JP2012185050A - Distance and speed measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance and speed measuring device using a spread spectrum system for highly accurately measuring distance and speed.SOLUTION: A modulation code acquired by calculating the logical sum of a PN code and a periodical code is used as a spread code that conducts intensity modulation of irradiation light. The period of the periodical code is set as 6 times the pulse width or above. Such a modulation code has a sharp peak in autocorrelation function thereof enabling accurate calculation of distance up to a target object. In addition, in sampling of a beat signal of local light and reflected light, as the signal strength does not become 0 at the timing of code 1 in the periodical code, the beat signal can be highly accurately calculated so that the speed of the target object can be also highly accurately measured.

Description

  The present invention relates to a distance-velocity measuring apparatus that simultaneously measures the distance and speed of a target by irradiating the target with light. In particular, the present invention relates to a spread spectrum that modulates and irradiates light using a spread code It depends on the method.

  A method of measuring the distance to a target by irradiating the target with light, receiving the reflected light from the target, and measuring the time from light emission to light reception is widely known. In this method, the measurement accuracy decreases due to scattering and the like, and it is impossible to measure to a long distance. As a method for solving this, a distance measurement method using a spread spectrum method is known (Patent Document 1). The spread spectrum system modulates light with a spreading code such as a PN code and irradiates the target, demodulates the spreading code from the received reflected light, takes a cross-correlation between the modulated spreading code and the demodulated spreading code, The distance from the position of the correlation peak to the target is measured. Japanese Patent Application Laid-Open No. 2004-228561 employs a method (direct modulation method) in which an output is directly modulated with a spread code by a drive circuit.

  Further, Patent Document 2 divides laser light into transmission light and local light, modulates the transmission light with a pseudo-random modulation signal, irradiates the target with the transmission light, and receives the reflected light. It describes that a beat signal of light and local light is generated and the distance and speed of a target are measured by analyzing the signal intensity and frequency of the correlation signal between the beat signal and the pseudo-random modulation signal.

JP 2002-368720 A JP 2000-338243 A

  When the distance and speed of the target are to be measured simultaneously in the spread spectrum method, when the beat signal is sampled for calculating the Doppler frequency, the light modulated by the spread code is irradiated. There was a possibility of sampling, and the speed could not be measured with high accuracy.

  Therefore, an object of the present invention is to realize an apparatus for measuring both distance and speed with high accuracy in a distance speed measurement apparatus that measures distance and speed simultaneously by a spread spectrum method.

  1st invention modulates light with a spreading code, irradiates the target, receives the reflected light from the target, and measures the distance to the target and the speed of the spread spectrum method for measuring the speed of the target In the measuring apparatus, a first spreading code generating means for generating a first spreading code in synchronization with a clock having a fixed period, and a periodic code having a period longer than 1 bit length of the first spreading code in synchronization with the clock. A periodic code generating means for generating; a second spreading code generating means for generating a second spreading code by taking the logical sum of the first spreading code and the periodic code; a light source for outputting the irradiation light; Transmitting means for modulating with a spreading code and irradiating the target, first receiving means for receiving the reflected light reflected by the target and generating a reception signal, and mixing the reflected light and irradiated light for reception Second receiving means for generating a beat signal; The distance to the target is measured by calculating the correlation function between the signal and the second spreading code generated by the second spreading code generation means, and the beat signal is sampled at the timing of the period code of 1 and Fourier transformed. And a distance speed calculation unit that measures a speed of a target by calculating a Doppler frequency that is a frequency of a beat signal.

  The second invention modulates light with a spread code to irradiate the target, receives the reflected light from the target, and measures the distance to the target and the speed of the target using the spread spectrum method. In the measuring apparatus, a first spreading code generating means for generating a first spreading code in synchronization with a clock having a fixed period, and a periodic code having a period longer than 1 bit length of the first spreading code in synchronization with the clock. A cyclic code generating means for generating, a second spreading code generating means for generating a second spreading code by taking the logical sum of the first spreading code and the periodic code, a light source, and a code of 0 according to the second spreading code. When the output is a first value b1, and when the code is 1, the light source is driven so that the output is a second value b2 that is larger than the first value b1, and modulated by the second spreading code. Generates irradiation light and sends the irradiation light to the target. Means, first receiving means for receiving the reflected light reflected by the target and generating a received signal, second receiving means for receiving the mixed reflected light and irradiated light and generating a beat signal, The distance to the target is measured by calculating the correlation function between the received signal and the second spreading code generated by the second spreading code generation means, and the beat signal is sampled at the timing of the period code of 1 and Fourier transformed. And a distance speed calculation unit that measures a speed of the target by calculating a Doppler frequency that is a frequency of a beat signal.

