JP6029287B2 - Distance measuring method and radar device - Google Patents

Description

  The present invention relates to a distance measuring method and a radar apparatus for measuring a distance to an object.

  Radar technology is known as a technology for measuring the distance to an object. A transmission radar signal is transmitted to the object, a reflection radar signal is received from the object, a delay time of the reflection radar signal with respect to the transmission radar signal is measured, and a distance to the object is measured. Based on the propagation speed c of the radar signal and the delay time τ of the reflected radar signal with respect to the transmitted radar signal, the distance to the object can be measured as L = cτ / 2.

  Specifically, during one period of radar signal transmission, a pulsed transmission radar signal is first transmitted, and then a reflected radar signal is received in the remaining period. Here, it is assumed that one period of radar signal transmission is T, and the pulse width of the transmission radar signal is w.

  The limit on the far side of the measurement distance is Lmax = cT / 2. When the measurement distance exceeds the limit on the long distance side, when a reflected radar signal is received in one cycle of a certain radar signal transmission, the transmission radar signal has already been transmitted in one cycle of the next radar signal transmission. This is because the two periods of radar signal transmission overlap.

  The limit on the short distance side of the measurement distance is Lmin = cw / 2. When the measurement distance exceeds the limit on the short distance side, when the reception of the reflected radar signal is started in one cycle of a certain radar signal transmission, the transmission of the transmission radar signal is completed in the one cycle of the radar signal transmission. This is because only the last part of the pulse can be received.

  In order to increase the signal-to-noise ratio, the pulse energy may be increased. Here, in order to increase the energy of the pulse, it is conceivable to increase the peak power of the pulse, but the peak power of the pulse is limited by the maximum transmission power. Therefore, in order to increase the pulse energy, it is desirable to increase the pulse width w.

  However, if the pulse width w is widened, it is convenient to measure the distance to the object at a long distance, but to measure the distance to the object at a short distance, the short distance side of the measurement distance It is inconvenient because of its limitations. Further, since the delay time τ of the reflected radar signal with respect to the transmission radar signal can only be measured indefinitely, there is a problem that the radar image is blurred.

  A pulse compression technique is known as a technique for sharpening a radar image even when the pulse width w is widened. In a radar using a pulse compression method, an uncorrelated signal is generally used as a transmission signal. An uncorrelated signal is a signal having a low correlation value between the signal waveform itself and a signal waveform obtained by time-shifting the signal waveform, and it is known that a pseudo-random noise signal has the property. . A configuration and a time chart of a conventional radar device using a pulse compression technique are shown in FIGS.

  A conventional radar device R of pulse compression technology includes an uncorrelated signal generation unit 1, a radar signal transmission unit 2, a speaker 3, a microphone 4, a radar signal reception unit 5, a correlation processing execution unit 6, a transmission timing switch 7T, and a reception timing switch. 7R and an operation timing switching unit 8.

  The uncorrelated signal generation unit 1 generates an uncorrelated signal as a pseudo random signal. The radar signal transmission unit 2 transmits a transmission radar signal to the object O. The speaker 3 irradiates the object O with a transmission radar signal. The microphone 4 collects a reflected radar signal from the object O. The radar signal receiving unit 5 receives a reflected radar signal from the object O.

The correlation processing execution unit 6 measures the distance to the object O by executing correlation processing between the transmission radar signal and the reflected radar signal. Specifically, the correlation processing execution unit 6 determines the delay time τ of the reflected radar signal R (t) with respect to the transmitted radar signal T (t) based on the transmitted radar signal T (t) and the reflected radar signal R (t). The correlation function d (τ) for is calculated.

  The transmission timing switch 7T determines the operation timing of the radar signal transmission unit 2. The reception timing switch 7R determines the operation timing of the radar signal receiving unit 5. The operation timing switching unit 8 switches the operation timing for the radar signal transmission unit 2 and the radar signal reception unit 5 only once during one period of radar signal transmission.

  That is, the operation timing switching unit 8 outputs the operation timing signal “1” and turns on the transmission timing switch 7T in the transmission period WT in one cycle T of radar signal transmission, while turning the reception timing switch 7R on. The radar signal transmission unit 2 is operated while the radar signal transmission unit 2 is operated while the radar signal reception unit 5 is not operated.

