Browsing by Author "Gezici, Sinan"
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Item Open Access Accuracy limits of distance estimation in visible light systems with RGB LEDs(IEEE, 2019-09) Demirel, İlker; Gezici, SinanThe distance estimation problem is investigated for visible light positioning (VLP) systems with red-green-blue (RGB) light emitting diodes (LEDs). The accuracy limits on distance estimation are calculated in terms of the Cramér-Rao lower bounds (CRLBs) for three different scenarios. Scenario 1 and Scenario 2 correspond to synchronous and asynchronous systems, respectively, with known channel attenuation formulas at the receiver. In Scenario 3, a synchronous systems is considered but channel attenuation formulas are not known at the receiver. The derived CRLB expressions reveal the relations among the distance estimation accuracies in the considered scenarios and provide intuitive explanations for the benefits of using RGB LEDs.Item Open Access Accurate positioning in ultra-wideband systems(Institute of Electrical and Electronics Engineers, 2011) Soganci, H.; Gezici, SinanAccurate positioning systems can be realized via ultra-wideband signals due to their high time resolution. In this article, position estimation is studied for UWB systems. After a brief introduction to UWB signals and their positioning applications, two-step positioning systems are investigated from a UWB perspective. It is observed that time-based positioning is well suited for UWB systems. Then time-based UWB ranging is studied in detail, and the main challenges, theoretical limits, and range estimation algorithms are presented. Performance of some practical time-based ranging algorithms is investigated and compared against the maximum likelihood estimator and the theoretical limits. The trade-off between complexity and accuracy is observed.Item Open Access Adaptation of two types of processing gains for UWB impulse radio wireless sensor networks(The Institution of Engineering and Technology, 2007) Güvenç, I.; Arslan, H.; Gezici, Sinan; Kobayashi, H.Ultrawideband impulse radio systems offer two kinds of processing gains that can be adapted based on the interference level in the system so that quality of service requirements are fulfilled. An adaptive assignment scheme for two types of multiple-access parameters in cluster-based wireless sensor networks is investigated. A mathematical framework is developed for asynchronous communications using a Gaussian approximation method to model the multiple-access interference in two cases: one with fixed frame duration, where the goal is to increase the average throughput, and the other with fixed symbol duration, where the goal is to increase the network lifetime. Extension of the analysis to multipath channels is carried out, and the validity of the Gaussian approximation is investigated using the Kullback-Leibler distance.Item Open Access Adaptive measurement matrix design for compressed DoA estimation with sensor arrays(IEEE, 2015) Özer, Berk; Lavrenko, A.; Gezici, Sinan; Römer, F.; Galdo, G. D.; Arıkan, OrhanIn this work we consider the problem of measurement matrix design for compressed 3-D Direction of Arrival (DoA) estimation using a sensor array with analog combiner. Since generic measurement matrix designs often do not yield optimal estimation performance, we propose a novel design technique based on the minimization of the Cramér-Rao Lower Bound (CRLB). We develop specific approaches for adaptive measurement design for two applications: detection of the newly appearing targets and tracking of the previously detected targets. Numerical results suggest that the developed designs allow to provide the near optimal performance in terms of the CRLB.Item Open Access Anchor placement in TOA based wireless localization networks via convex relaxation(IEEE, 2021-09-06) Öztürk, Cuneyd; Gezici, SinanA wireless source localization network consisting of synchronized target and anchor nodes is considered. An anchor placement problem is formulated to minimize the Cramér-Rao lower bound (CRLB) on estimation of target node positions by anchor nodes. First, it is shown that the anchor placement problem can be approximated as a minimization problem of the ratio of two supermodular functions. Due to the lack of a polynomial time algorithm for such problems, an anchor selection problem is proposed to solve the anchor placement problem. Via relaxation of integer constraints, the anchor selection problem is approximated by a convex optimization problem, which is used to propose two algorithms for anchor selection. Furthermore, extensions to quasi-synchronous wireless localization networks are discussed. To examine the performance of the proposed algorithms, various simulation results are presented.Item Open Access Average capacity maximization via channel switching in the presence of additive white Gaussian noise channels and switching delays(Institute of Electrical and Electronics Engineers Inc., 2016) Sezer, A. D.; Gezici, SinanThe optimal channel switching problem is studied