JP2014220857A - Terminal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for reducing collision probability of a packet signal.SOLUTION: A processing section 26 regulates such that a base station device is able to transmit a first type signal during a period of the beginning of each sub-frame and a terminal device is able to transmit a second type signal during a period of un-transmission of the first type signal in a frame. Also, the processing section 26 receives a first type signal from another base station device and a second type signal from the terminal device. Based on a received first type signal, a first specifying section 32 specifies a sub-frame used in another base station device. A second type signal includes information about the sub-frame when the terminal device receives a first type signal from another base station device. Based on information about a sub-frame, a second specifying section 34 specifies a sub-frame used in another base station device. Based on sub-frames specified in the first and second specifying sections 32 and 34, a third specifying section 42 specifies a sub-frame to be used.

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.

  In a radio communication system in which a mobile terminal apparatus can communicate, a large number of base station apparatuses are generally installed in various places. A mobile terminal apparatus existing in an area formed by each base station apparatus performs communication with the base station apparatus forming the area. When the mobile terminal device moves, the base station device with which the mobile terminal device communicates is changed. In order to smoothly move between base station apparatuses by a mobile terminal apparatus, it is necessary to ensure synchronization of transmission timing between adjacent base station apparatuses (see, for example, Patent Document 1).

JP 2009-177532 A

  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. For example, the roadside device notifies the vehicle-mounted device of information related to the situation of the intersection. On the other hand, vehicle-to-vehicle communication is defined separately from road-to-vehicle communication. In vehicle-to-vehicle communication, information related to the situation of an intersection is communicated between vehicle-mounted devices. For example, GPS (Global Positioning System) mounted on the vehicle detects current position information, and the position information is exchanged between the vehicle-mounted devices.

  In vehicle-to-vehicle communication, reduction of the collision probability of packet signals between vehicle-mounted devices is required, and in road-to-vehicle communication, reduction of the probability of collision of packet signals between roadside devices is required. When both vehicle-to-vehicle communication and road-to-vehicle communication are executed, it is also required to reduce the collision probability of packet signals between the vehicle-mounted device and the roadside device. In order to reduce the probability of occurrence of a collision, for example, each roadside device secures a period to be used for road-to-vehicle communication, and notifies control information including information on the period. The vehicle-mounted device recognizes a period to be used for road-to-vehicle communication based on the control information, and executes vehicle-to-vehicle communication in other periods.

  Under such circumstances, in order to reduce the collision probability of packet signals between roadside units, timing synchronization is required between roadside units. For example, a newly activated roadside machine receives a packet signal from an already activated roadside machine, and determines a transmission timing based on the received packet signal. However, there may be cases where obstacles such as buildings or tunnels cannot directly receive packet signals from surrounding roadside devices, and transmission timing can be determined without considering the transmission timing of surrounding roadside devices. . As a result, in the vehicle-mounted device, the collision probability of packet signals transmitted from a plurality of roadside devices increases. In the following description, the roadside device will be described as a base station device, and the vehicle-mounted device will be described as a terminal device.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for reducing the collision probability of packet signals.

  In order to solve the above-described problem, a terminal device according to an aspect of the present invention is a terminal device that communicates in a frame formed of a plurality of subframes, and the base station device is the first in the head period of each subframe. The first type signal from the base station device is defined so that the seed signal can be transmitted and the terminal device can transmit the second type signal in the non-transmission period of the first type signal in the frame. And a first type signal from the base station apparatus in a period other than receiving the first type signal and the second type signal at the receiving unit receiving the second type signal from the other terminal device And a transmission unit that transmits a second type signal including information on a subframe when the signal is received. The base station apparatus that is the transmission source of the first type signal received by the receiving unit (1) specifies a subframe used by another base station apparatus based on the received first type signal, and ( 2) Based on the received second type signal, identify subframes used by other base station apparatuses. (3) Based on the subframes identified in these, the subframes of unused subframes are identified. (4) The first type signal is transmitted in the head period of any one of the specified subframes, and the receiving unit receives the first type signal from the base station apparatus. Receive.

  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, the collision probability of packet signals can be reduced.

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 4E are diagrams showing frame formats defined in the communication system of FIGS. FIGS. 5A and 5B 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 data structure of the table memorize | stored in the memory | storage part of FIG. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. 1 and FIG. FIGS. 8A to 8C are diagrams showing the data structure of the table stored in the storage unit of FIG. It is a flowchart which shows the transmission procedure in the base station apparatus of FIG. It is a flowchart which shows the statistical processing procedure in the base station apparatus of FIG. It is a flowchart which shows the determination processing procedure in the base station apparatus of FIG. It is a figure which shows the structure of the base station apparatus which concerns on the modification of this invention. FIGS. 13A to 13B are diagrams showing a format of a MAC frame stored in a packet signal defined in the modification of the present invention. FIG. 13 is a diagram illustrating a data structure of a table stored in a storage unit in FIG. 12. It is a flowchart which shows the transmission procedure in the base station apparatus of FIG. It is a flowchart which shows the statistical processing procedure in the base station apparatus of FIG. It is a flowchart which shows the determination processing procedure in the base station apparatus of FIG. FIGS. 18A to 18B are diagrams showing a format of a MAC frame stored in a packet signal defined in another modification of the present invention.

  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. Further, as road-to-vehicle communication, the base station apparatus repeatedly defines a frame including a plurality of subframes. The base station apparatus selects any one of the plurality of subframes, and broadcasts a packet signal in which control information and the like are stored in 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 transmits 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. That is, when the terminal device recognizes the content of the control information, interference between road-vehicle communication and vehicle-to-vehicle communication is reduced. Here, the communication area formed by the base station apparatus 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, the terminal device transfers control information by inter-vehicle communication.

