JP6272154B2 - Sound wave reception time calculation device, method and program, and distance estimation system provided with the device - Google Patents

Description

  The present invention relates to a sound wave reception time calculation device, method, and program capable of accurately calculating the reception time of a direct wave by excluding the influence of the reflected wave even in a situation where the reflected wave is larger than the direct wave The present invention also relates to a distance estimation system including the device.

  Smart entry systems are beginning to spread mainly in automobiles. By using the smart entry system, the user can unlock the door only by approaching the door or touching the door knob without inserting the key into the door of the automobile. In addition, it is expected to be applied to unlocking doors at homes and common entrances in condominiums.

  A general smart entry system in an automobile includes a dedicated key carried by a user and a transceiver attached to the automobile. In Non-Patent Document 1, a response signal is transmitted when a dedicated key receives a transmission signal from a transceiver. When the transceiver receives the response signal, the door lock is released. The radio signal communication range of the transceiver is limited to a short distance of about 1 m. This solves a security problem such that a user away from the vehicle accidentally releases the door lock and a third party can enter the vehicle. The frequency band of the radio signal varies depending on the automobile manufacturer, but 125 kHz or 300 MHz is used.

  If a mobile terminal such as a mobile phone or a smartphone can be used instead of the dedicated key, the convenience of the user can be improved. Due to the widespread use of mobile terminals, many people usually wear mobile terminals, so there is no need to carry a dedicated key. A mobile terminal includes various wireless communication devices such as Bluetooth (registered trademark) and Wi-Fi (registered trademark). However, the communication range of the radio signal using these is as wide as about 5 m to 100 m, and the communication range may vary depending on the type of smartphone or mobile phone.

  To deal with such problems, Non-Patent Document 1 has dedicated hardware mounted on a mobile phone. Communication between automobiles and mobile phones uses radio waves of 125kHz and 300MHz, and the communication range of radio waves is limited to about 1m.

  On the other hand, from the viewpoint of avoiding the cost increase due to the addition of dedicated hardware to the mobile phone as described above, distance estimation is performed using a normal wireless communication device (radio wave and sound wave) having a wide communication range, There is an approach that allows security to be considered. In this case, high accuracy is required for distance estimation.

  Conventionally, as a typical method of distance estimation, there is a method of estimating a distance based on received signal strength when radio waves such as radio waves and sound waves are exchanged between terminals. However, since the received signal intensity varies depending on the sensitivity of the wireless device, ambient noise, and shielding, the estimation accuracy is not sufficient.

  As a typical method for distance estimation, the method using propagation time is less affected by the sensitivity and noise of the wireless device, and if the propagation time can be estimated with high accuracy, distance estimation can also be achieved with high accuracy. It is.

  In particular, Non-Patent Document 2 using a sound wave (ultrasonic wave) having a propagation time slower than that of an electromagnetic wave achieves an accuracy of an error number of 10 cm. Specifically, the distance is estimated by transmitting and receiving sound waves between the parent terminal and the child terminal, and the child terminal notifying the parent terminal of information on the transmission and reception times of the sound waves. A cross-correlation function is used to calculate the reception time. The waveform of the transmitted sound wave is shared between both terminals in advance and a reference signal is generated. The cross-correlation function between the received sound and the reference signal is calculated, and the peak point is determined as the sound wave reception time.

JP 2006-337279 A (Direct wave reflected wave determination method)

"Mobile phone with intelligent key" by Nissan, DOCOMO, Sharp http://www.itmedia.co.jp/mobile/articles/0810/02/news094.html Beepbeep: a high accuracy acoustic ranging system using cots mobile devices (international conference Sensys 2007)

  However, when the value of the cross-correlation function of the reflected wave is larger than that of the direct wave due to the influence of the reflected wave or human body shielding, there is a problem that the reception time of the sound wave is incorrect and the distance estimation result becomes larger than the actual result. In particular, when the direct wave and the reflected wave are received with time overlap, the reception time of the sound wave is often wrong.

  FIG. 1 schematically shows the situation that is the subject. In FIG. 1, there is a sound source S100 that generates a sound wave and a receiver R100 that receives the sound wave, and the shield O100 is on a straight line connecting them (that is, on the shortest path from the sound source S100 to the receiver R100). There is a wall W100 beside it.

  In this situation, the sound wave (direct wave) that goes straight from the sound source S100 shown in [1] to the receiver R100 is attenuated by the shield O100 and becomes a weak direct wave as shown in [2]. R100 will be reached. On the other hand, the direct wave in the other direction that is not attenuated by the shield O100 shown in [3] is reflected by the wall W100 as the reflection surface, and becomes a reflected wave that remains strong as shown in [4], and is reflected in the receiver R100. Will reach. As a result, the receiver R100 erroneously detects the strong reflected wave of [4] instead of the weak direct wave of [2] as a direct wave that has reached straight from the sound source S100. Then, when calculating the distance between the sound source S100 and the receiver R100 based on the erroneously detected reception time, the distance of the reflected wave path is calculated instead of the shortest path by the original direct wave, It becomes a value larger than the original distance.

  A specific example in which the situation shown in FIG. 1 occurs is shown in FIG. In FIG. 2, the sound source S100 is provided in the user's mobile terminal, and the receiver R100 is provided in the user's car, so that the smart entry that calculates the distance between the user having the mobile terminal and the car using the sound wave reception time. It is an example of a system. In such a situation, if the user puts the mobile terminal in the pocket on the back side of the user, and the user himself / herself faces straight toward the car, the user himself / herself against the direct wave emitted from the pocket. It becomes a shield, and the situation as shown in FIG. 1 is born. Alternatively, the user does not have the mobile terminal in his pocket and holds it in his hand, but when the user is facing away from the car, the user himself becomes a shield and the situation shown in FIG. 1 is born. .

