JP2021110591A - Radio wave arrival direction estimating device and position estimating system - Google Patents

Abstract

To enable a radio wave arrival direction to be estimated with high accuracy while suppressing an increase in the size of a device configuration for estimating the arrival direction.SOLUTION: A switching part 21 outputs one of receive signals inputted from a plurality of antennas 20. A control unit 10 calculates a reference correction value on the basis of a receive signal from a specific antenna having been acquired twice at a time interval td via the switching part 21. The control unit 10 generates a first correlation matrix on the basis of receive signals having been sequentially acquired one by one at the time interval td from each of the plurality of antennas 20 via the switching part 21. The control unit 10 removes a phase difference component due to the time interval td from the first correlation matrix using the reference correction value and thereby calculates a second correlation matrix. An estimation part estimates the arrival direction of a radio wave on the basis of the second correlation matrix.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a technique for estimating the arrival direction of radio waves.

Patent Document 1 discloses an arrival wave estimation system that estimates the arrival direction of radio waves by using the MUSIC (Multiple Signal Classification) method.
In this incoming wave estimation system, received signals from a plurality of antennas are sequentially input to a single high-frequency circuit one by one via a switching means. Such a configuration contributes to suppressing the increase in size of the system as compared with a configuration in which a high frequency circuit is individually provided for each antenna, for example.

Further, in this incoming wave estimation system, delay means are individually provided for each antenna so that the received signals sequentially input to the high frequency circuit are received at the same timing. The received signals from the plurality of antennas are input to the high frequency circuit via the corresponding delay means.

Japanese Unexamined Patent Publication No. 2002-214318

However, as a result of detailed examination by the inventor, the following problems have been found in the above-mentioned incoming wave estimation system.
That is, in the above-mentioned incoming wave estimation system, one high-frequency circuit is sufficient, but it is necessary to provide a delay means for each antenna. Therefore, the effect of suppressing the increase in size is limited.

Moreover, in the above-mentioned incoming wave estimation system, it is not easy to obtain a delay time with desired accuracy in each of the delay means for each antenna. If the accuracy of the delay time in each delay means is not sufficient, time-series variations will occur between the received signals for each antenna acquired via the high-frequency circuit. Such variation causes deterioration of the estimation accuracy in the arrival direction.

One aspect of the present disclosure is to make it possible to estimate the arrival direction with high accuracy while suppressing an increase in the size of the device configuration for estimating the arrival direction of the radio wave.

The radio wave arrival direction estimation device according to one aspect of the present disclosure includes a switching unit (21), a first output unit (10: S220 to S230), a first acquisition unit (10: S220 to S230), and a second output. Units (10: S230 to S260), second acquisition unit (10: S230 to S260), first generation unit (10: S310), reference correction value calculation unit (10: S300), and second generation unit. (10: S310) and an estimation unit (10: S330) are provided.

A reception signal of radio waves received by each of a plurality of antennas (20-1 to 20-N) arranged at regular intervals is input to the switching unit. A switching signal instructing the selection of any one of the received signals is input to the switching unit. The switching unit outputs one of the plurality of input received signals selected by the switching signal.

The first output unit outputs a switching signal for selecting a specific received signal. The first acquisition unit acquires the reception signal output from the switching unit twice at the time interval td according to the switching signal output by the first output unit.

The second output unit outputs a switching signal for sequentially selecting the reception signals from the plurality of antennas one by one at the time interval td. The second acquisition unit acquires reception signals from a plurality of antennas that are sequentially output from the switching unit one by one at a time interval td according to the switching signal from the second output unit.

The first generation unit generates the first correlation matrix. The first correlation matrix is a correlation matrix showing the two correlation characteristics of each of any two combinations of the received signals acquired by the second acquisition unit.

The reference correction value calculation unit calculates the reference correction value based on the two received signals acquired by the first acquisition unit. The reference correction value represents the phase difference between the two received signals caused by the time interval td.

The second generation unit generates a second correlation matrix based on the reference correction value calculated by the reference correction value calculation unit. The second correlation matrix is a correlation matrix in which the component of the phase difference due to the time interval td is removed from the first correlation matrix generated by the first generation unit.

The estimation unit estimates the arrival direction of the radio wave based on the second correlation matrix generated by the second generation unit.
The received signal refers to AC power that is induced in the antenna by the radio waves when the radio waves are received by the antenna (in other words, the radio waves are incident on the antenna) and is output from the antenna.

According to such a configuration, although there is a phase difference between the received signals acquired from each antenna due to switching at each time interval dt by the switching unit, the phase difference is removed from the second correlation matrix. Is generated. Then, the arrival direction is estimated using the second correlation matrix. Therefore, it is possible to estimate the arrival direction with high accuracy while suppressing an increase in the size of the device configuration for estimating the arrival direction of the radio wave.

The position estimation system according to another aspect of the present disclosure includes a radio wave arrival direction estimation device (10, 20, 21: S130) and a distance estimation device (10, 60, 61, 70, 71: S110, S120, S140). And a position estimation device (10: S150).

The distance estimation device includes a transmission unit (10, 70, 71: S110), a reception unit (10, 60, 61: S120), and a distance estimation unit (10: S140).
The transmission unit transmits a transmission signal to the mobile terminal (200) by the first radio wave. The receiving unit receives a response signal including reception strength information indicating the reception strength of the first radio wave in the mobile terminal, which is transmitted from the mobile terminal by the second radio wave in response to the reception of the first radio wave in the mobile terminal. do. The distance estimation unit estimates the distance from a predetermined reference position to the mobile terminal based on the reception intensity information included in the response signal received by the reception unit.

The radio wave arrival direction estimation device includes a plurality of antennas (20-1 to 20-N) arranged at regular intervals, a switching unit (21), a first output unit (10: S220 to S230), and a first acquisition. Units (10: S220 to S230), second output units (10: S230 to S260), second acquisition units (10: S230 to S260), first generation units (10: S310), and reference correction values. It includes a calculation unit (10: S300), a second generation unit (10: S310), and an estimation unit (10: S330).

The switching unit receives the reception signal of the second radio wave received by each of the plurality of antennas. A switching signal instructing the selection of any one of the received signals is input to the switching unit. The switching unit outputs one of the plurality of input received signals selected by the switching signal.

The first output unit outputs a switching signal for selecting a specific received signal. The first acquisition unit acquires the reception signal output from the switching unit twice at the time interval td according to the switching signal output by the first output unit.

The second output unit outputs a switching signal for sequentially selecting the reception signals from the plurality of antennas one by one at the time interval td. The second acquisition unit acquires reception signals from a plurality of antennas that are sequentially output from the switching unit one by one at a time interval td according to the switching signal from the second output unit.

The first generation unit generates the first correlation matrix. The first correlation matrix is a correlation matrix showing the two correlation characteristics of each of any two combinations of the received signals acquired by the second acquisition unit.

The reference correction value calculation unit calculates the reference correction value based on the two received signals acquired by the first acquisition unit. The reference correction value represents the phase difference between the two received signals caused by the time interval td.

The second generation unit generates a second correlation matrix based on the reference correction value calculated by the reference correction value calculation unit. The second correlation matrix is a correlation matrix in which the component of the phase difference due to the time interval td is removed from the first correlation matrix generated by the first generation unit.

The estimation unit estimates the arrival direction of the second radio wave based on the second correlation matrix generated by the second generation unit.
The position estimation device estimates the position of the mobile terminal based on the distance estimated by the distance estimation device and the arrival direction estimated by the radio wave arrival direction estimation device.

According to the position estimation system configured in this way, it is possible to estimate the position of the mobile terminal with high accuracy while suppressing an increase in the size of the device configuration for estimating the arrival direction of the second radio wave from the mobile terminal. It will be possible.

It is explanatory drawing which shows typically the arrangement position of various antennas in the vehicle of embodiment. It is a block diagram which shows the electrical structure of the electronic key system of embodiment. It is a flowchart which shows the terminal position estimation process. It is explanatory drawing which shows the estimation calculation processing. It is explanatory drawing which shows the waveform of the received signal received by each antenna, and an example of the sampling timing of the received signal in each phase.

Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.
[1. Embodiment]
(1-1) Outline of Vehicle In the present embodiment, an example in which the present disclosure is applied to the vehicle 100 shown in FIG. 1 will be described. The vehicle 100 may be any vehicle. The vehicle 100 may be provided with, for example, an internal combustion engine, and may be configured to travel by a driving force generated by the internal combustion engine. Further, for example, the vehicle 100 may be provided with an electric motor and may be configured to travel by the driving force generated by the electric motor.

As shown in FIG. 1, the vehicle 100 includes an electronic key system 1. The electronic key system 1 controls the locking and unlocking of the door of the vehicle 100 and permits the vehicle 100 to travel by performing predetermined communication with the mobile terminal 200 carried by the user of the vehicle 100. It has the function of.

Various functions included in the electronic key system 1 include a terminal position estimation function. The terminal position estimation function is a function of estimating the relative position of the mobile terminal 200 with respect to a predetermined reference position (for example, a predetermined position in the vehicle 100).

As shown in FIG. 1, the electronic key system 1 includes a first receiving antenna array 20, a second receiving antenna array 30, a third receiving antenna array 40, a fourth receiving antenna array 50, and a receiving antenna 60. It includes a first transmitting antenna 70, a second transmitting antenna 80, and a third transmitting antenna 90.

The first receiving antenna array 20 is provided near, for example, the right front corner of the vehicle 100. The second receiving antenna array 30 is provided, for example, near the right rear corner of the vehicle 100. The third receiving antenna array 40 is provided, for example, near the left front corner of the vehicle 100. The fourth receiving antenna array 50 is provided, for example, near the left rear corner of the vehicle 100. The receiving antenna 60 is provided, for example, in a substantially central portion of the vehicle 100. The receiving antenna 60 may be provided near the ceiling in the interior of the vehicle 100, for example. The first transmitting antenna 70 is provided near the door handle of the driver's side door of the vehicle 100, for example. The second transmitting antenna 80 is provided, for example, in the vicinity of the door handle of the passenger seat side door in the vehicle 100. The third transmitting antenna 90 is provided, for example, in front of the vehicle 100 in the room.

As shown in FIG. 2, the first receiving antenna array 20 has N antennas 20-1, 20-2, ... , 20-N. The second receiving antenna array 30, the third receiving antenna array 40, and the fourth receiving antenna array 50 are also configured in the same manner as the first receiving antenna array 20. In the present embodiment, the antennas 20-1 to 20-N are arranged at regular intervals, for example, along the front-rear direction of the vehicle 100. However, the antennas 20-1 to 20-N may be arranged along any direction. The antennas 20-1 to 20-N may be arranged along a straight line, may be arranged along a curved line, or may be arranged at equal angular intervals on the circumference. The same applies to the other receiving antenna arrays 30, 40, and 50.

The terminal position estimation function described above includes a terminal distance estimation function and an arrival direction estimation function. The terminal distance estimation function is a function of estimating the distance between the vehicle 100 and the mobile terminal 200. In the terminal distance estimation function, for example, the distance from the above-mentioned reference position to the mobile terminal 200 may be estimated.

The arrival direction estimation function is a function of estimating the arrival direction of radio waves incident on the receiving antenna arrays 20, 30, 40, and 50. In the present embodiment, for the arrival direction of the radio wave received by the first receiving antenna array 20, for example, as shown in FIG. 1, the arrival angle θa with reference to the left-right direction of the vehicle 100 as a reference (0 degree) is calculated. Estimated by. Further, the arrival direction of the radio wave received by the second receiving antenna array 30 is estimated by calculating the arrival angle θb with reference to the left-right direction of the vehicle 100, for example, as shown in FIG. The arrival direction of the radio waves received by each of the third receiving antenna array 40 and the fourth receiving antenna array 50 is also estimated by calculating the arrival angle in the same manner. In other words, the arrival direction estimation function is a function of estimating the direction of the position where the mobile terminal 200 exists as seen from each of the receiving antenna arrays 20, 30, 40, 50. The reference of the arrival angle may be different from the left-right direction of the vehicle 100.

(1-2) Configuration of Electronic Key System 1 A more specific configuration of the electronic key system 1 will be described with reference to FIG. Note that FIG. 2 shows an excerpt of a part of the electronic key system 1 for convenience of explanation. As shown in FIG. 2, the electronic key system 1 includes the above-mentioned first receiving antenna array 20, a second receiving antenna array 30, a receiving antenna 60, and a first transmitting antenna 70.

The electronic key system 1 further includes a control unit 10, a first changeover switch 21, a first reception circuit 22, a second changeover switch 31, a second reception circuit 32, a fifth reception circuit 61, and a first. A transmission circuit 71 is provided.

The control unit 10 includes a control unit 11 and a storage unit 12. The control unit 11 has, for example, a CPU. The storage unit 12 has a semiconductor memory such as a ROM, a RAM, an NVRAM, a flash memory, or an SSD. That is, the control unit 10 of the present embodiment includes a computer including a CPU and a semiconductor memory. Various programs, data, and the like are stored in the storage unit 12. The program stored in the storage unit 12 includes the terminal position estimation processing program of FIG. 3, which will be described later.

The control unit 11 realizes various functions by executing a program stored in a non-transitional substantive recording medium. In the present embodiment, the storage unit 12 corresponds to a non-transitional substantive recording medium in which the program is stored. The various functions realized by the control unit 11 are not limited to those realized by executing the program, and some or all of them may be realized by using one or a plurality of hardware.

When the first transmission circuit 71 receives the transmission data from the control unit 10, the first transmission circuit 71 converts the transmission data into an analog transmission signal and outputs the transmission data to the first transmission antenna 70. The transmission signal is converted into radio waves by the first transmission antenna 70 and radiated. The transmission signal is a predetermined carrier wave modulated by the transmission data.

The frequency of the transmitted signal may be any value. In the present embodiment, the frequency of the transmission signal is, for example, a frequency within the band of the LF (Low Frequency) band. The LF band may be, for example, in the range of 30 kHz to 300 kHz, or may be in a range different from this range.

In FIG. 2, the second transmitting antenna 80 and the third transmitting antenna 90 are not shown. For the second transmitting antenna 80 and the third transmitting antenna 90, a transmission signal is input from a transmission circuit (not shown) configured in the same manner as the first transmission circuit 71, and the transmission signal is radiated by radio waves.

The transmission signal transmitted from the first transmission antenna 70, the second transmission antenna 80, and the third transmission antenna 90 can be received by the mobile terminal 200. When the mobile terminal 200 receives any of the transmission signals, it detects the strength of the received transmission signal, that is, RSSI (Received Signal Strength Inspection).

Further, the transmission signal includes source information indicating the source of the transmission signal. That is, the transmission source information is information for identifying which of the first transmission antenna 70, the second transmission antenna 80, and the third transmission antenna 90 has transmitted the corresponding transmission signal. When the mobile terminal 200 receives any of the transmission signals, the mobile terminal 200 transmits a response signal. The response signal includes reception strength information indicating the detected RSSI and source information.

The frequency of the response signal may be any value. In the present embodiment, the frequency of the response signal is, for example, a frequency within the band of the UHF (Ultra High Frequency) band. The UHF band may be, for example, in the range of 300 MHz to 3 GHz, or may be in a range different from this range.

The response signal transmitted from the mobile terminal 200 is received by one or more of the first receiving antenna array 20, the second receiving antenna array 30, the third receiving antenna array 40, the fourth receiving antenna array 50, and the receiving antenna 60. Can be done.

When the response signal is received by the receiving antenna 60, the received signal is input to the fifth receiving circuit 61. The fifth reception circuit 61 performs various reception processes such as demodulation processing and AD conversion processing on the reception signal from the reception antenna 60, and outputs the reception data generated by these various reception processes to the control unit 10.

