Data-Aided Symbol Timing Estimation for Multiple-Access OFDM/OQAM Systems

In this paper we consider the problem of data-aided synchronization in the up-link of a multiple access (MA) orthogonal frequency division multiplexing (OFDM) system based on offset quadrature amplitude modulation (OQAM). In particular, the joint maximum-likelihood (ML) phase offset and symbol timing estimator exploiting a short known preamble embedded in the burst received from each of U users is derived. Since the waveforms of the different users are nearly orthogonal, the ML approach leads to U different joint phase offset and symbol timing estimators. Moreover, for each user the phase estimate is in closed form, and, then, the symbol timing estimator requires only an one-dimensional maximization procedure. The performance of the proposed ML estimator is assessed via computer simulations both in AWGN and multipath channel, and for three different allocation schemes.