| With increasing need of multi-media and real-time stream-media of people, both of high quality and high data rate will be required in the future wireless communication systems. New technology has proposed to achieve that target when the frequency spectrum resources are finite. Multi-input Multi-output(MIMO) technology can provide high throughput, Orthogonal Frequency Division Multiplexing(OFDM) can achieve high spectral efficiency and is robust to frequency selective fading. Owing to the advantage of MIMO and OFDM technology, the combination of OFDM and MIMO can offer solution of core technology for future wireless communication systems.Synchronization must be first solved for baseband signal process in the communication systems, and other signal process algorithms are based on synchronization. Because OFDM is a special multi-carrier system,the performance of OFDM system is easily affected by frequency offset, thus, correct timing and frequency offset estimate are important for OFDM system. Meanwhile, after combing MIMO technology with OFDM technology, there is severe inter-antenna interference as synchronization error existed. Hence, it is necessary to research synchronization in MIMO-OFDM system.In this thesis, synchronization algorithms for centralized MIMO-OFDM system and distributed MIMO-OFDM system are researched over multi-path environment ,new synchronization algorithms are proposed and compared with conventional algorithms. The main contributions of this thesis can be described as follows:(1) Introduce the background and meaning of MIMO-OFDM system. Summarize MIMO,OFDM technology and their combination. Overview existing MIMO-OFDM synchronization algorithm. Finally point out work arrangements of this thesis.(2) Introduce the basic model and the key technology of MIMO-OFDM system, get influences of synchronization error of OFDM system by simulation.(3) Study on synchronization algorithm for centralized MIMO-OFDM system. First present the synchronization model for centralized MIMO-OFDM system, then present several typical synchronization algorithms in detail. These algorithms have the defect that occupying system resources greatly and orthogonal easily affected by multi-path. Thus, a new synchronization algorithm is proposed, which makes the timing peak more obvious by introducing Zadoff-chu sequence and optimizing the structure of the orthogonal sequences. The new algorithm improves the synchronization performance under multi-path channel and is easily implemented with one OFDM symbol.(4) Study on synchronization algorithm for distributed MIMO-OFDM system. It is different from centralized MIMO-OFDM system. Different transmitter and receiver pairs have different timing and frequency offset value. A new algorithm is proposed after introducing several existing synchronization algorithm of distributed MIMO-OFDM system, which based on UPSP algorithm. Comparing with original UPSP algorithm, new algorithm improves synchronization accuracy under multi-path environment by setting up a more reasonable training sequence structure and utilizing the good auto-correlation property of zadoff-chu sequence.(5) Summarize the work of this thesis. Point out deficiencies and further work. |
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