The control unit 10 can recognize the area where the mobile terminal 200 exists based on the source information included in the received data input from the fifth receiving circuit 61. That is, when the transmission source information indicates, for example, the first transmission antenna 70, it can be recognized that the mobile terminal 200 exists in the area on the right side of the vehicle 100. When the source information indicates, for example, the second transmitting antenna 80, it can be recognized that the mobile terminal 200 exists in the area on the left side of the vehicle 100. When the source information indicates, for example, the third transmitting antenna 90, it can be recognized that the mobile terminal 200 exists in the room of the vehicle 100.

When the response signal from the mobile terminal 200 is received by the first receiving antenna array 20, the received signal is input to the first changeover switch 21. More specifically, the received signals of the first antenna 20-1 to the Nth antenna 20-N are input to the first changeover switch 21.

The first changeover switch 21 selects one of the input received signals and outputs it to the first receiving circuit 22. The first changeover switch 21 selects a received signal according to the changeover signal input from the control unit 10.

When the control unit 10 recognizes that the mobile terminal 200 exists in, for example, the area on the right side of the vehicle 100 (and can receive the response signal from the mobile terminal 200), the control unit 10 can receive the response signal from the mobile terminal 200. A changeover signal for estimating the arrival direction of the radio wave is output to the first changeover switch 21 and the second changeover switch 31. The specific contents of these switching signals, that is, the specific procedure for switching the selected received signal, and the like will be described later.

The first receiving circuit 22 includes an orthogonal demodulator 23, a local oscillator 24, a first AD converter 25, and a second AD converter 26. The local oscillator 24 outputs a sinusoidal oscillation signal having the same frequency as the carrier frequency of the response signal.

The orthogonal demodulator 23 orthogonally demodulates the received signal input from the first changeover switch 21 by using the oscillation signal from the local oscillator 24. The orthogonal demodulator 23 generates an in-phase component signal I-ch and an orthogonal component signal Q-ch by performing orthogonal demodulation. The common mode component signal I-ch is input to the first AD converter 25, and the orthogonal component signal Q-ch is input to the second AD converter 26.

The first AD converter 25 converts the input in-phase component signal I-ch into digital data. The I-ch reception data, which is the digital data converted by the first AD converter 25, is input to the control unit 10.

The second AD converter 26 converts the input orthogonal component signal Q-ch into digital data. The Q-ch reception data, which is the digital data converted by the second AD converter 26, is input to the control unit 10.

The control unit 10 receives radio waves (that is, response signals) received by the first receiving antenna array 20 based on the I-ch reception data and the Q-ch reception data input from the first reception circuit 22 as described later. Estimate the direction of arrival.

Although detailed description will be omitted, the second changeover switch 31 also functions in the same manner as the first changeover switch 21 with respect to the received signal from the second receiving antenna array 30. The second receiving circuit 32 also functions in the same manner as the first receiving circuit 22 with respect to the received signal from the second changeover switch 31. Then, the control unit 10 estimates the arrival direction of the radio wave received by the second receiving antenna array 30 based on the I-ch reception data and the Q-ch reception data input from the second reception circuit 32.

The control unit 10 performs a predetermined authentication process based on the received data input from the fifth receiving circuit 61. Then, if the authentication is successful, various processes such as permitting the unlocking and locking of the door of the vehicle and permitting the running of the vehicle are performed.

The control unit 10 further executes the terminal position estimation function described above in response to the response signal being received by the receiving antenna 60. Specifically, the distance between the vehicle 100 and the mobile terminal 200 is estimated by executing the terminal distance estimation function described above based on the reception intensity information included in the response signal. Further, by executing the above-mentioned arrival direction estimation function, the arrival direction of the radio wave of the response signal is estimated. For example, when the mobile terminal 200 exists in the area on the right side of the vehicle 100, it is the arrival direction of the radio wave received by the first receiving antenna array 20 based on the received data from the first receiving circuit 22. 1 Estimate the arrival direction (that is, the arrival angle θa). Further, based on the received data from the second receiving circuit 32, the second arrival direction (that is, the arrival angle θb), which is the arrival direction of the radio wave received by the second receiving antenna array 30, is estimated. Then, the position of the mobile terminal 200 is estimated based on the estimated distance, the first arrival direction, and the second arrival direction.

In FIG. 2, the third receiving antenna array 40 and the fourth receiving antenna array 50 are not shown. The third receiving antenna array 40 and the fourth receiving antenna array 50 are also provided with the same changeover switch as the first changeover switch 21 and the same receive circuit as the first receive circuit 22, respectively, and receive data from the receive circuit. Is input to the control unit 10.

When the control unit 10 recognizes that the mobile terminal 200 exists in the area on the left side of the vehicle 100, for example, based on the response signal from the mobile terminal 200, the control unit 10 is for estimating the arrival direction of the radio wave from the mobile terminal 200. The changeover signal is output to the changeover switch corresponding to each of the third receiving antenna array 40 and the fourth receiving antenna array 50. Then, in the same manner as described above, the arrival directions of the radio waves received by the third receiving antenna array 40 and the fourth receiving antenna array 50 are estimated.

(1-3) Arrival direction estimation function Next, the arrival direction estimation function will be specifically described. For the sake of simplification of the explanation, it is assumed that the radio wave is received by the first receiving antenna array 20 as an example. Then, how to estimate the arrival direction of the radio wave received by the first receiving antenna array will be described in detail below. Therefore, the arrival direction estimation function described below is similarly executed when estimating the arrival direction of the radio waves received by each of the second receiving antenna array 30, the third receiving antenna array 40, and the fourth receiving antenna array 50. Is to be done.

The received signal received by each of the antennas 20-1 to 20-N at time t is referred to as a received signal x _n (t) (where n = 1 to N). The received signal x _n (t) can be represented by a complex number as shown in the equation (1).

Each of the real part I of the received signal _x n (t) (t) and the imaginary part Q (t) is the received signal _x n (t) is obtained by being quadrature demodulation. That is, _{by orthogonally demodulating the received signal xn} (t), the above-mentioned in-phase component signal I-ch corresponding to the real part I (t) and the above-mentioned orthogonal component signal Q- corresponding to the imaginary part Q (t) ch and can be obtained.

_{Under ideal conditions, the received signal xn} (t) received by the antennas 20-1 to 20-N can be more specifically expressed by the equation (2).

The ideal condition means that, for example, only a single radio wave (that is, a desired wave) to be estimated in the direction of arrival is received by the antennas 20-1 to 20-N.
In the equation (2), τ _n is the time difference between the incident timing of the radio wave at the reference point (for example, the antenna 20-1) and the incident timing of the radio wave at the antenna 20-n. This time difference τ _n is caused by the difference in physical position (for example, distance) between the reference point and the antenna 20-n. ω is the frequency of the oscillation signal from the local oscillator 24, that is, the carrier frequency of the response signal from the mobile terminal 200. A is the amplitude of the received signal (that is, the amplitude of the received radio wave).

If the reception data of the radio waves received at the same timing by the antennas 20-1 to 20-N is acquired, the arrival direction of the radio waves is, for example, a correlation matrix Rxx based on the _{received signal xn (t).} It can be calculated and estimated by using a known arrival direction estimation method based on the correlation matrix Rxx. _{Specifically, when the received signals x n} (t) at the antennas 20-1 to 20-N are collectively displayed as a vector as shown in the equation (3), _{the correlation between any two received signals x n} (t) can be obtained. The correlation matrix Rxx shown is expressed by Eq. (4).

In equation (4), E represents an operation for obtaining an expected value (for example, time average).
Specifically, the correlation matrix Rxx derived by the equation (4) is expressed as the equation (5) under ideal conditions.

In equation (5), Ps represents the power of the received wave.
Therefore, if the correlation matrix Rxx is obtained based on the received signal _xn (t), the correlation matrix Rxx is used, and calibration is applied as necessary based on the correlation matrix Rxx, using, for example, a MUSIC (Multiple Signal Classification) algorithm. The direction of arrival of radio waves can be estimated.

However, as described above, the above estimation method is based on the assumption _{that all the received signals x n} (t) from the antennas 20-1 to 20-N are acquired at the same timing.
On the other hand, in the present embodiment, in order to reduce the size of the electronic key system 1, the received signals from the antennas 20-1 to 20-N are processed in time division by one first receiving circuit 22.

