Performance Improvement for Multichannel HARQ Protocol in Next Generation WiMAX System

Hybrid automatic repeat-request (HARQ) is critical to an IEEE 802.16e OFDMA network, as it can significantly improve the reliability of wireless link. However, as revealed by our simulation, the maximum number of parallel HARQ channels defined in the current system will render a potential bottleneck and preponderantly limit the overall system capacity of next generation WiMAX network, wherein the wireless link is anticipated to support much higher data rate. Moreover, the current IEEE 802.16 standard fails to tap into the considerable synergy inherent in HARQ and MAC layer fragmentation, as these two schemes have been designed separately. In order to enhance the throughput performance and improve the preparedness of multichannel HARQ protocol for adoption by future 802.16j and 802.16m system, we then propose two remedies, namely expansion of ACID field and an adaptive fragmentation scheme. The performance evaluation results further confirm that the ACID expansion readily doubles the link level throughput, while the adaptive fragmentation can effectively stave off the dismal degradation that plagues the IEEE 802.16e HARQ protocol in high bit error rate regime. Equally importantly, the two proposed schemes substantially reuse the existing mechanisms in the current 802.16 standard and only incur diminutive additional complexity, thereby speeding up the possible acceptance and implementation of the technology.