Low complexity estimation of carrier and sampling frequency offsets in burst-mode OFDM systems

Residual carrier frequency offset (CFO) and sampling frequency offset (SFO) in orthogonal frequency-division multiplexing (OFDM) transmission result in loss of orthogonality between the subcarriers, which severely degrades system performance. This makes effective CFO and SFO estimation methods essential for such systems. In this work, we address the joint estimation of CFO and SFO, focusing on burst-mode OFDM communications scenarios. We study communications under slowly varying channels, and consider three cases of knowledge of the channel impulse response (CIR): full knowledge, no knowledge, and partial knowledge of the CIR. By partial knowledge, we refer to knowing only either the CIR magnitudes or the CIR phases. It is known that obtaining the exact joint maximum-likelihood estimate (MLE) of the CFO and the SFO requires a two-dimensional search. Here, we present a new estimation method which uses the Taylor expansion of the MLE cost function, combined with the best linear unbiased estimator, to obtain a method which does not require such a search. The computational complexity of the new method is evaluated. Numerical simulations demonstrate that the new method approaches the corresponding Cramér-Rao bound for a wide range of signalto-noise ratios, and has superior performance compared to all other existing methods for approximating the solution for the joint MLE, while maintaining a low computational complexity. Copyright © 2015 John Wiley & Sons, Ltd.