Rate-Splitting Multiple Access for Spatial Non-Stationary Extremely Large-Scale Antenna Array

The extremely large-scale antenna array (ELAA) is recognized as a promising technology for the sixth-generation wireless communication systems. Besides the extended near-field region, the enlarged aperture introduces spatial non-stationarity, which is characterized by the visibility region (VR). When all the antenna elements in the ELAA are used indiscriminately, the spatial non-stationarity can result in the user receiving signals radiated by partial antenna elements, which cannot be ignored in designing an effective multiple access scheme. To address this, a rate-splitting multiple access (RSMA) scheme is designed for the ELAA with spatial non-stationarity in this paper, where antenna selection and RSMA are jointly exploited to alleviate the effect of the spatial non-stationarity. Then, an optimization problem (OP) is formulated to maximize the weighted sum-rate (WSR) by jointly optimizing user grouping, digital precoding, and the rate-splitting vector. To solve the formulated OP, antenna selection is initially performed, followed by the user grouping algorithm. Subsequently, given the user grouping result, the conditional optimal solutions are obtained by using the semidefinite relaxation method. Simulation results demonstrate that the proposed scheme achieves a higher WSR than the baseline schemes.