JP4247184B2 - Wireless communication terminal and wireless communication method - Google Patents

Description

  The present invention relates to a wireless communication terminal and a wireless communication method which are mounted on a vehicle such as an automobile and used for inter-vehicle communication.

  An automobile that constructs a LAN (Local Area Network) in a vehicle and manages the operation state of each part in the vehicle has already been realized, and so-called computerization is also progressing in the automobile. Linking information outside the vehicle includes road-to-vehicle communication and vehicle-to-vehicle communication, and efforts are being made to provide driving assistance and automatic driving using information equipment. For example, Patent Document 1 below describes road-to-vehicle communication using a fixed communication protocol.

  Inter-vehicle communication is wireless communication with other vehicles. Active research is being carried out for the purpose of exchanging driving conditions with vehicles traveling in the vicinity of the vehicle, exchanging entertainment information, and guiding the following vehicles. Efforts are also being made to form a network by forming a mesh network between not only vehicles positioned in front of and behind the vehicle, but also wireless communication devices mounted on the vehicles on the front, back, left and right.

On the other hand, there are various standards for wireless communication. IEEE is developing a standard called 802.15.4a for short-range, low-speed wireless for sensor networks. This short-range low-speed radio has a short radio wave reach of about several tens of meters and a bit rate of several kbps, but has a high distance measurement function and position detection function. If such wireless technology is used, a wireless device can be used as a radar, and a wireless device that combines an inter-vehicle communication device and an inter-vehicle radar may be realized. In addition, when wireless communication terminals for vehicle-to-vehicle communication are installed in many vehicles, considering the available channels, that is, the frequency is finite, the radio wave coverage is as much as possible within the practical range. Shorter is better.
JP 2000-253188 A

  Most of the inter-vehicle communication so far is communication between vehicles traveling in the same direction. Automobiles are usually moving at a high speed of 10km / h, and the relative speed when passing an oncoming car may exceed 100km / h. For this reason, inter-vehicle communication between oncoming vehicles is based on the fact that the communicable time from when the oncoming vehicle enters the communicable area until it leaves is short, and the Doppler shift that occurs when the vehicle moves is relative speed. It is known that the technology is difficult to realize due to the fact that it becomes very large corresponding to the above. In particular, in communication means with a short radio wave reach distance, the communicable time of less than one second is cut, and in communication between vehicles crossing at an intersection etc., due to the influence of shielding such as buildings outside the road, It has also been pointed out that communication cannot be started unless it is very close. In addition, when trying to realize vehicle-to-vehicle communication using the wireless communication technology as described above with a low bit rate and a short radio wave reach, the number of bits that can be transmitted is less than one second when the communication time is less than one second. There is a possibility that the communication start procedure may not be completed.

  Communication with front, rear, left and right vehicles moving in the same direction is easier than inter-vehicle communication between oncoming vehicles. However, vehicles that move in the same direction basically have similar information on vehicle operation, and the amount of information obtained by exchanging information is not very large (of course, exchanging entertainment information and guiding the following vehicles). Is effective.) On the other hand, when trying to obtain information about road conditions through inter-vehicle communication, it is easier to obtain useful information from oncoming vehicles and vehicles that intersect at intersections because they are driving different routes from their own. It is obvious. In vehicle-to-vehicle communication, communication with a nearby vehicle can be started ad hoc as necessary, and communication can be terminated when it is no longer necessary. This is a simple communication means that communication is possible even if there is no infrastructure such as a center or a base station as long as the communication devices have the same specifications. It is considered that there is a potentially high demand for obtaining a lot of useful information using such a simple communication means.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a wireless communication terminal and a wireless communication method capable of vehicle-to-vehicle communication between oncoming vehicles by short-range wireless communication.

