Ultra-wideband (UWB) Time-Difference-of-Arrival (TDoA) is a popular approach for indoor system localization due to its simplicity, efficiency, high performance, and low energy consumption. To solve the nonlinear multilateration problem associated with determining the transmitter’s coordinates based on data from synchronized receivers, the least-squares method with low computational complexity or its improved variants, in particular, the two-stage weighted least squares (WLS) method, are often used. However, these methods perform poorly on ill-conditioned matrices due to a specific mutual arrangement between the receiver and the transmitter. This paper proposes a parametric weighted least squares algorithm that is effective under these conditions and enables the determination of an entire family of solutions. It provides accurate and reliable position estimates even under complex conditions associated with system rank reduction. The efficiency of the proposed algorithm is analyzed under various scenarios, including Gaussian noise, synchronization errors at the reference node, and multipath interference, for different receiver configurations arranged in a square grid.
A method for calculating the dispersion characteristics of double-sided microstrip and balanced transmission lines has been developed. The method is based on a rigorous solution of an internal boundary value problem for the Helmholtz equation in a rectangular domain with a three-layer dielectric filling and two strip lines located on both sides of the dielectric substrate. The results of numerical calculations of the deceleration coefficients and wave impedance of microstrips for typical substrate material parameters (RT/Duroid 5880 and FR4) are presented. As an example, the scattering characteristics of smooth tapered transitions with an exponential profile between microstrip and balanced transmission lines, and the transition between two microstrip lines located on opposite sides of the substrate, were simulated, calculated, and experimentally measured. According to the measurement results, smooth transitions with an exponential profile between transmission lines of different types, calculated using the exact values of the deceleration coefficient and wave impedance for double-sided microstrip lines, enable ultrawideband signal transmission. Experimental results have shown that smooth transitions with an exponential profile in the 1–6 GHz frequency band achieve a reflection coefficient of –15 dB or better.
This paper proposes an enhancement to the existing methodology for employing Convolutional Neural Networks (CNNs) to identify parameters of the Long Range (LoRa) telecommunication standard. Building upon the approach of classifying signals using predefined combinations of modulation parameters, our method expands the detectable set by at least twofold through signal-processing modifications. Using the YOLO11 object detection model, our results demonstrate a notable improvement in Mean Average Precision (mAP50) to 93.5
Increased capacity, faster data rates, lower latency, and improved service quality are the primary goals in the fifth-generation (5G) and beyond era. Cellular network architectures must be significantly improved to meet these needs. To accomplish these goals, the presented analysis emphasizes the critical roles of 5G cellular network architecture, the substantial use of multiple-input multiple-output (MIMO) technology, and the integration of device-to-device communication. Despite being a promising option, free-space optics (FSO) struggles when used alone in challenging weather conditions. Because FSO systems rely on the line-of-sight connectivity, flying birds and trees do not affect them. Furthermore, unfavorable weather conditions, such as fog and snow, significantly affect FSO performance, resulting in a substantial decline. This study focuses on hybrid FSO/radio frequency (RF) communication systems and provides a comprehensive review of ongoing efforts in this field. Every method used in these models to attain the best possible data throughput and bit error rate (BER) performance for incorporation into 5G networks has been recorded and examined.
Characteristics of E-polarized wave scattering by systems of absolutely thin and conductive flat impedance strips, arranged according to the laws of construction of a perfect set with variable fractional dimension, have been investigated. The scattering problem statement is classically rigorous under certain assumptions. In this case, several classical methods, namely the method of integral equations and Lord Rayleigh’s asymptotic method, along with their modifications, have been used. Considerable attention is paid to two generalizations of the classical nowhere dense perfect set with dimension ln2/ln3, which significantly expand the possibilities for practical applications of such sets. A detailed mathematical analysis of the process of creating two different classes of nowhere dense perfect sets with variable fractional dimension is proposed. This analysis forms the basis for the creation of correct mathematical models of the scattering of plane electromagnetic waves by using strip systems. A simple asymptotic model of scattering of an E-polarized wave by narrow-strip sparsely filled gratings, ordered according to the laws of construction of perfect sets with variable fractional dimensions ln2/lnc (c > 2) and ln3/lnc (c > 3), has been developed. This model forms the basis for developing algorithms to calculate the direction patterns of certain classes of strip gratings ordered according to new mathematical laws. The study and modeling performed by the author can be useful for improving the performance quality of electronic devices that use antenna gratings.
