Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12469/47

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Citation - WoS: 2
Citation - Scopus: 3
Reliable Two-Path Successive Relaying
(2013) Basar, Ertugrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
Emerging two-path successive relaying protocols generally rely on error-free source-relay channels and/or interference-free inter-relay channels to achieve high-rate and full-diversity. In this paper by removing these optimistic assumptions a novel two-path successive relaying scheme that benefits from relay selection and distributed space-time block coding (STBC) and transfers the data from the source to the destination via relays in a reliable fashion is proposed. The proposed scheme can achieve full diversity without the requirement of perfect decoding at relays since not only the destination but also the relays benefit from distributed STBC and relay selection. As the target STBC coordinate interleaved orthogonal design (CIOD) for two transmit antennas is considered. The average symbol error probability of the proposed scheme is derived and its error performance is compared with reference systems. © 2013 IEEE.
Citation - WoS: 5
Citation - Scopus: 7
Power and Rate Adaptation Based on Csi and Velocity Variation for Ofdm Systems Under Doubly Selective Fading Channels
(IEEE-INST Electrical Electronics Engineers Inc, 2016) Dong, Zhicheng; Fan, Pingzhi; Lei, Xianfu; Panayırcı, Erdal
In this paper a novel joint continuous power and rate adaptation scheme is proposed fordoubly selective fading channels in orthogonal frequency division multiplexing (OFDM) systems based on terminal velocity and perfect or imperfect channel state information (CSI). The analysis and simulation results show that the continuous power and rate adaptation scheme is very effective and improve the performance of OFDM systems substantially under time-varying fading channels as compared with the traditional adaptation schemes operating without a priori knowledge of velocity and mobility adaptation without CSI.
Citation - WoS: 28
Citation - Scopus: 35
Design of Practical Matching Networks With Lumped Elements Via Modeling
(IEEE, 2007) Yarman, Sıddık Binboğa; Şengül, Metin Y.; Kılınç, Ali
It is a common practice to utilize commercially available software tools to design matching networks for wireless communication systems. Most of these tools require a properly selected matching network topology with good initial element values. Therefore in this paper a practical method is presented to generate matching networks with initial element values. In the implementation process of the proposed method first the driving point immitance data for the matching network is obtained in a straight forward manner without optimization. Then it is modeled as a realizable bounded-real input reflection coefficient which in turn yields the desired matching network with reasonable element values. Eventually the initial design is improved by optimizing the performance of the matched system employing the commercially available computer-aided design (CAD) packages. An example is given to illustrate the utilization of the proposed method. It is shown that new method provides excellent results as a front-end when utilized together with CAD tools.
Citation - WoS: 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 - WoS: 4
Citation - Scopus: 6
Channel Estimation for Realistic Indoor Optical Wireless Communication in Aco-Ofdm Systems
(Springer, 2018) Özmen, Atilla; Şenol, Habib
In this paper channel estimation problem in a visible light communication system is considered. The information data is transmitted using asymmetrical clipped optical orthogonal frequency division multiplexing. Channel estimation and symbol detection are performed by the Maximum Likelihood and the Linear Minimum Mean Square Error detection techniques respectively. The system performance is investigated in realistic environment that is simulated using an indoor channel model. Two different channels are produced using the indoor channel model. Symbol error rate (SER) performance of the system with estimated channels is presented for QPSK and 16-QAM digital modulation types and compared with the perfect channel state information. As a mean square error (MSE) performance benchmark for the channel estimator Cramer-Rao lower bound is also derived. MSE and SER performances of the simulation results are presented.
