Wireless Powered Cooperative Non-Orthogonal Multiple Access Transmission

Abstract

This paper considers a three-stage multiple-input single-output (MISO) downlink system with wireless powered cooperative non-orthogonal multiple access (NOMA) transmission. In the first stage, a transmitter and a user with the best-of-the-effort quality-of-service (QoS) requirement activate a passive user by wireless power transfer (WPT) via radio frequency (RF) signal. In the second stage, the information is sent to both users with NOMA scheme. Finally, the best- of-the-effort user forwards the information to the passive user with decode-and-forward (DF) protocol in the third stage. By jointly optimizing the time fraction of each stage, the transmitter's beamforming vectors and the user's forwarding power, the data rate of the best- of-the-effort user is maximized while satisfying the minimum signal-to-interference-plus- noise ratio (SINR) and data transmission requirement of the passive user. Analytic solutions of the time fraction and forwarding power are derived, while the beamforming vectors can be obtained either in closed-form, or by solving a semidefinite programming (SDP) problem. The numerical results validate the proposed algorithm, and the significant impact over the system performance due to the nonlinear energy harvesting model is also verified.