Next-generation O-RAN Edge: Energy-aware Joint Placement and Migration of CNF

The evolution of cellular mobile networks to Open Radio Access Network (O-RAN) architecture represents a paradigm shift in the deployment, management, and optimization of cellular infrastructure. This study examines the joint optimization of CNF placement and migration in the O-RAN edge cloud, considering both the conventional single-CU association model and a future many-to-many DU-CU connectivity association. We formulate the optimization problem as an Integer Linear Programming (ILP) model to minimize total energy consumption while enforcing F1 interface delay bounds and server-level resource constraints within a fat-tree data center. We also design a k-means-based heuristic. The evaluation shows that the multi-CU architecture offers superior energy performance, reducing consumption by 6.2% compared to the single-CU baseline in joint optimization scenarios. In addition, the proposed heuristic achieves near-optimal performance, with an average total energy gap of 8.6% for the single-CU model and 11.4% for the multi-CU model over 24 hours, effectively approximating ILP solutions while reducing computational complexity.