Journal of Communications Technology and Electronics最新文献

Abstract—

Multi-User Multiple Input Multiple Output (MU-MIMO) technology allows you to increase the channel throughput. However, its efficiency is reduced by overhead induced by frequent channel sounding and transmission of channel feedback frames. This article examines the problems of channel state information (CSI) compression in Wi-Fi networks using MU-MIMO with channel aging. The research aims to experimentally test the effectiveness of MU-MIMO technology in real use cases, considering the channel sounding procedures and CSI feedback transmission. Using an experimental setup, the channel has been recorded to analyze its behavior and the evolution of the signal received power under different conditions. In addition, the limits of the applicability of the TGax MU-MIMO channel model in the WLAN Toolbox have been investigated by comparing it with experimental results. The findings of this study are particularly useful in optimizing MU-MIMO performance under channel time evolution and CSI compression.

Abstract—An important step in solving the problem of classification and segmentation of 2D images is the extraction of local geometric features. Convolutional neural networks were widely used in recent years to solve problems in this field. Typically, the neighborhood of each pixel in an image is used to collect local geometric information. A convolutional neural network is used to extract the underlying geometric features of the neighborhood. In this work, we propose a neural network based on descriptor concatenation for two well-known neural networks to solve the problem of extracting local geometric features of mammographic images. To improve the accuracy of mammogram classification, feature filtering is used based on the calculation of joint information. Results of computer simulation are presented to illustrate the performance of the proposed method.

Abstract—The paper addresses capacitated clustering problems: (a) basic capacitated clustering problem, (b) capacitated centered clustering problem, (c) multicapacity clustering problem, and (d) related problems. The paper is based on the combinatorial clustering viewpoint. A survey on the problems, solving approaches, and some applications are presented. The optimization models of the basic capacitated clustering problem and multicriteria capacitated clustering problem are considered. An application of capacitated clustering as the handover minimization problem in mobile wireless networks is briefly described. Numerical examples illustrate problems and applications.

Abstract—Reconfigurable intelligent surface (RIS) is a promising technology that can increase the capacity and coverage of wireless networks. The effectiveness of a RIS is determined by its configuration, which can be made based on the information about location of the transceiver devices. In practice, there are two main types of RIS configurations: focusing the signal reflected from the RIS at the receiver location and redirecting the signal towards the receiver. Both types of RIS configuration become outdated in time due to changes in environmental parameters caused by the movement of transceiver devices and other objects in the surrounding environment. This paper examines outdating of RIS configurations made by focusing and redirection procedures in a system with spatially static transceiver devices. The paper shows that the difference in signal-to-noise ratio for the two types of configurations can reach up to 8 dB and has nonmonotonic features that can be explained by considering the near-field region of a RIS.

Abstract—The main task of the study is to improve the performance of existing computer diagnostic systems using new methods for classification of benign and malignant tumors using digital mammograms. Methods and algorithms for systems of computer diagnostics are being actively developed using deep neural networks. To achieve better results on the selected data set, we transform the data using autoencoders to obtain features with low intraclass and high interclass variance. The entire working cycle of the system consists of the following stages: extraction of features using a segmented part of the pathology, division of the data into two clusters, and feature transformations using linear discriminant analysis for minimization of intraclass variance and classification of pathologies. The results of this study show that the classification of pathologies using deep learning methods makes it possible to achieve high results.

Abstract—Reconfigurable intelligent surfaces (RISs) are promising devices capable of increasing the information capacity and coverage of new and available wireless networks. By now, most of these devices have been presented in the form of prototypes that have no environmental protection and are not adapted for use in real communication systems. Meanwhile, a protective coating can significantly affect the characteristics of a RIS and reduce its efficiency. This study considers the effect of thickness, permittivity, and dissipation factor of the most common protective coating materials on the frequency and phase responses of a RIS unit cell (UC). Recommendations on choosing a material and its thickness and on correcting UC sizes at constant parameters of a protective coating are provided.

Abstract

An algorithm is proposed for iterative symbol-by-symbol decoding of signal constructions based on orthogonal frequency-division multiplexing signals with the base increased using pseudorandom sequences and noise-immunity coding. The algorithm is based on the nonlinear transformation of the spectral components of the input implementation (constraining the spectral component amplitudes or their switching-off) in combination with the symbol-by-symbol decoding of the used class of noise-immune block codes. The results of the simulation of this decoding algorithm for the investigated signal constructions in the presence of the channel of narrow-band noise are reported and the stability of the signal constructions against the distorting effect of the discussed interference class is demonstrated. It is shown that a signal construction based on a low-density code in combination with the iterative symbol-by-symbol decoding algorithm is more efficient in terms of the noise immunity than a convolutional code in combination with the Viterbi decoding algorithm that implements the maximum likelihood rule. It is shown that the operation of switching-off the spectral components relative to their constraining is more efficient in terms of suppressing the distorting effect of the investigated noise complex.

Abstract

Based on the rigorous nonlinear theory of relativistic traveling wave tubes (TWTs) and backward wave oscillators BWOs on irregular hollow waveguides with cathode filter-modulators, taking into account both propagating and supercritical waves, taking into account losses in the walls of the waveguide and the inhomogeneity of the magnetostatic field guiding the electron flow, the influence of dynamic stratification of the electron flow on the efficiency of the generator is determined. The article shows a full compensation possibility on the influence of dynamic layering on efficiency by optimizing an electronic beam in inhomogeneous high frequency and magnetic fields and the corrugated irregular waveguide characteristics when electron beam layers depositing on it.

Abstract

The discrete sources method emerged in the 1980s as an alternative to the method of integral equations has become an effective tool for analyzing problems of diffraction of optical radiation on various physical objects. On the basis of the discrete sources method, a computer technology has been developed and implemented that makes it possible to solve fundamental and application tasks, specifically, to study the scattering properties of coarse atmospheric particles and erythrocytes, to build effective schemes of surface scanners for detecting and recognizing defects in silicon substrates, to measure the potential of interaction of colloidal particles in a solution with the surface of a layered substrate with the simultaneous determination of the distance to the substrate accurate to 1 nm, to develop an optimum design of a near-field microscope based on the effect of total internal reflection of waves, and to investigate the impact of quantum effects on the optical characteristics of nanoplasmonic structures taking into account the manifestation of the nonlocality and occurrence of a longitudinal electric field using the theory of a generalized nonlocal response. All these and other issues related to the use of the discrete sources method are discussed in the proposed review.

Abstract

A general method for mathematical modeling of the electromagnetic field emitted by infinite phase-scanned antenna arrays is proposed. Using the Floquet conditions and the partial radiation conditions, the problem in free space have been reduced to solving Maxwell’s equations in a bounded domain, where the incomplete Galerkin method proposed by Sveshnikov in 1963 is used to find an approximate solution.