Simultaneous Information and Power Transfer with RISs

Simultaneous wireless information and power transfer (SWIPT) has been recently proposed as a means to prolong the battery lifetime of low-power devices in next-generation networks, such as Internet-of-Things (IoT) terminals. At the same time, dynamic spectrum sharing is widely adopted recently by network operators and verticals, in order to improve spectrum utilization and accelerate network deployment at low cost. The emerging reconfigurable intelligent surface (RIS) technology can serve as an enabler of both aforementioned paradigms. In this chapter, we demonstrate this feature by considering an RIS-aided primary SWIPT system that is collocated with a secondary communication system under a spectrum underlay regime and focusing on the Joint Transmit/Reflect Beamforming and Power Splitting (JTRBPS) optimization problem in the context of transmit sum-energy minimization. Two penalty-based iterative optimization algorithms are presented: an alternating minimization algorithm that involves semi-definite relaxation in JTBPS design and successive convex approximation in RB optimization, and a block coordinate descent algorithm that employs the Riemannian conjugate gradient algorithm in RB updates. Numerical simulations highlight the performance gains of the proposed strategies over benchmarks, corroborate RIS’s benefits, and provide valuable insights.