JP5253112B2 - Notification method and radio apparatus - Google Patents

Description

  The present invention relates to a notification technique, and more particularly, to a notification method and a wireless device that notify a signal including predetermined information.

Road-to-vehicle communication is being studied to prevent collisions at intersections. In the road-to-vehicle communication, information on the situation of the intersection is communicated between the roadside device and the vehicle-mounted device. Road-to-vehicle communication requires the installation of roadside equipment, which increases labor and cost. On the other hand, if it is the form which communicates information between vehicle-to-vehicle communication, ie, onboard equipment, installation of a roadside machine will become unnecessary. In that case, for example, the current position information is detected in real time by GPS (Global Positioning System), etc., and the position information is exchanged between the vehicle-mounted devices so that the own vehicle and the other vehicle enter the intersection respectively. (See, for example, Patent Document 1).
JP 2005-202913 A

  In a wireless LAN (Local Area Network) compliant with a standard such as IEEE 802.11, an access control function called CSMA / CA (Carrier Sense Multiple Access Collision Aviation) is used. Therefore, in the wireless LAN, the same wireless channel is shared by a plurality of terminal devices. In such CSMA / CA, due to the distance between terminal devices and the influence of obstacles that attenuate radio waves, a situation occurs in which radio signals do not reach each other, that is, a situation where carrier sense does not function. When carrier sense does not function, packet signals transmitted from a plurality of terminal devices collide. In order to increase the communication speed, an OFDM modulation scheme is used in the wireless LAN.

  On the other hand, when a wireless LAN is applied to vehicle-to-vehicle communication, it is necessary to transmit information to an unspecified number of terminal devices. However, at intersections and the like, an increase in the number of vehicles, that is, an increase in the number of terminal devices, is expected to increase packet signal collisions. As a result, data included in the packet signal is not transmitted to other terminal devices. If such a situation occurs in vehicle-to-vehicle communication, the purpose of preventing a collision accident at the intersection encounter will not be achieved.

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

  In order to solve the above problems, a wireless device according to an aspect of the present invention includes an accepting unit that receives information about a frame including at least a plurality of slots from an access control device for controlling communication between wireless devices; A generation unit that generates a frame including at least a plurality of slots so as to be synchronized with a frame corresponding to information received in the reception unit, and at least one of the plurality of slots included in the frame generated in the generation unit And a notification unit for reporting data in the slot selected by the selection unit. The selection unit selects a slot having the same relative timing in the frame over a predetermined number of frames, and selects at least one slot again after the predetermined number of frames are completed.

  Another aspect of the present invention is a notification method. The method includes a step of receiving information on a frame including at least a plurality of slots from an access control device for controlling communication between wireless devices, and a plurality of frames so as to synchronize with a frame corresponding to the received information. Generating a frame including at least a slot; selecting at least one of a plurality of slots included in the generated frame; and notifying data in the selected slot. The selecting step selects a slot having the same relative timing within the frame over a predetermined number of frames, and selects at least one slot again after the predetermined number of frames.

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

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

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a communication system that performs data communication between terminal devices mounted on a vehicle. The terminal device broadcasts a packet signal that stores information such as the speed and position of the vehicle (hereinafter referred to as “data”). Further, the other terminal device receives the packet signal and recognizes the approach of the vehicle based on the data. Here, the terminal apparatus employs the OFDM modulation scheme for the purpose of increasing the communication speed. Under such circumstances, when the number of terminal devices increases at an intersection or the like, the generation probability of a packet signal increases. In order to cope with this, the communication system according to the present embodiment executes the following processing.

  The communication system according to the present embodiment includes an access control device in addition to a plurality of terminal devices, and the access control device is installed at an intersection, for example. The access control apparatus repeatedly defines a frame including a plurality of slots. Note that some of the plurality of slots included in each frame are reserved as control slots. In addition, the access control device specifies a control slot to be used, and includes information on the timing of the control slot and information for identifying the access control device (hereinafter referred to as “identification information”) in the control information. Further, the access control apparatus broadcasts a packet signal storing control information (hereinafter also referred to as “control information”) in the control slot. Here, the information on the timing of the control slot is, for example, information on how many times the control slot is arranged from the head of the frame (hereinafter referred to as “control slot information”).

