing within the frame. On the other hand, the terminal device existing outside the predetermined range from the base station device 10 recognizes the general vehicle period and executes CSMA during the general vehicle period. The control unit 30 controls processing of the entire 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. 8 shows a configuration of the terminal device 14 mounted on the vehicle 12. The terminal device 14 includes an antenna 50, an RF unit 52, a modem unit 54, a processing unit 56, and a control unit 58. Further, the processing unit 56 includes a timing specifying unit 60, an acquisition unit 62, a generation unit 64, a notification unit 70, a selection unit 90, and an instruction unit 92. The timing specifying unit 60 includes a control information extracting unit 66, a transmission processing determining unit 72, a slot determining unit 68, and a CSMA executing unit 74, and the selecting unit 90 includes a transfer number acquiring unit 110, an assigning unit 112, and a measuring unit 114. A transfer amount determination unit 116 and a transfer information determination unit 118. The antenna 50, the RF unit 52, and the modem unit 54 execute the same processing as the antenna 20, the RF unit 22, and the modem unit 24 in FIG. Therefore, these descriptions are omitted here.

  The acquisition unit 62 includes a GPS receiver (not shown), a gyroscope, a vehicle speed sensor, and the like. Based on data supplied from the GPS receiver, a vehicle 12 (not shown), that is, a vehicle 12 on which the terminal device 14 is mounted, Get direction, speed, etc. 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 62 outputs the acquired information to the generation unit 64.

  The control information extraction unit 66 receives a signal from the RF unit 52 or a demodulation result from the modem unit 54. In addition, the control information extraction unit 66 identifies the timing of the control slot. For example, the control information includes a known pattern, and the control information extraction unit 66 specifies the timing of the control slot when the known pattern is detected by the correlation process. In addition, the control information extraction unit 66 establishes synchronization of the frame, subframe, and slot with reference to the timing at which the control slot is received. That is, the control information extraction unit 66 generates a subframe and a frame so as to synchronize with the subframe including the control slot. The control information extraction unit 66 outputs information on the generated frame to the transmission process determination unit 72. In addition, the control information extraction unit 66 acquires information on empty slots and information on collision slots from each control information. The control information extraction unit 66 outputs the information regarding the empty slot and the information regarding the collision slot to the slot determination unit 68.

  The transmission processing determination unit 72 receives information about the frame from the control information extraction unit 66. The transmission processing determining unit 72 specifies the timing of each control slot based on the information regarding the frame, and measures the reception power in the specified control slot. This corresponds to measuring the received power of control information. At that time, the transmission processing determination unit 72 receives a signal from the RF unit 52. More specifically, the transmission processing determining unit 72 measures the reception power of the control slot included in each of the plurality of subframes, and selects the maximum reception power from the measurement. Further, the transmission process determination unit 72 receives the threshold value for transmission process determination shown in FIG. 7B from the control information extraction unit 66. For example, the transmission process determination unit 72 receives a transmission process determination threshold value included in the control information corresponding to the selected received power. The transmission process determination unit 72 compares the received power with a transmission process determination threshold value. Here, the threshold value for determining transmission processing is determined in consideration of propagation loss so as to correspond to a certain range from the base station apparatus 10.

  If the received power is larger than the threshold value for determining transmission processing, the transmission processing determining unit 72 estimates that the transmission power determining unit 72 exists within a certain range from the base station apparatus 10 and determines use of the priority vehicle slot. On the other hand, if the received power is not larger than the threshold value for determining the transmission process, the transmission process determining unit 72 estimates that the base station apparatus 10 is outside a certain range and uses the general vehicle period. decide. When the use of the priority vehicle slot is determined, the transmission processing determination unit 72 instructs the slot determination unit 68 to operate, and when the use of the general vehicle period is determined, the transmission processing determination unit 72 includes the CSMA execution unit 74. Instruct the operation.

  The slot determination unit 68 receives information on empty slots and information on collision slots from the control information extraction unit 66. For example, the slot determination unit 68 receives information regarding empty slots and information regarding collision slots included in the control information corresponding to the received power selected by the transmission processing determination unit 72. The slot determination unit 68 selects an empty slot from a plurality of priority vehicle slots based on the information on the empty slot. Even during the continuation of such processing, the control information extraction unit 66 continues to acquire information on empty slots and information on collision slots from the control information for each frame. The slot determination unit 68 confirms whether the slot number corresponding to the currently used priority vehicle slot is not a collision slot based on the information on the collision slot. If the slot is not a collision slot, the slot determination unit 68 continues to output the same slot number as before to the generation unit 64. On the other hand, if the slot is determined to be a collision slot, the slot determination unit 68 estimates the empty slot again based on the information regarding the empty slot, and outputs the slot number corresponding to the empty slot to the generation unit 64.

