RU2531387C2 - Method of detecting chirp signals - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: present method includes receiving spaced-apart signals emitted by a plurality of radio transmitters; performing linear FM heterodyning of the resultant signal and calculating fast Fourier transform (FFT); partially accumulating FFT readings using an adder during the detection session; finding, among the adder outputs, the maximum value r_h and the corresponding index j_p; based on a given false alarm probability, calculating a threshold value r_hthres; establishing a flag $$s_{\det }=\{\begin{array}{l}"Detected",at{r}_h>r_{hthres}\\ "Notdetected",at{r}_h\le r_{hthres}\end{array}$$

and, if s_det="Detected", using the index value j_p to determine the start time of the detected chirp signal and the length of the group propagation path thereof.

EFFECT: high reliability of detecting chirp signals and enabling determination of characteristics thereof in case of detection.

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Description

The invention relates to the field of radio communication technology, and more particularly to the detection of signals with linear frequency modulation (LFM) and can be used to build hardware and use the results of LFM sounding.

Closest to the proposed technical solution is a method of searching for complex signals, which consists in the fact that the signals emitted by a plurality of radio transmitters coherently receive spatially spaced receiving channels synchronously transform the ensemble of received signals into complex digital signals, sliding in time by converting digital signals with a given time resolution and frequency receive the complex spectral densities of the signals of each channel, remember the spectral densities, from integrated polices spectral densities are formed and stored complex mutual spectral density (WWW) signals of all the possible pairs of channels formed on an integrated WWW determined and stored time-frequency localization domain received signals.

The disadvantage of the prototype method is that the decision-making process on the detection of the chirp signal does not maximize the signal-to-noise ratio, since the initial data uses spectral characteristics that are calculated at intervals shorter than the duration of the observation interval, presumably equal to the duration of the desired signal, and in which, therefore, only part of the signal energy is taken into account.

The objective of the invention is that when deciding to detect a chirp signal, maximize the signal-to-noise ratio, taking into account the total energy of the received signal.

и, если s_обн=«Обнаружен», по величине индекса j_p определяют значения стартового времени обнаруженного ЛЧМ-сигнала и длины его группового пути распространения.The problem is achieved in that in the method of detecting signals with linear frequency modulation (LFM), which consists in receiving spatially separated signals emitted by a plurality of radio transmitters, according to the invention, perform LFM heterodyning of the total signal and calculate the fast Fourier transform (FFT), s using the adder during the detection session, the FFT counts are partially accumulated, then the maximum value r _{h is} found among the outputs of the adder, and the corresponding index j _p , for a given the false alarm probability value is calculated threshold value rh _then , set the flag $$s_{\mathrm{about}bn}=\{\begin{array}{l}"\mathrm{ABOUT}bn\mathrm{but}R\mathrm{at}\mathrm{well}en",PR\mathrm{and}{r}_h>r_{hP\mathrm{about}R}\\ "Ne\mathrm{about}bn\mathrm{but}R\mathrm{at}\mathrm{well}en",PR\mathrm{and}{r}_h\le r_{hP\mathrm{about}R}\end{array}$$

and, if s _obn = “Detected”, the values of the start time of the detected LFM signal and the length of its group propagation path are determined by the value of j _p .

Achievable technical result is to increase the reliability of detection of chirp signals and the ability to determine their characteristics in case of detection.

Figure 1 presents the structural diagram of the receiver of the LFM signals, providing the implementation of the proposed method, comprising a converter 1, a fast Fourier transform computer (FFT) 2, an adder 3, a solving circuit 4, a start time calculator 5.

The proposed method works as follows.

The converter 1 performs heterodyning the input signal to obtain a particular chirp signal of the difference frequency signal, the instantaneous frequency f _p which depends on the delay time τ _of propagation of radio waves on the path from the transmitting station to the infeed station:

$$f_p=\left(T_{n\mathrm{but}hg}-\left(T_{\mathrm{from}t}+{\tau }_s\right)\right)\cdot \beta -f_{n\mathrm{but}hg},\left(\mathrm{one}\right)$$

where T start _r is the value of the time the start of heterodyning;

T _article - the value of the starting time for the transmitting station;

β is the value of the rate of change of the instantaneous frequency of the probing chirp signal;

f _{beg g} - the value of the initial frequency of heterodyning.

The FFT calculator 2 performs a fast Fourier transform (FFT) and, as a result of the i-th iteration of the calculation, generates an output signal with a module m _ij at each j-th output. For an input signal with a difference frequency f _p , the maximum voltage is generated at the output of the FFT computer with the index f _p . In this case, the values of f _p and j _p will be related by the relation:

$$f_p=\{\begin{array}{l}\frac{j_p\times f_d}{N_{bPf}},PR\mathrm{and}0\le j_p<\frac{N_{bPf}}{2}\\ \frac{\left(j_p-N_{bPf}\right)\times F_d}{N_{bPf}}PR\mathrm{and}\frac{N_{bPf}}{2}\le j_p<N_{bPf}\end{array},\left(2\right)$$

where N _FFT is the length of the FFT;

F _d - the value of the sampling frequency in the process of computing the FFT.

