Low-Complexity Blind Symbol Timing Offset Estimation in OFDM Systems

Abstract

A low-complexity blind timing algorithm is proposed to estimate timing offset in OFDM systems when multiple symbols are received (the timing offset estimation is independent of the frequency offset one). Though the maximum-likelihood estimation (MLE) using two or three symbols is good in offset estimation, its performance can be significantly improved by including more symbols in our previous work. However, timing offset estimation requires exhaustive search and a priori knowledge of the probability distribution of the received data. The method we propose utilizes the second-order statistics embedded in a cyclic prefix. An information vector (IVR) with the same length as the cyclic prefix is formed based on an autocorrelation matrix (AM). The modulus of elements in the IVR is first quantized based on a threshold that is defined by the variance of OFDM symbols. The timing offset is then estimated based on the binary sequence of the IVR. Because the exhaustive search used in the MLE can be avoided, computational complexity is significantly reduced. In practice, the proposed scheme can be used as a coarse synchronization estimation that can rapidly provide a rough and contractible estimation range, which serves as the basis for a fine estimation like the MLE. The proposed estimator will be proved theoretically to be asymptotically unbiased and mean-squared consistent. Simulations and comparisons will be provided in the paper to illustrate the advantages of our design.

Keywords

• symbol timing offset estimation
• maximum-likelihood estimation
• frequency offset estimation
• blind estimation in OFDM communications.