| 1. |
- 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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| 2. |
- Callmer, Jonas, et al.
(författare)
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Robust Heading Estimation Indoors using Convex Optimization
- 2013
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Ingår i: 2013 16TH INTERNATIONAL CONFERENCE ON INFORMATION FUSION (FUSION). - Linköping : Linköping University Electronic Press. - 9786058631113 ; , s. 1173-1179
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The problem of estimating heading is central in the indoor positioning problem based on mea- surements from inertial measurement and magnetic units. Integrating rate of turn angular rate gives the heading with unknown initial condition and a linear drift over time, while the magnetometer gives absolute heading, but where long segments of data are useless in prac- tice because of magnetic disturbances. A basic Kalman filter approach with outlier rejection has turned out to be difficult to use with high integrity. Here, we propose an approach based on convex optimization, where segments of good magnetometer data are separated from disturbed data and jointly fused with the yaw rate measurements. The optimization framework is flexible with many degrees of freedom in the modeling phase, and we outline one design. A recursive solution to the optimization is derived, which has a computational complexity comparable to the simplest possible Kalman filter. The performance is evaluated using data from a handheld smartphone for a large amount of indoor trajectories, and the result demonstrates that the method effectively resolves the magnetic disturbances.
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| 3. |
- Gunnarsson, Fredrik, et al.
(författare)
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Estimation of the Carrier-to-Interference Ratio in Cellular Radio Systems
- 1999
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Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780355652 ; , s. 1312-1316 vol.2
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.
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| 4. |
- Gustafsson, Fredrik, et al.
(författare)
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Asymptotic Power and the Benefit of Under-Modeling in Change Detection
- 1995
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Ingår i: Proceedings of the 3rd European Control Conference. - Linköping : Linköping University. ; , s. 1237-1242
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- It is well-known from experience that low order models perform well in change detection problems even if the true system is quite complicated. By computing the asymptotic power function, it is here shown that common hypothesis tests proposed in literature attain their maximum power for a low order model under certain conditions on how much each parameter change.
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| 5. |
- Gustafsson, Fredrik, et al.
(författare)
-
Blind Equalization by Direct Examination of the Input Sequences
- 1991
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The authors' approach to blind equalization examines the possible input sequences directly by using a bank of filters and, in contrast to common approaches, does not try to find an approximative inverse of the channel dynamics. The identifiability question of a noise-free finite impulse response (FIR) model is investigated. A sufficient condition for the input sequence (persistently exciting of a certain order) is given which guarantees that both the channel model and the input sequence can be determined exactly in finite time. A recursive algorithm is given for a time-varying infinite impulse response (IIR) channel model with additive noise, which does not require a training sequence. The estimated sequence is an arbitrarily good approximation of the maximum a posteriori estimate. The proposed method is evaluated on a Rayleigh fading communication channel. It shows fast convergence properties and good tracking ability.
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| 6. |
- Gustafsson, Fredrik, et al.
(författare)
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Closed Loop Performance Monitoring in the Presence of System Changes and Disturbances
- 1995
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Ingår i: Proceedings of the 3rd European Control Conference. - Linköping : Linköping University. ; , s. 453-458
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper addresses issues in closed loop performance monitoring. Particular attention is paid to detecting whether an observed deviation from nominal performance is due to a disturbance or due to a system change. This is achieved by introducing a novel performance measure that allows feasible application of a standard CUSUM change detector. The paper includes explicit results on the probability of mistaking a disturbance for a system change and demonstrates the algorithm with a simulation study.
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| 7. |
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| 8. |
- Hol, Jeroen, et al.
(författare)
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A New Algorithm for Calibrating a Combined Camera and IMU Sensor Unit
- 2008
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Ingår i: Proceedings of the 10th International Conference on Control, Automation, Robotics and Vision. - Linköping : Linköping University Electronic Press. - 9781424422876 - 9781424422869 ; , s. 1857-1862
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper is concerned with the problem of estimating the relative translation and orientation between an inertial measurement unit and a camera which are rigidly connected. The key is to realise that this problem is in fact an instance of a standard problem within the area of system identification, referred to as a gray-box problem. We propose a new algorithm for estimating the relative translation and orientation, which does not require any additional hardware, except a piece of paper with a checkerboard pattern on it. Furthermore, covariance expressions are provided for all involved estimates. The experimental results shows that the method works well in practice.
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| 9. |
- 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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| 10. |
- Ninness, Brett, et al.
(författare)
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A Unifying Construction of Orthonormal Bases for System Identification
- 1994
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Ingår i: Proceedings of the 33rd IEEE Conference on Decision and Control. - Linköping : Linköping University. - 0780319680 ; , s. 3388-3393 vol.4
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we develop a general and very simple construction for complete orthonormal bases for system identification. This construction provides a unifying formulation of all known orthonormal bases since the FIR, Laguerre and Kautz model structures are restrictive special cases of our construction as is another construction method based on balanced realisations of all-pass functions. However, in contrast to these special cases, the basis vectors in our unifying construction can have nearly arbitrary magnitude frequency response according to the prior information the user wishes to inject into the problem. We also provide results characterising the completeness properties of our bases.
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