Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://gcris.khas.edu.tr/handle/20.500.12469/47

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Now showing 1 - 20 of 279

Citation Count: 1
Power transfer networks at RF frequencies "New design procedures with implementation roadmap"
(IEEE, 2006) Şengül, Metin Y.; Trabert, Johannes; Blau, Kurt; Yarman, B. Sıddık; Hein, Matthias
The purpose of this work is to provide the necessary background to design wide-band power transfer two-ports, or so-called broadband matching networks, at radio frequencies for wireless communication systems. The importance of the topic stems from the recent advances in the conceptual design and manufacturing technologies of the next-generation wireless and mobile communication systems, which will operate over ultra-wide frequency bands. In fact, for all communication systems, construction of wide-band power transfer networks is essential. Therefore, in this manuscript, new procedures to design broadband matching network are covered, and a design roadmap is given with relevant recommendations. As an example, the design of a compensation network for a RF switch matrix covering the band 17...23 GHz is presented, which employs the roadmap described in this work.
Citation Count: 0
Analysis and Optimization of Matching Networks-II Getting Started with Microwave Office
(Springer-Verlag Berlin, 2008) Şengül, Metin Y.
[Abstract Not Available]
Citation Count: 0
Analysis and Optimization of Matching Networks-I Getting Started with ADS
(Springer-Verlag Berlin, 2008) Şengül, Metin Y.
[Abstract Not Available]
Citation Count: 1
Design and Implementation of a Cellular Neural Network Based Oscillator Circuit
(World Scientific and Engineering Acad and Soc, 2009) Tander, Baran; Özmen, Atilla; Özçelep, Yasin
In this paper, a novel inductorless oscillator circuit with negative feedbacks, based on a simple version of a "Cellular Neural Network" (CNN) called "CNN with an Opposite Sign Template" (CNN-OST) is designed and implemented. The system is capable of generating quasi-sine oscillations with tuneable amplitude and frequency which can't be provided at the same time in the conventional oscillator circuits.
Citation Count: 0
Optimal On-Off Transmission Schemes for Full Duplex Wireless Powered Communication Networks
(IEEE, 2020) Şadi, Yalçın; Şadi, Yalçın; Coleri, Sinem
In this paper, we consider a full duplex wireless powered communication network where multiple users with radio frequency energy harvesting capability communicate to an energy broadcasting hybrid access point. We investigate the minimum length scheduling and sum throughput maximization problems considering on-off transmission scheme in which users either transmit at a constant power or remain silent. For minimum length scheduling problem, we propose a polynomial-time optimal scheduling algorithm. For sum throughput maximization, we first derive the characteristics of an optimal schedule and then to avoid intractable complexity. We propose a polynomial-time heuristic algorithm which is illustrated to perform nearly optimal through numerical analysis.
Citation Count: 4
Sparse Channel Estimation with Clipping Noise in DCO-OFDM Based VLC Systems
(IEEE, 2020) Bektaş, Ekin Başak; Panayırcı, Erdal
In this paper a new computationally efficient and high performance channel estimation algorithm is proposed for DC-biased optical OFDM (DCO-OFDM) systems in indoor visible light communications (VLC) in the presence of a clipping noise. The sparse structure of the channel is taken into consideration in the channel estimation algorithm. The algorithm has an iterative structure and aims at reducing the effect of the clipping noise, inevitably generated by the DCO-OFDM systems. In te algorithm, the clipping noise is estimated in the time-domain and compensated for its effect in the frequency-domain. The initial values of the channel, including sparse channel path gains and the path delays, are determined by the least-squares (LS) and the ESPRIT algorithms, respectively, by making use of the pilots. Computer simulations indicate that the proposed algorithm converge in 3 iterations at most and yields excellent bit error rate (BER) and mean-square error (MSE) performances for DC-biased optical OFDM (DCO-OFDM) based systems.