  In the calculation of the target distance in the first and second inventions, the correlation function between the received signal and the second spreading code is not directly calculated, but the second spreading code is decoded from the received signal and the decoded second A correlation function between the spread code and the second spread code generated by the second spread code generation means may be calculated.

  In a third aspect based on the second aspect, the distance / velocity calculation unit calculates the signal intensity in the interference time zone when the sign of the reflected light is 1 and the sign of the irradiated light is 0 out of the output of the beat signal. This is a distance / velocity measuring apparatus characterized by correcting by multiplying / b1.

  According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the beat signal is sampled twice or more at different sampling timings.

  According to a fifth aspect of the present invention, in the third aspect of the invention, the beat signal sampling is performed twice, at a timing delayed by π / 2 and a timing delayed by 3π / 2 from the clock phase. .

  A sixth aspect of the present invention is the distance velocity measuring apparatus according to any one of the first to fifth aspects of the present invention, wherein the period of the periodic code is 6 times or more the code pulse width.

  In a seventh aspect based on the first to sixth aspects, the period of the periodic code is set to λ / (4V) or less, where V is the maximum velocity of the target to be measured and λ is the wavelength of the light source. This is a characteristic distance velocity measuring device.

  According to the first and second inventions, when the beat signal is sampled, the signal intensity does not become zero at the timing of the code 1 of the periodic code, so that the speed of the target can be measured with high accuracy. In addition, since the period of the periodic pulse signal is longer than the 1-bit length of the first spreading code, the autocorrelation peak of the second spreading code is high, and accuracy may be deteriorated when measuring the distance of the target. Absent.

  Further, according to the third invention, the speed of the target can be measured with higher accuracy.

  Further, according to the fourth and fifth inventions, at least one sampling can be prevented from entering the rising edge or falling edge of the signal, so that the speed can be measured with higher accuracy.

  Further, according to the sixth and seventh inventions, the peak of the autocorrelation function of the second spreading code becomes sharper, so that the accuracy of distance measurement can be further improved.

The figure which showed the structure of the distance speed measuring apparatus of Example 1. FIG. The figure explaining the structure of a modulation code. The figure which showed the relationship between the autocorrelation function of a modulation code, and the period T of a period code. The figure which showed the waveform of the beat signal. The figure which showed the structure of the distance speed measuring apparatus of Example 2. FIG. The figure which showed the waveform of the beat signal. The figure which showed the result of having calculated the Doppler frequency by simulation. The figure which showed the result of having calculated the Doppler frequency by simulation. The figure which showed the relationship between a clock phase and a received signal. The figure which showed the relationship between a clock phase and a received signal. The figure which showed the relationship between a clock phase and a received signal. The figure which showed the relationship between a clock phase and a received signal.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating the configuration of the distance velocity measuring apparatus according to the first embodiment. The distance velocity measuring apparatus according to the first embodiment includes a laser 10, an intensity modulator 11, a code generation circuit 12, photodiodes 13A and 13B, a distance velocity calculation unit 14, and splitters 15 and 16. Yes.

  The laser 10 is a narrow-band laser light source that emits continuous light, and its center wavelength is, for example, 1500 nm. The light output from the laser 10 is divided by the splitter 15, one of which is used as irradiation light for irradiating the target and the other is used as local light for generating a beat signal. Local light is input to the photodiode 13A.

  The code generation circuit 12 generates a PN code (first spreading code in the present invention) and a periodic code in synchronization with a clock having a fixed period τ, and takes a logical sum of the PN code and the periodic code to generate a modulation code (the present invention). 2) (see FIG. 2). The periodic code is a periodic pulse having a period T and a pulse width τ. The period T is an integer multiple of the pulse width τ. The PN code is a code such as an M series or a Gold series having a pulse width (1 bit length) τ.

