Elektrik ve Elektronik Mühendisliği Bölümü / Department of Electrical & Electronics Engineering

Permanent URI for this collectionhttps://gcris3.etu.edu.tr/handle/20.500.11851/276

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Experimental Study on the Effects of Communication on Cooperative Search in Complex Environments
(Woodhead Publishing Limited, 2010) Çayirpunar, Ömer; Gazi, Veysel; Tavli, Bülent; Cervera, Enric; Witkowski, Ulf; Penders, Jacques S.J.H.
In this study we investigate the benefits of networked communication by experimentally evaluating the results of two search algorithms, which are spiral search and informed random search. Both simulations and real experiments are performed in order to obtain objective results. The robotic experiments were performed in an experimental area containing obstacles where the communication ranges were "simulated" with the help of an overhead camera. Each robot was allowed to keep an occupancy grid based local map of the environment also containing information about the cells it has visited and to exchange this information with the other robots within its communication range. The effect of the size of communication range on the performance of the system defined as the time of completion the search task (i.e. locating the target) was investigated. © Woodhead Publishing Limited, 2011. © 2013 Elsevier B.V., All rights reserved.
Introduction to Multiple Antenna Communications and Reconfigurable Surfaces
(now Publishers Inc., 2024) Björnson, Emil; Demir, Özlem Tuğfe
Wireless communication is the backbone of the digitized society, where everything is connected and intelligent. Access points and devices are nowadays equipped with multiple antennas to achieve higher data rates, better reliability, and support more users than in the past. This book gives a gentle introduction to multiple antenna communications with a focus on system modeling, channel capacity theory, algorithms, and practical implications. The basics of wireless localization, radar sensing, and controllable reflection through reconfigurable surfaces are also covered. The goal is to provide the reader with a solid understanding of this transformative technology that changes how wireless networks are designed and operated, today and in the future. The first three chapters cover the fundamentals of wireless channels, and the main benefits of using multiple antennas are identified: beamforming, diversity, and spatial multiplexing. The theory and signal processing algorithms for multiple-input multiple-output (MIMO) communications with antenna arrays at the transmitter and receiver are progressively developed. The next two chapters utilize these results to study point-to-point MIMO channels under line-of-sight (LOS) and non-LOS conditions, covering the shape of signal beams, impact of array geometry, polarization, and ways to achieve reliable communication over fading channels. The book then shifts focus to multi-user MIMO channels, where interference between devices is managed by spatial processing. The next chapter extends the theory to multicarrier channels and explains practical digital, analog, and hybrid hardware implementations. The last two chapters cover the role of multiple antennas in localization and sensing, and how reconfigurable surfaces can improve both communication and sensing systems. The text was developed as the textbook for a university course and builds on the reader's previous knowledge of signals and systems, linear algebra, probability theory, and digital communications. Each chapter contains numerous examples, exercises, and simulation results that can be reproduced using accompanying code.
