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Christian Renner

Foto von Christian Renner
Dr.-Ing. Christian Renner
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Von Juli 2008 bis September 2012 habe ich als wissenschaftlicher Mitarbeiter am Institut für Telematik gearbeitet und über das Thema "Sustained Operation of Sensor Nodes with Energy Harvesters and Supercapacitors" promoviert.

Seit Oktober 2012 arbeite ich als PostDoc am Institut für Technische Informatik der Universität zu Lübeck. Aktuelle Informationen befinden sich auf meiner persönlichen Seite.


CV

Projekte

Publikationen

Christian Renner und Volker Turau. State-of-Charge Assessment for Supercap-Powered Sensor Nodes: Keep it Simple Stupid!. In Proceedings of the International Workshop on Algorithms and Concepts for Networked Sensing Systems Powered by Energy Harvesters (EnHaNSS'12), Juni 2012. Antwerp, Belgium.
@InProceedings{Telematik_RT_2012_CapModels, author = {Christian Renner and Volker Turau}, title = {State-of-Charge Assessment for Supercap-Powered Sensor Nodes: Keep it Simple Stupid!}, booktitle = {Proceedings of the International Workshop on Algorithms and Concepts for Networked Sensing Systems Powered by Energy Harvesters (EnHaNSS'12)}, day = {11}, month = jun, year = 2012, location = {Antwerp, Belgium}, }
Abstract: Electric double-layer capacitors, also known as supercaps, have several advantages over traditional energy buffers: They do not require complex charging circuits, offer virtually unlimited charge-discharge cycles, and generally enable easy state-of-charge assessment. A closer look yet reveals that leakage and internal reorganization effects hamper state-of-charge assessment by means of terminal voltage, particularly after a charging cycle. Sophisticated models capture this effect at the cost of an increased calculation and parameter-estimation complexity. As this is hardly feasible on low-power, low-resource sensor nodes, we evaluate the performance of simple models on a real energy-harvesting sensor node platform. We show that model errors are as low as 1-2% on average and never exceed 5% in our experiments, supporting that there is no need to employ more complex models on common sensor node platforms, equipped with unreliable ADC readings and uncertain consumption due to hardware variation in the same order of magnitude.
Christian Renner, Florian Meier und Volker Turau. Holistic Online Energy Assessment: Feasibility and Practical Application. In Proceedings of the 9th IEEE International Conference on Networked Sensing Systems (INSS'12), Juni 2012. Antwerp, Belgium. Best Student Paper Award.
@InProceedings{Telematik_RT_2012_HolisticEnergyAssessment, author = {Christian Renner and Florian Meier and Volker Turau}, title = {Holistic Online Energy Assessment: Feasibility and Practical Application}, booktitle = {Proceedings of the 9th IEEE International Conference on Networked Sensing Systems (INSS'12)}, day = {11-14}, month = jun, year = 2012, location = {Antwerp, Belgium}, note = {Best Student Paper Award}, }
Abstract: Combining energy harvesting with energy-aware scheduling enables perpetually operating sensor networks. The practical realization of this goal yet requires reliable and precise holistic online energy assessment. While the building blocks--assessing residual energy, predicting energy intake, and tracing energy consumption--have been studied in detail, the analysis of their interaction on a real platform has been neglected. This paper answers the question, whether these techniques can be easily joined to give a precise and correct picture of a sensor node's energetic state and behavior. For this purpose, we model the energy flow of a prototype energy-harvesting sensor node and evaluate the joint performance of state-of-the-art energy assessment based on a field test. We verify the system model and show the feasibility of holistic energy assessment, which tolerates small configuration errors, achievable with a combination of generic configuration and online calibration. We also analyze the feasibility of forecasting a node's future energetic state, and find that the presented method gives sufficient results for uniformly distributed consumption profiles.
Christian Renner, Florian Meier und Volker Turau. Policies for Predictive Energy Management with Supercapacitors. In Proceedings of the 8th IEEE International Workshop on Sensor Networks and Systems for Pervasive Computing (PerSeNS'12), März 2012. Lugano, Switzerland.
