C-RAN is one of the more misunderstood acronyms in wireless as it is used to describe two different, but related architectures. C-RAN can describe cloud RAN or centralized RAN.
RAN stands for radio access network, the equipment that connects to cellular antennas, processes the signal and sends it to the core network. As the demand for connectivity has exploded, mobile operators have looked for ways to minimize the footprint and cost of their equipment. This has led to the move to centralize parts of the RAN.
Specifically, the baseband processing unit (BBU) is the part of the RAN that carriers may move to a central location from which multiple remote radio heads can be served. To date, carriers have been reluctant to share processing equipment, but one carrier may use the same equipment or equipment room to service more than one set of remote radio heads.
Fiber is typically used to connect BBUs to remote radio heads, and this connection is often referred to as “fronthaul.” In some architectures, the BBUs are linked and can share information, and in others they are simply located in the same building. Co-location of BBUs is increasingly popular for carriers that are deploying distributed antenna systems. Centralized DAS, or C-DAS, is seen by some analysts as a form of C-RAN.
“Today in DAS, the majority of the DAS has to have a head-end room inside the building, which takes up a lot of room and it’s really expensive if the building is in a dense metro area like Manhattan or Chicago downtown or wherever,” said analyst Earl Lum of EJL Wireless Research. “If you can move the head-end room away to some cheaper part of the city and run fiber back to each of the buildings that you want to connect, and have all of the signaling equipment from the operators in that one building, that’s essentially a baseband hotel or a form of C-RAN.”
Centralized RAN and centralized DAS both describe architectures in which the mobile operator maintains direct control and ownership of the baseband equipment. Cloud RAN implies this equipment is owned by another service provider, or the baseband processing is handled in software run on a generic “white box” server.
”From a network point of view cloud and centralized RAN are the same in terms of requirements (fronthaul for instance) and work in the same way,” said analyst Monica Paolini of Senza Fili Consulting. “The difference is in the ownership of equipment.”
Paolini foresees more uptake for centralized RAN than for cloud-based RAN in the months ahead.
“I think it is unlikely that operators would want to give control to a third party for the RAN baseband – ownership maybe, but not control,” Paolini said.
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