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Metis project the 5 g framework

  1. 1. IEEE Communications Magazine • May 201426 0163-6804/14/$25.00 © 2014 IEEE Afif Osseiran, Olav Que- seth, Hugo Tullberg, Bog- dan Timus, and Mikael Fallgren are with Erics- son. Federico Boccardi is with Vodafone. This work was carried out when he was with Alcatel-Lucent Bell Labs. Volker Braun is with Alcatel-Lucent Bell Labs. Katsutoshi Kusume and Hidekazu Taoka are with DOCOMO Euro-Labs. Patrick Marsch and Michal Maternia are with Nokia Solutions and Net- works. Malte Schellmann is with Huawei ERC. Hans Schotten is with the University of Kaiser- slautern. Mikko A. Uusitalo is with Nokia. INTRODUCTION Societal development will lead to changes in the way mobile and wireless communication systems are used. Essential services such as e-banking, e- learning, and e-health will continue to prolifer- ate and become more mobile. On-demand information and entertainment (e.g., in the form of augmented reality) will progressively be deliv- ered over mobile and wireless communication systems. These developments will lead to an avalanche of mobile and wireless traffic volume, predicted to increase a thousand-fold over the next decade [1, 2]. Furthermore, it is generally predicted that today’s dominating scenarios of human-centric communication will, in the future, be comple- mented by a tremendous increase in the num- bers of communicating machines. This so-called Internet of Things will make our everyday life more efficient, comfortable, and safe. There are forecasts of a total of 50 billion connected devices by 2020 [3]. The coexistence of human-centric and machine-type applications will lead to a large diversity of communication characteristics. Some of these applications can be supported by today’s mobile broadband networks and their future evo- lution. However, some other applications will impose additional and very diverse requirements on mobile and wireless communication systems that the fifth generation (5G) will have to support: • Far more stringent latency and reliability requirements are expected to be necessary to support applications related to health- care, security, logistics, automotive applica- tions, and mission-critical control. • A wide range of data rates has to be sup- ported, up to multiple gigabits per second, and tens of megabits per second need to be guaranteed with very high availability and reliability. • Network scalability and flexibility are required to support a large number of devices with very low complexity and requirements for very long battery lifetimes. One of the main challenges is to satisfy these requirements while at the same time addressing the growing cost pressure. Efficiency and scala- bility are therefore key design criteria, reflecting the need to respond to the expected explosion of traffic volume and number of connected devices. Based on lessons learned in the past, Mobile and Wireless Communications Enablers for the Twenty-Twenty Information Society (METIS) builds on the assumption that a single new radio access technology (RAT) will not be able to sat- isfy all these requirements or replace today’s ABSTRACT METIS is the EU flagship 5G project with the objective of laying the foundation for 5G sys- tems and building consensus prior to standard- ization. The METIS overall approach toward 5G builds on the evolution of existing technologies complemented by new radio concepts that are designed to meet the new and challenging requirements of use cases today’s radio access networks cannot support. The integration of these new radio concepts, such as massive MIMO, ultra dense networks, moving networks, and device-to-device, ultra reliable, and massive machine communications, will allow 5G to sup- port the expected increase in mobile data vol- ume while broadening the range of application domains that mobile communications can sup- port beyond 2020. In this article, we describe the scenarios identified for the purpose of driving the 5G research direction. Furthermore, we give initial directions for the technology components (e.g., link level components, multinode/multi- antenna, multi-RAT, and multi-layer networks and spectrum handling) that will allow the fulfill- ment of the requirements of the identified 5G scenarios. 5G WIRELESS COMMUNICATIONS SYSTEMS: PROSPECTS AND CHALLENGES Afif Osseiran, Federico Boccardi, Volker Braun, Katsutoshi Kusume, Patrick Marsch, Michal Maternia, Olav Queseth, Malte Schellmann, Hans Schotten, Hidekazu Taoka, Hugo Tullberg, Mikko A. Uusitalo, Bogdan Timus, and Mikael Fallgren Scenarios for 5G Mobile and Wireless Communications: The Vision of the METIS Project OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 26
  2. 2. IEEE Communications Magazine • May 2014 27 networks. Instead, METIS’s vision is that 5G networks will respond to the expected traffic vol- ume explosion and to the new and diverse requirements mentioned above through a flexi- ble combination of evolved existing technologies and new radio concepts, as illustrated in Fig. 1. METIS [4] is an integrated project partly funded by the European Commission under the FP7 research framework, and is considered the 5G flagship project [5]. The project started in November 2012 and has a 30-month duration. METIS is part of a long-term vision roadmap, as shown in Fig. 2. The roadmap can be divided into three phases: • The ongoing exploratory phase, which con- sists of laying the foundation for the 5G system • The optimization phase, which consists of system optimization and standardization • The implementation phase, which consists of pre-commercial trials The METIS consortium comprises 29 partners spanning telecommunication manufacturers, net- work operators, the automotive industry, and academia. Among these are five major global telecommunications manufacturers, five global operators, and 13 academic partners. METIS’s objective is to lay the foundation for the 5G mobile and wireless communications system. To achieve this objective, METIS is designing a sys- tem concept that delivers the necessary efficien- cy, versatility, and scalability. The project started by developing relevant scenarios from which requirements and key performance indicators (KPIs) were deduced. Research needs on spec- trum, network, multi-link, and radio link issues were identified, and the corresponding enabling technology components