Study On The Selection And Handoff Methods In Wireless Ubiquitous Environment

With the advance in various radio access technologies, the wireless ubiquitousnetwork, which features the efficient cooperation and composition amongheterogeneous wireless networks, is regarded as the trend of future networks. Becauseof the versatility and complexity of handoff processes in the wireless ubiquitousenvironments, those traditional handoff control mechanisms face severe challenges.Consequently, it is of great necessity to research new selection and handoff methodsapplicable to the future ubiquitous network.The existing algorithms of network selection and handoff mainly aim atmaintaining always-best-connection for the benefit of single user. Since they areoptimized at certain protocol layer and can not take full use of the resource sharingacross heterogeneous networks for maximizing the service ability of networks, probablelocal congestions happen frequently. Therefore, a resource allocation model based onoptimization theory, which applies to the environment of heterogeneous networks, isproposed first, and its optimal solution can be taken as the criterion of access networkselection and vertical handoff. Then, according to the result generated by this resourcesdistribution model, we improve the network selection method based on analytichierarchy process. The new method ensure the best connection of single user when theterminal is locate in the overlap of several heterogeneous networks, and the networkloads also approach to balance so that the congestions are prevented. At last, the handoffrequirements of mobile terminals in the wireless ubiquitous network are analyzed and anew vertical handoff method based on classified trigger events is proposed. It makes useof the convenience brought by the overlap of heterogeneous networks to executevertical handoff and employ different handlings to different events to develop theservice abilities of networks.OPNET network simulations demonstrate the efficiency of load balance and the callloss and connection-dropping ratio is dramatically reduced.