  The recently proposed open-radio access network (O-RAN) architecture embraces
cloudification and network function virtualization techniques to perform the
base-band function processing by dis-aggregated radio units (RUs), distributed
units (DUs), and centralized units (CUs). This enables the cloud-RAN vision in
full, where mobile network operators (MNOs) could install their own RUs, but
then lease on-demand computational resources for the processing of DU and CU
functions from commonly available open-cloud (O-Cloud) servers via open x-haul
interfaces due to variation of load over the day. This creates a multi-tenant
scenario where multiple MNOs share networking as well as computational
resources. In this paper, we propose a framework that dynamically allocates
x-haul and DU/CU resources in a multi-tenant O-RAN ecosystem with min-max
fairness guarantees. This framework ensures that a maximum number of RUs get
sufficient resources while minimizing the OPEX for their MNOs. Moreover, in
order to provide an access network architecture capable of sustaining
low-latency and high capacity between RUs and edge-computing devices, we
consider time-wavelength division multiplexed (TWDM) passive optical network
(PON)-based x-haul interfaces where the PON virtualization technique is used to
provide a direct optical connection between end-points. This creates a virtual
mesh interconnection among all the nodes such that the RUs can be connected to
the Edge-Clouds at macro-cell RU locations as well as to the O-Cloud servers at
the central office locations. Furthermore, we analyze the system performance
with our proposed framework and show that MNOs can operate with a better
cost-efficiency than baseline greedy resource allocation with uniform
cost-sharing.
