Synchronization for MIMO OFDM Systems with Loosely Synchronous (LS) Codes

This paper proposes a time and frequency synchronization technique for MIMO OFDM system by employing the loosely synchronous (LS) codes as the training sequences. The auto-correlation functions of all LS codes are ideal, and there exists an interference-free window (IFW) or a zero correlation zone (ZCZ) in their cross-correlation functions of the LS codes around the origin. These properties of the LS codes make the synchronization of the MIMO OFDM system easily and more accurate. The synchronization process proposed in this paper can be viewed as the four stage process of 1) segmented matched filter based coarse time acquisition, 2) the coarse frequency offset estimation by the fast Fourier transform (FFT) technique with quadratic interpolation in the frequency domain, 3) fine time acquisition and channel estimation by LS code coherent detection, 4) phase rotation based fine frequency offset estimation. Through the simulation, the synchronization algorithm shows satisfactory performance even at a low SNR, high frequency offset and in a frequency selective channel.