Research And Realization Of Downlink QoS In WiMAX System

Worldwide Interoperability for Microwave Access (WiMAX) is a Broadband Wireless Access Metropolitan Area Network technology based on IEEE 802.16 standard,and it provides a new solution to the problem of "Last mile".In order to satisfy the increasing QoS requirement of the the emerging services,a comparatively QoS mechanism is defined in WiMAX system.But the algorithms which implement the QoS support are not given in the standard and all of these issues are left to developer to implement.Because "Last mile" application is a typical asymmetric network,compared to the uplink direction,the traffic in the downlink direction is much heavier. So,the downklink QoS mechanism becomes more important.On the basis of researching the QoS mechanism in WiMAX system,this paper improves the admission control and Scheduling Algorithm which are the major mechenism to implement QoS in WiMAX system.(1) The study on optimal admission control policy of a comprehensive consideration of revenue,blocking rate and users' bandwidth utilization.Admission control plays a critical role to guarantee QoS, the current researches on optimal admission control policy mainly focus on maximizing the revenue of service providers, and pay little regard to the interest of users.In the admission control policy proposed in this paper,two constraints namely blocking rate and bandwidth utilization,which are related to the interests of users, are added to optimal revenue policy. And the algorithm to implement the policy is given as:First allocating bandwidth to each traffic class to guarantee blocking rate,then choosing the traffic class with the highest revenue rate for bandwidth allocation from traffic classes which can meet the requirment of utilization. Simulation result shows that the policy has good performance in revenue,blocking rate and bandwidth utilization, thus the interests of service providers and users are both given consideration.(2) The study on downlink realtime scheduling algorithm based on the type and average arrival rate of the service flow. Scheduling algorithm directly affects the delay and throughput of the system which are the key indicators of QoS. As the wide application of real-time services in networks,the downlink scheduling algorithm Round-Robin based on stations in WiMAX system, since the delay of real-time traffic can not be graranteed,can not meet the real-time request well.This paper proposes a new algorithm based on service type called Downlink Real-time Scheduling (DLRTS),which schedules services with higher real-time request first to guarantee the delay and then allocates the remaining time slots according to the average arrival rate of the service flow to improve the throughput. Simulation result shows that,compared to Round-Robin, DLRTS has better performance both in delay and throughput of the real-time services.