JP2010130565A - Informing method, and wireless device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a packet signal collision probability even when a communication quantity is increased. <P>SOLUTION: A control information extractor 66 accepts information on a frame including at least a plurality of slots from an access controller for controlling communication between wireless devices. The control information extractor 66 generates a frame including at least a plurality of slots so as to synchronize with the frame associated with the accepted information. A slot determiner 68 selects at least one of the plurality of slots included in the generated frame. A setter 82 sets a start timing of data notification in the selected slot. A modulator/demodulator 54 or the like notifies the data at the set timing. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 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 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 In the slot selected by the selection unit, a setting unit that sets a timing at which data notification should be started, and a notification unit that notifies data from the timing set by the setting unit.

  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. A step of generating a frame including at least a slot, a step of selecting at least one of a plurality of slots included in the generated frame, and a timing for starting data broadcasting in the selected slot are set. And a step of notifying data from the set timing.

  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”). At that time, the terminal device variably sets a period from the head of the selected slot to the broadcast transmission start timing (hereinafter referred to as “back-off period”). Further, the terminal apparatus performs carrier sense in the back-off period, and starts broadcast transmission if there is no interference signal.

  As described above, even in the slot, since the carrier sense is executed with the back-off period being variably set, the probability that data between a plurality of terminal apparatuses 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 an access control device 10, a first vehicle 12a, a second vehicle 12b, a third vehicle 12c, a fourth vehicle 12d, a fifth vehicle 12e, a sixth vehicle 12f, and a seventh vehicle 12g. 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 center. 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. Further, the terminal device determines a back-off period in the selected slot. For example, the back-off period is determined randomly. The terminal device performs carrier sense during the back-off period.

  As a result of carrier sense, if the interference power is lower than the threshold value, the terminal device broadcasts data after the back-off period ends. Note that the data length is defined so as to fit in the slot even in consideration of the back-off period. On the other hand, if the interference power is equal to or greater than the threshold value as a result of the carrier sense, the terminal device selects another slot again after the next frame and repeats the above-described processing. 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 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 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. 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.

  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 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 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 notifying unit 70. The timing specifying unit 60 includes a control information extracting unit 66, a slot determining unit 68, a carrier sense unit 80, and a setting unit. 82. 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 these, the location of the vehicle 12 (not shown), that is, the position of the vehicle 12 on which the terminal device 14 is mounted, the progress 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 80 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 80 measures the interference power for each slot. Carrier sense unit 80 outputs the result of carrier sense, that is, the interference power for each slot, to 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 80. 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 setting unit 82 specifies the slot to be transmitted based on the information from the slot determination unit 68. In addition, the setting unit 82 sets a timing (hereinafter referred to as “start timing”) at which data notification should be started in the specified slot. As shown in FIG. 3C, one slot is formed by a combination of a plurality of symbols. The setting unit 82 determines the timing shifted in symbol units as the start timing. Specifically, the setting unit 82 sets one of timings such as the first symbol, the second symbol,... As the start timing. That is, the start timing is defined as a value shifted in symbol units. Note that the guard time shown in FIG. 3C only needs to be arranged before the first symbol, but the guard time is omitted in the following description.

  6A to 6E show an outline of the start timing set in the setting unit 82. FIG. These correspond to the configuration of one slot, but the guard time is omitted. FIG. 6A shows a case where the start timing is set to the first symbol “t0”, and FIGS. 6B to 6E show the fifth symbol from the second symbol “t1” with the start timing. This is a case where each is set to “t4”. Further, as shown in these figures, the length of data is defined so that data transmission ends within the slot regardless of the start timing. Returning to FIG.

  Further, the period from the beginning of the slot to the start timing corresponds to the aforementioned back-off period. The detection unit 32 selects one from a plurality of start timings. For example, the setting unit 82 randomly selects the start timing for each arbitrary frame so as to select each start timing with a uniform probability. Note that the detection unit 32 may hold information related to the priority of the terminal device 14. Here, whether the vehicle is mounted on an emergency vehicle such as an ambulance is specified as the priority, and a higher priority is given to the emergency vehicle. The setting unit 82 shortens the back-off period for the higher priority. In other words, the higher priority uses the start timing closer to the beginning of the packet.

  Specifically, the start timing “t0” is assigned to the case where the vehicle is mounted on an emergency vehicle, and the start timing after the start timing “t1” is assigned to the case where the vehicle is mounted on another vehicle. It has been. Three or more priorities may be defined. At this time, a regulation is made such that the higher the priority, the shorter the back-off period. Here, the carrier sense unit 80 performs carrier sense over the back-off period. Carrier sense unit 80 outputs interference power during the back-off period to setting unit 82. If the interference power is smaller than the threshold value, the setting unit 82 notifies the generation unit 64 of the start timing. On the other hand, if the interference power is equal to or greater than the threshold value, setting unit 82 stops notification of the start timing to generation unit 64 and instructs slot determination unit 68 to select a new slot. The slot determination unit 68 selects a new slot by repeating the above-described processing after the next frame.

