In my new Heavy Reading report, C-RAN & LTE Advanced: The Road to "True 4G" & Beyond, I discuss the emergence of an important new radio access network (RAN) architecture that promises superior performance in coordinated systems such as LTE Advanced.

Standing for both centralized RAN and cloud RAN, the C-RAN concept is based around the idea of a centralized baseband processing pool serving n number of distributed radio access nodes.

Centralized baseband processing is primarily useful because it enables faster coordination of radio resources across distributed access nodes than a classic macro cell architecture. In systems such as Long Term Evolution (LTE) and LTE Advanced (LTE-A), where coordinated processing is important to performance improvements, the capability to manage resources centrally rather than via an external X2 interface between base stations could generate important capacity and end-user performance gains.

Indeed, in the context of hyper-densification of the RAN it is arguable that centralized, collaborative processing to reduce and manage inter-cell interference will become a hard requirement. Looking further ahead toward 5G and to the concept of integrated management of cloud and radio resources, the C-RAN model could become more attractive still.

The basic idea is shown below in this chart from China Mobile:

Figure 1:

Asian operators are -- unquestionably -- driving the pace of C-RAN development. China Mobile in particular is forcing an aggressive pace that combines substantial in-house development with collaborative R&D with specialist and large, integrated vendors. South Korean operators KT and SK Telecom are more reliant on vendor collaboration, but have been able to make rapid progress on base station hoteling (centralized RAN) and can transition this to shared baseband "cloud" model over time. And in Japan NTT Docomo is actively pursuing development of its Super Cell platform on which it will deploy LTE-A.

Over the past year or so, Western operators have started to take a much greater interest in C-RAN because of how the technology dovetails with the push toward LTE-A. Operator R&D departments have been familiar with the concept for a long time, but more recently the focus has shifted to thinking about potential implementation and deployment models. Thus operators such as Deutsche Telekom, Orange, AT&T, and Verizon are evaluating how C-RAN might apply to their networks.

Vendor perspectives on cloud RAN are mixed: All see the potential, but there is not yet a consensus about when and how this technology should be implemented commercially. We think the top six or seven vendors harbor similar perspectives, albeit articulated and marketed a little differently. Huawei, ZTE, and Alcatel-Lucent are more progressive in terms of trials and public communication. Ericsson and NSN are more conservative in their external communication, but are very much engaged in coordinated system development. And Samsung is arguably some way along the line towards a virtualized control-plane with its "smart scheduler" node, which runs on standard IT servers.

There are, of course, substantial challenges to overcome if C-RAN is to be widely deployed commercially (virtualized baseband and better "fronthaul" solutions, for example), but an emerging set of use-cases that scale down to smaller, more approachable deployments look encouraging.

C-RAN is typically thought of as a large-scale urban macro solution, but the concept of pooled baseband serving n number of radio access nodes can apply to a variety of scenarios, such as small cell underlays (using micro RRUs), so-called Super Cells, and outdoor/indoor hotzone systems. These models, identified and defined partly through the NGNM Alliance, could prove an attractive way to introduce and develop C-RAN technology.

— Gabriel Brown, Senior Analyst, Heavy Reading

C-RAN & LTE Advanced: The Road to "True 4G" & Beyond is available now from Heavy Reading. For more information, please contact:

David Williams
Global Director of Sales, Research
Heavy Reading
(858) 829-8612
[email protected]