Energy Efficiency Design in RIS-Assisted Satellite–Terrestrial Integrated Networks With NOMA

This letter proposes an reconfigurable intelligent surface (RIS)-assisted satellite-terrestrial integrated network with non-orthogonal multiple access (NOMA), in which an RIS is strategically deployed to establish additional links, enhancing the efficiency of downlink transmission. We formulate a novel problem focused on maximizing energy efficiency (EE), subject to the constraints of the maximum transmit power, successive interference cancellation (SIC) decoding order constraint and reflection constraints at the RIS. To effectively tackle the intricate challenges arising from the high coupling of optimization variables, we decompose the original joint optimization problem into two subproblems and employ the alternating optimization (AO) algorithm. Then, we handle the fractional objective function and non-convex constraints by incorporating auxiliary variables, successive convex approximation (SCA), and relaxation methods. Numerical results demonstrate that the proposed algorithm significantly enhances the EE compared to other benchmark schemes and confirm the effectiveness of the proposed algorithm.