RU2621329C1 - Method of radio signal imitation - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: result is achieved by providing imitation in real time of the signal reflected from spatially-distributed radiophysical scene, which is represented by fragments of the earth's surface with different roughness degree, and coordinates and motion parameters of electronic system carrier are set, boundaries of interaction area of radio emission with the area of the scattering surface are defined, the surface is approximated by basic platforms-facets, characteristic size, the parameters of roughness and electrical properties of which are determined on the basis of required accuracy of radiosignal synthesis and properties of the faceted polygon model, consisting of terrain layers, natural covers and artificial objects, and then the facets are chosen, simultaneously visible from the position of radiotechnical system antenna, wherein the antenna pattern of the radio system is in the form of a ray set inside space whose volume is determined by the form of the main and side lobes of antenna pattern; antenna pattern is divided into rays with the even pitch in angular deviations from the central ray, coinciding with the direction of antenna pattern axis, the amplitude of each ray is determined by the coefficient of antenna directivity pattern in a given direction, the number of rays is determined based on the required accuracy of radiosignal synthesis, each ray of ray set of antenna directivity pattern is put in corresponding elementary area on the facets of the faceted polygon model, with the subsequent calculation of ray incidence angle and effective specific scattering surface for each elementary area, and, to find the vector sum of complex dispersion coefficients, complex dispersion coefficients are calculated, in accordance with that selected and ranked in ascending order of quantized propagation delays of their partial signals elementary areas are sorted in groups of simultaneously irradiated elementary areas for each of formed group of elementary areas with consideration of delays of the partial signals, the Doppler frequency offsets, attenuations, forms of main and side lobes of antenna pattern.

EFFECT: Improve accuracy of imitation.

Description

The invention relates to the field of radar technology and can be used in a semi-natural simulation of the propagation of radio waves in the air-to-surface channel, taking into account reflections from the surface by providing a real-time simulation of the radio signal reflected from a spatially distributed radiophysical scene, which are fragments of the earth's surface with different the degree of roughness (relief, water surfaces, vegetation, artificial objects, etc.).

The difficulty in simulating a radio signal reflected from the earth’s surface that is adequate to the real one for the areas of radar and radio navigation lies in the fact that the desired signal is a superposition of the set of partial echo signals of the secondary emissions of the earth’s surface and various artificial objects, which, from the point of view of the processes of electromagnetic interaction with them fields, three-dimensional dynamic radiophysical scene.

To adequately simulate a radio signal reflected from the earth's surface, it is necessary to develop a method for generating a secondary multipath radiation signal in complex dynamic three-dimensional radiophysical scenes with the required resolution parameters, in real time, invariant to the parameters of the emitted radio signals, taking into account the technical characteristics of the radio systems (RTS) and the flight conditions of the RTS carrier. Moreover, this method should generate radio signals taking into account weather conditions, shading zones, reflected from various surface types (concrete, asphalt, various soil, grass cover, forests, ponds, snow, ice, artificial objects, etc.) located on the background of the selected relief of the earth's surface.

Known radio signal simulator [1], which allows you to simulate a complex radio environment and set a deterministic or randomly determined number of rays, values for the delays of Doppler frequency shifts, fading. However, this device does not allow the formation of radio signals when simulating movements along real routes in three-dimensional models of real conditions and conditions.

A known radio signal simulator [2], in which increasing the degree of adequacy of simulated radar signals reflected from the earth's surface is achieved by introducing reflection coefficients depending on the angle of incidence for each type of surface. The disadvantage of this method is the finite number of prepared terrain fragments and, as a result, the impossibility of physically generating an adequate radar signal reflected from a selected area of the earth’s surface in the simulation mode of an arbitrary flight of an RTS carrier.

As a prototype, a method for simulating a radio signal reflected from a spatially distributed radiophysical scene in real time was chosen [3].

This method of simulating a radar signal in real time is based on tracking the RTS antenna at the central point of the scan area [4]. As a result of this, the change in the impulse response of the scattering surface during the movement of the RTS carrier during the accumulation of the reflected signal at one angular position consists in changing the average propagation delay due to the average path length from the antenna to the group of simultaneously irradiated facets and back and Doppler frequency shifts of the signals reflected from the facets.

