The three fundamental stages to Cloud RAN are centralization of the current baseband equipment to clusters of sectors, splitting of processing between COTS equipment and specialized chips resulting in additional processing in the RRH and the BBU being made virtual, and total network virtualization.
Each of these stages has costs and benefits. Centralization of current baseband equipment can be done without major equipment changes. Clustering of cell sectors will enable more timely and expedient decision making and reduce operational costs, but it has limited efficiency benefits on the overall network.
In the second phase, most of the call processing that currently takes place on specialized chips can be moved off the BBU and put onto standard server style equipment. At the same time, some radio functions (Layer 1) can move into the RRHs from the BBU, enabling a lower-speed, higher-latency link between the core and the site. This design may allow non-dedicated links to exist, which will reduce cost and decrease installation issues.
The final stage of centralization virtualizes everything at the site except the digital to RF converters in the data center — from signal processing to analytic applications.
I expect phase two will be most common deployment scenario on a wide scale, operating as a sort of pseudo Cloud RAN. The control plane and the data plane from the baseband will be in some way separated, but it will have more latency than true Cloud RAN. Some of the intelligence will be out at the site, like today, and some of the intelligence will be brought into the centralized cloud.
There will also likely be semi-centralized sites that serve clusters of cells where some processing functions will be semi-centrally located. The equipment that remains out at the site will really be there for power management in both pseudo and full Cloud RAN.
It is interesting to note that 5G will be the first wireless technology designed with targets for energy efficiency, and the Cloud RAN network architecture will reflect that need.
Right now, the wireless industry is working out how to move the Layer 2 and Layer 3 radio functions to the cloud servers that sit further back in the core.
Morgan Kurk serves as the senior vice president and Wireless segment leader at CommScope.