Cloud RAN Network Technologies RAN

SK Telecom claims first true Cloud-RAN

Working with Nokia, Korean operator implements open IT platform for base stations in commercial LTE network, looks ahead to 5G slicing

The term C-RAN is being used almost as broadly as 5G, and several operators already claim to have ‘centralized RANs’ or ‘virtualized RANs’. Now SK Telecom of Korea, one of the companies which has been boasting about C-RAN for a couple of years, is claiming the world’s first true Cloud-RAN, and says it is ushering in the era of “All-IT”, to take the “All-IP” network towards 5G.

As in 5G, there is a hefty dose of semantics as operators look to outdo one another, but SK is also moving the terms of the C-RAN debate forward. There have been several major trials and even deployments of virtualized base stations, enabling a cluster of cell sites to be managed by a server running the baseband functions in software – Telefonica, NTT Docomo and KT are among the pioneers, while SK itself demonstrated vRAN functions, with Nokia, back in 2013.

But its latest test, conducted on a commercial LTE network, gets close to the fully fledged software defined RAN vision originally publicized by China Mobile (which may dispute SK’s claims to be first to achieve this milestone, given its own advanced work on Cloud-RAN with partners such as Intel). Like China Mobile and others, SK and Nokia have implemented a base station in which network functions are virtualized and centralized. This provides efficient, elastic use of network resources, which can be allocated to different cell sites according to demand; and it enhances quality of service with the split of functions between different locations and automatic error recovery.

Where SK goes further, and points to one of the key visions for 5G, is to implement a software-defined network with open interfaces, so that third parties – specifically small and medium enterprises (SMEs), in SK’s thinking – can develop their own functions for the RAN using Mobile Edge Computing.

This would be an enabler of network slicing, the concept which could, more than any other, justify the investment in 5G. This allows huge numbers of service providers and enterprises, including small ones, to use a virtualized, on-demand ‘slice’ of the network, optimized for their services and supporting the network capabilities they request.

SK Telecom is also referring to its lab network as a software-defined RAN (SDRAN), which – while adding yet another acronym to the overloaded area – is more descriptive than C-RAN. This is not just about running base station functions as virtual machines in the cloud – it is really about introducing open IT architectures that enable entirely new economics and business models, with elements such as an Ethernet fronthaul link.

The operator explained its definition of SDRAN as enabling “traditional base station functions to be implemented on a general purpose IT server, and its distinctive features include functional split between real time and non-real time processing functions, Ethernet-based interface, and intelligent operation.”

The use of an Ethernet link between the remote radio unit and the central baseband or digital unit (DU) is important to the economic viability of C-RAN, which was originally reliant on CPRI implemented on very high speed fiber links, which are unavailable or unaffordable for many operators. Fiber, especially dark fiber, will remain important to C-RAN implementations, and there are also emerging microwave CPRI options suited to some scenarios, but the main focus has been on an Ethernet solution. TIM is trialling Altiostar’s Ethernet-based C-RAN architecture in Italy, while the IEEE is working on its 1914 Next Generation Fronthaul standard, and in the UK, BT has trialled Ethernet fronthaul over copper links.

SK Telecom says its own Ethernet-based interface is “used for more efficient network configuration. The interface also better handles signal delays, so that when a delay occurs, it adjusts the timing of data transmission and prevents a slowdown in transmission speed. Accordingly, customers benefit from better data quality.”

The Korean operator says that, by applying general IT technologies to the interface, not just to the actual base station processing, it is opening up the architecture and making the RAN into an IT environment. Data center techniques such as intelligent operations can be applied to the mobile network – for instance, a base station can “self-detect systemic errors and automatically restore the virtual machine. Also, it dynamically generates or deletes the virtual resources of a base station, depending on the number of current users and traffic loads, for more efficient resource allocation.”

The partnership with Nokia is a close one. The two companies demonstrated virtualized RAN functions in 2013 and last year, they completed a field test of SDRAN, technology they have now applied to a commercial network. SK is feeding its virtualized base station work into ETSI’s NFV initiative.

Frank Weyerich, head of mobile networks products at Nokia, said in a statement: “This is a major milestone for Nokia; together with SK Telecom, we have for the first time implemented our AirScale Cloud RAN technology in a commercial network. We are paving the way towards 5G, and cloud-based radio networks delivering the scalability and flexibility required to allow operators such as SK Telecom to meet the future data demands of customers, enabling new levels of user experience at minimal cost and maximum operational efficiency.”

Park Jin-hyo, head of SK’s Network R&D Center, added: “Network innovation through convergence of telecommunication and IT is an urgent task to deal with explosive growth of data traffic.”

Along with arch-rival KT, SK has been an early adopter of many new network technologies from Cloud-RAN to dense small cell zones and HetNets. Whereas it once might have tried to define standards solo, as Docomo did in 3G, now it aims to assert its leadership by working with many partners round the world, punching above its weight in the standards and IPR processes while sharing the load of R&D funding, testing and political activity with others.

Last month, it announced a hat trick of 5G alliances – joining two groups led by AT&T and Verizon respectively, and extending a collaboration it announced at Mobile World Congress in February with Deutsche Telekom. The pair have attracted more supporters to their 5G program – most of these are the usual suspect vendors (Huawei, Nokia, Ericsson, Qualcomm and Samsung) but AT&T has also signed up.

The plan is to deploy a transcontinental pre-5G network incorporating many of the key technologies of the new networks (4G or 5G), such as NFV, software-defined infrastructure (SDI), distributed cloud and network slicing. The goal is to identify and test use cases and create a global business case for 5G services based on a reliable roaming experience. The partnership will also focus on Internet of Things (IoT) services, media platforms and new user experiences.

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