JP6880752B2 - Distance measurement system - Google Patents

Description

The present invention relates to a distance measuring system.

The distance between the in-vehicle communication device and the communication terminal is measured based on the reception level of radio waves transmitted and received between the in-vehicle communication device mounted on the vehicle such as an automobile and the communication terminal that performs wireless communication between the in-vehicle communication device and the communication terminal. There is a technique to do.

For example, in a wireless communication system including an in-vehicle communication device and a mobile wireless terminal, the in-vehicle communication device determines the distance to the mobile wireless terminal based on the received radio wave intensity of a response signal transmitted from the mobile wireless terminal with a constant intensity. A technique for calculating is known (see, for example, Patent Document 1).

JP 2015-072244

In the technique disclosed in Patent Document 1, the in-vehicle communication device measures the distance to and from the communication terminal based on the reception strength of the radio wave received from the communication terminal. Therefore, when the radio wave contains noise. , There is a problem that the error of the measurement distance increases.

An embodiment of the present invention has been made in view of the above problems, and is a case where noise is included in radio waves in a distance measuring system for measuring a distance between an in-vehicle communication device and a communication terminal. The purpose is to reduce the error of the measured distance in.

In order to solve the above problems, the distance measuring system according to the embodiment of the present invention measures the distance between the vehicle-mounted communication device and the communication terminal that performs wireless communication in the LF band. a measuring system, from the in-vehicle communication device, to generate a first magnetic field having a first attenuation characteristic, a first radio wave transmission unit for transmitting the first radio wave from the vehicle communication device, In order to generate a second magnetic field having a damping characteristic higher than that of the first damping characteristic, a second radio wave transmitting unit that simultaneously transmits a plurality of radio waves in the LF band and the first radio wave transmitting unit in the communication terminal. Correspondence between the level difference calculation unit that calculates the level difference between the reception level of radio waves in the magnetic field and the reception level of radio waves in the second magnetic field, and the level difference calculated by the level difference calculation unit and the distance. Based on the above, the vehicle has a distance calculation unit for calculating the distance between the vehicle-mounted communication device and the communication terminal.

With the above configuration, the distance measuring system determines the level difference between the reception level of the first radio wave having the first attenuation characteristic and the reception level of the second radio wave having the second attenuation characteristic in the communication terminal. The distance between the in-vehicle communication device and the communication terminal is measured based on the correspondence with the distance. Even if the radio wave contains noise, the effect on the level difference between the reception level of the first radio wave and the reception level of the second radio wave is small, and therefore, according to the present embodiment, it is included in the radio wave. It is possible to suppress an increase in the error of the measured distance due to noise.

In a distance measuring system that measures the distance between an in-vehicle communication device and a communication terminal, it is possible to reduce an error in the measured distance when the radio wave contains noise.

It is a block diagram which shows the structural example of the distance measurement system which concerns on one Embodiment. It is a figure for demonstrating the relationship between the distance which concerns on one Embodiment, and the difference of a reception level. It is a flowchart which shows the example of the distance measurement processing which concerns on one Embodiment. It is a figure for demonstrating the effect of the distance measuring method which concerns on one Embodiment.

Hereinafter, modes for carrying out the invention will be described with reference to the drawings.

<System configuration>
FIG. 1 is a block diagram showing a configuration example of a distance measurement system according to an embodiment. The distance measurement system 1 is, for example, a communication that performs wireless communication with an ECU (Electronic Control Unit) 11, an in-vehicle communication device 12 that performs wireless communication under the control of the ECU 11, and an in-vehicle communication device 12 mounted on a vehicle 10 such as an automobile. Includes terminal 20.

The ECU 11 is, for example, an electronic control device mounted on the vehicle 10, and has a CPU (Central Processing Unit), a RAM (Random Access Memory), a flash ROM (Read Only Memory), a control interface, and the like.

The ECU 11 can send and receive data by wireless communication with the communication terminal 20 by using the in-vehicle communication device 12 connected via the control interface. Further, the ECU 11 uses the vehicle-mounted communication device 12 to execute a measurement process for measuring the distance between the vehicle-mounted communication device 12 and the communication terminal 20.

The in-vehicle communication device 12 is connected to, for example, the control interface of the ECU 11, and performs data transmission / reception by wireless communication with the communication terminal 20 according to the control from the ECU 11. Further, the in-vehicle communication device 12 transmits two radio waves having different attenuation characteristics according to the control of the ECU 11. For example, the vehicle-mounted communication device 12 uses the first wireless communication device 13 to transmit a first radio wave having the first attenuation characteristic, and uses the second wireless communication device 14 to obtain the first attenuation characteristic. A second radio wave having a different second attenuation characteristic is transmitted.