  A wireless communication terminal according to an aspect of the present invention includes means for detecting another wireless communication terminal that has entered a communicable range, means for detecting the position of the other wireless communication terminal, and the other wireless communication terminal. Based on the detected position, the relative traveling direction, and the relative speed of the other wireless communication terminal, the means for detecting the relative traveling direction of the other wireless communication terminal, the means for detecting the relative speed of the other wireless communication terminal, Means for estimating a communicable time with the other wireless communication terminal; a plurality of protocol modules; a means for selecting one protocol module from the plurality of protocol modules according to the estimated communicable time; Means for communicating with the other wireless communication terminal using the selected protocol module.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communication terminal and radio | wireless communication method which can perform the vehicle-to-vehicle communication between the oncoming vehicles by short distance radio | wireless can be provided.

  FIG. 1 is a block diagram of a wireless communication terminal according to an embodiment of the present invention. The wireless communication terminal 1 is a terminal mounted on a vehicle such as an automobile. The wireless communication terminal 1 radiates radio waves from the antenna 8 and receives radio waves from the antenna 8, and communicates with radio communication terminals mounted on other vehicles. Car-to-vehicle communication. The reach of radio waves radiated from the antenna 8 is relatively short, about several tens to 100 m, and the wireless communication terminal 1 is a terminal for short-range communication. The radio wave reachable distance corresponds to the maximum distance at which a transmitted radio wave is received by other wireless communication terminals with a minimum reception sensitivity or higher.

  For example, in the case of inter-vehicle communication with a parallel vehicle, a preceding vehicle, or a subsequent vehicle, a relatively sufficient communication time can be secured, but in the inter-vehicle communication with an oncoming vehicle, the time that can be communicated with the oncoming vehicle is extremely short. . The bit rate is also low. In such a wireless communication terminal 1, the terminal detection unit 12 detects that another terminal has entered the communicable range of the terminal itself, that is, the range determined by the antenna pattern and the radiation power.

  Specifically, the terminal detection part 12 is implement | achieved as follows, for example. Each wireless communication terminal radiates radio waves regularly or continuously, especially during idle periods when no communication is performed with any of the other parties. When the terminal detection unit 12 detects that the radio wave received by the wireless communication terminal 1 includes the radio wave emitted by the other radio communication terminal, the other radio communication terminal has entered the communicable range. Detect that. In this case, the terminal detection unit 12 does not perform detection alone, but uses a function of a physical layer processing unit (PHY) 7 that performs transmission / reception physical layer (RF, IF, baseband, etc.) processing. In addition, when the own terminal is not radiating the same radio wave when receiving the radio wave of the counterpart terminal, it is preferable to immediately radiate the radio wave from the own terminal so as to notify the partner of the existence of the own terminal.

  As another method, when the wireless communication terminal 1 has a radar function or is connected to a radar device mounted on a vehicle, the following is performed. In other words, in response to the presence of an object or moving object within the communicable range from the radar measurement results, radio waves are emitted to confirm that the other party is a wireless communication terminal that can communicate with the own terminal. In response to the response, another wireless communication terminal is detected. Each wireless communication terminal is set to respond to such confirmation radio waves received by other terminals.

  When it is confirmed that another wireless communication terminal exists within the communicable range of the own terminal, the position detection unit 3 detects the relative position of the partner terminal with respect to the own terminal. This is realized as follows, for example. When the wireless communication terminal 1 has a radar function or is connected to a radar device mounted on a vehicle, the position is detected from the measurement result. Even if the radar function is not provided, for example, a function for detecting the radiation position of the radio wave can be provided as described below.

  FIG. 2 is a diagram illustrating an appearance of a vehicle equipped with the wireless communication terminal according to the present embodiment. As shown in the figure, the antennas 13-1 and 13-2 of the wireless communication terminals are provided at two locations of the vehicle 14, and immediately after the other terminal receives the radio wave emitted from the first antenna 13-1, or The delay time required for signal processing from reception to transmission is included in the data, and the radio wave is sent back. When it is received by the first antenna 13-1 of its own terminal, the distance to the other party is calculated from the round trip time or the propagation time obtained by subtracting the delay time included in the data from the round trip time. The second antenna 13-2 also receives radio waves from the other party. The arrival times of the radio wave received by the first antenna and the radio wave received by the second antenna are shifted depending on the position of the other party. The position of the partner terminal can be detected from the difference in arrival time and the distance to the partner. At this time, a plurality of points may be candidates in the calculation, but it is narrowed down to at least one on a two-dimensional plane by considering the directivity of the antenna and the shielding characteristic of the vehicle on which the terminal is mounted. be able to. If it is clear that the other party is a terminal mounted on the vehicle, the height of the wireless communication terminal is almost known, so if it can be fixed at one position on the two-dimensional plane, the other party's position can be identified with that. it can. In a system in which the communication partner of the wireless communication terminal may be other than the terminal mounted on the vehicle, the height of the partner can be determined if the type of the partner terminal is notified, so that the position of the partner can be specified.

