With the increase of the demand for last-generation of wireless communications systems, it has become necessary to increase the data rate, improve the spectrum efficiency, successive interference cancellation (SIC), and decrease the outage probability (OP) of user’s signals. For these reasons, the researchers in this domain are oriented and developed a novel method for multiple access (MAT), which is named non-orthogonal MAT. To improve the efficiency of this system more and more, the academics of mobile communications systems use other methods, such are: power allocation (PA) techniques, Multiple-Input Multiple-Output (MIMO) and Cooperative NOMA, ….. ect. This study aims to evaluate the effectiveness of various PA algorithms by combining MIMO and NOMA systems and we determine the best PA technique that is most appropriate for MIMO/NOMA technology. The efficiency of the MIMO/NOMA methodology compared to MIMO-Orthogonal MAT is investigated by the use of two parameters, such as: PA algorithms and OP. Based on preliminary simulation results, it has been determined that MIMO/NOMA, when utilizing enhanced PA techniques, can achieve the greatest achievable rate (AR) and reduce the probability of an outage when compared to traditional approaches (fixed, fairness, and MIMO–OMA).