JP2020106441A - Distance measuring device, communication device, and communication system - Google Patents

Abstract

To measure a distance by reducing influence of fading while using intensity of reception.SOLUTION: A distance measuring device 13 includes a first communication unit 121, a variation calculation unit 112, and a position determination unit 113. The first communication unit 121 receives a signal J2 continuing for a predetermined length of time, at a predetermined frequency. The variation calculation unit 112 determines the maximum value of the reception intensity of the signal J2 received by the first communication unit 121 in the predetermined length of time for each frequency of reception, and obtains the variation in a predetermined number of maximum values. When the variation is at least a threshold value, the position determination unit 113 determines that the source of sending the signal J2 is distant from the first communication unit 121 by at least a predetermined distance. When the variation is less than the threshold value, the position determination unit 113 determines that the source of sending the signal J2 is distant from the first communication unit 121 by less than the predetermined distance.SELECTED DRAWING: Figure 5

Description

The present invention relates to a distance measuring device.

To prevent the vehicle theft method commonly known as relay attack, do not unlock the vehicle or drive the vehicle if the key with the communication function (tentatively called "electronic key" below) and the vehicle are separated. Technology is proposed.

For example, a technique has been proposed in which an electronic key has a GPS function and the position information of the electronic key is transmitted from the electronic key to a device mounted on a vehicle (for example, Patent Document 1 below).

JP, 2014-150425, A

Because of its portability, electronic keys rely on a built-in battery to drive power. From the viewpoint of reducing the power consumption of the built-in battery, it is desirable to avoid the GPS function for determining whether or not the electronic key and the vehicle are separated.

It is also possible to evaluate the distance between the vehicle and the electronic key by using the intensity of the radio wave received by the communication device mounted on the vehicle from the electronic key. However, since this technique evaluates the distance from the reception strength itself, it is susceptible to fading. This influence causes a phenomenon in which the reception strength is reduced despite the fact that the distance is actually small, and increases the possibility of erroneously recognizing that the distance is large.

Therefore, an object of the present invention is to provide a technique for performing distance measurement while reducing the influence of fading while utilizing the reception intensity.

A first aspect of the present invention is a first communication unit that receives a signal that lasts for a predetermined period a predetermined number of times, and a maximum reception intensity of the signal received by the first communication unit within the predetermined period. A variation calculation unit that obtains a value for each number of times and obtains a variation of the predetermined number of the maximum values, and if the variation is a threshold value or more, the position of the signal transmission source is a predetermined distance or more from the first communication unit. The distance measuring device includes a position determining unit that determines that the position is closer than the predetermined distance from the first communication unit if the variation is less than the threshold value.

A second aspect of the present invention is the distance measuring apparatus according to the first aspect, wherein the standard deviation of the predetermined number of the maximum values is adopted as the variation.

A third aspect of the present invention includes the distance measuring device according to the first aspect or the second aspect, and a second communication unit having a configuration for performing communication with the transmission source, and the second communication unit. Is a communication device that communicates with the transmission source on condition that it is determined that the position is closer than the predetermined distance from the first communication unit.

A fourth aspect of the present invention is for performing communication with the communication device according to the third aspect, a third communication unit having a configuration for performing communication with the first communication unit, and communication with the second communication unit. And a second communication device functioning as the transmission source, the first communication unit transmitting a first signal to the third communication unit, and the third communication unit. Is a communication system that transmits a second signal as the signal in response to receiving the first signal.

With the distance measuring device according to the first aspect, distance measurement can be performed without depending on the reception intensity itself. According to the second aspect, the variation can be evaluated by a known method. According to the third and fourth aspects, it contributes to power saving of the transmission source.

It is a conceptual diagram which illustrates the communication system which concerns on embodiment. It is a graph which shows the relationship between the distance in free space and receiving intensity. It is a flow chart which illustrates operation of a communication apparatus. It is a flow chart which illustrates operation of a personal digital assistant. It is a block diagram which illustrates the structure of a communication apparatus. It is a block diagram which illustrates the structure of a portable terminal.

