Encrypted image transmission in OFDM-based VLC systems using symbol scrambling and chaotic DFT precoding

In this paper, a joint symbol-scrambling and chaotic discrete Fourier transform (DFT) precoding scheme is proposed for orthogonal frequency-division multiplexing (OFDM) visible light communication (VLC) systems for encrypted image data. In the proposed scheme, the original image data is first divided into sub-blocks and then an inter-block scrambling operation is applied to the resulting image data. Secondly, the real and imaginary parts of the transmitted QAM symbols are encrypted using two separate chaotic sequences generated from different chaotic maps. Thirdly, the resulting encrypted QAM signals are transformed into new signals using a chaotic DFT-precoding matrix in order to further improve the security and bit error rate (BER) performance of the OFDM signals. The mathematical model of our proposed encrypted OFDM-based VLC system is established and the BER formula is derived. The obtained BER formula is confirmed by our simulation results. Our simulation results also show that both symbol scrambling and image-block scrambling have no effect on the BER of the proposed DFT-precoded OFDM-based VLC system. The proposed scheme not only improves the quality of the transmitted image but also protects the transmitted image data from eavesdroppers.