That is, in this embodiment, from the received signal of the antenna 20-1 to the reception signal of the antenna 20-N, sequentially one by one at a time interval t _d, is input to the first receiving circuit 22. Then, the input received signal is orthogonally demodulated, AD-converted, or the like, and is taken into the control unit 10. For example, if the received signals _x 1 antenna 20-1 (t) is input to the first receiving circuit 22 at time t0, the antenna 20-n of the received signals _x 1 (t) is the time t0 + (n-1) It is input to the first receiving circuit 22 at t _d.

Therefore, in the present embodiment, the received signal x _n (t) corresponding to the received data input to the control unit 10 is represented by the equation (6) under ideal conditions.

In addition, in the formula (6), the second term of the exponent part may be _{"+ (n-1) t d".
The correlation matrix Rxx td} derived based on the _{received signal x n} (t) represented by the equation (6) is expressed as the equation (7).

つまり、時間間隔ｔ_ｄで１つずつ第１受信回路２２に入力される受信信号ｘ_ｎ（ｔ）に基づいて得られる相関行列Ｒｘｘ_ｔｄは、時間間隔ｔ_ｄの成分を含んでおり、この点で、上記式（５）に示す一般的な相関行列Ｒｘｘとは異なる。

In other words, the correlation matrix _{Rxx td} obtained based on the received signal _x n (t) input to the first receiving circuit 22 one by one at intervals _{t d} includes a component of the time interval _{t d,} the point Therefore, it is different from the general correlation matrix Rxx shown in the above equation (5).

Even if the _{correlation matrix Rxx td} containing the component of the _{time interval t d} is applied to the MUSIC algorithm in the same manner as the correlation matrix Rxx of the equation (5), the radio wave contains the component of the _{time interval t d.} The direction of arrival cannot be estimated.

Therefore, in the present embodiment, in order to remove the component of the time interval t _{d from the correlation matrix Rxx td} represented by the equation (7), _{the correction matrix C p1} described later is calculated. The correction matrix C _p1 is calculated based on the actual received signal.

Then, the second correlation matrix Rxxc, which will be described later, is calculated by performing the calculation of the correlation matrix Rxx _td and the correction matrix C _p1. This second correlation matrix Rxxx _{does not include the component of the time interval t d} , and is equivalent to the correlation matrix Rxx of the equation (5). Therefore, the arrival direction of the radio wave can be estimated by a known arrival direction estimation method such as the MUSIC algorithm using the second correlation matrix Rxxxc.

A method of removing the component of the time interval t _d from the correlation matrix Rxx _td , that is, a method of calculating the second correlation matrix Rxxc will be specifically described.
The arrival direction estimation method of the present embodiment includes a first phase and a second phase. In the first phase, a switching signal for inputting a reception signal from a certain antenna 20-n to the first receiving circuit 22 is input to the first switching switch 21. The received data based on the received signal from the antenna 20-n is two cycles (i.e. two) at time intervals t _d, is obtained.

In the present embodiment, in the first phase, for example, reception data based on the reception signal from the first antenna 20-1 is acquired. The main purpose of the first phase is to derive the _{correction matrix C p1.} In the first phase, _{in order to derive the correction matrix C p1} , the correction correlation matrix Rxx _p1, which will be described later, is derived.

In a second phase following the first phase, the received signal selected by the first selector switch 21 are sequentially switched at the N antenna 20-N time interval t _d to reception signals from the reception signal of the first antenna 20-1 .. That is, the control unit 10 causes the first changeover switch 21 is switched for every time interval t _d as described above outputs a switching signal to occur. Therefore, in the second phase, from the received data corresponding to the received signal of the first antenna 20-1 to the reception data corresponding to the received signal of the N antenna 20-N, it is sequentially acquired in a time interval t _d. The main purpose of the second phase is _{to derive the first correlation matrix Rxx p2,} which will be described later.

In the present embodiment, the reception data of the first antenna 20-1 acquired second time in the first phase is also used as the reception data of the first antenna 20-1 to be acquired first in the second phase. That is, in the present embodiment, the acquisition of the last received data in the first phase also serves as the acquisition of the first received data in the second phase.

_{The received signal x np2} (t) corresponding to each received data acquired in the second phase is expressed by the equation (8).

_{When the received signal x np2} (t) represented by the equation (8) is collectively displayed as a vector as shown in the equation (9), the first is a correlation matrix showing the correlation _{between any two received signals x nnp2 (t).} The correlation matrix Rxx _p2 is derived by Eq. (10).

_{The first correlation matrix Rxx p2} derived by the equation (10) is expressed as the equation (11) under ideal conditions.

つまり、時間間隔ｔ_ｄで１つずつ取得される受信信号ｘ_ｎｐ２（ｔ）に基づいて得られる第１相関行列Ｒｘｘ_ｐ２は、前述の式（７）の相関行列Ｒｘｘ_ｔｄと同じであり、時間間隔ｔ_ｄの成分を含んでいる。

That is, the first correlation matrix Rxx _{p2 obtained based on the received signals x np2} (t) acquired one by one at the time interval t _{d is the same as the correlation matrix Rxx td in the} above equation (7), and the time. It contains components at intervals t _d.

Therefore, in order to remove the component of the time interval t _d from the first correlation matrix Rxx _{p2 , the correction matrix C p1} is derived based on the two received data acquired in the first phase.
_{The received signals x 1p11} (t) and x _1p12 (t) corresponding to the first received data and the second received data acquired in the first phase are of the equations (12) and (13), respectively. It is expressed as.

In the equations (12) and (13), the first received signal x _1p11 (t) is received before the _{time interval t d before the second received signal x 1p12} (t). Is shown.
When these two received signals x _1p11 (t) and x _1p12 (t) are collectively displayed as a vector as shown in the equation (14), _{the correlation between these two received signals x 1p11} (t) and x _1p12 (t) is shown. _{The correction correlation line example Rxx p1} , which is a correlation matrix, is derived by Eq. (15).

_{The correction correlation matrix Rxx p1} derived by the equation (15) is expressed as the equation (16) under ideal conditions.

Equation (16) means ^{that e −jωtd} and e ^{+ jωtd} can be derived by calculating the _{correction correlation matrix Rxx p1.} Therefore, e ^−jωtd and e ^{+ jωtd} are derived from the calculated correction correlation matrix Rxx _{p1. That is, in the present embodiment, ωt d} is derived based on the two actually measured values in the first phase. In other words, it can be said that the first phase is a phase for actually measuring _{ωt d.} In addition, e ^−jωtd and e ^{+ jωtd} correspond to an example of the reference correction value in the present disclosure.

e ^−jωtd and e ^{+ jωtd} may be calculated by any method. e ^−jωtd and e ^{+ jωtd} can be calculated as follows, for example. That is, assuming that the 1-row 1-column component of _{the correction correlation matrix Rxx p1 is R 11} and the 1-row 2-column component is R ₁₂ , R ₁₁ and R ₁₂ are expressed as equations (17) and (18), respectively. ..

Therefore, e ^−jωtd can be obtained by the equation (19).

That is, by deriving the correction correlation matrix Rxx _p1 ^{, e −jωtd} can be calculated using the equation (19). Once e ^−jωtd is obtained, e ^{+ jωtd} can be easily obtained based on the fact that it has a complex conjugate relationship with e ^−jωtd. The calculation method using the formula (19) is an example, and e ^−jωtd and e ^{+ jωtd} may be calculated by other methods. For example, it may be calculated by using the 2-row 1-column component and the 2-row 2-column component of the correction correlation matrix Rxx _p1.

^{After e −jωtd} and e ^{+ jωtd} are calculated as described above, the _{correction matrix C p1} shown in the equation (20) is derived using the calculated values.

Each component in the correction matrix C _p1 indicates the phase difference of the received signal by the two antennas corresponding to the component. The phase difference is a phase difference caused by the time interval of switch switching, unlike _{τ n, which indicates the difference in arrival time.}

For example, the components of one row and two columns in the correction matrix C _p1 is the received signal and the received signal of the second antenna 20-2 of the first antenna 20-1, caused by the td is the time interval of the switch changeover Shows the phase difference. More generally, the component of the s row and t column in the correction matrix C _p1 is the switch switching interval between the received signal of the s antenna 20-s and the received signal of the t antenna 20-t td * ( The phase difference caused by st) is shown.