@InProceedings{Telematik_RT_2012_Epol, author = {Christian Renner and Florian Meier and Volker Turau}, title = {Policies for Predictive Energy Management with Supercapacitors}, booktitle = {Proceedings of the 8th IEEE International Workshop on Sensor Networks and Systems for Pervasive Computing (PerSeNS'12)}, day = {19-23}, month = mar, year = 2012, location = {Lugano, Switzerland}, }
Abstract: This paper presents an algorithm to dynamically determine the maximum supported uniform demand for energy of sensor nodes powered by energy harvesters using supercapacitors as energy buffers. Knowledge about the maximum uniform consumption is required to adapt the sensor node's duty cycle or task schedule to achieve uniform, utility-maximizing, and depletion-safe operation. Our algorithm makes use of a supercapacitors' relationship between state-of-charge and voltage, is particularly designed to handle the non-linear system model, and is lightweight enough to run on low-power sensor node hardware. We define three energy policies, evaluate their performance using a real-world solar-harvesting trace, and analyze the influence of the supercapacitor's capacity and errors of the energy forecast.
Christian Renner und Volker Turau. Adaptive Energy-Harvest Profiling to Enhance Depletion-Safe Operation and Efficient Task Scheduling. Sustainable Computing: Informatics and Systems, 2(1):43–56, März 2012.
@Article{Telematik_RT_2012_AdaptiveSlotting, author = {Christian Renner and Volker Turau}, title = {Adaptive Energy-Harvest Profiling to Enhance Depletion-Safe Operation and Efficient Task Scheduling}, pages = {43-56}, journal = {Sustainable Computing: Informatics and Systems}, volume = {2}, number = {1}, month = mar, year = 2012, issn = {2210-5379}, }
Abstract: Forecasting the expected energy harvest enables small-sized energy-harvesting sensor nodes to schedule tasks or adapt the radio duty cycle. This ability ensures depletion-safe and efficient operation. Most energy sources exhibit cyclic patterns of intensity, e.g., the sun. These patterns show periods with unequal--low versus high and stable versus varying--energy production and heavily depend on a node's location as well as seasonal and environmental changes. Existing forecast algorithms do not exploit these patterns, but create and update forecasts at static and arbitrary points in time, the main knob being the number of updates per cycle. We present a method enabling sensor nodes to adapt to harvesting patterns at runtime. It is designed for seamlessly replacing the static scheme to improve the accuracy of a wide range of existing forecast algorithms. In our evaluation, we show that (i) the adaptive method traces the energy pattern in real-world deployments accurately, (ii) reacts to seasonal and environmental changes, (iii) increases forecast accuracy, and (iv) reduces the number of prediction updates. These achievements enhance depletion-safe operation and efficient task scheduling with fewer recalculations and adjustments of the duty cycle. They also facilitate the exchange of harvesting forecasts for collaborative node tasks, since less information has to be shared.
Stefan Unterschütz, Christian Renner und Volker Turau. Opportunistic, Receiver-Initiated Data-Collection Protocol. In Proceedings of the 9th European Conference on Wireless Sensor Networks (EWSN'12), Februar 2012. Trento, Italy.
@InProceedings{Telematik_URT_2012_Orinoco, author = {Stefan Unterschütz and Christian Renner and Volker Turau}, title = {Opportunistic, Receiver-Initiated Data-Collection Protocol}, booktitle = {Proceedings of the 9th European Conference on Wireless Sensor Networks (EWSN'12)}, day = {15-17}, month = feb, year = 2012, location = {Trento, Italy}, }
Abstract: This paper presents and evaluates ORiNoCo, a novel data-collection and event-reporting protocol for sensor networks. ORiNoCo is built upon the asynchronous duty-cycle protocol RI-MAC and breaks with the tradition of exchanging extensive neighborhood information, a cornerstone of many competing collection protocols and one of their major source of communication overhead and energy expenditure. The merit of this venture is an opportunistic, energy-efficient, latency-reducing, and self-stabilizing protocol. ORiNoCo comes at virtually no extra costs in terms of memory demand and communication overhead compared to RI-MAC. We derive theoretical boundaries for the improvements in radio efficiency, latency, and energy-consumption. ORiNoCo is verified with these findings via simulation and compared with CTP. ORiNoCo achieves lower energy-consumption while reducing end-to-end delays.

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