Congestion-aware downlink scheduling for IEEE 802.16j multi-hop relay networks

In this paper, a congestion-aware downlink scheduling for IEEE 802.16j multi-hop relay networks is proposed. In the mechanism, a relay station (RS) can report its queue status of each downlink connection to the upstream station. Based on the reported information, the upstream station may properly schedule its downlink transmission and hence the system performance benefits. We focus on the following three issues to achieve the goal. First, to find a congested queue, we develop a measuring method to monitor queue statuses in a RS. Then, a report system is designed to carry the information. Finally, a congestion-aware downlink scheduling algorithm of a MR-BS and RS is devised to properly schedule the downlink transmission. According to the NS-2 simulation results, the proposed scheme effectively mitigates the congestion problem in a RS and improves the system performance. Compared with the contribution of downlink flow control presented in the IEEE 802.16j task group, the proposed scheduling scheme is able to increase the network throughput up to 60.11% and reduce the dropping ratio up to 26.21%.