RU2773481C1 - Method for determining the time delay between copies of a non-deterministic pseudo-random signal - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: invention relates to measuring and radio receiving technology and can be used in systems that measure the time delay between copies of a non-deterministic pseudo-random signal. The method includes several stages: fast Fourier transform (FFT) of input signals; alignment of input signals according to the power level of spectral components; formation of several control sum signals; FFT of sum signals; the introduction of additional auxiliary time delays that contribute to the expansion of the measurement range and the formation of IM in the spectra of control sum signals; the formation of a set of spectral intervals of IM in the sum spectra by means of phase shifts between the terms of control sum signals, the MPF of the set of spectral intervals of IM in the sum spectra; the calculation of the delay time based on the measurements of the intervals of IM in the control sum signals.

EFFECT: main signal processing consists in performing FFT and simple mathematical operations, which increases performance and simplifies the implementation of this method for determining the delay time.

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Description

The invention relates to measuring and radio receiving equipment and can be used in systems that measure the time delay between copies of a non-deterministic pseudo-random signal.

There is a spectral method for measuring time delays described in the sources (Gershman S.G. Tuzhilkin Yu.I. On the interference of broadband noise signals. - Acoustic journal. 1965, v.11; and patent RU No. 864167 dated 15.09.81 IPC G01R 23 / 00). This method is based on the fact that characteristic signs of interference appear in the total (multipath) signal; with a frequency representation of the signal, they will look like a sharp “dip” in the level of the spectral components at the interference minimum and a “rise” at the maximum.

The interference minimum (IM) and the maximum amplitudes of the total components of the spectrum are due to the values of the phase shift angles between the two terms, close to 180 and 0 degrees, respectively. One of the initial and total spectra are shown in Fig. one.

The frequency interval (dƒ) between the interference minima (MI) located on the total spectrum determines the value of the delay (dT) between the signals:

The possibility of the appearance of several MIs in the spectrum band (dF) of the signal is determined by the condition:

The disadvantage of the spectral method is the low accuracy of determining the delay time due to multipath, uneven group delay time of the signal and the irregular composition of the spectral components that determine the location of the IM on the frequency scale. The spectral composition of the signal is determined by the frequencies of the modulation signal. Errors in determining the value of the MI frequency lead to an error in determining the frequency interval and, accordingly, the calculated value of the delay time.

In the description of the invention (patent RU No. 864167 dated 15.09.81 IPC G01R 23/00) the shortcomings of the spectral method are analyzed and it is proposed to use a combined method to improve the accuracy of delay measurement - in addition to the spectral measurement, add directly the measurement of the MI interval in the time domain, highlighting these parts of the spectrum selective filters. The measured data are accumulated and then the delay time is determined from the most probable values.

We will take this modified spectral method for measuring the delay time as a method corresponding to the functional purpose as a prototype.

The disadvantage of this method is the low speed and the resulting low noise immunity in terms of changing the delay time. Also, the irregular composition of the modulation frequencies that determine the value of the MI interval in the time domain (the MI time interval is the intersection of the signal fluctuation with the zero mark) leads to “jitter” of the measured values of the time intervals, that is, to a decrease in the measurement accuracy.

The technical result of the claimed invention is to increase the speed and accuracy of determining the delay time between two copies of a pseudo-random non-deterministic signal.

The technical result is achieved by using a spectral-phase method that forms a “spectral-phase grid” (SPS) of MI, which is several MI intervals simultaneously created on a plurality of spectra of the total signal and shifted in frequency. This makes it possible to parallelize the process of measuring MI frequency intervals in all created spectra of sum signals and then, by averaging simultaneous measurements, to increase the accuracy of determining the delay time.

