JP2010081390A - Reporting method, and access controller for wide area and access controller for local area utilizing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the collision probability of packet signals even when a communication amount increases. <P>SOLUTION: A frame generation part 160 generates a frame including at least a plurality of slots. A processing part 156, a modulation and demodulation part 154 and an RF part 152 report wide area information relating to the generated frame to the access controller for a local area. In this case, the processing part 156 makes the access controller for the local area to which the wide area information is reported detect a slot usable for communication between terminal units from the plurality of slots included in the frame and report control information relating to the detected slot. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a notification technique, and more particularly to a notification method for notifying a signal including predetermined information, a wide area access control device and a local access control device using the notification method.

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 a form which communicates information between vehicles, 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 respectively enter the intersection. (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, so it is desirable that the signal be transmitted by broadcast. However, at intersections and the like, an increase in the collision of packet signals is assumed due to an increase in the number of vehicles, that is, an increase in the number of terminal devices. 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, a wide area access control device according to an aspect of the present invention includes a generation unit that generates a frame including at least a plurality of slots, and first information about the frame generated in the generation unit. A notification unit that notifies the access control device. The notification unit causes the local access control apparatus that has notified the first information to detect a slot that can be used for communication between wireless apparatuses from among a plurality of slots included in the frame, and 2 Information is notified.

  Another aspect of the present invention is a local access control apparatus. The apparatus includes: a reception unit that receives first information regarding a frame including at least a plurality of slots from the wide area access control device; and a plurality of slots so as to be synchronized with a frame corresponding to the first information received in the reception unit. Generating a frame including at least a frame, a detection unit detecting a slot usable for communication between wireless devices from a plurality of slots included in the frame generated by the generation unit, and detecting by the detection unit A notification unit for reporting second information about the slot.

  Yet another aspect of the present invention is a notification method. The method includes a step of generating a frame including at least a plurality of slots, and a step of notifying the local access control device of first information related to the generated frame. The notifying step causes the local access control apparatus that has notified the first information to detect a slot that can be used for communication between wireless apparatuses from among a plurality of slots included in the frame, and relates to the detected slot The second information is notified.

  Yet another embodiment of the present invention is also a notification method. In this method, at least a plurality of slots are included so as to synchronize with a frame corresponding to the received first information, and a step of receiving first information about a frame including at least a plurality of slots from the wide area access control device. Generating a frame, detecting a slot usable for communication between wireless devices from a plurality of slots included in the generated frame, and informing second information related to the detected slot, Prepare.

  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 a local access control device in addition to a plurality of terminal devices, and the local access control device is installed at an intersection, for example. The local access control apparatus repeatedly defines a frame including a plurality of slots. A part of the plurality of frames included in each frame is reserved as a control slot. The local access control device specifies a slot (hereinafter referred to as “empty slot”) that is not used for communication between a plurality of terminal devices by measuring the reception power in each slot. The empty slots are slots other than the control slot.

  Further, the local access control device includes frame configuration information and information on the specified slot in the control information, and stores the packet signal storing the control information (hereinafter also referred to as “control information”) in one slot. Broadcast transmission at. Here, one slot used for transmission of control information is selected from the control slots. The terminal device selects one of the empty slots based on the control information, and broadcasts a packet signal storing data (hereinafter also referred to as “data”) in the selected slot. When transmitting data over a plurality of frames, the terminal device uses slots having the same relative timing in each frame.

  The local access control device 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 devices collide in each slot. To do. The collision slot is also a slot other than the control slot. Further, the local access control apparatus also includes information regarding the identified slot in the control information. Based on the control information, the terminal device confirms whether or not a collision has occurred in the already used slot. When a collision has occurred, the terminal device selects another free slot based on the control information. Here, the local 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. To the last, the local access control device monitors the status of data communication between terminal devices, and reports information on empty slots and collision slots. That is, the local 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 a local access control device is installed at each of the adjacent intersections, it is necessary to consider interference between the local access control devices. If the control information broadcast from each local 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 local 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 the aforementioned control slots are secured. Each local 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.

  When a control slot is selected by carrier sense, other local access control devices may not be recognized depending on the position where the local access control device is installed. That is, the same phenomenon as the hidden terminal problem occurs. In order to cope with this, each access device broadcasts information for identifying the access device (hereinafter referred to as “identification information”) included in the control information. The terminal device broadcasts the data by including the information of the control slot (hereinafter referred to as “control slot information”) and the identification information in which the control information is transmitted. The access device recognizes the control slot used by another local access control device by receiving the data. Further, the local access control apparatus selects a control slot in consideration of the recognized control slot.

  In the description so far, the local access control device, for example, has set the vicinity of one intersection as an area to be controlled (hereinafter referred to as “local area”). The communication system according to the present embodiment further includes a wide area access control device that controls a wide area including a plurality of local areas (hereinafter referred to as “wide area”). The wide area access control device generates the above-described frame and secures a slot for the wide area access control device as a “wide area slot” from a plurality of slots included in the frame. The wide area access control device generates system information (hereinafter, referred to as “wide area information”) that stops the operation of the entire communication system, for example, and broadcasts the wide area information in the wide area slot. The local access control device described above receives the wide area information, generates a frame at a timing synchronized with the wide area slot, and executes the above-described processing. That is, the wide area access control device is installed to control a plurality of local access control devices. Since the wide area information is also received by the terminal device, the wide area access control device can also control the terminal device.

  FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. The communication system 100 includes a first local access control device 10a, a second local access control device 10b, a third local access control device 10c, and a fourth local access control device 10d, which are collectively referred to as the local access control device 10. , The Nth local access control device 10n, and the wide area access control device 16. As shown, a wide area 202 is formed by the wide area access control device 16. Further, the first local access control device 10a, the second local access control device 10b, the third local access control device 10c, the fourth local access control device 10d, and the Nth local access control device 10n A local area 200a, a second local area 200b, a third local area 200c, a fourth local area 200d, and an Nth local area 200n are formed.

