JP7250271B2 - POSITION DETECTION SYSTEM AND POSITION DETECTION METHOD - Google Patents

Description

The present invention relates to a position detection system and position detection method for detecting the positional relationship between a first communication device and a second communication device.

2. Description of the Related Art Conventionally, a position detection system that performs radio wave communication between a terminal and its operation target, measures the distance between them, and determines whether the measured distance is correct or not is well known (see Patent Document 1, etc.). For example, when the position detection system obtains a measurement value according to the distance between the terminal and its operation target, and determines that this measurement value is less than a threshold, for example, the wireless communication between the two parties Allow ID matching to be established. As a result, even if an unauthorized communication is attempted by connecting a terminal far away from the operation target using a repeater or the like, it is possible to detect this and prevent the ID collation from being established illegally.

JP 2017-38348 A

Further improvement in position detection accuracy has been desired in these position detection systems.
SUMMARY OF THE INVENTION An object of the present invention is to provide a position detection system and a position detection method capable of improving position detection accuracy.

A position detection system that solves the above problems is characterized in that, when the other receives radio waves transmitted at different frequencies from one of the first communication device and the second communication device, the different frequencies a phase difference calculation unit that calculates at least two sets of phase differences between radio waves for each combination of frequencies that are different from each other; and between the first communication device and the second communication device based on the at least two sets of phase differences and a distance estimator for determining a distance estimate, which is the distance of .

A position detection method for solving the above-mentioned problem is characterized in that, when radio waves transmitted at different frequencies from one of the first communication device and the second communication device are received by the other, the propagation characteristics of the radio waves are the frequencies different from each other. a step of calculating at least two sets of phase differences between radio waves by a phase difference calculating unit for each combination of frequencies different from each other; and based on the at least two sets of phase differences, the first communication device and the second communication determining a distance estimate, which is the distance between aircraft, by a distance estimator.

According to the present invention, position detection accuracy can be improved.

1 is a schematic diagram of a position detection system according to a first embodiment; FIG. The block diagram of a position detection system. A matrix diagram of a correlation matrix. The graph which shows the analysis result by computer simulation. FIG. 7 is a configuration diagram of a radio wave transmitting unit and a radio wave receiving unit according to the second embodiment; The block diagram of the element which calculates a distance estimated value. 4 is a flowchart showing a procedure for distance estimation; (a) is a power spectrum diagram of propagation characteristics, and (b) is a phase spectrum diagram of propagation characteristics. (a) to (c) are phase spectrum diagrams for explaining a phase DC component.

(First embodiment)
A first embodiment of a position detection system and a position detection method will be described below with reference to FIGS. 1 to 4. FIG.

As shown in FIG. 1, the position detection system 1 transmits radio waves Sa from the first communication device 2 to the second communication device 3, and returns the radio waves Sa received by the second communication device 3 to the first communication device 2. . The first communication device 2 receives this radio wave Sa and measures the positional relationship between the first communication device 2 and the second communication device 3 from the phase change of this received signal. Radio wave Sa is preferably a multi-carrier signal formed by mixing a plurality of signals. Also, it is preferable that the first communication device 2 is positioned as a base station and the second communication device 3 is positioned as a terminal.

As shown in FIG. 2 , the position detection system 1 includes a radio wave transmitter 4 and a radio wave receiver 5 . In the case of this example, the radio wave transmitter 4 and the radio wave receiver 5 are provided in the first communication device 2, the radio wave Sa transmitted from the first communication device 2 is received by the second communication device 3, and the radio wave Sa transmitted from the second communication device 3 is received by the second communication device 3. A similar radio wave Sa is returned. Then, the first communication device 2 receives the return radio wave Sa, and measures the positional relationship between the two parties from the time required for transmitting and receiving the radio wave Sa.

The radio wave transmission unit 4 includes a plurality of oscillators 9 , adders 10 , DA converters 11 and transmission antennas 12 . Oscillator 9 outputs complex signals to adder 10 as unmodulated continuous waves (CW waves) of different frequencies. A complex signal at each frequency is a signal having a real part and an imaginary part. Adder 10 adds the real parts of a plurality of complex signals to generate a synthesized signal, and outputs this to DA converter 11 . The signal after D/A conversion is transmitted from the transmitting antenna 12 as radio waves Sa.

The second communication device 3 receives the radio wave Sa transmitted from the first communication device 2 as a signal delayed by the propagation time τ. Then, the second communication device 3 transmits to the first communication device 2 a radio wave Sa similar to that received. This radio wave Sa also reaches the first communication device 2 with a delay of the propagation time τ.

The radio wave receiver 5 includes a receiving antenna 15 , an AD converter 16 , a complex generator 17 , a correlation calculator 18 and a correlation matrix calculator 19 . The receiving antenna 15 receives the radio wave Sa returned from the second communication device 3 as a signal delayed by the propagation time τ. This received signal is A/D converted by the AD converter 16 and output to the complexing section 17 . The complex generator generates a complex signal of the radio wave Sa based on the received signal. The correlation calculator 18 calculates the correlation between the complex signals and outputs the calculation result to the correlation matrix calculator 19 . A correlation matrix calculator 19 obtains a correlation matrix _Rxx from the calculation result of the correlation calculator 18 .

