JP2010093564A - Wireless communication apparatus and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication apparatus capable of reducing radio wave interference and realizing efficient wireless communication. <P>SOLUTION: The wireless communications apparatus has: a plurality of antennas 1 and 2 each of which has a different communication range; a propagation loss calculator 4 that receives a radio wave from a surrounding wireless communications apparatus, and calculates a propagation loss between transmission and reception based on a received radio wave strength; a communication target determination part 6 that determines whether or not each surrounding wireless communication apparatus becomes a communication target based on an antenna from which the radio wave is received and on the calculated propagation loss; and a communication controller 8 that decides the antenna with which wireless transmission is carried out and the transmission radio wave strength based on the propagation loss for the wireless communication apparatus as the communication target. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method.

  In CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) communication such as wireless LAN, it is confirmed whether a channel is available prior to transmission of radio waves. Then, after confirming that the channel is free, transmission of radio waves is started. Thus, while communication is being performed on one channel, communication from other terminals is awaited.

  Therefore, in order to reduce radio wave interference and optimize the communication environment, transmission power is controlled based on reception intensity (Patent Document 1). In addition to the reception intensity, it is disclosed that transmission power is controlled based on the degree of congestion of surrounding wireless communication, the relative speed with a counterpart terminal, and the like (Patent Documents 2 and 3).

In addition, if the process for determining transmission power between terminals is started before starting wireless communication, there is a problem that the start of communication is delayed due to this control. Further, when determining the transmission power based on the reception strength of a communication partner terminal needs to know whether to communicate with the advance which communication terminal.
Japanese Patent Laid-Open No. 2004-260753 JP 2005-039665 A JP 2007-006395 A

  An object of the present invention is to reduce radio wave interference and realize efficient wireless communication.

  The wireless communication apparatus according to the present invention includes a plurality of antennas, propagation loss calculation means, determination means, and communication control means. Each of the plurality of antennas has directivity and has a different communication range. The propagation loss calculation means receives a radio wave from a surrounding wireless communication device via an antenna, and calculates a propagation loss between transmission and reception from the received radio wave intensity. The determination means determines whether or not each of the surrounding wireless communication devices is to be a communication target, from which antenna the radio wave is received and from the propagation loss. The communication control means, when performing data transmission, determines which antenna is used for communication and how much transmission radio wave intensity is used for the transmission loss calculated for the wireless communication device determined to be a communication target. Determine based on.

  Note that the propagation loss can be calculated from, for example, the difference between the transmission power stored in the radio frame and the reception power at the time of reception. In addition, the determination unit can determine which wireless communication device should be a communication target because the existence direction of the counterpart device can be determined from the receiving antenna and the relative distance can be determined from the propagation loss. .

  According to the present invention, unnecessary radio wave transmission can be suppressed and interference can be suppressed. That is, wireless transmission cannot be performed from an antenna in which no wireless communication device to be communicated exists within the communication range. In addition, interference can be suppressed by setting the transmission radio wave intensity to the minimum radio wave intensity required for communication with the wireless communication device to be communicated.

  Note that it is desirable that the propagation loss calculation means periodically acquires the received radio wave intensity from surrounding wireless communication devices and stores the calculated propagation loss. Moreover, it is preferable that the determination means also determines whether or not the wireless communication device is a communication target each time a radio wave is received. By doing so, it is possible to always grasp which wireless communication device is a communication target. Therefore, it is possible to reduce the preprocessing to be performed at the time of data transmission, and it is possible to immediately transmit data. Thus, it is desirable that each wireless communication apparatus periodically transmit radio waves so that the received radio wave intensity can be measured periodically. Moreover, it is preferable that the determination unit performs the determination process every time a radio wave is received. However, depending on the reception frequency, the determination process may be performed less frequently.

  Here, the wireless communication apparatus according to the present invention performs multiple types of data transmission, and it is preferable to determine a communication target for each type of data transmission. That is, it is preferable that the determination unit and the communication unit determine whether or not to make a communication target for each type of data transmission, and determine the antenna for performing wireless communication and the transmission radio wave intensity.