  As a conventional technique for separating a direct wave and a reflected wave, Patent Document 1 proposes a technique for separating a direct wave and a reflected wave by using an array antenna and estimating an arrival angle of a received wave. Yes. However, this method is premised on the use of an array antenna, and there is a problem that it cannot be used with a general-purpose portable terminal such as a mobile phone or a smartphone.

  In view of the above-described problems of the prior art, the present invention does not require a special device such as an array antenna, and there is a reflected wave that is not attenuated with respect to a direct wave that is attenuated due to the influence of human body shielding or the like. An object of the present invention is to provide a sound wave reception time calculation device, method, and program capable of accurately calculating the reception time of a direct wave even when the reflected wave becomes larger than the direct wave depending on the situation of . Moreover, it aims at providing a distance estimation system provided with the said apparatus.

  In order to achieve the above object, the present invention provides a sound wave reception time calculation device, a sound wave receiving unit that receives sound waves and obtains sound wave reception data, and a first cross-correlation between the sound wave reception data and a predetermined reference signal A first calculation unit that calculates a function using a first window size, and calculates the first time when the value of the first cross-correlation function exceeds the first threshold and peaks as the first reception time; A second cross-correlation function between data in the predetermined range before the first reception time in the received data and the predetermined reference signal is calculated using a second window size smaller than the first window size, A second calculation unit that calculates a first reception time as a second reception time when there is a time at which the value of the two cross-correlation function exceeds the second threshold and reaches a peak; If the arrival time of the direct wave of the predetermined reference signal in the data is the second reception time when the second reception time is calculated, the first reception time when the second reception time is not calculated It is a first feature that the determination unit includes a determination unit.

  The present invention is also a method for calculating a sound wave reception time, wherein a sound wave reception step of receiving sound waves to obtain sound wave reception data, and a first cross-correlation function between the sound wave reception data and a predetermined reference signal Calculating using a window size, and calculating a first time when the first cross-correlation function value exceeds the first threshold and peaks as a first reception time; and A second cross-correlation function between data within a predetermined range before one reception time and the predetermined reference signal is calculated using a second window size smaller than the first window size, and the second cross-correlation function A second calculation step of calculating the first reception time as the second reception time when there is a time when the value exceeds the second threshold value and the peak, and in the sound wave reception data, The arrival time of the direct wave of the predetermined reference signal is the second reception time when the second reception time is calculated, and the first reception time when the second reception time is not calculated. As a second feature, a determination step for determining is provided.

  In addition, the present invention is a program that has a third feature of causing a computer to function as the sound wave reception time calculation device.

  In addition, the present invention is a distance estimation system that includes a parent device and a child device, and estimates a distance between the parent device and the child device, and is bidirectionally or unidirectionally specified between the parent device and the child device. By transmitting a sound wave as a reference signal of the above and receiving either or both of the sound wave transmitted in the bidirectional or unidirectional among the parent device and the child device, the sound wave reception time calculating device A fourth feature is that a reception time is calculated, and a distance between the parent device and the child device is estimated based on the calculated reception time.

  Furthermore, in the sound wave reception time calculation device, the determination unit may further determine the arrival time of the direct wave of the predetermined reference signal in the sound wave reception data when the second reception time is calculated. Instead of the second reception time, the value of the first cross-correlation function exceeds the third threshold value that is smaller than the first threshold value in a predetermined range around the second reception time, and the third peak is reached first. The fifth feature is to adopt the reception time.

  According to the first to fourth features, when there is no influence of the reflected wave, the first reception time as the peak time of the first cross-correlation function is determined as the direct wave reception time, and the influence of the reflected wave is If there is an overlap with the direct wave, calculate the second cross-correlation function with a window size smaller than the first cross-correlation function in a predetermined range before the first reception time, and the second reception as the peak time The time is determined as the reception time of the direct wave. Here, since the second reception time is calculated by reducing the influence of the overlapping portion of the reflected waves by reducing the window size, the direct wave reception time can be appropriately calculated.

  According to the fifth feature, by searching for the peak of the first cross-correlation function after setting the threshold value to a small value again around the second reception time, as a third reception time with further improved accuracy, The reception time excluding the influence of the reflected wave can be calculated.

It is a figure which shows typically the condition used as a subject. It is a figure which shows the specific example which the condition like FIG. 1 will generate | occur | produce. It is a functional block diagram of a sound wave reception time calculation system including a sound wave reception time calculation device according to an embodiment. It is a figure which shows the case where only a direct wave reaches | attains as a 1st type. It is a figure which shows the case where a strong reflected wave arrives after the attenuated direct wave as a 2nd type. It is a figure which shows the case where a strong reflected wave reaches | attains as a 3rd type and overlaps with the attenuated direct wave. It is a figure which shows typically the reception time of the original direct wave determined with each cross-correlation function in 1st-3rd type | molds collectively. It is a functional block diagram of the distance estimation system concerning one embodiment. It is a flowchart of the distance estimation by the distance estimation system of FIG. It is a figure for demonstrating four types of transmission / reception time. It is a functional block diagram of the distance estimation system which concerns on another one Embodiment. It is a flowchart of distance estimation by the distance estimation system of FIG.

  FIG. 3 is a functional block diagram of a sound wave reception time calculation system including a sound wave reception time calculation device according to an embodiment. The sound wave reception time calculation system 100 includes a sound wave reception time calculation device 10 and a sound wave transmission terminal 20. The sound wave reception time calculation device 10 includes a sound wave reception unit 11, a first calculation unit 12, a second calculation unit 13, and a determination unit 14. The sound wave transmission terminal 20 includes a sound wave transmission unit 21. The processing content of each part 11-14, 21 is as follows. In the following description, the processing contents themselves are first described formally, and then the substantial technical significance or meaning thereof is described.