The source data for solving the task in the prototype are information about the required resolution parameters, the parameters of the movement of the RTS carrier, the position of the RTS antennas, as well as the facet model of the polygon, tied to geographical coordinates.

In the prototype [3] the formation of the reflected radar signal was provided by the sequence of the following actions.

Create a facet model of a test site with the required discretization parameters, consisting of relief layers and natural covers.

Set the flight path of the RTS carrier with the points of the beginning and end of the RTS.

The boundaries of the area of interaction of the radiation pattern of the antenna of the RTS with the underlying surface (facet model of the test site) are determined for one angular position according to the coordinates of the location of the carrier of the RTS and the width of the RTS of the RTS.

Create an array of facets that are significant for the subsequent formation of the reflected radio signal. It was believed that the facet does not contribute to the resulting echo when one of the following conditions is met:

- the angle of incidence of the irradiating wave exceeds 90 °;

- the facet is in the shadow area of another facet;

- the level of the bottom line of the RTS in the facet direction is less than the threshold value.

They check the coordinates of each facet for observing the shading conditions between them in accordance with the principles of geometric optics, namely, the direct propagation of radiation.

The angle of incidence of the probing radio signal on the facet and the specific effective dispersion surface (EPR) for each significant facet are calculated.

The area of interaction between the DN and the surface is divided into a sequence of groups of simultaneously irradiated facets in accordance with a given sorting principle.

For each group, taking into account delays of the partial signals of the facets, their Doppler frequency shifts, attenuations, the complex dissipation coefficients of the facets are calculated, their vector sum is found, and the inverse Fourier transform of the sums obtained is calculated.

A convolution of the probing signal is performed with a sequence of readings of the impulse characteristics of the groups of simultaneously irradiated facets for the entire area of interaction between the beams and the underlying surface.

The disadvantage of this method [3] is the lack of consideration of the shape of the radiation pattern of the RTS when simulating in real time a radio signal reflected from a spatially distributed radiophysical scene.

Failure to take into account the shape of the main and side lobes of the RTS radiation pattern reduces the accuracy of real-time simulation of a radio signal reflected from a spatially distributed radiophysical scene.

The technical result of the invention is to increase the accuracy of real-time simulation of a radio signal reflected from a spatially distributed radiophysical scene by taking into account the shape of the main and side lobes of the radiation pattern of the RTS.

The technical result is achieved by the fact that in a method of simulating a radio signal reflected from a spatially distributed radiophysical scene in real time, which consists in setting the coordinates of the location and motion parameters of the carrier of the radio system, determining the boundaries of the region of interaction of radio emission with a portion of the scattering surface, which is approximated by elementary areas facets, characteristic dimensions, roughness parameters and electrical properties of which are determined on the basis of the required the accuracy of the synthesis of the radio signal and the properties of the facet model of the polygon, consisting of relief layers, natural covers and artificial objects, after which the choice of facets simultaneously visible from the position of the antenna of the radio engineering system, taking into account the parameters of the corresponding dispersion model, weather conditions, refraction, shading zones, movement of participants scenes with subsequent calculation of the angle of incidence of the radio beam and the specific effective scattering surface for each facet from the facet model of the polygon, the presentation of the formation mechanism I of the reflected radio signal as a superposition of signals scattered by a set of selected facets - sources of partial echoes of secondary radiation received by the radio system at fixed times, each of which on the antenna of the radio system simultaneously contains reflected partial signals from the group of facets with a difference in propagation delays, not exceeding half the magnitude of the resolution of the radio engineering system, in sorting facets selected and sorted by age Acknowledgment of quantized delays in the propagation of their partial signals over groups of simultaneously irradiated facets for each of the formed groups of facets, taking into account delays in partial signals, Doppler frequency shifts, attenuation, calculation of complex scattering coefficients and finding their vector sum, calculating from which the inverse Fourier transform, constructing as a result, sequences of complex samples of impulse characteristics of groups of facets defining complex samples of impulse character of the radiophysical scene, the formation by convolution of the emitted reflected radio signal of the emitted radio signal from the radio system, the radiation pattern of the radio system is represented as a set of rays inside the space, the volume of which is determined by the shape of the main and side lobes of the radiation pattern of the radio system. The radiation pattern of the radio system is divided into beams with a uniform pitch in angular deviations from the central beam, which coincides with the direction of the axis of the radiation pattern of the radio system. The amplitude value of each beam is determined by the gain of the radiation pattern of the radio system in a given direction, the number of rays is determined based on the required accuracy of the synthesis of the radio signal. Each beam from a set of beams of the radiation pattern of the radio system is associated with an elementary site on the facets of the facet model of the polygon, followed by calculation of the angle of incidence of the beam and the specific effective scattering surface for each elementary site. And to find the vector sum of the complex scattering coefficients, the complex scattering coefficients are calculated, according to which the elementary sites selected and ordered by increasing quantized propagation delays of their partial signals are sorted by groups of simultaneously irradiated elementary areas for each of the formed groups of elementary areas taking into account the delays of partial signals Doppler frequency shifts, attenuations, the shape of the main and side lobes laziness radio system.

