RU2623094C1 - Method of measuring mutual delay of msk signals of packet radio networks in difference-range positioning system - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: arrival time of the signal at the receiving point is measured by the time position of the posteriori probability density maximum constructed through the module of the resulting cross correlation function (CCF) calculated by means of partial CCF received at the receiving point with four harmonic oscillations of two frequencies with a duration equal to the duration of the received signal (packet). The CCF module is formed by elementary pulses of the modulating sequence, which makes it possible to obtain a narrow peak of the a posteriori probability density even with the unknown law of primary modulation. The phase increment for the duration of one elementary pulse of the modulating sequence is

.

EFFECT: increasing the accuracy of measuring the mutual delay of MSK signals of packet radio networks with the unknown law of primary modulation in the difference-range positioning systems due to the use of that MSK signal feature.

11 dwg

Description

The invention relates to the field of radio engineering and can be used in differential-ranging systems for determining the coordinates of radio emission sources (IRI), using the mutual delay of the received radio signals as a coordinate-informative parameter.

Known:

1. A method of measuring the mutual delay of signals with software tuning of the operating frequency (MFC) [1].

2. Difference-range measuring method for determining the coordinates of the source of radio emission [2].

3. Difference-range multi-position radio engineering systems [3, p. 228 ... 241].

4. Evaluation of the difference in the moments of arrival of signals by a grouping of spatially separated small spacecraft [4].

5. Determining the delay time of signal reception by spatially separated ultra-small spacecraft [5].

6. Determining the location of the noise-like signal source using the correlation function [7].

The main disadvantage of the above methods is that they require the relay of signals received at peripheral reception points (PPP) to the central point of reception and processing (CPPO), where they are jointly mutually correlated. In this case, the mutual signal delay (SCW) corresponds to the position of the maximum module of the cross-correlation function of these signals. Relay can be carried out both in analogue and in digital form. In this case, for digital relaying, a uniform time scale at all reception points is necessary [7]. The need to relay signals from peripheral points to the central one requires high-speed data channels. Namely, their absence is the main limiting factor for the widespread use of differential-ranging systems of positioning (RDS MO) in practice, since with this method of implementing RDS MO their throughput is very low.

Closest to the claimed method according to the totality of the matching essential features is the method [6, 7], which is selected as a prototype. The essence of this method is to measure the mutual delay of signals of an unknown shape, based on measuring the time of arrival of signals (IPN) [8] in each RFP RDS MO equipped with a single time subsystem (PSEV), and transmitting only the measurement results to the CPPO. This method is applicable to pulsed signals, which include signals of packet radio networks (including frequency hopping). This approach dramatically increases the throughput of RDS MO. But since the signal shape is unknown, the task of measuring the temporal position of the signal is reduced to measuring the temporal position of the envelope of the pulse signal (packet). The measured values of the IPN are transmitted to the CPPO, where the differences in the time of reception of these signals in the RFP and the CPPO are calculated as the differences corresponding to the IPN, and then the coordinates of the IRI are calculated. The structural diagram of the RDS MO, containing three PRPP, one CPPO and PSEV, shown in Fig. one.

Each peripheral point of reception of the IRI signal (IFR _i ), representing a set of devices emitting radio signals from the IRI against the background of interference, devices measuring IPN _i relative to the time scale, as well as devices organizing the transmission lines of the measured IPN _i , includes:

- antenna and digital radio receiver (TsRPU _i ) devices for receiving IRI signals;

- a device for measuring the time of arrival of the signal (UIVPS _i ) to highlight the envelope of the packet and measure its temporal position on a single time scale (UPU _i );

- radio transmitting (RPdU _i ) and antenna devices for transmitting the measured values of IPN _i to the CPPO, where i = 1, 2, 3.

The central point of reception and processing, representing a set of devices emitting radio signals from the IRI against the background of interference, a device measuring IPL ₀ relative to the time scale, as well as devices designed to extract useful information about the parameters of the IRI (mutual signal delay) by calculating the differences of the IPC _i in PPPi and TsPPO, includes:

- antenna and radio receivers (RPrU) for receiving information signals about IPN _i ;

- antenna and radio receiver (RPrU ₀ ) devices for receiving signals of IRI;

- central processing point (CPO).

The CPO assesses the mutual delays of the IRI signals at the receiving points by calculating the differences of the IPN _i in the RFP _i and the CPPO.

