MAC Protocol Analysis And QoS Technology Research Based On IEEE802.16

With the development of wireless communication technology, the contents of multimedia applications are expected to be enriched. QoS of different applications must be taken into consideration in Wireless Metropolitan Area Network (WMAN) which is a competitive technology of the next generation wireless network. QoS signaling mechanisms such as bandwidth request/allocation and scheduling service types were defined in IEEE802.16 standard.However, some important issues such as admission control,traffic conditioning and packet scheduling were undefined.These problems were expected to be solved by the developers.In this paper,the IEEE802.16 MAC layer and relevant QoS mechanism and services scheduling algorithm were studied.Then,integrating the merits of the QoS structure solutions which were proposed in some latest literature, an efficient QoS architecture which overcome the shortcomings existed in the current IEEE802.16 QoS structure was proposed.The traffic control module was added to the subscriber station (SS).In the base station (BS),an admission control module was defined,a contention timeslot allocation module was added, the UPS was equal to scheduling information module and packet scheduling module. In the physical layer,a link state monitoring module was added.The function of each module was described in detail. The admission control scheme and the packet scheduling algorithm of QoS structure were emphasized.Aiming at the shortages in the existing admission control algorithm and considering how to provide a better QoS for mobility, an admission control mechanism based on reserved bandwidth and priority degradation mode was proposed. In the algorithm, a certain bandwidth for real-time handoff connecting was reserved to reduce the blocking rate. At the same time, the reserved bandwidth could be dynamicly allocated to the Non-Real-Time Polling Service (nrtPS) which connected to the BS and did not get to the largest bandwidth in the system, so the bandwidth utility rate was enhanced. When the system goes short of bandwidth, bandwidth stealing can be realized to ensure the real-time needs by continuous degradation of nrtPS. The rule of degradation is according to the priority of nrtPS.Compared with nrtPS overall degradation mode, the algorithm can significantly improve the transmission capacity of nrtPS services. Finally, the performance of the algorithm was validated by the results simulated with Matlab. Considering the unfairness of low-priority service caused by the existing Priority Queue (PQ) hierarchical scheduling algorithm, we have made some improvements to the algorithm. that is , a certain bandwidth for the Unsolicited Grant Service(UGS) was reserved, then hierarchical scheduling algorithm for the other three type services were adopted and a Deficit Fair Priority Queue(DFPQ) algorithm was used in the first layer. The simulation results showed that the advanced hierarchical scheduling algorithm could satisfy the QoS need of different type services and improve the fairness for BE service.