Considering velocity-measure capabilities of vehicle terminals and high-speed mobile supporting features of WiMAX network

this paper proposes a speed adaptive vertical handoff algorithm with variable weight cost function for a vehicle terminal in heterogeneous networks.The proposed algorithm uses speed adaptive strategy in the discovery phase of vertical handoff

which overcomes the drawbacks of the fixed and single network discovery methods by the received signal strength.Moreover

a cost function weight-variable algorithm is used during handoff decision

which selects the network with the maximum cost function value as the handoff network.Simulation results show that the proposed algorithm can effectively improve the update rate

lower the blocking probability

reduce the switching frequency

ensure effectiveness and fairness of vertical handoff.