The single time subsystem is a collection of devices that serve to form a single time scale at all points of reception.

Calculation of AMS _i in the IFR _{i is} made in UIVPS _i as follows.

First, the envelope of the packet U _p (t) is highlighted. For this, the input real signal ξ (t, λ) = s (t, λ) + n (t), 0≤t≤T, which is the sum of the useful signal s (t, λ), which depends on several parameters λ = {λ ₁ , λ ₂ , ..., λ _n } and noise n (t), where T is the observation time, is converted into analytical using the Hilbert transform [9, p. 469-473].

- преобразование Гильберта ξ(t); Т - длительность наблюдения.Where

- Hilbert transform ξ (t); T is the duration of observation.

The envelope of the packet U _p (t) is defined as the modulus of the analytical signal

Then, the problem of determining the temporary position of the envelope of the packet [8, p. 189-200]. In accordance with the theory of optimal reception, the task of an ideal receiver designed to measure the temporal position of signal pulses is to develop a posterior probability density (AR) P _ps (τ) of parameter τ based on an analysis of the adopted realization ξ (t) taking into account a priori information about the signal and noise

where P _pr (τ) is the a priori probability density;

k is a coefficient selected from the normalization condition;

- likelihood function;

- I ₀ (⋅) is the modified Bessel function of zero order;

- the cross-correlation function between the envelope of the packet U _p (t) and the video pulse U ₀ (t) of duration T _p ;

N _W - the spectral power density of the noise floor of the receiver.

When evaluating the IPN - τ _{air force, it is} sufficient to use the central AR peak, approximating it in some way, for example, a polynomial.

Then the estimate of the signal arrival time will be found from the equation

where P _psm is the approximation of the central peak of the posterior probability density.

вычисляется по формулеAnd the desired VZS

calculated by the formula

и

- оценки ВПС в i-м и j-м ППП соответственно, i≠j.where -

and

- IPN estimates in the i-th and j-th SPP, respectively, i ≠ j.

If the a priori probability density is unknown, then the estimate for the maximum of the posterior probability density coincides with the most plausible estimate.

Oscillograms of the signals at the characteristic points of the UIVPS are shown in FIG. 2.

The main disadvantage of the prototype is the low accuracy of the measurement of IPN, since the measurement is performed along the envelope of the packet and the in-pulse modulation of the packet is not used.

The purpose of the invention is to increase the accuracy of the measurement of mutual delay MSK (minimum shift keying) of signals of packet radio networks with an unknown law of primary modulation in the RDS MO.

The specified technical result in the implementation of the proposed method is achieved by the fact that in the proposed method the actions are changed when measuring IPN in the RFP.

The essence of these changes is as follows.

[10, стр. 177-181], ВПС в ППП измеряется по временному положению максимума апостериорной плотности вероятности, построенной через модуль результирующей взаимно корреляционной функции (ВКФ), вычисляемой с помощью парциальных ВКФ принимаемого в точке приема сигнала с четырьмя гармоническими колебаниями двух частот

и

длительностью, равной длительности принимаемого сигнала (пакета) Т_р. Здесь ƒ_н - частота несущей, Т_с - длительность элементарного импульса модулирующей последовательности.Based on the fact that the phase gain on the elementary pulse of the modulating sequence of the MSK signal is

[10, p. 177-181], the IPN in the SPP is measured by the time position of the maximum a posteriori probability density constructed through the module of the resulting cross-correlation function (VKF) calculated using the partial VKF of the signal received at the receiving point with four harmonic oscillations of two frequencies

and

duration equal to the duration of the received signal (packet) T _p . Here ƒ _n is the carrier frequency, T _c is the duration of the elementary pulse of the modulating sequence.

Then the algorithm for constructing the reclosure P _ps (τ) in the proposed method will be described by the expressions

where A ₁ (τ), A ₀ (τ), B ₁ (τ), B ₀ (τ) are the partial CCFs of the signal received at the point of reception with four harmonic oscillations of two frequencies;

T is the time of observation;

D (⋅) is the straightening operator of the correlation integral;

P _pr (τ) is the a priori probability density τ;

I ₀ (⋅) is the modified zero-order Bessel function;

L (τ) is the likelihood function;

Z (τ) is the resulting cross-correlation function;

U _m is the signal amplitude;

N _W - the spectral power density of the noise of the receiver;

k is a coefficient selected from the normalization condition;

P _pr (τ) is the a priori probability density.

