Placement of 5G RAN Slices in Multi-tier O-RAN 5G Networks with Flexible Functional Splits

The network slicing concept has gained much attention with the development of software-defined network and network function virtualization technologies, enabling logically isolated networks for different purposes in the same network infrastructure. The virtualization of network functions enables the functional split of radio access network functions to fulfill different 5G radio access network requirements. Functional split can be expressed as deciding the distribution of radio access network functionalities between the radio unit placed at the edge of the network, the distributed unit placed close to the users, and the central unit placed centrally. The open radio access network concept is utilized to achieve a virtualized, interoperable radio access network among multiple vendors. In this work, we considered the placement of radio access network slices in a multi-tier 5G open radio access network architecture and formulated the problem as a Mixed-Integer Quadratically Constrained Programming, considering different functional split options for each network slice separately. Our results showed that flexible functional split utilizes physical network resources and satisfies different network slice requirements better than fixed functional split options.