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TMN 5 20Gbps per user, as well as applications that require very low latencies - such as virtual reality, self driving cars and industrial remote robotics. To meet these requirements, 5G introduces a range of capabilities to the network; Extreme throughput Very low latencies Support for high device density per km 2 Ubiquitous coverage The ability to adapt network QoS to different "vertical" use cases To achieve these goals, 5G networks will be designed very differently to current LTE networks. There will be a new air interface, or even air interfaces, based on a different waveform to LTE's ODFM interface. The architecture of the network will leverage Network Functions Virtualisation (NFV) and Software Defined Networks (SDN) technologies to construct control capabilities that can provide "slices" of service parameters across the network. This leveraging of virtualisation will spread to the Radio Access Network, where baseband capacity will be virtualised in both a centralised and edge-based architecture. Note too that small cells will be critical to meeting 5G's use case diversity and technical requirements. In each instance the inherent advantages of small cells - proximity to the end user or device, ability to enable spectrum re-use, ease of deployment, self-organising capabilities - are a great match. However, the small cell itself starts to look different in 5G as operators adopt not just new technologies within the small cell itself but new architectures within which to deploy those small cells. Virtualisation of the RAN will go hand in hand with adoption of Cloud-RAN architectures, where network functions are decomposed and sited where most appropriate - either in core or edge nodes, or even on the small cell itself at the extreme edge of the network. One iteration of this edge- based intelligence, with functions running as virtual instances on COTS hardware platforms, is known as Mobile Edge Computing. Mobile Edge Computing, by its very function, is designed to support very low latency applications, and will require small cells with the capability to act as "hosts" for service and application logic and network functions. This will be critical for applications that require sub- ms system latency, as it eliminates the round trip distance over fibre connections back to core networks that introduce the latencies currently present in LTE networks. This diversity in the choices of network architecture available to operators will require small cell platforms that can support different implementations of virtualisation. These are known as virtual/ physical "splits", with different "splits" proposals currently existing for MAC/ PHY, L2 and L3 splits, depending on the use case the operator is trying to meet. Different splits lend themselves to different latencies and downlink and uplink bandwidths. For example a MAC-PHY split can achieve 2-6ms one way latency, while a PDC-RLC split will be more like 30ms. The import of these splits is where they place features like mobility management, enhanced SON, RF coordination, security and policy enforcement in the network. Supporting this sort of functions decomposition in the network will require vendors to support an interface in the network based on the current nFAPI interface that the Small Cell Forum has outlined. Small cells in 5G networks will also be required to fit into a 5G Het Net and Network Slicing that combines licensed spectrum small and macro cells, as well as cells harnessing unlicensed spectrum, and even mmWave access cells to create various virtual networks catering to different 5G use cases. That will require small cells to sit within a new Het Net management capability in the network - itself a virtualised function that can be dynamically and flexibly deployed. So although there is little doubt that "5G starts to look a lot like small cells" as a senior Vodafone network strategy architect told the Small Cells World Summit in June, there is also no doubt that small cells developers will need to be able to support a variety of different form factors, virtualised "splits" and deployment options within the network. CONCLUSION Small cells are on a journey through the network from their current status as "special project" solutions meeting tightly defined use cases, through the adoption of 4.5G features as operators look to increase throughputs by enhancing spectral efficiency, harnessing new spectrum and supporting new MTC applications. That will be followed by small cells being absolutely critical to meeting the vastly diverse demands imposed on networks by 5G use cases. In this stage of development, small cells move from being a niche technology to being absolutely integral to the fabric of the 5G network. SMALL CELL EVOLUTION

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