In this way, in the first phase, two received signals x _1p11 (t) and _{x1p12 (t) are acquired from the same antenna at a time interval t d} , and a correction correlation matrix Rxx _p1 based on both is derived. Then, ωt _d is naturally derived. Each component in the correction matrix C _p1 corresponds to an example of the individual correction values in the present disclosure.

By correcting the first correlation matrix _{Rxx p2} using the correction matrix _{C p1} derived in this way, obtain a second correlation matrix Rxxc the components of the time interval _{t d} from the first correlation matrix _{Rxx p2} is removed be able to. Specifically, the second correlation matrix Rxxxc can be obtained by performing the calculation of the equation (21).

The second correlation matrix Rxxx obtained by the calculation of the equation (21) is an estimated value of the correlation matrix Rxx (see the above equation (5)) obtained based on _{the received signal xn (t) received at the same timing.} Can be regarded as. Theoretically, the second correlation matrix Rxxx is the same as the correlation matrix Rxx.

Once the second correlation matrix Rxxxc is obtained in this way, the arrival direction of the radio wave can be estimated using the second correlation matrix Rxxxc, for example, using a known arrival direction estimation algorithm such as the MUSIC algorithm.

For reference, the procedure for estimating the direction of arrival using the MUSIC algorithm will be described in a very general manner.
That is, the eigenvalues λ _{1 to λ N} (where λ ₁ ≧ λ ₂ ≧ ... λ _L > λ _{L + 1} = ... = λ _N = σ ² ) of the second correlation matrix Rxxc are calculated. Note that σ ² is the thermal noise power. Then, since the number of eigenvalues larger than the thermal noise power σ ² _{among these eigenvalues λ 1 to λ N} is L, it is estimated that the number of received radio waves is L. Moreover, to calculate the eigenvectors _{e L} + 1 _{~e N} corresponding to the thermal noise power eigenvalues equal to ^{_{σ 2 λ L + 1 ~λ N}} .

_{Then, a noise subspace matrix Ens} composed of eigenvectors corresponding to NL eigenvalues equal to the thermal noise power σ ² is defined by the equation (22). 1 Assuming that the complex response of the receiving antenna array 20 is represented by a (θ), the evaluation function _PMU (θ) shown in the equation (23) is obtained.

The angle spectrum (that is, the MUSIC spectrum) obtained from this evaluation function _PMU (θ) is set so as to diverge and have a sharp peak when the direction θ coincides with the arrival direction of the arrival wave. Therefore, the arrival angle theta ₁ through? _L of each receiving radio waves L wave is determined by detecting the peak of the MUSIC spectrum.
If only one radio wave is received from the mobile terminal 200, the arrival angle θ1 is uniquely determined as the arrival angle of the radio wave from the mobile terminal 200. When there are a plurality of received radio waves (that is, L is 2 or more), a desired wave (radio wave from the mobile terminal 200) can be detected by various methods. For example, the desired wave may be detected based on the relationship between each eigenvalue and a predetermined threshold value.

(1-4) Terminal Position Estimating Process Next, the terminal position estimation process executed by the control unit 10 will be described with reference to the flowchart of FIG. The terminal position estimation function described above includes executing the terminal position estimation process of FIG. The term "executed by the control unit 10" for the terminal position estimation process specifically means that the control unit 11 in the control unit 10 executes the terminal position estimation process. More specifically, for example, the control unit 11 executes the terminal position estimation process. It means that the CPU in the inside executes.

The control unit 10 repeatedly executes the terminal position estimation process shown in FIG. 3 at predetermined execution timings (for example, at a constant control cycle). When the control unit 10 starts the terminal position estimation process, the control unit 10 executes the LF signal transmission process in S110. Specifically, the above-mentioned transmission signal is transmitted by radio waves from the first transmission antenna 70, the second transmission antenna 80, and the third transmission antenna 90.

In S120, it is determined whether or not the response signal from the mobile terminal 200 to the transmission signal transmitted in S110 is received by the receiving antenna 60. If the response signal has not been received, the terminal position estimation process ends. When the response signal is received, the process proceeds to S130.

In S130, the arrival direction estimation process is executed. The arrival direction estimation process is a process for realizing the above-mentioned arrival direction estimation function. The arrival direction estimation process of S130 is performed, for example, as follows.

First, based on the source information included in the response signal, it recognizes from which transmitting antenna the transmission signal was received by the mobile terminal 200, in other words, in which area the mobile terminal 200 exists. do. Then, when it is recognized that the mobile terminal 200 exists in the area on the right side of the vehicle 100, the estimation calculation process shown in FIG. 4 is performed for each of the first receiving antenna array 20 and the second receiving antenna array 30. Execute. When it is recognized that the mobile terminal 200 exists in the area on the left side of the vehicle 100, the estimation calculation process shown in FIG. 4 is executed for each of the third receiving antenna array 40 and the fourth receiving antenna array 50. ..

The estimation calculation process of FIG. 4 will be described by assuming that the processing target is the first receiving antenna array 20 as an example. When the control unit 10 starts the estimation calculation process, the first parameter Cnt is set to the initial value 1 and the second parameter Cs is set to the initial value 2 in S210.

In S220, the first phase first sequence sampling process is executed. Specifically, a switching signal for inputting a reception signal from a certain antenna 20-n (hereinafter, referred to as "specific antenna") to the first receiving circuit 22 is input to the first switching switch 21. The specific antenna is, for example, the first antenna 20-1 in the present embodiment. Then, the received data based on the received signal from the specific antenna, that is, the data of the in-phase component (real part) and the orthogonal component (imaginary part) that the received signal is processed by the first receiving circuit 22 and input to the control unit 10. Is acquired over the number of sampling times M at the sampling interval ts. That is, the received data is sequentially acquired at each sampling timing Tm (m is 1 to M) of M times.

Note that FIG. 5 shows an example of the received signal waveform of each antenna when the first receiving antenna array 20 includes the first antenna 20-1, the second antenna 20-2, and the third antenna 20-3, and An example of the sampling timing of the received data in each phase is shown. In FIG. 5, the circles displayed superimposed on the waveform indicate that the received data is acquired at the corresponding sampling timing. Further, in FIG. 5, "P1" indicates the first phase, "P2" indicates the second phase, "seq1" indicates the first sequence, "seq2" indicates the second sequence, and "seq3" indicates the second phase. The third sequence is shown.

In S230, the first phase second sequence sampling process is executed. This first phase second sequence sampling process is the same as the first phase first sequence sampling process of S220. That is, the switching signal for inputting the reception signal from the specific antenna to the first receiving circuit 22 is input to the first switching switch 21. Then, the received data based on the received signal from the specific antenna is acquired over the sampling number M at each sampling interval ts.

However, the first sampling timing T1 in S230 is when the time interval t _d has elapsed from the first sampling timing T1 in S220. That is, the sampling timing Tm in S230 corresponds to the timing at which the _{time interval t d has elapsed from the sampling timing Tm in S220.}

The S220 and S230 and the processing of the first phase described above, i.e., the process of acquiring two periods the received data at time intervals t _d from a particular antenna is executed.
In S220 and S230, the number of sampling times M may be any number. Theoretically, the number of sampling times M may be one. The same applies to S240, which will be described later.

That is, if the received data is acquired only once for each of S220 and S230, the correction matrix C _p1 can be derived in S300 described later. However, in reality, it is not always possible to stably receive the response signal due to the influence of disturbance such as noise. Therefore, in the present embodiment, for each sequence of acquiring the received data from one antenna in each phase, the received data is not acquired only at a single timing, but a plurality of times (that is, the number of samplings) at the sampling interval ts. Acquire the received data over M). Then, by performing the time averaging calculation described later, it is finally realized that a highly reliable second correlation matrix Rxxxc is obtained.

In the present embodiment, since the specific antenna in the first phase is the first antenna 20-1, the first phase second sequence sampling process of S230 also serves as the second phase first sequence sampling process. The second phase first sequence sampling process is the process of the first sequence in the second phase, that is, the process of acquiring the received data from the first antenna 20-1.