for average capacity maximization in the presence of additive white Gaussian noise channels and channel switching delays. First, an optimization problem is formulated for the maximization of the average channel capacity, considering channel switching delays and constraints on average and peak powers. Then, an equivalent optimization problem is obtained to facilitate theoretical investigations. The optimal strategy is derived and the corresponding average capacity is specified when channel switching is performed among a given number of channels. Based on this result, it is shown that channel switching among more than two different channels is not optimal. In addition, the maximum average capacity achieved by the optimal channel switching strategy is formulated as a function of the channel switching delay parameter and the average and peak power limits. Then, scenarios under which the optimal strategy corresponds to the exclusive use of a single channel or to channel switching between two channels are described. Furthermore, sufficient conditions are obtained to determine when the optimal single channel strategy outperforms the optimal channel switching strategy. The numerical results are presented to provide the examples of the theoretical results and to illustrate the effects of channel switching delays. © 2002-2012 IEEE.Item Open Access Average Fisher information maximisation in presence of cost-constrained measurements(The Institution of Engineering and Technology, 2011) Dulek, B.; Gezici, SinanAn optimal estimation framework is considered in the presence of cost-constrained measurements. The aim is to maximise the average Fisher information under a constraint on the total cost of measurement devices. An optimisation problem is formulated to calculate the optimal costs of measurement devices that maximise the average Fisher information for arbitrary observation and measurement statistics. In addition, a closed-form expression is obtained in the case of Gaussian observations and measurement noise. Numerical examples are presented to explain the results.Item Open Access Average fisher information optimization for quantized measurements using additive independent noise(IEEE, 2010) Balkan, Gokce Osman; Gezici, SinanAdding noise to nonlinear systems can enhance their performance. Additive noise benefits are observed also in parameter estimation problems based on quantized observations. In this study, the purpose is to find the optimal probability density function of additive noise, which is applied to observations before quantization, in those problems. First, optimal probability density function of noise is formulated in terms of an average Fisher information maximization problem. Then, it is proven that optimal additive "noise" can be represented by a constant signal level. This result, which means that randomization of additive signal levels is not needed for average Fisher information maximization, is supported with two numerical examples. ©2010 IEEE.Item Open Access A Bayesian approach to respiration rate estimation via pulse-based ultra-wideband signals(IEEE, 2009) Soǧancı, Hamza; Gezici, Sinan; Arıkan, OrhanIn this paper, theoretical limits on estimation of respiration rates via pulse-based ultra-wideband (UWB) signals are studied in the presence of prior information about respiration related signal parameters. First, a generalized Cramer-Rao lower bound (G-CRLB) expression is derived, and then simplified versions of the bound are obtained for sinusoidal displacement functions. In addition to the derivation of the theoretical limits, a two-step suboptimal estimator based on matched filter (correlation) processing and maximum a posteriori probability (MAP) estimation is proposed. It is shown that the proposed estimator performs very closely to the theoretical limits under certain conditions. Simulation results are presented to investigate the theoretical results.Item Open Access Binary signaling under subjective priors and costs as a game(Institute of Electrical and Electronics Engineers Inc., 2019) Sarıtaş, S.; Gezici, Sinan; Yüksel, S.; Teel, A. R.; Egerstedt, M.Many decentralized and networked control problems involve decision makers which have either misaligned criteria or subjective priors. In the context of such a setup, in this paper we consider binary signaling problems in which the decision makers (the transmitter and the receiver) have subjective priors and/or misaligned objective functions. Depending on the commitment nature of the transmitter to his policies, we formulate the binary signaling problem as a Bayesian game under either Nash or Stackelberg equilibrium concepts and establish equilibrium solutions and their properties. In addition, the effects of subjective priors and costs on Nash and Stackelberg equilibria are analyzed. It is shown that there can be informative or non-informative equilibria in the binary signaling game under the Stackelberg assumption, but there always exists an equilibrium. However, apart from the informative and non-informative equilibria