Study On Virtual Extension Of L-Shaped Array And Beamforming

Beamforming technology is widely used in wireless communication systems.The conventional beamforming is easily limited by the number of elements of the array antenna,so the virtual expansion technology is produced accordingly.When the virtual array of interpolation transformation is used for beamforming,there are problems such as high side lobe,low output signal to interference noise ratio and "angle sensitivity".Therefore,in this thesis,aiming at the above mentioned problems,the beamforming algorithms of the L-shaped interpolation transform virtual extended array are studied.The main contents are as follows:1.In order to reduce the side lobe level of adaptive beamforming under virtual expansion of the L-shaped array antenna and improve its output signal to interference plus noise ratio,a beamforming algorithm combining covariance matrix sharpening and second order cone programming is given.The covariance matrix of the interpolation array is sharpened by mixing diagonal loading and Maillfoux-Zatman sharpening,and then the side lobe is constrained by the second order cone programming,and finally a new adaptive weight is constructed.The simulation results show that the above algorithm can effectively constrain the side lobe level of the L-shaped array virtual expansion,and obtain a larger output signal to interference plus noise ratio.At the same time,the algorithm has better robustness to the array mutual coupling error.2.Aiming at the problem of "angle sensitivity" in the interpolation transformation,a beamforming method with symmetrical expansion of the interpolation area is given and optimized.First,the array manifold matrix of the L-shaped array is processed symmetrically about the coordinate axis to realize the double symmetrical expansion of the interpolation area.Then,the beamforming weight vector is optimized through the improvement of the existing variable diagonal loading technology and Taylor weighting.The simulation results show that the above process can effectively expand the range of available interpolation angle to the system,restrict the side lobe level of the L-shaped extended array,and improve the output signal to interference plus noise ratio.3.Aiming at the problem that the performance of desired signal reception may be caused to decrease by excessive side lobe suppression,a beamforming algorithm of side lobe suppression under oblique projection is given.In the L-shaped array virtual expansion,the interference signal is first obliquely projected to the desired signal direction to reduce the influence of the interference signal.Then only the side lobe power in the vicinity of the main lobe is minimized to suppress the side lobe level.Finally,the beamforming weight vector for side lobe suppression under oblique projection is constructed.The simulation results show that the above algorithm can effectively improve the performance of suppressing interference and noise,while ensuring effective reception of the desired signal.And it has good robustness to mutual coupling.