Citation - WoS: 7
Citation - Scopus: 9
Detection of Interdependent Primary Systems Using Wideband Cognitive Radios
(Elsevier GMBH Urban & Fischer Verlag, 2013) Yılmaz, Burak; Erküçük, Serhat
Cognitive radios (CRs) may be sharing multiple frequency bands with primary systems if the CR is a wideband or an ultra wideband (UWB) system. In that case the CR should ensure all the coexisting primary systems in these bands are detected before it can start data transmission. In this work we study the primary system detection performance of a wideband CR assuming that there are multiple coexisting primary systems and that these primary systems may be jointly active. Accordingly we consider the implementation of energy detection scheme in multiple bands followed by two detection methods: (i) a maximum-a-posteriori (MAP) based detection (i.e. joint detection) that takes into account the statistics of simultaneously operating systems in independent bands and (ii) a Neyman-Pearson (NP) test based detection that optimizes the threshold values independently in each band (i.e. independent detection). For a simpler implementation of the independent detection we show that the threshold values obtained from joint detection can be used in order to achieve the optimum NP test based independent detection results. In addition to quantifying the gain of joint detection over independent detection in terms of probabilities of false alarm and detection for practical scenarios we also present the operation capability of CRs in terms of the fractions of time the CR can access the channel without interfering with the primary systems. The results are important for the practical implementation of multiband detection when the primary systems are known to be interdependent. (C) 2013 Elsevier GmbH. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 6
Code Shift Keying Impulse Modulation for Uwb Communications
(IEEE-INST Electrical Electronics Engineers Inc, 2008) Erküçük, Serhat; Kim, Dong In; Kwak, Kyung Sup
In this paper the system performance of M-ary code shift keying (MCSK) impulse modulation is studied in detail and compared to M-ary pulse position modulation (MPPM) under single- and multi-user scenarios. For that bounds on the semi-analytic symbol-error rate (SER) expressions are derived and simulation studies are conducted. When practical implementations of MCSK and MPPM are considered it is shown that MCSK can provide about 2 dB performance gain over MPPM as it reduces the effects of multipath delays on the decision variables by randomizing locations of the transmit pulse.
Citation - WoS: 1
Citation - Scopus: 1
Bayesian Estimation of Discrete-Time Cellular Neural Network Coefficients
(TUBITAK Scientific & Technical Research Council Turkey, 2017) Özer, Hakan Metin; Özmen, Atilla; Şenol, Habib
A new method for finding the network coefficients of a discrete-time cellular neural network (DTCNN) is proposed. This new method uses a probabilistic approach that itself uses Bayesian learning to estimate the network coefficients. A posterior probability density function (PDF) is composed using the likelihood and prior PDFs derived from the system model and prior information respectively. This posterior PDF is used to draw samples with the help of the Metropolis algorithm a special case of the Metropolis--Hastings algorithm where the proposal distribution function is symmetric and resulting samples are then averaged to find the minimum mean square error (MMSE) estimate of the network coefficients. A couple of image processing applications are performed using these estimated parameters and the results are compared with those of some well-known methods.
Citation - WoS: 40
Citation - Scopus: 49
Sparse Channel Estimation and Equalization for Ofdm-Based Underwater Cooperative Systemsw With Amplify-And Relaying
(IEEE-INST Electrical Electronics Engineers Inc, 2016) Panayırcı, Erdal; Şenol, Habib; Uysal, Murat; Poor, H. Vincent
This paper is concerned with a challenging problem of channel estimation and equalization for amplify-and-forward cooperative relay based orthogonal frequency division multi-plexing (OFDM) systems in sparse underwater acoustic (UWA) channels. The sparseness of the channel impulse response and prior information for the non-Gaussian channel gains modeled by an exact continuous Gaussian mixture (CGM) are exploited to improve the performance of the channel estimation algorithm. The resulting novel algorithm initially estimates the overall sparse complex-valued channel taps from the source to the destination as well as their locations using the matching pursuit (MP) approach. The effective time-domain non-Gaussian noise is approximated well as a Gaussian noise in the frequency-domain where the estimation takes place. An efficient and low complexity algorithm is developed based on a combination of the MP and the maximum a posteriori probability (MAP) based space-alternating generalized expectation-maximization technique to improve the estimates of the channel taps and their locations in an iterative manner. Computer simulations show that the UWA channel is estimated very effectively and the proposed algorithm exhibits excellent symbol error rate and channel estimation performance.
Citation - Scopus: 4
Pilot-Aided Bayesian Mmse Channel Estimation for Ofdm Systems: Algorithm and Performance Analysis
(2004) Şenol, Habib; Cirpan, Hakan Ali; Panayırcı, Erdal
This paper proposes a computationally efficient pilot-aided minimum mean square error (MMSE) channel estimation algorithm for OFDM systems. The proposed approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and estimates uncorrelated series expansion coefficients. Moreover optimal rank reduction is achieved in the proposed approach by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the estimation algorithm. The performance of the proposed approach is studied through analytical and experimental results. We first consider the stochastic Cramer-Rao bound and derive the closed-form expression for the random KL coefficients. We then exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. © 2004 IEEE.
Citation - WoS: 4
Citation - Scopus: 4
Reflectance-Based Foster Impedance Data Modeling
(Fachverlag Schiele Schon, 2007) Şengül, Metin Y.
