Distributed Multi‐IRS‐assisted 6G Wireless Networks: Channel Characterization and Performance Analysis

In this chapter, we study the channel modelling and characterization for multi-intelligent reconfigurable surface (IRS)-assisted wireless systems. Specifically, we consider a general system model, called a distributed multi-IRS (DMI)-assisted system, in which the IRSs have different geometric sizes and are distributively deployed to aid wireless communications. For the purposes of comprehensive channel modelling, we assume that wireless channels, associated with different IRSs, are independent but not identically distributed (i.n.i.d.). To statistically characterize such a channel, we propose a mathematical framework based on the moment-matching method to determine the distribution of the end-to-end (e2e) channel fading of the DMI system. We prove that the true distribution of the e2e channel magnitude can be approximated by either Gamma or log-normal distributions. Using the obtained approximate distributions, we derive tight approximate closed-form expressions of the ergodic capacity (EC) and outage probability (OP) of the DMI system. Numerical results show that the DMI system outperforms the conventional non-IRS-assisted system in terms of EC and OP. Furthermore, considering i.n.i.d. fading channels, the co-channel interference and the number of reflecting elements installed on each IRS have a significant impact on the DMI system performance.