Joint Symbol Timing and CFO Estimation for OFDM/OQAM Systems in Multipath Channels

Tilde Fusco,Mario Tanda,Angelo Petrella

doi:10.1155/2010/897607

Abstract

The problem of data-aided synchronization for orthogonal frequency division multiplexing (OFDM) systems based on offset quadrature amplitude modulation (OQAM) in multipath channels is considered. In particular, the joint maximum-likelihood (ML) estimator for carrier-frequency offset (CFO), amplitudes, phases, and delays, exploiting a short known preamble, is derived. The ML estimators for phases and amplitudes are in closed form. Moreover, under the assumption that the CFO is sufficiently small, a closed form approximate ML (AML) CFO estimator is obtained. By exploiting the obtained closed form solutions a cost function whose peaks provide an estimate of the delays is derived. In particular, the symbol timing (i.e., the delay of the first multipath component) is obtained by considering the smallest estimated delay. The performance of the proposed joint AML estimator is assessed via computer simulations and compared with that achieved by the joint AML estimator designed for AWGN channel and that achieved by a previously derived joint estimator for OFDM systems.

Highlights

In the last years, the interest for filter-bank multicarrier (FBMC) systems is increased, since they provide high spectral containment
The results show that both in AWGN and multipath channel A the approximate ML (AML) estimators assure a negligible degradation with respect to the perfectly synchronized system while the adoption of the Schmidl and Cox (SC) synchronization scheme leads to an error floor due essentially to the inaccuracy of the symbol timing (ST) estimates
The performance of the joint AML1 estimator for multipath channel has been assessed via computer simulations and compared with that achieved by the joint AML2 estimator designed for AWGN channel

Summary

Introduction

The interest for filter-bank multicarrier (FBMC) systems is increased, since they provide high spectral containment They have been taken into account for high-data-rate transmissions over both wired and wireless frequency-selective channels. Since the subchannel filters are obtained by complex modulation of a single filter, efficient polyphase implementations are possible Another fundamental difference between OFDM and OFDM/OQAM systems is the adoption in the latter case of pulse shaping filters very well localized in time and frequency [5, 6]. Carrier frequency-offset (CFO) and symbol timing (ST) estimation errors can lead to a performance degradation For this reason, it is very important to derive efficient synchronization schemes. In this paper we consider the problem of data-aided synchronization for OFDM/OQAM systems in multipath channels.

System Model

Joint Symbol Timing and CFO Estimator

Numerical Results and Comparisons

Conclusions