Vol 20, No 1 (2021)
Robotics, automation and control systems
Stability of Tracking the Delay of Phase-shift Keyed Signals with Spectrum Expanding in Synchronization Systems of Radio Engineering Systems
Abstract
The issues of ensuring the stability of delay tracking in synchronization systems of radio engineering systems when receiving phase-shift keyed signals with spectrum expansion based on pseudorandom sequences are considered. When working with moving objects, the delay of the received signal continuously changes, synchronization errors occur, and the quality of signal reception largely depends on the stability of the tracking scheme for the delay, characterized by the probability of tracking failure. Delay tracking is usually considered as the main task of the synchronization system of the considered radio systems with phase-manipulated signals with spectrum expansion based on pseudo-random sequences.
The effect of synchronization errors when tracking the delay of a received phase-shift keyed signal with a spectrum extension based on pseudorandom sequences on the probability of tracking failure is studied. The calculation method is used to obtain families of dependences of the probability of tracking failure on the values of random and systematic components of the delay tracking error, normalized to the capture band of the time discriminator of the delay tracking scheme for various combinations of these parameters. The areas of weak and strong influence of the value of tracking errors over the delay of the received signal on the probability of tracking failure are determined. The nature of impact of random and systematic components of tracking error on the probability of failure of tracking was analyzed and it was found that in the General case is the ambiguity of normalized mean square of tracking error as the optimization criterion while minimizing the likelihood of tracking loss.
Calculations performed for a wide range of changes in the normalized delay tracking errors show that to ensure a given quality of signal reception in a radio system with phase-shift keyed signals with spectrum expansion based on pseudorandom sequences, a joint choice of parameters of the delay tracking system that determine the value of random and systematic components of the tracking error is necessary. The results obtained can be used to analyze the characteristics of synchronization systems that monitor the parameters of received signals with a spectrum extension, and to justify the technical solutions of the synchronization system that provide the required quality of signal reception in information and measurement of radio-electronic systems.
Informatics and Automation. 2021;20(1):16-42
16-42
Holding Geostationary Satellite at Given Standing Point, Taking into Account Additional Phase Restrictions
Abstract
The active lifetime of orbital facilities in the geostationary orbit (GSO), which include stationary artificial earth satellites (SAES) for various purposes, can be more than 15 years. At the same time, in modern conditions of orbital grouping increment, the number of space debris, including those on the GSO, also increases: SAES, which have finished its active lifetime and were not transferred to disposal orbit for some reasons, shards of SAES appeared from collision with meteors or accidents. This leads to the increase of probability of collisions with active SAESs. The listed factors determine the need of considering not only the problem of keeping SAESs in vicinities of position, but also the task of avoiding collisions with space debris objects (SDO), while the costs of the working fluid should not increase.
A great attention is being paid to rational power units placing during the projection of new space shuttles, especially those with long useful lifetime. In this article, it is assumed that SESs are equipped with several correction motors, which make it possible to create control accelerations in only several directions, without changing the orientation of the SES itself. In other words, in this task it is assumed that the corrections of the parameters of the AES orbit do not affect the orientation of the SAES itself. This condition is a severe limitation in the synthesis of the SES’s control system.
In the considered methodological approach, the costs of the working fluid are set as a functionality from control, which are necessary to perform the next correction, after which the SAES will not have dangerous distances and approaching in projection horizon’s interval. This makes it possible to avoid situations when the decision on control is being made after the SES leaves the vicinity of the station point, and first of all, the approach to the SDO at a distance less than a liminal one. This article provides the results of modeling, which indicate the effectiveness of the proposed solutions.
An important advantage compared with the existing methods is the consideration of the movement of the SAES relatively not only to the stationary point, but also to several other objects located in its vicinity, both controlled and uncontrolled. Moreover, there can be any given number of objects.
Informatics and Automation. 2021;20(1):43-67
43-67
Increasing Efficiency of Over-the-Horizont Surface Wave Radars for Detecting Surface Objects based on the Antenna System Aperture
Abstract
Nowadays, over-the-horizon surface wave radars are used to solve the problems of monitoring the situation on the water surface adjacent to the border areas of the land. The main advantage of these means is the ability to detect surface objects beyond the optical horizon due to the propagation of an electromagnetic wave along the sea surface in the diffraction zone. However, the accuracy characteristics of such observations turn out to be extremely low due to the small signal-to-noise ratios of the reflected signal, which in turn are caused by the wide directivity pattern of the existing antenna systems. It leads to the prevalence of background reflection in the irradiated region over the radio echo of the target object. For the same reason, stationary targets are undetectable, for which there is no Doppler frequency shift in the reflected signal spectrum. The only way to increase the signal-to-noise ratio is to narrow the radiation pattern in the direction of the detected target (an increase in the antenna system directivity). The article proposes a solution for the described problem by the method of sequential accumulation of reflected signals and their summation according to the principle of optimization of the selection of phase relationships for adjacent pulses (synthesized ape rtures) corresponding to the ev entual front of electromagnetic waves focused in the direction of the hypothetical target. The solution of this problem will significantly narrow the antenna directional pattern, which leads to the achievement of direction finding accuracy that meets the requirements for some navigation systems. In this case, there is no need to change the design of the antenna arrays. Computer simulation of the synthesized antenna array was performed and its directional pattern was constructed. A quantitative assessment of the incre asing the angular resolution was performed in comparison with the potentially possible one determined by the Rayleigh criterion. This circumstance allows us to consider the possibility of using coastal over-the-horizon surface wave radars to detect stationary objects «invisible» by existing radars.
