Secure OFDM Transmission Precoded by Chaotic Discrete Hartley Transform

We propose a chaotic discrete Hartley transform (DHT) to enhance the physicallayer security and simultaneously improve the transmission performance of optical orthogonal frequency division multiplexing (OFDM) in passive optical network. The theoretical analysis and numerical simulation show that the chaotic DHT precoding matrix after independent row/column permutations can also effectively reduce the peak-to-average power ratio (PAPR) of OFDM signals, which can be generated for OFDM data encryption using digital chaos. The multifold data encryption provides a huge key space of ~10178to ensure the physical-layer confidentiality. An encrypted data transmission of 8.9 Gb/s 16-QAM optical OFDM signals is successfully demonstrated over 20 km standard single-mode fiber. Due to the effective reduction in PAPR by the chaotic DHT precoding matrix, the receiver sensitivity is improved by ~1.4 dB (BER@10-3). Moreover, the proposed scheme has low computational complexity, which also provides high spectral efficiency since no additional sideband information is required.