Konrad Jędrzejewski

Warsaw University of Technology

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Krzysztof Kulpa

Warsaw University of Technology

Mateusz Malanowski

Warsaw University of Technology

Szymon Buś

Warsaw University of Technology

Mariusz Pożoga

Centrum Badań Kosmicznych

ŁM

Ł. Małkiewicz

Warsaw University of Technology

Renata Plucińska

Warsaw University of Technology

Przemysław Guzik

Poznan University of Medical Sciences

АА

А. А. Платонов

Magnezit (Russia)

J. Jasnos

Warsaw University of Technology

Aleksander Droszcz

Warsaw University of Technology

Cooperative Institutions

Nonlinear Control Strategies (United States)

Warsaw University of Technology

Polish Academy of Sciences

Tele & Radio Research Institute

Gdańsk University of Technology

University of Warsaw

Technical University of Darmstadt

Weatherford College

Information Technology Institute

University of Pavia

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Beamforming of LOFAR Radio Telescope Antennas Used as Sensors in Passive Radiolocation System

Aleksander Droszcz Julia Kłos Konrad Jędrzejewski Krzysztof Kulpa Mariusz Pożoga

The paper presents the results of studies on analysis, implementation and testing of beamforming methods which can be used for enhancement of radiolocation capabilities of radioastronomical LOFAR station in the context of its use for passive radiolocation. Using the LOFAR system for passive radiolocation might be an highly cost-effective solution for location of objects due to the fact that most of the necessary equipment already exists. In this paper the location of planes by a single LOFAR station in Borowiec was considered as the proof of concept for a more complex system for localizing space objects in the future. The beamforming Phase-Shift algorithm used for passive radiolocation by means of LOFAR station was presented and thoroughly discussed. Beam patterns of steered antenna array of a LOFAR station and its single subapertures, known as tiles, were shown. Occurrence of grating lobes in presented beam patterns is also discussed. The results of preliminary experiments performed with real signals registered by the LOFAR station in Borowiec confirm the efficiency regarding enhancement of radiolocation capabilities, increasing radar's range and certainty of detection by means of beamforming.

LOFAR

Radio navigation

10.23919/irs48640.2020.9253779

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Citations (8)

Experimental verification of passive radar space object detection with a single low‐frequency array radio telescope

IET Radar Sonar & Navigation (2023)

Konrad Jędrzejewski Mateusz Malanowski Krzysztof Kulpa Mariusz Pożoga

Abstract The paper focuses on the results of experimental research on the possibility of passive space object detection using a single radio telescope from the European Low‐Frequency Array (LOFAR) network of astronomical radio telescopes. Commercial digital television (DVB‐T) transmitters were used as illuminators of opportunity in this radar system. In the conducted experiments, one LOFAR radio telescope served both as a surveillance receiver and reference receiver in a passive radar system. The greater part of the LOFAR telescope array was used to observe a space object, while a small part of the array was directed towards the illuminator of opportunity to record the reference signal. One of the most important problems to overcome with utilising the LOFAR radio telescope in such a solution was the effective suppression of the direct‐path component in a surveillance signal coming from the illuminator of opportunity, which was relatively close to the LOFAR radio telescope. The results regarding the passive detection of the International Space Station, included in the paper, confirm the possibility of observing the space object flying in Low‐Earth Orbit using the LOFAR telescope or another receiving system with a similar antenna array.

LOFAR

Passive Radar

Radio Astronomy

10.1049/rsn2.12481

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Influence of Feature Scaling and Number of Training Sessions on EEG Spectral-based Person Verification with Artificial Neural Networks

Renata Plucińska Konrad Jędrzejewski Urszula Malinowska Jacek Rogala

Research on using EEG as a biometric began over 20 years ago. However, compared to more traditional modalities like fingerprints, EEG is still relatively novel. Further studies on more extensive databases are necessary to properly verify proposed methods, accounting for temporary fluctuations in the EEG signal. The study focuses on the impact of methods of feature scaling on the efficiency of EEG spectral-based person verification using artificial neural networks. For our research, we used signals collected from 29 individuals, with 20 recording sessions, each performed on different days. Having such a database, the influence of a number of training sessions on the verification results was also investigated. We tested various methods for scaling estimates of power spectral density coefficients, including power normalization, 5–95 percentile normalization, interquartile range normalization, and raw PSD estimate coefficients converted to the decibel scale. The best results were obtained after converting them to the decibel scale, which resulted in the accuracy of EEG-based people verification equals to 96.6 %.

Normalization

Decibel

10.23919/spsympo57300.2023.10302695

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Citations (1)

Numerical analysis of signal distribution propagation in radar detection procedures

Konrad Jędrzejewski

The paper presents the results of research on a histogram-based approach to numerical analysis of statistical distributions of signals in radar detection systems. The idea of this method consists in the numerical calculation of histogram equivalents of probability density functions or cumulative density functions of signals after each stage of a signal processing path. The considerations are illustrated by simulation examples. Their results are compared to the results of Monte Carlo simulations.

