Research On OFDM Synchronization Technology In High Dynamic And Interference Environments

Orthogonal Frequency Division Multiplexing(OFDM),because of its high spectral efficiency and good resistance to multipath capability,which is widely used in practical communication systems.OFDM technology also has potential advantages in future telemetry systems.However,due to the low signal-to-noise ratio and high dynamic characteristics of telemetry communication,this will bring great challenges to the application of OFDM technology in telemetry communication system.In addition,in the non-authorized band,because a variety of communication systems can work in the band,resulting in this band becoming more crowded,so the WLAN system working in the environment will be susceptible to narrowband interference.The establishment of time-frequency synchronization is the premise of the application of OFDM technology,so this paper mainly studies the OFDM synchronization technology in high dynamic telemetry environment and narrowband interference environment.Aiming at the synchronization problem of OFDM system in high dynamic scene,this paper considers the application scenario and development requirement of telemetry communication system,and studies the OFDM synchronization algorithm which is suitable for low SNR and high dynamic environment.Firstly,the research background of OFDM technology and the significance of applying OFDM to telemetry system are studied.Then paper introduces some existing synchronization algorithms,including the ML algorithm based on cyclic prefix,the carrier synchronization algorithm based on frequency domain,such as Moose algorithm,Classen algorithm,the synchronization algorithm based on leading sequence,such as S&C algorithm,Minn algorithm,Park algorithm,and the synchronization algorithm based on CAZAC sequence.Their synchronization performance under different channel conditions is analyzed by MATLAB simulation,which proves that they are not suitable for high dynamic telemetry scene.Finally,based on the analysis of the existing synchronization algorithm,for the existence of large Doppler frequency offset and frequency offset rate in the telemetry channel,paper designs a new synchronous preamble structure and the scheme of timing detection and frequency offset estimation which are suitable for the telemetry channel.The simulation results show that the improved synchronization scheme can guarantee the accuracy of time acquisition and frequency offset estimation.Aiming at the problem that the OFDM system is susceptible to narrowband interference in the non-authorized frequency band,this paper next investigated the synchronization algorithm of OFDM system in narrowband interference environment.Firstly,the performance of OFDM with narrowband interference is analyzed,and taking the Park algorithm as an example,we illustrate the influence of NBI on the timing function of synchronization algorithm.Then,the narrowband interference cancellation technique based on time domain and frequency domain is studied respectively.And the performance of OFDM synchronization algorithm is tested by simulating different interference cancellation techniques.Finally,a new threshold setting method is proposed for frequency domain interference detection.Using this method can better filter out the subcarriers that are disturbed.The simulation shows that the improved method proposed in this paper could improve the performance of carrier synchronization.