  Then, the operation timing switching unit 8 outputs the operation timing signal “0” and turns off the transmission timing switch 7T in the reception period WR of one cycle T of the radar signal transmission, while the reception timing switch 7R is turned off. The radar signal transmission unit 2 is operated while the radar signal transmission unit 2 is not operated.

  The uncorrelated signal generation unit 1 generates an uncorrelated signal in all periods of one period T of radar signal transmission, but the speaker 3 only transmits the transmission period WT in one period T of radar signal transmission. In FIG. 3, a non-correlated signal is extracted and irradiated.

  Here, even if the transmission period WT of one period T of radar signal transmission is extended, the correlation function d (τ) regarding the delay time τ of the reflected radar signal R (t) with respect to the transmission radar signal T (t) is the target. It has a sharp peak at the delay time τ corresponding to the distance to the object O. Therefore, the pulse compression technique can make the radar screen clearer than the ordinary radar technique.

  Specific forms of the pulse compression technique are disclosed in Patent Document 1 and Patent Document 2. In Patent Document 1, in addition to the above, the sensing area can be made variable according to the surrounding situation by making the distance measurement cycle variable according to the surrounding situation. In Patent Document 2, in addition to the above, even if the object has a velocity component in the same direction as the direction of the transmission radar signal and the reception radar signal, the Doppler shift of the reception radar signal with respect to the transmission radar signal is compensated. As a result, the radar screen can be made clear.

Japanese Patent Laid-Open No. 9-21869 JP 2010-197241 A

  In radar using the pulse compression method, if the pulse width w is increased, the energy of the pulse can be increased, so that the object O at a long distance can be measured with high accuracy, but the short distance side of the measurement distance. Therefore, the object O at a short distance cannot be measured efficiently. On the other hand, if the pulse width w is narrowed, the limit on the short distance side of the measurement distance can be shortened, so that the object O at a short distance can be measured efficiently, but the pulse energy is reduced. Therefore, the object O at a long distance cannot be measured efficiently.

  By the way, radar technology using pulse compression technology can be applied to radar technology using ultrasonic waves, electromagnetic waves, or the like. In the following description, a problem to be solved in radar technology using pulse compression technology in radar technology using airborne ultrasonic waves will be described.

  In the radar technology using airborne ultrasonic waves, the propagation speed c of the radar signal is slow and the radar signal is greatly attenuated as compared with the radar technology using electromagnetic waves, so that it is practical only at a measurement distance of about 5 m. Therefore, in order to compensate for the attenuation of the radar signal, it is desired to increase the effective energy of the pulse by the pulse compression technique, but the following problem arises.

  In radar technology using airborne ultrasonic waves, a sounding / receiving element of 40 kHz to 60 kHz is usually used. Here, since the sound generation / sound receiving element is a resonator, it does not sound easily even if driving is started, and does not stop easily even if driving is stopped. Therefore, it is normal to set the pulse width w within or outside of w = 2 ms. The pulse width w includes 80 waves of 40 kHz and 120 waves of 60 kHz.

  Therefore, the pulse width w is set to w = 2 ms, and the pulse peak power is set to 1 W. Then, the limit on the short distance side of the measurement distance is Lmin = 340 m / s × 2 ms / 2 = 0.34 m. The energy of the pulse is 1 W × 2 ms = 2 mJ. However, at this level of energy, the measurement capability of a long-distance object is only about 5 m because of the attenuation of the radar signal.

  Therefore, the pulse width w is expanded, w = 32 ms is set, and the peak power of the pulse is set to 1 W. Then, the limit on the short distance side of the measurement distance is Lmin = 340 m / s × 32 ms / 2 = 5.44 m. The energy of the pulse is 1 W × 32 ms = 32 mJ. Since an object having a distance of about 5 m can be observed with this energy, when using a pulse with w = 32 ms, it is more efficient than using a pulse with w = 2 ms.

  In order to perform detection with higher accuracy, the pulse width w is further expanded, w = 64 ms is set, and the peak power of the pulse is set to 1 W. Then, the energy of the pulse is 1 W × 64 ms = 64 mJ. The limit on the short distance side of the measurement distance is Lmin = 340 m / s × 64 ms / 2 = 10 m. However, since a reflected wave from an object having a distance of about 5 m returns when 32 ms, which is half of w = 64 ms, has passed, the transmitter and the receiver cannot be driven simultaneously. Even in the case of 64 ms, only the same energy can be received as in the case of w = 32 ms, and the object detection capability is also equivalent. Therefore, there is a certain limit to the method of improving the detection capability of an object having a distance of about 5 m simply by increasing the pulse width.

