Cell-Free Processing for 5G Massive MIMO Deployments: Sleep Modes and User Stream Management

Cell-free massive MIMO (CF-M-MIMO) is heralded as a technological pillar for 6G mobile networks, outperforming the classical cellular-based M-MIMO architecture of 5G by bringing infrastructure closer to end users and leveraging interference cancellation through network-wide joint processing. However, the major drawback is the significant expense required to deploy and maintain numerous infrastructure sites and connect them to a central processing unit (CPU) for baseband processing. This paper proposes utilizing CF-M-MIMO processing atop existing micro/macrocellular deployments in current 5G networks. It suggests connecting all base stations (BSs) to a CPU via fronthaul links to enable joint processing of user equipment (UE) without the costly deployment of many scattered access points (APs). By jointly managing all transmit/receive points (TRPs) in the network, a novel switch on/off strategy is derived to maximize energy efficiency by exploiting the sleep mode capabilities of current baseband/RF hardware, adapting to changes in UE behavior and operator requirements. Additionally, the paper considers multiantenna user terminals, common in current 5G setups, and proposes a technique to manage the number of streams directed to each UE, balancing multiplexing gains and increased pilot contamination.