WO2019188892A1

WO2019188892A1 - Ranging system

Info

Publication number: WO2019188892A1
Application number: PCT/JP2019/012344
Authority: WO
Inventors: 佳樹大石; 健一古賀
Original assignee: 株式会社東海理化電機製作所
Priority date: 2018-03-29
Filing date: 2019-03-25
Publication date: 2019-10-03
Also published as: JP6839679B2; JP2019174416A; DE112019001642T5

Abstract

A ranging system (1) includes a waveform generating unit (8) which generates a periodic signal (Sk) comprising a periodic digital code, as a radio wave (Si) to be transmitted between a first communication device and a second communication device by means of Bluetooth communication. A DC component extracting unit (21) extracts a DC component propagation characteristic by interpolating the phase of a DC component on the basis of the phase in the vicinity the DC component in a frequency spectrum propagation characteristic obtained by subjecting the received radio wave (Si) to a Fourier transformation. A combining unit combines the extracted DC component propagation characteristics for a plurality of frequencies. A ranging unit calculates the distance between the first communication device and the second communication device from a calculation result obtained by subjecting the propagation characteristic resulting from the combination to a reverse Fourier transform.

Description

Ranging system

The present invention relates to a ranging system that measures the distance between two communication devices.

Conventionally, a distance measuring system that transmits and receives radio waves between two communication devices and calculates the distance between the two communication devices from the propagation time of the radio waves is well known (see Patent Document 1). In this distance measuring system, a radio wave is transmitted from a base station to a terminal, and the radio wave is returned from the terminal to the base station. Then, the distance between the base station and the terminal is calculated from the propagation time required for the exchange of radio waves at this time.

JP 2017-38348 A

By the way, the ranging system of Patent Document 1 does not specify that communication between two communication devices is Bluetooth communication. There was a need for technology development that can accurately calculate the distance between two communication devices for Bluetooth communication.

An object of the present invention is to provide a distance measuring system that improves the accuracy of distance calculation between the first communication device and the second communication device.

A ranging system that solves the above problem transmits radio waves from one of the first communication device and the second communication device to the other through Bluetooth communication, obtains propagation characteristics of the radio waves, and performs inverse Fourier transform on the propagation characteristics. Accordingly, the distance between the first communication device and the second communication device is calculated, and a periodic digital signal is transmitted as a radio wave transmitted between the first communication device and the second communication device. By interpolating the phase of the DC component based on the phase in the vicinity of the DC component in the propagation characteristics of the frequency spectrum obtained by Fourier transforming the received radio wave, and the waveform generation unit that generates a periodic signal composed of codes, the DC A DC component extracting unit for extracting component propagation characteristics; a combining unit for combining the extracted DC component propagation characteristics for a plurality of frequencies; and a reverse characteristic for the propagation characteristics obtained by combining. From the calculation result of the error transform, and a distance measuring unit for calculating a distance between said first communication device and the second communication device.

According to this configuration, a periodic signal composed of a periodic digital code is transmitted as a radio wave to perform distance measurement, so that a frequency spectrum required as a propagation characteristic stands periodically. For this reason, when the DC component of the phase spectrum is interpolated, it is possible to interpolate the phase of the DC component based on the tendency of the frequency spectrum that rises at a constant period, so that the SN (SN ratio: signal to noise ratio) It is possible to extract the phase of the DC component using only high data. Thereby, the calculation result of the inverse Fourier transform is obtained with high accuracy. Therefore, the distance between the first communication device and the second communication device can be obtained with high accuracy.

In the ranging system, the radio waves are transmitted through a plurality of channels by being transmitted through a plurality of channels, and the ranging unit is configured to transmit the first communication device based on a propagation characteristic measured from each channel. And calculating the distance between the second communication devices. According to this configuration, radio waves can be transmitted at a plurality of frequencies by a simple communication mode in which radio waves are transmitted through a plurality of channels.

