Active RIS-Enhanced Wireless Powered Communication Network in Hybrid Near- and Far-Field

In this paper, an active reconfigurable intelligent surface (ARIS)-enhanced wireless powered communication network (WPCN) in hybrid near- and far-field for Internet of Things (IoT) system is investigated. In detail, a sum throughput maximization optimization problem bounded by ARIS power expenditure constraints, transmission time slots constraints, and ARIS reflecting amplitude constraints is proposed by the joint design of the time slots and ARIS reflecting coefficients. To address the intractable non-convex optimization problem caused by the coupling of variables, the alternating optimization (AO) algorithm is applied to disassemble the problem into two sub-problems, in which the semi-definite programming (SDP) relaxation algorithm is explored to obtain the dedicated transmission time for each slot and the reflecting factors of ARIS in energy transfer period while the reflecting amplitudes of ARIS in information transfer slots are derived by solving a sequence of successive convex approximation (SCA) problems based on the optimal closed-form phase shifts. Finally, the simulation results demonstrate that the inclusion of distance domain in near-field channel enables it exceedingly suitable for energy transfer and unveil the effective role of ARIS in promoting system performance in hybrid near- and far-field.