摘要:

Orthogonal beamforming is the name given to certain high-resolution methods for estimating the spectra of a wave field received by an array of sensors. These methods use the eigenvalues and eigenvectors of the spectral matrix of the sensor outputs. The problem is to predict the behaviour of such methods when only an estimate of the matrix is known. The sensor outputs may consist of sensor noise, ambient noise and noise from a finite set of discrete sources. The properties of the eigensystem of the spectral matrix in the case of weak ambient noise motivate the methods of orthogonal beamforming, for example Pisarenko's nonlinear peak estimates and the projection estimates of Owsley and Liggett. If the spectral matrix is estimated by one of the classical methods, some asymptotic distributional properties of the matrix estimate and its eigensystem are well known. They can be used to determine asymptotic expressions, for example for the first and second moments of the peak estimators, and to approximate the distributions. The parameters, however, cannot be calculated in applications since the eigensystem of the exact spectral matrix is required. Therefore we recently developed bounds for the deviation of the peak estimates which only use limited knowledge about the matrix. We applied some results on perturbations of Hermitian operators. The asymptotic behaviour of the bounds for the projection estimator is investigated, and possibilities for their estimation are indicated. Finally, we report on extensive simulations with random matrices to evaluate the new bounds. As a result, we found that the projection estimator behaves stably and that there are tight bounds if the eigenvalues of interest are sufficiently separated from the rest.

DOI:10.1049/ip-f-1.1983.0043

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A power estimation technique is presented which is suitable for broadband detection of signals reaching a passive array of sensors. It is demonstrated that the technique provides a fixed beam pattern for all steering directions at low frequencies and that this may be used by an operator to aid detection. The effectiveness of the technique is demonstrated by comparison with two alternative approaches.

DOI:10.1049/ip-f-1.1983.0044

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The interference direction frequency response and cancellation capability of a broadband tapped delay line adaptive array are discussed. The frequency response is found to be an entire function in thes-plane, but the hypothesis is advanced that, for a given total time delay and number of degrees of freedom, it approximates to the rational frequency response function of a single uniformly tapped delay line for band- limited interference spectra. Some elementary expressions for the cancellation are derived.

DOI:10.1049/ip-f-1.1983.0045

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The problem of measuring the time delay (or difference in arrival times) of a signal emanating from a source and received at two separate locations is considered. Most existing techniques of time delay estimation assume identical receivers. The phase of the cross-spectrum between the receivers' outputs is then directly proportional to frequency, with the time delay as the proportionality constant. The paper develops a new estimator for receivers having unequal phase characteristics. Their phase differences are represented by a polynomial in frequency, with the coefficients of the polynomial approximately known. An augmented least-squares estimator, incorporating the approximate phase information, is developed to compute the time delay. Simulation results that serve to illustrate the method and confirm some of the theoretical findings are presented.

DOI:10.1049/ip-f-1.1983.0046

出版商:IEE    

年代:1983

数据来源: IET

摘要:

In the analysis of time/frequency domain signals, lattice filters have proved popular, providing significant advantages over conventional tapped delay line digital filters. Improvements in adaptation times and model order identification have been observed, and the modular structure of these filters allows a straightforward VLSI hardware implementation. In the paper, a lattice-structured spatial filter for use in adaptive arrays is described. This filter is shown to take on a triangular structure in the spatial domain which provides a step-by-step solution to the prediction problem. Several uses of the lattice filter in array processing are then discussed, particularly the extraction of high-resolution spatial spectral estimates from the parameters of the filter. These spatial spectral estimators include the maximum-entropy, maximum-likelihood and eigenvector (Pisarenko) based methods and are used to obtain high-resolution maps of the directional power incident upon an array of spatially distributed sensors. It is also shown how multiple look direction constraints may be applied to the lattice filter, providing the capability for enhancing desired signals in the presence of directional interference.

DOI:10.1049/ip-f-1.1983.0047

出版商:IEE    

年代:1983

数据来源: IET