JP5459247B2 - Wireless communication apparatus and wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication apparatus and a wireless communication system that wirelessly transmit data including a transmission time.

  Conventionally, in order to prevent data transmitted wirelessly from being falsified by a malicious third party, a method of transmitting a transmission data by adding a message authentication code (Message Authentication code) to the transmission data is known (for example, (See Patent Document 1).

JP 2010-258864 A

By the way, in the technique described in Patent Document 1, when transmission time information indicating a time for transmitting transmission data is added to the transmission data, data transmission is performed according to the following procedure.
First, when there is a transmission request for transmission data, current time information is acquired. Then, the current time information is added to the transmission data as transmission time information. Hereinafter, the transmission data with the transmission time information added is referred to as transmission time-added transmission data.

  Thereafter, a message authentication code is generated using transmission time-added transmission data as original data, and the generated message authentication code is added to the transmission time-added transmission data, and then wireless transmission is performed.

Therefore, there is a difference corresponding to the time required for generating the message authentication code between the time when the wireless transmission was actually performed and the transmission time indicated by the transmission time information added to the transmission data.
Therefore, when the wireless communication device that has received the transmission data synchronizes its own clock based on the transmission time information included in the data, the time of the clock of the wireless communication device that transmitted the data and the data are received. There is a problem that the above difference occurs between the time of the clock of the wireless communication device and the synchronization accuracy between the transmitting wireless communication device and the receiving wireless communication device cannot be obtained.

  The present invention has been made in view of these problems, and provides a technique for reducing the difference between the time when transmission data is actually transmitted and the transmission time indicated by the transmission time information added to the transmission data. For the purpose.

  The wireless communication device according to claim 1, wherein the wireless communication device according to claim 1 is configured to wirelessly transmit data using a predetermined communication channel, and the transmission time determination means is a data transmission time when the data is wirelessly transmitted. A transmission unit configured to determine a plurality of times and the generation unit includes transmission time information indicating a data transmission time and data different from the data transmission time for each of the plurality of data transmission times determined by the transmission time determination unit A message authentication code or an electronic signature is generated based on the time additional data. Then, the channel determination means determines whether or not the communication channel is free, and when the transmission means determines that the communication channel is free, the transmission time indicating the data transmission time closest to the current time Transmission data composed of transmission time additional data having information and a message authentication code or an electronic signature generated by the generation unit based on the transmission time additional data is wirelessly transmitted.

  In the wireless communication apparatus configured as described above, the transmission unit determines in advance the time (data transmission time) at which transmission data is wirelessly transmitted, and then based on the data to which transmission time information is added (transmission time additional data). Then, a message authentication code or an electronic signature is generated, and then transmission data including transmission time information indicating a data transmission time closest to the current time is transmitted when the communication channel is free.

  For this reason, the data transmission time indicated by the transmission time information included in the transmission time additional data is determined in advance in consideration of the time required for generating the message authentication code or the electronic signature and the usage status of the communication channel. Thus, the difference between the time when the wireless communication apparatus actually transmits data wirelessly and the data transmission time indicated by the transmission time information included in the transmission data wirelessly transmitted by the transmission unit can be minimized. .

  Therefore, the wireless communication device that has received the data transmitted from the wireless communication device synchronizes the time of its own clock with the data transmission time indicated by the transmission time information in the received data, thereby Synchronization accuracy can be improved.

  Further, the transmission time additional data including the transmission time information and the message authentication code or electronic signature generated based on the transmission time additional data correspond to each of a plurality of different data transmission times by the transmission means. It is generated in advance before wireless transmission.

  For this reason, after the channel determination means determines that the communication channel is free, a message authentication code or electronic signature corresponding to transmission time additional data including transmission time information indicating the data transmission time closest to the current time is generated. Corresponding to the transmission time additional data including transmission time information indicating the data transmission time closest to the current time immediately after the channel determination means determines that the communication channel is free without processing. Transmission data composed of the message authentication code or the electronic signature can be wirelessly transmitted. Therefore, the communication efficiency can be improved by the amount that the process of generating the message authentication code or the electronic signature can be omitted after the channel determination means determines that the communication channel is free.

  Further, in the wireless communication device according to claim 1, when the wireless communication device performs wireless transmission using a carrier sense multiple access / collision avoidance (CSMA / CA) method, the wireless communication device according to claim 2 In addition, a fixed generation time which is a fixed time set in advance as a time required for the generation means to generate a message authentication code or an electronic signature, and wireless transmission after the channel determination means determines that the communication channel is free. A time obtained by adding a fixed waiting time set in advance as a time to wait before starting is defined as a first fixed time, and a slot time which is a minimum unit time of backoff time in the CSMA / CA method is defined as a second fixed time. The data transmission time is tg, the current time is t0, the first fixed time is T1, the second fixed time is T2, n is a preset integer value, and i is from 0 When the integer value of n-1) to the transmission time determination means, the data transmission time, better to be determined by the following equation (1).

tg = t0 + T1 + i × T2 (1)
In the CSMA / CA method, when it is determined that the communication channel is free by the access control, a predetermined time DIFS (Distributed Inter Frame Space) and a randomly set back-off time are added. Data transmission starts after the time has elapsed. The back-off time is calculated by multiplying an integer value r (hereinafter referred to as a random value r) that is randomly generated in the range from 0 to the contention window CW and a slot time that is a fixed time.

  That is, in the radio communication apparatus according to the second aspect, a plurality of data transmission times are determined corresponding to a time interval for transmitting data in the CSMA / CA scheme. For this reason, the difference between the time when the wireless communication device actually wirelessly transmits data and the data transmission time indicated by the transmission time information included in the transmission data wirelessly transmitted by the transmission unit is very large. Occurrence can be suppressed. Furthermore, the processing load of the wireless communication apparatus is not generated without generating a lot of transmission time additional data and message authentication codes or electronic signatures corresponding to data transmission times of a time interval shorter than the data transmission interval in the CSMA / CA system. Can be reduced.

