RU2588057C1 - Method of locating objects for local navigation systems - Google Patents

Abstract

FIELD: radar and navigation.

SUBSTANCE: invention may be used in navigation systems and local area networks to control the movement of mobile objects in local zones navigation. Method is based on generation by a navigation object two high-frequency harmonic signals with different frequencies, their simultaneous radiation from navigation object and reception in several reference radio navigation points with known coordinates, generation in said points of differential frequency signals received from a navigation object high-frequency signals, transmitting generated differential frequency signals in central processing station, where phase difference of differential frequency signals coming from different reference points results of measurements of phase differences taking into account mutual arrangement of central receiving station and reference radio navigation points are recalculated in coordinates of navigation object, wherein both generated on navigation object harmonic signals, before radiation, are synchronously phase modulated with same pseudorandom binary sequence with phase deviation of 180°.

EFFECT: high noise-immunity.

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Description

The invention relates to radio navigation and can be used in local navigation systems and networks to control the movement of mobile objects in local navigation areas.

Known protected by RF patent No. 2204145, class. G01S 3/46, 2003 a method for determining the coordinates of a radiation source based on the reception of its signal by three antennas forming orthogonal bases.

Such an action as determining the direction to the radiation source is an essential sign of the proposed method.

Also known is protected by a patent of the Russian Federation No. 20133785, class. G01S 13/00, 1994 a method for determining the location of moving objects, which consists in emitting encoded signals by object transmitters, receiving signals at N spatially separated points, and then relaying them to a central receiving point and measuring the delays between the received signals.

The relay of signals to the central receiving point is an essential sign of the proposed method.

The reason that impedes the achievement in these analogues, protected by patents of the Russian Federation, of the technical result provided by the invention, is the need to use a rather complex system of uniform time.

The known differential-ranging method for determining the location of mobile objects, which consists in alternately emitting a network of navigation reference points located at points in space with known coordinates, coherent harmonic signals, receiving them on a mobile object, received from each reference object and calculating the coordinates of the mobile object from them [ Bakulev P.A., Sosnovsky A.A. Radar and radio navigation systems. - M .: Radio and communications, 1994, p. 211-214].

The measurement of the phase shifts of the signals and the calculation of the coordinates of the mobile object from them is an essential sign of the proposed method.

The reason that impedes the achievement in this analogue of the technical result provided by the invention is the need to use a high-precision scale of a single time at the navigation object and the difficulty of implementation at large distances between the reference radio navigation points and the navigation object.

The closest in technical essence to the claimed (prototype) is the method for determining the location of the navigation object described in patent application No. 2014116786 of 04.24.2014, the decision to grant a patent of 05.06.2015.

The method consists in generating and simultaneously emitting two high-frequency harmonic signals with different frequencies by the navigation object, receiving them at several reference radio navigation points with known coordinates, generating differential-frequency signals there from the received high-frequency signals, transmitting the generated differential-frequency signals to a central processing point where it is measured the phase difference of these differential frequency signals obtained from different reference radio navigation points, and the phase results New measurements are recalculated taking into account the relative position of the central receiving point and reference radio navigation points in the coordinates of the navigation object.

Such actions as the formation and simultaneous emission by the navigation object and the transmitter of two high-frequency harmonic signals with different frequencies, the receipt of these high-frequency signals at several reference radio navigation points with known coordinates, the formation of high-frequency signals received from the navigation object, differential frequency signals in them, measurement the phase differences of the signals of the differential frequency generated at different reference radio navigation points and the calculation of the measured phase differences to the coordinates of the navigation object, taking into account the relative position of the central processing point and reference radio navigation points, are essential features of the proposed method.

The reason that prevents the achievement of the technical result provided by the invention in the prototype method is the low level of noise immunity of the radio navigation systems implementing this method with respect to intentional interference from a possible attacker, due to the high spectral density of the signals emitted by the navigation object near the carrier frequency. This circumstance makes it easier for a potential attacker to detect the signals used in the system implementing the method in question and to measure the frequencies of these signals, as well as the possibility of suppressing these signals by active interference that is aimed at the frequency.

The technical problem to which the invention is directed is to increase the noise immunity of radio navigation systems that implement the proposed method.

