Cyclic-Based Estimators for Synchronization of Windowed OFDM Systems

Abstract

In many applications of OFDM systems it is necessary to use a transmitting window, with a proper roll-off, in order to reduce out of band spectral leakage. In this case, i.e. windowed OFDM, the conventional cyclic prefix based Maximum Likelihood (ML) estimator of timing and frequency offset is not optimal and suffers from an error floor. In this paper we derive the optimum ML estimator for the windowed OFDM systems. Furthermore we have shown that by adding an appropriate receiving window to conventional ML estimator an excellent approximation to the optimal ML estimator can be achieved. This window is independent of SNR, unlike the windows needed in the optimum estimator, and therefore highly reduces the complexity.

Joint Synchronization Using Cyclic Property

“…Equation (6) reveals that the only difference between the sampled received CB and its replica is a phase rotation of ΩT F , caused by the CFO, and a relative time shift consisting of the integer part m and the fractional part μ, originated from the SFO. Recalling (3) and (4) gives…”

“…The first type uses dedicated training sequence and the corresponding methods can be derived directly from the ML estimation, as shown in [2], [3]. Methods of the second type [4]- [6] resort to the cyclic property, which is usually possessed by the transmitted signal of block transmission systems, where each guard interval padded with a cyclic prefix (CP) or a fixed known sequence can be regarded as a cyclic block (CB). The synchronization scheme derived for OFDM systems in [4] was extended to SC systems with repeated training sequence in [5], and was improved to fit for time domain windowed OFDM systems in [6].…”