cases, under certain conditions, there does not exist a Nash equilibrium when the receiver is restricted to use deterministic policies. For the corresponding team setup, however, an equilibrium typically always exists and is always informative. Furthermore, we investigate the effects of small perturbations in priors and costs on equilibrium values around the team setup (with identical costs and priors), and show that the Stackelberg equilibrium behavior is not robust to small perturbations whereas the Nash equilibrium is.Item Open Access Birleşik sezim ve kestirim sistemlerinin gürültü ile geliştirilmesi(IEEE, 2014-04) Akbay, Abdullah Başar; Gezici, SinanBelirli koşullar altında, optimal olmayan bazı sezici ve kestiricilerin performansını girdilerine gürültü ekleyerek geliştirmek mümkündür. Bu çalışmada, birleşik bir sezim ve kestirim sisteminin gürültü eklenerek geliştirilmesi incelenmektedir. Sistem performansının maksimizasyonu bir optimizasyon problemi olarak tanımlanmaktadır. Optimal toplanır gürültü dağılımının istatiksel özellikleri belirlenmektedir. Sistem performansının gürültü ile iyileştirilemeyeceği bir koşul elde edilmektedir.Önerilen optimizasyon probleminin, bir doğrusal programlama (DP) problemi olarak yaklaşımı sunulmaktadır. Bir sayısal örnek üzerinde, kuramsal bulguları desteklemek amacıyla, gürültü eklenmiş sistem ile orijinal sistemin performansları karşılaştırılmaktadır.Item Open Access Centralized and decentralized detection with cost-constrained measurements(Elsevier B.V., 2017) Laz, E.; Gezici, SinanOptimal detection performance of centralized and decentralized detection systems is investigated in the presence of cost constrained measurements. For the evaluation of detection performance, Bayesian, Neyman–Pearson and J-divergence criteria are considered. The main goal for the Bayesian criterion is to minimize the probability of error (more generally, the Bayes risk) under a constraint on the total cost of the measurement devices. In the Neyman–Pearson framework, the probability of detection is to be maximized under a given cost constraint. In the distance based criterion, the J-divergence between the distributions of the decision statistics under different hypotheses is maximized subject to a total cost constraint. The probability of error expressions are obtained for both centralized and decentralized detection systems, and the optimization problems are proposed for the Bayesian criterion. The probability of detection and probability of false alarm expressions are obtained for the Neyman–Pearson strategy and the optimization problems are presented. In addition, J-divergences for both centralized and decentralized detection systems are calculated and the corresponding optimization problems are formulated. The solutions of these problems indicate how to allocate the cost budget among the measurement devices in order to achieve the optimum performance. Numerical examples are presented to discuss the results.Item Open Access Clutter detection algorithms for airborne pulse-Doppler radar(IEEE, 2010) Güngör, Ahmet; Gezici, SinanClutter detection is an important stage of target detection. Clutter may not always appear around zero Doppler frequency when realistic terrain models and moving platforms are considered. Two algorithms developed for clutter detection using range-Doppler matrix elements and their performance analysis are presented in this paper. The first algorithm has higher error rates but lower computational complexity whereas the second one has lower error rates but higher computational complexity. The algorithms detect clutter position by filtering range-Doppler matrix elements via non-linear filters. ©2010 IEEE.Item Open Access Coded-reference ultra-wideband systems(2008-09) Gezici, SinanTransmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems employ pairs of reference and data signals, which are shifted in the time and frequency domains, respectively, to facilitate low-to-medium data rate communications without the need for complex channel estimation and template signal generation. On the other hand, the recently proposed coded-reference (CR) UWB systems provide orthogonalization of the reference and data signals in the code domain, which has advantages in terms of performance and/or implementation complexity. In this paper, CR UWB systems are investigated. First, it is shown that a CR UWB system can be considered as a generalized non-coherent pulse-position modulated system. Then, an optimal receiver according to the Bayes decision rule is derived for CR UWB systems. In addition, the asymptotic optimality properties of the conventional CR UWB receivers are investigated. Finally, simulation results are presented to compare the performance of the optimal and conventional CR UWB receivers. ©2008 IEEE.Item Open Access Cognitive and Cooperative Wireless Networks(Springer-Verlag Italia s.r.l., 2012) Palazzo, S.; Dardari, D.; Dohler, M.; Gezici, Sinan; Giupponi, L.; Luise, M.; Pérez Romero, J.; Shamai, S.; Noguet, D.; Moy, C.; Asheid, G.The traditional approach of dealing