The wireless hierarchical token bucket: a channel aware scheduler for 802.11 networks

The paper proposes an architecture for a scheduling algorithm to be integrated in IEEE 802.11 access points (AP), able to take into account, besides the transport service class required by the destination user, the channel quality experienced by the destination mobile station (STA). The relevance of this topic is due to the observation that when one or more STAs experience poor radio channel conditions, they increase the time spent to transmit a single packet, due to the retransmission of corrupted frames and the adoption of transmission techniques at a lower bit rate, leading to an inefficient use of the shared medium. These phenomena give, as a consequence, a worsening of the performance of all the STAs sharing the wireless medium, independent of their radio channel conditions. The adoption of a scheduling algorithm able to manage information on channel quality permits these effects to be reduced, not penalizing the STAs experiencing good channel conditions and, as a consequence, their experienced throughput. As a result, only the STAs in bad channel conditions experience a reduction of throughput. A prototype of an AP equipment implementing the proposed architecture is presented: it was obtained by modifying the hierarchical token bucket (HTB) and is referred to as wireless hierarchical token bucket (WHTB). The performance of the presented prototype is evaluated experimentally and compared with those obtained with standard scheduling algorithms, which do not take into account information on channel quality.