Robust Synchronization Approach for MIMO-OFDM Systems with Space-Time Diversity

In this paper, we propose a robust timing and frequency synchronization scheme for MIMO-OFDM systems. Exploiting a preamble of two identical parts and proceeding in two stages, the proposed technique achieves synchronization under non-coherent detection. To take advantage from transmit diversity, we use differential Alamouti space time block coding which provides full-spatial diversity without requiring any channel knowledge in neither the transmitter nor the receiver. Two different replicas of the preamble are generated and sent simultaneously from dual-antenna transmitter. At the receiver side, a coarse synchronization is first carried onto the received signal to roughly localize the preamble respecting the famous Cox and Schmidl algorithm. Second, differential Alamouti decoding must be achieved to recover the transmitted signal. Then, a fine synchronization metric is calculated based on cross-correlating the recovered signal with the local known preamble to detect the exact preamble start. The fine metric is calculated over a short interval around the coarse time estimate which relaxes the computational complexity of this stage. As a byproduct, the fractional part of the frequency offset is estimated using the same timing metric. Computer simulations carried to evaluate the proposed technique show its robustness in the Rayleigh fading channel under non-coherent reception.