Flexible TXOP assignments for efficient QoS scheduling in IEEE 802.11e WLANs

A basic concept in 802.11e is Transmission Opportunities (TXOPs). The draft amendment of IEEE 802.11e includes a Simple Scheduler, in which a fixed length of TXOPs is assigned according to mean data rates. Since some traffic present bursts of variable size, several enhancements have been proposed previously; e.g., TXOPs are allocated according to the actual buffered data which is indicated through transmissions performed in the previous TXOP. Though the allocations are efficient in channel utilization, a delay could inevitably be incurred by packets, due to that new arrivals cannot be transmitted in the current TXOP, but have to wait until next. In this paper, an efficient scheduling scheme is proposed that aims at improving packet delay while maintaining high channel utilization. In the proposed scheme, maximal residual bandwidth is assigned to a station taking into account demands from all the other stations, and the unused portion is reclaimed. From extensive simulation results, it is shown that packet delay is effectively improved, compared to two previous enhancements of the Simple Scheduler, while achieving high throughput performance.