A method of simulating a radio signal is implemented as follows.

The initial data for the task are:

information about the required resolution parameters, the parameters of the movement of the RTS carrier, the position and parameters of the RTS antenna, as well as the facet model of the polygon, tied to geographical coordinates.

The preparation of the landfill is carried out using software using altitude matrixes and vector cover layers.

The resulting scattering field is defined as a superposition of the fields created by the individual layers. Using this model allows you to reduce time costs due to the fact that when making changes to the simulated conditions, reprocessing will need to be performed for only one or several layers.

The facets description is based on the following restrictions:

- the dimensions of the facet are selected so that the dimensions of the resolution element in range and azimuth are at least twice the characteristic dimensions of the facet;

- the facet dimensions are much larger than the irradiating wavelength;

- the height of the small irregularities of the facet is less than the length of the irradiating wave;

- the distance of the spatial correlation of facet irregularities, characterizing changes in the height of small and large irregularities on the facet surface, is significantly smaller than the facet size;

- the law of distribution of small and large irregularities over the entire facet surface is accepted as normal;

- the average height of small irregularities coincides with the surface of large, smoothed irregularities, and the average surface of large irregularities is the flat facet surface;

и

, причем

много больше

.- variances of large and small irregularities are equal, respectively,

and

, and

much more

.

The correlation functions of small and large irregularities are isotropic, and the correlation interval of coarse roughness l _{h1 is} much larger than the correlation interval of fine roughness l _h2 .

The radiation pattern of the RTS antenna is represented as a set of rays inside the space, the volume of which is determined by the shape of the main and side lobes of the beam.

They take for a central beam a beam that coincides with the direction of the axis of the beam.

Beams are divided into beams with a uniform step in angular deviations from the central beam, the amplitude value of each beam is determined by the gain of the beams in this direction.

The number of rays is determined based on the required accuracy of the synthesis of the radio signal.

Each beam from the set of MDs is assigned an elementary site on the facets of the facet model of the polygon. Each such beam is determined by the point of radiation and the point of intersection of the beam with the center of a particular elementary site.

It is assumed that each elementary site corresponds to an incident beam with a constant value of the gain of the beam.

The value of the gain of the NAM for each beam from the set of NAM is calculated as follows. From the known coordinates of the central beam of the beam and the current beam from the set of beam, the angle between these rays is calculated. Then, in accordance with a given shape of the pattern, the gain value of the pattern is determined, corresponding to the current angle.

The angle of incidence of the beam and the specific effective scattering surface (EPR) for each elementary site are calculated.

Represent the formation of the reflected signal as the passage of a radio signal through a linear system with distributed parameters. Then the process of obtaining the reflected signal will be ensured by convolution of the radio signal with the impulse response of the scattering surface, calculated for a sequence of fixed points in time in accordance with the initial conditions of the simulation. In this case, the dispersion surface is approximated by a set of facets on facets from the facet model of the polygon, the average level of small irregularities of which coincides with the surface of large (smoothed) irregularities.

The resulting reflected signal is represented as a superposition of reflected signals from individual elementary sites, each of which is equal to the radio signal delayed by the propagation time from the RTS antenna to the elementary site and from the elementary site to the RTS antenna and multiplied by some complex value.

