Generalized Sidelobe Canceller Structure Research Articles

Deep neural network-based generalized sidelobe canceller for dual-channel far-field speech recognition

The traditional generalized sidelobe canceller (GSC) is a common speech enhancement front end to improve the noise robustness of automatic speech recognition (ASR) systems in the far-field cases. However, the traditional GSC is optimized based on the signal level criteria, causing it not to guarantee the optimal ASR performance. To address this issue, we propose a novel dual-channel deep neural network (DNN)-based GSC structure, called nnGSC, which is optimized by using the objective of maximizing the ASR performance. Our key idea is to make each module of the traditional GSC fully learnable and use the acoustic model to perform joint optimization with GSC. We use the coefficients of the traditional GSC to initialize nnGSC, so that both traditional signal processing knowledge and large amounts of data can be used to guide the network learning. In addition, nnGSC can automatically track the target direction-of-arrival (DOA) frame-by-frame without the need for additional localization algorithms. In the experiments, nnGSC achieves a relative character error rate (CER) improvement of 23.7% compared to the microphone observation, 13.5% compared to the oracle direction-based super-directive beamformer, 12.2% compared to the oracle direction-based traditional GSC and 5.9% compared to the oracle mask-based minimum variance distortionless response (MVDR) beamformer. Moreover, we can improve the robustness of nnGSC against array geometry mismatches by training with multi-geometry data.

Low-Complexity Reduced-Dimension Space–Time Adaptive Processing for Navigation Receivers

In this paper, we propose a low-complexity adaptive reduced-rank interference suppression scheme based on alternating low-rank decomposition techniques for navigation receivers. The proposed scheme, which employs a generalized sidelobe canceler structure, makes use of a projection matrix for rank reduction followed by a reduced-dimension receive filter. An alternating optimization strategy based on recursive least squares is devised to compute the basis vectors of the projection matrix and the receive filter adaptively. Simulation results show that the proposed algorithm achieves a better performance than existing methods with a reduced computational complexity.

Reduced-dimension space-time adaptive processing with sparse constraints on beam-Doppler selection

Abstract State-of-the-art space-time adaptive processing (STAP) algorithms devised in the beam-Doppler domain are confined by fixing the beam-Doppler cells used for adaptation, which may suffer from performance degradation. To overcome this drawback, a novel STAP algorithm in the beam-Doppler domain is proposed. The proposed algorithm adopts a generalized sidelobe canceller structure, and the filter design is formulated as a sparse representation problem by imposing a sparse constraint on the weight vector. As the sparse constraint enforces most of the elements in the weight vector to be zero (or sufficiently small in amplitude), the proposed algorithm can adaptively select the best beam-Doppler cells for adaptation, and thus it falls under the category of reduced-dimension approach. Simulation results illustrate that the proposed algorithm outperforms the existing STAP approaches with fixed beam-Doppler localized processing.

An alternative to diagonal loading for implementation of a white noise array gain constrained robust beamformer

Diagonal loading is one of the most popular methods of robust adaptive beamforming, and the solution to many different problems aimed at producing beamformers which are robust to finite samples effects or/and steering vector errors. Among the latter, constraining the white noise array gain (WNAG) is a meaningful approach. However, relating the loading level to the desired WNAG is not straightforward. In this communication, using a generalized sidelobe canceler structure of the beamformer, we prove that the WNAG constraint can be encoded directly in the beamformer, and the latter can be obtained in a rather simple way from a specific eigenvector and without going through the diagonal loading step.

Broadband Adaptive Beamforming of Conformal Arrays for Wireless Communications Based on Generalized Sidelobe Canceller

Conformal arrays are increasingly used in recent wireless communication systems due to their flexibility in mounting on arbitrary surfaces. Many of such systems require working with broadband signals. However, designing conformal arrays has been limited mostly to pattern synthesis techniques due to the complexity imposed by the different contribution of individual antenna patterns to the overall array response. Such pattern synthesis techniques greatly confine the application of the beamformer in dynamic environments since they are fundamentally non-adaptive data independent methods. In this article, the conventional space–time broadband generalized sidelobe canceller (GSC) is used to develop an adaptive method for an arbitrarily-shaped conformal array. The constraint matrix assumed for the main beam of the conventional GSC structure is modified to incorporate the pattern of each individual element. This treatment allows the element responses to be directly involved in the weight adjustment algorithm and contribute to the array overall response without having any additional complexity. The proposed method can handle different types of the constraints, although the analysis presented here is based on the angle–frequency domain constraints which nevertheless eliminates the presence of the pre-steering delays and ensures a frequency invariant beampatterm required for wideband beamforming. The simulation results which are presented for a typical cylindrical array show that the proposed method can create the desired broadband beampattern with high performance and in an adaptive manner.

