| Orthogonal Frequency Division Multiplex(OFDM)technology can effectively combat multipath fading interference and improve the spectral efficiency of the system.Multi-Input Multiple-Output(MIMO)technology greatly improves the system throughput through transmit diversity,space division multiplexing and beamforming.The MIMO-OFDM system is widely used in various communication systems by combining the advantages of the two technologies.However,due to the use of multiple antennas,the time delay and frequency offset of signals received by different receiving antennas may be different,and the OFDM modulated signal is very sensitive to the timing offset and carrier frequency offset,and the synchronization process is easy to be affected by the passive or active interference of the communication system.Therefore,the time-frequency synchronization technology of the MIMO-OFDM system is optimized,it is of great significance to effectively deal with various interference environments.Aiming at the possible interference problems in MIMO-OFDM communication system,this paper studies the corresponding timing synchronization and frequency offset estimation and compensation algorithms,and considers the MIMO reception diversity requirements,and finally uses FPGA to realize the time-frequency synchronization process of MIMO-OFDM system.The paper first introduces the research background and significance of the subject,summarizes the research status at home and abroad in two parts,then introduces the principle and model of MIMO-OFDM system,analyzes the causes of timing synchronization error,carrier frequency offset,passive interference and active interference and the impact of these problems on the system,and build a simulation system based on the transmission and receiver algorithms of the Wireless Local Area Networks(WLAN)802.11 ax standard.Then,a detailed overview and analysis of frame synchronization algorithms,frequency offset estimation algorithms,and symbol synchronization algorithms for some typical MIMO-OFDM systems are presented.Based on this,new frame synchronization algorithms are proposed,which improve frequency offset estimation algorithms with higher accuracy and symbol synchronization algorithms with lower computational complexity.Subsequently,a new method for detecting and compensating inter antenna delay was proposed,and an interference detection method based on signal-to-noise ratio estimation was introduced.These algorithms are simulated in different signal-to-noise ratios,different channel models and different interference environments.The performance and complexity of the algorithms mentioned in this paper and the algorithms proposed in this paper are analyzed and compared according to the performance indicators such as the correct probability of frame synchronization,the mean square error of frequency offset estimation,the correct probability of symbol synchronization,the correct probability of inter-antenna delay compensation and the mean square error of signal-to-noise ratio estimation,and determine the time-frequency synchronization scheme for FPGA implementation.Finally,the proposed synchronization scheme is designed and simulated using Xilinx Vivado’s development kit System Generator,and the performance gap between fixed-point simulation and MATLAB floating-point simulation is analyzed and compared to provide data support and verification for the physical layer FPGA implementation.Then carry out FPGA implementation and function verification,optimize the system timing and hardware resource occupation with pipeline,parallelization and resource optimization algorithms,and finally obtain the FPGA hardware resource consumption report and timing report. |
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