Vol 61, No 12 (2016)

The method of contour integrals can be used to analyze interference in radio equipment of modern broadband radio-access systems resulting from the presence of nonlinear devices (NDs) with amplitude-to-phase conversion. Several nonlinear models of power amplifiers are considered as such devices. The analysis of interference is reduced to the determination of the interference power density at the ND output and the signal-to-interference ratio in the fundamental band of the signal.

The 1D problem related to the distortion of the rising edge of a carrier-free signal, which arise abruptly at the starting point, is examined. It is demonstrated that, in propagation through an arbitrary (including, absorbing) medium, the signal’s rising edge is not distorted and moves exactly with the speed of light in vacuum. Signals are revealed to attenuate with growing path length. Such attenuation occurs due to shortening of the time interval on which the rising part of the signal continues to hold its initial value without a decrease in its initial amplitude. The given time interval has been estimated.

A method for construction of a 2D radio image of an asteroid from the radar data obtained with the use of a continuous monochromatic signal has been tested. The method is based on the inverse focused synthesis of the antenna aperture due to the rotational motion of the object and reconstructive computeraided tomography. On the basis of the analysis of the echo signals from asteroid Golevka, a 2D distribution of its surface radio brightness has been constructed. Reconstruction of the asteroid silhouette confirmed that Golevka has a not very elongated angular body whose maximum diameter is 620 m and the minimum diameter is 460 m.

An algorithm for choosing the variable of integration providing a specified accuracy in each variable when solving the problem of electromagnetic-wave propagation in a two-dimensional inhomogeneous medium by the geometrical optics method is presented, and the accuracy of the algorithm is estimated.

The problem of protection of a voice-activated robotics control system against the acoustic noise similar to the speaker voice is investigated. A new algorithm for voice signal processing using the phonetic word decoding method and the (R+1) information element is proposed. The results of the experimental study of this algorithm are reported. It is shown that the developed algorithm reduces the false alarm ratio by and an order of magnitude or even more and retains high probability of correct voice recognition.

Comparative examination of magnetotransport properties of nonstoichiometric Si_1–xMn_x alloys with roughly the same (δх/x ≈ 7%) excess of Mn relative to silicides Mn₄Si₇ and MnSi has been performed. Films of Si_1–xMn_x (х ≈ 0.39 and 0.535) with a thickness of 60–70 nm have been fabricated by means of pulsed laser deposition on Al₂O₃ (0001) substrates at a temperature of 340°С. It has been found that the excess of Mn produces the strongest effect on the Curie temperature in the case of MnSi (Т_С increases from 30 K to 300 K and higher), while no such effect is observed in Mn₄Si₇. This may be attributed to strong nonmagnetic disorder in Si_1–xMn_x with x ≈ 0.39 and the associated unusual behavior of negative magnetoresistance (NMR): The NMR varies linearly with magnetic field at В ≤ 1.3 T and exhibits almost no temperature dependence at T = 40–85 K.

A prototype of gradiometer for detection and analysis of magnetic signals that are generated by defects in metal structures and materials in the presence of external magnetic bias is based on dc-current superconducting quantum interference device (SQUID). A prototype of single-channel SQUID gradiometer that contains a fiberglass nonmagnetic cryostat, measurement probe with the SQUID sensor and magnetic flux transformer (second-order axial gradiometer), SQUID electronics, and software for control of SQUID gradiometer is studied. The prototype exhibits stable operation under laboratory conditions in the absence of additional magnetic shielding. Upgrade of the SQUID sensors and remaining elements of the prototype of magnetometer is planned for application in nondestructive testing.

Planar microwave devices that make it possible to determine parameters of fabricated layers are developed and produced. The parameters are needed for correct numerical simulation based on the Mattis–Bardeen theory and may differ from the tabulated parameters of materials.

The problem concerning the aggregating of the forecasts of specialized expert strategies is examined using the mathematical theory of machine learning. Expert strategies are understood as the algorithms capable of successively predicting the components of a time series in the online mode. The specialized strategies can refrain from predictions at certain time instants—they make forecasts in compliance with the application area of the specific model of an object region forming their basis. An optimal algorithm whereby the forecasts of such expert strategies are aggregated into the single forecast is proposed. The algorithmic optimality consists in that, on average, its total losses are asymptotically less than those of any active prediction strategies on a set of time instants. The uppermost estimated error of the given mixing of predictions, i.e., the regret of aggregating strategies, is determined. The errors are estimated in the worst situation where no assumptions are made about the mechanism underlying the initial data source. The proposed algorithm is tested using the real information on the commodity circulation of a trading network. The numerical results and estimates of the regret are presented.

The majority of known methods for correction of multispectral images distorted by nonuniform illumination use the following distortion model: a certain part of the scene close to a directed light source is illuminated much brighter than the rest of the scene. However, another serious problem often arises in practice in the case of nonuniform illumination of 3D objects of the scene: extended heavily shadowed regions with a small area of transition from light to shadow are formed. In this study, a method for the locally adaptive correction of nonuniform illumination of multispectral digital images, which is based on an algorithm that imitates human visual perception, is proposed. The performance of the proposed method is compared to that of available algorithms for correction of color images distorted by both nonuniform illumination and the presence of shadow regions.

This paper deals with the irregular binary low-density parity-check (LDPC) codes and two iterative low-complexity decoding algorithms. The first one is the majority error-correcting decoding algorithm, and the second one is iterative erasure-correcting decoding algorithm. The lower bounds on correcting capabilities (the guaranteed corrected error and erasure fraction respectively) of irregular LDPC code under decoding (error and erasure correcting respectively) algorithms with low-complexity were represented. These lower bounds were obtained as a result of analysis of Tanner graph representation of irregular LDPC code. The numerical results, obtained at the end of the paper for proposed lower-bounds achieved similar results for the previously known best lower-bounds for regular LDPC codes and were represented for the first time for the irregular LDPC codes.

A method for optimization of parameters of a telecommunication and information network providing data processing and transmission in a mobile two-agent robotic system is considered. The first agent receives a Poisson stream of packets (information blocks) and retransmits them to the second agent for subsequent processing. The first agent loses the input packet if its buffer is overflown; the second agent does not admit the overflow of its buffer by sending a rejection message and requesting packet retransmission. The problem of minimization of input packet loss is solved in the steady-state mode under constraints on the processing time and energy consumption by controlling the transmission rate and rejection probability. Conditions in which the values of the objective and constraint functionals form a convex set are determined. The numerical synthesis of the control is implemented on the basis of the augmented Lagrangian method.

A new approach to automatic prediction of earthquakes is considered. The seismotectonic processes are represented using spatio-temporal fields. The parameters of prediction by several fields are the linear predictive function, the value of the alarm decision threshold, as well as the size of the spatio-temporal alarm domain. The considered approach is not bound to a specific data type. Simulation results show that the automatic prediction is available with the use of the Internet catalogues of earthquakes, feasible and rather efficient.

Mapping of the environment is one of the key functions of autonomous robots. An efficient mapping algorithm is needed for successful localization and path finding. Maps may be plotted on the basis of the data from various sensors. Cheap and easy-to-install sonars are typically used for this purpose. A sonar-based mapping algorithm based on continuous optimization methods is proposed. This algorithm may be used in real time, and its main advantages over the common methods are more accurate determination of the size of small (smaller than the sonar beam width or comparable to it) obstacles and more reliable detection of narrow passages (e.g., doorways).