Robust WSSR Maximization for Holographic RIS-aided RSMA Near-Field Systems

This work investigates the performance of rate splitting multiple access (RSMA) in a holographic reconfigurable intelligent surface (HRIS)-aided near-field (NF) driven downlink secure communication system under imperfect channel state information (iCSI) in the presence of an eavesdropper (Eve). We formulate a weighted sum secrecy rate (WSSR) while ensuring a minimum quality of service (QoS) at each node under the available resource constraints, such as the total power budget at the base station (BS). Since the optimization problem is nonconvex due to the coupling of the variables, we propose an iterative algorithm based on alternating optimization (AO) that jointly optimizes transmit beamforming at BS and phase shift at HRIS. Numerical results are shown to validate the effectiveness and convergence of the proposed algorithm. Furthermore, we also discuss the impact of the key system parameters, such as HRIS reflecting elements, minimum QoS constraint, transmit power budget, and number of users. The dominance of RSMA over conventional multiple-access technologies such as non-orthogonal multiple access (NOMA) and space division multiple access (SDMA) is also demonstrated.