RIS-assisted Cell-Free MIMO with Dynamic Arrivals and Departures of Users: A Novel Network Stability Approach

TL;DR

This paper investigates RIS-assisted cell-free MIMO systems with dynamic user mobility, proposing a stability-focused optimization framework that guarantees network stability and stabilizes a significant portion of the stability region.

Contribution

It introduces a novel phase shift optimization framework for RIS-assisted cell-free MIMO with dynamic users, ensuring network stability and providing theoretical and numerical validation.

Findings

Framework stabilizes the network when possible

Guarantees stabilization of over 78.5% of the stability region

Numerical results support theoretical stability claims

Abstract

Reconfigurable Intelligent Surfaces (RIS) have recently emerged as a hot research topic, being widely advocated as a candidate technology for next generation wireless communications. These surfaces passively alter the behavior of propagation environments enhancing the performance of wireless communication systems. In this paper, we study the use of RIS in cell-free multiple-input multiple-output (MIMO) setting where distributed service antennas, called Access Points (APs), simultaneously serve the users in the network. While most existing works focus on the physical layer improvements RIS carry, less attention has been paid to the impact of dynamic arrivals and departures of the users. In such a case, ensuring the stability of the network is the main goal. For that, we propose an optimization framework of the phase shifts, for which we derived a low-complexity solution. We then provide a theoretical analysis of the network stability and show that our framework stabilizes the network whenever it is possible. We also prove that a low complexity solution of our framework stabilizes a guaranteed fraction (higher than 78.5%) of the stability region. We provide also numerical results that corroborate the theoretical claims.