Latency-Aware Near-Real-Time RIC Deployment in User-Centric RAN With Cell-Free Massive MIMO: A Telecom Operator Perspective

The next-generation mobile networks will be developed based on virtualized and distributed radio access network (RAN), necessitating cost-effective and flexible deployment solutions to meet latency requirements without incurring excessive costs. The O-RAN alliance has defined the architecture for these future networks, where the RAN controller is split into the Non-Real-Time RAN Intelligent Controller (Non-RT RIC) and the Near-Real-Time RAN Intelligent Controller (Near-RT RIC). These controllers, virtualized and deployable on general-purpose processors at edge nodes, can be distributed across the entire geographical area covered by a mobile network. This is particularly vital for user-centric RAN with cell-free massive MIMO (CF-mMIMO). The inherent high control traffic overload, due to not only continuous access point (AP) cluster updates but also from extensive controls for the user-centric RAN, runs the risk of overloading the transport network. Therefore, controller deployment optimization becomes essential. Additionally, in scenarios involving critical applications, latency is a key factor to consider, adding to the optimization challenges. This paper addresses the Near-RT RIC deployment problem, considering latency requirements and transport network limitations. Mixed integer linear programming (MILP) is utilized to solve the deployment issue. The solution's effectiveness is validated against different network topologies and design parameters.