Ismail Amin Ali

Semi-reliable transport protocol for IPTV over mobile WiMAX

As Internet IPTV extends to mobile devices, suitable transport protocols are sought that can adapt streaming to wireless access networks. This paper proposes a semi-reliable video-rate protocol that provides selective retransmission of scalable video layers should channel packet loss occur. The semi-reliable protocol leads to good video quality and reduces end-to-end delay and start-up delay.

Content-aware intra-refresh for video streaming over lossy links

Insertion of intra-coded macroblocks (MBs) is a means of mitigating temporal error propagation in mobile video streaming using an H.264/AVC codec. This paper proposes that the insertion of a cyclic line of such intra-coded MBs can give considerable quality gain for less-active video sequences rather than the more common periodic insertion of intra-coded frames, which in its turn is shown to be favorable for more-active sequences. The paper finds that randomized insertion of intra-refresh MBs is always less suitable than a cyclic line of intra-coded MBs. The results are relevant to choice of content when streaming to/between smartphones.

A prioritization scheme for H.264/AVC video congestion resilience with IEEE 802.11e

Intra-refresh is an efficient technique to mitigate temporal error propagation resulting from network packet losses. However, while including intra-refresh macroblocks (MBs) can prevent error propagation, conversely when network congestion occurs, packets carrying this type of MBs should be dropped at wireless network access time, in preference to dropping packets containing data of other types of MBs. Exploiting this observation, the proposed network access prioritization scheme combines intra-refresh MB lines with the H.264/AVC codecs Flexible Macroblock Ordering (FMO) to enhance congestion resilience. The proposed scheme is shown to improve the resulting video quality by up to 4 dB during periods of congestion. As an application of the proposed algorithm, the paper applies a crosslayer mapping of video traffic to IEEE802.11e access categories. The potential gains are demonstrated both for random packet drops at input buffers and for a wireless sensor network scenario.

Video Intra Coding for Compression and Error Resilience: A Review

Intra-coding is the application of spatial prediction coding to video data either on a whole frame basis or on individual macroblocks. This paper outlines the growing sophistication in intra-coding within recent standard codecs, the topic which is primarily relevant to compression for data storage. It then specializes to intra-coding for error resilience and intra-refresh, the topic which is relevant to video streaming applications. Efficient intra coding is becoming important for real-time high-resolution video, due to the computational cost of inter-coding, as the paper will consider for recent codecs. The paper will compare error-resilience performance across a variety of schemes. There are choices, which the paper analyses, as to whether to protect: on a whole frame basis; by intra-coding selected macro-blocks; and whether to use an isolated region; a cyclic intra-refresh line; or randomized insertion of macroblocks. The paper contains over 100 references, including recent patents in this field.

Video streaming over an Ad Hoc network using data partitioning and path diversity

Multiple description video coding can exploit path diversity to improve error resiliency by generating several independently decodable video descriptions and sending them over different paths. Such paths are readily available in ad hoc wireless networks. To approach the original quality, all descriptions need to be successfully received. However, in a wireless channel, error bursts or link disruption may still affect one or more descriptions, resulting in significant drops in video quality. This article describes a lower complexity yet effective scheme for video streaming over such wireless networks. In order to improve error resiliency, the scheme combines unequal packet importance with the advantages of path diversity. The scheme can be implemented with a minimal increase in computational complexity, as spatial decomposition of video frames is employed to generate the descriptions. Experimental results for an ad hoc wireless network show that a significant objective quality gain can be achieved (up to 3 dB) in the presence of signal shadow fading.

Enhanced prioritization for video streaming over wireless home networks with IEEE 802.11e

Cyclic intra refresh is able to mitigate temporal error propagation. This paper exploits the unequal error sensitivity introduced within individual video frames when using a cyclic intra refresh line of macroblocks. Slice-level priority is proposed based on the relative position of a slice with respect to the intra-refresh line. Two in-frame prioritization schemes are investigated: a region-based priority assignment and a packet-based priority assignment. The region-based scheme assigns packet priorities in the order of bitstream arrival to the packetizer, whereas the packet-based scheme assigns priorities within regions and does not follow bitstream arrival order to the packetizer. The proposed schemes do not add any bitrate or computational overheads and no decoder modification is required. Simulation results for streaming high-definition video over a quality-of-service enabled home wireless network show that the packet-based scheme can achieve quality gains up to 3 dB over sending video without applying priorities.

Prioritized packetization for video with intra-refresh macroblock line

When transmitting video over low bandwidth networks a cyclic intra-refresh (IR) line is preferable to periodic intra frames as an error mitigation technique. This paper shows that IR lines introduce non-uniform error sensitivity among regions within a picture that are identifiable by the position of the IR line. To exploit this characteristic, a packet prioritization scheme is proposed in which priorities are assigned on a packet-level basis. Thus, higher priority packets can be given better protection. The proposed scheme is demonstrated for prioritized access to a congested IEEE 802.11e network. Experimental results indicate that, when compared with the classic non-prioritized packet access scheme, the proposed scheme can achieve quality gains of up to 3.6 dB for a 10% data loss rate.

Congestion-resistant scalable media stream mapping for an IEEE 802.11E sensor network

Mapping an H.264/SVC (Scalable Video Coding) bitstream to the IEEE 802.11e video service class may result in the decoder discarding an excessive number of packets. This is because of dependencies between the discarded packets and those dropped in the service queue. Instead, the paper proposes mapping SVC quality layers across multiple service classes, thereby reducing the impact of traffic congestion upon video quality. Video quality in the sensor network scenario tested was almost stabilized, despite up to 10% packet drops through traffic congestion. An added advantage of the mapping is that the end-to-end delay of the base layer packets was considerably reduced compared to the standard IEEE 802.11e mapping.

Error and Congestion Resilient Video Streaming over Broadband Wireless

In this paper, error resilience is achieved by adaptive, application-layer rateless channel coding, which is used to protect H.264/Advanced Video Coding (AVC) codec data-partitioned videos. A packetization strategy is an effective tool to control error rates and, in the paper, source-coded data partitioning serves to allocate smaller packets to more important compressed video data. The scheme for doing this is applied to real-time streaming across a broadband wireless link. The advantages of rateless code rate adaptivity are then demonstrated in the paper. Because the data partitions of a video slice are each assigned to different network packets, in congestion-prone wireless networks the increased number of packets per slice and their size disparity may increase the packet loss rate from buffer overflows. As a form of congestion resilience, this paper recommends packet-size dependent scheduling as a relatively simple way of alleviating the buffer-overflow problem arising from data-partitioned packets. The paper also contributes an analysis of data partitioning and packet sizes as a prelude to considering scheduling regimes. The combination of adaptive channel coding and prioritized packetization for error resilience with packet-size dependent packet scheduling results in a robust streaming scheme specialized for broadband wireless and real-time streaming applications such as video conferencing, video telephony, and telemedicine.

Distortion-based slice level prioritization for real-time video over QoS-enabled wireless networks

This paper presents a prioritization scheme based on an analysis of the impact on objective video quality when dropping individual slices from coded video streams. It is shown that giving higher-priority classified packets preference in accessing the wireless media results in considerable quality gain (up to 3 dB in tests) over the case when no prioritization is applied. The proposed scheme is demonstrated for an IEEE 802.11e quality-of-service- (QoS-) enabled wireless LAN. Though more complex prioritization systems are possible, the proposed scheme is crafted formobile interactive or user-to-user video services and is simply implemented within the Main or the Baseline profiles of an H.264 codec.