O-RIS Assisted NOMA-VLC System: Integrated Positioning and Communications

This work introduces an optimized integrated positioning and communications (IPAC) framework for a non-orthogonal multiple access (NOMA) based visible light communication (VLC) system, enhanced by the assistance of an optical-reconfigurable intelligent surface (O-RIS). First, a closed-form expression is derived for the variance of the positioning estimation error in the considered set up using the Cramer-Rao Lower Bound. Next, we formulate a multi-objective optimization problem aimed at efficiently allocating the O-RIS elements among the communication and target users. In this context, our objective is two-fold: i) to minimize the derived positioning error metric for the target users; ii) to maximize the achievable sum rate for the communication users, while ensuring the quality-of-service requirements. To address this optimization problem, we employ a modified iterative greedy approach and demonstrate significant improvements both in terms of the achievable sum rate and the positioning error. Indicatively, at a meaningful for VLC transmit signal-to-noise ratio of 140 dB, the sum rate increases by over 9.5%, whilst the positioning error reduces by more than 72% compared to non O-RIS systems.