A Selectivity Function Scheduler for IEEE 802.11e

The IEEE 802.11e standard defines a reference scheduler that allocates transmission opportunities (TXOP) to traffic streams based on mean data rate and minimum physical rate. However, the reference scheduler is only efficient for streams with strict constant bit rate (CBR) characteristics. This paper presents a scheduling scheme named as the selectivity function scheduler (SFS) for the IEEE 802.11e hybrid coordination function (HCF) controlled channel access (HCCA). The SFS enhances the procedure of computing the number of variable sized packets by not only considering the new arrivals, but also accounting for the packets remaining in the queue due to channel conditions. SFS incorporates a selectivity function that assigns polling priorities to already admitted streams based on their actual requirements. The performance of the proposed SFS is evaluated and compared with the reference scheduler defined by the standard. Simulation results show that the SFS outperforms the standard scheduler in terms of enhancing streams throughput, reducing the packet dropping ratio, and maintaining high fairness among different traffic streams.