Interference-Constrained Power Adaptive Decode-and-Forward Relaying Policy: Design and Performance Analysis

Power adaptation is a feasible and promising solution to avoid interference at the primary, caused by transmissions of secondary underlay cooperative spectrum sharing systems. For it, we propose a novel interference-constrained power adaptive decode-and-forward (IC-PADnF) relaying policy jointly with a simple probabilistic relay selection (PRS) policy. The proposed IC-PADnF relaying policy, apart from acting as a regenerative relay, adaptively sets its transmit power and gain to optimize the underlay cooperative spectrum sharing system's performance. Further, the relay selection policy is easy to implement due to less channel state information (CSI) requirements. To evaluate the proposed IC-PADnF policy's performance, we derive analytical expressions for optimal fading averaged spectral efficiency and optimal fading averaged energy efficiency. We also obtain upperbound to these essential performance measures. We perform Monte-Carlo simulations to validate the derived analytical results. Furthermore, we compared the proposed policy with benchmark policies to explicitly show the performance improvements and its applicability for cooperative spectrum sharing systems and networks. Lastly, we find that IC-PADnF relaying policy jointly with PRS policy outperforms the benchmark policies.