Synchronization techniques for multiple-input multiple-output OFDM systems

In this paper, We propose an effective synchronization scheme for MIMO-OFDM systems, where three stages are included: coarse time acquisition, fractional carrier frequency offset estimation, and fine time acquisition. The proposed coarse time acquisition method is accomplished by cross-correlating the received signal and the cyclic prefix part of the corresponding training sequence. The proposed coarse time acquisition method is able to provide each transmit-receive branch with a dedicated acquisition instant. With these acquisition instants, the proposed fractional carrier frequency offset estimator first estimates the frequency offset of each transmit-receive branch based on cyclic prefix, and then properly combines all estimates to form a more accurate result. The fine time acquisition stage is similar to the coarse time acquisition stage, except that the cross-correlation function is computed based on the received signal and the whole training sequence (without the cyclic prefix part). Computer simulation results show that, through the proposed coarse time acquisition method and the proposed fractional carrier frequency offset estimation method, significant performance gain can be obtained for frequency offset estimation. In addition, the proposed coarse-to-fine time acquisition estimator is able to provide accurate and comparable timing estimates regardless of the number of transmit antennas.