  A simultaneously transmitting and reflecting reconfigurable intelligent
surfaces (STAR-RISs) enhanced uplink non-orthogonal multiple access (NOMA)
communication system is proposed. A total power consumption minimization
problem is formulated by jointly optimizing the transmit-power of users,
receive-beamforming vectors at the base station (BS), STAR-beamforming vectors
at the STAR-RIS and time slots. Here, the STAR-beamforming introduced by
STAR-RIS consists of transmission- and reflection-beamforming. To solve the
formulated non-convex problem, an efficient penalty-based alternating
optimization (P-AltOp) algorithm is proposed. Simulation results validate the
effectiveness of the proposed scheme and reveal the effect of various system
parameters on the total power consumption.