A reflectance-based method is presented to model a set of given Foster impedance data as a lossless singly terminated two-port consisting of lumped-elements in short or open termination. The basis of the new method rests on the interpolation of the given data as a realizable bounded-real (BR) reflection function. The desired circuit model is obtained by synthesizing this function. An algorithm to generate the circuit model is presented and an example is included which illustrates the utilization of the proposed modeling method.
Citation - Scopus: 43
Orthogonal Frequency Division Multiplexing With Index Modulation in the Presence of High Mobility
(2013) Basar, Ertugrul; Aygölü, Ümit; Panayırcı, Erdal
In this paper a novel orthogonal frequency division multiplexing (OFDM) scheme which is called OFDM with index modulation (OFDM-IM) is proposed for frequency-selective fading channels in the presence of high mobility. In this scheme inspiring from the recently introduced spatial modulation concept for multiple-input multiple-output (MIMO) channels the information is conveyed not only by M-ary signal constellations as in classical OFDM but also by the indices of the subcarriers which are activated according to the incoming bit stream. Different low complexity transceiver structures based on maximum likelihood (ML) detection or log-likelihood ratio (LLR) calculation are proposed. It is shown via computer simulations that the proposed scheme achieves significantly better error performance than classical OFDM. © 2013 IEEE.
Citation - Scopus: 5
A Broadband Microwave Amplifier Design by Means of Immittance Based Data Modelling Tool
(IEEE, 2002) Kilinç, Ali; Pinarbaşi, Haci; Şengül, Metin Y.; Yarman, Sıddık Binboğa
In this paper a practical broadband microwave amplifier design algorithm is introduced utilizing the immittance data-modelling tool. In the course of design first the optimum input and output terminations for the active device are produced employing the real frequency technique. Then these terminations are modelled utilizing the new immittance-modelling tool to synthesize the front-end and back-end matching networks. An example is included to exhibit the implementation of the proposed design algorithm to construct a single stage BJT amplifier over a wide frequency band. It is expected that the proposed design algorithm will find applications to realize wideband microwave amplifiers put on MMIC for mobile communication.
Citation - WoS: 16
Citation - Scopus: 24
Qos-Constrained Semi-Persistent Scheduling of Machine-Type Communications in Cellular Networks
(IEEE, 2019) Karadağ, Göksu; Gül, Recep; Sadi, Yalçın; Ergen, Sinem Coleri
The dramatic growth of machine-to-machine (M2M) communication in cellular networks brings the challenge of satisfying the quality of service (QoS) requirements of a large number of M2M devices with limited radio resources. In this paper we propose an optimization framework for the semi-persistent scheduling of M2M transmissions based on the exploitation of their periodicity with the goal of reducing the overhead of the signaling required for connection initiation and scheduling. The goal of the optimization problem is to minimize the number of frequency bands used by the M2M devices to allow fair resource allocation of newly joining M2M and human-to-human communications. The constraints of the problem are delay and periodicity requirements of the M2M devices. We first prove that the optimization problem is NP-hard and then propose a polynomial-time heuristic algorithm employing a fixed priority assignment according to the QoS characteristics of the devices. We show that this heuristic algorithm provides an asymptotic approximation ratio of 2.33 to the optimal solution for the case where the delay tolerances of the devices are equal to their periods. Through extensive simulations we demonstrate that the proposed algorithm performs better than the existing algorithms in terms of frequency band usage and schedulability.
Design of Mixed-Element Networks Via Modeling
(IEEE, 2008) Şengül, Metin Y.; Yarman, Sıddık Binboğa
A new method is introduced to design mixed lumped and distributed element network
Citation - WoS: 6
Citation - Scopus: 8
Design of Broadband Single Matching Networks
(Elsevier GMBH Urban & Fischer Verlag, 2009) Şengül, Metin Y.
