| 1. |
- Bodin, Per, et al.
(författare)
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A frequency response estimation method based on smoothing and thresholding
- 1998
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Ingår i: International Journal of Adaptive Control and Signal Processing. - 0890-6327 .- 1099-1115. ; 12:5, s. 407-416
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Tidskriftsartikel (refereegranskat)abstract
- A standard approach for estimating the frequency function of a linear dynamical system is to use spectral estimation. Traditionally, this is done by smoothing the noisy frequency data using linear filters. The method has proved to be successful in most cases and is widely used. However, if the frequency response has fine details appearing only locally in frequency, the loss of resolution caused by smoothing might result in unacceptable errors. In this paper, a different method for frequency response estimation is suggested. The method utilizes recently proposed wavelet-based denoising schemes combined with traditional smoothing techniques. The wavelet transform is applied in the frequency domain in order to provide a suitable frequency window. Tested through simulations, this approach provides an alternative when traditional methods fail.
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| 2. |
- Bodin, Per, et al.
(författare)
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Algorithm for selection of best orthonormal rational basis
- 1997
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - San Diego, CA, USA. ; , s. 1277-1282
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Konferensbidrag (refereegranskat)abstract
- This contribution deals with the problem of structure determination for generalized orthonormal basis models used in system identification. The model structure is parameterized by a pre-specified set of poles. Given this structure and experimental data a model can be estimated using linear regression techniques. Since the variance of the estimated model increases with the number of estimated parameters, the objective is to find structures that are as compact/parsimonious as possible. A natural approach would be to estimate the poles, but this leads to nonlinear optimization with possible local minima. In this paper, a best basis algorithm is derived for the generalized orthonormal rational bases. Combined with linear regression and thresholding this leads to compact transfer function representations.
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| 4. |
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| 5. |
- Carlemairn, Catharina, et al.
(författare)
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Low complexity parameter estimation approach for fast time-delay estimation
- 1997
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Ingår i: Decision and Control, 1997., Proceedings of the 36th IEEE Conference on. ; , s. 1603-1608
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Konferensbidrag (refereegranskat)abstract
- Presents algorithms for time-delay estimation based on a parametric approach. The suggested methods combine an exhaustive search with a low complexity since they do not require filtering or correlation computations. Consequently, the problems with local minima of gradient search algorithms are avoided. The proposed detection schemes are experimentally verified by way of computer simulations. Furthermore, receiver operator characteristics are presented
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| 6. |
- Carlemalm, Catharina, et al.
(författare)
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Algorithms for time delay estimation using a low complexity exhaustive search
- 1999
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Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 44:5, s. 1031-1037
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the problem of time-delay estimation. Two new algorithms for time-delay estimation are developed and analyzed. The suggested methods combine an exhaustive search with a low complexity. Consequently, the problems with local minima of gradient search algorithms are avoided. The receiver operating characteristics (ROC) are computed, and together with simulation results these verify the performance of the estimation schemes.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Gustafsson, Fredrik, 1964-, et al.
(författare)
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Blind Equalization by Direct Examination of the Input Sequences
- 1995
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Ingår i: IEEE Transactions on Communications. - Linköping : Linköping University. - 0090-6778 .- 1558-0857. ; 43:7, s. 2213-2222
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a novel approach to blind equalization (deconvolution), which is based on direct examination of possible input sequences. In contrast to many other approaches, it does not rely on a model of the approximative inverse of the channel dynamics. To start with, the blind equalization identifiability problem for a noise-free finite impulse response channel model is investigated. A necessary condition for the input, which is algorithm independent, for blind deconvolution is derived. This condition is expressed in an information measure of the input sequence. A sufficient condition for identifiability is also inferred, which imposes a constraint on the true channel dynamics. The analysis motivates a recursive algorithm where all permissible input sequences are examined. The exact solution is guaranteed to be found as soon as it is possible. An upper bound on the computational complexity of the algorithm is given. This algorithm is then generalized to cope with time-varying infinite impulse response channel models with additive noise. The estimated sequence is an arbitrary good approximation of the maximum a posteriori estimate. The proposed method is evaluated on a Rayleigh fading communication channel. The simulation results indicate fast convergence properties and good tracking abilities.
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| 11. |
- Gustafsson, Fredrik, et al.
(författare)
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On the Problem of Detection and Discrimination of Double Talk and Change in the Echo Path
- 1996
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Ingår i: Proceedings of the 1996 IEEE International Conference on Acoustics, Speech and Signal Processing. - 0780331923 ; , s. 2742-2745 vol.5
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Konferensbidrag (refereegranskat)abstract
- The problem of detection and discrimination of double talk and change in the echo path in a telephone channel is considered. The phenomenon echo path change requires fast adaptation of the channel model to be able to equalize the echo dynamics. On the other hand, the adaption rate should be reduced when double talk occurs. Thus, it is critical to quickly detect a change in the echo path while not confusing it with double talk, which gives a similar effect. The proposed likelihood based approach compares a global channel model with a local one over a sliding window, both estimated with the recursive least squares algorithm.
