Ergodic Capacity of Passive and Active IRS-Aided MIMO Systems

The intelligent reflecting surface (IRS) has emerged as a promising solution to address the ever-increasing demand for reliable and high-speed communication in next-generation wireless communication systems. In this article, the ergodic capacity (EC) of IRS-aided multiple-input-multiple-output (MIMO) wireless systems is investigated. Analytical approximations for the ECs of active and passive IRS-aided MIMO systems are derived. As an application of the established theoretical approximations, an optimization problem is formulated to maximize the system’s energy efficiency (EE) by determining the optimal number of IRS elements and the optimal transmission power. It is shown that this problem can be readily solved using an alternative optimization technique applicable to both active and passive IRS configurations. Numerical results demonstrate the accuracy of the EC approximations. The results also clarify the impact of operational and environmental parameters on the system’s EC.