<Overall structure>
FIG. 1 is a conceptual diagram illustrating a communication system 100 according to the embodiment. The communication system 100 includes a communication device 10 and a mobile terminal 20. The mobile terminal 20 is configured to be able to communicate with the communication device 10.

FIG. 1 shows a situation in which the user 2 of the vehicle 1 leaves the vehicle 1. The fact that the communication device 10 is mounted on the vehicle 1 is indicated by a chain line connecting the two for convenience. For convenience, the user 2 carries the mobile terminal 20 with a chain line connecting them.

The communication device 10 transmits a signal J1 to the mobile terminal 20, and the mobile terminal 20 transmits a signal J2 to the communication device 10. The signals J1 and J2 are transmitted by radio waves, for example, radio waves having a frequency in the 2.4 GHz band. In the following description, the signals J1 and J2 themselves are treated as radio waves.

As a communication method of the signals J1 and J2, for example, a communication method conforming to the IEEE802.15.1 standard is adopted. The signal J1 is an advertising signal adopted in Bluetooth Low Energy (Bluetooth is a registered trademark), for example. The mobile terminal 20 transmits the signal J2 in response to the reception of the signal J1.

FIG. 2 is a graph showing the relationship between the distance and the reception intensity in free space when a 2.402 GHz signal is transmitted with a transmission intensity of 8 dBm. The distance is the distance between the source of the signal and the location where the signal was received. The reception strength is the reception strength at the position where the signal is received.

In FIG. 2, the broken line is the simulation result. The solid line will be described later. As a general tendency, the reception strength tends to decrease as the distance increases. The simulation result shows that due to the influence of fading, there is a distance in which the reception strength is remarkably reduced although the distance is short. Such a distance is commonly called a null point.

Referring to FIG. 2 in accordance with the signal J2, the fact that the communication device 10 that has received the signal J2 from the mobile terminal 20 measures the distance to the mobile terminal 20 only by the reception intensity (that is, distance measurement) means fading. It can be seen that it is not desirable in view of the influence of.

<Operation>
FIG. 3 is a flowchart illustrating the operation of the communication device 10, and FIG. 4 is a flowchart illustrating the operation of the mobile terminal 20. Each of the flowcharts illustrates only the portion related to distance measurement, does not illustrate all the operations of the communication device 10, and does not illustrate all the operations of the mobile terminal 20.

In FIG. 3, step S100 is a step of acquiring information around the vehicle 1. The information on the surroundings includes information on the surroundings where the vehicle 1 is located, such as an urban area or a countryside. Such information can be easily acquired by a known car navigation device, for example.

Step S101 is a process of detecting that the door of the vehicle 1 has been closed. Specifically, for example, when the mobile terminal 20 is close to the communication device 10, it detects that the door of the vehicle 1 is closed. It is not necessary to use the signals J1 and J2 to determine whether the mobile terminal 20 is in the vicinity of the communication device 10 when the door is closed, and a known method can be adopted. In other words, step S101 is executed using a known technique.

After the door is closed, the threshold value is set according to the above information in step S110. Since FIG. 2 shows the dependence of the reception intensity on the distance in free space, a smaller threshold value is set as compared with the case where the threshold value is determined according to FIG. This is because the environment around the vehicle 1 may reduce the reception intensity, but it is unlikely to increase it.

For example, when the vehicle 1 is located in an environment with many people, the threshold value is set to a value that is smaller by about 5 to 10 dBm than the threshold value determined in the free space. When the vehicle 1 is located in an environment where there are many vehicles such as a parking lot, the threshold value is set to a value that is about 30 dBm smaller than the threshold value determined in the free space. When the vehicle 1 is located in an environment where the influence of the building should be taken into consideration, the threshold value is set to a value that is about 20 dBm smaller than the threshold value determined in free space.

