Rate-Energy Tradeoff Analysis in RIS-SWIPT Systems With Hardware Impairments and Phase-Based Amplitude Response

This paper investigates the reconfigurable intelligent surface (RIS)-empowered dynamic power splitting designs for simultaneous wireless information and power transfer (SWIPT) systems while adopting various practical hardware issues. Specifically, we adopt the physical size of the RIS and the placement of the RIS plane to phase-align the reflected signals towards the desired direction. The analytical phase shift model for the reflecting elements is presented to characterize an intertwined relationship between amplitude and phase responses, which captures the amplitude variations depending on phase in RIS elements. Furthermore, an additive distortion noise incorporates the residual transceiver hardware impairments (RTHIs). The stringent signal-to-interference-plus-noise ratio requirement is facilitated using both the direct and indirect, i.e., RIS cascaded, links. To made complicated analysis become tractable, we exploit the statistical properties of the effective channel power which follows a Gamma distribution. The tight bounds for the achievable rates and residual energy are derived and the tradeoffs between the achievable rate and residual energy for the time switching and static power splitting designs are characterized. Finally, the numerical results confirm the accuracy of the developed framework and demonstrate the selection of the system parameters.