Here, the following description will be made assuming that the first wireless communication device 13 and the second wireless communication device 14 are different wireless communication devices, but the first wireless communication device 13 and the second wireless communication device 14 will be described below. 14 may be the same wireless communication device (one wireless communication device). Further, the first wireless communication device 13 and the second wireless communication device 14 may transmit radio waves using one antenna, or may transmit radio waves using a plurality of antennas. There may be.

In short, the in-vehicle communication device 12 can transmit and receive data by wireless communication with the communication terminal 20, and can transmit a first radio wave having a first attenuation characteristic and a second radio wave having a second attenuation characteristic. The configuration may be any configuration as long as it is.

The communication terminal 20 includes, for example, a microcomputer 21 having a CPU, RAM, a flash ROM, a control interface, and the like, and a third wireless communication device 22 that wirelessly communicates with the in-vehicle communication device 12 under the control of the microcomputer 21, for example. , Smart keys and other devices.

The communication terminal 20 transmits / receives data to / from the vehicle-mounted communication device 12 by wireless communication. Further, the communication terminal 20 measures the reception level of the first radio wave and the reception level of the second radio wave received from the in-vehicle communication device 12, and measures the reception level of the first radio wave and the second radio wave. The reception level is transmitted to the vehicle-mounted communication device 12 by wireless communication.

Although the example of FIG. 1 shows an example in which the communication terminal 20 is outside the vehicle 10, the communication terminal 20 is outside the vehicle 10, for example, a smart key of the vehicle 10. In some cases, it may be inside the vehicle 10.

<Functional configuration of ECU>
The ECU 11 executes, for example, a program stored in a flash ROM or the like by a CPU to execute a first radio wave transmission unit 111, a second radio wave transmission unit 112, a level difference calculation unit 113, a distance calculation unit 114, and a storage unit. Part 115 and the like are realized.

The first radio wave transmission unit 111 controls the vehicle-mounted communication device 12 to transmit the first radio wave having the first attenuation characteristic from the vehicle-mounted communication device 12. For example, the first radio wave transmitting unit 111 instructs the vehicle-mounted communication device 12 to transmit the first radio wave, and the vehicle-mounted communication device 12 follows the instruction from the first radio wave transmitting unit 111 to transmit the first radio wave. The first radio wave is transmitted using 13.

The second radio wave transmission unit 112 controls the vehicle-mounted communication device 12 to transmit a second radio wave having a second attenuation characteristic different from the first attenuation characteristic from the vehicle-mounted communication device 12. For example, the second radio wave transmitting unit 112 instructs the vehicle-mounted communication device 12 to transmit the second radio wave, and the vehicle-mounted communication device 12 follows the instruction from the second radio wave transmitting unit 112 to transmit the second radio wave. A second radio wave is transmitted using 14.

The level difference calculation unit 113 receives the reception level of the first radio wave and the reception level of the second radio wave transmitted from the communication terminal 20 via the in-vehicle communication device 12, and the first radio wave in the communication terminal 20. The level difference between the reception level of the second radio wave and the reception level of the second radio wave is calculated.

The distance calculation unit 114 communicates with the in-vehicle communication device 12 based on the correspondence relationship between the distance and the level difference between the reception level of the first radio wave and the reception level of the second radio wave calculated by the level difference calculation unit 113. Calculate (or specify) the distance to the terminal 20. For example, the distance calculation unit 114 calculates the distance between the in-vehicle communication device 12 and the communication terminal 20 by using the information previously stored in the storage unit 115 indicating the correspondence between the distance and the reception level difference.

FIG. 2 is a diagram for explaining the relationship between the distance and the difference in reception level according to the embodiment.

FIG. 2A is a graph 201 showing the relationship between the distance from the antenna and the reception level (magnetic field strength) of radio waves. In FIG. 2A, the first curve 202 shows the first attenuation characteristic in the first radio wave, and the second curve 203 shows the second attenuation characteristic in the second radio wave. .. In the example of FIG. 2A, since the attenuation characteristics of the first radio wave and the second radio wave are different, the level difference 204 between the reception level of the first radio wave and the reception level of the second radio wave changes depending on the distance. To do.

