RU2613369C1 - Method of aircraft navigation using high-precision single-phase direction finder and address-respond packet digital radio link in decameter waves range - Google Patents

Abstract

FIELD: aircraft engineering.

SUBSTANCE: invention relates to aircraft navigation using the passive radar method of determining location of an object, which is a source of electromagnetic radiation, and is intended to build independent and integrated navigation systems of aircraft. High-precision single-phase direction finder is a software-hardware complex equipped with an active phased antenna array, which receives radio signals, performs their synchronous demodulation by a multichannel quadrature receiver, conversion into digital format using a multichannel analogue-to-digital converter and further digital processing of the signals aimed to form a bearing angle using the optimum single-phase method of estimating parameters. One-stage estimation method involves formation of a decision function basing on the conditional density by maximum likelihood and its subsequent optimization; this method eliminates performing intermediate stages, at which sequential assessment of time and phase delays is performed.

EFFECT: technical result is the increase of accuracy of estimating the location of an aircraft owing to the use of a high-precision of the single-phase direction finder, faster navigation support due to the use of an address-respond packet digital radio link and reduced requirements to on-board computer complexes as main computations are performed in the ground equipment.

1 cl, 5 dwg

Description

Technical field

The invention relates to the field of navigation of aircraft using a passive radar method for determining the location of an aircraft based on the reception and digital processing of signals generated by a source of electromagnetic radiation placed on its board. The invention is intended to create autonomous and integrated navigation systems for aircraft and navigation systems, providing operational support for navigation and tracking of aircraft by transmitting measured coordinates to the aircraft. Such navigation systems are most valuable for navigation in sparsely populated and inaccessible areas, equipping them with standard technical systems can be expensive or technically difficult.

The invention is used to solve the technical problem of navigation support of an aircraft, consisting in determining the bearing on it and the coordinates of its location. Achievable technical result of the invention consists in increasing the accuracy of assessing the location of the aircraft, in increasing the speed of navigation support and reducing the requirements for on-board computer systems.

State of the art

The current level of flight safety requirements determines the need for systems that can determine with high accuracy the coordinates of aircraft of military and civil aircraft during their flight along a given route. There are several main ways to provide navigation support, which include inertial navigation systems (ANNs), satellite navigation systems (SNA), long-range navigation systems (NLS), interrogation-response navigation systems (AOS).

In the ANN, the location of an aircraft is determined by analog or digital integration of navigation parameters formed on the basis of inertial sensors, such as values of angular velocity and acceleration [1]. Due to its autonomy, the advantage of this navigation method is its high noise immunity, however, its drawback is the accumulation of errors in integrators over time, which may require periodic correction of the location of the aircraft due to the use of radio navigation methods: SNA or SDN.

In the SNA, the calculation of the navigation parameters of an aircraft is carried out using the signals of several navigation satellites forming a working constellation [2]. The advantages of the SNA-based method are the globality of its application and the high potential accuracy of the estimates obtained, while the disadvantages include low noise immunity, high (according to flight safety requirements) probability of failure: positioning using the SNA may not be possible if the satellite radio visibility zone An antenna of the aircraft will receive an insufficient number of navigation satellites. In practice, such a disadvantage as the low accuracy of estimating the vertical coordinate (height) of an aircraft is often noted, which is especially critical for maneuverable aircraft. It should be noted that they are also characterized by high variability of the visible working constellation of satellites during the flight.

Existing SDNs are based on a rangefinder or differential rangefinder method for determining the location of an aircraft [3]. Systems such as Loran-C and Omega involve the deployment on the ground of a base station system emitting bursts of coherent pulses of a known structure filled with a harmonic signal corresponding to kilometer (long) or myriameter (ultra-long) waves, the required range of which is ensured by signal propagation through surface waves. Signals from several emitting stations are received on board the aircraft, where they are processed, aimed at calculating the phase shifts between pulses of different sequences. Further calculations performed on the phase shifts in a digital computer or special computer, allow us to obtain location estimates with an accuracy of about 400 m in a single measurement.

AISSs are navigation systems, the principle of which is based on the formation of aircraft location estimates by a ground active or passive radar system and the subsequent transfer of the received estimates to the aircraft via a packet digital radio line. The advantage of the AISS is their independence from the conditions for receiving a signal by the on-board equipment and the possibility of generating accurate estimates through the use of computationally-expensive methods, the necessary calculations for which are carried out in a ground-based computer complex, which, unlike an on-board computer, is not subject to strict weight and size limitations by consumed electric power.

