Research On Radio Resource Management Method In Heterogeneous Wireless Networks

With the rapid development of communication industry, a large number of wireless access technologies which have distinctive features are emerging. Different wireless access technologies that were from different application backgrouds were originally designed for diverse types of traffics and needs. These wireless access technologies are continually evolving along respective technology roadmaps. As the scopes of various wireless networks are increasing, some geographical areas may be covered simultaneously by more than one type of wireless networks, namely heterogeneous wireless networks. Spontaneously some of these wireless networks have complementary features. In order to meet the diverse needs of traffics, mobile terminal which integrates multiple wireless interfaces has become the mainstream trend of development. Consequently, integrating heterogeneous wireless networks to provide satisfying services is one important direction of future mobile communication systems. The radio resource management in heterogeneous wireless networks can make good use of finite wireless resources to improve the system efficiency and meet various growing needs of users.Focusing on how to ensure the quality of service for users and improve the utilization of radio resources, this thesis makes detailedly analysis and intensive study of three key technologies of radio resource management in heterogeneous wireless networks, including connection admission control, load balancing and handover management. With the help of the theorys and methods such as multi-objective optimization, fuzzy math, multi-attribute decision making and Markov process, some novel algorithms for access control, load balancing and handover decision in heterogeneous wireless environment are proposed to improve the overall efficiency of radio resources and ameliorate the user’s service experience.In the aspect of connection admission control, a novel model based on cost is proposed to describe the coverage of heterogeneous wireless networks. Based on the access cost at the different geographical locations, this model devides the coverage of heterogeneous wireless networks into several subranges which can calculate the system performance more detailedly in a cellular. As a part of the radio resource management, on one hand connection access control should meet the user’s access request and select an appropriate access location according to the different traffics. On the other hand connection access control also needs to ensure the continuity of traffic and the experience of service for the serving users in order to enhance the overall network capability. For different optimal objects, an algorithm based on multi-objective optimization is proposed which considers both the user and network sides. The solution is turned to a Pareto optimal problem that can ensure the system throughput optimal, maintain the new connection blocking rate within the range of system requirement and reduce the number of handovers.In the aspect of load balancing, the influence on network load which is caused by users’ motion states is analyzed firstly. The impact on load can be concluded by transfering different types of traffics. And then, the network state is abstracted to a Markov process through the users states served by different wireless networks. The ergodic and existence of limit distribution of this Markov process are proved. In order to ensure the system to provide satisfying services for users, the time during which the system is unstable should be as short as possible. Hence a load balancing algorithm based on Markov chain is presented to balance the load between different wireless networks rapidly.In the aspect of handover, the handover solution can be solved as a multi-attribute decision making problem which considers the many factors for users’ traffics and preferences. Since analytic hierarchy process is difficult to guarantee the consistency of judgment matrix and solve the weight vector, a vertical handover decision algorithm based on fuzzy analytic hierarchy process is proposed. The algorithm has a better consistency with the human mind when the relative importance of various attributes is compared for judgment results. So the best handover position can be decided for user. To avoid frequent unnecessary handovers, namely ping-pong effect, a variable length timer is designed based on the states of user motion and load. During the timer, the attributes are eliminated. The efficiency of handover and system throughput are improved due to reducing the unnecessary handovers.