Holographic Active RIS-aided for Robust Secure Uplink Near-Field NOMA Networks

This article proposes a holographic active reconfigurable intelligent surface (HARIS)-aided near-field (NF)-driven uplink non-orthogonal multiple access (NOMA) secure communication system under imperfect channel state information (iCSI) in the presence of an eavesdropper (Eve). To ensure efficient resource utilization, a sum secrecy rate (SSR) maximization problem is formulated by jointly optimizing the combined vector at the base station (BS), the power allocation for each uplink user, and the HARIS phase profile under strict quality of service (QoS) requirements and limited power budgets at both the uplink users and HARIS. Due to the non-convex nature of the problem, an alternating optimization (AO)-based algorithm is proposed, which uses semidefinite programming (SDP), convex upper bound approximation, and semidefinite relaxation (SDR) techniques to optimize all variables iteratively. Extensive simulations validate the performance and convergence of the proposed algorithm. In addition, the effects of system parameters, such as the number of HARIS elements, minimum QoS per user, maximum BS receive power, and the HARIS amplification factor, are investigated.