Discrete and Continuous Optimization Methods for Self-Organization in Small Cell Networks - Models and Algorithms

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2016-08-25
Degree programme
93 + app. 89
Aalto University publication series DOCTORAL DISSERTATIONS, 150/2016
Self-organization is discussed in terms of distributed computational methods and algorithms for resource allocation in cellular networks. In order to develop algorithms for different self-organization problems pertinent to small cell networks (SCN), a number of concepts from discrete and continuous optimization theory are employed. Self-organized resource allocation problems such as physical cell identifier (PCI) assignment and primary component carrier selection are formulated as discrete optimization problems. Distributed graph coloring and constraint satisfaction algorithms are used to solve these problems. The PCI assignment is also discussed for multi-operator heterogeneous networks. Furthermore, different variants of simulated annealing are proposed for solving a graph coloring formulation of the orthogonal resource allocation problem. In the continuous optimization domain, a network utility maximization approach is considered for solving different resource allocation problems. Network synchronization is addressed using greedy and gradient search algorithms. Primal and dual decomposition are discussed for transmit power and scheduling weight optimizations, under a network-wide power constraint. Joint optimization over transmit powers and multi-user scheduling weights is considered in a multi-carrier SCN, for both maximum rate and proportional-fair rate utilities. This formulation is extended for multiple-input multiple-output (MIMO) SCNs, where apart from transmit powers and multi-user scheduling weights, the transmit precoders are also optimized, for a generic alpha-fair utility function. Optimization of network resources over multiple degrees of freedom is particularly effective in reducing mutual interference, leading to significant gains in network utility. Finally, an alternate formulation of transmit power allocation is considered, in which the network transmit power is minimized subject to the data rate constraints of users. Thus, network resource allocation algorithms inspired by optimization theory constitute an effective approach for self-organization in contemporary as well as future cellular networks.
Supervising professor
Tirkkonen, Olav, Prof., Aalto University, Department of Communications and Networking, Finland
Thesis advisor
Dowhuszko, Alexis, Dr., Aalto University, Department of Communications and Networking, Finland
Self-organization, optimization, small cell networks, resource allocation, graph coloring, network utility maximization, 4G, 5G
  • [Publication 1]: F. Ahmed, O. Tirkkonen, M. Peltomäki, J.-M. Koljonen, C.-H. Yu, and M. Alava. Distributed Graph Coloring for Self-Organization in LTE Networks. Journal of Electrical and Computer Engineering, vol. 2010, Article ID 402831, 10 pages, 2010. doi: 10.1155/2010/402831
  • [Publication 2]: F. Ahmed and O. Tirkkonen. Self Organized Physical Cell ID Assignment in Multi-operator Heterogeneous Networks. In Proceedings of IEEE Vehicular Technology Conference Spring, pages 1-5, May 2015. doi: 10.1109/VTCSpring.2015.7146077
  • [Publication 3]: F. Ahmed and O. Tirkkonen. Simulated Annealing Variants for Selforganized Resource Allocation in Small Cell Networks. Applied Soft Computing, vol. 38, pages 762-770, Jan. 2016. doi:10.1016/j.asoc.2015.10.028
  • [Publication 4]: F. Ahmed and O. Tirkkonen. Topological Aspects of Greedy Self Organization. In Proceedings of IEEE International Conference on Self-Adaptive and Self-Organizing Systems, pages 31-39, Sep. 2014. doi: 10.1109/SASO.2014.15
  • [Publication 5]: F. Ahmed, O. Tirkkonen, A. Dowhuszko, and M. Juntti. Distributed Power Allocation in Cognitive Radio Networks under Network Power Constraint. In Proceedings of IEEE International Conference on Cognitive Radio Oriented Wireless Networks and Communications, pages 492-497, June 2014. doi: 10.4108/icst.crowncom.2014.255738
  • [Publication 6]: F. Ahmed, A. Dowhuszko, and O. Tirkkonen. Distributed Algorithm for Downlink Resource Allocation in Multicarrier Small Cell Networks. In Proceedings of IEEE International Conference on Communications, pages 6802-6808, June 2012. doi: 10.1109/ICC.2012.6364716
  • [Publication 7]: F. Ahmed, A. Dowhuszko, and O. Tirkkonen. Distributed Downlink Resource Allocation for Multi-carrier MIMO Small Cell Networks. Submitted to IEEE Transactions on Vehicular Technology, 2016.
  • [Publication 8]: F. Ahmed, A. Dowhuszko, O. Tirkkonen, and R. Berry. A Distributed Algorithm for Network Power Minimization in Multicarrier Systems. In Proceedings of IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, pages 1914-1918, Sep. 2013. doi: 10.1109/PIMRC.2013.6666456