  As illustrated, the wide area 202 is wider than each local area 200, and the wide area 202 includes a plurality of local areas 200. The wide area access control device 16 generates a frame including at least a plurality of slots. Further, the wide area access control device 16 broadcasts information on the generated frame as the above-mentioned wide area information. Each local access control device 10, when receiving the wide area information from the wide area access control device 16, generates a frame including at least a plurality of slots so as to synchronize with a frame corresponding to the wide area information. The wide area access control device 16 detects a slot that can be used for communication between terminal devices (not shown) from a plurality of slots included in the generated frame. Here, the terminal device is mounted on a vehicle. The local access control device 10 broadcasts information on the detected slot as the control information described above. The terminal device identifies an empty slot based on the control information, and broadcasts data in the empty slot.

  The operation of the local access control device 10 described above will be described from the point of the wide area access control device 16. For the local access control device 10 that broadcasts wide area information, a usable slot is selected from a plurality of slots. It can be said that the control information is broadcasted and transmitted. Further, the wide area access control device 16 causes the terminal device that cannot receive the control information to receive the wide area information and use at least one of the plurality of slots included in the frame. Further, when the local access control device 10 cannot receive the wide area information from the wide area access control device 16, the local access control device 10 independently generates a frame and executes the above-described operation. In consideration of the relationship between the wide area 202 and the local area 200, the transmission power of the wide area access control device 16 is larger than the transmission power of the local access control apparatus 10. Note that the wide area access control device 16 may not only notify the timing of the frame or slot by the wide area information, but may include other information in the wide area information. For example, the wide area information includes an instruction for stopping the operation of the entire communication system 100 and information for changing the frame configuration.

  FIG. 2 shows another configuration of the communication system 100 according to the embodiment of the present invention. FIG. 2 is an enlarged view of the periphery of the first local access control device 10a and the second local access control device 10b shown in FIG. As shown in the drawing, one road that goes in the horizontal direction of the drawing, that is, the left and right direction intersects with two roads that go in the vertical direction of the drawing, that is, the vertical direction. 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”. Therefore, FIG. 2 corresponds to a case where two intersections are arranged side by side.

  The first local access control device 10a and the second local access control device 10b are installed at each intersection. As described above, the first local area 200a is formed by the first local access control device 10a, and the second local area 200b is formed by the second local access control device 10b. Further, the first local area 200a and the second local area 200b are partially overlapped. If a vehicle (not shown) exists in the overlapping part, the terminal device mounted on the vehicle receives the control information from the first local access control device 10a and the control information from the second local access control device 10b. Can receive. Therefore, a configuration for reducing interference with the control information from the two local access control apparatuses 10 is required.

  FIG. 3 shows still another configuration of the communication system 100 according to the embodiment of the present invention. This corresponds to a case where one intersection is viewed from above. The communication system 100 includes a local access control device 10, a first vehicle 12 a, a second vehicle 12 b, a third vehicle 12 c, a fourth vehicle 12 d, a fifth vehicle 12 e, a sixth vehicle 12 f, and a seventh vehicle 12. A vehicle 12g and an eighth vehicle 12h are included. Each vehicle 12 is equipped with a terminal device (not shown). A local area 200 is formed by the local access control device 10. Further, 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 local access control device 10 at the intersection. The local access control device 10 generates a frame including a plurality of slots so as to be repeated so as to synchronize with the frame included in the wide area information. Further, the local access control device 10 identifies an empty slot and a collision slot from among a plurality of slots. A method for identifying the empty slot and the collision slot will be described later. The local access control device 10 includes information on the identified empty slot and collision slot in the control information. Furthermore, the local access control apparatus 10 broadcasts control information in any of a plurality of control slots. The selection of the control slot will also be described later.

  The plurality of terminal devices receive the control information broadcast by the local access control device 10 and select one of the empty slots. Also, the terminal device broadcasts data in the selected slot. Here, the terminal device broadcasts data in a slot corresponding to the selected slot over a plurality of frames. For example, when the 10th slot from the beginning of the frame is selected, the 10th slot from the beginning of the frame is used in the next frame. Note that if the control information indicates that the slot used is a collision slot, the terminal device further selects another empty slot. The terminal device repeatedly executes the above process over a period in which the control information broadcast by the local access control device 10 can be received. That is, the terminal device monitors the control information, and detects that it has entered the local area 200 when it can receive the control information. Note that the terminal device may broadcast data even when the control information is not received. 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, wide area information broadcast from the wide area access control device 16 (not shown), control information broadcast from the local access control device 10, and data broadcast from the terminal device are both OFDM signals. use. However, these arranged subcarriers are not the same. Data is not placed on the aforementioned identification carrier. On the other hand, wide area information and identification information are arranged on an identification carrier in addition to a subcarrier on which data is arranged. As a result, even if the wide area information or the identification information collides with the data, the terminal device can detect the presence of the wide area information or the control information by observing the signal component of the identification carrier. In addition, the approach detection to the local area 200 by the above-mentioned terminal device may be made with respect to the identification carrier.

  FIG. 4 shows the configuration of the wide area access control device 16. The wide area access control device 16 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, and a control unit 162. 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 the information of time, 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 secured as “wide area slots”. For example, among the 200 slots included in one frame, the first slot is a wide area slot. The wide area slot is a slot used for the wide area access control device 16 to broadcast and transmit wide area information. Further, at least one slot different from the wide area slot is secured as a “control slot”. For example, out of 200 slots included in one frame, four slots from the second are set as control slots. The control slot is a slot used for the local access control apparatus 10 (not shown) 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. 5A to 5D show the format of a frame generated by the frame generation unit 160. FIG. FIG. 5A 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. 5B 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 wide area slot, and a section where the wide area slot is arranged is shown as a wide area 222. Further, a slot arranged after the wide area 222 corresponds to a control slot, and a section in which the control slot is arranged is shown as a control area 220.

  Here, the first slot is included in the wide area 222 as a wide area slot, and four slots from the second slot to the fifth slot are included in the control area 220 as control slots. FIG. 5C shows the configuration of one slot. As shown in the figure, guard times are provided in the front portion and the rear portion of the slot. Further, the remaining period of the slot is composed of N OFDM symbols. FIG. 5D 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.

