Power-Efficient Baseband-Function Placement in Latency-Constrained 5G Metro Access

Mobile operators face the challenge of deploying a flexible network to handle the requirements of emerging use cases. A new Radio Access Network (RAN) for 5G was proposed to provide more dynamic and energy-efficient network management, resource allocation, and service provisioning compared to 4G. The baseband functions, previously performed next to the antennas, are divided into different radio-network units – Radio Unit (RU), Distributed Unit (DU), Centralized Unit (CU) – according to functional splits, which define how to distribute the functions in the various units. The operators encounter the problem of placing these units over the network to minimize their cost and guarantee Quality of Service (QoS). In this work, we propose a Mixed Integer Linear Programming (MILP) formulation that minimizes the DU/CU placement power consumption subject to functional split, latency, and capacity constraints. We also develop a heuristic algorithm with reduced complexity for larger topologies. The results show that optimizing the DU/CU placement using either the MILP or the heuristic algorithms saves power compared to the fully decentralized scenario and guarantees compliance to all requirements. Moreover, despite not achieving the exact MILP result, we show that the heuristic placement reaches a similar power consumption and respects all constraints.