  Further, in the wireless communication device according to claim 1, when the wireless communication device performs wireless transmission using a carrier sense multiple access / collision avoidance (CSMA / CA) method, In addition, a fixed generation time which is a fixed time set in advance as a time required for the generation means to generate a message authentication code or an electronic signature, and wireless transmission after the channel determination means determines that the communication channel is free. A time obtained by adding a fixed waiting time set in advance as a time to wait before starting is set as a first fixed time, and a slot time which is a minimum unit time of backoff time in the CSMA / CA method is set as a second fixed time. The data transmission time is tg, the current time is t0, the first fixed time is T1, the second fixed time is T2, n is a preset integer value, and i is from 0 ( -1) integer value, T3 as a third fixed time preset to be longer than (T2 × n), m as a preset integer value, and j as an integer from 0 to (m-1) If it is a numerical value, the transmission time determination means may determine the data transmission time by the following equation (2).

tg = t0 + T1 + i × T2 + j × T3 (2)
In the wireless communication device configured as described above, the data transmission times are determined in the ascending order as shown in FIG. 10 based on the following equation (2).

  (T0 + T1), (t0 + T1 + T2), (t0 + T1 + 2 × T2), (t0 + T1 + 3 × T2),..., {T0 + T1 + (n−1) × T2}, (t0 + T1 + T3), (t0 + T1 + T3 + T2), (t0 + T1 + T3) t0 + T1 + T3 + 3 × T2),..., {t0 + T1 + T3 + (n−1) × T2}, (t0 + T1 + 2 × T3), (t0 + T1 + 2 × T3 + T2), (t0 + T1 + 2 × T3 + 2 × T2), (t0 + T1 + 2 × T3 + 3)・.

  Therefore, the difference between {t0 + T1 + (j−1) × T3 + (n−1) × T2} and (t0 + T1 + j × T3) (for example, {t0 + T1 + T3 + (n−1) × T2}) and (t0 + T1 + 2 × T3) The difference is the difference between {t0 + T1 + (j−1) × T3 + (n−1) × T2} and {t0 + T1 + (j−1) × T3 + n × T2} (for example, {t0 + T1 + T3 + (n−1) × T2}). And (difference between t0 + T1 + n × T2)).

  Therefore, according to the wireless communication device of the third aspect, when determining the data transmission time over a certain time range, the number of the data transmission times is compared with the determination of the data transmission time based on the formula (1). Can be reduced. For this reason, the number of transmission time additional data and message authentication codes or electronic signatures generated is smaller than that of the wireless communication device according to claim 2, and the processing load of the wireless communication device can be reduced.

  Further, in the wireless communication device according to claim 3, as described in claim 4, the estimation unit calculates the number of peripheral communication devices, which is the number of wireless communication devices existing around the wireless communication device, as the wireless communication device. N and m so that the value setting means has a positive correlation with the number of peripheral communication devices based on the number of peripheral communication devices estimated by the estimation means. Set at least one of the values.

  According to the wireless communication device configured as described above, as the number of peripheral communication devices increases, at least one of n and m increases, and the transmission time determination unit can determine a later data transmission time. . As a result, since the number of peripheral communication devices is large, it is possible to suppress the occurrence of a situation in which the communication channel is not free even when the latest time among the data transmission times determined by the transmission time determination means has elapsed.

  Further, in the wireless communication device according to any one of claims 1 to 4, as described in claim 5, the time when the transmission allowable time determination unit transmits the transmission data wirelessly by the transmission unit. And a difference between the data transmission time indicated by the transmission time information included in the transmission data is equal to or greater than a preset transmission allowable time, and the prohibited re-execution means transmits the transmission by the transmission allowable time determination means. When it is determined that the time is equal to or longer than the allowable time, wireless transmission by the transmission means of the transmission data used for the determination by the transmission allowable time determination means is prohibited, and the transmission time determination means may be executed again.

  In other words, when it is determined by the transmission allowable time determination means that the transmission allowable time is longer than the transmission allowable time, a plurality of new data transmission times are determined by the transmission time determination means, and a new data transmission time is added accordingly. Transmission data is generated. As a result, the difference between the time when the wireless communication apparatus actually transmits the data wirelessly and the data transmission time indicated by the transmission time information included in the transmission data wirelessly transmitted by the transmission means exceeds the allowable transmission time. It can suppress becoming very large.

A radio communication system according to a sixth aspect includes the radio communication device according to any one of the first to fifth aspects.
According to the wireless communication system configured as described above, the same effect as that of the wireless communication device according to any one of claims 1 to 5 can be obtained, and synchronization timing of the wireless communication system can be protected. A highly secure wireless communication system can be realized.

1 is an explanatory diagram showing an outline of a configuration and operation of a wireless communication system 1. FIG. It is a functional block diagram which shows the outline | summary of the process which communication apparatus 2A, 2B, 2C, ... performs. It is a flowchart which shows a regular frame transmission process. It is a flowchart which shows a random frame transmission process. It is a flowchart which shows a frame verification process. It is a timing chart explaining the difference of the frame transmission timing of the past and this invention. It is a flowchart which shows the random frame transmission process of 2nd Embodiment. It is a flowchart which shows a parameter setting process. It is a figure which shows the structure of a transmission possible time calculation parameter table | surface. It is a figure explaining the calculation method of data transmission time or transmission possible time tg.

(First embodiment)
A first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram showing an outline of the configuration and operation of the wireless communication system 1.

  As shown in FIG. 1 (a), the wireless communication system 1 of the present embodiment includes a plurality of communication devices 2A installed as road devices in the vicinity of a vehicle's traveling path, and mounted on the vehicle. It comprises communication devices 2B, 2C,... That perform wireless communication with other vehicles.

  The communication device 2A has a periodic transmission function for periodically transmitting various information such as traffic information to surrounding vehicles. The communication devices 2B, 2C,... Receive a transmission request from a control device mounted on the vehicle. Thus, it has a random transmission function (transmission function based on CSMA / CA access control) for transmitting the state of the host vehicle to road vehicles and other vehicles.

  For communication between these communication devices 2A, 2B, 2C,..., A common communication channel is used. When the communication devices 2B, 2C,. It is determined whether or not the communication channel is free by (CSMA / CA) access control, and data transmission is started when the communication channel is free.

