Optimization of Delay Constrained Wireless Communication Networks

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Traditionally, in order to address the many complex issues that arise in communication networks, a ``layered" approach has been taken. The different layers are typically assigned different ``responsibilities," so that the general network design problem can be decomposed into simpler, more manageable problems. However, the independent design of the different layers - which ignores the detailed nature of their mutual interactions, shared constraints, and cumulative impact on the network's overall performance - can lead to inefficiencies. Future wireless communication networks will be required to provide wide coverage and high capacity to mobile users generating bursty multi-media information. This heterogeneous traffic will impose upon the network time-varying quality of service (QoS) constraints. Since many multi-media applications have delay-sensitive information with varying reliability requirements, such as numerical data, voice, and video, the project will take end-to-end delay and data integrity as its dominant system constraints. The goal of this project is, in the broadest sense, to take a more global view of end-to-end performance, to better understand the interactions among the layers, to develop techniques that improve system performance through joint optimization over the various layers and to do so in the context of a end-to-end delay constraint. One key theme of the proposal involves the optimization of system performance in the context of multiple users, particularly in a system which does not employ a cellular-type architecture. This requires the development of techniques that, on the one hand, address the deleterious effects of multiple-user interference at the physical layer, yet also incorporate end-to-end QoS objectives, especially delay, just as with the development of routing and scheduling algorithms. Another major theme will be the determination of the optimal distribution and the real-time dynamics of error control functions implemented across t he layers of the network, subject to specified end-user requirements. This requires investigation of inherent tradeoffs between error-rate and decoding delay of FEC employed at the physical layer, as well as the interactions among error control functions, including retransmission strategies, invoked at higher levels.