JP5300459B2 - Access control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a packet signal collision probability even in the case where communication volume is increased. <P>SOLUTION: A processing section 156 generates timing information regarding timing to be synchronized when each terminal device reports a signal, during communication between terminal devices. A modulation/demodulation section 154, an RF section 152 and an antenna 150 report the generated timing information. Furthermore, the processing section 156 also generates cycle information regarding a report cycle in the case where each terminal device reports a signal, during communication between terminal devices. The modulation/demodulation section 154, the RF section 152 and the antenna 150 also report the generated cycle information together with the timing information. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a notification technique, and more particularly, to a notification method and an access control apparatus that notify 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. In order to increase the communication speed, an OFDM modulation scheme is used in the wireless LAN.

  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. However, at intersections and the like, an increase in the number of vehicles, that is, an increase in the number of terminal devices, is expected to increase packet signal collisions. 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 purpose of preventing a collision accident at the intersection encounter will not be achieved.

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

  In order to solve the above-described problem, an access control device according to an aspect of the present invention includes a generation unit that generates timing information related to a timing to be synchronized when each wireless device notifies a signal in communication between wireless devices; A notification unit that notifies the timing information generated in the generation unit. In the communication between the wireless devices, the generation unit also generates periodic information regarding a notification cycle when each wireless device notifies the signal, and the notification unit also notifies the periodic information generated in the generation unit together with the timing information.

  Another aspect of the present invention is a notification method. This method includes the steps of generating timing information related to the timing to be synchronized when each wireless device notifies a signal in communication between the wireless devices, and notifying the generated timing information. The generating step also generates period information related to a notification period when each wireless apparatus notifies a signal in communication between wireless apparatuses, and the notifying step notifies the generated period information together with timing information.

  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, it is possible to reduce the collision probability of packet signals even when the amount of communication increases.

  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. Here, the terminal apparatus employs the OFDM modulation scheme for the purpose of increasing the communication speed. Under such circumstances, when the number of terminal devices increases at an intersection or the like, the generation probability of a packet signal increases. 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 an access control device in addition to a plurality of terminal devices, and the access control device is installed at an intersection, for example. The access control apparatus repeatedly defines a frame including a plurality of slots. Note that some of the plurality of slots included in each frame are reserved as control slots. In addition, the access control device specifies a control slot to be used, and includes information on the timing of the control slot and information for identifying the access control device (hereinafter referred to as “identification information”) in the control information. Further, the access control apparatus broadcasts a packet signal storing control information (hereinafter also referred to as “control information”) in the control slot. Here, the information on the timing of the control slot is, for example, information on how many times the control slot is arranged from the head of the frame (hereinafter referred to as “control slot information”).

  The terminal device generates a frame corresponding to the control information by receiving the control information. The generated frame also includes a plurality of slots. Further, the terminal device recognizes a slot other than the control slot among the plurality of slots included in the frame. In the following description of the terminal device, a slot may indicate a slot excluding a control slot. The terminal apparatus estimates a slot (hereinafter referred to as “empty slot”) that is not used by another terminal apparatus by performing carrier sense for each of the plurality of slots. Here, there may be a plurality of empty slots. The terminal device randomly selects one slot to be used for transmitting data from the empty slots. In the selected slot, the terminal device broadcasts a packet signal storing data (hereinafter also referred to as “data”).

  Further, the terminal device uses relatively the same slot over a plurality of frames. Under such circumstances, if the number of terminal devices that transmit data increases, that is, if the traffic volume increases, the probability of occurrence of data collision increases. In order to cope with this, the access control apparatus measures the traffic volume and determines the data notification period according to the measured traffic volume. For example, the notification cycle is indicated as “1 frame”, “2 frames”, “3 frames”. Further, the access control apparatus broadcasts information related to the determined notification period (hereinafter referred to as “period information”) in the control information. The terminal device sets a notification cycle based on the cycle information.

  Here, the access control apparatus does not directly participate in data communication between terminal apparatuses, and does not directly specify a slot to be used for data communication. The access control device merely notifies the configuration of a frame including a slot to be used by a plurality of terminal devices. The terminal device performs data communication at the timing of the slot included in the notified frame. That is, the access control device controls communication between a plurality of terminal devices.

  Since the control information is also transmitted in one slot, there is a possibility that the data transmitted from the terminal device that cannot receive the control information collides with the control information. As a result, if other terminal devices cannot receive control information, it becomes difficult to execute the above processing. In order to cope with this, in an OFDM signal used to transmit data, data is not stored in some subcarriers and is set as a null carrier (hereinafter, such a subcarrier is referred to as an “identification carrier”. "). On the other hand, in the OFDM signal used for transmitting control information, a signal is also arranged on the identification carrier. Therefore, even if data and control information collide, the terminal device can detect the presence of control information by observing the signal component of the identification carrier.

  Furthermore, when an access control device is installed at each of adjacent intersections, it is necessary to consider interference between the access control devices. If the control information broadcast from each access control device interferes, the terminal device may not be able to receive the control information, and the above-described operation cannot be realized. Such interference can be avoided by assigning different frequency channels to each access control device, but if no other frequency channel is provided, another configuration is required to reduce the interference. In order to cope with this, a plurality of control slots are secured as described above. Each access control apparatus selects one control slot by performing carrier sense for each of a plurality of control slots, and broadcasts control information in the selected control slot.

