Study And Implementation In Smart Antenna Beamforming Based On LMS Algorithm

Smart antenna technology is one of key technologies of the third generation mobile communication system. It can remarkably increase the capacity of the communication system, and sufficiently utilize the limited frequency spectrum resource. The key of the smart antenna is the adaptive beamforming algorithm. It produces spatial and directional beam with the direction of the useful signal. The main beam aims at the coming direction of reference user and the side lobe or null points to the coming direction of interference user. So the signal of desired user will be enhanced, and the signal of interference user will be restrained.Beamforming algorithm also is named spatial filter. It looks like a general filter. Most of adaptive filter algorithms can be used in adaptive beamforming technology. Generally, research about adaptive beamforning is based on adaptive filter algorithm.Based on the adaptive filter algorithm, firstly, it analyze the original Least Mean Squares(LMS) algorithm, and researches the constringency and stabilization of the LMS algorithm. And it points out the direction of improving LMS algorithm. Based on the direction, it starts the research work of improving the LMS algorithm. And it does lots of simulation experimentations about the constringency of the LMS algorithm.Then, LMS algorithm is successfully utilized in the adaptive beamforming technology. Based on simulation experimentations, it has analyzed when modified method SVS_LMS algorithm is used in the adaptive beamforming technology, how is the SVS_LMS algorithm beamforming pattern. Compared the original LMS algorithm and the modified method SVS_LMS algorithm, the modified method SVS_LMS algorithm can beamform an enough null. At the same time, the SVS_LMS algorithm has fast constringency speed.Lastly, it designs an LMS adaptive beamformer based on FPGA. Different with the original beamforming structure, it integrates direct digital quadrature transformation technology based on polyphase filtering and adaptive beamforming technology. And it implements a direct IF sampling adaptive beamformer. In this method, it simples the hard design of the smart antenna. This is a successful application that the software radio technology is utilized in smart antenna.