UP	Paper 1380	US-M-W	DOWN
The performance of space-time coded cooperative diversity in an asynchronous cellular uplink
Vardhe,Kanchan		West Virginia University
Reynolds,Daryl		West Virginia University
Cooperative diversity which generalizes the conventional multiple-antenna system has generated a great deal of interest in the research community. Most of the prior work on cooperation assumes assignment of orthogonal channels to multiple users and synchronous communication between the signals transmitted from different cooperating terminals. Both of these assumptions may require an accurate coordination among the cooperating terminals causing significant overhead in wireless networks. The main purpose of this paper is to study the performance of space-time coded cooperative diversity while relaxing the constraints such as assignment of orthogonal channels to different users (inter-user orthogonality) and to focus on asynchronous communication. We consider a code division multiple access (CDMA) cellular uplink consisting of K users where users have been assigned non-orthogonal spreading codes. Note that since spreading codes are non-orthogonal, and we assume asynchronous communication between the relayed signals transmitted from cooperating terminals, we have non-orthogonality across the channels (inter-user non-orthogonality) and also within a channel. The crux of the problem is then to evaluate performance under these conditions and to design practical coding and reception schemes. In particular, we consider fully loaded, underloaded and overloaded CDMA. The outage probability results indicate spectral inefficiency of an underloaded system with respect to fully loaded CDMA system. The overloaded system is bandwidth efficient up to certain number of users but then exhibits worse performance than fully loaded CDMA. The proposed scheme shows a loss in spectral efficiency with respect to Laneman's scheme due to asynchronism and non-orthogonal spreading codes. But these constraints make our system practical and more flexible. We also present a practical system design and provide bit-error-probability simulations under the practical adaptive receiver design.
Kanchan G. Vardhe received the B.E. degree in electronics and telecommunications from Pune Institute of Computer Technology, University of Pune, India, in 2002 and the M.S. degree in electrical engineering from West Virginia University, Morgantown, in 2005. She is presently persuing the Ph.D. in electrical engineering at the West Virginia University, Morgantown. Her research interests include signal processing for wireless communications, communication theory and information theory. Dr. Daryl Reynolds received the B.S. degree in Electrical Engineering from the University of Colorado at Boulder in 1993. He received the M.S. and Ph.D. degrees in electrical engineering from Texas A&M University, College Station, TX in 1998 and 2002, respectively, where he also served as an assistant lecturer. In August 2002, he joined the Lane Department of Computer Science and Electrical Engineering at West Virginia University as an Assistant Professor. Dr. Reynolds' research interests fall in the general areas of communication theory and statistical signal processing.