Throughput and error probability improvement in downlink communication based on MIMO-NOMA using reconfigurable intelligent surface (RIS)

The user far from the base station (BS) can decode the signal via direct transmission or a relay network, but it cannot achieve higher throughput because of its high error probability. The MIMO-NOMA-Relay networks are replaced by MIMO-NOMA-RIS to achieve higher throughput in the proposal. The MIMO-NOMA-RIS sends a superimposed signal to the receiver using a multiple RIS beam scanning algorithm. They can improve the strength of the signal as well as improve the throughput and reduce the probability of error. As more reflecting surface area increases, the strength of the beam-forming signal also increases, which means that the user could receive more signal strength than the direct transmission, amplify and forward (A&F) relay network. In multi-user case, use the max-min power control algorithm (MMPCA) to allocate optimum power to a weaker channel strength user and achieve an optimum result. Method 1 used a single user with RIS to find the system equations. In both single-user and multi-user scenarios, we use MIMO-NOMA-RIS. Our proposed method's complexity is low because of its simplicity. In our proposed method, the MMPCA is used for optimum power allocation, and the resulting non-convex function is converted into a convex one by using successive convex approximations. The result section shows that the RIS achieved the highest throughput and the lowest probability of error.