  When two antennas are used, the PHY 7 is actually composed of two PHY 7-1 and PHY 7-2 as shown in FIG. 3, and the transmission data is appropriately distributed according to the position of the other party and the nature of communication, while the reception data is Merged in an appropriate way.

  Except in the case of connecting to an external radar device and receiving data from the radar device, most of the components of the position detection unit 3 are included in the PHY 7 and the position is calculated based on the data from the PHY 7. The function to perform is provided in a portion other than PHY 7, that is, in the position detection unit 3.

  The wireless communication terminal 1 further includes a traveling direction detection unit 11 and a relative speed detection unit 2 related to the partner wireless communication terminal. These will be described later. The parameter to be measured is at least a relative parameter such as how the other party moves with respect to the own terminal. Of course, absolute parameters may be measured to perform advanced control of vehicle travel, but relative parameters are sufficient if the purpose is limited to the purpose of calculating the communicable time.

  Receiving a notification from the terminal detection unit 12 that another wireless communication terminal has entered the communicable range, the communication possible time is estimated from the data provided from the position detection unit 3, the relative speed detection unit 2, and the traveling direction detection unit 11. The unit 4 calculates a communicable time with the other party. As shown in FIG. 4, the communicable time comes out after the vehicle 14-2 equipped with another terminal enters the communicable range 15 of the vehicle 14-1 with respect to the vehicle 14-1 equipped with the own terminal. Is calculated based on the traveling direction and the relative speed v. In FIG. 4, the communicable range 15 extends to the rear part of the vehicle 14-1. When the front antenna arrangement is as shown in FIG. 2, one or two antennas are arranged at the rear of the vehicle in order to ensure a communicable range at the rear. Alternatively, the antenna may be installed on the roof of the vehicle so that the radio wave is not shielded by the vehicle body, and the radio wave may reach the rear part.

  When the communicable time is predicted, the protocol selection unit 5 shown in FIG. 1 selects one of a plurality of protocols according to the length of the communicable time, and another wireless communication terminal detected at that time Used for communication with. In FIG. 1, there are three protocol modules, that is, protocol 1 (6-1), protocol 2 (6-2), and protocol 3 (6-3), and between the data storage / generation unit 9 and PHY 7, Connected through one. That is, for example, if the protocol selected by the protocol selection unit 5 is protocol 1 (6-1), the transmission data is input from the data storage / generation unit 9 to protocol 1 (6-1) and packetized, MAC layer processing such as header assignment is performed. The transmission data subjected to the MAC layer processing is wirelessly modulated by the PHY 7 and emitted from the antenna 8. On the other hand, for the received data, the radio wave received by the antenna 8 is demodulated by the PHY 7, the header is analyzed and the data is recombined by the protocol 1 (6-1), and sent to the data storage / generation unit 9. This data is accumulated in the data accumulating / generating unit 9, and real-time data such as sound and data not to be accumulated input / output to / from the outside (display etc.) are input / output via the data input / output unit 10. .

  Each of the plurality of protocols differs in the size of the header, the number of types of header objects, the types of processing and data that can be handled, the access method, and the like. Basically, several types are prepared according to the time required for transmission / reception of parts (access control packet, header part, etc.) other than information (payload) inherent to data.

