| 1. |
- Araujo, Jose, et al.
(författare)
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Experimental Validation of a Localization System Based on a Heterogeneous Sensor Network
- 2009
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Ingår i: ASCC. - NEW YORK : IEEE. - 9781424454402 ; , s. 465-470
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Konferensbidrag (refereegranskat)abstract
- The experimental implementation and validation of a localization system based on a heterogeneous sensor network is described. The sensor network consists of ultrasound ranging sensors and web cameras. They are used to localize a mobile robot under sensor communication constraints. Applying a recently proposed sensor fusion algorithm that explicitly takes communication delay and cost into account, it is shown that one can accurately trade off the estimation performance by using low-quality ultrasound sensors with low processing time and low communication cost versus the use of the high-quality cameras with longer processing time and higher communication cost. It is shown that a periodic schedule of the sensors is suitable in many cases. The experimental setup is discussed in detail and experimental results are presented.
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| 2. |
- Giani, A., et al.
(författare)
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The VIKING project : An initiative on resilient control of power networks
- 2009
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Konferensbidrag (refereegranskat)abstract
- This paper presents the work on resilient and secure power transmission and distribution developed within the VIKING (vital infrastructure, networks, information and control system management) project. VIKING receives funding from the European Community's Seventh Framework Program. We will present the consortium, the motivation behind this research, the main objective of the project together with the current status.
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| 3. |
- Henriksson, Erik, 1982-
(författare)
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Compensating for Unreliable Communication Links in Networked Control Systems
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Control systems utilizing wireless sensor and actuator networks can be severely affectedby the properties of the communication links. Radio fading and interferencemay cause communication losses and outages in situations when the radio environmentis noisy and low transmission power is desirable. This thesis proposes amethod to compensate for such unpredictable losses of data in the feedback controlloop by introducing a predictive outage compensator (POC). The POC is a filter tobe implemented at the receiver sides of networked control systems where it generatesartificial samples when data are lost. If the receiver node does not receive thedata, the POC suggests a command based on the history of past data. It is shownhow to design, tune and implement a POC. Theoretical bounds and simulationresults show that a POC can improve the closed-loop control performance undercommunication losses considerably. We provide a deterministic and a stochasticmethod to synthesize POCs. Worst-case performance bounds are given that relatethe closed-loop performance with the complexity of the compensator. We also showthat it is possible to achieve good performance with a low-order implementationbased on Hankel norm approximation. Tradeoffs between achievable performance,communication loss length, and POC order are discussed. The results are illustratedon a simulated example of a multiple-tank process. The thesis is concludedby an experimental validation of wireless control of a physical lab process. Herethe controller and the physical system are separated geographically and interfacedthrough a wireless medium. For the remote control we use a hybrid model predictivecontroller. The results reflect the difficulties in wireless control as well as theyhighlight the flexibility and possibilities one obtains by using wireless instead of awired communication medium.
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| 4. |
- Henriksson, Erik, et al.
(författare)
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Predictive Compensation for Communication Outages in Networked Control Systems
- 2008
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Ingår i: Proceedings of the 47<sup>th</sup> IEEE Conference on Decision and Control. - Cancun, Mexico. - 9781424431243 ; , s. 2063-2068
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Konferensbidrag (refereegranskat)abstract
- A predictive outage compensator co-located with the actuator node in a networked control system can be used to counteract unpredictable losses of data in the feedback control loop. When a new control command is not received at the actuator node at an appropriate time instance, the predictive outage compensator suggests a replacement command based on the history of past control commands. It is shown that a simple tuning phase together with the monitoring of the control history can lead to a compensator that can improve the closed-loop control performance under communication outages considerably compared to traditional schemes. Worst case performance bounds are given that relate the quality of the tuning phase and the complexity of the compensator with the length of the communication outage period. Zero-order-hold (holding the past control command if the current is lost) and applying an a priori decided constant signal (using a redefined value on the control command if the current is lost) are special cases of the more general compensation scheme presented. The predictive outage compensator is illustrated through computer simulation with communication outages.
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| 5. |
- Henriksson, Erik, et al.
(författare)
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Reduced-Order Predictive Outage Compensators for Networked Systems
- 2009
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Ingår i: Proceedings of the combined 48<sup>th</sup> IEEE Conference on Decision and Control and 28<sup>th</sup> Chinese Control Conference. - Shanghai, P.R. China. - 9781424438716 ; , s. 3775-3780
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Konferensbidrag (refereegranskat)abstract
- Control systems utilizing wireless sensor and actuator networks can be severely affected by the properties of the wireless links. Radio fading and interference may cause communication outage of several samples in situations when the radio environment is noisy and low transmission power is desirable. We propose a method to compensate for outages by introducing a predictive outage compensator (POC), which is a filter to be implemented at the receiver sides of networked control systems and that generates artificial samples during the outage. The main contribution of the paper is to show that a POC can be derived based on a Kalman filter formulation and that it is possible to achieve good performance with a low-order implementation based on Hankel norm approximation. Tradeoffs between achievable closed-loop performance, outage length, and POC order are discussed. The results are illustrated on a simulated example of a multiple-tank process.
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| 6. |
- Ramesh, Chithrupa, et al.
