The Experts below are selected from a list of 30693 Experts worldwide ranked by ideXlab platform
A B Gershman - One of the best experts on this subject based on the ideXlab platform.
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on the relationship between robust minimum variance Beamformers with probabilistic and worst case distortionless response constraints
IEEE Transactions on Signal Processing, 2008Co-Authors: Sergiy A Vorobyov, H H Chen, A B GershmanAbstract:An interesting relationship between the probability-constrained and worst-case optimization based robust minimum variance (MV) Beamformers has been discovered. It is shown that both in the cases of circularly symmetric Gaussian and worst-case distributions of the steering vector mismatch, the probability-constrained robust MV beamforming problem can be tightly approximated as a convex second-order cone programming (SOCP) problem. The latter problem is mathematically equivalent to that resulting from the deterministic worst-case approach and, therefore, probability-constrained Beamformers can be interpreted and implemented using their deterministic worst-case counterparts. However, an important advantage of the developed probability-constrained MV Beamformers with respect to their standard worst-case counterparts is that the former approaches enable to explicitly quantify the parameters of the uncertainty region in terms of the beamformer outage probability.
Richard Langley - One of the best experts on this subject based on the ideXlab platform.
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fast communication subband design of fixed wideband Beamformers based on the least squares approach
Signal Processing, 2011Co-Authors: Yong Zhao, Wei Liu, Richard LangleyAbstract:Subband method is an effective way to reduce the computational complexity of a wideband system and in this paper we study the subband design problem for fixed wideband Beamformers, with an emphasis on the design of frequency invariant Beamformers (FIBs). We first express the equivalent fullband beam response as a function of the subband beamformer coefficients and then formulate the design problem based on the least squares approach. One direct least squares formulation is first proposed for the design of a general wideband beamformer, and then extended to the FIB design case, followed by three further variations.
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SINR Analysis of the Subtraction-Based SMI Beamformer
IEEE Transactions on Signal Processing, 2010Co-Authors: Wei Liu, Richard LangleyAbstract:The sample matrix inversion (SMI) beamformer suffers from performance degradation due to the finite sample size effect and the arrival angle mismatch problem. A simple technique to provide robustness to the conventional SMI beamformer is to block the desired signal from the received data before calculating the beamformer's weight vector, which leads to the subtraction-based SMI (S-SMI) beamformer. In this correspondence, closed-form approximations of the expected value of the signal-to-interference-plus-noise ratio (SINR) for the S-SMI beamformer and the SMI beamformer are derived, where the effect of both finite sample size and arrival angle mismatch are considered. Simulations show that the derived approximations are close enough to represent the true values of the SINR, when the sample size is small and the arrival direction mismatch exists.
Yee Hong Leung - One of the best experts on this subject based on the ideXlab platform.
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Broadband Beamformer Design
SpringerBriefs in Electrical and Computer Engineering, 2016Co-Authors: Chiong Ching Lai, Sven Nordholm, Yee Hong LeungAbstract:A beamformer is a spatial filter used to achieve spatial selectivity. However, it can be combined with a temporal filter to achieve both spatial and temporal selectivity. Such combined filter is essentially a multidimensional filter which is normally known as broadband beamformer. Broadband Beamformers are useful in applications involving acoustic signal, for examples, speech acquisition for personal computers, teleconferencing and built-in hands-free communication in vehicles. Various design methods can be applied to design broadband Beamformers. One such method is an optimisation-based approach where different optimisation criteria can be used to design beamformer weights for target applications. Typical beamformer designs are based on either nearfield or farfield source model, resulting in nearfield-only or farfield-only Beamformers. However, it is possible to generalise the design formulation to cover both nearfield and farfield cases, thus achieving mixed nearfield–farfield Beamformers, i.e. Beamformers that work for both nearfield and farfield sources simultaneously.
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Steerable Broadband Beamformer Design
SpringerBriefs in Electrical and Computer Engineering, 2016Co-Authors: Chiong Ching Lai, Sven Nordholm, Yee Hong LeungAbstract:The design formulation for fixed broadband Beamformers can be extended to steerable broadband Beamformers using a polynomial filter structure to achieve beam steering. The main advantage of a steerable broadband beamformer is that once its coefficients are designed, its main beam can still be steered dynamically without the need to redesign the beamformer weights. This feature is useful in applications where a desired signal source does not always remain fixed at a single spatial location, but is moving. These electronically steerable broadband Beamformers allow the main beam to be beamed and locked onto the same signal source even if it moves to another spatial location.
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design of steerable spherical broadband Beamformers with flexible sensor configurations
IEEE Transactions on Audio Speech and Language Processing, 2013Co-Authors: Chiong Ching Lai, Sven Nordholm, Yee Hong LeungAbstract:In broadband beamformer applications with dynamically moving sources, it can be important to have a simple mechanism to steer the main-beam. It can also be desirable if the beampattern of the beamformer is invariant to the look direction. A number of design methods for such Beamformers, based on the spherical harmonic transform, have been reported in the literature. However, these methods require the sensor positions to satisfy a certain condition which may conflict with practical considerations. This paper proposes a design method which obviates this restriction thus allowing for spherical arrays with arbitrary sensor configurations. Moreover, for a comparable level of performance and computational complexity to the existing spherical harmonic Beamformers, the proposed beamformer requires fewer sensors. The trade-off is that the design of the beamformer now depends on the sensor positions. Other considerations, such as the effects of array mis-orientation and robustness, are also discussed in this paper and illustrated by design examples.
