Design and Analysis of Physical Layer Security Based on Ill-Posed Theory for Optical OFDM-Based VLC System over Real-Valued Visible Light Channel

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Due to the broadcast property of the visible light beam, visible light communication (VLC) systems may suffer from malicious attack or eavesdropping in public area. In this paper, we design and analyze the physical layer security mechanism with the aid of ill-posed theory and present a channel determined subcarrier shifting (CDSS) scheme with pre-equalization. The CDSS scheme exploits the real-valued and location-sensitive channel state information (CSI) of VLC channel and performs sorting operations on the CSI, which formulates a shifting matrix with the aid of chaotic sequences, to dynamically change the available subcarrier for the optical orthogonal frequency division multiplex (OOFDM) aided VLC system. Meanwhile, we combine the CDSS scheme with the preequalization module to further improve the bit error rate (BER) performance for legitimate users. Moreover, the analytical physical layer security model for VLC system is presented using ill-posed theory, which removes the requirements of known CSI and worse channel quality of malicious users when evaluating secrecy capacity. Theoretical and simulation results are provided and compared to prove the benefits achieved by the proposed CDSS scheme, which can enhance the security with no loss of BER, while the secrecy capacity performances are also evaluated to verify the effectiveness of our design.