In general commercially available software tools are preferred to design broadband matching networks for wireless communication systems. But they need a properly selected matching network topology with good initial element values. Therefore in this paper a new real frequency technique is presented to generate broadband single matching networks with suitable initial element values. In the proposed method load impedance is written in terms of ABCD-parameters of the desired matching network and the source resistor. Then free parameters are optimized which in turn yields the desired matching network with initial element values. It is not needed to select a circuit topology for the matching network which is the natural consequence of the matching processes. Also there is no need to select the desired transducer power gain level , the proposed technique naturally provides a gain curve fluctuating around the final available level. Eventually the initial design is improved by optimizing the performance of the matched system employing the commercially available computer-aided design (CAD) packages. An algorithm and two examples are given to illustrate the utilization of the proposed technique. (C) 2007 Elsevier GmbH. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 2
Performance of Mimo Enhanced Unipolar Ofdm With Realistic Indoor Visible Light Channel Models
(Institute of Electrical and Electronics Engineers Inc., 2016) Yeşilkaya, Anıl; Miramirkhani, Farshad; Basar, Ertugrul; Panayırcı, Erdal; Uysal, Murat
Visible light communication (VLC) involves the dual use of illumination infrastructure for high speed wireless access. Designing such optical based communication systems realistic indoor optical channel modeling becomes an important issue to be handled. In this paper first we obtain new realistic indoor VL channel characterizations and models in a multiple-input multiple-output (MIMO) transmission scenario using non-sequential ray tracing approach for the channel impulse responses (CIRs). Practical issues such as number of light emitting diode (LED) chips per luminary spacing between LED chips objects inside the room and cabling topology are also investigated. On the other hand since indoor optical channels exhibit frequency selectivity multi-carrier communication systems particularly orthogonal frequency division multiplexing (OFDM) is used to handle the resulting inter-symbol interference in VLC systems. Hence we propose a new MIMO-OFDM based VLC system called MIMO enhanced unipolar OFDM (MIMO-eU-OFDM) by combining MIMO transmission techniques with the recently proposed eU-OFDM scheme. The bit error rate (BER) performance of the proposed system is investigated in the presence of the 2×2 and 4×4 realistic MIMO VLC channels and its BER performance is compared with the reference optical MIMO-OFDM systems. © 2016 IEEE.
Partial Power and Rate Adaptation for Mqam/Ofdm Systems Under Cfo
(IEEE, 2014) Dong, Zhicheng; Fan, Pingzhi; Panayırcı, Erdal; Lei, Xianfu
In this paper a new partial power and rate adaptation scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed in the presence of carrier frequency offset (CFO). The conventional adaptive scheme is shown to be a special case of the partially adaptive scheme technique which enables the resulting non-convex optimization problem solved in a feasible way. It leads to a solution for optimal power adaptation that maximizes the spectral efficiency of an OFDM system using M-ary quadrature amplitude modulation (MQAM) under average power and instantaneous BER constraints. Closed-form expressions for the average spectral efficiency (ASE) of adaptive OFDM systems are derived. The theoretical results and computer simulations show that the range of the partial adaptation becomes narrow and the performance of constant power and continuous rate is very close to that of the partially adaptive power and continuous rate for higher CFO or high signal noise ratio (SNR) values.
Citation - WoS: 3
Citation - Scopus: 3
Explicit Synthesis Formulae for Cascaded Lossless Commensurate Lines
(Fachverlag Schiele Schon, 2008) Şengül, Metin Y.
In literature synthesis of cascaded lossless commensurate lines have been realized via some iterative methods. So to be able to obtain the value of an element which is not the first one the designer has to obtain all the values of the elements connected before the desired one. But in this paper explicit synthesis formulae of the networks containing cascaded lossless commensurate lines up to three have been derived analytically and all the element values can be calculated independently.
Citation - WoS: 3
Citation - Scopus: 3
Bayesian Compressive Sensing for Ultra-Wideband Channel Estimation: Algorithm and Performance Analysis
(Springer, 2015) Özgör, Mehmet; Erküçük, Serhat; Çırpan, Hakan Ali
Due to the sparse structure of ultra-wideband (UWB) channels compressive sensing (CS) is suitable for UWB channel estimation. Among various implementations of CS the inclusion of Bayesian framework has shown potential to improve signal recovery as statistical information related to signal parameters is considered. In this paper we study the channel estimation performance of Bayesian CS (BCS) for various UWB channel models and noise conditions. Specifically we investigate the effects of (i) sparse structure of standardized IEEE 802.15.4a channel models (ii) signal-to-noise ratio (SNR) regions and (iii) number of measurements on the BCS channel estimation performance and compare them to the results of -norm minimization based estimation which is widely used for sparse channel estimation. We also provide a lower bound on mean-square error (MSE) for the biased BCS estimator and compare it with the MSE performance of implemented BCS estimator. Moreover we study the computation efficiencies of BCS and -norm minimization in terms of computation time by making use of the big- notation. The study shows that BCS exhibits superior performance at higher SNR regions for adequate number of measurements and sparser channel models (e.g. CM-1 and CM-2). Based on the results of this study the BCS method or the -norm minimization method can be preferred over the other one for different system implementation conditions.

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