  Pulse compression radar cannot detect distant objects if the pulse width is reduced with an emphasis on the ability to detect near objects. Conversely, if the pulse width is increased with emphasis on the ability to detect a distant object, a close object cannot be detected with a certain capacity. In order to solve this problem, the present invention provides a radar technique using a pulse compression technique that measures an object at a long distance with high accuracy and also measures an object at a short distance with high precision. Objective.

  In order to achieve the above object, the operation timing is switched multiple times during one period of radar signal transmission for radar signal transmission and radar signal reception.

  Specifically, the present invention is characterized in that an uncorrelated signal is transmitted to an object while switching a state between a transmission state and a non-transmission state over a plurality of times during one period of radar operation. This is a distance measurement method.

  In addition, the present invention transmits an uncorrelated signal to an object while switching a state between a transmission state and a non-transmission state over a plurality of times during one cycle of the radar operation. While switching the state between the reception state and the non-reception state so as to be in the reception state in the non-transmission state while switching to the non-reception state in the transmission state over a plurality of times, the reflected radar signal The distance measuring method is characterized in that the distance to the object is measured by executing correlation processing between the uncorrelated signal transmitted and received from the object and the received reflected radar signal.

  In addition, the present invention includes a radar signal transmission unit that transmits an uncorrelated signal to an object while switching a state between a transmission state and a non-transmission state over a plurality of times during one period of radar operation. Is a radar device characterized by

  The present invention also provides a radar signal transmission unit that transmits an uncorrelated signal to an object while switching a state between a transmission state and a non-transmission state over a plurality of times during one period of the radar operation, and a radar operation. While switching the state between the reception state and the non-reception state so as to be in the non-reception state in the transmission state and the reception state in the non-transmission state over a plurality of times during one cycle of By executing a correlation process between the radar signal receiving unit that receives the reflected radar signal from the object, the uncorrelated signal transmitted by the radar signal transmitting unit, and the reflected radar signal received by the radar signal receiving unit. And a correlation processing execution unit that measures a distance to the object.

  According to this configuration, an object at a long distance can be measured with high accuracy, and an object at a short distance can also be measured with high accuracy.

  Further, the present invention is a distance measuring method characterized by changing a measurement sensitivity characteristic of the distance to the object by changing a state switching pattern between the transmission state and the non-transmission state.

  Further, the present invention is characterized in that the radar signal transmission unit changes a measurement sensitivity characteristic of a distance to the object by changing a state switching pattern between the transmission state and the non-transmission state. It is a radar device.

  According to this configuration, an object at any distance can be measured with high accuracy.

  The present invention is also the distance measurement method characterized in that the total time of the transmission state in one cycle of the radar operation is set to approximately 50% with respect to one cycle of the radar operation.

  Further, the present invention is the radar device characterized in that the radar signal transmission unit sets the total time of the transmission state during one cycle of the radar operation to approximately 50% with respect to one cycle of the radar operation. is there.

  According to this configuration, it is possible to receive and collect transmission power most efficiently.

  According to the present invention, in a radar technique using a pulse compression technique, an object at a long distance can be measured with high accuracy, and an object at a short distance can also be measured with high accuracy.

It is a figure which shows the structure of the radar apparatus of the conventional pulse compression technique. It is a figure which shows the time chart of the radar apparatus of the conventional pulse compression technique. It is a figure which shows the structure of the radar apparatus of this invention. It is a figure which shows the time chart of the radar apparatus of this invention. It is a figure which shows the simulation result of the sensitivity characteristic of the measurement distance in a comparative example. It is a figure which shows the simulation result of the sensitivity characteristic of the 1st measurement distance in this invention. It is a figure which shows the simulation result of the sensitivity characteristic of the 2nd measurement distance in this invention. It is a figure which compares the simulation result of the sensitivity characteristic of the 1st and 2nd measurement distance in this invention. It is a figure which shows the simulation result of the sensitivity characteristic of the measurement distance in a comparative example. It is a figure which shows the simulation result of the sensitivity characteristic of the 1st measurement distance in this invention. It is a figure which shows the simulation result of the sensitivity characteristic of the 2nd measurement distance in this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  First, an outline of the distance measurement method will be described. The radar signal transmission process and the radar signal reception process may be performed by the same entity or different entities.

