# Method of detecting and finding location of radio-frequency radiation

FIELD: radio engineering.

SUBSTANCE: method can be used for detection and finding of on-ground radio-frequency radiation sources. Method is based upon receiving of radio-frequency radiation in N≥3 points being distant from each other is space, transmission of data to central point, determination of R_{n}(x,y) distance from any point of (x,y) space to any n=1,2,...Nth point of receiving of data, measurement of efficient values f voltage of received radio signals U_{n}, transmission of the signals to central point where they are subject to transformation to spatial indeterminate function F(x,y). Availability of radiation and position of source are found from location and value of maximum of the function. Value and position of maximum of spatial indetermination are evaluated in neighborhood of point having coordinates to be equal to weighted average coordinates of reception points with weights being equal to measured efficient values of voltage of received radio signals raised to 4/p power. P parameter is determined while taking dependence of strength of source field into account on distance with standard value being equal to 1 or 2.

EFFECT: improved precision; increased efficiency; stabilization of false alarm level.

4 dwg

The invention relates to electrical engineering and can be used in monitoring systems to detect and determine the location of land-based sources of radio emission, in particular short-wave and ultrashortwave range.

There is a method to detect and locate the source of radio emission, including reception of radio-frequency radiation source in at least three spatially separated points of reception and subsequent transmission of the received radio signals to a Central point, measuring mutual delays between received signals and the calculation of coordinates on the mutual delays equal to zero, their sum on closed through the points of reception circuit (RF Patent No. 2013785, G 01 S 13/00, 1994).

For narrowband signals, having a broad correlation peaks, the method provides unacceptably low probability of detection and the accuracy of the positioning of the sources. The disadvantage of this method is the complexity associated with the need to transfer a large amount of information from spatially separated points of reception at the Central point.

Closest to the proposed to the technical essence and the achieved positive effect is the way to detect and locate the source of radio emission, based on the reception is ignal transmitter receivers installed at known fixed locations, the transmission from the receivers to the point of data about the detection signals, where the coordinates of the receivers receiving signals, determine the location of objects (French Patent No. 2630565, CL G 08 In 7/06, 1988).

In this way the amount of information transmitted is substantially less precision positioning does not depend on the width of the spectrum of radiation, but the ratio of the probability of detection and the accuracy of the positioning is contradictory. To reduce errors in the determination of coordinates it is necessary to increase the detection threshold to a level that ensures the registration of the source signal at only one point of reception. In this case decreases the probability of detection in the region between the points of reception. The lower threshold level trigger detectors multiple points of reception, and error location determination amounts to the removal of the object from the geometric center, formed by averaging the coordinates of collection points. The characteristics of reliability of detection and the accuracy of the positioning unstable, significantly depend on the power of the transmitter of the object, the noise power at the receiving points, fluctuations of the signal levels in the propagation of radio waves. So the m way the main disadvantages of this method are the low accuracy of the positioning and effectiveness of discovery of the source of radio emission.

The objective of the invention is to improve the location accuracy and detection efficiency emitters due to the stabilization of the level of false alarms.

This object is achieved due to the fact that in the known way to detect and locate the source of radio emission, including reception of the radio source N≥3 spatially separated points of reception and subsequent transmission of received radio signals to a Central point, a pre-determined distance R_{n}(x,y) of each point in space with coordinates (x,y) to each n=1, 2, ..., N-th receiving point, each point of the measured effective value of the voltage received radio signals U_{n}that, and transmit to a Central point where transform them in function of the spatial uncertainty of the form, the most of which are compared with the detection threshold and the position of the maximum detect the presence of radiation and the source location, and the reception of radio emission perform with identical receivers, and antennas, Omni-directional in the horizontal plane with the same you who otami raise above the surface of the Earth,
the parameter p determines on the basis of the dependence of the field strength of the source from a distance with a typical value of 1 or 2, and the detection threshold determined on the basis of a given false alarm probability, the number of collection points and their coordinates.

The value and position of the maximum of the function of spatial uncertainty estimate in the neighborhood of the point with coordinates equal to the weighted average of the coordinates of the points of reception with weights equal to the measured effective value of the voltage received radio signals in degrees.

