Non-Orthogonal DF Relaying for SWIPT over Fading Channels with Power Adaptation

This paper investigates two-phase non-orthogonal decode-and-forward (DF) relaying for simultaneous wireless information and power transfer (SWIPT) over fading channels. The source transmits in both phases, while the relay forwards the decoded information in the second phase and the destination employs power splitting in both phases. We jointly optimize the source-power allocation between the two phases and the power-splitting ratios to maximize the ergodic end-to-end achievable rate subject to a minimum average harvested-energy requirement. By exploiting the time-sharing property, the original nonconvex problem is solved using Lagrangian duality. Numerical results under Rayleigh fading show that the proposed adaptive scheme achieves a higher ergodic achievable rate and supports a wider range of feasible harvested-energy requirements than a conventional scheme employing a fixed power-splitting ratio, with the performance advantage becoming more pronounced under stringent harvested-energy requirements.