On Enhancing WiMAX Hybrid ARQ: A Multiple-Copy Approach

One major challenge in broadband wireless access networks is to provide fast, reliable services to time-sensitive communications. We propose an enhanced hybrid automatic repeat request (HARQ) scheme for the worldwide interoperability for microwave access (WiMAX). The new scheme follows the multi-channel stop-and-wait chase combining HARQ adopted by WiMAX, yet it enables the base station (BS) to proactively react to poor channel conditions. The BS would send multiple copies of the same data burst to the subscriber station (SS) over the multiple HARQ channels available to the SS. We design a novel method which would determine the number of multiple copies needed based on the channel feedback. The new HARQ scheme effectively reduces the total time needed for a successful transmission. Simulation results show that, comparing with the original WiMAX HARQ, the new scheme significantly reduces the waiting time for a successful transmission by up to 45%, while maintaining a comparable level of throughput. This work is most significant for time-critical applications that need fast, reliable services, such as VoIP and other interactive uses.