Angelo Petrella

Data-aided symbol timing and CFO synchronization for filter bank multicarrier systems

In this paper we consider the problem of data-aided joint symbol timing and carrier-frequency offset (CFO) estimation for filter bank-based multicarrier (FBMC) systems. As all multicarrier systems, FBMC systems are very sensitive to synchronization errors, since CFO and symbol timing errors cause interference between successive symbols and adjacent subcarriers which can lead to a severe performance degradation. Therefore, reliable and accurate synchronization algorithms must be designed for these systems. The approach herein presented is based on the deployment of appropriate training sequences. In particular, we propose a new joint symbol timing and CFO synchronization algorithm based on the least squares approach and exploiting the transmission of a training sequence made up of identical parts. The performance of the derived estimators, assessed by computer simulations, is compared with that of two data-aided synchronization algorithms previously proposed in the literature.

Sensitivity of multi-user filter-bank multicarrier systems to synchronization errors

In this paper we investigate the sensitivity of multiuser filter-bank multicarrier (FBMC) systems to synchronization errors in both the uplink and the downlink scenarios. In particular, the performance degradation caused by synchronization errors is evaluated analytically and with numerical simulations and compared with that of orthogonal frequency division multiplexing (OFDM) systems. It is shown that, as all multicarrier systems, FBMC systems are very sensitive to synchronization errors, since timing errors and carrier frequency offsets produce intercarrier interference and interference between successive symbols. However, in an asynchronous multi-user scenario FBMC systems are more robust than OFDM systems to time and frequency misalignments among the users.

Joint symbol timing and CFO estimation for OFDM/OQAM systems in multipath channels

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.

Blind CFO Estimation for Noncritically Sampled FMT Systems

In this correspondence, we consider the problem of blind carrier-frequency offset (CFO) estimation for noncritically sampled filtered multitone (FMT) systems. Specifically, a closed-form CFO estimator, based on the best linear unbiased (BLU) estimation principle, is derived. Although the proposed BLU estimator is derived under the hypothesis of additive white Gaussian noise channel, it demonstrates a remarkable robustness against multipath fading. Moreover, it does not require the knowledge of the symbol timing. The performance of the derived BLU estimator is compared with that of four recently proposed CFO estimators for FMT systems.

Joint symbol timing and CFO estimation in multiuser 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, carrier-frequency offset (CFO) and symbol timing (ST) estimator exploiting a short known preamble embedded in the burst received from each of U users is considered. Under the assumption that the CFO of each user is sufficiently small the considered approach leads to U different approximate ML (AML) joint phase offset, CFO and ST estimators. Specifically, the phase and CFO estimators are in closed form while the AML ST estimator requires a one-dimensional maximization procedure. The performance of the proposed joint AML estimator is assessed via computer simulations both in AWGN and multipath channel, and for three different allocation schemes.

Non-data-aided carrier-frequency offset estimation for pulse-shaping OFDM/OQAM systems

In this paper we consider the problem of blind carrier-frequency offset (CFO) estimation for pulse-shaping orthogonal frequency-division multiplexing (OFDM) systems based on offset quadrature amplitude modulation (OQAM). In particular, under the assumption of low signal-to-noise ratio, three maximum-likelihood (ML) CFO estimators for non-dispersive channels are derived. Due to their significant computational complexity a more feasible closed-form CFO synchronization algorithm is considered. The performance of the derived blind estimators is assessed via computer simulations and compared with that of a blind CFO estimator previously proposed in the literature, exploiting the second-order cyclostationarity property of the OFDM/OQAM signal.

A Data-Aided Symbol Timing Estimation Algorithm for OFDM/OQAM Systems

In this paper we deal with the problem of data-aided symbol timing estimation for orthogonal frequency division multiplexing systems based on offset-QAM modulation (OFDM/OQAM). Specifically, a data-aided joint phase offset and symbol timing estimator, based on the least squares (LS) approach, exploiting the conjugate-symmetry property of a properly designed training symbol, is derived. Since the phase estimate is in closed form, the symbol timing estimate requires only an one-dimensional maximization procedure. The derived LS estimator does not require the knowledge of the prototype filter and, moreover, its performance, is independent of the carrier frequency offset.

Blind carrier frequency offset estimation for non-critically sampled FMT systems in multipath channels

In this paper we consider the problem of blind carrier-frequency offset (CFO) estimation for non-critically sampled filtered multitone (FMT) systems in multipath channels. Specifically, by exploiting the statistical properties of the received FMT signal in the presence of multipath channels a closed-form blind CFO estimator is derived. The proposed algorithm does not require the knowledge of the channel impulse response and demonstrates a remarkable robustness in the presence of a non-ideal timing recovery. Computer simulation results are carried out to analyze the performance of the proposed CFO estimation algorithm.

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.

Blind symbol timing estimation for OFDM/OQAM systems

In this paper we consider the problem of blind symbol timing estimation for pulse shaping orthogonal frequency-division multiplexing (OFDM) systems based on offset quadrature amplitude modulation (OQAM). In particular, under the assumption of low signal-to-noise ratio, the joint ML phase offset and symbol timing estimator for AWGN channels is derived. Since the phase estimate is in closed form, the symbol timing estimate requires only a one-dimensional maximization procedure with respect to a continuous parameter. Specifically, the cost function to be maximized to obtain the desired symbol timing estimate depends on both the unconjugate and the conjugate correlation functions of the transmitted OFDM/OQAM signal. The performance of the proposed blind estimator is assessed via computer simulations in AWGN and multipath channel.