  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 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, which are collectively referred to as the access control device 10 and the vehicle 12. The 8th vehicle 12h is included. Each vehicle 12 is equipped with a terminal device (not shown). Further, an area 200 is formed by the access control device 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. 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 access control device 10 at the intersection. The access control device 10 generates a frame including a plurality of slots so as to be repeated based on a signal received from a GPS satellite (not shown). Here, a part of the plurality of slots corresponds to a control slot. The access control device 10 includes control slot information and identification information in the control information. Furthermore, the access control apparatus 10 broadcasts control information in the control slot. The selection of the control slot will be described later.

  The plurality of terminal apparatuses receive the control information notified by the access control 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 access control device 10. In addition, slots generated in each of the plurality of terminal devices are synchronized with each other. The terminal device performs carrier sense in each of the plurality of slots and estimates an empty slot. Also, the terminal device randomly selects one slot from the empty slots. Further, the terminal device broadcasts data in the selected slot. The terminal device continues to select slots having the same relative timing within the frame over a plurality of frames.

  The access control device 10 measures the traffic volume in communication between terminal devices. Further, the access control apparatus 10 determines a period when the terminal apparatus broadcasts data (hereinafter referred to as “notification period”) based on the traffic volume. Furthermore, the access control apparatus 10 notifies the information related to the notification period, that is, the above-described period information included in the control information. The terminal device sets the notification cycle according to the cycle information included in the control information. The terminal device broadcasts data using the selected slot in the frame corresponding to the broadcast cycle. In addition, even if it is a case where control information is not received, a terminal device may alert | report data. The terminal device that has received data from another terminal device recognizes the presence of the vehicle 12 on which the other terminal device is mounted based on the data.

  Here, both the control information broadcast from the access control apparatus 10 and the data broadcast from the terminal apparatus use OFDM signals. However, the subcarriers in which both are arranged are not the same. Data is not placed on the aforementioned identification carrier. On the other hand, the identification information is arranged on the identification carrier in addition to the subcarrier on which the data is arranged. As a result, even if data and identification information collide, the terminal device can detect the presence of control information by observing the signal component of the identification carrier. In addition, the approach detection to the area 200 by a terminal device may be made with respect to the identification carrier.

  FIG. 2 shows the configuration of the access control apparatus 10. The access control apparatus 10 includes an antenna 150, an RF unit 152, a modem unit 154, a processing unit 156, a GPS positioning unit 158, a frame generation unit 160, a control unit 162, and a period deriving unit 164. The period deriving unit 164 includes an estimating unit 166 and a determining unit 168. The GPS positioning unit 158 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 time information, description is abbreviate | omitted here. The GPS positioning unit 158 outputs time information to the frame generation unit 160.

  The frame generation unit 160 acquires time information from the GPS positioning unit 158. The frame generation unit 160 generates a plurality of frames based on the time information. For example, the frame generation unit 160 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. The frame generation unit 160 generates a plurality of slots by dividing each frame into a plurality of frames. For example, by dividing each frame into 200, 200 “500 μsec” slots are generated.

  Here, some of the plurality of slots included in the frame are reserved as “control slots”. For example, among the 200 slots included in one frame, the first five slots are set as control slots. The control slot is a slot used for the access control apparatus 10 to broadcast control information. Further, the remainder of the plurality of slots included in the frame is secured for communication between terminal devices (not shown). As described above, since the communication system 100 adopts the 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.

  FIGS. 3A to 3D show the format of a frame generated by the frame generation unit 160. FIG. FIG. 3A shows the structure of the frame. 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. 3B shows the configuration of one frame. As shown in the figure, one frame is composed of M slots. For example, M is “200”, and the period of each slot is “500 μsec”. A slot arranged at the head portion of the frame corresponds to a control slot, and a section where the control slot is arranged is shown as a control area 220.

  Here, five slots from the first slot to the fifth slot are included in the control area 220 as control slots. FIG. 3C 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. FIG. 3D 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.

  As reception processing, the RF unit 152 receives, in each slot, a packet signal transmitted in communication between other terminal devices (not shown) by the antenna 150. Here, the transmission source of the packet signal is, for example, a terminal device. The RF unit 152 performs frequency conversion on a radio frequency packet signal received via the antenna 150 to generate a baseband packet signal. Further, the RF unit 152 outputs a baseband packet signal to the modem unit 154. 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 152 also includes an LNA (Low Noise Amplifier), a mixer, an AGC, and an A / D conversion unit. As a transmission process, the RF unit 152 performs frequency conversion on the baseband packet signal input from the modem unit 154 in each slot to generate a radio frequency packet signal. Further, the RF unit 152 transmits a radio frequency packet signal from the antenna 150. The RF unit 152 also includes a PA (Power Amplifier), a mixer, and a D / A conversion unit.

  The modem unit 154 performs demodulation on the baseband packet signal from the RF unit 152 as reception processing. Further, the modem unit 154 outputs the demodulated result to the processing unit 156. In addition, the modem unit 154 performs modulation on the data from the processing unit 156 as a transmission process. Further, the modem unit 154 outputs the modulated result to the RF unit 152 as a baseband packet signal. Here, since the communication system 100 corresponds to the OFDM modulation scheme, the modem unit 154 also executes FFT (Fast Fourier Transform) as a reception process, and also executes IFFT (Inverse Fast Fourier Transform) as a transmission process.

