Quadrature Processing Research Articles

Method for reducing phase fluctuations of a precision frequency response meter for microwave quantum generators

The principle of operation of the device for measuring frequency characteristics is considered. Block diagram of a device for measuring the frequency characteristics of a digital frequency comparator with correlation quadrature processing and description of their components is illustrated. The block diagram of the frequency multiplier is given. The accuracy characteristics of the developed meter design are evaluated. They are compared with the characteristics of previously used devices. The Improve accuracy characteristics and increased stability of operation were found.

Remote Diagnostics of Vibrations of Dynamic Objects Using Doppler Microwave Sensors

This paper reviews methods used for measuring the vibration of dynamic objects, including a promising method for non-contact vibration diagnostics based on Doppler microwave sensors. The method involves actively irradiating an object with electromagnetic waves and applying a two-channel quadrature processing to the reflected signal received. The article also discusses modes of analysis of the subtle resulting signal using spectral or wavelet transformations depending on the nature of the active vibration. The advantages of this non-contact and remote vibration analysis method for studying complex dynamic objects are described. Finally, we evaluate the applicability of this method in machine learning and intelligent systems employed for the non-destructive continuous monitoring of the state of complex dynamic objects under vibration.

Navigation Doppler lidar sensor for precision landing of China's Chang'E-5 lunar lander.

Lidar technology is playing an important role in the application of autonomous navigation and hazard avoidance for the landing and cruising exploration on planetary bodies, such as landing on the moon, Mars, and asteroids. We report a Doppler lidar developed for Chang'E-5 mission in this paper. To meet high reliability and resource constraints, time-sharing measuring and in-phase and quadrature processing in this Doppler lidar system was provided and tested. Compared with the traditional linear frequency modulated systems, this lidar system provides excellent detection probabilities of false alarms, especially for the determination of velocity directions. Flight and vibration tests and plume experiments were carried out to further demonstrate the performance and feasibility during the landing mission in late 2020.

Identification of Energy-Hidden Chirp Signals of Telecommunication Systems in Conditions of Parametric Uncertainty

The ambiguity diagram of rectangular chirp RF pulse has been analyzed. The characteristic point of ambiguity diagram was identified. It was proposed to identify the signal on the basis of correlation level at the characteristic point of ellipsoidal ambiguity diagram built in a special coordinate system. The quasi-optimal autocorrelation algorithm with quadrature processing is proposed. This algorithm is resistant to a priori uncertainty of parameters of input energy-hidden signals with unknown waveform and unknown initial phase against the background of Gaussian stationary noise. The tuning parameters of identification scheme and the decision-making rule regarding the availability of chirp signal in the input mixture were determined. The simulation modeling of identification procedure was conducted using the software package Matlab R2016a. The simulation results confirmed the ability of the proposed algorithm to identify the chirp signal in the input mixture at small values of the signal-to-noise ratio.

Remote diagnostics of vibrations of dynamic objects by Doppler microwave sensors

This paper describes a promising method for non-contact vibration diagnostics based on the use of Doppler microwave sensors. In this case, active irradiation of the object with electromagnetic waves and the allocation of phase changes using two-channel quadrature processing of the received reflected signal are used. The modes of further fine analysis of the resulting signal using spectral or wavelet transformations depending on the nature of the active vibration are considered. The advantages of this non-contact and remote vibration analysis method for the study of complex dynamic objects are described. The convenience of the method for machine learning and use in intelligent systems of non-destructive continuous monitoring of the state of these objects by vibration is noted.