During one detection session (operation of the chirp signal receiver), adder 3 accumulates I times the voltage at each of the J outputs of the FFT 2 calculator (J≤N _FFT ) so that the voltage at the j-output of adder 3 by the time the session ends is

, $$r_j=\frac{h_j}{m_k}-\mathrm{one}$$

,

;Where $$h_j=\frac{{\displaystyle \sum _{i=0}^{I-\mathrm{one}}{m}_{ij}}}{I}$$

;

- среднее арифметическое значение всех элементов h_j. $$m_h=\frac{{\displaystyle \sum _{i=0}^{I-\mathrm{one}}{h}_j}}{J}$$

is the arithmetic mean of all elements h _j .

An example of a characteristic diagram of the values of r _j shown in figure 2.

The maximum value of r _h from all r _j will correspond to the value of j _{p of} index j, for which the response of the probing signal most often manifests itself in the output FFT values m _ij , and, therefore, to the value of f _{p of the} difference frequency, which is determined by expression (2).

The decision circuit 4 analyzes the values of r _j , finds the maximum value of r _h and the corresponding index j _p . In addition, the decision circuit 4 generates a flag s _obn set in the state of "Discovered" or in the state of "Not detected", according to the following rule:

$$s_{\mathrm{about}bn}=\{\begin{array}{l}"\mathrm{ABOUT}bn\mathrm{but}R\mathrm{at}\mathrm{well}en",PR\mathrm{and}{r}_h>r_{hP\mathrm{about}R}\\ "Ne\mathrm{about}bn\mathrm{but}R\mathrm{at}\mathrm{well}en",PR\mathrm{and}{r}_h\le r_{hP\mathrm{about}R}\end{array},\left(3\right)$$

;Where $$r_{hP\mathrm{about}R}={\sigma }_0\sqrt{-2\ln \left(\mathrm{one}-\exp \left(\frac{\ln \left(\mathrm{one}-P_{lt}\right)}{J}\right)\right)}$$

;

P _lt - the value of the regulated probability of false alarm;

.σ ₀ - the standard deviation of the value of r _j in the absence of response of the probe signal. For example, if we use the values of r _j for the current session of the chirp receiver, the value of σ ₀ can be defined as $$\sqrt{{\displaystyle \sum _{j=0}^{J-\mathrm{one}}\raisebox{1ex}{$r_j^2$}\!\left/ \!\raisebox{-1ex}{$J$}\right.}}$$

.

в виде функции от Р_лт приведены на фиг.3 для J=40, 400, 4000.The results of the calculation of normalized values $$\frac{r_{hP\mathrm{about}\mathrm{<figure-callout\; id="0"\; label="R\; \sigma "\; filenames="00000017.png"\; state="\{\{state\}\}">R\; </figure-callout>}}}{{\sigma }_{}}$$

as a function of P _lt are shown in figure 3 for J = 40, 400, 4000.

If the flag s _upd is set to "Detected", the start time calculator 5 defines the value of the difference frequency f _p according to the rule (2), the value of start time:

$$T_{\mathrm{from}t}=\left[\frac{\left(T_{\mathrm{from}t}+{\tau }_s\right)}{\Delta T_{\mathrm{from}t}}\right]\times \Delta T_{\mathrm{from}t},\left(\mathrm{four}\right)$$

where (T _st + τ _s ) = T _{beg g} - (f _p + f _{beg g} ) / β (see expression (1));

ΔT _article - the regulated step of the time grid for transmitting stations (for example, ΔТ _article = 1 s), the value of which is obviously greater than the possible value of τ _s ;

[x] is the operation of extracting the integer part of the quantity x,

and the value of the group path of propagation of radio waves along the path from the transmitting station to the receiving point:

$$L_{gR}=\left(\left(T_{\mathrm{from}t}+{\tau }_s\right)-\left[\frac{\left(T_{\mathrm{from}t}+{\tau }_s\right)}{\Delta T_{\mathrm{from}t}}\right]\times \Delta T_{\mathrm{from}t}\right)\times \mathrm{from},\left(5\right)$$

where [x] is the operation of extracting the integer part of the quantity x;

c = 3 × 10 ⁵ km / s is the propagation velocity of the electromagnetic wave.

Information sources

1. Z. No. 2009124999, G01S 5/00, publ. 01/10/2011.

Claims (1)

A method for detecting linear frequency modulated (LFM) signals, which comprises spatially separated signals emitted by a plurality of radio transmitters, characterized in that they perform LFM heterodyning of the total signal and calculate the fast Fourier transform (FFT) using an adder during the session detections partially accumulate FFT samples so that on each j-th output of the adder the value r _{j is formed} , then among all J outputs of the adder, an output with that index j _{p is found} , for which as a result ate accumulation obtained from the maximum values of r _j, and denoted as r _h, and which is uniquely associated with the value of the difference frequency f _p, then for a given false alarm probability value r calculated _hpor threshold value, a flag

and, if s _obn = “Detected”, the value of the starting frequency f _p determines the start time of the detected LFM signal and the length of its group propagation path.

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