WHAT ARE THE C-RAN CHALLENGES?
Mobile operators heavily rely on low-energy, flexible traffic management and reliable architecture*. A Cloud-RAN (C-RAN) has the advantage of centralizing task-processing intelligence for multiple radio stations in one single node. This main node may then process cells interference which is the number one issue for operators and users in the quest for quality of service optimization.
Centralized processing also allows increased capacity and enhanced productivity in network management, in a prediction-allowing way (the use of a main cluster** optimizes interference prevention since it gathers information for all transmission bridges). C-RAN has attracted some manufacturers’ interest, but not all of them are ready for this new kind of deployment and the issue is tackled in many different ways:
– Some manufacturers limit their solution to radio station aggregation, maintaining a CPRI (Common Public Radio Interface) link with RRH (Remote Radio Head) radio heads to achieve a C-RAN-like architecture. Even with relatively old hardware, it is possible to aggregate and interconnect it into a centralized processing unit. Within this approach, cells only report interference levels they detect and interact with other cells to limit interferences.
– Other manufacturers, more recent, small-sized and freshly started, have invented a completely new architecture, with a main controller common to multiple cells and with a high processing capacity. Their product transmits signals between the C-RAN and radio parts over Ethernet direct links (CPRI links operate with specific protocols).
It all depends on what type of deployment is targeted. If it’s for a football stadium or a high-density area, it is easy to deploy specific switches and optical fibers. However, if the C-RAN deployment is planned for a whole city without a fiber backbone, it’s better to use the existing Ethernet network for an optimized deployment. Manufacturers’ strategies will depend on their business strategies, if they target small areas with high-density or wider rural areas. The pre-existing landline network’s performances and availability in cities are a key point for C-RAN deployment.
To build a 3GPP compliant C-RAN architecture, it’s possible to separate a radio station into an RRH architecture and a remote processing unit. The bottom part of the station’s tower can be clustered somewhere else in the city and linked to the tower with an Ethernet link. Other manufacturers have considered a different way to separate the station for more flexibility on datacenter-antenna links. Each imagines its own way of separation but has to be equipped with the appropriate testing suits and tools adapted to the chosen mode: CPRI, Ethernet, C-RAN cluster, baseband controller.
Operators’ objectives should be to increase capacity, optimize the use of their very expensive spectrum, decrease installation costs, ease deployments, limit energy consumption and hence cut running costs of the chosen architecture, consider their environmental impact and especially manage interferences. Centralizing is the solution!
* http://www.fujitsu.com/downloads/TEL/fnc/whitepapers/CloudRANwp.pdf
** cluster: in this scope, an aggregation of processing units
