Ergodic Capacity and Outage Probability Analysis of Intelligent Reflecting Surface Aided Communication Systems

This paper investigates the ergodic capacity and outage probability performance of a single-input single-output (SISO) communication system aided by an intelligent reflecting surface (IRS) in mixed fading channels, where Rayleigh fading from the base station (BS) to the user and Rician fading from the BS to IRS as well as the RIS to receiver are all considered. Firstly, the approximate probability density function (PDF) of the cascaded channel gain from the BS to user via the IRS is derived by means of the moment matching method, which is more accurate than the existing PDF based on the central limit theorem (CLT). Then, with the obtained PDF, an approximation of ergodic capacity of the system is deduced by using the Taylor series expansion, also the approximate expression of outage probability is derived. The derived ergodic capacity has more accuracy than the existing one based on the Jensen's inequality. Moreover, the obtained outage probability has more accuracy than the existing one with CLT as well. Simulation results verify the effectiveness of the derived theoretical expressions, namely, the derived PDF and ergodic capacity as well as the outage probability can match the corresponding simulation better than the existing ones. Especially for small number of reflecting elements and/or large SNR, the accuracy is more obvious.