POVALAČ, A. Metody a systémy prostorové identifikace RFID etiket [online]. Brno: Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií. 2013.
The dissertation thesis submitted by Ales Povalac is aimed to the methodology, implementation and experimentally testing of a location system for RFID tags in UHF band. The topic of the thesis is presently indeed interesting and crucial in many practical applications not only in industry. Precision determination of tag position can to ensure more reliable identification of passage through gates, easy finding of items in a stock, e.g. books in a public library, or movement of persons in dangerous plants. A massive usage of this technology in practice needs cheap solution based on passive tags. On the other hand, application of inexpensive passive tags using backscattering principle brings many complications in comparison to active retransmission, namely in environment with multipath propagation of radio waves. The fundamental goal of this work has been an exploration of possibilities to use simple system for satisfactory accuracy of tag positioning in light of hardware, preferably to use commercial readers, with convenient minimal configuration of RX/TX antennas. In the last decade, several experiments and some practical solutions has been presented, but these results are not too sufficient in achieved accuracy or such systems use UWB techniques unfitting for passive backscattering. The most widely used method based on RSS can be successfully applied only in open-space environment without significant multipath. The PHD thesis with title "Spatial Identification Methods and Systems for RFID Tags" consists of 82 pages including annex. In the introduction, the applicant for Ph.D. degree performed the careful literature retrieval and put together the state of the art subsuming methods for estimation of distance to tag and angular direction to tag with respect to the reader antenna direction. As a fundamental question, adequate model of RFID channel became pivotal for comprehensive analysis of the RFID positioning system to determine channel impulse response, particularly for indoor usage. As an efficient method to reach reasonable accuracy in the UHF tag positioning has been qualified the phase difference of arrival method tailored to characteristics of UHF RFID systems. It can be regarded as the first original contribution. In addition, the analyses performed for these phase methods are supported by unique RFID channel emulator, in which several typical scenarios have been modelled. The significant part of the work was focused on experiments. The fundamental requirement for application of the phase method is the perfect coherency between receiving and transmitting subsystems and dynamic range, therefore an application of any common reader could not bring satisfactory results, and student built up RFID modular measurement system based on SDR which is able to perform on many kinds of measurement using different configuration of several antennas. Set of measurements including evaluation in the anechoic chamber and also in true scenarios represents next original contribution in this field. The final part of the thesis is focused on procedures to obtaining tag position. There can be also found aspects of originality, such as the interpolation of CIR by parabolic curve for improving wideband distance estimation. Generally, this dissertation work combines theoretical derivations supported by system modelling with extensive experimental verification. The obtained results indicate that proposed phase methods are efficient for accurate positioning of passive UHF tags in environments without strong multipath and they offers much better results in comparing with RSS-based method. For environments with significant multipath propagation, student presents methodical approaches to achievement of acceptable accuracy under the specific conditions for hardware parameters of reader and also tags, application of improvement methods, and continual calibration using calibration tags. In the conclusion, I must say that Ales Povalac represents a qualified professional, who is able to successfully solve any engineering and scientific task from wide spectra of electronics or communication systems. I would like to thanks him also for an excellent cooperation during his whole PHD study not only in field of research, but also for help in teaching, and of course for friendship, which always helped us.
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viz posudek ve formátu pdf
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