After step S110 is executed, the first signal (signal J1) is transmitted from the communication device 10 to the mobile terminal 20 M times in step S102. Referring to FIG. 4, it is determined in step S201 whether mobile terminal 20 has received the first signal. When the determination result is affirmative, in other words, when it is determined that the mobile terminal 20 has received the first signal, the process proceeds to step S202, and the second signal (signal J2) is transmitted to the communication device 10. .. The mobile terminal 20 is a communication device that functions as a transmission source of the second signal.

Referring again to FIG. 3, in step S103, the communication device 10 receives the second signal. In step S104, the maximum value of the reception intensity is acquired for each of the received second signals. Each of the second signals is a signal that lasts for a predetermined period, and the maximum value of the reception intensity for each of the second signals (hereinafter referred to as “period intensity maximum value”) is acquired in step S104.

Since the first signal is transmitted M times and the second signal is transmitted in response to receiving the first signal, the second signal is received M times in step S103 and the second signal is received M times in step S104. A period intensity maximum can be obtained for each of the signals. However, if N maximum intensity values for period are sufficient for the processing described later, the maximum intensity value for period in step S104 may be acquired N times under the condition of N≦M. In the following description, it is assumed that N maximum period intensity values are acquired. In other words, the transmission of the first signal in step S102 is performed at least N times.

Steps S103 and S104 can be processed in parallel. For example, the maximum value of the period intensity of the (k-1)-th second signal may be acquired in step S104 while receiving the k-th second signal in step S103.

After step S104, the standard deviation of N period intensity maximum values is calculated in step S105. After step S105, it is determined in step S106 whether the standard deviation is greater than or equal to the threshold value.

If the standard deviation is greater than or equal to the threshold, it is determined that the distance from the communication device 10 to the mobile terminal 20 is greater than or equal to the predetermined distance, and if the standard deviation is less than the threshold, the distance is less than or equal to the predetermined distance. .. That is, by comparing the standard deviation with the threshold value, the distance between the communication device 10 and the mobile terminal 20 is measured as the size of the predetermined distance.

In FIG. 2, the solid line illustrates the maximum value of the period intensity. The maximum value of the period intensity is not so remarkable as the simulation result, but the influence of fading appears. However, the maximum value of the period strength has less variation with respect to the distance than the reception strength when the distance is long. The variation of the reception intensity with respect to the distance can be considered as the variation of the maximum intensity of the period at a certain distance by allowing the error of the distance.

Due to the effect of fading, the reception strength is significantly reduced at and near the null point. Therefore, when the distance is measured using the reception intensity itself, the error in the distance measurement may increase not only in the null point but also in the vicinity thereof. On the other hand, by adopting the variation of the maximum intensity of the period, it is possible to measure the distance without depending on the reception intensity itself. This is advantageous from the viewpoint of reducing the influence of fading on distance measurement. Adopting the standard deviation as the index indicating the variation is advantageous from the viewpoint that the variation can be evaluated by a known method.

For example, the standard deviation of the maximum period intensity when the distance from the communication device 10 to the mobile terminal 20 is 2 to 5 m is about 0.48 to 1.8, and the standard deviation of the maximum period intensity when it is 45 to 48 m. Was about 5.42 to 19.40. Therefore, assuming that the predetermined distance is about 20 to 30 m, the threshold value of the standard deviation of the maximum value of the period intensity may be selected to be about 3.

If it is determined in step S106 that the standard deviation is less than the threshold value, the process returns to step S102, and the distance measuring operation is continued. If it is determined that the standard deviation is greater than or equal to the threshold value, the distance measuring operation ends, and no further first signal is transmitted. Therefore, the mobile terminal 20 also does not transmit the second signal, and thus the power consumption of the mobile terminal 20 is reduced.

