Indoor Localization Based on Visible Light Communication

With the increasing demand for accurate indoor localization and widespread deployment of light-emitting diodes (LEDs) for lighting, there has been a dramatic rise in research activities in many areas of indoor localization based on visible light communication (VLC), including modeling of VLC channels, localization methods, localization algorithms, and localization systems. In VLC based indoor localization systems, the reflection, interference and noise in the VLC channels cause the loss, fading and distortion of the transmitted signals. The bandwidth and the signal-to-noise ratio (SNR) of the channel directly affect the channel capacity, the design of modulation scheme, the transmitted power and the data rate. Therefore, it is imperative to capture the characteristics of different VLC channels and properly model them for dual purpose of illumination and localization. We start by a systematic investigation of the VLC channel models. We first investigate three possible configurations of indoor VLC links, and evaluate two widely used VLC channel models – the directed light-of-sight (LOS) optical channel and the nondirected LOS optical channel model. We next investigate the electrical SNR for VLC channels with intersymbol interference (ISI) and without ISI, and provide closed-form derivations to clarify some confusion on the electrical SNR in the literature.To help design and especially evaluate VLC localization schemes, we investigate, analyze and compare four possible localization methods applied to indoor VLC localization – time of arrival (TOA) methods, time difference of arrival (TDOA) methods, received signal strength (RSS) methods and angle of arrival (AOA) methods. For practicality, we consider intensity modulation and direct detection (IM/DD) and explore the dilution of precision (DOP) analysis, a metric that has been successfully deployed in GPS localization and AOA-based localization. For RSS-based indoor VLC localization, we establish a closed-form relation between positional DOP (PDOP) and the accuracy of RSS-based indoor VLC localization, use PDOP to analyze two localization scenarios with different LED grid patterns, and quantize the effect of LED grid patterns on the position errors. Simulation results confirm the effectiveness of the proposed approach

Doctor of Philosophy

dissertationWireless communication has become an essential part of everyday life. The hunger for more data, more phone calls, more video, and more access in more places, including vehicles, is growing massively. Communication in vehicles is particularly challenging because of their extremely high multipath environment. In addition, there is significant interest in reducing the number of wires in vehicles to reduce weight, complexity, maintenance, etc. and replace them with wireless systems. Preliminary research shows that MIMO systems take advantage of the extreme multipath environment found in aircraft and other vehicles and also provides more consistent channel capacity than SISO systems. The purpose of this research was to quantify complex channels (including the aircraft/vehicle environment) and their relation to other environments, evaluate MIMO in aircraft, provide design constraints for accurately modeling complex channels, and provide information to predict optimum antenna type and location to enable communication in aircraft/cars/buses/ships/trains/etc. and other extreme channels. The ability to evaluate and design MIMO technologies from the guidelines in this paper is potentially transformative for aircraft safety - enabling a new generation of location specific monitoring and maintenance. Average measured capacity was found to be between 18 and 21 bits/s/Hz using a 4x4 array of antennas, and had no direct relation to the size of the channel. Site-specific capacity showed a multipath rich channel, varying between 15 to 23 bits/s/Hz. The capacity decreased for increasing measurement distance, with exceptions near reflective objects that increase multipath. Due to these special circumstances for site-specific locations within complex channels, it is recommended that 3D ray tracing be used for modeling as it is more accurate than commonly used statistical models, within 1.1 bits/s/Hz. This showed that our 3D ray tracing is adaptable to various environments and gives a more accurate depiction than statistical models that average channel variations. This comes at the cost of greater model complexity. If increased complexity is not desirable, Nakagami 1.4 could be used as the next most accurate model. Design requirements for modeling different complex channels involve a detailed depiction of channel geometry, including height, width, length, shape (square, cylindrical, slanted walls, etc.), large windows, and reflective objects inside the channel space, especially those near the transmitter. Overall, the multipath rich channel found in vehicles is an excellent environment for MIMO systems. These complex channels can be simulated accurately without measurement and before they are even built using our sitespecific 3D ray tracing software combined with a detailed signal model to incorporate antenna effects