RU2542574C1 - Method of correlation reception of phase-manipulated signals - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed method comprises division of signals into identical components, their frequency conversion along with LF filtration of every said component. Strobes are shaped for time switching of data channels composed by the shift of local oscillator harmonic signals. Note here that said strobes are shaped from envelope beating originating at multiplication of input signal by local oscillator harmonic signals with constant phase shift there between. This is effected by double beating frequency is isolated to be subjected to LF filtration, limiting amplitude limitation, passage of digital logical elements that perform logical multiplication of digital logic input signal and signal obtained with the help of frequency digital divider.

EFFECT: efficient reception with no monitoring of current phase of carrier frequency.

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Description

The method relates to electrical communication technology, involves the correlation reception of phase-shifted signals in the absence of tracking the current phase of the carrier frequency with constant adjustment of the reference signals received by the correlation device. The method does not depend on the magnitude of the frequency mismatch between the input and reference signals, provided that the input signal of the receiving device is in the band of frequency-selective circuits, and therefore can be used in mobile data transmission systems with undefined deviations of the carrier frequency from the nominal value.

It is known that the frequency deviations of the received and reference signals during the correlation reception of phase-shifted signals can be compensated (detected) using various closed-loop tracking schemes for the current phase of the carrier wave [1], [2]. With large values of the mismatch, a preliminary adjustment is carried out using parallel and sequential search schemes.

In [1] and [2], in addition to the PLL system, a squaring circuit is considered that provides phase-locked loop in the absence of a constant component of a phase-shifted signal by squaring a phase-shifted signal, tuning using a double-frequency PLL loop and subsequent division.

In [2], a scheme is presented for recovering the carrier frequency by means of squaring to the fourth degree, which works on the same principle as squaring.

In [1], the in-phase-quadrature scheme, also called the Costas circuit [3], on which most of the existing synchronization solutions are based, is considered. This circuit includes two channels in which the input signal is demodulated by multiplying by carriers with a phase shift between them by 90 °, multiplying the demodulated signals provides tuning of the controlled generator through a loop filter.

The scheme adopted by us for the prototype [4] includes the separation of the signal into two equal components, in-phase and quadrature frequency conversion of both components, followed by low-pass filtering of each of the frequency-converted signal components, multiplying the filtered signals and finding the Fourier transform of the signal.

The disadvantage of the prototype, like most other solutions used in the correlation reception of phase-shifted signals, in one form or another, involving the use of tracking circuits to compensate for the frequency mismatch between the carrier signal and the reference generators, is the limited frequency adjustment speed and the limited capture band, which is determined by the presence of a rigid the relationship between the stability of closed loop systems with feedback, speed and tuning range.

The objective of the present invention is the ability to provide energy-efficient correlation reception of phase-shift signals in the absence of tracking the current phase of the carrier frequency.

The essence of the invention lies in the fact that the method of correlation receiving phase-shifted signals in the absence of synchronization on the carrier frequency includes the formation of gates that provide temporary switching of information channels. Information channels are formed as a result of the fact that the input information signal with a shifted carrier frequency is multiplied by the signals of the reference generators with phase shift. Gates are formed from the resulting signals in the information channels, consisting of an information signal with beats with different phases. To obtain gates, the double beat frequency is selected, filtered and the amplitude limit is limited. Pulses are formed from the received signals using digital logic elements, each of which marks the time of receiving the information signal from the channel with the corresponding beat phase.

The features of the method for the correlation reception of phase-shifted signals in the absence of synchronization on the carrier frequency are that the method

uses several receiving channels resulting from the multiplication of the input phase-manipulated signal by the signals of the reference oscillator with a different frequency and phases set at a certain step, in which binary information does not change the phase depending on the phase of the reference oscillation;

allows you to select the envelope of the beats in the frequency band determined by the upper frequency of the bandpass filters;

allows you to generate gating pulses from the envelope of the beats with a different phase;

the number of receiving channels is determined by the magnitude of the phase step and determines the amount of signal reduction at the output of the correlation device relative to the maximum value corresponding in time to the middle of the strobe pulse.

The difference between this solution and the well-known in-phase-quadrature circuit consists in the absence of a feedback loop for tuning the frequency of the reference oscillator.

Figure 1 shows a structural diagram of a device for the correlation reception of phase-shifted signals, where:

1) demodulators, consisting of multipliers and low-pass filters;

2) phase shift elements;

3) reference generator;

4) circuits emitting gating pulses in the channels;

5) delay elements;

6) a digital logic circuit providing temporary switching of channels.

Figure 2 shows a diagram of the selection of the strobe pulse from the channel with beats, where:

7) a signal module taking unit;

8) band-pass filter;

9) the block raising the signal to an even degree;

10) limit limiter;

11) multiplier;

12) a comparison unit with a threshold level;

13) threshold level generator;

14) limit limiter.

Figure 3 and figure 4 presents the output signal of the circuit for a special case where two quadrature channels are used for cases where the frequency of the information signal is higher than the beat frequency and when the frequency of the information signal is lower than the beat frequency.

The method is as follows.

