| 1. |
- Bergquist, Bjarne, et al.
(författare)
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A Bayesian analysis of unreplicated two-level factorials using effects sparsity, hierarchy, and heredity
- 2011
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Ingår i: Quality Engineering. - : Informa UK Limited. - 0898-2112 .- 1532-4222. ; 23:2, s. 152-166
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Tidskriftsartikel (refereegranskat)abstract
- This article proposes a Bayesian procedure to calculate posterior probabilities of active effects for unreplicated two-level factorials. The results from a literature survey are used to specify individual prior probabilities for the activity of effects and the posterior probabilities are then calculated in a three-step procedure where the principles of effects sparsity, hierarchy, and heredity are successively considered. We illustrate our approach by reanalyzing experiments found in the literature.
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| 2. |
- Birk, Wolfgang, et al.
(författare)
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Project: iRoad
- 2011
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Annan publikation (populärvet., debatt m.m.)
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| 3. |
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| 4. |
- Hostettler, Roland, et al.
(författare)
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A system identification approach to modeling of wave propagation in pavements
- 2012
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Ingår i: 16th IFAC Symposium on System Identification. - : IFAC, International Federation of Automatic Control. - 9783902823069 ; , s. 292-297
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Konferensbidrag (refereegranskat)abstract
- In this paper, modeling of the pavement as a wave propagation medium and estimation of the corresponding model parameters is approached from a system identification perspective. A model based on the physical background is proposed and the corresponding parameters are then estimated from measurement data. In order to achieve the latter, two estimators are proposed, their performance evaluated, and then applied to the measurement data. It is found that the proposed methods are applicable and the results show that different eigenmodes of the structure are excited.
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| 5. |
- Hostettler, Roland, et al.
(författare)
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Extended Kalman filter for vehicle tracking using road surface vibration measurements
- 2013
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Ingår i: IEEE 51st Annual Conference on Decision and Control. - Piscataway, NJ : IEEE Communications Society. - 9781467320658 - 9781467320641
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Konferensbidrag (refereegranskat)abstract
- This paper addresses a novel method for vehicle tracking using an extended Kalman filter and measurements of road surface vibrations from a single accelerometer. First, a measurement model for vibrations caused by vehicular road traffic is developed. Then the identifiability of the involved parameters is analyzed. Finally, the measurement model is combined with a constant speed motion model and the Kalman filter is derived. Simulation and measurement results indicate that the approach is feasible and show where further development is needed.
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| 6. |
- Hostettler, Roland, et al.
(författare)
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Feasibility of road vibrations-based vehicle property sensing
- 2010
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Ingår i: IET Intelligent Transport Systems. - : Institution of Engineering and Technology (IET). - 1751-956X .- 1751-9578. ; 4:4, s. 356-364
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Tidskriftsartikel (refereegranskat)abstract
- This article discusses a novel approach to vehicle property sensing based on traffic-induced road surface vibrations and investigates the feasibility of this approach. Road surface vibrations from real-life experiments are acquired using three-axis accelerometers and the data are analysed. Based on the assessment of the data, a first coarse scheme for axle detection of passing vehicles is developed. The scheme is then evaluated using measurement data from a highway with moderate traffic intensity but diverse traffic. It is found that the proposed approach is feasible and the estimation scheme yields promising results. Furthermore, delimitations, encountered problems and identified research challenges are discussed and future research directions are given.
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| 7. |
- Hostettler, Roland, et al.
