BER analysis and enhanced SIC for photon-counting NOMA in photon-limited OWC

Optical wireless communication (OWC) has emerged as a promising complementary technology to radio frequency systems. Particularly, under photon-limited channel conditions, despite the advantages of single-photon avalanche diodes (SPADs), their performance is limited by dead time and lack of photon-number resolution (PNR), which degrade signal detection in multi-user non-orthogonal multiple access (NOMA) systems. In this paper, we propose what is believed to be a novel posterior-probability-based adjusted threshold-successive interference cancellation (AT-SIC) algorithm to mitigate error propagation and multi-user interference in practical SPAD-based NOMA systems. We develop a comprehensive mathematical framework that incorporates dead time and the lack of PNR effects to derive exact closed-form bit error rate (BER) expressions for both downlink and uplink NOMA over photon-counting channels. The proposed AT-SIC algorithm achieves near-optimal performance with significantly reduced computational complexity. The numerical results validate the accuracy of the analytical model and demonstrate the effectiveness of the proposed method under various channel and power allocation conditions. This study offers a valuable tool for the design and optimization of photon-counting NOMA systems.