Power minimization of cooperative relay transmission with relay's private information

Power minimization of a cooperative decode-and-forward (DF) half-duplex relaying is considered in this paper. In the system considered, two source nodes (S) try to communicate with one destination (D). Recognizing the difference in link qualities, one of source nodes not only transmits its own information to D but also acts as a relay for the other S. An optimization problem is formulated to minimize total network power by adjusting transmission powers and a time sharing variable. Since the objective function is not convex, an optimal solution cannot be obtained with low complexity. Instead, we approximate the objective function by a convex function to obtain a suboptimum time sharing factor among transmission phases. Then, transmission power is calculated based on the obtained suboptimum time sharing factor. Power saving of the system considered is compared to multiple access channel (MAC) with optimum power allocation.