  The RF unit 152 receives, from the antenna 20, a packet signal transmitted in communication between other terminal devices (not shown) in each slot as reception processing. Here, the transmission source of the packet signal is, for example, the local access control device 10 or the terminal device (not shown). 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. Further, 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 modulation / demodulation unit 154 also executes FFT (Fast Fourier Transform) as a reception process, and also executes IFFT (Inverse Fast Fourier Transform) as a transmission process. In the following description, only transmission processing in the RF unit 152 and the modem unit 154 is executed. Therefore, the RF unit 152 and the modem unit 154 do not have to have a reception processing function.

  The processing unit 156 generates wide area information while including information related to the frame configuration and an instruction for stopping the entire communication system 100. The processing unit 156 receives information related to frames and slots from the frame generation unit 160. The processing unit 156 periodically assigns wide area information to wide area slots. The processing unit 156 outputs the wide area information to the modem unit 154 in the allocated wide area slot. Note that broadcast transmission of wide area information in a wide area slot determined in the communication system 100 corresponds to notifying the timing of the wide area slot in the frame. Further, since the relative position of the wide-area slot in the frame is known, the above also corresponds to notifying the timing of the frame.

  As described above, since the communication system 100 supports the OFDM modulation scheme, the processing unit 156 generates control information as an OFDM signal. Note that the OFDM signal is also used for control information generated in the local access control device 10 (not shown) and data communication between a plurality of terminal devices (not shown). Here, an OFDM signal in which wide area information and control information are arranged (hereinafter also referred to as “wide area information” and “control information”) and an OFDM signal in which data is arranged (hereinafter also referred to as “data”). Will be explained.

  FIGS. 6A to 6B show OFDM symbol formats used in the communication system 100. FIG. FIG. 6A corresponds to wide area information and control information, and FIG. 6B 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.

  Common to wide area information, control information, and data, subcarrier numbers “31” to “27”, “2”, “0”, “−2”, “−26” to “−32” are subcarriers, It is null. Of the wide area information and the control information, the subcarriers with subcarrier numbers “26” to “3” and “−3” to “−25” are also used in data, and the use of symbols is also used in these. Are the same. On the other hand, of the wide area information and the control information, the subcarrier numbers “1” and “−1” 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 between the subcarrier used in the data and the identification carrier, that is, the subcarrier numbers “2” and “−2” among the wide area information and the control information. The subcarriers with subcarrier numbers “−2” to “2” may be collectively referred to as “identification carriers”.

  Here, the processing unit 156 arranges information regarding 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 transmit the wide area information generated by the processing unit 156 in the wide area slot from the antenna 150. One of the destinations of the wide area information is the local access control device 10. The local access control device 10 that has received the wide area information detects a slot that can be used for communication between the terminal devices from the remaining slots reserved for communication between the terminal devices, and detects any slot in the control region 220. Then, the control information is broadcasted. Details of these processes will be described later. On the other hand, another destination of the wide area information is a terminal device. The terminal device that has received the wide area information executes processing according to the wide area information. The terminal device that cannot receive the control information recognizes the timing of each slot by receiving the wide area information, and uses at least one of the remaining slots reserved for communication between the terminal devices. The control unit 162 controls processing of the entire wide area access control device 16.

  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 the configuration of the local access control apparatus 10. The local 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, and a control unit 30. The processing unit 26 includes a detection unit 32, a frame generation unit 34, a signal 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, a collision slot. A specifying unit 44 is included. The selection unit 110 includes an information acquisition unit 112, an analysis unit 114, an estimation unit 116, a carrier sense unit 118, and an execution unit 120.

  The RF unit 22 receives, from the antenna 20, a packet signal transmitted in communication between other terminal devices (not shown) in each slot as reception processing. Note that the RF unit 22 receives a packet signal including wide area information from a wide area access control device 16 (not shown) in a wide area slot included in the wide area 222 as a reception process. The RF unit 22 also receives a packet signal including control information from another local access control apparatus 10 (not shown) in each control slot included in the control area 220. Since the processing in the RF unit 22 is the same as that in the RF unit 152, description thereof is omitted here. As described above, the PA transmission power in the RF unit 22 is smaller than the PA transmission power in the RF unit 152. Since the process in the modem unit 54 is the same as the process in the modem unit 154, the description is omitted here. The GPS positioning unit 28 is also the same as the GPS positioning unit 158 of FIG.

  The frame generation unit 34 receives wide area information in the wide area slot from the wide area access control device 16 (not shown) via the RF unit 22 and the modem unit 24. The frame generation unit 34 recognizes the configuration of FIG. 5B, and can recognize the configuration of a frame including a plurality of slots by recognizing reception in the wide area 222. That is, the frame generation unit 34 recognizes the configuration of the frame including the wide area 222, the control area 220, and other slots for communication between terminal devices by receiving the wide area information. The frame generation unit 34 generates a frame including a plurality of slots so as to synchronize with the recognized frame. Note that the frame generation unit 34 independently generates a frame based on the time information from the GPS positioning unit 28 when it does not accept the wide area information. Here, the frame is generated in the same manner as the frame generation unit 160 in FIG.

  The carrier sense unit 118 performs carrier sense for each control slot in the control area 220. That is, the carrier sense unit 118 receives the received signal for each control slot from the RF unit 22 or the modem unit 24 and measures the received power. As a result, the carrier sense unit 118 measures the received power for each of the plurality of control slots. Further, the carrier sense unit 118 stores a control slot threshold value in advance, and compares the received power with the control slot threshold value for each control slot. The carrier sense unit 118 selects a control slot having a reception power smaller than the control slot threshold value. The carrier sense unit 118 outputs the selected control slot number to the estimation unit 116.

  The information acquisition unit 112 receives, from the modem unit 24, a packet signal in communication between a plurality of terminal devices (not shown), that is, a packet signal broadcast from a predetermined terminal device. The information acquisition unit 112 receives a packet signal in a slot other than the control area 220 in the frame. The packet signal includes identification information and control slot information. The control information is information for identifying the local access control device 10 that broadcasts the control information referred to by the terminal device that has transmitted the packet signal. As a premise, it is assumed that identification information is included in the control information broadcast by each local access control device 10.

  The identification information corresponds to the position information where the local access control device 10 is set. For example, the position information is indicated by latitude / longitude, and the latitude / longitude is used as identification information. Further, a part of latitude / longitude, for example, a lower part may be used for the identification information. The control slot information is information regarding the control slot in which the control information referred to by the terminal device that transmitted the packet signal is broadcast and corresponds to the slot number in which the control information is arranged. For example, in FIG. 4B, it is shown as “second slot”. The information acquisition unit 112 outputs the identification information and the control slot information to the analysis unit 114.

