JP2019176437A - Communication system - Google Patents

Abstract

To provide a communication system that enables communication correctness determination with higher accuracy.SOLUTION: A phase characteristic is measured twice for the same channel, and a determination parameter Rx used for normality determination of communication is calculated by finding the absolute value of difference between values of the phase characteristic. The maximum value of the determination parameter Rx during normal communication is 2dθmax. On the other hand, the maximum value of the determination parameter Rx during unauthorized communication is 2π. If the determination parameter Rx is less than a threshold value, communication is determined to be normal communication and if the determination parameter Rx is equal to or greater than the threshold value, communication is determined to be unauthorized communication.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a communication system in which communication is established by two or more communication devices.

  Conventionally, as a method of improperly establishing wireless communication, there is an illegal act using a repeater (an illegal act using a repeater: see Patent Document 1). This fraudulent act is an act of establishing communication between these two parties by connecting the terminal to the communication master by a plurality of repeaters and relaying radio waves when the terminal is located far from the communication master. Therefore, since communication is established without the user's knowledge, there is a possibility that the communication master is illegally used by a third party.

JP 2006-161545 A

  Here, as a communication correctness determination method, for example, a method has been devised in which distance measurement is performed from the phase of the center frequency of each channel using Bluetooth (registered trademark) and communication correctness is determined from the measured distance. . However, in the case of this determination method, there is a possibility that a legitimate distance may be calculated by, for example, “spoofing”, so another determination method is required.

  An object of the present invention is to provide a communication system capable of determining whether communication is more accurate or not.

  A communication system that solves the above problems includes a radio wave transmission unit that transmits radio waves of the same frequency multiple times from one of the first communication device and the second communication device, and multiple transmissions at the same frequency from the radio wave transmission unit. A propagation characteristic measuring unit that measures the propagation characteristics of each of the radio waves to be transmitted, and a communication correctness determination unit that determines whether the communication is correct from the measurement result obtained by measuring the propagation characteristics of the same frequency a plurality of times.

  According to this configuration, by measuring the propagation characteristics at the same frequency a plurality of times, it is possible to obtain measurement results corresponding to each of normal communication and unauthorized communication. Therefore, in communication between the first communication device and the second communication device, it is possible to determine whether the communication is correct or not with higher accuracy.

  In the communication system, it is preferable that the propagation characteristic is a phase characteristic obtained by calculating a radio wave including a received complex signal. According to this configuration, it is possible to accurately determine whether communication is correct or not by using phase characteristics measured from received radio waves.

  In the communication system, the communication correctness determination unit calculates a difference between the propagation characteristics of each radio wave as a determination parameter from the propagation characteristics of each radio wave transmitted a plurality of times at the same frequency, and determines whether the communication is correct based on the difference. Is preferably determined. According to this configuration, it is possible to determine whether communication is correct or not by a simple calculation of obtaining a difference between propagation characteristics obtained by a plurality of measurements.

  In the communication system, the radio wave transmission unit includes a waveform generation unit that generates a periodic signal including a periodic digital code as a radio wave transmitted between the first communication device and the second communication device, The propagation characteristic measurement unit interpolates the phase of the DC component based on the phase in the vicinity of the DC component in the Fourier transform unit for Fourier transforming the received radio wave and the propagation characteristic of the frequency spectrum obtained by Fourier transforming the received radio wave. A DC component extraction unit that extracts a DC component propagation characteristic, and the communication correctness determination unit determines whether the communication is correct based on a plurality of the DC component propagation characteristics obtained at the same frequency. preferable. According to this configuration, since a periodic signal composed of a periodic digital code is transmitted as a radio wave to determine whether communication is correct or not, 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. Therefore, it is advantageous to accurately determine whether the communication is correct.

