A method has been proposed for synchronizing modems that use a system of cyclic amplitude-phase keyed signals encoded by multi-level numerical sequences with an ideal periodic autocorrelation function to transmit information. The method is based on the invariance of the phase structure of the zero cyclic shift and the inverse zero cyclic shift of the coding sequence to the fast discrete Fourier transform. This makes it possible to detect a synchronization signal based on the analysis of only the phase structure of the signal at the output of the phase detector and to carry out fast automatic adjustment of the receiver gain under conditions of an unknown initial amplitude of the amplitude-phase manipulated signal. The amplitude structure of the clock signal is restored using a special case of the fast discrete Fourier transform — the fast discrete cosine transform. Due to the integer values of the amplitudes, the symmetry around the center, and taking into account the cyclicity property, a single matched filter is used to distinguish orthogonal cyclic signals in a system containing N signals with the number of multipliers equal to the number of discrete amplitude variations, less than N/2 for even N or N/2–1 for odd N.

ATmega series AVR microcontrollers (e.g., ATmega8A or ATmega16A) and ARM microcontrollers with a Cortex M3 core (e.g., STM32F103С8T6) are among the most popular controllers used in solving engineering problems related to servicing various fire and security alarm sensors and devices for metering household and industrial power consumption. At the same time, to transfer the data via a twisted pair or AC voltage network, it needs to be encoded using Manchester 1 or Manchester 2 code, and said AVR and ARM microcontroller units (MCU) contain no hardware encoder and decoder for the Manchester code. The study aimed at solving the engineering problem of implementing the codec (encoder-decoder) of the Manchester code based on the hardware interfaces of low-performance microcontrollers. The direct implementation of the encoding algorithm with the Manchester code using a purely software-driven approach significantly decreases the information transfer rate. At the same time, among the hardware interfaces of the MCU, there is always a serial universal asynchronous data transceiver (UART). However, the UART data transfer protocol is not generally suitable for Manchester encoding and, therefore, needs to be software adapted. In order to adapt the UART protocol to the conditions of Manchester encoding, the 8N1 mode is selected at the hardware level, which means 8 data bits, 1 stop and 1 start bit. The software implementation of the encoder consists in the fact that out of the total possible volume of 256 code combinations, 16 are selected that satisfy the Manchester 2 code, while the start and stop conditions for data bytes transmitted in a row also satisfy the structure of the Manchester code. To maximize the efficiency of the program code, all code words are stored in the memory of the MCU in such a way that their serial number corresponds to the decimal interpretation of 4 bits of the input data. The decoding of the received data is also performed as efficiently as possible using the decoding table. The implementation of the software and hardware codec of the Manchester code significantly expands the scope of popular AVR and ARM microcontrollers and reduces the cost of the finished product by excluding any additional units that perform the function of encoding and decoding the Manchester code.

An optical signal is usually converted into an electrical one by using photosensitive matrices with a large number of discrete elements based on charge-coupled device (CCD) technology or CMOS technology. One of the disadvantages of CCD and CMOS technologies is the impulse conversion noise that appears on digitized images, impairing visual perception and significantly reducing the likelihood of correct identification in pattern recognition tasks. Traditionally, impulse noise is removed from images using median filters with a fixed aperture within each iteration of full-format processing. However, such filters reduce the sharpness of the reconstructed image at high noise levels or insufficiently suppress the interference under the same noise conditions. These setbacks call for a need to develop an adaptive median filtering algorithm, which would produce a reconstructed image as a joint result of processing with median filters with different apertures. The essence of this algorithm is to select image areas with different noise levels and process these areas with filters with different apertures. As an objective criterion for assessing the efficiency of the proposed filtering algorithm, the authors used the criterion of the maximum correlation coefficient between noise-free and non-noisy images at various values of the noise variance. The mathematical modeling performed in this study allowed finding that with an increase in the impulse noise variance, the gain of the adaptive median filtering algorithm increases exponentially, in comparison with the algorithms using the filters with a fixed aperture value. The proposed algorithm can be used for pre-preprocessing images intended for recognition by machine vision systems, scanning text, and improving subjective image characteristics, such as sharpness and contrast.

