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  • Research Article
  • Open Access

Opportunistic Scheduling for OFDM Systems with Fairness Constraints

EURASIP Journal on Wireless Communications and Networking20072008:215939

Received: 4 June 2007

Accepted: 3 November 2007

Published: 20 November 2007


We consider the problem of downlink scheduling for multiuser orthogonal frequency-division multiplexing (OFDM) systems. Opportunistic scheduling exploits the time-varying, location-dependent channel conditions to achieve multiuser diversity. Previous work in this area has focused on single-channel systems. Multiuser OFDM allows multiple users to transmit simultaneously over multiple channels. In this paper, we develop a rigorous framework to study opportunistic scheduling in multiuser OFDM systems. We derive optimal opportunistic scheduling policies under three QoS/fairness constraints for multiuser OFDM systems—temporal fairness, utilitarian fairness, and minimum-performance guarantees. Our scheduler decides not only which time slot, but also which subcarrier to allocate to each user. Implementing these optimal policies involves solving a maximal bipartite matching problem at each scheduling time. To solve this problem efficiently, we apply a modified Hungarian algorithm and a simple suboptimal algorithm. Numerical results demonstrate that our schemes achieve significant improvement in system performance compared with nonopportunistic schemes.


OFDM SystemMultiuser DiversityBipartite MatchHungarian AlgorithmFairness Constraint

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Authors’ Affiliations

Department of Electrical and Computer Engineering, Colorado State University, Ft. Collins, USA
QuantWorks, Inc, Oak Hill, USA


© Zhi Zhang et al. 2008

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.