THE MOBILE ACCESS NETWORK, BEYOND CONNECTIVITY. xran.org White Paper October 2016

Transcription

1 THE MOBILE ACCESS NETWORK, BEYOND CONNECTIVITY xran.org White Paper October 2016

2 Table of Contents Executive Summary... 2 The Need for a New Radio Access Network (RAN) Architecture... 3 Limitations of Current RAN Architecture... 5 Introducing the xran Architecture... 5 xran Optimizes Network Capacity and Quality of Experience... 8 Benefits of an xran Architecture... 9 Conclusion Executive Summary Traditional Radio Access Network (RAN) architectures fall short of what s required for next generation mobile applications and services. As a result, a broad industry effort formed to address the gap. xran.org offers a software defined approach to RAN architecture, xran, to evolve mobile network services beyond connectivity. With this initiative we propose to decouple the control and user planes in the RAN, standardize the user plane silicon and software with open interfaces, and logically centralize network intelligence and state and abstract the underlying network infrastructure from business applications. The xran architecture will build a reference system for LTE-A, with an eventual goal of defining and building the same architecture for 5G once the new air interface is finalized. As a result of this architecture, carriers will gain unprecedented programmability on the RAN, automation and network control, a supply chain of off-the-shelf components to build out their mobile access network; enabling them to build highly scalable, flexible radio access networks that they can rapidly adapt to changing business and traffic needs. xran promises to deliver substantial benefits to carriers and their network subscribers, including: Optimized end-user experience, as applications exploit programmable control to seamlessly adapt network behavior to user needs; Several fold increase in spectral efficiency through coordinated radio resource control to exploit interference; Rapid innovation with the ability to deliver new capabilities without configuring individual devices or wait for vendor releases; Increased value of carrier network, beyond connectivity, by applying intelligent services and control in the network; and 2016 xran.org. All rights reserved. 2

3 Tight alignment with carrier edge cloud infrastructure to allow dynamic orchestration of compute and storage with mobile network. An xran approach is well aligned with Network Function Virtualization (NFV) initiatives, and provides high-performance, fine-grained traffic control on standard x86 platforms and across multi-vendor radio access interfaces. Following in the footsteps of Software Defined Networking (SDN), xran is transforming today s static, highly proprietary RAN infrastructure into an extensible service delivery platform capable of rapidly responding to changing application and business needs. xran.org is a non-profit industry consortium that is leading the advancement of xran and standardizing critical elements of an xran architecture. The xran architecture is complementary to 3GPP and other standards bodies and hopes to provide a blueprint that these standards bodies can use for architecting the future RAN as the industry moves towards 5G. The Need for a New Radio Access Network (RAN) Architecture Mobile wireless networks today are faced with two conflicting trends. On the demand side, traffic is growing exponentially and becoming increasingly diverse. Several industry reports have showed that traffic has grown on order of magnitude over the last 3 years alone and is expected to continue at that pace with more and more video content being consumed over mobile networks. Further, the traffic mix will be diverse, ranging from voice, data and video to new applications such as smart grids, drones and automotive applications. Specifically, Mobile Video Streaming: High Definition (HD) video has become the norm and interruptions in video or audio are unacceptable to today s mobile video consumers. Brute force throttling approaches have proven to deliver a low user quality of experience and have created significant backlash for carriers taking this approach. Current RAN architecture rely heavily on the mobile device s signal strength alone to determine when cell-to-cell handoffs are made. But, signal strength is only one factor of many that can impact mobile video quality. Other factors include cell capacity, mobile device direction and speed, device video buffer size and state and video bit rate. A new architecture, which allows real-time control across multiple enodebs based on all these factors, weighted by carrier policies, is required to meet the mobile video consumer s expectations xran.org. All rights reserved. 3