  On the other hand, when packet signals transmitted from a plurality of base station apparatuses collide in road-to-vehicle communication, the error rate of packet signals in road-to-vehicle communication increases. Furthermore, since the terminal device cannot specify the road-to-vehicle transmission period, the packet signal collision probability in inter-vehicle communication also increases. In this situation, in order to cause each base station apparatus to select different subframes, the present embodiment executes the following processing.

  The base station apparatus receives a packet signal transmitted from another base station apparatus and acquires control information from the packet signal, thereby specifying a subframe used by the other base station apparatus. The base station apparatus selects a subframe other than the subframe used by another base station apparatus. On the other hand, due to the provision of obstacles such as buildings, there may be other base station apparatuses that are not close to each other but can receive packet signals. Such a subframe used by another base station apparatus is not recognized by the base station apparatus.

  In order to reduce the collision probability of packet signals in road-to-vehicle communication, the base station apparatus should also recognize subframes used by such other base station apparatuses. For this purpose, the base station apparatus also receives a packet signal from the terminal apparatus. The base station apparatus acquires control information stored in the packet signal, and recognizes a subframe used by another base station apparatus based on the control information. Furthermore, when selecting a subframe, the base station apparatus selects a subframe other than that used by another base station apparatus. The selected subframe is also used in the next frame.

  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 communication system 100 arranges the base station device 10 at an intersection. The base station device 10 repeatedly generates a frame including a plurality of subframes based on a signal received from a GPS satellite (not shown) and a frame formed by another base station device 10 (not shown). Here, the road vehicle transmission period can be set at the head of each subframe. The base station apparatus 10 selects a subframe in which the road and vehicle transmission period is not set by another base station apparatus 10 from among the plurality of subframes. The base station apparatus 10 sets a road and vehicle transmission period at the beginning of the selected subframe. The base station apparatus 10 stores control information including information on a road and vehicle transmission period in a packet signal. The base station apparatus 10 also stores predetermined data in the packet signal. The base station apparatus 10 notifies the packet signal in the set road and vehicle transmission period.

  The plurality of terminal apparatuses receive the packet signal broadcast by the base station apparatus 10 and generate 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 devices is synchronized with the frame generated in the base station device 10. In addition, the terminal device recognizes the road and vehicle transmission period set by each base station device 10 and specifies a period other than the road and vehicle transmission period in order to transmit the packet signal. The terminal device transmits a packet signal by executing CSMA / CA during the specified period.

  Specifically, the terminal device selects any one of the plurality of subframes, and specifies a period other than the road and vehicle transmission period in the selected subframe. Also, the terminal device selects subframes having the same relative timing in the next frame. Here, the terminal device acquires data and stores the data in a packet signal. The data includes, for example, information related to the location. The terminal device also stores control information in the packet signal. That is, the control information transmitted from the base station device 10 is transferred by the terminal device.

  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 transfers 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 transfers 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 transfers 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 preferentially transfers the control information.

  Here, it is assumed that the second base station apparatus 10b and the third base station apparatus 10c have already been activated and the first base station apparatus 10a is newly activated. Further, it is assumed that the first base station apparatus 10a can receive the packet signal from the second base station apparatus 10b, but cannot receive the packet signal from the third base station apparatus 10c. For example, an obstacle exists between the first base station apparatus 10a and the third base station apparatus 10c. The first base station apparatus 10a receives the packet signal from the second base station apparatus 10b, thereby generating a frame in synchronization with the frame generated in the second base station apparatus 10b.

  Further, the first base station apparatus 10a specifies a subframe used by the second base station apparatus 10b based on the control information from the second base station apparatus 10b. In addition, the first base station device 10a receives a packet signal from a terminal device mounted on the second vehicle 12b. The packet signal includes control information from the third base station apparatus 10c. The first base station apparatus 10a identifies the subframe used by the third base station apparatus 10c based on the control information. The first base station apparatus 10a selects a subframe other than the identified subframe, and sets a road and vehicle transmission period in the selected subframe.

  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 control unit 30, and a network communication unit 80. The processing unit 26 includes a first specifying unit 32, a measuring unit 38, a second specifying unit 34, an estimating unit 40, a generating unit 36, a third specifying unit 42, a storage unit 44, and a frame forming unit 46.

  The RF unit 22 receives a packet signal from a terminal device (not shown) or another 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 forming unit 46 receives a demodulation result from another base station apparatus 10 (not shown) via the RF unit 22 and the modem unit 24. The frame forming unit 46 repeatedly generates a frame formed by a plurality of subframes based on the demodulation result. 4A to 4E show frame formats defined in the communication system 100. FIG. FIG. 4A shows a frame configuration. 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 10, a subframe having a length of 10 msec is defined.

  FIG. 4B shows a configuration of a frame generated by the first base station apparatus 10a. The first base station apparatus 10a sets a road and vehicle transmission period at the beginning of the first subframe. In addition, the first base station apparatus 10a sets the vehicle transmission period from the second subframe to the Nth subframe. The vehicle transmission period is a period during which the terminal device can transmit a packet signal. That is, the first base station apparatus 10a can transmit a packet signal in a road and vehicle transmission period that is a head period of a predetermined subframe, and the terminal apparatus can transmit a frame signal in a vehicle transmission period other than the road and vehicle transmission period. It is defined that a packet signal can be transmitted.

