n the last year or so, significant momentum has started tobuild around the idea of a fifth generation (5G) for wire-

less communications technology. New research projects havestarted internationally, and research centers devoted to 5Gtechnology have begun to open. At the ICC 2013 conferencein Budapest, there were a number of keynote talks and specialinvited sessions addressing some of the key concepts around5G technology. This Special Issue was created by IEEE Com-munications Magazine to help readers understand the currentperspectives on 5G technology from both industry and aca-demic standpoints.

In the last five to ten years, the speed at which standardshave developed has been breathtaking. The first release of theThird Generation Partnership Project (3GPP) Long TermEvolution (LTE) system was frozen in December 2008, withcommercial deployments beginning a year or two after that.The first release of LTE-Advanced was in March 2011, whichmade LTE formally compliant with the International Telecom-munication Union (ITU) definition of the fourth generationof wireless technology, called IMT-Advanced. LTE also metthe requirements set out by the mobile-operator-led organiza-tion Next Generation Mobile Networks (NGMN). Furtherreleases of LTE-Advanced still continue. However, the stan-dards bodies and industry are now organizing a timeframe tostandardize 5G technology, which is expected to be between2016 and 2018, followed by initial deployments around 2020.

The development of 3G and 4G wireless technology wasmainly driven by demand for data services over the Internet.However, the drivers for 5G systems are likely to be muchmore diverse. There is still a demand for higher-capacity net-works, especially in Asia, where network operators face majorchallenges in meeting the demands of large populations. Newtraffic types and data services are emerging, notably machine-to-machine communications to support concepts such as thesmart grid, smart homes and cities, and e-health. These appli-cations have very diverse communications requirements, andproviding a single unified wireless technology to support themseamlessly alongside existing voice and Internet services willbe a major task. In addition, future networks should be muchmore energy-efficient than current networks in order to make5G a sustainable network technology in the long term. Ulti-mately, if 5G technology cannot offer a new paradigm overand above what can be achieved with LTE-Advanced, thetechnology will not be commercialized successfully.

This Call for Papers was timed in order to appear in printfor the Mobile World Congress 2014. In spite of the relativelyshort timescales, almost 70 independent submissions werereceived. After a rigorous review process, 18 manuscripts werefinally selected for publication. In order to present all of thesepapers, this Feature Topic has been split into two. The firstset of nine articles will appear in this issue, with the secondpart scheduled for publication in May 2014.

IEEE Communications Magazine February 201462

GUEST EDITORIAL

I

5G WIRELESS COMMUNICATION SYSTEMS:PROSPECTS AND CHALLENGES

Join the online discussion group for this Feature Topic here:http://community.comsoc.org/forums/commag-features-and-series

John Thompson Xiaohu Ge Hsiao-Chun Wu Ralf Irmer Hong Jiang

Gerhard Fettweis Siavash Alamouti

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IEEE Communications Magazine February 2014 63

The first article, Towards Green and Soft: A 5G Perspec-tive written by authors from China Mobile, presents an oper-ators perspective on 5G technology. They identify two majorthemes in their article relating to greener wireless networksand the wide adoption of software controlled networks fromthe radio base station through to the core network. In orderto deliver this vision, they then point to five key approachesthey believe will be adopted in 5G networks. The first of theseis the design of radio networks taking into account both ener-gy efficiency and spectral efficiency. The second approach isto abstract future cellular networks, where base station pro-cessing is moved to the Internet cloud: the so-called C-RANapproach. The third strand relates to the separation of dataand control channels following the software defined network-ing (SDN) principles now being adopted in wired networks.Fourth, they see a move toward large antenna arrays or mas-sive multiple-input multiple-output (MIMO) concepts inorder to provide much higher data capacities. Finally, theypredict the adoption of full duplex concepts in future radiosso that they are capable of transmitting and receiving in thesame frequencies simultaneously.

