Advanced mobility management techniques for hierarchical cell structure

Increasing demand for global wireless mobile communication services has motivated extensive research and development activities surging the way towards the 3rd generation personal communication systems, focusing in particular- on flexible control mechanisms and efficient mobility management. The Hierarchical Cell Structure (HCS)/multi layer cell architecture represents one of the most efficient techniques used in the radio environment to extend the coverage and provide greater capacity. It also offers flexibility to operators to tailor-fit capacity to match traffic demands in a growing market. However, the performance of such a system is influenced by many factors, dictating additional challenges in system design. This thesis focuses on enhanced mobility management, control mechanism, and relevant issues in a hierarchical cell structure in 3rd generation mobile communication system. The network integration issue in a multi-layer cell architecture, when each layer exploits different radio and network technologies, is thoroughly investigated. Various integration solutions are proposed. Within the selected scenario, location management, call routing, cell selection and handover are investigated and improved signalling message sequences are identified. New mobility management mechanisms leading to significant reduction of the signalling traffic in the integrated system are proposed. The handover issues in a two-layer cell architecture are also studied. New inter-system handover algorithms are proposed and their performances are analysed via both mathematical and simulation models. Novel methods are also proposed to optimise the inter-system handover performance in terms of reduction of unnecessary handover probability and mean number of handovers. The handover control mechanism and handover time, are thoroughly investigated and suitable control methods are suggested for such a system. The signalling load issue is examined and the performance of the proposed techniques is evaluated. Finally, the Grade of Service (GoS) issue is thoroughly investigated. The performance of the various overflow policies are examined through an analytical model and an optimum policy is recommended. The impacts of the proposed handover algorithms on the GoS are evaluated. A new methodology is also proposed to estimate the optimum channel allocation ratio between layers providing a uniform GoS between layers.