  In the communication system, the first communication unit includes a combining unit that combines the DC component propagation characteristics for a plurality of frequencies extracted by the DC component extraction unit, and a calculation result obtained by performing inverse Fourier transform on the propagation characteristics obtained by combining. And a distance measuring unit for calculating a distance between the second communication device and the second communication device. According to this configuration, the phase of the DC component is interpolated based on the frequency spectrum that rises at a constant period. Therefore, it is possible to extract the phase of the DC component using only data having a high SN (SN ratio: signal to noise ratio), and as a result, the calculation result of the inverse Fourier transform can be obtained with high accuracy. Therefore, the distance between the first communication device and the second communication device can be obtained with high accuracy.

  ADVANTAGE OF THE INVENTION According to this invention, in communication of a 1st communication apparatus and a 2nd communication apparatus, the correctness determination of communication with more sufficient accuracy can be performed.

The block diagram of the communication system of one Embodiment. 1 is a configuration diagram of a radio wave transmission unit and a radio wave reception unit of a communication system. The block diagram of the element which performs distance calculation in a communication system. The flowchart which shows the procedure of ranging. Power spectrum diagram. (A)-(c) is a phase spectrum figure. 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. The processing flow figure performed in the case of communication right / wrong determination. A calculation formula that determines the determination parameters for regular communication and unauthorized communication. Explanatory drawing of the range which a determination parameter can take by regular communication and unauthorized communication.

Hereinafter, an embodiment of a communication system will be described with reference to FIGS.
As shown in FIG. 1, the communication system 1 causes the first communication device 2 and the second communication device 3 to communicate wirelessly. 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).

  The communication system 1 includes a function (ranging system 4) that measures the distance L between the first communication device 2 and the second communication device 3 that perform wireless communication. The distance measuring system 4 of this example transmits and receives radio waves Si across a plurality of channels between the first communication device 2 and the second communication device 3 that are connected by radio, and the propagation characteristics (amplitude and phase) in each of these channels. Ask. 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.

  As shown in FIG. 2, the distance measuring system 4 includes a radio wave transmission unit 6 on the radio wave Si transmission side and a radio wave reception unit 7 on the radio wave Si reception side. 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 is composed of GFSK (Gaussian Frequency Shift Keying). The periodic signal Sk is modulated by the modulation unit 9, D / A converted by the DA converter 10, and then the baseband signal Sb is superimposed 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 propagation characteristic measuring 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 received radio wave to the baseband signal Sb by the mixer 17, and this is converted to the A / A by the AD converter 19. D-convert.

  The propagation characteristic measurement unit 20 includes a Fourier transform unit 21 and a DC component extraction unit 22. The Fourier transform unit 21 performs Fourier transform (FFT transform) on the signal after A / D conversion. The DC component extraction unit 22 extracts a DC component of propagation characteristics, and in this example, extracts a DC component of amplitude and phase (DC component propagation characteristics) as the propagation characteristics. In particular, the DC component extraction unit 22 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 transforming 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).

  The distance measuring system 4 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.

  As shown in FIG. 3, the ranging system 4 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 synthesizer 24 synthesizes 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 combined propagation characteristics. 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.

  The communication system 1 includes a function (communication fraud establishment prevention system 28) that determines whether communication established in the first communication device 2 and the second communication device 3 is correct or not and prevents establishment of unauthorized communication. The communication fraud establishment prevention system 28 of this example measures the propagation characteristics of the same frequency a plurality of times, and determines whether the communication is correct or not based on variations in the measurement results.

  In the case of this example, the radio wave transmitting unit 6 transmits the radio wave Si at the same frequency a plurality of times when determining communication correctness. The radio wave transmission unit 6 of this example operates so as to transmit a plurality of radio waves Si on the same channel. Note that the same channel used for determining whether communication is correct or not may be any channel set in the communication system 1 (ranging system 4).

  In addition, the propagation characteristic measurement unit 20 of this example measures the propagation characteristic of the radio wave Si transmitted from the radio wave transmission unit 6 a plurality of times when determining communication correctness. That is, the propagation characteristic measurement unit 20 measures the propagation characteristics of each of the radio waves Si when the radio wave transmission unit 6 transmits the radio wave Si multiple times on the same channel. As described above, the propagation characteristic is calculated by Fourier-transforming the received radio wave and extracting a DC component from the calculation result. The propagation characteristics are preferably phase characteristics (phase ∠θ (f)), for example.

