RU2810710C1 - Method for accumulating light-location signals - Google Patents

Abstract

FIELD: reception of optical signals.

SUBSTANCE: method for accumulating light-location signals, including N cycles of target probing, in each of which the signal reflected by the target is compared with a threshold level and the number M of exceeding the threshold is accumulated, by which the presence of a signal is judged, a series of N soundings is first performed N'(p,t,m) confirming a given probability of reliable measurement for signals exceeding a threshold value, where p is the permissible probability of missing a signal, t is the coefficient determined from the expression Ф(t)=γ /2,γ is the confidence probability, Ф(t) is the Laplace function, m is the specified permissible number of signal omissions in a preliminary series; the number of threshold M exceedances is determined in this series' and, if condition N'-M'≤ m is met, accumulation is stopped and a decision is made about the presence of a signal, whereas the volume of the preliminary series is determined by the formula where m=1, 2, 3….

EFFECT: optimal choice of accumulation mode depending on the nature of the location.

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Description

The invention relates to laser technology, namely to laser ranging, more specifically to the reception of light-location signals.

There is a known method for the incoherent accumulation of pulses when they are repeated many times, for example, to detect received signals during laser or radar probing of remote objects [1-5]. This method consists in performing a series of probing cycles; in each probing cycle, the received signal is compared with an analog threshold (binary quantization is performed), the number of times the analog threshold is exceeded, and a decision is made on the presence of a signal if this number exceeds a given number.

This method does not allow realizing the potential probability of signal detection due to the loss of information during binary quantization of the received signal.

The closest in technical essence to the proposed method is the method of incoherent accumulation of signals, including a series of probing cycles, in each probing cycle the reception of a reflected signal and comparison of the received signal with several analog threshold levels, the accumulation of the sum of excesses of analog threshold levels, by which, after completion of the series, the presence of a signal by comparing the sum of excesses with a threshold number [6].

The fixed storage volume inherent in this method limits its advantages due to excessive measurement time in conditions where this is not necessary, and unjustified consumption of the resource of the emitter and power source.

The objective of the invention is the optimal choice of accumulation mode depending on the nature of the location situation.

This problem is solved due to the fact that in the known method of accumulating light-location signals, including N cycles of target probing, in each of which the signal reflected by the target is compared with a threshold level and the number M of exceeding the threshold is accumulated, by which the presence of a signal is judged, a series of N'(p,t,m) soundings confirming a given probability of reliable measurement for signals exceeding a threshold value, where p is the permissible probability of missing a signal, t is a coefficient determined from the expression Ф(t)=γ/2, γ is confidence probability, Ф(t) - Laplace function, m - a given permissible number of signal omissions in a preliminary series, determine in this series the number of exceedings of the threshold M' and, if the condition N'-M'≤m is met, accumulation is stopped and a decision is made on the presence signal, and the volume of the preliminary series is determined by the formula where m=1, 2, 3…

When conducting a preliminary series, you can alternately assign the values 1, 2, etc. to parameter m, if in the previous series the condition N'-M'≤m is not met.

In fig. Figure 1 shows an example of a signal-noise mixture and two analog thresholds set symmetrically relative to the zero level.

In fig. Figure 2 shows examples of detecting a weak signal N=100, M=7 (Fig. 2a) and a strong signal N'=10, M=10 (Fig. 2b).

In fig. Figure 3 shows a variant of the structure for implementing the method.

The mixture of the received signal and noise (Fig. 1) forms a realization of a random process, which is analyzed by comparison with one or more analog thresholds. In the one shown in FIG. 1 two-level version [6], this implementation is compared with analog thresholds located symmetrically relative to the zero level. If in a given probing cycle in any discrete time the implementation crosses the positive threshold level u+up, then this is recorded by generating and adding the number +1 to the accumulated amount, and if the implementation crosses the negative threshold level u. down, then the number minus 1 is added to the accumulated sum. At the end of a series of N soundings in each discrete, the accumulated sum M is compared with the threshold number M* and, if this number is exceeded, a decision is made about the presence of a signal in this discrete (Fig. 2a) .

A preliminary accumulation series is carried out to identify strong reflected signals. In the presence of such a signal, determined by the accumulation volume N' according to the criterion N'-M'≤m, accumulation is stopped and a decision is made about the presence of a signal,

The volume N of the main series when weak signals are detected is set based on the permissible accumulation time, the expected amplitude of the reflected signals, determined by the nature of the target, the requirements for measurement accuracy and the energy potential of the location system [7, 8].

The volume N' of the preliminary batch is determined as follows.

The relative frequency of unreliable measurements corresponds to the Bernoulli scheme for random alternative events and is subject to a binomial distribution [3].

In this case, the mathematical expectation of the estimate W of the frequency of unreliable measurements m/n in a series of n tests

Dispersion of the estimate of the frequency of unreliable measurements

where p is the expected probability of the event.

Standard deviation of the estimate

When estimating W the probability of missing a signal by calculating the relative frequency of omissions [3] as the ratio of the number m* of omissions and the total volume of the series n, the acceptance quantity m*=m* _pr is determined by the expression

where p is the specified probability of missing; x**** - confidence coefficient.

With a minimally significant value m* _pr = 1 from (4) the minimum volume of the series follows

Where

According to the method of interval estimates [3], the upper limit of the confidence probability for n>>1 is described by the formula

where W=m/n;

t - confidence coefficient determined from the expression: Ф(t)=γ/2:

γ - confidence probability;

Ф(t) - Laplace function.

For W<<1, expression (6) is simplified

where

This technique allows you to set the minimum volume of the preliminary series, sufficient to carry out measurements with a given probability of correct detection D=1-W, that is, in the shortest possible time T'.