  The sound wave reception unit 11 includes a device having a function of receiving sound waves such as a microphone, records the received sound waves, records the data, and records the sound wave reception data rec (i) (i Is an integer of 1 ≦ i ≦ rec_length, and rec_length is the length of the sound wave reception data) to the first calculation unit 12 and the second calculation unit 13. In the following description of the present invention, when referring to the sound wave reception data, the sample number on the time axis is represented by the integer i as described above. (A value obtained by multiplying an integer i by a predetermined sampling interval is a real-time value, but the explanation is complicated, so it is referred to by an integer i. The same applies when using another letter such as j or k instead of i. .)

  Here, the reception time of the sound wave transmitted from the sound wave transmission unit 21 in the sound wave transmission terminal 20 is detected from within the sound wave reception data rec (i), but the transmission waveform of the sound wave to be detected is a reference. It is assumed that the signal ref (i) (i is an integer of 1 ≦ i ≦ ref_length and ref_length is the length of the reference signal) is known on the sound wave reception time calculation device 10 side.

  The sound wave transmitting unit 21 includes a device having a function of transmitting sound waves (including ultrasonic waves) such as a speaker, and transmits the reference signal ref (i).

  The first calculation unit 12 uses the first cross-correlation function cor1 (j) between the sound wave reception data rec (i) and the reference signal ref (i), using the first window size WS1 as in the following equation (1). The time j when the value of the first cross-correlation function cor1 (j) is the first peak passing the first threshold value TH1 (the time j of the peak position and the value cor1 ( The time j) when j) first exceeds the first threshold TH1 is calculated as the first reception time j = Tmax1.

  Here, WS1 = ref_length may be set. That is, the first window size WS1 may be a value equal to the reference signal length ref_length. In this case, all (1 ≦ k ≦ ref_length) of the reference signal ref (k) is used for the calculation of the cross correlation function. In general, when the window size is increased, the cross-correlation value with noise is decreased, the cross-correlation value with a sound wave as a detection target is increased, and robustness of sound wave detection with respect to noise is improved. By dividing by the denominator term in Equation (1), the absolute value of the cross-correlation function is normalized to 1 or less.

  The second calculation unit 13 should verify whether the calculated first reception time Tmax1 is an original direct wave reception time or an erroneous reception time affected by the reflected wave. The second cross-correlation function between the sound wave reception data and the reference signal is recalculated within a predetermined time range before the first reception time Tmax1, and the second reception time Tmax2 is calculated if it can be calculated. Note that the verification process itself is performed by the determination unit 14 described later in response to the result of the second calculation unit 13.

  Here, if the first reception time Tmax1 is incorrect due to the influence of the reflected wave, the original direct wave reception time is earlier than Tmax1 (that is, the past). The predetermined time range {j | Tmax1-Range1 ≦ j ≦ Tmax1} is a target for recalculating the second cross-correlation function.

  Here, Range1 is a parameter for designating a range in which the peak of the direct wave is included before the peak of the reflected wave. For this reason, the length may be approximately the same as the reference signal length. For example, an equal value such as Range1 = ref_length may be set. The peak relationship between the reflected wave and the direct wave will be described later with reference to FIG.

  Further, when the second calculation unit 13 recalculates the second cross-correlation function cor2 (j) in the range, the condition is different from the calculation of the first cross-correlation function cor1 (j) in the first calculation unit 12. To calculate.

Specifically, the second calculation unit 13 calculates the second cross-correlation function cor2 (j) using the second window size WS2, and the value of the second cross-correlation function cor2 (j) passes the second threshold value TH2. The time j that becomes the first peak is calculated as the second reception time j = Tmax2. Here, as shown in the following formulas (2) and (3), a predetermined value smaller than the first window size WS1 is used for the second window size WS2, and the first threshold TH1 is used for the second threshold TH2. The following predetermined values are used. (The meaning of using the predetermined value will be described later with reference to FIG. 6.)
WS2 <WS1 (2)
TH2 ≦ TH1… (3)

  Accordingly, the second cross-correlation function cor2 (j) calculated by the second calculation unit 13 is expressed by the following equation (4). That is, the reference signal ref (k) is not the whole (1 ≦ k ≦ ref_length) but only the first part (1 ≦ k ≦ WS2 <WS1 = ref_length).

  The second calculation unit 13 tries to calculate the second reception time Tmax2 from the calculated second cross-correlation function cor2 (j), but within the calculation range (Tmax1-Range1 ≦ j ≦ Tmax1), the second cross-correlation function cor2 If the value of (j) does not exceed the second threshold TH2, there is no one that satisfies the condition to be satisfied by the second reception time Tmax2, so that the second reception time Tmax2 cannot be calculated. .

  When the second reception time Tmax2 is calculated, the determination unit 14 erroneously calculates the first reception time Tmax1 due to the influence of the reception time of the reflected wave, and the second reception time Tmax2 is originally If the second reception time Tmax2 cannot be calculated, the first reception time Tmax1 was the original direct wave reception time without error. Judge as something.

  In the above, the processing content of each part 11-14 was demonstrated from the formal viewpoint. The meaning will be described below. That is, the types when the original reception time of the direct wave is calculated as the first reception time Tmax1 or the second reception time Tmax2 are described with reference to the simulation waveforms of FIGS. . 4 to 6 correspond to each other, and the transmission waveform (reference signal ref (i)) is common. Further, in the description of the relationship between the transmitted and received signals shown in the columns C51 to C53, the same symbols (sound source S100, receiver R100, etc.) as those in FIG. 1 are used.