  FIG.4 (c) shows the packet signal transmitted from the 1st base station apparatus 10a in a road and vehicle transmission period. The plurality of packet signals are continuously transmitted with a SIFS interval. Here, since the communication system 100 employs the OFDM modulation scheme, each packet signal is composed of a plurality of OFDM symbols. The OFDM symbol is composed of a guard interval (GI) and a valid symbol.

  FIG. 4D shows a configuration of a frame generated by the second base station apparatus 10b. The second base station apparatus 10b sets a road and vehicle transmission period at the beginning of the second subframe. Also, the second base station apparatus 10b sets the vehicle transmission period from the first subframe and the third subframe to the Nth subframe. FIG. 4E shows a configuration of a frame generated by the third base station apparatus 10c. The third base station apparatus 10c sets a road and vehicle transmission period at the beginning of the third subframe. Also, the third base station apparatus 10c sets the vehicle transmission period from the first subframe, the second subframe, and the fourth subframe to the Nth subframe. As described above, the plurality of base station apparatuses 10 select different subframes, and set the road and vehicle transmission period at the head portion of the selected subframe. Returning to FIG.

  The frame forming unit 46 detects control information from the demodulation result. The frame forming unit 46 specifies the reception timing of the control information. Since the reception timing of the control information is the reception timing of the packet signal including the control information, it corresponds to the start timing of the subframe in which the road and vehicle transmission period is arranged. In addition, the frame forming unit 46 acquires a subframe number included in the control information. Furthermore, a frame is generated based on the start timing of the subframe and the subframe number. Note that, when receiving packet signals from a plurality of base station apparatuses 10, the frame forming unit 46 selects a packet signal having the maximum received power and executes the above-described processing on the selected packet signal. . As described above, the frame forming unit 46 generates a frame synchronized with the frame generated in the other base station apparatus 10.

  When the frame forming unit 46 cannot receive a packet signal from another base station apparatus 10, the frame forming unit 46 may execute the following process. The frame forming unit 46 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 forming unit 46 generates a plurality of frames based on the time information. For example, the frame forming unit 46 generates 10 frames of “100 msec” by dividing the period of “1 sec” into 10 with reference to the timing of “0 msec”.

  The processing unit 26 inputs a demodulation result from another base station device 10 or a terminal device (not shown) via the RF unit 22 and the modem unit 24. Here, the configuration of the MAC frame stored in the packet signal will be described as a demodulation result. The MAC frame input to the processing unit 26 and the MAC frame output from the processing unit 26 have the same configuration. 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”, “RSU control header”, “application data”, and “CRC” are arranged in order from the top. The RSU control header corresponds to the control information described above. The application data stores data to be notified to the terminal device such as accident information.

  FIG. 5B shows the format of the RSU control header. The RSU control header includes “basic information”, “timer value”, “transfer count”, “subframe number”, “frame period”, “used subframe number”, “start timing & time length” in order from the top. Deploy. Note that the configuration of the RSU control header is not limited to that shown in FIG. 5B, and some elements may be excluded, or other elements may be included. The number of times of transfer indicates the number of times that the control information transmitted from the base station apparatus 10, particularly the content of the RSU control header, has been transferred by a terminal device not shown. Here, the base station device 10 corresponds to the base station device 10 for the MAC frame output from the processing unit 26, and the base station device 10 corresponds to the MAC frame input to the processing unit 26. Corresponds to another base station apparatus 10. This is common in the following description.

  For the MAC frame output from the processing unit 26, the generation unit 36 described later sets the transfer count to “0”. In addition, the number of transfers for the MAC frame input to the processing unit 26 is set to “1” or more. The number of subframes indicates the number of subframes forming one frame. The frame period indicates the period of the frame, and is set to, for example, “100 msec” as described above. The used subframe number is a number of a subframe in which the base station device 10 sets a vehicle transmission period. As shown in FIG. 4A, the subframe number is set to “1” at the head of the frame. In the start timing & time length, the start timing of the road and vehicle transmission period at the head of the frame and the time length of the road and vehicle transmission period are indicated. Returning to FIG.

  The first specifying unit 32 extracts a MAC frame whose transfer count is set to “0” from the MAC frames input to the processing unit 26. This corresponds to a packet signal directly transmitted from another base station apparatus 10. The first specifying unit 32 specifies the value of the used subframe number among the extracted MAC frames. This corresponds to specifying a subframe used by another base station apparatus 10. The first identification unit 32 notifies the measurement unit 38 and the third identification unit 42 of information regarding the identified subframe.

  The measurement unit 38 measures the reception power of the packet signal received by the RF unit 22 in units of packet signals. In addition, the measurement unit 38 extracts the received power of the packet signal arranged at the head of the subframe specified by the first specification unit 32. This corresponds to extracting the received power of the packet signal from the other base station apparatus 10. Note that the measurement unit 38 also receives information on the road-to-vehicle transmission period from the first specifying unit 32, and averages the received power of the packet signal included in the road-to-vehicle transmission period, so that packets from other base station devices 10 are received. The received power of the signal may be derived. The measuring unit 38 outputs the extracted received power to the third specifying unit 42.

  The second specifying unit 34 extracts MAC frames whose transfer count is set to “1” or more from the MAC frames input to the processing unit 26. This corresponds to a packet signal transmitted from the other base station apparatus 10 and then transferred by the terminal apparatus. The second specifying unit 34 specifies the value of the used subframe number among the extracted MAC frames. This corresponds to specifying a subframe used by another base station apparatus 10. The terminal device transfers the subframe number when the terminal device receives a packet signal from another base station device 10. The second specifying unit 34 notifies the estimation unit 40 and the third specifying unit 42 of information regarding the specified subframe.

