A Sustainable Paradigm of RIS-Aided Cell-Free MIMO for IoT Networks

Abstract

Cell-free (CF) large multiple-input multiple-output (MIMO) with reconfigurable intelligent surfaces (RIS) systems and energy harvesting (EH) have garnered considerable attention in the development of 6G Internet of Things (IoT) networks. To tackle the joint optimization difficult problems, the study first develops a block coordinate alternating optimization to decompose the problem into multiple smaller sub-problems. The proposed alternating optimization algorithm with the Intermediate Value Theorem (IVT), namely AO-IVT, efficiently solves the non-convex task. Simulations verify that the deployment of RISs in CF-IoT scenarios improves the IoT connectivity, and the proposed joint design can further improve this connectivity. For instance, compared to a conventional situation (equal power and random phase shift) for a 5% anticipated rate outage, the suggested method shows a notable improvement of over 83% in terms of minimum target rate (increase from 0.24 to 1.5 nat/s/Hz) in a particular condition.