Calibration-Based Polynomial-Fit Non-Uniformity Correction on Thermal Imaging Systems
(2023) Önver, Ahmet Yasin; Özdür, İbrahim Tuna
Infrared Focal Plane Arrays (IRFPAs) are used in many areas today as they provide the imaging ability to electro-optical systems. However, the raw images acquired from IRFPAs are usually not useful forthwith since there exist several undesired effects. Non-uniformity (NU) is one of these undesired effects which is caused by several factors such as the cosine-fourth-power effect, photo-detectors on IRFPA being nonidentical, fixed-pattern noise, etc. To eliminate NU and obtain a clearer image, an appropriate nonuniformity correction (NUC) procedure must be applied to the raw image. There are fundamentally two different types of NUC methods that are scene-based and calibration-based. Calibration-based methods rely on adjusting the responsivity of each photo-detector on IRFPA by calibrating the photo-detector response with the help of a uniform radiation source, while scenebased methods rely on correcting the image based on scenery by adjusting NUC parameters in run time with the help of neural-network algorithms, Kalman filter, etc. In this study, a calibrationbased Polynomial-Fit NUC (PFNUC) method is presented and compared to a 2-point NUC (2PNUC) method that is currently used in a serial production thermal imaging system. 2PNUC is one of the most common NUC methods used in thermal imaging systems, where the response of the IRFPA is calibrated based on the raw images taken from a blackbody (BB) at two different temperatures. A gain factor and an offset value are calculated for each photo-detector by using digital signal levels (well-fill level) of the raw image. Ultimately, a gain and an offset table (NUC tables) are formed and applied to the raw image. In serial production systems, each system is usually calibrated at constant BB temperatures. However, this is not appropriate since there may be a considerable amount of variance in the average responsivity of IRFPAs used in systems that may be caused by a couple of reasons such as the different optical transmissions in optics due to imperfection in optical coatings, primitive methods during focus and alignment of the optics, slightly different gain factors on the read-out circuits of the IRFPAs, etc. Given that, when 2PNUC is performed at constant BB temperatures, it leads to both systems being calibrated at different well-fill levels and having different residual NU (RNU) over their dynamic range, which is quite an unwanted characteristic from systems of the same production line. RNU is a measure of how non-uniform is the response of the IRFPA when a uniform radiation source is present in its field of view and an evaluation metric for the NUC method. Despite the average responsivity variance in IRFPAs, the well-fill curve characteristics are quite similar, so it is possible to perform a polynomial fitting. Given that a PFNUC method is proposed and the responses of IRFPAs are calibrated based on a third-order polynomial-fit estimation in which the well-fill levels of each photo-detector are fitted to the median values of IRFPA at four different raw BB images over the dynamic range. By doing so, the coefficients of the fitted polynomial are calculated and the PFNUC tables are formed. A third order PFNUC covers the polynomial characteristics of photo-detectors’ responsivities on IRFPA greatly and it decreases the total RNU by around 50% on average.
Asymmetric terahertz spoof surface plasmon polariton antennas with end-fire radiation
(SPIE, 2024) Songur, Ahmet Canberk; Demircioglu, Mesut; Akcay, Beyza; Sakin, Ahmet Oguz; Ünlü, Mehmet
[No Abstract Available]
Detection of the Coordinates of the Bee Swarm in the Sky Through Image Processing
(2023) Karahan, Mehmet; Lacınkaya, Furkan; Inal, Mertcan; Dilmen, Alperen; Akay, Ahmet Nuri; Kasnakoğlu, Coşku
By scattering pollen to flowers, bees allow plants and trees to bear fruit and disperse their seeds. This important task of bees in life continues the oxygen cycle, which is vital for humans. To put it briefly, a large part of life on earth depends on bees doing their job. In recent years, there has been an annual decrease in the number of bee colonies. For this reason, it is of great importance to keep the bee population under control and to prevent its decline. In this study, the x and y coordinates of a bee swarm in the sky were obtained using the MATLAB program. For this purpose, erosion, one of the morphological image processing methods, was used. In this way, objects other than bees in the photograph used in image processing were removed. With the developed algorithm, the coordinates were determined in the photograph where only the bees were visible. The obtained coordinates are written on the command line of the MATLAB program. Thus, the instantaneous location of the bees could be determined properly.
