Boost in number of wireless sensors which do not need high data rate alongside ever-increasing traffic demand of the users, made a heterogeneity in network demands that is hard to fulfill by existing cellular telecommunication systems. Additionally, efficient usage of the system resources is another important issue of the next generation of networks. Due to the unique features of non-orthogonal multiple access(NOMA) systems, they are able to increase system spectral efficiency; meanwhile, they can fairly support a wide range of connectivities in order to serve the whole network users, based on their requirements. Hence, NOMA is one of the notable techniques to define the framework of 5G. On the other hand, for the sake of mobility of users, processing errors and noise, it is important to consider imperfect CSI assumption to approach the practical scenarios. Thus, in this thesis the effect of imperfect channel state information (CSI) on a downlink MIMO-NOMA in presence of co-channel interference resources has been investigated. Inter-pair interference is one of the most important factors that can result in system performance degradation. In order to cancel this interference, signal alignment technique is used by designing suitable detection vectors and precoding matrice that can remove inter-pair interference from the user's received signal. Using signal alignment and considering channel estimation error, the exact and upper-bound formulas for the outage probability of the users are achieved. Then, closed-form expression for the outage probability is derived using some theorems. Closed-form expression is independent of the stochastic parameters of system and can pave the way to optimize the other parameters in future researches. Simulation results indicates the amount of channel estimation error effect on the performance of the system users in two different conditions of with/without the presence of interference resources. Another figure in simulation results depicts the outage probability of the system users according to different values of the power allocation coefficients. Key Words: on-Orthogonal Multiple Access, Imperfect CSI, Signal Alignment, MIMO System