FIG. 3 illustrates a case where step S107 is provided in the middle of the flow of returning from step S106 to step S102. In step S107, a predetermined communication process is performed. In step S107, known communication such as authentication and vehicle control is performed between the communication device 10 and the mobile terminal 20, for example. In FIG. 1, such communication is indicated by signal J3.

If it is determined in step S106 that the standard deviation is greater than or equal to the threshold, it is determined that the distance from the communication device 10 to the mobile terminal 20 is greater than or equal to the predetermined distance, and thus step S107 is not executed. Such non-execution of step S107 is also advantageous from the viewpoint of reducing the power consumption of the mobile terminal 20.

<Device configuration>
FIG. 5 is a block diagram illustrating the configuration of the communication device 10. The communication device 10 is mounted on the vehicle 1. The communication device 10 includes a body control module 11 and a communication module 12. The communication module 12 has a first communication unit 121. The body control module 11 has a door contact detection unit 111, a fluctuation calculation unit 112, a position determination unit 113, an LF band transmission unit 114, and a UHF band reception unit 115. The door contact detection unit 111, the variation calculation unit 112, the position determination unit 113, the LF band transmission unit 114, and the UHF band reception unit 115 operate in cooperation with each other using a known technique.

The door contact detection unit 111 executes the process of step S101 shown in the flowchart of FIG. Information indicating that step S101 has been executed is transmitted from the door contact detection unit 111 to the communication module 12. The communication module 12 receives the information and operates the first communication unit 121.

The first communication unit 121 executes the processing of steps S102 and S103. Speaking of step S102, the first communication unit 121 transmits the first signal in the 2.4 GHz band, for example. The first communication unit 121 receives, for example, a second signal in the 2.4 GHz band. In view of this function, in FIG. 5, the first communication unit 121 is additionally described as “2.4 GHz band transmission/reception unit”. The signals J1 and J2 can be used as the first signal and the second signal, respectively.

Speaking of step S103, the second signal is received by the first communication unit 121 at least N times. If the second signal is the signal J2, it can be said that the first communication unit 121 receives the signal J2 in the 2.4 GHz band that lasts for a predetermined period a predetermined number of times (N times).

The fluctuation calculation unit 112 executes the process of step S105. The fluctuation calculation unit 112 obtains the maximum period intensity value of the signal J2 received by the first communication unit 121 for each number of times, and obtains the variation of N period intensity maximum values by the standard deviation.

The process of step S104 may be executed by the first communication unit 121 or the fluctuation calculation unit 112.

The position determination unit 113 executes the processing of steps S110 and S106. The position determination unit 113 determines whether the variation calculated as the standard deviation is equal to or more than the threshold value set in step S110. If the standard deviation is equal to or more than the threshold value, it is determined that the position of the mobile terminal 20 is separated from the first communication unit 121 by a predetermined distance or more. In other words, the distance from the first communication unit 121 to the mobile terminal 20 (this may be regarded as the distance from the communication device 10 to the mobile terminal 20 or the distance from the vehicle 1 to the user 2). Is greater than or equal to a predetermined distance. If the standard deviation is less than the threshold value, it is determined that the position of the mobile terminal 20 is closer than the predetermined distance from the first communication unit 121.

The determination result of step S106, that is, the result of distance measurement is given from the position determination unit 113 to the LF band transmission unit 114. If it is determined that the position of the mobile terminal 20 is closer than the predetermined distance from the first communication unit 121 (that is, the distance from the first communication unit 121 to the mobile terminal 20 is less than the predetermined distance), the LF band transmission unit 114 is determined. It becomes possible to operate. This corresponds to the process of step S107. That is, the communication indicated by the signal J3 in FIG. 1 can be executed by the LF band transmission unit 114. The LF band transmitter 114 handles signals using radio waves in the LF band (30 to 300 kHz).

The first communication unit 121, the fluctuation calculation unit 112, and the position determination unit 113 can be collectively considered as the distance measuring device 13 that measures the distance from the communication device 10 to the mobile terminal 20 using the predetermined distance as a threshold.