In this paper, the problem of synthesizing and studying the properties of transmission line dual-mode resonators characterized by a single dimension is solved for the first time. The initial samples for the synthesis are stepped-impedance resonators (SIR) with different numbers of composite sections N, and characteristic impedances Z0i, i = 1, 2, …, N. Four dual-mode resonators were synthesized, which represent a meander with alternating sections of high Z0max and low Z0min characteristic impedance. In two resonators, dual-mode oscillation arises from the mutual convergence of the resonant frequencies f01 and f02, forming a meander with three sections. The other two resonators represent a meander with five sections. In these resonators, dual-mode oscillation arises from the convergence of the resonant frequencies f02 and f03, enabling operation at higher frequencies without reducing their length. Both ends of these resonators can be either open-circuited or short-circuited. A simple analytical dependence of the even fe and odd fo modes on the parameter m = Z0max/Z0min of synthesized meander dual-mode resonators was established. The larger the parameter m, the closer fe and fo modes are. Their convergence can be as low as 4
The paper discusses the improvement of the caterpillar Singular Spectrum Analysis (SSA) method by using the surrogate data technology to increase the accuracy of time series reconstruction in the presence of additive noise. The use of the Attractor Trajectory Surrogates (ATS) algorithm to generate surrogate realizations is proposed, which effectively reduces residual noise in observations after processing with the caterpillar SSA method. The simulation results show that the use of surrogate data technology, combined with the caterpillar-SSA method, yields higher-quality time-series signal reconstruction than the baseline method, particularly under high-noise conditions. In the process of analyzing the quality of signal reconstruction, SG statistics was calculated, and the recovery coefficient was determined, which made it possible to obtain numerical values for the SG (Savit and Green) predictability index. These values were used to process the data, both by the baseline caterpillar SSA method and by its refined version using the ATS algorithm. The proposed approach is shown to reduce the dependence of time series restoration quality on the number of singular decomposition components, increase the stability of the results, and minimize the final noise level.
In the case of an acousto-optic delay line, the procedure for measuring the cut-off frequency is quite complex. This paper considers the influence of the light beam diameter and the acoustic wave propagation velocity in a photoelastic medium on the time constant of the transient response of the acousto-optic delay line. Based on the results obtained, an express method for measuring the cut-off frequency of an acousto-optic delay line is proposed. Some aspects of the practical application of this method are discussed. Relevant numerical examples are presented. The proposed express method for determining the cut-off frequency of the acousto-optic delay line has been experimentally verified, and the scatter in the obtained measurements has been estimated.
Steganography is one of the most effective and powerful modern means of information protection. One of the main requirements for a steganographic system is resistance to attacks on the embedded message. Given the current state of information technology, such attacks can be carried out without specialized software or hardware, making the task of countering them extremely relevant. The properties of the container used, which in this study is a digital image, play an important role in organizing a hidden (steganographic) communication channel. By selecting a container, the characteristics of steganographic system can be improved without changing the steganographic method used. The purpose of this study is to increase the robustness of a steganographic system against attacks targeting the embedded message by improving the container selection method previously proposed by the authors. The goal is achieved by improving the determination of the key parameter for container selection, i.e., the volume of protected embedded information, as well as by applying the process of primary filtering of a set of potential containers, which allows us to filter out conditional background digital images that do not provide adequate resistance to disturbing actions for the corresponding steganographic message. This increased the efficiency of container selection by 2.3