It is not essential that the first phase second sequence sampling process also serves as the second phase first sequence sampling process. Even if the received data from the first antenna 20-1 is acquired in the first phase second sequence sampling process and then the received data from the first antenna 20-1 is acquired again in the first sequence in the second phase process. good.

In S240, the second phase second Cs sequence sampling process is executed. Specifically, a changeover signal for causing the first reception circuit 22 to input the reception signal from the Cs antenna 20-Cs is input to the first changeover switch 21. Then, the received data based on the received signal from the Cs antenna 20-Cs is acquired over the sampling number M at the sampling interval ts. The first sampling timing T1 in S240 that is executed first following S230 is when the time interval t _d has elapsed from the first sampling timing T1 in S230.

The initial value of the second parameter Cs is 2. Therefore, in the process of S240 which is executed first after starting the estimation calculation process of FIG. 4, the received data corresponding to the received signal from the second antenna 20-2 is acquired.

In S250, it is determined whether or not the currently set second parameter Cs is equal to N. The process of S250 is a process of determining whether or not the process of S240 has been executed for all of the first antenna 20-1 to the N antenna 20-N in the second phase, that is, the second phase, the first sequence to the second phase. It can be said that this is a process for determining whether or not all the Nth sequences have been executed.

If the second parameter Cs currently set in S250 is different from N, the process proceeds to S260. In S260, the second parameter Cs is incremented by one to shift to S240. The first sampling timing T1 in the transition from S260 to S240 is when the time interval t _d has elapsed from the first sampling timing T1 in the previous S240.

By the processing of S230 to S260, the processing of the second phase, that is, from the received data corresponding to the received signal of the first antenna 20-1 to the received data corresponding to the received signal of the Nth antenna 20-N at a time interval t _d . It is realized to acquire sequentially.

If the second parameter Cs currently set in S250 matches N, the process proceeds to S270. In S270, the first parameter Cnt is incremented by one. In S280, it is determined whether or not the current first parameter Cnt exceeds the specified number of times.

In S280, when the first parameter Cnt is less than or equal to the specified number of times, the process proceeds to S290. In S290, the second parameter Cs is initialized to 2, and the process shifts to S220. That is, the first phase and the second phase following the first phase are collectively regarded as one data acquisition process, and the data acquisition process is repeated a predetermined number of times. Assuming that the specified number of times is Nd, the data acquisition process is executed Nd times. FIG. 5 shows up to the point where the third data acquisition process is started after the data acquisition process is started.

If the first parameter Cnt exceeds the specified number of times in S280, the process proceeds to S300. In S300, the correction matrix calculation process is executed. The mobile terminal 200 may transmit the response signal to be transmitted in response to receiving the transmission signal from the vehicle 100 for any period of time. In the present embodiment, the mobile terminal 200 is configured to continuously transmit a response signal, for example, for a period required until an affirmative determination is made in S280 in at least the estimation calculation process of FIG. Conversely, as an affirmative decision is made at S280 while the response signal from the mobile terminal 200 is transmitted, a predetermined number of times Nd and the time interval t _d may be set as appropriate.
_{Specifically, in S300, the correction matrix C p1} is calculated individually for each Nd data acquisition process based on the received data acquired in the first phase, that is, the received data acquired in S220 and S230.

The calculation method of the _{correction matrix C p1} based on the received data acquired in one data acquisition process in the correction matrix calculation process of S300 will be described more specifically. _{That is, the correction correlation matrix Rxx p1} is calculated based on the equation (15) using the received data acquired at the same sampling timing Tm in each of the first sequence and the second sequence. For example, first, using the received data acquired at the sampling timing T1 in the first sequence and the received data acquired at the sampling timing T1 in the second sequence, for correction corresponding to the sampling timing T1 based on the equation (15). Calculate the correlation matrix. Next, using the received data acquired at the sampling timing T2 in the first sequence and the received data acquired at the sampling timing T2 in the second sequence, the correction correlation corresponding to the sampling timing T2 is used based on the equation (15). Calculate the matrix. Finally, in the same procedure, a total of m correction correlation matrices corresponding to each of the sampling timings T1 to Tm are calculated. _{Then, the correction correlation matrix Rxx p1} is calculated by performing, for example, time averaging the components corresponding to each other in the m correction correlation matrices. When the number of samplings M is 1, it is not necessary to perform the time averaging calculation as a matter of course.
Then, based on the calculated correction correlation matrix Rxx _{p1 , for example, the correction matrix C p1} represented by the equation (20) is derived by performing the calculation or the like shown in the above equation (19). By performing such an operation for each Nd data acquisition process, a correction matrix C _p1 corresponding to each of the Nd data acquisition processes is obtained.

In S310, the correlation matrix calculation process is executed. This correlation matrix calculation process is a process for calculating the second correlation matrix Rxxx. Specifically, in S310, individual calculation processing and time averaging processing are performed.
In the individual calculation process, the second correlation matrix Rxxxc is calculated individually for each Nd data acquisition process. The second correlation matrix Rxxc for each data acquisition process calculated by the individual calculation process is hereinafter referred to as an "individual second correlation matrix". In the time averaging process, the second correlation matrix Rxxxc is obtained by performing the time averaging calculation of Nd individual second correlation matrices calculated by the individual calculation process.
The calculation method of the individual second correlation matrix based on the received data acquired in one data acquisition process in the individual calculation process will be described more specifically. _{That is, first, the first correlation matrix Rxx p2} is calculated using the received data corresponding to each of the antennas 20-1 to 20-N acquired in the second phase. The first correlation matrix Rxx _p2 can be calculated, for example, based on the above equation (10). The calculation of the first correlation matrix Rxx _p2 is also calculated by the time averaging calculation in the same manner as the calculation of the correction correlation matrix Rxx _{p1. That is, the first correlation matrix Rxx p2} is calculated based on the equation (10) using the received data acquired at the same sampling timing Tm in each of the first sequence to the Nth sequence in the second phase.

Then, by correcting the calculated first correlation matrix Rxx _{p2 using the correction matrix C p1} corresponding to the same data acquisition process calculated in S300, the components of the time interval t _d can be obtained from the first correlation matrix Rxx _p2. The removed individual second correlation matrix is calculated. For example, for the first correlation matrix Rxx _{p2 based on the received data acquired in the xth data acquisition process, the correction matrix C p1} obtained based on the received data acquired in the same xth data acquisition process is used. The individual second correlation matrix is calculated by correction. Specifically, the calculation of the individual second correlation matrix is performed by the calculation of the Hadamard product shown in the above equation (21).
By performing such an operation for each Nd data acquisition process, Nd individual second correlation matrices corresponding to each of the Nd data acquisition processes are obtained.
Then, in the time averaging calculation, for example, one second correlation matrix in which the Nd individual second correlation matrices are averaged by performing the time averaging of the components corresponding to each other in the Nd individual second correlation matrices. Obtain Rxxx.
The specified number of times Nd may be any value. The specified number of times Nd may be, for example, twice or more, or may be, for example, once. When the specified number of times Nd is 1, the above-mentioned time averaging calculation is unnecessary in the correlation matrix calculation process of S310.
In the present embodiment, the specified number of times Nd is set to 2 times or more (for example, 4 times). The reason why the specified number of times Nd is set to 2 times or more, in other words, the main reason for obtaining the second correlation matrix Rxxx by the time averaging calculation of a plurality of individual second correlation matrices is the error caused by the movement of the mobile terminal 200 (the error caused by the movement of the mobile terminal 200 ( That is, this is to suppress a decrease in calculation accuracy). That is, in order to suppress the influence of the movement of the mobile terminal 200 on the phase shift between the N antennas included in the receiving antenna array, the specified number of times Nd is set to 2 times or more. If the source of the radio wave is stationary, the second correlation matrix Rxxx calculated regardless of the specified number of times Nd is the same, so it can be said that one time is sufficient for the specified number of times Nd.
In S320, a calibration process is performed. For example, the error component included in the second correlation matrix Rxxc calculated in S310 is removed by using the known correlation matrix Rxx0 corresponding to the specific arrival direction.