with spectrum management in wireless communications has been the definition of a licensed user granted with exclusive exploitation rights for a specific frequency. While it is relatively easy in this case to ensure that excessive interference does not occur, this approach is unlikely to achieve the objective to maximize the value of spectrum, and in fact recent spectrum measurements carried out worldwide have revealed a significant spectrum underutilization, in spite of the fact that spectrum scarcity is claimed when trying to find bands where new systems can be allocated. Just to mention some examples of measurements, different studies can be found in [1-6], revealing that overall occupation in some studies for frequencies up to 7GHz could be in the order of only 18%.Item Open Access Cognitive-radio systems for spectrum, location, and environmental awareness(IEEE, 2010) Celebi, H.; Güvenç, I.; Gezici, Sinan; Arslan, H.In order to perform reliable communications, a system needs to have sufficient information about its operational environment, such as spectral resources and propagation characteristics. Cognitive-radio technology has capabilities for acquiring accurate spectrum, location, and environmental information, due to its unique features such as spectrum, location, and environmental awareness. The goal of this paper is to give a comprehensive review of the implementation of these concepts. In addition, the dynamic nature of cognitive-radio systems - including dynamic spectrum utilization, transmission, the propagation channel, and reception - is discussed, along with performance limits, challenges, mitigation techniques, and open issues. The capabilities of cognitive-radio systems for accurate characterization of operational environments are emphasized. These are crucial for efficient communications, localization, and radar systems.Item Open Access Comparative theoretical analysis of distance estimation in visible light positioning systems(Institute of Electrical and Electronics Engineers Inc., 2016) Keskin, M. F.; Gezici, SinanIn this paper, theoretical limits and estimators are studied for synchronous and asynchronous visible light positioning (VLP) systems. Specifically, the Cramér-Rao lower bounds (CRLBs) and maximum likelihood estimators are investigated for distance estimation based on time-of-arrival (TOA) and/or received signal strength (RSS) parameters. Hybrid TOA/RSS-based distance estimation is proposed for VLP systems, and its CRLB is compared analytically against the CRLBs of TOA-based and RSS-based distance estimation. In addition, to investigate the effects of sampling, asymptotic performance results are obtained under sampling rate limitations as the noise variance converges to zero. A modified hybrid TOA/RSS-based distance estimator is proposed to provide performance improvements in the presence of sampling rate limitations. Numerical examples are presented to illustrate the theoretical results. © 2015 IEEE.Item Open Access Comparison of low complexity UWB range estimators based on experimental data(IEEE, 2012) Soğancı, Hamza; Gezici, Sinan; Tan, A.S.In this paper, performances of low complexity time based range estimators that are employed for ultra wide-band (UWB) systems are compared using experimental data. These estimators are widely used in practical applications due to their low complexity. However, performances of these estimators vary depending on the choice of certain parameters such as the threshold value and window size. The optimal values for these parameters are investigated for several situations using the data acquired in the experiments. © 2012 IEEE.Item Open Access A concave-convex procedure for TDOA based positioning(IEEE, 2013) Gholami, M. R.; Gezici, Sinan; Strom, E. G.This letter investigates the time-difference-of-arrival based positioning problem in wireless sensor networks. We consider the least-mean absolute, i.e., the ℓ1 norm, minimization of the residual errors and formulate the positioning problem as a difference of convex functions (DC) programming. We then employ a concave-convex procedure to solve the corresponding DC programming. Simulation results illustrate the improved performance of the proposed approach compared to existing methods. © 1997-2012 IEEE.Item Open Access A confidence ellipsoid approach for measurement cost minimization under Gaussian noise(IEEE, 2012-06) Dülek, Berkan; Gezici, SinanThe well-known problem of estimating an unknown deterministic parameter vector over a linear system subject to additive Gaussian noise is studied from the perspective of minimizing total sensor measurement cost under a constraint on the log volume of the estimation error confidence ellipsoid. A convex optimization problem is formulated for the general case, and a closed form solution is provided when the system matrix is invertible. Furthermore, effects of system matrix uncertainty are discussed by employing a specific but nevertheless practical uncertainty model. Numerical examples are presented to discuss the theoretical results in detail.