On frequency offset estimation for flat-fading channels

We consider the problem of estimating the frequency offset between transmit ter and receiver in flat-fading communication channels using a training seq uence. In [1] and [2], two frequency estimators were proposed to solve the aforementioned problem. They rely on weighted linear regression for the pha ses of the correlation sequence [1] or their differences [2]. The method in [1] needs phase unwrapping and both methods require knowledge of the corre lation of the fading process. In this letter, two simple methods which do n ot require any of these assumptions are proposed. The first is the unweight ed version of the method of [2]. The second is drawn from the array process ing framework. It is based on a nonlinear least-squares approach that assum es an unstructured correlation of the fading process. The performance of th e proposed methods is as good as that of the methods in [1] and [2], but th e robustness of our methods to modeling errors is much enhanced.