New Kind of Mother Constellation for SCMA Systems

Abstract—Sparse code multiple access (SCMA) is a variation of the nonorthogonal multiple access (NOMA) technology. SCMA communication systems use codebooks based on multidimensional constellations, which are generated using original mother constellations. The properties of these constellations largely determine the efficiency of SCMA communication systems. This paper proposes new mother constellations for use in SCMA systems. The proposed constellations were synthesized using a new analytical method for describing tabular functions in the form of a functional dependence of the signal on the vector of binary variables. This representation made it possible to reveal some patterns and determine the characteristics of constellations that affect the efficiency of their use. In particular, a new type of two-dimensional constellation with a parametric description, called Arrow constellations, is proposed. The proposed constellations belong to the class of multidimensional constellations and can be used both independently and in codebook synthesis in SCMA systems. The best effect from using these constellations is observed in SCMA systems with a turbo receiver, in which both the demodulator and the decoder are operated with the same feedback.