  The analysis unit 114 sequentially acquires combinations of identification information and control slot information from the information acquisition unit 112. The analysis unit 114 statistically analyzes the combination of identification information and control slot information. More specifically, the analysis unit 114 accumulates the number of acquisitions for each combination over a predetermined period. In addition, the analysis unit 114 determines a threshold value for the number of times in advance, and compares the number of acquisition times with the threshold value for the number of times for each combination. Furthermore, the analysis unit 114 extracts a combination corresponding to the number of acquisition times that is larger than the number-of-times threshold.

  The analysis unit 114 derives position information from the identification information included in the combination. The analysis unit 114 stores in advance position information where the local access control device 10 is installed, and derives a distance between the two based on the position information of both. Furthermore, the analysis unit 114 stores a distance threshold value in advance, and compares the distance with the distance threshold value. The analysis unit 114 is a combination for the local access control device 10 having a distance larger than the distance threshold, that is, the local access installed at a position farther from the local access control device 10 than the distance threshold. The combinations for the control device 10 are excluded from the integration targets. The analysis unit 114 outputs the extracted combination to the estimation unit 116.

  The estimation unit 116 receives the number of the selected control slot from the carrier sense unit 118 and also receives the combination extracted as the analysis result from the analysis unit 114. Based on the control slot information included in the combination, the analysis unit 114 specifies a control slot that is not used by another local access control device 10. Specifically, a control slot other than the slot number indicated in the control slot information is specified. Furthermore, the estimation unit 116 estimates a control slot that is not used by another access control device in the control region 220 based on the identified control slot and the control slot selected by the carrier sense unit 118. Specifically, a control slot that is the specified control slot and selected by the carrier sense unit 118 is an unused control slot. Here, there may be a plurality of unused control slots. The estimation unit 116 outputs the estimation result to the execution unit 120.

  The execution unit 120 receives the estimation result from the estimation unit 116, and selects one of the unused control slots. The selection may be made by an arbitrary method. That is, the execution unit 120 selects one control slot from the control area 220 in order to broadcast control information. The antenna 20 outputs information on the selected control slot to the signal 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 wide area slot and 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. Again, the slot corresponds to a slot other than the wide area slot and 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 from among a plurality of slots other than the wide area 222 and the control area 220 as an empty slot. 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 signal 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 signal generation unit 36.

  The signal 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 signal 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 signal 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, the signal generation unit 36 includes the slot number of the collision slot included in the previous frame as information on the collision slot in the control information. In addition to these, the signal generation unit 36 stores the identification information of the local access control device 10, includes the identification information in the control information, receives information on the control slot from the execution unit 120, and information on the control slot Is also included in the control information. Since the identification information is as described above, description thereof is omitted here. Further, the signal generation unit 36 receives information on frames and slots from the frame generation unit 34. The signal generator 36 periodically assigns control information to the control slots indicated in the information regarding the control slots. The signal generation unit 36 outputs control information to the modem unit 24 in the assigned control slot.

  The modem unit 24 and the RF unit 22 broadcast the control information generated by the signal generation unit 36 from the antenna 20. In addition, the terminal device using the slot according to the information regarding the empty slot and the information regarding the collision slot included in the control information uses the slot corresponding to the slot over a plurality of frames. For example, the slot with the slot number “10” is continuously used. The control unit 30 controls processing of the local access control apparatus 10 as a whole.

  FIG. 8 shows a configuration of the terminal device 14 mounted on the vehicle 12. The terminal device 14 includes an antenna 50, an RF unit 52, a modem unit 54, a processing unit 56, and a control unit 58. The processing unit 56 includes a timing specifying unit 60, an acquiring unit 62, a generating unit 64, and a notification unit 70. The timing specifying unit 60 includes a control information extracting unit 66, a wide area information extracting unit 72, 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 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 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. The control information extraction unit 66 includes valid data in the subcarrier portion corresponding to the identification carrier, and extracts the slot number included in the identification carrier. When the slot number is included in the control area 220, the control information extraction unit 66 recognizes that the slot including the control information, that is, the control slot is received. That is, the control information extraction unit 66 recognizes that control information is received in the control slot. 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. As described above, since the frame generated in the local access control device 10 is synchronized with the frame corresponding to the wide area information, the above processing is synchronized with the frame generated in the wide area access control device 16. Is equivalent to establishing

  More specifically, the control information extraction unit 66 identifies a control slot in which the received demodulation result is arranged based on information on the control slot included in the control information, and generates a frame based on this control slot. To do. Furthermore, the control information extraction unit 66 acquires information on empty slots, information on collision slots, and identification information 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 control information extraction unit 66 outputs information on the control slot as control slot information to the slot determination unit 68 and also outputs identification information to the slot determination unit 68.

  Similar to the control information extraction unit 66, the wide area information extraction unit 72 monitors the subcarrier portion corresponding to the identification carrier. When the slot number is included in the wide area 222, the wide area information extraction unit 72 recognizes that the slot including the wide area information, that is, the wide area slot is received. That is, the wide area information extraction unit 72 recognizes that wide area information is received in the wide area slot. Similarly to the control information extraction unit 66, the wide area information extraction unit 72 establishes frame and slot synchronization with reference to the timing at which a slot including the wide area information is received. The wide area information extraction unit 72 outputs the frame and slot timings to the slot determination unit 68. Further, when the wide area information includes an instruction for stopping the operation of the entire communication system 100, the wide area information extraction unit 72 outputs the instruction to the control unit 58. When receiving the instruction, the control unit 58 stops the processing of the entire terminal device 14.

  When the control information extraction unit 66 can receive the control information, the slot determination unit 68 receives information regarding the empty slot and information regarding the collision slot from the control information extraction unit 66. The slot determination unit 68 also receives control slot information and identification information from the control information extraction unit 66. The slot determination unit 68 selects one empty slot from slots other than the wide area 222 and the control area 220 in the frame based on the information regarding the empty slot. It should be noted that an empty slot may be selected arbitrarily. The slot determination unit 68 outputs information on the selected empty slot, control slot information, and identification information to the generation unit 64.

