IRS Deployment in Wireless Powered Communication Network with Nonlinear Energy Harvesting

In this paper, we have studied a wireless powered communication network with practically nonlinear energy harvesting (EH). An intelligent reflecting surface (IRS) has been deployed to assist both energy transfer and data transmissions. In particular, we assume there are two users with diverse communication types and the whole operation period is divided to two slots. In the first slot, one user behaves as downlink device requesting data from the access point (AP), while the other user acts as a rechargeable device collecting wireless energy from AP for harvesting its energy buffer. In the second slot, the rechargeable user will deploy harvested energy for supporting the data uploading to the AP. The IRS is applied for intelligently modifying the radio environment in both slots. Taking nonlinear EH model into account, we formulate a joint IRS beamforming and service slot optimization problem maximizing the uplink throughput with a given downlink throughput constraint. Subsequently, to deal with the design difficulty in nonlinear EH, we propose a variable substitution based problem reformulation and construct a series of convex approximations for iteratively approaching a suboptimal of the considered problem. Finally, via simulations, we validate the convergence of our proposed algorithm and illustrate the benefits of IRS beamforming in assisting wireless powered communication communication.