Adaptive beamformer

About: Adaptive beamformer is a research topic. Over the lifetime, 4934 publications have been published within this topic receiving 93100 citations.

Main-Lobe Jamming Suppression Method of using Spatial Polarization Characteristics of Antennas

Abstract: As interferences are introduced from a main-lobe direction, which results in target signals being masked by interference, traditional adaptive beamforming and eigen-subspace projection methods cannot suppress main-lobe interferences effectively. A novel interference suppression method is proposed that processes the sample data by using the scanning property of a single polarized antenna. The orthogonal polarization decomposition and polarization estimation of the receiving signal based on the spatial polarization characteristics of the antenna are realized so that the interference is diminished. The effect of an elevation measurement error on interference suppression performance is eliminated by design spatial multinotch virtual polarization filtering. Theoretical and simulation results show that it made single polarized radar own a polarization information processing ability that improved radar working performance.

Advanced Beamformers for Cochlear Implant Users: Acute Measurement of Speech Perception in Challenging Listening Conditions

Abstract: Objective To investigate the performance of monaural and binaural beamforming technology with an additional noise reduction algorithm, in cochlear implant recipients. Method This experimental study was conducted as a single subject repeated measures design within a large German cochlear implant centre. Twelve experienced users of an Advanced Bionics HiRes90K or CII implant with a Harmony speech processor were enrolled. The cochlear implant processor of each subject was connected to one of two bilaterally placed state-of-the-art hearing aids (Phonak Ambra) providing three alternative directional processing options: an omnidirectional setting, an adaptive monaural beamformer, and a binaural beamformer. A further noise reduction algorithm (ClearVoice) was applied to the signal on the cochlear implant processor itself. The speech signal was presented from 0° and speech shaped noise presented from loudspeakers placed at ±70°, ±135° and 180°. The Oldenburg sentence test was used to determine the signal-to-noise ratio at which subjects scored 50% correct. Results Both the adaptive and binaural beamformer were significantly better than the omnidirectional condition (5.3 dB±1.2 dB and 7.1 dB±1.6 dB (p<0.001) respectively). The best score was achieved with the binaural beamformer in combination with the ClearVoice noise reduction algorithm, with a significant improvement in SRT of 7.9 dB±2.4 dB (p<0.001) over the omnidirectional alone condition. Conclusions The study showed that the binaural beamformer implemented in the Phonak Ambra hearing aid could be used in conjunction with a Harmony speech processor to produce substantial average improvements in SRT of 7.1 dB. The monaural, adaptive beamformer provided an averaged SRT improvement of 5.3 dB.

A novel adaptive beamformer for MEG source reconstruction effective when large background brain activities exist

Abstract: This paper proposes a novel prewhitening eigenspace beamformer suitable for magnetoencephalogram (MEG) source reconstruction when large background brain activities exist. The prerequisite for the method is that control-state measurements, which contain only the contributions from the background interference, be available, and that the covariance matrix of the background interference can be obtained from such control-state measurements. The proposed method then uses this interference covariance matrix to remove the influence of the interference in the reconstruction obtained from the target measurements. A numerical example, as well as applications to two types of MEG data, demonstrates the effectiveness of the proposed method

Shrinkage Linear and Widely Linear Complex-Valued Least Mean Squares Algorithms for Adaptive Beamforming

Abstract: In this paper, shrinkage linear complex-valued least mean squares (SL-CLMS) and shrinkage widely linear complex-valued least mean squares (SWL-CLMS) algorithms are devised for adaptive beamforming. By exploiting the relationship between the noise-free a posteriori and a priori error signals, the SL-CLMS method is able to provide a variable step size to update the weight vector for the adaptive beamformer, significantly enhancing the convergence speed and decreasing the steady-state misadjustment. On the other hand, besides adopting a variable step size determined by minimizing the square of the augmented noise-free a posteriori errors, the SWL-CLMS approach exploits the noncircular properties of the signal of interest, which considerably improves the steady-state performance. Simulation results are presented to illustrate their superiority over the CLMS, complex-valued normalized LMS, variable step size, recursive least squares (RLS) algorithms and their corresponding widely linear-based schemes. Additionally, our proposed algorithms are more computationally efficient than the RLS solutions though they may have a slightly slower convergence rate.

Beamforming With Dominant Mode Rejection

Abstract: High resolution adaptive beamforming of a spatial array of sensors has traditionally been formulated in terms of a minimum noise variance, distor tionless response (MVDR) optimality criterion . This approach results in a constrained spatial Wiener filter structure which requires the estimation and inversion of either the array space-time correlation matrix for time domain implementation or the array cross­ spectral density matrix (CSDM) for a frequency domain implementation 1. In the situation where the array acoustic environment consists of a limited number of dominant modes the full matrix inversion procedure is both numerically and statistically inadvisable. In this case, the technique of point source interference null steering can be generalized to the nulling of dominant modes without prior knowledge of the mode structure . In effect, a reduced rank version of the spatial Wiener filter is produced which is realized as a generalized mode nulling beamformer .