  In this way, the communication target can be changed for each type of data transmission. In other words, data can be transmitted only to a partner within an appropriate range according to the data type.

  In the present invention, it is preferable that a communication target range is determined for each type of data transmission, and the determination unit determines that a wireless communication device existing in the communication target range is a communication target. In this case, the determination means calculates in which direction the surrounding wireless communication device exists depending on which antenna the radio wave is received from, calculates a relative distance from the propagation loss, and calculates the calculated existence direction and relative distance. It is preferable to determine based on the communication target range. In this way, it is possible to determine a wireless communication device to be communicated for each data transmission type.

  In the present invention, it is preferable to determine a modulation scheme to be used for each type of data transmission, and to determine the transmission radio wave intensity in consideration of the modulation scheme. Since a modulation scheme with higher communication efficiency requires stronger reception strength, it is preferable to determine the transmission radio wave strength accordingly.

  In this way, a modulation scheme corresponding to the data type can be used. In addition, when the reception sensitivity of the communication target is sufficiently good, data transmission may be performed using a modulation scheme that is more efficient than the modulation scheme predetermined for the data type.

  The present invention can be understood as a wireless communication apparatus having at least a part of the above means. The present invention can also be understood as a wireless communication method including at least a part of the above processing or a program for realizing the method. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

For example, the present invention is a wireless communication method in a wireless communication device including a plurality of antennas each having a different communication range,
A propagation loss calculating step of receiving radio waves from surrounding wireless communication devices by the plurality of antennas and calculating a propagation loss between transmission and reception from the received radio wave intensity;
For each of the surrounding wireless communication devices, a determination step of determining whether to make a communication target, from which antenna the radio wave is received and from the propagation loss,
Based on the propagation loss for the wireless communication device to be communicated, a communication control step for determining an antenna for performing wireless transmission and a transmission radio wave intensity;
It can be grasped as a wireless communication method characterized by including.

  According to the present invention, it is possible to reduce radio wave interference and realize efficient wireless communication.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

<Configuration>
The present embodiment is an inter-vehicle communication system in which a wireless communication device is mounted on a vehicle and wireless communication is performed between the vehicles. Each vehicle includes a plurality of antennas each having a different communication range. In the present embodiment, one antenna is disposed at each of the front and rear of the vehicle, and each has directivity in the front direction and the rear direction.

  An in-vehicle wireless communication apparatus according to this embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating functional blocks of a wireless communication device according to the present embodiment. As described above, the wireless communication apparatus includes the antenna 1 whose communication range is the front of the vehicle and the antenna 2 whose communication range is the rear of the vehicle. The transmission / reception unit 3 performs modulation / demodulation processing, digital-analog conversion processing, frequency conversion processing, and the like. In the present embodiment, a wireless communication system conforming to IEEE802.11j that uses an OFDM (Orthogonal Frequency Division Multiplexing) system in the 5 GHz band is adopted. Note that the modulation scheme (subcarrier modulation scheme) and transmission power for wireless transmission are determined by an instruction from the communication control unit 8.

  The propagation loss calculation unit 4 acquires the received power intensity of radio waves transmitted from surrounding vehicles. Here, the propagation loss calculation unit 4 is intended to estimate the distance from the opponent vehicle from the intensity of the received radio wave. Therefore, the propagation loss calculation unit 4 calculates the propagation loss of radio waves from the acquired reception sensitivity. In the present embodiment, transmission power is stored in control information of a radio frame, and information is transmitted. FIG. 2 is a diagram illustrating a configuration of a radio frame used in the present embodiment. As shown in the figure, the radio frame used in the present embodiment is composed of a preamble 11, a unique word 12, control information 13 and data 14, and the control information 13 includes a transmission vehicle ID 15 and transmission power 16. Therefore, the propagation loss calculation unit 4 refers to the transmission vehicle ID 15 to determine which vehicle the radio wave is from, and compares the transmission power information in the acquired radio frame with the received radio wave intensity to determine the propagation loss. calculate.

