Optimal Joint Functional Split and Network Function Placement in Virtualized RAN With Splittable Flows

Jointly choosing a functional split of the protocol stack and placement of network functions in a virtualized RAN is critical to efficiently using the access network resources. This problem represents the latest advancement in 5G networks research, which involves the challenge of optimal choosing simultaneously the virtualized functions placement, routing (considering latency and throughput requirements), and resource usage (considering vRAN centralization). In this letter, we solve the problem as a Mixed-Integer Linear Programming (MILP) problem, in which is possible up to two functional splits per base station, there is a generic set of viable next-generation RAN configurations, and vRAN functions can be flexibly positioned in the computing resources. In this formulation, we aim to minimize the computing resources and maximize the centralization of vRAN functions. Our contribution is to consider splittable flows between vRAN functions that improve the vRAN efficiency regarding computing resource usage, network resources usage, and vRAN centralization. We illustrate the benefits of our flexible approach by evaluating its performance by employing functional splits recommended by O-RAN specifications.