Asymmetric signaling constellations for phase estimation

In digital communication systems, most commonly used signaling constellations are symmetric. Without a pilot tone or known training sequence, an arbitrary phase rotation cannot be identified from a symmetric constellation. The standard approach to overcome the phase ambiguity is to use differential encoding. We introduce the notion of using an asymmetric constellation instead of a symmetric constellation with differential encoding. The absolute phase of an asymmetric constellation can be determined using blind statistics of processed channel outputs. Through simulation and analysis, we study the trade-offs between asymmetry and other features of a constellation, such as data rate, power, and symbol separation