In the ranging system, it is preferable that the DC component extraction unit obtains the phase of the DC component by taking an average of phases before and after the DC component in a phase spectrum obtained as the propagation characteristic. According to this configuration, the phase of the DC component can be extracted by a simple process of averaging the DC component of the phase spectrum before and after.

In the ranging system, the digital code is preferably a binarized code. According to this configuration, it is possible to generate a transmission radio wave from a simple data array signal constructed from “0” and “1”.

In the ranging system, it is preferable that the periodic signal is a signal in which the binary code “0” and “1” are repeated. According to this configuration, it is possible to construct a periodic signal from a simple data group in which “0” and “1” are simply repeated.

It is preferable that the ranging system further includes a modulation unit that performs GFSK modulation on the periodic signal when the periodic signal is transmitted. According to this configuration, since the spectrum of the periodic signal is shaped before the signal modulation, it is possible to reduce the spectrum bandwidth and the out-of-band spectrum. Therefore, it is possible to remove power from adjacent channels.

In the distance measuring system, the first communication device and the second communication device transmit and receive radio waves when calculating a distance between them, and the distance measuring unit transmits the second communication from the first communication device. It is preferable to calculate the distance based on propagation characteristics obtained by transmitting radio waves to a machine and propagation characteristics obtained by sending radio waves from the second communication device to the first communication device. According to this configuration, the propagation characteristic obtained by transmitting radio waves from the first communication device to the second communication device is multiplied by the propagation characteristics obtained by transmitting radio waves from the second communication device to the first communication device, etc. Through the calculation, it is possible to cancel the phase error of the opposite sign. Therefore, it is further advantageous for improving the accuracy of the distance calculation.

According to the present invention, the accuracy of distance calculation between the first communication device and the second communication device can be improved.

1 is a model diagram of a communication device in which a distance measuring system according to an embodiment is used. The block diagram of the radio wave transmission part and radio wave reception part of a ranging system. The block diagram of the element which performs distance calculation in a ranging system. The flowchart which shows the procedure of ranging. Power spectrum diagram. (A) to (c) are phase spectrum diagrams. The phase spectrum figure which shows the phase of the interpolated DC component. The characteristic view which shows the amplitude and phase of several channels. The wave form diagram which shows the calculation result of an inverse Fourier transform.

Hereinafter, an embodiment of a ranging system will be described with reference to FIGS.
As shown in FIG. 1, the ranging system 1 measures a distance L between a first communication device 2 and a second communication device 3 that perform wireless communication. The distance measuring system 1 of this example transmits and receives the radio wave Si over a plurality of channels between the first communication device 2 and the second communication device 3 connected by radio, and the propagation characteristics (amplitude and amplitude) of the radio wave Si in each of these channels. (Phase). Then, by combining the obtained propagation characteristics of a plurality of channels and performing inverse Fourier transform on the propagation characteristics obtained by the synthesis, an impulse propagation time Tx, that is, a distance L is calculated equivalently. In this example, for example, the first communication device 2 is an electronic key of a vehicle, and the second communication device 3 is a vehicle, for example. The communication between the first communication device 2 and the second communication device 3 is preferably, for example, Bluetooth (registered trademark).

As shown in FIG. 2, the distance measuring system 1 includes a radio wave transmission unit 6 that is a transmission side of the radio wave Si and a radio wave reception unit 7 that is a reception side of the radio wave Si. The radio wave transmission unit 6 includes a waveform generation unit 8, a modulation unit 9, a DA converter 10, a mixer 11, an oscillator 12, and a transmission antenna 13.

The waveform generation unit 8 generates a periodic signal Sk composed of a periodic binarized code as the radio wave Si transmitted between the first communication device 2 and the second communication device 3, and outputs this to the modulation unit 9 To do. The periodic signal Sk is a signal in which “0” and “1” of the binarized code are switched every period T. The modulation unit 9 includes GFSK (GaussianussFrequency Shift Keying). The periodic signal Sk is modulated by the modulator 9, D / A converted by the DA converter 10, superposed on the carrier wave of the oscillator 12 by the mixer 11, and transmitted from the transmission antenna 13.