Partial signals from elementary sites sorted by increasing propagation delays are sorted. At the same time, it is believed that at fixed times at the antenna’s location point there are partial signals of a group of elementary platforms at the same time, the difference in propagation delays of which does not exceed half the magnitude of the resolving power of the receiving device provided that the elementary areas are in the visibility range of the RTS antenna (there is no shadowing by one elementary areas others). Therefore, it is accepted that the propagation delays of partial signals of such facets can be considered the same.

представляют в следующем виде:Reflection Expression

present in the following form:

,

,

where N is the number of groups of elementary sites with the same propagation delays;

- излучаемый радиосигнал;

- radiated radio signal;

- комплексные множители;

- complex factors;

t _dn is the signal delay time corresponding to the nth group.

Complex factors h _n coincide with a finite impulse response of length N samples of a discrete filter. Thus, the simulated reflected signal is actually a convolution of the emitted radio signal with a sequence of discrete samples of the impulse response of the scattering surface, which coincides with a sequence of impulse characteristics of the groups of irradiated elementary areas, provided that the distance between adjacent samples of the impulse response of the irradiated surface does not exceed half the resolution receiving device.

представляют в виде геометрической суммы полей, рассеянных отдельными разно наклоненными элементарными площадками

:Scattering field from a group of irradiated elementary sites

represent as a geometric sum of fields scattered by separate differently inclined elementary areas

:

,

,

where N is the number of elementary sites in the group.

Then the total scattering field is expressed as follows:

,

,

,

,

- матрица рассеяния группы элементарных площадок;Where

- scattering matrix of a group of elementary sites;

- вертикальная, горизонтальная плоскости;

- vertical, horizontal plane;

- поле излучаемого радиосигнала;

- field of the emitted radio signal;

- соответствующий элемент матрицы рассеяния элементарной площадки.

- the corresponding element of the scattering matrix of the elementary site.

Each element of this matrix is a complex quantity, depending on:

- properties of the elementary site (taking into account various types of surface),

- the location of the elementary site relative to the radiation point (taking into account the shading zones and Doppler frequency),

- orientation of the elementary site to the direction of irradiation (taking into account the backscatter pattern (DOR) of the surface for a given direction),

- the distance between the elementary site and the receiving point (taking into account weather conditions),

- deviation of the beam incident on this elementary site from the central beam of the beam (gain of the beam of the beam of the RTS for a given direction).

[5] можно записать в следующем виде:Scattering matrix of a single elementary site

[5] can be written as follows:

,

,

where R _0k is the distance from the receiving point to the center of the corresponding elementary site;

S _pk is the area of the elementary site;

σ _ijk are the values of the specific EPR of an individual elementary site.

The scattering properties of an elementary site are determined by the type of scattering surface, therefore, to calculate the values of the specific EPR of each facet, they choose their scattering model, which depends on the dielectric properties of the surface and the characteristic dimensions of small and large irregularities.

, после соответствующих преобразований в элементы матрицы эффективной длины

по формулеElements of the scattering matrix of the group of irradiated elementary sites

, after appropriate transformations into elements of a matrix of effective length

according to the formula

,

,

where R ₀ is the average distance to the group facets, in fact, they represent the frequency characteristics of the group of elementary sites, from which, using the inverse Fourier transform, complex samples of the impulse response of the group of irradiated elementary sites are obtained.

The resulting impulse response of the scattering surface is a sequence of discrete samples in time, which actually coincide with the sequence of impulse characteristics of the groups of irradiated elementary sites.

A convolution of the probing radio signal is performed with a sequence of readings of the impulse characteristics of the groups of simultaneously irradiated elementary sites and an imitation of reflected from a spatially distributed surface is obtained.

Thus, the method of simulating a radio signal has a number of significant advantages over the analogue and prototype, since the accuracy of the simulation is significantly increased by taking into account the shape of the main and side lobes of the bottom of the RTS.

The proposed method allows you to generate radio signals taking into account weather conditions, shading zones, reflected from various types of surfaces (concrete, asphalt, various soil, grass cover, forests, ponds, snow, ice, artificial objects, etc.) located on the background of the selected terrain relief.

The proposed method allows you to generate a radio signal of secondary multipath radiation in complex dynamic three-dimensional radiophysical scenes with the required resolution parameters, in real time, invariant to the parameters of the emitted radio signals.

