Single-cell and hierarchical wireless data broadcast systems: Modeling, performance analysis, and optimal scheduling.

摘要

Wireless Data Broadcast (WDB) is known as a highly efficient information delivery mechanism of nearly unlimited scalability. Over the last few years, due to the appealing properties and a wide area of possible application, a large number of new solutions and ideas related to WDB have been proposed. However, most of those solutions employ overly simplified assumptions concerning the system operation and user behaviour, and therefore fail to provide a broader insight into the nature and performance of WDB as found in the real world.; The work presented in this thesis aims to overcome the main limitations of the previous published research works on WDB. In particular, the following contributions are made. (1) We propose a new model of TDM-based single-cell WDB systems, which extends over both broadcast and unicast data retrieval principles, and assumes realistic-impatient user behaviour patterns. Based on this model, we define and derive exact mathematical expressions for several performance measures that seem most appropriate for the analysis of WDB systems. Consequently, we prove that there exists a single broadcast scheduling scheme (S_optimal), which can ensure the optimal system performance with respect to all of the measures at once, as well as the system's throughput, QoS and GoS. (2) The actual search for S_optimal, both in WDB systems of uniform and variable user mobilities, turns out to be a complex non-linear double inequality-constrained optimization problem, without a tractable closed-form solution. However, by exploiting some mathematical properties of the main cost function, we prove that the given optimization problem can be considerably simplified. Based on this simplification, we derive a closed form approximate expression for S_optimal and, consequently, we propose an algorithm for fast, CPU conserving estimation of S_optimal . Experimental results verify that the proposed algorithm requires minimum computation, while providing performance almost identical to S_optimal obtained through numerical estimation. (3) For the completeness of our discussion on single-cell WDB systems, we also consider the possibility of frequency-division-multiplexing (FDM) WDB. We prove that for any given FDM-based broadcast schedule there exists a TDM-based broadcast schedule that results in a better overall system performance. With this proof, we ultimately justify our initial decision to make TDM-WDB the main focus of this work. (Abstract shortened by UMI.)