The radio wave receiving unit 7 includes a receiving antenna 16, a mixer 17, an oscillator 18, an AD converter 19, and a Fourier transform unit 20. When the radio wave reception unit 7 receives the radio wave Si of the periodic signal Sk transmitted from the radio wave transmission unit 6 by the reception antenna 16, the radio wave reception unit 7 converts the reception signal into the baseband signal Sb by the mixer 17, and this is converted to the A / D-convert. Then, the signal after A / D conversion is converted (FFT conversion) by the Fourier transform unit 20, whereby the frequency spectrum (propagation characteristic) of the received signal is measured. The propagation characteristics are each amplitude and phase data of the transmitted and received radio wave Si.

The ranging system 1 performs the measurement of the propagation characteristics during communication on all the channels to be communicated. When the communication is Bluetooth, there are a plurality of channels (for example, 40 channels), and therefore propagation characteristics are measured in all channels (CH1, CH2,..., CHn). Thus, in this example, the radio wave Si is transmitted at a plurality of frequencies by transmitting the radio wave Si through a plurality of channels. In the case of this example, the radio wave Si is transmitted from the first communication device 2 to the second communication device 3 to measure the propagation characteristics, and the radio wave Si is also transmitted from the second communication device 3 to the first communication device 2. To measure the propagation characteristics. That is, the propagation characteristics are measured by both the first communication device 2 and the second communication device 3. In this case, both the first communication device 2 and the second communication device 3 are provided with the radio wave transmission unit 6 and the radio wave reception unit 7, respectively.

The radio wave receiving unit 7 includes a DC component extracting unit 21 that extracts a DC component of propagation characteristics. The DC component extraction unit 21 extracts amplitude and phase DC components (DC component propagation characteristics) as propagation characteristics. In particular, the DC component extraction unit 21 of this example interpolates the phase of the DC component based on the phase near the DC component in the propagation characteristics of the frequency spectrum obtained by Fourier transform of the received radio wave Si, and propagates the DC component. Calculate the characteristics. The DC component is a characteristic value when the frequency is “0” in the frequency spectrum after Fourier transform (after FFT transform).

As shown in FIG. 3, the ranging system 1 includes a multiplying unit 23, a combining unit 24, an inverse Fourier transform unit 25, and a ranging unit 26. Note that the function group of the multiplication unit 23, the synthesis unit 24, the inverse Fourier transform unit 25, and the distance measurement unit 26 may be provided in any of the first communication device 2 and the second communication device 3.

The multiplication unit 23 has propagation characteristics measured by transmitting radio waves from the first communication device 2 to the second communication device 3, and propagation characteristics measured by transmitting radio waves from the second communication device 3 to the first communication device 2. Multiply As described above, the multiplication unit 23 of this example transmits the radio wave from the first communication device 2 to the second communication device 3 and transmits the radio wave from the second communication device 3 to the first communication device 2. Multiply the obtained FFT result.

The combining unit 24 combines the extracted DC component propagation characteristics for a plurality of channels. The synthesizing unit 24 in this example obtains frequency data H (f) including a vector in which the propagation characteristics of each channel are arranged.

The inverse Fourier transform unit 25 performs inverse Fourier transform on the propagation characteristics after synthesis. The inverse Fourier transform unit 25 performs inverse Fourier transform on the frequency data H (f) obtained by the synthesis unit 24, and obtains time data y (t) as a calculation result.

The distance measuring unit 26 calculates the distance L between the first communication device 2 and the second communication device 3 from the calculation result obtained by performing inverse Fourier transform on the propagation characteristics obtained by the synthesis (calculation result of the inverse Fourier transform unit 25). To do. The distance measuring unit 26 of this example calculates the distance L between the first communication device 2 and the second communication device 3 from the time data y (t) obtained by the inverse Fourier transform unit 25.

