Non-Orthogonal Multiple Access via Non-binary Factor Graphs

In this paper we propose a novel non-orthogonal multiple access (NOMA) scheme via non-binary factor graphs by introducing operations over Galois field GF(q). By utilizing sparse GF(q) spreading, the proposed scheme benefits from an improved diversity of the superimposed symbols and accordingly a lower probability of constellation overlapping. Meanwhile, the coordination with high-order modulation helps to reduce the interference at the receiver, and therefore a better error performance can be expected. Iterative belief-propagation (BP) detection based on log-domain probabilities is derived for the GF(q) NOMA. The upper bounds of maximum likelihood (ML) detection and simulation results in terms of symbol error rate are provided, which demonstrate the superiority of the proposed scheme to its binary counterparts.