  The communication system 1 includes a communication correctness determination unit 29 that determines the correctness of communication from the measurement result obtained by measuring the propagation characteristics of the same frequency a plurality of times. The communication correctness determination unit 29 of this example determines a determination parameter Rx used for communication correctness determination from a plurality of propagation characteristics obtained by transmitting the radio wave Si at the same frequency a plurality of times and measuring the propagation characteristics thereof. Calculation is performed, and whether the communication is right or wrong is determined based on the determination parameter Rx.

Next, operations and effects of the distance measuring system 4 according to the present embodiment will be described with reference to FIGS.
[Ranging operation]
As shown in FIG. 4, in step 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 the 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 baseband signal Sb D / A converted by the DA converter 10 is carried on a carrier wave by the mixer 11 and transmitted as a radio wave Si from the transmission antenna 13. 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 21. The Fourier transform unit 21 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, and based on this propagation characteristic, the propagation characteristic of the center frequency of the received radio wave received by the radio wave receiver 7 can be measured.

  As shown in FIGS. 5 and 6, the propagation characteristics are constructed from amplitude data P (f) (see FIG. 5) and phase data ∠θ (f) (see FIG. 6) as frequency spectrum elements. 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 22 extracts the amplitude P0 of the DC component (frequency “0”) from the power spectrum after the Fourier transform. Hereinafter, amplitude data and amplitude are synonymous, and phase data and phase are synonymous.

  As shown in FIG. 6, 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. The reason why only the DC component propagation characteristic is used for distance measurement is that there is no error in the phase of the DC component, but there is an error in the other components, and therefore it cannot be used.

  Therefore, as shown in FIG. 7, the DC component extraction unit 22 of this example calculates the phase θ0 of the DC component by using the phases θm and θp immediately before and after the DC component (frequency “0”) of the phase spectrum. To do. 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 θ0 (= (θm + θp) / 2) of the DC component. In this way, the DC component extraction unit 22 of the present 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 22 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 θ0 of the DC component, it is possible to extract the phase θ0 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 noise ratio) can be used, and the phase θ0 is a highly accurate value with little variation.

  Returning to FIG. 4, in step 102, the second communication device 3 transmits the radio wave Si to the first communication device 2 to cause 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 the round trip of communication between the first communication device 2 and the second communication device 3, the multiplication unit 23 transmits the radio wave from the first communication device 2 to the second communication device 3, and the propagation measured. The characteristic (FFT result) is 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. 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 4, these errors appear as phase errors of opposite signs on the transmitting side and the receiving 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 represents the amplitude characteristic and whose phase angle represents the phase characteristic. The propagation characteristic H (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 103, the distance measuring system 4 (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 104, 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 105, 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.

  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.

[Activation of unauthorized communication detection]
As shown in FIG. 10, in step 201, the radio wave transmission unit 6 transmits the radio wave Si at the same frequency a plurality of times in order to obtain the propagation characteristic (DC component propagation characteristic) through the same processing as in the distance measurement (this example). 2 times). In this example, the radio wave transmission unit 6 transmits the radio wave Si a plurality of times on the same channel. If radio wave transmission has been completed once by distance measurement, only the remaining necessary number of radio wave transmissions may be performed in this step.

  In step 202, the communication correctness determination unit 29 acquires each propagation characteristic of the radio wave Si having the same frequency. That is, since the DC component propagation characteristics of the same frequency are measured a plurality of times by the propagation characteristic measurement unit 20, these DC component propagation characteristics are acquired. In the case of this example, it is assumed that the DC component propagation characteristic used for determining whether communication is correct is the phase characteristic (phase ∠θ (f)) of a plurality of DC components at the same frequency (same channel).

In step 203, the communication correctness determination unit 29 calculates a determination parameter Rx used for communication correctness determination based on a plurality of DC component propagation characteristics having the same frequency. The determination parameter Rx in this example is an absolute value of the difference between the measured plurality of DC component propagation characteristics. Here, when the number of measurement of the DC component propagation characteristic is “2 times”, the determination parameter Rx includes the phase ∠θ (f) ₁ measured at the first time and the phase ∠θ (f) measured at the second time. The absolute value of the difference from ₂ is “| ∠θ (f) ₁ −∠θ (f) ₂ |”.