Adaptive Widely Linear Constrained Constant Modulus Reduced-Rank Beamforming

We propose a blind adaptive reduced-rank widely linear beamforming algorithm using the generalized sidelobe canceller structure for interference suppression. A structured Krylov-subspace-based approach is devised to construct the dimensionality reducing transformation matrix, and a recursive least-squares algorithm is developed according to the widely linear constrained constant modulus criterion to update the reduced-rank filter. We analyze the convergence and complexity of the proposed algorithm and validate its performance gains through simulations.

Adaptive set membership constant modulus algorithm with a generalized sidelobe canceler based on dynamic bounds for beamforming

In this study, we propose an adaptive set membership constant modulus (SM-CM) algorithm with a generalized sidelobe canceler (GSC) structure for blind beamforming. We develop a stochastic gradient (SG) type algorithm based on the concept of SM filtering to facilitate an adaptive implementation. The filter weights are updated only if the constraint cannot be satisfied. In addition, we also propose an extension of two schemes of time-varying bounds for beamforming with a GSC structure where we incorporate parameter and interference dependency to characterize the environment, which improves the tracking performance of the proposed algorithm in dynamic scenarios. A convergence analysis of the proposed adaptive SM filtering technique was performed. The simulation results showed that the proposed adaptive SM-CM-GSC algorithm with dynamic bounds delivered superior performance compared with previously reported methods and at a reduced update rate.

A Low Complexity 1D-Based Successive GSC Structure for 2D Adaptive Beamformer Implementation

In this study, we propose a one dimensional (1D) based successive generalized sidelobe canceller (GSC) structure for the implementation of 2D adaptive beamformers using a uniform rectangular antenna array (URA). The proposed approach takes advantage of the URA feature that the 2D spatial signature of the receive signal can be decomposed into an outer product of two 1D spatial signatures. The 1D spatial signatures lie in the column and the row spaces of the receive signal matrix, respectively. It follows that the interferers can be successively eliminated by two rounds of 1D-based GSC structure. As compared to the conventional 2D-GSC structure, computer simulations show that in addition to having significantly low computational complexity, the proposed adaptive approach possesses higher convergence rate.

Low‐complexity robust adaptive generalized sidelobe canceller detector for DS/CDMA systems

AbstractA novel low computational complexity robust adaptive blind multiuser detector, based on the minimum output energy (MOE) detector with multiple constraints and a quadratic inequality (QI) constraint is developed in this paper. Quadratic constraint has been a widespread approach to improve robustness against mismatch errors, uncertainties in estimating the data covariance matrix, and random perturbations in detector parameters. A diagonal loading technique is compulsory to achieve the quadratic constraint where the diagonal loading level is adjusted to satisfy the constrained value. Integrating the quadratic constraint into recursive algorithms seems to be a moot point since there is no closed‐form solution for the diagonal loading term. In this paper, the MOE detector of DS/CDMA system is implemented using a fast recursive steepest descent adaptive algorithm anchored in the generalized sidelobe canceller (GSC) structure with multiple constraints and a QI constraint on the adaptive portion of the GSC structure. The Lagrange multiplier method is exploited to solve the QI constraint. An optimal variable loading technique, which is capable of providing robustness against uncertainties and mismatch errors with low computational complexity is adopted. Simulations for several mismatch and random perturbations scenarios are conducted in a rich multipath environment with near–far effect to explore the robustness of the proposed detector. Copyright © 2008 John Wiley & Sons, Ltd.

