  This paper studies an intelligent reflecting surface (IRS)-assisted multiuser
multiple-input single-output (MISO) simultaneous wireless information and power
transfer (SWIPT) system. In this system, a multi-antenna access point (AP) uses
transmit beamforming to send both information and energy signals to a set of
receivers each for information decoding (ID) or energy harvesting (EH), and a
dedicatedly deployed IRS properly controls its reflecting phase shifts to form
passive reflection beams for facilitating both ID and EH at receivers. Under
this setup, we jointly optimize the (active) information and energy transmit
beamforming at the AP together with the (passive) reflective beamforming at the
IRS, to maximize the minimum power received at all EH receivers, subject to
individual signal-to-interference-plus-noise ratio (SINR) constraints at ID
receivers, and the maximum transmit power constraint at the AP. Although the
formulated SINR-constrained min-energy maximization problem is highly
non-convex, we present an efficient algorithm to obtain a high-quality solution
by using the techniques of alternating optimization and semi-definite
relaxation (SDR). Numerical results show that the proposed IRS-assisted SWIPT
system with both information and energy signals achieves significant
performance gains over benchmark schemes without IRS deployed and/or without
dedicated energy signals used.