  When the control information extraction unit 66 cannot receive the control information and the wide area information extraction unit 72 can receive the wide area information, the slot determination unit 68 performs the wide area information according to the frame and slot timing from the wide area information extraction unit 72. One slot is selected from a plurality of slots other than the area 222 and the control area 220. The slot determination unit 68 outputs information regarding the selected slot to the generation unit 64. That is, the slot determination unit 68 preferentially uses control information out of control information and wide area information regarding slot selection. The slot determination unit 68 performs carrier sense via the RF unit 52 and the modem unit 54 when the control information extraction unit 66 cannot receive control information and the wide area information extraction unit 72 cannot receive wide area information. By executing, the timing which should transmit data is specified. The slot determination unit 68 outputs the identified timing to the generation unit 64.

  The generation unit 64 receives information from the acquisition unit 62 and also receives (1) control slot information and control information from the slot determination unit 68, (2) information about the selected slot, and (3) specified timing. Here, any one of (1) to (3) is input to the generation unit 64 in accordance with the operation of the slot determination unit 68 described above. The generation unit 64 generates data based on the information. Here, the data is formed as shown in FIG. In the case of (1), the data includes control slot information and control information. The generation unit 64 outputs data to the modulation / demodulation unit 54 in an empty slot according to an instruction regarding an empty slot from the slot determination unit 68. Note that the processor 56 may perform carrier sense before outputting data. In addition, the generation unit 64 outputs data in the slot having the same slot number in the next frame. In the case of (2), the generation unit 64 outputs data to the modem unit 54 in the selected slot. In the case of (3), the generation unit 64 outputs data to the modem unit 54 at the specified timing.

  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 selects one empty slot again based on the information regarding the empty slot. That is, a slot different from the slot selected so far is selected. The slot determination unit 68 outputs information regarding the selected empty slot to the generation unit 64. Thereafter, the generation unit 64 performs similar processing. 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) according to the contents 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. 9 shows an outline of the operation of the communication system 100. The horizontal direction in the drawing corresponds to time, and the first local access control device 10a to the third local access control device 10c are shown in the vertical direction in the drawing. 9 shows only the wide area 222 and the control area 220 in FIG. 5B. As described above, here, one wide area slot is arranged in the wide area 222 and four control slots are arranged in the control area 220. “Control” in the figure corresponds to control information. The first local access control device 10a uses the second slot, the second local access control device 10b uses the fifth slot, and the third local access control device 10c uses the third slot. Is used. As a result, interference between control information broadcast from each local access control apparatus 10 is reduced.

  FIG. 10 shows another operation outline of the communication system 100. 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 the wide-area slot is omitted, one control slot is included in one frame, and 15 slots are included in one frame. As shown in the figure, the local access control apparatus 10 broadcasts control information in the first slot of each frame. “Control” in the figure corresponds to control information. In the lower part, information on empty slots and information on collision slots included in the control information are shown while being associated with the slots. “Empty” in the figure corresponds to an empty slot, and “attack” corresponds to a collision slot.

  Furthermore, the lower part shows the timing at which the first terminal apparatus 14a to the fourth terminal apparatus 14d broadcast 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 and transmit 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 broadcast from both collide with each other. The local 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 local 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 apparatus 14c and the fourth terminal apparatus 14d broadcast data in the selected empty slot. Since all data does not collide, the collision slot is not indicated in the control information broadcast-transmitted from the local access control device 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. 11 shows still another operation outline of the communication system 100. FIG. 11 is shown similarly to FIG. Here, as a premise, it is assumed that the second terminal device 14b cannot receive the control information from the local access control device 10 and further cannot receive the wide area information from the wide area access control device 16. Therefore, the second terminal apparatus 14b transmits data without grasping the frame configuration. The local access control apparatus 10 broadcasts control information in the first slot of the frame. On the other hand, the second terminal apparatus 14b broadcasts data in the first slot of the frame. As a result, control information and data collide in the slot. Here, the first terminal device 14a, the third terminal device 14c, and the fourth terminal device 14d can control information by observing the signal component of the identification carrier in the control information even when a collision occurs. The presence of can be detected.

  FIG. 12 is a flowchart showing a frame generation procedure in the local access control apparatus 10. If the RF unit 22 and the modem unit 24 can receive the wide area information (Y in S200), the frame generation unit 34 generates a frame synchronized with the frame corresponding to the wide area information (S202). The control unit 30 executes processing according to the wide area information (S204). On the other hand, if the RF unit 22 and the modem unit 24 cannot receive the wide area information (N in S200), the frame generation unit 34 generates a frame based on the time information from the GPS positioning unit 28 (S206). .

  FIG. 13 is a flowchart showing a control slot selection procedure in the local access control apparatus 10. The carrier sense unit 118 performs slot selection by carrier sense (S100). The information acquisition unit 112, analysis unit 114, estimation unit 116, and carrier sense unit 118 execute slot selection based on the control slot information and the identification information (S102).

  FIG. 14 is a flowchart showing a control slot selection procedure based on carrier sense. This corresponds to the processing in step 100 of FIG. The number of control slots included in the control area 220 is “S-2”. The carrier sense unit 118 sets the slot number m to 2 (S120). The carrier sense unit 118 measures received power (S122). If the received power is smaller than the control slot threshold (Y in S124), the carrier sense unit 118 identifies the slot with the slot number m as empty (S126). If the received power is not smaller than the control slot threshold (N in S124), the carrier sense unit 118 skips the process of step 126. If the slot number m is not the maximum number S-1 (N in S128), the carrier sense unit 118 adds 1 to the slot number m (S130) and returns to step 122. On the other hand, if the slot number m is the maximum number S-1 (Y in S128), the process is terminated.