(författare)
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The pavement as a waveguide: modeling, system identification, and parameter estimation
- 2014
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 63:8, s. 2052-2063
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents modeling of wave propagation in pavements from a system identification point of view. First, a model based on the physical structure is derived. Second, experiment design and evaluation are discussed and maximum-likelihood estimators for estimating the model parameters are introduced, assuming an error-in-variables setting. Finally, the proposed methods are applied to measurement data from two experiments under varying environmental conditions. It is found that the proposed methods can be used to estimate the dispersion curves of the considered waveguide and the results can be used for further analysis
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| 8. |
- Isoz, Oscar
(författare)
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Interference detection and localization in the GPS L1 frequency band
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of Global Navigation Satellite Systems (GNSS) in general and the American GPS in particular increases everyday and so does the number of applications where it is used. The GNSS receivers relies on receiving signals from satellites orbiting the earth at an altitude of about 20 000 km and the signals received by the receiver are signicantly weaker then the background noise. Due to the weak signals it is fairly easy to intentionally or accidentally make it very hard or even impossible for a receiver to detect and track the satellites.With this in mind there is a need to develop cost eective methods to detect and localize interference so that appropriate counter measures can be taken. A number of methods have been proposed to detect and localize these sources. The complexity of these methods ranges from requiring future cellphones to contain software to monitor the GNSS environment to dedicated systems with multiple antennas and complicated hardware. In this thesis, two complementary methods will be presented which can detect and also localize interference in the GNSS bands using minimum amount of equipment. The equipment is based around a type of GNSS "receiver" that only samples the GNSS frequency so that it can be processed using a software dened GNSS eceiver. It will be shown that it is capable of detecting and localizing interference sources while also be cost eective and easily deployable. The rst technique is based on measuring the received power level. Since the GNSS signals are below the noise oor, the number of visible satellites will not aect the received power level. Instead the received power level will be aected by changes in the spectrum and changes in the receiver hardware. The GNSS signal is fairly robust against interference so an interferer usually has to have a signicantly higher signal power than the received power from the satellites in order to cause problems for the receiver. By monitoring the received signal power using multiple receivers it is possible to both detect interference and estimate the position of the transmitter. This method requires very little bandwidth but since the signal is measured in the analog domain it is sensitive to process variations between dierent receivers. Also, the nonlinear behaviour of the analog components in the receiver limits the accuracy of the position estimations. To improve the accuracy of the interference localization, a second method has been evaluated. In this method the GNSS samples recorded by dierent receivers at different locations is compared. When a GNSS receiver calculates a position it is actually calculating the time it takes for the signals to travel from the satellite to the receiver. This made it possible to synchronize data from multiple independent receivers both in time and frequency and then estimate the time dierence of arrival of the interfering signal between the dierent receivers. Both localization methods were evaluated during experiments done with assistance from the Swedish armed forces research agency (FOI). It will be shown that the signal power measurement can be used as a detector for interference and that the GPS signal can be used to synchronize data from independent stations so that the dierence in distance to a wideband transmitter can be estimated. To determine the amount of interference in the GPS L1 band two measurement campaigns were made. The rst campaign, measured where interference might be present in an urban area using a car mounted receiver. The other campaign took place at two airports in the summer and fall of 2011 and measured the interference level from xed antennas over an extended period of time.All research was done using the GPS L1 signal but the methods can easily be applied to other GNSS signals as well.
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| 9. |
- Johansson, Gustav, et al.
(författare)
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Simulation of post-ADC digital beamforming for large aperture array radars
- 2010
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 45:RS3001
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.
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| 10. |
- Lin, Jing, et al.
(författare)
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Bayesian survival analysis in reliability for complex system with a cure fraction
- 2011
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Ingår i: International Journal of Performability Engineering. - 0973-1318. ; 7:2, s. 109-120
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Tidskriftsartikel (refereegranskat)abstract
- In traditional methods for reliability analysis, one complex system is often considered as being composed by some subsystems in series. Usually, the failure of any subsystem would be supposed to lead to the failure of the entire system. However, some subsystems' lifetimes are long enough and even never fail during the life cycle of the entire system. Moreover, such subsystems' lifetimes will not be influenced equally under different circumstances. In practice, such interferences will affect the model's accuracy, but it is seldom considered in traditional analysis. To address these shortcomings, this paper presents a new approach to do reliability analysis for complex systems. Here a certain fraction of the subsystems is defined as a "cure fraction" under the consideration that such subsystems' lifetimes are long enough and even never fail during the life cycle of the entire system. By introducing environmental covariates and the joint power prior, the proposed model is developed within the Bayesian survival analysis framework, and thus the problem for censored (or truncated) data in reliability tests can be resolved. In addition, a Markov chain Monte Carlo computational scheme is implemented and a numeric example is discussed to demonstrate the proposed model
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| 11. |
- Lin, Jing, et al.