Next, a method for calculating the correlation matrix _Rxx will be specifically described. The radio wave transmitting unit 4 of the first communication device 2 mixes and transmits M equal-amplitude sinusoidal signal waves of equal-interval frequencies f ₁ , . . . , f _M . In this example, it is assumed that this multicarrier signal is received in a multiple wave environment of L waves, that is, in a multipath environment. The radio wave receiver 5 samples the received signal at the sampling frequency _Fs to obtain _Np × _Ns sample data. Here, N _p is the number of samples for correlation calculation, and N _s is the number of snapshots of correlation calculation values. It is assumed that this signal has a frequency error f _dif when it is transmitted by the terminal due to a clock error occurring in a digital circuit within the terminal. The received signal C(t) at this time is represented by the following equation (A).

但し、式(A)において、ｓ_０ｌとτ_ｌは、第ｌ到来波（遅延波）の複素振幅（全マルチキャリアは同じ振幅）と伝搬遅延時間とする。また、ｎ_ｌ(t)は、外部ノイズを含む雑音である。

However, in equation (A), s _0l and _τl are the complex amplitude (same amplitude for all multicarriers) of the l-th arriving wave (delayed wave) and the propagation delay time. Also, n _l (t) is noise including external noise.

_Correlation calculation section 18 calculates N _s pieces of correlation value data x _m (n ₎ (n=1, . , . . . , M). Then, by arranging them in order of frequency, a snapshot of the M-dimensional input vector is generated as shown in the following equation (B). In equation (B), n is the number of snapshots and m is the frequency carrier number.

さらに、異なるキャリア間の信号の相関値はゼロであるとすると、式(B)で示す周波数アレーデータは、ベクトル表記により次式(C)で表される。

Furthermore, assuming that the correlation value of signals between different carriers is zero, the frequency array data shown in equation (B) is represented by the following equation (C) in vector notation.

ここで、式(C)において、ａ(τ_ｌ)は、遅延時間τ_ｌを含むベクトルであり、アレー応答ベクトルと呼ばれる。また、Ａは、アレー応答行列と呼ばれる。ｓ(n)は、信号応答ベクトルであり、ｎ(n)は、各周波数の雑音成分から成る雑音ベクトルである。

Here, in equation (C), a(τ _l ) is a vector containing the delay time τ _l and is called an array response vector. A is also called the array response matrix. s(n) is the signal response vector and n(n) is the noise vector consisting of the noise components at each frequency.

The input vector has the same form as for direction estimation, and the method of direction of arrival estimation can be used to estimate the propagation delay time, ie, the terminal distance. A correlation matrix based on N _s snapshot data is represented by the following equation (D).

また、式(D)のアレーデータの相関行列Ｒ_ｘｘは、次式(E)に展開することができる。

Also, the array data correlation matrix R _xx in equation (D) can be developed into the following equation (E).

式(E)の行列Ｓは、信号（波源）相関行列と呼ばれ、到来波が全て互いに無関係であれば、次式(F)で表される。

Matrix S of formula (E) is called a signal (wave source) correlation matrix, and if all incoming waves are mutually unrelated, it is represented by the following formula (F).

ここで、Ｐ_lは、各到来波の入力電力であり、σ^２は、雑音ｎ(n)の平均電力である。但し、ここでは簡単のため、雑音成分は各周波数において独立で等電力としている。このようにして、本例の相関行列算出部１９は、相関行列Ｒ_ｘｘを求める。そして、この相関行列Ｒ_ｘｘを用いて、第１通信機２及び第２通信機３の間の距離である距離推定値ｄが求められる。

where P _l is the input power of each incoming wave and ^σ2 is the average power of the noise n(n). However, for the sake of simplicity, the noise components are assumed to be independent and of equal power at each frequency. In this manner, the correlation matrix calculator 19 of this example obtains the correlation matrix _Rxx . Then, using this correlation matrix _Rxx , the estimated distance value d, which is the distance between the first communication device 2 and the second communication device 3, is obtained.

The position detection system 1 includes a phase difference calculator 22 and a distance estimator 23 . The phase difference calculator 22 of the present example determines that the propagation characteristics of the radio waves Sa transmitted from one of the first communication device 2 and the second communication device 3 at frequencies different from each other are different from each other when the other receives the radio waves Sa. At least two sets of phase differences between radio waves of frequencies are calculated for each different combination of frequencies. The distance estimator 23 obtains a distance estimation value d, which is the distance between the first communication device 2 and the second communication device 3, based on at least two pairs of phase differences.

Based on the correlation matrix _Rxx obtained by the correlation matrix calculator 19, the position detection system 1 calculates the propagation time τ required for the round trip of the radio waves Sa, that is, the estimated distance value d, by the group delay method. The group delay method generally differentiates the phase difference φ between an input waveform and an output waveform with respect to each frequency ω=2πf, and is expressed by the following equation (1) where τ is the propagation time.

