Non-Equiprobable APSK Constellation Labeling Design for BICM Systems

The previously proposed amplitude phase shift keying (APSK) with Gray labeling achieves a considerable shaping gain in comparison with conventional square quadrature amplitude modulation. In this letter, by reducing the number of points on the inner rings of Gray-APSK and introducing a non-equiprobable (NE) bit-to-symbol labeling, a novel NE-APSK constellation labeling is proposed. NE-APSK provides additional 0.1 dB shaping gain over Gray-APSK without any complexity increase, as illustrated by the mutual information analysis and verified by the bit error rate simulation.