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| 12. |
- Halvarsson, Susanne, et al.
(författare)
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Test statistics for low complexity change detection in dynamic systems based on averaged filter models
- 1996
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - Atlanta, GA, USA : IEEE. - 0780331923 ; , s. 2845-2848
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new method to detect and discriminate between abrupt changes in dynamics and sudden changes in disturbance levels in dynamic systems. It is assumed that a normalized least mean square (NLMS) adaptive filter estimates the system. The detection method is based on the observation that the estimated taps behave differently in the two studied events. The convergence behavior of the taps is modeled using averaging theory, giving an exponential convergence behavior for each tap. Kalman filtering techniques, based on this model, are then used in order to design a new detection scheme.
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| 13. |
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| 14. |
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| 15. |
- Homer, John, et al.
(författare)
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Improved LMS Estimation via Structural Detection
- 1995
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Ingår i: Information Theory, 1995. Proceedings., 1995 IEEE International Symposium on.
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In various adaptive estimation applications, the unknown channel is characterized by an impulse response which consists of extended regions of negligible response or `inactivity'. We consider the LMS estimation of a channel that may be well approximated by an FIR (filter) model with only a few nonzero tap coefficients within a given delay horizon or tap length n. When the number of nonzero tap coefficients m is small compared to the delay horizon n, the performance of the LMS estimator is greatly enhanced when this specific structure is exploited. We propose a consistent algorithm that performs identification of nonzero taps only
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| 16. |
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| 17. |
- Viberg, Mats, et al.
(författare)
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Analysis of state space system identification methods based on instrumental variables and subspace fitting
- 1997
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Ingår i: Automatica. - 0005-1098 .- 1873-2836. ; 33:9, s. 1603-1616
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Tidskriftsartikel (refereegranskat)abstract
- Subspace-based state-space system identification (4SID) methods have recently been proposed as an alternative to more traditional techniques for multivariable system identification. The advantages are that the user has simple and few design variables, and that the methods have robust numerical properties and relatively low computational complexities. Though subspace techniques have been demonstrated to perform well in a number of cases, the performance of these methods is neither fully understood nor analyzed. Our principal objective is to undertake a statistical investigation of subspace-based system identification techniques. The studied methods consist of two steps. The subspace spanned by the extended observability matrix is first estimated. The asymptotic properties of this subspace estimate are derived herein. In the second step, the structure of the extended observability matrix is used to find a system model estimate. Two possible methods are considered. The simplest one only uses a certain shift-invariance property, while in the other method a parametric representation of the null-space of the observability matrix is exploited. Explicit expressions for the asymptotic estimation error variances of the corresponding pole estimates are given.
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| 18. |
- Wahlberg, Bo, 1959-, et al.
(författare)
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On approximation of stable linear dynamical systems using Laguerre and Kautz functions
- 1996
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 32:5, s. 693-708
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Tidskriftsartikel (refereegranskat)abstract
- Approximation of stable linear dynamical systems by means of so-called Laguerre and Kautz functions, which are the Laplace transforms of a class of orthonormal exponentials, is studied. Since the impulse response of a stable finite dimensional linear dynamical system can be represented by a sum of exponentials (times polynomials), it seems reasonable to use basis functions of the same type. Assuming that the transfer function of a system is bounded and analytic outside a given disc, it is shown that Laguerre basis functions are optimal in a mini-max sense. This result is extended to the "two-parameter" Kautz functions which can have complex poles, while the poles of Laguerre functions are restricted to the real axis. By conformal mapping techniques the "two-parameter" Kautz approximation problem is recast as two Laguerre approximation problems. Thus, the well-developed theory of Laguerre functions can be applied to analyze Kautz approximations. Unilateral shifts are used to further develop the connection between Laguerre functions and Kautz functions. Results on H2 and H∞ approximation using Kautz models are given. Furthermore, the weighted L2 Kautz approximation problem is shown to be equivalent to solving a block Toeplitz matrix equation.
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| 19. |
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| 20. |
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| 21. |
- Zhao, Yimin, et al.
(författare)
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Comments on "Experimental and theoretical comparison of some algorithms for beamforming in single receiver adaptive arrays" [with reply]
- 1995
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Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 43, s. 1348-1349
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Tidskriftsartikel (refereegranskat)abstract
- B.G. Wahlberg, I.M.Y. Mareels, and I. Webster (see ibid., vol.39, no.1, p.21, 1991) present a simple algorithm to estimate the covariance matrix by perturbing the weights W. Zhao and Ju point out that section II of the paper contains two errors. The basic error is in equation (17). This leads to errors in equation (18). Wahlberg et al. reply to the Comments.
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