  The performance of Simultaneous Wireless Information and Power Transfer
(SWIPT) is mainly constrained by the received Radio-Frequency (RF) signal
strength. To tackle this problem, we introduce an Intelligent Reflecting
Surface (IRS) to compensate the propagation loss and boost the transmission
efficiency. This paper proposes a novel IRS-aided SWIPT system where a
multi-carrier multi-antenna Access Point (AP) transmits information and power
simultaneously, with the assist of an IRS, to a single-antenna User Equipment
(UE) employing practical receiving schemes. Considering harvester nonlinearity,
we characterize the achievable Rate-Energy (R-E) region through a joint
optimization of waveform, active and passive beamforming based on the Channel
State Information at the Transmitter (CSIT). This problem is solved by the
Block Coordinate Descent (BCD) method, where we obtain the active precoder in
closed form, the passive beamforming by the Successive Convex Approximation
(SCA) approach, and the waveform amplitude by the Geometric Programming (GP)
technique. To facilitate practical implementation, we also propose a
low-complexity design based on closed-form adaptive waveform schemes.
Simulation results demonstrate the proposed algorithms bring considerable R-E
gains with robustness to CSIT inaccuracy and finite IRS states, and emphasize
the importance of modeling harvester nonlinearity in the IRS-aided SWIPT
design.