  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 start timing in the slot selected by the slot determination unit 68 from the setting unit 82 and outputs data to the modem unit 54 at the start timing corresponding to the information. As a result, the modem unit 54, the RF unit 52, and the antenna 50 notify the data at the start timing set in the setting unit 82.

  If data to be transmitted remains after the data is notified, the setting unit 82 sets the start timing in the same slot as that already used in the subsequent frames. Here, the same slot corresponds to a slot having the same relative timing in the frame. As described above, the setting unit 82 randomly selects a start timing for each arbitrary frame. 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. 7 shows an outline of the operation 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. 7 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. 8 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 (S100). The slot determination unit 68 selects a slot (S102). The setting unit 82 sets the start timing (S104). Here, the same value is held for an arbitrary frame as the start timing. The arbitrary number of frames is, for example, “1” or “2” or more. If the data cannot be notified as a result of the carrier sense (N in S106), the process returns to step 102. If the data can be notified (Y in S106), the modem 54 and the like notify the data (S108). If there is data to be notified (Y of S110), the process returns to step 104. If there is no data to be notified (N of S110), the process is terminated.

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

  The access control apparatus also includes information on the specified empty slot and collision slot in the control information. The terminal device 14 selects one of the empty slots based on the control information, and broadcasts data in the selected slot. At that time, the above-described start timing is set. Based on the control information, the terminal device 14 confirms whether or not a collision has occurred in the already used slot. If a collision has occurred, the terminal device 14 selects one of the other empty slots based on the control information. In the above description, the terminal device 14 sets the start timing in the identified slot as described above. The communication system 100 and the terminal device 14 according to the modification are the same types as those in FIGS. Here, the difference will be mainly described.

  FIG. 9 shows the configuration of the access control apparatus 10 according to a modification of the present invention. The access control device 10 includes an antenna 20, an RF unit 22, a modem unit 24, a processing unit 26, a GPS positioning unit 28, and a control unit 30. The processing unit 26 includes a detection unit 32, a frame definition unit 34, a generation unit 36, and a selection unit 110. The detection unit 32 includes a power measurement unit 38, a quality measurement unit 40, an empty slot identification unit 42, and a collision slot identification. Part 44 is included. The antenna 20, the RF unit 22, the modem unit 24, the GPS positioning unit 28, the control unit 30, and the frame defining unit 34 are the antenna 150, the RF unit 152, the modem unit 154, the GPS positioning unit 158, the control unit 162, and the frame shown in FIG. Since it corresponds to each of the generation units 160, description thereof is omitted here.

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

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

  The empty slot identifying unit 42 receives the received power in slot units from the power measuring unit 38. The empty slot specifying unit 42 compares each received power with a threshold (hereinafter referred to as “empty slot threshold”), and specifies a slot whose received power is smaller than the empty slot threshold. That is, the empty slot specifying unit 42 detects a slot that can be used for communication between a plurality of terminal devices as an empty slot from a plurality of slots other than the control area 220. Here, when there are a plurality of empty slots, the empty slot specifying unit 42 specifies them. The empty slot specifying unit 42 outputs information regarding the specified empty slot to the generating unit 36.

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

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

  The generation unit 36 receives information on frames and slots from the frame definition unit 34. The generation unit 36 periodically assigns control information to one of the control slots. The generation unit 36 outputs control information to the modem unit 24 in the assigned control slot.

  In the embodiment, the slot determination unit 68 of the terminal device 14 selects one slot based on the carrier sense result in the carrier sense unit 80. On the other hand, in the modification, the slot determination unit 68 selects one slot based on the information regarding the empty slot and the information regarding the collision slot included in the control information. Here, processing in the terminal device 14 according to the modification will be described.

  The control information extraction unit 66 receives control information from the modem unit 54. The control information extraction unit 66 acquires information on empty slots and information on collision slots from the control information. The control information extraction unit 66 outputs the information regarding the empty slot and the information regarding the collision slot to the slot determination unit 68. The slot determination unit 68 receives information on empty slots and information on collision slots from the control information extraction unit 66. The slot determination unit 68 selects one empty slot from slots other than 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 regarding the selected empty slot to the setting unit 82. Processing ahead of the setting unit 82 is performed in the same manner as in the embodiment.

  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 setting unit 82. 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 setting unit 82.

