Rateless scalable video coding for overlay multisource streaming in MANETs q T. Schierl a, * , S. Johansen b , A. Perkis b , T. Wiegand a a Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute (HHI), Einsteinufer 37, D-10587 Berlin, Germany b Centre for Quantifiable Quality of Service in Communications Systems, Norwegian University of Science and Technology, Trondheim, Norway article info Article history: Received 2 December 2007 Accepted 19 June 2008 Available online 28 June 2008 Keywords: Channel coding Scalable video coding Distributed streaming Network reliability Rate allocation Mobile Ad Hoc Networks abstract Recent advances in forward error correction and scalable video coding enable new approaches for robust, distributed streaming in Mobile Ad Hoc Networks (MANETs). This paper presents an approach for distri- bution of real time video by uncoordinated peer-to-peer relay or source nodes in an overlay network on top of a MANET. The approach proposed here allows for distributed, rate-distortion optimized transmis- sion-rate allocation for competing scalable video streams at relay nodes in the overlay network. The approach has the desirable feature of path/source diversity that can be used for enhancing reliability in connectivity to serving nodes and/or attaining a higher throughput. The distributed approach reduces signaling overhead as well as avoiding scalability issues that come with centralized processing in MAN- ETs. Results show a significant performance gain over both single-server systems and previously pro- posed multi-source systems. Ó 2008 Elsevier Inc. All rights reserved. 1. Introduction Recently, MANETs [1] based on the ad hoc mode of IEEE 802.11 WLAN [2] or the emerging IEEE 802.16j WiMAX Mobile Multihop Relay [3] and IEEE 802.11s [4] standards have gained interest for delivery of multimedia content and other mobile services. Similar to ‘push’ services in 3G networks, new services can be introduced based on ad hoc groups built on top of MANETs. MANETs are attractive due to low infrastructure costs, especially in areas with high user density. The coverage area for mobile services can gener- ally be extended through cooperation with neighboring nodes. In MANETs, user terminals in a mobile network are conceptually not assumed to be receivers only, but can also be used as routing nodes in order to build a dynamic network infrastructure. User nodes building an on-demand MANET are by definition as- sumed to be mobile, which results in highly dynamic characteris- tics for this type of network. Thus, a topology built upon a MANET cannot be truly robust against network separation, route/ path losses and packet losses. Therefore, clients typically experi- ence connection losses to serving nodes [5]. Multimedia delivery services in MANETs can be implemented using non-real-time downloads or real-time streaming. Download delivery in general does not relate to the usual timing constraints for media data. By using appropriate end-to-end protocols (e.g. [6]), one could more easily deal with connectivity loss and longer outages in MANETs in order to provide full reliability. For real-time delivery, on the other hand, timely delivery is crucial. In this case, where the associated delay constraints [5] are of prime impor- tance, reliability is much harder to achieve. Furthermore, the avail- able throughput in MANETs is typically orders of magnitude lower than other wireless (and certainly wired) networks, leading to in- creased congestion and contention. When simply using common point-to-point transmission techniques such as link layer forward error correction or retransmission protocols, sufficiently good ser- vice quality in MANETs is often not possible. Hence, solutions for satisfying the different connectivity requirements of real-time streaming in MANETs are needed. The solution to this problem presented here is based on enhanc- ing source connectivity by using source node diversity (i.e. stream- ing from multiple sources concurrently) combined with the use of a family of ‘rateless’ forward error correction codes (also known as ‘fountain’ codes) [8]. The proposed approach exploits the benefits of cooperative interaction between peers in an overlay network on top of a MANET for maximizing video quality, adapting to vary- ing network conditions and connectivity. For improving application layer QoS, scalable video coding and application layer forward error correction is employed. In general, a scalable video stream allows for flexibility in rate allocation and adaptation at peers in the overlay network, as peer nodes may de- cide to forward or not to forward a network stream in order to adapt the transmission rate. By using an efficient and flexible FEC code, the Raptor code [7][8], in combination with scalable video coding, reception of real time video data from uncoordinated peers is realized. 1047-3203/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jvcir.2008.06.004 q The authors thank C. Hellge (Fraunhofer HHI, Berlin, Germany), T. Stockhammer (Nomor Research, Bergen, Germany) and Shpend Mirta (Fraunhofer HHI, Berlin, Germany) for their contributions to the work presented in this paper. * Corresponding author. Fax: +49 30 392 7200. E-mail addresses: schierl@hhi.fhg.de (T. Schierl), stianjo@q2s.ntnu.no (S. Johansen), andrew@q2s.ntnu.no (A. Perkis), wiegand@hhi.fhg.de (T. Wiegand). J. Vis. Commun. Image R. 19 (2008) 500–507 Contents lists available at ScienceDirect J. Vis. Commun. Image R. journal homepage: www.elsevier.com/locate/jvci