Fuzzy Layer Selection Method in Hierarchical Cellular Systems

Hierarchical cellular systems are proposed to accommodate mobile users of different speeds. While the micro layer serve the slow users, the macro layer serve the fast users. After a handoff is initiated, we must make a decision determining whether it should go to the micro or macro cell. In this paper, this problem is tackled by making use of past cell dwell time and occupancies in the target micro and macro cell. Heuristically, we want those mobile users with small cell dwell time, i.e. fast velocity, to join the macro layer. It is also desirable to select the target cell which has lower occupancy, in order to prevent call blocking. These heuristics are incorporated in a fuzzy layer selection algorithm, which is devised in terms of fuzzy set and fuzzy logic. The performance is compared to the popular threshold method in the literature by simulation.