Pulsed laser rangefinders prove to be cost-effective and practical devices when used at distances of several tens of kilometers due to their compactness, portability and energy efficiency. However, the measurement accuracy is significantly reduced by the presence of pulsed interference affecting the input of the optical receiver both during the sensing period and when the reflected signal is being received. Using the algorithms with the accumulation and subsequent processing of the results of several successive measurements reduces the speed of decision-making and does not guarantee the convergence of the results to the real value of the distance. The paper proposes a structural diagram of a laser rangefinder with the ability to detect pulsed interference in the range interval and correct errors that occur in the structure of the signal reflected from the target. The basis of the rangefinder circuit is a logical consistent filter, the structure of which contains multipliers (multiplication operations). The following requirements were formulated for the structure of the probe signal: — the first element should always be set to +1 to synchronize the receiver decider; — the weight of the coding sequence is equal to half its length; — the length of the coding sequence is even. Based on the requirements for coding sequences, the optimal structures of binary probing signals of length 8 were found, providing the best corrective ability. Comparison of the correlation properties of the found sequences and the sequences that are constructed using the Walsh functions showed the advantage of the optimal sequences by the criterion of the minimum level of the ACF side lobes. The simulation of the rangefinder under pulsed noise conditions has shown that the logical filter is advisable to use for those cases when the duration of the obstacle does not exceed 1/3 of the duration of the probing signal.

The paper considers typical designs of surveillance devices for acousto-optic leakage channels. To assess the quality of the channel, it is proposed to use the criterion of the minimum permissible power of the information signal at the input. To analyze the processes that occur while the probe signal propagates to the pick-up point and back to the surveillance device, the authors propose a detailed model of the information leakage channel with the indication of the main transformations of the intercepted signal. The paper presents the main criteria for the correct reception of an optical signal and for the extraction of acoustic information from it. A number of assumptions are formulated regarding the practical implementation of the optoelectric converter of the receiving device, and a simplified equivalent functional model of the optical information transmission channel is developed. The authors also propose a method for calculating the voltage at the load of the photodiode depending on the distance to the vibrating surface, power and the coefficient of directional action of the transmitter emitter. The numerical dependences of the voltage at the load of the photodiode on the distance are obtained for specific numerical values of the load resistance, supply voltage, directional coefficient of the emitter and receiver, as well as the geometric dimensions of the information interception zone. A simplified technique is developed that allows determining the signal level at the input of the sensitive element of a photodetector under idealized conditions, if the minimum permissible optical signal power condition is met and there is no background illumination of the photodetector of the surveillance device.

In order to increase the efficiency of dedicated frequency channels, i.e. to increase the specific data transfer rate, multipositional quadrature phase shift keying (QPSK, aka 4-PSK) should be used. The problems with QPSK signal demodulation is a rotation of the signal constellation plane by an angle multiple of 90° and a slow response of the carrier oscillation recovery scheme. The study considers the existing methods for eliminating the phase ambiguity of the recovered carrier frequency in typical QPSK modems, and identifies the shortcoming of a low-speed response oscillation recovery circuit. The authors propose a QPSK demodulator circuit with a fast adjustment of the reference oscillator, which is due to the fact that no loop filter is used in the feedback and that a digital calculator of the required phase shift is used. An algorithm for the frame synchronization restoration with the simultaneous elimination of the phase ambiguity multiple of 90° was also developed using synthesized binary sequences with an ideal non-periodic autocorrelation function (NACF) at even shifts that do not have the rotary symmetry property. The phase ambiguity elimination algorithm proposed in the article can be used as an alternative to standard modems with differential coding.