are now being devel- oped. These technology components are being integrated into a system concept that is evaluat- ed using link- and system-level simulators. Hard- ware testbeds provide proof-of-concept demonstrations of selected technology compo- nents essential to the system concept. METIS has taken a leading role in exploring the funda- mentals of the 5G mobile and wireless communi- cations system, and it will ensure an early global consensus prior to global standardization activi- ties, also involving major external stakeholders. This is achieved, for example, by initiating and addressing work in relevant fora such as the International Telecommunication Union Rado- communication Standards Sector (ITU-R), to prepare for WRC-15 and provide input to WRC- 18, as well as in national and regional regulatory bodies. For instance, METIS has been contribut- ing to the ITU-R 2020 vision document [6]. A similar approach was taken in the WINNER project [7], where important technology compo- nents were developed prior to standardization/ regulations of Long Term Evolution (LTE) in the Third Generation Partnership Project (3GPP) and IMT-Advanced in ITU-R. This article aims at introducing the work in METIS and contains two main sections. We describe the 5G scenarios and requirements as well as the methodology used for investigating them. Furthermore, we explain METIS’s tech- nology approach toward 5G. In particular, it gives initial directions of the technology compo- nents most likely able to fulfill the requirements of the 5G scenarios. METHODOLOGY, REQUIREMENTS, AND SCENARIOS METHODOLOGY METIS technology innovation follows a push- pull approach. In a bottom-up process, new radio concepts are developed and optimized to support future application needs. In a top-down approach, relevant use cases as well as service and application needs are evaluated in order to Figure 1. The 5G roadmap: revolution, evolution, and complementary new technologies. 4G 3G WiFi Existing technologies in 2012 5G future Integration of access technologies into one seamless experience Mobile, reliable D2D communications 10-100 higher typical user rate 1000 higher mobile data volume per area 10 longer battery life for low-power M2M 10-100 higher number of connected devices 5 reduced E2E latency Respond to traffic explosion Extend to novel applications Complementary new technologies Evolution Revolution Massive MIMO Ultra-dense networks Moving networks Higher frequences Ultra-reliable communications Massive machine communications a nd/or and/o r By using a technolo- gy agnostic scenario description, METIS has avoided tailoring scenarios to specific potential technolo- gies that it wants to evaluate. Many inter- esting and challeng- ing applications can be identified by fol- lowing current trends and projecting them into 2020. OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 27
  3. 3. IEEE Communications Magazine • May 201428 derive the requirements that 5G has to meet. In particular, the top-down process is based on an end-user perspective. Moreover, by using a technology agnostic scenario description, METIS has avoided tailoring scenarios to specif- ic potential technologies that it wants to evalu- ate. Many interesting and challenging applications can be identified by following cur- rent trends and projecting them into 2020. METIS has selected a dozen test cases (i.e., applications or use cases) that are expected to span the space of possible future uses. These exemplary applications have been clustered into five scenarios, each illustrating a fundamental challenge. Some of these challenges are typical of conventional mobile broadband applications (e.g., very high traffic volume and experienced data rate); others are essential for applications that are not properly handled in today’s net- works, such as extremely low power consumption and low latency. Many test cases share many of the challenges identified. The fundamental chal- lenges and requirements are described. We describe the five scenarios, and illustrate them with numeric examples from a few selected test cases. More details of the test cases within each scenario can be found in [8]. REQUIREMENTS The identified scenarios and test cases are pre- sented from an end-user (human or machine) perspective. Therefore, the requirements and KPIs are primarily related to the end user. To evaluate and compare the different technology components addressing the METIS scenarios, some solution-agnostic KPIs [8] are introduced. The KPIs taken as a basis for assessment of the radio link related requirements from the end- user perspective are as follows: traffic volume density, experienced end-user throughput, laten- cy, reliability, availability, and retainability.1 Fur- thermore, some KPIs reflecting an energy or economic perspective are needed to assess the final system solution. We consider energy con- sumption (or efficiency) and cost. Each KPI is given a qualitative and mathematical definition [8]. The technical objective of METIS that reflects the 5G requirements is to develop tech- nical solutions toward a system concept that sup- ports [9]: • 1000 times higher mobile data volume per area • 10 to 100 times higher number of connected devices • 10 to 100 times higher user data rate • 10 times longer battery life for low-power massive machine communication (MMC) • 5 times reduced end-to-end latency These requirements shall be fulfilled at simi- lar cost and energy dissipation as today. In order to derive the corresponding requirements and KPIs, the identified scenarios and applications are analyzed. The selected key requirements are summarized in Table 1. The complete analysis can be found in [8]. SCENARIOS METIS has analyzed the above mentioned chal- lenges regarding mobile and wireless infra- structure for beyond 2020 in detail. In order to tackle these challenges and target the right enabling technology components, the following five scenarios have been specified: • “Amazingly fast” focuses on providing very high data rates for future mobile broadband users to experience instantaneous connec- tivity without delays. • “Great service in a crowd” focuses on pro- viding reasonable mobile broadband experi- ences even in crowded areas such as stadiums, concerts, and shopping malls. • “Best experience follows you” focuses on providing end users on the move (e.g., in cars or trains) with high levels