Showing papers on "Adaptive beamformer published in 1983"

Adaptive signal processor for interference cancellation

Abstract: The present invention relates to an adaptive signal processor for reducing interference in ranging and communication systems resulting from jamming or multipath reception. More particularly, an optical signal processor is provided in which a first time correlation is performed between the receive signal derived from a direction antenna and an interference signal derived from one or more auxiliary omnidirectional antennas in an acousto-optical device to obtain one or more corresponding weighting functions stored as a function of signal delay. The auxiliary signal is then correlated in a spatial correlation process in which the auxiliary signals are delayed and multiplied with the weights and the result spatially integrated to derive the predicted interference. The predicted interference is then subtracted from the main signal in an adaptive feedback loop wherein the predicted signal is made to approach equality with the interference. The system achieves good cancellation by correcting for multiple arrival times and by retaining the phase and amplitude information of the original carriers throughout the optical process.

UHF circular arrays incorporating open-loop null steering for communications

Abstract: The paper describes an experimental wideband antenna and adaptive signal processing system which has the ability to exhibit an omnidirectional azimuth radiation pattern which can be modified in real time to minimise the effects of unwanted interference. The philosophy behind the use of circular antenna arrays for this system and brief details of their directional properties are given. To enable the adaptive signal processing system to be used in existing communication links, with standard receivers and no extra-special encoding of wanted signals, a simple form of open-loop adaptive control has been devised. This concept has been implemented in an experimental system based upon a four-element circular array and capable of electronically steering a single directional null against high-level interference. Finally, results from an experimental array operating over the 200–400 MHz band are presented to illustrate and qualify the concepts and theoretically predicted results.

New Principle of Array Processing in Underwater Passive Listening

Abstract: : One of the main function of an underwater passive listening system is the reckoning of the number of present sources as well as the characteristic parameters of everyone. To do so, the noises transmitted by the sources are used when recorded on the sensors of an array. The basic tool is the spatial processing. The traditional tool is the classical beamforming. Then, in view of improving the performance, one came to adaptive beamforming of a sensor array. As a result, this method brings an improvement -an array gain- which is asymptotically bound by the signal to noise ratio of the source noises, when measured on a particular sensor. More recently have appeared more powerful methods called high resolution. The improvement in performance as compared to previous processing is at the cost of one more assumption on the medium. Nevertheless, these methods carry the possibility to include free parameters in the medium model, and that make more flexible the assumptions to be accepted.

Source-oriented adaptive beamforming

Abstract: A system concept expected to improve sonar multiple target detection and classification performance in severe directional interference environments is presented. Adaptive nulling of undesired strong interference sources and detection of desired weak sources are achieved by utilizing constrained adaptive processing techniquestogether with conventional processing techniques. The adaptive processing functions are incorporated in the overall system architecture in a manner which maintains the computational complexity and storage requirementslinearly proportional to the product of the number of interference sources and the number of adaptive weights per interference source. In addition, a detailed discussion is provided concerning the importance of certaina priori assumptions on constrained adaptive algorithm performance.

Performance of stochastic gradient descent adaptive beamforming using sonar data

Abstract: Using sonar data characterised by the presence of a strong interference, adaptive beamforming is performed by the stochastic gradient descent algorithm in the frequency domain. The weights are constrained to have a unity response in the look direction. Convergence rates are estimated from averaged adaption curves, and, in most cases, these are found to be in reasonable agreement with theoretical values. It is conjectured that a marked discrepancy in one case is due to phase errors in the data covariance matrix.

A New Adaptive Antenna System for Coherent Signals and Interference.

Abstract: : In this paper the authors introduce a new adaptive antenna system able to work well even when the desired signal and the interference are coherent. The present adaptive beamformers fail to operate in these cases. The results of simulations appear to confirm the theoretical predictions. (Author)

Detection of narrowband sources by an array

Abstract: Adaptive array techniques which seek to optimise the passive detection of an acoustic narrowband source under ideal conditions are well established. The paper gives details of a frequency-domain technique which has modest hardware requirements and yet is capable of operation in a highly nonstationary environment. In addition, the algorithm enhances both signal/noise gain and detectability when mismatch occurs, particularly for the important case of low input signal/noise ratio. The suggested technique includes linear interpolation, and yet is shown to give near-optimal performance.

Applications of adaptive signal processing to the reduction of flow-induced noise in small underwater vehicles

Abstract: We analytically and experimentally investigate the effectiveness of adaptive filtering for reducing flow-induced sonar interference in small underwater vehicles. Noise and signal fields are modeled and applied to an array whose beamformer is designed to maximize signal to noise ratio. The beamformer output is applied to an adaptive processing system with two auxiliary channels, one for a spatial sample, and one for a temporal sample of interference. Noise, signal, and adaptive filter parameters are examined analytically to define design guidelines for the system and assess performance in a variety of realistic signal and noise situations. The hardware implementation emphasizes architectures that meet the performance requirements and are responsive to the physical constraints of small underwater vehicles. A digital high speed, pipelined transversal filter is used to produce the noise cancelling signal, and the computations for error signal and filter weights are performed in parallel by high speed microprocessors.

Signal separation theory by using adaptive array

Abstract: Signal separation theory by using adaptive arrays is a new thesis in array data processing. The model considered in this paper is that the array consists of N elements and the number of signal sources, which are separated in spatial location, is M and M \leq N . By using the Hilbert transform of input signal and the directional incident angle matrix, a signal separation processor is formed. In each output channel of this processor have only one incident signal. The results of system simulation experiment in digital computer has proved that this theory is effective for separating signal in certain situation.

Digital extrapolation beamforming

Abstract: More sensors are usually required in order to enhance the resolution of a beamformer and to improve its beam pattern. Due to physical and/or economical constraints this requirement cannot be met. This paper presents the results of an analytical and experimental study of the use of a signal extrapolation method in order to "synthetically" (without adding more physical sensors) enhance the beamformer resolution. A simple model for the extrapolation error has been obtained experimentally. The beam pattern has been extensively improved. Further improvements can be achieved by combining other techniques such as windowing, temporal interpolation, etc. to the spatial extrapolation.

An escalator structure for adaptive beamforming

Abstract: The standard LMS algorithms for adaptive beamforming though straightforward, suffer from the main draw back of having slow, convergence rate This is normally attributed to the wide range of spread of eigenvalues of the input signal vector correlation matrix By properly pre-whitening the input signal vector these eigenvalues can be equalized thereby improving the convergence rate An Escalator structure recently proposed for linear prediction problems is used to pre-whiten the input signal vector This whitened signal vector is now fed to a beam former with desired main beam shape The overall adaptive array is computationally efficient and exhibits faster convergence rate than the conventional LMS algorithms