Smart antenna

Smart Antenna (also known as adaptive 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, 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,Matrix Pencil method 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. Matrix Pencil is very efficient in case of real time systems, and under the correlated sources.

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. This can be done with a simple FIR tapped delay line filter. The weights of the 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.

Types of Smart Antennas

Two of the main types of smart antennas include switched beam smart antennas and adaptive array smart antennas. Switched beam systems have several available fixed beam patterns. A decision is made as to which beam to access, at any given point in time, based upon the requirements of the system. Adaptive arrays allow the antenna to steer the beam to any direction of interest while simultaneously nulling interfering signals.

Extension of Smart Antennas

Smart antenna systems are also a defining characteristic of MIMO systems, such as the proposed IEEE 802.11n standard. Conventionally, smart antennas is an unit of a wireless communication system and performs spatial singal processing with multiple antennas. Multiple antennas can be used at either the transmitter or receiver. Recently, the technology has been extended to use the multiple antennas at both the transmitter and receiver, which is called especially as MIMO. As extended Smart Antennas technologies, MIMO supports spatial information processing, relative that conventional researches on Smart Antennas have foucsed on how to provide a beamforming advantage by the use of spatial signal processing in wireless channels. Spatial information processing includes spatial information coding suh as Spatial multiplexing and Diversity Coding, as well as beamforming.