Signal Processing Technology Of Agile Waveform For OFDM Radar

As a new type of radar system rising in recent years,Orthogonal Frequency Division Multiplexing(OFDM)radar has the advantages of flexible waveform design,high frequency spectrum utilization and easy digital processing,and is widely used in the field of internetwork communication and target detection.However,with the increasing complexity of electromagnetic countermeasure environment,the anti-jamming capability of OFDM radar will also face severe challenges.To address this problem,the frequency agility technology was introduced into the OFDM radar.The time-frequency characteristics of the transmitted subcarriers are complex and agile,which makes it difficult for an enemy to accurately estimate signal parameters and effectively implement jamming,and are thus conducive to radar target detection and robust tracking in complex jammed background.Based on this,this paper studies the signal processing technology of agile waveform for OFDM radar.After analyzing the characteristics of agile waveform for OFDM radar,we develop two target range-velocity estimation methods,and study the main lobe interference suppression method and target Direction of Arrival(DOA)estimation method.The main research of the study includes the following works:(1)The time-frequency domain,ambiguity function and Peak to Average Power Ratio(PAPR)characteristics of agile waveform for OFDM radar are analyzed.An agile OFDM signal model is constructed,and the ambiguity functions of OFDM waveforms with stepped frequency and agile frequency are compared.The experimental results show that the agile OFDM waveform has higher range resolution.(2)Two range-velocity estimation methods for high-speed multi-target based on Frequency Agility-OFDM(FA-OFDM)radar are proposed.First,the FA-OFDM radar signal model is established,and the target high-resolution range profile synthesis methods on the basis of the Compressed Sensing(CS)and Iterative Adaptive Approach(IAA)are compared.Then the Expectation Maximization(EM)algorithm and Random Sample Consensus(Ransac)algorithm are employed to fit multiple lines simultaneously for the observation data constituted by high-resolution range at each pulse time,and the target velocity is estimated according to the slope rate of the line.Simulation results verify the effectiveness of the two algorithms,and the results show that compared with the EM algorithm,Ransac algorithm is still applicable under the condition of low Signal to Noise Ratio(SNR)thresholds.(3)The main lobe interference suppression and target DOA estimation methods based on MIMO-OFDM agile radar are studied.First,a signal model of MIMO-OFDM agile radar is established.Then,the Blind Source Separation(BSS)method is introduced to suppress the main lobe interference of noise suppressed and dense false targets.The effectiveness of the method is verified by a collection of simulation expriments.Finally,the high-resolution subspace-based methods for DOA estimation are also studied.The simulation results show that the DOA estimation with the Estimating Signal Parameters via Rotational Invariance Techniques(ESPRIT)has better spatial resolution.