  The terminal device generates a frame corresponding to the control information by receiving the control information. The generated frame also includes a plurality of slots. Further, the terminal device recognizes a slot other than the control slot among the plurality of slots included in the frame. In the following description of the terminal device, a slot may indicate a slot excluding a control slot. The terminal device selects one slot to be used for transmitting data by performing carrier sense for each of the plurality of slots. In the selected slot, the terminal device broadcasts a packet signal storing data (hereinafter also referred to as “data”). Also, the terminal device uses slots having the same relative timing in each frame over a predetermined number of frames. After a predetermined number of frames have elapsed, the terminal device performs the above-described carrier sense again and repeatedly executes the above-described processing.

  As described above, when a predetermined number of frames have elapsed, the slot is changed, so that occurrence of a situation in which data from a plurality of terminal devices continues to collide with each other is reduced. Here, the access control apparatus does not directly participate in data communication between terminal apparatuses, and does not directly specify a slot to be used for data communication. The access control device merely notifies the configuration of a frame including a slot to be used by a plurality of terminal devices. The terminal device performs data communication at the timing of the slot included in the notified frame. That is, the access control device controls communication between a plurality of terminal devices.

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

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

  FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. This corresponds to a case where one intersection is viewed from above. The communication system 100 includes a first vehicle 12a, a second vehicle 12b, a third vehicle 12c, a fourth vehicle 12d, a fifth vehicle 12e, a sixth vehicle 12f, and a seventh vehicle 12g, which are collectively referred to as the access control device 10 and the vehicle 12. The 8th vehicle 12h is included. Each vehicle 12 is equipped with a terminal device (not shown). Further, an area 200 is formed by the access control device 10.

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

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

  Therefore, the communication system 100 arranges the access control device 10 at the intersection. The access control device 10 generates a frame including a plurality of slots so as to be repeated based on a signal received from a GPS satellite (not shown). Here, a part of the plurality of slots corresponds to a control slot. The access control device 10 includes control slot information and identification information in the control information. Furthermore, the access control apparatus 10 broadcasts control information in the control slot. The selection of the control slot will be described later.

  The plurality of terminal apparatuses receive the control information notified by the access control apparatus 10 and generate a frame based on the control information. As a result, the frame generated in each of the plurality of terminal devices is synchronized with the frame generated in the access control device 10. As a result, the slots generated in each of the plurality of terminal devices are synchronized with each other. The terminal device performs carrier sense in each of the plurality of slots and selects one slot. 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 predetermined number 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. After a predetermined number of frames have elapsed, the terminal device executes the above-described process again. In addition, even if it is a case where control information is not received, a terminal device may alert | report data. The terminal device that has received data from another terminal device recognizes the presence of the vehicle 12 on which the other terminal device is mounted based on the data.

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

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

  The frame generation unit 160 acquires time information from the GPS positioning unit 158. The frame generation unit 160 generates a plurality of frames based on the time information. For example, the frame generation unit 160 generates 10 frames of “100 msec” by dividing the period of “1 sec” into 10 with reference to the timing of “0 msec”. By repeating such processing, the frame is defined to be repeated. The frame generation unit 160 generates a plurality of slots by dividing each frame into a plurality of frames. For example, by dividing each frame into 200, 200 “500 μsec” slots are generated.

  Here, some of the plurality of slots included in the frame are reserved as “control slots”. For example, among the 200 slots included in one frame, the first five slots are set as control slots. The control slot is a slot used for the access control apparatus 10 to broadcast control information. Further, the remainder of the plurality of slots included in the frame is secured for communication between terminal devices (not shown). As described above, since the communication system 100 adopts the OFDM modulation scheme, each slot is defined to be composed of a plurality of OFDM symbols. The OFDM symbol is composed of a guard interval (GI) and a valid symbol. A guard time may be provided in the front part or the rear part of each slot. Here, a group of a plurality of OFDM symbols included in the slot corresponds to the aforementioned packet signal.

  FIGS. 3A to 3D show the format of a frame generated by the frame generation unit 160. FIG. FIG. 3A shows the structure of the frame. As shown in the figure, it is defined that a plurality of frames are repeated such as the i-th frame to the (i + 2) -th frame. The period of each frame is “100 msec”, for example. FIG. 3B shows the configuration of one frame. As shown in the figure, one frame is composed of M slots. For example, M is “200”, and the period of each slot is “500 μsec”. A slot arranged at the head portion of the frame corresponds to a control slot, and a section where the control slot is arranged is shown as a control area 220.

  Here, five slots from the first slot to the fifth slot are included in the control area 220 as control slots. FIG. 3C shows the configuration of one slot. As shown in the figure, guard times are provided at the front portion and the rear portion of the slot. The remaining period of the slot is composed of N OFDM symbols. FIG. 3D shows the configuration of one OFDM symbol. As shown in the figure, one OFDM symbol is composed of a GI and an effective symbol. Returning to FIG.