When demodulating signals in communication systems with QPSK modulation operating in the pulsed mode, the following problems arise: rapid elimination of the reference oscillator phase ambiguity and ensuring reliable frame synchronization for a given noise immunity. In most QPSK modems, the carrier frequency recovery and synchronization recovery tasks are separated and solved with the help of different functional modules, which is not the optimal solution from the point of view of increasing the energy efficiency. In this paper, we propos a fast algorithm for frame synchronization and recovery of the carrier frequency of a QPSK modem using Barker sequences as synchronization signals in conjunction with the coordinated processing. The simulation of the combined circuit is performed, which allows to eliminate the phase ambiguity of the reference oscillation with the simultaneous formation of the frame synchronization signal for various combinations of binary sync codes of the length N = 7. To obtain a reference oscillation, a stable quartz oscillator is used. An external adjustable phase shifter block abruptly changes the phase of the oscillator, and the phase ambiguity, which is multiple of 90°, is eliminated by parallel analysis of all possible rotations of the signal constellation plane in the units, each of which contains a pair of filters matched to the signal distributed over in two quadratures. The timing for the proposed scheme does not depend on the initial phase difference between the received and the initial signal constellations, while the circuit realization of a non-tunable oscillator is much simpler than that for a voltage controlled oscillator.

Increase of the operation reliability of the frame synchronization schemes of communication systems affected by interferences might be achieved by using sync sequences optimal according to the minimax criterion and having the best ratio of the maximum side-lobe level to the main peak of the non-periodic autocorrelation function. Obviously, the longer the minimax sequence, the higher its correction ability. However, with the increase in the length of the sync code, a conflict arises between the corrective ability and the speed of data transfer. This is caused by the decrease in the duration of the information section of the frame. At the same time, as the length of the code increases, the complexity of the technical implementation of the decoder synchronization scheme increases as well. This means that when developing an information transmission system, it is necessary to find a compromise between the complexity of the technical implementation of the decoder and the required noise immunity. To solve this problem, it is necessary to study the correcting ability of binary sync codes. The purpose of this work was to study the correcting ability of binary sequences with good non-periodic auto-correlation properties using a reception scheme with matched processing. This article discusses the possibility of using Barker sequences of lengths 7, 11, and 13 and M-sequences as corrective sync codes. The authors carry out an analysis of the correcting ability of the decoder model with matched processing for Barker codes of different lengths under the conditions of a one, two, and threefold error. Analytical expressions have been obtained to determine the decoding error probability of a binary minimax code depending on the length of the sync code. The dependence of the corrective ability of the code and the maximum level of the side lobe on the length of the sync code in the range from 4 to 128 with the best nonperiodic autocorrelation functions (NPAF) is obtained. It has been established that there are length ranges for minimax sequences within which their correction ability remains constant, that is, a sync code of shorter length has the same correction ability as a longer code. Thus, the research results allow us to optimize the complexity of the technical implementation of a sync signal decoder depending on the requirements for general noise immunity and information transfer rate in a communication system. The proposed approach can be successfully used to modify the existing synchronization schemes of communication systems with code division of channels.

The authors have developed a device for imitation of the signal-interference environment for radars, equipped with the plan-position indicator (PPI) «Picket», which does not require a PC for operation. Thanks to the use of the original method of forming marks from targets, it was possible to significantly reduce the amount of memory, required to store information about the scenario that reliably imitates the operation of the radar in real conditions. The device provides simultaneous operation of twelve indicators of a circular survey and is intended for equipping training centers for the training of air control operators.

The information efficiency of communication systems using quadrature amplitude modulation is reduced because of the costs for data transmission necessary to provide frame synchronization and the required time to search for the sync signal and to go into the tracking mode of the synchronization system. One of the most effective schemes of constructing a frame synchronization system is the correlation diagram. In order for this diagram to operate, signal-code constructions with good aperiodic autocorrelation properties are required. The aim of this study is to develop an effective frame synchronization system for quadrature modulation communication systems based on binary signal-code sequences with an ideal sectioned non-periodic autocorrelation function. In this paper, we propose a frame synchronization scheme for QPSK modulation based on binary sequences of even length with an ideal autocorrelation function. All binary synchronous sequences of length N = 8 with the idealness of the autocorrelation function are analytically found in the study. On the basis of the chart of the code distance spectrum in the Hamming metric for binary sequences of N = 8 length, it was established that such sequences have a correcting ability that allows correcting single errors. Based on the structural properties of binary sequences of N = 8 length, sequences of a larger multiple length (N = 16, N = 32, etc.) can be synthesized. The practical value of the proposed scheme of frame synchronization is to reduce the complexity of technical implementation and increase the overall noise immunity of the communication system. The proposed approach can be successfully used to synchronize communication systems with QAM modulation with a large number of signal positions such as QAM 16, QAM 64, etc.

