Joint Reflection and Power Splitting Optimization for RIS-assisted OAM-SWIPT

Simultaneous wireless information and power transfer (SWIPT) can enhance the spectrum and power efficiencies of wireless communications networks. Line-of-sight (LOS) transmission is a typical SWIPT scenario. However, the strong channel correlation limits the spectrum and energy efficiencies of SWIPT in the LOS channel. Due to the orthogonal wavefronts, orbital angular momentum (OAM) waves can facilitate the SWIPT in LOS channels. With the assistance of the reconfigurable intelligent surface (RIS), both the energy efficiency and capacity can be further improved for the OAM-SWIPT systems. In this paper, we model the RIS-assisted OAM-SWIPT transmission and derive the optimal reflection coefficients and power splitting ratio for it. We first give the system and channel models. Then, we propose the transmission scheme. Based on the transmission scheme, we formulate the capacity and energy harvesting (EH) trade-off problem. We solve the problem by developing an alternating optimization algorithm. Simulations validate the capacity and EH enhancements brought by the RIS for OAM-SWIPT.