Electrical characterization of ALD grown HfO2 memristive devices and their noise analysis
(Koç University, 2024) Köymen, Itır; Bozat, Özgür; Öztoprak, İlker; Gökçe, Aisha; Chan, (Sam) Yun Fu; Brown, Gavin; Douglas, Robert
[No Abstract Available]
Delta Bağlantı Fırçasız Motor için Alan Odaklı Kontrol kullanan Sistemin FPGA Tasarımı ve Gerçeklemesi
(BIDGE Publications, 2024) Öncüler, Mustafa Emre; Kasnakoğlu, Coşku
This paper presents FPGA(Field Programmable Gate Array) design and implementation method of system using FOC (Field Oriented Control) for delta connection BLDC (BrushLess Direct Current) motor. Brushless direct current motors are electro-mechanical units commonly used in daily life, industry, military and space applications. FOC method is used in applications that need constant torque of these motor types. FOC algorithm can use various PWM (Pulse With Modulation) methods while controlling BLDC motors. SPWM (Sinusoidal Pulse Width Modulation) is one of the most common methods for 3 phase inverter applications. FPGA’s that provide timewise certainty, high reliability, high speed performance and process simultaneous operation are intelligent units useful for motor applications. In this work, it was used Mojo V3 development board that had an FPGA from Xilinx Spartan-6 family. Mojo V3 development board can be used easily because programmer connecting with usb to computer is provided on board. FPGA was designed and implemented by using VHDL language through design flexibility and robustness. While implemention of FPGA, UART module, Telemetry/Telecommand module, FOC calculation module, PID controller module, Speed calculation module, SPI (Serial Peripheral Interface) communication module, SPWM module are designed by VHDL. As the result of this work has been compared delta connection brushless motor and star connection brushless motor difference when FPGA implements FOC method.
Fault Tolerant Controller Design for Multirotor Systems
(International Institute of Academic Research & Publications (IIARP), 2023) İnal, Mertcan; Kasnakoğlu, Coşku
Purpose: The use area of Unmanned Aerial Vehicles (UAVs) is increasing day by day. Especially Quadcopters are applicable for wide range of potential applications such as security, traffic surveillance, natural risk management, environmental exploration, agriculture and military. However, engine failures, sensor failures or communication failures may occur in quadcopters and it cause both serious accidents in vehicles and damage the environment or surroundings. The purpose of this study aims to develop a fault-tolerant controller design for a quadcopter to enhance its reliability and stability in the presence of component failures or malfunctions. Methodology: The proposed fault-tolerant controller design involves the following key steps: Quadrotor System Design: The mathematical position equations of the quadrotor unmanned aerial vehicle to be designed in the MATLAB Simulink program are extracted using the Euler rotation formulation. Model design is done in MATLAB Simulink by determining the dynamic equations. The designed model also includes the effects of external disturbances and possible failures. Fault Detection: Proposed system has a closed loop control system in order to detect the anomalies in the sensors, motors and critical communication modules. After realizing the anormalities, a fault identification algorithm determines the specific components responsible for the observed anormal behavior. In this study, motors failures and abnormalities are examined. Fault Isolation: In order to prevent motors having faulty behaviors from distorted signals, PID feedback control system is proposed. Quadcopter roll, pitch, yawn movements are tested by reference signal. Originality: Proposed PID controller has ability to fix errors under disturbances; however, nonlinear controller methods have better ability to control the control system. The proportional controller is dependent on the current error, the integral controller is the sum of past errors and the derivative controller is an estimation of future errors. When we tune the PID controller values, we can achieve better state responses but curve settlement time increases. On the other hand, when we decrease the curve settlement time, we observed more aggressive system behavior. For more robust system error isolation, nonlinear quadcopter system will be tested with nonlinear controllers, such as sliding mode control.
STSeqGNN - Konum-Zaman Tabanli Hareket Karakterizasyonu
(IEEE, 2024) Keresteci, Emin; Bulut, M. Eren; Akgün, M. Burak; Tavlı, Bülent
Konum-zaman tabanlı parmak-izi çıkarımı, güncel ve gezginlik (mobility) analizi alanında kritik kabul edilen bir konudur. TUL (Trajectory-user linking) adı altında, LBSN verisi üzerinde çalışan bir çok yapay sinir ağı modeli ortaya konmuştur. Fakat bildiğimiz kadarıyla GPS gibi sıralı konum-zaman verisi ile çalışan yapay sinir ağı üzerinde bir çalışma vücuda gelmemiştir. Bu çalışmada, sıralı konum-zaman verisi işleyebilen, STSeqGNN modelini sunuyoruz. Modelimiz, hem haritanın çizge yapısını, hem de verinin zaman boyutunu verimli ve başarılı bir şekilde işlemektedir. Modelimiz ayrıca güzergahların hareket bilgileri ve temel istatistiksel değerlerini de kullanabilmektedir. Test sonuçlarımızı k tahminde doğruluk metriği ile göstermiş bulunmaktayız. Modelimiz farklı veri kümelerinde %99’un üzerinde başarı yakalamaktadır.