To achieve the specified technical result in a known method for determining the location of a navigation object, which consists in generating two high-frequency harmonic signals with different frequencies by the navigation object, simultaneously emitting them from the navigation object and receiving at several reference radio navigation points with known coordinates, generating difference frequency signals at these points from the high-frequency signals received from the navigation object, to the transmission of the generated differential frequency signals to the center the processing point, where the phase difference of the difference frequency signals from different reference points is measured, and the results of the phase difference measurements, taking into account the relative position of the central receiving point and the reference radio navigation points, are converted to the coordinates of the navigation object, both of which are generated on the navigation object harmonic signals before radiation phase-modulated by the same pseudo-random binary sequence with a phase deviation of 180 °.

The invention is illustrated in the drawing, which shows:

- in FIG. 1 - the relative position of the navigation object and the three reference radio navigation points;

- in FIG. 2 - structure of a differential frequency signal driver.

To implement the method requires at least three reference radio navigation points with known coordinates.

The operation of the method is illustrated in FIG. 1, which shows a mobile navigation object (MO) located at a point with unknown coordinates X and Y, and reference radio navigation points ORT1, ORT2 and ORT3, located at points with known coordinates X ₁ and Y ₁ , X ₂ and Y ₂ and X ₃ and Y _3, respectively. There are also shown the distances D ₁ , D ₂ , D ₃ between the navigation object and the reference radio navigation points, as well as the direction N to the north.

Using the transmitter installed on the navigation object, two harmonic signals with frequencies ω ₀ and ω ₁ are generated in the direction of the points OPT1, OPT2 and OPT3, synchronously modulate them in phase with a phase deviation of 180 ° by the same binary random sequence r (t) summarize the obtained phase-manipulated oscillations and emit the resulting high-frequency broadband signal (the sum of two broadband phase-shifted FM-2 signals with frequencies ω ₀ and ω ₁ ) from the navigation object

where r (t) is a binary pulse sequence taking the values "+1" and "-1" at random times. Both signals have the same amplitude A and random initial phases φ ₀ and φ ₁ .

This signal is received at points ORT1, ORT2 and ORT3 at distances D ₁ , D ₂ and D _3, respectively, from the navigation object:

where c = 3 · 10 ⁸ m / s is the velocity of propagation of radio waves in the atmosphere.

In each of the reference radio navigation points ORT1, ORT2 and ORT3, the difference frequency signals are generated from the received signals s ₁ (t), s ₂ (t) s ₃ (t).

.The structure of the differential frequency signal generator is shown in FIG. 2. It is a series-connected multiplier (balanced mixer) and a narrow-band bandpass filter tuned to the differential frequency

.

. Принятый сигнал подается одновременно на оба входа перемножителя (балансного смесителя), в котором происходит демодуляция фазоманипулированного сигнала:A signal s _i (t) is received at each of the reference radio navigation points

. The received signal is fed simultaneously to both inputs of the multiplier (balanced mixer), in which the demodulation of the phase-shifted signal occurs:

Thus, at the output of the multiplier, a signal is formed containing the following spectral components:

1) a signal with a zero frequency (constant component);

2) harmonic signals with doubled frequencies 2ω ₀ and 2ω ₁ ;

3) a harmonic signal with a total frequency ω _Σ = ω ₀ + ω ₁ ;

4) harmonic signal with difference frequency

All these signals, with the exception of the signal with a difference frequency ω _p , are suppressed by the filter.

The difference frequency signals generated in each of the reference radio navigation points are:

It is easy to see that the signals generated in each of the reference radio navigation points differ in phase, which are determined by the distances D ₁ , D ₂ and D _3, respectively. These signals are transmitted to the central reception center (CPP). As such, for example, one of the reference radio navigation points can be used. For definiteness, let us assume that geographically the CPP is located at the point of ORT2.

Thus, the following three difference frequency signals are received from the reference radio navigation points in the DPC.

1) The signal received from ORT1,

where R ₂₁ is the distance between the reference radionavigation point ORT1 and CPP;

v is the propagation speed of the radio signal in the communication line connecting ORT1 and CPP.

