Blind CFO estimation for OFDM with constant modulus constellations: Performance bounds and algorithms

In this paper, we derive the Cramér-Rao bound for blind carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) with constant modulus constellations. A blind maximum likelihood CFO estimator is also proposed. It achieves highly accurate frequency synchronization with a single OFDM block, regardless of multipath fading and without the need for null-subcarriers. The approach is thus very attractive for time and frequency (i.e., doubly) selective channels where the CFO may be time varying. If sufficient additional pilot information is available, maximum likelihood estimates of channel parameters and transmitted data can be obtained as a byproduct. Finally, performance bounds are evaluated for several commonly encountered scenarios.