  The estimation unit 40 measures the received power of the packet signal input to the second specifying unit 34. Moreover, the estimation part 40 estimates that the measured received signal is the received power of the packet signal from the other base station apparatus 10 to which control information was transferred by the packet signal. Note that the second specification unit 34 and the estimation unit 40 may exclude the subframe specified by the first specification unit 32 from the processing target. The estimation unit 40 outputs the received power to the third specification unit 42.

  The third specifying unit 42 receives information on subframes from the first specifying unit 32 and the second specifying unit 34, and receives received power from the measuring unit 38 and the estimating unit 40. The third specifying unit 42 collects information on subframes and received power in a table. The third specifying unit 42 stores the table in the storage unit 44. FIG. 6 shows the data structure of the table stored in the storage unit 44. As shown in the figure, a subframe number column 220, a used size column 222, a received power column 224, and a type column 226 are included. In the subframe number column 220, subframe numbers corresponding to FIG. The use size column 222 indicates a road and vehicle transmission period arranged in each subframe.

  The received power column 224 shows the received power measured by the measurement unit 38 or the received power estimated by the estimation unit 40. If the measuring unit 38 measures the received power corresponding to the subframe number, the third specifying unit 42 enters the received power measured by the measuring unit 38 in the received power column 224 corresponding to the subframe number. . On the other hand, if the measurement unit 38 does not measure the received power corresponding to the subframe number and the estimation unit 40 estimates, the third specifying unit 42 enters the received power column 224 corresponding to the subframe number. The received power estimated by the estimation unit 40 is entered. If there is no received power corresponding to the subframe number, the third specifying unit 42 enters “unused” in the received power column 224 corresponding to the subframe number.

  The type column 226 indicates whether the received power entered in the received power column 224 is a value measured by the measurement unit 38 or a value estimated by the estimation unit 40. The former corresponds to a state in which a packet signal is directly received from another base station apparatus 10, and the latter does not receive a packet signal directly from another base station apparatus 10, and the packet signal transferred by the terminal apparatus is not received. Corresponds to the state being received. In the former case, “base” is indicated in the type column 226, and “end” is indicated in the type column 226 in the latter case. Returning to FIG.

  The third specifying unit 42 specifies the subframe in which the road and vehicle transmission period is to be set while referring to the table stored in the storage unit 44. Specifically, the third specifying unit 42 confirms whether there is an “unused” subframe in the received power column 224 of the table. If present, the third specifying unit 42 selects one of the “unused” subframes. Here, when a plurality of subframes are unused, the third specifying unit 42 selects one subframe at random. That is, the third specifying unit 42 specifies any of the unused subframes based on the subframe specified by the first specifying unit 32 and the subframe specified by the second specifying unit 34. . Note that the reception power of the packet signal from the terminal device may be measured, and a subframe with a small reception power may be selected.

  When there is no unused subframe, that is, when each of the plurality of subframes is used, the third specifying unit 42 refers to the received power column 224 of the table. The third specifying unit 42 specifies a subframe to be used based on the received power measured by the measuring unit 38 and the received power estimated by the estimating unit 40. Specifically, the third specifying unit 42 preferentially specifies a subframe with low received power. As described above, the third specifying unit 42 specifies a subframe to be used based on the subframe specified by the first specifying unit 32 and the subframe specified by the second specifying unit 34. The third specifying unit 42 outputs the specified subframe number to the generating unit 36.

  The generation unit 36 receives the specified subframe number from the third specification unit 42. In addition, the generation unit 36 sets a road and vehicle transmission period at the beginning of the subframe having the received subframe number. The generation unit 36 generates a MAC frame to be stored in the packet signal. In that case, according to the setting of the road and vehicle transmission period, the production | generation part 36 determines the value of the RSU control header of a MAC frame. The generation unit 36 acquires predetermined information via the network communication unit 80 and includes the predetermined information in the application data. Here, the network communication unit 80 is connected to a network 202 (not shown). The generation unit 36 causes the modem unit 24 and the RF unit 22 to transmit a packet signal during the road and vehicle transmission 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. 7 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 extraction unit 66 and a CSMA execution unit 74, and the selection unit 90 includes a transfer number acquisition unit 110, an extraction number measurement unit 112, a management unit 114, a storage unit 116, and a comparison unit 118. Including. 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 the packet signal from the RF unit 52 or the demodulation result from the modem unit 54. Further, when the demodulation result is a packet signal from the base station apparatus 10 (not shown), the control information extraction unit 66 specifies the timing of the subframe in which the road and vehicle transmission period is arranged. . Further, the control information extraction unit 66 generates a frame based on the timing of the subframe and the content of the RSU control header. The generation of the frame may be performed in the same manner as the above-described frame forming unit 46, and thus description thereof is omitted here. As a result, the control information extraction unit 66 generates a frame synchronized with the frame formed in the base station apparatus 10. Moreover, the control information extraction part 66 specifies a road and vehicle transmission period based on the content of the RSU control header. Furthermore, the control information extraction unit 66 selects one of the plurality of subframes, and identifies a period other than the road and vehicle transmission period among the selected subframes as the vehicle and vehicle transmission period. The control information extraction unit 66 outputs information on frame and subframe timing and vehicle transmission period to the CSMA execution unit 74.

  The CSMA execution unit 74 inputs information regarding the timing of frames and subframes and the vehicle transmission period from the control information extraction unit 66. The CSMA execution unit 74 executes CSMA during the vehicle transmission period. Specifically, the CSMA execution unit 74 measures the interference power by executing 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. 5A to 5B is used, and the generation unit 64 stores the measured location in the application data. The generation unit 64 broadcasts a packet signal including data via the modem unit 54, the RF unit 52, and the antenna 50 at the transmission timing determined by the CSMA execution unit 74. The notification unit 70 acquires a packet signal from the base station device 10 (not shown) in the road and vehicle transmission period, and acquires a packet signal from another terminal device 14 (not shown) in the vehicle and vehicle transmission period. The notification unit 70 notifies the driver of the approach of another vehicle 12 (not shown) to the driver via a monitor or a speaker in accordance with the content of data stored in the packet signal.

