Power Control in Cellular Radio Systems
Sammanfattning: The primary goal of cellular radio systems, is to provide communication services to a large number of mobile users. Due to the rapid expansion of the market in this area, the available resources have to be used efficiently. The main issue in this thesis is methods to assign appropriate transmission powers, given coarsely quantized measurements, in order to meet the quality requirements from the users despite various disturbances.We propose a concept of a power regulator comprising the steps of estimating relevant quantities, handling quality specications, and controlling the powers. With this setting, the power controlling component relates directly to the mainstream of the algorithms proposed to date.For practical reasons, it is necessary to control the powers in a distributed fashion, and these distributed algorithms can be seen as local control loops. The effects of time delays and power output constraints in these loops are analyzed with respect to stability, using root locus techniques and describing functions. We emphasize the importance of identifying these time delays and constraints in order to choose the appropriate controller parameters for stable operation. The relevance of the local stability results on the overall system level is discussed, and further analyzed in a simulation environment, which has been developed.The literature is surveyed, and the contributions are classified with respect to a common framework in order to stress their similarities and differences. We show that an integrating controller forms the basis for the most popular algorithms. Methods for convergence analysis are investigated and related to the theory of linear systems. These methods are applied when proving global convergence of the integrating controller.The power control strategies are evaluated under more realistic circumstances in an environment simulating the operation of a GSM system. Comparing the results when using different power control algorithms we note that the proposed concept performs better than the algorithms proposed to date, both in terms of transmission quality of service and capacity.
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