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Sensors 2014, 14(12), 23176-23204; doi:10.3390/s141223176

Delay Tracking of Spread-Spectrum Signals for Indoor Optical Ranging

1
Department of Electronics, University of Alcalá, Madrid 28871, Spain
2
Communication Engineering Department, University of Málaga, Campus de Teatinos, Málaga 29010, Spain
3
Institute of Geodesy and Photogrammetry, ETH Zürich, Zürich 8093, Switzerland
*
Author to whom correspondence should be addressed.
Received: 27 August 2014 / Revised: 22 November 2014 / Accepted: 27 November 2014 / Published: 5 December 2014
(This article belongs to the Section Physical Sensors)
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Abstract

Delay tracking of spread-spectrum signals is widely used for ranging in radio frequency based navigation. Its use in non-coherent optical ranging, however, has not been extensively studied since optical channels are less subject to narrowband interference situations where these techniques become more useful. In this work, an early-late delay-locked loop adapted to indoor optical ranging is presented and analyzed. The specific constraints of free-space infrared channels in this context substantially differ from those typically considered in radio frequency applications. The tracking stage is part of an infrared differential range measuring system with application to mobile target indoor localization. Spread-spectrum signals are used in this context to provide accurate ranging while reducing the effect of multipath interferences. The performance of the stage regarding noise and dynamic errors is analyzed and validated, providing expressions that allow an adequate selection of the design parameters depending on the expected input signal characteristics. The behavior of the stage in a general multipath scenario is also addressed to estimate the multipath error bounds. The results, evaluated under realistic conditions corresponding to an 870 nm link with 25 MHz chip-rate, built with low-cost up-to-date devices, show that an overall error below 6% of a chip time can be achieved. View Full-Text
Keywords: optical ranging; spread-spectrum; delay-locked loop; multipath mitigation; indoor positioning optical ranging; spread-spectrum; delay-locked loop; multipath mitigation; indoor positioning
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Salido-Monzú, D.; Martín-Gorostiza, E.; Lázaro-Galilea, J.L.; Martos-Naya, E.; Wieser, A. Delay Tracking of Spread-Spectrum Signals for Indoor Optical Ranging. Sensors 2014, 14, 23176-23204.

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