  The propagation loss storage unit 5 stores the propagation loss calculated by the propagation loss calculation unit 4 together with the vehicle ID. FIG. 3 is a diagram illustrating a configuration example of the propagation loss storage unit 5. As shown in the figure, the propagation loss storage unit 5 stores a vehicle ID 51, an antenna 52, and a propagation loss 53. Thus, by referring to the propagation loss storage unit 5, it is possible to grasp how far away each vehicle is located in which antenna orientation.

  The contents of the propagation loss storage unit 5 preferably hold the latest information as much as possible. Therefore, it is preferable that the propagation loss calculation unit 4 updates the propagation loss storage unit 5 every time a radio frame is received. Further, regarding the propagation loss 53, if it is determined based on only the latest one received signal, there is a risk that the variation will increase due to the influence of fading or the like. Therefore, it is preferable to use a value obtained by averaging the propagation loss in the latest predetermined period.

The communication information database 7 stores setting information as to which range and in which modulation method the data is transmitted according to the type of data to be transmitted, and the data transmission destination vehicle at the present time. FIG. 4 shows a configuration example of the communication information database 7. The communication information database 7 stores a data type 71, an antenna 72, a required transmission distance 73, a modulation method 74, and a target vehicle ID 75. For example, the data type “green signal start promotion” notifies the vehicle ahead when the signal changes to blue, and the range within 30 m using the front antenna, that is, the front 30
Within m is set as the communication range. At this time, the modulation scheme is set to use 64QAM.

  Depending on the data type, there may be a communication range only in front or rear, and a communication range in front or rear. The data type (in FIG. 4, “lane change” is equivalent to “lane change” in FIG. 4) for both the front and rear communication ranges may be changed in the required transmission distance and the modulation method for each of the front and rear. good. As for the target vehicle ID 75, the target vehicle ID is stored for each antenna.

  Here, it is assumed that the data type 71, the antenna 72, the required transmission distance 73, and the modulation method 74 are fixed data and are not changed, but the target vehicle ID 75 is updated as needed.

  The communication target determining unit 6 determines whether or not to include a vehicle whose propagation loss, that is, a relative distance can be acquired by the propagation loss calculating unit 4 as a communication target vehicle for various data transmissions. The relationship between the propagation loss and the communication distance can be estimated based on the propagation loss estimation formula. Here, as the propagation loss estimation formula, a free space model, a two-wave model, or other empirical estimation formulas can be used. If there is a parameter used in the propagation loss estimation formula, it may be stored in association with the map information and used depending on the location where the vehicle is traveling, or by wireless communication from an external device such as a roadside device. Parameters may be acquired and used.

  In this way, the communication target determining unit 6 estimates in which range (azimuth and distance) the vehicle that has received the radio wave is located, and determines whether or not the position is within the assumed communication range. Judge every. When the vehicle is located within the communication target range of the data type, the vehicle ID is stored in the target vehicle ID 75 of the communication information database 7. Conversely, if the vehicle is not located within the communication target range and the target vehicle ID 75 of the communication information database 7 is stored, the vehicle ID is deleted.

  When transmitting data, the communication control unit 8 refers to the propagation loss storage unit 5 and the communication information database 7 to determine the antenna to be used for communication, the transmitted radio wave intensity and the modulation method, and transmit / receive Notify part 3. The antenna and modulation method used for communication can be obtained as they are by referring to the communication information database 7. The transmission radio wave intensity is determined as follows.

  That is, the communication control unit 8 first acquires a vehicle to be communicated with reference to the communication information database 7. Next, the vehicle located farthest among the vehicles to be communicated (having a large propagation loss) is obtained with reference to the propagation loss storage unit 5. Then, the transmission intensity is set as an intensity that can be received by the vehicle located farthest away. That is, the transmission radio wave intensity is determined as the intensity obtained by adding the propagation loss of the farthest vehicle to the minimum reception sensitivity determined by the modulation method. At this time, the transmission radio wave intensity obtained in this way may be provided with a slight margin and may be slightly stronger.