  FIG. 4 shows only a direct wave from the sound source S100 (that is, the sound wave transmitting unit 21) to the receiver R100 (that is, the sound wave reception time calculating device 10) as the first type, as shown in the column C51. It is a figure which shows the case where it arrives and a reflected wave does not exist.

  In the case of the first type, the first calculation unit 12 calculates the first reception time Tmax1, the second calculation unit 13 cannot calculate the second reception time Tmax2, and the determination unit 14 determines the first reception time Tmax1. Is determined as the reception time of the direct wave.

  An example of the transmission waveform in the case of the first type (that is, the reference signal ref (i)) is shown in the column C100, the received signal (that is, the sound wave reception data rec (i)) and the first cross-correlation function cor1 (j). An example is shown in column C101. As shown in the column C100, the transmission waveform ref (i) is a predetermined waveform having a predetermined length of 0.01 seconds (10 milliseconds). If the sampling frequency to be set is 44.1 kHz, the number of samples ref_length = 441 in the reference signal ref (i) for 10 milliseconds is obtained. Hereinafter, when referring to the number of samples, the sampling frequency is assumed to be the setting.

  On the other hand, the received signal rec (i) and the first cross-correlation function cor1 (j) in the range of 0.02 seconds (sample number rec_length = 882) are shown in the column C101. Note that noise (white noise) having the same sound pressure as the received direct wave is added to the received signal on the upper side of the column C102 in order to simulate a real environment. The first cross-correlation function on the lower side of the column C101 is calculated from the received signal and the transmitted signal, and the first peak exceeding the threshold is calculated using the first threshold TH1 (here TH1 = 0.3) as indicated by the horizontal line L101. The time is obtained as indicated by the vertical line T101, and the time is the first reception time Tmax1. As is clear from comparison with the upper waveform, the time of the direct wave is appropriately calculated as the first reception time.

  FIG. 5 shows, as a second type, a direct wave that reaches the receiver R100 from the sound source S100 but is attenuated by the shield O100, while being directly attenuated by the wall W100. The reflected wave that is stronger than the wave also reaches the receiver R100 in a situation where it reaches the receiver R100. It is a figure which shows the case where it exists in the relationship which does not exist.

  Also in the case of the second type, the first calculation unit 12 calculates the first reception time Tmax1, the second calculation unit 13 cannot calculate the second reception time Tmax2, and the determination unit 14 Tmax1 is determined as the reception time of the direct wave.

  In the case of the second type, the transmission waveform is the same as the example shown in the column C100 of FIG. 4, and the received signal rec (i) and the first cross-correlation function in the column C201 in the range of 0.03 seconds (sample number rec_length = 1323) An example of cor1 (j) is shown. As shown in the upper part of column C201, in the received signal rec (i), in order to imitate the real environment, received attenuated direct wave and noise of the same sound pressure (white noise) are added, and the attenuated direct wave A reflected wave with 3 times the sound pressure reaches the propagation path book with a difference of about 3.5 m (that is, a reception time difference of about 10 milliseconds). Since the 10 milliseconds is the length of the transmission waveform, the direct wave and the reflected wave do not overlap in the reception signal rec (i).

  As shown on the lower side of the column C201, in the calculated first cross-correlation function cor1 (j), the first threshold TH1 (TH1 = 0.3 as in FIG. 4) is used as shown by the horizontal line L201. The exceeding first peak is obtained as indicated by the vertical line T201, and this time becomes the first reception time Tmax1. Note that the second peak exceeding the first threshold TH1 (= 0.3) also exists as indicated by the vertical line T202, which corresponds to the reception time of the reflected wave. Thus, as is apparent from the comparison with the waveform on the upper stage, the reception time of the direct wave is appropriately calculated as the first reception time by the first threshold TH1 (= 0.3) without making a mistake with the reflected wave.

  As shown in FIG. 6, as the third type, the direct wave attenuated by the shield O100 arrives from the sound source S100 to the receiver R100, as in the case of the second type, as shown in the column C53 in the relationship between transmission and reception signals. In a situation where a reflected wave that is stronger than this also arrives, unlike the case of the second type, the arrival time relationship is such that both the attenuated direct wave and the strong reflected wave overlap with each other and reach the receiver R100. It is a figure which shows the case where it exists in the relationship which carries out.

  In the case of the third type, the first calculation unit 12 calculates the first reception time Tmax1, but the time is affected by the reflected wave and is not the arrival time of the original direct wave. In order to correct this, the second calculation unit 13 succeeds in calculating the second reception time Tmax2, and the determination unit 14 determines the second reception time Tmax2 as the reception time of the direct wave.

  In the case of the third type, the transmission waveform is the same as the example (length 10 milliseconds) shown in the column C100 in FIG. 4, and the received signal rec (i in the range 0.02 seconds (number of samples rec_length = 882) is stored in the column C301. ) And a first cross-correlation function cor1 (j) and a second cross-correlation function cor2 (j) are shown. Note that the second cross-correlation function cor2 (j) actually does not have to be calculated over the entire range of 0.02 seconds as described in Equation (4), but the example shown on the lower side of column C301 The figure shows the values calculated over the entire range from the viewpoint of promoting understanding through comparison with the upper and middle stages.

  As shown in the upper part of column C301, in the received signal rec (i), noise of the same sound pressure as that of the attenuated direct wave to be received is added to imitate the real environment, and the sound is three times the attenuated direct wave. The reflected wave of pressure arrives with a propagation path length difference of about 1 m (that is, a reception time difference of about 3 milliseconds). That is, in the example of FIG. 6, the sound pressure relationship between the direct wave, the reflected wave, and the noise is the same as that of the example of FIG. 5, and the relationship of the arrival time is narrower than that of the example of FIG. There was an overlap of direct and reflected waves that did not exist. Thus, in the received signal rec (i), the portion of the rear side of about 7 milliseconds out of the attenuated direct wave having a length of 10 milliseconds overlaps with the strong reflected wave.

