Cross-layer per-flow QoE evaluation for VoIP in wireless system
Gholibeigi, Mozhdeh (2011)
Master's Degree Programme in Information Technology
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The Internet as the biggest worldwide network provides a huge range of facilities and conveniences. Different types of communication applications are one of the most manifest conveniences provided up to date. Among others wireless VoIP as one of the most adhered applications which compliances anywhere/anytime communication capability is of special interest and attention. Performance optimization in the context of real-time applications such as VoIP is one of the most principal and yet challenging issues. Wireless environments aggravate conditions and tensity of issues due to inherent uncertainties, vulnerabilities and time-varying characteristics. The layered structure of the communication protocol stack is not well-suited for wireless environments by setting isolated layers and encumbering limitations. Whereas, if different layers of the protocol stack not only neighbouring ones can communicate and exchange information and make appropriate functionality decisions based on obtained information may be it becomes more straightforward to achieve optimized performance at any given instant of time. This is the basis for cross-layer design. In this thesis work we proposed a cross-layer performance evaluation frame work for a wireless VoIP flow of interest from the end-user perspective. As, quality perception is the most momentous aspect of it. In this frame work we used the E-model for formulating and measurement of perceived speech quality. In our work we considered the effect of underlying layers parameters and processes contributing in performance evaluation on the performance provided to the IP layer. As, performance evaluation is carried out at the IP layer. IP packet loss probability and transmission delay as the effects of the wireless channel, FEC and ARQ error concealment mechanisms at the data-link layer, queuing process at the IP layer, losses due to buffer overflow and at the end perceived quality evaluation through simple packet loss rate model and the integrated loss metric model (Clark s model) were considered through extensive simulations. We realized that the Clark s model which takes into account the effect of loss correlation provides more accurate performance estimates. As a general and important result we concluded that by designing and developing dynamic performance control systems such as rate control or resource allocation which dynamically adapt to time-varying real-time traffic and wireless channel conditions we can achieve better performance at any given instant of time. This can be considered as further studies and as an extension of this thesis work. /Kir11