An adaptive beamformer is a system that performs adaptive spatial

signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as audio signal processing, sound, image processing, images, Scalar potential, potential fields, Seismic tomograph ...

with an array of transmitters or receivers. The signals are combined in a manner which increases the signal strength to/from a chosen direction. Signals to/from other directions are combined in a benign or destructive manner, resulting in degradation of the signal to/from the undesired direction. This technique is used in both radio frequency and acoustic arrays, and provides for directional sensitivity without physically moving an array of receivers or transmitters.

Motivation/Applications

Adaptive beamforming was initially developed in the 1960s for the military applications of sonar and radar. There exist several modern applications for beamforming, one of the most visible applications being commercial wireless networks such as

LTE LTE may refer to: Science and technology * LTE (telecommunication) (Long-Term Evolution), a mobile telephony standard ** LTE Advanced, an enhancement ** LTE Advanced Pro, a further enhancement * Compaq LTE, a line of laptop computers * Leukotrie ...

. Initial applications of adaptive beamforming were largely focused in radar and electronic countermeasures to mitigate the effect of signal jamming in the military domain. *

Radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

uses can be seen here

Phased array radar A phaser is an electronic sound processor used to filter a signal by creating a series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs of the waveform being affected is typically modulated by an interna ...

. Although not strictly adaptive, these radar applications make use of either static or dynamic (scanning) beamforming. * Commercial wireless standards such as 3GPP Long Term Evolution (

LTE (telecommunication) In telecommunications, long-term evolution (LTE) is a standard for wireless broadband communication for cellular mobile devices and data terminals. It is considered to be a "transitional" 4G technology, and is therefore also referred to as 3 ...

) and

IEEE 802.16 IEEE 802.16 is a series of wireless broadband standards written by the Institute of Electrical and Electronics Engineers (IEEE). The IEEE Standards Board established a working group in 1999 to develop standards for broadband for wireless metropo ...

WiMax Worldwide Interoperability for Microwave Access (WiMAX) is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide physical layer (PHY) and media access control (MAC) options. The WiMA ...

rely on adaptive beamforming to enable essential services within each standard.

Basic Concepts

An adaptive beamforming system relies on principles of wave propagation and phase relationships. See

Constructive interference In physics, interference is a phenomenon in which two coherence (physics), coherent waves are combined by adding their intensities or displacements with due consideration for their phase (waves), phase difference. The resultant wave may have ...

, and

Beamforming Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles ...

. Using the principles of superimposing waves, a higher or lower amplitude wave is created (e.g. by delaying and weighting the signal received). The adaptive beamforming system dynamically adapts in order to maximize or minimize a desired parameter, such as

Signal-to-interference-plus-noise ratio In information theory and telecommunication engineering, the signal-to-interference-plus-noise ratio (SINR) (also known as the signal-to-noise-plus-interference ratio (SNIR)) is a quantity used to give theoretical upper bounds on channel capacity ...

Adaptive Beamforming Schemes

There are several ways to approach the beamforming design, the first approach was implemented by maximizing the signal to noise ratio (

SNR The initialism SNR may refer to: * Signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio ...

) by Applebaum 1965. This technique adapts the system parameters in order to maximize the receive signal power, while minimizing noise (such as interference or jamming). Another approach is the Least Mean Squares (LMS) error method implemented by Widrow, and Maximum Likelihood Method (MLM), developed in 1969 by Capon. Both the Applebaum and the Widrow algorithms are very similar, and converge toward an optimal solution. However, these techniques have implementation drawbacks. In 1974, Reed demonstrated a technique known as Sample-Matrix Inversion (SMI). SMI determines the adaptive antenna array weights directly, unlike the algorithms of Applebaum and Widrow. A detailed explanation of the adaptive techniques introduced above can be found here: *

Least Mean Squares Least mean squares (LMS) algorithms are a class of adaptive filter used to mimic a desired filter by finding the filter coefficients that relate to producing the least mean square of the error signal (difference between the desired and the actua ...

Algorithm * Sample Matrix Inversion Algorithm * Recursive Least Square Algorithm *

Conjugate gradient method In mathematics, the conjugate gradient method is an algorithm for the numerical solution of particular systems of linear equations, namely those whose matrix is positive-semidefinite. The conjugate gradient method is often implemented as an it ...

* Constant Modulus Algorithm

References

{{DEFAULTSORT:Adaptive Beamformer Signal processing Multidimensional signal processing

Motivation/Applications

Basic Concepts

Adaptive Beamforming Schemes

See also

References