RU2365053C2 - Method of inverse-quadrature restoration of carrier frequency phase-shift keyed signals of any frequency rate - Google Patents

Abstract

FIELD: physics; radio.

SUBSTANCE: invention concerns radio engineering and can be used at demodulation of PSK signals of various frequency rates. The essence of the method is characterised by restoration of carrier frequency of the phase-shift keyed signals by forming of inverse-quadrature components of the inphase and quadrature channels with use of the tunable oscillator of sinusoidal fluctuations on the doubled frequency concerning carrier frequency of a received phase-shift keyed signal.

EFFECT: increase of noninterference and maintenance of carrier restoration at any frequency rate of phase-shift keyed (PSK) signals.

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Description

The invention relates to the field of radio engineering and can be used for demodulation of phase-shifted signals with a complex structure of FM2, FM4, FM4S, FM8, KAM16, KAM32, KAM64, KAM128, KAM256.

One of the main operations performed during demodulation of FM signals and determining the quality of demodulation is the carrier frequency recovery operation.

The following methods for recovering a carrier frequency are known:

1. The method of squaring is the multiplication of the signal itself (1 - J. Spilker “Digital Satellite Communication; M .: Communication, 1979). This method has low noise immunity due to a decrease in its energy potential by 6 dB (1, p. 351), as well as due to autocorrelation when multiplying the components that occur in the transmission path and accompany the useful signal.

2. The method of synchronous detection (2 - Japan patent No. 52-4902 "Method for the synchronous detection of phase-shift signals"). This method is preferable to the squaring method due to its lower sensitivity to center frequency shifts and the ability to operate over a wide range of input signal speeds. However, this method also has a significant drawback associated with the fact that when generating an error signal, information components penetrate the control circuit of a frequency-tunable generator, which leads to a decrease in its noise immunity (3 - E.D. Vitterby “Principles of coherent communication”, Soviet radio , 1973).

3. The method of inverse-quadrature recovery of the carrier frequency (4 - Patent No. 2187901 "Method of inverse-quadrature recovery of the carrier frequency of FM signals").

This method is most effective, but has a drawback - it provides carrier recovery only for two-phase signals (2FM).

4. Currently, in almost all demodulating devices of both domestic and foreign production, the in-phase quadrature multiplication method is used - the Kostas method (1, p. 276), taken as a prototype and providing carrier recovery for types of modulation FM2, FM4, FM4S, FM8, KAM16 ... KAM256. The method is less sensitive to shifts of the central frequency and ensures operation in a wide range of input signal speeds.

According to the method of Kostas perform the following sequence of operations:

- reception and branching of the signal into two directions;

- generation of a sinusoidal signal at a frequency close to the carrier of the input signal;

- quadrature-coherent detection of a part of the FM signal by multiplying it with a 90 ° phase-shifted generated signal in the first direction of signal branching;

- in-phase-coherent detection of a part of the FM signal by multiplying it with the in-phase-generated signal in the second direction of signal branching;

- filtering (in the band of modulating frequencies) the results of each detection;

- multiplication of the quadrature components of the filtered signals (as part of the likelihood maximum assessment device);

- integration of the multiplication results in order to generate an error signal for synchronization of the generated signal (in this case, the frequency and phase of the generated signal in the synchronization mode are set equal to the carrier wave of the received signal).

However, this method has significant disadvantages:

- penetration into the control circuit of a frequency-tunable generator of information components (especially when a series of zeros or ones appears in the signal), which leads to a decrease in its noise immunity (3, p. 40);

- correlation of interference in the band of the monitored signal, which also impairs its noise immunity.

The aim of the invention is to increase the noise immunity of the method of recovering the carrier frequency of the FM signals and providing carrier recovery for an arbitrary multiplicity of FM signals.

To achieve this goal, a method is proposed for inverse-quadrature reconstruction of the carrier frequency of phase-manipulated signals of arbitrary multiplicity, in which the signal is received and two processing paths are generated: the first and second, generate a tunable signal with a frequency close to the carrier frequency of the phase-manipulated signal, perform a sinusoidal signal, and perform quadrature-coherent detecting part of the FM signal by multiplying part of the signal along the first processing path with the generated sinusoidal shifted by 90 ° signal, carry out in-phase-coherent detection of part of the FM signal by multiplying part of the signal along the second processing path with the in-phase-generated sinusoidal signal, filter and multiply the obtained results in the process of maximum likelihood estimation, form the maximum likelihood estimate, filter and form the control signal for tuning the generated sinusoidal signal. According to the invention, two more processing paths are formed: the third and fourth, a sinusoidal signal is generated at a frequency not close to the carrier, but at a double frequency to the carrier, as a result of which the inverse-quadrature signal is obtained in the first processing path, which is multiplied with part of the original signal along the third processing path, and in the second path, an inverse common-mode signal is obtained, which is multiplied with a part of the initial signal by the fourth processing path, while the signal of the reconstructed carrier form comfort by dividing by two the frequency generated by the established value of the signal at double the frequency, and the recovered carrier signal is formed by dividing into two steady-state value of frequency of the generated signal.

The combination of distinctive features and properties of the proposed method from the available literature are unknown, therefore, it meets the criterion of novelty and inventive level.

