Abstract
In this paper, we present multiple techniques for phase-based narrowband backscatter tag localization in three-dimensional space with planar antenna arrays or synthetic apertures. Beamformer and MUSIC localization algorithms, known from near-field source localization and direction-of-arrival estimation, are applied to the 3D backscatter scenario and their performance in terms of localization accuracy is evaluated. We discuss the impact of different transceiver modes known from the literature, which evaluate different send and receive antenna path combinations for a single localization, as in multiple input multiple output (MIMO) systems. Furthermore, we propose a new Singledimensional-MIMO (S-MIMO) transceiver mode, which is especially suited for use with mobile robot systems. Monte-Carlo simulations based on a realistic multipath error model ensure spatial correlation of the simulated signals, and serve to critically appraise the accuracies of the different localization approaches. A synthetic uniform rectangular array created by a robotic arm is used to evaluate selected localization techniques. We use an Ultra High Frequency (UHF) Radiofrequency Identification (RFID) setup to compare measurements with the theory and simulation. The results show how a mean localization accuracy of less than 30 cm can be reached in an indoor environment. Further simulations demonstrate how the distance between aperture and tag affects the localization accuracy and how the size and grid spacing of the rectangular array need to be adapted to improve the localization accuracy down to orders of magnitude in the centimeter range, and to maximize array efficiency in terms of localization accuracy per number of elements.
Highlights
The origins of phase-based near-field source localization (NFSL) are firmly grounded in direction-of-arrival (DOA) estimation
The basic principles needed for the design of phase-based narrowband localization systems for backscatter tags have been discussed and evaluated by simulations and measurements
The simulations simulations show which localization accuracies can be expected from a uniform rectangular arrays (URA) aperture for different show which localization accuracies can be expected from a URA aperture for different localization localization algorithms, transceiver modes, noise and multipath conditions
Summary
The origins of phase-based near-field source localization (NFSL) are firmly grounded in direction-of-arrival (DOA) estimation. Signal-strength-based localization approaches compare the measured RSSI at multiple antenna positions with an EM-propagation-model to estimate the tag positions [5,6], whereas phase based localization approaches evaluate the signal phase of the narrow band receive signal [7]. This paper addresses multiple approaches from phase-based NFSL, DOA and UHF. We conduct simulations to compare the performance of different localization algorithms, transceiver modes and antenna geometries in terms of localization error and system complexity. We present a new and beneficial approach in which we numerically analyze localization accuracies for UHF RFID with the aid of a realistic multipath model incorporating spatial signal correlation.
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