Non-orthogonal Multiple Access (NOMA) method, due to its improved spectral efficiency and cooperative system due to its reduced fading effect, are two important methods to meet the requirements for increasing capacity in next-generation in wireless communications systems. On the other hand, considering the limitation in energy consumption due to environmental issues as well as the cost of providing energy, optimizing energy efficiency has become an important issue in recent years. \\\\ Therefore, in this thesis, a system based on cooperative communications with non-orthogonal multiple access is provided by considering two users including a central user and a cell edge user. In this system model, the central user acts both as a user as well as a relay for the base station to increase the signal quality of the cell edge user. Considering the importance of the energy issue, energy efficiency in the proposed system model is examined. Since the joint optimization problem for finding precoding matrices in base station and relay, which targeting energy efficiency, is difficult. The problem is solved individually for each variable by fixing other variables. For some variables, when the problem is in fractional form, the Dinklabach algorithm is used. The results shows that the proposed method provides higher energy efficiency compared to ZF precoding and random precoding for different number of antenna and different location of relay. کلیدواژه انگلیسی: Non-orthogonal Multiple Access , Cooperative Communications , Energy Efficiency