Adaptation techniques in optical wireless communications

The need for high-speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on optical wireless communication. Optical wireless systems boast some advantages over radio frequency (RF) systems, including a large unregulated spectrum, freedom from fading, confidentiality and immunity against interference from electrical devices. They can satisfy the dual need for mobility and broadband networking. However, optical wireless links are not without flaws. They are affected by background noise (artificial and natural light sources) and suffer from multipath dispersion. The former can degrade the signal-to-noise ratio, while the latter restricts the maximum transmission rate available. The aim of this thesis is to investigate a number of techniques to overcome these drawbacks and design a robust high-speed indoor optical wireless system with full mobility. Beam delay and power adaptation in a multi-spot diffusing system is proposed in order to increase the received optical signal, reduce the delay spread and enable the system to operate at higher data rates. The thesis proposes employing angle diversity receivers and imaging diversity receivers as in order to reduce background noise components. Moreover, the work introduces and designs a high-speed fully adaptive optical wireless system that employs beam delay, angle and power adaptation in a multi-spot diffusing configuration and investigates the robustness of the link design in a realistic indoor office. Furthermore, a new adaptive optical wireless system based on a finite vocabulary of stored holograms is introduced. This method can effectively optimise the spots’ locations and reduce the design complexity of an adaptive optical wireless system. A fast adaptation approach based on a divide-andconquer methodology is proposed and integrated with the system to reduce the time required to identify the optimum hologram. The trade-off between complexity and performance enhancement of the adaptive finite holograms methods compared with the original beam power and angle adaptation is investigated

Holograms in Optical Wireless Communications

Adaptive beam steering in optical wireless communication (OWC) system has been shown to offer performance enhancements over traditional OWC systems. However, an increase in the computational cost is incurred. In this chapter, we introduce a fast hologram selection technique to speed up the adaptation process. We propose a fast delay, angle and power adaptive holograms (FDAPA-Holograms) approach based on a divide and conquer methodology and evaluate it with angle diversity receivers in a mobile optical wireless (OW) system. The fast and efficient fully adaptive FDAPA-Holograms system can improve the receiver signal to noise ratio (SNR) and reduce the required time to estimate the position of the receiver. The adaptation techniques (angle, power and delay) offer a degree of freedom in the system design. The proposed system FDAPA-Holograms is able to achieve high data rate of 5 Gb/s with full mobility. Simulation results show that the proposed 5 Gb/s FDAPA-Holograms achieves around 13 dB SNR under mobility and under eye safety regulations. Furthermore, a fast divide and conquer search algorithm is introduced to find the optimum hologram as well as to reduce the computation time. The proposed system (FDAPA-Holograms) reduces the computation time required to find the best hologram location from 64 ms using conventional adaptive system to around 14 ms

Uplink Design in VLC Systems with IR Sources and Beam Steering

The need for high-speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on visible light communication (VLC) systems. Although VLC systems provide lighting and communications simultaneously from light emitting diodes, LEDs, the uplink channel design in such a system is a challenging task. In this paper, we propose a solution in which the uplink challenge in indoor VLC is resolved by the use of an Infrared (IR) link. We introduce a novel fast adaptive beam steering IR system (FABS-IR) to improve the uplink performance at high data rates while providing security for applications. The goal of our proposed system is to enhance the received optical power signal, speed up the adaptation process and mitigate the channel delay spread when the system operates at a high transmission rate. The channel delay spread is minimised from 0.22 ns given by hybrid diffuse IR link to almost 0.07 ns. At 2.5 Gb/s, our results show that the imaging FABS-IR system accomplished about 11.7 dB signal to noise ratio (SNR) in the presence of multipath dispersion, receiver noise and transmitter mobility