Secure Image Transmission in Orthogonal Frequency Division Multiplexing Visible Light Communication Systems

In this paper, a novel physical layer security based on two-level encryption is proposed for orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) systems. In the two-level encryption scheme, the bit signal, which is generated from image data, is first scrambled by a chaotic sequence. After the encrypted bit signal is mapped into 16 QAM symbols, the real and imaginary components of the resulting symbols are encrypted again by two separate chaotic sequences, respectively. A mathematical model is established to securely transmit images in OFDM-based VLC systems based on encryption. Based on the established mathematic model, the bit error rate (BER) formula to securely transmit OFDM-VLC is derived over the dispersive visible light communication (VLC) channel. A theoretical analysis shows that the encryption does not degrade the BER performance of the systems. Additionally, the validity of the BER formula obtained is verified by computer simulation. Theoretical and simulation results both show that the encryption operation has no effect on the BER of the proposed system. However, encryption is helpful for reducing the peak-to-average power ratio (PAPR) of the image-based OFDM. The simulation results show that the security of the image-based OFDM is enhanced and the PAPR is reduced.