AoI Minimization in RIS-Aided SWIPT Systems

This paper studies the age of information (AoI) minimization design in a reconfigurable intelligent surface (RIS)-aided simultaneous wireless information and power transfer (SWIPT) system. The non-orthogonal multiple access (NOMA) scheme is adopted in the uplink (UL) phase. We formulate an AoI minimization problem to optimize the transmit/receive beamformers, phase shift vector, information-user (IU) selection, UL/downlink (DL) time allocation and decoding order subject to the power budget constraint of the base station, the unit-modulus constraints of the reflecting elements and the energy harvesting (EH) constraints of the energy users. The considered problem is decomposed into three subproblems, and then solved by a proposed alternating optimization-based algorithm. The computational complexity of the proposed algorithm is analyzed. Simulation results demonstrate the impacts on AoI by adopting RIS and NOMA as well as the system parameters. Besides, the trade-off between information freshness and the EH is revealed through the impact of EH requirement on the IU selection and UL/DL time allocation.