A Pilot Assisted Beamforming Scheme with Interference Resistant Angle of Arrival Estimation for OFDM Systems

In this paper, we propose an angle of arrival (AOA)-based beamforming structure with strong interference resistant capability for OFDM systems. First, we present novel interference resistant angle of arrival (AOA) estimation schemes for each multipath without training sequences or symbols as the pre-processing of the proposed structure. The generalized sidelobe canceler (GSC) structure is thus applied with the AOA information to avoid calculating the beamforming weight vector individually on a per subcarrier basis, wherein the GSC structure with the reduced-rank multistage Wiener filter (MSWF) is adopted. We also propose a signal transformation scheme to improve performance before the signals are fed into the GSC receiver. The proposed receiver offers better performance than the GSC form of the constrained Wiener filter-based receiver due to the faster convergence property of reduced rank processing and the signal transformation scheme.

A robust adaptive generalized sidelobe canceller with decision feedback

Conventional generalized sidelobe canceller (GSC) is sensitive to a mismatch between the estimated and actual direction of arrival (DOA) of the desired signal. Such a mismatch induces signal cancellation in the GSC, and it severely degrades the beamforming performance. In this paper, we propose a new decision feedback (DF) technique to increase the robustness against the DOA mismatch. Our new scheme introduces a blind equalizer and a feedback filter in the GSC structure. We first derive Wiener solutions for the DF-GSC with perfectly matched and mismatched DOA and show that the problem of signal cancellation can be avoided. Then, we consider the adaptive GSC implementation in which the least-mean-square (LMS) algorithm is used for weight adaptation. In addition to the improved robustness, the proposed scheme also remedies the slow convergence problem inherent in the conventional adaptive GSC structure. The convergence behavior of the LMS-based DF-GSC is fully analyzed and the analytic signal-to-interference-plus-noise ratio (SINR) is also derived. Finally, simulation results demonstrate that while the proposed structure can considerably enhance the overall performance, it has greatly improved robustness as compared to other existing robust adaptive beamformers.

A Decision Aided CDMA Receiver with Partially Adaptive DecorrelatingMulti-User Interference Cancellation

A CDMA receiver with enhanced multiple access interference (MAI) suppression is proposed for a pilot symbols assisted system over multipath channels. The design of the receiver involves the following procedure. First, blind adaptive correlators are constructed at different fingers based on the scheme of generalized sidelobe canceller (GSC) to collect the multipath signals and suppress MAI. A low-complexity partially adaptive (PA) realization of the GSC correlators is proposed which incorporates multi-user information for reduced rank processing. By a judiciously designed decorrelating procedure, a new GSC structure is obtained in which the MAI are decorrelated and suppressed individually. The next step is then a simple coherent combining of the correlator outputs with pilot aided channel estimation. Finally, further performance enhancement is achieved by an iterative scheme in which the signal is reconstructed and subtracted from the GSC correlators input data, leading to faster convergence of the receiver. The proposed low-complexity PA CDMA multi-user receiver is shown to be robust to multipath fading and channel errors, and achieve nearly the same performance of the ideal maximum SINR and MMSE receivers by using a small number of pilot symbols.

Adaptive H∞ robust beamforming for imperfect antenna array

The inherent robustness of the H ∞ algorithm in dealing with modeling disturbances is used to improve the performance of imperfect antenna array with the generalized sidelobe canceller structure. The modeling disturbances include sensor gain perturbation, initial condition error, and colored noise contamination. The influence of modeling disturbances, which is not involved in the recursive least squares (RLS) algorithm, is lumped into the estimation error minimization of the adaptive H ∞ algorithm. Thus, an H ∞-based beamformer converges faster and is more robust to imperfect antenna array than an RLS-based beamformer. Computer simulation results have been provided to show the robustness feature of the proposed technique when applied to an imperfect antenna array.

The constrained conjugate gradient algorithm

Based on the condition for equivalence between linearly constrained minimum-variance (LCMV) filters and their generalized sidelobe canceler (GSC) implementations, we derive the new constrained conjugate gradient (CCG) algorithm. We discuss the use of orthogonal and nonorthogonal blocking matrices for the GSC structure and how the choice of this matrix may affect the relationship with the LCMV counterpart. The newly derived algorithm was tested in a computer experiment for adaptive multiuser detection and showed excellent results.

