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Ahlén, Anders
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Publications (10 of 63) Show all publications
Olofsson, T. & Ahlén, A. (2018). Computing probability density functions of compound distributions: A comparative investigation. In: : . Paper presented at IEEE International COnference on Communications, ICC, Kansas City, USA.
Open this publication in new window or tab >>Computing probability density functions of compound distributions: A comparative investigation
2018 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-363239 (URN)
Conference
IEEE International COnference on Communications, ICC, Kansas City, USA
Available from: 2018-10-15 Created: 2018-10-15 Last updated: 2018-10-15
Biswas, S., Knorn, S., Dey, S. & Ahlén, A. (2018). Quantized non-Bayesian quickest change detection with energy harvesting. In: : . Paper presented at IEEE Globecom2018 SPC.
Open this publication in new window or tab >>Quantized non-Bayesian quickest change detection with energy harvesting
2018 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-363299 (URN)
Conference
IEEE Globecom2018 SPC
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2018-10-16
Herman, I., Knorn, S. & Ahlén, A. (2017). Disturbance scaling in bidirectional vehicle platoons with different asymmetry in position and velocity coupling. Automatica, 82, 13-20
Open this publication in new window or tab >>Disturbance scaling in bidirectional vehicle platoons with different asymmetry in position and velocity coupling
2017 (English)In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 82, p. 13-20Article in journal (Refereed) Published
Abstract [en]

This paper considers a string of vehicles where the local control law uses the states of the vehicle's immediate predecessor and follower. The coupling towards the preceding vehicle can be chosen different to the coupling with the following vehicle, which is referred to as an asymmetric bidirectional string. Further, the asymmetry for the velocity coupling can be chosen differently to the asymmetry in the position coupling. It is investigated how the effect of the disturbance on the control errors in the string depends on the string length. It is shown, that in case of symmetric position coupling and asymmetric velocity coupling, linear scaling can be achieved. For symmetric interactions, the errors scale quadratically in the number of vehicles. When the coupling in position is asymmetric, exponential scaling may occur or the system might even become unstable. The paper thus gives a comprehensive overview of the achievable performance in linear, asymmetric, bidirectional platoons. The results reveal that symmetry in the position coupling and asymmetry in velocity coupling qualitatively improve the performance of the string. Extensive numerical results illustrate the theoretical findings.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
Keywords
Port-Hamiltonian systems, Vehicular platoons, Multi-vehicle systems, Scaling, Asymmetry
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-328962 (URN)10.1016/j.automatica.2017.04.010 (DOI)000403984300002 ()
Available from: 2017-09-12 Created: 2017-09-12 Last updated: 2017-09-12Bibliographically approved
Leong, A. S., Quevedo, D. E., Tanaka, T., Dey, S. & Ahlén, A. (2017). Event-Based Transmission Scheduling and LQG Control Over a Packet Dropping Link. In: Denis Dochain, Didier Henrion, Dimitri Peaucelle (Ed.), 20th IFAC World Congress: . Paper presented at 20th World Congress of the International-Federation-of-Automatic-Control (IFAC),Toulouse, France, July 9-14, 2017. (pp. 8945-8950). Elsevier
Open this publication in new window or tab >>Event-Based Transmission Scheduling and LQG Control Over a Packet Dropping Link
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2017 (English)In: 20th IFAC World Congress / [ed] Denis Dochain, Didier Henrion, Dimitri Peaucelle, Elsevier, 2017, p. 8945-8950Conference paper, Published paper (Refereed)
Abstract [en]

This paper studies a joint transmission scheduling and controller design problem, which minimizes a linear combination of the control cost and expected energy usage of the sensor. Assuming that the sensor transmission decisions are event-based and determined using the random estimation error covariance information available to the controller, we show a separation in the design of the transmission scheduler and controller. The optimal controller is given as the solution to an LQG-type problem, while the optimal transmission policy is a threshold policy on the estimation error covariance at the controller.

Place, publisher, year, edition, pages
Elsevier, 2017
Series
IFAC-PapersOnLine, E-ISSN 2405-8963 ; 50:1
National Category
Control Engineering
Identifiers
urn:nbn:se:uu:diva-330703 (URN)10.1016/j.ifacol.2017.08.1311 (DOI)000423964900477 ()
Conference
20th World Congress of the International-Federation-of-Automatic-Control (IFAC),Toulouse, France, July 9-14, 2017.
Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-05-16Bibliographically approved
Knorn, S. & Ahlén, A. (2016). Deviation bounds in multi agent systems described by undirected graphs. Automatica, 67, 205-210
Open this publication in new window or tab >>Deviation bounds in multi agent systems described by undirected graphs
2016 (English)In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 67, p. 205-210Article in journal (Refereed) Published
Abstract [en]

