Browsing by Subject "Positioning accuracy"

Now showing 1 - 2 of 2

Open Access
Enhanced position estimation via node cooperation
(IEEE, 2010) Sahinoglu, Z.; Gezici, Sinan
Two-way time-of-arrival (TW-ToA) is a widely used ranging protocol that can provide the distance between two devices without time synchronization. One drawback of the TW-ToA is poor positioning accuracy in the absence of a sufficient number of reference ranging devices. Also, for a self-positioning system with a limited battery life, it might be necessary to limit the number of transmissions while satisfying accuracy constraints. In this paper, a cooperative positioning protocol [1] is studied, which can improve positioning accuracy compared to the conventional TW-ToA based positioning systems and also facilitate positioning with fewer packet transmissions; hence, it can prolong battery life on average. The maximum likelihood estimator is obtained for the cooperative technique and the limits on the positioning accuracy are quantified in terms of the Cramer-Rao lower bound (CRLB). Simulation results are provided in order to show performance improvements. ©2010 IEEE.
Open Access
Magnetic resonance imaging assisted by wireless passive implantable fiducial e-markers
(Institute of Electrical and Electronics Engineers, 2017) Gokyar, S.; Alipour, A.; Unal, E.; Atalar, Ergin; Demir, Hilmi Volkan
This paper reports a wireless passive resonator architecture that is used as a fiducial electronic marker (e-marker) intended for internal marking purposes in magnetic resonance imaging (MRI). As a proof-of-concept demonstration, a class of double-layer, sub-cm helical resonators were microfabricated and tuned to the operating frequency of 123 MHz for a three T MRI system. Effects of various geometrical parameters on the resonance frequency of the e-marker were studied, and the resulting specific absorption rate (SAR) increase was analyzed using a full-wave microwave solver. The B1 + field distribution was calculated, and experimental results were compared. As an exemplary application to locate subdural electrodes, these markers were paired with subdural electrodes. It was shown that such sub-cm self-resonant e-markers with biocompatible constituents can be designed and used for implant marking, with sub-mm positioning accuracy, in MRI. In this application, a free-space quality factor ( Q -factor) of approximately 50 was achieved for the proposed resonator architecture. However, this structure caused an SAR increase in certain cases, which limits its usage for in vivo imaging practices. The findings indicate that these implantable resonators hold great promise for wireless fiducial e-marking in MRI as an alternative to multimodal imaging.