Research Of Time-Frequency Synchronization Technology Based On OFDM System In Complex Environment

With the increasing demand for high-speed data transmission and high spectrum utilization,the development of broadband wireless communication has become increasingly mature and has become a research hotspot in the field of wireless communication.OFDM(Orthogonal Frequency Division Multiplexing)technology has received extensive attention and application in broadband wireless communications due to its strong adaptability,high frequency band utilization,and strong anti-multipath capability.The time-frequency synchronization,as one of the most critical technologies of OFDM,affects the reliability of the data transmission.In this paper,suitable time-frequency synchronization methods are proposed for high dynamic environment and complex electromagnetic environment respectively.The specific research content and contributions can be divided into the following three points.1)The performance of three classical time-frequency synchronization algorithms is first analyzed,and then the impact of time-varying,multipath and large frequency offset of channel in high dynamic environment is studied.The simulation results show that these impacts cause the dispersion of delay-correlated peak in time-frequency synchronization based on preamble with repetitive structure,dramatically degrading synchronization performance.Meanwhile,the influence of complex electromagnetic environment on communication equipment is also analyzed.2)In order to solve the failure of traditional time-frequency synchronization methods in high dynamic environments,this paper proposed a new time-frequency synchronization algorithm through detecting the peak of differential cross-correlation between local stored sequence(LSS)and the corresponding received signal.At the same time,a new normalization method for differential correlation calculation is proposed to overcome the influence of the near-far effect on the received signal.In addition,a new timing metric is defined to combat multipath effects.Finally,the fast Fourier transform is applied in calculating the differential cross-correlation to reduce the complexity.Simulation show that the proposed method achieves better timing estimation,higher precision of frequency offset estimation and larger frequency offset estimation range than the baseline schemes,which has good adaptation to high dynamic environments..3)For improving the performance of synchronization in the complex electromagnetic interference environment,this paper proposed a time-frequency synchronization method with self-orchestrable spectrum based on cognitive radio NC-OFDM(Non-Contiguous Orthogonal Frequency Division Multiplexing).Meanwhile,a new timing metric function is defined,greatly improving the synchronization performance of NC-OFDM.Finally,the FPGA implementation scheme of the time-frequency synchronization module of autonomous frequency selection system in complex electromagnetic environment is proposed.Experiment results verify the engineering feasibility of the proposed conjugate symmetric synchronization algorithm,significantly reducing the consumption of hardware resources.