Research On Adaptive Antenna Null Broadening Beamforming Technique Based On Fourth Order Statistics

With the rapid development of communication technology,adaptive antenna has been more and more widely used.Adaptive beamforming technology makes the adaptive antenna produce the maximum response in the desired signal direction but the minimum response in the interference direction,so as to reduce the impact of interference on the antenna system receiving the desired signal.However,in the real environment,if the interference signal moves relative to the adaptive antenna,the beam null position will be inconsistent with the interference direction,which will reduce the suppression ability of the adaptive antenna to the interference signal.At this time,the null needs to be broaden.The complex transmission environment results in large mismatch error in the estimated value of the desired signal steering vector,which reduces the output signal-to-interference noise ratio of the adaptive antenna null broadening algorithm.In addition,if the array antenna needs to suppress too many interferences,the conventional null broadening algorithm will degrade the null broadening performance due to the lack of the degree of freedom of the array antenna.Beamforming technology based on fourth order statistics can construct virtual array elements and increase the degree of freedom of array antenna.Therefore,it can well deal with the problem that the null broadening algorithm consumes too many degrees of freedom of array.Aiming at the existing problems,this paper studies the adaptive antenna null broadening beamforming technology based on fourth order statistics to improve the null broadening performance of adaptive beamforming technology.The main innovations of this paper are as follows:1.Aiming at the problems of narrow null of conventional adaptive beamforming algorithm and poor ability to suppress interference that occurs relative to null,a null broadening beamforming algorithm based on projection transformation and fourth order statistics(PT-FOS)is proposed.The algorithm processes the array received signal through the projection transformation matrix,increases the interference incident information in the covariance matrix,so as to broaden and deepen the null.Then,the fourth order statistics are introduced to increase the degree of freedom of the array and improve the null broadening performance of the algorithm when the number of interference is large.At the same time,the introduction of fourth order statistics can further deepen the null depth.2.Aiming at the problem that the null broadening performance of the conventional null broadening algorithm seriously degrade when the mismatch error of the desired signal steering vector estimation occurs,two highly robust null broadening beamforming algorithms are proposed.Firstly,a null broadening beamforming algorithm based on interference subspace reconstruction and fourth order statistics(ISR-FOS)is proposed,which constructs the interference subspace matrix through the interference signal information,and uses the interference subspace to process the sampling covariance matrix.Then,a more accurate desired signal steering vector is obtained by using the re-estimation method,by introducing fourth order statistics extended covariance matrix and array steering vector.The linear constrained sector suppressed approach is also combined for adaptive beamforming.Compared with the conventional null broadening algorithm,the null broadening beamforming performance of ISRFOS algorithm is greatly improved and has high robustness in the face of the mismatch of the desired signal steering vector.Then a simplified ISR-FOS null broadening(SIFNB)algorithm is proposed.The algorithm constructs the fourth order steering vector correlation matrix by introducing covariance matrix taper technology,which simplifies the calculation process.However,compared with ISR-FOS algorithm,the null broadening performance of SIFNB algorithm degrades.It is suitable for application scenarios where the interference motion speed changes rapidly and the requirements for null broadening performance are not strict.