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GUEST EDITORIAL
HETEROGENEOUS AND SMALL CELL NETWORKS: PART 1
Ismail Guvenc
D
Tony Q.S. Quek
riven by a new generation of wireless user equipment and the proliferation of bandwidth-intensive applications, user data traffic and the corresponding network load are increasing in an exponential manner. Most of this new data traffic is being generated indoors, which requires increased link budget and coverage extension to provide satisfactory user experience. As a result, current cellular networks are reaching their breaking point, and conventional cellular architectures that are devised to cater to large coverage areas and optimized for homogeneous traffic are facing unprecedented challenges to meet these user demands. In this context, there has been increasing interest in deploying relays, distributed antennas, and small cell access points (e.g., picocells and femtocells) in residential areas, subways, and offices. These network architectures, commonly referred to as heterogeneous networks (HetNets), are either operator-deployed and/or consumerdeployed, and are made up of a mix of low-power cells underlying the macrocell network. By deploying additional network nodes within the local area range and bringing the network closer to end users, HetNets can potentially improve spatial reuse and coverage, thus allowing future cellular systems to achieve higher data rates, while retaining the seamless connectivity and mobility of cellular networks. Inspired by the attractive features and potential advantages of HetNets, their development and deployment have been gaining momentum in the wireless industry and research communities in the last few years. It has also attracted the attention of standardization bodies, such as the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)-Advanced. However, HetNets also come with their own challenges, and there are significant technical issues that still need to be addressed for successful rollout and operation of these networks. The goal of this Feature Topic was to solicit contributions from experts working in this area to motivate further interest in heterogeneous and small cell networks. We received a large number of submissions, and it has been a challenging task to select the best and best adapted papers. The accepted arti-
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Marios Kountouris
David Lopez-Perez
cles in this Feature Topic will be published in two issues of IEEE Communications Magazine, in this issue and the next, in June 2013. In this first feature topic issue, we have six accepted papers that address self-organization, mobility, energy efficiency, and small cell discovery issues in HetNets. The first two articles are related to self-organization and automatic network planning in HetNet deployments. The article by Peng et al. provides a comprehensive survey of self-organizing networks (SONs) in 3GPP LTE-Advanced HetNet systems and follows by investigating several self-configuration and self-optimization issues in HetNets. With a testbed for HetNets, the performance gain of SON algorithms is verified. The article by Guo et al. provides an overview of different cell site planning approaches based on deterministic models, Monte Carlo simulation, and stochastic geometry-based models. An automated framework for outdoor and indoor deployment of low-power nodes is presented and validated through using real network data. Smaller and denser deployments of HetNets introduce challenging problems related to mobility management, which are covered by the next two articles. The article by Munoz et al. is on traffic steering in HetNets, which allows operators to modify user distributions across different network tiers. Different mechanisms of traffic steering are introduced for both idle and connected mode scenarios, in which mobility parameters can be adjusted by a cellular operator to achieve specific goals. A fuzzy-logic-based SON algorithm to meet specified traffic steering goals is also proposed, which adapts the thresholds for inter-radio access technology (RAT) handovers using a reinforcement learning algorithm. In the next article by Pedersen et al., mobility enhancements in HetNets are investigated considering a inter-site carrier aggregation scenario. In the proposed approach, macrocell mobility is network controlled, while the users autonomously decide small cell addition, removal, and change without any explicit signaling of measurement events to the network. As a result, signaling overhead for small cell handover is reduced, as illustrated by their system-level simulation results.
IEEE Communications Magazine • May 2013
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GUEST EDITORIAL Energy efficiency is another important challenge in HetNet deployments, which is addressed by the last two articles in our Feature Topic. In the article by Prasad et al., the authors present various cell detection techniques designed for energy-efficient discovery of small cells deployed in a different carrier than the umbrella macrocell. The drawbacks of currently standardized mechanisms are analyzed, and new flexible schemes are proposed. Results show that adaptive schemes lead to significant user equipment power savings at the expense of insignificant losses in offloading opportunities. In the last article by Xu et al., the authors propose a two-layer network functionality separation scheme, targeted at low control signaling overhead and flexible network reconfiguration for future mobile networks. Numerical results show that the proposed scheme achieves significant energy reduction over traditional LTE networks, and can be recommended as a candidate solution for future green mobile networks.
