An adaptive traffic control scheme for hierarchically structured CDMA cellular systems

The hierarchical cell structure (HCS) describes a system where at least two types of cells (e.g. macrocell and microcell) operate one upon another. Due to increasing demand in the capacity of future cellular systems, HCS is expected to be an increasingly popular trend in cellular system design. We have proposed a traffic control mechanism for CDMA HCS, which dynamically adapts to a varying traffic environment by redistributing traffic between the macrocell and microcell. The proposed scheme dynamically adjusts the coverage area of the microcell to maintain a required signal to interference ratio in both the microcell and macrocell. The performances were measured in terms of the call blocking probability and call failure probability. The call blocking rate improves when the system is lightly loaded and the loads are unbalanced between the macrocell and microcell. Performance improvements were significant in terms of the call failure rate.