Comparative analysis of the claimed solution with the prototype shows that the proposed method differs from the known presence of, first, new actions on signal: measure the effective value of the voltage of received signals, determine the distance from each point of space to each point of the reception, converts the measured effective value of the voltage in function of spatial uncertainty, the presence of radiation and the coordinates of the source is determined by the maximum of the function of spatial uncertainty and its situation, and secondly, new procedures, equipment and conditions of action: transmit to the Central point of the measured value of the voltage of the received radio signal, the receiving radio will is complementary with identical receivers and identical Omni-directional in the horizontal plane antennas with the same lifting heights above the Earth's surface, the parameter p determines on the basis of the dependence of the field strength of the source from a distance with a typical value of 1 or 2, the detection threshold determined on the basis of a given false alarm probability, the number of collection points and their coordinates, the value and position of the maximum of the function of spatial uncertainty estimate in the neighborhood of the point with coordinates equal to the weighted average of the coordinates of the points of reception with weights equal to the measured effective value of the voltage received radio signals in degrees.

The study of other known technical solutions in the field of equipment specified set of features that distinguish the invention from the prototype, was not identified.

The physical basis of the positive effect is to account for the dependence of the field strength of the source distance, which is inversely proportional to the first power of the distance R=1 in the propagation of radio waves in free space or over the roofs of tall buildings, and second-degree p=2 in the propagation of radio waves near the earth's surface [Grodinsky G.P. Propagation of radio waves. M: Vyshla, 1975, page 71, 200], [Appl. Radio engineering. V.42, M., SCREW, 1991, pages 9-16, 56, 87-88].

Statistical synthesis taking into account the relationship with uncertainty about the spatial is ulozhenie radiation source, the amplitude and phase of the signals at points of reception of the noise variance, the variation of the signal levels in the propagation of radio waves leads to the necessity of processing of a set of effective values of the voltage of received signals in accordance with the proposed order.

The transformation of the sufficient statistic (effective values of voltage signals) in a crucial statistics according to the invention (the transformation of the effective values of the voltage signals in function of the spatial uncertainty) provides accounting information about the signals of all items. The view of the crucial statistics in the form of relationships provides its invariance to the noise variance, which allows to stabilize the level of false alarm, and join in deciding the statistics information about the aggregate of the effective values of the voltage of the received radio signal to increase the probability of correct detection and the accuracy of the measurements.

It is integral based on the signals of all points of reception and the dependence of the field strength of the source distance in accordance with the proposed new activities and the order of their execution allows to increase the accuracy of determining the location of the source of radio emission at stabilizing the level of false alarms.

Figure 1 shows the structural diagram of the system detect the Oia and locate the source of radio emission, implementing the proposed method, figure 2 - an example of a function of spatial uncertainty, figure 3 - arrangement of reception points in the rectangular coordinate system (circles shows the placement of acceptance points, plus - emitters, x - assess the location, square - estimation of location), figure 4 - program research model in the system Mathcad 2000.

The system that implements the proposed method contains spatially separated points of reception 1.1-1.N, each of which includes a receiving antenna 2.1 (2.N)connected to the first input of the measuring receiver 3.1 (3.N), the output connected to the first input data transmission equipment 4.1 (4.N), and the Central point 5, containing the data communications apparatus 6, the equalizing tank 7, a persistent storage device 8, a buffer memory device 9, the Quad 10.1-10.3, multipliers 11.1-11.2, accumulate adders 12.1-12.3, the divider 13, memory unit 14, the determination device the maximum of 15, the threshold element 16.

The first outputs data transmission equipment 4.1 (4.N) each of the collection points 1.1 to 1.N are connected by communication lines to the input data transmission equipment 6 Central point 5. The second output of the data transmission equipment 6 is connected with the second inputs of the data-transmission equipment 4.1 (4.N), the second outputs of which soy is inany with the second input of the measuring receiver 3.1 (3.N). The first output of the data transmission equipment 6 is connected to the input of the averager 7 and the buffer memory device 9, the output of which is connected to the input of the Quad 10.2 and the first input of the multiplier 11.1. The output of the averager 7, through a permanent storage device 8 is connected to the input of the Quad 10.1 and the second input of multiplier 11.1. Output Quad 10.1, accumulating adder 12.1 and the first input of the multiplier 11.2 are connected in series. The output of multiplier 11.1 through accumulating adder 12.2 and squarer 10.3 connected to the first input of the divider 13, the second input of which is connected to the output of the multiplier 11.2. Output Quad 10.2 through accumulating adder 12.3 connected to the second input of the multiplier 11.2. The output of the divider 13 is connected through an operational storage device 14 to the input device, determining maximum of 15 and through its first output to the input of the threshold element 16. The second output of the device determine the maximum 15 is the first system output (the source location), and the output of the threshold element is a second system output (the discovery).