  Specifically, when it is determined that the communication channel is free due to the access control, a time obtained by adding a predetermined time DIFS (Distributed Inter Frame Space) and a randomly set back-off time thereafter. After the elapse of time, data transmission is started. Note that the back-off time is obtained by multiplying an integer value r (hereinafter referred to as a random value r) that is randomly generated in a range from 0 to a contention window CW (15 in this embodiment) and a slot time that is a fixed time. Calculated. As a result, it is possible to suppress the occurrence of a situation in which the communication devices 2B, 2C,... Start data transmission at the same time, and to reduce the probability that transmission data from the communication devices 2B, 2C,.

  The communication device 2A performs regular transmission. The period of this periodic transmission is determined in advance, and the communication device 2A is assigned which period within one periodic transmission cycle is used for regular transmission. Yes.

  The communication device 2A notifies the assigned regular transmission period to the other communication devices 2B, 2C,... By regular transmission, and the other communication devices 2B, 2C,. Prohibits random transmission.

  That is, in the present embodiment, the communication device 2A having a periodic transmission function, as shown in FIG. 1B, transmits a frame composed of transmission time data, periodic transmission data, and a MAC (Message Authentication code) or an electronic signature. , Send regularly to the surroundings. The transmission time data is information indicating the time at which the communication device 2A transmits a frame. The regular transmission data includes various information such as traffic information, and regular transmission period information indicating the start timing of the regular transmission period and the length (period length) of the regular transmission period. The MAC or electronic signature is generated using a transmission message composed of transmission time data and regular transmission data as original data.

  Then, when the other communication devices 2B, 2C,... Having the random transmission function receive the frame transmitted by the communication device 2A, they are shown in FIG. 1 (c) based on the periodic transmission period information included in the frame. As described above, the random transmission prohibition period is set so that the random transmission is not started within the regular transmission period of the communication device 2A, and the random transmission period is set within the period other than the random transmission prohibition period (random transmission period). Send.

  In addition, as shown in FIG. 1A, the communication device 2B is located in an area (area indicated by hatching in the drawing) where the transmission radio wave from the communication device 2A reaches, and the communication device 2C is located outside the area. The periodic transmission data transmitted from the communication device 2A does not reach the communication device 2C, the communication device 2C starts random transmission within the regular transmission period of the communication device 2A, and on the communication device 2B side, the communication devices 2A, 2C It is conceivable that the transmission radio waves from the radio waves arrive at the same time and the respective transmission data cannot be received.

  Therefore, in this embodiment, when the communication devices 2B, 2C,... Receive the periodic transmission data, the periodic transmission data is retransmitted to notify the other communication devices away from the communication device 2A of the periodic transmission period information. Have been to.

  In order to set the random transmission prohibition period based on the periodic transmission period information on the communication devices 2B, 2C,..., The periodic transmission cycle recognized on the communication device 2A side, and the communication devices 2B, 2C,. It is necessary to match the periodical transmission period recognized in (1).

  Therefore, in the present embodiment, when the communication devices 2B, 2C,... Transfer the periodic transmission period information, the transmission time is read from its own clock, and a frame composed of at least transmission time data and the periodic transmission period information is read. Generate and send. Then, the communication devices 2B, 2C,... That have received the frame including the transmission time data and the periodical transmission period information compare the transmission time in the received frame with the reception time read from its own clock. The time of the clock is synchronized with the time of the communication device 2A, 2B,... That has transmitted the periodic transmission period information.

  That is, for example, in FIG. 1A, the periodic transmission period information transmitted from the communication device 2A reaches the communication device 2B, and the communication device 2B transfers the periodic transmission period information to the communication device 2C. When the communication devices 2B and 2C receive the periodic transmission period information, the periodic transmission period information is obtained by synchronizing the time of its own clock with the clock of the communication devices 2A and 2B that transmitted the periodic transmission period information. The clocks of the received communication devices 2B, 2C,... Are all time-synchronized so that they are all at the same time as the clock of the communication device 2A.

As a result, each of the communication devices 2A, 2B, 2C,... Can detect one periodic transmission cycle at the same timing using its own clock.
FIG. 2A is a functional block diagram illustrating an outline of processing executed by the communication device 2A.

As illustrated in FIG. 2A, the communication device 2 </ b> A includes a data input unit 11, a data processing unit 12, a MAC / electronic signature processing unit 13, and a transmission unit 14.
Among these, the data input unit 11 is configured to be able to input data by wire or wirelessly with an information station installed outside the communication device 2A. From this information station, data indicating various information such as traffic information is input. Then, the data is transmitted to the data processing unit 12.

  The data processing unit 12 generates a transmission message by adding transmission time data to the data received from the data input unit 11, transmits the generated transmission message to the MAC / electronic signature processing unit 13, and transmits the MAC / electronic signature. The MAC or electronic signature received from the processing unit 13 is added to the transmission message to generate a frame, and the generated frame is transmitted to the transmission unit 14. The data processing unit 12 includes a clock (not shown) that counts time by counting the internal clock, and uses this clock to determine the transmission time indicated by the transmission time data.

  The MAC / electronic signature processing unit 13 generates a MAC or electronic signature using the transmission message received from the data processing unit 12 as original data, and transmits the generated MAC or electronic signature to the data processing unit 12.

The transmission unit 14 receives a frame from the data processing unit 12 and transmits the frame wirelessly.
Note that the communication device 2A is configured around a well-known microcomputer including a CPU, ROM, RAM, I / O, and a bus line that connects these components. Based on a program stored in the ROM, the communication device 2A The data input unit 11, the data processing unit 12, the MAC / digital signature processing unit 13, and the transmission unit 14 are executed.

FIG. 2B is a functional block diagram illustrating an outline of processing executed by the communication devices 2B, 2C,.
As shown in FIG. 2B, the communication devices 2B, 2C,... Have a data input / output unit 21, a data processing unit 22, a MAC / electronic signature processing unit 23, a transmission / reception unit 24, a synchronization processing unit 25, and a data storage. Part 26 is provided.

