H.264 Video over 802.11a WLANs with Multipath Fading: Parameter Interplay and Delivered Quality

Emerging as the method of choice for compressing video over WLANs, the AVC/H.264 standard is a suite of coding options and parameters whose values are to be chosen for specific videos and channel conditions. We investigate the tradeoffs in performance across the quantization parameter (QP), the group of picture size (GOPS), the payload size (PS), physical layer (PHY) data rate in 802.11a, and the average channel SNR for multipath fading channels. The interesting and sometimes surprising results are: the delivered video quality is very sensitive to the change in PSs and in many cases the PS optimizing PHY throughput cannot yield acceptable video quality; although lower QP yields better video quality when there is no packet loss, when the quality is corrupted heavily due to packet losses, there is no advantage gained for finer quantization and higher bit rate; lower GOPS, i.e., to refresh I-frames more frequently does not necessarily improve the delivered video quality and in many cases medium values of GOPS should be chosen; different types of videos have dramatically different delivered quality in the same channel which should be taken into account in network evaluation and design.