  The CSMA execution unit 74 executes CSMA during the general vehicle period. Specifically, the CSMA execution unit 74 measures the interference power by carrier sense. Also, the CSMA execution unit 74 estimates transmission timing based on the interference power. Specifically, the CSMA execution unit 74 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 CSMA execution unit 74 determines the transmission timing. The CSMA execution unit 74 notifies the generation unit 64 of the determined transmission timing.

  The generation unit 64 generates data so as to include the information acquired by the acquisition unit 62. At that time, the MAC frame shown in FIGS. 7A to 7B is used, and the generation unit 64 stores the measured location in the MSDU. The generation unit 64 broadcasts data via the modulation / demodulation unit 54, the RF unit 52, and the antenna 50 at the priority vehicle slot specified by the slot determination unit 68 or the transmission timing determined by the CSMA execution unit 74. The notification unit 70 acquires data from the base station device 10 (not shown) in the road and vehicle slots, and acquires data from other terminal devices 14 (not shown) in the priority vehicle slot and the general vehicle period. The notification unit 70 notifies the driver of the approach of another vehicle 12 (not shown) or the like via a monitor or speaker according to the contents of the data.

  As described above, each of the plurality of subframes forming the frame includes a control slot and a road and vehicle slot (hereinafter referred to as “first period”), a priority vehicle slot and a general vehicle period (hereinafter referred to as “second period”). ")". In addition, the first period included in each of the plurality of subframes is used for different base station apparatuses 10. The antenna 50, the RF unit 52, the modulation / demodulation unit 54, and the processing unit 56 receive control information and data from the base station apparatus 10 in each first period, and exchange data with other terminal apparatuses 14 in each second period. Send and receive.

  The control information extraction unit 66 extracts control information that is control information for which the base station device 10 is an information source and that indicates the first period used by the base station device 10. Here, as described above, the control information extraction unit 66 extracts the direct transmission control information (hereinafter referred to as “first type control information”) from the base station apparatus 10, and is further transferred by another terminal apparatus 14. The control information included in the data (hereinafter referred to as “second type control information”) is also extracted. Here, the first control information and the second type control information may be collectively referred to as “control information”. Since the second type control information corresponds to the extended MAC header shown in FIG. 7B, it does not include information on empty slots and information on collision slots. Here, in the second type control information, the number of transfers is set to a value of “1 or more”. Further, since the subframe number is not changed when transferred by the terminal apparatus 14, the base station apparatus 10 serving as the information source is specified by referring to the subframe number. Note that the control information extraction unit 66 may extract at least one of the first type control information and the second type control information.

  The transfer count acquisition unit 110 acquires information regarding the transfer count included in the first control information and the second control information for each base station apparatus 10 serving as an information source. More specifically, the transfer count acquisition unit 110 sequentially acquires the transfer counts corresponding to the subframe number “1”, and executes the same processing for the transfer counts corresponding to other subframe numbers. . Further, for each base station device 10 serving as an information source, the transfer number acquisition unit 110 obtains the smaller transfer number, for example, the value of the minimum transfer number from the information related to the transfer number related to the base station device 10. get. That is, the transfer count acquisition unit 110 acquires the minimum transfer count corresponding to the subframe number “1”, the minimum transfer count corresponding to the subframe number “2”, and the like. When the control information extraction unit 66 extracts the first control information, the minimum value of the number of transfers is “0”.

  The assigning unit 112 receives the transfer number acquired by the transfer number acquiring unit 110 and the control information extracted by the control information extracting unit 66. The assigning unit 112 assigns a priority order to each control information based on the number of transfers. Here, the assigning unit 112 assigns to the control information a priority that increases as the number of transfers decreases. When there are a plurality of pieces of control information having the same number of transfers, the assigning unit 112 assigns priority to the control information so that the lower the subframe number, the higher the priority. The assigning unit 112 outputs the control information assigned with the priority order to the transfer information determining unit 118.

