High-Security Physical Layer Encryption Scheme for SCMA-FBMC in Four-Mode Fiber

This paper proposes a high-security physical layer encryption scheme for sparse code multiple access filter bank multi-carrier (SCMA-FBMC) in weakly coupled four-mode fiber. Due to the multiplexing of four modes and the overload of SCMA, the number of users connected by the proposed method is increased by six times. To improve the security of the SCMA-FBMC system, the Logistic mapping parameters are employed as the public key that is distributed to all users and is utilized for frequency masking to protect against illegal receivers' attacks. The 6D Duffing_Lu model acts as a private key of optical network units (ONUs) to prevent other ONUs from eavesdropping. A 60 Gb/s (4 × 15 Gb/s) encrypted SCMA-FBMC signal transmission over 5 km weakly coupled four-mode fiber is experimentally demonstrated. The experimental results show that there is no discernible difference in the signal's bit error rate (BER) performance before and after encryption. The sensitivity between different ONUs is less than 0.5 dB. In addition, the proposed scheme's key space can reach up to 10 ¹¹⁰ , which effectively guarantee the physical layer security of the system. This scheme has application prospects in future short-distance optical access due to the growing number of connections and good security performance.