| 1. |
- Akcay, H., et al.
(författare)
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On the choice of norms in system identification
- 1996
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Ingår i: IEEE Transactions on Automatic Control. - Linköping : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286. ; 41:9, s. 1367-1372
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we discuss smooth and sensitive norms for prediction error system identification when the disturbances are magnitude bounded. Formal conditions for sensitive norms, which give an order of magnitude faster convergence of the parameter estimate variance, are developed. However, it also is shown that the parameter estimate variance convergence rate of sensitive norms is arbitrarily bad for certain distributions. A necessary condition for a norm to be statistically robust with respect to the family F(C) of distributions with support [-C, C] for some arbitrary C > 0 is that its second derivative does not vanish on the support. A direct consequence of this observation is that the quadratic norm is statistically robust among all ℓp-norms, p ≀ 2 < ∞ for F(C). ©1996 IEEE.
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| 2. |
- Andersson, Mats T., et al.
(författare)
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Controllable 3-D Filters for Low Level Computer Vision
- 1993
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Ingår i: SCIA8. - Linköping, Sweden : Linköping University, Department of Electrical Engineering.
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional data processing is becoming more and more common. Typical operations are for example estimation of optical flow in video sequences and orientation estimation in 3-D MR images. This paper proposes an efficient approach to robust low level feature extraction for 3-D image analysis. In contrast to many earlier algorithms the methods proposed in this paper support the use of relatively complex models at the initial processing steps. The aim of this approach is to provide the means to handle complex events at the initial processing steps and to enable reliable estimates in the presence of noise. A limited basis filter set is proposed which forms a basis on the unit sphere and is related to spherical harmonics. From these basis filters, different types of orientation selective filters are synthesized. An interpolation scheme that provides a rotation as well as a translation of the synthesized filter is presented. The purpose is to obtain a robust and invariant feature extraction at a manageable computational cost.
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| 3. |
- Andersson, Torbjörn, et al.
(författare)
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Estimation of Residence Time in Continuous Flow Systems with Dynamics
- 1994
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Ingår i: Proceedings of the 10th IFAC Symposium on System Identification. - Linköping : Linköping University. ; , s. 401-406
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Konferensbidrag (refereegranskat)abstract
- A method for estimation of residence time in continuous flow systems with varying dynamics is presented. By resampling, i.e., choosing time instants different from the given sampling instants, and interpolation between measured data points, we obtain a continuous flow system with constant residence time expressed in the new resampled time vector. We assume the flow patterns in the systems are invariant. The new data set is then used for identification of parameters in a chosen model structure. From the identified model, the residence time is readily calculated and a procedure for that is briefly described. The presented method is readily extended to enable use in recursive identification. In that case, however, as an improvement of tracking ability of an ordinary recursive routine.
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| 4. |
- Andersson, Torbjörn, et al.
(författare)
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Identification Aspects of Inter-Sample Input Behavior
- 1994
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Ingår i: Proceedings of the 10th IFAC Symposium on System Identification. - Linköping : Linköping University. - 9780080422251 ; , s. 137-142
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Konferensbidrag (refereegranskat)abstract
- In this contribution aspects of inter-sample input signal behavior are examined. The starting point is that parametric identification always is performed on basis of discrete-time data. This is valid for identification of discrete-time models as well as continuous-time models. The usual assumptions on the input signal are; i) it is band-limited, ii) it is piecewise constant or iii) it is piecewise linear. One point made in this paper is that if a discrete-time model is used, the best possible (in the model structure) adjustment to data is made. This is independent of the assumption on the input signal. However, a transformation of the obtained discrete model to a continuous one is not possible without additional assumptions on the input signal. The other point made is that the frequency functions of the discrete models very well coincides with the frequency functions of the discretized continuous time models and the continuous time transfer function fitted in the frequency domain.
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| 5. |
- Axehill, Daniel, et al.