従って、群遅延法を用いた距離推定法とは、送信信号と受信信号との間に生じている位相回転量を周波数ごとに求め、さらに隣り合う周波数における位相回転の差を抽出し、距離を推定する手法である。ここでは、先行波のみのマルチキャリア信号を受信した場合について説明する。

Therefore, the distance estimation method using the group delay method obtains the amount of phase rotation occurring between the transmission signal and the reception signal for each frequency, extracts the phase rotation difference between adjacent frequencies, and calculates the distance. It is a method of estimating. Here, the case of receiving a multicarrier signal consisting of only preceding waves will be described.

Correlation with other frequency components contained in the received signal is sufficiently suppressed by performing correlation calculation using all samples of the received signal C(t) and the frequency _fm component of the transmitted signal. As a result, x _m representing changes in the amplitude and phase of the frequency f _m component is obtained as shown in the following equation (2).

なお、式(2)において、τは、伝搬時間であり、ｓは、マルチキャリア信号の複数素数幅（全キャリア同じ値）であり、Ｎ_ｐは、相関演算用のサンプル数であり、Ｎ_ｓは、相関演算用のスナップショット数である。また、式(2)において、Ｍは、キャリア数、Ｆ_ｓは、サンプリング周波数であり、ｆ_difは、周波数誤差であり、ｎ(ｔ)は、各周波数の雑音成分からなる雑音ベクトルである。

In equation (2), τ is the propagation time, s is the multiple prime number width of the multicarrier signal (same value for all carriers), N _p is the number of samples for correlation calculation, and N _s is the number of snapshots for correlation calculation. Also, in equation (2), M is the number of carriers, _Fs is the sampling frequency, f _dif is the frequency error, and n(t) is a noise vector consisting of noise components of each frequency.

If there is no frequency error in the received signal (if f _dif =0), then x _m has a form that does not include the number of data samples t, and averaging with respect to t extracts the phase change in the frequency f _m components. can. At this time, _xm is represented by the following equation (3).

このｘ_ｍに対して、各々の周波数成分ごとに隣り合う周波数との位相差を抽出し、距離ｄ_ｍを次式(4)から求める。なお、式(4)のｃは、光速であり、［・］^＊は、共役複素数を示す。

For this _xm , the phase difference between adjacent frequencies is extracted for each frequency component, and the distance _dm is obtained from the following equation (4). Note that c in equation (4) is the speed of light, and [·] ^* indicates a conjugate complex number.

距離推定値ｄは、各々の周波数成分ごとに求めた距離ｄ_ｍの平均値から得られる。よって、距離推定値ｄは、次式(5)により求まる。

A distance estimate d is obtained from the average value of the distances _dm determined for each frequency component. Therefore, the estimated distance value d is obtained by the following equation (5).

また、式(5)は、次式(6)のように表すこともできる。

Expression (5) can also be expressed as the following expression (6).

しかし、式(5)や式(6)において、例えば周波数誤差が発生する場合、ｘ_ｍは、データサンプル数ｔを含む形となり、ｔに関する平均化により、低下或いは消失する。よって、このとき周波数成分ごとの位相回転量を正しく抽出することができず、推定精度が悪化する懸念があった。また、距離推定値ｄは、隣接するキャリアとの位相差のみ使用するため、ノイズ等により、推定精度が低下し易い問題もあった。

However, in equations (5) and (6), for example, if a frequency error occurs, _xm will include the number of data samples t, and will drop or disappear due to averaging with respect to t. Therefore, at this time, the amount of phase rotation for each frequency component cannot be correctly extracted, and there is a concern that the estimation accuracy will deteriorate. In addition, since the distance estimation value d uses only the phase difference with the adjacent carrier, there is also a problem that the estimation accuracy tends to decrease due to noise or the like.

Therefore, in the case of this example, in estimating the distance, first, the phase rotation amount data vector X is used to obtain the correlation matrix _Rxx . Note that the correlation matrix _Rxx is obtained by the following equation (7).

そして、この相関行列Ｒ_ｘｘについて、相関行列Ｒ_ｘｘの各対角線に沿って平均処理を行い、各キャリア間の位相差を含む複素数ｘ_Δｐを得る。この複素数ｘ_Δｐは、次式(8)によって表される。

Then, this correlation matrix _Rxx is averaged along each diagonal line of the correlation matrix _Rxx to obtain a complex number _xΔp including the phase difference between each carrier. This complex number x _Δp is represented by the following equation (8).

ここで、係数ｚを次式(9)のように定義する。

Here, the coefficient z is defined as in the following equation (9).

この係数ｚは、次式(10)のように表すことができる。

This coefficient z can be expressed as in the following equation (10).

そして、このｚ_ｐを用いて、次式(11)の多項式を定義する。

Then, using this _zp , the polynomial of the following equation (11) is defined.

式(11)において、ｚが往復の伝搬時間２τに対応する値をとるとき、式(11)の各項は、ゼロをとる。このため、式(9)の条件のとき、式(11)が成立することは明らかである。従って、式(11)のｚに関する多項式の解を求めれば、伝搬時間τの推定値、すなわち距離推定値ｄが得られることになる。しかし、式(11)は、ｚ^＊を含み、ｚのみの多項式ではないため、式(11)をゼロにする解を求めるのが難しくなる。そこで、求めたいものは、｜ｚ｜＝１の解（ｚｚ^＊＝１の解）であるので、ｚ^＊＝ｚ^－１とおくと、式(11)は、次式(12)に変換することができる。

In equation (11), each term in equation (11) is zero when z takes a value corresponding to the round trip propagation time 2τ. Therefore, it is clear that the formula (11) is established under the condition of the formula (9). Therefore, the estimated value of the propagation time τ, that is, the distance estimated value d can be obtained by solving the polynomial for z in Equation (11). However, since equation (11) contains z ^* and is not a polynomial of only z, it becomes difficult to find a solution that makes equation (11) zero. Therefore, what we want to find is the solution of |z| ^{=1 (solution of zz* = 1} ). be able to.