  Among these, the data input / output unit 21 inputs transmission data from the control device mounted on the automobile, transmits the data to the data processing unit 22, and transmits transmission data (control data) from the data processing unit 22 to the control device. When received, control data is transmitted to the control device.

  Further, when receiving data from the data input / output unit 21, the data processing unit 22 generates a transmission message by adding additional information such as a header to the received data, and the generated transmission message is subjected to MAC / electronic signature processing. The frame is generated by adding the MAC or electronic signature received from the MAC / electronic signature processing unit 23 to the transmission message, and the generated frame is transmitted to the transmission / reception unit 24.

  Further, when the data processing unit 22 receives the frame and the reception time from the transmission / reception unit 24, the data processing unit 22 transmits a verification request message including the received frame and the verification command to the MAC / electronic signature processing unit 23, and the verification result (acceptance or rejection). ), And when the data processing unit 22 receives acceptance from the MAC / electronic signature processing unit as a verification result, the message included in the received frame is stored in the data storage unit 26. Further, the data processing unit 22 calculates a difference between the transmission time included in the frame and the reception time (attached by the transmission / reception unit 24), and transmits a time correction command to the synchronization processing unit 25 together with the calculated difference time.

  Further, when it is necessary to transmit control data to the control device, the data processing unit 22 receives a message from the data storage unit 26, generates control data from the received message, and transmits the generated control data to the data input / output unit. To 21.

  The MAC / electronic signature processing unit 23 verifies the MAC or electronic signature of the received frame of the verification request message received from the data processing unit 22, and transmits a verification result (acceptance or rejection) to the data processing unit 22.

  In addition, when the frame is received from the data processing unit 22, the transmission / reception unit 24 wirelessly transmits the frame. When the frame is wirelessly received, the transmission / reception unit 24 transmits the frame to the data processing unit 22 together with the reception time of the frame. Send.

  The synchronization processing unit 25 includes a clock (not shown) that counts the time by counting the internal clock. Then, the synchronization processing unit 25 receives the difference time and the time correction command from the data processing unit 22 and corrects the clock (internal clock) of the own device so that the difference becomes zero.

  In addition, when the data processing unit 22 receives acceptance as a verification result from the MAC / electronic signature processing unit, the data storage unit 26 stores a message included in the received frame, and stores the stored message as a data processing unit. 22 to send.

  The communication devices 2B, 2C,... Are mainly composed of a well-known microcomputer comprising a CPU, ROM, RAM, I / O and a bus line connecting these components. Based on the data input / output unit 21, the data processing unit 22, the MAC / digital signature processing unit 23, the transmission / reception unit 24, the synchronization processing unit 25, and the data storage unit 26.

  In the wireless communication system 1 configured as described above, the communication device 2A executes a periodic frame transmission process for transmitting a frame within a periodic transmission period. Further, the communication devices 2B, 2C,... Execute a random frame transmission process for transmitting a frame within a random transmission period and a frame verification process for verifying the received frame.

  First, the procedure of the periodic frame transmission process executed by the communication device 2A will be described with reference to FIG. FIG. 3 is a flowchart showing the regular frame transmission process. This periodic frame transmission process is a process that is started when the CPU of the communication device 2A is activated.

  When the periodic frame transmission process is executed, the communication device 2A first receives input data from the outside of the communication device 2A in S10.

  When the input data is received, the transmission order instruction value i is set to 1 in S20, and the current time t0 is acquired from the clock included in the data processing unit 12 in S30. Thereafter, in S40, the future transmission time ti is acquired. The future transmission time ti indicates the i-th frame transmission time based on the current time t0. In the present embodiment, in the communication apparatus 2A, the transmission time within one periodic transmission period is set so that the frame is transmitted only once after a preset fixed time tf has elapsed from the start of the periodic transmission period. ing. That is, the time at which the communication device 2A transmits a frame has already been determined. Then, assuming that the periodic transmission cycle is Tp, the future transmission time ti is expressed by the following equation (3). Note that i is an integer of 1 or more.

ti = t1 + Tp × (i−1) (3)
In S50, the difference between the future transmission time ti and the current time t0 is calculated as the transmission grace time Δt. In S60, the data received in the process of S10, the information indicating the future transmission time ti, and the periodic transmission are performed. Based on the data length of the original data, the time required to generate the MAC or electronic signature using the transmission message composed of the period information as the original data (hereinafter referred to as the first MAC / electronic signature generation processing time tm1) is calculated. To do.

  Thereafter, in S70, it is determined whether or not the transmission delay time Δt is longer than the first MAC / electronic signature generation processing time tm1. If the transmission delay time Δt is not longer than the first MAC / electronic signature generation processing time tm1 (S70: NO), the transmission order instruction value i is incremented (added by 1) in S80, and the process proceeds to S30. Then, the above process is repeated.

  On the other hand, when the transmission delay time Δt is longer than the first MAC / electronic signature generation processing time tm1 (S70: YES), the predicted transmission time ts is set to the future transmission time ti in S90. Thereafter, in S100, a MAC or an electronic signature is generated with the transmission message composed of the data received in the process of S10, the predicted transmission time information indicating the predicted transmission time ts, and the periodic transmission period information as original data. In S110, a frame composed of the predicted transmission time information, the data received in the process of S10, the periodic transmission period information, and the MAC or electronic signature generated in the process of S100 is generated.

  Thereafter, in S120, it is determined whether or not the current time is the predicted transmission time ts. If the current time is not the predicted transmission time ts (S120: NO), the process of S120 is repeated, and the process waits until the current time becomes the predicted transmission time ts. On the other hand, when the current time is the predicted transmission time ts (S120: YES), in S130, the frame generated in the process of S110 is wirelessly transmitted, and the process returns to data reception waiting (S10).

  Next, a procedure of random frame transmission processing executed by the communication devices 2B, 2C,... Will be described with reference to FIG. FIG. 4 is a flowchart showing random frame transmission processing. This random frame transmission process is a process that is started when the CPUs of the communication devices 2B, 2C,.

  When this random frame transmission process is executed, communication devices 2B, 2C,... First receive transmission data from the control device mounted on the vehicle in S210.

