Cloud RAN: A Centralized Solution for Mobile Operators Seeking Improved Network Efficiency

By NFVZone Special Guest
Renuka Bhalerao, Senior Product Line Manager, Radisys
December 19, 2014

The wireless network evolution is defined by users’ voracious appetites for increased bandwidth and coverage, marked by the uptick in bandwidth-hungry smartphone applications. This trend is placing significant strain on mobile operators’ networks, making the addition of a cloud concept for the RAN a necessary next step for mobile operators seeking cost-effective and efficient ways to address their overloaded networks.

Simultaneously, the telecom industry is embracing Network Functions Virtualization (NFV) to reduce cost and complexity, while speeding up deployment of new applications and services. NFV is also being applied to the access network with RAN functions moving from macro and pico eNodeBs to centralized, general-purpose servers—an architectural approach called Cloud RAN (C-RAN).

C-RAN is one option for centralizing the components of the RAN to deliver improved network efficiency and Total Cost of Ownership (TCO). Complementary to Software-Defined Networking (SDN) and NFV, the C-RAN stands out because it is based on open-platform and base station virtualization, enabling processing aggregation and dynamic allocation of resources from a centralized processing unit. It also reduces the power consumption and increases the utilization rate of processing resources, making it an energy-efficient infrastructure that adapts to exploding mobile connectivity needs.

Figure 1: Options in Radio Access Network (RAN)

RAN Architecture Tradeoffs: 

Centralization in C-RAN vs. Distribution in eNodeBs

Given C-RAN’s cost-reducing and efficiency-raising capabilities, the question for mobile operators isn’t whether they should implement it, but how to do so efficiently and cost effectively. RAN functions can be split up between the cell site and the C-RAN in different ways and with varying amounts of centralized functionality.

Figure 2: Scenarios for distributing RAN network functions

There are challenges and tradeoffs associated with varying implementation scenarios, which range from centralizing all subgroups in the C-RAN to only centralizing the L3 control plane layer.          

Example C-RAN Migration Scenario #3:

  • Keep L1 Physical Layer and L2 Real-Time Processing in eNodeB
  • Centralize L2 Non-Real-Time and L3 Control Plane in C-RAN

Early C-RAN solutions are expected to migrate non-real-time functions out of the eNodeBs into a centralized NFV architecture. This scenario maintains L2 real-time downlink/uplink scheduling, in addition to the physical layer, near the cell site. As a result, the time critical part of the eNodeB remains closer to the cell site, leaving the rest of L2 and L3 for migration into the C-RAN.

This architecture reduces the dependency on expensive backhaul technology, allowing operators to meet the aggregate cell throughput requirements by using a number of backhaul technologies, such as gigabit Ethernet, microwave links and Wi-Fi.

One disadvantage to this RAN function distribution scenario is that the L1 and L2 downlink/uplink scheduling functions are not virtualized.  

C-RAN: Setting the Stage for Future Reduced Costs, Improved Efficiency

Exploding smartphone usage is pressuring mobile operators to add capacity at a time when the cost of building, operating and upgrading the RAN is becoming more expensive. C-RAN provides several different deployment options, as well as the opportunity to reduce energy and TCO costs, improve spectral and resource efficiency, and facilitate the deployment of services at the edge.

Developers of C-RAN solutions must decide how much L1 and L2 functionality, along with L3, can be centralized in the C-RAN. Regardless of the architectural approach, Cloud RAN developers should have a flexible platform that can support a variety of centralized vs. distributed function scenarios, while delivering performance for virtualized workloads. Radisys, Wind River and Intel have developed a carrier-grade, application-ready C-RAN platform that is specially designed to maximize the speed of network functions running in a virtualized environment. Mobile operators that deploy a C-RAN-ready platform can accelerate their cloud deployments and realize the benefits of virtualized network functions.

Renuka Bhalerao is Senior Product Line Manager for software and solutions at Radisys with her primary focus on 3G and LTE wireless technologies. Prior to Radisys, Renuka worked as a Senior Architect at Continuous Computing and previously at Intel Corporation. As a Senior Architect at Continuous Computing Renuka was focused on the company’s Trillium Software product line. Renuka has an extensive experience working in Telecom Software and Systems with expertise in wireless and VoIP areas. Renuka holds a bachelor’s degree in Computer Science and Engineering from Regional College of Engineering, India.

Edited by Alisen Downey

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