сигналов по предлагаемому методу, на фиг.5 поясняется процесс проникновения сигнала той же помехи, расположенного в полосе модулирующих частот входного сигнала, в продукты взаимного перемножения каналов I и Q по способу Костаса.Figure 1 shows a block diagram of a device that implements this method, figure 2 is a block diagram of Costas (shown for comparing operations and devices of the proposed method and prototype), figure 3 is a basic element of maximum likelihood assessment (5 - B .M. Botashev, N.G.Parkhomenko “Estimation of the phase of the carrier wave of multi-position phase-shifted signals”, Questions of radio electronics, issue 17, 1991), figure 4 explains the process of not penetrating the interference signal located in the modulating frequency band of the input signal, into the products of mutual multiplication FM and

signals according to the proposed method, figure 5 explains the process of penetration of the signal of the same interference, located in the modulating frequency band of the input signal, into the products of the mutual multiplication of channels I and Q according to the Kostas method.

The device according to the proposed method contains a four-way splitter 1, the first output of which is connected to the input of a series-connected mixer 2, a multiplier 3, a filter 4, a maximum likelihood estimator 5, a proportionally integrating filter (feedback filter) 6, a generator controlled by voltage 7, phase shifter (90 °) 8; the second output of the splitter 1 is connected to the input of the second mixer 9, the second multiplier 10, the filter 11, the output of which is connected to the second input of the maximum likelihood estimator 5, the third output of the splitter 1 is connected to the second input of the first multiplier 3; the fourth output of the splitter 1 is connected to the second input of the second multiplier 10, while the output of the phase shifter 8 is connected to the second input of the first mixer 2, and the output of the generator 7 is also connected to the second input of the second mixer 9 and to the input of the divider into two 12, which is the output of the device.

The operation of the device is based on the use of the amplitude and phase symmetry properties of the spectrum of FM signals relative to the carrier frequency. For amplitude this is a clear symmetry, for a phase it is fuzzy (6 - “Noise-like signals in information transmission systems” edited by Professor Pestryakov, M .: Sov. Radio, 1973).

When converting the input FM signal using a reference signal with a frequency twice the frequency of the carrier FM signal, a frequency-inverse FM signal is formed (with symmetric mutual permutation of the spectral components relative to the carrier frequency of the original FM signal), orthogonal in phase and completely equivalent to the original signal.

When the source and frequency-inverse FM signals are multiplied, a control signal is generated that provides synchronization of the generator frequency (VCO) with respect to the received carrier oscillation. In this case, the noise accompanying the signal in the initial and frequency-inverse spectra of the FM signals turns out to be symmetric with respect to the signal carrier, and their cross-correlation is filtered out by proportionally-integrating filters of the control circuit, which minimizes their contribution to the control signal and thereby increases the noise immunity of the device.

The device (figure 1) works as follows. The received signal in the splitter 1 branches into four processing paths. In the first path, the signal goes to mixer 2, the second input of which receives a signal from the VCO 7 at a double frequency relative to the signal carrier through the phase shifter 8, as a result of which a frequency-inverse copy of the Q channel of the input signal is generated at the output of the mixer 2, which is fed to the multiplier 3 , the second input of which receives the original signal from the third processing path. The result of the multiplication is filtered in block 4 and fed to the first input of the estimator of the maximum likelihood 5.

The operation of the device along the second and fourth processing paths is similar to that described above, except that the signal from the VCO 7 is fed directly to the second mixer 9, as a result of which a frequency inverse copy of channel I of the input signal is generated at its output. The output of channel I filter 11 is supplied to the second input of block 5, the control voltage from which is supplied to the proportionally integrating filter 6, and from it to the control input of the VCO 7 and maintains it in synchronism mode, the signal from the output of the VCO 7 is fed to a two-twelve-factor divider, the output of which is the output of the device. The basic element of the likelihood estimator (Fig. 3) contains a first multiplier, an adder, a subtractor, a second multiplier, while the output of channel Q from the device (Fig. 1) is connected to the first inputs of the first multiplier, an adder, and a subtracter, and the output of channel I is connected to the second inputs of the first multiplier, adder and subtractor; the outputs of the adder and subtractor are connected respectively to the first and second input of the second multiplier. The output of the first multiplier goes to the input of the proportionally integrating filter 6 and to the input of the subsequent base element, the output of the second multiplier goes to the second input of the subsequent base element. The number of series-connected basic elements is determined by the modulation ratio. For FM4 - one basic element, for FM8 - two, for Kam16 - three, for KAM 256 - seven.

Claims (1)

A method of inverse-quadrature reconstruction of the carrier frequency of phase-manipulated signals of arbitrary multiplicity, in which, according to the Kostas method, the signal is received and branched, a frequency-tunable sinusoidal signal is generated, quadrature-coherent detection of the phase-manipulated signal is performed by multiplying it with a 90 ° phase-shifted generated sinusoidal signal subsequent filtering in the first direction of signal branching, in-phase-coherent phase detection is carried out of the manipulated signal by multiplying it with the in-phase generated signal and then filtering in the second direction of the signal branching, form a signal for evaluating the maximum likelihood by multiplying the obtained results in the first and second directions of branching, filter the result and form the control signal for tuning the sine signal generator, characterized in that the generation of a sinusoidal signal is carried out at a double frequency to the carrier of the input signal, as a result, an inverse-quadrature signal is obtained in the first branching direction, and an inverse-in-phase signal in the second branching direction, and before filtering in the third branching direction, the phase-manipulated signal is multiplied with the inverse-quadrature signal of the first branching direction, and in the fourth branching direction multiply the phase-shifted signal with the inverse common-mode signal of the second branching direction, and the signal is restored th carrier is obtained by dividing by two steady-state frequency values of the generated sinusoidal signal at twice the frequency.

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