(författare)
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Spares demand system with consideration of integration management and optimization
- 2011
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Ingår i: 2011 International Conference on Mechanical, Industrial, and Manufacturing Engineering. - 9780983169314 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- Inventory management differs from other manufacturing inventory managements, mainly due to its specialists in function with maintenance. So far, enormous attention has been paid by standing on spares’ manufacturingfactories, sales companies, end users’ purchasing departments, or maintenance engineers, separately. However, not only “bullwhip effect” in forecasting spares demands, but also deteriorated relationships among the spares supply chains have shown that, spares optimization strategies with isolated consideration couldonly bring short-term or partial improvements. In this paper, the spares demand system with consideration of integration management is promoted, the new Solid-Net relationships among four main components are elaborated. Then, the root causes of ineffective in spares demand system are analyzed. Also, distinctoptimization policies are illustrated. What’s more, successful stories in practice are cited.
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| 12. |
- Ling, Jun, et al.
(författare)
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Efficient channel equalization for MIMO underwater acoustic communications
- 2010
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Ingår i: 2010 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM). - Piscataway, NJ : IEEE Communications Society. - 9781424489787 - 9781424493951 ; , s. 73-76
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Konferensbidrag (refereegranskat)abstract
- Linear minimum mean-squared error (LMMSE)-based channel equalization is widely used in multi-input multioutput (MIMO) underwater acoustic communications (UAC). The practical challenge of LMMSE based schemes is the necessity of matrix inversion which generally imposes heavy computational burden on the receiver. To obtain the LMMSE filters efficiently, we exploit the conjugate gradient method and the diagonalization properties of circulant matrices. The proposed scheme is based on fast Fourier transform operations and can be implemented in parallel, which makes it a promising candidate for real-time MIMO underwater acoustic communications. Both numerical and SPACE'08 experimental examples are presented to demonstrate the effectiveness of the proposed approach.
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| 13. |
- Ling, Jun, et al.
(författare)
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Multi-input multi-output underwater communications over sparse and frequency modulated acoustic channels
- 2011
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 130:1, s. 249-262
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses multi-input multi-output (MIMO) communications over sparse acoustic channels suffering from frequency modulations. An extension of the recently introduced SLIM algorithm, which stands for sparse learning via iterative minimization, is presented to estimate the sparse and frequency modulated acoustic channels. The extended algorithm is referred to as generalization of SLIM (GoSLIM). The sparseness is exploited through a hierarchical Bayesian model, and because GoSLIM is user parameter free, it is easy to use in practical applications. Moreover this paper considers channel equalization and symbol detection for various MIMO transmission schemes, including both space-time block coding and spatial multiplexing, under the challenging channel conditions. The effectiveness of the proposed approaches is demonstrated using in-water experimental measurements recently acquired during WHOI09 and ACOMM10 experiments.
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| 14. |
- Ling, Jun, et al.
(författare)
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On Bayesian channel estimation and FFT-based symbol detection in MIMO underwater acoustic communications
- 2014
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Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 39:1, s. 59-73
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Tidskriftsartikel (refereegranskat)abstract
- Reliable channel estimation and effective interference cancellation are essential for enhancing the performance of multiple-input-multiple-output (MIMO) underwater acoustic communication (UAC) systems. In this paper, an efficient user-parameter-free Bayesian approach, referred to as sparse learning via iterative minimization (SLIM), is presented. SLIM provides good channel estimation performance along with reduced computational complexity compared to iterative adaptive approach (IAA). Moreover, RELAX-BLAST, which is a linear minimum mean-squared error (MMSE)-based symbol detection scheme, is implemented efficiently by making use of the conjugate gradient (CG) method and diagonalization properties of circulant matrices. The proposed algorithm requires only simple fast Fourier transform (FFT) operations and facilitates parallel implementations. These MIMO UAC techniques are evaluated using both simulated and in-water experimental examples. The 2008 Surface Processes and Acoustic Communications Experiment (SPACE08) experimental results show that the proposed MIMO UAC schemes can enjoy almost error-free performance even under severe ocean environments.