  Hereinafter, the transfer of the RSU control header by the terminal device 14 will be described. The control information extraction unit 66 extracts an RSU control header from a packet signal for which the base station apparatus 10 is an information source. As described above, when the packet signal is directly transmitted from the base station apparatus 10, the number of transfers is set to “0”, but when the packet signal is transmitted from another terminal apparatus 14. The number of transfers is set to a value of “1 or more”. Here, since the used subframe number is not changed when transferred by the terminal apparatus 14, the subframe used in the base station apparatus 10 serving as the information source is specified by referring to the used subframe number. The

  The transfer count acquisition unit 110 acquires information on the transfer count 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 then executes the same processing for the transfer counts corresponding to other subframe numbers. To do. 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.

  The extraction number measurement unit 112 measures the number of extractions of the RSU control header, that is, control information, for each base station apparatus 10 that is an information source. In addition, the extraction count measurement unit 112 selects, for each base station apparatus 10 serving as an information source, the control information extraction count including the transfer count value acquired by the transfer count acquisition unit 110. More specifically, the extraction count measuring unit 112 measures the number of control information extractions for each transfer count for one subframe number. As a result, for example, for the subframe number “1”, the number of times control information is extracted is “0”, and the number of times control information is extracted is “4”. ", And the number of times control information is extracted is" 6 "times. If the transfer count acquired by the transfer count acquisition unit 110 is “1”, the extraction count measurement unit 112 selects the extraction count “4” of the control information including this transfer count. The extraction number measurement unit 112 outputs the selected number of extractions to the management unit 114 for each base station apparatus 10 serving as an information source.

  The management unit 114 receives the number of transfers from the transfer number acquisition unit 110 and the number of extractions from the extraction number measurement unit 112. The management unit 114 stores the subframe number, the transfer count, and the extraction count in the storage unit 116 in association with each other. In addition, the management unit 114 updates the storage content in the storage unit 116 when the number of transfers or the number of extractions is updated. The storage unit 116 stores the subframe number, the number of transfers, and the number of extractions in association with each other according to an instruction from the management unit 114. 8A to 8C show the data structure of the table stored in the storage unit 116. FIG. These correspond to the data structure of the table stored in the storage unit 116 in another terminal device 14, for example, the storage unit in the terminal device 14 mounted in each of the first vehicle 12a to the third vehicle 12c. 116.

  Each table includes a subframe number column 210, a transfer count column 212, and an extraction count column 214. In the subframe number column 210, the value shown in the used subframe number in FIG. The number of transfers acquired by the transfer number acquisition unit 110 is input to the transfer number column 212, and the number of extractions acquired by the extraction number measurement unit 112 is input to the extraction number column 214. In FIG. 8A, the control information using the base station apparatus 10 corresponding to the subframe number “1” as the information source is extracted “4” times with the transfer count “1” as the minimum transfer count. On the other hand, in FIG. 8A, the control information using the base station apparatus 10 corresponding to the subframe number “2” as the information source is extracted “15” times with the transfer count “0” as the minimum transfer count. . Returning to FIG.

  The comparison unit 118 acquires the number of transfers and the number of extractions for each base station device 10 by accessing the storage unit 116. The comparison unit 118 selects control information corresponding to at least one base station apparatus 10 as control information to be transferred based on the number of transfers and the number of extractions. Specifically, the comparison unit 118 compares the number of extractions after comparing the number of transfers to the plurality of base station apparatuses 10. That is, after selecting the control information with the smaller number of transfers, for example, the control information with the minimum number of transfers, the control information with the larger number of extractions and the maximum number of extractions are selected from the selected control information. Selected control information is selected. In the case of FIG. 8B, since the minimum transfer count is “0” corresponding to the subframe numbers “2” and “3”, the comparison unit 118 sets the subframe number “2” as the first step. The control information “3” is selected. Subsequently, the number of extractions of the subframe number “2” is “9”, the number of extractions of the subframe number “3” is “20”, and the latter extraction number is larger. Selects the control information of the subframe number “3” as the second stage.

  In this way, the control information having the minimum number of transfers and the control information having the maximum number of extractions corresponding to the number of transfers is selected by the comparison unit 118. It can be said that control information is received near the base station apparatus 10 which becomes an information source, so that the frequency | count of transfer is small. In addition, it can be said that the control information is received in a situation where the variation in the wireless environment is smaller as the number of extractions is larger. Therefore, it can be said that the terminal device 14 has selected the control information from the base station apparatus 10 installed as close as possible by selecting the control information that satisfies the above-described situation.

  In FIG. 2, the terminal device mounted on the first vehicle 12a transfers control information from the second base station device 10b to the vehicle (not shown) traveling behind the first vehicle 12a. This corresponds to causing the terminal device mounted to receive control information. In addition, the terminal device mounted on the second vehicle 12b corresponds to causing the terminal device mounted on the first vehicle 12a to receive the control information by transferring the control information from the third base station device 10c. . Further, the terminal device mounted on the third vehicle 12c transfers the control information from the first base station device 10a, so that the terminal device mounted on a vehicle (not shown) traveling behind the third vehicle 12c. Corresponds to receiving control information.

