High security and low complexity SCMA-OFDM transmission system based on dual three-dimensional memory hyperchaotic in seven-core optical fibers

This paper proposes a physical layer encryption scheme with high security and low complexity for sparse code multiple access (SCMA) in weakly coupled seven-core optical fibers, using orthogonal frequency division multiplexing (OFDM) modulation to improve the link quality of a single user. Due to the overload rate of SCMA and space division multiplexing, the number of users connected to the proposed system scheme has increased to 10.5 times. To improve the security of the SCMA-OFDM system, this paper adopts a memory triangular mapping (MTM) hyperchaotic model. After data preprocessing, its chaotic sequence is used to perturb the SCMA codebook, constellation, subcarriers, symbols, and time slots, and multidimensional scrambling is performed to prevent illegal users from eavesdropping. The key is placed behind the signal to achieve key accompanying signal transmission. The sphere decoding-based message passing algorithm (SD-MPA) is adopted at the receiver to solve the problem of high computational complexity. Experiments have proved that the encryption scheme for SCMA-OFDM signal transmission of 34.9 Gb/s effective information over 2 km of 7-core optical fiber has a key space of 10 ³⁴³ , verifying the security and robustness of the transmission system. In addition, the detection effects of different multiuser detection algorithms in SCMA-OFDM multicore optical fiber transmission systems are also studied.