An evaluation of quality of service for H.264 over 802.11e WLANs

802.11 wireless local area networks are now a common feature in the home. In order to meet the quality of service (QoS) demands for the increasing number of multimedia applications on these home networks the 802.11e amendment was developed. A suitable video coding standard for these multimedia applications is H.264 due to its high compression and error resilience. In this paper we investigate how the quality of H.264 video is affected as the number of concurrent video streams sent over a multi-rate 802.11e network is increased. Several packet mapping schemes are compared. We show that the mapping schemes which differentiate video packets based on their frame type are more successful at maintaining acceptable video quality when congestion occurs, providing a more gradual quality degradation as congestion increases rather than the cliff-edge quality drop that tends to occur with the other mapping schemes. These differentiated schemes are more successful for videos that do not have a high amount of temporal activity. We also identify that impairments caused by congestion tend to occur towards the bottom of each frame when the flexible macroblock ordering (FMO) feature of H.264 is not used but the use of FMO can reduce this effect.