  In the radar signal transmission process, an uncorrelated signal is transmitted to the object while switching the state between the transmission state and the non-transmission state over a plurality of times during one period of the radar operation. Here, the transmission state is a state in which a non-correlated signal is extracted and transmitted, and the non-transmission state is a state in which not only a non-correlated signal is transmitted but also a waveform signal is not transmitted.

  In the radar signal reception process, the reflected radar signal is received from the object while switching the state between the reception state and the non-reception state over a plurality of times during one period of the radar operation. Here, the state is switched between the reception state and the non-reception state so that the transmission state becomes the non-reception state while the non-transmission state becomes the reception state.

  In the correlation processing execution stage, the distance to the object is measured by executing correlation processing between the transmitted uncorrelated signal and the received reflected radar signal.

  Here, the measurement sensitivity characteristic of the distance to the object can also be changed by changing the state switching pattern between the transmission state and the non-transmission state.

  Furthermore, the total transmission state time during one period of radar operation can be set to approximately 50% with respect to one period of radar operation.

  Next, details of the radar device will be described. The radar signal transmission unit and the radar signal reception unit may be arranged in the same device or may be arranged in different devices. In the following embodiments, the former case will be described.

  The configuration and time chart of the radar apparatus of the present invention are shown in FIGS. The radar apparatus R of the present invention includes an uncorrelated signal generation unit 1, a radar signal transmission unit 2, a speaker 3, a microphone 4, a radar signal reception unit 5, a correlation processing execution unit 6, a transmission timing switch 7T, a reception timing switch 7R, and nothing. It comprises a correlation signal switch 7C and an operation timing switching unit 8. In the present invention, compared with the prior art, the operation timing switching unit 8 executes a different process, and a non-correlated signal switch 7C is newly added.

  The uncorrelated signal generation unit 1 generates an uncorrelated signal as a pseudo random signal. As a non-correlated signal, a frequency chirp signal, a signal modulated with a pseudo random pulse such as an M (Maximum length) sequence, a multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) signal, and the like are known. The radar signal transmission unit 2 transmits a transmission radar signal to the object O. The speaker 3 irradiates the object O with a transmission radar signal. The microphone 4 collects a reflected radar signal from the object O. The radar signal receiving unit 5 receives a reflected radar signal from the object O.

The correlation processing execution unit 6 measures the distance to the object O by executing correlation processing between the transmission radar signal and the reflected radar signal. Specifically, the correlation processing execution unit 6 determines the delay time τ of the reflected radar signal R (t) with respect to the transmitted radar signal T (t) based on the transmitted radar signal T (t) and the reflected radar signal R (t). The correlation function d (τ) for is calculated.

  The transmission timing switch 7T determines the operation timing of the radar signal transmission unit 2. The reception timing switch 7R determines the operation timing of the radar signal receiving unit 5. The operation timing switching unit 8 switches the operation timing for the radar signal transmission unit 2 and the radar signal reception unit 5 a plurality of times during one period of radar signal transmission.

  That is, the operation timing switching unit 8 outputs the operation timing signal “1” in the transmission periods WT1, WT2, and WT3 in one period T of radar signal transmission, and turns on the transmission timing switch 7T while receiving the signal. The timing switch 7R is turned OFF to operate the radar signal transmission unit 2, while the radar signal reception unit 5 is not operated.

  Then, the operation timing switching unit 8 outputs the operation timing signal “0” in the reception period other than the transmission periods WT1, WT2, and WT3 in one period T of the radar signal transmission, and turns off the transmission timing switch 7T. On the other hand, the reception timing switch 7R is turned ON, and the radar signal receiving unit 5 is operated while the radar signal transmitting unit 2 is not operated.

  The uncorrelated signal generation unit 1 generates an uncorrelated signal in all periods of one period T of radar signal transmission, but the speaker 3 transmits a transmission period WT1 in one period T of radar signal transmission, In WT2 and WT3, an uncorrelated signal is extracted and irradiated.

  The uncorrelated signal switch 7C generates the same signal as the transmission radar signal when the correlation processing execution unit 6 executes the correlation processing of the transmission radar signal and the reflected radar signal.