  The intensity modulator 11 transmits the irradiation light output from the laser 10 almost through the irradiation hole with the code 1 by the modulation code generated by the code generation circuit 12, and intensity-modulates the light intensity to 0 with the code 0. The modulated irradiation light is irradiated to the target through the lens 17.

  FIG. 3 is a diagram showing the relationship between the autocorrelation function of the modulation code and the period T of the periodic code. It can be seen that the peak of the autocorrelation function becomes sharper as the period T increases. In particular, when the period T is 6τ or more, the peak of the autocorrelation function is sufficiently sharp, and distance measurement can be performed with high accuracy.

  The reflected light that is irradiated and reflected by the target is received through the lens 18 and divided by the splitter 16, one of which is input to the photodiode 13B, and the other is mixed with the local light and input to the photodiode 13A. In the photodiode 13 </ b> B, the reflected light is converted into a received signal that is an electrical signal, and the received signal is input to the distance / speed calculator 14. In the photodiode 13 </ b> A, the beat signal is converted into a beat signal by mixing the local light and the reflected light, and the beat signal is input to the distance speed calculation unit 14.

  Instead of the photodiodes 13A and 13B, other light receiving elements such as phototransistors may be used. An optical fiber can be used for the optical transmission path from the laser 10 to the lens 17 and the photodiode 13A and the optical transmission path from the lens 18 to the photodiodes 13A and B. Of course, space may be propagated. Further, an optical coupler may be used in place of the splitters 15 and 16.

  The distance / velocity calculation unit 14 calculates the distance of the target as follows using the received signal from the photodiode 13B. The distance speed calculation unit 14 includes a decoder and a correlator, and decodes a modulation code from the received signal. Then, a cross-correlation between the decoded modulation code and the modulation code from the code generation circuit is calculated by a correlator. From the peak position of the cross-correlation function, the time until the irradiated light is reflected by the target and returned can be known, and the distance to the target can be calculated. Here, since the modulation code is a code with a sharp peak of the autocorrelation function as shown in FIG. 3, the distance of the target can be calculated with high accuracy.

  On the other hand, the distance speed calculation unit 14 calculates the frequency of the beat signal by sampling the beat signal from the photodiode 13A and performing FFT, and calculates the speed of the target from the frequency (Doppler frequency). As shown in FIG. 4, the beat signal is a signal in which the signal strength is maintained at the timing of the code 1 of the modulation code and the signal strength is 0 at the timing of the code 0 in the sine wave signal. Here, since the modulation code is a code obtained by ORing the PN code and the periodic code, the signal strength is always held at the timing of the period T that is the code 1 of the periodic code. Therefore, by sampling the beat signal at the timing of the code 1 of the periodic code, it is possible to always sample the state in which the signal strength is maintained while avoiding the timing when the signal strength becomes 0, and the frequency of the beat signal is increased. It can be calculated with accuracy. The period T is preferably λ / (4V) or less, where λ is the wavelength of the irradiation light and V is the maximum velocity of the target. When a spectrum analysis is performed on the droop frequency fd = 2V / λ generated by the velocity V using Fourier analysis, the sampling frequency fs ≧ 2fd = 4V / λ and the cycle T = 1 / fs ≦ 1 / (2fd) = λ / (4V ).

  The beat signal sampling procedure will be described in more detail. First, sampling is performed twice by shifting the timing of the phase difference π / 2 at the period τ. In FIG. 4, the timing is indicated by dotted arrows and straight arrows. The reason for sampling twice is to prevent sampling at the rise and fall timing of the beat signal because the timing at which the reflected light reaches the photodiode 13A is indefinite. If sampling is performed twice, at least one of the two sampling data obtained thereby can avoid the rise and fall of the beat signal. Of course, sampling may be performed twice or more. The timing of the two samplings is, for example, the timing of π / 2 and 3π / 2 of the clock phase. In consideration of the time delay between the local light and the reflected light, the sampling timing may be delayed by the delay time.

