Abstract:

A timing synchronization scheme using constant amplitude zero auto correlation sequence as training sequence is proposed for multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in multipath fading channels. A modified cyclic delay sequence is used in each antenna. The cross correlation between local sequence and received signal and the symmetrical correlation of received signal are calculated respectively. The two correlations are then combined together to detect the time offset of each transmitter element. Furthermore, multipath backward searching technique is employed at the receivers to cope with the situation where the first path is not the strongest. The threshold is variable at different signal to noise ratios in order to guarantee acceptable synchronization performance. Performance of this proposed scheme is verified and compared by simulations in both additive white gaussian noise and multipath fading channels.

Key words:  multiple input multiple output, orthogonal frequency division multiplexing, timing synchronization, constant amplitude zero auto correlation, multipath backward searching