The quality of wireless network depends essentially on the directional characteristics of the antennas, the most important of which are the amplitude radiation pattern (RP) and the frequency response (FR), which is understood as a change of the gain coefficient in the working frequency band. At the same time, equipment for measuring the characteristics of the antennas in real conditions is very expensive, difficult to deploy, configure and maintain. In most cases, the measurement accuracy requirements are significantly lower than in laboratory measurements. This fact allows using the equipment which is part of the wireless network itself. The aim of this work is to develop a simplified procedure for measuring the amplitude RP and frequency characteristics of antennas for the rapid assessment of electromagnetic environment during deployment of wireless networks, when the requirements for measurement accuracy are not critical. In this article we propose to use as a UHF calibrated power generator a standard Wi-Fi router with a coaxial output, i.e. with the possibility to connect an external antenna. Certified routers 802.11n standard of 2.4 GHz band, regardless of the manufacturer, provide the following parameters: output power range of 20-100 mW, receiver sensitivity of 80-85 dBm, dynamic range of the receiver - 90 dBm. Using system settings of the router allows one to rapidly change the frequency in the range of 2400-2483.5 MHz with a step of 5-20 MHz. The practical value of the proposed methodology for measuring Wi-Fi antennas characteristics consists in substantial saving of time and costs during deployment and adjusting of wireless networks. This method can be successfully used for testing city wireless video surveillance systems and public access points to the local and global resources of city network.

Directivity pattern (DP) or graphical representation of the dependence of gain factor (directivity gain) of antennas on the direction of the antenna in the target plane is the main characteristic that describes its directional properties. Running DP measurements directly in the microwave range is very expensive. While generating and receiving devices for the acoustic frequency range are reasonably priced. In this paper, we propose a method for measuring the amplitude directivity pattern of parabolic mirrored antennas on the basis of sound equivalent, which is based on the identity of the numerical values of the directivity gain of microwave range, and at audio frequencies. The paper presents analytical expressions for the calculation of equivalent frequency and defines the requirements for the minimum size of the antenna. The paper contains a modified block diagram for an amplitude directivity pattern meter for parabolic mirrored antennas in the audio frequency range.

Digital television systems need to ensure that all digital signals processing operations are performed simultaneously and consistently. Frame synchronization dictated by the need to match phases of transmitter and receiver so that it would be possible to identify the start of a frame. As a frame synchronization signals are often used long length binary sequence with good aperiodic autocorrelation function. Aim: This work is dedicated to the development of the algorithm of random length sequences synthesis. Materials and Methods: The paper provides a comparative analysis of the known sequences, which can be used at present as synchronization ones, revealed their advantages and disadvantages. This work proposes the algorithm for the synthesis of binary synchronization sequences of random length with good autocorrelation properties based on noise generator with a uniform distribution law of probabilities. A "white noise" semiconductor generator is proposed to use as the initial material for the synthesis of binary sequences with desired properties. Results: The statistical analysis of the initial implementations of the "white noise" and synthesized sequences for frame synchronization of digital television is conducted. The comparative analysis of the synthesized sequences with known ones was carried out. The results show the benefits of obtained sequences in compare with known ones. The performed simulations confirm the obtained results. Conclusions: Thus, the search algorithm of binary synchronization sequences with desired autocorrelation properties received. According to this algorithm, the sequence can be longer in length and without length limitations. The received sync sequence can be used for frame synchronization in modern digital communication systems that will increase their efficiency and noise immunity.

