Synchronization Algorithms for MIMO OFDMA Systems

We propose in this paper a maximum likelihood (ML) estimator to jointly obtain time and frequency synchronization together with channel estimation in a MIMO OFDMA system. The proposed algorithm is planned to be implemented in a base station (BS) environment and so it is mainly devoted to uplink asynchronous transmission schemes. We propose a new EM based procedure which enables to convert a multidimensional maximization problem into a number of substantially smaller separate maximization problems. Simulation results are presented which clearly show the accuracy of our estimator and its ability to combat the near-far effect.