Amplify-and-Forward Relay Sharing for Both Primary and Cognitive Users

In this paper, we propose and investigate four amplify-and-forward (AF) relaying schemes for both the primary user (PU) and the cognitive user (CU), depending on whether both users transmit their signals to the common relay in parallel or serially and whether the relay forwards their signals to the respective receivers in parallel or serially. The advantage of the proposed schemes is that both users can share the same relay, which is different from previous works. Our goal is to minimize the normalized total power consumption while guaranteeing the quality of service (QoS) of both users and their individual transmit power constraints. Based on the feasible conditions for the optimization problem (OP), we define a new performance metric called relay sharing (RS) probability to characterize proposed schemes and derive closed-form expressions for asymptotically tight approximation and exact performance analysis. Simulations results demonstrate the effectiveness of the proposed schemes in terms of low power consumption and high RS probability.