  For example, in the example of FIG. 1, protocol 1 is a protocol that is easy to access because it has a light processing and header, and corresponds to an opponent such as an oncoming vehicle passing at a high speed and having a significantly short communication time. Protocol 2 is a protocol that is used when the communicable time is short compared to the oncoming vehicle, although the communicable time is short, such as when passing by a vehicle stopped at a relatively low speed, More complex processing than protocol 1 is possible.

  Protocol 3 is a protocol used when communication with a vehicle traveling in the same direction is performed and the predicted value of the communicable time is long and communication can be performed without time limitation. It is a protocol capable of advanced processing equivalent to the protocol used.

  Specifically, the access method of protocol 1 is, for example, ALOHA. Aloha is known. The header of the communication frame is about the size of an Ethernet (registered trademark) header, and there are few types of objects that can be inserted into the header. The other party is not authenticated and radio waves can be exchanged with the other party, that is, a data link is formed with the other party.

  The access method of protocol 2 is, for example, CSMA / CA (carrier sense multiple access with collision avoidance). CSMA / CA is also known in the same manner as Aloha. Before forming a data link with the other party, the other party is authenticated. Therefore, there are more types of objects that can be inserted into the header than in Protocol 1.

  For example, the protocol 3 has a frame in which an access time of each terminal is assigned. A network can be formed as well as a data link, and authentication for entering the network and authentication for exchanging data with a specific terminal in the network are performed. Of course, there are many types of header objects. In some cases, the MAC layer is divided into several sub-layers, and fine control is possible. Furthermore, data can be encrypted as necessary.

  As described above, by selecting a plurality of protocols having different communication procedures and different processing burdens or processing times corresponding to the communication procedures according to the communication available time, even if the communication available time is short, Communication with the terminal is possible. Further, when the communicable time is long, sufficient authentication or the like is performed, and more advanced data exchange such as a voice call can be performed.

  These multiple protocols may be completely different protocols, but for ease of implementation, the function modules to be used and the range of options corresponding to each protocol are selected within one protocol module. It is preferable to define. FIG. 5 shows a configuration example of one protocol module corresponding to the above example. As shown in the figure, the range of header options and specific function modules (internal modules of one protocol module) that can be used according to each protocol is different.

  For example, in protocol 1 (16-1), a packet is simply generated, a minimum header such as a transmission source address, a destination address, a frame length, and a checksum is added, and the packet is transmitted. Since ALOHA is a protocol that can send packets at any time, ALOHA can be made substantially ALOHA by removing modules for access control such as framing and collision avoidance (CSMA / CA). Protocol 2 adds a collision avoidance module to CSMA / CA and includes an authentication module for authenticating the other party. Protocol 3 further includes a networking module, a framing module, an encryption module, and the like. In Protocol 3, the intention to join the network for the first time includes a collision avoidance module because there is a possibility of access by CSMA / CA during the free access period in the frame. Each header option has a range corresponding to the option to be used. In such a protocol module, a range is selected in accordance with an instruction from the protocol selection unit 5, and data from the data storage / generation unit 9 and the PHY 7 is processed within the range.

  When implementing a plurality of protocols, the configuration in which the usage range in one protocol module is determined according to each protocol eliminates the need to manufacture each module separately, thereby reducing manufacturing costs. In addition to being easy, there is an advantage that the memory space for mounting can be reduced. In addition, since it is basically based on the same protocol, when identifying a partner at the start of communication with another wireless communication terminal, there is a procedure for searching whether the protocol used by the partner can be used by the terminal. This eliminates the need for easy and quick identification of the partner communication terminal.

  Of course, the module shown in FIG. 5 only illustrates a part of the function of the actual protocol corresponding to the above example, and there are actually a large number of function modules and options including large and small, The range of their use varies depending on each protocol. In FIG. 5, the protocol with a large range includes all the small protocols. However, for example, there may be an option or a function module that is not used in a heavy protocol due to a light protocol. In fact, there is a high possibility that not all will be included as shown in the figure.

