A Fair-Oriented Two-Level Scheduling Scheme for QoS Guarantee in WiMAX

As the standard of worldwide interoperability for microwave access (WiMAX) technology, IEEE 802.16 defined five classes of traffic services, which are UGS, rtPS, ertPS, nrtPS, and BE, respectively, and introduced a supporting mechanism for quality of services (QoS) into medium access control (MAC) layer. But it did not propose the corresponding scheduling algorithm. In order to provide various multimedia communications with QoS guarantee effectively, a two-level scheduling scheme is proposed based on the orthogonal frequency division multiple access (OFDMA) technology and adaptive modulation and coding (AMC) mechanism. This scheduling scheme employes the cross-layer design methodology and can be used in the point-to-multipoint (PMP) WiMAX downlink. According to the value of QoS priority, the first-level scheduler schedules the head of line (HOL) packets in different service class buffers to satisfy the rtPS maximum delay restriction and nrtPS minimum rate requirement simultaneously. After accomplishing the first-level scheduling, the second-level scheduler schedules the HOL packets in different user buffers according to the AMC information and users’ state message for obtaining the users’ rate fairness. Simulation results show that the proposed two-level scheme can meet various QoS requirements of multimedia services well without sacrificing users’ rate fairness, and meanwhile, get the preferable WiMAX system throughput.