Comparative study of the estimation techniques for direction of signal arrival in smart antennas

Abstract

A smart antenna system combines multiple antenna elements with a signal processing capability to optimize its radiation pattern automatically in response to the signal environment. Widespread interest of smart antenna has continued for several decades due to their use in numerous applications. As a whole Smart Antennas examine all aspects of array signal processing, delivering a detailed treatment of antenna array processing schemes, adaptive algorithm to adjust weighting, direction of arrival (DOA) estimation methods, and diversity combining methods that combat fading and reduce error. The objective of this work is to provide a comprehensive study on various techniques concerning estimation of received signals on directions of arrival (DOA).The goal is to achieve maximum SNR, resolution, sensitivity by comparing some techniques. In order to obtain the best possible cancellation of unwanted interferences the gain of the low noise amplifier (LNA) must be adjusted. For optimum processing the typical objective is to maximize the output signal to noise ratio (SNR). For an array with a specified response in the direction of the desired signal, this is achieved by minimizing the mean output power of the processor subject to be specified constraint. In the absence of errors, the beam pattern of the optimized array has the desired response in the signal direction and reduced response in the direction of unwanted interference. In this research work the three types of DOA estimation method are considered. Firstly conventional method includes spectral estimation, minimum variance distortion less response estimator. Secondly optimal method includes linear prediction, maximum entropy, and maximum likelihood. Finally various Eigen structure methods are also described which includes different versions of multiple signal classification (MUSIC) methods, minimum norm methods, estimation of signal parameters via rotational invariance technique (ESPRIT) method and the weighted subspace fitting method. The power and beam pattern expressions of various techniques have been computed and the output has been analyzed to compare the various estimation methods. It has been found that the structured estimation techniques give the better resolution, better sensitivity than the conventional and optimal methods.