  In this way, since the weak direct wave overlaps the strong reflected wave, the direct wave part in the first cross-correlation function is greatly affected by the reflected wave part, and its peak value is higher than the original value. It gets smaller. That is, in the first cross-correlation function cor1 (j) shown in the middle part of the column C301, the first peak exceeding the threshold is indicated by the vertical line T302 using the first threshold TH1 (= 0.3) as shown by the horizontal line L301. Thus, even if the time is calculated as the first reception time Tmax1, the first reception time Tmax1 is clearly compared with the waveform of the reception signal on the upper stage, so that the original direct wave arrival time is However, it is influenced by the arrival time of the reflected wave. The original arrival time of the direct wave is the time of the peak position indicated by the vertical line T301 (or in the vicinity of the time), but the peak value has decreased due to the overlapping of the reflected waves, and the peak time Is not detected at the first threshold TH1 (= 0.3) indicated by the horizontal line L301.

  Therefore, the second cross-correlation function cor2 (j) is calculated as shown on the lower side of the column C301, and the second threshold TH2 equal to or lower than the first threshold TH1 (= 0.3) of the first cross-correlation function as shown by the horizontal line L401. (= 0.25) is used to analyze a predetermined range ahead of the first reception time Tmax1 (= position of the vertical line T302 = position of the vertical line T402) (= the range of the length of Range1 in Expression (4)) Thus, the second reception time Tmax2 is calculated as indicated by the vertical line T401 as the peak position that first exceeds the second threshold TH2 (= 0.25) within the range. As is clear from the waveform of the received signal on the upper side, the first cross-correlation function cor1 (j) is buried in the reflected wave by the analysis of the second cross-correlation function cor2 (j) as described above. The arrival time of the direct wave can be appropriately calculated as the second reception time.

  As apparent from the example of FIG. 6, the second window size WS2 smaller than the first window size WS1 used for the analysis of the first cross-correlation function is used in the analysis of the second cross-correlation function. This is because, in a situation where the corresponding portion on the side overlaps with the reflected wave and is buried, only the first portion that is not buried because there is no direct wave overlap is used for detection. The reason why the second threshold value TH2 is set to be equal to or less than the first threshold value TH1 is to achieve more reliable detection because there is a relationship that the robustness generally decreases when the window size is reduced. Since it is “below”, TH2 = TH1 may be set.

  As a specific numerical example, in the example of the column C301 in FIG. 6, the first window size WS1 = ref_size = 441 samples (= 10 milliseconds) and the second window size WS2 = 100 samples (≈2.3 milliseconds). ). Since the second window size WS2 is shorter than 3 milliseconds which is the length of the portion where the direct wave is not buried in the reflected wave, it is possible to appropriately detect the direct wave of the portion not buried.

  4 and 5, the first reception time Tmax1 is already the original reception time of the direct wave, and (accidentally, other similar sound sources existed. Unless there is an exceptional situation like this), there is no meaningful signal in the predetermined part (the length of Range1) before this, so calculate the second cross-correlation function cor2 (j) However, the second reception time Tmax2 as the peak position exceeding the second threshold TH2 is not calculated. Therefore, it is determined that the first reception time Tmax1 is a direct wave reception time.

  FIG. 7 is a diagram schematically showing the cross-correlation functions in the first to third types described above with reference to FIGS. 4 to 6 and the reception time of the original direct wave determined. In the first type shown in [1], only the attenuated or non-attenuated direct wave arrives, and the first reception time Tmax1 is calculated as the position where the first cross-correlation function exceeds the first threshold TH1 for the first time, and this is used as it is. The reception time of the direct wave is determined. In the second type shown in [2], a strong direct wave arrives after the arrival of the attenuated direct wave, but since there is no overlap on the time axis, the first reception time Tmax1 is also determined as the direct wave reception time. The In the third type shown in [3], sound wave reception is performed in such a way that the second half side of the attenuated direct wave is buried in a strong reflected wave, and not the first reception time Tmax1, but the second threshold TH2 (and the second cross-correlation function). The second reception time Tmax2 based on the second window size WS2) is determined as the direct wave reception time.

  As described above, according to the present invention, by analyzing both the first and second cross-correlation functions, the direct wave reception time can be normally obtained at the first reception time Tmax1 as in the first and second types. If the value is calculated, the result is used as it is. If an incorrect reception time is calculated due to the influence of the reflected wave as in the third type, the result is corrected to the second reception time Tmax2. By doing so, it is possible to correct the reception time of the original direct wave.

  In other words, according to the present invention, in calculation of the sound wave reception time that requires particularly high accuracy in applications such as distance measurement, the direct wave is buried in the reflected wave having a higher received sound pressure than itself due to the influence of human body shielding and reflection. Even in this case, it is possible to calculate the reception time of the direct wave by adjusting the window size of the cross-correlation function, and to reduce an increase in the error of the sound wave reception time.

  In order to further improve the accuracy of the corrected second reception time Tmax2, the third reception time Tmax3 obtained by the following additional processing in the determination unit 14 is changed to the final direct wave instead of the second reception time Tmax2. You may make it be the reception time of.

  That is, the cross-correlation function when the first window size WS1 is used in the range from Tmax2-Range2 to Tmax2 + Range2 (that is, the first cross-correlation function cor1 (j) already calculated by the first calculation unit 12) ) Is first calculated as the third reception time Tmax3 of the direct wave, and the final result is substituted for the second reception time Tmax2.

