A Cross-Layer Solution for Ultrawideband Based Wireless Video Sensor Networks L. Campelli CEFRIEL Politecnico di Milano Milan 20133, Italy Email: Luca.Campelli@cefriel.it I. F. Akyildiz Broadband Wireless Networking Laboratory Georgia Institute of Technology Atlanta, GA 30332, USA Email: ian@ece.gatech.edu L. Fratta, M. Cesana Dipartimento di Elettronica e Informazione Politecnico di Milano Milan 20133, Italy Email: {fratta, cesana}@elet.polimi.it Abstract—A cross-layer communication protocol called VSN- Module is introduced for Wireless Video Sensor Networks based on UltraWideBand (UWB) radio technology at the physical layer. The core of our solution is a distributed path reservation scheme which routes video traffic from sources (sensors) to a sink. The path establishment takes into account the specific requirements of video flows such as bandwidth, end-to-end delay and jitter, as well as the current status of the traversed devices such as the available bandwidth, the energy consumption, and the quality of the wireless channels. Simulation experiments are carried out and the performance of the VSN-Module is evaluated in terms of maximum end-to-end delivery delay, maximum delay jitter, and power consumption, under different video flow requirements. I. I NTRODUCTION Wireless Video Sensor Networks (WVSNs) are composed of interconnected, battery-powered miniature video cameras, each packed with a low-power wireless transceiver that is capable of processing, sending, and receiving data. Video sensors will be used to enhance and complement existing surveillance systems against crime and terrorist attacks. Large scale networks of video sensors can extend the ability of law enforcement agencies to monitor areas, public events, private properties and borders. There exist several other applications of WVSNs [1]. Several of these applications require the sensor network paradigm to be re-thought in view of the need for mechanisms to deliver video content with a certain level of Quality of Service (QoS). Since the need to minimize the energy con- sumption has driven most of the research in sensor networks so far, mechanisms to efficiently deliver application-level QoS, and to map these requirements to network-layer metrics such as latency and jitter, have not been primary concerns in mainstream research on classical sensor networks. Moreover, the challenging goal of delivering video over resource-limited infrastructure requires a wise optimization of all the communi- cation protocols involved in the process. To this end, a cross- layer approach is highly favorable. Cross-layering in WSNs has been recently becoming an effective alternative solution to traditional layered protocol architectures. Cross-layering stands for joint design of network protocols, with the clear advantages over layered protocol design in terms of limited overhead and possibility to optimize jointly different protocol functionalities. Although several papers are focused on cross-layer design [2], a systematic methodology to accurately model and leverage cross-layer interactions is still missing. Most of the existing studies [3][4] decompose the resource allocation problem at different layers, and consider allocation of the resources at each layer separately. In many other cases [5][6][7], resource allocation problems are treated either heuristically, or without consider- ing cross-layer interdependencies, or by considering pairwise interactions between isolated pairs of layers. In this paper we introduce the Video Sensor Networks Module VSN-Module, a cross-layer communication protocol which provides QoS support. The VSN-Module is based on a distributed path reservation scheme, which is able to set up multi-hop routes from the video traffic source to the traffic sink, while satisfying the flow requirements (bandwidth, end- to-end delay, delay jitter). VSN-Module is designed according to a cross-layer solution of different protocol functionalities in different layers. Due to the high bandwidth requirements of video applica- tions, we argue that the physical layer must be integrated into (and exploited by) the upper layer functionalities of medium access, routing and transport layer. Thus, the VSN-Module adopts the Ultrawideband (UWB) technology at the physical layer, and couples the channel access with the physical trans- mission parameters. The main contribution of our work is the development of a cross layer communication protocol module to support video flows in energy and resource constrained video sensor networks. In particular, we propose: • a cross-layer approach capturing the interdependencies and functionalities of medium access control, routing, congestion control and UWB radio transceivers. • a distributed path reservation scheme for video flows. The remainder of the paper is organized as follows. In Section II, we present the network architecture and the feature of the video applications. In Section III we explain the func- tionalities of the VSN-Module, whose performance is evaluated in Section IV. Our concluding remarks are given in Section V. II. NETWORK ARCHITECTURE We refer to heterogeneous and hierarchical network sce- narios where sensor nodes are distinguished for the type of This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2008 proceedings. 978-1-4244-2324-8/08/$25.00 © 2008 IEEE.