Sergiy A Vorobyov - One of the best experts on this subject based on the ideXlab platform.
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on the relationship between robust minimum variance Beamformers with probabilistic and worst case distortionless response constraints
IEEE Transactions on Signal Processing, 2008Co-Authors: Sergiy A Vorobyov, H H Chen, A B GershmanAbstract:An interesting relationship between the probability-constrained and worst-case optimization based robust minimum variance (MV) Beamformers has been discovered. It is shown that both in the cases of circularly symmetric Gaussian and worst-case distributions of the steering vector mismatch, the probability-constrained robust MV beamforming problem can be tightly approximated as a convex second-order cone programming (SOCP) problem. The latter problem is mathematically equivalent to that resulting from the deterministic worst-case approach and, therefore, probability-constrained Beamformers can be interpreted and implemented using their deterministic worst-case counterparts. However, an important advantage of the developed probability-constrained MV Beamformers with respect to their standard worst-case counterparts is that the former approaches enable to explicitly quantify the parameters of the uncertainty region in terms of the beamformer outage probability.
Israel Cohen - One of the best experts on this subject based on the ideXlab platform.
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Combined Beamformers for robust broadband regularized superdirective beamforming
IEEE Transactions on Audio Speech and Language Processing, 2015Co-Authors: Reuven Berkun, Israel Cohen, Jacob BenestyAbstract:Superdirective fixed Beamformers are known to attain high directivity factors, but are extremely sensitive to uncorrelated noise and slight errors in the array elements, which are modeled by the beamformer white noise gain measure. The delay-and-sum beamformer, on the other hand, manages to maximize the white noise gain, but suffers from a very low directivity factor. In this paper, we discuss the design of a broadband beamformer which controls both the directivity factor and the white noise gain. We combine a regularized version of the superdirective beamformer together with the delay-and-sum beamformer to create a robust regularized superdirective beamformer. We derive analytic closed-form expressions of the beamformer gain responses, and extend them to derive a beamformer with full control of the desired white noise gain or the directivity factor. The proposed approach offers a simple and robust broadband beamformer with controllable characteristics, shown here through persuasive simulation results.
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low complexity addition or removal of sensors constraints in lcmv Beamformers
IEEE Transactions on Signal Processing, 2012Co-Authors: Shmulik Markovichgolan, Sharon Gannot, Israel CohenAbstract:We address the application of the linearly constrained minimum variance (LCMV) beamformer in sensor networks. In signal processing applications, it is common to have a redundancy in the number of nodes, fully covering the area of interest. Here we consider suboptimal LCMV Beamformers utilizing only a subset of the available sensors for signal enhancement applications. Multiple desired and interfering sources scenarios in multipath environments are considered. We assume that an oracle entity determines the group of sensors participating in the spatial filtering, denoted as the active sensors. The oracle is also responsible for updating the constraints set according to either sensors or sources activity or dynamics. Any update of the active sensors or of the constraints set necessitates recalculation of the beamformer and increases the power consumption. As power consumption is a most valuable resource in sensor networks, it is important to derive efficient update schemes. In this paper, we derive procedures for adding or removing either an active sensor or a constraint from an existing LCMV beamformer. Closed-form, as well as generalized sidelobe canceller (GSC)-form implementations, are derived. These procedures use the previous beamformer to save calculations in the updating process. We analyze the computational burden of the proposed procedures and show that it is much lower than the computational burden of the straightforward calculation of their corresponding Beamformers.
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The MVDR Beamformer for Speech Enhancement
Springer Topics in Signal Processing, 2010Co-Authors: Emanuel A P Habets, Jacob Benesty, Sharon Gannot, Israel CohenAbstract:The minimum variance distortionless response (MVDR) beamformer is widely studied in the area of speech enhancement and can be used for both speech dereverberation and noise reduction. This chapter summarizes some new insights into the MVDR beamformer. Specifically, the local and global behaviors of the MVDR beamformer are analyzed, different forms of the MVDR beamformer and relations between the MVDR and other optimal Beamformers are discussed. In addition, the tradeoff between dereverberation and noise reduction is analyzed. This analysis is done for a mixture of coherent and non-coherent noise fields and entirely non-coherent noise fields. It is shown that maximum noise reduction is achieved when the MVDR beamformer is used for noise reduction only. The amount of noise reduction that is sacrificed when complete dereverberation is required depends on the directto- reverberation ratio of the acoustic impulse response between the source and the reference microphone. The performance evaluation demonstrates the tradeoff between dereverberation and noise reduction.
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WASPAA - On the application of the LCMV beamformer to speech enhancement
2009 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, 2009Co-Authors: Emanuel A P Habets, Jacob Benesty, Patrick A. Naylor, Sharon Gannot, Israel CohenAbstract:In theory the linearly constrained minimum variance (LCMV) beamformer can achieve perfect dereverberation and noise cancellation when the acoustic transfer functions (ATFs) between all sources (including interferences) and the microphones are known. However, blind estimation of the ATFs remains a difficult task. In this paper the noise reduction of the LCMV beamformer is analyzed and compared with the noise reduction of the minimum variance distortionless response (MVDR) beamformer. In addition, it is shown that the constraint of the LCMV can be modified such that we only require relative transfer functions rather than ATFs to achieve perfect cancellation of coherent interferences. Finally, we evaluate the noise reduction performance achieved by the LCMV and MVDR Beamformers for two coherent sources: one desired and one undesired.