Measuring receivers 3.1-3.N tuned to the frequency of the object are controlled and synchronized by the Manager (second) input signals from the equipment data 6 Central point via the second output data transmission equipment 4.1-4.N points p is Yama, provide measurement of the effective values of the voltage signals. As such can be used for measuring receivers of known composition meter field strength type FSM-8 [Mounds PS, Balls EE Technique of measuring the field strength of radio waves. M.: Radio and communication, 1982, pp. 47-48]. Information in a persistent storage device 8 in the form of values, the inverse of the degree p of the distance from each point in space to each point, entered before beginning operation of the system. The parameter p determines on the basis of the dependence of the field strength of the source from a distance with a typical value of 1 or 2. The threshold value in the element 15 is fixed, is set regardless of the settings of signals and noise, based on an acceptable level of false alarms, the number of collection points and their coordinates. Averager 7 provides averaging of the coordinates of the points of reception with a weight equal to arriving at its input the measured effective value of the voltage received radio signals in degrees. Receivers 3.1-3.N and antenna 2.1-2.N identical, the latter is omnidirectional in the horizontal plane with the same height of the elevation above the Earth's surface. The specified identity and sameness equivalent heights of raising the antennas may be provided pre-calibrated si the topics on the signals from the transmitter with known coordinates and the introduction of appropriate adjustments of the transfer coefficients of the receivers.

The principle of functioning of the system consists in the following. Radio frequency energy source take in points of reception 1.1-1.N using antennas 2.1-2.N, converting the radio signals S_{n}(t), where n=1, 2, ..., N is the number of the point, t is the current time. In the measuring receivers 3.1-3-N measure the effective value of the voltage signal, for example by a quadratic detection

where T is the time constant of integration, is smaller values of the inverse width of the signal spectrum.

The measured voltage are independent random variables, and their average value is proportional to the distance in degree p to the points of reception

where x0,V0 - coordinates of the source of radio emission.

The coefficient R is equal to 1 when the propagation of radio waves in free space or over the roofs of tall buildings and second-degree p=2 in the propagation of radio waves near the earth's surface [Appl. Radio engineering. V.42, M., SCREW, 1991, pages 9-16, 56, 87-88].

Constant μ is determined by a number of factors

where P is the transmitter power, h is the height of elevation of the antenna receiving points, h_{0}- the height of the elevation of the antenna of the object, H is the effective height of the antenna reception centers, λ - wavelength radiation.

Value intercept the options μ when an unknown transmitter power is also unknown. The dispersion of the measured values of the voltage is determined by the signal-to - noise ratio at the point of reception, as well as random changes in the parameter μ wave propagation. Fluctuations in the levels of the signals and, respectively, constants μ in the propagation of UHF radio waves in peri-urban areas according to [the Results of science and technology. Radio engineering. V.42, M., SCREW, 1991, page 56] is 0.5-1.0 dB.

Under the assumption of unknown constants μ and the dispersion of the measured values of voltage statistically optimal treatment involves the maximization of unknown function coordinates of uncertainty

Ambiguity function (4) determines the joint processing of the set of measurement results. Therefore, the measured voltage is passed through channels of communication with data transmission equipment 4.1-4.N, 6 the Central point 5, and the subsequent conversion of the measured voltages is as follows.

For measured values voltage averager 7 determine an initial estimate of the source location as a point with coordinates equal to the weighted average of the coordinates of the points of reception with weights equal to the measured effective value of the voltage received radio signals in degrees :

where X_{n}, Y_{n}- coordinates of the points of reception.

Operation (5) is not a necessary condition for the implementation of the method, but it reduces post-processing the search area of the maximum of the function uncertainty. For systems "cell" type 3 error location (5) within a cell does not exceed 50% of the radius of the cell.

In this implementation provided by way of actions on signals carried out at discrete points in space, which is restricted to within 0.5 of the radius of cells in the neighborhood of the initial estimate of the location of the source. Given the working area of the system pre-quantum, with a quantization step determined by the condition of providing the required accuracy of positioning, determine the distancefrom each point in space with coordinates (x,y) to each n=1, 2, ..., N-th receiving point, and then the values of the inverse of the degree p of the distance from each point in space to each point of receptionThe calculation results remember in the storage device 8.

For each point of the space in the vicinity of the initial estimate of the location of the source coming from the averager 7, read the values back a step and R the distance from each point in space to each point of reception (Q(x,y)), and multiply them in the multiplier 11.1 on the measured voltage. These voltage measured pre-memorize the device 9 at the time of receipt of the totality of the measured voltages and perform the initial evaluation in (7).