  That is, the operation timing switching unit 8 outputs the operation timing signal “1” in the transmission periods WT1, WT2, and WT3 in one period T of the radar signal transmission, turns on the uncorrelated signal switch 7C, and sets the uncorrelated signal. Is output to the correlation processing execution unit 6.

  Then, the operation timing switching unit 8 outputs the operation timing signal “0” in the reception period other than the transmission periods WT1, WT2, and WT3 in one period T of the radar signal transmission, and turns off the uncorrelated signal switch 7C. The uncorrelated signal is not output to the correlation processing execution unit 6.

  In order to measure the object O at a short distance, the reflected radar signal may be received a short time after the transmission radar signal is transmitted. For example, a reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT1 may be received in the reception period WR1 between the transmission period WT1 and the transmission period WT2. Alternatively, a reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT2 may be received in the reception period WR2 between the transmission period WT2 and the transmission period WT3. Alternatively, a reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT3 may be received in the reception period WR3 after the transmission period WT3.

  In order to measure the object O at a long distance, the reflected radar signal may be received a long time after transmitting the transmission radar signal. For example, if a reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT1 is received in the reception period WR2 between the transmission period WT2 and the transmission period WT3 or received in the reception period WR3 after the transmission period WT3 Good. Alternatively, the reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT2 is received in the reception period WR3 after the transmission period WT3, or the reception period WR1 after the transmission period WT1 in the transmission period of the next radar signal. Can be received.

  That is, in one period T of radar signal transmission, since the transmission period is secured by the sum of the transmission periods WT1, WT2, and WT3, the pulse energy can be increased, and the object O at a long distance can be increased. It can be measured with high accuracy. And in one cycle T of radar signal transmission, since the transmission period is ensured by division like the transmission periods WT1, WT2, and WT3, the limit on the short distance side of the measurement distance can be shortened, and the short distance A certain object O can also be measured with high accuracy. Thus, the radar apparatus R of the present invention can be applied to both long distance measurement and short distance measurement.

  Here, if the total of the divided transmission periods is 50% of one period T of radar signal transmission, the total of the divided reception periods is also 50% of one period T of radar signal transmission. At this time, transmission power can be received and collected most efficiently.

  In one cycle T of radar signal transmission, the operation timing switching pattern may be periodic or aperiodic. For example, in the time chart shown in FIG. 4, in one cycle T of radar signal transmission, a switching pattern of the transmission period WT1 and the reception period WR1, a switching pattern of the transmission period WT2 and the reception period WR2, and a transmission period WT3 and The switching pattern of the reception period WR3 may be the same or different.

  By the way, in the detection of an object at an intermediate distance between the long distance and the short distance, the reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT1 is received in the non-reception period wr12 which is the same period as the transmission period WT2. Cannot be received, and cannot be received in the non-reception period wr23, which is the same period as the transmission period WT3. The reflected radar signal corresponding to the transmission radar signal transmitted in the transmission period WT2 cannot be received in the non-reception period wr23, which is the same period as the transmission period WT3, and the transmission period in the transmission period of the next radar signal It cannot be received in the non-reception period wr31 which is the same period as WT1. Therefore, depending on the measurement distance, there are measurement distances with high measurement sensitivity and measurement distances with low measurement sensitivity.

  However, the operation timing switching unit 8 can change the sensitivity characteristic of the measurement distance by changing the operation timing switching pattern. In other words, even if the measurement sensitivity at a certain measurement distance is increased, the operation timing switching unit 8 increases the operation sensitivity switching pattern for decreasing the measurement sensitivity at another measurement distance and the measurement sensitivity at the other measurement distance. In addition, an operation timing switching pattern that lowers the measurement sensitivity at a certain measurement distance is selectively used according to the target measurement distance. Therefore, the radar apparatus R of the present invention can increase the measurement sensitivity at the certain measurement distance, can also increase the measurement sensitivity at the other measurement distance, and can accurately detect the object O at any distance. Can be measured.

σ（ｔ）は、レーダー信号送信部２の動作タイミング信号であり、σ（ｔ）＝１のときには、レーダー信号送信部２は動作し、σ（ｔ）＝０のときには、レーダー信号送信部２は停止する。ρ（ｔ）は、レーダー信号受信部５の動作タイミング信号であり、ρ（ｔ）＝１−σ（ｔ）が成立し、ρ（ｔ）＝１のときには、レーダー信号受信部５は動作し、ρ（ｔ）＝０のときには、レーダー信号受信部５は停止する。ｘは、測定距離である。Ｐは、送信電力である。Ｕ（ｘ）は、測定距離の感度特性である。簡単のため、Ｐ＝１かつｃ／２＝１とすれば、測定距離の感度特性は、数式４のように表わされる。

Here, the sensitivity characteristic of the measurement distance is expressed as Equation 3.

