In this work, we develop an indoor visible light communications (VLC) system based on a transmitted precoded (TPC)-aided, coded generalized space shift keying (GSSK) system with physical layer security (PLS) capability in the presence of dimming. A new design of the encoder and decoder of linear codes is given to improve the error-correcting capability of the system as well as to enable random selection of the activated indices in the GSSK automatically. The PLS of the system is guaranteed by the appropriate selection of the power allocation coefficients for randomly activated photodiodes (PDs). At the receiver, the unknown channel and dimming coefficients are jointly estimated in the legitimate users with a new pilot-aided estimation technique. Then, the optimal detection of the spatial symbols is implemented using the maximum likelihood (ML) criterion in the presence of dimming. It is shown that the dimming coefficients, unknown to the eavesdropper, provide additional PLS for the legitimate user. The computer simulations show that the legitimate user achieves excellent bit error performance mainly due to the linear coding employed that serves for error correction and selection of the best GSSK constellation in the system. In contrast, the bit error performance of the potential eavesdroppers is significantly degraded.
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