of service experience. • “Super real-time and reliable connections” focuses on new applications and use cases with very strict requirements on latency and reliability. • “Ubiquitous things communicating” focuses on the efficient handling of a very large number of devices (including, e.g., machine type devices and sensors) with widely vary- ing requirements. The scenarios are illustrated in Fig. 3 and described in more detail below. Further details can be found in [8]. Figure 2. The 5G timeline. WRC ’18 2020 ImplementationExploring new paradigms, fundamentals, system concepts Optimization/ standardization Further developments on fundamentals WRC ’15WRC ’12 201820152012 1 Retainability is a special aspect of availability, in which a service has been made available as long as the user needs the service [8, Sec.4.2]. The end user will focus on the experi- ence, rather than on the underlying tech- nology. The flash behavior will be a key factor for the success of cloud ser- vices and applica- tions, and an enabler for the future devel- opment of new applications. OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 28
  4. 4. IEEE Communications Magazine • May 2014 29 Amazingly Fast — This scenario targets the end-user experience of instantaneous connec- tivity, where all used applications will have a “flash” behavior: a single click and the response is perceived as instantaneous. Conse- quently, the end user will focus on the experi- ence, rather than on the underlying technology. The flash behavior will be a key factor in the success of cloud services and applications, and an enabler for the future development of new applications. An example METIS test case for this sce- nario is the “virtual reality office,” where giga- bytes of data — for instance, high-resolution 3D data — are exchanged to enable interactive work among people in remote locations, proving the experience “as if one were there.” To support that, end users should experience data rates of at least 1 Gb/s and 5 Gb/s in 95 and 20 percent of office locations, respectively, and during 99 per- cent of the busy period [8]. Great Service in a Crowd — This scenario addresses end-user needs for connectivity even in very crowded places such as stadiums, shop- ping malls, open air festivals, other public events that attract lots of people, or unexpected traffic jams and crowded public transportation. Today’s mobile communication systems are designed so that a user is provided with a rea- sonable mobile broadband experience just when there are few users requesting the ser- vice. In the case of large crowds, today’s users typically suffer from service denials due to net- work overload. However, in the future, it is likely that users will expect at least reasonably good service even in very crowded places, which poses a significant challenge to future communications system design. As an example, for a METIS test case within this scenario, the test case “Stadium” foresees a traffic volume per subscriber of 9 Gbytes/h during busy peri- ods, and an experienced user data rate between 0.3 and 20 Mb/s even in a completely filled sta- dium [8]. Best Experience Follows You — This sce- nario strives to bring the same good user expe- rience for an end user on the move as for one at home or in the office. Users on the move shall have the impression that “the network infrastructure follows them,” in situations where they suffer from poor coverage today. High data rate coverage is expected at every location of the service area, even in remote rural areas. High data rate services such as video stream- ing and file downloads in “blind spots” (i.e., locations with bad coverage) are typical applica- tions for this scenario. The end users should be able to experience a data rate of at least 100 Mb/s in the downlink and 20 Mb/s in the uplink, while maintaining end-to-end latencies below 100 ms. Availability must be as high as 95 per- cent in blind spots [8]. The technical challenge is to provide robust and reliable connectivity solutions as well as the ability to efficiently manage mobility with low battery consumption of end-user terminals and at low cost. Super Real-Time and Reliable Connec- tions — The reliability and latency in today’s communication systems have been designed with the human user in mind. For future wire- less systems, it is envisioned to have new appli- cations based on machine-to-machine (M2M) communication with real-time constraints, enabling new functionalities for traffic safety and traffic efficiency, or mission-critical con- trol for industrial applications. These new applications will require much higher reliabili- ty and lower latency than today’s communica- tion systems. The METIS test case “Traffic efficiency and safety” is a typical application for a super real- time and reliable connections scenario where traffic accidents are avoided by cooperative intelligent traffic systems that require timely and reliable exchange of information with less than 5 ms end-to-end (E2E) latency. “Telepro- tection in smart grid networks” is considered as another relevant application demanding reliable information transfer between power grid sub- stations within the range of a few milliseconds. Smart grid networks may require real-time monitoring and alerting functionalities, and immediate response to altered system condi- tions. The expected payload sizes are rather moderate, say up to about 1500 bytes, while the messages shall be transferred with 99.999 per- cent reliability with about 8 ms delay on the application layer [8]. Key technical challenges lie in reducing the E2E latency while providing high accessibility and reliability of the communication services. Ubiquitous Things Communicating — This scenario addresses the communication needs of ubiquitous machine-type devices, ranging from low-complexity devices (e.g., sensors and actua- tors) to more advanced devices (e.g., medical devices). The resulting requirements vary wide- ly, for example, in terms of payload size, fre- quency of transmission, complexity (cost), Table 1. A selection of the key requirements and respective application examples. Requirements Desired value Application example Data rate 1 to 10 Gb/s Virtual reality office Data volume 9 Gbytes/h in busy period 500 Gbytes/mo/sub- scriber Stadium Dense urban information society Latency Less than 5 ms Traffic efficiency and safety Battery life One decade Massive deployment of sensors and actuators Connected devices 300,000 devices per AP Massive deployment of sensors and actuators Reliability 99.999% Teleprotection in smart grid net- work Traffic efficiency and safety OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 29