A robust generalized sidelobe canceller with a blocking matrix using leaky adaptive filters

A new robust generalized sidelobe canceller structure suited to adaptive microphone arrays is proposed. In the proposed structure, the blocking matrix incorporates leaky adaptive filters whose input signals are the output of the fixed beamformer. The leaky adaptive filters alleviate the influence of phase error, which results in the robustness. Undesirable target-signal cancellation is avoided in the presence of array imperfections such as target-direction error and microphone-position error. The proposed structure can pick up a target signal with little distortion when the error in the sight direction from the target direction is large. It can be implemented with a small number of microphones. Simulations demonstrate that the proposed structure, designed to allow 20° directional error, reduces interference by more than 18 dB. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(8): 56–65, 1997

An effective quiescent pattern control strategy for GSC structure

A new quiescent pattern control strategy for the generalized sidelobe canceller (GSC) structure is presented. The synthesis technique is based on the constrained optimization algorithm with a penalty function used to design the quiescent array. The proposed quiescent array beampattern is highly directional with which an effective cancellation of multiple interference signals can be achieved. The design technique also permits the adaptive dimension of the GSC to be reduced significantly while preserving the quiescent beampattern. Numerical results showed that the new GSC structure is able to reject strong directional interference as compared to the full processor.

Effect of random weight errors on the performance of partially adaptive array beamformers

This paper analyzes the effect of random weight errors on the performance of array beamformers with partial adaptivity. Based on the structure of the generalized sidelobe canceller (GSC), three different beamformers, namely, element space, eigenspace, and beam space partially adaptive beamformers are considered. Theoretical formulas representing the beamformer's performance sensitivity to random errors of the adaptive weights are derived. These formulas show that the performance sensitivity to the random weight errors increases as the number of the adaptive weight increases in each case of the three different beamformers. Furthermore, we find that the choice of the signal blocking matrix required in the GSC structure also affects the performance of the array beamformers in the presence of random weight errors. Computer simulations confirming the theoretical analyses are provided. In dieser Arbeit wird die Answirkung zufälliger Gewichtsfehler auf die Wirkungsweise von Arrays mit partieller Adaptivität untersucht. Basierend auf der Struktur der verallgemeinerten Auslöschung von Nebenmaxima werden drei verschiedene Strahlformer betrachtet: Elementraum-, Eigenraum- und Strahlraumformer mit teilweiser Adaptivität. Theoretische Formeln für die Empfindlichkeit bezüglich zufälliger Fehler der adaptiven Gewichte werden abgeleitet. Sie zeigen, daβ die Empfindlichkeit bzgl. der zufälligen Gewichtsfehler mit steigender Zahl der adaptiven Gewichte in allen drei Fällen zunimmt. Weiterhin zeigt es sich, daβ die benötigte Signalblockmatrix ebenfalls die Wirkungsweise des Strahlformers beeinfluβt, falls zufällige Gewichtsfehler vorliegen. Rechnersimulationen, die die theoretischen Untersuchungen bestätigen, werden präsentiert. Cet article analyse l'effet d'erreurs de pondération aléatoires sur les performances de formateurs de voie en réseau à adaptativité partielle. Sur la bas de la structure de l'annulateur de lobe secondaire généralisé (GSC) trois formateurs de voie différents, à savoir les formateurs partiellement adaptatifs dans l'espace des éléments, dans l'espace propre, et dans l'espace de voie sont considérés. Nous dérivons des formules théoriques représentant la sensibilité des performances du formateur de voie vis-à-vis d'erreurs aléatoires dans les coefficients de pondération adaptatifs. Ces formules montrent que la sensibilité des performances vis-à-vis des erreurs de pondération aléatoires augmente lorsque le nombre de coefficients de pondération adaptif augmente dans les trois cas de formateur envisagés. De plus, nous montrons que le choix de la matrice de signal bloquante requise dans la structure GSC affecte également les performances des formateurs vis-à-vis des erreurs de pondération aléatoires. Nous fournissons des résultats de simulation confirmant les analyses théoriques.

Broad-band beamforming and the generalized sidelobe canceller

This correspondence identifies general conditions under which the generalized sidelobe canceller (GSC) structure implements a linearly constrained minimum variance (LCMV) broad-band beam-former. In previously published work, conditions have been presented for the case in which the linear constraint is restricted to fixed gain in the steer direction. Here, that work is extended to include general linear constraints. A geometric interpretation is presented to provide insight into the relationship between the GSC structure and LCMV beamformers, and several recent developments in broad-band beam-forming are reviewed and related to the GSC structure.