Abstract
In this thesis, we investigate power allocation for a downlink non-orthogonal multiple access (NOMA) system with a base station and two users, where the user with a larger channel gain is called the strong user and the other one is called the weak user. We first formulate an optimization problem for power allocation to maximize the sum capacity of both users under the constraints that the weak one must have greater transmit power than the strong one (i.e., the NOMA principle) and the minimum rate requirements of each user must be satisfied. Then we derive two closed-form power allocation solutions for the two users based on the Karush-Kuhn-Tucker conditions. Simulation results show that the proposed schemes can significantly outperform an arbitrary power allocation method. Also, as compared to the optimal approach described in a recent work, the proposed approaches achieve the same sum capacity with much lower computational complexity; in contrast to the suboptimal method, they provide better performance with similar complexity.