A Downlink NOMA System Based on Combinatorial Design

It is known that the Non-Orthogonal Multiple Access (NOMA) system is capable of obtaining higher spectral efficiency and massive connectivity owing to the fact that multiple users are superimposed over each resource. However, as the number of users is more than that of resources, the resultant surjective-only mapping and expanded constellation increase the multiuser detection (MUD) complexity at the receiver inherently. In this paper, a downlink code-domain NOMA design based on combinatorial structures with balanced incomplete block design (BIBD) is studied. The unique discretizing distribution of BIBD provides an inherent mapping pattern for the linear combination of multiuser data. To accommodate with our system, a heuristic constellation forming paradigm is proposed. Message Passing Algorithm (MPA) is used at the receiver in this design. Simulation results on additive white Gaussian (AWGN) and Rayleigh fading channel demonstrate that our system obtain an equivalent even better performance compared with other similar code-domain NOMA techniques with much lower design complexity.