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It is well known that the performance of adaptive beamformers may degrade in the presence of steering errors or lack of training data. Diagonal loading of the sample covariance matrix is a popular technique applied to the minimum variance/minimum power distortionless response beamformer to increase robustness of the array system. However, this technique induces a trade-off between sidelobe suppression...
Large sensor arrays are prone to element failures which can seriously degrade their performance. In the event of sensor failures, conventional non-adaptive re-design of array weights for the resulting non-uniform or even sparse array often leads to undesirable mainlobe-versus-sidelobe level trade-offs. Alternatively, adaptive array processing techniques can be employed but for large arrays it can...
We develop a wideband adaptive beamformer with an improved robustness against presteering errors. The proposed beamformer employs the presteered broadband array processor and models the uncertainty in the array manifold as norm-bounded phase errors at the outputs of the presteering delay filters. A state-space model is developed for this robust beamforming problem, and an extended Kalman filter (EKF)...
The performance of Krylov subspace-based dimensionality reduction for adaptive beamforming is analyzed using a simple second-order Taylor series approximation to the mean output signal-to-noise ratio (SNR). It is shown that the predicted SNRs accurately follow the experimentally measured SNR and explain the threshold effects when the angles or spacing are varied between the signal mode (subspace)...
It is well known in array processing that general multiple signal model based approaches for direction of arrival estimation, such as maximum likelihood (ML) or maximum a posteriori (MAP) estimation, are optimal. The major drawbacks of these approaches, is that not only do we need to know the number of signals a priori, but these methods also involve multivariate nonlinear maximizations which can...
In this paper, three main criteria for the adaptive beamformer design are discussed: maximal signal-to-interference-plus-noise ratio (MSINR), minimal mean-squared error (MMSE), and minimal least-square error (MLSE). Although in the case of exactly known power and steering vector of the signal-of-interest (SOI), there are beamformers that can simultaneously meet the MMSE and MSINR criteria, this is...
The design of optimal reduced-rank minimum variance beamformers based on the Krylov-subspace spanned by the covariance matrix of the array observations is addressed. We concentrate on finite sample-support situations that naturally appear in practice when the number of antennas and the sample-size are comparable in magnitude. The design of the coefficients of the resulting polynomial expansion is...
This paper describes methods for broadening the beam of a phased array antenna using phase-only element weights. This type of broadening can be valuable for improving the search occupancy and/or reducing the search frame time for large phased arrays, when transmit beam broadening is combined with multiple simultaneous receive beams. Phase-only broadening is required for typical solid-state (active...
This paper is concerned with new fast adaptive beamforming algorithms which are based on the internal model principle, to deal with fast fading environment to track the desired signal changes and suppress the interferences. The LMS and RLS algorithms for constructing nulls are derived by incorporating an AR model into the weight dynamics, and then can track fast fading environment. The convergence...
In this paper, a new direction of arrival (DOA) tracking algorithm is presented. We assume that the signals exhibit cyclostationarity, which is exploited to perform signal selective DOA tracking. A least squares (LS) tracking algorithm is first presented. Then a Kalman filter is applied to this algorithm to improve the performance of DOA tracking. Simulations are carried out to demonstrate the effectiveness...
Direction of arrival (DOA) estimation from time differences of arrival (TDOA) is used in several array systems. In some cases, practical constraints may necessitate the use of heavily quantized TDOA estimates. The quantization in TDOAs also causes the directional estimate to be quantized. This paper proposes a lattice-based representation for the quantization scenario. This representation can be used...
In this paper we propose an algorithm for angle and polarization estimation of non-coherent sources using real-world polarimetric antenna arrays. In order to construct an accurate model of an antenna array, we exploit its effective aperture distribution function (EADF). This model contains information on the array response for a vertical and horizontal excitation, the directional characteristic of...
In this paper, we describe a rectangular window subspace tracking algorithm, which tracks the r largest singular values and corresponding left singular vectors of a sequence of n times c matrices in O(nr2) time. This algorithm is designed to track rapidly changing subspaces. It uses a rectangular window to include a finite number of approximately stationary data columns. This algorithm is based on...
The resolving ambiguity of phase interferometer is necessary when the baseline separation between elements exceeds half wavelength since the phase difference between elements can only be measured modulo 2pi. It is difficult to meet the condition the minimum distance between two antennas is less than half wavelength for avoiding ambiguity in wideband operation. In this paper, we propose a simple and...
Several anti-jam techniques for GPS receivers rely on the direction-of-arrival (DOA) of the satellite signals. These angles change with moving GPS receiver platforms and, as such, they should be constantly estimated for the purpose of jammer nulling and beamforming. In this paper, we propose a new approach for directional finding for multi-antenna GPS receivers. This approach is based on a new unitary-cyclic...
On small platforms, angle-of-arrival (AOA) estimation of an E-M signal can be accomplished with colocated antennas measuring multiple components of the propagating wave. An electrically small vector sensor (VS) antenna constructed above and below the wing of a small UAV measures three components of the propagating wave. Determining the AOA involves fitting known "calibration" AOAs and corresponding...
A multi-channel detector for narcotics and explosives using nuclear quadrupole resonance (NQR) is developed. Multiple measurement coils are used to estimate the radio frequency interference that is often present. The temperature dependency of the NQR frequencies is incorporated in the detector, allowing for uncertainties in the temperature estimate of the sample. In addition, the detector considers...
A wide range of applications involve matrix decompositions which can be computed using givens rotations. A programmable processor for givens rotations offers more flexibility than highly tailored systolic array hardware implementations. The programmable processor design presented in this paper employs an approximate rotations method to compute givens rotations. Instantiations of this programmable...
In this paper, we consider the problem of detecting and locating buried landmines and subsurface objects by using seismic waves measured with sources and receivers on the surface. An imaging algorithm is proposed which uses the separated forward and reflected waves obtained via a Prony-based spectrum analysis technique. The imaging algorithm is followed by an energy detector. The resulting algorithms...
In this paper the working principle of the human eye is studied since uses very simple detectors, cones and rods, to provide an impressive high angular resolution without using any kind of scanning technique. Usually the resolution capability of the human eyes has been attributed to the complexity of the brain, but it is quite difficult to understand that something, specially small details, that it...
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