Probabilistic Shaping and High-Security Transmission Enabled by Non-Uniform Key-Based Hierarchical Modulation

In this study, a non-uniform key-based hierarchical modulation scheme for power domain multiplexing (PDM) systems is presented. In contrast to traditional secure communication methods based on fixed keys, we employ a Logistic chaotic system to encrypt the data stream, with dynamic key updates enabled via in-band key transmission. During the encoding process, bit-level probability allocation is applied to the key stream, and superposition coding (SC) is employed to generate a probabilistic shaped 16-Quadrature Amplitude Modulation (PS16QAM) signal with a non-uniform distribution, thereby enhancing transmission quality. At the receiver, to ensure both transmission performance and the accuracy of key information, we implemented a key decision method to demodulate the key information. To evaluate the system's performance, the proposed scheme was experimentally validated on a 2km 7-core fiber, achieving accurate transmission of signals at a net rate of 102.54 Gb/s. The experimental results indicate that the PS-16QAM signal with non-uniform key distribution achieves gain of over 0.45 dB compared to uniform 16QAM.