  The processing unit 156 receives information about the timing of the frame and the timing of the slot included in the frame from the frame generation unit 160. The processing unit 156 identifies the timing of the control slot among the plurality of slots included in the frame. In the case of FIG. 3A, five control slots included in the control area 220 are specified. The processing unit 156 performs carrier sense for each control slot via the antenna 150, the RF unit 152, and the modem unit 154. Since a known technique may be used as carrier sense, description thereof is omitted here. Note that the processing unit 156 may receive the received signal from the RF unit 152 without going through the modem unit 154. The processing unit 156 selects one of the five control slots based on the carrier sense result. For example, the control slot with the smallest interference power is selected.

  The processing unit 156 generates control slot information regarding the selected control slot. Further, the processing unit 156 generates control information while including control slot information and identification information. The processing unit 156 assigns control information to the selected control slot. The processing unit 156 outputs control information to the modem unit 154 in the assigned control slot. Note that broadcasting the control information in the control slot determined in the communication system 100 corresponds to notifying the timing of the control slot in the frame. Further, since the relative position of the control slot in the frame is included in the control slot information, the above also corresponds to notifying the timing of the frame. The frame timing here corresponds to a timing to be synchronized when each terminal device broadcasts data in communication between terminal devices.

  As described above, since the communication system 100 supports the OFDM modulation scheme, the processing unit 156 generates control information as an OFDM signal. An OFDM signal is also used for data communication between a plurality of terminal devices (not shown). Here, an OFDM signal for arranging control information (hereinafter also referred to as “control information”) and an OFDM signal for arranging data (hereinafter also referred to as “data”) are compared. explain. FIGS. 4A and 4B show OFDM symbol formats used in the communication system 100. FIG. 4A corresponds to control information, and FIG. 4B corresponds to data.

  Here, in both, a vertical direction shows a frequency and a horizontal direction shows time. In the vertical direction, numbers “31”, “30”,... “−32” are shown in order from the top, but these numbers are given to identify subcarriers (hereinafter referred to as “subcarriers”). Carrier number). Further, in the OFDM signal, the frequency of the subcarrier of subcarrier number “31” is the highest, and the frequency of the subcarrier of subcarrier number “−32” is the lowest. In the figure, “D” corresponds to a data symbol, “P” corresponds to a pilot symbol, and “N” corresponds to null.

  In common with control information and data, subcarriers with subcarrier numbers “31” to “27”, “2”, “0”, “−2”, “−26” to “−32” are null. is there. In the control information, subcarriers with subcarrier numbers “26” to “3” and “−3” to “−25” are also used in data, and the symbols are used for the same purpose in both cases. . On the other hand, the subcarrier numbers “1” and “−1” in the control information are not used in the data. These correspond to the aforementioned identification carrier. That is, the identification carrier is arranged on a subcarrier near the center frequency in the OFDM signal. Furthermore, a guard band is provided in the control information between the subcarrier used in the data and the identification carrier, that is, in the subcarrier numbers “2” and “−2”. The subcarriers with subcarrier numbers “−2” to “2” may be collectively referred to as “identification carriers”.

  Here, the processing unit 156 arranges information on the frame and the slot number on the identification carrier. Further, the processing unit 156 may preferentially arrange information with high importance on the identification carrier. A known signal is arranged in the OFDM symbol in front of the packet signal. Such a known signal is used for AGC in the terminal device and estimation of transmission path characteristics. The processing unit 156 may arrange the known signal on the identification carrier over a period of a part of the predetermined slot. Such a known signal is used like UW (Unique Word), for example. Returning to FIG.

  The modem unit 154 and the RF unit 152 broadcast the control information generated by the processing unit 156 from the antenna 150 in the control slot. One of the destinations of the control information is a terminal device. The terminal device that has received the control information recognizes the timing of each slot, and uses at least one of the slots reserved for communication between the terminal devices. Further, when reporting data over a plurality of frames, the terminal device uses slots having the same relative timing within the frame.

  The estimation unit 166 inputs a signal notified from each terminal device via the antenna 150 and the RF unit 152. The estimation unit 166 measures received power for each slot. In addition, the estimation unit 166 holds a threshold value in advance, compares the received power for each slot with the threshold value, and determines that the slot whose received power is larger than the threshold value is “in use”. As a result, the estimation unit 166 acquires the ratio and number of slots in use (hereinafter referred to as “used slots”) among the plurality of slots included in the frame. This corresponds to estimating the amount of traffic in communication between terminal devices.

  The determination unit 168 determines the notification period according to the traffic amount estimated by the estimation unit 166, that is, the ratio and number of used slots. Here, a case where the notification period is determined according to the ratio of the used slots will be described. The determining unit 168 derives the ratio of used slots per frame by dividing the number of used slots per frame by the total number of slots. Here, the total number of slots corresponds to the total number of slots included in one frame or the number of slots obtained by subtracting the number of control slots from the total number of slots.

