Imposing pattern nulls on broadband array responses

Abstract

(Received ) This paper considers the problem of altering a quiescent design for an array of omnidirectional sensors so that the altered design rejects a far eld broadband signal from a given direction. This problem occurs where microphone arrays are to be used to acquire speech signals for telecommunication and interfering signals must be rejected. Three main results are presented in this paper. Firstly, conditions for imposing an exact broadband null upon any given quiescent array response are derived. Secondly, an analysis of the sensitivity of exact nulling array responses to sensor positionerror is presented. Thirdly, frequency domain formulations for broadband nulls are obtained and it is shown that these are less restrictive t h a n t h e exact null conditions which are imposed in the time domain. A Lagrange multiplier approach is used to impose the null conditions upon a quiescent array response to minimize the square error between the quiescent and nulled responses. A design example is given.

Wideband Laguerre adaptive array with pre‐steering constraints

“…Of course, assuming less attenuation for the less disturbing signal would give us more freedom in setting other requirements in the pattern. Thus far, even ensuring to have a null at a given direction in the LCMV algorithm has been a difficult task [27–29]. Let us assume a beamformer with 10 antennas a desired signal at 88° with 0 dB power, and two interferences at 40° and 140° with 10 dB and 0 dB power, respectively.…”

“…Of course, assuming less attenuation for the less disturbing signal would give us more freedom in setting other requirements in the pattern. Thus far, even ensuring to have a null at a given direction in the LCMV algorithm has been a difficult task [27][28][29].…”

Non-linear, adaptive array processing for acoustic interference suppression

“…MVDR, for example, attempts to accomplish this by minimizing the variance of the beamformer output under a distortionless constraint. In cases where the bearing angle to an interferer is known, a fixed null beamformer 8,9 can be used to suppress contributions to the beamformer output from that specific direction. In most applications however, the locations of interfering sources are not known a priori.…”

Array signal processing techniques for broadband beamforming

“…The two-dimensional Fourier transform [62], weighted Chebyshev approximation [63], eigenfilters [64], second-order cone programming (SOCP) [65][66][67][68], vector space projections [69], and some other approaches [70][71][72], have been proposed to synthesize broadband beampatterns. References [73,74] are examples designing broadband beamformers with specified nulls.…”