Over the past twenty years, completely different ways have been found to improve the performance of navigation systems. So, the patent [4] proposes the use of an integrated approach consisting in the joint use of three methods (ANN, SNA, DLS) for obtaining navigation information, in which the results obtained by one of the methods serve as a rough approximation and are refined by another method; The selection of the coarse measurement method is determined by the current flight situation.

In the patent [5], a method is proposed for improving the accuracy of estimates of navigational parameters by using a reference terrain map compiled in a known manner prior to the movement of aircraft, selecting a measured terrain of a reference map, compiling a current map of measuring parameters of a measured portion of a reference map using radio waves, comparing values of the measured portion of the current and reference maps, the calculation of the signal correction of the trajectory of motion based on the determination of the results of multipath measurements by t it coordinates.

In the patent [6], a similar method is proposed for solving the problem of direction finding of a signal for determining the location of an aircraft, which consists in the fact that the signal of the airborne transmitter is received using antennas that form an annular array located near and parallel to the earth's surface. In the proposed method, the azimuth of the object is determined by the signals received by the lattice antennas by converting the measurements to the angular spectrum by multiplying by complex conjugate antenna patterns and then summing the results of cross-products across the entire set of antennas and determining the square of the sum module. However, the proposed method is not optimal because the averaging does not take into account the signal-to-noise ratio in each measurement channel, which leads to the formation of an ineffective coordinate estimate (i.e., there is another coordinate estimate in the class of unbiased and consistent estimates that has the smallest dispersion) .

Disclosure of invention

The technical task of the invention is to provide the pilot and / or aircraft control system with the exact coordinates of the location of the aircraft.

The result is achieved by evaluating bearings in a ground-based system, consisting of high-precision one-stage direction finders, as well as by generating a location estimate based on bearing estimates in a ground computing center and transmitting the generated coordinates to the aircraft via an address-response packet digital radio line operating in DCMV range.

In FIG. 1 is a structural diagram explaining the implementation of the proposed method. Aircraft (LA) (1) has on its board a radio emission source (IRI) (2), which can be either a source specially established for direction finding that generates a signal with specified spectral and correlation characteristics, or a standard radio emission source, for example, such as an aircraft-to-ground radio transmitter. Reception centers equipped with one-stage direction finders (OP) are located on the earth’s surface (3), the structure of which includes an antenna system based on an active phased antenna array, a digital receiver, and a digital signal processing unit based on a universal digital computer. Reception points are connected by ground or radio-relay communication lines (LS) (4) with a central processing point (CPO) (5), which can be located both locally and combined with one of the reception points equipped with OP (3). In the CPO, the formation of estimates of the location of the aircraft is based on the combination of the estimates obtained by individual OPs. The generated location estimates are transmitted over the communication line to the transmitter of the address-response radio line (PrdAORL) (6), which transmits in the DKMV band a radio signal containing useful location information addressed to the receiver (the aircraft whose location is estimated) in the form of digital data packets.

The source of radio emission (IRI) (2) generates an electromagnetic signal, for the description of which a model of a Gaussian radio signal is used:

- несущая частота,

- частоты учитываемых составляющих в спектре комплексной огибающей, a_k и b_k - коэффициенты, являющиеся гауссовскими попарно некоррелированными случайными величинами. Такой сигнал соответствует случаю стохастической модели случайного процесса, лежащего в формировании радиосигнала. Применение для построения алгоритма модели (1) способно обеспечить работу алгоритма пеленгации в условиях наименьшей доступной априорной информации.where K is the number of components taken into account,

- carrier frequency

are the frequencies of the components taken into account in the spectrum of the complex envelope, a _k and b _k are the coefficients, which are Gaussian pairwise uncorrelated random variables. Such a signal corresponds to the case of a stochastic model of a random process lying in the formation of a radio signal. The use of model (1) for constructing the algorithm is capable of ensuring the operation of the direction finding algorithm under the conditions of the least available a priori information.

The emitted radio signal in the form of a plane electromagnetic wave is received by a one-stage direction finder (OP), implemented according to the principle of a narrow-base subsystem (UP) [8]. According to this principle, the OP is a technically unified receiving station that implements multichannel reception of an electromagnetic wave through separate receiving points (TP), the placement of which in the structure of the antenna system of the UE meets the following two conditions:

1. The distance between the TP of the same UE is significantly less than the distance between the UE and IRI. This condition provides a flat wavefront at the receiving points and the same level of attenuation of signals received by different TPs.