  5. 5. IEEE Communications Magazine • May 201430 energy consumption, transmission power, and latency, and cannot be fully met by today’s cel- lular networks. “Massive deployment of sensors and actua- tors” is a typical application where small sensors and actuators are mounted to stationary or mov- able objects and enable a wide range of applica- tions connected to monitoring, alerting or actuating. The requirements will be to provide connectivity for 300,000 devices within one cell, enable long battery life (on the order of a decade) and low cost device implementations, so as to support the billions of connected devices expected by 2020 [8]. The technical challenge is to integrate the communication of ubiquitous things in mobile networks and to manage the overhead created by the high number of devices. We note that some METIS test cases cannot be mapped to a single scenario, but rather repre- sent a combination of different scenarios and their underlying challenges. For instance, the test case “dense urban information society” does not require the extreme data rates of the “virtual reality office” case or the latency connected to “traffic efficiency and safety,” but foresees both humans and machines enjoying reasonably high data rates at reasonably low latencies, both indoors and outdoors, and also when devices are moving jointly in crowds (e.g., on a pedestrian sidewalk). The key difficulty here is thus to address the product of multiple requirements under constrained network deployment costs. In particular, the requirement will be to enable in 95 percent of locations and time an experienced data rate of 300 Mb/s and 60 Mb/s in the down- link and uplink, respectively, and a data rate of 10 Mb/s between, say, sensors and devices. Ulti- mately, the network is required to provide the above date rate while sustaining an average traf- fic volume of 500 Gbytes per device and per month. This corresponds to about 1000 times today’s average monthly traffic volume per sub- scriber [8]. THE METIS TECHNOLOGY APPROACH TOWARD 5G The challenges described earlier will be addressed by a combination of different solu- tions. Each of these solutions may include sever- al novel technological building blocks and technological enablers. THE METIS HORIZONTAL TOPICS METIS uses so-called horizontal topics (HTs) to build the overall system concept. An HT inte- grates a subset of the technology components to provide the most promising solution to one or more test cases. The HT-specific solutions will be integrated into the overall METIS system concept. Poten- tial overlaps between HTs, trade-offs, and inter- dependencies between technology components will be identified and analyzed with respect to their impact on overall system performance. The performance of the proposed concept will be evaluated according to the research objectives and KPIs. The research work will be directed by the concept development to ensure consistent integration of the developed technology compo- nents. The METIS HTs are described below. Additional HT(s) can be added to capture emerging market, societal, technical, and eco- nomical trends. Direct device-to-device (D2D) communication refers to direct communication between devices, without user-plane traffic going through any net- work infrastructure. Under normal conditions the network controls the radio resource usage of the direct links to minimize the resulting inter- ference. The goals are to increase coverage, offload backhaul, provide fallback connectivity, and increase spectrum utilization and capacity per area. Massive machine communication (MMC) provides up- and down-scalable connectivity solutions for tens of billions of network-enabled Figure 3. The 5G scenarios defined in METIS. 1 Gb/s 5 Gb/s Amazingly fast Great service in a crowd Operator A Operator B Local content provider Cloud service provider A Cloud service provider B Operator C Cloud service provider Ubiquitous things communicating Wired and fire sensors Super real-time and reliable connections People communicating and exchanging content Wind and humidity sensors Best experience follows you Data storage Emerging servicesReal time services 100 Mb/s 10 Mb/s 1 Mb/s Data access Ultra low latency Ultra high reliability Ultra low latency Ultra high reliability Ultra low latency Ultra high reliability OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 30
  6. 6. IEEE Communications Magazine • May 2014 31 devices, which is vital for future mobile and wireless communication systems. Machine-relat- ed communications have a wide range of charac- teristics and requirements (e.g., data rate, latency, and cost) that often differ substantially from those of human-centric communication. Moving networks (MNs) enhance and extend coverage for potentially large populations that are part of jointly moving communication devices. An MN node or a group of such nodes can form an MN that communicates with its environment, that is, other nodes, fixed or mobile, inside or even outside the moving entity. Ultra-dense networks (UDNs) address the high traffic demands via infrastructure densifica- tion. The goals are to increase capacity, increase energy efficiency of radio links, and enable bet- ter exploitation of spectrum. UDNs are orders of magnitude denser than today, assuming, for instance, several access nodes per room indoors and an access node on each lamppost outdoors, which of course raises severe interference and mobility challenges, and increased pressure on cost per access node. Ultra-reliable communication (URC) will enable high degrees of availability. METIS aims to provide scalable and cost-efficient solutions for networks supporting services with extreme requirements on availability and reliability. Architecture (Arch) provides a consistent architectural framework integrating different centralized and decentralized approaches. METIS will research and introduce a novel architectural concept that can take advantage of the developed technology components in a scal- able way. TECHNOLOGY COMPONENTS In order to develop the connectivity solutions and mobile communications system for society