Power Allocation and User Pairing Based Beam Reuse in a NOMA System

In this paper, the non-orthogonal multiple access (NOMA) principle is applied to reuse existing beams to serve additional far users, in the premise of a multi-antenna BS has designed the precoding for near users in an existing space division multiple access (SDMA) network. Specifically, the same beam serves three users, including the existing near user and two far users to be selected. In order to maximize the sum capacity of far users while ensuring the near user’s rate requirements, a power allocation optimization problem is formulated and successfully solved by applying the branch-and-bound (BB) algorithm. Furthermore, for the far users pairing, three user pairing strategies: random user pairing (RP), most distinctive user pairing (MDP), and top two user pairing (TTP), are adopted. The results show that the same beam can serve two additional far users, which is more suitable in scenarios where the number of BS antennas is not significantly large. Additionally, the TTP strategy proves to be more advantageous in this scenario.