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Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. Signal processing is the analysis interpretation and manipulation of signals Signals of interest include sound, images, biological signals such as This spatial selectivity is achieved by using adaptive or fixed receive/transmit beampattern. The improvement compared with an omnidirectional reception/transmission is known as the receive/transmit gain (or loss). An omnidirectional antenna is an antenna system which radiates power uniformly in one plane with a directive pattern shape in a perpendicular plane In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a

Beamforming can be used for both radio or sound waves. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. It has found numerous applications in radar, sonar, seismology, wireless communications, radio astronomy, speech, and biomedicine. Adaptive beamforming is used to detect and estimate the signal-of-interest at the output of a sensor array by means of data-adaptive spatial filtering and interference rejection.

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Beamforming techniques

Beamforming takes advantage of interference to change the directionality of the array. In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern When transmitting, a beamformer controls the phase and relative amplitude of the signal at each transmitter, in order to create a pattern of constructive and destructive interference in the wavefront. The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0 Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system When receiving, information from different sensors is combined in such a way that the expected pattern of radiation is preferentially observed.

For example in sonar, to send a sharp pulse of underwater sound towards a ship in the distance, simply transmitting that sharp pulse from every sonar projector in an array simultaneously fails because the ship will first hear the pulse from the speaker that happens to be nearest the ship, then later pulses from speakers that happen to be the further from the ship. Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate The beamforming technique involves sending the pulse from each projector at slightly different times (the projector closest to the ship last), so that every pulse hits the ship at exactly the same time, producing the effect of a single strong pulse from a single powerful projector. The same thing can be carried out in air using loudspeakers, or in radar/radio using antennas. For the Marty Friedman album see Loudspeaker (album A loudspeaker, speaker, or speaker system is an electroacoustical An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into

In passive sonar, and in reception in active sonar, the beamforming technique involves combining delayed signals from each hydrophone at slightly different times (the hydrophone closest to the target will be combined after the longest delay), so that every signal reaches the output at exactly the same time, making one loud signal, as if the signal came from a single, very sensitive hydrophone. A hydrophone (Greek "hydro" = "water" and "phone" = "sound" is a Microphone designed to be used underwater for recording or listening Receive beamforming can also be used with microphones or radar antennas.

With narrow-band systems the time delay is equivalent to a "phase shift", so in this case the array of antennas, each one shifted a slightly different amount, is called a phased array. This article is about general theory and electromagnetic phased array A narrow band system, typical of radars, is one where the bandwidth is only a small fraction of the centre frequency. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships With wide band systems this approximation no longer holds, which is typical in sonars.

In the receive beamfomer the signal from each antenna may be amplified by a different "weight. " Different weighting patterns (e. g. , Dolph-Chebyshev) can be used to achieve the desired sensitivity patterns. A main lobe is produced together with nulls and sidelobes. As well as controlling the main lobe width (the beam) and the sidelobe levels, the position of a null can be controlled. This is useful to ignore noise or jammers in one particular direction, while listening for events in other directions. A similar result can be obtained on transmission.

For the full mathematics on directing beams using amplitude and phase shifts, see the mathematical section in phased array. This article is about general theory and electromagnetic phased array

Beamforming techniques can be broadly divided into two categories:

Conventional beamformers use a fixed set of weightings and time-delays (or phasings) to combine the signals from the sensors in the array, primarily using only information about the location of the sensors in space and the wave directions of interest. Smart antennas (also known as adaptive array antennas multiple antennas and recently MIMO) are Antenna arrays with smart signal processing algorithms used to identify Smart antennas (also known as adaptive array antennas multiple antennas and recently MIMO) are Antenna arrays with smart signal processing algorithms used to identify In contrast, adaptive beamforming techniques, generally combine this information with properties of the signals actually received by the array, typically to improve rejection of unwanted signals from other directions. This process may be carried out in the time or frequency domains.

As the name indicates, an adaptive beamformer is able to adapt automatically its response to different situations. An adaptive beamformer is a Signal processing system often used with an array of Radar antennas (or Phased array) in order to transmit or receive signals Some criterion has to be set up to allow the adaption to proceed such as minimising the total noise output. Because of the variation of noise with frequency, in wide band systems it may be desirable to carry out the process in the frequency domain. Frequency domain is a term used to describe the analysis of Mathematical functions or signals with respect to frequency

Beamforming can be computationally intensive. Sonar phased array has a data rate slow enough that it can be processed in real-time in software, which is flexible enough to transmit and/or receive in several directions at once. In contrast, radar phased array has a data rate so fast that it usually requires dedicated hardware processing, which is hard-wired to transmit and/or receive in only one direction at a time. Hardware is a general term that refers to the physical artifacts of a Technology. However, newer field programmable gate arrays are fast enough to handle radar data in real-time, and can be quickly re-programmed like software, blurring the hardware/software distinction. FPGAs should not be confused with the Flip-chip pin grid array, a form of integrated circuit packaging

Sonar beamforming requirements

Sonar itself has many applications, such as wide-area-search-and-ranging, underwater imaging sonars such as side-scan sonar and acoustic cameras. Side-scan sonar (also sometimes called side scan sonar, sidescan sonar, side looking sonar, side-looking sonar and bottom classification

Sonar beamforming implementation is similar in general technique but varies significantly in detail compared to electromagnetic system beamforming implementation. Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate Sonar applications vary from 1 Hz to as high as 2 MHz, and array elements may be few and large, or number in the hundreds yet very small. This will shift sonar beamforming design efforts significantly between demands of such system components as the "front end" (transducers, preamps and digitizers) and the actual beamformer computational hardware downstream. High frequency, focused beam, multi-element imaging-search sonars and acoustic cameras often implement fifth-order spatial processing that places strains equivalent to Aegis radar demands on the processors.

Many sonar systems, such as on torpedoes, are made up of arrays of up to 100 elements that must accomplish beamsteering over a 100 degree field of view and work in both active and passive modes.

Sonar arrays are used both actively and passively in 1, 2, and 3 dimensional arrays.

Sonar differs from radar in that in some applications such as wide-area-search all directions often need to be listened to, and in some applications broadcast to, simultaneously. Thus a multibeam system is needed. In a narrowband sonar receiver the phases for each beam can be manipulated entirely by signal processing software, as compared to present radar systems that use hardware to 'listen' in a single direction at a time.

Sonar also uses beamforming to compensate for the significant problem of the slower propagation speed of sound as compared to that of electromagnetic radiation. In side-look-sonars, the speed of the towing system or vehicle carrying the sonar is moving at sufficient speed to move the sonar out of the field of the returning sound "ping". In addition to focusing algorithms intended to improve reception, many side scan sonars also employ beam steering to look forward and backward to "catch" incoming pulses that would have been missed by a single sidelooking beam.

Beamforming schemes

Beamforming history in cellular standards

Beamforming techniques used in cellular phone standards have advanced through the generations to make use of more complex systems to achieve higher density cells, with higher throughput. Global System for Mobile Communications (AKA GSM, around 80–85 % market share and IS-95 (AKA cdmaOne around 10–15 % market share are the

See also

Beamforming solutions

Related issues

References

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