The LF band transmission unit 114 and the UHF band reception unit 115 can be collectively considered as the second communication unit 14 having a configuration for communicating with the mobile terminal 20. The second communication unit 14 communicates with the mobile terminal 20 on the condition that the position of the mobile terminal 20 is determined to be closer than the predetermined distance from the first communication unit 121.

It can be understood that the communication device 10 includes the distance measuring device 13 and the second communication unit 14.

FIG. 6 is a block diagram illustrating the configuration of the mobile terminal 20. The mobile terminal 20 includes a third communication unit 22, an LF band receiving unit 23, and a UHF band transmitting unit 24, which operate in cooperation with each other using a known technique. The third communication unit 22 has a configuration for communicating with the first communication unit 121. The third communication unit 22 executes steps S201 and S202. Specifically, the second signal (signal J2) is transmitted in response to the reception of the first signal (signal J1).

The LF band receiving unit 23 handles signals using LF band radio waves, and the UHF band transmitting unit 24 handles signals using UHF band radio waves (0.3 to 3 GHz). The communication indicated by the signal J3 in FIG. 1 can be executed by the LF band reception unit 23 and the UHF band transmission unit 24. The LF band receiving unit 23 and the UHF band transmitting unit 24 can be collectively considered as a fourth communication unit 25 having a configuration for communicating with the second communication unit 14.

It can be understood that the mobile terminal 20 includes the third communication unit 22 and the fourth communication unit 25.

{Modification}
As an index for evaluating the variation of the signal J2, an unbiased standard deviation may be used instead of the standard deviation, a variance or an unbiased variance may be used, or another index may be adopted.

The signal J2 may have the same content as the signal J1 or may have a different content. The signals J1, J2 may employ multiple frequencies. The signal J1 may employ multiple frequencies and the signal J2 may employ one frequency. 2.402 GHz, 2.426 GHz, and 2.480 GHz are given as examples of frequencies.

The mobile terminal 20 may be realized by, for example, an electronic key commonly called FOB, or at least the third communication unit 22 may be realized by a smartphone. The communication device 10 may be realized by modularizing the body control module 11 and the communication module 12 together.

The configurations described in the above-described embodiment and each modification can be appropriately combined unless they contradict each other.

Although the present invention has been described in detail as above, the above description is an example in all aspects, and the present invention is not limited thereto. It is understood that innumerable variants not illustrated can be envisaged without departing from the scope of the invention.

10 communication device 13 ranging device 14 second communication unit 20 mobile terminal (communication device, transmission source)
22 3rd communication part 25 4th communication part 100 Communication system 112 Fluctuation calculation part 113 Position determination part 121 1st communication part

Claims (4)

A first communication unit that receives a signal that lasts for a predetermined period a predetermined number of times;
A variation calculation unit that obtains the maximum value of the reception intensity of the signal received by the first communication unit within the predetermined period for each of the number of times, and obtains the variation of the predetermined number of the maximum values;
If the variation is equal to or more than a threshold, it is determined that the position of the signal source is away from the first communication unit by a predetermined distance or more, and if the variation is less than the threshold, the position is the first A distance measuring device comprising: a position determination unit that determines that the position is closer than the predetermined distance from a communication unit. The distance measuring device according to claim 1,
The distance measuring device wherein the standard deviation of the predetermined number of the maximum values is adopted as the variation. A distance measuring device according to claim 1 or 2;
A second communication unit having a configuration for communicating with the transmission source,
The communication device, wherein the second communication unit communicates with the transmission source on condition that the position is determined to be closer than the predetermined distance from the first communication unit. A communication device according to claim 3;
A third communication unit having a configuration for performing communication with the first communication unit and a fourth communication unit having a configuration for performing communication with the second communication unit are provided, and function as the transmission source. A second communication device,
The first communication unit transmits a first signal to the third communication unit,
A communication system in which the third communication unit transmits a second signal as the signal in response to receiving the first signal.

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