Citation Count: 0
Smart Stethoscope
(IEEE, 2020) Çevik, Mesut; Özmen, Atilla; Tander, Baran; Demirel, Mücahit; Özmen, Atilla; Tander, Baran; Çevik, Mesut
In this study, a device named smart stethoscope that uses digital sensor technology for sound capture, active acoustics for noise cancellation and artificial intelligence (AI) for diagnosis of heart and lung diseases is developed to help the health workers to make accurate diagnoses. Furthermore, the respiratory diseases are classified by using Deep Learning and Long Short-Term Memory (LSTM) techniques whereas the probability of these diseases are obtained.
Citation Count: 9
Complete density calculations of q-state Potts and clock models: Reentrance of interface densities under symmetry breaking
(Amer Physical Soc, 2020) Artun, E. Can; Berker, A. Nihat
All local bond-state densities are calculated for q-state Potts and clock models in three spatial dimensions, d = 3. The calculations are done by an exact renormalization group on a hierarchical lattice, including the density recursion relations, and simultaneously are the Migdal-Kadanoff approximation for the cubic lattice. Reentrant behavior is found in the interface densities under symmetry breaking, in the sense that upon lowering the temperature, the value of the density first increases and then decreases to its zero value at zero temperature. For this behavior, a physical mechanism is proposed. A contrast between the phase transition of the two models is found and explained by alignment and entropy, as the number of states q goes to infinity. For the clock models, the renormalization-group flows of up to 20 energies are used.
Citation Count: 0
Hybrid MEMS-Based molecular communication system
(Institute of Electrical and Electronics Engineers Inc., 2019) Baykaş, Tunçer; Erküçük, Serhat; Zeshan, Arooba; Pusane, Ali Emre
In this paper, we consider a molecular communication link integrated in a micro-electro mechanical system (MEMS) based environment. We apply acoustic tweezing techniques to the molecular communication system to increase communication reliability. We use finite element methods to simulate this hybrid system. By deriving the symbol error rate as the performance metric, we show that the proposed system facilitates reliable communication in the presence of fluid flow and its performance is robust against external factors, such as temperature.
Citation Count: 7
Channel Modeling for Visible Light Communications
(Springer-Verlag Berlin, 2016) Miramirkhani, Farshad; Uysal, Murat; Panayırcı, Erdal
In this chapter, we present a novel and realistic channel modeling approach for visible light communications that overcomes the limitations of previous works. In our work, we consider wavelength dependency, effect of realistic light sources as well as different types of reflections such as specular and mixed cases of diffuse and specular. We use nonsequential ray tracing algorithms to calculate the detected power and path lengths from source to detector for each ray. These are then processed to yield the channel impulse responses for various indoor environments. We further present a channel characterization study where channel parameters such as channel DC gain, root mean square delay spread, coherence bandwidth, mean excess delay are calculated for different environments.
Citation Count: 112
IEEE 802.15.7r1 Reference Channel Models for Visible Light Communications
(IEEE-Inst Electrical Electronics Engineers Inc, 2017) Baykaş, Tunçer; Narmanlıoğlu, Ömer; Baykas, Tuncer; Uysal, Murat; Panayırcı, Erdal
The IEEE has established the standardization group 802.15.7r1 "Short Range Optical Wireless Communications", which is currently in the process of developing a standard for visible light communication (VLC). As with any other communication system, realistic channel models are of critical importance for VLC system design, performance evaluation, and testing. This article presents the reference channel models that were endorsed by the IEEE 802.15.7r1 Task Group for evaluation of VLC system proposals. These were developed for typical indoor environments, including home, office, and manufacturing cells. While highlighting the channel models, we further discuss physical layer techniques potentially considered for IEEE 802.15.7r1.
