UBC Theses and Dissertations

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UBC Theses and Dissertations

Coordinated transmission for visible light communication systems Ma, Hao


Visible light communication (VLC) is an emerging optical wireless communication technology that employs the light-emitting diode (LED) as the data transmitter. It has great potential to alleviate the strain on the radio-frequency (RF) spectrum in the indoor environment. The integration of VLC into indoor communication networks establishes optical attocells, responsible for the downlink traffic from the network to user terminals. These attocells could be easily deployed wherever LEDs are adopted for general illumination, including in electromagnetic interference sensitive areas like hospitals and airplanes. Although opaque bounds effectively contain light signals, VLC attocells would generally not operate free of interference. Illumination designers aim to have a uniform illumination at a certain height in the indoor environment, which mandates a rich overlap between the emissions of luminaires and results in unavoidable inter-attocell interference (IAI) from a communications perspective. This reality encourages us to propose the coordination of multiple VLC attocells (i.e., VLC-enabled LED luminaires) to turn the problem of overlap and thus interference into an advantage. In this thesis, we study how the coordination of VLC attocells can be employed to improve the user performance. Two coordinated VLC architectures, both of which utilize single-carrier transmission but differ at the coordination level, are investigated first. The analysis primarily focuses on the beamforming design subjected to the limited dynamic range of LED transmitters. The design of robust beamformers is also considered to combat the uncertainty of channel information at the transmitter. Finally, we propose a multi-carrier coordinated VLC architecture that uses power lines as the backbone network for the VLC front-end. Several subcarrier allocation schemes with varying degrees of tradeoff among hardware, computational complexity, and performance for meaningful variations of this hybrid system are proposed. The system designs developed throughout the thesis enable the collaboration among multiple LED transmitters in VLC systems, and our results indicate that these collaborative designs can significantly improve the performance of indoor VLC systems.

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