  The measuring unit 114 measures the amount of packet signals received by the antenna 50, the RF unit 52, and the modem unit 54, that is, the amount of demodulated packet signals. Here, the packet signal to be measured includes control information and data. More specifically, the measurement unit 114 sets a window for a certain period and measures the amount of packet signal received in the window. FIG. 9 shows an outline of processing in the measurement unit 114. In FIG. 9, the horizontal axis indicates time. “Reception” corresponds to a period during which a packet signal of control information or data is received, “unreceived” corresponds to a period during which no packet signal is received, and “T” is set in the measurement unit 114. Indicates the window period. The measurement unit 114 sets a window starting from the timing t1, and measures the amount of packet signal received in the window. The measuring unit 114 also sets a window at the timing t2 obtained by shifting the timing t1 backward, and measures the amount of packet signal received within the window. In this way, the measurement unit 114 sequentially measures the amount of packet signals in the past certain interval by setting the window while shifting the timing.

  FIGS. 10A to 10B show another processing outline in the measurement unit 114. 10 (a)-(b) are shown in the same manner as FIG. 10A corresponds to the case where the amount of packet signals received within the window is relatively small, and FIG. 10B corresponds to the case where the amount of packet signals received within the window is relatively large. To do. Returning to FIG. Note that the measurement unit 114 may measure the ratio of the packet signal in the window period. The measuring unit 114 sequentially outputs the measured amount of packet signal to the transfer amount determining unit 116.

  The transfer amount determination unit 116 receives the amount of packet signal measured by the measurement unit. The transfer amount determination unit 116 determines the amount of control information to be transferred according to the amount of packet signals. More specifically, the transfer amount determination unit 116 stores in advance a table indicating a correspondence relationship between the amount of packet signals and the amount of control information to be transferred. FIG. 11 shows the data structure of the correspondence table stored in the transfer amount determination unit 116. As shown in the figure, a received information amount column 210 and a control information amount column 212 to be transferred are included. The received information amount column 210 indicates the range of the received packet signal amount, and the transferred control information amount column 212 indicates the amount of control information to be transferred.

  Here, the amount of control information to be transferred is defined so as to correspond to the range indicated in the received information amount column 210. For example, if the amount of received packet signals is in the range of “0 to 49 packets”, the amount of control information to be transferred is set to “3”. Note that “3” may be defined as the number per frame, or may be defined as the number per window period T described above. As is clear from FIG. 11, a correspondence relationship is defined such that the greater the amount of measured packet signals, the smaller the amount of control information to be transferred. Returning to FIG. The transfer amount determination unit 116 determines the amount of control information to be transferred from the amount of received packet signals by referring to the table shown in FIG. The transfer amount determination unit 116 outputs information regarding the amount of control information to be transferred to the transfer information determination unit 118.

  The transfer information determining unit 118 receives control information to which priority is given from the assigning unit 112, and receives information related to the amount of control information to be transferred from the transfer amount determining unit 116. The transfer information determination unit 118 determines the control information to be transferred by selecting the control information in order from the control information with the higher priority according to the amount of control information to be transferred. For example, if the amount of control information to be transferred is “1”, the transfer information determination unit 118 selects the control information with the highest priority. If the amount of control information to be transferred is “3”, the transfer information determination unit 118 selects the third control information with the highest priority. Here, since the priority is given so as to increase as the number of transfers decreases, it can be said that the transfer information determination unit 118 preferentially selects control information with a small number of transfers. The transfer information determination unit 118 outputs control information to the instruction unit 92.

  The instruction unit 92 instructs the generation unit 36 to transmit the packet signal storing the control information determined by the transfer information determination unit 118 in the priority vehicle slot or the general vehicle period. Specifically, the instruction unit 92 instructs the generation unit 64 to store the control information selected by the transfer information determination unit 118 in the extended MAC header of the data. When a plurality of control information is selected by the transfer information determination unit 118, the instruction unit 92 instructs the generation unit 64 to provide an extended MAC header corresponding to each control information. That is, the selected number of extended MAC headers are provided in the packet signal. As a result, the length of the packet signal becomes longer as the number of extended MAC headers increases. Or when the length of a packet signal is fixed, the capacity | capacitance of MSDU is reduced, so that the number of extended MAC headers increases. Further, the instruction unit 92 increases the number of transfers in the information regarding the number of transfers when storing the control information in the extended MAC header. In response to such an instruction, the generation unit 64 stores the control information selected by the transfer information determination unit 118 in the data and increases the number of transfers. The generation unit 64 broadcasts data in the same manner as described above. This corresponds to transferring control information. The control unit 58 controls the operation of the entire terminal device 14.