  After receiving the transmission data (S210), the current time t0 is acquired from the clock included in the synchronization processing unit 25 in S220. In S230, a time tg (hereinafter referred to as a transmittable time tg) at which there is a possibility of acquiring a frame transmission opportunity by CSMA / CA access control is calculated.

This transmittable time tg is expressed by the following equation (4) using the current time t0, the first fixed time T1 (described later), and the second fixed time T2 (described later).
tg = t0 + T1 + i × T2 (4)
As shown in the following formula (5), the first fixed time T1 in the formula (4) is a MAC or electronically based on a transmission message composed of transmission data input from the control device and periodic transmission period information as original data. This is a time obtained by adding a time required to generate a signature (hereinafter referred to as second MAC / electronic signature generation processing time tm2) and a time corresponding to DIFS (hereinafter referred to as DIFS time td). The second MAC / electronic signature generation processing time tm2 and the DIFS time td are fixed values set in advance.

T1 = tm2 + td (5)
The second fixed time T2 in the equation (4) is a slot time. Moreover, i in Formula (4) is an integer value from 0 to (CW-1). As described above, CW is a contention window, and in this embodiment, CW = 15. Therefore, in S230, CW (= 15) transmittable times tg are calculated.

  Thereafter, in S240, a transmission message (hereinafter referred to as “transmittable time additional data”) including each of the CW pieces of transmittable time information indicating the transmittable time tg and the data received in the process of S210 is generated. That is, CW transmittable time additional data is generated according to each transmittable time tg.

  In S250, a MAC or an electronic signature is generated using the CW pieces of transmission available time additional data as original data. That is, CW MACs or electronic signatures are generated according to each transmission possible time tg.

Further, in S260, the CW frames are generated by adding the MAC or electronic signature generated in S250 to each of the CW transmittable time additional data.
Thereafter, in S270, it is determined whether or not an opportunity for frame transmission has been acquired. Here, when the frame transmission opportunity has not been acquired (S270: NO), the processing of S270 is repeated, and the process waits until the frame transmission opportunity is acquired. On the other hand, when the opportunity of frame transmission is acquired (S270: YES), the current time t0 is acquired from the clock included in the synchronization processing unit 25 in S280.

  In S290, the CW frames generated in the process of S260 are wirelessly transmitted from the CW frames to which the transmission possible time tg with the smallest difference from the current time t0 acquired in S280 is added, and the transmission data The process returns to the reception town (S210).

  Next, the procedure of frame verification processing executed by the communication devices 2B, 2C,... Will be described with reference to FIG. FIG. 5 is a flowchart showing the frame verification process. This frame verification process is a process that is started when the CPUs of the communication devices 2B, 2C,.

  When this frame verification process is executed, the communication devices 2B, 2C,... First receive a frame from the communication device 2A in S410.

  On the other hand, when a frame is received (S410: YES), a transmission message (that is, transmission time data and periodic transmission shown in FIG. 1B) is transmitted from the frame determined to be received in S410 in S420. Data) and MAC or electronic signature. In step S430, the received message MAC or digital signature is verified.

  In S440, the process is divided depending on whether or not the verification in S430 is accepted. When the verification in S430 is rejected (S440: NO), in S450, the frame received in the process of S410 is discarded, and the process returns to the frame reception wait (S410).

  On the other hand, when the verification of S430 is accepted (S440: YES), the reception processing of the message included in the received frame (outputs the message from the data input / output unit 11) is performed at S460, and further at S470. The clock included in the synchronization processing unit 25 is synchronized with the time indicated by the transmission time data extracted in the process of S420, and the process returns to the frame reception wait (S410). Here, the order of the processes of S460 and S470 may be reversed.

  In the communication device 2A of the wireless communication system 1 configured as described above, first, the predicted transmission time ts for wirelessly transmitting the frame is determined (S30 to S90), and the input data, the predicted transmission time information, and the periodic transmission period information are used. A message authentication code (MAC) or electronic signature is generated based on the configured transmission message (S100). When the predicted transmission time ts is reached (S120: YES), a frame composed of a transmission message and a message authentication code (MAC) or an electronic signature is wirelessly transmitted (S130).

  In the communication apparatus 2A configured as described above, a time for transmitting a frame is determined in advance, and then a message authentication code (MAC) or an electronic signature is obtained based on data (transmission message) to which predicted transmission time information is added. After that, when a predicted transmission time ts is reached, a frame composed of a message authentication code (MAC) or electronic signature and a transmission message is wirelessly transmitted. For this reason, the time when the communication device 2A actually wirelessly transmits the frame can be matched with the predicted transmission time ts indicated by the predicted transmission time information included in the transmitted frame.

  Therefore, the communication devices 2B, 2C,... That have received the data transmitted from the communication device 2A synchronize their clock time with the time indicated by the predicted transmission time information in the received data, thereby enabling the communication device 2A. Synchronization accuracy can be improved.

  Further, the communication devices 2B, 2C,... Calculate a plurality of times tg (transmittable times tg) at which frame transmission opportunities may be obtained by CSMA / CA access control (S230) and a plurality of transmissions. For each possible time tg, a MAC or electronic signature is generated based on transmittable time information indicating the transmittable time tg and transmittable time additional data composed of data different from the transmittable time tg (S250). . Then, it is determined whether or not an opportunity for frame transmission has been acquired (S270). When it is determined that an opportunity for frame transmission has been acquired (S270: YES), the transmission possible time tg with the smallest difference from the current time t0 is determined. The frame to which is added is wirelessly transmitted (S290).

  In the communication devices 2B, 2C,... Configured as described above, the MAC or electronic signature is determined based on the data (transmittable time additional data) to which the transmittable time tg is added after the transmittable time tg is determined in advance. After that, when a communication channel is available, a frame including transmittable time information indicating the transmittable time tg closest to the current time is transmitted.

  For this reason, the transmittable time tg indicated by the transmittable time information included in the transmittable time additional data is determined in advance in consideration of the time required to generate the MAC or electronic signature and the usage status of the communication channel. This minimizes the difference between the time when the communication devices 2B, 2C,... Actually transmit the frame wirelessly and the transmittable time tg indicated by the transmittable time information included in the wirelessly transmitted frame. Can do.