FIG. 2B shows an example of information (hereinafter referred to as correspondence information) 205 showing a correspondence relationship between the distance from the antenna shown in FIG. 2A and the reception level difference 204. In the present embodiment, for example, the corresponding information 205 as shown in FIG. (B) is created in advance by actual measurement (or calculation) or the like and stored in the storage unit 115. As a result, the distance calculation unit 114 can specify the distance corresponding to the difference 204 of the reception levels by using the correspondence information 205 stored in the storage unit 115.

In FIG. 2B, the “distance” indicates the distance between the vehicle-mounted communication device 12 and the communication terminal 20. The "difference in reception level (dBμV / m)" is the difference in reception level (dB) between the reception level of the first radio wave (dBμV / m) and the reception level of the second radio wave (dBμV / m). Is shown. The "difference in reception level (μV conversion)" is the difference (dB) between the reception level of the first radio wave (dBμV / m) and the reception level of the second radio wave (dBμV / m). The value converted to μV is shown.

For example, in the example of FIG. 2B, when the difference in reception level between the reception level of the first radio wave and the reception level of the second radio wave is 28.0 dB, the in-vehicle communication device 12 and the communication terminal It can be determined that the distance between 20 and 20 is 25 cm.

When the difference in reception level does not match the corresponding information 205 in FIG. 2B (for example, 29.0 dB), the distance calculation unit 114 has, for example, a reception level difference of 28.0 dB to 29.5 dB. The range may be determined as a distance of 25 cm. Further, as another example, the distance calculation unit 114 calculates a distance corresponding to, for example, 28.2 dB by an operation of interpolating between two points where the difference in reception level is 28.0 dB and 29.5 dB. It may be something to do.

Here, returning to FIG. 1, the description of the functional configuration of the ECU 11 will be continued.

The storage unit 115 is realized by, for example, a flash ROM of the ECU 11 and a program executed by the CPU of the ECU 11, and stores the corresponding information 205 as shown in FIG. 2B, for example.

(About radio wave attenuation characteristics)
In the present embodiment, the first damping characteristic and the second damping characteristic may be different damping characteristics, and the method for realizing the damping characteristics is not particularly limited. However, some examples will be shown and an outline will be described here. ..

In a system such as a smart key of a vehicle 10, radio waves in the LF (Low Frequency, long wave) band are often used as radio waves transmitted from the in-vehicle communication device 12 to the communication terminal 20. In the LF band, communication is performed using the magnetic field component of the radio wave, and in the near field of λ / 2π (λ is the wavelength) or less, the radio wave is attenuated in inverse proportion to the cube of the distance (hereinafter referred to as cube attenuation). )It is known. For example, this cube attenuation can be used as the first attenuation characteristic.

Further, in the LF band, jamming can be performed by transmitting a plurality of radio waves at the same time, and the attenuation characteristic of the radio wave in the near field can be changed to another attenuation characteristic having a higher degree of attenuation than the cube attenuation. As an example, another attenuation characteristic having a higher degree of attenuation than the cube attenuation due to the plurality of radio waves can be used as the second attenuation characteristic.

Further, as another example, it is conceivable to transmit the first radio wave and the second radio wave by using the electric field component of the radio wave. Radio waves that communicate using electric field components have different attenuation characteristics depending on the wavelength (frequency) of the radio waves even in the near field. Therefore, by using the first radio waves and the second radio waves that have different frequencies, they can be used with each other. Different first damping characteristics and second damping characteristics can be obtained.

<Functional configuration of communication terminal>
In FIG. 1, the communication terminal 20 realizes the reception level measurement unit 211 and the reception level transmission unit 212 by, for example, executing a program stored in the flash ROM or the like of the microcomputer 21 on the CPU of the microcomputer 21. ..

The reception level measuring unit 211 measures (or acquires) the reception level of the first radio wave and the second radio wave received by the third wireless communication device 22. For example, the reception level measuring unit 211 acquires a signal or information representing the reception level output from the third wireless communication device 22, and converts it into a reception level of a predetermined format.

The reception level transmission unit 212 transmits the reception level of the first radio wave and the reception level of the second radio wave measured by the reception level measurement unit 211 to the vehicle-mounted communication device via the third wireless communication device 22. To do.

With the above configuration, in the distance measurement system 1 according to the present embodiment, the vehicle-mounted communication device 12 has a first radio wave having a first attenuation characteristic and a second attenuation characteristic different from the first attenuation characteristic. It transmits a second radio wave. Further, the communication terminal 20 measures the reception level of the first radio wave and the reception level of the second radio wave transmitted from the vehicle-mounted communication device 12, and measures the reception level of the first radio wave and the second radio wave. The reception level of is transmitted to the vehicle-mounted communication device 12.

