Research And Application Based On The Lms Algorithm For Smart Antenna Beamforming

Smart antenna is recognized as a key technology in the4G mobile communications for higher user capacity in wireless networks by effectively reducing multipath fading and co-channel interference. Because of function powerful, low-cost, digital processing components and the development of software-based techniques has made smart antenna systems used in both base station and mobile station of a cellular communications systems. In the mobile communication system, the use of smart antenna can improve the performance of the system, such as:reduce the bit error rate, increase system coverage and spectrum efficiency and so on.The core technology of smart antenna is adaptive beamforming algorithm, that the desired signals can be extracted and at the same time interferences can be suppressed. On the basic of the basic principles of smart antennas and adaptive beamforming technology in this thesis, pays much attention to analyze and discuss the modified algorithms of LMS. In view of the analysis and comparison of the variable step size algorithm, Gives an improved algorithm, which make use of the e(n)e(n-1) correlation values and the regulation of factor p(i) multiplied by the cumulative value of error signal correlation values before n sample time, builded a non-linear relationship with the step-size function. Furthermore, computer simulation verification and comparison are provided to the algorithm.Considering the practical application of smart antenna, this thesis integrates smart antenna with the Orthogonal Frequency Division Multiple (OFDM), to effectively compensate for the lack of OFDM technology, and improve the performance of the system.The combination of smart antenna and OFDM has two structure:Time-domain beamforming is called Pre-FFT because the array processing is done before the FFT step in time domain and frequency-domain beamforming can be called Post-FFT because the array processing is done after the FFT step in frequency domain. On the basic of their analysis and discussion, a new modified Pre-FFT system architecture is provided, it is based on the time domain and frequency domain of hybrid beam formation, it verified by simulation and performance analysis found that the modified Pre-FFT system architecture has a lower bit error rate than Pre-FFT system architecture.