  The decision unit 168 has two threshold values, a threshold value that is a reference for extending the notification cycle (hereinafter referred to as “extension threshold value”) and a threshold value that is a reference for shortening the notification cycle. (Hereinafter referred to as “shortening threshold”) is held in advance. Here, the extension threshold is defined to be larger than the shortening threshold. For example, the extension threshold is set to “80%”, and the shortening threshold is set to “30%”. The determination unit 168 compares the extension threshold value and the shortening threshold value with the ratio of used slots.

  When the ratio of the used slots is larger than the extension threshold value, the determination unit 168 determines extension of the notification cycle. For example, the determination unit 168 determines to extend the notification period by one frame, and determines to change to “3 frames” if the current notification period is “2 frames”. On the other hand, when the ratio of the used slots is smaller than the shortening threshold value, the determination unit 168 determines to shorten the notification cycle. For example, the determination unit 168 determines to shorten the notification cycle by one frame, and determines to change to “2 frames” if the current notification cycle is “3 frames”. In the extension of the notification cycle, the maximum value of the notification cycle may be defined as “5 frames”. The determination unit 168 does not extend the notification cycle when the current notification cycle is the maximum value. Further, when the current notification cycle is “1 frame”, the determination unit 168 does not shorten the notification cycle. Note that the determination unit 168 may increase the notification cycle by an integral multiple or decrease it by a fraction of an integer. The determination unit 168 outputs the determined notification cycle to the processing unit 156.

  When the processing unit 156 receives the notification cycle from the determination unit 168, the processing unit 156 generates cycle information related to the notification cycle. The processing unit 156 also stores the cycle information in the control information. As a result, period information is also notified. Here, the processing unit 156 may also generate restriction information regarding the terminal device to be controlled by the period information. For example, the processing unit 156 generates position information about the existing position where the terminal device to be controlled should exist as the restriction information. The position information is generated so as to indicate a partial region in the area 200 of FIG. The terminal device existing in the area adjusts the notification period according to the period information. On the other hand, a terminal device that does not exist in the area uses a predetermined notification cycle without following the cycle information.

  Moreover, the process part 156 produces | generates the speed information about the moving speed at the time of the terminal device used as control object moving as restriction | limiting information. The speed information is defined as, for example, a speed value (hereinafter referred to as “hourly threshold value”). A terminal device having a speed lower than the hourly threshold adjusts the notification period according to the period information. On the other hand, a terminal device having a speed equal to or higher than the hourly speed threshold uses a predetermined notification cycle without following the cycle information. Furthermore, the expiration date of the cycle information may be included in the control information as the expiration date information. The control unit 162 controls processing of the access control apparatus 10 as a whole.

  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. 5 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. The processing unit 56 includes a timing specifying unit 60, an acquiring unit 62, a generating unit 64, and a notification unit 70, and the timing specifying unit 60 includes a control information extracting unit 66 and a slot determining unit 68. The antenna 50, the RF unit 52, and the modem unit 54 perform the same processing as the antenna 150, the RF unit 152, and the modem unit 154 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 demodulation result from the modem unit 54. Further, the control information extraction unit 66 monitors the subcarrier portion corresponding to the identification carrier in the demodulation result. When valid data is included in the subcarrier portion corresponding to the identification carrier, the control information extraction unit 66 recognizes that the slot including the control information, that is, the control slot is received. Further, the control information extraction unit 66 establishes frame and slot synchronization with reference to the timing at which the slot including the control information is received.

  More specifically, the control information extraction unit 66 identifies a control slot in which the received demodulation result is arranged based on the control slot information included in the control information, and generates a frame based on this control slot. If the control slot information corresponds to the third slot in FIG. 3B, the control information extraction unit 66 generates a frame with reference to the third slot. That is, the control information extraction unit 66 generates a frame including a plurality of slots so as to synchronize with the frame corresponding to the control slot information. This corresponds to the control information extraction unit 66 extracting information regarding the timing of the frame and the timing of the slot included in the frame from the control information.

  In addition, the control information extraction unit 66 also extracts period information included in the control information. As described above, the notification cycle corresponding to the cycle information is determined according to the traffic volume in the communication between the terminal devices. If the control information includes restriction information and time limit information, the control information extraction unit 66 also extracts the restriction information and time limit information. The control information extraction unit 66 outputs information regarding the generated frame to the slot determination unit 68. Further, the control information extraction unit 66 also outputs period information, restriction information, and time limit information to the slot determination unit 68.

  The slot determination unit 68 measures the interference power for each of the plurality of slots included in the frame generated by the control information extraction unit 66 by carrier sense. Further, the slot determination unit 68 estimates an empty slot based on the interference power. More specifically, the slot determination unit 68 stores a predetermined threshold value in advance, and compares the interference power in each slot with the threshold value. Further, the slot determination unit 68 estimates a slot having interference power smaller than the threshold as an empty slot, and randomly identifies one of them. Note that the slot determination unit 68 may identify a slot with the smallest interference power. As a result, the slot determination unit 68 determines a slot that is synchronized with the control slot information and arrives at the frame period.

  Moreover, the slot determination part 68 specifies a slot so that it may arrive at the alerting | reporting period according to period information. For example, when the notification cycle is “2 frames”, when the slot determination unit 68 specifies one slot included in a predetermined frame, the slot determination unit 68 does not specify a slot included in the next frame, and further Identify one slot contained in the frame. As described above, the specified slots have the same relative timing in the frame.