Next, operations and effects of the distance measuring system 1 according to the present embodiment will be described with reference to FIGS.
As shown in FIG. 4, in step S <b> 101, the first communication device 2 transmits the radio wave Si to the second communication device 3 to cause the second communication device 3 to measure propagation characteristics. In the case of this example, the waveform generation unit 8 first generates a periodic signal Sk in which “0” and “1” are periodically repeated, and outputs this to the modulation unit 9. The modulation unit 9 performs GFSK modulation on the periodic signal Sk of the repetitive signals “0” and “1”, and outputs this to the DA converter 10. The DA converter 10 D / A converts the modulated signal. The signal D / A converted by the DA converter 10 is put on a carrier wave by the mixer 11 and transmitted from the transmission antenna 13 as radio wave Si. When the radio wave Si is transmitted through a plurality of channels, the radio wave Si of each channel is transmitted on a corresponding carrier.

The second communication device 3 receives the radio wave Si transmitted from the first communication device 2 by the reception antenna 16. A signal received by the receiving antenna 16 is converted into a baseband signal Sb through the mixer 17. The baseband signal Sb is A / D converted by the AD converter 19 and output to the Fourier transform unit 20. The Fourier transform unit 20 performs Fourier transform on the signal after A / D conversion, and measures the frequency spectrum (propagation characteristic) of the baseband signal Sb. Thereafter, the DC component propagation characteristic of the baseband signal Sb is obtained for each channel, and based on this propagation characteristic, the propagation characteristic of the center frequency of the signal received by the radio wave receiver 7 can be measured.

As shown in FIGS. 5 and 6 (a), the propagation characteristics include amplitude data P (f) (see FIG. 5) and phase data ∠θ (f) (see FIG. 6 (a)) as elements of the frequency spectrum. Built from. The amplitude data P (f) is represented by a power spectrum as shown in FIG. In the case of this example, since the periodic signal Sk in which “0” and “1” are repeated in the period T is transmitted and the distance is measured, the power spectrum takes a waveform in which the spectrum stands in the 1 / T period. That is, the power spectrum has a waveform whose value changes along a parabola with the frequency component “0” being a DC component at the top. The DC component extraction unit 21 extracts the amplitude P0 of the DC component (frequency “0”) from the power spectrum after the Fourier transform.

The phase data ∠θ (f) is represented by a phase spectrum as shown in FIG. In the case of this example, since the periodic signal Sk in which “0” and “1” are repeated in the period T is transmitted and the distance is measured, the phase spectrum takes a waveform in which the spectrum stands in the 1 / T period. Here, as shown in FIG. 6A, for example, the phase change characteristic due to the propagation of the baseband signal Sb is linear so that the value increases proportionally. By the way, a delay occurs at the time of A / D conversion or D / A conversion sampling timing during radio wave transmission / reception. If a delay occurs, the slope of the phase change characteristic as shown in FIG. Changes, but the phase of the frequency “0”, which is a DC component, does not change. As described above, since a delay error does not appear in the phase of the frequency “0”, it is understood that the delay error can be canceled by extracting this phase as the phase of the radio wave (the center frequency of the transmission channel). However, as shown in FIG. 6C, an error due to an offset occurs in the component of frequency “0”, and the “0” component cannot be correctly extracted. As described above, only the propagation characteristics of the DC component are used for distance measurement, but no delay error occurs in the phase of the DC component, but the other components contain delay errors, and thus cannot be used. Because.

