Abstract
Mobile WiMAX (Worldwide Interoperability for Microwave Access), namely IEEE 802.16-2005, is a kind of multiuser OFDM systems that can support both mobile and fixed broadband wireless services. The main challenge in Mobile WiMAX is to design an efficient traffic scheduler for resource assignment to the entire users in the system. A practical scheduler for Mobile WiMAX should have the following essentials: 1) it can provide guaranteed quality-of-service (QoS) for real-time and non-real-time packets without violating fairness; 2) it should take the channel properties of both fixed and mobile broadband networks into account when allocating resource. To meet these two requirements, we purpose a cross-layer design for the Mobile WiMAX scheduler based on joint considerations of the physical and medium access control (MAC) layers, with each user employing adaptive modulation/coding (AMC) based on the desired packet error rate. For the AMC algorithm, we derive new closed-form relations between the packet error rate (PER) and the received signal-to-noise ration (SNR) in the Mobile WiMAX system over AWGN and Nakagami-m fading channels. With the derived PER formulas and the target PER requirement, we can obtain the boundary SNR values for changing modulation/coding modes. The mode changing information is then cross-layer utilized in the design of the purposed QoS-guaranteed scheduler to maximize the system throughput. The proposed scheduler, referred to as Pre-Processing Scheduler, aims at providing the most appropriate treatments to data connections based on their QoS requirements as well as reducing processing needs at the beginning of transmission of each time frame. By exploiting the feature of the Mobile WiMAX standard that the duration of each TDD frame is fixed, the proposed scheduler can predict the starting instant of each frame and then pre-assign appropriate frames and subchannels for transmitting real-time packets based on their transmission deadlines and the corresponding channel responses. After this, the remaining resources are allocated to non-real-time packets. Computer simulation results show that the proposed scheduler can grantee QoS for real-time packets and attain a higher throughput for non-real-time packets, as compared to the conventional scheduling approach.