  FIG. 10 shows an outline of the operation of the communication system 100 according to the modification of the present invention. The horizontal direction in the figure corresponds to time, and three frames from the i-th frame to the i + 2th frame are shown as described in the uppermost stage. For the sake of clarity, it is assumed that one control slot is included in one frame and 15 slots are included in one frame. As shown in the figure, the access control device 10 broadcasts control information in the first slot of each frame. “Control” in the figure corresponds to control information. In the lower part, information on empty slots and information on collision slots included in the control information are shown while being associated with the slots. “Empty” in the figure corresponds to an empty slot, and “attack” corresponds to a collision slot.

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

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

  FIG. 11 is a flowchart showing a procedure for notifying an empty slot in the access control apparatus 10. The detector 32 sets the slot number m to s (S10). The power measuring unit 38 measures received power (S12). If the received power is smaller than the empty slot threshold (Y in S14), the empty slot specifying unit 42 specifies the slot with the slot number m as an empty slot (S16). If the received power is not smaller than the empty slot threshold (N in S14), the empty slot specifying unit 42 skips the process of step 16. If the slot number m is not the maximum number M (N in S18), the detection unit 32 adds 1 to the slot number m (S20), and returns to Step 12. On the other hand, if the slot number m is the maximum number M (Y in S18), the generation unit 36 includes the slot number of the empty slot in the control information (S22). The modem unit 24 and the RF unit 22 notify the control information (S24).

  FIG. 12 is a flowchart illustrating a collision slot notification procedure in the access control apparatus 10. The detection unit 32 sets the slot number m to s (S40). The power measuring unit 38 measures the received power, and the quality measuring unit 40 measures the error rate (S42). If the received power is greater than the first threshold and the error rate is greater than the second threshold (Y in S44), the collision slot identifying unit 44 identifies the slot with the slot number m as a collision slot (S46). ). If the received power is not greater than the first threshold value or the error rate is not greater than the second threshold value (N in S44), the collision slot specifying unit 44 skips the process of step 46. If the slot number m is not the maximum number M (N in S48), the detection unit 32 adds 1 to the slot number m (S50), and returns to Step 42. On the other hand, if the slot number m is the maximum number M (Y in S48), the generation unit 36 includes the slot number of the collision slot in the control information (S52). The modem unit 24 and the RF unit 22 notify the control information (S54).

  FIG. 13 is a flowchart showing a data transmission procedure in the terminal device 14 according to the modification of the present invention. The control information extraction unit 66 acquires control information (S70). If the slot to be used has already been specified (Y in S72), the slot determination unit 68 checks whether or not a collision has occurred in the slot. If a collision has occurred (Y in S74), the slot determining unit 68 changes the slot (S76). If no collision has occurred (N in S74), step 76 is skipped. On the other hand, if the slot to be used is not already specified (N in S72), the slot determining unit 68 specifies an empty slot (S78). The generation unit 64 transmits data in the specified slot (S80). In step 80, the processing in steps 104 and 106 in FIG. 8 is also executed.

  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. In addition, since the data is notified in the slot, 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 broadcast in the slot, the frame utilization efficiency can be reduced. In addition, since carrier sense is executed over the backoff period in the specified slot, the collision probability of packet signals can be reduced even when the amount of communication increases. In addition, if the backoff period is set at random and the interference signal is detected, the data notification is stopped, so that the occurrence of data collision can be avoided. Also, the higher the priority, the shorter the back-off period, so that data from a terminal device with a higher priority can be preferentially notified.

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

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

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

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

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

  In the embodiment of the present invention, control information notified from the access control 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. 6A to 6E are diagrams showing an outline of the start timing set in the setting unit in 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 access control apparatus which concerns on the modification of this invention. It is a figure which shows the operation | movement outline | summary of the communication system which concerns on the modification of this invention. 10 is a flowchart showing a procedure for notifying an empty slot in the access control apparatus of FIG. 10 is a flowchart showing a collision slot notification procedure in the access control apparatus of FIG. 9. It is a flowchart which shows the transmission procedure of the data in the terminal device which concerns on the modification of this invention.

Explanation of symbols

  10 access control device, 12 vehicle, 14 terminal device, 50 antenna, 52 RF unit, 54 modulation / demodulation unit, 56 processing unit, 58 control unit, 60 timing identification unit, 62 acquisition unit, 64 generation unit, 66 control information extraction unit, 68 slot determination unit, 70 notification unit, 80 carrier sense unit, 82 setting 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 (3)

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;
In the slot selected by the selection unit, a setting unit for setting a timing to start data notification;
An informing unit for informing data from the timing set in the setting unit;
A wireless device comprising: A holding unit that holds information about the priority of the wireless device;
The setting unit shortens a period from the head of the slot selected by the selection unit to a timing at which data notification should be started, as the priority held in the holding unit is relatively higher. The wireless device according to claim 1. 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;
Within the selected slot, setting a timing for starting data broadcasting; and
A step of notifying data from the set timing; and
A notification method comprising:

Images