| 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. |
- Wahlberg, Bo, et al.
(author)
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Robust Signal Parameter Estimation in the Presence of Array Perturbations
- 1991
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In: Proc. of 1991 International Conference on Acoustics, Speech, and Signal Processing, 1991. ICASSP-91.. - Linköping : IEEE. ; , s. 3277-3280
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Conference paper (peer-reviewed)abstract
- Signal parameter estimators which are less sensitive to perturbations in the array manifold are presented. A parametrized stochastic model for the array uncertainties is introduced. The unknown array parameters can include the individual gain and phase responses of the sensors as well as their positions. Based on this model, a maximum a posteriori (MAP) estimator is formulated. This results in a fairly complex optimization problem which is computationally expensive. The MAP estimator is simplified by exploiting properties of the weighted subspace fitting method. An approximate method that further reduces the complexity is also presented, assuming smallarray perturbations. A compact expression for the MAP Cramer-Rao bound (CRB) on the signal and arrayparameter estimates is derived. A simulation study indicates that the proposed robust estimation procedures achieve the MAP-CRB even for moderate sample sizes.
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| 3. |
- Eriksson, Anders, 1953-
(author)
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Derivatives of tangential stiffness matrices for equilibrium path descriptions
- 1991
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In: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 32:5, s. 1093-1113
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Journal article (peer-reviewed)abstract
- The paper describes how several procedures, based on expressions from analytical elastic stability theory, are introduced as numerical tools in a general Finite Element program for geometrically non-linear structural analysis. Especially is discussed how derivatives of the tangential stiffness matrix can be utilized in several contexts in the solution algorithm. These include improved predictions for the step-wise solution of equilibrium states, identification of critical points and accurate descriptions of initial post-bifurcation behaviour. For two plane beam and bar elements, formulations have been developed giving analytical expressions for these derivatives. The corresponding numerical approximations, needed in other element types, are also discussed. The paper discusses the relative efficiency of higher order predictions in relation to these different element types and different solution strategies. Some numerical examples, showing different types of behaviour, are analysed and discussed.
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| 4. |
- Eriksson, Anders, 1953-
(author)
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Fold lines for sensitivity analyses in structural instability
- 1994
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In: Computer Methods in Applied Mechanics and Engineering. - 0045-7825 .- 1879-2138. ; 114:1-2, s. 77-101
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Journal article (peer-reviewed)abstract
- The paper describes how a two-parameter formulation of a structural equilibrium problem can be used for a more accurate description of the occurring critical states. A fold line concept is used to evaluate the dependence of these states on an added variable, describing a disturbing load case or a disturbed geometry. The concept describes the local behaviour for small disturbances, but can also be used for parameter dependence analyses, e.g. in connection with optimization algorithms. Two different augmentations of the equilibrium relations are discussed; they describe the criticality of a solution state in different ways. Numerical adoption for a general equilibrium path following algorithm is discussed. A postponed factorization method for solution of the augmented sets of equations is proposed. Two simple examples are used to show the properties and the possibilities of the fold line concept. It is concluded that the suggested numerical procedure can give a better description of critical structural behaviour, especially with respect to imperfections in the structure and idealizations in the model. © 1994.
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| 5. |
- Eriksson, Anders, 1953-
(author)
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On a thin shell element for non-linear analysis, based on the isoparametric concept
- 1992
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In: Computers & structures. - 0045-7949 .- 1879-2243. ; 42:6, s. 927-939
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Journal article (peer-reviewed)abstract
- This paper discusses a finite element method model for the large displacement, moderate strain analysis of thin shells. The model is based on an 'adapted' reference configuration for a displaced element, separating the displacements into rigid body displacements and strain-producing deformations. A strategy is developed, making use of the isoparametric concept for both the choice of reference configuration and in the element formulation. This makes the use of arbitrarily shaped elements possible. The model is shown to give accurate results for a range of relevant problems. Some problems in the general application of this type of model are discussed. © 1992.
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| 6. |
- Eriksson, Anders, 1953-
(author)
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On accurate descriptions for primary and secondary paths in equilibrium problems
- 1992
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In: Computers & structures. - 0045-7949 .- 1879-2243. ; 44:1-2, s. 229-242
-
Journal article (peer-reviewed)abstract
- The paper describes how several procedures, based on ideas and expressions from the analytical elastic stability theory, have been introduced as numerical tools in a general finite element program for geometrically non-linear structural analysis. Derivatives of the tangential stiffness matrix are utilized for improved predictions in the step-wise solution of equilibrium states, for identification of critical points and for accurate descriptions of initial post-bifurcation behaviour. The methods are used in a general solution algorithm, based on a parameterizing component formulation. For some element types, analytical expressions for these derivatives can be developed. The corresponding numerical approximations, needed in other element types, are also discussed. Other practical details in the numerical implementation are given. Two numerical frame examples, showing different types of limit and bifurcation behaviours, are used to discuss the numerical properties of the methods. © 1992.
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| 7. |
- Eriksson, Anders, 1953-
(author)
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On improved predictions for structural equilibrium path evaluations
- 1993
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In: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 36:2, s. 201-220
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Journal article (peer-reviewed)abstract
- The paper describes how several procedures for higher-order predictions have been introduced in order to improve the convergence speed in a general finite element program for non-linear structural analysis. In addition to higher-order Taylor expansions earlier discussed, Lagrangian extrapolations and some methods commonly used for the integration of initial value problems have been introduced. The methods are used for improved predictions in the stepwise solution of equilibrium states and for accurate descriptions of the initial post-bifurcation behaviour. They are used in a general solution algorithm, based on a parameter formulation. The methods are discussed in the light of the strategies for re-creation of the tangential stiffness matrix, used for equilibrium iterations. Numerical examples, exhibiting different limit and bifurcation behaviours for trusses, frames and shells, are used to evaluate the numerical properties and efficiencies of the methods. The paper concludes that the overall efficiency in the algorithm can be improved by introduction of more accurate predictions than the standard Euler prediction. In terms of reliability combined with efficiency, an implicit generalized Simpson method is the preferred method.
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| 8. |
- 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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| 10. |
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