соответствующей центральной или несущей частоте принимаемого радиосигнала

а под с понимается скорость распространения сигнала от ИРИ до УП, принимаемая в радиолокации равной скорости света.2. The distance between the TP of the same UE does not exceed half the wavelength

corresponding center or carrier frequency of the received radio signal

and c means the propagation speed of the signal from the IRI to the UE, taken in radar equal to the speed of light.

The structural diagram of the station, implemented on the basis of the UE principle, is presented in FIG. 2. So, the UE consists of an antenna-feeder system (AFS) (21), a block of low-noise amplifiers (LNA) (22), a multi-channel synchronous quadrature receiver (MSC) (23), a block of analog-to-digital converters (ADC) (24) and a digital computer (DEC) (25) connected by a communication line (LAN) (5) to the CPO. The LNA block carries out preliminary amplification of the signals before it is transmitted to the MSCP input. Blocks MSCP, ADC are program-controlled, the mode of operation of which is set by the control signals of the computer. When receiving, electromagnetic waves are transformed by the antenna system into an analog electric radio signal, which is fed to the LNA input, from which the radio signal is fed to the MSCP input. As a result of synchronous detection, an analog video signal is generated at the output of the MSCP, which is supplied in the form of pairs of quadrature to the ADC input, at the output of which a digital signal is generated in the form of digital samples.

A computer is implemented on the basis of a high-performance multiprocessor workstation equipped with at least two multi-core universal Intel Xeon processors with an operating frequency of at least 1.8 GHz and a random access memory (RAM) of at least 8 GB. The computer in the structure of the OP performs all the necessary functions for managing the operation of the OP units by setting the required functional modes and operation parameters. In addition, the PCs separate OP controls the transmission of data over communication lines (4), connecting the OP with the CPO, including compression and, if necessary, encryption of data before transmission over the communication line.

A distinctive feature of the proposed navigation method is that the computer system as part of the CPO estimates the coordinates of the aircraft by combining the estimates of high-precision direction finders, forming estimates of the bearing on the IRI, located on board the aircraft, using a one-stage method, the content of which is as follows.

Let the IRI be located at a point in space whose coordinates are given by the vector r = (X, Y, Z) ^T. Then the signal received by the m-th TP, consisting in the structure of the n-th OP, is the sum of the delayed and weighted useful signal and additive noise:

- время прохождения сигнала от ИРИ до условного фазового центра (УФЦ) n-й УП;

- координаты УФЦ n-го ОП; χ_n - ошибка привязки сигнала по времени;

- время прохождения сигнала от УФЦ до ОП (от ОП до УФЦ, если ς_nm<0);

- координаты m-й ТП n-го ОП;

; α_n, β_n - азимут и угол места луча, направленного из n-го ОП на ИРИ; с - скорость распространения сигнала.where a _n is the amplitude of the signal at the inputs of the TP of the n-th OP;

- the signal transit time from the IRI to the conditional phase center (UFC) of the nth unitary enterprise;

- UFC coordinates of the n-th OP; χ _n is the error of the signal binding in time;

- signal propagation time from UFZ to OP (from OP to UFZ, if ς _nm <0);

- coordinates of the m-th TP of the n-th OP;

; α _n , β _n - azimuth and elevation angle of the beam directed from the n-th OP to IRI; c - signal propagation speed.

Digital samples of all received signals are transmitted via high-speed communication lines to a data center located in the structure of the CPU. Digital signals received by individual TPs of each OP are considered together and form a multidimensional digital signal.

Coordinates are estimated using the goniometric estimation method, in which the entire distributed system is considered as a passive radar system, consisting of narrow-base subsystems (PSUP). The essence of the estimation method of such a system is to calculate the estimate of the difference in the arrival of signals based on the correlation reception by the maximum likelihood method, which is presented in two papers for two reception points [7].

The development of the theoretical foundations of the correlation method for the possibility of its application to the solution of the IRI location problem based on direction finders is described in [8]. Based on the above approach, the proposed method performs the construction of the objective function relative to the vector of estimated parameters r, containing three coordinates of the radiation source, the expression of which in a compact form can be written in the form:

- несущая частота,

- полоса анализа сигнала. Через

обозначены фазовые задержки m-й ТП в n-м ОП, зависимости которых

от r выражаются следующим образом:where Re denotes the operation of finding the real part of the complex number, N is the number of used OPs, M _n is the number of receiving points (antenna elements) in each OP (can be either the same or different number of TPs),

- carrier frequency

- signal analysis band. Across

the phase delays of the m-th TP in the n-th OP are indicated, the dependences of which

from r are expressed as follows:

where c is the speed of light, r _n is the radius vector of the center of the n-th OP, and r _nm is the radius of the vector of the m-th receiving point, which is part of the n-th OP.

