Packet handling strategies to improve video QoS over 802.11e WLANs

In this paper we look at several techniques that can allow for the quality of downloaded video streams to be maintained when an 802.11e MAC becomes congested. These techniques come from two distinct groups: Packet mapping schemes and packet dropping schemes. The packet mapping schemes determine which 802.11e enhanced distributed channel access (EDCA) queue each video packet joins. One mapping scheme treats all packets equally, while the other differentiates the video packets of different slice types. The packet dropping schemes aim to avoid MAC layer congestion by dropping some of the packets before arriving at the MAC. Two packet dropping schemes are used which both differentiate video packets by trying to drop the lower importance packets first. One packet dropping scheme applies an even amount of loss to each video stream while the other applies an even statistic which results in an uneven amount of loss to each video stream. Results show that all of the schemes that differentiate video packets allow for a more gradual video quality degradation than would otherwise occur. The packet dropping schemes also provide the best delay performance. Results for each scheme are content dependant and the packet dropping scheme that results in uneven amounts of packet losses is the only scheme which treats all types of content well. We show that at high loads this scheme can offer a system performance with a mean opinion score that is at least 0.5 greater than any of the other schemes can provide.