Outage Probability Analysis and Minimization in Intelligent Reflecting Surface-Assisted MISO Systems

Intelligent reflecting surface (IRS) is gradually being recognized as a promising technology for improving spectral and energy efficiency of wireless systems. In this letter, we study an IRS-assisted multiple-input single-output (MISO) system where a base station (BS) with multiple antennas arranged in a uniform rectangular array (URA) serves a single-antenna user with the help of an IRS with multiple elements arranged in a URA. We consider a Rician fading model, where the non-line of sight (NLoS) components vary slowly and the line of sight (LoS) components do not change. To reduce costs for channel estimation and phase adjustment, we adopt fixed maximum-ratio transmission (MRT) at the BS, fixed phase shifts at the IRS and constant rate transmission. First, we obtain the expression of the outage probability. Then, we minimize the outage probability by optimizing the phase shifts of the IRS. Finally, we obtain the expression of the asymptotically optimal outage probability in the high signal-to-noise ratio (SNR) regime. We also characterize the impacts of several key system parameters on the optimal outage probability to reveal important design insights.