Study On Position-Based Vertical Handoff Algorithm In Heterogeneous Networks

Vertical handoff is the key characteristic and technology of Wireless Mobile network.Traditional handoff mechanism can not be directly applied to heterogeneous network.Based on the systematical summary and analysis of the latest researches on vertical handoff,uses the heterogeneous network in which TD-SCDMA and WiMAX coexist as the background,this dissertation focuses on the issues of performance analysis of the heterogeneous network vertical handoff and heterogeneous network positioning algorithm.The major contributions of this dissertation are as follows:(1) Performance analysis of representative algorithms.The existing handoff algorithms are analyzed and a set of performance evaluation models for vertical handoff in heterogeneous networks are provided.Two metrics,matching ratio and ping-pong number,were defined to evaluate the performance of vertical handoff algorithms.Based on the proposed models and metrics,the performance of two vertical handoff algorithms was compared:hysteresis based algorithm and dwelling-timer based algorithm.Simulation results show this switch of single decision-making does not necessarily guarantee the reasonableness of handoff,we need to study a new method of analysis.(3) The QoS optimization algorithm based on AHP and its improvement.This dissertation uses AHP to analysis multiple attribute decision-making,provides a QoS optimization algorithm.Furthermore,this dissertation makes improvement of the QoS optimization algorithm combined with the combination of location information. The algorithm can evaluate the performance of network links comprehensively and select the most appropriate one for user's services requirement.Simulation results show that this algorithm can reduce the number of handoffs,as well as make mobile nodes switch to a better network link.(4) A TOA location algorithm under NLOS conditions is presented in the end. We determine the location of the nodes in different network,use comprehensive results of the independent node position to get the nodes' location.Simulation results show that some factors have obviously impact to localization accuracy,such as the number and location of base station.The TOA location algorithm will achieve a comparable result when there are more WiMAX base stations in network.