The input signal along lines 1 ₁ -1 _N goes to the inputs 1 ₁ -1 _{N of} demodulators 1 ₁ -1 _N , and the reference signal from the generator 3 along lines 2 ₁ -2 _N goes to the inputs 1 ₁ -1 _N of phase shift elements 2 ₁ -2 _N , providing a delay of the reference signal into phases with a constant step,

the delayed signals of the reference generator from the outputs 2 ₁ -2 _{N of the} elements of the phase shift 2 ₁ -2 _N go to the inputs 2 ₁ -2 _{N of} demodulators 1 ₁ -1 _N , where they are multiplied and subjected to low-pass filtering, as a result of which channels 1-N are allocated information signal with envelope beats having a different phase,

from the outputs 3 ₁ -3 ₁ demodulators 1 ₁ -1 _N signals along the lines 4 ₁ -4 _N are supplied to the inputs 1 ₁ -1 _{N of} identical circuits that emit gating pulses in the channels, the structure of which is described below,

from the outputs 3 ₁ -3 _N demodulators 1 ₁ -1 _N signals along the lines 5 ₁ -5 _N go to the inputs 1 ₁ -1 _N delay elements 5 ₁ -5 _N , which ensure the appearance of the maximum signal in the channel at the moment when the strobe is highlighted -pulse,

strobe pulses from outputs 2 ₁ -2 _{N of} circuits 4 ₁ -4 _N are fed to inputs 1 ₁ -1 _{N of} digital logic circuit 6, where, using frequency dividers and logic gates, a sequence is formed that controls the switching of information signals from outputs 2 ₁ -2 _N delay elements 5 ₁ -5 _N along lines 7 ₁ -7 _N to the inputs 2 ₁ -2 _{N of the} digital logic circuit 6.

The information signal with envelope beats along line 4 is fed to input 1 of the capture unit of module 7,

from the output 2 of the block taking module 7 on line 8, the signal is fed to input 1 of the bandpass filter 8, where the beat signal is highlighted,

from the output 2 of the bandpass filter 8 along line 9, the signal is fed to the input 1 of the block raising to an even degree 9, which determines the width of the generated strobe pulses,

from the output 2 of the bandpass filter 8 along line 10, the signal is fed to input 1 of the limiter 10,

from the output 2 of the block raising to an even power of 9 on line 11, the signal goes to input 1 of the multiplier 11, from the output 2 of the limiter 10 along line 12, the signal goes to input 2 of the multiplier 11,

from the output 3 of the multiplier 11, the signal on line 13 is fed to the input 1 of the comparison unit with the threshold level 12,

from the output 1 of the block forming the threshold level 13 on line 14 is input 2 of the comparison unit with the threshold level 12,

from the output 3 of the comparison unit with the threshold level 12 along line 15, the signal is fed to input 1 of the limiter 14, which generates short strobe pulses, which are transmitted from output 2 of the limiter 14 via line 6 to the switching circuit.

Examples of the method for the case of using two quadrature channels are shown in FIGS. 3 and 4. In the first case, the mismatch value is chosen to be much larger than the frequency of the information signal, in the second case, much smaller. For both cases, the method is as follows:

The received phase-shift input signal has the form

V _BX (t) = A _BX sin (ω ₀ t + θ (t _k )),

where A _BX is the amplitude of the input signal, and θ (t _k ) is the phase of the signal at time t _k , taking values 0 and π.

The local oscillator signal differs from the frequency ω _{0 of the} input signal by δω and has an amplitude A _G and phase φ

V _Г (t) = A _Г sin (ω ₀ t + δω) + φ).

Then the signal after the mixer and the suppression of the high-frequency component is

Thus, when using two quadrature channels with a phase shift of the reference generator by 90 °, two resulting signals are formed, which are proportional to the amplitude of the input signal and the amplitude of the harmonic signal with a frequency δω acting as a carrier for the information signal.

The transmission of these two signals to the switching circuit is controlled by strobe pulses obtained from the same signals. In the amplitude detection of an information signal with an envelope determined by the magnitude of the frequency mismatch of the carrier, the module of such a signal is allocated. Filtering in a wide band, determined by possible values of the carrier frequency mismatch, makes it possible to isolate the double mismatch frequency for the subsequent limiting limitation, as a result of which in two channels sequences of pulses of equal length, opposite in phase, are formed.

Using a frequency divider, pulses with a mismatch frequency are extracted. When they are multiplied by a sequence of pulses in each channel, strobe pulses of different polarity are formed, and at those moments when the signal amplitude in the channel is maximum, the pulse takes alternating values 1 and -1, and when the signal amplitude in the channel is minimal, it is 0. Since the maximum of one channel coincides with the minimum of the other; multiplication of information in each channel by the received control signal and subsequent addition allow obtaining information with losses not exceeding 3 dB. Such losses will occur at the minimum points of the received signal corresponding to an envelope phase of 45 °.

Obviously, with an increase in the number of channels, which correspond to a decrease in the phase shift of the reference signals, the losses decrease.

The advantages of the proposed method include:

increased bandwidth of the processed frequency mismatch compared to previously existing solutions,

stable operation after completion of transient filter processes,

independence of signal power loss from mismatch of the carrier frequency and the frequency of the reference oscillator.

Information sources

1. B. Sklyar. Digital communication. Theoretical foundations and practical application. - M.: Williams Publishing House, 2004. Chapter 10.

2. J. Spilker. Digital satellite communications. - M.: Communication, 1979.

3. US patent No. 3047660, 1960.

4. RF patent No. 2234810, 2002. - Prototype.

Claims (1)

A method for correlating receiving phase-manipulated signals, including dividing the signal into equal components, frequency converting these components, followed by low-pass filtering of each of the frequency-converted signal components, characterized in that the method includes forming gates providing temporary switching of information channels formed by shifting the initial phase of harmonic signals of reference generators, while the gates are formed from the envelopes of the beats that occur when multiplying the input signal to the harmonic signals of the reference generators with a constant phase shift between them, by isolating the double beat frequency, its low-pass filtering, maximum amplitude limitation and the passage of digital logic elements, including the logical multiplication of the input signal of digital logic and the signal obtained using a digital frequency divider .

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