A New Adaptive Distributed Space-Time-Coding Scheme for Cooperative Relaying

A non-regenerative dual-hop wireless system based on a distributed space-time-coding strategy is considered. It is assumed that each relay station retransmits an appropriate scaled space-time coded version of the received signals. The main goal of this paper is to provide an analytical study of an optimum power allocation strategy in relay stations in order to satisfy the quality of service requirements. In the high signal-to-noise ratio (SNR) regime for the relay-destination link, it is shown that the optimum power allocation strategy in each relay that minimizes the outage probability is to remain silent, if its direct channel gain with the source is less than a prespecified threshold level. The Monte-Carlo simulations show that the optimum power allocation scheme in each relay in order to minimize the outage probability or the frame-error rate is the thresholdbased on-off power scheme (i.e., the relay which its channel gain with the source is above a certain threshold transmits at full power). Also, the numerical results show a dramatical improvement in the system performance by using this scheme in comparison with the case that the relay stations forward their received signals with full power. Index Terms Cooperative relaying, space-time-block-code, outage probability, multi-hop wireless networks. Financial support provided by Nortel and the corresponding matching funds by the Natural Sciences and Engineering Research Council of Canada (NSERC), and Ontario Centres of Excellence (OCE) are gratefully acknowledged. The authors are affiliated with the Coding and Signal Transmission Laboratory, Electrical and Computer Engineering Department, University of Waterloo, Waterloo, ON, N2L 3G1, Canada, Tel: 519-884-8552, Fax: 519-888-4338, Emails: {jabouei, hbagheri, khandani}@cst.uwaterloo.ca.