A Robust Blind Time Synchronization Method in OFDM Systems over Multipath Fading Channels

Abstract:
In Orthogonal Frequency Division Multiplexing (OFDM) systems, symbol timing errors may lead to a significant performance degradation. For this reason, it is very important to achieve a high precision time synchronization. With the absence of pilot symbols, blind synchronization algorithms using different metric functions or statistics of the received signal can be used. This paper investigates blind synchronization over multipath fading channels by utilizing the redundant information contained in the cyclic prefix. Whereas some proposed methods require channel information, a Maximum Likelihood method is developed for the joint estimation of the symbol timing offset and the channel length. Analysis shows that the obtained Log-Likelihood function exhibits a plateau and not a global maximum, leading to significant fluctuations in the estimated parameters. Interestingly, the symbol timing offset and the channel dispersion characterize the position and dimensions of this plateau. Based on this finding, a novel blind method is developed for the joint estimation of the symbol timing offset and the channel length. To demonstrate the performance of the proposed method, Monte Carlo simulations are conducted over Rayleigh multipath fading channels of various delay spreads. The results show that the proposed algorithm outperforms considerably other algorithms in related work and is robust to varying channel conditions.