Secure Transmission for Intelligent Reflecting Surface Assisted MISO Systems: Achievable Rate and Optimal Time Allocation

In this paper, we study the Physical Layer Security (PLS) problems in intelligent reflecting surface (IRS) multiple-input singleoutput (MISO) communication systems. A novel transmission scheme aimming to minimize the system energy consumption is proposed by jointly optimizing the phase shift matrix at the IRS and the beamforming vectors at the base station (BS). Furthermore, the maximum secrecy capacity is obtained by designing the time allocation between channel training and information transmission. Theory analysis and numerical results validate that the time ratio value depends on the signal-to-noise ratio (SNR) at the intended receiver.