そして、式(12)の両辺にｚ(M－１)をかけて整理すると、次式(13)に式変形することができる。

By multiplying both sides of the equation (12) by z(M−1), the equation can be transformed into the following equation (13).

式(13)に示されるように、２(Ｍ－１)次の多項式が得られる。ここで、もしｚ＝ｒｅ^ｊβ（なお、ｒが大きさ、βが偏角）が式(13)の解であれば、ｚ＝（１／ｒ）ｅ^ｊβも式(13)の解である。このように、ｚ平面、すなわち複素平面の式(13)の解は、必ず同じ偏角をもつ解が単位円を挟んで複数存在する。その中で、単位円上にある２重解が求める解である。こうして得られたｚに対し、次式(14)に示すように往復伝搬距離の距離推定値ｄを得ることができる。

As shown in equation (13), a polynomial of order 2(M-1) is obtained. Here, if z=re ^jβ (where r is the magnitude and β is the argument) is the solution of equation (13), then z=(1/r)e ^jβ is also the solution of equation (13). . Thus, in the z-plane, that is, in the complex plane, there are always a plurality of solutions with the same angle of argument across the unit circle. Among them, the solution to be sought is the double solution on the unit circle. For z obtained in this manner, the estimated distance d of the round-trip propagation distance can be obtained as shown in the following equation (14).

ここで、図３に示すように、チャネルのキャリア数の具体例を挙げて、距離推定値ｄの算出の仕方を説明する。ここでは、チャネルのキャリア数を「Ｎ」とし、ｘ_ｎを各キャリアの伝搬特性として、Ｎ＝４の例を示す。

Here, as shown in FIG. 3, a specific example of the number of carriers in a channel will be given to explain how to calculate the distance estimated value d. Here, an example of N=4 is shown where the number of carriers in the channel is "N" and _xn is the propagation characteristic of each carrier.

The phase difference calculator 22 calculates the phase difference between adjacent carriers skipping one or more. In this correlation matrix _Rxx , diagonal elements are components at the same frequency interval. In the case of the example of FIG. 3, the group indicated by the dashed-dotted line in the same figure is the phase difference θ with the one-adjacent carrier, and the group indicated by the two-dotted dashed line in the same figure is the phase difference with the two-adjacent carrier. The phase difference θ′ is the phase difference θ′, and the phase difference θ″ with the three adjacent carriers is indicated by the three-dot chain line in FIG.

The phase difference calculator 22 averages the elements of the correlation matrix _Rxx for each component with the same frequency interval to calculate phase differences θ, θ′, and θ″ between carriers. Here, these θ, θ′ and θ″ are represented by the following equation (15).

距離推定部２３は、式(15)のθ、θ’、θ’’について、それぞれ指数関数をとり、次式(16)のａ、ｂ、ｃを定義する。

The distance estimator 23 takes exponential functions for θ, θ′, and θ″ in Equation (15), and defines a, b, and c in Equation (16) below.

距離推定部２３は、式(11)の考え方に沿って次式(17)を立てて、｜ｚ｜＝１となる解（｜ｚ｜＝１に最も近い解）を算出する。

The distance estimating unit 23 formulates the following equation (17) in line with the concept of equation (11), and calculates a solution that satisfies |z|=1 (the solution closest to |z|=1).

そして、距離推定部２３は、算出したｚ（＝exp(ｊ２πΔｆτ)）の位相を用い、式(14)から距離推定値ｄを算出する。

Then, the distance estimation unit 23 uses the calculated phase of z (=exp(j2πΔfτ)) to calculate the estimated distance value d from Equation (14).

FIG. 4 shows the analysis results by computer simulation. The figure shows the SNR characteristics (signal-noise ratio) of the estimated value RMSE (Root Mean Squared Error). Tables 1 and 2 show the specifications of the simulation. In Table 2, B is the bandwidth of the filter, and T is the symbol length of the FSK signal.

図４では、従来の位置推定手法の場合の特性を一点鎖線で示し、本例の位置推定手法の特性を実線で示す。同図に示されるように、本例で述べたように、距離推定に全キャリア間隔の情報を用いれば、高い推定精度を確保できることが分かる。このことからも、周波数が隣り合う電波間の位相差のみならず、周波数が隣り合わない電波間の位相差も用いて距離推定値ｄを求める本例の手法は、位置検出精度が高いと言える。

In FIG. 4, the characteristic of the conventional position estimation method is indicated by a dashed line, and the characteristic of the position estimation method of this example is indicated by a solid line. As shown in the figure, it can be seen that high estimation accuracy can be ensured by using information on all carrier intervals for distance estimation, as described in this example. From this, it can be said that the method of this example for obtaining the distance estimation value d using not only the phase difference between radio waves with adjacent frequencies but also the phase difference between radio waves with non-adjacent frequencies has high position detection accuracy. .

