Non-Orthogonal Multiple Access (NOMA) has proven itself as a serious candidate for multiple access schemes in the 5th generation of wireless communication systems. In this paper, we propose new resource allocation techniques that allow the coupling of NOMA with multiple-input-multiple-output (MIMO) systems. As in most of downlink NOMA systems, the proportional fairness (PF) scheduler is used. As for power allocation (PA), most previous works assume an equal PA between antennas and subbands, which is sub-optimal. In this paper, we first propose a technique to reduce the complexity of the PF scheduler, and then we introduce an iterative waterfilling-based power allocation to the Single-User MIMO (SU-MIMO) case. Extensive simulations show that the novel PA technique improves the quality of experience of users suffering from bad channel conditions, as well as the user fairness.