STAR-RIS Assisted Hybrid Far- and Near-Field SWIPT

A simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted hybrid far- and near-field (HFNF) simultaneous wireless information and power transfer (SWIPT) framework is proposed, where the energy users are located in the near-field region while the information users are located in the far-field region. The weighted harvested power of near-field energy users is maximized by jointly optimizing the active beamforming of base station (BS) and the passive beamforming of STAR-RIS, subject to the communication quality of far-field communication users. To solve this non-convex problem, a two-layer penalty-based algorithm is proposed. For the inner layer, the concave-convex procedure (CCCP) technique is invoked to address non-convex difference-of-convex (DC) expressions. For the outer layer, the penalized approach is used to guarantee the rank-1 solution. Numerical results show that: 1) the proposed algorithm achieves significant energy harvesting enhancement; 2) the STAR-RIS outperforms both reflecting-only and transmitting-only RIS; and 3) in contrast to far-field beamformers, near-field beamformers enable energy to be concentrated directly around energy users, thereby improving energy harvesting performance.