Research And Improve Of Downlink Sechedule Of WiMAX Multi-Traffic

WiMAX is a technology of next generation WAN which was defined by a series of IEEE802.16 standards. One of its superiorities is that IEEE802.16 standard's QoS guarantee scheme can assign the bandwidth source according to the service requirement.A series of IEEE802.16 standards defined several kinds of QoS schedule types, such as UGS, rtPS, nrtPS, BE etc., but it did not give the detail of how to implement them. The system schedule scheme mainly decides the quality of the whole system.This paper proposed a downlink schedule policy for WiMAX PMP networks. Based on multi-level scheduling, we present a new rule named 'VARLS+LUCT+I-EDF'that will supply better service not only for real-time flow, but also for lower priority service. VARLS (Voice Actively Rejecting Lower-Priority Serving) is aiming at improving the QoS of VoIP. When the QoS of VoIP decreases, the scheduler will reject new access request, or decrease the time serving the low priority services. And the other one is LUCT (Lowest-rate UGS based Cross-level Transfer) which is about to improve the efficient of WiMAX system when the throughput of UGS service flow is bigger. I-EDF is improved from EDF algorithm, which will play a good role on managing the centrol queue. We simulate this scenario on NS2 and prove the downlink schedule schanism.