LiU-ITN-TEK-A--12/034--SE Load Balancing in Heterogeneous LTE-A Networks Wondmeneh Awoke Mengistie Kennedy Ronoh 2012-06-18 Department of Science and Technology Institutionen för teknik och naturvetenskap Linköping University Linköpings universitet SE-601 74 Norrköping, Sweden 601 74 Norrköping LiU-ITN-TEK-A--12/034--SE Load Balancing in Heterogeneous LTE-A Networks Examensarbete utfört i elektroteknik vid Tekniska högskolan vid Linköpings universitet Wondmeneh Awoke Mengistie Kennedy Ronoh Handledare Qing He Examinator Di Yuan Norrköping 2012-06-18 Upphovsrätt Detta dokument hålls tillgängligt på Internet – eller dess framtida ersättare – under en längre tid från publiceringsdatum under förutsättning att inga extra- ordinära omständigheter uppstår. Tillgång till dokumentet innebär tillstånd för var och en att läsa, ladda ner, skriva ut enstaka kopior för enskilt bruk och att använda det oförändrat för ickekommersiell forskning och för undervisning. 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The online availability of the document implies a permanent permission for anyone to read, to download, to print out single copies for your own use and to use it unchanged for any non-commercial research and educational purpose. Subsequent transfers of copyright cannot revoke this permission. All other uses of the document are conditional on the consent of the copyright owner. The publisher has taken technical and administrative measures to assure authenticity, security and accessibility. According to intellectual property law the author has the right to be mentioned when his/her work is accessed as described above and to be protected against infringement. For additional information about the Linköping University Electronic Press and its procedures for publication and for assurance of document integrity, please refer to its WWW home page: http://www.ep.liu.se/ © Wondmeneh Awoke Mengistie, Kennedy Ronoh Abstract LTE-A is the latest cellular network technology. One feature of LTE-A is the use of heterogeneous networks (HetNets) which consist of macro-cells and low power nodes (LPNs). One of the objectives of heterogeneous networks is to increase capacity especially in hotspot areas where there is high density of users. Due to their low transmit power, very few users associate with LPNs and this will result in load imbalance between LPNs and macro- cells. Load balancing is therefore key issue in HetNets so as to maximize cell splitting gains and ensure even user experiences. Cell range extension (CRE) is a technique that can be used to achieve load balancing in HetNets. Under CRE, an offset is added to LPNs during cell selection so as to expand the range of LPNs and offload more users from macro-cells to LPNs. CRE usually involves the use of uniform offsets. The use of uniform offsets results in some degree of load balancing in a HetNet which is not optimal. This arises because different LPNs require different offsets due to varying conditions such as user distribution and propagation environment in different hotspots. The use of cell-specific offsets is necessary for improving the level of load balancing in HetNets. In this thesis a heuristic load balancing algorithm that is used to assign cell-specific offsets to LPNs is designed. The algorithm makes use of a range optimization framework which applies the concept of cell load coupling. Our results show that the use of the cell-specific offsets results in not only a high degree of load balancing as measured by Jain’s fairness index but also more even user experiences in terms of throughput. i Acknowledgements We would like to thank: Mobile Telecommunications research group in Linköping University for giving us an opportunity to work with them. Our supervisor, Qing He, for the useful ideas she gave us and guidance during the project. Our examiner, Professor Di Yuan, for the support he gave us during the project and for the useful ideas that form a core part of this thesis. Our parents for the moral and financial support they gave us. It is through their sacrifices that we have been able to complete not only this thesis but indeed our entire studies at Linköping University. ii iii Table of Contents Table of Contents Abstract...............................................................................................................................................i Acknowledgements ............................................................................................................................ii List of Figures ..................................................................................................................................... v List of Tables ..................................................................................................................................... vi Acronyms ......................................................................................................................................... vii 1. Introduction ...................................................................................................................................1 1.1 Thesis goals ...............................................................................................................................1 1.2 Method .....................................................................................................................................2 1.3 Thesis Overview ........................................................................................................................2 2. LTE-A and Heterogeneous Networks ..............................................................................................3 2.1 Background of LTE-A .................................................................................................................3 2.2 System Requirements and Key Features ....................................................................................4 2.3 System Architecture ..................................................................................................................5 2.4 LTE Time-frequency Grid ...........................................................................................................6 2.5 Multiple Access Schemes...........................................................................................................7 2.5.1 OFDMA and OFDM .............................................................................................................7 2.5.2 SC-FDMA ............................................................................................................................9 2.6 Multi –antenna Techniques ..................................................................................................... 10 2.7 LTE-A Heterogeneous Networks .............................................................................................. 11 2.7.1 Traditional Network and its Shortcomings....................................................................... 11 2.7.2 Benefits of Heterogeneous Networks ............................................................................... 12 2.7.3 HetNets Network Architecture and Deployment ............................................................. 12 2.7.4 Types of LPNs.................................................................................................................. 13 3. Radio Resource Management in LTE-A ......................................................................................... 15 3.1 Scheduling............................................................................................................................... 16 3.1.1 Channel Quality Information ............................................................................................. 16 3.1.2 Link Adaptation and Power Allocation .............................................................................. 17 3.1.3 Buffer Status Information ................................................................................................. 17 3.2 Load Balancing ........................................................................................................................ 17 3.3 RRM techniques for Interference Management in LTE-A HetNets ............................................ 17 3.3.1 Static Resource Partitioning .............................................................................................. 18 3.3.2 Adaptive Resource Partitioning ......................................................................................... 18 3.4 Handover Control ...................................................................................................................