Research On Direction Finding And Beamforming Technology Based On Multi Antenna Array

Array signal processing is an important branch in the field of signal processing.It is widely used in wireless communication,sonar detection,seismic sensing and many other scenarios.Signal direction finding and beamforming are the key technologies to improve the reliability of antenna array system.The former realizes the estimation of signal incidence direction,and the latter realizes the suppression of interference signals.Although signal direction finding and beamforming technologies have been widely studied,there are still problems such as high computational complexity,limited application scenarios and simple array structure.In view of these phenomena,the direction finding and beamforming technologies of multi-antenna array are studied in this thesis.The specific work and contributions are as follows:First of all,considering that the traditional direction finding algorithm based on the comparison of multi-beam amplitudes is cumbersome and not universal,this thesis proposes an improved multi-beam amplitudecomparison direction finding algorithm without adopting a lookup table.By constructing the ergodic function and using the gain of each beam pattern,the amplitude comparison is implemented.At the same time,in order to reduce the impact of SNR and bandwidth on the recognition accuracy,the time-domain algorithm is extended to the frequency domain by comparing the amplitude of each frequency point.The simulation results show that the proposed algorithm is robust to the varying signal bandwidth and environmental noise,and its computational complexity is far lower than the existing algorithms.Moreover,the beam transmitted by the scheme is not constrained by the array structure,and its performance is only related to the beam width and the number of beams,which is more flexible.Secondly,considering that the beamforming algorithm based on the linear constrained minimum variance(LCMV)criterion involves matrix inversion,this thesis realizes a fixed-step LCMV-LMS adaptive beamforming algorithm implemented by the least mean square(LMS)iterative method,which avoids the high-complexity inversion operation.In order to improve the convergence effect of the algorithm,this thesis further proposes a variable step size LCMV-LMS algorithm.The simulation results show that when compared with the fixed-step algorithm,the proposed one can better control the convergence speed and avoid the divergence of convergence results.Finally,the proposed algorithm is extended to wideband beamforming by dividing whole wideband into numbers of sub-bands.The simulation results show that the proposed wideband LCMV-LMS algorithm can effectively retain the desired signal at each frequency point in the bandwidth and suppress the interference signal.Finally,the proposed multi-beam amplitude-comparison direction finding algorithm is implemented on the FPGA platform.According to the characteristics of the FPGA platform,the methods of zero-point smoothing and ping-pong operation are adopted to optimize the design,which effectively reduces the resource consumption on the premise of ensuring the operation efficiency.The result of the key modules show that the FPGA platform implemented in this thesis can correctly identify the signal incidence angle,which is consistent with the expectation.To sum up,the signal direction finding and beamforming algorithms proposed in this thesis can effectively detect the direction of the incoming signal and form an anti-interference targeted beam.Their complexity is lower than that of the existing algorithms.The FPGA platform for amplitude comparison and direction finding meets the requirements of signal direction finding efficiently.Therefore,the research in this thesis makes some contributions to the practical applications.