RU2451950C1 - Method for timing pulsed optical location signal - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of timing a pulsed optical location signal to a clock frequency signal, which is synchronised with a probing pulse, involves generating an array of sampled signal values and subsequent timing by comparing with a digital template corresponding to the shape of the probing pulse. The digital template is formed by digitising the probing pulse, which results in formation of base array of sampled values of the probing pulse. Further, the array is interpolated with a smooth function and additional arrays are formed. When timing the optical location signal, the array of its sampled values is compared with each of the additional arrays to obtain estimates which characterise proximity of the base and additional arrays, e.g., in form of total absolute deviation. The index number for which the estimate most characterises proximity of arrays is determined and an adjustment of timing relative the clock frequency pulse coinciding with the beginning of the signal is generated.

EFFECT: high accuracy of determining range to a target.

3 dwg

Description

The invention relates to laser technology, namely to laser ranging.

Known location methods for measuring the distance to distant objects. A known method of measuring the distance to the target [1], including sending to the target a probe laser pulse S _L (tt ₀ ), where t is the current time, t ₀ is the moment of sending, recording the moment of sending t ₀ , receiving the radiation reflected by the target S (tt _D ), recording the time of reception t _D and determining the time interval τ = t _D -t ₀ , which is used to judge the distance D to the target by the formula D = cτ / 2, where c is the speed of light. According to this method, the moments of radiation of the probe pulse and reception of the reflected signal (time reference) are recorded at the moment the signal exceeds a predetermined threshold (edge reference). With this method, the error of the timing is large - of the order of the duration of the signal front [2]. Another disadvantage of the method described in [1] is the low accuracy of determining the time interval τ, since the first generation meters used analog methods for measuring time intervals.

The closest in technical essence to the proposed method is a method for temporarily linking a pulsed radar signal S (tt _D ) to a clock signal synchronized with a probe pulse S _L (t) by counting the number of periods T of the clock frequency from the moment of radiation of the probe pulse, which consists in the formation of the array {S _i } of sample values of the signal S (tt _D ), with the sampling period T, and the subsequent time reference by comparison with the digital template {S _Li } corresponding to the probe pulse [3].

. Значение Р, при котором корреляционная зависимость R(P) принимает максимальное значение, считают соответствующим временному положению принятого сигнала и определяют дальность до цели по формуле D=cPT/2, где c - скорость света. Максимальное количество шагов р=I_max соответствует предельной измеряемой дальности D_max и определяется выражением I_max=2D_max/cT.In the indicated source, the comparison of the arrays {S _Li } and {S _j } is performed by sequentially shifting the array {S _i } by p = 1, 2, ..., I _max steps corresponding to the period T of the clock sequence and determining the correlation coefficient at each step

. The value of P, at which the correlation dependence R (P) takes the maximum value, is considered to correspond to the temporary position of the received signal and the distance to the target is determined by the formula D = cPT / 2, where c is the speed of light. The maximum number of steps p = I _max corresponds to the maximum measured range D _max and is determined by the expression I _max = 2D _max / cT.

With this method of fixing the temporary position of the received signal S (t), represented by an array of its sample values {S _i }, the accuracy of the range measurement is determined by the discreteness of the clock signal T.

, определяют порядковый номер w*, при котором оценка R_w в наибольшей степени характеризует близость массивов {S_1i}_w и {S_2i}, и формируют поправку T_t временной привязки относительно импульса тактовой частоты, совпадающего с началом сигнала S(t), по формуле T_t=ΔN·T, где ΔN=(w*-1)/W, T - период тактовой частоты.The objective of the invention is to increase the accuracy of determining the range. This problem is solved due to the fact that in the known method for temporarily linking a pulsed radar signal S (t), where t is the current time, to a clock signal with a period T synchronized with a probe pulse S _L (t), which consists in forming an array { S _i} of sample S (t) signal values with period sample T, and the subsequent temporary binding by comparison with a digital pattern corresponding to the shape of the probe pulse, the digital pattern is formed by digitizing the S _L (t) probe pulse with a period T, as the result of which form the basic array {S _{Li} 0} sample values of the probe pulse _{S Ti = S L (i ·} T), where i = 1, ..., I - digitizing index; I = t _and / T is the number of samples in the array {S _Li } ₀ ; t _and - pulse duration; after that, the array {S _Li } _{0 is} interpolated with the smooth function S _L * (t), and then the arrays {S _Li } _{w are formed} , where w = 1, 2, ..., W, formed by the formula S _Liw = S _L * (t _iw ), where t _iw = (w-1) T / W + (i-1) T, and when forming the array {S _Li } ₀ , the time t = 0 starts so that for the period from this moment to the top of the probe pulse accounted for not less than two clock period T, the number of additional arrays W is selected from the condition 2≤W≤T / Δ _T, where Δ _T - instrumental error unrecoverable timing, and during the timing with svetolokatsionnogo drove the array of its sample values are compared with each of the array {S _{Li} w} resulting form W ratings _{R w = R ({S 1i} } w, {S 2i}), characterizing proximity array {S _{1i} w} and {S _2i }, for example, in the form of a total absolute deviation

, determine the serial number w * at which the estimate R _w characterizes the closeness of the arrays {S _1i } _w and {S _2i } to the greatest extent, and form a correction T _{t of the} timing relative to the clock pulse coinciding with the beginning of the signal S (t), according to the formula T _t = ΔN · T, where ΔN = (w * -1) / W, T is the period of the clock frequency.

Figure 1 presents the timing diagram of the sensing process, its binding to the clock frequency and the formation of arrays {S _Li } and {S _i }. Figure 2 illustrates the principle of the formation of arrays {S _Li } _{w = 1} and {S _Li } _{w = w} . Figures 3a) and b) show the results of the representation of the function S _L * (t), respectively, by cubic splines and by the least squares method.