In this way, the lighter protocol is like a general wireless communication protocol with a reduced function. Functions such as bandwidth guarantee by authentication, encryption, or framing are cut according to each protocol, and there may be a need to impose restrictions on the nature and content of data that can be transmitted. In other words, the authentication and possibilities and the data that you do not want the feed is present without encryption, without bandwidth guarantee, or a short communication available time can be of the data can not be sent. In preparation for such a case, in this embodiment, as shown in FIG. 6, the protocol selection unit 5 controls the data accumulation / generation unit 9 corresponding to the selected protocol, that is, the communicable time, Data that can be transmitted by the data storage / generation unit 9 and a range of interfaces for inputting and outputting data are selected.

  FIG. 7 is an example showing in detail the periphery of the data storage / generation unit 9. In the data accumulation / generation unit 9, the accumulated data is classified. For example, data A is class 1-3, and data B is class 3. The class corresponds to the selected protocol. In protocol 1, class 1 designated data can be transmitted, and in protocol 3, class 3 designated data can be transmitted.

  Further, the data input / output unit 10 for inputting / outputting data to / from the data accumulating / generating unit 9 is divided into several interfaces as shown in detail, and the classification is similarly performed corresponding to each interface. ing.

  In addition, if data entering and exiting from the interface is data with low real-time characteristics that is temporarily stored in the data storage / generation unit 9, classification may be instructed to data input from the interface. Furthermore, even if not for each interface, real-time data such as voice and vehicle control information may be recorded in the data accumulating / generating unit 9 for further classification of data at the end of the interface. In addition, the stored data is not only classified by individual data, but may be classified by classifying the data into groups according to properties.

  When the selected protocol is notified from the protocol selection unit 5, the data storage / generation unit 9 selects data that can be transmitted correspondingly. Of course, what is sent in what order is determined in advance by a higher layer, for example, the intention of the human being in contact with the application or a request from the other terminal (or determined on the spot) Only data that can be supported by the selected protocol is selected and sent to the protocol module. In this way, it is possible to perform control such that transmission of data that should not be transmitted without authentication or encryption according to the protocol is permitted only when authentication or encryption is performed. In addition, it is possible to avoid wasting a short communication time by trying to send data that cannot be actually transmitted because the communication time is short.

  Furthermore, by such classification, when data that is not originally sent without authentication from a partner wireless communication terminal is sent using an unauthenticated protocol, such data is uncertain. It is possible to treat the data as untrustworthy, limit the range of use of the data, and warn the user to that effect.

  Next, a method for realizing the traveling direction and relative speed of the counterpart terminal will be described. The wireless communication terminal according to the present embodiment has at least a function of detecting the position of the counterpart terminal. The simplest method for realizing this is to perform position detection twice with a small time difference ΔT as shown in FIG. That is, when the terminal of the vehicle 14-1 wants to measure the relative speed and traveling direction of the terminal of the vehicle 14-2, the position is detected twice with an interval of ΔT. When position detection is performed, a difference between two relative position vectors is obtained and set as a difference vector. The direction of the difference vector is the traveling direction, and the relative speed is obtained by dividing the length L of the difference vector by ΔT. This method can be measured very simply.

  The following can be considered as another method applicable when the wireless communication terminal has a radar function or the vehicle is equipped with a radar and the wireless communication terminal can operate in cooperation with the radar. That is, the Doppler shift amount and the time differential value of the Doppler shift amount when the radio wave radiated as the radar bounces off the vehicle on which the counterpart terminal is mounted are detected.

  FIG. 9 is a graph illustrating how Doppler shifts occur when passing an oncoming vehicle in an adjacent lane as shown in FIG. At time 0, a frequency shift due to the Doppler shift appears by Δf, and after the time dt, the shift amount changes by df. Therefore, the differential value is df / dt. If Δf and df / dt and the position of the partner terminal are known, the traveling direction and relative speed of the partner terminal can be obtained on the assumption that the traveling speed v of the partner terminal does not change within dt. The differential value needs to be obtained from the frequency transition between multiple pulses if the radar radio wave is a short pulse, but if it is a long pulse or CW (continuous wave) radar, it can be measured with dt, and in a short time Can measure.

