| With the development of communication technology and the widely use of the2G,3G,4G cellular networks and WLAN, the next generation wireless communication networks will be heterogeneous networks with a variety of access means. Each network is different in access technology and interface protocol from others. It has always been the problem for many researchers that how to make the users choose the suitable networks in a complex network environment to obtain better services. Like the horizontal handoff in homogeneous networks, the vertical handoff is also a key research issue in mobility management for wireless networks. The handoff decision in heterogeneous networks is changing from network-controlled to terminal-controlled, which make it possible for users to make the decision.The most existing Algorithms are based on horizontal handoff algorithms, which will always make the results unsatisfied in a vertical handoff environment. The network capability and the state of the terminal are two factors that should be emphatically considered in vertical handoffs, while user willing based selection could always leads to a disastrous result such as communication interrupt. This paper took the heterogeneous network with UMTS network and WLAN network for example, built a network model with OPNET, and designed a dual-mode mobile terminal for simulating and comparing. By analyzing the advantages and disadvantages of several handoff algorithms that has been presented so far, this paper put forward a multiple index decision algorithm based on fuzzy logic, with decision factors that includes received signal strength, bandwidth and velocity of the terminal, considering the state of the network and the terminal, using fuzzy inference, to make the handoff decision. Simulation result proves that:Compared with the traditional RSS based algorithm, this algorithm could avoid unnecessary handoffs, reduce the overhead of the host, improve throughput on the basis of QoS guarantee. |
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