Мікросистеми, Електроніка та Акустика: науково-технічний журнал, Т. 29, № 1(126)
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Документ Відкритий доступ Evaluation of the Limitation of Operational Parameters of the IEEE 802.11 ac Network in the 20MHz Channel(КПІ ім. Ігоря Сікорського, 2024) Omelianets, O. O.; Lazebnyi, V. S.IEEE 802.11 wireless network technologies are widely used to create corporate and personal local networks for data exchange and access to Internet resources. The main principle of operation of IEEE 802.11 networks is the principle of competitive access, according to which all wireless network users have the same access rights to the information transmission environment. This method of access leads to the occurrence of collisions in networks with a large number of users, which complicates the process of network functioning and leads to the degradation of quality indicators. The purpose of the study is to estimate the limit values of the operational characteristics of the IEEE 802.11 ac wireless network in the mode with the highest transmission rate (MCS8) in a frequency channel of 20 MHz with one spatial stream, provided that the network has a significant number of active stations with a saturated load. An alternative model of processes in IEEE 802.11 networks based on the concept of a virtual competitive window is used for research. According to the concept of virtual contention window (VCW), the process of data transmission in a network with competitive access is considered as a quasistationary process. Numerical data were obtained and graphs of channel bandwidth, transmission delay, and delay nonuniformity were given in the presence of one to sixteen active stations with a saturated load in the network, in the case of transmission of frames with a data volume of 512 or 1500 bytes. The maximum possible bandwidth of the channel with a frequency band of 20 MHz (68.387 bit/s) was determined, in the case of using frames with the maximum load (11454 bytes) provided by the standard. Estimated data on the number of collisions occurring in a network with a saturated load and the number of frames transmitted at various stages of channel access are also provided. The frame transmission delay increases almost proportionally to the number of active stations and varies from 0.605 ms to 5.293 ms, in the case of loading all data frames of 512 bytes, and from 0.785 to 6.41 ms, in the case of a load of 1500 bytes, for changes in the number of active stations in the network from 2 to 16. The unevenness of the delay exceeds the average delay and grows non-linearly, in the case of an increase in the number of active stations from 1 to 6 (CWmin=15), and linearly — with a further increase in the number of stations (over 6). The obtained results are useful for reasonable planning of wireless networks and configuration of network equipment parameters.Документ Відкритий доступ Determination of Signs of Sleep Apnea Using Machine Learning Methods in Combination with Reducing the Dimensionality of Heart Rate Variability Features(КПІ ім. Ігоря Сікорського, 2024) Samsonenko, A. S.; Popov, A. O.Obstructive Sleep Apnea Syndrome (OSAS) is a clinically significant disorder characterized by recurrent episodes of upper airway obstruction, manifesting as either apnea or hypopnea, predominantly occurring at the pharyngeal level. Despite the preservation of respiratory muscle function during these episodes, OSAS poses considerable health risks, including cardiovascular complications and cognitive impairment. In recent years, a growing body of literature has explored novel methodologies to discern and diagnose OSAS, with a particular focus on cardiac activity analysis through Heart Rate Variability (HRV). This study contributes to the existing literature by conducting a comprehensive HRV analysis aimed at identifying indicative patterns of sleep apnea. The analysis incorporates diverse parameters within both time and frequency domains, facilitating a nuanced understanding of the complex interplay between cardiac dynamics and respiratory disruptions during sleep. In an effort to enhance the interpretability of the data, various scaling and dimensionality reduction techniques, such as Principal Component Analysis (PCA), t-distributed Stochastic Neighbor Embedding (t-SNE), and Uniform Manifold Approximation and Projection (UMAP), were applied. The dataset utilized in this investigation comprises records from 70 patients, sourced from the Apnea-ECG Database on the Physionet platform. To discern the optimal classification model, several machine learning algorithms were employed after the dimensionality reduction, including k-Nearest Neighbors (k-NN), logistic regression, Support Vector Machine (SVM), Decision Tree, Random Forest, and Gradient Boosting. Intriguingly, the results demonstrate a remarkable 100% accuracy across all classifiers when utilizing the UMAP dimensionality reduction method. A distinctive feature of the proposed methodology lies in its amalgamation of machine learning techniques with HRV parameters post-dimensionality reduction. This approach not only enhances the interpretability of the complex physiological data but also underscores the potential applicability of the developed model in real-world scenarios for the detection of OSAS. The robustness of the proposed approach, as evidenced by its high accuracy rates, positions it as a promising tool for advancing diagnostic capabilities in the realm of sleep medicine. Future research endeavors may further refine and validate this methodology, paving the way for its integration into clinical practice and contributing to the broader landscape of sleep disorder diagnostics.