  If the control information includes restriction information, the slot determination unit 68 determines whether the position information and speed information indicated by the restriction information are satisfied. As described above, the slot determining unit 68 uses the period information when satisfied, and does not use the period information when not satisfied. Further, when the time limit information is included in the control information, the slot determination unit 68 may select a slot so that it arrives at the notification period corresponding to the period information until the expiration date indicated by the time limit information. After the expiration date has passed, the slot determination unit 68 uses the default value as the notification period.

  Moreover, the slot determination part 68 may adjust a timing by making the alerting | reporting period according to period information into the minimum period. When the notification period is set to “2 frames” in the period information, the slot determination unit 68 may determine the notification period of “3 frames”. At that time, the slot determination unit 68 determines the notification cycle according to the application used in the terminal device 14. Finally, the slot determination unit 68 outputs information on the selected slot to the generation unit 64.

  The notification unit 70 acquires data from another terminal device 14 (not shown), and notifies the driver of the approach of another vehicle 12 (not shown) via a monitor or a speaker according to the content of the data. The processing in the notification unit 70 is not limited to this. 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. 6 shows an operation outline of the communication system 100. The horizontal direction in the drawing corresponds to time, and the first access control device 10a to the third access control device 10c are shown in the vertical direction in the drawing. FIG. 6 shows only the control area 220 in FIG. As described above, here, it is assumed that five control slots are arranged in the control area 220. “Control” in the figure corresponds to control information. The first access control device 10a uses the first control slot, the second access control device 10b uses the fifth control slot, and the third access control device 10c uses the third control slot. As a result, interference between control information broadcast from each access control apparatus 10 is reduced.

  FIG. 7 is a flowchart showing a control information notification procedure by the access control apparatus 10. The estimation unit 166 estimates the traffic volume (S100). If the ratio of the used slots is larger than the extension threshold (Y in S102), the determination unit 168 determines to extend the notification cycle by one frame (S104). On the other hand, when the ratio of the used slots is not larger than the extension threshold (N in S102) and the ratio of the used slots is smaller than the shortening threshold (Y in S106), the determining unit 168 sets the notification cycle to 1 The frame is shortened (S108). If the ratio of used slots is not smaller than the shortening threshold (N in S106), the determination unit 168 does not change the notification cycle. The processing unit 156 includes the notification cycle in the control information (S110). The modem unit 154, the RF unit 152, and the antenna 150 broadcast control information (S112).

  FIG. 8 is a flowchart showing a procedure for generating control information by the access control apparatus 10. This corresponds to an operation when information other than control slot information, identification information, period information, and the like is included in the control information. If there is a restriction on the existing position (Y in S130), the processing unit 156 includes the position information in the control information (S132). If there is no restriction on the location (N in S130), step 132 is skipped. If there is a restriction on the moving speed (Y in S134), the processing unit 56 includes the speed information in the control information (S136). If there is no restriction on the moving speed (N in S134), step 136 is skipped. If there is an expiration date (Y in S138), the processing unit 156 includes the expiration date in the control information (S140). If there is no expiration date (N in S138), step 140 is skipped.

  FIG. 9 is a flowchart illustrating a data notification procedure performed by the terminal device 14. The control information extraction unit 66 receives the control information (S160), generates a frame (S162), and specifies a notification cycle (S164). If the notification cycle is not the same as the current one (N in S166), the slot determination unit 68 changes the notification cycle (S168). If the notification cycle is the same as the current one (Y in S166), step 168 is skipped. The determination unit 168 identifies the slot (S170). The production | generation part 64 alert | reports data (S172).

  FIG. 10 is a flowchart illustrating a notification cycle setting procedure by the terminal device 14. If there is position information or speed information (Y in S190) and the condition is satisfied (Y in S192), the slot determination unit 68 sets a notification cycle (S194). On the other hand, if there is no position information or speed information (N in S190), step 192 is skipped. The slot determination unit 68 sets a notification cycle (S194). If there is an expiration date (Y in S196), the slot determination unit 68 sets the expiration date (S198). If there is no expiration date (N in S196), step 198 is skipped. If the condition is not satisfied (N in S192), steps 194 to 198 are skipped. When the expiration date has expired or when control information from the access control device 10 is no longer received, the slot determination unit 68 returns the notification cycle to the original value.

  Next, a modified example of the present invention will be described. The modification is a communication system 100 including the access control device 10 and the terminal device 14 as in the embodiment. In the embodiment, the access control device 10 notifies the frame timing and the notification cycle using the control information. On the other hand, in the modified example, in order to realize further reduction of the data collision probability, the access control device 10 notifies the control information by including further information. The access control apparatus 10 specifies a slot (hereinafter referred to as “empty slot”) that is not used for communication between a plurality of terminal apparatuses by measuring the reception power in each slot. The empty slots are slots other than the control slot. The access control apparatus 10 identifies a slot in which a collision occurs (hereinafter, referred to as a “collision slot”) by measuring whether or not packet signals transmitted from a plurality of terminal apparatuses collide in each slot. . The collision slot is also a slot other than the control slot.