The main operation in constructing the partial VKF is the operation of calculating the correlation integral (KI), of which the final VKF consists of the final values for various τ. The calculation of CI in an algorithm that implements the proposed method has some features. Let's consider them in more detail.

So, when calculating the correlation integrals in expressions (8, 9), 2 cases are possible: 1 - when there is an even number of pulses of a different frequency between pulses of one frequency, and 2 - when the number of pulses is odd. In the first case, the calculation of the correlation integral (CI) will occur normally. In the second case, when calculating the correlation integral, a “fracture” occurs (Fig. 3 and Fig. 4), while the angle at which the CI increased was the same in magnitude. Only the direction is changing. Thus, in the process of calculating the CI in each channel, it is necessary to analyze it in order to search for "fractures" and change the angle of inclination mirror-image relative to the horizontal line passing through the point of "fracture" (Fig. 5 and Fig. 6). This is possible due to the fact that the form of the correlation integral is a priori known (it always increases in absolute value). The KI rectification operator in (10) and (11) is denoted as D (⋅). The final view of the rectified KI is shown in FIG. 7 and FIG. 8.

When evaluating IPN, as in the prototype, it is enough to use the central peak of the AR, approximating it in some way. In FIG. 9 shows the process of approximating the central peak of the posterior probability density and estimating the signal arrival time. Here, the peak is approximated by a polynomial of the fourth degree.

The estimate of the signal arrival time is found from the solution of the equation

where P _psm is the approximation of the central peak of the posterior probability density.

вычисляется по формулеSeeking VZS

calculated by the formula

и

- оценки ВПС в первом и втором пространственно-разнесенных пунктах приема соответственно, i≠j.where -

and

- IPN estimates at the first and second spatially separated points of reception, respectively, i ≠ j.

Comparing the envelopes of the VKF Z (τ) of the prototype (Fig. 3) and the VKF of the proposed method (Fig. 10), it can be seen that the envelope of the VKF of the proposed method has a multimodal structure. In this case, the accuracy of measuring the IPN by the proposed method is determined by the width of the central peak of the envelope of the VKF, which is much narrower than the envelope of the VKF of the prototype, since it is formed by elementary pulses of the modulating sequence of duration T _s , while the envelope of the VKF of the prototype is formed by the envelope of the packet of duration T _p . The spectrum of the modulating sequence is much wider than the spectrum of the envelope of the packet. This explains the gain in the accuracy of the measurement of IPN by the proposed method.

The invention is illustrated by drawings, which depict:

in FIG. 1 is a structural diagram of the RDS MO;

in FIG. 2 - waveforms of signals at the characteristic points of the prototype;

in FIG. 3 - illustration of the fracture KI for frequency ƒ ₁ ;

in FIG. 4 - illustration of the fracture of the CI for a frequency of ƒ ₀ ;

in FIG. 5 - illustration of the rectification of KI for frequency ƒ ₁ ;

in FIG. 6 - illustration of the rectification of KI for frequency ƒ ₀ ;

in FIG. 7 - illustration of the rectified KI for frequency ƒ ₁ ;

in FIG. 8 - illustration of the rectified KI for frequency ƒ ₀ ;

in FIG. 9 - the process of approximating the central peak of the posterior probability density and estimating the signal arrival time;

in FIG. 10 - waveforms of signals at characteristic points of the proposed method;

in FIG. 11 - graphs of the dependence of the estimation error of the mutual delay of the signals on the signal-to-noise ratio.

To study the accuracy characteristics of the proposed method and compare it with the prototype and its analogues, a simulation model of UIVPS is created. In the simulation, the following signal parameters were used: carrier frequency - 100 MHz, packet duration - 6.4 μs, the number of pulses of the modulating pseudorandom sequence (PSP) - 32, the clock frequency of the PSP - 5 MHz, the type of modulation - MSK. The simulation results are shown in FIG. 11, which shows graphs of the dependence of the estimation error of the mutual delay of the signals on the signal-to-noise ratio at the input of the IUPS. The numbers indicate: 1 - graph for the prototype; 2 - for the proposed method; 3 - for analogues using relaying of received signals from the RFP to the CPPO.

As can be seen from the drawings, in comparison with the prototype, the proposed method provides a gain in accuracy of 2 to 10 times, depending on the signal-to-noise ratio. Thus, the goal is achieved.