Citation Count: 1
Busy Tone Based Power Control for Coordination of IFFY 802.11af and 802.22 System
(IEEE, 2017) Baykaş, Tunçer; Erküçük, Serhat; Karatalay, Onur; Baykas, Tuncer
In this paper, a new power control algorithm based on busy tone approach has been proposed for the coordination of IEEE 802.22 and IEEE 802.11af systems in TV white space. Different from the earlier studies, in addition to both 802.11af access point and clients listening to the busy tone, they also adjust their communication power according to the location information and use hopping for communication, if needed Acccordingly, interference caused to 802.22 systems has been reduced while the 802.11af systems are still able to communicate. This study quantifies the 802.11af and 802.22 system performances in terms of interfering packet rate and succesful packet transmission rate for different scenarios considering the communication parameters and channel models adapted for the standards.
Citation Count: 0
Design of Phase Shifters with Ladder Stubs Via Real Frequency Technique
(World Scientific, 2020) Şengül, Metin Y.
Generally at high frequencies, lumped-elements are not preferred because of their limited range of values. Therefore, in this work, a kind of phase shifter formed with ladder stubs is studied and a new approach to design phase shifter's low pass and high pass sections which are composed of series or shunt connected open-ended or short-ended stubs is proposed. In the approach, since the main focus is to form low pass and high pass two-port sections, switching process is not considered. First, the designer selects the section type and the total number of stubs in the sections; it is not necessary to fix the two-port section topologies and not necessary to derive the characteristic impedance and delay expressions for the stubs. In the example, 5-stub two-port sections of a 180∘ phase shifter are designed by means of the proposed approach.
Citation Count: 0
Mixed Element Networks With Series Capacitors Separated By Unit Elements
(World Scientific, 2020) Şengül, Metin Y.; Çakmak, Gökhan
In this work, high-pass mixed-element networks with series capacitors separated by unit elements are analyzed. First, the description of the networks via two frequency variables is given. Then, explicit coefficient relations for the descriptive polynomials are derived in terms of the single-variable boundary polynomial coefficients. Finally, the derived relations are used to design a high-pass mixed-element matching network. The series capacitors can be converted to short-ended stubs by means of Richard's transformation. Thus, the obtained network is suitable for microstrip production.
Citation Count: 18
Physical-layer security in visible light communications
(Institute of Electrical and Electronics Engineers Inc., 2020) Şadi, Yalçın; Erküçük, Serhat; Erküçük, Serhat; Şadi, Yalçın; Panayırcı, Erdal; Haas, Harald; Poor, Harold Vincent
Optical wireless communications (OWC) and its potential to solve physical layer security (PLS) issues are becoming important research areas in 6G communications systems. In this paper, an overview of PLS in visible light communications (VLC), is presented. Then, two new PLS techniques based on generalized space shift keying (GSSK) modulation with spatial constellation design (SCD) and non-orthogonal multiple access (NOMA) cooperative relaying are introduced. In the first technique, the PLS of the system is enhanced by the appropriate selection of a precoding matrix for randomly activated light emitting diodes (LEDs). With the aid of a legitimate user's (Bob's) channel state information (CSI) at the transmitter (CSIT), the bit error ratio (BER) of Bob is minimized while the BER performance of the potential eavesdroppers (Eves) is significantly degraded. In the second technique, superposition coding with uniform signaling is used at the transmitter and relays. The design of secure beamforming vectors at the relay nodes along with NOMA techniques is used to enhance PLS in a VLC system. Insights gained from the improved security levels of the proposed techniques are used to discuss how PLS can be further improved in future generation communication systems by using VLC.