Further, the ECU 11 of the vehicle 10 calculates the level difference between the reception level of the first radio wave and the reception level of the second radio wave received via the in-vehicle communication device 12, and obtains the calculated level difference and distance. The distance between the vehicle-mounted communication device 12 and the communication terminal 20 is measured based on the correspondence between the above.

The configuration of the distance measurement system 1 shown in FIG. 1 is an example, and the distance measurement system 1 according to the present embodiment can have various system configurations. For example, the level difference calculation unit 113 may be possessed by the communication terminal 20. In this case, the reception level transmission unit 212 of the communication terminal 20 transmits the level difference between the reception level of the first radio wave and the reception level of the second radio wave calculated by the level difference calculation unit 113 to the in-vehicle communication device 12. .. Further, the distance calculation unit 114 of the ECU 11 receives the level difference between the reception level of the first radio wave and the reception level of the second radio wave via the vehicle-mounted communication device 12, and uses the received level difference to mount the vehicle. The distance between the communication device 12 and the communication terminal 20 is calculated.

Further, for example, the communication terminal 20 may have a level difference calculation unit 113 and a distance calculation unit 114, and may transmit the distance calculated by the distance calculation unit 114 to the in-vehicle communication device 12.

Further, the distance calculation unit 114 replaces the correspondence information 205 stored in the storage unit 115 with a predetermined calculation formula (for example, cube attenuation, 4) corresponding to the first attenuation characteristic and the second attenuation characteristic. The distance corresponding to the level difference may be calculated by using (multiplication attenuation, etc.).

<Processing flow>
Subsequently, the processing flow of the distance measurement method executed by the distance measurement system 1 according to the present embodiment will be described.

(Distance measurement process)
FIG. 3 is a flowchart showing an example of the distance measurement process according to the embodiment. This process shows an example of the process of measuring the distance between the in-vehicle communication device 12 and the communication terminal 20 in the distance measurement system 1.

In step S301, the first radio wave transmission unit 111 of the ECU 11 controls the vehicle-mounted communication device 12 to transmit the first radio wave having the first attenuation characteristic from the vehicle-mounted communication device 12.

In step S302, the second radio wave transmission unit 112 of the ECU 11 controls the vehicle-mounted communication device 12 to transmit a second radio wave having a second attenuation characteristic different from the first attenuation characteristic from the vehicle-mounted communication device 12. To do.

In step S303, the level difference calculation unit 113 calculates the level difference between the reception level of the first radio wave and the reception level of the second radio wave in the communication terminal 20.

For example, the communication terminal 20 measures the reception level of the first radio wave and the reception level of the second radio wave, and sets the measured reception level of the first radio wave and the reception level of the second radio wave as the in-vehicle communication device. Send to 12. Further, the level difference calculation unit 113 of the ECU 11 receives the reception level of the first radio wave and the reception level of the second radio wave in the communication terminal 20 via the in-vehicle communication device 12, and receives the reception level of the first radio wave. And the level difference between the reception level of the second radio wave is calculated.

Further, as another example, as described above, when the communication terminal 20 has the level difference calculation unit 113, the level difference calculation unit 113 receives the first radio wave measured by the reception level measurement unit 211. The level difference between the level and the reception level of the second radio wave is measured. In this case, the reception level transmission unit 212 of the communication terminal 20 transmits the calculated level difference between the reception level of the first radio wave and the reception level of the second radio wave to the in-vehicle communication device 12.

In step S304, the distance calculation unit 114 of the ECU 11 uses the level difference between the reception level of the first radio wave and the reception level of the second radio wave calculated in step S303 to use the in-vehicle communication device 12 and the communication terminal. Calculate the distance to 20.

For example, the distance calculation unit 114 determines the level difference between the reception level of the first radio wave and the reception level of the second radio wave from the correspondence information 205 stored in the storage unit 115 as shown in FIG. 2 (b). Find the corresponding distance.

By the above processing, the ECU 11 receives the communication terminal 20 between the vehicle-mounted communication device 12 and the communication terminal 20 based on the level difference between the reception level of the first radio wave and the reception level of the second radio wave. The distance can be measured.