beyond 2020 with its broad range of service and application requirements, METIS develops the following technology components where signifi- cant progress beyond the state of the art is required: radio links, multi-node/multi-antenna technologies, multi-layer and multi-RAT net- works, and spectrum usage. These technology components are briefly described below. Radio Links — To efficiently support the vast range of identified use cases and scenarios, an air interface providing a “one-size-fits-all” solution no longer seems to be the favorable choice. Instead, the air interface for the future mobile radio system should become more flexible, pro- viding different solutions for particular use cases and applications under a common umbrella framework [10]. For a UDN, where the system is expected to support a large range of carrier fre- quencies, flexibility is brought to the system by an air interface with a scalable frame structure, pro- viding a low-cost solution for adapting the system to the signal conditions specific to the utilized bands. The efficient support of machine-type communication in parallel to human-centric com- munication is enabled by an optimized signaling structure, reducing the signaling overhead for MMC. Requirements of car-to-car applications are addressed by solutions aiming to improve reliability and quality of transmission at high vehicular speeds, also embracing novel approach- es to channel estimation and prediction. For the physical layer, a particular challenge is the efficient support of a broad range of data rates going from low-rate sensor applications up to ultra-high-rate multimedia services. For this purpose, waveforms, coding and modulation schemes, and suitable transceiver structures are investigated. Faster than Nyquist (FTN) trans- mission is studied as a technique for increasing the data rate at the cost of higher complexity of the receiver design. Filtered and filter-bank- based multi-carrier schemes are considered potential new waveform candidates for the future mobile radio system because they allow for effi- cient use of fragmented spectrum, and facilitate spectrum sharing with other services and appli- cations. In the context of advanced transceiver design, full duplex transmission seems to be a promising technology, allowing a node to simul- taneously transmit and receive a signal, thus increasing the spectral efficiency of the link. The new scenarios will also yield the intro- duction of new classes of devices and services, which should be efficiently supported by appro- priate multiple access (MA), medium access control (MAC), and radio resource management (RRM) techniques. Non- and quasi-orthogonal MA techniques are investigated, where the num- ber of users is no longer limited by the set of orthogonal resources, thus allowing the spectrum to be overloaded. In the area of MAC, research covers contention-based schemes for efficient access to a massive number of machine-type devices and distributed techniques for the syn- chronization of a set of nodes if no or only limit- ed access to the network is available. Deadline-driven hybrid automatic repeat request (HARQ) concepts address the needs of URC, as they guarantee to deliver a packet within a speci- fied deadline. Detailed descriptions of all radio link research topics can be found in METIS deliver- able D2.2 [14], and results from their assessment in deliverable D2.3 [15]. Multi-Node/Multi-Antenna Transmission — In METIS, improvements on multi-node/multi- antenna technologies are addressed to achieve the performance and capability targets of 5G wireless systems [11], by looking at both evolu- tions of 4G technologies and disruptive changes at both the node and architectural levels (Fig. 4). Massive multiple-input multiple-output (MIMO) is studied in order to deliver very high data rates and spectral efficiency, as well as enhanced link reliability, coverage, and/or energy efficiency. Part of the work is dedicated to assessing the impact of real-world challenges, such as channel estimation and pilot design, antenna calibration, link adaptation, and propa- gation effects. Another part of the work is dedi- cated to studying the effect of new types of array deployments. An additional part of the work is further exploring the theoretical limits of mas- sive MIMO [11]. Finally, the use of massive MIMO solutions in millimeter-wave bands is also considered. Advanced inter-node coordination is expect- ed to achieve significant increases in spectrum In METIS, improve- ments on multi- node/multi-antenna technologies are addressed to achieve the performance and capability targets of 5G wireless systems, by looking at both evolutions of 4G technologies and disruptive changes at both the node and architectural levels. OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 31
  7. 7. IEEE Communications Magazine • May 201432 efficiency and user throughput, and improve- ments for users with unfavorable radio condi- tions. METIS is currently exploring three different broad research directions related to inter-node coordination. The first one is further improvement of classical coordination tech- niques. Different from previous studies, coordi- nation is designed as a core characteristic of the network, rather than as an add-on feature (e.g., LTE Rel. 10). The second broad research direc- tion explored within METIS is interference alignment. The third research direction is coor- dination with enhanced network and UE capa- bilities. For example, METIS is investigating the possibility for 5G UEs to take a more active role in the network (e.g., selecting the set of serving base stations, performing advanced interference rejection, or exploiting local cooperation). Network densification, reliability, and support of moving networks may make relaying and mul- tihop communications one of the central ele- ments in the wireless architecture (in contrast to existing wireless networks where multihop com- munications have been considered as an addi- tional feature). METIS’s research approach addresses network densification through the use of infrastructure-deployed relays and techniques for wireless backhauling. Specifically, wireless network coding, buffer-aided relaying, and joint processing of interfering flows are considered by METIS promising research directions to make wireless relaying a viable option for efficient in- band backhauling. Heterogeneous