Channel Gain Modeling Through an Intelligent Reflecting Surface

Recently, Intelligent Reflecting Surfaces (IRSs) with controllable substructures have attracted attention due to their ability to manipulate electromagnetic wave reflections. A key benefit of IRSs is their capacity to enhance signal gain at the receiver. In this article, we propose a general channel gain model suitable for various wireless communication setups. We start with the gain models for the basic Single-Input Single-Output (SISO) case, progressing to the general model in the Multiple-Input Multiple-Output (MIMO) scenario. The models simplify for specific parameter choices. Also, we determine the optimal phase of IRS atoms for maximizing gain.