Blind estimation of frequency offset in the presence of unknown multipath

We address the problem of blind estimation of carrier offset in the presence of an unknown multipath propagation channel for linearly modulated signals. The goal is to decouple the two estimation problems. Here, we capitalize on the second and higher (typically fourth-) order noncircularity of the transmitted signals. We focus on QAM and PSK-type signals. We analyze both frequency and phase estimators. We study the performance of the proposed estimators, and compare them with the corresponding Cramer-Rao bounds which are also derived. The theoretical results are verified via simulations.