The proposed method for simulating a radio signal reflected from a spatially distributed dynamic radiophysical scene in real time allows you to expand the technical capabilities of the known virtual reality technologies by physically synthesizing the reflected radio signal. A significant advantage of the proposed method is a unified approach to the implementation of the synthesis of the reflected radio signal for the areas of radio navigation, radar (air-to-surface mode) and radio communications in multipath tasks.

Information sources

1 RF Patent No. 2094815, IPC G01S 7/40. A simulator of radio signal sources // Inventions. Useful models. - 1997 - Publ. 10/27/1997.

2 A.S. No. 474508, IPC G01S 7/40. A device for simulating radar signals reflected from the earth's surface // 1975 - Publ. 06/25/1975. - Bull. Number 23.

3 RF Patent No. 2386143, IPC G01S, Method for simulating a radio signal reflected from a spatially distributed dynamic radiophysical scene in real time // Inventions. Useful models. - 2010. - Publ. 04/10/2010. - Bull. No. 10. (prototype).

4 Yu.V. Kiseleva, A.N. Krenev, Analysis of the influence of the movement of the BRS carrier on the quality of the formation of the frame of the radio image in the mapping mode. Bulletin of the Yaroslavl Anti-Aircraft Missile Institute of Air Defense: A Collection of Scientific Papers / JAZRI Air Defense, Yaroslavl, 2002, Issue 3, p. 14-18.

5 Yu.V. Kiseleva, A.N. Krenev. The study of reflections from the earth's surface by mathematical modeling. Collection of reports of the VII International Scientific and Technical Conference "Radar Navigation Communications". Volume 3, Voronezh, April 24-26, 2001

Claims (1)

A real-time method of simulating a radio signal reflected from a spatially distributed radiophysical scene, which consists in setting the coordinates of the location and motion parameters of the carrier of the radio system, determining the boundaries of the area of interaction of the radio emission with a portion of the scattering surface, which is approximated by elementary facets, facets , the roughness parameters and electrical properties of which are determined based on the required accuracy of the synthesis of the radio signal and properties facet model of the polygon, consisting of relief layers, natural covers and artificial objects, after which facets are selected that are simultaneously visible from the position of the antenna of the radio engineering system, taking into account the parameters of the corresponding dispersion model, weather conditions, refraction, shading zones, movement of scene participants and then calculating the angle the radio beam incidence and the specific effective scattering surface for each facet, from the facet model of the polygon, the mechanism for the formation of the reflected radio signal is presented as a superposition of signals scattered by a set of selected facets - sources of partial echo signals of secondary radiation received by the radio system at fixed times, each of which simultaneously reflects the partial signals from the group of facets on the antenna of the radio system with a propagation delay difference of not more than half the resolution capabilities of the radio system, according to which the propagation delays selected and ordered by increasing quantized delays of their partial signals, the facets are sorted by groups of simultaneously irradiated facets for each of the formed groups of facets, taking into account the delays of partial signals, Doppler frequency shifts, attenuation, complex scattering coefficients are calculated and their vector sum is calculated, from which the inverse Fourier transform is calculated, as a result of which build a sequence of complex samples of the impulse characteristics of the groups of facets that determine the complex samples of the impulse response of the radiophysical prices, by convolving them with a sequence of samples of the emitted radio signal system of the radio signal, a simulated reflected radio signal is generated, characterized in that the antenna pattern of the radio system is represented as a set of rays within the space, the volume of which is determined by the shape of the main and side lobes of the antenna pattern, the antenna pattern is broken rays with a uniform step in angular deviations from the central beam, coinciding with the direction of the grams of antenna directivity, the amplitude value of each beam is determined by the gain of the antenna pattern in this direction, the number of rays is determined based on the required accuracy of the synthesis of the radio signal, each beam from the set of beams of the antenna pattern is assigned an elementary site on the facets of the facet model of the polygon, followed by by calculating the angle of incidence of the beam and the specific effective scattering surface for each elementary site, and to find the vector sum of complex scattering coefficients calculate the complex scattering coefficients, according to which the elementary sites selected and ordered by increasing quantized propagation delays of their partial signals are sorted by groups of simultaneously irradiated elementary sites for each of the formed groups of elementary sites taking into account delays of partial signals, Doppler frequency shifts, attenuation, the shape of the main and side lobes of the antenna pattern.