  The access control device 10 also includes information on the identified empty slot and collision slot in the control information. The terminal device 14 estimates an empty slot based on the control information, and randomly selects one slot from the empty slots. Further, the terminal device 14 broadcasts data in the selected slot. The communication system 100 and the terminal device 14 according to the modification are the same types as those in FIGS. Here, the difference will be mainly described.

  FIG. 11 shows the configuration of the access control apparatus 10 according to a modification of the present invention. The access control device 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 period deriving unit 164. The processing unit 26 includes a detection unit 32, a frame definition unit 34, a generation unit 36, and a selection unit 110. 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. The period derivation unit 164 includes an estimation unit 166 and a determination unit 168. The antenna 20, the RF unit 22, the modem unit 24, the GPS positioning unit 28, the control unit 30, the frame defining unit 34, and the period deriving unit 164 are the antenna 150, the RF unit 152, the modem unit 154, the GPS positioning unit 158 of FIG. Since they correspond to the control unit 162, the frame generation unit 160, and the period derivation unit 164, description thereof is omitted here.

  The selection unit 110 performs carrier sense for each of the plurality of control slots in the control region 220, and selects one control slot based on the result of carrier sense. The processing of the selection unit 110 is the same as the processing performed in the processing unit 156 of FIG. The selection unit 110 outputs information on the selected control slot to the generation unit 36.

  The power measuring unit 38 receives the received signal from the RF unit 22 or the modem unit 24 and measures the received power. Here, the received power is measured in slot units. The slot corresponds to a slot other than the control slot. Therefore, the power measuring unit 38 measures the received power for each of the plurality of 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 and measures the signal quality for each of the plurality of slots. Here, the error rate is measured as the signal quality. The slot corresponds to a slot other than the control slot. 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 the error rate 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 (hereinafter referred to as “empty slot threshold”), and specifies a slot whose received power is smaller than the empty slot threshold. That is, the empty slot specifying unit 42 detects a slot that can be used for communication between a plurality of terminal devices as an empty slot from a plurality of slots other than the control area 220. 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 identifying unit 44 identifies, as a collision slot, a slot whose received power is larger than the first threshold and whose error rate is worse than the second threshold. That is, the collision slot specifying unit 44 recognizes a slot having a large received power but having deteriorated communication quality as a collision slot. As described above, the collision slot specifying unit 44 detects, as a collision slot, a 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 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 slots included in the frame is assigned a number (hereinafter referred to as “slot number”) that is “1” and “2” in order from the front. The generation unit 36 includes the slot number of the empty slot included in the previous frame as information on the empty slot in the control information. Further, upon receiving the notification cycle from the determination unit 168, the generation unit 36 generates cycle information related to the notification cycle. The generation unit 36 also stores the cycle information in the control information. The same applies to the restriction information and the like, but the description is omitted here. In addition, the generation unit 36 receives information on frames and slots from the frame definition unit 34. The generation unit 36 periodically assigns control information to one of the control slots. The generation unit 36 outputs control information to the modem unit 24 in the assigned control slot.

  In the embodiment, the slot determination unit 68 of the terminal device 14 estimates an empty slot based on the result of carrier sense. On the other hand, in the modification, the slot determination unit 68 estimates the empty slot based on the information on the empty slot and the information on the collision slot included in the control information. Here, processing in the terminal device 14 according to the modification will be described.

  The control information extraction unit 66 receives control information from the modem unit 54. The control information extraction unit 66 acquires information on empty slots and information on collision slots from the 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 slot determination unit 68 receives information on empty slots and information on collision slots from the control information extraction unit 66. The slot determination unit 68 selects an empty slot from slots other than the control area 220 in the frame based on 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 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 on the empty slot. That is, the slot determination unit 68 repeatedly executes the processes so far.

  If the control information received by the control information extraction unit 66 does not include information on empty slots, the slot determination unit 68 may execute the operation of the embodiment. This corresponds to the case where the control information from the access control device 10 in FIG. 2 is notified instead of the control information from the access control device 10 in FIG. At that time, the slot determination unit 68 performs carrier sense in each of the plurality of slots included in the frame generated by the control information extraction unit 66. When the control information extraction unit 66 does not accept information regarding an empty slot, the slot determination unit 68 estimates an empty slot based on the carrier sense execution result.

  FIG. 12 shows an outline of the operation of the communication system 100 according to the modification of the present invention. 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. For the sake of clarity, it is assumed that one control slot is included in one frame and 15 slots are included in one frame. As shown in the figure, the access control device 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 access control device 10 detects the occurrence of a collision in the slot. In the (i + 1) th frame, the control information broadcast from the access control device 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 slots that have already been used, the slots having the same slot number are 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 already used slot. 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 access control 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 use again the slot having the same slot number as the already used slot.

  FIG. 13 is a flowchart showing a procedure for notifying an empty slot in the access control apparatus 10. The detector 32 sets the slot number m to s (S10). 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 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 illustrating a collision slot notification procedure in the access control 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). If 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 slot with the slot number m as a 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 showing a data transmission procedure in the terminal device 14 according to the modification of the present invention. The control information extraction unit 66 acquires control information (S70). If the slot to be used has already been specified (Y in S72), the slot determination unit 68 checks whether or not a collision has occurred in the slot. If a collision has occurred (Y in S74), the slot determining unit 68 changes the slot (S76). If no collision has occurred (N in S74), step 76 is skipped. On the other hand, if the 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 randomly (S78). The generation unit 64 transmits data in the specified slot (S80).