СТАТИСТИЧНІ ХАРАКТЕРИСТИКИ ЕНЕРГЕТИЧНО ПРИХОВАНОГО ФАЗОМАНІПУЛЬОВАНОГО СИГНАЛУ

The law of distribution of the output effect differs from the normal one at the output of the receiving path realized on the basis of autocorrelation algorithm with quadrature processing. When there is no signal at the input of the receiver, the distribution of the output effect corresponds to Rayleigh’s or Rayleigh – Rice’s law in condition of its presence. The probability density distribution at the output of an incoherent auto correlation receiver with quadrature processing is considered in relation to the input level of the energy-concealed phase-manipulated signal. In order to detect a useful signal it is necessary that, at the output of the receiver, the signal / noise ratio exceeds the detection threshold determined by the Neumann – Pearson criterion according to the given probability of false alarm. The level of the signal-to-noise ratio at the output of an incoherent autocorrelation receiver with quadrature processing has been calculated. A characteristic feature of the presented graphs is the linear dependence of the output signal / noise ratio relative to the input signal. This feature is observed in the input signal / noise ratio which is less than one. The curves for the distribution of the probability density of the input signal mix and noise corresponding to the generalized Rayleigh’s law (Rayleigh-Rice) are constructed in the book. There is a shift of curves for the abscissa axis according to the given probabilities of false alarms and accumulation time (observation). It is evident from the given graphs that the offset of the abscissa of the input signal value / noise ratio significantly depends on the accumulation of the input mixture time. The curves for detecting an energy-concealed phase-manipulated signal by a non-coherent autocorrelation receiver with quadrature processing on the basis of the probability density distribution are obtained. The results of the calculations indicate that detection of a phase-manipulated signal on the background of "white" noise is possible in case of an input-to-noise ratio of less than one, that is, up to -32 dB in real time (up to 0.1 s).

QUADRATURE MEASUREMENT METHOD FOR COMPLEX PARAMETERS OF MICROWAVE TWO-POLES

A new method based on direct frequency conversion is developed for measuring complex reflection coefficient of microwave two-poles. The method is based on the use of quadrature synchronous detection of the signal branched by omnidirectional probe with subsequent quadrature processing of the detected signal components. Such approach makes it possible to solve measuring task by simultaneously analyzing both amplitude and phase distribution of the field in transmission line which leads to redundancy. In addition, the use of direct frequency conversion provides the detection linearity in considerably higher dynamic range of the levels of the signal forwarded from the transmission line. So, both of these factors can improve the measurement accuracy. The method is performed by excitation of probing harmonic microwave oscillation in transmission line and formation of reference microwave oscillation with the same frequency. The reference signal and the signal branched from the transmission line by omnidirectional mobile probe are fed to the inputs the quadrature synchronous detector. At its outputs, I and Q components of the detected signal are formed. By means of these components, the amplitude and phase field distribution in the trans-mission line is obtained. It is followed by calculation of module and phase estimations using the expressions presented in the paper. The measurement result is obtained as arithmetic average of these estimations. A mathematical model of the proposed method is developed. The relations for the module and phase of the complex reflection coefficient are derived based on the analysis of both the amplitude and phase distribution of electromagnetic field in the transmission line. The paper describes the experimental unit in the form of vector measuring line that implements the quadrature method of measurement. The experimental analysis of the amplitude and phase distribution of the field in microwave path is carried out for standard loads with different parameters. Based on the analysis results, the estimations of measured parameters are calculated and measurement errors are defined. It is shown that highprecision measuring instruments can be designed using the proposed method.

