RU2390724C2 - Method for light-range finding - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method for light-range finding through non-coherent accumulation involves a series of probing cycles in each of which a laser probing pulse is sent to a target. After emission of the probing pulse, time is quantised into samples, the pulse reflected by the target is received and in each time sample the hypothesis on absence or presence of signal is processed through threshold transformation of the received signal and noise mixture. A number corresponding to the hypothesis is formed and the formed numbers are accumulated in form of sums for each time sample. At the end of accumulation, time samples where accumulation during a series of probing cycles the sum exceeds a given number are selected and the distance to the target is determined from these accumulated sums.

EFFECT: increased maximum range and accuracy of measuring range without increasing the required clock frequency and number of independent accumulation channels in order to make a portable device with long range of operation.

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Description

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

A known method of radar range determination [1]. The specified method consists in sending a laser probe pulse to the target, receiving the signal reflected by the target, and determining the time interval between the probe and reflected pulses by which the distance to the target is judged. This method does not allow to provide the required range when using semiconductor lasers, preferred for portable equipment.

The closest in technical essence to the proposed method is a method of radar range determination by the method of incoherent accumulation, including a series of sensing cycles, in each of which a laser probe pulse is sent to the target, after the radiation of the probe pulse, time is quantized to discrete, receive the pulse reflected by the target, generate in each from the time discrete, the hypothesis of the absence or presence of a signal by threshold transformation of the received mixture of signal and noise, the formation corresponds present hypothesis and accumulation of generated numbers as sums for each sample time, the accumulation completion secrete those discrete unit of time where accumulated over a series of cycles sensing sum exceeds a predetermined number, and these accumulated sums are judged on the target range [2].

In this method, the procedure of digital incoherent accumulation [3], which implements the method of statistical testing of hypotheses [4]. The disadvantage of this method is the need for a large amount of high-speed digital recording equipment required for its implementation. So, with a time discrete width of ΔT = 6.667 ns, which corresponds to a range of 1 m, the sampling clock rate should be 1 / ΔТ = 150 MHz, and the number of statistically independent storage channels is K = 2R _max / cΔT, where R _max is the range of measured ranges; c is the speed of light. For example, for the given example at R _max = 5 km K = 5000. In addition, in the described method, the duration of the signal must correspond to the duration of the time samples, which limits the energy of the probing signal, and therefore the maximum measured range.

The objective of the invention is to increase the maximum measured range and accuracy of range measurement without increasing the required clock frequency and the number of independent accumulation channels in order to create portable equipment with a high range.

The problem is solved due to the fact that in the known method of radar range determination by the method of incoherent accumulation, which includes a series of sensing cycles, in each of which a laser probe pulse is sent to the target, after the radiation of the probe pulse, the time is quantized to discrete, the pulse reflected by the target is received, and the each time discrete hypothesis of the absence or presence of a signal by threshold conversion of the received mixture of signal and noise, the formation of the corresponding hypothesis h In the case of accumulation of generated numbers in the form of sums for each time discrete, at the end of the accumulation, those time discrete are selected where the accumulated amount during the series of sensing cycles exceeds the specified number, and the distance to the target is judged from these accumulated sums, in each sounding cycle the pulse is emitted for a duration of several time discrete, at the end of the accumulation, a time discrete is allocated in which the accumulated sum is maximum, the delay T of the signal reflected by the target is determined but the moment of sending the probe pulse as the first initial moment of the array of accumulated sums in the vicinity of the allocated time discrete and from this delay determine the distance to the target R by the formula R = c (T-T _o ) / 2, where c is the speed of light, T _about is the instrumental constant.

The number of time samples in the vicinity of the selected samples to the left and to the right of it can correspond to the duration of the leading and trailing edges of the laser probe pulse. Moreover, the accumulation efficiency, that is, the degree of improvement of the signal-to-noise ratio, is close to the maximum value.

The duration of the time samples is set in the range from 0.1 to 0.5 of the duration of the laser probe pulse at a level of 0.1. With a shorter duration, the discrete requirements for the volume and speed of the equipment increase, and with a greater duration, the advantages of the proposed method are lost.

On figa and 1b are examples of filling the data array after accumulation, respectively, with a signal to noise ratio of 1 and 10.

Figure 2 shows two examples of filling the data array in the absence of a signal.

The analysis of the proposed method for the two-level accumulation mode with the following initial data.

Accumulation volume N = 200 cycles.

The ratio of the signal amplitude to the standard deviation σ of noise from 1 to 200.

The levels of the first and second analog thresholds are respectively + σ and -σ.

The duration of the signal at the base of t _and = 6ΔT.

The duration of the leading edge of the signal t _fr = 2ΔT.

