Optimization approach for the radio frequency spectrum management in cellular mobile communication systems

Abstract

Recently, in cellular mobile communication systems, the traffic demand has remarkably increased in spite of the limited radio frequency spectrum. Hence it is a very critical problem to use the limited spectrum in the most economical way. As an effort to solve this problem, this study investigates efficient algorithms for frequency assignment problem (FAP) in the cellular systems.

First, this study considers the FAP in a cellular system with a maximal distance of channel interference. This special structure is observed in most cellular systems. To handle the considered FAP, we use a new concept, the pattern approach which fits naturally to the problem. On the basis of this approach, we are able to formulate the considered FAP into a manageable optimization problem and propose a two phase heuristic algorithm for the problem. Computational experiments show that the two phase algorithm performs much better in both solution quality and computational time than the recently developed algorithms for the FAP. In addition, some theoretical results about the pattern approach are provided, which opens a meaningful viewpoint on the frequency assignment. That is, we can give explanations on the theoretical relationships between the two phase algorithm and the other algorithms for the FAP. Since the considered FAP well reflects most cellular systems, the two phase algorithm can be applied to many practical situations.

Second, this study proposes a new dynamic channel assignment (DCA) algorithm for microcellular systems. The microcells are indispensable to the future mobile communication systems under a huge communication traffic. In developing the algorithm, we provide a mathematical formulation of maximal packing (MP), which takes actual propagation conditions into account. Our algorithm is based on this formulation and adopts Lagrangean relaxation technique. This is, to our knowledge, the first mathematical programming approach in this area. Simulation results show that...