In S330, the arrival angle calculation process is executed. Specifically, the arrival angle θa of the radio wave is calculated by using the second correlation matrix Rxxc calibrated in S320 and using a known arrival direction estimation algorithm such as the MUSIC algorithm. The arrival angle θa calculated in this way is used as an estimation result of the arrival direction of the radio wave received by the first receiving antenna array 20. The calibration process of S320 is not essential, and the S330 arrival angle calculation process may be performed using the second correlation matrix Rxxx calculated in S310.

In the arrival direction estimation process of S130, the arrival direction is estimated by executing the estimation calculation process of FIG. 4 for each receiving antenna array to be calculated. In this embodiment, for example, the arrival angles θa and θb are estimated. Then, when the estimation of the arrival direction is completed for all the receiving antenna arrays to be estimated, the process proceeds to S140 (see FIG. 3). In S140, the terminal distance estimation process is executed. Specifically, the distance between the vehicle 100 and the mobile terminal 200 is estimated by executing the terminal distance estimation function described above based on the reception intensity information included in the response signal.

In S150, the terminal position specifying process is executed. Specifically, the position of the mobile terminal 200 is specified based on the arrival direction estimated in S130 and the distance estimated in S140. It is exemplified that the position of the mobile terminal 200 shown in FIG. 1 is the position specified in S150 based on the fact that the arrival angle θa and the arrival angle θb are estimated in S130 and the distance D is estimated in S140. is doing.

The position specified in S150 is used in various processes as a result of estimating the position of the mobile terminal 200. For example, by periodically estimating the position of the mobile terminal 200, the movement locus of the mobile terminal 200 can be detected. Then, various processes based on the movement locus can be performed. For example, when it is detected by the movement locus that the mobile terminal 200 is gradually separated from the vehicle 100, each door of the vehicle 100 may be automatically locked.

(1-5) Effects of the Embodiment According to the embodiment described above, the following effects are obtained.
In the present embodiment, although there is a phase difference between the received signals acquired from each of the antennas 20-1 to 20-N due to the switching of each time interval dt by the first changeover switch 21, the phase difference thereof. The second correlation matrix Rxxc from which is removed is generated. Then, the arrival direction of the radio wave is estimated using the second correlation matrix Rxxxc. Therefore, it is possible to estimate the arrival direction with high accuracy while suppressing an increase in the size of the device configuration for estimating the arrival direction of the radio wave.

The control unit 10 switches the switch by itself at the time interval t _d. Further, the angular frequency ω of the local oscillation signal from the local oscillator 24 is known. That is, the design values of the angular frequency ω and the time interval t _{d are known.} Therefore, for example, it is theoretically possible to remove the component of the time interval td from the first correlation matrix Rxx _{p2 by using the design known ω and t d.}

However, the actual angular frequency ω does not always exactly match the design value, and the actual angular frequency ω may deviate from the design value. Regarding the time interval t _d , the interval at which the first changeover switch is actually switched does not always exactly match the design value, and the actual time interval t _d may deviate from the design value.

When estimating the arrival direction of a radio wave using an arrival direction estimation method such as the MUSIC algorithm _{, an error between the angular frequency ω and the actual value of the time interval t d} can greatly affect the estimation accuracy. That is, even if the error is small, the estimation accuracy may be significantly reduced.

Therefore, in the present embodiment, the correction matrix C _p1 based on the actual angular frequency ω and the time interval t _d is calculated by actually measuring the received signal by the same antenna at the time interval t _{d in the first phase.} Then, using the correction matrix C _p1 , the component of the time interval td is removed from the first correlation matrix Rxx _p2. This makes it possible to obtain a highly accurate estimation result that reflects the actual angular frequency ω and the time interval t _d.

Further, in the present embodiment, the correction matrix is calculated based on the reference correction value, and the second correlation matrix is calculated by correcting the first correlation matrix by the correction matrix. Therefore, the correction from the first correlation matrix to the second correlation matrix can be efficiently performed.

Further, in the present embodiment, the first phase second sequence sampling process (S230) also serves as the second phase first sequence sampling process. Therefore, it is possible to shorten the time required for estimating the arrival direction.

Further, in the present embodiment, in addition to estimating the direction of arrival of radio waves from the mobile terminal 200, the distance to the mobile terminal 200 is also estimated. Then, the position of the mobile terminal 200 is estimated based on the estimated distance and the direction of arrival. Therefore, it is possible to estimate the position of the mobile terminal 200 with high accuracy while suppressing an increase in the size of the system configuration for estimating the position of the mobile terminal 200.

[2. Other embodiments]
Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and can be implemented in various modifications.

(2-1) In the above embodiment, the order of acquiring the received data in the second phase is the order of the first antennas 20-1 to 20-N, but this order is an example. For example, contrary to the above embodiment, in the second phase, the received data may be acquired in the order of the Nth antenna 20-N to the first antenna 20-1, or may be in a different order. ..

(2-2) In the above embodiment, the acquisition of the last received data in the first phase also serves as the acquisition of the first received data in the second phase. On the other hand, after acquiring the two received data in the first phase, the received data of each of the N antennas may be acquired again in the second phase. That is, the second phase may be completely distinguished from the first phase.

(2-3) The received data acquired in the first phase is not limited to the received data from the first antenna 20-1. That is, the specific antenna described above may be any antenna.
(2-4) In order to estimate the position of the mobile terminal 200, it is not essential to estimate the arrival angles θa and θb in the two receiving antenna arrays. The arrival angle may be estimated only by any one of the receiving antenna arrays, and the position of the mobile terminal 200 may be estimated based on the arrival angle and the distance. Conversely, the arrival angle may be estimated for each of the three or more receiving antenna arrays. For example, a receiving antenna array may be further provided between the first receiving antenna array 20 and the second receiving antenna array 30, and the arrival angle may be estimated for each of these three receiving antenna arrays. Then, the position of the mobile terminal 200 may be estimated based on the estimated three arrival angles and the distance.

(2-5) The receiving antenna arrays 20, 30, 40, and 50 may be provided at any position on the vehicle 100, respectively. Further, three or less receiving antenna arrays may be provided, or five or more receiving antenna arrays may be provided. The receiving antenna 60 and each of the three transmitting antennas 70, 80, 90 may be provided at any position on the vehicle 100, or may be provided in any number.
(2-6) In the terminal position estimation process of FIG. 3, it is not essential to execute the terminal distance estimation process of S140. That is, in order to specify the position of the mobile terminal 200, the distance between the mobile terminal 200 and the vehicle 100 is not always necessary. For example, the position of the mobile terminal 200 may be specified based on the arrival angles of each receiving antenna array estimated in S130 (for example, two arrival angles θa and θb in the present embodiment) without estimating the distance.

(2-7) The present disclosure is not limited to application to a technique for estimating the direction of arrival of radio waves from the mobile terminal 200. That is, the present disclosure is not limited to the application to the electronic key system 1, and is not limited to the application to the vehicle 100. The present disclosure can be applied to estimate the direction of arrival of radio waves in any scene where radio waves arrive.

(2-8) The control unit 10 and methods thereof described in the present disclosure are provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. It may be realized by a dedicated computer. Alternatively, the control unit 10 and its method described in the present disclosure may be realized by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control unit 10 and its method described in the present disclosure is a combination of a processor and memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. It may be realized by one or more dedicated computers configured by. The computer program may also be stored on a computer-readable non-transitional tangible recording medium as an instruction executed by the computer. The method for realizing the functions of each part included in the control unit 10 does not necessarily include software, and all the functions may be realized by using one or a plurality of hardware.

(2-9) A plurality of functions possessed by one component in the above embodiment may be realized by a plurality of components, or one function possessed by one component may be realized by a plurality of components. May be good. Further, a plurality of functions possessed by the plurality of components may be realized by one component, or one function realized by the plurality of components may be realized by one component. Further, a part of the configuration of the above embodiment may be omitted. In addition, at least a part of the configuration of the above embodiment may be added or replaced with the configuration of the other above embodiment.