  Therefore, the communication device that has received the data transmitted from the communication devices 2B, 2C,... Communicates by synchronizing the time of its own clock with the transmittable time tg indicated by the transmittable time information in the received frame. The accuracy of synchronization with the devices 2B, 2C,... Can be improved.

  Further, the transmission possible time additional data including the transmission possible time information and the MAC or the electronic signature generated based on the transmission possible time additional data correspond to each of a plurality of transmission possible times tg different from each other. Is generated in advance before wireless transmission.

  For this reason, a process of generating a MAC or electronic signature corresponding to transmittable time additional data including transmittable time information indicating the transmittable time tg closest to the current time after determining that a frame transmission opportunity has been acquired. Immediately after determining that the opportunity of frame transmission has been acquired without performing the transmission, the transmission possible time additional data including the transmission possible time information indicating the transmission possible time tg closest to the current time and the transmission possible time additional data are supported. A frame composed of a MAC or an electronic signature can be transmitted wirelessly.

  For example, as shown in FIG. 6, in the conventional communication device C11, when the control device E11 mounted on the vehicle V11 outputs the transmission data D11 to the communication device C11 mounted on the vehicle V11 (see time t11). ) After generating the MAC or electronic signature (see generation time T11), frame transmission is performed (see time t12). When the control device E11 outputs the transmission data D12 to the communication device C11, when the communication device C12 mounted on the vehicle V12 located around the vehicle V11 is transmitting a frame (at time t13). The communication device C11, after the end of frame transmission by the communication device C12 (see time t14), after the waiting time T12 based on CSMA / CA access control (see time t15) has elapsed, An electronic signature is generated (see generation time T13), and a frame is transmitted (see time t16).

  On the other hand, in the communication device C13 to which the system of the present embodiment is applied, when the control device E13 mounted on the vehicle V13 outputs the transmission data D13 to the communication device C13 mounted on the vehicle V13, When the communication device C12 mounted on the vehicle V12 located in the vicinity is transmitting a frame (see time t13), a MAC or an electronic signature is generated immediately after the transmission data D13 is input (see generation time T14). From the end of frame transmission by the communication device C12 (see time t14), frame transmission is performed after a standby time T12 based on CSMA / CA access control has elapsed (see time t15).

Accordingly, the communication efficiency can be improved by the amount that the process of generating the MAC or electronic signature after determining that the opportunity of frame transmission has been acquired can be omitted.
Further, the communication devices 2B, 2C,... Calculate the transmittable time tg according to the equation (4). That is, a plurality of transmittable times tg are determined in correspondence with the time interval for transmitting data in the CSMA / CA system. Therefore, the difference between the time when the communication devices 2B, 2C,... Actually transmit data wirelessly and the transmittable time tg indicated by the transmittable time information included in the wirelessly transmitted transmission frame is very large. The occurrence of the situation can be suppressed. In addition, a large number of transmittable time additional data and MACs or electronic signatures corresponding to transmittable times with a time interval shorter than the data transmission interval in the CSMA / CA system are not generated, and the communication devices 2B, 2C,. Processing load can be reduced.

  In the embodiment described above, the communication devices 2B, 2C,... Are the wireless communication devices in the present invention, the processing in S230 is the transmission time determining means in the present invention, the processing in S250 is the generating means in the present invention, and the processing in S270 is the present invention. The channel determination means in S290 and the process of S290 are transmission means in the present invention.

  The transmission possible time tg is the data transmission time in the present invention, the transmission possible time information is the transmission time information in the present invention, the transmission possible time additional data is the transmission time additional data in the present invention, and the second MAC / electronic signature generation processing time tm2 is The fixed generation time and DIFS time td in the present invention are the fixed standby time in the present invention.

(Second Embodiment)
A second embodiment of the present invention will be described below with reference to the drawings. In the second embodiment, only parts different from the first embodiment will be described.

  In the wireless communication system 1 according to the second embodiment, the random frame transmission process is changed, and the parameter setting process for setting a parameter for calculating the transmittable time tg is executed by the communication devices 2B, 2C,. Except for this, the second embodiment is the same as the first embodiment.

  Next, the procedure of random frame transmission processing according to the second embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing random frame transmission processing according to the second embodiment. This random frame transmission process is a process repeatedly executed while the CPUs of the communication apparatuses 2B, 2C,.

  When this random frame transmission process is executed, the communication devices 2B, 2C,... First receive transmission data from the control device mounted on the vehicle in S510 (S510).

  After receiving the transmission data, the current time t0 is acquired from the clock provided in the synchronization processing unit 25 in S520. In S530, a time tg (hereinafter referred to as a transmittable time tg) at which there is a possibility of acquiring a frame transmission opportunity by the CSMA / CA access control is calculated.

This transmittable time tg is expressed by the following equation (6) using the current time t0, the first fixed time T1 (described later), the second fixed time T2 (described later), and the third fixed time T3 (described later). .
tg = t0 + T1 + i × T2 + j × T3 (6)
The first fixed time T1 in the equation (6) is a time required to generate a MAC or an electronic signature using a transmission message composed of transmission data input from the control device and periodic transmission period information as original data, This is the time obtained by adding the time corresponding to DIFS. The first fixed time T1 is a value set in the parameter setting process (described later).

  Further, the second fixed time T2 in the equation (6) is a slot time. Moreover, i in Formula (6) is an integer value from 0 to (n-1). The second fixed time T2 and the integer value n are values set in the parameter setting process (described later).

  Further, the third fixed time T3 in the equation (6) is a value set in advance so as to be longer than (T2 × n). Furthermore, j in the formula (6) is an integer value from 0 to (m−1). The third fixed time T3 and the integer value m are values set in the parameter setting process (described later).

Therefore, in S530, n × m transmittable times tg are calculated.
Thereafter, in S540, a transmission message (hereinafter referred to as “transmittable time additional data”) composed of each of the n × m pieces of transmittable time information indicating the transmittable time tg and the data determined to be input in the process of S510. Generated). In other words, n × m pieces of transmission available time additional data are generated according to each transmission available time tg.

