Resource Allocation for RIS-Assisted Wireless Powered Sensing and Communication

Abstract

Reconfigurable intelligent surface (RIS)-assisted wireless-powered communication networks (WPCNs) introduce a new degree of freedom: the same passive beamforming array can concentrate the downlink energy toward harvesting devices and simultaneously shape the uplink interference environment. In this paper, we study a system where the base station (BS) waveform serves the dual role of wireless energy transfer (WET) and passive target sensing. Using the position error bound (PEB) derived from the equivalent Fisher information matrix (EFIM) as the sensing quality metric, we formulate a joint resource allocation problem that maximizes weighted uplink sum-rate subject to a PEB constraint, energy-causality, block-time sharing, and unit-modulus RIS phase constraints. Focusing on the practically important WET-only sensing case, we show that the problem separates into four tractable subproblems and propose a block coordinate descent (BCD) algorithm: (i) closed-form water-filling for WIT time-power allocation, (ii) semidefinite relaxation (SDR) with Dinkelbach iterations for per-slot WIT-RIS beamforming, (iii) golden-section search for the optimal WET duration, and (iv) a convex SDP for WET-RIS optimization under a PEB constraint. The BCD iterates converge monotonically. Simulations confirm a fundamental rate–sensing tradeoff and demonstrate significant gains from joint RIS-assisted optimization.