(författare)
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A Low-Complexity High-Performance Preprocessing Algorithm for Multiuser Detection using Gold Sequences
- 2008
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Ingår i: IEEE Transactions on Signal Processing. - Linköping : IEEE Signal Processing Society. - 1053-587X .- 1941-0476. ; 56:9, s. 4377-4385
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Tidskriftsartikel (refereegranskat)abstract
- The optimum multiuser detection problem can be formulated as a maximum likelihood problem, which yields a binary quadratic programming problem to be solved. Generally this problem is NP-hard and is therefore hard to solve in real time. In this paper, a preprocessing algorithm is presented which makes it possible to detect some or all users optimally for a low computational cost if signature sequences with low cross correlation, e.g., Gold sequences, are used. The algorithm can be interpreted as, e.g., an adaptive tradeoff between parallel interference cancellation and successive interference cancellation. Simulations show that the preprocessing algorithm is able to optimally compute more than 94,% of the bits in the problem when the users are time-synchronous, even though the system is heavily loaded and affected by noise. Any remaining bits, not computed by the preprocessing algorithm, can either be computed by a suboptimal detector or an optimal detector. Simulations of the time-synchronous case show that if a suboptimal detector is chosen, the bit error rate (BER) rate is significantly reduced compared with using the suboptimal detector alone.
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| 6. |
- Axholt, Magnus, et al.
(författare)
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Optical See-Through Head Mounted Display : Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise
- 2010
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Ingår i: Proceedings of the 54th Annual Meeting of the Human Factors and Ergonomics Society. - Linköping : Linköping University Electronic Press. - 9780945289371
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Konferensbidrag (refereegranskat)abstract
- The correct spatial registration between virtual and real objects in optical see-through augmented reality implies accurate estimates of the user’s eyepoint relative to the location and orientation of the display surface. A common approach is to estimate the display parameters through a calibration procedure involving a subjective alignment exercise. Human postural sway and targeting precision contribute to imprecise alignments, which in turn adversely affect the display parameter estimation resulting in registration errors between virtual and real objects. The technique commonly used has its origin incomputer vision, and calibrates stationary cameras using hundreds of correspondence points collected instantaneously in one video frame where precision is limited only by pixel quantization and image blur. Subsequently the input noise level is several order of magnitudes greater when a human operator manually collects correspondence points one by one. This paper investigates the effect of human alignment noise on view parameter estimation in an optical see-through head mounted display to determine how well astandard camera calibration method performs at greater noise levels than documented in computer vision literature. Through Monte-Carlo simulations we show that it is particularly difficult to estimate the user’s eyepoint in depth, but that a greater distribution of correspondence points in depth help mitigate the effects of human alignment noise.
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| 7. |
- Bauer, Dietmar
(författare)
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On Data Preprocessing for Subspace Methods
- 2000
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Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control. - Linköping : IEEE. - 0780366387 ; , s. 2403-2408
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Konferensbidrag (refereegranskat)abstract
- In modern data analysis often the first step is to perform some data preprocessing, e.g. detrending or elimination of periodic components of known period length. This is normally done using least squares regression. Only afterwards black box models are estimated using either pseudo-maximum-likelihood methods, prediction error methods or subspace algorithms. In this paper it is shown, that for subspace methods this is essentially the same as including the corresponding input variables, e.g. a constant or a trend or a periodic component, as additional input variables. Here essentially means, that the estimates only dier through the choice of initial values.
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| 8. |
- Bauer, Dietmar, et al.
(författare)
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Subspace Algorithm Cointegration Analysis - an Application to Interest Rate Data
- 2000
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Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 0780366387 ; , s. 146-151
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Konferensbidrag (refereegranskat)abstract
- In this paper the application of so called subspace methods for the specication and estimation of cointegrated systems is examined. This method, which is based on the state space representation, is suited for the analysis of general cointegrated systems of order one, i.e. is not limited to autoregressive models, as is e.g. Johansen's method. To assess the empirical usefulness of the method we apply it to perform a cointegration analysis of the US term structure of interest rates.
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| 9. |
- Björkman, Mattias, et al.
(författare)
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A New Concept for Motion Control of Industrial Robots
- 2008
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Ingår i: Proceedings of the 17th IFAC World Congress. - Linköping : Linköping University Electronic Press. - 9783902661005
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Konferensbidrag (refereegranskat)abstract
- This paper gives a short summary of an industrial development work on model-based motion control. This development has resultet in high robot motion performance simultaneously with an efficient use of the installed drive system of the robot.
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| 10. |
- Blom, Jonas, et al.
(författare)
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Pole Placement Design of Power Control Algorithms
- 1999
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Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780355652
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Konferensbidrag (refereegranskat)abstract
- Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.
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