Superposed 3D-256CAP Constellation Design Based on Geometrically Shaped 3D-16QAM

Geometric shaping (GS) can significantly enhance the performance of the transmission system. In this paper, a novel 16-ary three-dimensional (3D) constellation structure with a high constellation figure of merit (CFM) is designed by GS. Moreover, a scheme of 3D-GS-256CAP superposed constellation is proposed. Firstly, a 3D-16QAM is superposed with two identical 2D-4QAM to form 3D-256QAM, and then three orthogonal shaping filters are utilized in order to filter the mapping symbols to generate a 3D-GS-256CAP. The results of the simulation indicate that the proposed 16-ary 3D constellation and the superposed 3D-GS-256CAP have superior performance in bit error rate (BER) when compared to other traditional constellations.