  FIG. 15 is a flowchart showing a control slot selection procedure based on control slot information and identification information. This corresponds to the processing in step 102 of FIG. The analysis unit 114 integrates the number of acquisitions in a certain period using the control slot information and the identification information as one combination (S150). If there is a combination in which the integrated value of the number of acquisitions is larger than the threshold for the number of times (Y in S152), the analysis unit 114 extracts the combination (S154). If there is a combination that is further than the distance threshold (Y in S156), the analysis unit 114 excludes the combination (S158). If there is no combination farther than the distance threshold (N in S156), step 158 is skipped. The estimation unit 116 identifies an empty slot (S160). On the other hand, if there is no combination in which the integrated value of the number of acquisitions is greater than the threshold for the number of times (N in S152), the processing from step 154 to 160 is skipped. The execution unit 120 selects a slot reflecting the carrier sense result (S162).

  FIG. 16 is a flowchart showing a procedure for notifying an empty slot in the local access control apparatus 10. The detection unit 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 signal 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. 17 is a flowchart illustrating a collision slot notification procedure in the local access control apparatus 10. The detector 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 signal generator 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. 18 is a flowchart illustrating a data transmission procedure in the terminal device 14. When the control information extraction unit 66 receives the control information (Y in S220), the slot determination unit 68 and the generation unit 64 transmit data based on the control information (S222). On the other hand, when the control information extraction unit 66 does not receive the control information (N in S220) and the wide area information extraction unit 72 receives the wide area information (Y in S224), the wide area information extraction unit 72 acquires the timing of the slot. (S226). The slot determination unit 68 and the generation unit 64 select a slot and transmit data (S228). When the wide area information extraction unit 72 does not receive the wide area information (N in S224), the slot determination unit 68 and the generation unit 64 execute data transmission by carrier sense (S230).

  FIG. 19 is a flowchart illustrating a data transmission procedure based on the control information in the terminal device 14. This corresponds to step 222 in FIG. 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 is not already specified (N in S72), the slot determining unit 68 specifies an empty slot (S78). The generation unit 64 transmits data while including the control slot information and the identification information in the specified slot (S80).

  Next, a modified example will be described. The modified example also relates to a communication system including a wide area access control device, a local access control device, and a terminal device, as in the embodiment. In the modification, the frame configuration and the signal arrangement of the OFDM signal are different from those in the embodiment. The frame is formed of a plurality of slots, but the frame includes a control slot and other slots, and does not include a wide area slot. Here, control information is transmitted in the control slot, and data is transmitted in other slots. On the other hand, control information and data do not use an identification carrier. Moreover, wide area information is arrange | positioned only at an identification carrier. That is, time division multiplexing is performed on the control information and data, and frequency division multiplexing is performed on the combination of the control information and data and the wide area information. The configurations of the communication system 100, the wide area access control device 16, the local access control device 10, and the terminal device 14 according to the modification are the same types as those in FIGS. 1 to 3, FIG. 4, FIG. 7, and FIG. Here, the difference will be mainly described.

  In the wide area access control device 16 in FIG. 4, the frame generation unit 160 generates a frame including a plurality of slots. Here, the frame generation unit 160 reserves a part of the plurality of slots included in the frame as a control slot, that is, for the OFDM signal from the local access control apparatus 10. The frame generation unit 160 reserves the remainder of the plurality of slots for the OFDM signal in communication between the terminal devices 14. Note that the OFDM signal from the local access control device 10 corresponds to a control signal, and the OFDM signal in communication between the terminal devices 14 corresponds to data. The same subcarrier is used for the control signal and data in the OFDM signal. More specifically, the control signal and data are configured as shown in FIG.

  FIG. 20 shows a frame format in the modification of the present invention. In FIG. 20, the frame includes M slots as in FIG. However, in FIG. 20, unlike FIG. 5B, the wide area 222 is not arranged at the beginning of the frame, but the control area 220 is arranged. The control area 220 includes, for example, five control slots. The remaining slots are used for communication between the terminal devices 14. Returning to FIG.

  The processing unit 156 generates wide area information as an OFDM signal as in the embodiment. Here, the processing unit 156 uses the remaining subcarriers that are not used in the control information and data in the OFDM signal for wide area information. Specifically, the processing unit 156 uses the identification carrier for wide area information. FIG. 21 shows an OFDM symbol format in the wide area information in the modification of the present invention. As shown, only the subcarrier numbers “1” and “−1” are used. The length of the wide area information is defined to fit the slot. Further, the length of the wide area information may be defined to fit a plurality of slots. Furthermore, the length of the wide area information may be defined so as not to be related to the length of the slot. Returning to FIG. The modem unit 154 and the RF unit 152 broadcast transmit the wide area information generated by the processing unit 156 from the antenna 150. The modem unit 154 and the RF unit 152 cause the local access control device 10 and the terminal device 14 to receive wide area information using the identification carrier.

  In the local access control device 10 in FIG. 7, the frame generation unit 34 receives wide area information arranged on the identification carrier from the wide area access control device 16 (not shown) via the RF unit 22 and the modem unit 24. Here, it can be said that the identification carrier is a remaining subcarrier that is not used in the OFDM signal in the control information and data. The signal generation unit 36 selects a control slot from the control area 220 and outputs control information in the selected control slot. Note that the content of the control information is the same as that in the embodiment, and thus the description thereof is omitted here. The signal generation unit 36 uses subcarriers other than the identification carrier in the OFDM signal, that is, subcarriers shown in FIG. 6B for control information.

  In the terminal device 14 in FIG. 8, the control information extraction unit 66 receives control information in subcarriers other than the identification carrier in the OFDM signal in the control region 220 of the plurality of slots included in the frame. . The wide area information extraction unit 72 receives wide area information on an identification carrier in the OFDM signal. When the control information extraction unit 66 can receive the control information, the slot determination unit 68 selects at least one of the available slots in the slots other than the control region 220 among the plurality of slots included in the frame. select.

  Next, another modification will be described. Similar to the communication system 100 in the embodiment, the communication system 100 in another modification includes a plurality of local access control devices 10. The analysis unit 114 of the local access control device 10 according to the embodiment identifies an empty control slot by accumulating the combinations, that is, by executing statistical processing. On the other hand, the analysis unit 114 in another modified example does not execute statistical processing. A communication system 100, a local access control device 10, and a terminal device 14 according to another modification are the same as those in FIGS. 1 to 3, FIG. 7, and FIG. Therefore, here, the difference will be mainly described.