Multi-RAT and Multi-Layer Networks — In 5G wireless systems, we will see a co-existence of legacy RATs and new access technologies, as well as very dense multi-layer networks consisting of cells of very different sizes. Both aspects raise novel challenges in the field of interference and mobility management, which call for new approaches in how cellular systems are handled in general. For instance, the very dense deployments expected beyond 2020 will lead to fewer users per cell, and traffic will therefore be more bursty, which suggests the usage of time-division duplex (TDD) for more efficient usage of radio resources. In conjunction with possible wide- spread usage of direct D2D and vehicle-to-X (V2X) communication, the interference constel- lations will be different than observed today. In this respect, METIS proposes schemes to identify and predict interference. Furthermore, METIS is investigating a diverse portfolio from highly cen- tralized to distributed or fully decentralized RRM concepts, and assessing this regarding the achieved trade-off between system performance, minimized infrastructure, signaling overhead, as well as with respect to scalability. Of course, highly densified networks and a more prominent role of D2D communication lead to new mobility management challenges. METIS is tackling these challenges by developing novel schemes tailored specifically for moving cells, or low-power and low-cost machine-type devices. Here, a wide range of approaches is considered, including user autonomous, network assisted, or fully network driven service connectivity management. To address both interference and mobility management aspects in 5G in one holistic frame- work, METIS is also considering a complete redesign of control and user plane functionality, and novel cell concepts, for example, phantom or virtual cells that are fully or partially transpar- ent to the device. One clear differentiator between a 5G system and earlier generations will be that one will move toward proactive management of demand, mobility, and interference instead of simply reacting to instantaneous channel, demand, and network conditions. This will be made possible by an extensive prediction and exploitation of device and application context. Clearly, novel multi-RAT and multi-layer solutions require novel infrastructure enablers such as new network management interfaces, which are also investigated in METIS as the most promising technology components are becoming clear. Furthermore, the partners are also investigating the integration of nomadic cells (e.g., access nodes mounted on vehicles) with the static infrastructure. Ultimately, the aim of the multi-RAT and multi-layer activities is to find answers to funda- mental questions regarding interference and mobility management in 5G, such as to what extent centralized approaches will be needed Figure 4. Multi-node/multi-antenna transmission research in METIS. Massive antennaNetwork coding Advanced inter-node coordination Massive machine communication Multihop communications Device-to-device communication P1 P2 P2 ⊕ P2 OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 32
  8. 8. IEEE Communications Magazine • May 2014 33 and what implications on the network infra- structure these bring. First investigation results, such as assessing the gains of context awareness and enablers for cost- and energy-efficient net- work operations, can be found in [13]. Spectrum Usage — METIS has been investi- gating ways to enable and secure sufficient access to spectrum for wireless communication systems beyond 2020 by developing innovative spectrum- sharing concepts. This should lead to substantial improvements in overall spectrum utilization and result in significantly increased spectrum usage efficiency from a spectrum-oriented as well as an economic point of view. In the beginning, the focus has been on fre- quency-band analysis in order to identify new spectrum resources and understand their charac- teristics, and on a scenario analysis of future wireless communication systems in order to understand spectrum requirements for systems beyond 2020. Frequency band analysis has been looking for opportunities even up to 275 GHz. In a second step, innovative concepts and enablers for shared spectrum usage and flexible spectrum management have been initially devel- oped. Here, some examples of novelty include identification of required enablers for ultra- dense network deployments operating at high frequencies as well as spectrum management for autonomous and network-assisted D2D commu- nication supporting high mobility. The frequency range 380–5925 MHz is cur- rently used by many different services. Possibili- ties to accommodate additional IMT bands are being considered in the scope of the ITU-R WRC-15 preparation process in detail. Thus, no in-depth investigation of this frequency range is necessary within the METIS project. It should be noted that any radio access system aiming at providing coverage in an extended area must use this frequency range for technical and economic reasons. Therefore, most of the METIS scenar- ios and test cases will need to use at least one RAT in this frequency range. Additionally, in order to fulfill the requirements of the described test cases, the communicating devices must also be equipped with RATs that can access higher frequency ranges with large bandwidths [12]. The highest priority for the next work for fre- quencies above 6 GHz is on frequencies between 40 and 90 GHz. Initial analysis [12] indicates that not only are more spectrum and more efficient spectrum usage concepts required, but also spectrum engi- neering with respect to guaranteeing coexistence, compatibility, and coverage due to the broader range of application requirements. CONCLUSIONS In this article, the 5G mobile communications scenarios were identified. These scenarios reflect the foreseen challenges such as high data rate, accessibility, mobility, massive amounts of devices, low latency, and reliability. Further- more, the scenarios and test cases were present- ed from an end-user (human or machine) perspective, and the requirements and solution- agnostic KPIs were introduced. To target each scenario, research is carried out on technology components such as link-level components, multi-node/multi-antenna, multi- RAT and multi-layer networks, and spectrum handling. The METIS overall