  Since we want to estimate the communicable time before entering the communicable range of the wireless communication terminal and further communicate, we want to shorten the time used for estimating the communicable time as much as possible. In particular, in the case of communication with an oncoming vehicle, it is significant that the time required for estimating the communicable time can be saved.

  If the measurement range of the radar function is different from the radio wave arrival range of the wireless communication terminal, and the radar measurement range is larger, the vehicle on which the other party's terminal is installed communicates with the time within the radio communication terminal's radio wave arrival range. It is advisable to estimate the possible time before entering the radio wave reachable range. As a result, it is possible to take a longer communication time. However, since it cannot be detected in advance whether or not the partner vehicle is equipped with a wireless communication terminal capable of communicating with the own terminal, a procedure of confirming it at the moment of entering the communicable range is required.

  If the wireless communication terminal does not have a radar function and is not equipped with a radar that can cooperate with the vehicle, for example, the same detection can be performed by measuring the Doppler shift amount of the radio wave radiated by the counterpart terminal and its differential value. Is possible. However, the differential value of the Doppler shift amount can be detected with high accuracy. However, in order to detect the absolute value of the Doppler shift amount, it is necessary to synchronize the oscillator of the own terminal and the oscillator of the other terminal, which is difficult. There are many.

  Therefore, for example, the Doppler shift amount and its differential value may be detected as follows. That is, the wireless communication terminal has a function of radiating a radio wave in frequency synchronization with the received radio wave, and when the counterpart terminal receives the radio wave from its own terminal, it sends it back in synchronism with the frequency. The own terminal receives the returned radio wave and detects the Doppler shift amount and the differential value. Note that it is preferable to set a short time constant of the feedback loop when frequency synchronization is performed. This is because the received radio wave can quickly follow the synchronization with the Doppler shift already possessed.

  When the partner terminal receives radio waves from the terminal itself, the terminal is moving at a high relative speed with respect to the partner terminal, so a Doppler shift has already occurred. In this state, the partner terminal can synchronize only with the radio wave in which the Doppler shift occurs.

  In the passing method as shown in FIG. 4, the Doppler shift amount changes from moment to moment. If the time constant of the loop is slow, it synchronizes with the average value of the frequency that changes every moment. Even if the radio wave having such a synchronized frequency is sent back, the terminal itself does not know the average value at which point in time, and consequently, the absolute amount of Doppler shift cannot be detected without much difference from the case of not synchronizing. On the other hand, if the time constant is shortened and the synchronized signal is sent back enough to follow the change in the received Doppler shift, the returned radio wave received by the terminal is effectively amplified and reflected by the partner vehicle. It can be handled like a radar radio wave, and the absolute amount of Doppler shift can be measured.

  Depending on the configuration of the position detection unit 3, the position of the counterpart terminal may not be determined between the two points before and after the vehicle on which the terminal is mounted. In such a case, there is a high possibility that one of the two points cannot be detected when the Doppler shift is detected. However, the communicable time due to the vehicle on which the own terminal is mounted and the vehicle on which the partner terminal is mounted does not change in the relative speed or direction of travel, regardless of which of the partner terminal is in front or back. As long as it is calculated the same, there is no effect.

  The problem that the absolute amount of Doppler shift cannot be detected only by receiving radio waves normally radiated by the counterpart terminal can also be solved by the following method. For example, each wireless communication terminal is informed of the traveling speed of the vehicle from a device that monitors the traveling state of the vehicle on which the wireless communication terminal is mounted, and periodically or if necessary, information on the traveling speed is transmitted by radio waves. Send to other terminals. If another terminal is detected within the communicable range of the own terminal, the traveling speed of the own vehicle is transmitted or a notification is requested to the partner terminal. If the traveling speed of the partner terminal side vehicle (partner vehicle) can be known, the traveling direction of the partner vehicle can be detected based on the position of the partner vehicle and the differential value of the Doppler shift amount. At this time, the differential value of the Doppler shift amount may be measured by using a radio wave for the partner terminal to notify the traveling speed, and the progress of the vehicle on which the partner terminal is mounted is transmitted by a relatively simple method of sending data. Know the direction and relative speed. It should be noted that the protocol used for requesting and sending the progress speed data may be fixed, for example, using the protocol with the lightest processing load.