  In step S550, a MAC or electronic signature is generated using n × m pieces of transmission-available time additional data as original data. That is, n × m MACs or electronic signatures are generated in accordance with each transmittable time tg.

In S560, the MAC or electronic signature generated in S550 is added to each of the n × m transmittable time additional data to generate n × m frames.
Thereafter, in S570, it is determined whether a frame transmission opportunity has been acquired. If the frame transmission opportunity has not been acquired (S570: NO), the process of S570 is repeated, and the process waits until the frame transmission opportunity is acquired. On the other hand, when a frame transmission opportunity is acquired (S570: YES), the current time t0 is acquired from the clock included in the synchronization processing unit 25 in S580.

  In S590, from the n × m frames generated in the process of S560, the difference between the transmittable time tg having the smallest difference from the current time t0 acquired in S580 and the current time t0, that is, It is determined whether or not the minimum absolute value of the difference between the n × m transmittable times tg and the current time t0 (hereinafter referred to as the minimum transmission time difference) is less than a preset transmission allowable determination value. To do.

  Here, when the transmission time difference minimum value is equal to or larger than the transmission permission determination value (S590: NO), the process proceeds to S520 and the above-described processing is repeated. On the other hand, when the transmission time difference minimum value is less than the transmission allowance determination value (S590: YES), in S600, the current acquired in S580 from the n × m frames generated in the process of S560. The frame with the transmission possible time tg with the smallest difference from the time t0 is wirelessly transmitted, the (n × m−1) frames that have not been transmitted are discarded, and the reception of transmission data is awaited (S510). Return.

  Next, the procedure of parameter setting processing executed by the communication devices 2B, 2C,... Will be described with reference to FIGS. FIG. 8 is a flowchart showing the parameter setting process. FIG. 9 is a diagram showing the configuration of the transmittable time calculation parameter table. This parameter setting process is a process repeatedly executed while the CPUs of the communication devices 2B, 2C,.

  When this parameter setting process is executed, the communication devices 2B, 2C,... First, in S810, based on the number of received frames per unit time wirelessly received by the transmission / reception unit 24, the number of communication devices existing in the vicinity. (Hereinafter referred to as the number of peripheral communication devices) is estimated. For example, when each of the communication devices 2B, 2C,... Normally transmits about 10 frames per unit time (for example, 1 second), the number of received frames per unit time wirelessly received by the transmission / reception unit 24 is 100. In this case, it is estimated that the number of peripheral communication devices is ten.

  In S820, it is determined whether or not the adoption flag of the row corresponding to the number of peripheral communication devices estimated in S810 (hereinafter referred to as the estimated number of peripheral communication devices) is set to 1 in the transmittable time calculation parameter table. To do. The transmittable time calculation parameter table is stored in advance in the data storage unit 26, and includes a first fixed time T1 and a second fixed time corresponding to each of a range of a plurality of peripheral communication devices and a range of the number of peripheral communication devices. A combination of T2, a third fixed time T3, an integer value n, an integer value m, and an adoption flag (see FIG. 9). The first fixed time T1, the second fixed time T2, the third fixed time T3, the integer value n, and the integer value m are fixed values. Further, the value of the adoption flag can be rewritten to 0 or 1.

  If the adoption flag of the row corresponding to the estimated number of peripheral communication devices is set to 1 (S820: YES), the process proceeds to S850. On the other hand, when the adoption flag of the row corresponding to the estimated number of peripheral communication devices is set to 0 (S820: NO), in S830, the first fixed time T1, the second fixed time T2, and the third fixed time. T3, integer value n, and integer value m are set to the values in the row corresponding to the estimated number of peripheral communication devices in the transmittable time calculation parameter table.

Thereafter, in S840, in the transmittable time calculation parameter table, the adoption flag of the row corresponding to the estimated number of peripheral communication devices is set to 1, and the adoption flag of the other rows is set to 0, and the process proceeds to S850.
When the process proceeds to S850, the process waits for a preset transmission time calculation parameter change interval ΔT (for example, 1 second), and then returns to S810.

The thus configured communication devices 2B, 2C,... Calculate the transmittable time tg according to the equation (6). That is, as shown in FIG. 10, the data transmission times are determined as follows in ascending order.
(T0 + T1), (t0 + T1 + T2), (t0 + T1 + 2 × T2), (t0 + T1 + 3 × T2),..., {T0 + T1 + (n−1) × T2}, (t0 + T1 + T3), (t0 + T1 + T3 + T2), (t0 + T1 + T3) t0 + T1 + T3 + 3 × T2),..., {t0 + T1 + T3 + (n−1) × T2}, (t0 + T1 + 2 × T3), (t0 + T1 + 2 × T3 + T2), (t0 + T1 + 2 × T3 + 2 × T2), (t0 + T1 + 2 × T3 + 3)・.

  Since the third fixed time T3 is set to be longer than (T2 × n), the relationship between {t0 + T1 + (j−1) × T3 + (n−1) × T2} and (t0 + T1 + j × T3) The difference (for example, the difference between {t0 + T1 + T3 + (n−1) × T2} and (t0 + T1 + 2 × T3)) is {t0 + T1 + (j−1) × T3 + (n−1) × T2} and {t0 + T1 + (j−1) ) × T3 + n × T2} (for example, the difference between {t0 + T1 + T3 + (n−1) × T2} and (t0 + T1 + n × T2)).

  Therefore, when the data transmission time is determined over a certain time range, the number of data transmission times can be reduced as compared with the determination of the data transmission time based on Expression (4). For this reason, the number of generations of the transmittable time additional data and the MAC or the electronic signature is smaller than the wireless communication devices 2B, 2C,... Described in the first embodiment, and the processing load on the communication devices 2B, 2C,. Can be reduced.

  Further, the number of wireless communication devices (number of peripheral communication devices) existing around the communication devices 2B, 2C,... Is estimated based on the data reception status of the communication devices 2B, 2C,. Based on the number of peripheral communication devices (estimated peripheral communication device number), the value of m is set so as to have a positive correlation with the number of peripheral communication devices. In the present embodiment, m = 0 is set when the estimated number of peripheral communication devices is less than 10, and m = 2 is set when the estimated number of peripheral communication devices is 10 or more and less than 20.