  The operation of the communication system 100 configured as above will be described. FIG. 12 shows an outline of the operation of the communication system 100. Here, only the control slot and the priority vehicle slot are shown in FIG. The horizontal direction in the figure corresponds to time, and three frames from the i-th frame to the i + 2th frame are shown as described in the uppermost stage. Further, for the sake of clarity, it is assumed that 15 priority vehicle slots are included in one frame. As illustrated, the base station apparatus 10 broadcasts control information in the first slot of each frame. “Control” in the figure corresponds to control information. In the lower part, information on empty slots and information on collision slots included in the control information are shown while being associated with the slots. “Empty” in the figure corresponds to an empty slot, and “attack” corresponds to a collision slot.

  Furthermore, the lower part shows the timing at which the first terminal device 14a to the fourth terminal device 14d notify the data. “De” in the figure corresponds to data. The first terminal device 14a to the fourth terminal device 14d refer to the control information and select an empty slot. In the i-th frame, the first terminal device 14a to the fourth terminal device 14d broadcast data in the selected empty slot. At this time, since the empty slots selected in the third terminal device 14c and the fourth terminal device 14d are the same, the data notified from both collide. The base station apparatus 10 detects the occurrence of a collision in the slot. In the (i + 1) th frame, the control information broadcast from the base station apparatus 10 indicates the slot in which the collision occurred as information on the collision slot.

  Since the first terminal device 14a and the second terminal device 14b do not collide in the already used priority vehicle slot, the priority vehicle slot having the same slot number is used again. On the other hand, the third terminal device 14c and the fourth terminal device 14d select another empty slot again because a collision has occurred in the priority vehicle slot already used. The third terminal device 14c and the fourth terminal device 14d notify the data in the selected empty slot. Since all data does not collide, the collision slot is not indicated in the control information broadcast from the base station apparatus 10 in the (i + 2) th frame. Therefore, in the (i + 2) th frame, the first terminal device 14a to the fourth terminal device 14d again use the priority vehicle slot having the same slot number as the already used priority vehicle slot.

  FIG. 13 is a flowchart showing a procedure for notifying an empty slot in the base station apparatus 10. The detector 32 sets the slot number m to s (S10). Here, s is a slot number where the priority vehicle slot is started. The power measuring unit 38 measures received power (S12). If the received power is smaller than the empty slot threshold (Y in S14), the empty slot specifying unit 42 specifies the priority vehicle slot with the slot number m as an empty slot (S16). If the received power is not smaller than the empty slot threshold (N in S14), the empty slot specifying unit 42 skips the process of step 16. If the slot number m is not the maximum number M (N in S18), the detection unit 32 adds 1 to the slot number m (S20), and returns to Step 12. On the other hand, if the slot number m is the maximum number M (Y in S18), the generation unit 36 includes the slot number of the empty slot in the control information (S22). The modem unit 24 and the RF unit 22 notify the control information (S24).

  FIG. 14 is a flowchart showing a collision slot notification procedure in the base station apparatus 10. The detection unit 32 sets the slot number m to s (S40). The power measuring unit 38 measures the received power, and the quality measuring unit 40 measures the error rate (S42). When the received power is greater than the first threshold and the error rate is greater than the second threshold (Y in S44), the collision slot identifying unit 44 identifies the priority vehicle slot with slot number m as the collision slot. (S46). If the received power is not greater than the first threshold value or the error rate is not greater than the second threshold value (N in S44), the collision slot specifying unit 44 skips the process of step 46. If the slot number m is not the maximum number M (N in S48), the detection unit 32 adds 1 to the slot number m (S50), and returns to Step 42. On the other hand, if the slot number m is the maximum number M (Y in S48), the generation unit 36 includes the slot number of the collision slot in the control information (S52). The modem unit 24 and the RF unit 22 notify the control information (S54).

  FIG. 15 is a flowchart illustrating a transmission process determination procedure in the terminal device 14. The transmission process determining unit 72 measures the received power of each control information (S100). If the maximum received power is larger than the threshold value for determining transmission processing (Y in S102), the transmission processing determining unit 72 determines use of the priority vehicle slot (S104). On the other hand, if the received power is not greater than the threshold value for determining the transmission process (N in S102), the transmission process determining unit 72 determines the use of the general vehicle period (S106).