Therefore, as shown in FIG. 7, the DC component extraction unit 21 of this example uses the phases θm and θp immediately before and after the DC component (frequency “0”) of the phase spectrum to calculate the phase θ _{0 of the} DC component. calculate. In this example, the average of the phase θm of the phase spectrum immediately before the DC component (frequency “0”) and the phase θp of the phase spectrum immediately after the DC component (frequency “0”) is obtained. Is determined as the phase θ ₀ (= (θm + θp) / 2) of the DC component. In this manner, the DC component extraction unit 21 of this example extracts the DC component propagation characteristic by interpolating the phase of the DC component based on the phase near the DC component in the propagation characteristic of the frequency spectrum. Then, the DC component extraction unit 21 calculates the DC component of the power spectrum and the DC component of the phase spectrum obtained by interpolation as DC component propagation characteristics.

Thus, in the case of this example, when measuring the propagation characteristics, the radio wave Si generated based on the periodic signal Sk in which the binary codes “0” and “1” are repeated at intervals of the period T is transmitted. Therefore, in the frequency spectrum (power spectrum and phase spectrum) obtained as the propagation characteristics, the spectrum components stand periodically at 1 / T intervals. For this reason, when interpolating the phase θ ₀ of the DC component, it is possible to extract the phase θ ₀ through, for example, an arithmetic operation of averaging the binary values θm and θp before and after the DC component. For this reason, only data having a high SN (SN ratio: signal to noise ratio) can be used, and the phase θ ₀ is a highly accurate value with little variation.

Returning to FIG. 4, in step S102, the second communication device 3 transmits the radio wave Si to the first communication device 2, and causes the first communication device 2 to measure the propagation characteristics (amplitude and phase). That is, the radio wave Si is transmitted from the second communication device 3 to the first communication device 2, and the propagation characteristics (amplitude and phase) are also measured in the first communication device 2. Note that the measurement of the propagation characteristics is the same as that performed when radio waves are transmitted from the first communication device 2 to the second communication device 3, and thus description thereof is omitted.

When the propagation characteristics are measured in each round trip of communication between the first communication device 2 and the second communication device 3, the multiplier 23 is measured by transmitting radio waves from the first communication device 2 to the second communication device 3. The propagation characteristic (FFT result) multiplied by the propagation characteristic (FFT result) measured by transmitting a radio wave from the second communication device 3 to the first communication device 2 is multiplied. As a result, even if a clock error or an initial phase error of the PLL occurs in each device of the distance measuring system 1, these errors appear as phase errors of opposite signs on the transmission side and the reception side. These errors are canceled by multiplying.

Here, as shown in FIG. 8, for example, when radio waves of channel CH1 are communicated, the propagation characteristic H (f1) of the center frequency f1 of CH1, that is, the DC component propagation characteristic of the baseband signal Sb of CH1 is obtained. It is done. The propagation characteristic H (f1) is obtained as a complex number whose magnitude (power) represents an amplitude characteristic and whose phase angle represents a phase characteristic. The propagation characteristic H1 (f1) is expressed by the following equation (1). In the following equation, P (f1) is the amplitude data of CH1, and ∠θ (f1) is the phase data.

H (f1) = P (f1) ∠θ (f1) (1)
Returning to FIG. 4, in step S103, the ranging system 1 (the first communication device 2 and the second communication device 3) sequentially measures the propagation characteristics in each channel of communication. When the communication is Bluetooth, there are a plurality of channels (for example, 40 channels), so the propagation characteristics of communication (round trip) are measured in all of the channels. Therefore, for example, when radio waves of CH2 to CHn are transmitted and received, the propagation characteristics H (f2) to H (fn) of the center frequencies f2 to fn of each channel are obtained. The reason why the propagation characteristics of a plurality of frequencies are measured is that an impulse cannot be created with the propagation characteristics of one frequency.

In step S104, the combining unit 24 combines the round-trip propagation characteristics of all channels. In this example, the synthesis unit 24 creates a vector in which the propagation characteristics of each channel are arranged. In this example, [H (f1), H (f2),..., H (fn)] is obtained as a vector in which the propagation characteristics of each channel are arranged, that is, frequency data H (f).

