Research Of Anti-jamming Receiving Technology For OFDM Links

In recent years,the orthogonal frequency division multiplexing has been widely used in military and civil broadband wireless communication systems.For the application scenarios with malicious interference,how to effectively reduce malicious interference in OFDM receivers and ensure the reliability of data transmission in OFDM wireless communication links is worth studying.Aiming at several kinds of typical time-frequency domain interference,this paper studies the interference detection and suppression technology of OFDM link receiver,and the key technology of signal detection after interference suppression processing.Firstly,this paper introduces the research background in the second chapter.Combining with the basic characteristics of OFDM,the channel model and interference model are briefly introduced.Aiming at the requirements of channel coherence and bandwidth,the calculation and design methods of key parameters and indicators such as pilot symbols,subcarrier spacing,cyclic prefix and suffix,system rate in OFDM waveform are given.Next,in the third chapter,aiming at the two kinds of frequency domain interference: monotone and narrowband Gauss,the forward consecutive mean excision algorithm is used to detect the interference subcarriers,and the interference is suppressed by scaling the data of the interfered subcarriers.In this paper,the effects of different scaling coefficients and different bandwidth interference on the performance of OFDM links are studied by simulation and comparison.The results show that the frequency domain interference suppression algorithm adopted in this paper can improve the system performance.In Chapter 4,a method for detecting and suppressing time-domain Gauss pulse interference based on FCME is presented.In interference detection,this paper compares the direct detection,slope detection and smoothing detection techniques of amplitude sequence,and determines that smoothing detection has better detection performance by analyzing the ranking results under different detection.On the basis of interference detection,time-domain pulse interference is suppressed by limiting and extinguishing methods,and threshold fluctuation in interference suppression is solved by adjusting the amplitude sequence smoothing window size and smoothing the front and back thresholds.The influence of noise distribution after two kinds of interference suppression on system performance is further analyzed.The simulation results show that the analysis is correct and the proposed method has good performance in time domain interference detection and suppression.In the fifth chapter,the signal detection technology after interference suppression is presented.Aiming at the channel estimation problem affecting the performance of soft demodulation,this paper proposes a FFT noise reduction method for various channel types based on least squares estimation taking advantage of the characteristics of free subcarriers in OFDM waveforms.Aiming at the problem of noise variance estimation which affects the performance of soft demodulation,two noise estimation methods in frequency domain and time domain are presented in this paper.Frequency domain noise estimation uses idle subcarriers to estimate noise variance.The simulation results show that this method can improve the system performance under time domain impulse interference.Time-domain noise estimation uses the IFFT transform of frequency-domain channel estimation to estimate the noise variance by selecting the data after the maximum multipath delay of the channel in time-domain.In this paper,the mean square error performance of time domain and frequency domain estimation is compared by simulation.It is verified that both methods have good estimation accuracy,but when there is frequency domain interference,time domain noise estimation has stronger adaptability.