IRS-aided SWIPT systems with power splitting and artificial noise

Intelligent reflecting surface (IRS) is regarded as a promising technology because it can achieve higher passive beamforming gain. In particular, the IRS assisted simultaneous wireless information and power transfer (SWIPT) system can make the information decoding receivers (IDRs) have a higher signal-to-noise ratio (SNR), and the energy harvesting receivers (EHRs) have the guarantee of minimum harvested energy threshold. Motivated by the above, in this paper, we use the power splitting (PS) at the user and introduce artificial noise (AN) into the access point (AP), so that the user in system can harvest energy and decode information simultaneously, further improve the security of user. We jointly optimize the beamforming matrix at AP, the reflection phase shift at IRS and the PS ratio, in order to maximize the user's achievable secrecy rate, subject to the user's minimum harvested energy threshold and AP's transmission power. Due to the introduction of PS ratio, the coupling between variables is increased, and the complexity of the problem is significantly increased. Furthermore, the problem is non-convex, so we propose an efficient algorithm based on Taylor Formula, semi-definite relaxation (SDR) and alternating optimization (AO) to get the solution. Numerical results show that the proposed IRS-SWIPT system with PS and AN achieves significant performance improvement compared with other benchmark scheme.