| In recent years, wireless mobile communication technology and related applications start booming, but the spectrum scarcity has become a bottleneck problem for the further development of wireless mobile communication system. How to improve channel capacity and spectrum efficiency on the premise of guarantee the reliability become the focus of research in the field of wireless mobile communication. Depend on the spatial reuse technology,multiple input multiple output(MIMO) system can greatly improve the data transmission rate and increase communication system capacity. Orthogonal frequency division multiplexing system adopts multi-carrier modulation technology, each subcarrier orthogonal to others and can provide higher spectrum efficiency. MIMO- OFDM system has the advantages of both systems at the same time, the system is sensitive to synchronization error, however, not ideal synchronization will significantly reduce system performance, thus the precise time and frequency synchronization is especially important for the system. The purpose of this paper is to explore the blind time-frequency synchronization technology in centralized non-cooperative MIMO-OFDM system. The main work of this paper is as follows:1. First, introduced the MIMO system model and the channel capacity and also introduced the basic principle of OFDM technology and its advantages and disadvantages. Secondly, the MIMO- OFDM system model and its key technology were introduced. Finally, Detailed introduces the mobile wireless channel, and the mathematical modeling.2. The cooperative MIMO-OFDM wireless mobile communication system model is established. Depend on the time domain signal model, and analyses the influence of the non-ideal timing synchronization demodulation, and computer simulation have been carried out to verify the result of the analysis. This paper introduces the existing commonly used Mody and Zelst&Schenk synchronization algorithms on cooperative communication.3. Design blind estimation MIMO-OFDM system symbol length algorithm, relies on physical frame structure characteristics of cyclic prefix. Analyzes the shortcomings of the maximum likelihood algorithm and improved it. Put forward the blind frame length and timing synchronization joint estimation algorithm based on delay coefficient ofcorrelation sets. First of all, defines the delay coefficient of correlation sets, with two-dimensional search within the effective range to determine the physical length of the frame, and according to the change rule of the rendered to determine timing synchronization position. Finally, the validity and reliability of the proposed algorithm is verified by computer simulation.4. Analyzed the non-ideal frequency synchronization effects on MIMO-OFDM systems and introduces the existing scheme of frequency is commonly used in cooperative communication. Through in-depth analysis of mathematical characteristics of the received signal model under the multipath channel, This paper proposes an adaptive blind time and frequency synchronization algorithm based on clustering analysis The algorithm does not need priori information such as channel parameters,the type of space-time coding, and can overcome the influence of the multipath to obtain good performance. Is verified that can achieve high precision time and frequency synchronization in not-cooperation mobile communication scenarios by computer simulation. |
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