Cloud RAN ( C-RAN ) : Cell densification paradigm @ LTE A to 5 G !!


All Telco engineers know that in a typical mobile deployment, each base station serves all the mobile devices within its reach. Each base station has its digital component manage its radio resources, handoff, data encryption and decryption and an RF component which transforms the digital information into analog RF. The RF elements are connected to a passive antenna that transmits the signals to the air. Each base station should be placed in the geographical center of its coverage area. But even when such locations are selected, the mobile operators may have difficulty in renting the real estate, finding proper powering options, securing the location and protecting the equipment from weather conditions. Those cell sites carry with them a continuous stream of OPEX to address the high rental rates for real estate, electrical expenses, cost of backhaul for the cell site and security measures to protect the location from intruders.

Enter a novel architectural paradigm : C RAN !!! The basic premise of Cloud RAN is to change the traditional RAN architecture so that it can take advantage of technologies like cloud computing, Software-Defined Network (SDN) approaches, and advanced remote antenna/radio head techniques.C-RAN architecture is not bound to a single RAN air interface technology. In essence, conventional terrestrial cell site base stations are replaced with remote clusters of centralized virtual base stations which can support up to a hundred remote radio / antenna units. This is achieved by centralizing RAN functionality into a shared resource pool or “cloud” (the digital unit – DU, or baseband unit – BBU) which is then connected via fibre to advanced remote radio heads (“Radio Units” – RU) sited in different geographical locations in order to provide full coverage of an area. The radical concept can even use banks of x86 servers to connect cellular calls rather than traditional wireless base stations.

From a business perspective,C-RAN will deliver significant reductions in Opex and Capex due to reduced upgrading costs. A major reason for this is the aggregation and pooling of the DU computing power which can be assigned specifically where needed e.g. the load situation over time and space for indoor/outdoor cells, am/pm hours, weekday/weekend, and so on. As a result, single cells do not need to be dimensioned for peak hour demands, but rather the processing power can be pooled and assigned on an on-demand basis. The processing power savings achieved should also leave processing headroom for any further potential technology enhancements (e.g., LTE-A features) without the need for further CAPEX. C-RAN skips the need for a high-bandwidth, low latency (X2), synchronized interface between the geographically distributed base station because the computing resources of the multiple transmission points’ BBUs are all located within the same hardware.C-RAN slashes capex because fewer BBUs are needed, which reduces opex because fewer BBUs means less energy consumption and diminished maintenance costs. The reduced energy consumption makes C-RAN a “green” alternative, with China Mobile estimating 71 percent power savings vs. traditional RANs.

Furthermore, interference management will also benefit from C-RAN network architecture as technologies like dynamic eICIC schemes will be enabled, especially in a HetNet deployment.Heterogeneous networks will require small cells to be independent, intelligent and ubiquitous to avoid the cross- interference mayhem, yet be in synch and orchestrated with macro cells (including Cloud – RAN topology).Small cells are poised to become the most commonly used node for cellular access in the next-generation HetNet. C RANs will likely take their place beside traditional base stations and emerging small-cell base stations as another tool for building cellular nets.The success of many new 4G network deployments will depend on the use of outdoor and indoor small cells to extend coverage and increase capacity in areas poorly served by macrocell networks.

Cloud-RAN economics will only be realized by harnessing standards to ensure interoperability and reduce cost. That, in turn, will create a whole new ecosystem, and operators must resist any attempts by their suppliers to hijack standards for software-defined networking or cell site equipment. Otherwise, this fledgling architecture will remain confined to a few pioneers with the resources to build their own ecosystems, like China Mobile. China Mobile, the world’s largest carrier with 700 million subscribers, has been spearheading trials and plans to deploy systems as early as 2015. Japan’s NTT Docomo said it will follow in 2016, and a third unnamed carrier is now preparing plans for C-RANs. China Mobile aims to lower the cost of C-RANs to less than $30 per LTE sector, down from about $10,000 two years ago.

As MNOs face rising CAPEX bills to meet mobile data demand combined with falling ARPU, they must explore radical new network designs. With Cloud-RAN, they can virtualize baseband processing functions for hundreds of sites on a server or base station hotel. By consolidating individual Base-station processing into a single or regional server farm Investments on Cloud Radio Access Network (RAN) Infrastructure are expected to exceed $6 Billion by 2020, according to a new report from SNS Research. Distributed antenna technologies ( DAS ) will get a new lease on life, supporting coverage extension for C-RAN sites. This sector will open up $1.3bn in new revenues for antenna providers.

Pure C-RAN faces many barriers, such as overreliance on fiber to link sites and basebands and immature standards, but most operators will inch towards C-RAN using hybrid models. Development of microwave fronthaul technologies will be critical to improve the C-RAN business model . Whatever the challenges C-RAN offers a revolutionary approach to next-generation cellular networks deployment, management and performance. Fiber, needed for fronthaul, is crucial to C-RAN deployment, so it is no wonder that fronthaul is constantly brought up as Cloud RAN’s biggest challenge. Fronthaul connects RRHs to the aggregated BBUs, with traffic then backhauled from the BBUs to the IP core or evolved packet core (EPC).

NTT DOCOMO Japan,announced it will begin developing high-capacity base stations built with advanced C-RAN architecture for DOCOMO’s coming next-generation LTE-Advanced (LTE-A) mobile system. The new architecture will enable quick, efficient deployment of base stations, especially in high-traffic areas such as train stations and large commercial facilities, for significantly improved data capacity and throughput.

Advanced C-RAN architecture, a brand new concept proposed by DOCOMO, will enable small “add-on” cells for localized coverage to cooperate with macro cells that provide wider area coverage. This will be achieved with carrier aggregation technology, one of the main LTE-Advanced technologies standardized by the Third Generation Partnership Project (3GPP). The small add-on cells will significantly increase throughput and system capacity while maintaining mobility performance provided by the macro cell.

For NTT DoCoMo high-capacity base stations utilizing advanced C-RAN architecture will serve as master base stations both for multiple macro cells covering broad areas and for add-on cells in smaller, high-traffic areas. The base stations will accommodate up to 48 macro and add-on cells at launch and even more later. Carrier aggregation will be supported for cells served by the same base station, enabling the flexible deployment of add-on cells. In addition, maximum downlink throughput will be extendible to 3Gbps, as specified by 3GPP standards.

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. 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.

Korean operator SK Telecom is planning to implement a cloud RAN model in cooperation with Nokia, in what is claimed to be the world’s first commercial deployment. The approach, which SKT describes as a software-defined RAN, allows traffic to be scaled more effectively and network resources to be allocated across different cell sites according to demand. It also provides third-party access to the SKT network for users such as SMEs to develop their own applications.

Bottom Line : 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.You can build out a network faster provide greater coverage at a lower cost with C RAN !!

Sadiq Malik ( Telco Strategist )


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