  According to the embodiment of the present invention, since the access control apparatus notifies the notification period when the data is notified, the notification period of the terminal device can be controlled. In addition, since the notification cycle of the terminal device is controlled, the amount of communication traffic between the terminal devices can be controlled. Further, since the traffic volume of communication between terminal devices is controlled, the collision probability of packet signals can be reduced even when the traffic volume increases. Further, since the notification cycle is determined according to the estimated traffic volume, control suitable for the current traffic volume can be executed. Moreover, since the notification cycle is determined according to the estimated traffic volume, the traffic volume can be reduced when the traffic volume increases. In addition, since the amount of traffic is reduced, the collision probability of packet signals can be reduced.

  Moreover, since the restriction information regarding the terminal device to be controlled by the period information is also notified, only some terminal devices can be controlled. Further, since only some terminal devices can be controlled, the communication system can be operated flexibly. Moreover, since the location where the terminal device to be controlled should be present is notified as the restriction information, only the terminal device existing in the predetermined area can be controlled. In addition, since the moving speed when the terminal apparatus to be controlled moves is notified, only the terminal apparatus moving at a predetermined speed can be controlled. In addition, since the notification cycle of the terminal device having a low moving speed is controlled, the traffic amount of the terminal device having a long stay period in the area can be controlled.

  In addition, since the notification cycle is controlled based on the cycle information, a notification cycle according to the desire of the access control device can be realized. Further, since the notification cycle is controlled according to the cycle information considering the traffic volume in the entire area, the traffic volume in the entire area can be controlled. In addition, since the timing is adjusted with the notification period corresponding to the period information as the minimum period, the amount of traffic can be further reduced. Further, since the traffic volume is further reduced, the collision probability of packet signals can be further reduced.

  Since data is reported in the slot generated according to the control information from the access control device, synchronization between a plurality of terminal devices can be established. In addition, since synchronization between a plurality of terminal devices is established, the data collision probability can be reduced. In addition, since the data is notified in the slot, it is possible to reduce the occurrence of a situation where a part of a plurality of data overlaps and collides. Further, since data is broadcast in the slot, the frame utilization efficiency can be reduced. Also, since the empty slot is estimated and any one of the empty slots is selected, the collision probability of the packet signal can be reduced even when the traffic is increased. Moreover, since the empty slot is estimated based on the result of carrier sense, it is possible to estimate the empty slot according to the situation around the terminal device.

  Moreover, since the empty slot is estimated based on the control information, it is possible to estimate the empty slot according to the situation around the access control apparatus. Further, since carrier sense is executed if the information regarding the empty slot is not included in the control information, processing according to various access control devices can be executed. Also, among the control information, the identification carrier is not used for data, and the remaining subcarriers are also used for data, so that even if the control information collides with the data signal, the signal component of the control information is observed. Thus, the presence of the control information can be detected. In addition, since a guard band is provided between the identification carrier and other subcarriers, interference between the two can be reduced, and the arrival probability of information transmitted on the identification carrier can be improved. Moreover, since important information is arranged on the identification carrier, the arrival probability of important information can be improved. Moreover, since UW is arrange | positioned at an identification carrier, the detection accuracy of an identification carrier can be improved.

  Also, since the control area is reserved for the control slot among the plurality of slots included in the frame, interference between control information and data can be reduced. In addition, since a plurality of control slots are arranged in the control area, it is possible to reduce interference between control information from a plurality of access control apparatuses. Moreover, since interference is reduced, deterioration of the quality of control information can be suppressed. Moreover, since the deterioration of the quality of control information is suppressed, the content of control information can be transmitted accurately. Moreover, since interference between a plurality of control information is reduced, a plurality of access control devices can be arranged. Further, since a plurality of access control devices are arranged, the collision probability of packet signals at each intersection can be reduced. In addition, since a control slot that is not used by another access control apparatus is estimated, interference between a plurality of pieces of control information can be reduced.

  Moreover, since the slot which can be used for communication between several terminal devices is alert | reported from several slots, the occurrence probability of the collision in the communication between several terminal devices can be reduced. In addition, since the probability of collision in communication between a plurality of terminal devices is reduced, the collision probability of packet signals can be reduced even when the amount of communication increases. Further, since empty slots are identified based on the received power for each of the plurality of slots, the identification 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. In addition, since the terminal device using the empty slot uses a slot corresponding to the slot over a plurality of frames, the processing can be simplified. Further, since the access control device does not participate in the data communication between the terminal devices, but only notifies the index regarding the empty slot, it can be easily applied to a communication system based on CSMA / CA.

  In addition, since a slot in which a collision has occurred due to a plurality of terminal apparatuses transmitting a signal redundantly is notified from among a plurality of slots, the probability of occurrence of a collision in communication between the plurality of terminal apparatuses can be reduced. Further, since the collision slot is specified based on the received power for each of the plurality of slots and the signal quality for each of the plurality of slots, the specification 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 access control apparatus does not participate in data communication between terminal apparatuses and only notifies an index related to a collision slot, the access control apparatus can be easily applied to a communication system based on CSMA / CA.