  The third threshold TH3 is set as TH3 <TH1. By setting the third threshold TH3 to be smaller than the first threshold TH1, the peak of the direct wave buried by the influence of the reflected wave is detected. For the value of Range2 that defines the search range, for example, as Range2 = ref_length / 2 (ie, 2 * Range2 = ref_length), as in the case of Range1 that is the confirmation range of the second cross-correlation function cor2 (j), A range similar to the length may be set.

  In the embodiment using the above third reception time Tmax3 as a result instead of the second reception time Tmax2, in the example of FIG. 6, T401 was found as the peak position of the second cross-correlation function shown in the column C301. Later, by confirming the periphery of the position using the third threshold TH3 in the first cross-correlation function, the peak position T301 that could not be found at the beginning using the first threshold TH1 is adopted as the final result. It corresponds to that.

  In addition, the determination unit 14 tried to calculate the third reception time Tmax3 by the additional processing described above, but if the corresponding condition was not found, the second reception time Tmax2 was determined as the final result of the direct wave. What is necessary is just to employ | adopt as reception time.

  As described above, the sound wave reception time calculation device 10 of FIG. 3 can be applied to any system in which it is necessary to accurately calculate the reception time of a direct wave of a sound wave whose waveform is known in its application. By excluding the influence of the reflected wave at, it is possible to contribute to the calculation of the accurate reception time of the direct wave. Hereinafter, a distance estimation system will be introduced as an example of a system to which the sound wave reception time calculation device 10 is preferably applied.

  FIG. 8 is a functional block diagram of the distance estimation system 200 according to an embodiment. The distance estimation system 200 includes a parent device P10 and a child device C10, and the distance estimation unit 15P estimates the distance between the parent device P10 and the child device C10 using the method of Non-Patent Document 2 (Beepbeep) described above. Base unit P10 includes a control signal transmission / reception unit 5P, a sound wave reception time calculation device 10P, a sound wave transmission unit 21P, and a distance estimation unit 15P. The subunit C10 includes a control signal transmission / reception unit 5C, a sound wave reception time calculation device 10C, and a sound wave transmission unit 21C.

  Between the control signal transmission / reception units 5P and 5C, by transmitting and receiving radio signals to and from each other, a control signal required in the Beepbeep method between the parent device P10 and the child device C10 (such as time synchronization for sound wave transmission / reception timing setting), Information necessary for distance calculation (information of sound wave signal data to be transmitted / received and sound wave transmission / reception times at both sides) is transmitted / received. The wireless signal can be a radio wave such as Wi-Fi or Bluetooth, or communication via a base station such as 3G or LTE. Further, a predetermined standard sound wave / ultrasonic wave capable of transmitting and receiving information may be used for the radio signal.

  The sound wave reception time calculation devices 10P and 10C and the sound wave transmission units 21P and 21C are respectively common to the sound wave reception time calculation device 10 and the sound wave transmission unit 21 described in FIG. 3, and are reflected within the framework of the Beepbeep technique. The reception time excluding the influence of the wave is calculated. That is, regarding the sound wave transmitted from the child device C10 to the parent device P10 side, the sound wave reception time calculating device 10P receives the sound wave transmitted by the sound wave transmitting unit 21C, and calculates the reception time by excluding the influence of the reflected wave. . Similarly, regarding the sound wave transmitted from the parent device P10 to the child device C10 side, the sound wave reception time calculation device 10C receives the sound wave transmitted by the sound wave transmission unit 21P, and calculates the reception time by excluding the influence of the reflected wave. To do.

  FIG. 9 is a flowchart of distance estimation by the distance estimation system 200. In step S1, a communication channel is established between the control signal transmission / reception units 5P and 5C, and information on sound waves (information on the reference signal ref (i)) transmitted and received between each other in step S3 described later is transmitted between the parent device P10 and the child device C10. The clocks are shared with each other and the clocks are set with a predetermined accuracy, and then the process proceeds to step S2. In step S1, authentication or the like may be performed according to the use of the distance estimation system 200. Note that a sound wave transmitted from the parent device P10 is a sound wave P, and a sound wave transmitted from the child device C10 is a sound wave C.

  In step S2, after notifying the control signal transmission / reception unit 5C of the slave unit C10 from the control signal transmission / reception unit 5P of the parent device P10, a signal to start sound transmission / reception in the next step S3 in the Beepbeep method, Proceed to S3. Note that, by starting recording in base unit P10 and handset C10 in accordance with the signal, it is possible to prepare the above-described received signal rec (i) as having a predetermined length rec_length on both sides.

In step S3, sound waves are transmitted / received between the parent device P10 and the child device C10 by the Beepbeep method, and the transmission / reception times thereof are obtained from each other. As here shown, in the base unit P10, it obtains a transmission time T _{P_S} of waves P by itself, and the reception time T _{P_r} of waves C that are transmitted from the child device C10 side. Similarly, the slave device C10 _obtains the transmission time T _{C_S} of the sound wave C by itself and the reception time T _{C_R} of the sound wave P transmitted from the parent device P10 side.

FIG. 10 is a diagram for explaining the four types of transmission / reception times. The base unit P10 includes a speaker PS that transmits sound waves P and a microphone PM that records sound waves P and C. The handset C10 includes a speaker CS that transmits sound waves C and a microphone CM that records sound waves P and C. And. As shown in the figure, in the parent device P10, the transmission time T _{P_S of} the sound wave P by itself is the time when the microphone PM received the sound wave P transmitted by its own speaker PS and is transmitted from the child device C10 side. The reception time _{TP_R of} the sound wave C is the time at which the microphone PM of the sound wave C transmitted from the speaker CS of the other party is received. Similarly, in the child device C10, the transmission time T _{C_S of} the sound wave C by itself is the time when the microphone CM receives the sound wave C transmitted by the speaker CS, and the sound wave transmitted from the parent device P10 side. The reception time T _{C_R of} P is the time when the microphone CM of itself receives the sound wave P transmitted from the speaker PS on the other side.