In step S105, the inverse Fourier transform unit 25 performs inverse Fourier transform on the combined propagation characteristics (frequency data H (f)). In the case of this example, a vector (frequency data H (f)) is used as input data, and this is subjected to inverse Fourier transform to obtain the calculation result. The calculation result of the inverse Fourier transform can be acquired as time data y (t). The time data y (t) is represented by [y (t1), y (t2), ..., y (tn)]. Note that t1 to tn are time data corresponding to the propagation characteristics H (f1) to H (fn).

As shown in FIG. 9, the distance measuring unit 26 calculates the propagation time Tx of the radio wave Si, that is, the distance L between the first communication device 2 and the second communication device 3 based on the calculation result of the inverse Fourier transform. . When inverse Fourier transform is calculated, a pulse 30 as shown in the figure can be obtained. If a plurality of pulses 30 appear due to the influence of multipath, the pulse having the shortest time (pulse 30a) is acquired as the target pulse. The distance measuring unit 26 calculates the propagation time Tx from the position of the pulse 30a and converts this to the distance L.

Note that the selection of the pulse 30 is not limited to the method of selecting the pulse with the shortest time. For example, the pulse 30 having the highest peak value may be acquired as the target pulse. As described above, various methods can be employed for selecting the pulse 30.

By the way, for example, when ranging is performed by transmitting a bit signal in which binary codes “0” and “1” are randomly arranged as the periodic signal Sk, the frequency spectrum (phase spectrum) randomly spreads over the entire band. For this reason, when the phase θ _{0 of the} DC component is to be interpolated, for example, the entire spectrum is averaged to extract the phase θ _{0 of the} DC component. In this case, the average of a large number of data rising at random is taken. Since an operation for extracting a value is performed, an accurate value cannot be obtained, and the SNR deteriorates. For this reason, the phase data of a portion having a low SN is also used, which causes a problem that the accuracy of distance measurement cannot be ensured.

On the other hand, in the case of this example, the periodic signal Sk composed of a periodic binarized code is transmitted as a radio wave to perform distance measurement, so that a frequency spectrum required as a propagation characteristic stands periodically. For this reason, when interpolating the DC component of the phase spectrum, it becomes possible to interpolate the phase θ _{0 of the} DC component based on the tendency of the frequency spectrum that rises at a constant period, so only data with a high SN is used. Thus, the phase θ _{0 of the} DC component can be extracted. In particular, in the case of this example, a simple average of the phases θm and θp before and after the DC component may be obtained. Thereby, the calculation result of the inverse Fourier transform is obtained with high accuracy. Therefore, the distance L between the first communication device 2 and the second communication device 3 can be obtained with high accuracy.

The radio wave Si is transmitted at a plurality of frequencies by being transmitted at a plurality of channels. The distance measuring unit 26 calculates the distance L between the first communication device 2 and the second communication device 3 based on the propagation characteristics measured from each channel. Therefore, radio transmission at a plurality of frequencies can be realized by a simple communication mode in which the radio wave Si is transmitted through a plurality of channels.

The digital code is composed of a binary code. Therefore, a transmission radio wave (radio wave Si) can be generated from a simple data array signal constructed from “0” and “1”.
The periodic signal Sk is a signal in which “0” and “1” of the binary code are repeated. Therefore, the periodic signal Sk can be constructed from a simple data group in which “0” and “1” are simply repeated.

The radio wave transmission unit 6 includes a modulation unit 9 that performs GFSK modulation on the periodic signal Sk. For this reason, since the spectrum of the periodic signal Sk is shaped before signal modulation, it becomes possible to reduce the spectrum bandwidth and the out-of-band spectrum. Therefore, it is possible to remove power from adjacent channels.

