  In this paper, a novel intelligent reflecting surface (IRS)-assisted wireless
powered communication network (WPCN) architecture is proposed for
power-constrained Internet-of-Things (IoT) smart devices, where IRS is
exploited to improve the performance of WPCN under imperfect channel state
information (CSI). We formulate a hybrid access point (HAP) transmit energy
minimization problem by jointly optimizing time allocation, HAP energy
beamforming, receiving beamforming, user transmit power allocation, IRS energy
reflection coefficient and information reflection coefficient under the
imperfect CSI and non-linear energy harvesting model. On account of the high
coupling of optimization variables, the formulated problem is a non-convex
optimization problem that is difficult to solve directly. To address the
above-mentioned challenging problem, alternating optimization (AO) technique is
applied to decouple the optimization variables to solve the problem.
Specifically, through AO, time allocation, HAP energy beamforming, receiving
beamforming, user transmit power allocation, IRS energy reflection coefficient
and information reflection coefficient are divided into three sub-problems to
be solved alternately. The difference-of-convex (DC) programming is used to
solve the non-convex rank-one constraint in solving IRS energy reflection
coefficient and information reflection coefficient. Numerical simulations
verify the superiority of the proposed optimization algorithm in decreasing HAP
transmit energy compared with other benchmark schemes.