, который обусловлен прохождением расстояния R₂₁, разделяющего ОРТ1 и ЦПП (в рассматриваемом случае точку ОРТ2).S _21p (t) differs from the signal S _1P (t) in amplitude and an additional phase shift

, which is due to the passage of the distance R ₂₁ separating ORT1 and CPP (in this case, the point ORT2).

This signal can be represented as follows:

.Where

.

2) The signal received directly at the point ORT2 (CPP),

In this case, there is no additional phase shift, since the distance between the point OPT2 and the CPT is zero.

This signal can also be represented as

s _22p (t) = A ₂₂ cos (ω _p t + ψ ₂₂ ),

.Where

.

3) The signal received from ORT3,

This signal can also be written as:

.Where

.

We find the phase difference Δψ ₂₁ = ψ ₂₂ -ψ _{21 of the} signals S _22p (t) and S _21p (t) and the phase difference Δψ ₂₃ = ψ ₂₂ -ψ _{23 of the} signals S _22p (t) and S _23p (t):

From these expressions it follows that the considered differences do not depend on random initial phases φ ₀ and φ ₁ .

и

, получим окончательные выражения для расчета координат объекта навигации разности Δφ₂₁ фаз сигналов разностной частоты, сформированных во второй и первой опорных точках, а также для расчета разности Δφ₂₃ сигналов разностной частоты, сформированных во второй и третьей опорных точках:Excluding the known phase shifts from the last expressions for Δψ ₂₁ and Δψ ₂₃

and

, we obtain the final expressions for calculating the coordinates of the navigation object of the difference Δφ of ₂₁ phases of difference frequency signals generated at the second and first reference points, as well as for calculating the difference Δφ of ₂₃ difference frequency signals generated at the second and third reference points:

Thus, the parameter Δφ ₂₁ is the phase difference of the difference frequency signals between the second and first reference points, and the parameter Δφ ₂₃ is between the second and third reference points. The indicated phase differences uniquely correspond to the differences of the ranges D ₂ -D ₁ and D ₂ -D ₃ respectively.

This allows us to conclude that, according to the results of measurements of the parameters Δφ ₂₁ and Δφ ₂₃ , the parameters D ₁ , D ₂ and D ₃ can be calculated - the distances between the navigation object and reference radio navigation points, and, consequently, the coordinates of the navigation object.

Below is the algorithm for converting the results of measuring the phase difference of the signals of the differential frequency into the coordinates of the navigation object. This algorithm is applicable for local navigation systems when it is permissible to neglect the sphericity of the Earth, and the propagation velocity of radio waves in the coverage area of the navigation system can be considered constant.

The initial data for the calculation are:

- the difference Δφ of ₂₁ phases of the signals of the differential frequency for the first and second radio navigation points;

- the difference Δφ of ₂₃ phases of the signals of the differential frequency for the third and second radio navigation points.

In addition, the following constants are used in the calculation:

- the value of the first high frequency ω ₀ ;

- the value of the second high frequency ω ₁ ;

- the propagation velocity of radio waves in the atmosphere with;

- the distance between the first and second reference radio navigation points R ₂₁ ;

- the distance between the third and second reference radio navigation points R ₂₃ .

The calculation procedure is as follows.

1. The differences of distances from the navigation object to the reference points are calculated

Here D ₁ , D ₂ , D ₃ are the distances from the navigation object (MO) to the first ORT1, second ORT2 and third ORT3 of the radio navigation aids in accordance with FIG. one.

2. The values ΔD ₂₁ and ΔD ₂₃ are normalized by the lengths of the baselines and the parameter γ is calculated:

3. The constant parameters are determined:

a = α ₂₁ -α ₂₃ ; b = γ Δd ₂₃ -Δd ₂₁ ,

where α ₂₁ is the angle between the north direction and the baseline R ₂₁ ;

α ₂₃ - the angle between the north direction and the base line R ₂₃ .

4. An equation is compiled to calculate the angle β ₂₃ between the base line R ₂₃ and the direction of the navigation object:

cos (a-β ₂₃ ) -γ cosβ ₂₃ = b

This equation is solved with respect to angle β _{23 by} any of the numerical iterative methods, for example, by dividing a segment in half.