Документ Відкритий доступ Application of k-Nearest Neighbors Method for Drug Concentraiton and Cardiotoxicity Classification Using Extracellular Field Potentials and Reconstructed Action Potentials of Cardiac Cells(КПІ ім. Ігоря Сікорського, 2024) Shpotak, M. O.; Ivanushkina, N. H.Micro-electrode array (MEA) systems are important for measuring extracellular field potentials (FP) of cardiac cells, which is a crucial step in cardiotoxicity assessment. However, without modification, the MEA system is only capable of recording FPs. This limits the number of parameters for cardiotoxicity assessment only to FP parameters, while the action potential (AP) parameters remain unused. To address this issue the MEA systems are often modified to use electroor optoporation to record the local extracellular APs (LEAPs), which allows to reliably quantify the AP morphology. As an alternative to MEA modification and cell membrane stimulation the AP can be reconstructed mathematically.This study explores how using additional parameters from reconstructed action potentials (RAPs), derived from FPs, can improve the accuracy of k-NN machine learning models for drug concentration and potential cardiotoxicity classification. The k-NN classifier was trained using combinations of FP and RAP parameters. The k-NN models were evaluated using five-fold stratified cross-validation and cross-channel validation. Their performances were compared using error rate, macro precision, macro recall and macro F1 score accuracy metrics. The results indicated that ncorporating RAP parameters into the feature set increased the F1 score of k-NN model for DMSO concentration classification by up to 10.78% compared to the training set with only FP features.Документ Відкритий доступ Inductor-Less Broadband Energy-Efficient Active Balun up to 60GHz(КПІ ім. Ігоря Сікорського, 2024) Baluta, T. O.; Meyer, A.; Issakov, V.; Vountesmery, Yu. V.The paper presents a non-inductive broadband energy-efficient active balun based on a differential pair, intended for use in the input block of a frequency divider for 22 nm technology. The developed device can operate in the frequency range from 2 GHz to 60 GHz with a supply voltage of 0.8 V and consume less than 3 mA. The special feature of the developed active balun is that it does not have inductive components, which reduces its size and signal loss. Amplitude of the output signal in working frequency range is from 450 mV to 200 mV. Signal gain in the range from 1-60 GHz varies from -10 dB up to 4 dB. The size of the circuit on the chip is 48x34 um. The device allows you to receive a stable signal at high data transfer rates and provides energy savings due to low current consumption.Документ Відкритий доступ Formation of the Spectral Composition of the Output Voltage of Converters for Nuclear Magnetic Resonance(КПІ ім. Ігоря Сікорського, 2024) Zahranychnyi, A. V.In this paper, we consider the construction of an asynchronous control system for semiconductor converters for nuclear magnetic resonance. The relevance of research in this direction, main problems that arise during the construction of these systems are shown. Derived the mathematical model of the inverter, on the basis of which a control system with asynchronous pulse-width modulation is constructed. Proposed an equivalent converter circuit with a constant structure, constant parameters, and an equivalent EMF generator. Established correspondence between the equivalent circuit of the converter and its mathematical model in the form of differential equations. On the basis of mathematical equations, a structural diagram of the converter with a control system was developed and the principle of operation of the device was described according to it. To develop an algorithm for the control system, the dependence of the frequency change relative to the resonant frequency on the phase shift between the current through the filter and the voltage on the antenna circuit is determined. For which the model was built in Simulink and the corresponding simulation was carried out. Numerical dependences of reference signal frequency change and phase shift were obtained. The increase in efficiency of device for nuclear magnetic resonance is considered due to the use of multilevel inverters with tuning the frequency of operation to the frequency of the resonant circuit. Simulation of a three-level diode-clamped inverter showed that when the capacitance of the resonant circuit changes and, therefore, the resonant frequency of the circuit, the input current increases. The work obtained specific numerical dependencies. Time diagrams of voltages and currents on the main elements of the converter are given, which illustrate the implementation asynchronous pulse-width modulation in the control system. After working out the automatic frequency control algorithm, the increase in current consumption can be leveled off. The simulation results also show that it is possible to reduce the amplitude of the third harmonic. The disadvantages of the proposed system include the fact that the frequency of the converter is adjusted at each subsequent period of its operation. At the same time, the parameters of the filter can change again, which leads us to believe that adjusting the frequency will never give a 100% result, but will only allow to get as close as possible to the set parameters of the sounding signal. The work also indicates that it is possible to improve the spectral composition of the probing voltage generated by the converter by using more levels of a diode-clamped multi-level inverter. However, increasing the number of levels reduces the action speed of the system and complicates the control system itself. Therefore, the need to maintain a balance between the number of levels of the inverter and the complexity of the system is indicated.