3 results for Abdulla, WH

  • Effects of Imperfect Secondary Path Modeling on Adaptive Active Noise Control Systems

    Tabatabaei Ardekani, I; Abdulla, WH (2011)

    Journal article
    The University of Auckland Library

    Implementation of adaptive active noise control (ANC) systems requires an estimate model of the secondary path to be uploaded onto digital control hardware. In practice, this model is not necessarily perfect; however, to avoid mathematical difficulties, theoretical analysis of these systems is usually conducted for a perfect secondary path model. This paper conducts a stochastic analysis on performance of Filtered-x LMS (FxLMS)-based ANC systems when the actual secondary path and its model are not identical. This analysis results in a number of mathematical expressions, describing effects of a general secondary path model on stability, steady-state performance and convergence speed of FxLMS-based ANC systems. As a surprising result, it is found that intentional misadjustment of secondary path models can enhance performance of ANC systems in practice. Theoretical results are found to be in a good agreement with the results obtained from numerical analysis. Also, experimental results confirm the validity and accuracy of the theoretical results.

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  • Filtered weight FxLMS adaptation algorithm: Analysis, design and implementation

    Tabatabaei Ardekani, Iman; Abdulla, WH (2011-11)

    Journal article
    The University of Auckland Library

    In the Filtered-x Least-Mean-Square (FxLMS)-based Active Noise Control (ANC), the convergence speed of the adaptation process has a direct relationship to a scalar parameter, called the step size. There is a theoretical upper-bound for the step size beyond which the system becomes unstable. However, the step size is usually set to a number smaller than its upper-bound in practice. This is because for relatively large step sizes, the adaptation process becomes very sensitive to any non-stationary change in acoustic noise. Owing to this trade-off, real-time implementation of high-performance ANC systems becomes challenging. To overcome this problem, this paper develops a novel ANC algorithm in which a recursive filter compensates for influences of the step size increase on the system performance. It is shown that this filter can efficiently increase the step size upper-bound; consequently, the performance of the system is improved. This improvement is demonstrated using computer simulation. Also, experimental results shows the preference of the proposed algorithm to the traditional FxLMS-based ANC algorithm in practice.

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  • On the convergence of real-time active noise control systems

    Tabatabaei Ardekani, Iman; Abdulla, WH (2011-05)

    Journal article
    The University of Auckland Library

    Available convergence analyses of adaptive active noise control systems apply to only theoretical cases with broad-band white noise or pure delay secondary paths. In order to investigate convergence behaviors of these systems in more practical conditions, this paper conducts a new convergence analysis for filtered-x LMS-based active noise control systems with band-limited white noise and moving average secondary paths. A linear model for the adaptation process is developed. Based on this model, the upper-bound of the adaptation step-size is derived. Also, the adaptation step-size leading to the fastest convergence rate is derived. In addition to the computer simulation, a fully implemented real time active noise control system is used to verify the validity of the analytical results.

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