Multi-User Video Streaming Using Unequal Error Protection Network Coding in Wireless Networks

In this article, we investigate a multi-user video streaming system applying unequal error protection (UEP) network coding (NC) for simultaneous real-time exchange of scalable video streams among multiple users. We focus on a simple wireless scenario where users exchange encoded data packets over a common central network node (e.g., a base station or an access point) that aims to capture the fundamental system behaviour. Our goal is to present analytical tools that provide both the decoding probability analysis and the expected delay guarantees for different importance layers of scalable video streams. Using the proposed tools, we offer a simple framework for design and analysis of UEP NC based multi-user video streaming systems and provide examples of system design for video conferencing scenario in broadband wireless cellular networks. Introduction Real-time multi-user (or multi-party) video streaming refers to a scenario where multiple users, interconnected by a common communication network, perform real-time exchange of video streams [1,2]. Each of the users continuously creates its own video stream and is interested in the continuous and real-time recovery of the streams generated by a subset or the set of all the other users. Application examples include video conferencing, multiview video systems, multi-party peer-to-peer (P2P) video exchange, emerging multimedia-oriented social networking (e.g., “see-what-i-see” applications), etc. However, designing robust and efficient multi-user video streaming systems over wireless networks faces a number of challenges, most notably, the strict delay limits enforced by real-time requirements and time-variable wireless channel conditions responsible for frequent packet losses. Network coding (NC) is a novel information processing technique applied in network nodes in which, instead of simple forwarding of received data packets, the data packets are combined and resulting network coded packets are transmitted instead. The idea was first introduced for the single-source multicast problem, where it was shown that, *Correspondence: [email protected] 1Department of Power, Electronics and Communication Engineering, University of Novi Sad, Trg D. Obradovića 6, Novi Sad, Serbia Full list of author information is available at the end of the article unlike routing, it achieves the capacity of the multicast connection [3]. For the single-source multicast problems represented by directed acyclic graphs with unit-capacity error-free edges, the class of linear network codes achieves the multicast connection capacity [4]. Furthermore, random linear codes over sufficiently large finite fields open the way for simple and fully distributed network code design [5]. The random linear coding (RLC) approach is adapted for practical implementation in lossy packet networks [6,7], and suggested in a number of wireless networking applications [8,9]. To increase throughput and improve error resilience, NC has been recently suggested for applications in multimedia streaming [10-14], and in particular, for multi-user video conferencing [15-17]. In [15], which is closest to our work, RLC is investigated for multi-party video conferencing in wireless broadband cellular systems. This study demonstrates that RLC applied within the central node possess a potential to reduce the end-to-end delay, increase throughput and improve the transmission reliability and system fairness. In this article, we explore analytical tools for the design and analysis of a real-time multi-user video streaming system that applies scalable video coding and unequal error protection (UEP) RLC. We focus on a simple scenario where wireless users exchange video streams over a common central node with the goal of capturing © 2012 Vukobratović and Stanković; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Vukobratović and Stanković EURASIP Journal onWireless Communications and Networking 2012, 2012:218 Page 2 of 13 http://jwcn.eurasipjournals.com/content/2012/1/218 the fundamental system behaviour. This work builds upon our recent theoretical analysis of UEP RLC schemes for erasure channels [18]. Addressing a specific UEP RLC application, the real-time multi-user video streaming, this article extends the layer decoding probability analysis of UEP RLC addressed in previous work to include additional performance measures such as expected decoding delays of different video layers and evolution of the expected received video quality of exchanged scalable video streams over time. Using the presented set of analytical tools, we offer a simple framework for the design and analysis of UEP RLC based real-time multi-user scalable video streaming systems. The framework provides flexible approach for reliable exchange of layered video streams over dynamically changing wireless channels. The application of the proposed framework and the benefits over the standard RLC approach applied in [15] are demonstrated through the distortion-optimized system design examples. The article is organized as follows. Section “RLC: an overview and UEP extension” provides a background on RLC and its UEP extensions, and provides a decoding performance analysis of the UEP RLC. The proposed multi-user video streaming setup is introduced in Section “Multi-user video streaming using UEP NC”. The same section formulates the distortion-based optimization of the multi-user video streaming system based on UEP NC. Selected UEP NC code design examples are discussed in Section “System optimization and results”. The article is concluded in Section “Conclusions”. RLC: an overview and UEP extension Background andmotivation For wireless broadcasting, NC is usually motivated by the two-user packet exchange example in Figure 1 (see e.g., [19]). Instead of replicating and independently transmitting each user packet, the central node XORs the incoming user packets and broadcasts a single coded packet. As a result, the number of packet transmissions required for two-way packet exchange between users reduces from four to three. The two-user example can be extended to multi-user scenarios using opportunistic binary NC (XOR-ing) for