| With the development of the mobile communication technologies, a heterogeneous network composed of different types of wireless communication network is inevitable. How to select an appropriate wireless network to provide mobile users with multimedia services with guaranteed QoS is one of the key problems. Network selection algorithms and vertical handoff schemes, as key technologies to guarantee QoS, have been studied extensively and are also the focuses of this paper.On the basis of investigating different international standard organizations'research and standardizations on QoS, this paper presents key technologies to guarantee QoS and its future study in the heterogeneous networks. Being aimed at weakness of completeness, robustness, objectivity and accuracy of existing network selection algorithms, an intuitionistic fuzzy-based network selection algorithm (IFMADM) and a deviation degree-based MADM algorithm are proposed. The simulation results show that the proposed IFMADM algorithm can enhance the resolution among different networks greatly while ensuring the accuracy of the network selection result, and it also avoids the ranking abnormality problem. Theoretical analysis shows that deviation degree-based MADM algorithm can avoid ranking abnormality and enhance the resolution among different networks to some extent. In addition, a sensitive analysis method is presented to evaluate the performance of network selection algorithm, and it is used to analyse the performance of IFMADM.In order to meet the demands for vertical handoff optimization, a sensitivity-controlled vertical handoff scheme is proposed based on the study mentioned above. The scheme is designed to reduce the times of handoff by controlling the sensitivity of the network selection algorithm. The simulation results show that when the user is moving in the overlap area where there are several access networks, the proposed scheme can reduce the times of handoff while assuring the users' QoS. |
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