| Orthogonal Frequency Division Multiplexing (OFDM) is a promising technology for its robustness to selective fading and high spectral efficiency. Multi-Input Multi-Output (MIMO) technology can achieve high throughput. So OFDM and MIMO now become key technologies for the next generation mobile communication system. However both OFDM and MIMO-OFDM systems are very sensitive to time and frequency synchronization errors which can affect the systems greatly. Correct time and frequency synchronization are necessary for MIMO-OFDM system, this thesis focuses on that.Firstly, the principals of OFDM technology and MIMO technology are described, the model of MIMO-OFDM system is given, the influence of time and frequency synchronization errors to MIMO-OFDM system is analyzed, and the influences on signal to interference energy ration in the receiver are investigated by computer simulations.Secondly the thesis pays much attention on time and frequency synchronization algorithms, especially on the data-aid methods. To get better time synchronization performance, a joint time synchronization scheme of Schmidl&Cox algorithm and Park algorithm is applied. Frame synchronization can be achieved by Schmidl & Cox algorithm, and symbol synchronization can be achieved by Park algorithm. So in the joint algorithm, with a combination of the two algorithms, accurate time synchronization can be achieved. Computer simulations show that the joint algorithm has better performance than that of Schmidl&Cox algorithm.Finally based on the joint algorithm, a time and frequency synchronization scheme suitable for centralized MIMO-OFDM system is proposed. By USRP platform, a 2×2 MIMO-OFDM system is realized, and the valid of the time and frequency synchronization scheme is verified in the system. |
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