Channel assignment and layer selection in hierarchical cellular system with fuzzy control

We consider a hierarchical system which consists of a macrolayer and a microlayer. The macrocells accommodate fast mobile users. However, if we direct too many mobile users to the macrocells, the system capacity is low. On the other hand, the microcells are designed to increase capacity, but they cause a large number of handoffs. Our aim is to maximize the system capacity while keeping the amount of handoff small. We minimize the handoff rate by a fuzzy layer selection algorithm which makes use of the past cell dwell times of a user and the channel occupancy of the target cell. To maximize the capacity, we propose a distributed channel assignment algorithm to dynamically allocate the channels among the two layers. Exchange of information is allowed between neighboring macrocells. The state of channel assignment in a macrocell and its interfering cells are tabulated in a channel allocation table, which provides all the information required in the integrated resource allocation scheme. The performance is evaluated by simulation and compared with the popular layer selection scheme known as the threshold method.