As described above, according to this example, among the radio waves Sa of each frequency transmitted in the position detection communication, the phase differences between the radio waves whose frequencies are not adjacent, in this example, the phase differences θ′ and θ″ are obtained. A distance estimation value d is obtained using the phase differences θ′ and θ″. Therefore, it is possible to calculate the estimated distance value d from a large amount of phase difference information. Therefore, position detection accuracy can be improved.

The phase difference calculator 22 calculates the phase difference between radio waves having adjacent frequencies, which is the phase difference θ in this example. The distance estimating unit 23 uses the phase difference θ between radio waves with adjacent frequencies and the phase differences θ′ and θ″ between radio waves with non-adjacent frequencies as at least two sets of phase differences to obtain the estimated distance value d Ask for Therefore, it is possible to obtain the estimated distance value d using more phase difference information, which further contributes to improving the accuracy of position detection.

A plurality of radio waves Sa are transmitted at equally spaced frequencies. Therefore, from the propagation characteristics of the radio waves Sa transmitted at equally spaced frequencies, it is possible to perform highly accurate position detection using a technique such as the group delay method.

In the correlation matrix _Rxx obtained from the propagation characteristics, the phase difference calculator 22 calculates the average of the components located on the diagonal line of the correlation matrix _Rxx as phase differences θ, θ′, and θ″ between propagations. Therefore, it is possible to easily and accurately calculate the estimated distance d using the correlation matrix _Rxx obtained from the propagation characteristics.

The distance estimating unit 23 obtains the average value of the phase difference for each component of the same frequency interval as a complex number x _Δp as shown in equations (8) to (11), and each complex number x _Δp exists in a separate term. Formula (11) and (17) Then, the distance estimating unit 23 calculates the "z" of the solution that makes these equations zero, and obtains the estimated distance value d from the "z" of this solution. Therefore, the distance estimation value d can be obtained with high accuracy by calculating the distance estimation value d by obtaining "z" of the solution of the equation.

(Second embodiment)
Next, a second embodiment will be described with reference to FIGS. 5 to 9. FIG. The second embodiment differs from the first embodiment in that it uses BLE (Bluetooth Low Energy) communication of Bluetooth (registered trademark) instead of using multi-carrier signals. This is an example of Therefore, the same reference numerals are assigned to the same parts as in the first embodiment, detailed description thereof will be omitted, and only the different parts will be described in detail.

As shown in FIG. 5, the position detection system 1 measures the time it takes for the radio waves Sa to travel between the first communication device 2 and the second communication device 3 . For communication in this example, for example, Bluetooth is used. The position detection system 1 of this example transmits radio waves Sa through a plurality of channels between the first communication device 2 and the second communication device 3, obtains the propagation characteristics of the radio waves Sa of these channels, A distance estimate d, which is the separation distance between the second communication devices 3, is measured.

The radio wave transmitter 31 includes a waveform generator 32 , a modulator 33 , a DA converter 34 , a mixer 35 , an oscillator 36 and a transmission antenna 37 . The waveform generation unit 32 generates a periodic signal Sk composed of a periodic binary code as the radio wave Sa transmitted between the first communication device 2 and the second communication device 3, and outputs this to the modulation unit 33. do. It is preferable that the periodic signal Sk is a signal in which the binarized code "0" and "1" are switched every period T. FIG. The modulation unit 33 consists of GFSK (Gaussian Frequency-Shift Keying). The periodic signal Sk is modulated by the modulator 33 , D/A converted by the DA converter 34 , superimposed on the carrier wave of the oscillator 36 by the mixer 35 , and transmitted from the transmission antenna 37 .

A radio wave receiver 40 , a receiving antenna 41 , a mixer 42 , an oscillator 43 and an AD converter 44 are provided. When the radio wave receiving unit 40 receives the radio wave Sa transmitted from the radio wave transmitting unit 31 by the receiving antenna 41, the received signal is converted into a baseband signal Sb by the mixer 42 based on the signal of the oscillator 43, and this baseband signal The signal Sb is A/D converted by the AD converter 44 .

The radio wave receiving unit 40 includes a measuring unit 45 that measures the propagation characteristics of the received radio waves Sa. The measuring unit 45 measures at least the phase of the radio waves Sa as the propagation characteristics of the radio waves Sa transmitted at a plurality of frequencies from one of the first communication device 2 and the second communication device 3 when the other receives the radio waves Sa. . The measurement unit 45 of this example measures the propagation characteristics of the received radio wave Sa using the signal after A/D conversion. The propagation characteristics are preferably the amplitude and phase of the radio waves Sa, for example.

The measurement unit 45 has a Fourier transform unit 46 and a DC component extraction unit 47 . The Fourier transform unit 46 measures the frequency spectrum of the received signal by Fourier transforming the A/D converted signal. The frequency spectrum is data of the amplitude and phase of the transmitted/received radio wave Sa. The Fourier transform unit 46 outputs the frequency spectrum data group obtained from the Fourier transform to the DC component extractor 47 .

