In this paper, we address two major issues regarding architectural migration of radio access network (RAN). Firstly, an overview and explicit interpretation of how different enabling technologies over generations are brought up and coordinated for migration from a distributed, to a centralized, and then to a virtualized RAN for 5G and beyond cellular; and secondly, the proof-of-concept (PoC) evaluation to understand the feasibility of these enabling technologies, are addressed. In doing so, we first give an overview of major enabling technologies and discuss their impact on RAN migration. We then evaluate the PoC of major enabling technologies proposed mainly for 5G CRAN, namely functional split options, TDM-PON systems, and virtualization techniques using a mobile CORD based prototype in LTE systems with ideal fronthauls. PoC experimental results with split options 2 and 5 are presented and compared using TCP and UDP traffic. Experimentally, it is shown that the throughput improvement is significant for TCP as compared to UDP with virtualized BBUs, which are about 30%-40% and 40%-45% higher in mean throughputs respectively in downlink and uplink with split 5 than that with split 2. Finally, we point out the major experimental limitations of PoC and future research directions.