The second article, Five Disruptive Technology Directionsfor 5G, is written by authors from an equipment manufactur-er, Alcatel-Lucent Bell Labs, supported by academic colleagues.In response to the challenges of 5G, they also identify fivemajor directions for future research and standardization. Theirfirst point is to argue that network design should move awayfrom being cell-centric toward being device-centric andfocus on the needs of user terminals. They also argue that 5Gshould adopt higher-frequency millimeter wave bands wheremuch more bandwidth is available, albeit signal propagationmay be less favorable. Third, they also point toward largeantenna arrays or massive MIMO as a key 5G technology.Fourth, they argue for more intelligent terminals that are capa-ble of mitigating interference and communicating directly withother devices without network assistance. Finally, they point tothe requirement for 5G to support machine-to-machine com-munications in an effective and integrated manner.

The third article, Network Densification: The dominanttheme for Wireless Evolution into 5G, is written by authorsfrom Qualcomm. They argue that the network needs to densifyin three ways: spatial densification, spectral aggregation, andbackhaul densification. Spatial densification covers the movetoward more heterogeneous network deployments of macro-cells, picocells, relays, and small cells as well as direct device-to-device communication. Spectral aggregation implies that futuredevices are capable of communicating on multiple frequenciessimultaneously, as well as adopting new portions of spectrumsuch as the millimeter-wave bands. Finally, backhaul aggrega-tion identifies the requirement that the backhaul connectionfrom different cells into the core network must also improve tomeet the higher demands 5G networks will place on it.

The fourth article, Networks and Devices for the 5GEra, is co-authored by researchers from Intel and presentstheir vision for 5G. They draw attention to three majorparadigm shifts related to the change in cellular network lay-out, changes in understanding mobile performance, and thegrowth in the number of radio technologies and devices. Theybring attention to the growth of heterogeneous network archi-tectures, such as combining macrocells, small cells, and relayswith a variety of radio technologies including both cellularand wireless local area networks. They also envisage the adop-tion of new technologies such as massive MIMO, full duplextechnology, and device-to-device communications. Futuremobile terminals will have much improved context awareness,with knowledge of the users requirements, the surrounding

environment, and the network. The article also provides ahelpful discussion on user terminal design and requirements,alongside radio spectrum issues.

The fifth article, 5GNOW: Non-Orthogonal, Asyn-chronous Waveforms for Future Mobile Applications, pre-sents the perspective of a European 5G research project.Their focus is on how 5G will support machine-to-machinecommunications and the Internet of Things properly. Theyidentify five major features that are required for this to hap-pen. First, they propose a unified frame structure for thephysical layer that can support both existing high data rateapplications and machine-to-machine data traffic. Second,they support novel non-orthogonal waveforms that will pro-vide better performance for the physical layer. Third, theypropose the use of sparse signal processing that can decodebursty data traffic in an energy-efficient manner. Fourth, theyhighlight the importance of robust wireless systems that canperform well with real world limitations such as limited con-trol channel bandwidth and imperfect channel knowledge.Finally, they highlight the importance of reducing the end-to-end delay of wireless links from tens of milliseconds to around1 ms in order to meet the requirements of new machine-to-machine services.

The sixth article, Millimeter-Wave Beamforming as anEnabling Technology for 5G Cellular Communications: Theo-retical Feasibility and Prototype Results, is written by authorsfrom Samsung. This article describes their initial studies on thefeasibility of using the 30 GHz band for data transmission.Their work shows that the use of antenna arrays can counter-act the expected higher path loss at higher frequencies,enabling these bands to be used for cellular communications.They also describe a beamforming algorithm and discuss theirinitial field trial results of a practical 30 GHz antenna arraysystem tested in Korea. Results show that good cellular cover-age was achieved for both outdoor-outdoor and outdoor-indoor communication scenarios. These show the highpotential of using millimetre-wave frequencies for 5G systems.

The seventh article, Applications of Self-InterferenceCancellation in 5G and Beyond, is written by authors fromKumu Networks. They are developing self-interference can-cellation techniques for wireless receivers. This will enablefull-duplex communications, where a radio can transmit andreceive at the same time on the same frequency. Their articledescribes the basic self-interference cancellation radio archi-tecture. It also shows how this approach can lead to moreflexible spectrum use, including the concept of using the samefrequencies for mobile terminals and backhaul links. Finally,they discuss how self-interference cancellation will affectfuture standardization.