Ahe problem of technical implementation of phased array antennas (PAR) with the required radiation pattern (RP) is the complexity of the construction of the beamforming device that consists of a set of controlled attenuators and phase shifters. It is possible to simplify the technical implementation of PAR, if complex representation of coefficients of amplitude-phase distribution of the field along the lattice is approximated by real values in the synthesis stage. It is known that the amplitude distribution of the field in the aperture of the antenna array and the radiation pattern are associated with Fourier transform. Thus, the amplitude and phase coefficients are first calculated using the Fourier transform, and then processed according to the selected type of circuit realization of attenuators and phase shifters. The calculation of the inverse Fourier transform of the modified coefficients allows calculating the synthesized orientation function. This study aims to develop a search algorithm for amplitude and phase coefficients, taking into account the fact that integer-valued amplitudes and phases are technically easier to implement than real ones. Synthesis algorithm for equidistant linear array with a half-wavelength irradiators pitch (&l;/2) is as follows. From a given directivity function the discrete Fourier transform (DFT) in the form of an array of complex numbers is found, the resulting array is then transformed into a set of attenuations for attenuators and phase shifts for phase shifters, while the amplitude coefficients are rounded off to integers, and phases are binarizated (0, ?). The practical value of this algorithm is particularly high when using controlled phase shifters and attenuators integrally. The work confirms the possibility of a thermoelectric converter of human body application for an electronic medical thermometer power supply.

Solving the problem of character information recognition is relevant in the analysis of text documents, identification of the character information on printed circuit boards and electronic components, recognition of labels on containers and railway cars, etc. Optimal matching algorithm, which provides the highest probability of a correct distinction, lies in calculating the correlation coefficient between the recognizable character and a set of all templates. A simple noise-immune algorithm for character information recognition that does not use the procedure of pre-segmentation and contour filtering, based on the combination of the correlation method and the minimum code distance criterion was proposed in the paper. The proposed algorithm allows significantly improve the probability of correct character recognition by slight complication of the processing algorithm and allows to determine the coordinates of characters, corresponding to one given pattern for one iteration. The obvious advantage of this algorithm is the absence of multiplication operations. Herewith, the computational complexity of the algorithm is reduced due to the lack of multiplication operations and decrease in the total number of addition operations.

Solving the problem of character information recognition is relevant in the analysis of text documents, identification of the character information on printed circuit boards and electronic components, recognition of labels on containers and railway cars, etc.Optimal matching algorithm, which provides the highest probability of a correct distinction, lies in calculating the correlation coefficient between the recognizable character and a set of all templates.A simple noise-immune algorithm for character information recognition that does not use the procedure of pre-segmentation and contour filtering, based on the combination of the correlation method and the minimum code distance criterion was proposed in the paper.The proposed algorithm allows significantly improve the probability of correct character recognition by slight complication of the processing algorithm and allows to determine the coordinates of characters, corresponding to one given pattern for one iteration.The obvious advantage of this algorithm is the absence of multiplication operations. Herewith, the computational complexity of the algorithm is reduced due to the lack of multiplication operations and decrease in the total number of addition operations.

Рассмотрен алгоритм распознавания символьной информации, не использующий процедуры предварительной сегментации и контурной фильтрации. Проведен сравнительный анализ с известными алгоритмами распознавания символьной информации. Показано, что предложенный алгоритм требует выполнения меньшего числа арифметических операций и обладает низкой сложностью технической реализации

Currently in machine vision systems a problem of recognition of the character information has become urgent. The solution to this problem is necessary for the recognition of license plates, labels on containers and railway cars, analysis of text documents, identification of the character information on printed boards and electronic components, etc. Optimum matching algorithm providing the highest probability of correct discrimination consists in calculating of the correlation coefficient between the recognizable symbol and the set of all patterns.The article presents a simple algorithm to recognize the character information that does not use the advance segmentation and contour filtering.The proposed recognition algorithm allows in one iteration to determine the coordinates of the characters corresponding to one specific pattern. The obvious advantage of this algorithm is the absence of multiplications. his reduces the computational complexity of the algorithm due to the lack of multiplication operations and reduction of the total number of additions.Thus, the proposed algorithm has low complexity of the technical implementation