SIGNAL (programming language)

Radar detection

10.1109/irs.2016.7497395

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A new approach to drift compensation in adaptive feedback communication systems

Konrad Jędrzejewski

A new approach to drift compensation in adaptive feedback communication systems is presented in the paper. The proposed approach is based on application of the extended multidimensional algorithm that estimates simultaneously the value of a transmitted sample and the value of an unknown drift rate. The knowledge of a drift rate enables compensation of drifts and improves transmission efficiency of systems suffering problems with drifts.

Adaptive system

10.1109/icses.2012.6382240

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ECG-Derived Respiration - Complete Implementation and its Evaluation with Use of Clinical Data

Szymon Buś Konrad Jędrzejewski

The paper presents the results of studies devoted to development of the complete (end-to-end) and effective implementation of the method for reconstruction of a respiration signal from electrocardiogram (ECG). The methods for deriving a reliable information about patient's respiration activity without a necessity to make measurements other than ECG are generally referred to as ECG-derived respiration (EDR). Several well recognized signal processing techniques used in the subsequent stages of ECG signal processing for deriving the respiratory signal were analyzed and evaluated with use of clinical data. It allowed us to select the adequate solutions for our implementation. The results of evaluations obtained with three different variants of EDR are presented and discussed. The implementation was tested with clinical data containing simultaneously recorded 2-channel ECG signals and reference respiration signals registered with use of chest belt and strain gauge.

SIGNAL (programming language)

10.1109/icses.2018.8507332

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Consideration of component imperfections in new digitally assisted sub-ranging A/D converters

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2013)

Konrad Jędrzejewski

The paper presents the results of investigations on the new approach to optimization of sub-ranging analog-to-digital converters (ADCs) working with the assumed level of their components imperfections caused by technological dispersions, errors, noises or disturbances. The suggested approach is based on application of digital estimation algorithms that take into consideration the anticipated parameters of the components imperfections. Implementation of the approach is possible in the sub-ranging ADCs whose digital parts permit to calculate output codes of ADCs by means of simple mathematical operation. The performance of ADCs operating according to this approach is analyzed for the imperfections of different ADC components in simulation experiments. The results obtained for the proposed ADC are compared with the results obtained for the conventional pipeline ADC employing the identical analog components.

Ranging

Component (thermodynamics)

10.1117/12.2034307

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Citations (1)

Projektowanie i analiza laboratoryjnego prototypu cyklicznego przetwornika A/C wykorzystującego nową zasadę konwersji

A. Płatonow Zbigniew Jaworski Konrad Jędrzejewski Ł. Małkiewicz J. Jasnos

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Adaptive Active Noise Cancelling System for Headphones on Raspberry Pi Platform

Piotr Sykulski Konrad Jędrzejewski

In recent years, a lot of headphones with active noise control systems have appeared on the consumer market. Most of these systems make use of specialized digital signal processors designed specifically to process audio signals in real-time. In this article, we present an active noise control headphone system based on the general use Raspberry Pi computer with ARMv8 processor and Linux operating system. This platform is not designed for performing real-time digital signal processing neither in terms of hardware nor software. But with the help of techniques such as multithreading and low-level audio programming in Linux, we created a real-time active noise cancelling system and compared it in terms of noise reduction with different commercial headsets.

Headphones

Active Noise Control

Raspberry Pi

10.23919/spw49079.2020.9259141

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Statistical and Diagnostic Properties of pRRx Parameters in Atrial Fibrillation Detection

Journal of Clinical Medicine (2022)

Szymon Buś Konrad Jędrzejewski Przemysław Guzik

Background: We studied the diagnostic properties of the percentage of successive RR intervals differing by at least x ms (pRRx) as functions of the threshold value x in a range of 7 to 195 ms for the differentiation of atrial fibrillation (AF) from sinus rhythm (SR). Methods: RR intervals were measured in 60-s electrocardiogram (ECG) segments with either AF (32,141 segments) or SR (32,769 segments) from the publicly available Physionet Long-Term Atrial Fibrillation Database (LTAFDB). For validation, we have used ECGs from the Massachusetts Institute of Technology–Beth Israel Hospital (MIT–BIH) Atrial Fibrillation Database. The pRRx distributions in AF and SR in relation to x were studied by histograms, along with the mutual association by the nonparametric Spearman correlations for all pairs of pRRx, and separately for AF or SR. The optimal cutoff values for all pRRx were determined using the receiver operator curve characteristic. A nonparametric bootstrap with 5000 samples was used to calculate a 95% confidence interval for several classification metrics. Results: The distributions of pRRx for x in the 7–195 ms range are significantly different in AF than in SR. The sensitivity, specificity, accuracy, and diagnostic odds ratios differ for pRRx, with the highest values for x = 31 ms (pRR31) rather than x = 50 (pRR50), which is most commonly applied in studies on heart rate variability. For the optimal cutoff of pRR31 (68.79%), the sensitivity is 90.42%, specificity 95.37%, and the diagnostic odds ratio is 194.11. Validation with the ECGs from the MIT–BIH Atrial Fibrillation Database confirmed our findings. Conclusions: We demonstrate that the diagnostic properties of pRRx depend on x, and pRR31 outperforms pRR50, at least for ECGs of 60-s duration.

10.3390/jcm11195702

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Citations (8)