The eighth article, Cellular Architecture and Key Tech-nologies for 5G Wireless Communication Networks, is jointlyco-authored by researchers from the United Kingdom andChina. The article presents a future cellular network architec-ture using a combination of macrocells for outdoor coverageand relays, and small cells for indoor coverage. The articlealso identifies several key technologies for 5G systems. Theseinclude the use of massive MIMO and spatial modulation,which is a simple approach to increasing the capacity ofantenna array systems. The article also discusses the use ofcognitive radio as a means to use radio spectrum more effec-tively in the future. The mobile small cell concept is proposedwhere devices are installed on cars and trains along with theidea of promoting greener communications. The article con-cludes with some key research challenges to enable 5G.

The final article in this special issue is entitled Cache inthe Air: Enabling the Green Multimedia Caching and Deliv-

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IEEE Communications Magazine February 201464

ery for 5G Systems and is written by researchers at the Uni-versity of British Columbia. It deals with data storage orcaches through the mobile network, which can preemptivelyprovide popular data requests, improving quality of serviceand reducing delay. The article describes different levels ofcaching that may be used in a mobile network. It also providesperformance results to show the reduction in data delay thatcan be achieved and some examples of the potential savings innetwork costs due to caching.

Two of the Editors (Fettweis and Alamouti) have co-authored a separate article accepted through the magazinesopen call route, entitled 5G: Personal Mobile InternetBeyond What Cellular Did to Telephony. This article appearsalongside this Feature Topic. It discusses some key historicaltrends in wireless communications and looks forward to someof the major challenges that will necessitate new 5G stan-dards. These include providing high bandwidth content withspeeds in excess of 10 Gb/s. Furthermore, emerging monitor-ing and control applications should be integrated into 5G withvery low wireless data rates combined with very low energyconsumption. A third major trend is to develop new applica-tions through the tactile wireless Internet, with total end-to-end delays of less than 1 ms.

In conclusion, the Editors would like to thank all authorswho submitted manuscripts to this Feature Topic. Space con-straints have meant that only nine of the 18 high-qualitymanuscripts accepted for this issue appear this month; theother nine will be published in the May 2014 issue. This willfeature articles from new European research projects such asMETIS and iJOIN, alongside contributions from Samsung,the Fraunhofer Heinrich Hertz Institute, the Chinese Acade-my of Sciences, and the University of Waterloo. The Editorswish to thank the reviewers who helped to review all of thepapers in a very short timescale. They are grateful to the Edi-tor-in-Chief, Sean Moore, for his encouragement and supportto organize this special issue. They would also like to thankthe publication staff, Joseph Milizzo and Jennifer Porcello,along with Richard Fritzsche of TU Dresden for their assis-tance. We finish this editorial by noting that two related Fea-ture Topics on millimeter-wave technology and on end-to-endarchitectures for 5G are due to appear in the magazine in thesecond half of 2014.

BIOGRAPHIESJOHN THOMPSON (john.thompson@ed.ac.uk) currently holds a personal Chairin Signal Processing and Communications at the School of Engineering inthe University of Edinburgh. He specializes in antenna array processing,cooperative communications systems, and energy-efficient wireless commu-nications. His work in these areas is highly cited, and his h-index is currently18 according to the Web of Science. He is an elected Member-at-Large forthe Board of Governors of the IEEE Communications Society from20122014, the second largest IEEE Society. He was a Technical ProgramCo-Chair for the 2013 IEEE Vehicular Technology Spring Conference in Dres-den, Germany, and serves as a track chair on Green Communications for the2014 IEEE ICC in Sydney, Australia. He is lead Editor for this Feature Topic.

XIAOHU GE is currently a professor with the Department of Electronics andInformation Engineering at Huazhong University of Science and Technology(HUST), China. He received his Ph.D. degree in communication and informa-

tion engineering from HUST in 2003. He has worked at HUST since Novem-ber 2005. His research interests are in the area of mobile communications,traffic modeling in wireless networks, green communications, and interfer-ence modeling in wireless communications. He has published about 80papers in refereed journals and conference proceedings, and has beengranted about 15 patents in China. He is leading several projects funded byNSFC, China MOST, and industry. He is taking part in several internationaljoint projects, such as the RCUK funded UK-China Science Bridges: R&D on(B)4G Wireless Mobile Communications .

