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Research Article Power Allocation Strategies for Distributed Space-Time Codes in Amplify-and-Forward Mode | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2009 Article ID612719 13 pages doi 2009 612719 Research Article Power Allocation Strategies for Distributed Space-Time Codes in Amplify-and-Forward Mode Behrouz Maham1 2 and Are Hjorungnes1 1 UNIK-University Graduate Center University of Oslo 2027 Kjeller Norway 2 Department of Electrical Engineering Stanford University Stanford CA 94305 USA Correspondence should be addressed to Behrouz Maham behrouz@ Received 22 February 2009 Revised 28 May 2009 Accepted 23 July 2009 Recommended by Jacques Palicot We consider a wireless relay network with Rayleigh fading channels and apply distributed space-time coding DSTC in amplify-and-forward AF mode. It is assumed that the relays have statistical channel state information CSI of the local source-relay channels while the destination has full instantaneous CSI of the channels. It turns out that combined with the minimum SNR based power allocation in the relays AF DSTC results in a new opportunistic relaying scheme in which the best relay is selected to retransmit the source s signal. Furthermore we have derived the optimum power allocation between two cooperative transmission phases by maximizing the average received SNR at the destination. Next assuming M-PSK and M-QAM modulations we analyze the performance of cooperative diversity wireless networks using AF opportunistic relaying. We also derive an approximate formula for the symbol error rate SER of AF DSTC. Assuming the use of full-diversity space-time codes we derive two power allocation strategies minimizing the approximate SER expressions for constrained transmit power. Our analytical results have been confirmed by simulation results using full-rate full-diversity distributed space-time codes. Copyright 2009 B. Maham and A. Hjorungnes. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and