Research On Airborne Ultrashort Wave Resistant Narrowband Interference

With the development of communication technology,electronic countermeasures and electromagnetic interference further deteriorate the complex military battlefield electromagnetic environment,and also bring great challenges to airborne communication.Airborne aeronautical communication system usually adopts direct sequence spread spectrum communication system,also known as direct expansion system.The capability of the airborne communication system to suppress weak narrow band interference is usually proportional to the processing gain of the direct spread communication system.However,in practical applications,the processing gain of the direct expansion system is limited and cannot be done very high.Therefore,when dealing with strong and narrowband interference signals,relying solely on the system's own anti-jamming capability is far from enough.In order to get better anti-jamming ability,some interference suppression technique is needed.Aiming at the traditional narrow-band interference suppression technique,this paper optimizes the algorithm,reduces the complexity of the algorithm,improved anti-interference ability.The main research contents are as follows:In order to solve the problem that the traditional energy limiting factor recognition algorithm requires prior knowledge,this paper proposes an improved energy limiting factor identification algorithm.Firstly,the receiving signal spectrum is segmented and the energy value of each segment is calculated.Then select the segment with the smallest energy value and multiply it by the number of segments to get the energy estimate of the spread spectrum signal.Finally,the energy limiting factor is obtained according to the estimated value,and the existence of narrowband interference is determined by comparing the energy limiting factor with the threshold value.The experiment show that the improved algorithm can accurately identify the narrowband interference signal without prior knowledge.In order to solve the problem that the traditional FCME algorithm is too large in calculating the threshold value,this paper proposes a segmented detection method to calculate the threshold value.Firstly,the spectral lines are segmented,and the maximum values of each segment are compared,and the minimum values of these maximum values are obtained.Then,the initial threshold value is obtained by multiplying the minimum value and threshold coefficient,and the value is compared with the remaining spectral line,so as to update the threshold set.Finally,the threshold value of the spectrum is obtained by repeated iterative operation.The experiment shows that the segmented detection algorithm can significantly reduce thecomplexity of the algorithm compared with FCME algorithm while ensuring the accuracy of the requested threshold.In order to solve the problem that the double threshold interference suppression algorithm can not adapt to the large-scale dynamic change SNR environment,this paper proposes an interference suppression algorithm based on the three threshold.Firstly,according to the spectrum mean and threshold coefficient,the three threshold values of high,middle and low are obtained.Then,the signal to noise ratio is determined by comparing the frequency points in the cluster with the frequency points of narrowband interference.Finally,different threshold values were used to suppress the signal-to-noise ratio of different strengths and weaknesses.The experiment shows that the three-threshold interference suppression algorithm can adapt the system to a wide range of dynamic SNR environment.