Virtualized Cloud Radio Access Network for 5G Transport

Current radio access networks (RANs) need to evolve to handle diverse service requirements coming from the growing number of connected devices and increasing data rates for the upcoming 5G era. Incremental improvements on traditional distributed RANs cannot satisfy these requirements, so the novel and disruptive concept of a cloud RAN (CRAN) has been proposed to decouple digital units (DUs) and radio units (RUs) of base stations (BSs), and centralize DUs into a central office, where virtualization and cloud computing technologies are leveraged to move DUs into the cloud. However, separating RUs and DUs requires low-latency and high-bandwidth connectivity links, called "fronthaul," as opposed to traditional backhaul links. Hence, design of the 5G transport network, that is, the part of the network that carries mobile data traffic between BSs and the core network and data centers, is key to meet the new 5G mobile service requirements and effectively transport the fronthaul traffic. Today, consensus is yet to be achieved on how the fronthaul traffic will be transported between RUs and DUs, and how virtualization of network resources will occur from a radio network segment to the centralized baseband processing units. In this article, we present a new 5G architecture, called virtualized cloud radio access network (V-CRAN), moving toward a cell-less 5G network architecture. We leverage the concept of a virtualized BS (V-BS) that can be optimally formed by exploiting several enabling technologies such as software defined radio (SDR) and coordinated multipoint (CoMP) transmission/reception. A V-BS can be formed on a per-cell basis or per-user basis by allocating virtualized resources on demand. For the fronthaul solution, our approach exploits the passive optical network (PON), where a wavelength can be dynamically assigned and shared to form a virtualized passive optical network (VPON). Several use cases of the V-CRAN are presented to show how network architecture evolution can enhance system throughput, energy efficiency, and mobility management.