Spiral Constellations for Nonlinear Channels

In this letter, we propose a novel constellation design, specifically tailored to contrast the effect of nonlinear channels. The proposed constellations are based on a spiral expression, which, unlike other unstructured designs, makes them easy to build and optimize. Our design approach allows to optimize the distance between symbols in the angular and radial directions, resulting in a constellation that is robust to the nonlinearities, which affect more severely symbols with higher magnitude. Simulation results show that the proposed constellations outperform the solutions usually adopted for nonlinear channels, especially when the constellation size increases.