  As reception processing, the RF unit 152 receives, in each slot, a packet signal transmitted in communication between other terminal devices (not shown) by the antenna 150. Here, the transmission source of the packet signal is, for example, a terminal device. The RF unit 152 performs frequency conversion on a radio frequency packet signal received via the antenna 150 to generate a baseband packet signal. Further, the RF unit 152 outputs a baseband packet signal to the modem unit 154. In general, baseband packet signals are formed by in-phase and quadrature components, so two signal lines should be shown, but here only one signal line is shown for clarity. Shall be shown.

  The RF unit 152 also includes an LNA (Low Noise Amplifier), a mixer, an AGC, and an A / D conversion unit. As a transmission process, the RF unit 152 performs frequency conversion on the baseband packet signal input from the modem unit 154 in each slot to generate a radio frequency packet signal. Further, the RF unit 152 transmits a radio frequency packet signal from the antenna 150. The RF unit 152 also includes a PA (Power Amplifier), a mixer, and a D / A conversion unit.

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

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

  The processing unit 156 generates control slot information regarding the selected control slot. Further, the processing unit 156 generates control information while including control slot information and identification information. The processing unit 156 assigns control information to the selected control slot. The processing unit 156 outputs control information to the modem unit 154 in the assigned control slot. Note that broadcasting the control information in the control slot determined in the communication system 100 corresponds to notifying the timing of the control slot in the frame. Further, since the relative position of the control slot in the frame is included in the control slot information, the above also corresponds to notifying the timing of the frame.

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

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

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

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

  The modem unit 154 and the RF unit 152 broadcast the control information generated by the processing unit 156 from the antenna 150 in the control slot. One of the destinations of the control information is a terminal device. The terminal device that has received the control information recognizes the timing of each slot, and uses at least one of the remaining slots reserved for communication between the terminal devices. The control unit 162 controls processing of the access control apparatus 10 as a whole.

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

  FIG. 5 shows a configuration of the terminal device 14 mounted on the vehicle 12. The terminal device 14 includes an antenna 50, an RF unit 52, a modem unit 54, a processing unit 56, and a control unit 58. The processing unit 56 includes a timing specifying unit 60, an acquiring unit 62, a generating unit 64, and a notification unit 70. The timing specifying unit 60 includes a control information extracting unit 66, a slot determining unit 68, a counter 80, and a carrier sense unit 82. including. The antenna 50, the RF unit 52, and the modem unit 54 perform the same processing as the antenna 150, the RF unit 152, and the modem unit 154 in FIG. Therefore, these descriptions are omitted here.

  The acquisition unit 62 includes a GPS receiver (not shown), a gyroscope, a vehicle speed sensor, and the like. Based on data supplied from the GPS receiver, a vehicle 12 (not shown), that is, a vehicle 12 on which the terminal device 14 is mounted, Get direction, speed, etc. The existence position is indicated by latitude and longitude. Since a known technique may be used for these acquisitions, description thereof is omitted here. The acquisition unit 62 outputs the acquired information to the generation unit 64.

  The control information extraction unit 66 receives the demodulation result from the modem unit 54. Further, the control information extraction unit 66 monitors the subcarrier portion corresponding to the identification carrier in the demodulation result. When valid data is included in the subcarrier portion corresponding to the identification carrier, the control information extraction unit 66 recognizes that the slot including the control information, that is, the control slot is received. Further, the control information extraction unit 66 establishes frame and slot synchronization with reference to the timing at which the slot including the control information is received.

  More specifically, the control information extraction unit 66 identifies a control slot in which the received demodulation result is arranged based on the control slot information included in the control information, and generates a frame based on this control slot. If the control slot information corresponds to the third slot in FIG. 3B, the control information extraction unit 66 generates a frame with reference to the third slot. That is, the control information extraction unit 66 generates a frame with a plurality of slots so as to synchronize with the frame corresponding to the control slot information. The control information extraction unit 66 outputs information regarding the generated frame to the slot determination unit 68.

  The carrier sense unit 82 performs carrier sense for each of the slots other than the control slot among the plurality of slots included in the frame generated by the control information extraction unit 66. That is, the carrier sense unit 82 measures the interference power for each slot. The carrier sense unit 82 outputs the result of carrier sense, that is, the interference power for each slot, to the slot determination unit 68.