  The instruction unit 92 instructs the generation unit 36 to generate the RSU control header based on the control information selected by the comparison unit 118. The instruction unit 92 increases the number of transfers in the information regarding the number of transfers when storing the control information in the RSU control header. In response to such an instruction, the generation unit 64 generates an RSU control header based on the control information selected by the comparison unit 118 and increases the number of transfers at that time. The instruction unit 92 notifies the management unit 114 that the number of transfers has been increased, and the management unit 114 controls the storage unit 116 so as to increase the number of transfers of the corresponding 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. 9 is a flowchart showing a transmission procedure in the base station apparatus 10. The RF unit 22, the modem unit 24, and the processing unit 26 search for a signal (S10), and the second specifying unit 34 and the third specifying unit 42 statistically process base station apparatus information from the terminal device 14 (S12). . Here, the base station apparatus information corresponds to the contents included in the RSU control header described above. If packet signals from other base station devices 10 are received (Y in S14) and packet signals from a plurality of base station devices 10 are received (Y in S16), the third specifying unit 42 The other base station apparatus 10 with large received power is selected (S18). If packet signals from a plurality of base station apparatuses 10 are not received (N in S16), step 18 is skipped.

  The 3rd specific | specification part 42 hold | maintains the frame-synchronization timing of the other selected base station apparatus 10 (S20), and searches the sub-frame which the other base station apparatus 10 is not using (S22). If no packet signal has been received from another base station apparatus 10 (N in S14), steps 16 to 22 are skipped. The 2nd specific | specification part 34 performs the determination process of the base station apparatus information from a terminal device (S24). If there is no selected base station apparatus 10 (N in S26), the third specifying unit 42 selects another base station apparatus 10 and holds the frame synchronization timing (S28). If there is a selected base station apparatus 10 (Y in S26), step 28 is skipped. If the other base station apparatus 10 has an unused subframe (Y in S30) and the terminal apparatus 14 also has an unused subframe (Y in S32), the third specifying unit 42 The device 10 and the terminal device 14 randomly select a subframe from the unused subframes (S34).

  If there is no unused subframe in the terminal device 14 (N in S32), the third specifying unit 42 determines whether the other base station device 10 is unused and the terminal device 14 is in use. A subframe with a small reception power of the terminal device 14 is selected (S36). If no other base station apparatus 10 has an unused subframe (N in S30), the third specifying unit 42 receives the received power of the packet signal among the subframes determined by the other base station apparatus 10 to be in use. The subframe with the smallest is selected (S38). The generation unit 36, the modem unit 24, and the RF unit 22 transmit a packet signal in the selected subframe (S40).

  FIG. 10 is a flowchart showing a statistical processing procedure in the base station apparatus 10. This corresponds to step 12 in FIG. The third specifying unit 42 initializes a table generated based on the information received in the previous frame (S50). The third specifying unit 42 describes the received power of the other base station apparatus 10 for each subframe number and uses size for each received frame signal according to the subframe number set in the RSU control header of the terminal apparatus 14. Is also updated (S52).

  FIG. 11 is a flowchart illustrating a determination processing procedure in the base station apparatus 10. This corresponds to step 24 in FIG. The second specifying unit 34 sets X to 1 (S60). When X is N or less (Y in S62), the information of subframe X is not directly received from another base station apparatus 10 (N in S64), and the received power is equal to or greater than the threshold value (S66). Y), the second specifying unit 34 newly determines that the subframe X is being used (S68). If the information of subframe X is received directly from another base station apparatus 10 (Y in S64) or the received power is not equal to or greater than the threshold value (N in S66), step 68 is skipped. The second specifying unit 34 adds 1 to X (S70). Thereafter, the process returns to step 62. If X is not less than or equal to N (N in S62), the process is terminated.

  Next, a modified example of the present invention will be described. The modified example of the present invention is a communication that performs inter-vehicle communication between terminal devices mounted on a vehicle and also performs road-to-vehicle communication from a base station device installed at an intersection or the like to a terminal device, as in the embodiment. About the system. In addition, as in the embodiment, a frame is also configured, and a road and vehicle transmission period is set at the beginning of the subframe. The base station apparatus which concerns on an Example has selected the sub-frame for setting a road and vehicle transmission period based on the received power from another base station apparatus. On the other hand, the base station apparatus which concerns on a modification selects the sub-frame for setting a road and vehicle transmission period based on the distance with another base station apparatus. A communication system 100 according to the modification is of the same type as that shown in FIGS.

  FIG. 12 shows the configuration of the base station apparatus 10 according to a modification of the present invention. The base station apparatus 10 includes an antenna 20, an RF unit 22, a modem unit 24, a processing unit 26, a control unit 30, and a network communication unit 80. The processing unit 26 includes a first specifying unit 32, a second specifying unit 34, an acquiring unit 48, a generating unit 36, a third specifying unit 42, a storage unit 44, and a frame forming unit 46. Here, it demonstrates centering on difference with the base station apparatus 10 shown in FIG.

  The acquisition unit 48 includes a GPS receiver, a gyroscope, a vehicle speed sensor, and the like (not shown), and acquires position information related to the position where the base station apparatus 10 is installed based on data supplied from these. The position information is indicated by latitude and longitude. Since a known technique may be used for these acquisitions, description thereof is omitted here. The acquisition unit 48 outputs the acquired position information to the acquisition unit 48.

