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UBC Theses and Dissertations

Physical-layer security for visible-light communication systems Mostafa, Ayman


Visible-light communication (VLC) is an enabling technology that exploits the lighting infrastructure to provide ubiquitous indoor broadband coverage via high-speed short-range wireless communication links. On the other hand, physical-layer security has the potential to supplement conventional encryption methods with an additional secrecy measure that is provably unbreakable regardless of the computational power of the eavesdropper. The lack of wave-guiding transmission media in VLC channels makes the communication link inherently susceptible to eavesdropping by unauthorized users existing in areas illuminated by the data transmitters. In this thesis, we study transmission techniques that enhance the secrecy of VLC links within the framework of physical-layer security. Due to linearity limitations of typical light-emitting diodes (LEDs), the VLC channel is more accurately modelled with amplitude constraints on the channel input, rather than the conventional average power constraint. Such amplitude constraints render the prevalent Gaussian input distribution infeasible for VLC channels, making it difficult to obtain closed-form secrecy capacity expressions. Thus, we begin with deriving lower bounds on the secrecy capacity of the Gaussian wiretap channel subject to amplitude constraints. We then consider the design of optimal beamformers for secrecy rate maximization in the multiple-input single-output (MISO) wiretap channel under amplitude constraints. We show that the design problem is nonconvex and difficult to solve, however it can be recast as a solvable quasiconvex line search problem. We also consider the design of robust beamformers for worst-case secrecy rate maximization when channel uncertainty is taken into account. Finally, we study the design of linear precoders for the two-user MISO broadcast channel with confidential messages. We consider not only amplitude constraints, but also total and per-antenna average power constraints. We formulate the design problem as a nonconvex weighted secrecy sum rate maximization problem, and provide an efficient search algorithm to obtain a solution for such a nonconvex problem. We extend our approach to handle uncertainty in channel information. The design techniques developed throughout the thesis provide valuable tools for tackling real-world problems in which channel uncertainty is almost always inevitable and amplitude constraints are often necessary to accurately model hardware limitations.

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Attribution-NonCommercial-NoDerivatives 4.0 International