A robust timing and frequency synchronization for OFDM systems

Abstract

Abstract-A robust symbol-timing and carrier-frequency synchronization scheme applicable to orthogonal frequency-division-multiplexing systems is presented. The proposed method is based on a training symbol specifically designed to have a steep rolloff timing metric. The proposed timing metric also provides a robust sync detection capability. Both time domain training and frequency domain (FD) training are investigated. For FD training, maintaining a low peak-to-average power ratio of the training symbol was taken into consideration. The channel estimation scheme based on the designed training symbol was also incorporated in the system in order to give both fine-timing and frequency-offset estimates. For fine frequency estimation, two approaches are presented. The first one is based on the suppression of the interference introduced in the frequency estimation process by the training symbol pattern in the context of multipath dispersive channels. The second one is based on the maximum likelihood principle and does not suffer from any interference. A new performance measure is introduced for timing estimation, which is based on the plot of signal to timing-error-induced average interference power ratio against the timing estimate shift. A simple approach for finding the optimal setting of the timing estimator is presented. Finally, the sync detection, timing estimation, frequency estimation, and bit-error-rate performance of the proposed method are presented in a multipath Rayleigh fading channel.

Low Complexity Time Synchronization Algorithm for OFDM Systems with Repetitive Preambles

“…Given that the numerator of metric Q can be characterized as a central chisquared random variable of 2L degrees scaled by the signal power, we can follow a similar reasoning to [9] and [13], and approximate metric Q by a Gaussian random variable with mean (14) and variance (15). In this case, the false alarm probability is given by:…”

Multi-user Synchronisation in ad hoc OFDM-based Wireless Personal Area Networks

“…Besides, in [18] the use of hermitic sub-parts is explored. In [7], based on those ideas and others from the authors [19], they proposed a two stage synchronisation: coarse and fine with a preamble divided into N L sub-parts weighted by a sign pattern. For the coarse stage the preamble is used, then channel is estimated and the synchronisation is refine using the channel estimation in the fin stage.…”

“…For the coarse stage the preamble is used, then channel is estimated and the synchronisation is refine using the channel estimation in the fin stage. Those ideas from [7] have been taken for the peer-to-peer synchronisation part with small variations in our leader procedure.…”

“…The two firs symbols are devoted to acquisition, Automatic Gain Control (AGC) and synchronisation. The proposed preamble and algorithm for the coarse synchronisation are based on a slight modificatio of [7]. The preamble is divided into N L = 8 sub-parts and the sequence pattern is p s = [+ + − + + + −+].…”

“…The difference with respect to [7] lies in the correlation P prop [n] (Equation 7) that is performed with the original sequence S S instead of the received one, in order to reduce the MUI. Besides, the sign pattern is also slightly different.…”