(författare)
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LQG and Medium Access Control
- 2009
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Ingår i: Proceedings of the 1st IFAC Workshop on Estimation and Control of Networked Systems (NecSys2009). ; , s. 328-333
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Konferensbidrag (refereegranskat)abstract
- The communication channel is a shared resource in networked control systems, and channel access at every instant cannot be guaranteed. In this paper, we propose a novel architecture for control over wireless networks with integrated medium access control (MAC).We evaluate the impact of constrained channel access on the cost of controlling a single plant over a network and establish that the separation principle holds under certain conditions on the MAC. We arrive at a classification of random access methods for networked control systems and identify a structure for each method. Then, by evaluating the increase in cost compared to a conventional setup, we identify an adaptive random access method which uses a threshold-based decision criteria on the current data to determine channel access. Finally, we give stability criteria for control applications using these medium access methods.
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| 7. |
- Ramesh, Chithrupa, et al.
(författare)
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Multiple access with attention-based tournaments for monitoring over wireless networks
- 2009
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Ingår i: Proceedings of the European Control Conference 2009. - : EUCA. - 9789633113691 - 9783952417393 ; , s. 4302-4307
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Konferensbidrag (refereegranskat)abstract
- Wireless sensor networks for control and moni- toring applications introduce critical constraints on the design of multiple access schemes. Controlling dynamic processes requires that priority must be given to critical systems for the use of the wireless medium. Tournaments in the medium access control (MAC) layer are presented as a way to evaluate priorities and assign channel resources in a distributed manner. The priorities are dynamically assigned based on the attention that each data packet requires. A mathematical formulation of attention is presented together with the corresponding performance analysis of the multiple access scheme. Priorities based on the attention emphasize the information content in the data to be transmitted and the related process dynamics. It is shown that under certain conditions, the performance of this distributed scheme converges to a scheduling policy based on minimizing the per-sample variance of the error in the estimates obtained with limited communication resources. Sustainable data rates for a cluster of linear processes are also derived.
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| 8. |
- Sandberg, Henrik, et al.
(författare)
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Estimation over heterogeneous sensor networks
- 2008
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. ; , s. 4898-4903
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Konferensbidrag (refereegranskat)abstract
- Design trade-offs between estimation performance, processing delay and communication cost for a sensor scheduling problem is discussed. We consider a heterogeneous sensor network with two types of sensors: the first type has low-quality measurements, small processing delay and a light communication cost, while the second type is of high quality, but imposes a large processing delay and a high communication cost. Such a heterogeneous sensor network is common in applications, where for instance in a localization system the poor sensor can be an ultrasound sensor while the more powerful sensor can be a camera. Using a time-periodic Kalman filter, we show how one can find an optimal schedule of the sensor communication. One can significantly improve estimation quality by only using the expensive sensor rarely. We also demonstrate how simple sensor switching rules based on the Riccati equation drives the filter into a stable time-periodic Kalman filter. ￜ 2008 IEEE.
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| 9. |
- Aspeborg, Henrik, et al.
(författare)
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Carbohydrate-active enzymes involved in the secondary cell wall biogenesis in hybrid aspen
- 2005
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 137:3, s. 983-997
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Tidskriftsartikel (refereegranskat)abstract
- Wood formation is a fundamental biological process with significant economic interest. While lignin biosynthesis is currently relatively well understood, the pathways leading to the synthesis of the key structural carbohydrates in wood fibers remain obscure. We have used a functional genomics approach to identify enzymes involved in carbohydrate biosynthesis and remodeling during xylem development in the hybrid aspen Populus tremula x tremuloides. Microarrays containing cDNA clones from different tissue-specific libraries were hybridized with probes obtained from narrow tissue sections prepared by cryosectioning of the developing xylem. Bioinformatic analyses using the sensitive tools developed for carbohydrate-active enzymes allowed the identification of 25 xylem-specific glycosyltransferases belonging to the Carbohydrate-Active EnZYme families GT2, GT8, GT14, GT31, GT43, GT47, and GT61 and nine glycosidases (or transglycosidases) belonging to the Carbohydrate-Active EnZYme families GH9, GH10, GH16, GH17, GH19, GH28, GH35, and GH51. While no genes encoding either polysaccharide lyases or carbohydrate esterases were found among the secondary wall-specific genes, one putative O-acetyltransferase was identified. These wood-specific enzyme genes constitute a valuable resource for future development of engineered fibers with improved performance in different applications.
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| 10. |
- Aspeborg, Henrik, 1970-, et al.
(författare)
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Vegetabile material, plants and a method of producing a plant having altered lignin properties
- 2008
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Patent (populärvet., debatt m.m.)abstract
- The present invention is related to a set of genes, which when modified in plants gives altered lignin properties. The invention provides DNA construct such as a vector useful in the method of the invention. Further, the invention relates to a plant cell or plant progeny of the plants and wood produced by the plants according to the invention Lower lignin levels will result in improved saccharification for bio-refining and ethanol production and improved pulp and paper. Increased lignin levels will utilise lignin properties for energy production. The genes and DNA constructs may be used for the identification of plants having altered lignin characteristics as compared to the wild-type. According to the invention genes and DNA constructs may also be used as candidate genes in marker assisted breeding.
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