The proposed spectral-phase method for measuring the delay, based on the creation of a “spectral-phase grid” of MI, which is a set of total spectra (dF wide), each of which contains intervals of the MI spectral envelopes (dƒ), shifted from each other in frequency (BP Sequential shift in the frequency of MI intervals is carried out using a certain phase increment (Δf) of one of the terms of the signals.The value of the phase increment Δf in degrees, giving a frequency shift Δƒ, is determined by the formula:

The total spectra with frequency-shifted MI spectral envelope intervals are shown in Fig. 2, 3, 4, 5. Increasing the accuracy of determining the delay time is achieved by averaging a set of simultaneously measured frequency intervals in the spectra of the sum signals.

The method includes several steps:

- fast Fourier transform (FFT) of input signals;

- alignment of input signals according to the level of spectral components;

- formation of several control total signals;

- FFT of total signals;

- the introduction of auxiliary time delays, contributing to the expansion of the measurement range of time delays and the formation of IM in the spectra of control total signals;

- formation of SPS interference minima of the spectrum;

- averaging the values of the phase interference minima of the spectrum over frequency and time;

- determination of the delay time based on the results of the averaged values of the interference minima.

A block diagram that implements this method for measuring the delay time is shown in Fig. 6.

One of the input signals is fed to the controlled attenuator 1, which equalizes the power levels of the spectral components, then the signal is fed to the controlled delay line 2, in which an additional time delay is set, which makes it possible to form interference minima in the spectrum of the total signal. Then, after branching in circuit 3, the signals are fed to a line of controlled phase shifters - circuit 4. Controlled phase shifters, by setting a certain phase shift in them, perform frequency positioning of the intervals of the MI spectral envelopes in the spectra of the sum signals. Signals with certain phase shifts are fed to one of the inputs of the adders 5. The second input signal, after equalization in circuit 1, setting the time delay in circuit 2 and the formation of a phase shift in circuit 4, is fed to the other input of the adders 5. The total signals thus formed are fed to the circuits 6 that perform a Fast Fourier Transform (FFT). The spectral data about the signals are fed to circuit 7, which measures the intervals of the spectral envelopes of the MI and performs the calculation of the delay time.

The device operation algorithm that implements this delay measurement method includes the following steps:

- to increase the range of the measured delay time, and the possibility of obtaining interference minima, a time delay is introduced into one of the pair of signals;

- to improve accuracy, N number of measurements of MI frequency intervals are performed simultaneously

in the N number of total signals (which have the same delay and a certain specified phase shift of the terms of the signals forming the MI frequency shift);

- the sum signals are simultaneously subjected to fast Fourier transforms. Thus, N is formed - the number of control and measurement spectra, which, due to a certain phase shift between the terms of the signals, have different frequency-shifted intervals of the spectral envelopes of the MI. This allows from N number of control-measuring spectra at one time to obtain N number of measurements of the values of the intervals dƒ _i MI;

- based on the data obtained on the values of the intervals dƒ _i IM, the average value of the delay time dT is calculated using the formula:

The maximum practical value N, which determines the accuracy of the calculation of the delay time, is determined by the formula:

where R is the frequency resolution of the spectrum analyzer (number of FFT points per unit frequency).

When calculating the device operation algorithm, the main signal processing will be to perform a fast Fourier transform and simple mathematical operations, which will increase performance and simplify the implementation of this method for determining the delay time.

Claims (2)

A method for measuring time-delayed pseudo-random non-deterministic signals, in which two signals, presented in the form of a frequency spectrum, leveled in level, forming several interference minima (IMs) in the control total spectra, which makes it possible to determine the delay time by the value of the frequency difference of neighboring IMs, which differs in that , which, in order to increase the range of the measured delay time, introduces a discrete time delay into one of the signals, to increase the measurement accuracy, it generates N the number of total signals having a fixed time delay and a different defined phase shift of the terms, simultaneously subjecting the total signals to fast Fourier transforms and thus forming N is the number of control total spectra having the same time delay and different phase shift terms; allowing to make in the control summary spectra at one time N the number of measurements shifted in frequency of the values of the intervals dƒ _i -IM, and based on the measured data dƒ _i providing the average value of the delay time dT according to the formula

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