How Will Cell-Free Systems Be Deployed?

The cell-free system has recently been investigated as a way to achieve uniform communication performance over the 5G cellular system. However, deploying cell-free systems in commercial mobile networks is a challenging task. One major bottleneck is the need to install access points (APs) on a large scale. APs will be gradually introduced into the mobile system and will need to be compatible with the existing cellular system. As a solution, we propose a transitional system architecture for beyond 5G, where the cell-free system and the legacy cellular system coexist. We call the proposed system a cell-free and legacy coexistence network (CLCN). In this article, the discussion focuses on technical challenges, design considerations, and practical CLCN system layouts. Simulations confirm that the gradual installation of APs in legacy cellular systems can reduce the performance gap between users and improve the average spectral efficiency of the system. The results show that CLCN can provide users uniformly high performance, which has long been a challenge for cellular systems.