Date of Award

Spring 2006

Document Type

Thesis

Degree Name

Master of Science in Telecommunications - (M.S.)

Department

Electrical and Computer Engineering

First Advisor

Ali N. Akansu

Second Advisor

Edip Niver

Third Advisor

Nirwan Ansari

Abstract

RFID tag location estimation in a 3D environment is investigated. The location of the tag with unknown coordinates can be estimated with certain accuracy. However, accuracy can be improved using the knowledge based on measurement of additional reference tags with known location. This thesis studies the mathematical formulation and practical realization of location sensing using RFID tags.

Deviating from the standard use of RFID technology which employs one tag reader to identify the presence of tag, here multiple tag readers with known location are used to estimate the physical location of an individual tag, with/without the help of few reference tags with known locations.

Mathematical model of this concept has been developed based on distance variations in terms of signal strength. Experimental approach with limited range passive tags has been carried out. Since the range of the RFID system was limited only to a few inches, signal strength variations were insignificant. Instead, time domain measurements with the help of an external antenna were conducted. The composite signal width including of the wake up signal of the interrogator, travel time between the interrogator and tag, and the tag's response was measured and quantified. It was observed that the width of the signal was proportional to the distance between the tag reader and the tag. It was noticed that the use of four RFID tag readers yielded fairly accurate results to identify the location the tag based on the mathematical formulation developed here.

Additionally, concept of trilateration has also been extended for tracking the tag of unknown location without the use of reference tags. Archival data set corresponding to all tag location due to four different tag readers was compiled. The unknown tag was probed with four tag readers and matching the data to the archival data set yielded unique and accurate results for its unknown location. It was demonstrated that both approaches were proved to be cost-effective techniques and estimation of the location of a specific tag has been achieved with sufficient accuracy.

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