Citation - Scopus: 8
Localization in Massive Mimo Networks: From Far-Field To Near-Field
(Wiley, 2024) Ramezani, P.; Demir, Özlem Tuğfe; Björnson, E.
Source localization is the process of estimating the location of signal sources based on the signals received at different antennas of an antenna array. It has diverse applications, ranging from radar systems and underwater acoustics to wireless communication networks. Subspace-based approaches are among the most effective techniques for source localization due to their high accuracy, with Multiple SIgnal Classification (MUSIC) and Estimation of Signal Parameters by Rotational Invariance Techniques (ESPRIT) being two prominent methods in this category. These techniques leverage the fact that the space spanned by the eigenvectors of the covariance matrix of the received signals can be divided into signal and noise subspaces, which are mutually orthogonal. Originally designed for far-field source localization, these methods have undergone several modifications to accommodate near-field scenarios as well. This chapter aims to present the foundations of MUSIC and ESPRIT algorithms and introduce some of their variations for both far-field and near-field localization by a single array of antennas. We further provide numerical examples to demonstrate the performance of the presented methods. © 2025 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.
Citation - Scopus: 3
Efficient Channel Estimation With Shorter Pilots in Ris-Aided Communications: Using Array Geometries and Interference Statistics
(IEEE-Inst Electrical Electronics Engineers inc, 2025) Demir, Özlem Tuğfe; Bjornson, Emil; Sanguinetti, Luca
Accurate estimation of the cascaded channel from a user equipment (UE) to a base station (BS) via each reconfigurable intelligent surface (RIS) element is critical to realizing the full potential of the RIS's ability to control the overall channel. The number of parameters to be estimated is equal to the number of RIS elements, requiring an equal number of pilots unless an underlying structure can be identified. In this paper, we show how the spatial correlation inherent in the different RIS channels provides this desired structure. We first optimize the RIS phase-shift pattern using a much-reduced pilot length (determined by the rank of the spatial correlation matrices) to minimize the mean square error (MSE) in the channel estimation under electromagnetic interference. In addition to considering the linear minimum MSE (LMMSE) channel estimator, we propose a novel channel estimator that requires only knowledge of the array geometry while not requiring any user-specific statistical information. We call this the reduced-subspace least squares (RS-LS) estimator and optimize the RIS phase-shift pattern for it. This novel estimator significantly outperforms the conventional LS estimator. For both the LMMSE and RS-LS estimators, the proposed optimized RIS configurations result in significant channel estimation improvements over the benchmarks.
Citation - Scopus: 4
Multi-Target Integrated Sensing and Communications in Massive Mimo Systems
(Ieee-inst Electrical Electronics Engineers inc, 2025) Topal, Ozan Alp; Demir, Ozlem Tugfe; Bjornson, Emil; Cavdar, Cicek
Integrated sensing and communications (ISAC) allows networks to perform sensing alongside data transmission. While most ISAC studies focus on single-target, multi-user scenarios, multi-target sensing is scarcely researched. This letter examines the monostatic sensing performance of a multi-target massive MIMO system, aiming to minimize the sum of Cram & eacute;r-Rao lower bounds (CRLBs) for target direction-of-arrival estimates while meeting user equipment (UE) rate requirements. We propose several precoding schemes, comparing sensing performance and complexity, and find that sensing-focused precoding with power allocation for communication achieves near-optimal performance with 20 times less complexity than joint precoding. Additionally, time-sharing between communication and sensing outperforms simple time division, highlighting the benefits of resource-sharing for ISAC.
Distributed Strain Sensing by Frequency-Selective Fading in Phase-Otdr
(Optical Society of America, 2024) Yildiz M.K.; Uyar F.; Kartaloglu T.; Ozbay E.; Ozdur I.
