Security-enhanced layered coding multiple access for heterogeneous QoS requirements in IMDD-PONs.

A secure layered coding multiple access (LCMA) scheme based on power division multiplexing (PDM) is proposed for low-cost intensity modulation direct detection (IMDD) passive optical networks (PONs). The proposed PDM-LCMA scheme achieves layered modulation by deconstructing heterogeneous user data into a shared layer and a dedicated layer, enabling flexible adjustment of the signal structure based on differentiated quality of service (QoS) requirements. Experimental results demonstrate that the LCMA-PON signal exhibits high robustness over a 25 km standard single-mode fiber (SSMF) transmission at a data rate of 18.23 Gb/s. Compared with conventional power-domain non-orthogonal multiple access (NOMA), the average receiver sensitivity of the two users is improved by approximately 3.5 dB and 2 dB at γ=2 and γ=3, respectively, at the 3.8 × 10-3 hard-decision forward error correction (HD-FEC) threshold; even under high heterogeneity (γ=5), LCMA maintains a performance advantage of approximately 0.75 dB. Specifically, robust demodulation is still achieved in extreme scenarios where NOMA fails, given nearly identical QoS requirements. Furthermore, it is demonstrated that the introduced chaotic-driven dual-layer subcarrier scrambling mechanism enhances physical-layer security to a certain extent without degrading transmission performance, offering potential application value and technical support for the evolution of future PON systems that must coexist with high-capacity, service-flexible, and high-security requirements.