Research Of MDP-based Admission Control Algorithm In Heterogeneous Wireless Networks

With the advent of various radio access technologies(RATs), mobile communication system will develop into heterogeneous wireless networks consisting of different RATs,in order to provide more and better service experiences for users. Call admission control(CAC) is one of the key technologies of heterogeneous wireless networks. It achieves joint radio resource management and plays a crucial role in reducing network congestion, improving resource utilization rate and the end to end quality of service.This thesis is mainly on research of the admission control algorithm in heterogeneous wireless network. First, the thesis briefly introduces two coupling architectures(tight coupling mode and loose coupling mode) of heterogeneous wireless networks, then introduces the key technologies(vertical handoff, joint radio resource management, admission control) of heterogeneous wireless networks. This thesis gives a definition of the call admission control in heterogeneous wireless networks, also illustrates and compares the existing call admission control algorithms in heterogeneous wireless networks. The major jobs and innovations of this thesis are as follows:(1) Proposes a priority admission control algorithm based on Markov decision process under the CDMA/WLAN heterogeneous wireless network environment. The call admission control algorithm is formulated as a Markov decision process, and defines the state space and the action sets, the transition probability and the reward function of Markov decision process in detail. Improves reward function by analyzing the possible actions of the new call, vertical handoff call, real time and non real time calls. At the same time, the optimal call admission control policy is solved by the value iteration algorithm.(2) It introduces the network initiated vertical handoff strategy to the admission control mechanism to balance the load of the network and access more new services. To allocate resources among new users, switches the users from overlapping coverage area to light load network. This strategy reduces the new call blocking probability and utilizes the system resources in a more efficient way.(3) A multi-threshold bandwidth allocation scheme is proposed to optimize the admission control. Multiple threshold bandwidth allocation improves the admission control algorithm based on different types of services and designates different priorities to the different services by setting the bandwidth threshold. The improved admission control algorithm not only reduces the vertical handoff call dropping rate effectively, but also improves the satisfaction of users greatly.Compared with other algorithms, the simulation results show that proposed scheme is more superior in reducing the new call blocking probability and vertical handoff call dropping rate, and improving the overall network reward. But the algorithm still has some shortcomings,the services that algorithm considering are not thorough and the computational complexity of the algorithm needs to be further researched.In the end, sums up all of the content, gives suggestion for further research of the admission control algorithm.