Optimisation approaches to distributed multi-cell radio resource management
This PhD project was carried out in collaboration with Ericsson Research.
People
The PhD student was Mikael Fallgren with Anders Forsgren (CIAM/KTH) as the advisor. In addition to the adviser, the reference group consisted of Johan Håstad (CIAM/KTH), Gabor Fodor (Ericsson Research), and Mikael Prytz (Ericsson Research).
Financing
The project was fully funded by CIAM.
Status
The project was completed in 2011-10-07 when Fredrik Carlsson successfully defended his PhD thesis at the Optimization and Systems Theory, Department of Mathematics, KTH School of Engineering Sciences.
Background
Radio Resource Management (RRM) is the system level control of co-channel interference and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems. It involves strategies and algorithms for controlling parameters such as transmit power, channel allocation, data rates, handover criteria, modulation scheme, error coding scheme, etc. The objective is to utilise the limited radio spectrum resources and radio network infrastructure as efficiently as possible. Dynamic RRM schemes adaptively adjust the radio network parameters to the traffic load, user positions, quality of service requirements, etc. Dynamic RRM schemes are considered in the design of wireless systems, in view to minimise expensive manual cell planning and achieve 'tighter' frequency reuse patterns, resulting in improved system spectral efficiency. This calls for the development of optimisation-based approaches for dynamic RRM.
Goals
To formulate optimisation-based approaches to distributed, for dynamic RRM applied on existing and future cellular systems. In particular one seeks to maximise the user with minimum data throughput (Shannon capacity) or to maximise the total system throughput, referred to as the max-min and max-sum problem, respectively.
Scientific achievements
In the first paper of the thesis, an overall joint cell, channel and power allocation max-min problem is formulated. It is shown that the decision problem is NP-hard and that the optimisation 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 optimisation 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 optimisation problem, although the problem is in general not convex. In the following two papers, heuristics for solving the overall problem are proposed. The second paper considers the single channel problem and the third paper investigates the multiple channel setting. 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.