Energy Efficient Power Allocation in MIMO-NOMA Systems with ZF Receiver Beamforming in Multiple Clusters

In this paper, a method for allocating optimal power to each user in a communication system is examined. This operation maximizes energy efficiency (EE). The system in question is a multiple-input multiple-out (MIMO) with non-orthogonal multiple access (NOMA) system. The characteristics of the used channel are determinative in this system. Some key parameters that have not considered in most of the works, are examined in this paper, such as: the path loss, the zero forcing (ZF) beamforming, and the channel estimation error. In solving this problem, there are two constraints on the minimum user rate and maximum transmission power which means that the total users’ power should be less than the maximum transmission power. The problem of optimization is aimed at maximizing the EE of the system, which is generally non-convex and constrained problem. First, it is converted to a convex problem using the convex optimization theory. Next, by employing the Lagrange dual function, the constraints of the problem are eliminated. By doing so, the problem becomes a convex unconstraint problem, and the term of Karush-Kuhn-Tucker (KKT) are used to obtain the optimal power of the users. The results obtained in the simulations section show that the proposed method has better results than the methods of other papers.