Browsing by Subject "Lambertian pattern"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
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 Direct and two-step positioning in visible light systems(IEEE, 2018) Keskin, Musa Furkan; Gezici, Sinan; Arıkan, OrhanVisible light positioning (VLP) systems based on light emitting diodes can facilitate high accuracy localization services for indoor scenarios. In this paper, direct and two-step positioning approaches are investigated for both synchronous and asynchronous VLP systems. First, the Cramér-Rao lower bound (CRLB) and the direct positioning-based maximum likelihood estimator are derived for 3-D localization of a visible light communication receiver in a synchronous scenario by utilizing information from both time delay parameters and channel attenuation factors. Then, a two-step position estimator is designed for synchronous VLP systems by exploiting the asymptotic properties of time-of-arrival and received signal strength estimates. The proposed two-step estimator is shown to be asymptotically optimal, i.e., converges to the direct estimator at high signal-to-noise ratios. In addition, the CRLB and the direct and two-step estimators are obtained for positioning in asynchronous VLP systems. It is proved that the two-step position estimation is optimal in asynchronous VLP systems for practical pulse shapes. Various numerical examples are provided to illustrate the improved performance of the proposed estimators with respect to the current state-of-the-art and to investigate their robustness against model uncertainties in VLP systems.Item Open Access Direct positioning in synchronous and asynchronous visible light systems(IEEE, 2018) Keskin, Musa Furkan; Gezici, Sinan; Arıkan, OrhanIn this paper, direct positioning approaches are investigated for both synchronous and asynchronous visible light systems. First, the maximum likelihood estimator (MLE) and the Cramér-Rao lower bound (CRLB) are derived for the synchronous scenario by considering the information from both channel attenuation factors and time delay parameters. Then, asynchronous visible light positioning (VLP) systems are investigated and the corresponding CRLBs and MLEs are obtained based on received signal strength (RSS) information. It is shown that the direct and two-step position estimators are equivalent in the asynchronous scenario under mild conditions. Numerical examples are provided to illustrate the theoretical results.Item Open Access Fundamental limits on localization in single input multiple output visible light systems(2017-09) Kökdoğan, FurkanVisible light systems have recently been considered as an e ective and promising solution for indoor positioning. In this thesis, 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 Cram er-Rao lower bound (CRLB) is derived for both a generic three-dimensional scenario and speci c con gurations 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. Asymptotic analysis and accuracy of derived compact expression is investigated for this con guration of the system. In addition, the optimal placement of the PDs at the receiver is investigated by taking the e ects of the elevation angle parameter of the PDs into consideration. The optimal values are obtained theoretically and also veri ed by simulations. Numerical examples are presented to illustrate the impacts of system parameters on localization accuracy, namely radius of the uniform circular layout, elevation angle and number of PDs. Finally, theoretical limits are compared against the maximum likelihood estimator (MLE) as a benchmark to evaluate the performance of receiver position estimation.Item Open Access Improved lower bounds for ranging in synchronous visible light positioning systems(Institute of Electrical and Electronics Engineers Inc., 2016) Keskin, M. F.; Gonendik, E.; Gezici, SinanIn this study, the Ziv-Zakai bound (ZZB) is derived for synchronous visible light positioning (VLP) systems. The proposed ZZB extracts ranging information from the prior information, the time delay parameter, and the channel attenuation factor based on the Lambertian pattern. In addition to the ZZB, the Bayesian Cram�r-Rao bound (CRB) and the weighted CRB (WCRB) are calculated for synchronous VLP systems. Furthermore, a closed-form expression is obtained for the expectation of the conditional CRB (ECRB). Numerical examples are presented to compare the bounds against each other and against the maximum a posteriori probability (MAP) estimator. It is observed that the ZZB can provide a reasonable lower limit on the performance of MAP estimators. On the other hand, the WCRB and the ECRB converge to the ZZB in regions of low and high source optical powers, respectively; however, they are not tight in other regions. � 2016 IEEE.