  The processing unit 26 inputs a demodulation result from another base station device 10 or a terminal device (not shown) via the RF unit 22 and the modem unit 24. Here, the configuration of the MAC frame stored in the packet signal will be described as a demodulation result. The MAC frame input to the processing unit 26 and the MAC frame output from the processing unit 26 have the same configuration. FIGS. 13A to 13B show the format of the MAC frame stored in the packet signal defined in the modification of the present invention. FIG. 13A shows the configuration of the MAC frame, which is the same as that shown in FIG. FIG. 13B shows the configuration of the RSU control header. In the RSU control header shown in FIG. 13B, position information is added as compared with the RSU control header shown in FIG. The position information is information regarding the position where the base station apparatus 10 is installed. Returning to FIG.

  The frame forming unit 46 generates a frame in the same manner as in the embodiment, and the first specifying unit 32 and the second specifying unit 34 specify a subframe in the same manner as in the embodiment, and thus description thereof is omitted here. The third specifying unit 42 extracts position information from the packet signals received from other base station devices 10 and terminal devices 14. The position information is position information regarding another base station apparatus 10. The third specifying unit 42 derives the distance from the base station apparatus 10 to another base station apparatus 10 based on the extracted position information and the position information acquired by the acquisition unit 48. For example, vector calculation is used for the derivation of the distance.

  The 3rd specific | specification part 42 puts together the information and distance regarding a sub-frame on a table. The third specifying unit 42 stores the table in the storage unit 44. FIG. 14 shows the data structure of the table stored in the storage unit 44. As shown in the figure, a subframe number column 220, a use size column 222, a distance column 228, and a position column 230 are included. The subframe number column 220 and the used size column 222 are the same as those in FIG. The distance column 228 shows the distance derived by the third specifying unit 42. In the position column 230, position information about the other base station apparatus 10 extracted by the third specifying unit 42 is shown. Returning to FIG.

  The third specifying unit 42 specifies the subframe in which the road and vehicle transmission period is to be set while referring to the table stored in the storage unit 44. Specifically, the third specifying unit 42 confirms whether there is an “unused” subframe. If present, the third specifying unit 42 selects one of the “unused” subframes. Here, when a plurality of subframes are unused, the third specifying unit 42 selects one subframe at random. That is, the third specifying unit 42 specifies any of the unused subframes based on the subframe specified by the first specifying unit 32 and the subframe specified by the second specifying unit 34. . Note that the reception power of the packet signal from the terminal device may be measured, and a subframe with a small reception power may be selected.

  When there is no unused subframe, that is, when each of the plurality of subframes is used, the third specifying unit 42 refers to the distance column 228 of the table. The third specifying unit 42 specifies a subframe to be used based on the distance. Specifically, the third specifying unit 42 selects another base station device 10 having a long distance, and preferentially specifies the subframe used by the selected base station device 10. As described above, the third specifying unit 42 specifies the subframe to be used based on the distance between the subframe specified by the first specifying unit 32, the subframe specified by the second specifying unit 34, and the distance. The third specifying unit 42 outputs the specified subframe number to the generating unit 36.

  FIG. 15 is a flowchart showing a transmission procedure in the base station apparatus 10. The RF unit 22, the modem unit 24, and the processing unit 26 search for signals (S80), and the second specifying unit 34 and the third specifying unit 42 statistically process the base station apparatus information from the terminal device 14 (S82). . Here, the base station apparatus information corresponds to the contents included in the RSU control header described above. If the packet signal from the other base station apparatus 10 is received (Y of S84) and the packet signal from the plurality of base station apparatuses 10 is received (Y of S86), the third specifying unit 42 Another base station apparatus 10 with a short distance is selected (S88). If packet signals from a plurality of base station apparatuses 10 have not been received (N in S86), step 88 is skipped.

  The third specifying unit 42 holds the frame synchronization timing of the selected other base station device 10 (S90), and searches for subframes that are not used by the other base station device 10 (S92). If no packet signal is received from another base station apparatus 10 (N in S84), Step 86 to Step 92 are skipped. The 2nd specific | specification part 34 performs the determination process of the base station apparatus information from a terminal device (S94). If there is no selected base station apparatus 10 or no distance update is required (N in S96), the third specifying unit 42 selects another base station apparatus 10 and holds the frame synchronization timing (S98). If there is a selected base station apparatus 10 and distance update is not required (Y in S96), step 98 is skipped. If another base station apparatus 10 has an unused subframe (Y in S100) and the terminal apparatus 14 also has an unused subframe (Y in S102), the third specifying unit 42 The device 10 and the terminal device 14 randomly select a subframe from the unused subframes (S104).

  If there is no unused subframe in the terminal device 14 (N in S102), the third specifying unit 42 determines whether the other base station device 10 is unused and the terminal device 14 is in use. A subframe with a small reception power of the terminal device 14 is selected (S106). If the other base station apparatus 10 has no unused subframe (N in S100), the third specifying unit 42 determines the base having the maximum distance among the subframes determined by the other base station apparatus 10 to be in use. The subframe used by the station apparatus 10 is selected (S108). The generation unit 36, the modem unit 24, and the RF unit 22 transmit a packet signal in the selected subframe (S110).

  FIG. 16 is a flowchart showing a statistical processing procedure in the base station apparatus 10. This corresponds to step 82 in FIG. The third specifying unit 42 initializes a table generated based on the information received in the previous frame (S120). The 3rd specific | specification part 42 describes a shortest distance based on position information for every sub-frame number according to the sub-frame number set to the RSU control header of the terminal device 14 regarding all the received packet signals. At the same time, the use size is updated (S122).

