Abstract
Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is a transmission scheme that combines MIMO signal processing and OFDM techniques. This transmission scheme can increase data rate and link reliability in wireless environments. A MIMO-OFDM system is much more sensitive to the carrier frequency offset than an OFDM system, and the conventional synchronization techniques used for OFDM systems cannot be directly applied. In this thesis, we propose an effective synchronization scheme for MIMO-OFDM systems, where three stages are included: coarse time acquisition, carrier frequency offset estimation, and fine time acquisition. The proposed coarse time acquisition for a transmit-antenna signal at a receiver antenna is accomplished by finding the maximum value of the cross-correlation function between the received signal and the cyclic prefix part of the corresponding training sequence. Since we can obtain the approximate arrival time of each transmit-antenna’s signal at the receiver by using the proposed coarse time acquisition method, the carrier frequency offset of each transmit-antenna’s signal can be estimated and then properly combined to form a more accurate estimate. 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). The proposed scheme can simultaneously synchronize all the signals from the transmit antennas at the receiver. Computer simulation results show that the proposed synchronization scheme reaches better performance for MIMO-OFDM systems than a previously described method.