The DC component extractor 47 extracts the DC component of the amplitude and phase of the frequency spectrum, which is the Fourier transform result. This DC component is a characteristic value when the frequency is "0" in the frequency spectrum after Fourier transform. Also, the DC component is preferably extracted by interpolating a value based on the phase difference around the DC component. In this way, the propagation characteristics of the radio waves Sa transmitted and received by the first communication device 2 and the second communication device 3 are obtained.

As shown in FIG. 6, the position detection system 1 includes a multiplier 48 and a combiner 49 in addition to the phase difference calculator 22 and the distance estimator 23 described above. Note that these function groups may be provided in either the first communication device 2 or the second communication device 3 .

The multiplication unit 48 combines the propagation characteristics measured by transmitting radio waves from the first communication device 2 to the second communication device 3 and the propagation characteristics measured by transmitting radio waves from the second communication device 3 to the first communication device 2. Multiply by . Thus, in the case of this example, radio waves are transmitted from the first communication device 2 to the second communication device 3 to measure the propagation characteristics, and radio waves are also transmitted from the second communication device 3 to the first communication device 2 to propagate. Properties are measured and position estimation is performed from these propagation properties.

A synthesizing unit 49 synthesizes the multiplied propagation characteristics for a plurality of channels. By this synthesis, the synthesizing unit 49 calculates a phase rotation amount data vector X composed of a vector in which the radio wave characteristics of each channel are arranged.

The phase difference calculator 22 uses the phase of the propagation characteristics measured by the measuring unit 45 to calculate at least the phase difference between radio waves whose frequencies are not adjacent to each other. Based on the phase rotation amount data vector X acquired from the synthesizing unit 49, the phase difference calculator 22 of this example calculates the phase difference θ between radio waves with adjacent frequencies and the phase difference θ′ between radio waves with non-adjacent frequencies. , θ''.

Based on the phase difference obtained by the phase difference calculator 22, the distance estimator 23 obtains a distance estimated value d, which is the distance between the first communication device 2 and the second communication device 3. FIG. The distance estimating unit 23 of this example uses both the phase difference θ between radio waves with adjacent frequencies and the phase differences θ′ and θ″ between radio waves with non-adjacent frequencies to calculate the estimated distance value d. do.

Next, the operation and effects of the position detection system 1 of this embodiment will be described with reference to FIGS. 7 to 9. FIG.
As shown in FIG. 7, in S101 (“S” is an abbreviation for step, the same shall apply hereinafter), the first communication device 2 transmits the radio wave Sa to the second communication device 3, and the second communication device 3 receives the propagation characteristic is measured. In this example, a radio wave Sa based on the periodic signal Sk is transmitted from the transmitting antenna 37 of the first communication device 2 and received by the receiving antenna 41 of the second communication device 3 . In the second communication device 3, the frequency spectrum of the center frequency of the bandwidth of the channel is obtained from the baseband signal Sb of the received signal of the radio wave Sa. By extracting the DC component of this frequency spectrum, the propagation of the radio wave Sa is Properties are measured.

As shown in FIGS. 8A and 8B, the frequency spectrum elements include amplitude data P(f) and phase data θ(f). The amplitude data P(f) is represented by a power spectrum as shown in FIG. 8(a). Here, in the case of this example, in the position detection communication, a periodic signal Sk whose period T is repeated at "0" and "1" is transmitted. For this reason, the power spectrum has a parabolic waveform that stands at 1/T periods and has a peak at the frequency "0", which is a DC component. The DC component extractor 47 extracts the amplitude _P0 of the DC component from this power spectrum.

As shown in FIG. 8(b), the phase data .theta.(f) are represented by a phase spectrum as shown in the figure. Here, in the case of this example, in the position detection communication, a periodic signal Sk whose period T is repeated at "0" and "1" is transmitted. Therefore, the phase spectrum has a waveform in which the spectrum rises at a period of 1/T and the value increases proportionally.

Here, as shown in FIG. 9A, when a delay occurs in the sampling timing of A/D conversion or D/A conversion during radio wave transmission/reception, the slope of the phase change characteristic changes. However, as shown in the figure, even if the phase change characteristic tilts, the DC component, that is, the phase when the frequency is "0" does not change. Thus, since no delay error appears in the phase of frequency "0", the delay error can be canceled by extracting this phase as the phase of the center frequency of the radio wave Sa. However, as shown in FIG. 9B, an error due to the offset occurs in the frequency "0" component, and the "0" component cannot be extracted correctly.

Therefore, as shown in FIG. 9(c), the DC component extraction unit 47 of this example uses the phases θm and θp immediately before and after the DC component of the phase spectrum to calculate the phase _θ0 of the DC component. In this example, the average of the phase θm of the phase spectrum immediately before the DC component and the phase θp of the phase spectrum one after the DC component is obtained, and this is obtained as the phase _θ0 of the DC component. The amplitude P ₀ and phase θ ₀ of the C component obtained as described above are measured as the propagation characteristics of the radio wave Sa.

