Power Allocation and Passive Beamforming Design for RIS Aided NOMA in THz Communications

In some specific transmission scenarios, the mobile users are blocked by the buildings or trees, which will lead to occasionally disconnect for the direct transmission links. As for the solution, reconfigurable intelligent surface (RIS) technique can provide supplementary links which aims to guarantee the quality of transmissions. In order to enhance the coverage area and spectrum efficiency in Terahertz (THz) networks, RIS aided non-orthogonal multiple access (NOMA) is conceived. Then, to maximize energy efficiency under the constraints of the users' quality of service (QoS), rate fairness and transmit power budget, a joint power allocation and RIS beamforming optimization is established. For the sake of solving this non-convex optimization, an alternating iterative algorithm has been introduced by decoupling the problem into two independent subproblems. According to the simulation results, the performances of energy efficiency and energy consumption calculated by our proposed algorithm outperform other benchmarks.