  As a result, the later transmission possible time tg can be calculated as the number of peripheral communication devices increases. As a result, since the number of peripheral communication devices is large, the occurrence of a situation where the communication channel is not freed even when the latest transmission time tg has elapsed is suppressed, and unnecessary calculation by the communication device is reduced. can do.

  Further, it is determined whether or not the difference between the transmittable time tg having the smallest difference from the current time t0 and the current time t0 is equal to or larger than a preset transmission allowable determination value (S590), and is equal to or larger than the transmission allowable determination value If it is determined (S590: NO), the wireless transmission of the frame used for this determination is prohibited, and the processes of S520 and S530 are executed again. That is, if it is determined in the process of S590 that the transmission allowable value is exceeded, a plurality of new transmittable times tg are calculated in the process of S530, and accordingly, a frame to which a new transmittable time tg is added. Is generated.

  As a result, the difference between the time when the communication devices 2B, 2C,... Actually transmit the frame wirelessly and the transmittable time tg indicated by the transmittable time information included in the wirelessly transmitted transmission frame is the transmission allowance determination value. It can be suppressed from becoming very large beyond. That is, it is possible to suppress deterioration in time synchronization accuracy between communication devices. In addition, the wireless communication band can be effectively used by suppressing the transmission of frames that can degrade the synchronization accuracy.

  In the embodiment described above, the processing in S810 is the estimation means in the present invention, the processing in S830 is the value setting means in the present invention, the processing in S590 is the transmission allowable time determination means in the present invention, and the branch when the determination in S590 is NO Is the prohibition re-execution means in the present invention, and the transmission permission judgment value is the transmission permission time in the present invention.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, As long as it belongs to the technical scope of this invention, a various form can be taken.
For example, in the above-described embodiment, the present invention is applied to a device that wirelessly transmits data outside a periodic transmission period that is repeated at regular intervals. However, the present invention is not limited to this, and data including a transmission time is included. Any wireless communication device that performs wireless transmission may be used.

  In the above embodiment, the value of m is set so as to have a positive correlation with the number of peripheral communication devices. However, n is set so as to have a positive correlation with the number of peripheral communication devices. A value may be set.

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 2A, 2B, 2C ... Communication apparatus, 11 ... Data input part, 12 ... Data processing part, 13 ... MAC and electronic signature processing part, 14 ... Transmission part, 21 ... Data input / output part, 22 ... Data processing unit, 23... MAC / electronic signature processing unit, 24... Transmission / reception unit, 25.

Claims (6)

A wireless communication device that wirelessly transmits data using a predetermined communication channel,
Transmission time determining means for determining a plurality of data transmission times, which are times for wirelessly transmitting data;
For each of the plurality of data transmission times determined by the transmission time determination means, based on transmission time additional data configured from transmission time information indicating the data transmission time and data different from the data transmission time, Generating means for generating a message authentication code or electronic signature;
Channel determining means for determining whether or not the communication channel is empty;
When the channel determination means determines that the communication channel is free, the transmission time additional data having transmission time information indicating the data transmission time closest to the current time, and the transmission time additional data based on the transmission time additional data A wireless communication apparatus comprising: a transmission unit configured to wirelessly transmit transmission data including the message authentication code or the electronic signature generated by the generation unit. The wireless communication device performs wireless transmission using a carrier sense multiple access / collision avoidance (CSMA / CA) method,
The generation means is a fixed generation time which is a fixed time set in advance as a time required for generating the message authentication code or the electronic signature, and the wireless after the channel determination means determines that the communication channel is free. A time obtained by adding a fixed waiting time set in advance as a time to wait before starting transmission is a first fixed time,
The slot time, which is the minimum unit time of the backoff time in the CSMA / CA method, is set as the second fixed time.
The data transmission time is tg, the current time is t0, the first fixed time is T1, the second fixed time is T2, n is a preset integer value, and i is an integer value from 0 to (n-1). Then,
The transmission time determining means includes
The data transmission time is determined by the following equation (1). Tg = t0 + T1 + i × T2 (1)
The wireless communication apparatus according to claim 1. The wireless communication device performs wireless transmission using a carrier sense multiple access / collision avoidance (CSMA / CA) method,
A fixed generation time that is a fixed time set in advance as a time required for the generation means to generate the message authentication code or the electronic signature, and after the channel determination means determines that the communication channel is free A time obtained by adding a fixed waiting time set in advance as a time to wait before starting wireless transmission is defined as a first fixed time,
The slot time which is the minimum unit time of the backoff time in the CSMA / CA method is set as the second fixed time,
The data transmission time is tg, the current time is t0, the first fixed time is T1, the second fixed time is T2, n is a preset integer value, and i is an integer value from 0 to (n-1). , Where T3 is a third fixed time preset to be longer than (T2 × n), m is a preset integer value, and j is an integer value from 0 to (m−1).
The transmission time determining means includes
The data transmission time is determined by the following equation (2). Tg = t0 + T1 + i × T2 + j × T3 (2)
The wireless communication apparatus according to claim 1. Estimating means for estimating the number of peripheral communication devices, which is the number of wireless communication devices existing around the wireless communication device, based on the data reception status of the wireless communication device;
Value setting means for setting at least one value of the n and the m so as to have a positive correlation with the number of peripheral communication devices based on the number of the peripheral communication devices estimated by the estimation means; The wireless communication apparatus according to claim 3, further comprising: Whether the difference between the time when the transmission means wirelessly transmits the transmission data and the data transmission time indicated by the transmission time information included in the transmission data is equal to or greater than a preset allowable transmission time A transmission allowable time determination means for determining
When it is determined by the transmission allowable time determination means that the transmission allowable time is longer than the transmission allowable time, the transmission data used for the determination by the transmission allowable time determination means is prohibited from being wirelessly transmitted by the transmission means, and The wireless communication apparatus according to claim 1, further comprising a prohibition re-execution unit that executes the transmission time determination unit again.   A wireless communication system comprising the wireless communication device according to any one of claims 1 to 5.