  1, 3, and 6, the wireless communication terminal is illustrated as a set of functional components. However, as described above, these use some functions of the PHY or other functions of the vehicle. This is a means for calculating each parameter from information obtained by using or the like. Therefore, these can be part of the function of the control unit that performs such various calculations. A configuration closer to the mounting image is shown in FIG.

  The wireless communication terminal control unit 18 shown in FIG. 10 is a part that controls the entire wireless communication terminal, and performs such calculation simultaneously. Further, switching is determined and instructions are given to other blocks. The wireless terminal control unit 18 is connected to the PHY 7, controls this, causes the PHY 7 to perform measurement using the PHY 7, and sucks up the result from the PHY 7. Further, as described above, when the protocol switching is realized by changing the use range of the function module or option in one protocol module, as shown in FIG. Then, the wireless communication terminal control unit 18 instructs and changes the use range. The instruction to the data accumulation / generation unit 9 is similarly performed. Further, when receiving data from other functions of the vehicle in which the wireless communication terminal 1 is mounted, for example, a function for monitoring the running state of the vehicle, a radar function, etc., the wireless terminal control unit 18 stores and generates data. This is performed via the unit 9 and the data input / output unit 10. Furthermore, data necessary for starting communication transmitted by radio waves is also taken up from the data storage / generation unit 9.

  If any of the parameters cannot be measured well and the estimation of the communicable time fails, several methods can be used. For example, simply select the lightest protocol. Or what is necessary is just to determine a protocol by the case classification based on known information. For example, if only the relative position can be detected, if it is known that the position of the partner terminal is in the opposite lane, the lightest protocol is selected. You can see that you are driving, so choose a heavy protocol.

  According to the embodiment of the present invention described above, before a wireless communication terminal mounted on a vehicle starts communication with a terminal mounted on another vehicle, the position or relative speed of the counterpart terminal is detected. A communication possible time is estimated, and a protocol to be used is selected according to the estimated result. When the communicable time is long, a general protocol capable of authentication, network formation, encryption, and the like is selected. On the other hand, when the estimated communication possible time is short, a protocol with a light processing load is selected. Thereby, although there is a restriction in function, data exchange is possible, and a short-range wireless communication terminal capable of inter-vehicle communication between oncoming vehicles can be realized.

  Further, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram of a wireless communication terminal according to an embodiment of the present invention. The figure which shows the external appearance of the vehicle carrying the said wireless communication terminal The block diagram which shows the more detailed structure of the said radio | wireless communication terminal Diagram for explaining possible communication time Diagram showing how to implement multiple protocols The block diagram which shows the modification of the said radio | wireless communication terminal Diagram showing the configuration of the data storage / generation unit Diagram for explaining the measurement method of relative speed and direction of travel Diagram for explaining Doppler shift and its derivative The block diagram which shows the mounting image of the wireless communication terminal which concerns on one Embodiment of this invention

Explanation of symbols

1 ... wireless communication terminal;
2 ... Relative speed detector;
3 ... position detector;
4 ... Communication time estimation unit;
5 ... Protocol selection part;
6 ... Protocol module;
7: Physical layer processing unit;
8 ... Antenna;
9: Data accumulation / generation unit;
10: Data input / output unit;
11 ... Traveling direction detection unit;
12 ... terminal detection unit;
13 ... Antenna;
14 ... Vehicle;
15 ... Communication range;
16 ... protocol;
17 ... Data interface;
18 ... wireless communication terminal control unit;
19 ... Protocol module

Claims (12)