The paper presents the construction principles and the mathematical model of the mm-wave noise generator. It combines a thermal noise generator (TNG) and an avalanche transit-time (IMPATT) diode noise generator, thereby significantly increasing the output power range and expanding its application scope. In particular, such a device can serve as a reference signal source in radiometric systems (RS) for medical applications, earth surface sensing equipment, baggage control systems at airports, and for studying processes in plasma physics, etc. The proposed mathematical model enables the determination of the generator’s parameters and characteristics during its operation as part of the ultra-high-frequency path of RS. Experimental studies of the noise signal generator have confirmed the adequacy of the developed model and the high accuracy of calculations for the main parameters of the generator. The conducted studies provide the possibility of constructing a reference noise signal generator with a dynamic range of up to 40 dB and an error of output power reproduction of no more than 10
This paper considers the problem of creating compact, fully shielded microstrip BPFs implemented on a thick substrate and a low-mounted screen, capable of implementing narrow passbands (<3
Reverberation time is one of the most important characteristics of room acoustics. In particular, reverberation time estimates are used to analyze the speech intelligibility and overall acoustic perception in premises. This paper discusses the problem of obtaining unbiased reverberation time estimates using the inverse integration method in the presence of background noise. Two measurement methods using the inverse integration method are compared. In the first method, the tail of the room’s impulse response is not accounted for during integration. In the second method, the average value of the square of the background noise is subtracted from the square of the impulse response of the room during integration. For the first method, analytical expressions are proposed for selecting the optimal value of reverberation time estimate in terms of the minimal bias of the estimates, the value of the truncation point, which separates the decaying part of the impulse response of the room from the section with the background noise, The computer simulation has confirmed the validity of the results obtained and has also shown the feasibility of adjusting the value of the truncation point to compensate the effect of filtering on the measurement results when using both methods.
Non-orthogonal multiple access (NOMA), a pivotal scheme for sixth generation (6G), will revolutionize wireless communication by facilitating massive connectivity, spectral efficiency (SE), and user fairness. Power-domain multiplexing and successive interference cancellation (SIC) enable NOMA to support multiple users within the same time-frequency resource block, unlike orthogonal multiple access (OMA). The inherent broadcast nature of wireless communication presents significant challenges for physical layer security (PLS). Secure beamforming, artificial noise (AN) injection, reconfigurable intelligent surfaces (RIS), and cooperative jamming are analyzed strategies to improve PLS in NOMA deployments. This study examines advanced PLS methodologies for NOMA across several operational scenarios, including massive multiple-input multiple-output (M-MIMO), full-duplex (FD) relaying, millimeter-wave (mmWave) communications, RIS, vehicular communication, and unmanned aerial vehicle (UAV)-assisted communication. Investigations examine novel methodologies for secure power allocation and user pairing algorithms, employing deep learning (DL) and deep reinforcement learning (DRL). The study encompasses pioneering academic research on how these contributions mitigate eavesdropping, ensure data confidentiality, and enhance secure transmission across various fading scenarios. This research indicates that secure NOMA could be integrated with Terahertz (THz) communication, integrated sensing and communication (ISAC), quantum-resilient protocols, and energy-efficient green paradigms in 6G. The research investigates RIS NOMA and DL NOMA in scenarios of elevated node velocity in time-selective Nakagami-m and κ–μ fading channels. This study provides a basis for advancing secure NOMA-enabled wireless networks.
Experimental research has been conducted on deliberate interference in GNSS signals by the retransmitted radio frequency interference of the meaconing type. In an experimental setup, GPS, GLONASS, Galileo, and BeiDou signals were received and processed across four frequency bands. Radio frequency interference (RFI) is relayed from a separate antenna and fed to the receiver input via a microwave adder. A microwave amplifier and attenuator control the power of the interference. Regular satellite signals also reach the receiver input via a microwave adder. It has been shown that this procedure is equivalent to feeding both regular signals and radio-frequency interference to the receiver via a single antenna. Measurement results have shown that in a GNSS system containing GPS, GLONASS, Galileo, and BeiDou operating in all frequency bands, when smoothly entering the RFI zone of the meaconing type, signs of deliberate interference in regular satellite signals may be sudden changes in the position, signal-to-noise ratio, root mean square deviation of phase and code pseudoranges, and the difference between phase and code pseudoranges.