Informatics and Automation. 2021;20(1):68-93
68-93
Artificial intelligence, knowledge and data engineering
Classification Methods for EEG Patterns of Imaginary Movements
Abstract
The review focuses on the most promising methods for classifying EEG signals for non-invasive BCIs and theoretical approaches for the successful classification of EEG patterns. The paper provides an overview of articles using Riemannian geometry, deep learning methods and various options for preprocessing and "clustering" EEG signals, for example, common-spatial pattern (CSP). Among other approaches, pre-processing of EEG signals using CSP is often used, both offline and online. The combination of CSP, linear discriminant analysis, support vector machine and neural network (BPNN) made it possible to achieve 91% accuracy for binary classification with exoskeleton control as a feedback. There is very little work on the use of Riemannian geometry online and the best accuracy achieved so far for a binary classification problem is 69.3% in the work. At the same time, in offline testing, the average percentage of correct classification in the considered articles for approaches with CSP – 77.5 ± 5.8%, deep learning networks – 81.7 ± 4.7%, Riemannian geometry – 90.2 ± 6.6%. Due to nonlinear transformations, Riemannian geometry-based approaches and complex deep neural networks provide higher accuracy and better extract of useful information from raw EEG recordings rather than linear CSP transformation. However, in real-time setup, not only accuracy is important, but also a minimum time delay. Therefore, approaches using the CSP transformation and Riemannian geometry with a time delay of less than 500 ms may be in the future advantage.
Informatics and Automation. 2021;20(1):94-132
94-132
Geometric Piecewise Cubic Bézier Interpolating Polynomial with C2 Continuity
Abstract
Bézier curve is a parametric polynomial that is applied to produce good piecewise interpolation methods with more advantage over the other piecewise polynomials. It is, therefore, crucial to construct Bézier curves that are smooth and able to increase the accuracy of the solutions. Most of the known strategies for determining internal control points for piecewise Bezier curves achieve only partial smoothness, satisfying the first order of continuity. Some solutions allow you to construct interpolation polynomials with smoothness in width along the approximating curve. However, they are still unable to handle the locations of the inner control points. The partial smoothness and non-controlling locations of inner control points may affect the accuracy of the approximate curve of the dataset. In order to improve the smoothness and accuracy of the previous strategies, а new piecewise cubic Bézier polynomial with second-order of continuity C2 is proposed in this study to estimate missing values. The proposed method employs geometric construction to find the inner control points for each adjacent subinterval of the given dataset. Not only the proposed method preserves stability and smoothness, the error analysis of numerical results also indicates that the resultant interpolating polynomial is more accurate than the ones produced by the existing methods.
Informatics and Automation. 2021;20(1):133-159
133-159
Digital information telecommunication technologies
Models and Methods for Discovery of Local Area Network Topology with Incomplete Data
Abstract
A lot of network management tasks require a description of the logical and physical computer network topology. Obtaining such a description in an automatic way is complicated due to the possibility of incompleteness and incorrectness of the initial data on the network structure. This article provides a study on the properties of incomplete initial data on network device connectivity on the link layer. Methods for generalized handling of the heterogeneous input data on the link layer are included. We describe models and methods for deriving a missing part of the data, as well as the condition in which it is possible to get a single correct network topology description. The article includes algorithms for building a link layer topology description from incomplete data when this data is possible to fulfill up to the required level. Also, we provide methods for detecting and resolving an ambiguity in the data and methods for improving incorrect initial data. Tests and evaluations provided in the article demonstrate the applicability and effectiveness of the build methods for discovering various heterogeneous real-life networks. Additionally, we show advantages of the provided methods over the previous analogs: our methods are able to derive up to 99% data on link layer connectivity in polynomial time; able to provide a correct solution from an ambiguous data.
Informatics and Automation. 2021;20(1):160-180
160-180
Method for Protection of Copyright on Vector Data
Abstract
The paper proposes a method of copyright protection for vector maps, based on the embedding of raster digital watermarks. The method combines original ideas, namely, a vector data watermarking approach that does not distort the coordinate information of vector objects and embedding of noise-like images that encode a binary sequence. The use of noise-like carrier allows to simplify the verification procedure, and also to ensure the resistance of the hidden bit sequence to distortions, including interpolation errors. In comparison with previous investigations made by the authors when solving problems of vector data protection, the robustness of the embedded noise-like digital watermarks has been significantly increased by developing a new algorithm for detection of the binary sequence hidden in the spectrum of a noise-like image. The purpose of the experimental studies was to assess the attainable probability of correct sequence extraction for various parameters and embedding conditions. The study of information capacity showed that the potential amount of information embedded in each polygon without distorting the watermark sequence depends on the type of a map, namely on the number of vertices that make up each polygon. An experimental study on robustness against potentially possible transformations aimed at maliciously deleting the digital watermark from the vector map is performed. The developed method demonstrates resistance to affine transformations, cropping, addition, removal and reordering of vertices / objects, and, thus, seems to be the optimal solution to the problem of copyright protection for vector data. The analysis of the method quality according to the criteria of accuracy, durability, information capacity, and computational complexity is performed. The results of all conducted studies confirm the efficiency and the effectiveness of the proposed method for vector map protection, as well as its distinct advantage over the prior art.
Informatics and Automation. 2021;20(1):181-212
181-212