Abstract
With low cost, easy deployment, and flexible connectivity, the deployments of wireless networks have become widespread and fast-growing everywhere. However, the challenges of coping with the time-varying error rate and fluctuating bandwidth of a wireless network bring out the need of error resilient video transport. The packet loss problem may lead to serious video quality degradation, which not only affects the quality of current frame, but also leads to error propagation to subsequent frames due to the motion-compensated prediction and entropy coding used in current standard video coders. Using error resilience coding/transcoding tools to add redundancy to protect video data is a common strategy to handle the problem of packet loss. Besides, video transport over wireless networks usually requires retransmissions to successfully deliver video data to a receiver in case of packet loss, leading to increased delay time for the data to arrive at the receiver. Delay constraint is, however, one of the most important requirements in real-time applications since a video packet arriving later than the presentation time will become useless for the client.In this thesis, we propose efficient error protection techniques to address the problems of video transport in a three-tier streaming framework which involve hybrid wireline and wireless networks. We first propose a multiple-description fine granularity scalability (MD-FGS) coder that combines scalable coding with multiple description coding (MDC) to enhance error resiliency while retaining good temporal prediction efficiency for video transport. An adaptive soft handoff algorithm is also proposed to effectively mitigate video quality degradation caused by transient channel switching when a mobile client roams in wireless networks.We then propose a two-pass error-resilience transcoding scheme based on adaptive intra-refresh for inserting error resilience features to a compressed video at the intermediate transcoder of a three-tier streaming system. The proposed transcoder adaptively adjusts the intra-refresh rate according to the video content and the channel’s packet loss rate to protect the most important macroblocks against packet loss. In this work, we consider the problem of multicast of video to multiple clients with disparate channel loss profiles. We propose a minimax loss rate estimation scheme to determine a single intra-refresh rate for all the clients in a multicast group. For the scenario that a quality variation constraint is imposed on the users, we also propose a grouping method to partition a multicast group of heterogeneous users into a minimal number of sub-groups to minimize the channel bandwidth consumption while meeting the quality variation constraint.Finally, we propose a cross-layer content-aware retry limit adaptation scheme for video streaming over IEEE 802.11 wireless LANs (WLANs). In our method, video packets of different importance are unequally protected with different retry limits at the MAC layer. The error propagation effect of each packet is estimated to guide the determination of its retry limit. More retry numbers are allocated to packets of higher loss impact to achieve unequal error protection. Our scheme also analyzes the backoff time for each retry and then takes into account the estimated backoff time for retransmission scheduling.Experimental results demonstrate that the proposed MD-FGS coder can increase the temporal prediction efficiency without introducing severe drifting error when packet loss occurs. Furthermore, the use of path diversity as temporary step for roaming can provide significant benefits for error protection. The proposed error resilience transcoder effectively reduces the mean and variance of penalty distortion as well as achieves fairness among clients in video multicasting with heterogeneous channel conditions. Furthermore, the proposed retry limit adaptation scheme can effectively mitigate the error propagation due to packet loss and assure the on-time arrival of packets for presentation.