  The high reflect beamforming gain of the intelligent reflecting surface (IRS)
makes it appealing not only for wireless information transmission but also for
wireless power transfer. In this letter, we consider an IRS-assisted wireless
powered communication network, where a base station (BS) transmits energy to
multiple users grouped into multiple clusters in the downlink, and the
clustered users transmit information to the BS in the manner of hybrid
non-orthogonal multiple access and time division multiple access in the uplink.
We investigate optimizing the reflect beamforming of the IRS and the time
allocation among the BS's power transfer and different user clusters'
information transmission to maximize the throughput of the network, and we
propose an efficient algorithm based on the block coordinate ascent,
semidefinite relaxation, and sequential rank-one constraint relaxation
techniques to solve the resultant problem. Simulation results have verified the
effectiveness of the proposed algorithm and have shown the impact of user
clustering setup on the throughput performance of the network.