  The analysis unit 114 sequentially acquires combinations of identification information and control slot information from the information acquisition unit 112. The analysis unit 114 derives position information from the identification information included in the combination. The analysis unit 114 stores in advance position information where the local access control device 10 is installed, and derives a distance between the two based on the position information of both. Furthermore, the analysis unit 114 stores a distance threshold value in advance, and compares the distance with the distance threshold value. The analysis unit 114 is a combination for the local access control device 10 having a distance larger than the distance threshold, that is, the local access installed at a position farther from the local access control device 10 than the distance threshold. Combinations for the control device 10 are excluded. The analysis unit 114 outputs the remaining combinations to the estimation unit 116.

  FIG. 22 is a flowchart showing a control slot selection procedure based on control slot information and identification information in another modification of the present invention. This corresponds to the processing in step 102 of FIG. The analysis unit 114 acquires the control slot information and the identification information as one combination (S180). If there is a combination that is further than the distance threshold (Y in S182), the analysis unit 114 excludes the combination (S184). If there is no combination farther than the distance threshold (N in S182), step 184 is skipped. The estimation unit 116 identifies an empty slot (S186). The execution unit 120 selects a slot reflecting the carrier sense result (S188).

  According to the embodiment of the present invention, since a slot usable for communication between a plurality of terminal devices is notified from among a plurality of slots, the probability of occurrence of a collision in communication between the plurality of 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 local access control device does not participate in the data communication between the terminal devices, but only notifies the index relating to 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. Further, since the local access control device does not participate in the data communication between the terminal devices, but only notifies the index regarding the collision slot, it can be easily applied to a communication system based on CSMA / CA.

  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, interference between control information from a plurality of local access control apparatuses can be reduced. Moreover, since interference can be 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. Further, since the contents of the control information are transmitted accurately, it is possible to accurately notify the empty slot information and the like. Moreover, since interference between a plurality of control information is reduced, a plurality of local access control devices can be installed. Also, since a plurality of local access control devices are installed, the packet signal collision probability at each intersection can be reduced. In addition, since a control slot that is not used by another local access control apparatus is estimated, interference between a plurality of pieces of control information can be reduced.

  Further, since the information and the identification information regarding the selected control slot are included in the control information, the information regarding the selected control slot and the identification information can be notified to the terminal device. In addition, since information regarding the selected control slot is included in the control information, any one of the plurality of control slots can be freely used. Further, since the control slot information and the identification information are received from the terminal device, it is possible to indirectly recognize the presence of the local access control device that cannot directly recognize the presence. Further, since the presence of the local access control device that cannot directly recognize the presence is indirectly recognized, the hidden terminal problem can be solved. Further, since the presence of the local access control device that cannot directly recognize the presence can be indirectly recognized, the accuracy of selection of the control slot can be improved. In addition, since the accuracy of control slot selection is improved, interference between a plurality of pieces of control information can be reduced.

  In addition, since statistical processing is performed on the combination of control slot information and identification information, the estimation accuracy of an empty control slot can be improved. In addition, since the local access control devices that are separated from each other are excluded from the objects of statistical processing, it is possible to increase the number of control slots that can be selected while suppressing deterioration in quality due to interference. Further, since the number of selectable control slots is increased, the degree of freedom in selecting control slots can be improved. In addition, since a control slot that is not used in a local access control device other than the local access control device that is far away is selected, interference between a plurality of pieces of control information can be reduced.

  In addition, since a frame including a plurality of slots is generated and wide area information about the generated frame is notified to the local access control device, a common frame can be used by the plurality of local access control devices. . In addition, since a plurality of local access control devices use a common frame, synchronization between the plurality of local access control devices can be easily established. In addition, since the synchronization between the plurality of local access control devices is established, the frame utilization efficiency can be improved. Further, since the terminal device that cannot receive the control information is caused to receive the wide area information and use at least one of the plurality of slots included in the frame, it is possible to reduce the transmission of a signal that spans the plurality of slots. . In addition, since the transmission of signals over a plurality of slots is reduced, the frame utilization efficiency can be improved. Moreover, since wide area information is alert | reported to the local access control apparatus and a terminal device, a common instruction | indication can be notified to the whole communication system. In addition, since a common instruction is notified to the entire communication system, the entire communication system can be stopped simultaneously. In addition, since the entire communication system is stopped all at once, even if a failure occurs, the influence on other systems can be reduced.

  Also, a part of a plurality of slots included in the frame is reserved for wide area information, at least one other slot is reserved for control information, and the rest is reserved for communication between terminal devices. Therefore, it is possible to accurately notify wide area information and control information. In addition, since a wide slot, a control slot, and other slots are secured separately, the purpose of information placed in the slot can be clarified. Further, since the purpose of the information arranged in the slot becomes clear, reception processing can be facilitated. Further, since the terminal device that cannot receive the control information is made to receive the wide area information in the wide area slot, the reception probability of the wide area information can be improved. In addition, since the reception probability can be improved, the slot configuration can be notified. Further, since the slot configuration is notified, the slot utilization efficiency can be improved.

  Also, some of the slots included in the frame are reserved for control information, the rest are reserved for data, and slots for wide area information are not reserved, so they are used for control information and data. The number of slots that are played can be increased. Moreover, since a subcarrier different from the subcarrier used for control information and data is used for wide area information, interference with wide area information can be reduced. Also, since the period of the wide area information can be set regardless of the slot length, the degree of freedom in setting the period of the wide area information can be improved. In addition, since the terminal device that cannot receive the control information is caused to receive the wide area information by the identification carrier, the reception probability of the wide area information can be improved.

  Further, since the frame is generated so as to be synchronized with the frame corresponding to the wide area information from the wide area access control device, the frame can be easily generated. In addition, when the wide area information is not received, the frame is generated autonomously based on the received signal from the GPS satellite, so that some frame can be generated. In addition, since the wide area slot, the control slot, and the data slot are separately defined, the reception probability of the wide area information can be improved. In addition, since the reception probability of the wide area information is improved, the probability that a frame synchronized with the frame corresponding to the wide area information is generated can be improved. In addition, since the wide area information is arranged on the identification carrier that is not used in the control information and data, the reception probability of the wide area information can be improved. Also, if the wide area information is transmitted a plurality of times per frame, the period until the wide area information is received can be shortened. If the period until the wide area information is received is shortened, the period until frame synchronization can be shortened.

