Frequency assignment for cellular mobile systems using constraint satisfaction techniques

This paper presents a new algorithm for solving frequency assignment problems in cellular mobile systems using constraint satisfaction techniques. The characteristics of this algorithm are as follows: 1) instead of representing each call in a cell (a unit area in providing communication services) as a variable, we represent a cell (which has multiple calls) as a variable that has a very large domain, and determine a variable value step by step, 2) a powerful cell-ordering heuristic is introduced, 3) a branch-and-bound search that incorporates forward-checking is performed, and 4) the limited discrepancy search is introduced to improve the chance of finding a solution in a limited amount of search. Experimental evaluations using standard benchmark problems show that this algorithm can find optimal or semi-optimal solutions for these problems, and most of the obtained solutions are better than or equivalent to those of existing methods using simulated annealing, tabu search, or neural networks. These results show that state-of-the-art constraint satisfaction/optimization techniques are capable of solving realistic application problems when equipped with an appropriate problem representation and heuristics.