<Processing flow>
Next, a flow of processing performed by the wireless communication apparatus according to the present embodiment will be described.

-Radio wave reception processing First, processing performed when radio waves from surrounding vehicles are received will be described with reference to FIG. When the transmission / reception unit 3 receives radio waves (S10), the propagation loss calculation unit 4 measures the received power intensity at that time (S11). Then, the propagation loss is calculated by comparing the received power intensity with the transmission power intensity stored in the received radio frame, and the vehicle ID is stored in the propagation loss storage unit 5.
And stored in association with each other (S12). The communication target determining unit 6 estimates the relative distance from the transmission source vehicle from the propagation loss estimation formula (S13). Since the location of the transmission source vehicle is known from the received antenna and relative distance, it is determined for each data transmission type whether the vehicle is located within the data transmission range (S14). The communication target determining unit 6 updates the communication information database based on the determination result (S15). That is, if the transmission source vehicle is located within a transmission range for a certain data type, the vehicle ID is stored in the target vehicle ID 75 of the communication information database 7. On the other hand, if the transmission source vehicle is not located within the transmission range, the vehicle ID is deleted from the target vehicle ID 75.

-Radio wave transmission processing Next, processing performed when data is transmitted will be described with reference to the flowchart of FIG. First, when data transmission is required by using information from the outside as a trigger, the type of data to be transmitted is determined (S20). The communication control unit 8 refers to the communication information database 7 and acquires which vehicle is used as a communication target from which antenna to transmit data (S21). Next, the communication control unit 8 refers to the propagation loss storage unit 5 and determines a vehicle having the largest propagation loss among the communication target vehicles (S22). Further, the modulation method is acquired with reference to the communication information database 7 (S23). Since the minimum reception sensitivity required for each modulation method is determined, the radio wave intensity obtained by adding the maximum propagation loss obtained in step S22 to the minimum reception sensitivity is determined as transmission power (S24). When radio waves are transmitted from a plurality of antennas, transmission power is determined for each antenna.

  The communication control unit 8 transmits data with the transmission power determined in this way (S25). After the data transmission, ACK indicating that the communication partner has received the data correctly is received (S26). If there is a vehicle that does not return an ACK among the communication target vehicles (S27-YES), it is determined whether the transmission power can be increased (S28). That is, it is determined whether the upper limit of the transmission output is exceeded even if the radio field intensity is increased by a predetermined value (X dB) from the latest transmission output. If the transmission output can be increased (S28-YES), the transmission power is increased by this predetermined value (S29), and data transmission is attempted again.

<Operation example>
A specific operation example in the situation as shown in FIG. 7 will be described. In the situation shown in FIG. 7, vehicle ID2-5 is located ahead of the own vehicle (vehicle ID1), and vehicle ID6-9 is located behind. In such a case, the vehicle IDs 2 to 5 receive radio waves only from the front antenna, and the vehicle IDs 6 to 9 receive radio waves only from the rear antenna. Since the degree of radio wave attenuation (propagation loss) increases with increasing distance from the vehicle, data stored in the propagation loss storage unit 5 in this example is as shown in FIG. If a free space model is adopted as an estimation formula for the propagation loss, for example, the loss is 76 dB at a distance of 30 m, 80 dB at a distance of 50 m, and 86 dB at a distance of 100 m. Thus, the distance to each vehicle can be grasped from the propagation loss.

  Next, it is assumed that the transmission ranges of various data transmissions in this embodiment are defined in FIG. Here, five data types are defined. For example, “green signal start promotion” is a notification for prompting another vehicle to start when the signal changes to blue, and the transmission range is within 30 m ahead. Here, "Progress green start" and "Danger of frontal collision" are transmitted only in the front, "Front traffic jam" and "Brake braking" are transmitted only in the rear, and "Change lane" is transmitted in both the front and rear. The range.

