| 1. |
- Andersson, Sören, et al.
(author)
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An adaptive array for mobile communication systems
- 1991
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In: IEEE Transactions on Vehicular Technology. - Toronto, Ont, Can : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 40:1 pt 2, s. 230-236, s. 3289-3292
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Journal article (peer-reviewed)abstract
- The use of adaptive antenna techniques to increase the channel capacity is discussed. Directional sensitivity is obtained by using an antenna array at the base station, possibly both in receiving and transmitting modes. A scheme for separating several signals at the same frequency is proposed. The method is based on high-resolution direction-finding followed by optimal combination of the antenna outputs. Comparison with a method based on reference signals is made. Computer simulations are carried out to test the applicability of the technique to scattering scenarios that typically arise in urban areas. The proposed scheme is found to have great potential in rejecting cochannel interference, albeit at the expense of high computational requirements.
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| 2. |
- Gunnarsson, Svante, et al.
(author)
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Some asymptotic results in recursive identification using Laguerre models
- 1990
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In: Proceedings of the IEEE Conference on Decision and Control. - Honolulu, HI, USA : Linköping University. ; , s. 1068-1073
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Conference paper (peer-reviewed)abstract
- Frequency domain expressions for the quality of recursively identified Laguerre models are presented. These models generalize finite impulse response (FIR) models by using a priori information about the dominating time constants of the system to be identified. Expressions for the model quality are derived under the assumptions that the system varies slowly, that the model is updated slowly, and that the model order is high. The model quality is evaluated by investigating the properties of the estimated transfer function, and explicit expressions for the mean square error (MSE) of the transfer function, and explicit expressions for the mean square error of the transfer function estimate are derived.
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| 3. |
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| 4. |
- Viberg, Mats, et al.
(author)
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A statistical perspective on state-space modeling using subspace methods
- 1991
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In: Proceedings of the 30th IEEE Conference on Decision and Control. - Linköping : Linköping University. - 0780304500 ; , s. 1337-1342
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Conference paper (peer-reviewed)abstract
- The authors investigate aspects of subspace-based state-space identification techniques from a statistical perspective. They concentrate their efforts on a simple approach which is based on finding the range-space of the observability matrix of a state-space representation. The system description is then found using the shift-invariance property of the observability matrix. It is shown that this results in a consistent system description for multivariable output-error models if the measurement noise is white in time and independent from output to output. The asymptotic covariance of the estimated poles of the system is also derived. In the test case studied, the subspace technique performs comparably with the statistically efficient PE (prediction error) method, whereas the IV (instrumental variable) method does notably worse. Hence, the subspace technique may be a strong candidate for determining initial values for the optimization in the efficient PE method.
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| 5. |
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| 6. |
- Wahlberg, Bo, 1959-
(author)
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Identification of resonant systems using Kautz filters
- 1991
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In: Proceedings of the 30th IEEE Conference on Decision and Control Part 1 (of 3). - Linköping : Linköping University. - 0780304500 ; , s. 2005-2010
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Conference paper (peer-reviewed)abstract
- It is pointed out that by approximating the impulse response of a linear time-invariant stable system by a finite sum of given exponentials, the problem of estimating the transfer function is considerably simplified. The author shows how the complexity can be reduced further by using orthogonalized exponentials. The analysis is based on the result that the corresponding normal equations will then have a Toeplitz structure. The z-transform of orthogonalized exponentials corresponds to discrete Kautz functions, which generalize discrete Laguerre functions to the several, possibly complex, poles case. Hence, by appropriate choice of time constants Kautz models give low-order useful approximations of many systems of interest. In particular, resonant systems can be well approximated using Kautz models with complex poles. Several basic results on transfer function estimation are extended to discrete Kautz models, for example, frequency-domain quality properties and efficient numerical techniques.
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| 7. |
- Gunnarsson, Svante, et al.
(author)
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Some asymptotic results in recursive identification using Laguerre models
- 1991
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In: International Journal of Adaptive Control and Signal Processing. - : Wiley. - 0890-6327 .- 1099-1115. ; 5:5, s. 313-333
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Journal article (peer-reviewed)abstract
- This paper deals with recursive identification of time-varying systems using Laguerre models. Laguerre models generalize finite impulse response (FIR) models by using a priori information about the dominating time constants of the system to be identified. Three recursive algorithms are considered: the stochastic gradient algorithm, the recursive least squares algorithm and a Kalman-filter-like recursive identification algorithm. Simple and explicit expressions for the model quality are derived under the assumptions that the system varies slowly, that the model is updated slowly and that the model order is high. The derived expressions show how the use of Laguerre models affects the model quality with respect to tracking capability and disturbance rejection.
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| 8. |
- Gustafsson, Fredrik, et al.
(author)
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Blind Equalization by Direct Examination of the Input Sequences
- 1992
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In: Proceedings of the 1992 IEEE International Conference on Acoustics, Speech and Signal Processing. - 0780305329 ; , s. 701-704 vol.4
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Conference paper (peer-reviewed)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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| 9. |
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| 10. |
- Homer, John, et al.
(author)
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LMS Estimation of Sparsely Parametrized Channels via Structural Detection
- 1994
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In: Proceedings of the 33rd IEEE Conference on Decision and Control. - 0780319680 ; , s. 257-262 vol.1
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Conference paper (peer-reviewed)abstract
- Considers the LMS estimation of “long” channels which have time domain impulse responses consisting of sparsely spaced nonzero taps or groups of taps. Standard LMS estimation of such long sparsely parametrized channels, in which all taps are estimated, suffers from poor transient and/or asymptotic performance. Analyses carried out by the authors indicate that performance improvements can be achieved by estimating only those taps which are nonzero or “active”. The authors develop a simple procedure, based on the least squares method, which for sufficiently large N (the number of sample intervals) detects the correct number and position of active taps. Using this structure detection procedure the authors propose an LMS based estimation algorithm. Simulations indicate that this “LMS-structure detection” algorithm provides considerable performance improvement over the standard LMS algorithm.
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