The first communication device 2 and the second communication device 3 transmit and receive the radio wave Si in calculating the distance L between them. The distance measuring unit 26 is obtained by transmitting the radio wave Si from the first communication device 2 to the second communication device 3 and transmitting the radio wave Si from the second communication device 3 to the first communication device 2. The distance L is calculated based on the propagation characteristics. By the way, a clock error and an initial phase error of the PLL are generated in each device of the distance measuring system 1. These errors appear as phase errors of opposite signs on the transmission side and the reception side. For this reason, calculation such as multiplying the propagation characteristic obtained by radio wave transmission of the first communication device 2 → the second communication device 3 and the propagation characteristic obtained by radio wave transmission of the second communication device 3 → the first communication device 2 is performed. As a result, the phase error of the opposite sign can be canceled. Therefore, it is further advantageous for improving the accuracy of the distance calculation.

The first communication device 2 and the second communication device 3 transmit radio waves through a plurality of channels from one to the other. The distance measuring unit 26 obtains propagation characteristics in each channel and calculates a distance L from these propagation characteristics. For this reason, for example, communication can be performed while avoiding noise through frequency hopping or the like. Therefore, it is advantageous for improving communication establishment.

The distance measuring unit 26 obtains DC component propagation characteristics (amplitude data and phase data) in a plurality of channels, combines these propagation characteristics, performs inverse Fourier transform on the propagation characteristics obtained by the synthesis, and calculates the distance from the calculation result. L is calculated. Therefore, the distance L between the first communication device 2 and the second communication device 3 can be accurately obtained from the calculation result obtained by performing inverse Fourier transform on the power spectrum and the phase spectrum obtained by combining the propagation characteristics of a plurality of channels.

In addition, this embodiment can be implemented with the following modifications. The present embodiment and the following modifications can be implemented in combination with each other within a technically consistent range.
The processing is not limited to using all channels, but may be a mode in which only some channels are used.

· The periodic signal Sk is not limited to a signal in which “0” and “1” are repeated. For example, the combination of “0” and “1” can be appropriately changed as long as the binarized code is periodically repeated, such as a signal in which a data group of “0”, “0”, and “1” is repeated. .

The periodic signal Sk is not limited to a periodic signal of “0” and “1”, and may be a signal of only “0” or “1”, for example.
The order of operations is not limited to the order of Fourier transform, DC component extraction, and multiplication. For example, the order may be changed to Fourier transform, multiplication, and DC component extraction.

-Phase (theta) ₀ of DC component is not limited to the value which took the average before and behind DC component. For example, not only before and after the DC component, some phases may be extracted, and the phase θ _{0 of the} DC component may be obtained from these values.

The first communication device 2 may be a high function mobile phone having an electronic key function.
The radio wave transmission at a plurality of frequencies is not limited to transmitting the radio wave Si through a plurality of channels. For example, one channel may be used for radio wave transmission. In this case, for example, the baseband signal Sb of the radio wave Si to be transmitted is frequency-shifted by up-converting the baseband signal Sb by a prescribed amount and transmitted. Then, ranging may be performed using the propagation characteristics measured from the baseband signal Sb that is not frequency shifted and the propagation characteristics measured from the baseband signal Sb that is frequency shifted.

For example, an arbitrary frequency may be set to “0”, and this may be added to the frequency data H (f) at the time of inverse Fourier transform. For example, H (f) = [H (f1), H (f2), H (f3),..., H (fn)] is changed to H (f) = [H (f1), 0, H (f2), 0, H (f3), 0,..., 0, H (fn)] may be inverse Fourier transformed. By doing so, the number of time data samples after the inverse Fourier transform can be increased. In the case of the above example, the number of samples is “n” → “2n−1”.

・ Various frequencies can be used for radio waves.
The digital code is not limited to the binary code, and may be changed to another code on the assumption that modulation such as QPSK (Quadrature Phase Shift Keying) is used.