  The slot determination unit 68 selects one of a plurality of slots included in the frame generated by the control information extraction unit 66. Specifically, the slot determination unit 68 selects one slot based on the interference power from the carrier sense unit 82. For example, the slot determination unit 68 selects a slot having the lowest interference power. The slot determination unit 68 outputs information regarding the selected slot to the generation unit 64.

  The generation unit 64 receives information from the acquisition unit 62. The generation unit 64 generates data based on information from the acquisition unit 62. Here, the data is formed as shown in FIG. The generation unit 64 also receives information on the selected slot from the slot determination unit 68 and outputs data to the modem unit 54 in the slot corresponding to the information. As a result, the modem unit 54, the RF unit 52, and the antenna 50 broadcast data in the slot selected by the slot determination unit 68.

  The counter 80 causes the counter value to be added for each frame starting from the timing at which the slot is selected by the slot determination unit 68. That is, the counter 80 derives the number of frames from the timing when the slot is selected by the slot determination unit 68. The counter 80 outputs the counter value to the slot determination unit 68. Note that the counter 80 resets the counter value every time a new slot is selected by the slot determination unit 68. As described above, the slot determination unit 68 receives a counter value from the counter 80 after selecting a slot. Here, the slot determination unit 68 predefines a threshold value for the counter value. Until the counter value from the counter 80 becomes larger than the threshold value, the slot determination unit 68 continues to select the same slot.

  When the counter value from the counter 80 becomes larger than the threshold value, the slot determination unit 68 repeatedly executes the above-described processing to select a new slot. That is, the slot determination unit 68 selects slots having the same relative timing within the frame over a predetermined number of frames, and selects the slot again after the predetermined number of frames are completed. 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. 6 shows an operation outline of the communication system 100. The horizontal direction in the drawing corresponds to time, and the first access control device 10a to the third access control device 10c are shown in the vertical direction in the drawing. FIG. 6 shows only the control area 220 in FIG. As described above, here, it is assumed that five control slots are arranged in the control area 220. “Control” in the figure corresponds to control information. The first access control device 10a uses the first control slot, the second access control device 10b uses the fifth control slot, and the third access control device 10c uses the third control slot. As a result, interference between control information broadcast from each access control apparatus 10 is reduced.

  FIG. 7 is a flowchart illustrating a data notification procedure performed by the terminal device 14. The control information extraction unit 66 generates a frame based on the control information (S10). The slot determination unit 68 selects a slot based on the carrier sense result (S12). The counter sets the counter value i to 1 (S14). The generating unit 64, the modem unit 54, the RF unit 52, and the antenna 50 broadcast data in the selected slot (S16). If there is data to be notified (Y in S18), the counter 80 adds 1 to the counter value i (S20). If i is not larger than the threshold value N (N in S22), the process returns to step 16. On the other hand, if i is larger than the threshold value N (Y in S22), the process returns to step 12. If there is no data to be notified (N in S18), the process is terminated.

  Next, a modified example of the present invention will be described. Similar to the embodiment, the modified example is a communication system 100 including an access control device 10 and a terminal device 14, and the terminal device 14 generates a frame based on a control signal from the access control device 10, Select one of the slots. The terminal device 14 uses slots having relatively the same timing in the frame over a predetermined number of frames. In the embodiment, it is assumed that a predetermined number of frames have a predetermined fixed value. On the other hand, the terminal device 14 according to the modification randomly determines a predetermined number of frames. The communication system 100, the access control device 10, and the terminal device 14 according to the modification are the same types as those in FIGS. 1, 2, and 5, respectively. Here, the difference will be mainly described.

  FIG. 8 shows a configuration of the timing specifying unit 60 according to a modification of the present invention. The timing identification unit 60 includes a control information extraction unit 66, a slot determination unit 68, a counter 80, a carrier sense unit 82, a random number generation unit 84, and a usage period determination unit 86. The control information extraction unit 66, the counter 80, and the carrier sense unit 82 are the same as those in FIG. The random number generation unit 84 generates a random number at the timing when the slot is selected by the slot determination unit 68, that is, the timing when the counter 80 is reset. Since a known technique may be used to generate the random number, description thereof is omitted here. The random number generation unit 84 outputs the generated random number to the usage period determination unit 86.

