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The Scientific World Journal
Volume 2014 (2014), Article ID 857540, 8 pages
http://dx.doi.org/10.1155/2014/857540
Research Article

On the Multiuser Diversity of Relay-Aided Downlink Systems Using Reduced Feedback

1Agency for Defense Development, Daejeon 305-600, Republic of Korea
2Department of Computer Science and Engineering, Dankook University, Yongin 448-701, Republic of Korea

Received 29 May 2014; Accepted 13 October 2014; Published 10 November 2014

Academic Editor: Antonio Martinez Gonzalez

Copyright © 2014 Yong-Up Jang and Won-Yong Shin. 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.

Abstract

We introduce an efficient multiuser scheduling method using amplify-and-forward relaying in relay-aided downlink systems, consisting of one base station (BS), one relay station, and multiple mobile stations (MSs). In our scheme, the BS opportunistically selects both the transmission mode, that is, either one- or two-hop transmission, and the desired user (i.e., the desired MS). Closed-form expressions for the average achievable rates are derived for the two transmission modes with multiuser scheduling, and its asymptotic solutions are also analyzed in the limit of large number of MSs. Based on the analysis, we propose a feedback-efficient two-step multiuser scheduling algorithm: the transmission mode selection followed by the user selection that only needs a partial feedback for instantaneous signal-to-noise ratios (SNRs) to the BS. We also analyze the average SNR condition such that the multiuser diversity gain is fully exploited for two-hop transmission. The proposed two-step scheduling algorithm exhibits the quite comparable achievable rates to those of the optimal one using full feedback information, while its required feedback information is reduced by half of the optimal one.