HSIAO-CHUN WU received his B.S.E.E. degree from National Cheng Kung Uni-versity, Tainan, Taiwan, in 1990, and M.S. and Ph.D. degrees in electricaland computer engineering from the University of Florida, Gainesville, in1993 and 1999, respectively. From March 1999 to January 2001, he waswith Motorola Personal Communications Sector Research Laboratories as asenior electrical engineer. Since January 2001, he has been with the facultyof the School of Electrical Engineering and Computer Science, LouisianaState University, Baton Rouge. He has published more than 170 peer-refer-eed technical journal and conference articles in electrical and computerengineering. His current research interests include the areas of wirelesscommunications and signal processing. He is an IEEE Distinguished Lecturerand is currently an Associate Editor for several IEEE journals.

RALF IRMER is currently leading Wireless Access Research in Vodafone GroupR&D, United Kingdom. He received his Dr.-Ing. (Ph.D.) degree from Technis-che Universitt Dresden in 2005 after studies in Dresden and Edinburgh.He joined Vodafone in 2005, where his major achievements were workingwith Verizon Wireless, China Mobile, and others to make LTE a global stan-dard meeting operator requirements. He defined the Wi-Fi and small cellstrategies and the future wireless network blueprint for Vodafone. He wasalso responsible for proving key strategies in pre-commercial trials, such asLTE TDD, LTE-Advanced, and 3G/LTE/WiFi small cells including backhaul. Hecurrently leads the 5G activities in Vodafone. He holds several patents, andhas published over 30 conference and journal publications, covering coordi-nated multipoint, multiuser MIMO, relaying, heterogeneous networks, andquality of user experience.

HONG JIANG is a researcher and project leader with Alcatel-Lucent Bell Labsin Murray Hill, New Jersey. He received his B.S. degree from SouthwestJiaotong University, Chengdu, China; M. Math. from the University ofWaterloo, and Ph.D. from the University of Alberta, Canada. His researchinterests include signal processing, digital communications, and image andvideo compression. He invented key algorithms for VSB demodulation andHDTV video processing in the first generation ATSC system, which won aTechnology and Engineering Emmy Award. He pioneered hierarchical mod-ulation for satellite communication that resulted in commercialization ofvideo transmission. He has published more than 50 articles in peer-reviewed scientific and engineering journals, and more than 40 U.S.patents in digital communications and video processing.

GERHARD FETTWEIS [F] earned his Ph.D. under H. Meyrs supervision fromRWTH Aachen in 1990. After one year at IBM Research in San Jose, Califor-nia, he moved to TCSI Inc., Berkeley, California. Since 1994 he is VodafoneChair Professor at TU Dresden, Germany, with 20 companies from Asia,Europe, and the United States currently sponsoring his research on wirelesstransmission and chip design. He coordinates two DFG centers at TU Dres-den, cfAED and HAEC. He is a member of acatech, has an honorary doctor-ate from TU Tampere, and has received multiple awards. In Dresden he hasspun out 11 start-ups, and set up funded projects of close to 0.5 billionvolume. He has helped organize IEEE conferences, most notably as TPCChair of IEEE ICC 2009, IEEE TTM 2012, and General Chair of VTC Spring2013 and DATE 2014.

SIAVASH ALAMOUTI received B.A.Sc. and M.A.Sc. degrees in electrical engi-neering from the University of British Columbia. He is currently an indepen-dent entrepreneur helping to build new companies with a focus on mobilepersonalization. He was Group R&D director for Vodafone from March2010 until September 2013. Before that he was an Intel Fellow and CTO ofthe Mobile Wireless Group. Prior to joining Intel in 2004, he was the CTOof Vivato, and held various positions at Cadence, AT&T, and MPR Teltech.He is most well known for the invention of the Alamouti Code.

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