Therefore, the transmission time T _{P_S} and the reception time T _{P_R} are times based on the clock managed in the recording of the parent device P10, and the transmission time T _{C_S} and the reception time T _{C_R} are clocks managed in the recording of the child device C10. It is time based on. According to the Beepbeep method, even if there is a predetermined shift between both the watches, it is possible to estimate the distance with high accuracy by absorbing the shift.

Here, in particular, when calculating the reception times T _{P_R} and T _{C_R} , it is possible to calculate the reception time of the direct wave in a form excluding the influence of the reflected wave by the sound wave reception time calculation devices 10P and 10C. . In general, the microphone and speaker are considered to be sufficiently close together in the case in both the base unit P10 and the base unit C10, so there is an influence of reflected waves when calculating the transmission times _{TP_S} and _{TC_S.} Although it is difficult to imagine, the influence of the reflected wave may be excluded by the sound wave reception time calculation devices 10P and 10C when obtaining the transmission time.

  As is clear, the speaker described in FIG. 10 corresponds to the sound wave transmitting units 21P and 21C in FIG. Further, the microphone described in FIG. 10 corresponds to the sound wave receiving unit 11 in FIG. 3 as a functional block in the sound wave reception time calculation devices 10P and 10C in FIG.

Returning to the description of FIG. 9, in step S4, the control signal transmission / reception unit 5C of the slave unit C10 transfers the control signal transmission / reception unit 5P of the master unit P10 to the transmission / reception time (transmission time _{TC_S} and reception) in step S3. After notifying the time T _{C_R} ), the process proceeds to step S5.

In step S5, the distance estimation unit 15P estimates the distance between the parent device P10 and the child device C10. The estimation is as shown in the following expression (5) to (8), after calculating the transmission and reception interval T _C in transmission and reception intervals in the base unit P10 side T _P and the slave unit C10 side, the difference of the two intervals The distance D is estimated by calculating the sound wave propagation time ToF and multiplying by the sound velocity c.

T _P = T _{P_R} -T _{P_S} (5)
T _C = T _{C_S} -T _{C_R} (6)
ToF = (T _P -T _C ) / 2 (7)
D = ToF * c… (8)

  Note that the principle of calculating the distance D between the parent device P10 and the child device C10 as described above is disclosed and well known in the above-mentioned Non-Patent Document 2 (Beepbeep) and others, and the description thereof will be omitted. This principle is also common to the clock adjustment principle in the well-known NTP (Network Time Protocol).

  As described above, according to the distance estimation system 200 according to the embodiment of FIGS. 8 and 9, the distance D between the master unit P10 and the slave unit C10 is not accurately set by the Beepbeep method even if the clock is not accurately set. Can be estimated. At this time, the sound wave reception time calculation devices 10P and 10C can accurately estimate the distance D calculated based on the transmission / reception time by accurately calculating the reception time of the direct wave without the influence of the reflected wave. Is possible.

  Next, a distance estimation system 300 according to another embodiment that estimates the distance D between the master device P10 and the slave device C10 on the premise of performing highly accurate time adjustment will be described. FIG. 8 is a functional block diagram of a distance estimation system 300 according to another embodiment. The distance estimation system 300 includes a parent device P10 and a child device C10. Base unit P10 includes control signal transmission / reception unit 5P, sound wave transmission unit 21P, and distance estimation unit 15P. The subunit | mobile_unit C10 is provided with the control signal transmission / reception part 5C and the sound wave reception time calculation apparatus 10C.

  In the distance estimation system 300 shown in FIG. 11, unlike the distance estimation system 200 in FIG. 8, it is premised on highly accurate time adjustment, so that sound waves need to be transmitted and received only in one direction, not in both directions. The sound wave transmission unit 21P and the sound wave reception time calculation device 10C are responsible for the unidirectional transmission and reception, and the functions are the same as those of the sound wave transmission unit 21 and the sound wave reception time calculation device 10 shown in FIG. The control signal transmission / reception units 5P and 5C shown in FIG. 11 transmit and receive the same wireless signal as shown in FIG. 8, but information according to the embodiment is transmitted and received. The distance estimation unit 15P illustrated in FIG. 11 estimates the distance D by a method according to the embodiment.

  FIG. 12 is a flowchart of distance estimation by the distance estimation system 300. In step S11, a communication channel is established between the control signal transmission / reception units 5P and 5C, and in step S13, which will be described later, information on sound waves transmitted in a single direction from the parent device P10 to the child device C10 (information on the reference signal ref (i)) ) To the transmitting-side slave unit C10, and after performing high-precision clock alignment with each other, the process proceeds to step S12. In step S11, authentication or the like may be performed according to the use of the distance estimation system 300.

  In step S12, the control signal transmitting / receiving unit 5P of the parent device P10 notifies the control signal transmitting / receiving unit 5C of the child device C10 of a signal to start transmission of the unidirectional sound wave, and then proceeds to step S13. In response to the signal, the slave unit C10 starts recording, and the received signal rec (i) described above can be prepared as having a predetermined length rec_length.

In step S13, obtains the transmission time T _S along with wave transmitting unit 21P in the master unit P10 sends the sound waves, the receiving time T _R determined wave reception time calculation apparatus 10C in the slave unit C10 has received the wave Then, go to step S14. In step S14, to the control signal transmission and reception unit 5P of the master unit P10 from the control signal transmitting and receiving section 5C of the slave unit C10, from the notification reception time T _R at step S3, the process proceeds to step S15.