The theory of port-Hamiltonian systems is used to derive upper bounds for the state deviations in multi agent systems described by undirected graphs pinned to a reference signal. The upper bounds for the deviations in networks of first or second order agents, respectively, depend on the minimal eigenvalue of the extended Laplacian of the system. In networks of first order agents, the deviations decay exponentially with a rate depending on the same minimal eigenvalue. In case networks of second order systems meet specific design properties, it can be shown that the deviations also decay exponentially with half the rate compared to first order systems.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-283644 (URN)10.1016/j.automatica.2016.01.038 (DOI)000373540300023 ()
Available from: 2016-04-14 Created: 2016-04-14 Last updated: 2017-11-30Bibliographically approved
Olofsson, T., Ahlén, A. & Gidlund, M. (2016). Modeling of the fading statistics of wireless sensor network channels in industrial environments. IEEE Transactions on Signal Processing, 64(12), 3021-3034
Open this publication in new window or tab >>Modeling of the fading statistics of wireless sensor network channels in industrial environments
2016 (English)In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 64, no 12, p. 3021-3034Article in journal (Refereed) Published
Abstract [en]

This paper presents an investigation of how to model the statistical properties of radio channels arising in industrial environments over long time horizons, e.g., hours and days. Based on extensive measurement campaigns, conducted at three different factory buildings, it is shown that for mobile transceivers the fading characteristics are Rayleigh or close to Rayleigh. However, for transceivers mounted at fixed locations, the use of conventional single fading distributions is not sufficient. It is shown that a suitable model structure for describing the fading properties of the radio channels, as measured by power, is a mixture of gamma and compound gamma-lognormal distributions. Furthermore, the complexity of the model generally increases with the observation interval. A model selection approach based on a connection between Kullback's mean discrimination information and the log-likelihood provides a robust choice of model structure. We show that while a (semi)-Markov chain constitute a suitable model for the channel dynamics the time dependence of the data can be neglected in the estimation of the parameters of the mixture distributions. Neglecting the time dependence in the data leads to a more efficient parametrization. Moreover, it is shown that the considered class of mixture distributions is identifiable for both continuous and quantized data under certain conditions and under those conditions a maximum likelihood under independence assumption estimator is shown to give consistent parameters also for data which are not independent. The parameter estimates are obtained by maximizing the log likelihood using a genetic and a local interior point algorithm.

Keywords
Fading; channel modelling; wireless sensor networks; wireless control; maximum likelihood estimation; identifiability
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-283642 (URN)10.1109/TSP.2016.2539142 (DOI)000375594800002 ()
Available from: 2016-04-14 Created: 2016-04-14 Last updated: 2017-11-30Bibliographically approved
Bahne, A. & Ahlén, A. (2016). Optimizing the similarity of loudspeaker: Room responses in multiple listening positions. IEEE Transactions on Audio, Speech, and Language Processing, 24(2), 340-353
Open this publication in new window or tab >>Optimizing the similarity of loudspeaker: Room responses in multiple listening positions
2016 (English)In: IEEE Transactions on Audio, Speech, and Language Processing, ISSN 1558-7916, E-ISSN 1558-7924, Vol. 24, no 2, p. 340-353Article in journal (Refereed) Published
Abstract [en]

A shortcoming of multichannel sound reproduction standards, such as stereo or 5.1 surround, is their incompatibility with multiple off-axis listening positions. Accurate reproduction of virtual sound sources can only be experienced in the sweet spot, which is located equidistant to the loudspeakers. We here present a novel methodology to compensate audio systems such that the channel similarity is optimized in several listening positions simultaneously. To that end we propose a novel MIMO personal audio filter design framework based on feed-forward control. By proper design choices, filters that successfully compensate for multiple offaxis positions and irregularities in the frequency sum responses are obtained. The design choices include allpass filters with appropriate phase shifts as target for each listening position in addition to a weighted similarity requirement. Evaluations based on measurements of two four-channel car audio systems show that the proposed method significantly improves timbral sound reproduction and phantom center reproduction in several listening positions simultaneously.

Keywords
Acoustic signal processing; audio systems; equalizers; loudspeakers; multiple sweet spots; psychoacoustics; virtual center
National Category
Engineering and Technology
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-267311 (URN)10.1109/TASLP.2015.2496156 (DOI)000367950900007 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2006.0152
Available from: 2015-11-20 Created: 2015-11-20 Last updated: 2017-12-01Bibliographically approved
Knorn, S., Dey, S., Ahlén, A. & Quevedo, D. E. (2015). Distortion Minimization in Multi-Sensor Estimation Using Energy Harvesting and Energy Sharing. IEEE Transactions on Signal Processing, 63(11), 2848-2863
Open this publication in new window or tab >>Distortion Minimization in Multi-Sensor Estimation Using Energy Harvesting and Energy Sharing
2015 (English)In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, no 11, p. 2848-2863Article in journal (Refereed) Published
Abstract [en]

