A Survey of Positioning Systems Using Visible LED Lights

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.As Global Positioning System (GPS) cannot provide satisfying performance in indoor environments, indoor positioning technology, which utilizes indoor wireless signals instead of GPS signals, has grown rapidly in recent years. Meanwhile, visible light communication (VLC) using light devices such as light emitting diodes (LEDs) has been deemed to be a promising candidate in the heterogeneous wireless networks that may collaborate with radio frequencies (RF) wireless networks. In particular, light-fidelity has a great potential for deployment in future indoor environments because of its high throughput and security advantages. This paper provides a comprehensive study of a novel positioning technology based on visible white LED lights, which has attracted much attention from both academia and industry. The essential characteristics and principles of this system are deeply discussed, and relevant positioning algorithms and designs are classified and elaborated. This paper undertakes a thorough investigation into current LED-based indoor positioning systems and compares their performance through many aspects, such as test environment, accuracy, and cost. It presents indoor hybrid positioning systems among VLC and other systems (e.g., inertial sensors and RF systems). We also review and classify outdoor VLC positioning applications for the first time. Finally, this paper surveys major advances as well as open issues, challenges, and future research directions in VLC positioning systems.Peer reviewe

Light generation, transport, mixing and extraction in luminescent solar collectors

University of Technology, Sydney. Faculty of Science.The difficulty of directing daylight deep into the heart of buildings means that much artificial lighting is required during the day, which substantially increases energy costs for lighting and air conditioning. This thesis explores the feasibility of daylighting with luminescent solar collectors. An LSC is a stack of thin sheets of polymer doped with fluorescent dyes. Sunlight entering the sheets is absorbed and emitted isotropically at longer wavelengths. 75% of this emission is trapped by total internal reflection and propagates towards the sheets’ edges. A special coupler channels some of this light into a flexible optical fibre that guides it to a remote luminaire. High quality white light with zero excess heat is produced by appropriate dye use. LSC’s collect both diffuse and specular sunlight, so their luminous output is only weakly affected by light clouds. The best previous LSC’s for daylighting gave an outdoor-to-indoor lumens-to-lumens efficiency of only 0.2%. This project achieved an efficiency of 5%. The basic tool for optical design was étendue analysis. Key results are: i) the system’s cross sectional area must not decrease along the optical path, ii) the collector sheets need a high aspect ratio, and iii) an often neglected requirement for a solid optical system with no air gaps. Other optical design problems solved include high-efficiency flat-collector-sheet to cylindrical-optical-fibre couplers and high-efficiency light extractors (which boost output by approximately 50%). Major advances in mechanical design resulted in several new practical solutions including: strong, enduring optical joints; mass produced collector-sheet to optical-fibre couplers using injection moulding with demonstrated efficiencies of 96%; affordable flexible light guides; high-performance cover materials; roof and façade mounting; and reduced mass. Required system performance is impossible without high quality LSC sheets. Maximising fluorescence yield involves detailed understanding of the roles of: dye quantum efficiency, Stokes shift, long wavelength absorption “tails”, dye dispersion, light transport inside a sheet and long term sheet stability. A substantial improvement in the performance of collector sheets was achieved. Solutions to all the key problems for daylighting with practical LSC systems have been demonstrated using outdoor mounted collectors channeling light to indoor spaces, with one key exception: the increase in absorption tails over the long term. Techniques were developed for measuring this weak tails absorption, which significantly reduces light output from the required long collector sheets. Suggestions are made as to its cause, and possible methods of its reduction

Design of Visible-light driven catalysts for water oxidation and VOC degradation

The PhD thesis involves one or more articles that are either published,submitted or in the process of manuscript preparation. These all chapters are eloborated in context to the understandings and advancements involved during the PhD period. The whole thesis involves insights about synthesis and characterization of BiVO4 in the form of powder as well as thin films. It also describes the ability of BiVO4 powders and thin films in water splitting and volatile organic compound degradation