обозначают нормализованные спектры в m-й точке приема n-го ОП:Expressions in the formula (1)

denote the normalized spectra at the mth point of reception of the n-th OP:

измеренный спектр,

- спектральная плотность мощности, а

- отношение сигнал-шум.Where

measured spectrum

- spectral power density, and

- signal to noise ratio.

вычисляются с использованием алгоритма быстрого преобразования Фурье:Complex spectra

are calculated using the fast Fourier transform algorithm:

где

- период дискретизации; x_nm[l] - отсчеты сигнала, получаемые на выходе АЦП, связанные с отсчетами принятого сигнала соотношением

where T _n - time of observation; ν is the number of the frequency channel; L is the number of samples of the signal, calculated as the integer part of the ratio

Where

- sampling period; x _nm [l] - signal samples obtained at the ADC output, associated with the samples of the received signal by the ratio

Then, the maximum (by argument r) of the objective function (3) is searched using known methods [9], such as the first-order descent method or the second-order Newton method. The vector r _max delivering the maximum of the objective function is assumed to be the solution to the location problem. This assessment method is one-stage, i.e. it eliminates the calculation of intermediate estimates for the delay times and bearing angles, which reduces the likelihood of anomalous errors that can occur in multi-stage methods [10] with signal-to-noise ratios less than 15 dB.

размерностью N(N-1)/2, а на втором этапе сформированный вектор Т будет пересчитан в вектор координат r с использованием, например, таких подробно известных процедур, как среднеквадратическое приближение, представленное для этой задачи в [11]. Каждой паре задержек при этом соответствует своя линия пеленга; однако вследствие присутствия неустранимых шумов все линии положения не могут пересечься в одной и той же точке. При выполнении одноэтапного оценивания ищется непосредственно та единственная точка пересечения, которая определяется из минимального числа функционально независимых задержек, что проиллюстрировано фиг. 4. При этом поиск такой точки ведется путем численной оптимизации целевой функции (3) посредством разбиения всей области поиска на ячейки малой площади и вычисления целевой функции (3) в каждой из них; так, ячейка с максимальным значением определяет положение с точностью до размера ячейки.The main difference between the proposed method based on a one-stage direction finder and multi-stage direction finders (two or more stages of estimation) is the formation of an estimate that obviously satisfies all pairwise phase delays in the sense of the best (in the mean-square sense) approximation. To explain the differences between the one-stage method and the two-stage method, a graphic diagram is constructed for a two-dimensional direction-finding estimator based on the difference-ranging principle. Performing the two-step evaluation illustrated in FIG. 3 is performed as follows: at the first stage, the vector of mutual delays between N receiving stations is measured

dimension N (N-1) / 2, and at the second stage the generated vector T will be converted into the coordinate vector r using, for example, such well-known procedures as the mean-square approximation presented for this problem in [11]. In this case, each pair of delays has its own bearing line; however, due to the presence of unrecoverable noise, all position lines cannot intersect at the same point. When performing a one-step estimation, that single intersection point is directly sought, which is determined from the minimum number of functionally independent delays, as illustrated in FIG. 4. In this case, the search for such a point is carried out by numerically optimizing the objective function (3) by dividing the entire search area into small-area cells and calculating the objective function (3) in each of them; so, the cell with the maximum value determines the position accurate to the size of the cell.

The generated location estimate is transmitted to a point equipped with an address-response radio line transmitter (PrdAORL), which can be either a separately placed transmitting station or be included in the radio complex of a reception center equipped with an OP. In the latter case, the transmitter and the direction finder can share the same antenna system by switching it to receive / transmit.

The choice of the decameter (DKMV) range of the radio line operation is due to the advantages that this range provides when communicating with remote subscribers due to the reflection of radio waves from the ionosphere. A radio link in the DKMV range provides the ability to transmit over long distances using relatively small powers (up to 2 kW), determines the use of antennas located on low (up to 20 m) masts, and also allows for directional data transmission [12].