The modulation unit 9 is not limited to GFSK, and may be changed to other members such as simple FSK.
The first communication device 2 is not limited to the electronic key and the second communication device 3 is the vehicle. For example, the first communication device 2 may be a wireless communication personal computer, and the second communication device 3 may be a wireless LAN router.

The distance measuring system 1 is not limited to a system that performs distance measurement by transmitting and receiving radio waves in both directions. For example, it is good also as a single direction which transmits a radio wave only to the other from one side of the 1st communication apparatus 2 and the 2nd communication apparatus 3, and performs ranging. In addition, the first communication device 2 and the second communication device 3 transmit and receive radio waves, and once again transmit radio waves from one of the first communication device 2 and the second communication device 3 to obtain the propagation characteristics. Then, ranging between the two may be performed.

The ranging system 1 is not limited to being used in an electronic key system that wirelessly authenticates an electronic key for a vehicle, and may be applied to various systems and devices.
-A communication system is not limited to Bluetooth, For example, it is good also as other communications, such as wireless LAN and UWB.

Next, a technical idea that can be grasped from the above embodiment and modified examples will be described.
(A) By transmitting a radio wave from one of the first communication device and the second communication device to the other through Bluetooth communication, obtaining a propagation characteristic of the radio wave, and performing inverse Fourier transform on the propagation characteristic, the first communication device And a distance measuring method for calculating a distance between the second communication devices, wherein a periodic signal composed of a periodic digital code is used as a radio wave transmitted between the first communication device and the second communication device. A step of generating a DC component propagation characteristic by interpolating a phase of the DC component based on a phase near the DC component in a propagation characteristic of a frequency spectrum obtained by performing Fourier transform on the received radio wave; and A step of combining the extracted DC component propagation characteristics for a plurality of frequencies, and a calculation result obtained by performing inverse Fourier transform on the propagation characteristics obtained by the combination, Ranging method comprising the step of calculating the distance between the signal device and the second communication device.

Claims

By transmitting radio waves from one of the first communication device and the second communication device to the other through Bluetooth communication, obtaining the propagation characteristics of the radio waves, and performing inverse Fourier transform on the propagation characteristics, the first communication device and the first communication device A distance measuring system for calculating a distance between two communication devices,
As a radio wave transmitted between the first communication device and the second communication device, a waveform generation unit that generates a periodic signal composed of a periodic digital code,
A DC component extraction unit that extracts the DC component propagation characteristic by interpolating the phase of the DC component based on the phase near the DC component in the propagation characteristic of the frequency spectrum obtained by Fourier transforming the received radio wave;
A combining unit that combines the extracted DC component propagation characteristics for a plurality of frequencies;
A distance measuring system comprising: a distance measuring unit that calculates a distance between the first communication device and the second communication device from a calculation result obtained by performing inverse Fourier transform on the propagation characteristics obtained by combining.
The radio wave is transmitted through a plurality of frequencies by being transmitted through a plurality of channels,
The distance measuring system according to claim 1, wherein the distance measuring unit calculates a distance between the first communication device and the second communication device based on propagation characteristics measured from each channel.
The ranging system according to claim 1, wherein the DC component extraction unit obtains a phase of the DC component by taking an average of phases before and after the DC component in a phase spectrum obtained as the propagation characteristic.
The ranging system according to any one of claims 1 to 3, wherein the digital code is a binary code.
The distance measuring system according to claim 4, wherein the periodic signal is a signal in which the binarized code is “0” and “1”.
The ranging system according to any one of claims 1 to 5, further comprising a modulation unit that performs GFSK modulation on the periodic signal when the periodic signal is transmitted.
The first communication device and the second communication device transmit and receive radio waves in calculating the distance between them,
The distance measuring unit includes a propagation characteristic obtained by transmitting radio waves from the first communication device to the second communication device, and a propagation characteristic obtained by transmitting radio waves from the second communication device to the first communication device. The distance measuring system according to any one of claims 1 to 6, wherein the distance is calculated based on