Visible light communication (VLC) systems have become promising candidates to complement conventional radio frequency (RF) systems due to the increasingly saturated RF band and the potentially high data rates that can be achieved by VLC systems. Over the last decade, significant research effort has been directed towards the development of VLC systems due to their numerous advantages over RF systems, such as the availability of simple transmitters (light emitting diodes, LEDs) and receivers (silicon photo detectors), better security at the physical layer, improved energy efficiency due to the dual functionally (i.e., illumination and communication) and hundreds of THz of license-free bandwidth. However, there are several challenges facing VLC systems to achieve high data rates (multi gigabits per second). These challenges include the low modulation bandwidth of the LEDs, co-channel interference (CCI), inter symbol interference (ISI) due to multipath propagation and the light unit (i.e., VLC transmitter) should be ‘‘ON’’ all the time to ensure continuous communication. This thesis investigates a number of techniques to overcome these challenges to design a robust high-speed indoor VLC system with full mobility. A RGB laser diode (LD) is proposed for communication as well as illumination. The main goal of using LD is to enable the VLC system to achieve multi-gigabits data rates when employing a simple modulation technique (such as on-off keying (OOK)), thus adding simplicity to the VLC system. A delay adaptation technique (DAT) is proposed to reduce the delay spread and enable the system to operate at higher data rates (10 Gb/s in our case). The thesis proposes employing angle diversity receivers (ADR) and imaging diversity receivers to mitigate the impact of ISI, CCI, reduce the delay spread (increase the channel bandwidth) and increase the signal to noise ratio (SNR) when the VLC system operates at high data rates (5 Gb/s and 10 Gb/s) under the effects of mobility and multipath dispersion. Moreover, the work introduces and designs three new VLC systems, an ADR relay assisted LD-VLC (ADRR-LD), an imaging relay assisted LD-VLC (IMGR-LD) and a select-the-best imaging relay assisted LD-VLC (SBIMGR-LD), which are modelled and their performance is compared at 10 Gb/s in two VLC room sizes (5m × 5m × 3m and 4m × 8m × 3m). As well as modelling in two different room scenarios: an empty room and a realistic environment were considered. The work also introduces and designs a high-speed fully adaptive VLC system that employs beam steering and computer generated holograms (CGHs), which has the ability to achieve 20 Gb/s with full receiver mobility in a realistic indoor environment. Furthermore, a new high-speed fast adaptive VLC system based on a divide-and-conquer methodology is proposed and integrated with the system to reduce the time required to identify the optimum hologram. The new system has the ability to achieve 25 Gb/s in the worst case scenario. This thesis also proposes four new infrared (IR) systems to support VLC systems when the light is totally turned off. In addition, it introduces the concept of a collaborative VLC/IR optical wireless (OW) system and investigates the impact of partial dimming on the VLC system performance. An adaptive rate technique (ART) is proposed to mitigate the impact of light dimming. Finally, an IROW system (cluster distributed with beam steering) is introduced to collaborate with a VLC system to maintain the target data rate in the case of partial dimming.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:701713 |
| Date | January 2016 |
| Creators | Hussein, Ahmed Taha |
| Contributors | Elmirghani, Jaafar |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.whiterose.ac.uk/15894/ |
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