Example 1

p=0,l; m=1; t~2 (corresponds to a confidence probability of 0.95) [3, p. 226)].

Minimum volume

That is, if in the trial series there were no omissions or one omission occurred, then the range to the target is considered measured, and accumulation is stopped.

Comment. With the specified parameters of the preliminary series and with the selected optimal [7] threshold values relative to the root-mean-square noise level, the event N'-M'≥m due to noise emissions in the absence of a signal is practically impossible due to the proximity to zero of the probability of such an event.

If more than one omission occurred in the preliminary series, then the series can be continued until condition (8) is met.

Example 2

p=0.1; m=2; t=2.

Example 3

p=0.1; m=16; t=2.

In a similar way, you can continue to gradually increase the preliminary series until the volume N' reaches the maximum volume N'=N.

In fig. Figure 3 shows a diagram of the method. The device that implements it contains a frequency laser emitter 1, a photodetector 2, an amplifier 3, threshold devices 4 and 5, a multi-channel storage device 6 and a decision device 7. At the output of the threshold device 5 there is a counter 8 with a timing circuit 9. The system is synchronized by the control unit 10.

On command from control unit 10, laser 1 is launched, periodically emitting probing pulses towards the target. The signals reflected by the target are received by photodetector 2. A mixture of signal and noise through amplifier 3 is supplied to the inputs of threshold devices 4 and 5. Threshold devices [6, 7] have identical thresholds of different polarities (Fig. 1). When threshold device 4 is triggered, minus 1 is sent to the drive, and when device 5 is triggered, plus 1 is sent. The average value of the accumulated noise is thus equal to zero. The signal has a positive polarity and, when probing is repeated, gradually increases the average value of the accumulated sum, until the accumulated sum exceeds the threshold number in the range channel (sample) in which the signal is located. The number of this sample, corresponding to the delay of the reflected signal, is transmitted to the decision device 7, where the range to the target is calculated. Simultaneously with the start of accumulation, timing circuit 9 is launched, which determines the required accumulation volume N' during the preliminary accumulation time. The counter 8, connected at the output of the threshold device 5 with a positive threshold, registers operations from strong signals and, if during the preliminary accumulation the number of these operations M' differs from the number N' by no more than a given value m, then the decisive device completes the measurement, accumulation stops, and the measured range is output to the solver. If during the preliminary accumulation time the number of omissions m exceeds the permissible value, then the counter 8 outputs a signal to the timing circuit, which increases the preliminary accumulation time according to condition (8), and the accumulation process continues until a measurement result with the specified confidence characteristics is obtained.

The proposed method has the following advantages.

1 This procedure for isolating a signal from a background of noise provides a minimum processing time with given detection characteristics, close to the theoretical limit provided by criterion (8).

2 Reducing the volume of signal accumulation helps preserve the resource of the equipment, primarily the emitter and power source.

3 Reducing processing time to a minimum allows the method to be used not only for single measurements, but also in the frequency mode, for example, when measuring target speed [9].

4 The proposed method for separating a signal from noise is resistant to noise of an explosive nature, for example, to microplasma pulses arising in a photodetector (avalanche photodiode) [10].

5 The method is implemented with the simplest hardware, allowing it to be implemented in miniature equipment operated in a wide range of environmental conditions.

Thus, the solution to the problem is ensured - the optimal choice of accumulation mode depending on the nature of the location situation.

Information sources

1 Ya.D. Shirman, V.N. Golikov. “Fundamentals of the theory of detecting radar signals and measuring their parameters.” Ed. “Soviet Radio”, M., 1963, p. 179.

2 Ya.D. Shirman, V.N. Manjos. Theory and technology of processing radar information against a background of interference. M., “Radio and Communications”, 1981, p. 81-83.

3 V.E. Gmurman. Theory of Probability and Mathematical Statistics. M., “Higher School”, 1977, 479 p.

4 V.G. Vilner. Design of threshold devices with noise threshold stabilization. Optical-mechanical industry, 1984, No. 5, p. 39-41.

5 Patent WO 2005/006016 A1 "Laser rangefinder and method thereof.

6 RF Patent No. 2359226 according to law No. 2007137271 on 10.10.2007. "Method of incoherent accumulation of light-location signals." - Prototype.

7 V.G. Vilner et al. Evaluation of the capabilities of a light-location pulse range meter with accumulation. Photonics, 2007, No. 6, p. 22-27.

8 V.G. Vilner et al. Reliability of pulse laser rangefinder measurements. Photonics, 2013, No. 3, p. 42-60.

9 V.G. Vilner et al. Ways to achieve extreme accuracy of a laser speedometer. World of Measurements, 2010, No. 7, p. 17-21.

10 Filachev A.M., Taubkin I.I., Trishenkov M.A. Solid-state photoelectronics. Physical foundations. M., Fizmatkniga. 2007, p. 345.

Claims (2)

1. A method for accumulating light-location signals, including N cycles of target probing, in each of which a comparison is made of the signal reflected by the target with a threshold level and accumulation of the number M of exceeding the threshold by which the presence of a signal is judged, characterized in that a series of N'(p ,t,m) soundings confirming a given probability of reliable measurement for signals exceeding a threshold value, where p is the permissible probability of missing a signal, t is the coefficient determined from the expression Ф(t)=γ/2, γ is the confidence probability, Ф( t) is the Laplace function, m is the specified permissible number of signal omissions in the preliminary series, the number of exceedances of the threshold M' is determined in this series and, if the condition N'-M'≤m is met, accumulation is stopped and a decision is made on the presence of a signal, and, the volume of the preliminary series is determined by the formula where m=1, 2, 3… 2. The method according to claim 1, characterized in that when conducting a preliminary series, the parameter m is alternately assigned the values 1, 2, etc., if in the previous series the condition N'-M'≤m is not met.

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