Applications of “Cross-Layer” in Video Communications over Wireless Networks

Applications of “Cross-Layer” in Video Communications over Wireless Networks

Martin Fleury (University of Essex, UK), Rouzbeh Razavi (University of Essex, UK), Laith Al-Jobouri (University of Essex, UK), Salah M. Saleh Al-Majeed (University of Essex, UK) and Mohammed Ghanbari (University of Essex, UK)
Copyright: © 2012 |Pages: 16
DOI: 10.4018/978-1-4666-0960-0.ch009
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Because of the impact of noise, interference, fading, and shadowing in a wireless network, there has been a realization that the strict layering of wireline networks may be unsuitable for wireless. It is the volatility over time that demands an adaptive solution and the basis of adaptation must arise by communication of the channel conditions along with the datalink settings. Video communication is particularly vulnerable because, except when reception is decoupled from distribution as in multimedia messaging, there are real-time display and decode deadlines to be met. The predictive nature of video compression also makes it susceptible to temporal error propagation. In this chapter, case studies from the authors’ experiences with broadband wireless access networks and personal area wireless networks serve to illustrate how information exchange across the layers can benefit received video quality. These schemes are all adaptive and serve as a small sample of a much greater population of cross-layer techniques. Given the importance of multimedia communications as an engine of growth for networked communication, “cross-layer” should be the first consideration in designing a video application.
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Traditional network design has largely taken place independently of the application. This form of design preserves protocol layering as a way of providing a well-defined interface between the layers and of isolating errors. Because of this, in network design it becomes easier to replace one protocol with another within the same layer. However, multimedia applications with real-time constraints and limited tolerance of data loss can significantly benefit from cross-layer design and optimization (Schaar, 2007). A cross-layer approach allows the exchange of information across protocol-layer boundaries and in some cases the approach allows system-wise optimization of performance. For example, sensor networks benefit from system-wise optimization (Jurdak, 2007), as they usually run dedicated applications such as video surveillance. The same applies to ad hoc networks in general, where video streaming can benefit (Setton, et al., 2005) from cross-layer design. Widening the remit, IEEE 802.11 wireless LANs (Schaar, et al., 2005) have also proved a fertile ground for multimedia applications of cross-layer design.

There are penalties in applying a cross-layer scheme (Kawadia & Kumar, 2003), namely it may result in a monolithic application that is hard to modify or evolve. However, for wireless communication (Srivastav & Motani, 2005) an adaptive scheme that leverages information across the layers can cope with the volatile state of the channel due to fading and shadowing and the constrained available bandwidth of the channel. It is not necessary to abandon layering altogether in a ‘layerless’ design but simply to communicate between the layers. Video applications break protocol boundaries with limited objectives in mind, though improvements in performance remain the goal. Performance may be defined variously in terms of reduction of delay, reduction of errors, throughput efficiency, and, in wireless networks, reduction of energy consumption. This list by no means exhausts the possible trade-offs that can be engineered through cross-layer exchange of information.

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