LAUSR

Different from conventional reconfigurable intelligent surface, simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) can provide service for the users within 360° coverage. In this letter, we discuss a power minimization problem for STAR-RIS-empowered uplink non-orthogonal multiple access (NOMA) system. For the purpose of minimizing total transmit power, a joint optimization scheme of each user’s transmit power, transmission and reflection beamformers at the STAR-RIS, and time allocation is developed. To proceed, we derive the relationship between the phase shifts and the power allocation coefficients, then a near-optimal solution is proposed by invoking the semi-definite relaxation. It is shown by simulation results that the developed transmission-and-reflection scheme achieves better performance than the existing ones.