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. Due to the number of unknown quantities, frequency offset estimation together with time synchronization and channel estimation for each user constitute a very complex problem. We propose an EM based procedure which enables to convert a multidimensional maximization problem into 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.