A cross-layer packet scheduling scheme that streams pre-encoded video over wireless downlink packet access networks to multiple users is presented. The scheme can be used with the emerging wireless standards such as HSDPA and IEEE 802.16. A gradient based scheduling scheme is used in which user data rates are dynamically adjusted based on channel quality as well as the gradients of a utility function. The user utilities are designed as a function of the distortion of the received video. This enables distortion-aware packet scheduling both within and across multiple users. The utility takes into account decoder error concealment, an important component in deciding the received quality of the video. We consider both simple and complex error concealment techniques. Simulation results show that the gradient based scheduling framework combined with This work was supported by the Motorola Center for Seamless Communication at Northwestern University. The authors are with the Electrical Engineering and Computer Science Department at Northwestern University. the content-aware utility functions provides a viable method for downlink packet scheduling as it can significantly outperform current content-independent techniques. Further tests determine the sensitivity of the system to the initial video encoding schemes, as well as to non-real-time packet ordering techniques.
The emergence of 3G and 4G wireless networks brings with it the possibility of streaming high quality video content on-demand to mobile users. Wireless video applications require appropriate scheduling techniques that make use of the specific characteristics of video content, as well as the well known gains from multiuser diversity. While fast and frequent channel feedback is available in the new generation of wireless networks, the channel estimates cannot be perfect, and channel losses should be taken into account in the packet scheduling and resource allocation. The proposed scheme is formulated as a joint optimization over the resource allocation and channel loss protection, in order to minimize the distortion of the received video sequences. The distortion is a function of the packets deliberately dropped at the transmission queue due to congestion, as well as of random channel losses. The scheme makes use of a packet prioritization strategy that orders video packets based on their contribution to reducing the expected distortion of the received video sequence. Simulation results show that the proposed technique significantly outperforms content-independent packet scheduling schemes.
Abstract-This paper presents an improved technique for estimating the end-to-end distortion, which includes both quantization error after encoding and random transmission error, after transmission in video communication systems. The proposed technique mainly differs from most existing techniques in that it takes into account filtering operations, e.g. interpolation in subpixel motion compensation, as introduced in advanced video codecs. The distortion estimation for pixels or subpixels under filtering operations requires the computation of the second moment of a weighted sum of random variables. In this paper, we prove a proposition for calculating the second moment of a weighted sum of correlated random variables without requiring knowledge of their probability distribution. Then, we apply the proposition to extend our previous error-resilient algorithm for prediction mode decision without significantly increasing complexity. Experimental results using an H.264/AVC codec show that our new algorithm provides an improvement in both rate-distortion performance and subjective quality over existing algorithms. Our algorithm can also be applied in the upcoming high efficiency video coding (HEVC) standard, where additional filtering techniques are under consideration.
Demand for multimedia services, such as video streaming over wireless networks, has grown dramatically in recent years. The downlink transmission of multiple video sequences to multiple users over a shared resource-limited wireless channel, however, is a daunting task. Among the many challenges in this area are the time-varying channel conditions, limited available resources, such as bandwidth and power, and the different transmission requirements of different video content. This work takes into account the time-varying nature of the wireless channels, as well as the importance of individual video packets, to develop a cross-layer resource allocation and packet scheduling scheme for multiuser video streaming over lossy wireless packet access networks. Assuming that accurate channel feedback is not available at the scheduler, random channel losses combined with complex error concealment at the receiver make it impossible for the scheduler to determine the actual distortion of the sequence at the receiver. Therefore, the objective of the optimization is to minimize the expected distortion of the received sequence, where the expectation is calculated at the scheduler with respect to the packet loss probability in the channel. The expected distortion is used to order the packets in the transmission queue of each user, and then gradients of the expected distortion are used to efficiently allocate resources across users. Simulations show that the proposed scheme performs significantly better than a conventional content-independent scheme for video transmission.
Wireless video transmission is prone to unpredictable degradations due to time-varying channel conditions. Such degradations are difficult to overcome using conventional video coding techniques. Scalable video coding offers a flexible bitstream that can be dynamically adapted to fit the prevailing channel conditionq Within .1 qcibhle vidpeo ccndino frrmneprioritized according to their importance. The prioritization needed to occur in real-time in order to be optimal. In this paper, we explore means by which a scalable coded bitstream can be prioritized offline without knowledge of the specific channel realization. The proper method for prioritization is not immediately clear due to the effects of temporal scalability and error concealment. work,1.weVdevelopVsImple pc prorti.ti s.tratew h Previous work on multi-user video streaming can be found wok edvlpsml pake proiizto staeis which in [2] and [3]. They, however, do not specifically address the when combined with a reasonable error concealment scheme [2 an 3.Te,hwvr ontseiial drs h issue of scalable video encoding. In [4], temporal scalabiland a content-aware resource allocation technique, provide i for robust video transmission over time-varying channels. The ability, in the form of progressive refinement through FGS packet prioritization as well as the calculation of the content-abliy in th for ofporsierfnmn.hog G (Fine Granularity Scalability), is considered. Comparing the aware scheduling metric can be performed offline and sig-emerging scalable coding extension of H264 MPEG4-AVC, naled to the wireless scheduler. termed SVC (Scalable Video Coding), to the AVC standard Index Terms-Scalable video coding, wireless video stream-without scalable video coding, the authors show that signifing, cross-layer design icant improvement can be made in wireless multiuser video streaming through the use of SVC. A simple packet drop-1. INTRODUCTION ping strategy is used for buffer management and maximum
As wireless technology evolves towards its fourth generation (4G) of development, the prospect of offering multimedia services such as on‐demand video streaming and video conferencing to wireless mobile clients becomes increasingly more viable. The eventual success of such applications depends on the efficient management of the limited system resources while taking into account the time‐varying wireless channel conditions as well as the varying multimedia source content. In this paper, we review some of the recent advances in cross‐layer design schemes, which aim at providing significant gains in performance for video streaming systems through content‐aware resource allocation. Advances in both, real‐time video streaming, where the video is encoded and transmitted in real‐time, as well as, on‐demand video streaming, where the video is pre‐encoded in a media server, are considered. Copyright © 2007 John Wiley & Sons, Ltd.
The goal of video summarization is to select key frames from a video sequence in order to generate an optimal summary that can accommodate constraints on viewing time, storage, or bandwidth. While video summary generation without transmission considerations has been studied extensively, the problem of rate-distortion optimized summary generation and transmission in a packet-lossy network has gained little attention. We consider the transmission of summarized video over a packet-lossy network such as the Internet. We depart from traditional rate control methods by not sacrificing the image quality of each transmitted frame but instead focusing on the frames that can be dropped without seriously affecting the quality of the video sequence. We take into account the packet loss probability, and use the end-to-end distortion to optimize the video quality given constraints on the temporal rate of the summary. Different network scenarios such as when a feedback channel is not available, and when a feedback channel is available with the possibility of retransmission, are considered. In each case, we assume a strict end-to-end delay constraint such that the summarized video can be viewed in real-time. We show simulation results for each case, and also discuss the case when the feedback delay may not be constant.
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