Exploiting the MAC layer flexibility of WiMAX to systematically enhance TCP performance

TCP performance over wireless network has been extensively studied in the literature and many cross-layer optimization schemes are proposed. Nevertheless, new technologies such as WiMAX, based on IEEE 802.16, offer new dimensions for system optimization that limited research has explored. In this paper, we show that the flexible WiMAX MAC layer allows cross-layer optimization to be done at the fine granularity of each connection or each service class. We also highlight that in a WiMAX broadband wireless access network, aggregate system performance is more important than the performance of an individual application instance, particularly from a network operator point of view. To this end, we propose an asymmetric link adaptation strategy for TCP-based applications. Coupled with ARQ, the aggregate system performance is enhanced without significantly compromising the performance of individual TCP flow. In addition, we argue that schedulers should be designed specifically for different service classes. We propose a scheduler for TCP-based best-effort service class that achieves both good aggregate throughput and fairness. The proposed design concepts not only help to achieve a good end-to-end TCP performance along with enhanced spectral efficiency, but also open many possibilities for optimizing the performance of other applications with similar techniques in WiMAX