5. The coordinates of the navigation object in the local rectangular coordinate system are calculated, the origin of which is at the point ORT2:

If necessary, the coordinates of the navigation object are converted to the original rectangular coordinate system;

Thus, in the proposed method retains all the possibilities of measuring the coordinates of the navigation object, as in the prototype method. In addition, due to the phase modulation of the emitted signals by a random binary sequence of short pulses with a phase deviation of 180 °, the spectrum emitted by the navigation object significantly expands. As a result of this, their spectral density decreases as many times. In addition, in the spectrum of the emitted signals there are no spectral components with frequencies ω ₀ and ω ₁ . The width of the spectrum of the emitted signals can be increased tens of times. Accordingly, the spectral density of these signals decreases by the same amount.

The degree of expansion of the spectrum and, accordingly, the degree of decrease in spectral density is determined by the average pulse duration of a random binary sequence used for phase modulation of the emitted signals.

The low spectral density of the emitted signals, the absence of components with carrier frequencies in their spectrum, together with a short signal emission time, make it difficult for their detection and measurement of frequencies ω ₀ and ω _{1 by a} potential attacker. As a result of this, the ability to suppress the operation of radio navigation systems using the proposed method is substantially hindered. This significantly increases the noise immunity of the equipment that implements the method, compared with the prototype.

The technical implementation of the method does not cause difficulties. As an example of implementation, we consider the implementation of the proposed method for constructing a local navigation system for controlling traffic in high-risk areas where high-precision location of high-speed moving objects is required: on critical sections of their movement paths (for example, when approaching switch points on railway tracks, near steep closed turns of highways). For the implementation of the system, a frequency range of 1200-1400 MHz can be selected. The coverage area of the local navigation system can be several hundred meters.

The formation of two high-frequency phase-modulated signals at a navigation object can be implemented on the basis of two frequency synthesizers synchronized by a common reference oscillator, and an adder, balanced modulators, and a pseudorandom binary sequence generator, for example, an M-sequence generator based on a feedback register with a shift register. As frequency synthesizers, for example, ADF4360-5 type microcircuits can be used, which make it possible to generate two highly stable harmonic signals with a frequency spacing of (0.1-100) MHz, as a reference oscillator - a NT3225SA thermostabilized crystal oscillator.

To receive signals at navigation reference points, you can use integrated microwave amplifiers - microcircuit type SPF5122Z, to normalize the received signals in amplitude - AD8309 logarithmic amplifier, as a unit for generating a differential frequency signal - a mixer on a BFP620 transistor, whose load is a low-pass filter with a frequency slice equal to the difference frequency. The transmission of difference frequency signals from the navigation reference points to the central receiving point can be realized either via wired channels (at small distances between the reference navigation points and the central receiving point - about 100 m), or via radio channels with frequency separation (for more significant distances between reference navigation points and a central receiving point).

The separation of the phase difference of the signals of the difference frequency in the Central receiving point is based on a phase detector (for example, on a SYPD-1 chip or the like).

Analog signals from the output of the phase detector are fed through analog-to-digital converters to the input ports of the STM type microprocessor, which implements the solution of the navigation problem according to the above algorithm.

The method may find application for constructing local navigation systems for controlling traffic in high-risk areas where high-precision location of high-speed moving objects is required, at critical sections of their movement paths (for example, when approaching switch points on railway tracks, near sharp closed turns highways).

Claims (1)

The method for determining the location of objects for local navigation systems, which consists in generating two high-frequency harmonic signals with different frequencies by the navigation object, emitting them simultaneously from the navigation object and receiving at several reference radio navigation points with known coordinates, generating at these points differential frequency signals from received from the object navigation of high-frequency signals, transferring the generated differential-frequency signals to a central processing point, where the phase difference of the difference frequency signals received from different reference points, and the results of measurements of phase differences, taking into account the relative position of the central receiving point and the reference radio navigation points, are converted to the coordinates of the navigation object, characterized in that both harmonic signals generated on the navigation object are synchronously modulated before radiation phase of the same pseudo-random binary sequence with phase deviation of 180 °.

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