  FIG. 17 is a flowchart illustrating a determination processing procedure in the base station apparatus 10. This corresponds to step 94 in FIG. The second specifying unit 34 sets X to 1 (S130). If X is less than or equal to N (Y in S132), the information of subframe X is not received directly from another base station apparatus 10 (N in S134), and if the distance is less than or equal to the threshold value (in S136) Y), the second specifying unit 34 newly determines that the subframe X is being used (S138). If the information of subframe X is directly received from another base station apparatus 10 (Y in S134), or the distance is not less than the threshold value (N in S136), step 138 is skipped. The second specifying unit 34 adds 1 to X (S140). Thereafter, the process returns to step 132. If X is not less than or equal to N (N in S132), the process is terminated.

  FIGS. 18A and 18B show the format of a MAC frame stored in a packet signal defined in another modification of the present invention. 18 (a)-(b) can be said to be another pattern of the format of the MAC frame shown in FIGS. 13 (a)-(b). In FIG. 18A, a MAC header, an RSU control header, an upper header, application data, and a CRC are arranged. Here, the MAC header, the RSU control header, and the application data are the same as those in FIGS. On the other hand, the upper header includes position information and an identification number of the base station apparatus 10 corresponding to the position information. Only position information may be included, or information other than these may be included. In FIG. 18B, a MAC header, an upper header, an application header, and a CRC are arranged. Here, the upper header corresponds to the RSU control header shown in FIGS. Note that the upper header may not include a part of the information in FIG.

  According to the embodiment of the present invention, a plurality of subframes are provided in a frame, and a road-to-vehicle transmission period is provided at the head portion of the subframe, so that interference between road-to-vehicle communication and vehicle-to-vehicle communication can be reduced. Also, since the subframe used by the other base station apparatus is specified based on the packet signal received from the terminal apparatus as well as the packet signal directly received from the other base station apparatus, The frame identification accuracy can be improved. In addition, since the accuracy of identifying subframes in use is improved, the probability of collision between packet signals transmitted from the base station apparatus can be reduced. Moreover, since the collision probability between packet signals transmitted from the base station apparatus is reduced, the terminal apparatus can accurately recognize the control information. Further, since the control information is accurately recognized, the road and vehicle transmission period can be accurately recognized. Further, since the road and vehicle transmission period is accurately recognized, the collision probability of the packet signal can be reduced.

  In addition, since a subframe other than the currently used subframe is used preferentially, it is possible to reduce the possibility of transmitting a packet signal at a timing overlapping with packet signals from other base station apparatuses. Further, when any subframe is used by another base station apparatus, a subframe with low received power is selected, so that the influence of packet signal interference can be suppressed. Further, since the received power of the terminal device is used as the received power from another base station device that is the transmission source of the control information relayed by the terminal device, the received power estimation process can be simplified.

  In addition, since the subframe is selected based on the distance between the base station apparatus and another base station apparatus, it is possible to select a subframe in consideration of the arrangement of the base station apparatus and the other base station apparatus. Further, since the subframe used by another base station apparatus having a long distance is selected, the influence of interference can be suppressed. Moreover, since the influence of interference is suppressed, it is possible to suppress the deterioration of the packet signal reception probability.

  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 third specifying unit 42 uses received power when selecting a subframe. However, the present invention is not limited to this. For example, the third specifying unit 42 may use signal quality instead of received power. As the signal quality, an error rate is measured. Further, as the signal quality, instead of the error rate, EVM (Error Vector Magnet) or the like may be measured. According to this modification, the degree of freedom in design can be improved.

  In the modification of the present invention, the third specifying unit 42 uses the distance when selecting a subframe. However, the present invention is not limited to this. For example, the third specifying unit 42 may use the received power in addition to the distance. At that time, the processing unit 26 includes a measurement unit 38 and an estimation unit 40 as in FIG. The measurement unit 38 measures the received power of the packet signal from the other base station device 10, and the estimation unit 40 uses the packet signal from the estimation unit 40 to determine the packet signal from the other base station device 10. Estimate the received power. The 3rd specific | specification part 42 compares the distance with other base station apparatuses 10, and a threshold value, and selects the other base station apparatus 10 with a distance longer than a threshold value. Moreover, the 3rd specific | specification part 42 pinpoints a sub-frame with low receiving power, when selecting two or more other base station apparatuses with distance longer than a threshold value. According to the present modification, the subframe is specified based on the distance and the received power, so that the specifying accuracy can be improved.

  10 base station apparatus, 20 antenna, 22 RF unit, 24 modulation / demodulation unit, 26 processing unit, 30 control unit, 32 first specifying unit, 34 second specifying unit, 36 generating unit, 38 measuring unit, 40 estimating unit, 42 th 3 specifying unit, 44 storage unit, 46 frame forming unit, 80 network communication unit, 100 communication system.

Claims (2)

A terminal device that communicates in a frame formed of a plurality of subframes,
It is defined that the base station apparatus can transmit the first type signal in the head period of each subframe, and that the terminal apparatus can transmit the second type signal in the untransmitted period of the first type signal in the frame. A receiving unit that receives the first type signal from the base station device and the second type signal from another terminal device;
The second type signal including information on the subframe when the first type signal is received from the base station apparatus in a period other than the reception of the first type signal and the second type signal in the receiving unit. And a transmission unit for transmitting
The base station apparatus that is the transmission source of the first type signal received by the receiving unit (1) specifies a subframe used by another base station apparatus based on the received first type signal, (2) Based on the received second type signal, identify subframes used in other base station apparatuses, and (3) Unused subframes based on the subframes identified in these. (4) The first type signal is transmitted in the head period of any one of the specified subframes, and the receiving unit receives the first type from the base station apparatus. A terminal device that receives a signal. The second type signal transmitted from the transmission unit and the first type signal received by the reception unit include a header in a common format,
The terminal apparatus according to claim 1, wherein information on subframes is included in a header of the second type signal transmitted from the transmission unit.

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