A wireless communication terminal mounted on a vehicle,
Means for detecting a wireless communication terminal mounted on another vehicle that has entered the communicable range;
Means for detecting a position of a wireless communication terminal mounted on the other vehicle ;
Means for detecting a relative traveling direction of a wireless communication terminal mounted on the other vehicle ;
Means for detecting a relative speed of a wireless communication terminal mounted on the other vehicle ;
Position of the radio communication terminal mounted to the detected other vehicle, relative moving direction, and based on the relative velocity, and means to estimate the communication time of the wireless communication terminal mounted on said other vehicle ,
A plurality of protocol modules having different time required for access control processing or time required for transmission / reception of the packet header, and
Means for selecting one protocol module from the plurality of protocol modules according to the estimated communicable time;
A wireless communication terminal comprising: means for communicating with a wireless communication terminal mounted on the other vehicle using the selected protocol module. The plurality of protocol modules are:
A first protocol selected when processing is simplest and the estimated available time is significantly shorter;
A second protocol that is selected when the processing is more complicated than the first protocol and the estimated communication possible time is more than the first protocol selection;
The third protocol is selected when the processing is more complicated than the first and second protocols and the estimated communication possible time is sufficiently long. Wireless communication terminal.   The wireless communication terminal according to claim 2, wherein the first protocol forms a data link without authentication of a communication partner.   The wireless communication terminal according to claim 3, wherein the first protocol is ALOHA.   3. The wireless communication terminal according to claim 2, wherein the second protocol has a function of authenticating the communication partner before forming a data link with the communication partner, and a packet collision avoidance function.   6. The wireless communication terminal according to claim 5, wherein the collision avoidance function is CSMA / CA. The third protocol is:
A function of authenticating the communication partner before forming a data link with the communication partner;
Packet collision avoidance function,
The ability to follow frame-based access time allocation,
The ability to form a network,
A function of performing authentication for entering the network or performing communication with a specific terminal in the network;
The wireless communication terminal according to claim 2, further comprising a data encryption function.   8. The wireless communication terminal according to claim 1, wherein each of the plurality of protocol modules includes different combinations of function modules and header options related to protocol processing. 9. Data to be transmitted to a wireless communication terminal mounted on another vehicle depends on the communication possible time corresponding to each of the plurality of protocol modules, presence / absence of an authentication function, presence / absence of an encryption function, presence / absence of a bandwidth guarantee function Means for classifying and storing;
The apparatus further comprises means for selecting a class of data to be transmitted to a wireless communication terminal mounted on the other vehicle corresponding to the estimated communication possible time and the selected protocol module. Item 9. A wireless communication terminal according to any one of Items 1 to 8. Data input / output interface means classified according to communication possible time corresponding to each of the plurality of protocol modules, presence / absence of authentication function, presence / absence of encryption function, presence / absence of bandwidth guarantee function,
9. The radio according to claim 1, further comprising means for selecting a class of the data input / output interface corresponding to the estimated communication possible time and the selected protocol module. Communication terminal. A radio wave radiating means for radiating a radio wave synchronized in frequency with the received radio wave;
The means for detecting the relative speed of the radio communication terminal mounted on the other vehicle is configured to detect a radio wave emitted by the radio communication terminal mounted on the other vehicle in frequency synchronization with the radio wave emitted by the radio wave radiation means. The wireless communication terminal according to claim 1, wherein the relative speed is detected by detecting a differential value of the Doppler shift amount. In a wireless communication method between a wireless communication terminal mounted on another vehicle by a wireless communication terminal mounted on a vehicle provided with a plurality of protocol modules with different time required for access control processing or transmission / reception required time of the packet header part,
Detecting a wireless communication terminal mounted on the other vehicle that has entered the communicable range;
Detecting a position of a wireless communication terminal mounted on the other vehicle ;
Detecting a relative traveling direction of a wireless communication terminal mounted on the other vehicle ;
Detecting a relative speed of a wireless communication terminal mounted on the other vehicle ;
Position of the radio communication terminal mounted to the detected other vehicle, relative moving direction, and based on the relative velocity, the step of inferring the communicable time with the radio communication terminal mounted on said other vehicle ,
Selecting one protocol module from the plurality of protocol modules according to the estimated communicable time;
And a step of communicating with a wireless communication terminal mounted on the other vehicle using the selected protocol module.

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