In step S15, the distance estimation unit 15P estimates the distance D between the parent device P10 and the child device C10 by the following equation (9). Since assuming the time adjustment is performed in step S11 described above with high precision, it is sound propagation time of the difference between the receiving time T _C in the clock of the transmission time T _R and the slave unit C10 side in clock of the master unit P10 side Equation (9) is obtained by multiplying by the sound velocity c.
D = (T _R -T _S ) * c (9)

  Hereinafter, supplementary matters in the present invention will be described.

  (1) In the distance estimation systems 200 and 300 described with reference to FIGS. 8 and 11, the distance estimation unit 15P is described as being provided on the parent device P10 side, but may be provided as the distance estimation unit 15C on the child device C10 side. Alternatively, it may be provided in both the parent device P10 and the child device C10.

  (2) In the distance estimation systems 200 and 300 described with reference to FIGS. 8 and 11, the parent device P10 and / or the child device C10 may execute a predetermined function based on the distance D estimated by the distance estimation unit 15P. . For example, when the parent device P10 is installed in the user's car and the child device C10 is realized as the user's mobile terminal, when the distance D is equal to or less than the threshold value, the vehicle door is unlocked and is larger than the threshold value. In some cases, it may be locked to function as a smart entry system. In this case, it is preferable to estimate the distance D periodically at a predetermined interval.

  (3) The sound wave reception time calculation device 10, the sound wave transmission terminal 20, the parent device P10, the child device C10, and the like in the present invention each have a known hardware configuration such as a CPU (Central Processing Unit), a memory, and various input / output interfaces. It can be realized with a computer. In this case, the computer functions as each device. The present invention can also be provided as a program that causes a computer to function as each of the devices. In this case, the program is read and the computer executes instructions corresponding to the functional units shown in FIGS.

  DESCRIPTION OF SYMBOLS 10 ... Sound wave reception time calculation apparatus, 11 ... Sound wave reception part, 12 ... First calculation part, 13 ... Second calculation part, 14 ... Determination part, 21 ... Sound wave transmission part, 200,300 ... Distance estimation system, P10 ... Master machine, C10 ... cordless handset

Claims (8)

A sound wave receiving unit for receiving sound waves and obtaining sound wave reception data;
A first cross-correlation function between the sound wave reception data and a predetermined reference signal is calculated using a first window size, and the first time when the value of the first cross-correlation function exceeds the first threshold and peaks A first calculation unit that calculates the first reception time;
A second cross-correlation function between the predetermined reference signal and the data in the predetermined range before the first reception time in the sound wave reception data is calculated using a second window size smaller than the first window size, A second calculation unit that calculates the first reception time as the second reception time when there is a time at which the value of the second cross-correlation function exceeds the second threshold and peaks;
If the arrival time of the direct wave of the predetermined reference signal in the sound wave reception data is the second reception time when the second reception time is calculated, the arrival time of the direct wave of the predetermined reference signal is the second reception time when the second reception time is calculated. A sound wave reception time calculation apparatus comprising: a determination unit that determines that the reception time is one reception time.   In the case where the second reception time is calculated, the determination unit further replaces the first reception time with the first reception time as the arrival time of the direct wave of the predetermined reference signal in the sound wave reception data. The third reception time at which the cross correlation function value first peaks in a predetermined range around the second reception time exceeding a third threshold value smaller than the first threshold value is employed. The sound wave reception time calculation device described in 1.   The sound wave reception time calculating device according to claim 1 or 2, wherein the first window size is set to coincide with a length of the predetermined reference signal.   The second calculation unit calculates the second cross-correlation function using a portion of the predetermined reference signal having a length of the second window size on the first side. 4. A sound wave reception time calculation device according to any one of claims 1 to 3. A distance estimation system that includes a parent device and a child device and estimates a distance between the parent device and the child device,
Transmitting sound waves as predetermined reference signals in both directions or unidirectional between the parent device and the child device,
Among the master unit and the slave unit, both or one of receiving the sound waves transmitted in the bidirectional or unidirectional manner includes the sound wave reception time calculating device according to any one of claims 1 to 4, Calculate the received time,
A distance estimation system that estimates a distance between the parent device and the child device based on the calculated reception time. A sound wave receiving stage for receiving sound waves and obtaining sound wave reception data;
A first cross-correlation function between the sound wave reception data and a predetermined reference signal is calculated using a first window size, and a time at which the value of the first cross-correlation function exceeds a first threshold and first peaks is calculated. A first calculation stage for calculating the first reception time;
A second cross-correlation function between the predetermined reference signal and the data in the predetermined range before the first reception time in the sound wave reception data is calculated using a second window size smaller than the first window size, A second calculation step of calculating the first time to be the peak as the second reception time when there is a time at which the value of the second cross-correlation function exceeds the second threshold and becomes a peak;
If the arrival time of the direct wave of the predetermined reference signal in the sound wave reception data is the second reception time when the second reception time is calculated, the arrival time of the direct wave of the predetermined reference signal is the second reception time when the second reception time is calculated. And a determination step of determining that the reception time is one reception time.   In the determination step, when the second reception time is calculated, the arrival time of the direct wave of the predetermined reference signal in the sound wave reception data is replaced with the first reception time instead of the second reception time. 7. The third reception time at which the value of the cross-correlation function first peaks after exceeding a third threshold value smaller than the first threshold value in a predetermined range around the second reception time is adopted. The sound wave reception time calculation method according to 1.   A program for causing a computer to function as the sound wave reception time calculating device according to any one of claims 1 to 4.