4 Connected Cars: Transportation is going through a major shift this decade. Cars have moved beyond being mechanical creations to complex pieces of connected software that are remotely controlled. Connected cars will impose stringent requirements on the network, needing high bandwidth connectivity to both deliver content to the passengers in the car as well as stream high resolution telemetry back to an automated driving system in the cloud. Moreover, for self-driving cars to scale, the network will have to become the conduit for remote control of cars from the cloud. Thus, the network becomes critical to safe driving, delivering a high bandwidth, low latency connection to thousands of cars is necessary. Current RANs cannot deliver such consistent, low-latency connectivity. The consequences of this unreliability can be seen in the current crop of self-driving car designs, they strive to pack together all the sensing and co-ordination locally which makes the cars unaffordable. A programmable RAN that can be tailored for connected cars can open the doors for simpler self-driving cars where the complexity of automated driving and co-ordinations across cars can be delegated to the cloud. Virtual and Augmented Reality: Today s VR infrastructure requires significant compute and storage, directly tethered to bulky head gear and motion sensing systems that spatially restrictive. The vision of how Virtual Reality (VR) and Augmented Reality (AR) will evolve is going to require the RAN infrastructure to become smarter. Compute, storage and fined grained spatiotemporal sensing will move to the carrier network edge in order to reduce size and cost of wearable VR/AR systems. In parallel the RAN architecture must evolve to take a broader view of the applications it serves. RAN control will no longer be distributed to enodebs and limited to maintaining connectivity. It must become tightly integrated into a programmable control platform for orchestrating the low-latency compute, storage and motion sensing system required for a high-quality VR/AR experience. However, on the supply side, available spectrum and spectral efficiency (i.e. the maximum throughput achievable per Hz of spectrum) are flattening out. In fact, the spectral efficiency of 4G LTE PHY is fairly close to (within 20% of) the Shannon capacity limit, and further improvements are likely very expensive to implement and will only provide limited gains. To cope, future wireless networks have to change in two fundamental ways. First, network deployments have to get dense and tightly coordinated. This is motivated by a simple observation: The surest way to increase per-user capacity is to make cells small and bring the base station closer to the mobile client, since this improves per link SNR and reduces the number of users per 2016 xran.org. All rights reserved. 4

5 cell. But since this increases interference, the network has to be tightly coordinated at per TTI timescales. Second, since there is no one-size-fits-all network stack, networks have to dynamically adapt to meet the distinct requirements of diverse applications. They will have to dynamically switch between providing low latency connectivity for automotive applications, to predictable high throughput connectivity for video, persistent reliable connectivity for data, etc. These points by themselves are not particularly novel observations; with the advent of femto/micro-cells, current networks are slowly moving towards denser deployments and the discussion on slicing in 5G is primarily motivated by the need to support new business applications beyond just connectivity. Limitations of Current RAN Architecture Current radio access network architectures are ill-equipped to support a dense and application driven wireless infrastructure. Specifically, Proprietary, vendor specific SW and HW: Current networks are hard to program, network stack software is realized in a tightly coupled fashion on proprietary hardware and its quite difficult to adapt to the requirements of new applications. Vendor interfaces are coarse grained at best, and proprietary to them, making it difficult for carriers to build multi-vendor infrastructure that s easy to evolve. Chaotic infrastructure: Second, since it will be impossible to obtain regularly placed cell sites for an infrastructure with much higher density, base stations will be deployed wherever possible in a chaotic fashion. However, a chaotic and dense wireless deployment will be very complex to manage, since it will experience highly variable loads and unpredictable inter-cell interference among other things. High CAPEX & OPEX: Finally, a dense infrastructure is very expensive to deploy and operate. Due to the proprietary and diverse nature of the HW and SW platforms used to build base stations, economies of scale that have been available in other networking domains such as datacenters are not possible in the RAN. Further, there is very little vendor interoperability, limiting operator choice and therefore increasing costs. Introducing the xran Architecture Our goal is to build a new network architecture for designing future dense and programmable wireless infrastructure. At its core, xran is guided by the principle of decoupling service definition from hardware by designing generic, programmable substrates that can flexibly realize multiple network 2016 xran.org. All rights reserved. 5

