Abstract not found

We present an “opportunistic ” transmission scheduling policy that exploits time-varying channel conditions and maxi-mizes the system performance stochastically under a certain resource allocation constraint. We establish the optimality of the scheduling scheme, and also that every user experiences a performance improvement over any non-opportunistic scheduling policy when users have independent performance values. We demonstrate via simulation results that the scheme is robust to es-timation errors, and also works well for nonstationary scenarios, resulting in performance improvements of 20–150 % compared with a scheduling scheme that does not take into account channel conditions. Last, we discuss an extension of our opportunistic scheduling scheme to improve “short-term ” performance.

Study of Distributed Fair Scheduling in Wireless Local Area Networks. (August 2000) Seema Gupta, M.Sc., Indian Institute of Technology Chair of Advisory Committee: Dr. Nitin H. Vaidya A Fair Scheduling policy is required to support dierentiated QoS requirements of contending ows in a wireless channel. This thesis presents a study of the Distributed Fair Scheduling (DFS) algorithm proposed for wireless Local Area Networks. The thesis evaluates DFS protocol and studies the unfairness in IEEE 802.11 standard. The wireless channel capacity varies with time and location due to the presence of location-dependent wireless errors. Therefore, the error-free scheduling specication is not sucient for fair allocation of channel capacity amongst contending ows in an error-prone wireless channel. This thesis borrows the idea of dynamic weight adjustment from prior work and applies it in the Distributed Fair Scheduling algorithm to provide long-term fairness in the presence of wireless errors. iv To my mother, father, brother and sisters v ACKNOWLEDGMENTS I would like to express my sincere thanks to my advisor Dr. Vaidya for his guidance, comments and encouragement. Without his advice, enthusiasm and help, my graduate school experience would not have been so fullling. I would like to thank Dr. Victor Bahl of Microsoft Research for his guidance and comments during the course of work. I thank Dr. Bettati and Dr. Reddy for being part of my advisory committee. I would like to thank Ms. Bhaskaran for her help during the course of work. I would like to thank NSF and Sun Microsystems for supporting me nancially to carry out my research. I would like to thank my parents for their constant encouragement and support. vi TABLE OF CONTENTS CHAPTER Page I

Routers are expected to play an important role in the IPbased wireless data network. Although a substantial number of techniques have been proposed to improve wireless network performance under dynamic wireless channel conditions and host mobility, a system support framework is still missing. In this paper, we describe DIRAC, a software-based router system that is designed for wireless networks to facilitate the implementation and evaluation of various channeladaptive and mobility-aware protocols. DIRAC adopts a distributed architecture that is composed of two parts: a Router Core (RC) shared by the wireless subnets, and a Router Agent (RA) at each access point/base station. RAs expose wireless link-layer information to the RC and enforce the control commands issued by the RC. This approach allows the router to make adaptive decisions based on linklayer information feedback. It also permits the router to enforce its policies (e.g., policing) more e#ectively through underlying link-layer mechanisms. As showcases, we implement under DIRAC the prototypes of three wireless network services: link-layer assisted fast handover, channeladaptive scheduling, and link-layer enforced policing. Our implementation and experiments show that our distributed wireless router provides a flexible framework, which enables advanced network-layer wireless services that are adaptive to channel conditions and host mobility.