Abstract: A method to maximize energy efficiency is proposed for uplink non-orthogonal multiple access (NOMA) systems assisted by simultaneously transmitting and reflecting intelligent surface(STAR-RIS). Firstly, the optimization problem of maximizing energy efficiency is constructed, with base station beamforming, STAR-RIS phase shift, users’ power and time allocation as variables. Then, the optimization problem is sim-plified by deducing the relationship between beamforming and STAR-RIS phase shift and the minimum power required by the users. Finally, an iterative method is proposed to optimize STAR-RIS phase shift, power al-location and time allocation alternately. In each iteration, semi-definite programming method (SDP) is used to optimize STAR-RIS phase shift, Dinkelbach algorithm to optimize power allocation, and function extremal method to optimize time allocation. The simulation results show that for the time switching protocol, time allocation has little effect on energy efficiency, while random phase shift has great effect on energy efficiency.

Key words: NOMA, STAR-RIS, energy efficiency, power, phase shift