| Recently, MIMO OFDM has become a research hotspot in the field of mobile communications. But the performance of MIMO OFDM systems is very sensitive to carrier frequency offset, so synchronization, particularly frequency synchronization, is one of the key techniques in MIMO OFDM systems. In this paper, we focus on synchronization in MIMO OFDM systems, and frequency synchronization is of our main interest. The combination of MIMO and OFDM enables mobile systems to be more robust to frequency selective fading and attain higher frequency spectrum efficiency, and will be widely applied in future mobile communication systems. In Chapter 1 of this paper, the fundamental principles of MIMO OFDM systems are introduced. We address the main advantages and disadvantages of MIMO OFDM, and point out that its sensitivity to carrier frequency offset is one of the major disadvantages of MIMO OFDM systems, which accounts for the importance of frequency synchronization in MIMO OFDM systems. In Chapter 2, the problem of synchronization in MIMO OFDM systems is described. First, the main characteristics of mobile wireless channels are introduced in detail. Then the main synchronization problems in OFDM systems are modeled, and their effects on the system performance are analyzed, which shows that frequency synchronization is the major problem of synchronization in OFDM systems. Finally, the basic model of synchronization in MIMO OFDM systems is presented and some assumptions are made. In Chapter 3, the research status of synchronization in MIMO OFDM systems is summarized. Firstly several classic synchronization methods in OFDM systems with a single antenna are presented, and their advantages and disadvantages are compared. Then some papers on synchronization in MIMO systems are introduced. In MIMO OFDM systems, Doppler spread due to time variation of mobile wireless channels leads to a loss of subcarrier orthogonality, which causes inter-carrier interference (ICI) and degrades the system performance. In Chapter 4, we analyze theoretically the ICI power in MIMO OFDM systems with the spatial multiplexing (SM) architecture, and the system performance is also evaluated based on the average... |
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