Citation Count: 10
Flexible physical layer based resource allocation for machine type communications towards 6G
(Institute of Electrical and Electronics Engineers Inc., 2020) Şadi, Yalçın; Erküçük, Serhat; Panayırcı, Erdal
The exponential growth of Internet of Things applications necessitates the design of next generation cellular systems to provide native support for machine type communications (MTC). While 5G aims at providing this native support under domain of massive MTC (mMTC) as one of the three major domains it focuses; i.e., enhanced mobile broadband, ultra reliable low latency communication, and mMTC, the enabling technologies and communication architectures are still limited and incomplete considering the nearly standardized efforts under 3GPP Releases 15 and 16. Studies towards 6G should elaborate on enabling truly massive MTC flexibly to support fast growing machine-to-machine (M2M) services with massive number of devices and very diverse quality of service (QoS) requirements. In this paper, we study radio resource allocation for mMTC based on the envisioned flexible physical layer architecture for 5G and beyond, possibly including 6G. We first present an overview of the 5G New Radio physical layer aspects particularly focusing on multiple numerologies and discuss the 3GPP features in Releases 15-17 as possible enablers of a flexible radio resource allocation scheme. Then, we propose a polynomial-time persistent resource allocation scheme for M2M communications aiming at meeting diverse QoS requirements of the M2M applications while achieving spectral efficiency. Finally, we present some numerical results and discuss future research directions for access schemes to enable truly massive MTC.
Citation Count: 1
Anomaly Detection in Walking Trajectory
(IEEE, 2018) Öğrenci, Arif Selçuk
Analysis of the walking trajectory and the detection of anomalies in this trajectory, provide important benefits in the fields of health and security. In this work, two methods to detect anomalies in trajectories, are compared. Firstly, an unsupervised method is used where the conformance among trajectories are taken into consideration. Trajectories that deviate from others are qualified as anomalies. Secondly, the points in the trajectories are considered as a time series. Artifical neural networks performing supervised learning based on the backpropagation algorithm are used. The results are compared, and the points to be enhanced are highlighted.
Citation Count: 0
RGB Color Based Occupancy Rate Detection of Indoor Spaces
(IEEE, 2018) Özmen, Atilla; Demir, Kubilay; Özmen, Atilla
In this study, a system has been developed to detect the human density of indoor spaces such as libraries, banks, shopping malls. The RGB images used in this work was obtained from the real-life space. First and second order color moments were used as feature extractor.
Citation Count: 0
The Effect of Data Augmentation on ADHD Diagnostic Model using Deep Learning
(IEEE, 2019) Özmen, Atilla; Özmen, Atilla; Akan, Aydin
Attention Deficit Hyperactivity Disorder (ADHD) is a neuro-behavioral hyperactivity disorder. It is frequently seen in childhood and youth, and lasts a lifetime unless treated.The ADHD classification model should be objective and robust. Correct diagnosis usually depends on the knowledge and experience of health professionals. In this respect, an automated method to be developed for the ADHD classification model is of great importance for clinicians. In this study, the effect of data augmentation on ADHD classification model with deep learning was investigated. For this purpose, magnetic resonance images were taken from NPIstanbul NeuroPsychiatry Hospital and ADHD-200 database. Since the images were not sufficient in terms of training, data augmentation methods were applied and by convolutional neural network (CNN) architecture, these data were classified and tried to reveal the diagnosis of the disease independently from the non-objective experiences of the health professionals.
Citation Count: 0
A Novel Transmit Array Structure for Optical Spatial Modulation
(IEEE, 2019) Çoğalan, Tezcan; Haas, Harald; Panayırcı, Erdal
The performance of multiple input single output (MISO) and multiple input multiple output (MIMO) systems is limited by spatial channel correlation. This limitation becomes particularly severe in light lidelity (LiFi) systems, which use intensity modulation/direct detection (IM/DD) for data transmission, because light emitting diodes (LEDs) can only emit incoherent light. This paper proposes a novel transmitter structure that provides spatially separated channels and enables optical MISO/MIMO spatial modulation (SM) transmission without the need for a power allocation algorithm or a transmit precoding technique. A single LED array, which consists of multiple LEDs with different characteristics, is considered in an indoor environment. Different numbers of transmit LEDs are chosen for SM transmission based on the relation between channel correlation and bit error probability. It is shown that the proposed structure provides reliable SM transmission when the modulation order for M-ary pulse amplitude modulation (PAM) is considered as 2 and 4. Computer simulations also show that higher modulation order, e.g., 8-PAM, can be supported but at a slightly degraded bit error ratio (BER) performance.

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