Integration of Reconfigurable Intelligent Surfaces (RISs) in D-MIMO Networks for 6G

Abstract

Abstract The distributed MIMO (D-MIMO) systems are one of the potential technique to densify the ever-evolving 5G networks and beyond (6G) technologies. However, the scalability of D-MIMO systems to large-scale networks in a practical scenario is very challenging. The aim towards sustainability and other economic challenges in the upcoming 6G networks resulted in the exploitation of cost-effective and energyefficient dynamic access point (AP) clustering techniques and use of densification enablers for providing high performance and reliability for its users. Reconfigurable intelligent surface (RIS) is a technology that is well known for its low-cost, rapid deployability, and energy-efficient properties, which can add extra diversity to the spatial domain if deployed in a network. This work explores the benefits gained by integrating RIS into a D-MIMO system in terms of major KPIs of focus, i.e., energy efficiency and service coverage of the system. In this study, we focus an indoor use case with a high UE density where the service coverage is very scarce due to high obstacle density that results in huge pathloss and shadowing. Towards the end, we propose dynamic user-centric AP clustering and RIS placement techniques adapted for addressing such high UE demands in an indoor D-MIMO system. Here, for configuring RIS phase-shifts we use an alternating optimization method which is a sub-optimal solution to lower the computational complexity. Finally, we compare an RIS-assisted D-MIMO system with a conventional D-MIMO system to prove that the integration of RISs in D-MIMO system is a potential approach to enhance the service coverage and energy efficiency, while satisfying the scalability requirement in 5G and beyond (6G) technologies.