For each aircraft, the location of which was estimated using a one-stage direction finder, a radiation pattern of the antenna array used by PrdAORL in the direction of the aircraft with respect to the transmitting point is formed. The composition of the message transmitted on board the aircraft may include information on the coordinate vector of the aircraft in three-dimensional space, information on the accuracy of the estimates obtained, information on bearings to the reference points of the terrain, measurement time and other overhead information. The information packet can be encrypted using symmetric or asymmetric encryption algorithms to prevent third-party recipients from accessing information.

The general scheme of the proposed navigation method is shown in FIG. 5. At the first stage (51), a radio signal is emitted from the aircraft, which enters the antenna systems of N one-stage direction finders, the processing of which directly includes (52) receiving a signal, which consists in generating a digital sequence of samples of the signal at each receiving point. Processing (53) of the received signals consists in generating normalized spectra according to expression (5), which are then transmitted (54) to the CPO (5), where the formation of the aircraft location estimates (55) is generated based on minimizing the function given by expression (3). The found estimate of the location of the aircraft, together with the information for forming the radiation pattern, is transmitted (56) to the point where the transmitter of the response-address radio line is located. The generated message is transmitted (57) by a digital information packet via a radio link in the DKMV band. The received coordinate information is used (58) on board the aircraft by the pilot and / or control systems to adjust the course of the aircraft.

Information sources

1. Roger R.M. Applied mathematics in integrated navigation systems. AIAA, 2007.

2. Network satellite radio navigation systems / Shebshaevich B.C., Dmitriev PP, Ivantsevich N.V. et al. Ed. B.C. Shebshaevich. 2nd ed. M .: Radio and communication, 1993.408 s.

3. Aviation radio navigation. Handbook Ed. Sosnowski Α.Α., M .: Transport, 1990.

4. Pat. 2558699 A comprehensive method for navigating aircraft / Baburov V.I., Halperin TB, Gerchikov A.G., Orlov V.K., Sauta O.I., Sokolov A.I., Yurchenko Yu.S.; patent holder: CJSC "VNIIRA-Navigator" - 2014120782/28; declared 05/22/2014; publ. 08/10/2015, bull. 22. - 31 p.

5. Pat. 2338158 Aircraft navigation method / Khrustalev A.A., Koltsov Yu.V., Egorov C.H .; patent holder: FSUE FNPC "Research Institute of Measuring Systems named after Y. Sedakov" - 2007118460/28; declared 05/17/2007; publ. 11/10/2008, bull. 31. - 13 p.

6. Pat. 2567850 Method of direction finding of an air object / Ufaev V.A .; patent holders: Russian Federation (Ministry of Defense of the Russian Federation), Federal State-Funded Educational Institution of Higher Professional Education "Air Force Research Center" Air Force Academy named after Professor N.E. Zhukovsky and Yu.A. Gagarin "- 2014125677/07; declared. 06.24.2014; publ. 10.11.2015, bull. 31. - 13 p.

7. Knapp C.H., Carter G.C., The Generalized Correlation Method for Estimation of Time Delay // IEEE Transactions on Acoustic, Speech and Signal Processing, 1976, vol. 24, no. 4, pp. 320-327.

8. Dubrovin A.B., Sosulin Yu.G. One-stage estimation of the location of a source of radio emission by a passive system consisting of narrow-base subsystems // Radio Engineering and Electronics, 2004, v. 49, No. 2, p. 156-170.

9. Nocedal J., Numerical Optimization, 2 ^nd ed., Springer, 664 pp.

10. Chernyak B.C. Multiposition radar. - M .: Radio and communications, 1993 .-- 416 p.

11. Torrieri D.J., Statistical Theory of Passive Location Systems // IEEE Transactions on Aerospace and Electronic Systems, 1984, vol. 20, no. 2, pp. 183-198.

12. Nikolsky V., Nikolskaya T. Electrodynamics and propagation of radio waves - M .: Librocom, 2014. - 544 p.

Claims (1)

A method of navigating aircraft, which consists in generating an estimate of the location by digitally processing the radio signals emitted from the aircraft by a ground direction finder and transmitting the generated estimates to the aircraft through an address-response packet digital radio line operating in a decameter (DKMV) wavelength range, characterized in that to obtain an estimate of the location of the aircraft uses a high-precision one-stage direction finder, consisting of an act an explicit phased antenna array, a digital receiver, and a digital signal processing unit constructed on the basis of a universal digital computer and implementing a one-stage method for estimating bearings and spatial coordinates of radio emission sources based on maximizing the decisive function based on the maximum likelihood method without intermediate steps with respect to bearings and spatial coordinates for known samples of the spectra of signals received by elements of an active phased antenna array.

Images