BIOGRAPHIES ISMAIL GUVENC [SM’10] (
[email protected]) received his Ph.D. degree in electrical engineering from the University of South Florida in 2006, with an outstanding dissertation award. He was with Mitsubishi Electric Research Labs during 2005, and with DOCOMO Innovations Inc. between 2006 and 2012, working as a research engineer. Since August 2012, he has been an assistant professor with Florida International University. His recent research interests include heterogeneous wireless networks and future radio access beyond 4G wireless systems. He has published more than 70 conference and journal papers, and several standardization contributions. He coauthored/co-edited three books for Cambridge University Press, is an Editor for IEEE Communications Letters and IEEE Wireless Communications Letters, and was a Guest Editor for three special issue journals/magazines on heterogeneous networks. He is an inventor/co-inventor of 17 U.S. patents, and has another 9 pending U.S. patent applications. T ONY Q.S. Q UEK [SM’12] (
[email protected]) received B.E. and M.E. degrees in electrical and electronics engineering from the Tokyo Institute of Technology in 1998 and 2000, respectively. At MIT, he earned his Ph.D. in
IEEE Communications Magazine • May 2013
electrical engineering and computer science in February 2008. Currently, he is an assistant professor with the Information Systems Technology and Design Pillar at Singapore University of Technology and Design. He is also a scientist with the Institute for Infocomm Research. He is currently an Editor for IEEE Transactions on Communications and IEEE Wireless Communications Letters. He received the Singapore Government Scholarship in 1993, Tokyu Foundation Fellowship in 1998, and the A*STAR National Science Scholarship in 2002. He was honored with the 2008 Philip Yeo Prize for Outstanding Achievement in Research, the IEEE GLOBECOM 2010 Best Paper Award, the 2011 JSPS Invited Fellow for Research in Japan, the CAS Fellowship for Young International Scientists in 2011, and the 2012 IEEE William R. Bennett Prize. M ARIOS K OUNTOURIS [M’08] (
[email protected]) received his Diploma in electrical and computer engineering from the National Technical University of Athens, Greece in 2002, and his M.S. and Ph.D. degrees in electrical engineering from the Ecole Nationale Supérieure des Télécommunications, Paris, France, in 2004 and 2008, respectively. In 2008–2009 he was a research associate at the University of Texas at Austin. Since June 2009, he has been an assistant professor at the Department of Telecommunications at Ecole Supérieure d’Electricité, France. He has published more than 60 journal and conference papers, and has served as organizer and technical program committee member for several top international conferences and workshops. He is currently an Editor for the EURASIP Journal on Wireless Communications and Networking. He also received the 2012 IEEE SPS Signal Processing Magazine Award and the Best Paper Award in Communication Theory Symposium at IEEE GLOBECOM in 2009. He is a Professional Engineer of the Technical Chamber of Greece. DAVID LOPEZ-PEREZ (
[email protected]) is a member of technical staff at Bell Laboratories, Alcatel-Lucent, Dublin, Ireland. He earned his Ph.D. in wireless networking from the University of Bedfordshire, United Kingdom, in 2011. In 2010–2011, he was a postdoctoral research associate at King's College London, United Kingdom, and in 2005–2006, he was with VODAFONE Spain, working in the area of network planning and optimization. In 2011 and 2009, he was invited researcher at DOCOMO USA Labs, Palo Alto, California, and CITI INSA, Lyon, France, respectively. He has published more than 50 book chapters, and journal and conference papers, all in recognized venues, and filed a number of patents. He is a founding member of IEEE TSCGCC, and has been awarded as an Exemplary Reviewer for IEEE Communications Letters. He is an author and/or editor of several books, and he is or has been a Guest Editor of IEEE Communications Magazine, ACM/Springer MONE, and EURASIP JCNC. He is or has been a TPC member of major IEEE conferences, as well as a co-chair of several IEEE workshops.
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