Power-time resource allocation for downlink SWIPT-assisted cooperative NOMA systems

We study a downlink cooperative non-orthogonal multiple access (NOMA) system in which a base station (BS) serves two paired users on the same frequency band simultaneously, and the near user acts as an energy-constrained relay for the far user since there is no direct link between the BS and the far user due to physical obstacles or heavy shadowing. To replenish energy of the near user for relaying, we enable the near user to harvest energy from BS signals by adopting the simultaneous wireless information and power transfer (SWIPT) technique. Different from the linear energy harvesting (EH) model used in most of the existing literature, we adopt a non-linear model for EH. By considering the non-linear features of the practical circuits, we aim to minimize the BS energy consumption while ensuring the minimum required transmission rate of both users. Since the formulated problem contains coupled power and time resource variables, it is challenging to solve it directly. Thus, we propose an optimal power-time resource allocation algorithm by decoupling the variables properly. Simulation results verify the theoretical analysis and show the performance of the considered system.