  In addition, when wide area information and control information can be received, control information is used preferentially, so information such as empty slots can be used effectively. Even if the control information cannot be received, the slot information can be acquired because the wide area information is used if the wide area information can be received. In addition, since the slot timing is acquired, the frame can be used effectively. Further, when the wide area information and the control information are not received, carrier sense is executed, so that the influence on other devices can be reduced. In addition, since carrier sense is executed, data can be transmitted without acquiring slot timing.

  Further, since the wide area slot, the control slot, and the slot for data are separately defined, the reception probability of the wide area information or the control information can be improved. Further, since the reception probability of control information is improved, the probability of effectively using information such as empty slots can be improved. In addition, since the reception probability of the wide area information is improved, the probability of acquiring the slot timing can be improved. In addition, since the control slot and the data slot are separately defined and the wide area information is arranged on a subcarrier different from the subcarrier used for the control slot, the reception probability of the wide area information or the control information can be improved. . Moreover, since only wide area information uses an identification carrier, the influence by control information and data can be reduced.

  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 and the frame generator 34 generate a frame formed by a plurality of slots. However, the present invention is not limited to this. For example, the frame generation unit 160 and the frame generation unit 34 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 local access control apparatus 10 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, wide area information broadcast from the wide area access control device 16, control information broadcast from the local access control device 10, and data broadcast from one terminal device 14 are stored in one slot. Assigned to. However, the present invention is not limited to this. For example, wide area information, control information, and data may be allocated to two or more slots. According to this modification, the communication speed of wide area information, 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 identification information of the local access control device 10 is associated with the position information of the local access control device 10. However, the present invention is not limited to this. For example, the identification information may be given regardless of the position information. According to this modification, it is possible to improve the degree of freedom of giving identification information. That is, different identification information may be given to different local access control devices 10.

  In an embodiment of the present invention, wide area information and control information also use an identification carrier, and data does not use an identification carrier. However, the present invention is not limited to this. For example, only the wide area information may use the identification carrier, and the control information and data may not use the identification carrier. According to this modification, the reception probability of wide area information can be improved.

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 another 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 for wide areas of FIG. FIGS. 5A to 5D are diagrams illustrating a format of a frame generated in the frame generation unit of FIG. FIGS. 6A and 6B are diagrams showing the format of the OFDM symbol used in the communication systems of FIGS. It is a figure which shows the structure of the local access control apparatus of FIGS. 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 FIGS. It is a figure which shows another operation | movement outline | summary of the communication system of FIGS. It is a figure which shows another operation | movement outline | summary of the communication system of FIGS. It is a flowchart which shows the production | generation procedure of the frame in the local access control apparatus of FIG. It is a flowchart which shows the selection procedure of the control slot in the local access control apparatus of FIG. It is a flowchart which shows the selection procedure of the control slot by the carrier sense of FIG. It is a flowchart which shows the selection procedure of the control slot by the control slot information and identification information of FIG. It is a flowchart which shows the notification procedure of the empty slot in the local access control apparatus of FIG. It is a flowchart which shows the notification procedure of the collision slot in the local access control apparatus of FIG. It is a flowchart which shows the transmission procedure of the data in the terminal device of FIG. It is a flowchart which shows the transmission procedure of the data based on the control information in the terminal device of FIG. It is a figure which shows the format of the flame | frame in the modification of this invention. It is a figure which shows the format of the OFDM symbol in the wide area information in the modification of this invention. It is a flowchart which shows the selection procedure of the control slot by the control slot information and identification information in another modification of this invention.

Explanation of symbols

  10 local access control device, 14 terminal device, 16 wide area access control device, 20 antenna, 22 RF unit, 24 modem unit, 26 processing unit, 28 GPS positioning unit, 30 control unit, 32 detection unit, 34 frame generation unit , 36 signal generation unit, 38 power measurement unit, 40 quality measurement unit, 42 empty slot identification unit, 44 collision slot identification unit, 50 antenna, 52 RF unit, 54 modulation / demodulation unit, 56 processing unit, 58 control unit, 60 timing identification Unit, 62 acquisition unit, 64 generation unit, 66 control information extraction unit, 68 slot determination unit, 70 notification unit, 72 wide area information extraction unit, 100 communication system, 110 selection unit, 112 information acquisition unit, 114 analysis unit, 116 estimation Part, 118 carrier sense part, 120 real Department, 150 antenna, 152 RF unit 154 modem unit, 156 processing unit, 158 GPS positioning unit, 160 frame generation unit, 162 controller.

Claims (6)

A generating unit that generates a frame including at least a plurality of slots;
A notification unit that notifies the local access control device of the first information related to the frame generated in the generation unit;
The notification unit causes the local access control device that has notified the first information to detect a slot that can be used for communication between wireless devices from among a plurality of slots included in the frame, and relates to the detected slot A wide area access control apparatus characterized by notifying second information.   The notification unit causes a wireless device that cannot receive the second information from the local access control device to receive the first information and use at least one of a plurality of slots included in the frame. The wide area access control apparatus according to claim 1. A receiving unit that receives first information about a frame including at least a plurality of slots from the wide area access control device;
A generating unit that generates a frame including at least a plurality of slots so as to be synchronized with a frame corresponding to the first information received in the receiving unit;
A detecting unit for detecting a slot usable for communication between wireless devices from a plurality of slots included in the frame generated by the generating unit;
An informing unit for informing the second information about the slot detected in the detecting unit;
A local access control device comprising:   The local access control apparatus according to claim 3, wherein the generation unit generates the frame autonomously when the reception unit does not accept the first information. Generating a frame including at least a plurality of slots;
Notifying the first information on the generated frame to the local access control device,
The notifying step causes the local access control device that has notified the first information to detect a slot that can be used for communication between wireless devices from among a plurality of slots included in the frame, and detects the detected slot The notification method characterized by making 2nd information regarding be notified. Receiving first information on a frame including at least a plurality of slots from a wide area access control device;
Generating a frame including at least a plurality of slots so as to synchronize with a frame corresponding to the received first information;
Detecting a slot usable for communication between wireless devices from a plurality of slots included in the generated frame;
Informing the second information about the detected slot;
A notification method comprising:

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