At time t = 0, a probe pulse S _L (t) 1, represented by arrays of their sample values {S _Li } _w , is sent in the direction of the target. One of these arrays 2 is shown in FIG. The moment t = 0 of the radiation of the probe pulse 1 is tied to the clock sequence 4 by assigning to the pulse the clock sequence coinciding with the moment t = 0, serial number i = 0. Clock pulses are generated using a highly stable source with a frequency F _T = 1 / T, where T is the repetition period of clock pulses.

After the probe pulse is emitted, the target S (t) 3 pulse is received and digitized with a period of the clock frequency T. The digitization results are stored in the array {S _i } 5, which is then compared with each of the arrays {S _Li } _w , formed as follows .

The base array {S _Li } ₁ 6 is formed by preliminary digitization of the probe signal 1, which consists in the probe radiation of the probe signal 1, its conversion into an electrical signal, the selection and registration of its sample values 6 with a period T, as shown in figa). Following this, the array {S _Li } _{0 is} interpolated with the smooth function S _L * (t). This function 7 is shown in FIG. Having built the function S _L * (t), form W arrays of its sample values 2. Each of these arrays is formed by the formula

;

.

;

.

The formation of a template in the form of W arrays formed by the formula (1), and the implementation of temporal binding of the array {S _i } by alternately comparing it with each of these arrays {S _Li } _w, makes it possible to reduce the discreteness of range measurement by a factor of W, since the results of such comparisons depend on the sequence number of the array {S _Li } _w . Due to this, the measurement accuracy is significantly increased without increasing the clock frequency F _T.

The considered method of template generation allows digitization of the probing signal by standard technical means without increasing the clock frequency and without the need for multiple test soundings with the introduction of the digitization shift t _w = wT / W for each such sounding. This allows us to eliminate the hardware errors of the template formation associated with the error in setting the shift t _w , the ambiguity in reproducing the amplitude and waveform of each test probe, the effects of interference and other factors inherent in analog-to-digital processing. Figure 3 shows examples of interpolation of the probe signal S _L (t) 1, represented by an array of its sample values {S _Li } ₀ 6, using cubic splines (curve 9) and the least-square approximation (curve 11) [4]. The approximation errors are shown on the same graphs on a scale of 50: 1 — curve 10 for spline interpolation and curves 12, 13 — for approximation by polynomials of degrees 7 and 9, respectively. For any of the approximation methods, the proposed method for digitizing arrays {S _Li } _w provides an error of the order of 0.1% or less. Such accuracy is unattainable with direct analog-to-digital conversion of the probe signal.

This method is implemented in an experimental sample of a laser rangefinder with the following characteristics. The clock frequency F _T = 25 MHz (the clock period T = 40 ns, which corresponds to the discreteness in range ΔD = 6 m). The number of arrays is W = 100. The total number of samples in each array {S _Li } _w K = 5. The standard error of the range measurement does not exceed 0.06 m and is determined by the fatal error of the time reference. For known rangefinders, the measurement error is tens of times greater than this value.

The proposed method, in comparison with known methods, provides a much more accurate estimate of the position of the reflected signal by the array of its sample values under the influence of noise, including multiple sounding and data accumulation. The result is a significant increase in the accuracy of determining the range to the target.

Information sources

1. V.A. Volokhatyuk, V.M. Kochetkov, P.P. Krasovsky. Optical location issues. - M.: Soviet Radio, 1971, p.176.

2. E.A. Meleshko. Integrated circuits in nanosecond nuclear electronics. - M .: Atomizdat, 1977, p.77.

3. United States Patent No. 5805468, September 8, 1998, Method and apparatus for determining the light transit time over a measurement path arranged between a measuring apparatus and a reflecting object. - The prototype.

4. I.N. Bronstein, K.A. Semendyaev. A reference book in mathematics for engineers and students of technical colleges. - M.: Science, 1986.

Claims (1)

A method for temporarily referencing a pulsed radar signal S (t), where t is the current time, to a clock signal with a period T synchronized with a probe pulse S _L (t), which consists in forming an array {S _i } of sample values of the signal S (t) with a sampling period T and subsequent timing by comparison with a digital template corresponding to the shape of the probe pulse, characterized in that the digital template is formed by digitizing the probe pulse S _L (t) with a period T, resulting in a base array {S _Li } ₀ sample values of the probe pulse S _Ti = S _L (i · T), where i = 1, ..., I is the index of digitization; I = t _and / T is the number of samples in the array {S _Li } ₀ ; t _and - pulse duration; after that, the array {S _Li } _{0 is} interpolated with the smooth function S _L * (t), and then the arrays {S _Li } _{w are formed} , where w = 1, 2, ..., W, formed by the formula S _Liw = S _L * (t _iw ), where t _iw = (w-1) T / W + (i-1) T, and when forming the array {S _Li } ₀ , the time t = 0 starts so that for the period from this moment to the top of the probe pulse there were at least two periods T of the clock frequency, the number W of additional arrays was chosen from the condition 2≤W≤T / Δ _T , where Δ _T is the fatal error of the time reference, and during the time reference of the radar with The ignal array of its sample values is compared with each of the arrays {S _Li } _w , as a result of which W estimates are formed R _w = R ({S _1i } _w , {S _2i }) characterizing the proximity of the arrays {S _1i ) _w and {S _2i }, for example, in the form of a total absolute deviation

, determine the serial number w *, in which the estimate R _w characterizes the closest proximity of the arrays {S _1i } _w and {S _2i }, and form the correction T _{t of the} timing relative to the clock pulse coinciding with the beginning of the signal S (t), according to the formula T _t = ΔN · T, where ΔN = (w * -1) / W, T is the clock frequency period.

Images