6 service definitions. Further, it decouples the control plane of network services from the user/data planes and defines open interfaces between them. xran has three core components: Decoupled Data/User Plane: xran decouples the control plane from the user plane and defines standardized interfaces to make the user plane programmable. This has two key benefits. First, it standardizes the workload implementing the user plane, making it more predictable since most of the variation comes from the control plane. Hence, silicon vendors can invest in smaller geometry silicon that can be quite power efficient and produce one piece of silicon for all vendors, rather than a fragmented catalog of silicon for each vendor. Second, a programmable data plane enables the operator to customize the network stack for different applications or to realize new functionalities without depending on vendors. The xran approach is well aligned with carrier Network Function Virtualization (NFV) initiatives, and provides high-performance, finegrained traffic control, interference management and radio resource control on standard x86 platforms and across multi-vendor radio access interfaces. This approach enables flexible placement of enb functions and hybrid split-control plane with a scheduler to handle variable front-haul latency and programmable control. Software Defined Control Plane: xran decouples the control plane from the data plane by leveraging the standardized interfaces to program the data plane and provide a software-defined control plane abstraction. This provides the flexibility required to simplify management of complex networks. Traditional wireless infrastructure design embeds much of the control plane into the design of the base station hardware itself, making it difficult to dynamically modify and manage network operation. Instead, in xran the control plane interacts with the data plane via a programmatic interface that allows network operators to dynamically handle different classes of traffic and manage the network efficiently. By defining an open, standardize interface between the control and user planes, operators can realize a multi-vendor ecosystem in the RAN. This migration of control, formerly tightly bound to RAN hardware devices, into accessible computing devices allows the underlying RAN to be more efficiently orchestrated as a logical pool of capacity. Base station software is decoupled from vendor specific hardware, inspiring innovation in both software and hardware cooperatively, but independently. Slicing Plane: The last piece of the infrastructure redesign is a slicing plane that provides a mechanism to share the same physical infrastructure among multiple applications with customized network stacks, thus supporting the diverse needs of future apps and allowing the network to 2016 xran.org. All rights reserved. 6

7 evolve beyond just providing connectivity. In doing so, the slicing plane should provide strong isolation and performance guarantees to the slices exposed to different applications. In traditional RAN Architecture (See Figure 1), the Control-Plane and Data- Plane are tightly coupled at the enodeb, which decentralizes the controlplane. The RAN is a collection of distributed end-points, and does not benefit from end-to-end context. The X2 interface allows for limited coordination and information exchange between enodebs, but it falls short of the operator expectation to treat the RAN as a programmable platform designed to optimize customer Quality of Experience (QoE). Figure 1 Current RAN Architecture Figure 2 xran Architecture 2016 xran.org. All rights reserved. 7

8 The xran approach decouples the control plane from the data plane. (See Figure 2). The control plane in the xran Architecture is: Centralized view: Operating as a cloud-based cluster, the controller has a scale-out design Context-aware: Both on the radio network side (UE behavior, channel, load, interference) as well as end-to-end application QoE demands and SLAs Shared: across the entire RAN (or a cluster of enodebs). Easily upgradable: New features can be added by an operator with a quick software upgrade in the cloud. Multi-vendor: Offing an open-interface supporting multiple compatible enodeb vendors. Instead of providing individual control-plane functionalities as in the current architecture, the xran-architecture treats the entire RAN as a common pool of resources which can be optimized to end user application. Supporting SDN principles, full programmability offers customization to align carrier policies with network demands, and evolve to support next generation applications. xran Optimizes Network Capacity and Quality of Experience The xran controller manages control plane functionality to optimize the network for end-to-end QoE, including: SON optimization/configuration: Programmatically optimizes various thresholds and configuration parameters within enodebs Managing UE-level Connectivity: Manages which UE connects to which cell. This allows the controller to optimize UE connections, and hand-offs to optimize both network capacity and user QoE through load balancing, for example. Managing Bearer-level connectivity: This is similar to the point-above, however leveraging fine-grained control at bearer (data-flow) level. The controller uses LTE features like Dual-connectivity/Carrier Aggregation, through which a UE can be simultaneously receiving/transmitting to more than one cell, one of them serving as primary cell, and the others as the secondary cell. The xran controller can provide a central, context-aware, and end-to-end-aware way of orchestrating this scenario xran.org. All rights reserved. 8