  FIG. 16 is a flowchart illustrating a data transmission procedure in the terminal device 14. This corresponds to the case where the priority vehicle slot is used. The control information extraction unit 66 acquires control information (S70). If the priority vehicle slot to be used has already been specified (Y in S72), the slot determination unit 68 confirms whether or not a collision has occurred in the slot. If a collision has occurred (Y in S74), the slot determination unit 68 changes the priority vehicle slot (S76). If no collision has occurred (N in S74), step 76 is skipped. On the other hand, if the priority vehicle slot to be used has not already been specified (N in S72), the slot determining unit 68 estimates the empty slot and then specifies the empty slot at random (S78). The generation unit 64 transmits data in the identified priority vehicle slot (S80).

  FIG. 17 is a flowchart showing a control information transfer procedure in the terminal device 14. The measuring unit 114 measures the amount of packet signal received in a certain period (S120). The transfer amount determination unit 116 determines the amount of control information to be transferred according to the amount of packet signals (S122). The transfer information determination unit 118 instructs the generation unit 64 to store control information corresponding to the determined amount of control information in the packet signal (S124).

  According to the embodiment of the present invention, since the control slot, road vehicle slot, priority vehicle slot, and general vehicle period are provided in the frame, the transmission timing can be varied depending on the use of the signal. Moreover, since the road and vehicle slot is provided differently from the priority vehicle slot and the general vehicle period, it is possible to reduce the mutual influence between the inter-vehicle communication and the road-to-vehicle communication. Further, since the frame is divided into a plurality of subframes and the control slots are multiplexed by the plurality of subframes, it is possible to cope with a case where a plurality of base station apparatuses are installed in proximity. Further, since the road and vehicle slot in the subframe using the control slot is used, the road and vehicle slot can also be multiplexed.

  Further, since one base station apparatus uses the first period including the control slot and the road and vehicle slot in one subframe, the influence of interference between the base station apparatuses can be reduced. Moreover, since the control information including the information regarding the first period is notified by the base station apparatus, the terminal apparatus can be informed of the first period. Moreover, since the terminal device transfers the control information including the information related to the first period, the transmission area of the information related to the first period can be expanded. Moreover, since the transmission area of the information regarding the first period is expanded, the number of terminal devices that recognize the first period can be increased. In addition, since the number of terminal devices that recognize the first period increases, communication according to the original purpose of the slot can be executed.

  In addition, since the amount of control information to be transferred is determined according to the amount of received packet signals, an amount of control information corresponding to the amount of traffic can be transferred. Also, if the traffic volume is small, the amount of control information is increased, so that various control information can be transferred. Also, if the traffic volume is large, the amount of control information is reduced, so that the influence on data communication can be reduced. In addition, since the control information is transferred according to the priority order, necessary control information can be transferred with priority. In addition, since the priority of control information with a small number of transfers is increased, the priority of control information necessary for other terminal devices can be increased. In addition, when transferring control information from the base station apparatus, it is possible to control an increase or decrease in traffic and maintain an optimal traffic amount.

  Further, in each subframe other than the subframe including the control slot being used, the control slot and the road and vehicle slot are added to the detection target as the priority vehicle slot, so that the number of priority vehicle slots can be increased. Moreover, since the priority vehicle slot which can be used for communication between terminal devices is notified from among a plurality of priority vehicle slots, the probability of occurrence of a collision in communication between terminal devices can be reduced. In addition, since the probability of collision in communication between terminal devices is reduced, the collision probability of packet signals can be reduced even when the amount of communication increases. Moreover, since the empty slot is specified based on the received power for each of the plurality of vehicle slots, the specification can be easily performed.

  In addition, since the number of the empty slot included in the previous frame is notified, the instruction to the terminal device can be surely executed. Moreover, since the terminal device using the empty slot uses the priority vehicle slot corresponding to the slot over a plurality of frames, the processing can be simplified. In addition, since the priority vehicle slot in which a collision has occurred due to a plurality of terminal devices transmitting duplicate signals from a plurality of priority vehicle slots is notified, occurrence of a collision in communication between the plurality of terminal devices Probability can be reduced. Further, since the collision slot is identified based on the received power for each of the plurality of priority vehicle slots and the signal quality for each of the plurality of priority vehicle slots, the identification can be easily performed. In addition, since the number of the collision slot included in the previous frame is notified, the instruction to the terminal device can be reliably executed.