approach to 5G is to build on the evolution of existing technologies complemented by the integration of complemen- tary concepts and, when needed, new radio access technologies. The integration of new radio concepts such as massive MIMO, ultra-dense networks, moving networks, direct device-to-device communica- tion, ultra-reliable communication, massive machine communication, and others, and the exploitation of new spectrum bands will allow support of the expected dramatic increase in the mobile data volume while broadening the range of application domains that mobile communica- tions can support beyond 2020. ACKNOWLEDGMENTS Part of this work has been performed in the framework of the FP7 project ICT-317669 METIS, which is partly funded by the European Union. The authors would like to acknowledge the contributions of their colleagues in METIS. REFERENCES [1] Cisco, “Global Mobile Data Traffic Forecast Update,” 2010–2015 White Paper, Feb. 2011. [2] Nokia Siemens Networks 2011, “2020: Beyond 4G Radio Evolution for the Gigabit Experience,” White Paper, Feb. 2011, http://nsn.com/sites/default/files/docu- ment/nokia_siemens_networks_beyond_4g_white_paper _online_20082011_0.pdf. Figure 5. Heterogeneous multi-RAT and multi-layer networks research scope in METIS. ? 1 Device to device Moving networks Interference management Smart mobility managementSmart radio resource management Management interfaces Novel cell concepts Context awareness The integration of the new radio con- cepts and the exploitation of new spectrum bands will allow support of the expected dramatic increase in the mobile data volume while broadening the range of applica- tion domains that mobile communica- tions can support beyond 2020. OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 33
  9. 9. IEEE Communications Magazine • May 201434 [3] Ericsson, “More than 50 Billion Connected Devices,” White Paper, Feb. 2011, http://www.ericsson.com/res/ docs/whitepapers/wp-50-billions.pdf. [4] METIS, Mobile and Wireless Communications Enablers for the Twenty-Twenty Information Society, EU 7th Framework Programme project, http://www.metis2020.com. [5] EU Press Release, “€50 Million EU Research Grants in 2013 to Develop ‘5G’ Technology,” Feb. 2013, http://europa.eu/rapid/press-release_IP-13-159_en.htm. [6] ITU-R M.[IMT.VISION], “IMT Vision — Framework and Overall Objectives of the Future Development of IMT for 2020 and Beyond,” ITU Working Document 5D/TEMP/224-E, July 2013 [7] WINNER Project IST 2004-507581, WINNER II Project IST-4-027756 and WINNER+ Project CELTIC CP5-026, http://projects.celtic-initiative.org/winner+/. [8] ICT-317669 METIS Project, “Scenarios, Requirements and KPIs for 5G Mobile and Wireless System,” Del. D1.1, May 2013, https://www.metis2020.com/docu- ments/deliverables/. [9] A. Osseiran et al., “The Foundation of the Mobile and Wireless Communications System for 2020 and Beyond Challenges, Enablers and Technology Solutions,” VTC- Spring 2013, June 2–5, 2013. [10] ICT-317669 METIS Project, “Requirements and General Design Principles for New Air Interface,” Del. D2.1, Aug. 2013, https://www.metis2020.com/documents/deliver- ables/. [11] ICT-317669 METIS project, “Positioning of Multi- Node/Multi-Antenna Transmission Technologies,” Del. D3.1, July 2013, https://www.metis2020.com/docu- ments/deliverables/. [12] ICT-317669 METIS project, “Intermediate Description of the Spectrum Needs and Usage Principles,” Del. D5.1, Aug. 2013, https://www.metis2020.com/docu- ments/deliverables/. [13] ICT-31766 METIS project, “Summary on Preliminary Trade-Off Investigations and First Set of Potential Net- work-Level Solutions,” Del. D4.1, Sept. 2013, https://www.metis2020.com/documents/deliverables/. [14] ICT-317669 METIS project, “Novel Radio Link Concepts and State of the Art Analysis,” Del. D2.2, Oct. 2013, https://www.metis2020.com/documents/deliverables/. [15] ICT-317669 METIS project, “Components of A New Air Interface — Building Blocks and Performance,” Del. D2.3, Apr. 2014, https://www.metis2020.com/docu- ments/deliverables/. BIOGRAPHIES AFIF OSSEIRAN [SM] is director of radio communications within the Industry Area Telecom at the Ericsson CTO office. He holds a doctorate degree from the Royal Insti- tute of Technology (KTH), Stockholm, Sweden. Since 1999 he has been with Ericsson, Sweden. From April 2008 to June 2010, he was the Technical Manager of the Eureka Celtic project WINNER+. From November 2012 to April 2014, he managed METIS, the EU project on 5G. He has published over 50 technical papers in international journals and conferences. He has co-authored two books on IMT- Advanced with Wiley. FEDERICO BOCCARDI is a principal engineer in the Vodafone Group. He received his M.Sc and Ph.D. degrees in telecom- munication engineering from the University of Padova, Italy, in 2002 and 2007, respectively, and his postgraduate diploma in strategy and innovation from the Oxford Saïd Business School in 2014. Before joining Vodafone, he was with Bell Labs (Alcatel-Lucent) UK from 2006 to 2010 and with Bell Labs Germany from 2010 to 2013. He participat- ed and held leadership positions in different EU collabora- tive projects and in the 3GPP standardization activity for LTE and LTE-Advanced. He holds more than 100 issued or pending patents, peer reviewed iternational research papers, and 3GPP contributions. His interests fall in the intersection between technology innovation and strategy, and he is currently working on different aspects related to 5G. VOLKER BRAUN (Ph.D.) is with Alcatel-Lucent Bell Labs (for- merly Alcatel Research & Innovation), Stuttgart, Germany, since 1999. He led the development of the base station software for the HSPA fast radio resource management, and defined and integrated an LTE pre-standard prototype system used for early customer mobility trials. He further pioneered the concept of outdoor infrastructure small cells. Currently he is working on various 5G research aspects. KATSUTOSHI KUSUME received his M.Sc. and Dr.-Ing. degrees from the Munich University of Technology (TUM) in 2001 and 2010, respectively. In 2002, he joined DOCOMO Euro- Labs and is currently manager of the Wireless Research Group. He received the best paper award at IEEE GLOBE- COM in 2009. His research interests include multiple anten- na systems, multicarrier transmissions, iterative techniques, ad hoc networking, and device-to-device communications. PATRICK MARSCH received his Dipl.