  Next, one of the two sets of sampling data is selected and the other is discarded. Referring to the reception time of the reference light at the correlator, it is determined whether the reception time is close to kT + T / 4 or kT + 3T / 4. If it is close to kT + T / 4, sampling is performed at the timing of 3π / 2 delay of the clock. If it is close to kT + 3T / 4, the data sampled at the timing of the π / 2 delay of the clock is held. Here, k is a positive integer and T is the period of the periodic code.

  As shown in FIG. 9, when the reception time of the beat signal (heterodyne signal) is between 0 and π / 2 of the clock phase, there is a possibility that the rise of the beat signal may be entered at the timing of clock rise or π / 2 delay. And cannot be used as sampling time. On the other hand, sampling is possible at the timing of clock rise or 3π / 2 delay. Also, as shown in FIG. 10, when the beat signal reception time is between π / 2 to π of the clock phase, the timing of π / 2 delay or π delay is the same because of the possibility of entering the rise of the beat signal. It cannot be used as the sampling time, and the clock rise cannot be used because spike noise may occur. Therefore, only 3π / 2 delay timing can be used. In addition, as shown in FIG. 11, when the reception time is between π and 3π / 2, the timing of the clock falling or 3π / 2 delay can be used as the sampling time because of the possibility of entering the rising of the beat signal. In addition, the clock rise cannot be used because spike noise may occur. Therefore, only clock π / 2 delay timing can be used. Also, as shown in FIG. 12, when the reception time is 3π / 2 to 2π, the timing of 3π / 2 delay or the clock rise cannot be used as the sampling time because of the possibility of entering the rise of the signal. Therefore, the clock π / 2 delay or the clock rise timing can be used as the sampling timing. 9 to 12, if sampling is performed at two timings of the clock π / 2 delay and 3π / 2 delay, even if there is a phase shift in the reception time, at least one of the two timings is correct. It can be seen that sampling is possible.

  Next, of the sampling data, only the data at the timing of code 1 of the periodic code is left. As a result, the sampling period is converted from τ to T.

  Next, the Doppler frequency fd is calculated by performing FFT on the sampling data whose period is converted to T, and the velocity of the target is calculated from the Doppler frequency fd by λ * fd / 2 (λ is the wavelength of the irradiation light).

  As described above, according to the distance velocity measuring apparatus of the first embodiment, in the spread spectrum distance velocity measuring apparatus, the Doppler frequency can be calculated with high accuracy, and the speed of the target can be measured with high accuracy. Further, since the peak of the autocorrelation function of the modulation code that modulates the irradiation light is sharp, the distance of the target can also be measured with high accuracy.

  The figure shows the configuration of the distance velocity measuring apparatus of the second embodiment. The distance velocity measuring apparatus according to the second embodiment includes a laser 20, a drive circuit 21, a code generation circuit 22, photodiodes 23A and B, a distance velocity calculation unit 24, and splitters 25 and 26. . The code generation circuit 22 is the same as the code generation circuit 12 of the first embodiment, and generates a modulation code by taking a logical sum of a PN code and a periodic code.

  The laser 20 is a narrow-band laser light source that emits continuous light, and the light intensity is controlled by the drive circuit 21. Based on the modulation code from the code generation circuit 22, the drive circuit 21 has the light intensity of the irradiation light output from the laser 20 as the light intensity b 2 for the code 1 and the light intensity b 1 (<b 2 for the code 0). ). Irradiation light output from the laser 20 is divided by a splitter 25, one of which is used as irradiation light for irradiating a target and the other is used as local light for generating a beat signal. The irradiation light is irradiated onto the target through the lens 27, and the local light is input to the photodiode 13A.

  The reflected light irradiated and reflected on the target is received through the lens 28 and divided by the splitter 26. One is input to the photodiode 23B, and the other is mixed with the local light and input to the photodiode 23A. In the photodiode 23 </ b> B, the reflected light is converted into a received signal that is an electrical signal, and the received signal is input to the distance / speed calculator 24. Further, in the photodiode 23 </ b> A, the beat signal is converted into a beat signal by mixing local light and reflected light, and the beat signal is input to the distance speed calculation unit 24.