  In addition, since the terminal device that controls the transmission timing according to the control information and the terminal device that autonomously controls the transmission timing are arranged in different periods, it is possible to separate terminal devices having different transmission timing control methods. . In addition, since terminal devices with different transmission timing control methods are separated, it is possible to reduce the collision probability of packet signals from terminal devices with different transmission timing control methods.

  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, control information and data broadcast from the base station apparatus 10 and data broadcast from one terminal apparatus 14 are allocated to one slot. However, the present invention is not limited to this. For example, control information and data may be assigned to two or more slots. According to this modification, the communication speed of control information and data can be improved.

  In the embodiment of the present invention, the base station apparatus 10 detects empty slots and collision slots and includes information related to them in the control information. However, the present invention is not limited to this. For example, the base station device 10 may detect only empty slots without detecting a collision slot. At that time, the collision slot specifying unit 44 and the like are omitted. According to this modification, the configuration and processing of the base station device 10 can be simplified.

  In the embodiment of the present invention, the instruction unit 92 instructs the generation unit 64 to provide a plurality of extended MAC headers in one packet signal when transferring a plurality of control information. However, the present invention is not limited to this. For example, the instruction unit 92 may provide only one extended MAC header for one packet signal and change the transmission frequency of the packet signal when transferring a plurality of control information. When transferring three pieces of control information, the instruction unit 92 instructs the generation unit 64 to transmit three packet signals in one frame, and when transferring one piece of control information, the instruction unit 92 has one instruction unit 92. The generation unit 64 is instructed to transmit one packet signal in the frame. According to this modification, the format of the packet signal is fixed, so that the processing can be simplified.

  In the embodiment of the present invention, the measurement unit 114 measures the amount of the demodulated packet signal. However, the present invention is not limited to this. For example, the measurement unit 114 may measure the amount of packet signals by using the received power and the carrier sense result in the RF unit 52. When the reception power at the RF unit 52 is used, the measurement unit 114 measures a period during which the reception power exceeds a predetermined threshold. When using the carrier sense result, the measurement unit 114 measures the number of slots in communication. According to this modification, various processes can be used.

  10 base station device, 12 vehicle, 14 terminal device, 20 antenna, 22 RF unit, 24 modulation / demodulation unit, 26 processing unit, 28 GPS positioning unit, 30 control unit, 32 detection unit, 34 frame definition unit, 36 generation unit, 38 Power measurement unit, 40 quality measurement unit, 42 empty slot identification unit, 44 collision slot identification unit, 50 antenna, 52 RF unit, 54 modulation / demodulation unit, 56 processing unit, 58 control unit, 60 timing identification unit, 62 acquisition unit, 64 Generation unit, 66 control information extraction unit, 68 slot determination unit, 70 notification unit, 72 transmission processing determination unit, 74 CSMA execution unit, 80 network communication unit, 90 selection unit, 92 instruction unit, 100 communication system, 110 transfer number acquisition Part 112 giving part 114 measuring part 11 Transfer amount determination unit, 118 transfer information determination unit.

Claims (4)

Each of a plurality of subframes forming a frame includes a first period and a second period, and the first period included in each of the plurality of subframes forming the frame is different from each other in the base station apparatus. A communication unit that is used, receives a signal from the base station apparatus in each first period, and transmits / receives a signal to / from another terminal apparatus in each second period;
An extraction unit that extracts control information indicating a first period used by the base station device, which is control information used by the base station device as an information source, from the signal received by the communication unit;
A measurement unit for measuring the amount of signal received in the communication unit;
A determination unit that determines control information to be transferred while changing the amount of control information to be transferred among the control information extracted by the extraction unit according to the amount of signal measured by the measurement unit;
An instruction unit for instructing the communication unit to transmit a signal storing the control information determined by the determination unit in a predetermined second period;
The terminal unit extracts at least one of control information transmitted directly from a base station device and control information transferred by another terminal device.   The terminal device according to claim 1, wherein the measurement unit sets a window for a certain period and measures the amount of a signal received in the window.   The terminal device according to claim 1, wherein the determination unit reduces the amount of control information to be transferred as the amount of the signal measured by the measurement unit increases.   The determination unit obtains information on the number of transfers included in the control information extracted by the extraction unit for each base station device serving as an information source, and gives priority to control information with a small number of transfers as control information to be transferred. The terminal device according to claim 1, wherein the terminal device is selected automatically.

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