Smart antenna

Smart antenna

An antenna system that focuses its beam on a desired signal to reduce interference. A wireless network employs smart antennas at its base stations in an effort to reduce the number of dropped calls, improve call quality and improve channel capacity. (Cingular)

Smart Antenna refers to a system of antenna arrays with smart signal processing algorithms that are used to identify the direction of arrival (DOA) of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on the mobile/target. The antenna could optionally be any sensor.

Smart antenna techniques are used notably in acoustic signal processing, track and scan RADAR, Radio astronomy and Radio telescopes Radio Telescopes, and mostly in cellular systems like W-CDMA and UMTS.

Smart antennas have two main functions

1. DOA estimation
2. Beamforming

DOA estimation

The smart antenna system estimates the direction of arrival of the signal, using any of the techniques like MUSIC (Multiple Signal Classification) or ESPRIT (Estimation of Signal Parameters via Rotational Invariant Techniques) algorithms, or their derivatives. They involve finding a spatial spectrum of the antenna/sensor array, and calculating the DOA from the peaks of this spectrum. MUSIC involves calculation of eigenvalues and eigenvectors of an autocorrelation matrix of the input vectors from the receiving antenna array. These calculations are computationally intensive

Beamforming

Beamforming is the method used to create the radiation pattern of the antenna array by adding constructively the phases of the signals in the direction of the targets/mobiles desired, and nulling the pattern of the targets/mobiles that are undesired/interfering targets. We basically implement a simple FIR tapped delay line filter to do this. The weights of this FIR filter may also be changed adaptively, and used to provide optimal beamforming, in the sense that it reduces the MMSE between the desired and actual beampattern formed. Typical algorithms are the steepest descent, and LMS algorithms. Beamforming is a latest technology being used for various purposes.

(Wikipedia)