THE PROCESSING OF THE ELLIPTICALLY POLARIZED SIGNAL IN RADAR STATIONS WITH DIGITAL SYNTHESIS OF THE ANTENNA APERTURE

The processing of the elliptically polarized reflected signal in the Earth remote sensing systems makes it possible to obtain additional advantages when solving problems of recognition of the observable objects on the ground and under the ground. Full polarization reception implemented in radar stations with digital synthesis of the antenna aperture when remote sensing of the Earth increases the information content of such radars (the radar image of the investigated surface is detailed, the contrast of objects in the field of view is improved, and various negative effects of the image are minimized). The paper considers the quadrature processing of the reflected elliptically polarized signal in radar stations with digital synthesis of the antenna aperture in the mode of lateral survey of the terrestrial (water) surface. The processing of the reflected signal using the methods of radio polarimetry opens new possibilities for such radars while solving problems of remote sensing of the surface and recognition of radar targets. In addition, radar stations with digital synthesis of the antenna aperture with processing of an elliptically polarized signal have a higher interference immunity compared to radars, where a linearly polarized signal is processed. In the article, mathematical modeling is performed in the part of demodulation of the in-phase and quadrature components of the trajectory signal when the geometric parameters of the polarization ellipse change. The obtained analytical expressions allow estimating the influence of the geometric parameters of the polarization ellipse on the trajectory signal being processed. It is analytically confirmed that the angle of ellipticity affects the energy characteristics, and the orientation angle of the polarization ellipse introduces an additional phase shift in the characteristics of the trajectory signal being processed. Not taking into account these nuances while designing digital units and systems of such radars can lead to the loss of all the benefits of processing an elliptically polarized signal. The paper presents a structural scheme of the polarization radar station with digital synthesis of the antenna aperture.

Tutorial: GPS receiver architectures, front-end and baseband signal processing

This tutorial provides an overview of the hardware architectures and signal processing that form the core of satellite-based navigation receivers such as GPS. The concepts of spread spectrum and code division multiple access are introduced along with their roles in signal acquisition and tracking. The super-heterodyne front-end architecture will be described as well as the baseband architecture that utilizes in-phase and quadrature processing. Tracking loops are discussed along with measurement generation. The tutorial concludes with a brief look at so-called modernized satellite-based navigation signals.

THE DISCRETIZATION OF THE POLARIZED SIGNAL

Often, the monitoring systems solution of remote sensing problems, recognition (classification, discrimination) of radar objects using radio polarimetry methods is required in real time mode with the display of the current information on the radar monitor. Monitoring systems can be either stationary (more often terrestrial) or mobile (based on various transport vehicles). When designing such systems, along with ensuring the required speed and performance of the computer, it is also important to ensure the unification of the units and assemblies, the reduction of weight and size characteristics, simplification of the tuning, increase of the operational reliability. In this case, the use of blocks of digital information processing is required. When digitally processing polarized signals, it is necessary to convert the input analog signal to digital form, i.e. to sampled by time and frequency and perform level quantization. The peculiarities of the discretization of the radar polarized signal over time are considered in the article. Analytical expressions for the input polarized signal are derived with considering the geometric parameters of the polarization ellipse. Formulas are given for the in-phase and quadrature components of the polarized signal, for a complex signal envelope. It is alleged that quadrature processing of the polarized signal leads to a decrease in the requirements for analog-to-digital conversion chips due to a significant reduction in the sampling frequency. After the transformations presented in the article, electronic components, which are already in production by Russian companies in the radio electronic industry, can be used in monitoring systems. The transformations of a polarized signal in the time domain described in the article lead to certain transformations in the frequency domain. We are talking about converting the two-side signal spectrum into a one-side spectrum with its transfer to the video frequency region. Such a conversion helps to reduce the sampling rate from gigahertz to megahertz. Analytic expressions in the time domain are accompanied in the article by a graphic interpretation of the signal spectra in the frequency domain. A scheme for demodulating the in-phase and quadrature components of the polarized signal is given. Functional features of filtering units in the scheme are described, the attention of the designers of the digital signal processing systems to the requirements of the Kotel'nikov's sampling theorem is emphasized.

РЕЗУЛЬТАТИ МОДЕЛЮВАННЯСХЕМИ ВИЗНАЧЕННЯ СЕРЕДНЬОЇ ЧАСТОТИЛІНІЙНО-ЧАСТОТНО-МОДУЛЬОВАНОГО СИГНАЛУЗ НИЗЬКОЮ СПЕКТРАЛЬНОЮ ЩІЛЬНІСТЮ ПОТУЖНОСТІ

During last time noticed a trend to the implementation radio electronic systems (RES) for various purposes with a spread spectrum signals. For contraction RES with aggregated signals, wideband and noise-like signals very often utilized radio emission with chirp signals. The research some issues of determining the parameters of such signals are not solved yet for the present time. The author suggested a decisive rule of the algorithm measurement average frequency for a discrete model of an autocorrelation receiver with quadrature processing. In the article also considers options for reducing the error in its determination, which is confirmed by the results of the experiment.