Using a thin wire approximation, a numerical and analytical solution was obtained for the problem of current distribution in regular and biconical dipoles with constant and variable distributed surface impedance and arbitrary excitation located in free space. The input characteristics and radiation fields of the given antenna structures have been investigated. The reliability of the solution has been confirmed by the satisfactory agreement between the experimental and numerical results, with known literature sources, and by comparison with calculated data obtained using commercial software packages. Numerical results are presented for the input admittance, the reflection coefficient in the feed line, and electromagnetic fields excited in the surrounding space by dipoles with symmetrical and asymmetrical distributed surface impedance.
The ever-increasing demand for 5G networks necessitates innovative solutions to optimize network efficiency. In this study process, we approached conventional Random User Selection (RUS) and Maximum Channel Gain (MCG) based on which we developed a new method called Distance User Selection (DUS). In DUS, the users are selected based on the distance where the nearest user is chosen first and assigned to the available antennas at the base station. This method prioritizes users closer to the serving base station for association, exploiting stronger signal strength and reducing path loss. Additionally, it employs optimized antenna selection algorithms to improve the signal quality and resource allocation further. We evaluated the proposed method through simulations and compared its performance with conventional approaches regarding throughput, sumrate, and energy efficiency. Our results demonstrate significant improvements in network efficiency, highlighting the potential of DUS and antenna selection to enhance 5G network performance and user experience.
A promising direction in the development of neural networks for the analysis and classification of biomedical signals is the use of trainable activation functions, known as AAFs (Adaptive Activation Functions). The use of such functions enables heterogeneous data to be adapted, thereby improving classification accuracy. This paper considers the application of AAFs for the classification of low-amplitude components of electrocardiogram (ECG), specifically ventricular late potentials (VLP) and atrial late potentials (ALP), which are important for the early detection of cardiac tachyarrhythmias. To evaluate the impact of AAF on the quality of VLP and ALP detection, two fully connected neural networks with different numbers of hidden layers were developed. The study established that using AAF increases the accuracy of VLP and ALP classification and the speed of neural network model training compared to non-adaptive activation functions. To minimize the problems of “vanishing” or “exploding” gradients in the loss function, as well as the effects of “dead” neurons that arise during neural network training, a new activation function has been developed that normalizes weight coefficients, preventing excessively high or low gradients. Using the developed activation function increases the speed and stability of neural network training. It improves the recognition accuracy of low-amplitude ECG components compared to other activation functions. Using the developed AAF, the highest classification accuracy was obtained for VLP (94.7
In the second part of the article, the electric field distribution, electron beam trajectories, and their focal parameters are calculated using the known analytical expressions to determine the plasma boundary position relative to the cathode surface. The sequential upper relaxation method, the current tube method, the fourth-order Runge–Kutta method, and extreme analysis numerical methods are used to determine the electric field distribution in the electrode system, to calculate the spatial charge, to calculate the electron trajectories in the free drift region in the anode plasma, and to estimate the thickness of the electron beam in focus, respectively. The iterative calculation relations for the electric field distribution and electron beam trajectories are expressed as arithmetic-logical expressions and recurrence matrices to simplify program code implementation. The obtained relative difference between calculated and experimental data for the thickness of the electron beam in focus doesn’t exceed 15–20
The structures of scalar field sources described by zonal spherical wave functions have been studied. Such functions are used, in particular, in problems of electrodynamics and acoustics when a spherical surface limits the domain. The values of the fields under consideration depend not only on the distance to the source, but also on the angular coordinate, which indicates the multipole nature of such a source. Therefore, the study of their structures is an interesting theoretical problem. A multipole source is a set of monopoles (zero-order field sources) located within a specific infinitely small region. In this study, an expression has been first obtained that relates the zero-order field to the fields of subsequent orders. The differential nature of this expression shows that the size of the multipole, unlike the dimensionless monopole, is an infinitesimally small quantity. By assigning this quantity small finite values, it is demonstrated that monopoles in a multipole are located along a short segment. The amplitudes of these monopoles are also found. The resulting multipole is called linear. Next, based on the well-known addition theorem, other values of monopole amplitudes are determined, at which the initial field corresponding to the zonal spherical wave function is described more accurately. A generalization of the linear multipole for the case of a larger number of monopoles is also given. Based on the same addition theorem, it is further shown that the initial field can also be described by monopoles, which, unlike the previous cases, are located on the surface of a small radius sphere.
