Performance Research Of Broadband Access PMP WMAN MAC Layer

In recent vears,several last mile high-speed technologies have been explored to provide Internet access and multimedia services to users.For fixed Broadband Wireless Access(BWA)systems,IEEE 802.16d was developed and published in June 2004.The standard defines the air interface for wireless metropolitan area networks(WMAN).IEEE standard 802.16d MAC protocol was designed to support point-to-multipoint architecture and QoS mechanisms taking advantage of request/grant MAC scheduling mechanisms.Specific algorithm about key mechanisms ir QoS and scheduling was not given in the protocol for providing more flexibility to manufacturers.In this thesis IEEE802.16d MAC layer protocol was analyzed in detail, including protocol model,construction and transmission of MAC PDU, MAC layer elementary characteristic.The thesis established a soft model for fixed accessing PMP WMAN to simulate MAC performance.An improved backoff algorithm was also proposed.In this algorithm,by predicting the number of request messages in next uplink frame,BS controlled the optimal backoff ranges dynamically.As a result,the successful rate of sending requested messages in each frame was increased. Simulation results demonstrated that improved algorithm made an obvious improvement in data throughput and the mean access delay compared with the original BFB algorithm.