Research On Mobility Management In Heterogeneous Wireless Networks

As the prensent and future development trend, heterogeneous wireless networksconsist of various kinds of wireless technologies and terminals to provide ubiquitousservices. Mobility management in heterogeneous networks faces a number ofchallenges such as users’ locomotion, ubiquitous services, and seamless handoffbetween different networks. This thesis addresses several key problems on mobilitymanagement in heterogeneous networks, including strategy and framework for locationmanagement, location database stucture, paging and vertical handoff, and theoptimization in application circumstances. The main achievements of this thesis are asfollows:First, a unified location management structure based on the position and a newdynamic location management strategy based on the geographic coordinates areintroduced in this dissertation. This unified location management structure matches asingle geographic position with those addresses in the different kinds of networks andassigns a unified address over all the networks to this geographic position withoutchanging the architecture of the existing wireless networks. Our study shows that theproposed structure is qualified as a better framework in terms of database size and thecost of wireless system, and meets the needs on compatibility, opening and scalabilityfor practical networks. The strategy based on the geographic coordinates integrates theLEO network into the ground heterogenous networks, by which each user terminalobtains its coordinates itself, computes its optimal updating radius, without therestriction of the cell. The study shows that this strategy reduces resource cost and hasbetter performance than the existing ones.Next, the dissertation further presents a new3-layer database structure byconsidering the users’ velocity in motion. This database adds a pointer database, setsdifferent home databases, visits databases to corresponding location areas for the userswith different speeds, and treats them dissimilarly. The study shows that the proposeddatabase structure has better performance in system cost than that of the existing2-layer structure and the tree structure. In addition, under the framework proposed before, the dissertation introduces areversing paging process of called users and a network selection strategy based on thetime-series forecasting of future network traffic. In the reversing paging process, weintegrate the paging and the vertical handoff processes such that the users can choosethe best networks to set up the communication and page with the best coveragenetworks in view of the problem of multiple coverages and the difficulty for collectingall users’ information. The study shows that, in terms of system cost, average timedelay and call success rate, the proposed process plays better than the existing one thatpages first and then handoffs vertically. Meanwhile, in view of the self-similarity ofservices in heterogeneous networks, in the network selection strategy based on thetime-series forecasting, it chooses the second best network to access when the bestnetwork might be congested. The study shows that the proposed strategy decreases thecongestion capacity, the capacity of handoff interrupting, and the cost of the network.Finally, the dissertation proposes a polymerizing algorithm in the public transportscenario according to the pertinence among multiple users, which adopts the operationsof cluster head to replace other users in the logical cluster. The study shows that theproposed algorithm decreases the cost of location updating without increasing the costof paging and could be used accompanied with other optimizing algorithms together.Compared with other similar methods such as network mobility, it does not requireadditional equipment and does not limit the users’ access and hence has betterperformance on system cost.The research in this thesis extends the existing researches on mobilitymanagement in heterogeneous wireless networks. The results have some theoreticaland practical values, and provide effective reference for engineering applications．...