The Research Of Hierarchical Cellular System & Soft Handover Scheme In HCS

The thesis introduces a hierarchical cellular system. In this kind of system, a set of contiguous microcells are overlaid with a macrocell. High-speed mobile stations are serviced in the macrocells to minimize the number of handoffs while low-speed mobile stations are serviced in the microcells to increase the system capacity.To achieve an efficient hierarchical handoffs, the thesis proposes a dynamic velocity estimation algorithm which based on overlapping cell sojourn time called OA algorithm. Considering the direction change of mobile stations, OA algorithm reduces the measuring region of cell sojourn time. The smaller measuring region for sojourn time is, the lower probability of changing direction in that region is. Moreover, OA algorithm uses time parameter instead of speed parameter when mobile stations measuring cell sojourn time. It makes OA algorithm more feasible. Furthermore, the thesis proposes a dynamic hierarchical handoff scheme base on mobile velocity called SDOH scheme. Considering the different tranamitting power between macrocell base station and microcell base station, SDOH scheme uses velocity property as intertier's handoff rule while uses the pilot signal strength as intratier's handoff rule. As well as it, SDOH scheme puts the high speed handoff voice call queuing algorithm on handoff voice call reserved channel algorithm. It reduces the handoff failure probability of high speed mobile stations and improves communication QoS.From the simulation results, the conclusion is given that the new scheme takes good advantage of the hierarchical cellular architecture. It not only ensures low handoff failure probability to high speed mobile services but also enhances the capacity of hierarchical system, and optimizes the resource management of high speed handoff services.