(2-10) In addition to the electronic key system 1 described above, a system having the electronic key system 1 as a component, a program for executing various functions in the electronic key system 1, a semiconductor memory recording this program, and the like. The present disclosure can also be realized in various forms such as a non-transitional substantive recording medium and a specific method for realizing various functions in the electronic key system 1.

1 ... Electronic key system, 10 ... Control unit, 11 ... Control unit, 12 ... Storage unit, 20 ... 1st receiving antenna array, 20-1 to 20-N ... 1st antenna to Nth antenna, 21 ... 1st switching Switch, 22 ... 1st receiving circuit, 23 ... Orthogonal demodulator, 24 ... Local oscillator, 25 ... 1st AD converter, 26 ... 2nd AD converter, 30 ... 2nd receiving antenna array, 31 ... 2nd changeover switch, 32 ... reception circuit, 40 ... third receiving antenna array, 50 ... fourth receiving antenna array, 60 ... receiving antenna, 61 ... fifth receiving circuit, 70 ... first transmitting antenna, 71 ... first transmitting circuit, 100 ... vehicle, 200 ... Mobile terminal.

Claims (8)

A switching unit (21) configured to input a reception signal of radio waves received by each of a plurality of antennas (20-1 to 20-N) arranged at regular intervals, and any one of them. A switching unit configured to input a switching signal instructing the selection of the received signal, and to output one of the plurality of input received signals selected by the switching signal.
A first output unit (10: S220 to S230) configured to output the switching signal for selecting one specific received signal, and
A first acquisition unit (10: S220 to S230) configured to acquire the received signal output from the switching unit twice at a time interval td in response to the switching signal output by the first output unit. When,
A second output unit (10: S230 to S260) configured to output the switching signal for sequentially selecting the received signals from the plurality of antennas one by one at the time interval td.
A second acquisition unit configured to acquire the received signals from the plurality of antennas, which are sequentially output one by one from the switching unit at the time interval td in response to the switching signal from the second output unit. (10: S230 to S260) and
A first generation unit configured to generate a first correlation matrix which is a correlation matrix showing the two correlation characteristics in each of any two combinations of the received signals acquired by the second acquisition unit (1st generation unit). 10: S310) and
A reference correction configured to calculate a reference correction value representing the phase difference between the two received signals caused by the time interval td based on the two received signals acquired by the first acquisition unit. Value calculation unit (10: S300) and
Based on the reference correction value calculated by the reference correction value calculation unit, the component of the phase difference due to the time interval td is removed from the first correlation matrix generated by the first generation unit. A second generator (10: S310) configured to generate a two-correlation matrix, and
An estimation unit (10: S330) configured to estimate the arrival direction of the radio wave based on the second correlation matrix generated by the second generation unit.
A radio wave arrival direction estimation device equipped with. The radio wave arrival direction estimation device according to claim 1.
The second acquisition unit is configured to acquire the received signal second acquired by the first acquisition unit as the first received signal to be acquired by the second acquisition unit. Direction estimator. The radio wave arrival direction estimation device according to claim 1 or 2.
Further, based on the reference correction value calculated by the reference correction value calculation unit, the position of the two received signals caused by the time difference between the acquisition of the two corresponding received signals in each of the combinations. It is provided with an individual correction value calculation unit (10: S300) configured to calculate an individual correction value representing a phase difference.
The second generation unit is configured to generate the second correlation matrix based on at least the individual correction value calculated by the individual correction value calculation unit.
Radio wave arrival direction estimation device. The radio wave arrival direction estimation device according to claim 3.
Further, a correction matrix configured to generate a correction matrix in which the individual correction values corresponding to each of the combinations are arranged by using the individual correction values calculated by the individual correction value calculation unit. Equipped with a calculation unit (10: S300)
The second generation unit is configured to generate the second correlation matrix by performing an operation between the first correlation matrix and the correction matrix calculated by the correction matrix calculation unit.
Radio wave arrival direction estimation device. The radio wave arrival direction estimation device according to claim 4.
The second generation unit is a radio wave arrival direction estimation device configured to generate the second correlation matrix by calculating the Hadamard product of the first correlation matrix and the correction matrix. The radio wave arrival direction estimation device according to claim 4 or 5.
Further, a receiving circuit (22) configured to input the received signal output from the switching unit is provided.
The receiving circuit
An orthogonal demodulator (23) configured to input the received signal output from the switching unit, and the received signal is represented by a complex number by quadrature demodulating the input received signal. An orthogonal demodulator configured to generate an in-phase component signal corresponding to the real part in the case and an orthogonal component signal corresponding to the imaginary part when the received signal is represented by a complex number.
A first AD converter (25) configured to perform AD conversion of the in-phase component signal generated by the orthogonal demodulator, and
A second AD converter (26) configured to perform AD conversion of the orthogonal component signal generated by the orthogonal demodulator, and
With
The first acquisition unit and the second acquisition unit are configured to acquire the reception signal via the reception circuit.
Radio wave arrival direction estimation device. The radio wave arrival direction estimation device according to any one of claims 1 to 6.
The radio wave arrival direction estimation device is mounted on the vehicle (100).
The vehicle includes a transmission unit (10, 70, 71: S110) configured to transmit a transmission signal to the mobile terminal (200) by a first radio wave.
The mobile terminal is configured to transmit a response signal on the second radio wave in response to receiving the first radio wave.
The plurality of antennas are configured to receive the second radio wave.
The estimation unit is configured to estimate the arrival direction of the second radio wave received by the plurality of antennas.
Radio wave arrival direction estimation device. Radio wave arrival direction estimation device (10, 20, 21: S130) and
With the distance estimation device (10, 60, 61, 70, 71: S110, S120, S140),
Position estimation device (10: S150) and
It is a position estimation system equipped with
The distance estimation device is
A transmission unit (10, 70, 71: S110) configured to transmit a transmission signal to a mobile terminal by the first radio wave, and
A response signal including reception strength information indicating the reception strength of the first radio wave in the mobile terminal, which is transmitted from the mobile terminal by the second radio wave in response to the reception of the first radio wave by the mobile terminal. A receiver (10, 60, 61: S120) configured to receive, and
A distance estimation unit (10: S140) that estimates the distance from a predetermined reference position to the mobile terminal based on the reception intensity information included in the response signal received by the reception unit.
With
The radio wave arrival direction estimation device is
Multiple antennas (20-1 to 20-N) arranged at regular intervals,
The switching unit (21) configured to input the reception signal of the second radio wave received by each of the plurality of antennas, and the switching signal instructing the selection of any one of the received signals is A switching unit configured to be input and to output one of the plurality of input received signals selected by the switching signal.
A first output unit (10: S220 to S230) configured to output the switching signal for selecting one specific received signal, and
A first acquisition unit (10: S220 to S230) configured to acquire the received signal output from the switching unit twice at a time interval td in response to the switching signal output by the first output unit. When,
A second output unit (10: S230 to S260) configured to output the switching signal for sequentially selecting the received signals from the plurality of antennas one by one at the time interval td.
A second acquisition unit configured to acquire the received signals from the plurality of antennas, which are sequentially output one by one from the switching unit at the time interval td in response to the switching signal from the second output unit. (10: S230 to S260) and
A first generation unit configured to generate a first correlation matrix which is a correlation matrix showing the two correlation characteristics in each of any two combinations of the received signals acquired by the second acquisition unit (1st generation unit). 10: S310) and
A reference correction configured to calculate a reference correction value representing the phase difference between the two received signals caused by the time interval td based on the two received signals acquired by the first acquisition unit. Value calculation unit (10: S300) and
Based on the reference correction value calculated by the reference correction value calculation unit, the component of the phase difference due to the time interval td is removed from the first correlation matrix generated by the first generation unit. A second generator (10: S310) configured to generate a two-correlation matrix, and
An estimation unit (10: S330) configured to estimate the arrival direction of the second radio wave based on the second correlation matrix generated by the second generation unit.
With
The position estimation device is configured to estimate the position of the mobile terminal based on the distance estimated by the distance estimation device and the arrival direction estimated by the radio wave arrival direction estimation device. ,
Position estimation system.

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