Software-defined radio technology in the problem concerning with the successive sounding of HF ionospheric communication channels

The problem concerning new software-defined radio technology is investigated as applied to the successive sounding of HF ionospheric communication radio channels. The algorithm for quadrature processing of chirp signals subjected to elementwise compression in the frequency domain is developed. It is established that a channel scattering function and a delay power profile are related to a compressed-signal spectrum and their basic parameters. Data on the key characteristic of HF communications modems are presented. The efficiencies of different modems are estimated using the experimental data on channel parameters. It is demonstrated that the aforementioned technology can be used to estimate not only HF communication channel parameters from the pass band of a radio line but also select the optimal one and, furthermore, makes it possible to combine communications and radio sounding systems in the single device.

Verification procedure for radar quadrature processing unit with stepwise frequency modulation of the probing signal

The paper presents a verification procedure developed for the quadrature processing unit of radar with stepwise frequency modulation of the probing signal. The computer simulation and experiments on verifying the developed and manufactured quadrature processing unit were performed for the cases of placing a single stationary point object at distances 9 and 24 meters. The effect of inaccuracy in setting the phase shift between the reference oscillations of quadrature mixer on the waveform of spatial reflectogram was investigated by using the developed verification procedure; and it was shown that phase shift errors could lead to the generation of false responses.

The performance of direct-sequence spread spectrum with complex processing and quaternary data modulation

The receiver processing that is often employed for direct-sequence spread spectrum with quaternary data modulation operates separately on in-phase and quadrature components of the spread-spectrum signal. Previous results on complex quaternary sequences, which are also referred to as four-phase sequences, provide a strong motivation to employ alternative processing methods that permit the receiver to benefit from the correlation properties of these sequences. With this goal in mind we present receiver architectures that use complex processing and are capable of demodulating the signals proposed for the third-generation mobile cellular code-division multiple-access systems. The performance of the proposed receiver architecture with complex processing is shown to be determined by the complex aperiodic correlation functions for the spreading sequences. Comparisons are made with systems in which the quaternary sequences are derived from pairs of common binary spreading sequences and the receiver employs separate in-phase and quadrature processing. We find that in spite of their superior periodic crosscorrelation properties, the previously developed quaternary sequences do not provide significantly smaller error probabilities in multiple-access systems.

A Wideband Interferometric Wavelength Shift Demodulator of Fiber Bragg Grating Strain Sensor

The performance of a fiber Bragg grating strain sensor constructed with 3 $\times$ 3 coupler is investigated. A 3 $\times$ 3 coupler Mach-Zehnder (M/Z) interferometer is used as wavelength discriminator, interrogating strain-induced Bragg wavelength shifts. Two quadrature-phase-shifted intensities are synthesized from the as-coupled interferometer outputs, and digital arctangent demodulation and phase unwrapping algorithm are applied to extract the phase information proportional to strain. Due to the linear relation between the input strain and the output of quadrature signal processing, signal-fading problems eliminated. In the experiment, a fiber grating that was surface adhered on an aluminum beam was strained in different ways, and the photodetector signals were transferred and processed in a computer-controlled processing unit. A phase recovery fo 7.8 $\pi$ pk-pk excursion, which corresponds to ~650 $\mu$ strain pk-pk of applied strain, was demonstrated. The sensor system was stable over the environmental intensi쇼 perturbations because of the self-referencing effect in the demodulation process.

