Performance Analysis of the LMS Adaptive Algorithm for Adaptive Beamforming

摘要

The demand for higher capacity wireless communication networks has motivated research in the techniques of adaptive beamforming using smart antennas. The technique is to radiate narrow beams in a desired direction and to suppress interferences. Antenna array beamforming is a fundamental technique for directional signal transmission and reception[1]. The LMS algorithm has been identified as a suitable technique that optimises the SNR of the desired signal in a particular direction. The proposed adaptive beamforming scheme uses an array of antennas to realise maximum reception in a specified direction. This is achieved by adjusting the weights of each of the antennas with changing signal environment. This paper analyses the performance of the LMS adaptive algorithm in terms of the convergence rate of the Mean Square Error (MSE), also the effect of some antenna array elements like the number of elements and the spacing between elements, based on the Direction of Arrival (DOA), but also the special case when the interference is correlated to the desired user. The simulation results show that increasing the number of antenna elements results in narrower beams reduces the correlation of the interference DOA on the desired user direction, and the optimum value of separation distance between elements is half wavelength for which the MSE gives an optimum error in a particular direction. Also, increasing the SNR of the interference over the desired signal affects the convergence performance of the algorithm. The convergence of the LMS algorithm remains unchanged even the initial weight vector changes. The results are simulated using MATLAB.