Research On Network Access Selection Strategy In Heterogeneous Networks

The widespread success of wireless and mobile communications has resulted in the development of a large variety of mobile and wireless technologies,including 3G? 4G?WLAN and WiMAX.At the same time,Heterogeneous network can significantly improve the service guarantee and access capability of a single network,has thus become a significant topic.Furthermore,the selection of a network is the first step and the key preparatory work before connection of the user terminal and the network,is an important behavior and decision procedure to determine user service will use which network to fulfill their communication needs.Therefore,users rely on a various aspects of outstanding and intelligent network selection strategy,help they complete the access network selection has become one of the key problems to be solved in heterogeneous network environment.The existing heterogeneous network selection strategy is rarely consideration the user characteristics and network characteristics comprehensively to design the network selection.For this situation,we study the access selection problem of high mobility users and low mobility users on the heterogeneous networks of macro and micro dual base stations in this paper.And The optimization strategy of network selection based on user terminal is given.Mobility is the most essential attributes of users.Therefore,in the design of high speed mobile user's network selection strategy,It is necessary to avoid unreasonable frequent switching,but also need to consider the merits of the system throughput performance,and the complexity is hard to find.In addition,the existing research has always modeled the base station location as the traditional regular hexagon,ignoring the actual coverage situation.Faced with these problems,this paper combined with random geometric theory modeling of heterogeneous network scenarios,Study on the high speed mobile users on the micro cellular dwell time may be very small,And part of the high speed users who want to connect to the macro cellular but are located in the microcell coverage area,Their bandwidth reservation and bandwidth allocation issues in access selection.We use the system capacity of the high and low speed terminal to reduce the switching cost,and get the utility function about the whole network revenue.Then it is proved that the optimal solution of the utility function is a convex optimization problem with restricted conditions.Then,by using the gradient descent method,the optimal solution of the reserved bandwidth and the allocation bandwidth and the access probability of the users with high speed and low moving speed on the macro and micro cellular networks are obtained.On the other hand,considering the fact that the traditional MDP decision model is used for vertical handoff in real time and non real time in overlapping region is often ignores the difference of QoS,which leads to the problem that the resource is not fully utilized.In thispaper,we present an improved result of the action set in the Markov decision process.Combining the improved MDP decision process with the redesigned bandwidth reservation mechanism,a joint call admission strategy based on the whole network is proposed.Simulation results show: The optimization scheme of the call selection strategy for the user terminal and the whole network have good performance and improvement in the new call blocking rate,handoff dropping rate,and the whole network capacity benefit.