Returning to FIG. 7, in S102, the second communication device 3 transmits the radio wave Sa to the first communication device 2 to cause the first communication device 2 to measure the propagation characteristics. That is, the radio waves Sa are transmitted from the second communication device 3 to the first communication device 2 as well, and the propagation characteristics of the first communication device 2 are similarly measured. Note that the method of measuring the propagation characteristics at this time is the same as in the case of radio wave transmission from the first communication device 2 to the second communication device 3, so description thereof will be omitted.

When the propagation characteristics are measured by both the first communication device 2 and the second communication device 3, the multiplier 48 multiplies these propagation characteristics. As a result, even if a clock error or an initial phase error of the PLL occurs in each device of the position detection system 1, these errors appear as phase errors with opposite signs on the transmitting side and the receiving side. Errors can be canceled by multiplication.

In S103, the first communication device 2 and the second communication device 3 sequentially measure propagation characteristics on each communication channel. In the case of Bluetooth communication, for example, there are a plurality of channels (40 channels), so propagation characteristics are measured in each channel.

In S104, the synthesizing unit 49 synthesizes the propagation characteristics of all channels. In this example, the synthesizing unit 49 obtains a vector in which the propagation characteristics of each channel are arranged, that is, a phase rotation amount data vector X. FIG.

In S105, the phase difference calculating unit 22 and the distance estimating unit 23 use the phase rotation amount data vector X obtained by the synthesizing unit 49 to estimate the propagation time τ required for the round trip of the radio wave Sa, that is, the distance estimation by the group delay method. Calculate the value d. As described above, even in the case of a communication system using BLE, it is possible to obtain the distance estimated value d with high accuracy.

In addition, this embodiment can be changed and implemented as follows. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
[Regarding countermeasures when radio waves Sa are unevenly spaced]
・In each embodiment, the group delay method is based on the premise that the frequency intervals of the radio wave Sa to be transmitted are equal. It is also assumed that information cannot be obtained. In order to deal with this, when the frequencies of the radio waves Sa are unevenly spaced, the distance estimating unit 23 sets the phase difference between the radio waves at which the frequencies are unevenly spaced to zero, and performs an operation to obtain the estimated distance value d. . Specifically, when the frequencies of the radio waves Sa are unevenly spaced, the correlation matrix _Rxx is generated by setting the nonexistent frequency radiowave components to zero, and the phase differences θ, θ′, and θ″ are generated from the correlation matrix _Rxx . Calculate In this case, even if the frequencies of the radio waves Sa are unevenly spaced, the estimated distance value d can be calculated with high accuracy.

[Regarding radio waves Sa transmitted in position detection communication]
- In each embodiment, the bandwidth of each frequency of the radio waves Sa can be appropriately used as desired.

- In each embodiment, when the radio waves Sa are transmitted at a plurality of frequencies, each frequency may be transmitted in order.
- In each embodiment, when the radio wave Sa is transmitted at multiple frequencies, it may be transmitted as a mixed wave in which each frequency is superimposed.

- In each embodiment, the radio waves Sa are not limited to radio waves with the same frequency interval, and may be radio waves with non-same frequency intervals.
[Regarding the phase difference calculator 22]
- In each embodiment, the phase of the propagation characteristic is not limited to the phase of the DC component. For example, a value other than the DC component may be used.

- In each embodiment, the phase difference calculator 22 may calculate the phase difference from the propagation characteristics without multiplication or combination. In this case, the multiplier 48 and the combiner 49 can be omitted.
- In each embodiment, the phase difference may be calculated, for example, by calculating only the phase difference between non-adjacent radio waves.

[Regarding the distance estimation unit 23]
- In each embodiment, the equation for obtaining the distance estimated value d is not limited to the equations (11), (17), etc., and various equations can be applied as long as the distance estimated value d can be calculated.

・In each embodiment, the method of calculating the estimated distance value d is a method of obtaining the solution "z" using equations (11) and (17) as described in the embodiment and deriving the estimated distance value d. Not limited. That is, methods other than the method of solving equations (11) and (17) can also be applied.

[Regarding the first communication device 2 and the second communication device 3]
- In each embodiment, the radio wave Sa may be transmitted from the second communication device 3 to the first communication device 2, and the distance estimation unit 23 may be calculated through this communication.

- In each embodiment, the 1st communication apparatus 2 and the 2nd communication apparatus 3 are good also as a mode which transmits radio wave Sa only from one to the other, and measures a propagation characteristic.
- In each embodiment, either of the first communication device 2 and the second communication device 3 may be used as a base station, and either may be used as a terminal.

[Regarding the periodic signal Sk]
- In the second embodiment, the periodic signal Sk is not limited to a signal in which 0 and 1 are alternately repeated. good.

- In the second embodiment, the periodic signal Sk is not limited to a periodic signal in which "0" and "1" are switched at the period T, but may be an aperiodic signal.
[Regarding position detection system 1]
- In each embodiment, the method of distance estimation is not limited to the group delay method, and other methods such as the beamformer method, the MUSIC method, and the Root-MUSIC method may be used.

- Communication used in the position detection system 1 is not limited to Bluetooth, and other methods such as WiFi may be used.
- In each embodiment, various frequencies can be used as the frequency of the radio waves Sa used in the position detection system 1 .

[others]
- In each embodiment, the position detection system 1 is not limited to a vehicle, that is, an in-vehicle key system.