Dynamic range of quadrature radio-frequency time-integrating acousto-optic correlator

A new time-integrating acousto-optic correlator (TIAOC) was developed. It combines relatively low complexity with an exceedingly wideband of signals analyzed. The main feature of the architecture is the use of the light beams interference to provide the quadrature processing channel. The dynamic range (DR) of the new TIAOC is calculated for the active and passive operating modes. Parameter optimization to achieve the maximum DR is performed. The photodetector charge handling capacity is shown to be the main DR limiter.

Speech signal processing circuit and method for decoding a coded speech signal by controlling operation of a band synthesis filter

A speech signal processing circuit includes an input buffer for receiving inverse quantization samples and for temporarily storing those samples. The circuit also includes a band synthesis filter for reading the inverse quantization samples stored in the input buffer one by one, and for conducting quadrature conversion processing and sum-of-product operation processing to decode the samples into speech signals. The circuit further includes a control circuit for controlling operation of the band synthesis filter. When the inverse quantization samples are recognized as being stored in the input buffer, the control circuit controls the band synthesis filter to execute, as an initial operation, the quadrature conversion processing of the inverse quantization samples as many times as a number corresponding to an operation delay time of the band synthesis filter. After completion of the initial operation, the control circuit control the band synthesis filter to continue, as a steady operation, the quadrature conversion processing of the inverse quantization samples stored in the input buffer, as well as to conduct the sum-of-product operation processing with respect to the results of the quadrature conversion processing.

Subband processing for broadband microphone arrays

This paper considers array processing for wideband signals. The optimization techniques and associated performance results correspond to steerable but fixed beam microphone arrays, to be used in hearing aid applications, both in free-space and reverberant conditions. We first review the results on maximum energy (ME) broadband arrays. We subsequently formulate optimization criteria for array subband processing. The uniformly spaced subband and the non-uniformly spaced subband using quadrature mirror filter approaches are treated. Finally, various simulation results for free-space and reverberant conditions are presented to demonstrate the usefulness of this class of microphone arrays, as well as the feasibility of quadrature mirror filter-based subband processing.

Efficient quadrature multichannel processor algorithms for MCD applications

The forthcoming third generation of satellites incorporating multichannel demodulator (MCD) processors, and the needs apparent within aviation systems, induce the requirement for efficient band processing algorithms with specific regard to the quadrature processing arrangement. This paper presents a coherent z-domain formulation of the pertinent digital transmultiplexer algorithms for the on-board processing (OBP) scenario, with a view to establishing a set of desirable algorithmic properties suitable for the preferred complex oriented quadrature processing algorithms. Stemming from the principles set forth, an ensemble of new algorithms based upon mixes of Hilbert transforming and real transform algorithms is presented, wherein the established concepts relating to the telephone network transmultiplexer algorithms are able to be exploited in certain cases. Further, the computational load of one of the methods is lower than that of a known prominent OBP related technique. The computational necessities of the various algorithms are laid down for comparative purposes in addition to the mathematical descriptions.

Effect of feedback on the frequency responses of systems containing nonrecursive digital filters

Nonrecursive digital filters (NDF) constitute a widely used element in systems for digital signal processing. They are implemented by means of integrated circuits, solid-state devices based on surface acoustic waves (SAW), and devices with charge coupling (see [1]). In a number of cases the necessity arises of controlling the amplitude- frequency response (AFR) of systems, which is usually carried out by changing the coefficients of the NDF; this is difficult from the engineering standpoint, especially for solid-state implementations. Therefore, methods which allow the AFR of a system to be varied without altering the internal structure of the NDF are of interest. Such a result may be achieved by commutation of filters having known AFR (see [2]), but under these conditions hardware expenditures increase. The control of the system passband by means of quadrature processing of the input signal may be effectively accomplished only for NDF which are close to ideal differentiators or Hilbert converters and requires the presence of two such filters (see [3]). In radioelectronics, extensive use is made of feedback (FB) in order to control AFR. The use of FB converts an NDF into a recursive filter, but the AFR of such a structure has not been considered in the theory of recursive filters.