-Ing. and Dr.-Ing. degrees from Technische Universität Dresden, Germany, in 2004 and 2010, respectively. He was the Technical Project Coor- dinator of the project EASY-C, where the world’s largest research testbeds for LTE-Advanced were established. After heading a research group at TU Dresden, he is now man- aging a research department within Nokia Solutions and Networks in Wrocław, Poland. He has (co-)authored 50+ journal and conference papers, received three best paper awards, been editor of or contributor to several books, and has been awarded the Philipp Reis Prize for pioneering research in the field of coordinated multipoint (CoMP). He has co-organized multiple IEEE workshops and served on various technical program committees, for instance, serving as Symposium Co-Chair of IEEE VTC-Spring 2013. MICHAL MATERNIA received his Master’s in optical telecom- munications from Wroclaw Technical University. He started his career at NSN in 2006, where he has been involved in multiple research projects focused on system-level aspects of 3G, 4G, and beyond 4G. His research has ranged from mobility aspects through deployment research and interfer- ence management. Since 2013 he has been leading the Multi-RAT/Multi-Layer work package in the 5G project METIS. OLAV QUESETH received his M.Sc. in computer engineering from Chalmers University, Sweden, in 1995 and a Ph.D. degree on radio communications networks from KTH in 2005. In 2007 he joined Ericsson and currently holds a senior researcher position. He has worked in 3GPP stan- dardization and regulatory fora, mainly on radio prefor- mance and spectrum issues. Since 2012 he has been leading the dissemination work in METIS. He became the METIS Project Coordinator in April 2014. MALTE SCHELLMANN received his Dipl.-Ing. (M.S.) degree in electrical engineering from Technische Universität München in 2003 and his Dr.-Ing. (Ph.D.) degree from Technische Universität Berlin in 2009. While working at Fraunhofer Heinrich Hertz Institute, Berlin (2004–2009), he contributed to the European research projects WINNER, WINNER II, and WINNER+. Since 2009 he has been a senior research engi- neer at Huawei European Research Center (ERC) in Munich, focusing on radio access technology research for 5G. In METIS, he is leading the research on radio link concepts. HANS SCHOTTEN is a full professor and head of the Institute for Wireless Communications and Navigation at the Univer- sity of Kaiserslautern, and scientific director and member of the Management Board of the German Research Centre for Artificial Intelligence (DFKI GmbH). In 1997, he received a Ph.D. in electrical engineering from Aachen University of Technology RWTH, Germany. He held positions as senior researcher, project manager, and head of research groups at Aachen University of Technology, Ericsson Corporate Research, and Qualcomm Corporate R&D. At Qualcomm he has also been director for Technical Standards and coordi- nator of Qualcomm's activities in European research pro- grams. He is the author of more than 160 publications. His main interests are mobile communications, algebraic cod- ing, and industrial communication solutions. HIDEKAZU TAOKA received his B.S. and M.S. degrees from the Department of Physics of Kyoto University, Japan, in 1998 and 2000, and received his Dr. Eng. degree from Tohoku University, Sendai, Japan, in 2009. In 2000, he joined NTT DOCOMO, Inc. Since joining NTT DOCOMO, he has been engaged in the research and development of wireless access technologies, including multiple-antenna transmis- sion techniques, relaying and network coding techniques, and future radio access techniques for next generation mobile communication systems. From 2006 to 2010, he was also engaged in standardization in 3GPP RAN1 as a delegate in multiple antenna technologies. From 2010 to 2013, he worked at DOCOMO Communications Laborato- ries Europe GmbH, Munich, Germany, as an expatriate from NTT DOCOMO, Inc. From 2012 to 2013, he served as OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 34
  10. 10. IEEE Communications Magazine • May 2014 35 a work package leader to an EU funded research project on 5G radio access, METIS, to define scenarios and require- ments for future radio access. He is now manager of the General Affairs Department of NTT DOCOMO, Inc. HUGO TULLBERG is the Technical Coordinator of the EU FP7 project METIS. He received his M.Sc. degree in electrical engineering from Lund University, and his Ph.D. degree in electrical engineering, communication theory, and systems, from the University of California at San Diego (UCSD). He has held positions as project manager and research man- ager in various areas related wireless communication. He is currently a senior researcher at Ericsson Research, where he works with 5G communication systems. His research inter- ests include communication and information theory, infer- ence systems, cognitive radio, and ad hoc networking. MIKKO A. UUSITALO [SM] is a principal researcher at Nokia Research Center Finland in the area of radio access sys- tems. He is also a Fellow of WWRF. He obtained his M.Sc. (engineering) and Dr.Tech. from Helsinki University of Tech- nology in 1993 and 1997, and hisB.Sc. (economics) from Helsinki School of Economics in 2003. Before his current role, he was head of International Cooperation at Nokia Research. He has over 30 peer reviewed publications and around 80 pending or granted patents. BOGDAN TIMUS [M] is a senior researcher at Ericsson Research, Stockholm, Sweden, in the area of wireless access networks. He received an M.Sc. degree from Chalmers University of Technology in 1997 and a Ph.D. degree from KTH in 2009. He has been with Ericsson Research since 1997. He has been Secretary of the IEEE ComSoc/VTC Chapter in Sweden. His research interests include evolution of radio communication networks and techno-economic analysis of deployment strategies. MIKAEL FALLGREN received an M.Sc. degree in engineering physics and a Ph.D. degree in applied and computational mathematics from KTH in 2006 and 2011, respectively. He has been an experienced researcher at Ericsson Research, Stockholm, Sweden, in the area of wireless access net- works since 2011. He has led the Scenarios, Requirements and KPIs task of the EU FP7 project METIS since 2013. OSSEIRAN_LAYOUT_Layout 5/7/14 11:17 AM Page 35

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