Here, it is assumed that the radio wave from the vehicle ID 3 is received by the front antenna 1 and the propagation loss is 75 dB. In this case, it can be seen that the vehicle ID 3 is located within 30 m ahead of the host vehicle. Therefore, the communication information database 7 is used as a communication target vehicle for the front antenna of “green signal start”, “frontal collision”, and “lane change”. Stored. Further, it is assumed that the vehicle ID 8 receives a radio wave from the rear antenna and has a propagation loss of 83 dB. In this case, since it can be seen that the vehicle ID 8 is located about 65 m behind the host vehicle, the vehicle ID 8 is stored as a communication target vehicle for the rear antenna of the “rapid brake braking”. In addition, it is determined from the propagation loss shown in FIG. 3 which data transmission target each vehicle is.

  Next, based on the communication information database 7 created in this way, a method for determining transmission power when performing each data transmission will be specifically described. For example, when transmitting the “green signal start promotion” data, referring to the communication information database 7, it can be seen that it is only necessary to transmit from the front antenna 1 by the 64QAM method. Further, the communication target vehicles are IDs 3, 4 and 5, and the vehicle farthest among them is the vehicle ID 3, and it can be determined by referring to the propagation loss storage unit 5 that the propagation loss is 75 dB. . Since the minimum reception sensitivity in the case of transmitting in the 64QAM system is -74 dBm, it can be determined that transmission with an output of 1 dBm is sufficient to suppress the transmission of unnecessary radio waves while including the vehicle ID 3 in the communication range. For other data types, the transmission output is determined in the same way, but for the notification of “lane change” with both the front and rear communication ranges, the transmission output transmitted from the front and rear antennas is determined individually. To do.

<Operation / Effect of Embodiment>
According to the present embodiment, since the transmission output can be adjusted so that the radio wave reaches only the communication target vehicle when performing the radio communication, it is possible to reduce the interference of the radio wave and realize efficient radio communication. Further, since this communication range can be set individually for each data type, the communication range can be set flexibly according to the importance of data.

  In addition, since the communication information database 7 is regularly updated, it can be easily determined by referring to this database which vehicle should be communicated when data is transmitted. Further, since the calculation of the transmission output can be obtained by a simple calculation based on the propagation loss stored in the propagation loss storage unit 5, less processing is performed before data transmission. Therefore, the transmission can be executed promptly after the data needs to be transmitted.

<Modification>
The above embodiment is merely an example of the present invention. The scope of the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the technical idea.

  For example, each of the wireless communication devices mounted on the vehicle includes two antennas whose communication ranges are the front and rear of the vehicle, but may include three or more antennas. For example, it is also preferable to provide four antennas and set the front, rear, right side, and left side as communication ranges.

  Further, although the description has been given assuming that the modulation scheme is fixed for each data type, the modulation scheme may be adaptively changed. Data types that need to be communicated to relatively long distances are set to use modulation schemes that require low reception sensitivity. For example, in the example of FIG. 4, QPSK is used when notifying “frontal collision risk” or “sudden braking” that needs to be communicated up to 100 meters away. However, if the vehicle to be communicated exists only near the host vehicle, communication is possible even if a more efficient modulation method is used.

  In order to adaptively change the modulation method in this way, when the communication control unit 8 determines the transmission power (step S24 in FIG. 6), the communication information database with the vehicle farthest from the host vehicle is used. It is only necessary to determine whether communication is possible even with a modulation scheme having a larger multi-value number than the modulation scheme defined in FIG.

  Also, the communication range may be changeable according to the situation. For example, the communication range may be widened or narrowed according to the time zone or surrounding traffic conditions. In this case, each vehicle may grasp the surrounding situation by a sensor or the like and change autonomously, or may receive a change instruction from a roadside device or the like and change it accordingly.

