Broadcast Scheduling in Information Delivery Networks

Title of Dissertation: BROADCAST SCHEDULING IN INFORMATION DELIVERY NETWORKS Majid Raissi-Dehkordi, Doctor of Philosophy, 2002 Dissertation directed by: Professor John S. Baras Department of Electrical and Computer Engineering The continuous growth in the demand for access to information and the increasing number of users of the information delivery systems have sparked the need for highly scalable systems with more efficient usage of the bandwidth. One of the effective methods for efficient use of the bandwidth is to provide the information to a group of users simultaneously via broadcast delivery. Generally, all applications that deliver the popular data packages (traffic information, weather, stocks, web pages) are suitable candidates for broadcast delivery and satellite or wireless networks with their inherent broadcast capability are the natural choices for implementing such applications. In this dissertation, we investigate one of the most important problems in broadcast delivery i.e., the broadcast scheduling problem. This problem arises in broadcast systems with a large number of data packages and limited broadcast channels and the goal is to find the best sequence of broadcasts in order to minimize the average waiting time of the users. We first formulate the problem as a dynamic optimization problem and investigate the properties of the optimal solution. Later, we use the bandit problem formulation to address a version of the problem where all packages have equal lengths. We find an asymptotically optimal index policy for that problem and compare the results with some well-known heuristic methods. Since the equal file length assumption is not appropriate for applications such as cache broadcasting in the Internet delivery systems, we also investigate an extension of the problem where the files have random lengths. After investigating some of the properties of the optimal solution, we derive an asymptotically optimal index policy for that case as well. Also, through simulation studies, the performance of the policy is compared with that of some other heuristic polices designed by intuitive arguments. The index policy is also extended to systems with deterministic, unequal file sizes and its performance is evaluated and compared to other policies via simulation studies. The formulation and analytical procedures used in deriving the index policies in this dissertation allow for introduction of other extensions of the problem like assigning weights to the data files (studied in Chapter 3) or taking into account the channel errors and correlation between the arrivals. We will present our formulation of the last two extensions and discuss some of the numerical results to motivate future work on these problems. BROADCAST SCHEDULING IN INFORMATION DELIVERY NETWORKS by Majid Raissi-Dehkordi Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2002 Advisory Committee: Professor John S. Baras, Chairman/Advisor Dr. Richard J. La Dr. Tzong-yow Lee Professor Armand M. Makowski Dr. Babis Papadopoulos c ©Copyright by Majid Raissi-Dehkordi 2002