The delay of the reflected signal T _s is determined by the formula of the first initial moment [5], in the general case, with weight coefficients for the values of the accumulated sums

Where

j is the number of time discretes in which the accumulated sum is maximum;

K _(a) is the accumulated amount in the (a) -th discrete;

k _(a) is the weight coefficient of the (a) -th discrete;

m = t _fr / ΔТ is the number of discretes corresponding to the duration of the leading edge of the laser pulse;

t _fr - the duration of the leading edge of the laser pulse;

q = t _and / ΔT is the number of discretes corresponding to the pulse duration;

t _and is the duration of the laser pulse;

p is the correction number characterizing the time point of the signal;

ΔT is the duration of the samples.

In the considered variant, the length of the analyzed array is taken equal to the pulse duration, i.e. 6 discrete discrete weights, discrete weight coefficients k _(a) = 1, correction number p = 3. The duration of the discrete is conventionally taken equal to ΔT = 1. Thus, the evaluation of the pulse delay is carried out in accordance with the algorithm

In the considered example, ΔT = 1 numerically corresponds to a range discrete of 1 m, therefore, the delay estimate T _s ≡ R, where ≡ is the sign of numerical equality, R is the range estimate. The range estimate is formed by the formula R = cT _s / 2, where c is the speed of light.

As follows from figa and 1b, the estimate of the delay of the received signal by the proposed method (shown by the index on the time axis) approximately corresponds to the maximum of the signal and maintains its position in a wide range of amplitudes of the received signal (when the signal to noise ratio is from the threshold to the level of overflow adders in drive channels).

Figure 2 shows examples of filling the drive in the absence of a signal when the sums accumulated in the range discretes do not exceed the threshold value of 20-25. Given that with a signal-to-noise ratio = 1, the maximum accumulated sum is 140, in this case there is a margin of amplitude about 6 times, i.e. the threshold signal-to-noise ratio at the drive input is 0.15. Moreover, as the simulation showed, the root-mean-square error of the delay estimate does not exceed 0.4 discretes at asynchronous start (when the moment of emission of the probe laser pulse is not tied to the sampling clock frequency) and does not exceed 0.25 discretes during synchronous start, when the probe pulse is emitted at the arrival of the next clock pulse. This allows measurements at a lower clock speed compared with known solutions.

Compared with the methods of radar range determination, in which the duration of the probe pulse corresponds to the duration of the time discrete, the proposed method allows several times to increase the effectively used energy of the probe laser pulse, increasing it due to a significant increase in the pulse duration. In the above example, this allows you to increase the effective signal-to-noise ratio by about two times, due to which the actually measured range will increase by 1.3-1.5 times.

Thus, the proposed method of radar range measurement allows you to increase the maximum measured range and accuracy of range measurement without increasing the required clock frequency and the number of independent storage channels, which allows you to create portable equipment with a high range.

Information sources

1. V.A. Volokhatyuk, V.M. Kochetkov, P.P. Krasovsky "Issues of optical location". Ed. "Soviet Radio", Moscow, 1971, p. 177.

2. Patent WO 2005/006016 A1 "Laser rangefinder and method thereof - prototype.

3. Ya. D. Shirman, VN Manzhos “Theory and technique of processing radar information against the background of interference”. Ed. “Radio and communications”, M., 1981, pp. 81-83.

4. V.E. Gmurman "Probability Theory and Mathematical Statistics." Ed. "Higher School", Moscow, 1977, p. 281.

5. I. N. Bronstein, K. A. Semendyaev, “A Handbook of Mathematics for Engineers and Students of Technical Universities,” Ed. "Science", Moscow, 1986, p. 466.

Claims (3)

1. The method of radar-ranging determination by the method of incoherent accumulation, including a series of sensing cycles, in each of which a laser probe pulse is sent to the target, after the probe pulse is emitted, the time is quantized to discrete, the reflected pulse is received, the hypothesis of absence or the presence of a signal by threshold conversion of the received mixture of signal and noise, the formation of the corresponding number hypothesis and the accumulation of the generated numbers in the form of sums for each time samples, upon completion of accumulation, those time samples are selected where the sum accumulated during the series of sensing cycles exceeds a predetermined number, and the distance to the target is judged by these accumulated sums, characterized in that in each sensing cycle the laser probe pulse is emitted for several time discrete, at the end of accumulation, a time discrete is allocated in which the accumulated sum is maximum, the delay T of the signal reflected by the target relative to the moment of sending the probing impulse is determined lsa as the first initial point array of accumulated sums in the vicinity of the selected discrete unit of time and thus delay determined target range R by the formula R = c (TT _o) / 2, where c - velocity of light; T _about - hardware constant. 2. The method according to claim 1, characterized in that the amount of time discrete in the vicinity of the allocated discrete to the left and right of it corresponds to the duration of the leading and trailing edges of the laser probe pulse. 3. The method according to claim 1, characterized in that the duration of the time samples is set in the range from 0.1 to 0.5 of the duration of the laser probe pulse at a level of 0.1.

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