Intra-Refresh and Data-Partitioning for Video Streaming over IEEE 802.11e

Intra-Refresh and Data-Partitioning for Video Streaming over IEEE 802.11e

Ismail Ali (University of Essex, UK), Sandro Moiron (University of Essex, UK), Martin Fleury (University of Essex, UK) and Mohammed Ghanbari (University of Essex, UK)
DOI: 10.4018/978-1-4666-4715-2.ch012
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Intra-refresh macroblocks and data partitioning are two error-resilience tools aimed at video streaming over wireless networks. Intra-refresh macroblocks avoids the repetitive delays associated with periodic intra-coded frames, while also arresting temporal error propagation. Data-partitioning divides a compressed data stream according to the data importance, allowing packet prioritization schemes to be designed. This chapter reviews these and other error-resilience tools from the H.264 codec. As an illustration of the use of these tools, the chapter demonstrates a wireless access scheme that selectively drops packets that carry intra-refresh macroblocks. This counter-intuitive scheme actually results in better video quality than if packets containing transform coefficients were to be selectively dropped. Dropping only occurs when in the presence of wireless network congestion, as at other times the intra-coded macroblocks protect the video against random bit errors. Any packet dropping takes place under IEEE 802.11e, which is a quality-of-service addition to the IEEE 802.11 standard for wireless LANs. The chapter shows that, by this scheme, when congestion occurs, it is possible to gain up to 2 dB in video quality over assigning a stream to a single IEEE 802.11e access category. The scheme is shown to be consistently advantageous in indoor and outdoor wireless scenarios over other ways of assigning the partitioned data packets to different access categories. The chapter also contains a review of other research ideas using intra-refresh macroblocks and data-partitioning, as well as a look at the research outlook, now that the High Efficiency Video Codec (HEVC) has been released.
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Video compression depends for most of its coding gain on temporal predictive coding, involving motion estimation followed by motion compensation. Consequently, errors in a distorted frame will propagate to the following frames, as error concealment (backward error correction) at the decoder may not repair some distorted areas. As video compression efficiency improves with successive codec standards, error sensitivity increases, which in turn results in quality degradation when transmitting over wireless channels. Thus, ways are sought to arrest spatio-temporal error propagation and intra-refresh techniques provided by the video codec itself are a way to do so (as discussed in this Chapter), along with other forms of error resilience (Stockhammer & Zia, 2007) such as data partitioning (Stockhammer & Bystrom, 2004) (as also discussed in this Chapter). Data-partitioning divides a compressed bitstream into prioritized data. This allows packetisation strategies and/or unequal error protection to improve the reconstruction quality of the video. This Chapter examines intra-refresh techniques and data-partitioning by means of a detailed case study in the context of IEEE 802.11e wireless LAN (Grilo & Nunes, 2002) quality-of-service provision.

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