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Báo cáo hóa học: " Research Article Opportunistic Scheduling for OFDM Systems with Fairness Constraints"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Opportunistic Scheduling for OFDM Systems with Fairness Constraints | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2008 Article ID 215939 12 pages doi 10.1155 2008 215939 Research Article Opportunistic Scheduling for OFDM Systems with Fairness Constraints Zhi Zhang 1 Ying He 2 and Edwin K. P Chong1 1 Department of Electrical and Computer Engineering Colorado State University Ft. Collins CO 80523 USA 2 QuantWorks Inc. Oak Hill VA 20171 USA Correspondence should be addressed to Edwin K. P. Chong edwin.chong@colostate.edu Received 4 June 2007 Accepted 3 November 2007 Recommended by F. K. Jondral 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. Copyright 2008 Zhi Zhang et al. 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. 1. INTRODUCTION .