(effect)
FIG. 4 is a diagram for explaining the effect of the distance measuring method according to the embodiment. Here, as an example for explanation, the following description will be given assuming that the distance between the vehicle-mounted communication device 12 and the communication terminal 20 is 50 cm and 20 dB of noise is mixed in the radio wave.

FIG. 4A shows an example in which the vehicle-mounted communication device 12 measures the distance between the vehicle-mounted communication device 12 and the communication terminal 20 based on the reception level of the radio wave received from the communication terminal 20. ing. In the example of FIG. 4A, the reception level of the radio wave received by the communication terminal 20 is increased by about 20 dB due to the influence of noise, so that the reception level 412, which is 20 dB higher than the actual reception level 411, is measured by the in-vehicle communication device 12. Will be done. In this case, although the actual distance between the vehicle-mounted communication device 12 and the communication terminal 20 is 50 cm, the vehicle-mounted communication device 12 measures the distance as 25 cm. In this way, when the vehicle-mounted communication device 12 measures the distance between the vehicle-mounted communication device 12 and the communication terminal 20 based on the reception level of the radio wave received from the communication terminal 20, due to the influence of noise contained in the radio wave. , There is a problem that the error of the measurement distance increases.

In FIG. 4B, for example, the vehicle-mounted communication device 12 transmits two radio waves having the same radio wave attenuation characteristics, and the ECU 11 uses the reception level of the two radio waves received from the communication terminal 20. An example of measuring the distance between 12 and the communication terminal 20 is shown.

As shown in FIG. 4B, even if 20 dB of noise is superimposed on the reception level 421 of the first radio wave and the reception level 422 of the second radio wave, the reception levels 421 and the second of the first radio wave The effect on the level difference (10 dB) from the radio wave reception level 422 is small. However, in the example of FIG. 4B, even if the distance changes, the level difference between the reception level 421 of the first radio wave and the reception level 422 of the second radio wave does not change. The level difference cannot be used to measure the distance between the vehicle-mounted communication device 12 and the communication terminal 20. Therefore, even in the example shown in FIG. 4B, the problem that the error of the measured distance increases due to the influence of noise contained in the radio wave cannot be solved.

FIG. 4C shows that in the distance measurement system 1 according to the present embodiment, two radio waves having different radio wave attenuation characteristics are transmitted, and the ECU 11 communicates with the vehicle by using the level difference between the two radio waves in the communication terminal 20. An example of measuring the distance between the device 12 and the communication terminal 20 is shown.

In the example of FIG. 4C, even if 20 dB of noise is superimposed on the reception level 431 of the first radio wave and the reception level 432 of the second radio wave, the reception level 431 of the first radio wave and the second radio wave The effect on the level difference (34 dB) from the reception level 422 of is small. Further, in the distance measurement system 1 according to the present embodiment, since the first attenuation characteristic of the first radio wave and the second attenuation characteristic of the second radio wave are different, the vehicle-mounted communication device 12 and the communication terminal 20 are used. The level difference between the first radio wave and the second radio wave is different depending on the distance between them. Therefore, the ECU 11 uses, for example, the correspondence information 205 as shown in FIG. 2B and the level difference between the reception level of the first radio wave and the reception level of the second radio wave to be used in the in-vehicle communication device. The distance between 12 and the communication terminal 20 can be estimated.

As described above, according to the present embodiment, in the distance measuring system 1 for measuring the distance between the in-vehicle communication device 12 and the communication terminal 20, the error of the measured distance when the radio wave contains noise is determined. It can be reduced.

1 Distance measurement system 12 In-vehicle communication device 20 Communication terminal 111 First radio wave transmission unit 112 Second radio wave transmission unit 113 Level difference calculation unit 114 Distance calculation unit

Claims (1)

A distance measuring system that measures the distance between an in-vehicle communication device and a communication terminal that performs wireless communication in the LF band.
A first radio wave transmission unit that transmits a first radio wave in order to generate a first magnetic field having a first attenuation characteristic from the vehicle-mounted communication device.
A second radio wave transmission unit that simultaneously transmits a plurality of radio waves in the LF band in order to generate a second magnetic field having an attenuation characteristic higher than that of the first attenuation characteristic from the in- vehicle communication device.
In the communication terminal, a level difference calculating section for calculating a level difference between the signal reception level in said first radio wave reception level in the magnetic field the second magnetic field,
A distance calculation unit that calculates the distance between the in-vehicle communication device and the communication terminal based on the correspondence between the level difference and the distance calculated by the level difference calculation unit.
Distance measurement system with.

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