Next, technical ideas that can be grasped from the above embodiment and modifications will be described.
(b) In the position detection system, it is preferable that the distance estimating section obtains an average of the phase differences for components with the same frequency interval, and obtains the estimated distance value from the average.

1 Position detection system 2 First communication device 3 Second communication device 22 Phase difference calculator 23 Distance estimator Sa Radio wave θ, θ′, θ″ Phase difference d ... distance estimate, R _xx ... correlation matrix.

Claims (11)

As the propagation characteristics of the radio waves transmitted from one of the first communication device and the second communication device at frequencies different from each other when the other receives the radio waves, the phase difference between the radio waves of the different frequencies is A phase difference calculation unit that calculates at least two sets for each combination of
a distance estimating unit that calculates a distance estimation value that is a distance between the first communication device and the second communication device based on the at least two sets of phase differences ;
The position detection system, wherein the phase difference calculation unit calculates, as a phase difference between radio waves, an average of components positioned on a diagonal line of the correlation matrix in the correlation matrix obtained from the propagation characteristics. As the propagation characteristics of the radio waves transmitted from one of the first communication device and the second communication device at frequencies different from each other when the other receives the radio waves, the phase difference between the radio waves of the different frequencies is A phase difference calculation unit that calculates at least two sets for each combination of
a distance estimating unit that calculates a distance estimation value, which is a distance between the first communication device and the second communication device, based on the at least two sets of phase differences;
with
The distance estimating unit obtains the average of the phase differences for each component of the same frequency interval as a complex number, formulates an equation in which each complex number exists in a separate term, calculates a solution that makes the equation zero, and calculates the solution. A position detection system that determines said distance estimate from. 3. The position detection system according to claim 1, wherein a plurality of said radio waves are transmitted at equally spaced frequencies. 3. The position detection system according to claim 1 , wherein the radio wave is transmitted by synthesizing a plurality of equally spaced frequencies. As the propagation characteristics of the radio waves transmitted from one of the first communication device and the second communication device at frequencies different from each other when the other receives the radio waves, the phase difference between the radio waves of the different frequencies is A phase difference calculation unit that calculates at least two sets for each combination of
a distance estimating unit that calculates a distance estimation value, which is a distance between the first communication device and the second communication device, based on the at least two sets of phase differences;
with
The position detection system, wherein, when the frequencies of the radio waves are unevenly spaced, the distance estimating unit performs an operation for obtaining the estimated distance value by setting a phase difference between the radio waves having the uneven frequencies to be zero. The radio waves are transmitted in a plurality at equally spaced frequencies,
When the frequency intervals of the radio waves to be transmitted are equal and the frequency intervals of the radio waves are unequal, the distance estimating unit sets the phase difference between the radio waves with the unequal frequencies to zero. , to determine the distance estimate. The radio wave is transmitted by combining a plurality of equally spaced frequencies,
When the frequency intervals of the radio waves to be transmitted are equal and the frequency intervals of the radio waves are unequal, the distance estimating unit sets the phase difference between the radio waves with the unequal frequencies to zero. , to determine the distance estimate. The phase difference calculation unit calculates the phase difference between radio waves having adjacent frequencies,
The distance estimating unit obtains the estimated distance value using the phase difference between radio waves with adjacent frequencies and the phase difference between radio waves with non-adjacent frequencies as the at least two sets of phase differences. 8. The position detection system according to any one of 1 to 7 . As the propagation characteristics of the radio waves transmitted from one of the first communication device and the second communication device at frequencies different from each other when the other receives the radio waves, the phase difference between the radio waves of the different frequencies is A step of calculating at least two sets by the phase difference calculation unit for each combination of
obtaining, by a distance estimator, a distance estimation value, which is the distance between the first communication device and the second communication device, based on the at least two sets of phase differences ;
The position detection method, wherein the phase difference calculator calculates, as a phase difference between radio waves, an average of components positioned on a diagonal line of the correlation matrix in the correlation matrix obtained from the propagation characteristics. As the propagation characteristics of the radio waves transmitted from one of the first communication device and the second communication device at frequencies different from each other when the other receives the radio waves, the phase difference between the radio waves of the different frequencies is A step of calculating at least two sets by the phase difference calculation unit for each combination of
obtaining, by a distance estimator, a distance estimation value, which is a distance between the first communication device and the second communication device, based on the at least two sets of phase differences;
with
The distance estimating unit obtains the average of the phase differences for each component of the same frequency interval as a complex number, formulates an equation in which each complex number exists in a separate term, calculates a solution that makes the equation zero, and calculates the solution. A location method for determining said distance estimate from. As the propagation characteristics of the radio waves transmitted from one of the first communication device and the second communication device at frequencies different from each other when the other receives the radio waves, the phase difference between the radio waves of the different frequencies is A step of calculating at least two sets by the phase difference calculation unit for each combination of
obtaining, by a distance estimator, a distance estimation value, which is a distance between the first communication device and the second communication device, based on the at least two sets of phase differences;
with
The position detection method, wherein, when the frequencies of the radio waves are unevenly spaced, the distance estimating unit performs a calculation for obtaining the estimated distance value by setting a phase difference between the radio waves at which the frequencies are unevenly spaced to zero.

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