  The distance / velocity calculation unit 24 calculates the distance of the target using the received signal from the photodiode 23B in the same manner as in the first embodiment. Since the modulation code is a code with a sharp peak of the autocorrelation function as in the first embodiment, the distance of the target can be calculated with high accuracy.

  The distance speed calculation unit 24 calculates the frequency of the beat signal by sampling the beat signal from the photodiode 23A and performing FFT, and calculates the speed of the target from the frequency (Doppler frequency).

  Here, in the case of the first embodiment, the local light is continuous light, but in the second embodiment, the local light is light whose intensity is modulated by a modulation code. Therefore, the waveform of the beat signal of the second embodiment is a waveform that is more distorted from the sine wave than the waveform of the beat signal of the first embodiment, and the measurement accuracy of the frequency of the beat signal is deteriorated. Such waveform collapse is caused by interference between the code 0 of the local light modulation code and the code 1 of the reflected light modulation code, or between the code 1 of the local light modulation code and the modulation code of the reflected light. This is because there is a case of interference with the code 0. Of these two cases, the beat signal is sampled at the timing of code 1 of the modulation code of the reflected light (detailed sampling method will be described later). In this case, the signal intensity is multiplied by b2 / b1. Thus, the frequency of the beat signal can be calculated more accurately by making the waveform closer to a sine wave. FIG. 6 is a diagram showing the waveform of the beat signal subjected to this correction. It can be seen that a waveform close to a sine wave is obtained. This correction is performed after sampling the beat signal described below.

  The beat signal sampling procedure will be described in more detail. The beat signal is sampled twice with a different sampling timing, as in the first embodiment. As shown in FIG. 6, in the beat signal after correction, spike noise may occur at the rising and falling portions of the local light. Therefore, it is necessary to perform sampling to avoid this. Therefore, the sampling timing is performed twice, that is, π / 2 and 3π / 2 of the clock phase. Thereby, it is possible to perform sampling while avoiding spike noise. In consideration of the time delay between the local light and the reflected light, the sampling timing may be delayed by the delay time. That is, sampling may be performed at a timing of (π / 2) + φ and (3π / 2) + φ of the clock phase, where φ is the delay time.

  Next, one of the two sets of sampling data sampled at the timings of π / 2 and 3π / 2 of the clock phase is selected, and the other is discarded. This is selected in the same manner as described in the first embodiment.

  Next, of the sampling data, only the data at the timing of code 1 of the periodic code is left. As a result, the sampling period is converted from τ to T. When the data interferes with the code 0 of the local light modulation code and the code 1 of the reflected light modulation code, and when the data interferes with the code 1 of the local light modulation code and the code 1 of the reflected light modulation code. Data.

  Next, when the sampled data interferes with code 0 of the local light modulation code and code 1 of the reflected light modulation code, code 1 of the local light modulation code and code 1 of the reflected light modulation code, It is determined whether the interference occurs in the case of. In the case of data in the case of interference between the code 0 of the local light modulation code and the code 1 of the reflected light modulation code, correction is performed to increase the signal intensity by b2 / b1. In the case of data in the case of interference between code 1 of the local light modulation code and code 1 of the reflected light modulation code, the signal intensity is maintained without correction.

  Next, the Doppler frequency is calculated by performing FFT on the corrected sampling data, and the speed of the target is calculated from the Doppler frequency.

  FIG. 7 shows the result of the simulation of the Doppler frequency when the speed of the target is 1 m / s, and FIG. 8 shows the Doppler frequency when the speed is 11.11 m / s. The 1-bit length τ is 5 ns, and the period T of the periodic code is 30 ns. In each case, the simulation was performed with no noise and four SNRs of 0 dB, −10 dB, and −20 dB. When the target speed is 1 m / s, there is an error of 0.2485 MHz with respect to the actual Doppler frequency of 1.29 MHz, and with 11.11 m / s, there is an error of 0.15 with respect to the actual Doppler frequency of 14.337 MHz. There was an error of 011 MHz. From this result, it can be seen that the speed of the target can be measured with high accuracy by the distance velocity measuring apparatus of the second embodiment. Moreover, it is guessed that it can measure with high precision, so that the speed of a target object is high. In addition, it can be seen that the speed of the target can be measured without being affected by noise in the range of SNR up to -20 dB.