  The usage period determination unit 86 receives a random number from the random number generation unit 84. The use period determining unit 86 determines a period in which the same slot should be used based on the random number. This corresponds to determining the threshold value in the slot determining unit 68. For example, the use period determining unit 86 uses the value of the random number as a threshold value as it is. Further, a table in which the random number value and the threshold value are associated with each other is stored in advance, and the use period determining unit 86 determines the threshold value based on the random number value while referring to the table. The usage period determining unit 86 outputs the threshold value to the slot determining unit 68. Slot determination unit 68 receives a threshold value from usage period determination unit 86. The slot determination unit 68 executes the above-described processing while using the received threshold value. That is, the slot determination unit 68 adjusts the number of frames for selecting slots having the same relative timing within the frame so as to be random.

  Next, another modification of the present invention will be described. Similarly to the modified example, the terminal device 14 according to another modified example sets the number of frames that use slots having relatively the same timing in the frame as a variable value. The terminal device 14 in the modified example randomly determines the number of frames. On the other hand, the terminal device 14 according to another modified example determines the number of frames based on the moving speed of the vehicle 12 on which the terminal device 14 is mounted. The communication system 100, the access control device 10, and the terminal device 14 according to another modification are the same types as those in FIGS. 1, 2, and 5, respectively. Here, the difference will be mainly described.

  FIG. 9 shows a configuration of a timing specifying unit 60 according to another modification of the present invention. The timing identification unit 60 includes a control information extraction unit 66, a slot determination unit 68, a counter 80, a carrier sense unit 82, a usage period determination unit 86, and a moving speed acquisition unit 88. The control information extraction unit 66, the counter 80, and the carrier sense unit 82 are the same as in FIG. 5, and the slot determination unit 68 is the same as in FIG. The moving speed acquisition unit 88 acquires information related to the moving speed of the vehicle 12 on which the terminal device 14 is mounted. The moving speed acquisition unit 88 is configured by a known speed sensor, for example. Moreover, the moving speed acquisition part 88 may acquire a moving speed from the change rate of the positional information acquired by GPS etc. The movement speed acquisition unit 88 outputs the movement speed to the use period determination unit 86.

  The use period determination unit 86 receives the movement speed from the movement speed acquisition unit 88. The use period determining unit 86 determines a period during which the same slot should be used based on the moving speed. This corresponds to determining the threshold value in the slot determining unit 68. For example, the use period determining unit 86 stores a table in which the moving speed and the threshold are associated with each other in advance, and the using period determining unit 86 determines the threshold based on the moving speed while referring to the table. Here, it is specified that the threshold value decreases as the moving speed decreases. In other words, the lower the moving speed, the shorter the number of frames for selecting slots with the same relative timing within the frame. The usage period determining unit 86 outputs the threshold value to the slot determining unit 68.

  Next, still another modification of the present invention will be described. Further, the terminal device 14 according to another modification example sets the number of frames that use slots having relatively the same timing in a frame as a variable value, similarly to the modification examples and the other modification examples. The terminal device 14 in the modified example or another modified example randomly determines the number of frames or determines the number of frames according to the moving speed. On the other hand, the terminal device 14 according to yet another modification uses information regarding the number of frames included in the control information. Further, the communication system 100, the access control device 10, and the terminal device 14 according to another modification are the same types as those in FIGS. 1, 2, and 5, respectively. Here, the difference will be mainly described.

  FIG. 10 shows a configuration of a timing specifying unit 60 according to still another modification of the present invention. The timing specifying unit 60 includes a control information extracting unit 66, a slot determining unit 68, a counter 80, a carrier sense unit 82, and a usage period determining unit 86. The counter 80 and the carrier sense unit 82 are the same as those in FIG. 5, and the slot determination unit 68 is the same as that in FIG.

  As described above, the control information extraction unit 66 receives a control signal from the access control device 10 (not shown). The control signal includes information on the number of frames for which slots with the same relative timing within the frame should be selected. Such information is set by the access control device 10. The control information extraction unit 66 extracts information on the number of frames from the control information. The control information extraction unit 66 outputs information regarding the number of frames to the slot determination unit 68. The usage period determination unit 86 receives information on the number of frames from the control information extraction unit 66. Here, when the information regarding the number of frames is indicated as the threshold value, the use period determining unit 86 determines the threshold value based on the received information. The usage period determining unit 86 outputs the threshold value to the slot determining unit 68.

