Reader Forum: The emergence of C-RAN for LTE-A deployments

Editor’s Note: Welcome to our weekly Reader Forum section. In an attempt to broaden our interaction with our readers we have created this forum for those with something meaningful to say to the wireless industry. We want to keep this as open as possible, but we maintain some editorial control to keep it free of commercials or attacks. Please send along submissions for this section to our editors at: dmeyer@rcrwireless.com.
Today’s mobile operators are facing widespread challenges. As smartphone users consume ever-expanding network resources, operators are re-doubling their efforts to provide networks that meet subscriber demand. Additionally, the cost to build, operate and upgrade the radio access network is becoming increasingly expensive and unwieldy, while the average revenue per unit is flattening within the existing RAN infrastructure.
The traditional RAN architecture has limitations, as each base station is built on a proprietary platform as a vertical solution and only connects to a fixed number of sector antennas that cover a small area and only support transmission/reception signals within that coverage area. Base station processing power cannot be shared, and building additional base station sites to accommodate growing traffic requires increasing capital and operating expenses.
Add to that the fact that mobile data traffic is trending upward and is projected to continue this trajectory, underscoring the need for timely and efficient build-out of networks and service offerings. Operators are rushing to find innovative and cost-effective ways to roll out their LTE-Advanced deployments so they can improve data rates, enhance cell edge performance and improve radio interference mitigation and spectrum re-use. However, a successful LTE-A rollout involves having both optimal use of centralized processing power and strategic coordination among base stations.
Enter the cloud. The telecom industry saw heightened focus on the cloud and virtualization techniques in 2013. On the RAN side, operators are seeing the cloud enable an efficient use of network resources, while adding the baseband pooling. This helped designate 2014 as a proof-of-concept year for the cloud radio access network, with expected deployments in 2015. C-RAN expands upon the growing utility of the RAN, wherein the radio frequency and physical layer/baseband are decoupled, providing more flexibility and efficiency in managing baseband functionality. Complementary to software-defined networking and network functions virtualization, C-RAN is based on open-platform and base station virtualization, enabling processing aggregation and dynamic allocation of resources from a centralized processing unit. Simultaneously, it reduces the power consumption and increases the utilization rate of processing resources, making it an energy-efficient infrastructure that adapts to changing requirements. When virtual base stations are idle at night and most of the processing power is not needed, they can be selectively turned off, or be reduced to a lower power state, without affecting service. Combining radio and baseband with a real-time cloud infrastructure, C-RAN architecture is a centralized, general-purpose processing solution that enables the network to respond efficiently, dynamically and on demand.
C-RAN provides the flexibility of allocating resources where and when needed by keeping the processing power away from the antennas and nearer to the core as a centralized pool of resources. C-RAN decouples the base band function from the front antenna system, enabling software-defined capacity and scaling. This trait allows the utilization of SDN and NFV by pooling network resources as needed. If traffic surges, there is increased access to processing power needed. If traffic recedes, the network resource utilization decreases concurrently. This concept of network elasticity also gives a path to operators for network sharing.
Cloud infrastructures allow mobile operators to reduce capex and opex, increasing spectral efficiency and providing a revenue-generating platform. Supporting advanced network coverage, new services, and lower support costs, C-RAN also enables better use of processing power, improved coordination among base stations and ideal architecture for certain LTE-A functionality – primarily for interference mitigation for heterogeneous networks. Thus, the C-RAN evolution, combined with the known benefits of general purpose processing in macro base stations, offers operators a complementary approach for effective deployment of LTE-A functionality.
C-RAN deployments do not come without challenges (both real and perceived) for the mobile operator. First, when separating the baseband from the rest of the processing of the base station, the link between the two must not be limited by the latency. Secondly, the addition of C-RAN to operators’ existing infrastructure can be daunting, as there is an element of uncertainty about the on current network architecture. However, in order to remain competitive in the migration to LTE-A, major carriers across the globe are readying for incorporating the cloud into their existing RAN platforms.
Small cells are crucial in global LTE-A deployments and will strengthen the key features of the technology, such as carrier aggregation, coordinated multipoint and LTE-A relay. Additionally, small cells benefit from key interference management features, including enhanced inter-cell interference coordination and range extension, which are both part of the LTE-A body of standards. Although small cells impose a limit on how many users they can support, they provide full base station functionality and capacity addition without much additional investment.
C-RAN further widens the possibilities by utilizing heightened resource management and processing capabilities. C-RAN also uses multiple antennas that are closer to the end user, bringing more intelligence to the network to drive a coordinated cluster of small cells and support LTE-A functionality. Considering small cells’ base station functionality and ease of capacity addition, as well as C-RAN’s flexibility and efficiency, the optimal LTE-A deployments will include a combination of the two working in tandem to provide a “best of both worlds” approach.
Given the traditional RAN’s coverage restrictions and limitations of transmission and reception signal support, the benefits of deploying a C-RAN infrastructure are clear. The C-RAN, as a centralized, general purpose processing solution, enables the efficient use of network resources. Based on open-platform and base station virtualization, C-RAN provides an ideal architecture for LTE-A functionality as well as being complementary to next-generation SDN and NFV deployments. Many major mobile operators across the globe are preparing to incorporate the cloud into their existing RAN platforms. We anticipate that 2014 will move the C-RAN beyond the “cloud hype” as operators gain a competitive edge through integrating the C-RAN in their LTE-A migration.