The Vertical Handoff And Network Selection Algorithms Based On QoS In Heterogeneous Wireless Networks

With the rapid development of technology,mobile communication system has shown two different standards.The one is mobile communication system,based on the cellular mobile communication technology,such as 2G,3G,4G.The other one is wireless access system,based on the wireless access technology,such as WLAN,WMAN.And one kind of communication standard can also develop different types of network because of the differences among countries,regions as well as mobile operators,for example,CDAM2000 and TD-SCDMA belong to 3G network.Thus leads to that different wireless network exist together.In order to make a good experience environment for users,mobile terminals must be able to connect all kinds of wireless networks to ensure application can seamlessly switch to different networks.So next generation network must be heterogeneous wireless network integration of different kinds of wireless networks.As different networks have different using standards,different traffic classes have different requirements for performance parameters of network.Thus vertical handoff in heterogeneous wireless networks becomes a hot and difficult problem.Vertical handoff is divided into three steps,namely,networking discovery,hand-off decision making,handoff execution.handoff decision making is the most important part of vertical handoff,and network selection is the most important part of handoff decision making.Because it determines which network the mobile terminal selects.In this paper,two vertical handoff network selection algorithms is proposed.The first one is the network selection algorithm based on distinguish traffic classes(NSADTC).It takes bandwidth,latency,packet loss ratio and service cost as network attributes.Weight computing includes average importance of attributes as subjective weight and standard deviation of attributes as objective weight,and chooses the network having the smallest distance to positive ideal solution(PIA)as the target network.The experiment shows that it can choose the most suitable wireless network as the target according to current traffic classes.The second one is the network selection algorithm based on utility function(NSAUF).It calculates the utility value of different attribute firstly.Then the weight combines the subjective weight which is determined by AHP and the objective weight which is determined by entropy method.Finally it is concluded total utility value of different network and choose the network with the maximum utility value as the target network.And it can be seen from the experiment that the target network selected according to different traffic classes is same as AHP-TOPSIS.