The obtained average works in nakaplivaya the adder 12.2 in overall reception points, the average of the square in the Quad 10.3. Simultaneously with the application of Quad 10.1 and accumulating adder 12.1 average over the set of points of reception values, return the degree of p•2 distances, and separately using Quad 10.2 and accumulating adder 12.3 - squares of the measured values of voltage. The average of the squares of the measured values of voltage (output unit 12.3) and average inverse degree R•2 distances (output unit 12.1), Peremohy in the multiplier 11.2. The result of squaring (output unit 10.3) divided by the product of the results of averaging (output unit 11.2), receiving the ambiguity function (4)whose values for all discrete points in space (in the vicinity of the initial evaluation) is recorded in the storage device 14.

The function of uncertainty shown in figure 2. This function has the following properties. In the absence of measurement errors, the maximum of the function is located in a point and the true location of the object, the function value is 1. When there is no signal and the measured voltage values are random and distributed according to Rayleigh (single sample, the product of the time integration in (1) the width of the spectrum of the signal is equal to 1), the position of the maximum random, and the value of the function (4) does not depend on the noise intensity and has a beta distribution

with parameters of the form

where G(·) is the gamma function,

The difference of the function values of uncertainty in the presence of a signal and its absence caused by a change of the type of functional relationship between the received radio frequency signal (voltage measured is inversely proportional to the degree of p and about the same distance respectively), which serves as the basis for detection.

In block 15 determines the maximum value of the crucial statistics among all points in space and the position of the maximum

Since the search area is limited, the value and position of the maximum of the function of spatial uncertainty estimate in the neighborhood of point (5) with coordinates equal to the weighted average of the coordinates of the points of reception with weights equal to the measured effective value of the voltage taken the radio to the extent .

The maximum value of the threshold element 16 is compared with a previously calculated threshold above which decide about the presence of radio emission with delivery on the system output of the detection (output 1 system) and the coordinates of the source(the output of the two systems, from the second output unit 15).

The detection threshold determined on the basis of the set RL false alarm probability, the number of collection points and their coordinates by the formula

where qbeta(•,•,•) - the callback function of the beta density, α, β, defined by the formula (8) with the replacement of its magnitude m(x,y) at its maximum among all points in spaceFor cell type (N=7) figure 3 the value of m=0,628. When this threshold value is equal To=0,98407 when the probability of false alarm RL=10^{-3}.

The effectiveness of the invention is expressed in increasing the location accuracy and detection efficiency emitters due to the stabilization of the level of false alarms. For a quantitative evaluation of the modeling method. Simulated the system of the seven points of reception hosted according to figure 3 (circles shows the placement of acceptance points, plus - emitters, x - score location, quadrati the om -
initial assessment of the location). The program models in the system Mathcad 2000 is shown in figure 4. Adopted the following basic parameters: the cell radius of 5 km, the signal-to-noise (amplitude sinusoidal signal to the average RMS value of the noise) in the peripheral points of reception when placing the object in the center of the system is 5, the fluctuation of the signal level in the propagation of UHF radio waves are consistent with the terms of suburban zone 1 dB, the probability of false alarm 10^{-4}(detection threshold=0,98407). In the simulation found that the method provides an error location about 10% of the cell radius when an object is deleted from the centre 5 km, while the probability of correct detection is about 0.9. The probability of false alarm corresponds to the specified value. Errors are reduced to 2.5% or less, and the detection probability is close to 1 when the object is deleted up to 4 km Relative to the prototype method improved the accuracy of the positioning of the emitters is approximately at guaranteeing the 10^{-4}level of false alarms.

1. The way to detect and locate the source of radio emission, including reception of the radio source N≥3 spatially separated points of reception followed before the whose information received radio signals to a Central point,
wherein the pre-determined distance R_{n}(x,y) of each point in space with coordinates (x,y) to each n=1, 2, ..., N-th receiving point, each point of the measured effective value of the voltage received radio signals U_{n}that, and transmit to a Central point where transform them in function of the spatial uncertainty of the formthe most of which are compared with the detection threshold and the position of the maximum detect the presence of radiation and the source location, and the reception of radio emission perform with identical receivers, and antennas, Omni-directional in the horizontal plane with the same height of the elevation above the Earth's surface, the parameter p determined from the dependence of the field strength of the source from a distance with a typical value of 1 or 2, and the detection threshold determined on the basis of a given false alarm probability, the number of collection points and their coordinates.

2. Method for detection and location of emitters according to claim 1, characterized in that the value and position of the maximum of the function of spatial uncertainty estimate in the neighborhood of the point with coordinates equal to the weighted average of the coordinates of the points of reception with weights equal to the measured effective value of the voltage passed the x signal in degrees .

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