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 Bit Loading Algorithms for Cooperative OFDM Systems | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2008 Article ID 476797 9 pages doi 2008 476797 Research Article Bit Loading Algorithms for Cooperative OFDM Systems Bo Gui and Leonard J. Cimini Jr. Department of Electrical and Computer Engineering University of Delaware Newark DE 19716 USA Correspondence should be addressed to Bo Gui guibo@ Received 18 May 2007 Revised 9 August 2007 Accepted 25 September 2007 Recommended by Hikmet Sari We investigate the resource allocation problem for an OFDM cooperative network with a single source-destination pair and multiple relays. Assuming knowledge of the instantaneous channel gains for all links in the entire network we propose several bit and power allocation schemes aiming at minimizing the total transmission power under a target rate constraint. First an optimal and efficient bit loading algorithm is proposed when the relay node uses the same subchannel to relay the information transmitted by the source node. To further improve the performance gain subchannel permutation in which the subchannels are reallocated at relay nodes is considered. An optimal subchannel permutation algorithm is first proposed and then an efficient suboptimal algorithm is considered to achieve a better complexity-performance tradeoff. A distributed bit loading algorithm is also proposed for ad hoc networks. Simulation results show that significant performance gains can be achieved by the proposed bit loading algorithms especially when subchannel permutation is employed. Copyright 2008 B. Gui and L. J. Cimini Jr. 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 In cooperative systems a group of single-antenna nodes transmits as a virtual antenna array obtaining diversity gain without requiring multiple .