We demonstrate a novel approach using frequency-selective fading in phase-OTDR systems to measure dynamic strain on a fiber optic cable. We present the measurements of 200 Hz, 0.03 µe strain at 2 kHz interrogation frequency. © Optica Publishing Group 2024, © 2024 The Author(s)
Citation - Scopus: 1
User-Centric Cell-Free Massive Mimo With Ris-Integrated Antenna Arrays
(Ieee, 2024) Demir, Özlem Tuğfe; Bjornson, Emil
Cell-free massive MIMO (multiple-input multiple-output) is a promising network architecture for beyond 5G systems, which can particularly offer more uniform data rates across the coverage area. Recent works have shown how reconfigurable intelligent surfaces (RISs) can be used as relays in cell-free massive MIMO networks to improve data rates further. In this paper, we analyze an alternative architecture where an RIS is integrated into the antenna array at each access point and acts as an intelligent transmitting surface to expand the aperture area. This approach alleviates the multiplicative fading effect that normally makes RIS-aided systems inefficient and offers a cost-effective alternative to building large antenna arrays. We use a small number of antennas and a larger number of controllable RIS elements to match the performance of an antenna array whose size matches that of the RIS. In this paper, we explore this innovative transceiver architecture in the uplink of a cell-free massive MIMO system for the first time, demonstrating its potential benefits through analytic and numerical contributions. The simulation results validate the effectiveness of our proposed phase-shift configuration and highlight scenarios where the proposed architecture significantly enhances data rates.
Citation - Scopus: 2
Spatial Correlation Modeling and Rs-Ls Estimation of Near-Field Channels With Uniform Planar Arrays
(Ieee, 2024) Demir, Özlem Tuğfe; Kosasih, Alva; Bjornson, Emil
Extremely large aperture arrays (ELAAs) can offer massive spatial multiplexing gains in the radiative near-field region in beyond 5G systems. While near-field channel modeling for uniform linear arrays has been extensively explored in the literature, uniform planar arrays-despite their advantageous form factor-have been somewhat neglected due to their more complex nature. Spatial correlation is crucial for non-line-of-sight channel modeling. Unlike far-field scenarios, the spatial correlation properties of near-field channels have not been thoroughly investigated. In this paper, we start from the fundamentals and develop a near-field spatial correlation model for arbitrary spatial scattering functions. Furthermore, we derive the lower-dimensional subspace where the channel vectors can exist. It is based on prior knowledge of the three-dimensional coverage region where scattering clusters exists and we derive a tractable one-dimensional integral expression. This subspace is subsequently employed in the reduced-subspace least squares (RS-LS) estimation method for near-field channels, thereby enhancing performance over the traditional least squares estimator without the need for having full spatial correlation matrix knowledge.
An Experimental Design-Based Approach for Modelling of Weapon Engagement Zone of an Air-To Missile
(Taylor & Francis Ltd, 2024) Topbas, Eren; Karaca, H. Deniz; Yazicioglu, Yigit; Kasnakoğlu, Coşku
It is vital for pilots to have precise information about missile ranges during air-to-air combat. The Weapon Engagement Zone (WEZ), or Dynamic Launch Zone (DLZ) for air missions, represents these ranges based on the flight conditions of both the launching and target aircraft. Generating accurate, real-time WEZ functions requires high-fidelity simulations under various engagement scenarios. Classical approaches often require numerous simulations due to uncertainty in sample requirements and complexities like nonlinearities. To address this, the study proposes a method that treats WEZ modeling as a computer experiment, using a surrogate model developed through sequential experimental design and deep neural networks (DNN). This iterative approach optimizes the number of simulations needed, minimizing the loss of model accuracy. The method's effectiveness is validated by comparing it to classical factorial designs, showing that the proposed approach achieves similar accuracy with significantly fewer sample points, making it a more efficient solution for WEZ modeling.