σ (t) is an operation timing signal of the radar signal transmission unit 2. When σ (t) = 1, the radar signal transmission unit 2 operates, and when σ (t) = 0, the radar signal transmission unit 2. Stops. ρ (t) is an operation timing signal of the radar signal receiving unit 5, and ρ (t) = 1−σ (t) is established. When ρ (t) = 1, the radar signal receiving unit 5 operates. , Ρ (t) = 0, the radar signal receiver 5 stops. x is a measurement distance. P is transmission power. U (x) is a sensitivity characteristic of the measurement distance. For simplicity, if P = 1 and c / 2 = 1, the sensitivity characteristic of the measurement distance is expressed as Equation 4.

フーリエ級数ｕ_ｋ、σ_ｋ、ρ_ｋは、数式８のように、関係付けることができる。ここで、ρ_ｋ ^＊はρ_ｋの複素共役を表す。

Since radar signal transmission is repeated in one period T, U (x), σ (t), and ρ (t) are respectively Fourier series u _k , σ _k , ρ as shown in Equations 5, 6, and 7, respectively. _k can be expanded. Here, ω ₀ = 2π / T.

The Fourier series u _k , σ _k , and ρ _k can be related as shown in Equation 8. Here, ρ _k ^* represents a complex conjugate of ρ _k .

数式９の見通しを良くするため、単発の送信レーダー信号のみを取り出せば、Ｕ（ｘ）は、数式１０のように、フーリエ変換することができる。

Ｕ^〜（ω）は、Ｕ（ｘ）のフーリエ変換である。σ^〜（ω）は、σ（ｔ）のフーリエ変換である。δ（ω）は、ディラックのデルタ関数である。 because it is ρ (t) = 1-σ (t), the Fourier series _{u k} is expressed as in Equation 9. Here, η is the total duty ratio of the divided transmission periods (for example, transmission periods WT1, WT2, and WT3 in FIG. 4) for one period T of radar signal transmission.

If only a single transmission radar signal is extracted in order to improve the visibility of Equation 9, U (x) can be Fourier transformed as in Equation 10.

U ^~ (ω) is the Fourier transform of U (x). σ ^~ (ω) is the Fourier transform of σ (t). δ (ω) is a Dirac delta function.

To calculate the sigma (t) from U (x) is than applying Equation 4 calculates the ^{U ~} (ω) by applying the equation 10, ^{U ~} a (omega) to U (x) Inverse Fourier transform is more efficient. From Equation 9, it can be seen that _uk is a real number, and from Equation 5, U (x) is an even function and is line symmetric with respect to x = cT / 4 when 0 ≦ x ≦ cT / 2.

  Next, the simulation result of the sensitivity characteristic of the measurement distance when the propagation attenuation is not taken into consideration will be shown. FIG. 5 shows the simulation result of the sensitivity characteristic of the measurement distance in the comparative example, and FIGS. 6 and 7 show the simulation result of the sensitivity characteristic of the first and second measurement distances in the present invention, respectively.

  A comparative example will be described. As shown in the upper part of FIG. 5, the operation timing switching unit 8 switches the operation timing for the radar signal transmission unit 2 and the radar signal reception unit 5 only once during one period of radar signal transmission. T = 250 ms and η = 12.5%.

  As shown in the middle part of FIG. 5, at η = 12.5%, U (x) indicates a flat sensitivity characteristic, and the maximum sensitivity is U (x) ˜15. As shown in the lower part of FIG. 5, the maximum sensitivity U (x) increases as η increases from 12.5% to 25%, 37.5%, and 50%, and η = 50% , U (x) indicates a sensitivity characteristic having only one peak, and the maximum sensitivity is U (x˜22 m) ˜60. It can be seen that simply increasing η does not improve the detection capability of the proximity object beyond a certain level.

  The present invention will be described. 6 and 7, σ (t) is different.

  As shown in the upper part of FIG. 6, the operation timing switching unit 8 periodically performs the radar signal transmission unit 2 and the radar signal reception unit 5 about three times during one period of radar signal transmission. Switch the operation timing. T = 250 ms and η = 50%.

