A New Blind Joint Timing and Frequency Offset Estimator for OFDM Systems Over Multipath Fading Channels

Abstract

A blind joint timing and frequency synchronization algorithm is derived for orthogonal frequency-division multiplexing (OFDM) signals transmitting over multipath fading channels. The proposed estimator requires neither the knowledge of the signal-to-noise ratio (SNR) nor the power delay profile of the fading channels, except that the maximum delay spread <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> should be known and should be shorter than the guard interval. In the proposed estimator, the transmitted time-domain OFDM samples are modeled as an independent Gaussian random sequence, and the received time-domain OFDM samples are partitioned into a few subsets in such a way that the neighboring entries in each subset are uncorrelated. This is achieved by picking out OFDM samples that are spaced <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> samples apart into each subset. By modeling the channel gains as unknown deterministic variables, a joint symbol timing and frequency offset (FO) estimation algorithm is derived based on these subsets. Simulation results show that, in terms of lock-in probability, the proposed blind ST estimator achieves better performance than the estimators studied by Van De Beek and Speth , as well as the approximate maximum-likelihood estimator described by Lee and Cheun when the SNR is sufficiently high. For FO estimation, in terms of mean square error (MSE), the proposed estimator outperforms the estimators studied by Van De Beek and Speth at medium and high SNR. In terms of bit error rate (BER), the proposed estimator is superior to the estimators studied by Van De Beek and Speth Furthermore, the simulation results show that the performance of the proposed estimator is tolerant to the variation in the number of delay paths. This means that the proposed estimator will still adequately perform, even when the number of delay paths is time varying and is not estimated at the receiver. Finally, simulation results show that the use of virtual subcarriers has negligible performance loss in the proposed estimator.