Author: Liu, Zhongxu
Title: Investigations of novel indoor visible light positioning schemes
Advisors: Yu, Changyuan (EIE)
Degree: M.Sc.
Year: 2020
Subject: Indoor positioning systems (Wireless localization)
Optical communications
Hong Kong Polytechnic University -- Dissertations
Department: Department of Electronic and Information Engineering
Pages: xi, 58 pages : color illustrations
Language: English
Abstract: Due to low accuracy, high complexity, and electromagnetic interference, conventional wireless positioning technologies are hard to meet the growing demand for location-based service (LBSs). As a green technology, visible light positioning (VLP) uses light-emitting diodes (LEDs) to provide the functions of illumination and positioning. The VLP is a promising candidate for achieving effective and efficient positioning since it can offer many advantages, such as high positioning accuracy, no electromagnetic interference, and low installment cost. In this thesis, the comparisons between VLP systems based on different multiple access methods are discussed firstly. The principle and simulation results of time division multiple access (TDMA) and frequency division multiple access (FDMA), and code division multiple access (CDMA) are analyzed. Although conventional CDMA does not occupy the time resources and frequency bandwidth compared to TDMA and FDMA, it still needs the strict synchronization of VLP systems. For mitigating the demand for synchronization of positioning systems, an asynchronous CDMA scheme for VLP is proposed. Cyclic orthogonal Walsh-Hadamard code (COWHC) and pseudo-noise (PN) code are used to generate orthogonal pseudo-random code (OPRC) which has zero periodic cross-correlation and multiple peak-valued autocorrelation functions. By using the proposed scheme, accurate positioning can be realized even when the VLP system loses synchronization. The simulation results show that more than 99% positioning error less than 6cm at the sampling frequency of 100MHz. Besides, the proposed scheme also can simultaneously achieve the functions of positioning and communication when the LEDs transmit signals at the same time. More than 99% positioning error can be reduced to 4cm at the high sampling frequency and the positioning performance is well in all areas of the room including the corners. A two-LED indoor VLP model is also demonstrated in this thesis. By using a mirror to replace one LED, two LEDs can generate four signals to realize the trilateration algorithm for positioning. This overcomes the limitation of using at least three LEDs for conventional trilateration algorithms. At the transmitter, two LEDs alternately transmit orthogonal frequency division multiplexing (OFDM) training signals via time division multiplex (TDM). Then by the channel estimation at the receiver, the channel direct current (DC) gains can be obtained and used for positioning. According to the simulation results, this method can achieve reliable indoor VLP with location error < 5cm within 90% of the tested area.
Rights: All rights reserved
Access: restricted access

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