PERFORMANCE COMPARISON OF BEAM FORMING TECHNIQUE USING LMS AND SMI ALGORITHMS

Abstract

The main objective is to analyse adaptive beam forming approach based on smart antenna. Several algorithms have been developed based on different criteria to compute the complex weights. In this paper the comparison of the performance of algorithms namely Least Mean Square algorithm (LMS) and Sample Matrix Inversion algorithm (SMI) are presented. The main advantage of these algorithms is its simplicity with a minimal loss of accuracy. This paper describes the design of an adaptive antenna array after receiving the signals from the desired and interfering directions. Then the weight vector is evaluated to minimize the error that provides an appropriate beam pattern to each subscriber. For these two algorithms the mean square error and Array factor are evaluated and compared. Simulation results revealed that Least Mean Squares (LMS) are best for beam forming (to form main lobes) towards desired user but they have limitations towards interference rejection. While Sample Matrix Inversion Algorithm (SMI) has satisfactory response towards beam forming and it gives better outcome for interference rejection. It is verified that convergence rate of SMI is faster than LMS so SMI is proved the best choice. The effect of changing number of elements on Array factor for SMI algorithm has also been studied. Keywords— Antenna Arrays, Adaptive Algorithms, Beam forming, Interference, Smart antenna, Least Mean Squares (LMS), Sample Matrix Inversion Algorithm (SMI).