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| 15. |
- Lundberg Nordenvaad, Magnus, et al.
(författare)
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A map based estimator for inverse complex covariance matricies
- 2012
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Ingår i: 2012 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). - 1520-6149. - 9781467300469 ; , s. 3369-3372
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Konferensbidrag (refereegranskat)abstract
- A novel approach to estimate (inverse) complex covariance matrices is proposed. By considering the class of unitary invariant estimators, the main challenge lies in estimating the underlying eigenvalues from sampled versions. By exploiting that the distribution of the sample eigenvalues can be derived in closed form, a Maximum A Posteriori (MAP) based scheme is then derived. The performance of the derived estimator is simulated and results indicate that the proposed scheme shows performance similar to one of the best estimators known to date. The main advantage lies in that the proposed solution only requires numerical optimization over a P-dimensional space where P is the size of the covariance matrix.
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| 16. |
- Lundberg Nordenvaad, Magnus, et al.
(författare)
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Broadband synchronization of underwater acoustic communication signals using superimposed pilots
- 2012
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Ingår i: OCEANS, 2012 - YEOSU. - 9781457720918
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Konferensbidrag (refereegranskat)abstract
- A low-complex methodology to synchronize broadband underwater acoustic channels is proposed. The aim of the scheme is to process the received signal in such a way that the highly time-varying discrete-time channel turns time-invariant. Suggested is an LMS-like strategy based on superimposed pilots. Simulations on realistic models show that the proposed scheme is able to maintain very stable channel properties throughout long data frames. This indicates that the derived strategy is a highly attractive component for various underwater communication applications as channel variation is often the limiting factor in system performance.
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| 17. |
- Nordenvaad, Magnus Lundberg
(författare)
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A hierarchical approach to noise-adaptive estimation
- 2010
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Ingår i: 2010 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM). - Piscataway, NJ : IEEE Communications Society. - 9781424493951 - 9781424493951 ; , s. 161-164
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Konferensbidrag (refereegranskat)abstract
- This paper presents a noise-adaptive estimator for the linear model. The strategy is based on a hierarchical approach where in each step, a decreasing number of unbiased estimates for the parameter of interest is produced. In this way, the complexity is greatly reduced compared to standard estimators, like the adaptive maximum likelihood (AML) estimator. Also, since the method combines solutions to sub-problems of smaller dimensionality, the required size of the noise training data set is also reduced. As a result, the derived scheme performs better than AML for small sample support. The results are verified by simulations and show that the derived scheme is a very appropriate choice for a large class of problems with high dimensionality.
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| 18. |
- Svensson, Lennart, 1976, et al.
(författare)
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The Reference Prior for Complex Covariance Matrices With Efficient Implementation Strategies
- 2010
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Ingår i: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 58:1, s. 53-66
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Tidskriftsartikel (refereegranskat)abstract
- The paper derives the reference prior for complex covariance matrices. The reference prior is a noninformative prior that circumvents some of the weaknesses of common alternatives in multidimensional settings. As a consequence, inference based on this prior renders well-behaving solutions that in many cases outperform traditionally used approaches. The main obstacle is that inference based on this prior require integration over high-dimensional spaces which have no closed form solutions. A focus of the paper is therefore to discuss efficient implementation strategies based on Markov chain Monte Carlo methods. It is identified that certain structures can be treated analytically both for the case where the parameter of interest is the covariance matrix itself but also for cases in which the covariance matrix is a nuisance parameter that characterizes noise color. Evaluation in both these settings also verify the superior performance obtained by using the proposed prior as compared to traditional techniques to treat unknown covariance matrices.
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