An Analysis of Delay-Constrained Opportunistic Scheduling for Cellular Wireless Systems

Base station schedulers in 3G and evolving 4G cellular systems use knowledge of the time-varying channel conditions of mobile users to exploit the multiuser diversity inherent in wireless networks. Although such opportunistic schedulers significantly improve the system throughput by scheduling users when their channel conditions are most favorable, they could degrade the user experience as a result of unfair resource allocation and increased variability in the scheduled rate and delay. The growing need to provide service differentiation between delay-sensitive multimedia traffic and non real-time data traffic over packet switched air-interfaces underscores the need for these schedulers to incorporate delay constraints. In this work, we focus primarily on the trade-off between the realization of multiuser diversity gain and the provision of delay guarantees. Our main contribution is an analytical characterization of the distributions of the delay and rate offered by an opportunistic scheduler. The scheduling metric used in the algorithm combines the rate requested by the user and scheduling delay in a general form. Our analysis of a wireless system with a finite number of users in discrete time is strongly supported by system simulations of a time-slotted cellular downlink shared by multiple mobile users with independent, fading channels. We also compute closed form expressions for the scheduler statistics using a continuous approximation. The results in this paper can be used to evaluate system performance and provision resources to support Quality of Service (QoS) guarantees in broadband wireless networks

Utilization-based delay guarantee techniques and their applications

Many real-time systems demand effective and efficient delay-guaranteed services to meet timing requirements of their applications. We note that a system provides a delay-guaranteed service if the system can ensure that each task will meet its predefined end-to-end deadline. Admission control plays a critical role in providing delayguaranteed services. The major function of admission control is to determine admissibility of a new task. A new task will be admitted into the system if the deadline of all existing tasks and the new task can be met. Admission control has to be efficient and efficient, meaning that a decision should be made quickly while admitting the maximum number of tasks. In this dissertation, we study a utilization-based admission control mechanism. Utilization-based admission control makes an admission decision based on a simple resource utilization test: A task will be admitted if the resource utilization is lower than a pre-derived safe resource utilization bound. The challenge of obtaining a safe resource utilization bound is how to perform delay analysis offline, which is the main focus of this dissertation. For this, we develop utilization-based delay guarantee techniques to render utilization-based admission control both efficient and effective, which is further confirmed with our data. We develop techniques for several systems that are of practical importance. We first consider wired networks with the Differentiated Services model, which is wellknown as its supporting scalable services in computer networks. We consider both cases of providing deterministic and statistical delay-guaranteed services in wired networks with the Differentiated Services model. We will then extend our work to wireless networks, which have become popular for both civilian and mission critical applications. The variable service capacity of a wireless link presents more of a challenge in providing delay-guaranteed services in wireless networks. Finally, we study ways to provide delayguaranteed services in component-based systems, which now serve as an important platform for developing a new generation of computer software. We show that with our utilization-based delay guarantee technique, component-based systems can provide efficient and effective delay-guaranteed services while maintaining such advantages as the reusability of components