Optimization and Systems Theory Seminar
September 30, at 11.00, room 3721, Lindstedtsvägen 25, KTH:

Ph.D. Seminar

Mikael Fallgren,
Division of Optimization and Systems Theory
Department of Mathematics

He will present his thesis that will be defended October 7:

Optimization of Joint Cell, Channel and Power Allocation in Wireless Communication Networks

In this thesis we formulate joint cell, channel and power allocation problems within wireless communication networks. The objectives are to maximize the user with minimum data throughput (Shannon capacity) or to maximize the total system throughput, referred to as the max-min and max-sum problem respectively. The complexity is studied together with proposed optimization- and heuristic-based approaches. In the first paper an overall joint cell, channel and power allocation max-min problem is formulated. We show that the decision problem is NP-hard and that the optimization problem is not approximable unless P is equal to NP, for instances with a sufficiently large number of channels. Further, it follows that for a feasible binary cell and channel allocation, the remaining continuous power allocation optimization problem is still not approximable unless P is equal to NP. In addition, it is shown that first-order optimality conditions give global optimum of the single channel power allocation optimization problem, although the problem is in general not convex. In the following two papers heuristics for solving the overall problem are proposed. In the second paper we consider the single channel problem with convex combinations of the max-min and the max-sum objective functions. This variable utility provides the ability of tuning the amount of fairness and total throughput. The third paper investigates the multiple channel setting. On a system with three cells, eight mobile users and three channels, we perform an exhaustive search over feasible cell and channel allocations. The exhaustive search is then compared to the less computationally expensive heuristic approaches, presenting potential earnings to strive for. A conclusion is that several of the proposed heuristics perform very well. The final paper incorporates fixed relay stations into the overall joint cell, channel and power allocation max-min problem. The complexity is inherited from the formulation without relay stations. Further, we propose a heuristic channel allocation approach that shows good performance, compared to an optimization based approach, in numerical simulations on the relay setting.

Calendar of seminars Last update: September 5, 2011.