  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 frame generator 160 defines a frame formed by a plurality of slots. However, the present invention is not limited to this. For example, the frame generation unit 160 may provide periods other than a plurality of slots in the frame. Specifically, a plurality of slots may be arranged in a partial period of the frame, and CSMA / CA may be performed between the plurality of terminal apparatuses 14 in the remaining period. At this time, the access control apparatus does not detect an empty slot or a collision slot during the CSMA / CA period. According to this modification, since the terminal device 14 can select communication by slot and communication by CSMA / CA, the degree of freedom of communication can be improved. That is, the frame only needs to include at least a plurality of slots.

  In the embodiment of the present invention, control information notified from the access control apparatus 10 and data notified 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 identification carrier corresponds to two subcarriers. Further, the identification carrier is arranged on a subcarrier near the center frequency of the OFDM symbol. However, the present invention is not limited to this. For example, the identification carrier may correspond to two or more subcarriers, and the identification carrier may be arranged on a subcarrier other than the vicinity of the center frequency of the OFDM symbol. At this time, the identification carrier may include information on empty slots and information on collision slots. According to this modification, the degree of freedom in designing the communication system 100 can be improved.

  In the embodiment of the present invention, the access control device 10 defines a frame including a plurality of slots, and defines a notification cycle in units of frames. However, the present invention is not limited to this, and for example, a frame including a plurality of slots may not be defined. At that time, the notification cycle is indicated as time. According to this modification, the present invention can be applied to various communication systems.

  In the embodiment of the present invention, the determination unit 168 determines the notification period according to the ratio of used slots. However, the present invention is not limited to this. For example, the determination unit 168 may determine the notification cycle according to the number of used slots and the number of unused slots in a frame. When the number of unused slots becomes smaller than the extension threshold value, the determination unit 168 determines to extend the notification cycle by one frame. On the other hand, when the number of unused slots becomes larger than the shortening threshold, the determination unit 168 determines to shorten the notification cycle by one frame. In this case, the extension threshold value is defined to be smaller than the shortening threshold value. According to the present modification, the processing amount can be reduced because the process of counting the number of unused slots may be executed.

  In the embodiment of the present invention, period information and the like are stored in the control information. However, the present invention is not limited to this. For example, the control information may include information on the type of vehicle on which the terminal device 14 is mounted (hereinafter referred to as “vehicle information”). In the vehicle information, automobiles, bicycles, and the like are shown, but pedestrians may be shown. Furthermore, the notification cycle is determined for each type of vehicle, and the cycle information may be generated so as to include the notification cycle. According to this modification, the notification cycle can be controlled in detail.

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the access control apparatus of FIG. FIGS. 3A to 3D are diagrams illustrating a format of a frame generated by the frame generation unit of FIG. FIGS. 4A to 4B are diagrams showing the format of the OFDM symbol used in the communication system of FIG. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. It is a figure which shows the operation | movement outline | summary of the communication system of FIG. It is a flowchart which shows the alerting | reporting procedure of the control information by the access control apparatus of FIG. It is a flowchart which shows the production | generation procedure of the control information by the access control apparatus of FIG. It is a flowchart which shows the alerting | reporting procedure of the data by the terminal device of FIG. It is a flowchart which shows the setting procedure of the alerting | reporting period by the terminal device of FIG. It is a figure which shows the structure of the access control apparatus which concerns on the modification of this invention. It is a figure which shows the operation | movement outline | summary of the communication system which concerns on the modification of this invention. 12 is a flowchart showing a procedure for notifying an empty slot in the access control apparatus of FIG. 12 is a flowchart showing a collision slot notification procedure in the access control apparatus of FIG. It is a flowchart which shows the transmission procedure of the data in the terminal device which concerns on the modification of this invention.

Explanation of symbols

  10 access control device, 12 vehicle, 14 terminal device, 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, 100 communication system, 150 antenna, 152 RF unit, 154 modulation / demodulation unit, 156 processing unit, 158 GPS positioning unit, 160 frame generation unit, 162 control unit, 164 period derivation unit, 166 estimation unit 168 Determination unit.

Claims (3)

A generation unit that repeatedly generates frames and generates timing information related to the timing of frames to be synchronized when each wireless device broadcasts a signal in communication between wireless devices;
A notification unit for reporting the timing information generated in the generation unit,
In the communication between wireless devices, the generation unit also generates cycle information about a cycle from when each wireless device broadcasts a signal to when it is broadcast next , and indicated by an integer multiple of a synchronized frame. And
The notification unit also notifies the period information generated in the generation unit together with timing information ,
This access control device
An estimation unit for estimating a traffic volume in communication between wireless devices;
An access control apparatus , further comprising: a determination unit that determines a period from a signal notification to a next notification in accordance with the traffic amount estimated by the estimation unit. The generation unit also generates restriction information related to a wireless device to be controlled by cycle information,
The access control apparatus according to claim 1, wherein the notification unit also notifies the restriction information generated in the generation unit together with period information. The access control apparatus according to claim 2 , wherein the generation unit generates position information about an existing position where a wireless device to be controlled should exist as restriction information.

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