  As indicated by the solid line in the lower part of FIG. 6, U (x) indicates a sensitivity characteristic having three peaks, and the maximum sensitivity is U (x˜7 m) ˜U (x˜36 m) ˜60. And U (x to 22 m) to 55. Although the comparative example and the case of η = 48% are shown by the lower broken line in FIG. 6, the measurement sensitivity is improved in the present invention in comparison with the comparative example at x to 7 m and x to 36 m.

  As shown in the upper part of FIG. 7, the operation timing switching unit 8 performs the aperiodic operation on the radar signal transmission unit 2 and the radar signal reception unit 5 three times during one period of the radar signal transmission. Switch the operation timing. T = 250 ms and η = 50%.

  As shown by the solid line in the lower part of FIG. 7, U (x) represents a sensitivity characteristic having two peaks, and the maximum sensitivity is U (x-10 m) to U (x-34 m) to 55. It is. The lower broken line in FIG. 7 shows the comparative example and the case of η = 48%. However, in x to 10 m and x to 34 m, the measurement sensitivity is improved in the present invention compared to the comparative example.

  6 and 7 are compared. FIG. 8 compares the simulation results of the sensitivity characteristics of the first and second measurement distances in the present invention. In FIG. 6, U (x) has a maximum sensitivity at x to 7 m, 22 m, and 36 m. In FIG. 7, U (x) has maximum sensitivity at x to 10 m and 34 m. Thus, when σ (t) is a different pattern, U (x) can have different sensitivity characteristics. The σ (t) to be applied can be selected according to the target measurement distance, that is, according to the target U (x).

  Next, the simulation result of the sensitivity characteristic of the measurement distance in the case of considering propagation attenuation will be shown. The simulation result of the sensitivity characteristic of the measurement distance in the comparative example is shown in FIG. 9, and the simulation result of the sensitivity characteristic of the first and second measurement distances in the present invention is shown in FIGS. 10 and 11, respectively.

Ｄは、伝搬距離である。ａ（Ｄ）は、伝搬減衰率である。Ｄ^２に反比例する項は、球面波としての波動の拡散を表わしており、指数関数的に減衰する項は、空気による音響エネルギーの吸収を表わしている。数式１１は、周波数５０ｋＨｚ、温度２０℃、気圧１００ｋＰａ及び相対湿度６０％の条件を考慮して、作成したものである。 Here, the propagation attenuation factor is expressed as Equation 11.

D is the propagation distance. a (D) is a propagation attenuation factor. Term inversely proportional to D ² represents the diffusion of the wave as a spherical wave, terms exponentially decaying represents the absorption of acoustic energy by air. Formula 11 is created in consideration of the conditions of a frequency of 50 kHz, a temperature of 20 ° C., an atmospheric pressure of 100 kPa, and a relative humidity of 60%.

  The object O having the same reflectivity was placed at a distance of 5 m and 8 m from the radar device R. White noise was added so that SNR = 1/6 (−7.8 dB) within the signal band.

  A comparative example will be described. As shown in FIG. 5, T = 250 ms and η = 50%, and σ (t) that switches the operation timing only once during one period of radar signal transmission was used. The uncorrelated signal is a chirp signal that shifts in frequency from (50-12.5) kHz to (50 + 12.5) kHz during a half period T / 2 of radar signal transmission.

  The object O placed at a distance of 5 m from the radar device R (shown as “A” in FIG. 9) is detected, but the object O placed at a distance of 8 m from the radar device R (“B” in FIG. 9). Was not detected due to the large propagation attenuation.

  The present invention will be described. 10 and 11, σ (t) is different.

In FIG. 10, T = 250 ms and η = 50% shown in FIG. 6, and σ (t) that periodically switches the operation timing over about three times during one period of radar signal transmission is used. In FIG. 11, T = 250 ms and η = 50% shown in FIG. 7, and σ (t) that switches the operation timing aperiodically three times during one period of radar signal transmission is used. An uncorrelated signal is a carrier wave modulated by a PN code. The PN code was generated by a 12th order M-sequence generator. Of the repetition length of 2 ¹² −1 = 4095 bits, the first 3125 bits were used. The carrier wave had a center frequency of 50 kHz. BPSK was used as the modulation method. One period T of radar signal transmission is 3125 / (50/4) = 250 ms.