Citation - Scopus: 1
Optimizing Intelligent Reflecting Surfaces With Discrete Phase Shifts and Pilot Overhead Reduction Using Deep Learning
(Institute of Electrical and Electronics Engineers Inc., 2024) Tok, Y.E.; Demirtaş, Ali Murat
Intelligent Reflecting Surface (IRS) is a cost-effective technology for future wireless communication systems to achieve high spectrum and energy efficiency. If the IRS elements are adjusted properly, the surface can provide a power gain proportional to the square of the number of IRS elements. Optimizing the phase shifts of IRS elements is a challenging task since they are not equipped with active RF chains. Previous studies have mostly assumed that the phase shifts of the elements take continuous values, which is practically difficult to implement due to hardware constraints. In addition, a large number of elements at the IRS may result in substantial training overhead. The study presents a Deep Learning approach for configuring discrete phase shifts of IRS elements. The proposed method uses the pilot signals reflected by the IRS as the model input and provides the optimum discrete phase shift values as its output. The model is trained using different lengths of pilot symbol blocks, and numerical results are presented. © 2024 IEEE.
Citation - Scopus: 9
Distributed Versus Centralized Sensing in Cell-Free Massive MIMO
(Ieee-inst Electrical Electronics Engineers inc, 2024) Zou, Qinglin; Behdad, Zinat; Demir, Özlem Tuğfe; Cavdar, Cicek
This letter investigates single-target detection in an integrated sensing and communication (ISAC) system, implemented within a cell-free massive multiple-input multiple-output (MIMO) setup, based on a cloud radio access network (C-RAN) architecture. Unlike previous centralized approaches where sensing is processed in the central cloud, we propose a distributed approach where sensing partially occurs at the receive access points (APs). We consider two scenarios based on the knowledge available at receive APs: i) fully-informed, with complete access to transmitted signal information, and ii) partly-informed, with access only to transmitted signal statistics. We introduce a maximum a posteriori ratio test detector for both distributed sensing scenarios and assess the signaling load for sensing. The fully-informed scenario's performance aligns with the centralized approach in terms of target detection probability. However, the partly-informed scenario requires an additional 13 dBsm variance on the target's radar cross section (RCS) for a detection probability above 0.9. Distributed sensing significantly reduces signaling load, especially in the partly-informed scenario, achieving a 70% reduction under our system setup.
Performance Analysis for Isac Systems With 1-Bit Dacs
(IEEE, 2024) Salman, Murat Babek; Demir, Özlem Tuğfe; Bjornson, Emil
Low-resolution quantization constrains the maximum achievable gains of multiple-input multiple-output (MIMO) systems. While the adverse effects and mitigation strategies have been thoroughly analyzed for communication systems, the impact of low-resolution quantization on integrated sensing and communication (ISAC) systems remains insufficiently explored in the existing literature. In this paper, we propose an analysis and design framework to investigate and mitigate the effects of 1-bit digital to analog converters (DACs) for ISAC systems. Firstly, an analytical sensing signal-to-noise ratio (SNR) expression is derived by using the Bussgang decomposition. Furthermore, two different methodologies are proposed to design a transmit waveform that satisfies both communication and sensing requirements simultaneously. The first method uses a separate constant modulus (CM) sensing signal since CM signals are known to be more robust to nonlinear distortion than orthogonal frequency division multiplexing (OFDM) modulated signals. The second method employs the squared-infinity norm Douglas-Rachford splitting (SQUID) approach to construct the transmit waveform using nonlinear quantized precoding. Finally, the performance of the proposed methods are validated via numerical simulations to indicate the complexity-performance tradeoff between two different methods.
Citation - Scopus: 1
Terahertz Photoconductive Antenna Array With Beam Steering and Time-Domain Analysis for 6g and Beyond
(Ieee, 2024) Songur, Ahmet Canberk; Sakin, Ahmet Oguz; Ünlü, Mehmet
In this study, a beam-steering photoconductive antenna array operating in the terahertz band, which is an important potential candidate for 6G and beyond communication systems, was developed. The designed terahertz source incorporates a 4 x 1 spiral antenna array with broad-spectrum radiation capabilities, enabling beam steering within a range of +/- 60 degrees in the 0.8 - 2 THz band, and featuring an antenna gain of 12.7 dBi. The terahertz antenna array design and radiation were charaterized in time domain.

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