This paper investigates an optimal energy allocation problem for multisensor estimation of a random source where sensors communicate their measurements to a remote fusion center (FC) over orthogonal fading wireless channels using uncoded analog transmissions. The FC reconstructs the source using the best linear unbiased estimator (BLUE). The sensors have limited batteries but can harvest energy and also transfer energy to other sensors in the network. A distortion minimization problem over a finite-time horizon with causal and noncausal centralized information is studied and the optimal energy allocation policy for transmission and sharing is derived. Several structural necessary conditions for optimality are presented for the two sensor problem with noncausal information and a horizon of two time steps. A decentralized energy allocation algorithm is also presented where each sensor has causal information of its own channel gain and harvested energy levels and has statistical information about the channel gains and harvested energies of the remaining sensors. Various other suboptimal energy allocation policies are also proposed for reducing the computational complexity of dynamic programming based solutions to the energy allocation problems with causal information patterns. Numerical simulations are included to illustrate the theoretical results. These illustrate that energy sharing can reduce the distortion at the FC when sensors have asymmetric fading channels and asymmetric energy harvesting processes.

Keywords
Energy allocation, energy harvesting, energy sharing, fading channels, multisensor estimation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-256216 (URN)10.1109/TSP.2015.2416682 (DOI)000354382100010 ()
Available from: 2015-07-06 Created: 2015-06-22 Last updated: 2017-12-04Bibliographically approved
Nourian, M., Dey, S. & Ahlén, A. (2015). Distortion Minimization in Multi-Sensor Estimation With Energy Harvesting. IEEE Journal on Selected Areas in Communications, 33(3), 524-539
Open this publication in new window or tab >>Distortion Minimization in Multi-Sensor Estimation With Energy Harvesting
2015 (English)In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 33, no 3, p. 524-539Article in journal (Refereed) Published
Abstract [en]

This paper presents a design methodology for optimal energy allocation to estimate a random source using multiple wireless sensors equipped with energy harvesting technology. In this framework, multiple sensors observe a random process and then transmit an amplified uncoded analog version of the observed signal through Markovian fading wireless channels to a remote station. The sensors have access to an energy harvesting source, which is an everlasting but unreliable random energy source compared to conventional batteries with fixed energy storage. The remote station or so-called fusion centre estimates the realization of the random process by using a best linear unbiased estimator. The objective is to design optimal energy allocation policies at the sensor transmitters for minimizing total distortion over a finite-time horizon or a long term average distortion over an infinite-time horizon subject to energy harvesting constraints. This problem is formulated as a Markov decision process (MDP) based stochastic control problem and the optimal energy allocation policies are obtained by the use of dynamic programming techniques. Using the concept of submodularity, the structure of the optimal energy allocation policies is studied, which leads to an optimal threshold policy for binary energy allocation levels. Motivated by the excessive communication burden for the optimal control solutions where each sensor needs to know the channel gains and harvested energies of all other sensors, suboptimal decentralized strategies are developed where only statistical information about all other sensors' channel gains and harvested energies is required. Numerical simulation results are presented illustrating the performance of the optimal and suboptimal algorithms.

Keywords
Wireless sensor networks, distributed estimation, best linear unbiased estimator (BLUE), energy/power control, energy harvesting, Markov decision processes, dynamic programming (DP), threshold policy
National Category
Telecommunications
Identifiers
urn:nbn:se:uu:diva-252012 (URN)10.1109/JSAC.2015.2391691 (DOI)000351741200013 ()
Available from: 2015-05-05 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
Brännmark, L.-J. & Ahlén, A. (2015). Multichannel Room Correction with Focus Control. Journal of The Audio Engineering Society, 63(1-2), 21-30
Open this publication in new window or tab >>Multichannel Room Correction with Focus Control
2015 (English)In: Journal of The Audio Engineering Society, ISSN 0004-7554, ISSN 1549-4950, Vol. 63, no 1-2, p. 21-30Article in journal (Refereed) Published
Abstract [en]

Digital equalization of audio systems is mostly performed on a channel-by-channel basis, i.e., loudspeakers are equalized separately and independently of each other. In reverberant rooms the spatial variability of the loudspeaker room transfer function puts a limit on what can be achieved with such single-channel approaches, and considerably more far-reaching results can be obtained with multichannel methods. In this paper we present a multichannel equalizer design method where the loudspeaker to be equalized is assisted by several support loudspeakers that act in combination to improve the response of the main loudspeaker while suppressing the reverberation of the listening room. However, since a full dereverberation may not always be desirable, we shall here study the proposed method from the perspective of how to control the amount of room correction for a given number of contributing support loudspeakers. The amount of correction is controlled by a scalar parameter that we interpret as a "focus control," enabling the user to slide seamlessly between a single-channel equalizer and a full multichannel inversion of the room.

National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-248653 (URN)000349743200003 ()
Note

Print version: ISSN 1549-4950

Available from: 2015-04-12 Created: 2015-04-06 Last updated: 2017-12-04Bibliographically approved
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