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Abstract: This paper introduces a new robust four way LMS and variable step size NLMS beam forming algorithm to reduce interference in a smart antenna system. This algorithm is able to resolve signals arriving from narrowband sources propagating plane waves close to the array end fire. The results of previously used adaptive algorithm have the fixed step size NLMS will result in a trade-off issue between convergence rate and steady-state MSE of NLMS algorithm. This issue is solved by using four way LMS and VSSNLMS which will improve the efficiency of the convergence point. The proposed algorithm implemented reduces the mean square error (MSE) and shows faster convergence rate when compared to the conventional NLMS.

Keywords: Adaptive Antenna, Beamforming, Means Square Error (MSE), Convergence

I.   Introduction

A.      Introduction

In today’s world numbers of mobile users are increasing day by day, hence it is necessary to serve such a huge market of mobile users with high QOS even though the spectrum is limited. This becomes a major challenging problem for the service providers to solve. A major limitation in capacity and performance is co-channel interference caused by the increasing number of users and the multipath fading and delay spread. Research efforts investigating effective technologies to mitigate such effects have been going on and among these methods Adaptive antenna employment is the most promising technology. This project works on Adaptive Antenna which ensures high capacity providing with the same Quality of Service(QOS).In a normal scenario currently the mobile towers employ parabolic dish or a horn antenna but this suffers if the SNR is low the signals have to be repeatedly retransmitted from mobile station to base station. The use of Adaptive Antenna considers an array of antennas in which the antenna will receive the delayed versions of the electromagnetic wave and adds them to achieve high SNR.

B.      Problem Statement

In the earlier antenna radiation was directed based on frequency or time, Therefore spectrum was not utilized efficiently because as the number of users increases the quality of service decreases. Hence, in this work a solution to use the Adaptive antenna frameworks have been proposed and used as an efficient means to meet the quickly expanding the  traffic volume. This issue of Technology has discusses the importance of various advanced antenna schemes for improving the same amount of spectrum and provides service to the large amount of mobile users is deduced. This is done by separating the users with respect to direction.

II.                Adaptive antenna

Adaptive antenna is the one which adapts itself to pick the user signal in any direction without user intervention , basically it undergoes through a two phase process:

  • Direction detection Estimation (DDE) using a suitable algorithm and sensor data.
  • Beam forming which forms a beam in the desired direction and nulls in the interference direction.

Direction Detection Estimation (DDE) methods are used to detect the incoming wave and the other signals which arrive from different parts of the space can be processed to extract different type of data including direction desired incoming signal falling on the antenna array.

Beam forming is a process of forming the Main beam in the desired direction and nulls in the direction of jammers direction. The block diagram is shown in  Figure1 shows an adaptive antenna structure with N antenna elements, DDE blocks, Adaptive signal processor algorithms to make adaptive antenna system smart, where incoming signal is processed by beam forming algorithms the figure also shows main beam formed in the direction of desired signal and nulls in the jammers direction.


Fig. 1: Adaptive Antenna