To appear in ACM Journal of Mobile Networks and Applications (MONET) Vol. 9, No. 3, June 2004 1 A Packet Scheduling Approach to QoS Support in Multihop Wireless Networks Haiyun Luo * , Songwu Lu * , Vaduvur Bharghavan † , Jerry Cheng * , Gary Zhong † * Computer Science Dept. † Coordinated Science Laboratory University of California University of Illinois Los Angeles, CA 90095 Urbana, IL 61801 {hluo,slu,chengje,gzhong}@cs.ucla.edu bharghav@crhc.uiuc.edu Abstract Providing packet-level quality of service (QoS) is critical to support both rate-sensitive and delay-sensitive applica- tions in the bandwidth-constrained, shared-channel, mul- tihop wireless networks. Packet scheduling has been a very popular paradigm to ensure minimum throughput and bounded delay access for packet flows. This work describes a packet scheduling approach to QoS provisioning in mul- tihop wireless networks. Besides minimum throughput and delay bounds for each flow, our scheduling disciplines seek to achieve fair and maximum allocation of the shared wireless channel bandwidth. However, these two criteria can poten- tially be in conflict in a generic-topology multihop wireless network where a single logical channel is shared among mul- tiple contending flows and spatial reuse of the channel band- width is possible. In this paper, we propose a new schedul- ing model that addresses this conflict. The main results of this paper are the following: (a) a two-tier service model that provides a minimum “fair” allocation of the channel bandwidth for each packet flow and additionally maximizes spatial reuse of bandwidth, (b) an ideal centralized packet scheduling algorithm that realizes the above service model, and (c) a practical distributed backoff-based channel con- tention mechanism that approximates the ideal service within the framework of the CSMA/CA protocol. Keywords Wireless Scheduling, Fair Queueing, Ad-hoc networks, Wireless MAC 1 Introduction In recent years, researchers have developed numerous re- source management algorithms and protocols for wireless mobile networking environments [1, 2, 3, 4, 5, 6], e.g., QoS oriented MAC layer design, packet scheduling, mobility management, admission control and resource reservation to name a few. The end goal of all these proposals is to devise effective management schemes for capacity-constrained and highly dynamic wireless networks in order to support com- munication intensive applications with QoS that are compa- rable to their wireline counterparts. In many of these pro- posed designs, fair distribution of bandwidth and maximiza- tion of resource utilization have been identified as two impor- tant design goals, notably for scheduling disciplines [2, 3, 7]. Fairness is critical to ensure that well-behaved users are not penalized because of the excessive resource demands of ag- gressive users. Maximizing resource utilization is critical to effectively support communication-intensive applications, e.g., web browsing, video conferencing and remote trans- fer of large files, which can easily stress the bandwidth- constrained wireless channel. Achieving both fairness and maximization of channel uti- lization in packet scheduling is particularly challenging in a shared-medium multihop wireless network. Since wireless transmissions are locally broadcast in the shared physical channel, location-dependent contention exists among flows in a neighborhood [8]. How to ensure fair channel alloca- tion among spatially contending packet flows through packet scheduling has not been addressed in related literature. Be- sides, the multihop nature of a shared-channel wireless net- work makes spatial channel reuse possible [2, 4]. How to maximize channel reuse, and hence the aggregate network capacity, poses another challenge. Unfortunately, the two goals of ensuring fairness and maximizing resource utiliza- tion have inherent conflicts in shared-medium multihop wire- less networks, as we will illustrate in this paper. Two extreme approaches for resolving this conflict are to either maximize the aggregate channel utilization without any fairness consid- erations (potentially starving some packet flows), or enforce strict notions of fairness across all flows in the network at the cost of possibly significant reductions in the aggregate chan- nel utilization. In this paper, we investigate a model for packet scheduling that arbitrates these two design criteria in order to resolve the inherent conflict between them. The main results of this