  In the above example, the wireless communication system conforming to IEEE802.11j has been described as an example. However, other wireless LAN standards such as IEEE802.11a, b, g, and n may be used. Other wireless communication methods such as 802.20 may be used.

It is a figure which shows the functional block of the radio | wireless communication apparatus which concerns on embodiment. It is a figure which shows the structure of the radio | wireless frame utilized by embodiment. It is a figure which shows the example of the table structure of a receiving intensity memory | storage part. It is a figure which shows the example of the table structure of a communication information database. It is a flowchart which shows the flow of the process performed when an electromagnetic wave is received from the surrounding vehicle. It is a flowchart which shows the flow of the process at the time of performing data transmission. It is a figure explaining the example of the positional relationship of a vehicle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front antenna 2 Back antenna 3 Transmission / reception part 4 Propagation loss calculation part 5 Propagation loss memory | storage part 6 Communication object judgment part 7 Communication information database 8 Communication control part

Claims (10)

A plurality of antennas each having a different communication range;
Propagation loss calculating means for receiving radio waves from surrounding wireless communication devices by the plurality of antennas and calculating propagation loss between transmission and reception from the received radio wave intensity;
For each of the surrounding wireless communication devices, determination means for determining whether or not to be a communication target from which antenna the radio wave is received and the propagation loss,
Based on the propagation loss for the wireless communication device to be communicated, an antenna for performing wireless transmission and a communication control means for determining a transmission radio wave intensity;
A wireless communication device comprising: The wireless communication apparatus according to claim 1, wherein the communication control unit determines an antenna that performs wireless transmission and a transmission radio wave intensity so that radio wave interference does not occur in a wireless communication apparatus other than a communication target. Multiple types of data transmission,
The determination unit and the communication control unit determine, for each type of data transmission, whether to make a communication target, and determine an antenna for performing wireless communication and a transmission radio wave intensity. Item 3. The wireless communication device according to Item 1 or 2. A communication target range is determined for each of the plurality of types of data transmission,
The determination means calculates the presence azimuth according to which antenna the radio wave is received from around the surrounding wireless communication device, calculates the relative distance from the propagation loss, and the calculated presence azimuth and relative distance are the communication targets of the data transmission. It is judged whether it is a range. The radio | wireless communication apparatus of Claim 3 characterized by the above-mentioned. The modulation scheme to be used is determined for each of the plurality of types of data transmission,
The wireless communication apparatus according to claim 3 or 4, wherein the communication control means determines a transmission radio wave intensity in consideration of a modulation method. A wireless communication method in a wireless communication device including a plurality of antennas each having a different communication range,
A propagation loss calculating step of receiving radio waves from surrounding wireless communication devices by the plurality of antennas and calculating a propagation loss between transmission and reception from the received radio wave intensity;
For each of the surrounding wireless communication devices, a determination step of determining whether to make a communication target, from which antenna the radio wave is received and from the propagation loss,
Based on the propagation loss for the wireless communication device to be communicated, a communication control step for determining an antenna for performing wireless transmission and a transmission radio wave intensity;
A wireless communication method comprising: The wireless communication method according to claim 6, wherein, in the communication control step, an antenna for performing wireless transmission and a transmission radio wave intensity are determined so that radio wave interference is not caused in radio communication apparatuses other than the communication target. Multiple types of data transmission,
The wireless communication method according to claim 6 or 7, wherein the determination step and the communication control step are executed for each data transmission. A communication target range is determined for each of the plurality of types of data transmission,
In the determining step, for the surrounding wireless communication devices, the existence direction is calculated according to which antenna the radio wave is received from, the relative distance is calculated from the propagation loss, and the calculated existence direction and the relative distance are the communication targets of the data transmission. It is judged whether it is a range. The radio | wireless communication method of Claim 8 characterized by the above-mentioned. The modulation scheme to be used is determined for each of the plurality of types of data transmission,
The wireless communication method according to claim 8 or 9, wherein, in the communication control step, a transmission radio wave intensity is determined in consideration of a modulation method.

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