Browsing by Author "Erdem, Osman"
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Item Open Access Cooperative localization in hybrid infrared/visible light networks: Theoretical limits and distributed algorithms(Institute of Electrical and Electronics Engineers, 2019) Keskin, M. Furkan; Erdem, Osman; Gezici, SinanLight emitting diode (LED) based visible light positioning (VLP) networks can provide accurate location information in environments where the global positioning system (GPS) suffers from severe signal degradation and/or cannot achieve high precision, such as indoor scenarios. In this manuscript, we propose to employ cooperative localization for hybrid infrared/visible light networks that involve multiple LED transmitters having known locations (e.g., on the ceiling) and visible light communication (VLC) units equipped with both LEDs and photodetectors (PDs) for the purpose of cooperation. In the considered scenario, downlink transmissions from LEDs on the ceiling to VLC units occur via visible light signals, while the infrared spectrum is utilized for device-to-device communications among VLC units. First, we derive the Cramer-Rao lower bound (CRLB) and the maximum likelihood estimator (MLE) for the localization of VLC units in the proposed cooperative scenario. To tackle the nonconvex structure of the MLE, we adopt a set-theoretic approach by formulating the problem of cooperative localization as a quasiconvex feasibility problem, where the aim is to find a point inside the intersection of convex constraint sets constructed as the sublevel sets of quasiconvex functions resulting from the Lambertian formula. Next, we devise two feasibility-seeking algorithms based on iterative gradient projections to solve the feasibility problem. Both algorithms are amenable to distributed implementation, thereby avoiding high-complexity centralized approaches. Capitalizing on the concept of quasi-Fej\'er convergent sequences, we carry out a formal convergence analysis to prove that the proposed algorithms converge to a solution of the feasibility problem in the consistent case. Numerical examples illustrate the improvements in localization performance achieved via cooperation among VLC units and evidence the convergence of the proposed algorithms to true VLC unit locations in both the consistent and inconsistent cases. IEEEItem Open Access Cooperative visible light positioning systems(Bilkent University, 2017-12) Erdem, OsmanLight emitting diode (LED) based visible light positioning (VLP) systems o er an alternative approach to commonly used radio frequency (RF) based positioning systems. In the literature, VLP studies are performed only for noncooperative systems. In this thesis, received signal strength (RSS) based cooperative localization is proposed for visible light systems. The e ects of cooperation on the localization accuracy of visible light positioning systems are illustrated based on a Cram er-Rao lower bound expression. The obtained expression is generic for any three-dimensional con guration and covers all possible cooperation scenarios via de nitions of connectivity sets. In addition, a low-complexity positioning algorithm is proposed for cooperative location estimation. Numerical results are presented to investigate the signi cance of cooperation and to evaluate performance of the proposed algorithm in various scenarios.Item Open Access Effects of cooperation on visible light positioning(IEEE, 2018) Erdem, Osman; Keskin, Musa Furkan; Gezici, SinanIn this paper, cooperative localization is proposed for visible light systems. The effects of cooperation on the localization accuracy of visible light positioning systems are illustrated based on a Cramér-Rao lower bound expression. The obtained expression is generic for any three-dimensional configuration and covers all possible cooperation scenarios via definitions of connectivity sets. Numerical results are presented to investigate significance of cooperation in various scenarios.Item Open Access Theoretical limits on localization in single input multiple output (SIMO) visible light systems(Elsevier, 2018) Kökdoğan,Furkan; Erdem, Osman; Gezici, SinanIn this work, a theoretical accuracy analysis is conducted for position estimation in visible light systems based on received signal strength (RSS) measurements. Considering a single light emitting diode (LED) at the transmitter and multiple photo-detectors (PDs) at the receiver, the Cramér-Rao lower bound (CRLB) is derived for both a generic three-dimensional scenario and specific configurations of the PDs at the receiver. For the special case in which the height of the receiver is known, a compact expression is derived for the CRLB, considering a uniform circular layout and the same elevation angle for all the PDs. In addition, the optimal placement of the PDs at the receiver is investigated by taking the effects of the elevation angle parameter of the PDs into consideration. The optimal values are obtained theoretically and also verified by simulations. Numerical examples are provided to illustrate the impacts of various system parameters on localization accuracy and to compare the theoretical limits against the maximum likelihood estimator (MLE) for the receiver position.