  10 and 11, the object O (shown as “A” in FIGS. 10 and 11) placed at a distance of 5 m from the radar device R is also detected and placed at a distance of 8 m from the radar device R. The object O (shown as “B” in FIGS. 10 and 11) was also detected despite the large propagation attenuation.

One specific example of the method for generating the switching timing waveform applied to this method will be described. The radar repetition period is divided into N small parts. For T = 250 ms, 16 to 24 is appropriate for N. Each divided section is defined as a transmission period or a reception period. For each waveform of the generated sigma (t), we obtain the complex Fourier series sigma _k using Equation 6, obtains the complex Fourier series u _k using Equation 9, by substituting the complex Fourier series u _k in Equation 5, the distance sensitivity performance Find U (x). The above-described processing is repeated for each waveform of the generated σ (t) until σ (t) where U (x) satisfies the predetermined distance sensitivity performance is obtained. By using FFT for Fourier transform and inverse Fourier transform, this method can be implemented at a sufficiently high speed.

  A waveform of approximately η = 50% is used in this method. Also, the time origin is shifted with respect to a certain σ (t) and circulated with a period T, the time sequence is reversed with respect to a certain σ (t), and the transmission / reception timing with respect to a certain σ (t) In which the distance is reversed has the same distance sensitivity characteristic as the certain σ (t). Using this property, the number of comparisons as σ (t) can be limited. It is only necessary to compare 257 ways for N = 16 division, 2518 ways for N = 20 division, 8359 ways for N = 22 division, and 28968 cases for N = 24 division. It can be executed with.

  The distance measuring method and the radar apparatus R of the present invention can be applied to radar technology using ultrasonic waves, electromagnetic waves, or the like. Examples of radar technology using airborne ultrasonic waves include an automatic door human sensor and a vehicle back sensor. As a radar technique using underwater ultrasonic waves, for example, a medical diagnostic device, a fish detector, and the like can be given.

  The distance measuring method and radar apparatus of the present invention can be widely applied to radar technology using airborne ultrasonic waves, underwater ultrasonic waves, electromagnetic waves, and the like.

R: Radar device O: Object 1: Uncorrelated signal generation unit 2: Radar signal transmission unit 3: Speaker 4: Microphone 5: Radar signal reception unit 6: Correlation processing execution unit 7T: Transmission timing switch 7R: Reception timing switch 7C : Uncorrelated signal switch 8: Operation timing switching unit

Claims (6)

No change having one period equal to one period of the radar operation while switching the state between the transmission state and the non-transmission state over a plurality of times during one period of the radar operation that determines the far side of the measurement distance. Send the correlation signal to the object,
A state between the reception state and the non-reception state so as to be in a non-reception state in the transmission state and a reception state in the non-transmission state over a plurality of times during one period of the radar operation. , Receiving the reflected radar signal from the object,
A distance measurement method comprising measuring a distance to the object by executing a correlation process between the transmitted uncorrelated signal and the received reflected radar signal. By changing the state switching pattern between the transmitting state and the non-transmission state, the distance measuring method according to claim 1, characterized in that to change the measurement sensitivity of the distance to the object. 3. The distance measuring method according to claim 1, wherein a total time of the transmission state in one period of the radar operation is set to approximately 50% with respect to one period of the radar operation. No change having one period equal to one period of the radar operation while switching the state between the transmission state and the non-transmission state over a plurality of times during one period of the radar operation that determines the far side of the measurement distance. A radar signal transmitter for transmitting a correlation signal to an object;
A state between the reception state and the non-reception state so as to be in a non-reception state in the transmission state and a reception state in the non-transmission state over a plurality of times during one period of the radar operation. A radar signal receiving unit that receives a reflected radar signal from the object,
A correlation processing execution unit that measures the distance to the object by executing correlation processing of the uncorrelated signal transmitted by the radar signal transmission unit and the reflected radar signal received by the radar signal reception unit;
A radar device comprising: The radar signal transmitting unit, by changing the state switching pattern between the transmitting state and the non-transmission state, according to claim 4, characterized in that to change the measurement sensitivity of the distance to the object Radar equipment. The radar signal transmission unit, wherein the total time of the transmission state during one cycle of the radar operation, to claim 4 or 5, characterized in that set to approximately 50% relative to one period of the radar operation Radar equipment.

Images