  As shown in FIG. 11, the phase measured for the first time during normal communication is “θ1”, the phase measured for the second time during normal communication is “θ2”, and is measured for the first time during illegal communication. Let “θ1 ′” be the phase and “θ2 ′” be the second phase measured during illegal communication. In the case of regular communication, there should be no significant difference between the phase θ1 and the phase θ2. Therefore, when the error from the true value of the phase θ1 is “dθ1” and the error from the true value of the phase θ2 is “dθ2”, the difference (absolute value of the difference) between the phases θ1 and θ2 is taken as the determination parameter Rx. However, it can be a difference between the errors dθ1 and dθ2 from the true value. That is, when the maximum value of dθ1 is dθ1max and the maximum value of dθ2 is dθ2max, these are dθmax that is the maximum value of error, and the maximum value of the determination parameter Rx (the absolute value of the difference between the phases θ1 and θ2) is the error. It should be twice the maximum value dθmax.

  On the other hand, as a method of unauthorized communication, for example, when a phase rotation (delay) is randomly added to each channel, if the difference between the phase θ1 ′ and the phase θ2 ′ is taken, this is a simple binary difference. It will not be. That is, the error from the true value generated in the regular communication system 1 in the phase θ1 ′ is “dθ1 ′”, and the error from the true value generated in the regular communication system 1 in the phase θ2 ′ is “dθ2 ′”. When the value of the first phase rotation at the time of unauthorized communication is “φ1” and the value of the second phase rotation at the time of unauthorized communication is “φ2,” the difference (difference) between the phases θ1 ′ and θ2 ′ as the determination parameter Rx. Is the absolute value of the difference between dθ1 ′ and dθ2 ′ plus the phase rotation difference (φ1−φ2). Therefore, the maximum value of the determination parameter Rx (the absolute value of the difference between the phases θ1 ′ and θ2 ′) is 2π.

  For this reason, as shown in FIG. 12, the determination parameter Rx during normal communication falls within a small value of 2dθmax. On the other hand, the determination parameter Rx at the time of unauthorized communication takes a large value of “2π” at the maximum. Therefore, if the determination parameter Rx is less than the threshold value Rk, it can be identified whether the communication is regular communication or unauthorized communication. Note that the threshold value Rk is preferably a value that allows variations in measured values during normal communication.

  Returning to FIG. 10, in step 204, the communication correctness determination unit 29 determines whether or not the determination parameter Rx is less than the threshold value Rk. At this time, if the determination parameter Rx is less than the threshold value Rk, the process proceeds to step 205, and if the determination parameter Rx is equal to or greater than the threshold value Rk, the process proceeds to step 206.

  In step 205, the communication correctness determination unit 29 determines that communication between the first communication device 2 and the second communication device 3 is normal communication when the determination parameter Rx is less than the threshold value Rk. For this reason, the distance L calculated at the time of distance measurement is validated. Therefore, for example, when authentication is performed between the first communication device 2 and the second communication device 3, if the authentication is established, wireless communication between the first communication device 2 and the second communication device 3 is established. To be migrated.

  In step 206, when the determination parameter Rx is equal to or greater than the threshold value Rk, the communication correctness determination unit 29 determines that communication between the first communication device 2 and the second communication device 3 is unauthorized communication. For this reason, even if the distance L calculated at the time of distance measurement is invalidated and the first communication device 2 and the second communication device 3 are authenticated by radio, the authentication does not shift to establishment. Therefore, unauthorized communication establishment is prevented.

  Now, in the case of this example, the measurement result according to each communication of regular communication and unauthorized communication is obtained by measuring a propagation characteristic in multiple times in the same frequency. Therefore, in communication between the first communication device and the second communication device, it is possible to determine whether the communication is more accurate or not.