Compared with analogues with a large signal-to-noise ratio (more than 40), the error of the proposed method exceeds the error of analogues by an average of 35%. With a decrease in the signal-to-noise ratio, the difference gradually decreases, and with a value of q≈12, the proposed method is compared in accuracy with analogs. With a further decrease in the signal-to-noise ratio, the picture changes and the error of analogues, compared with the proposed method, increases sharply, while the gain of the proposed method reaches 50%. This fact is very important, since radio monitoring is carried out, as a rule, at low signal-to-noise ratios.

и

длительностью, равной длительности принимаемого сигнала (пакета) T_p, что до сих пор нигде не применялось. Таким образом, заявляемый способ соответствует критерию "новизна".A comparative analysis of the proposed technical solution with the prototype shows that the proposed method differs from the known one when constructing the VCF, namely, that the resulting VCF is calculated using the partial VCF received at the receiving point of the signal with four harmonic oscillations of two frequencies

and

duration equal to the duration of the received signal (packet) T _p , which until now has not been applied. Thus, the claimed method meets the criterion of "novelty."

Information sources

1. Patent RU No. 2335781, publ. 10/10/2008

2. Patent RU No. 2539968, publ. 01/27/2015 g.

3. Kondratiev B.C. et al. Multiposition radio engineering systems / Edited by prof. V.V. Tsvetnova. - M .: Radio and communications, 1986. - 264 p.

4. Gromov V.A., Voroshilin E.P., Mironov M.V. Estimation of the difference in the moments of arrival of signals by a grouping of spatially separated small spacecraft. - Tomsk, TU SUR // Reports of TUSUR, No. 2 (22), part 2, December 2010. S. 7-13.

5. Voznyuk V.V., Zaitsev S.A., Tolstoukhov D.A., Bulaev O.A., Gusakov N.V. Determining the delay time of signal reception by spatially spaced ultra-small spacecraft // Izv. Universities. Instrument making. 2008.Vol. 51, No. 3. S. 13-17.

6. Radzievsky V.G., Orphan A.A. Theoretical foundations of electronic intelligence. 2nd ed., Rev. and add. - M .: Radio engineering, 2004 .-- 432 p.

7. Fayt A.V. Determining the location of a noise-like signal source using the correlation function // Materials of the conference "Scientific and technical problems in industry". - St. Petersburg: Research Institute "Vector", 2012, May 29-31. S. 21-22.

8. Ipatov V.P. et al. Search, detection and measurement of signal parameters in radio navigation systems / Edited by Yu.M. Kazarinova. - M .: Owls. Radio, 1975 .-- 296 p.

9. Bendat J., Piersol A. Applied analysis of random data: Per. from English - M .: Mir, 1989 .-- 540 p.

10. Grigoriev V.A. Signals of foreign telecommunication systems. - SPb .: YOU, 2007, 2007. - 368 p.

Claims (6)

A method for measuring the mutual delay MSK (minimum shift keying) of packet radio network signals in a differential ranging system of location, which consists in the fact that at the peripheral points of receiving a differential ranging ranging system, MSK signals of packet radio networks are received, and the signal arrival time (IPN) is measured relative to a single time scales according to the position of the maximum of the posterior probability density constructed through the module of the cross-correlation function (CCF) of the received signal and the reference oscillation, and along the lines of communication transmit measured values to the central receiving and processing, where the calculated mutual delay signal

where -

and

- IPN estimates at the i-th and j-th spatially separated receiving points, respectively, i ≠ j, characterized in that the module of the resulting VKF Z (τ) is calculated using the partial VKF of the signal received at the receiving point with four harmonic oscillations of two frequencies

and

the duration equal to the duration of the received signal (packet) T _p :

B (τ) = B ₁ (τ) + B ₀ (τ); A (τ) = A ₁ (τ) + A ₀ (τ);

Where

- carrier frequency; T _with - the duration of the elementary pulse of the modulating sequence; A ₁ (τ), A ₀ (τ), B ₁ (τ), B ₀ (τ) - partial VKF of the signal received at the point of reception with four harmonic oscillations of two frequencies; T is the observation time;

;

; Z (τ) is the module of the resulting VKF; D (⋅) is the operator of straightening the correlation integral (CI), which searches for “fractures” and changes the angle of inclination of the CI mirror image relative to a horizontal line passing through the point of “fracture”.

Images