One of the most challenges of 4G network is to have a unified network ofheterogeneous wireless networks. To achieve seamless mobility in such a diverseenvironment, vertical hand off is still a challenging problem. In manysituations handover failures and unnecessary handoffs are triggered causingdegradation of services, reduction in throughput and increase the blockingprobability and packet loss. In this paper a new vertical handoff decisionalgorithm handover necessity estimation (HNE), is proposed to minimize thenumber of handover failure and unnecessary handover in heterogeneous wirelessnetworks. we have proposed a multi criteria vertical handoff decision algorithmbased on two parts: traveling time estimation and time threshold calculation.Our proposed methods are compared against two other methods: (a) the fixed RSSthreshold based method, in which handovers between the cellular network and theWLAN are initiated when the RSS from the WLAN reaches a fixed threshold, and(b) the hysteresis based method, in which a hysteresis is introduced to preventthe ping-pong effect. Simulation results show that, this method reduced thenumber of handover failures and unnecessary handovers up to 80% and 70%,respectively.
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