  The propagation characteristic used for the determination of fraudulent correctness is a phase characteristic (phase ∠θ (f)) obtained by calculating the radio wave Si composed of the received complex signal. Therefore, it is possible to accurately determine whether the communication is correct by using the phase characteristic (phase ∠θ (f)) measured from the received radio wave.

  The communication correctness determination unit 29 calculates a difference (absolute value) of the propagation characteristics of each radio wave Si as a determination parameter Rx from the propagation characteristics of each radio wave Si transmitted multiple times at the same frequency, and based on the difference Judge whether communication is right or wrong. Therefore, it is possible to determine whether the communication is correct or not by a simple calculation of obtaining a difference between propagation characteristics obtained by a plurality of measurements.

  The radio wave transmission unit 6 includes a waveform generation unit 8, and the propagation characteristic measurement unit 20 includes a Fourier transform unit 21 and a DC component extraction unit 22. The communication correctness determination unit 29 determines the correctness of communication based on a plurality of DC component propagation characteristics obtained at the same frequency. In the case of this example, since a periodic signal Sk consisting of a periodic digital code (binary code) is transmitted as the radio wave Si to determine whether the communication is correct or not, the frequency spectrum required as the 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. Therefore, it is possible to accurately determine whether communication is correct or not.

  The communication system 1 is provided with a function of measuring the distance L between the first communication device 2 and the second communication device 3 (compositing unit 24 and ranging unit 26). In the case of this example, the phase ∠θ (f) of the DC component is interpolated based on the frequency spectrum that rises at a constant period. Therefore, it is possible to extract the phase of the DC component using only data having a high SN (SN ratio: signal to noise ratio), and as a result, the calculation result of the inverse Fourier transform can be 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.

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 communication correctness determination is not limited to being performed on only one channel, and may be performed on a plurality of channels. In this case, the validity of the determination parameter Rx can be confirmed in each channel, which is further advantageous in ensuring the accuracy of the communication correctness determination.

  A plurality of determination parameters Rx may be calculated by measuring three or more propagation characteristics on the same channel, and communication correctness determination may be performed from these determination parameters Rx. As a determination method in this case, for example, the determination parameter Rx that is less than the threshold value (below the threshold value) is less than a certain number, or the determination parameter Rx that exceeds the threshold value (more than the threshold value) is greater than a certain number. When established, the communication may be determined as unauthorized communication. Further, it may be determined whether the communication is right or wrong based on the ratio between the number of determination parameters Rx that are less than the threshold and the number of determination parameters Rx that are greater than or equal to the threshold.

  -The final determination result may be determined by repeating the re-communication until the result of the communication correctness determination satisfies a specific condition. For example, when unauthorized communication determination results occur n times (n consecutive occurrences), unauthorized communication determination is confirmed, and when regular communication determination results occur k times (k consecutive occurrences), regular communication determination The communication may be repeated until either of them is satisfied. In addition, when a determination result of unauthorized communication or regular communication comes out, communication is performed again, and if the same determination is made continuously a certain number of times or more, the determination result may be confirmed.

  The threshold value Rk of the determination parameter Rx is not limited to one, and two or more threshold values may be provided. For example, when two threshold values Rk are provided (first threshold value and second threshold value having a relationship of first threshold value <second threshold value), if the determination parameter Rx is less than the first threshold value, normal communication is determined, and the first If it is equal to or greater than the threshold and less than the second threshold, communication is performed again to determine whether the communication is correct. If the determination parameter Rx is equal to or greater than the second threshold in the determination at this time, it may be determined that the communication is unauthorized.

  The determination parameter Rx is not limited to the difference between the binary phase characteristics. For example, various values can be applied as long as the parameters represent variations in measured values, such as dispersion and standard deviation when a plurality of propagation characteristics are measured (measured three or more times) on the same channel.

The determination parameter Rx may be a complex number calculated not only from the phase） θ (f) but from both the amplitude P (f) and the phase ∠θ (f).
The threshold value Rk can be set to any value as appropriate according to the assumed environment, system, logic used for determining whether communication is correct, and the like.