  According to the embodiment of the present invention, data is reported in the slot generated according to the control information from the access control device, so that synchronization between a plurality of terminal devices can be established. In addition, since synchronization between a plurality of terminal devices is established, the data collision probability can be reduced. Since the data is notified at the slot timing, it is possible to reduce the occurrence of a situation in which a part of a plurality of data overlaps and collides. Further, since data is notified at the slot timing, the frame utilization efficiency can be reduced. In addition, since a new slot is selected when a predetermined number of frames have elapsed, the occurrence of a situation where data continues to collide can be reduced. In addition, since the occurrence of a situation where data continues to collide is reduced, the collision probability of packet signals can be reduced even when the amount of communication increases.

  Since slots having the same timing are used over a predetermined number of frames, an effective slot can be selected by carrier sense. In addition, since the selection and switching of the slot are executed in the terminal device, the access control device only notifies the timing of the frame, and the processing can be simplified. Further, since the predetermined number is a fixed value, the processing can be simplified. Further, since the predetermined number is determined at random, the collision probability can be reduced. Further, since the predetermined number is determined according to the moving speed, it is possible to determine the slot switching according to the moving speed. Further, when the moving speed is lowered, the predetermined number is reduced, so that the possibility that the slots continuously collide can be reduced.

  Also, among the control information, the identification carrier is not used for data, and the remaining subcarriers are also used for data, so that even if the control information collides with the data signal, the signal component of the control information is observed. Thus, the presence of the control information can be detected. In addition, since a guard band is provided between the identification carrier and other subcarriers, interference between the two can be reduced, and the arrival probability of information transmitted on the identification carrier can be improved. Moreover, since important information is arranged on the identification carrier, the arrival probability of important information can be improved. Moreover, since UW is arrange | positioned at an identification carrier, the detection accuracy of an identification carrier can be improved.

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

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

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

  In the embodiment of the present invention, control information notified from the access control device and data notified from one terminal device 14 are allocated to one slot. However, the present invention is not limited to this. For example, control information and data may be assigned to two or more slots. According to this modification, the communication speed of control information and data can be improved.

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

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the access control apparatus of FIG. FIGS. 3A to 3D are diagrams illustrating a format of a frame generated by the frame generation unit of FIG. FIGS. 4A to 4B are diagrams showing the format of the OFDM symbol used in the communication system of FIG. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. It is a figure which shows the operation | movement outline | summary of the communication system of FIG. It is a flowchart which shows the alerting | reporting procedure of the data by the terminal device of FIG. It is a figure which shows the structure of the timing specific part which concerns on the modification of this invention. It is a figure which shows the structure of the timing specific | specification part which concerns on another modification of this invention. It is a figure which shows the structure of the timing specific | specification part which concerns on another modification of this invention.

Explanation of symbols

  10 access control device, 14 terminal device, 50 antenna, 52 RF unit, 54 modem 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, 80 counter, 82 carrier sense unit, 100 communication system, 150 antenna, 152 RF unit, 154 modulation / demodulation unit, 156 processing unit, 158 GPS positioning unit, 160 frame generation unit, 162 control unit.

Claims (4)

A receiving unit for receiving information on a frame including at least a plurality of slots from an access control device for controlling communication between wireless devices;
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 information received in the receiving unit;
A selection unit that selects at least one of a plurality of slots included in the frame generated by the generation unit;
A notification unit for reporting data in the slot selected by the selection unit;
The accepting unit also accepts information on the number of frames from which the slots having the same relative timing in the frame should be selected from the access control device,
The selection unit determines the number of frames to select slots having the same relative timing within the frame based on the information on the number of frames received by the reception unit, and includes the frame within the predetermined number of frames. A wireless device, wherein slots having the same relative timing are selected and at least one slot is selected again after completion of the predetermined number of frames.   The radio apparatus according to claim 1, wherein the selection unit randomly determines the number of frames to select slots having the same relative timing within a frame. An acquisition unit for acquiring information related to the moving speed of the wireless device;
The radio apparatus according to claim 1, wherein the selection unit determines the number of frames in which slots having the same relative timing within a frame are to be selected according to the moving speed acquired by the acquisition unit. . Receiving information on a frame including at least a plurality of slots from an access control device for controlling communication between wireless devices;
Generating a frame including at least a plurality of slots so as to be synchronized with a frame corresponding to the received information;
Selecting at least one of a plurality of slots included in the generated frame;
And informing the data in the selected slot,
The step of accepting also accepts information on the number of frames from the access control device that should select slots having the same relative timing within the frame,
The selecting step determines the number of frames to select slots having the same relative timing in the frame based on the information on the received number of frames , and determines the relative number in the frame over the predetermined number of frames. A notification method, wherein slots having the same timing are selected and at least one slot is selected again after completion of the predetermined number of frames.

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