  As described above, according to the distance-velocity measuring apparatus of the second embodiment, sampling is performed so as to avoid spike noise and the signal intensity is corrected in the spread-spectrum-type distance-velocity measuring apparatus. The speed of the target can be measured with high accuracy. Further, the distance of the target can be measured with high accuracy in the same manner as the distance velocity measuring apparatus of the first embodiment. Since the intensity modulator used in the distance velocity measuring apparatus according to the first embodiment is expensive, the distance velocity measuring apparatus according to the second embodiment that does not use the intensity modulator can be manufactured at a lower cost than the distance velocity measuring apparatus according to the first embodiment. .

  The present invention can be applied to an on-vehicle radar device and the like.

DESCRIPTION OF SYMBOLS 10, 20: Laser 11: Intensity modulator 12, 22: Code generation circuit 13A, B, 23A, B: Photodiode 14, 24: Distance speed calculation part 15, 16, 25, 26: Splitter 21: Drive circuit

Claims (7)

In a distance velocity measuring apparatus by a spread spectrum method that modulates light with a diffusion code and irradiates a target, receives reflected light from the target, and measures the distance to the target, and the velocity of the target,
First spreading code generating means for generating a first spreading code in synchronization with a clock of a fixed period;
Periodic code generating means for generating a periodic code having a period longer than one bit length of the first spreading code in synchronization with the clock;
Second spreading code generating means for generating a second spreading code by taking the logical sum of the first spreading code and the periodic code;
A light source that outputs irradiation light;
Transmitting means for modulating the irradiation light with the second spreading code and irradiating the target;
First receiving means for receiving reflected light reflected by the target and generating a received signal;
A second receiving means for receiving the mixed reflected light and the irradiated light and generating a beat signal;
The distance to the target is measured by calculating a correlation function between the received signal and the second spreading code generated by the second spreading code generation means, and the beat signal is a timing at which the periodic code is 1. A distance speed calculation unit that measures the speed of the target by calculating a Doppler frequency, which is a frequency of the beat signal,
A distance velocity measuring device characterized by comprising: In a distance velocity measuring apparatus by a spread spectrum method that modulates light with a diffusion code and irradiates a target, receives reflected light from the target, and measures the distance to the target, and the velocity of the target,
First spreading code generating means for generating a first spreading code in synchronization with a clock of a fixed period;
Periodic code generating means for generating a periodic code having a period longer than one bit length of the first spreading code in synchronization with the clock;
Second spreading code generating means for generating a second spreading code by taking the logical sum of the first spreading code and the periodic code;
A light source;
According to the second spreading code, when the code is 0, the output is the first value b1, and when the code is 1, the output is the second value b2, which is larger than the first value b1. Driving means for generating irradiation light modulated by the second spreading code and irradiating the target with the irradiation light;
First receiving means for receiving reflected light reflected by the target and generating a received signal;
A second receiving means for receiving the mixed reflected light and the irradiated light and generating a beat signal;
The distance to the target is measured by calculating a correlation function between the received signal and the second spreading code generated by the second spreading code generation means, and the beat signal is a timing at which the periodic code is 1. A distance speed calculation unit that measures the speed of the target by calculating a Doppler frequency, which is a frequency of the beat signal,
A distance velocity measuring device characterized by comprising:   The distance speed calculation unit corrects the signal intensity in the interference time zone when the sign of the reflected light is 1 and the sign of the irradiation light is 0 out of the output of the beat signal by b2 / b1. The distance velocity measuring apparatus according to claim 2.   The distance / speed measuring device according to any one of claims 1 to 3, wherein the beat signal is sampled twice or more at different sampling timings.   4. The distance / velocity measuring apparatus according to claim 3, wherein the beat signal is sampled twice at a timing delayed by π / 2 and a timing delayed by 3π / 2 from a clock phase.   6. The distance-velocity measuring apparatus according to claim 1, wherein a period of the periodic code is 6 times or more a pulse width of the code.   The period of the periodic code is set to λ / (4V) or less, where V is the maximum velocity of the target to be measured and λ is the wavelength of the light source. The distance velocity measuring device described in 1.

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