  The threshold value Rk is not limited to a fixed value, and may be a variable value. In this case, for example, the noise generated in the communication environment may be monitored, and the threshold value Rk corresponding to the noise may be set.

  -After determining whether the communication is correct or not based on the phase characteristic, the fluctuation of the amplitude characteristic may also be determined, and a final determination may be made as to “influence by unauthorized communication” or “influence by noise”. For example, when the determination parameter Rx obtained from the phase characteristic is equal to or greater than the threshold value Rk, if the fluctuation of the amplitude characteristic is large, it is determined that the fluctuation is affected by noise. If the fluctuation of the amplitude characteristic is small, it is determined that the influence is due to unauthorized communication. To do. In this way, when the determination parameter Rx is equal to or greater than the threshold value Rk, it can be determined whether the determination parameter Rx is due to unauthorized communication or noise.

The communication correctness determination is not limited to being performed after distance measurement, and the timing to be performed is not particularly limited before distance measurement or during distance measurement.
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.

  The phase θ0 of the DC component is not limited to a value obtained by taking an average before and after the DC component. For example, not only before and after the DC component, some phases may be extracted, and the DC component phase θ0 may be obtained from these values.

The second communication device 3 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 “0” and 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 becomes “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 a vehicle and the second communication device 3 is an electronic key. 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 4 is not limited to a system that performs distance measurement by transmitting and receiving radio waves. 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 communication 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) A step of transmitting a radio wave of the same frequency from one to the other of the first communication device and the second communication device a plurality of times, and a propagation characteristic of each of the radio waves transmitted from the radio wave transmission unit a plurality of times at the same frequency A communication method comprising: a step of measuring; and a step of determining whether communication is correct or not from a measurement result obtained by measuring a propagation characteristic of the same frequency a plurality of times.

  DESCRIPTION OF SYMBOLS 1 ... Communication system, 2 ... 1st communication apparatus, 3 ... 2nd communication apparatus, 4 ... Ranging system, 6 ... Radio wave transmission part, 8 ... Waveform generation part, 20 ... Propagation characteristic measurement part, 21 ... Fourier transform part, DESCRIPTION OF SYMBOLS 22 ... DC component extraction part, 24 ... Synthesis | combination part, 26 ... Distance measurement part, 28 ... Communication fraud establishment prevention system, 29 ... Communication correctness determination part, Si ... Radio wave, Ra ... Determination parameter, Sk ... Periodic signal, L ... Distance .

Claims (5)

A radio wave transmitter that transmits radio waves of the same frequency multiple times from one to the other of the first communication device and the second communication device;
A propagation characteristic measurement unit that measures the propagation characteristics of each of the radio waves transmitted at the same frequency from the radio wave transmission unit multiple times;
A communication system including a communication correctness determination unit that determines whether communication is correct or not based on a measurement result obtained by measuring propagation characteristics of the same frequency a plurality of times. The communication system according to claim 1, wherein the propagation characteristic is a phase characteristic obtained by calculating a radio wave including a received complex signal. The communication correctness determination unit calculates a difference between the propagation characteristics of each radio wave as a determination parameter from the propagation characteristics of each radio wave transmitted a plurality of times at the same frequency, and determines whether the communication is correct based on the difference. The communication system according to 1 or 2. The radio wave transmitter is
As a radio wave transmitted between the first communication device and the second communication device, a waveform generation unit that generates a periodic signal consisting of a periodic digital code,
The propagation characteristic measurement unit is
A Fourier transform unit for Fourier transforming the received radio wave;
A DC component extraction unit that extracts the DC component propagation characteristic by interpolating the phase of the DC component based on the phase in the vicinity of the DC component in the propagation characteristic of the frequency spectrum obtained by Fourier transforming the received radio wave ,
The communication system according to any one of claims 1 to 3, wherein the communication correctness determination unit determines the correctness of communication based on a plurality of DC component propagation characteristics obtained at the same frequency. A synthesis unit that synthesizes the DC component propagation characteristics for a plurality of frequencies extracted by the DC component extraction unit;
The communication system according to claim 4, further 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.