Dual chaotic encryption scheme for index modulation orthogonal time frequency space PON system

In the OTFS-IM system, physical layer security (PLS) and peak-to-average power ratio (PAPR) are two critical issues that will affect the safe transmission and efficiency of the system. This paper uses dual chaotic encryption on the index bits and data bits of the index modulation orthogonal time frequency space (OTFS-IM) system. Besides, a peak-to-average power ratio optimized encryption scheme using random interleaved partitioning time segmentation (RIPTS) is also proposed to reduce autocorrelation. To verify the PAPR and encryption performance of the proposed scheme, a Back-to-back (B2B) and 80 km standard single-mode fiber (SSMF) transmission passive optical network (PON) system is conducted. The simulation and experimental results show that compared to the OTFS-IM without PAPR optimization, the proposed RIPTS scheme can improve 4.3 dB PAPR performance. Moreover, compared with partial transmit sequence (PTS), interleaved PTS (IPTS), and random PTS (RPTS) schemes, it can also improve 0.8 dB, 0.6 dB, and 0.5 dB PAPR performance and effectively reduce the inter-carrier interference(ICI). In addition, the dual chaotic encryption system is controlled by six parameters, so the total key space can be up to 10⁹⁰, respectively. The research in this paper provides a reliable solution to the PLS problem of the OTFS-IM PON system and optimizes the system transmission performance.