High Throughput Multi-User Visible Light Communication with LEDs for High-speed Wireless Data Networks

Abstract

With the advancement of light emitting diode (LED) technology, visible light communication (VLC) emerged as a novel way of providing data communication. Using visible light as the communication medium, VLC possesses many advantages over conventional RF communications, such as large unlicensed spectral bandwidth, usability at RF-prohibited areas. Since data transmission is done via LEDs using intensity modulation techniques, VLC is able to provide data rates faster than the LED switching rate, which is a several hundred of Megahertz. This thesis provides a design of an indoor multi-user (MU) VLC system and it analyses the system addressing some of the important issues in indoor VLC. Moreover, the thesis provides a fundamental analysis of the VLC system in the aspects of indoor illumination, power reception and channel dispersion in the indoor environment. The ultimate target of designing the indoor MU-VLC system is achieved by conducting the study in four sections. In the first study, a decision feedback equalizer (DFE) with adaptive recursive least square (RLS) algorithm is analyzed for the reduction in the length of the training sequence (TS) used in the DFE. The reduced TS length allows more data bits to be transmitted, and hence facilitates higher bit rate. The use of RLS-DFE also enables the VLC system to reduce the multipath induced inter-symbol interference (ISI) that helps to increase data rate with improved bit error rate performance (BER). Secondly, the thesis presents the studies on multilevel pulse amplitude modulation (PAM) with RLS-DFE for VLC systems. The PAM scheme supports higher throughput andthe RLS-DFE facilitates to use fewer bits for the TS, so that the data rate can be increased over the limitation of LED modulation speed. The simulation results of the outage area probability show that the VLC system supports high data rate transmission at nearly errorfree rates for most areas in indoor environments. As a promising way of reducing the multipath effects, the third study employs orthogonal frequency division multiplexing (OFDM) in the indoor VLC system. The original OFDM signal inherently composed with signal peaks with high power, causing high peak-to-average power ratio (PAPR). At the transmission of this high PAPR signal, the LEDs are overheated due to the limited output power and the transmitted signal is also distorted due to the nonlinear characteristics of the LEDs. Therefore, it is crucial to reduce the PAPR of the OFDM signal before it is fed into the LEDs. The third study of the thesis presents the analysis of μ-law CT and exponential CT schemes in terms of PAPR reduction and it also proposes a novel CT scheme that can be efficiently used for the reduction of PAPR in VLC-OFDM. The simulations comparatively analyze the performances of each CT scheme with other CT schemes. It shows from the results that the CT schemes perform with significant PAPR reduction in VLC-OFDM signal providing excellent BER performances. The MU-VLC system is designed in the last study, proposing a novel MU-VLC system exploiting the visible light spectrum. The proposed scheme is defined as color-clustered multiuser VLC and the study makes sure that the MU-VLC system is complete in that it encompasses transmission and detection methods for multiple user access, while ensuring a color-controlled flicker free illumination. The simulations demonstrate that the proposed MU-VLC system provides an efficient multiuser VLC platform with significant performances over various transmission scenarios.