UP	Paper 1522	US-W-AB	DOWN
Position Dependant Power Allocation Strategies in Cooperative Relay Networks
Reynolds,Daryl		Computer Science and Electrical Engineering, West Virginia University
Datta Gupta,Somak		Computer Science and Electrical Engineering, West Virginia University
In fading wireless channels, relays are often used with the aim of achieving diversity and thus overall performance gain. Various forwarding techniques like amplify and forward (AF) and decode and forward (DF) are used at the relay to achieve this. In a power constrained environment, the performance can be bettered by using an optimal power allocation strategy. The relative position of the relay with respect to the source and destination also has an immense effect on the efficacy of the relay. We have considered AF and DF strategies at the relay and coherent demodulation. To simplify and facilitate the problem of power allocation, a single relay and half-duplex system model is used. Transmission from the source and that from the relay is assumed to be time-orthogonal. The first time slot uses a fraction of the total power to transmit the signal. In the second time slot the relay retransmits with the remaining fraction of power using one of the forwarding strategies. The distance between source and destination is normalized to one and we also assume a fixed noise power. The relay is placed at various positions in a planar grid with the position of source and destination being fixed. Analytical expressions of the instantaneous SNR at the destination are derived for both AF and DF. These expressions are numerically optimized to obtain an optimum power allocation strategy for each position of the relay in both the AF and DF schemes. BER performances of AF and DF are then compared. These results help us identify the regions where the relay would provide some performance improvement and where using a relay provides no benefits. Depending on the position, the relay will also have the option to decide what forwarding strategy would be most rewarding. So not only can the performance be bettered by using optimal power allocation and switching between forwarding techniques, we can also decide when it is advantageous to use a relay and when we should switch it off.
Somak Datta Gupta received his B.E. degree in Electronics and Communication Engineering from Visvesvaraya Technological University, India in 2002. He is currently a graduate student, pursuing his M.S. in the Lane Department of Computer Science and Electrical Engineering at West Virginia University. His research interests are in the fields of communication theory and signal processing in general and optimizing relay communications in particular. 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.