9 Benefits of an xran Architecture xran WHITE PAPER Interference management: The controller manages inter-cell interference through CoMP (coordinated multipoint) techniques, such as coordinated scheduling. Dynamic Scheduler Policy: The xran architecture allows for a softwareupgradable scheduler, that allows it to easily adapt to different network/user-demand conditions. Programmability to support 5G applications: In the current RAN architecture, upgrades to carrier networks to support the latest 5G applications with well-defined QoS parameters would require vendorspecific upgrades enodeb schedulers. In an xran architecture, the xran controller allows simple SDN-like programmability of the scheduler on demand. For carriers, an xran architecture makes it possible to address the highbandwidth, low latency and spatiotemporal nature of next generation mobile applications and services. The software-based architectural approach delivered by xran allows carriers to reduce complexity, innovate more quickly and significantly reduce operational and capital costs. The benefits that carriers can achieve through and xran architecture include: Optimize RAN utilization: The xran architecture has been shown to support RAN utilization optimization. Simulations, using actual data from enodebs collected across 100 cells in a metro area, resulted in a 30-50% increase in capacity, with no added physical RAN capacity. This result was achieved by allowing the xran controller to orchestrate the distribution of UEs across enodebs to more efficiently distribute the load. Fine grained control: The xran architecture enables control decisions to be based on second and millisecond time scales, across several adjacent enodebs. This allows the xran controller to balance optimization of infrastructure utilization and subscriber quality of experience. With unprecedented real-time programmability and control of the RAN infrastructure the xran architecture readily supports next generation mobile applications and business services Increased user experience: xran enables carriers to optimized end-user experience, as applications exploit programmable control, end-to-end network slicing to dynamically adapt the RAN to user needs. By managing the network as a pool of connectivity and capacity, an xran controller optimizes user experience by placing and/or moving UEs based on UE requirements in real-time xran.org. All rights reserved. 9

10 Speed of software innovation: xran adoption accelerates innovation by allowing carriers to reprogram the RAN infrastructure in real-time to meet rapidly evolving business and customer needs. Programmable control allows carriers and potentially applications to tailor the behavior of the RAN and introduce new services and network capabilities on demand. Supports NFV objectives: The xran architecture is designed to operate on commodity hardware and support standard RAN components. This architecture allows RAN capacity to elastically scale and supports carrier NFV objectives to reduce infrastructure capital costs and improve operational efficiency. Conclusion xran.org was formed by carriers to develop, standardize and promote an open alternative to the traditionally closed, hardware-based RAN architecture. Current RAN architectures result in sub-optimal use of scarce spectrum and radio resources. This inefficient utilization of the RAN hinders the efforts of carriers to customize or quickly innovate to meet emerging customer needs. Amid exploding demand for bandwidth and intense competition, carriers need an alternative approach to protect profits now being eroded by escalating capital and operational costs of the existing design. Global trends such as mobile video streaming, connected cars and virtual and augmented reality applications require high-bandwidth and low-latency from carrier networks. xran provides a new, software-based approach that delivers next generation RAN capabilities resulting in an intelligent mobile network platform that offers services and capabilities beyond connectivity The future of mobile networking will inevitably be more flexible, more intelligent and more programmable. xran.org and its members are dedicated to promoting a software-based, extensible Radio Access Network (xran) and to standardizing critical elements of the xran architecture. The xran architecture will transform today s static, highly proprietary RAN infrastructure into an extensible, software-based service delivery platform capable of rapidly responding to changing user, application and business needs. For more information and to stay up-to-date, visit and register to receive updates and news xran.org. All rights reserved. 10