Topic
Adaptive beamformer
About: Adaptive beamformer is a research topic. Over the lifetime, 4934 publications have been published within this topic receiving 93100 citations.
Papers published on a yearly basis
Papers
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TL;DR: This paper utilizes multiple small uncertainty sets, instead of using a single large set, to cover the whole large uncertainty region, and results indicate that the proposed method offers a significant performance improvement in case of large steering vector mismatch.
25 citations
21 Mar 2004
TL;DR: It is shown, however, that the adaptive modulation based approach is too sensitive to channel estimation errors and that its performance is worse than the adaptive frequency-domain power allocation approach under imperfect CSI.
Abstract: Dynamic resource allocation combined with adaptive antenna arrays at both the transmitter and receiver can achieve further QoS improvement in conventional OFDM systems. In this paper, we propose two different dynamic resource allocation algorithms with adaptive beamforming for MIMO/OFDM systems and investigate their performance over multipath fading channels under perfect and imperfect CSI. These proposed approaches involve the use of adaptive modulation and adaptive frequency-domain power allocation. By employing this proposed methodology, significant performance improvement can be achieved as compared to the conventional adaptive antenna arrays based on OFDM systems. It is shown, however, that the adaptive modulation based approach is too sensitive to channel estimation errors and that its performance is worse than the adaptive frequency-domain power allocation approach under imperfect CSI.
25 citations
TL;DR: The proposed adaptive beamforming schemes for orthogonal frequency-division multiplexing (OFDM) communication systems are shown to be suitable in scenarios of narrow angular spread with exponential power delay profile.
Abstract: In this paper, we propose adaptive beamforming schemes for orthogonal frequency-division multiplexing (OFDM) communication systems. After applying the discrete-Fourier-transform operation to the output of each antenna, one estimates the signal-plus-interference spatial correlation matrix by selecting the samples at ldquononzero-valuedrdquo subcarriers and the interference-alone spatial correlation matrix by choosing those samples at ldquozero-valuedrdquo subcarriers (also known as virtual carriers). The beamforming weight vector is the ldquolargestrdquo generalized eigenvector of the resulting matrix pencil, wherein the solution is computed in a batch fashion. By using a limited number of samples, the proposed scheme offers competitive performance compared with that of the scheme using optimal beamforming weight vectors that are calculated for each subcarrier under small-angular-spread scenarios. The adaptive solution for calculating the beamforming weight vector is also derived. The proposed schemes are shown to be suitable in scenarios of narrow angular spread with exponential power delay profile. The simulations that are presented here employ the OFDM signal model to illustrate the efficacy of the proposed algorithms.
25 citations
TL;DR: Generally, although the noise-reduction performance of the system is degraded by target misalignment and modest reverberation, the system still provides positive advantage at input target-to-jammer ratios up to about 0 dB, in contrast to the degrading target-cancellation effect.
Abstract: We describe the results of computer simulations of a multimicrophone adaptive-beamforming system as a noise reduction device for hearing aids. Of particular concern was the system's sensitivity to violations of the underlying assumption that the target signal is identical at the microphones. Two-and four-microphone versions of the system were tested in simulated anechoic and modestly-reverberant environments with one and two jammers, and with deviations from the assumed straight-ahead target direction. Also examined were the effects of input target-to-jammer ratio and adaptive-filter length. Generally, although the noise-reduction performance of the system is degraded by target misalignment and modest reverberation, the system still provides positive advantage at input target-to-jammer ratios up to about 0 dB. This is in contrast to the degrading target-cancellation effect that the system can have when the equal-target assumption is violated and the input target-to-jammer ratio is greater than zero.
25 citations
TL;DR: An extension of the method described in Leshem, 2000, is developed which eliminates pattern-distortion-induced PSD bias and spatial response errors over the long-term PSD averaging window and will enable PSD estimation using multi-antenna sensors and adaptive interference cancellation for radio astronomy, remote sensing, and other sensitive radiometry applications where cancellation has not been feasible.
Abstract: We address the issue of computing power spectral density (PSD) estimates at the output of a beamforming sensor array in the presence of strong moving interference. It is shown that the time-varying spatial response of an adaptive beamformer (ldquopattern rumblerdquo) causes estimation bias in the PSD of both the signal of interest (SOI) and noise. In applications such as radio astronomy with stringent sensitivity requirements, even small pattern variations can be problematic because the resulting higher variance noise spectrum estimates make it impossible to detect signals of interest which are many decibels below the noise floor. Distortion in beam mainlobe shape also introduces errors in SOI direction estimates. To overcome this problem, an extension of the method described in Leshem , 2000, is developed which eliminates pattern-distortion-induced PSD bias and spatial response errors over the long-term PSD averaging window. Both simulated and real data experiments demonstrate algorithm effectiveness in realizing an undistorted effective (average) beam spatial response while maintaining a low noise floor level. This algorithm will enable PSD estimation using multi-antenna sensors and adaptive interference cancellation for radio astronomy, remote sensing, and other sensitive radiometry applications where cancellation has not been feasible.
25 citations