Mr. Prof. Dr. Horst Hellbrück
|Position||Professor and Head of Center of Excellence CoSA|
Lübeck University of Applied Sciences, Electrical Engineering and Computer Science
|Phone||+49 (0)451 300-5042|
During the Semester: Monday 16:00h -17:00h & Wednesday 16:30h - 17:00h (On Request)
In the Semester Break on Request only. Please check actual schedule in the calendar.
The Center of Excellence CoSA (Communications - Systems - Applications) deals with Communication Networks, Distributed Systems and their applications. My interest are modern structures like wireless mobile networks and sensor networks. Of special interest are sensor networks in various application fields from medical applications to underwater technologies.
Lumen II (2016 - 2018) funded by BMBF
ROSIE (2016 - 2018) funded by BMWi
LOCIC (2014 - 2016) funded by BMWi
m:flo (2014 - 2016) funded by BMWi
BOSS-COGNET (2013 - 2017) funded by BMWi
SoCor (2012 - 2016) funded by DAAD
Lumen (2012 - 2015) funded by BMBF
DataCast (2010 - 2013) funded by BMBF
Real World G-Lab (2009 - 2012) Part of Glab funded by BMBF
SoFT (2009 - 2012) funded by BMBF
TriSOS (2008) funded by Schleswig-Holstein
AutoNomos (2005 - 2011) in SPP Organic Computing funded by DFG
MarathonNet (2005 - 2007) funded by KTS
Symposium and Organizations
- since 2005 Active Member of KuVS Distributed Systems Group of the GI (Gesellschaft für Informatik)
- 2006 4. German KuVS Summer School 2006 - Selforganisation, Organisation and Chair of the Workshop
- 2008 Multi Conference (Mensch & Computer, DeLFI, Cognitive Design, Usability Professionals), Exhibition Chair
- since 2009 Leitungsgremium der GI/ITG-Fachgruppe KuVS
- 2009 GI Jahrestagung Lübeck, Exhibition Chair
- 2011 KiVS Kiel, Workshop Chair
- since 2011 Reviewer for Acquin Accreditation agency
- since 2011 Reviewer for BMBF
- since 2012 program manager for the international study program in Electrical Engineering (ISE) at the Lübeck University of Applied Sciences
- from 2013 to 2019 Vice Chairman Life Science Nord e.V.
- since 2013 Member of ITG 5.2.1 System Architectures and Traffic Engineering
- since 2013 Head of Center of Excellence CoSA.
- since 2018 program manager for the master program in Electrical Engineering (AIT) at the Lübeck University of Applied Sciences
- since 2019 Chairman of VDI of Regional Association VDI in Schleswig-Holstein
- Reviewer for Journals
- Member of several international Program Committees
- IADIS WWW/Internet (ICWI)
- IASTED International Conference on Telematics
- IASTED RTA International Conference on Robotics, Telematics and Applications
- LOCALGOS (Workshop on Localized Algorithms and Protocols for Wireless Sensor Networks)
- LOCAN (Workshop on Localized Communication and Topology Protocols for Ad hoc Networks)
- WMAN (Workshop on Mobile Ad Hoc Networks)
- born October 23rd, 1967
- Abitur 1986 at the Johannes Kepler Gymnasium Lebach
- Diploma (equiv. to Master Degree) in Electrical Engineering in 1994 at the University of Saarland
- Software Development 1994-1998 at Dräger in Lübeck
- International Product Marketing 1998-2000 at eupec in Warstein
- Research Associate in 200-2004 at International University in Germany, Bruchsal
- Dissertation in Computer Science 2004 at Technical University in Braunschweig
- Leader of the Automation Group in a Pharma-Projekt 2004-2005 at Roche Diagnostics GmbH in Mannheim
- From February 2005 until January 2008: Research Assistant at the Institute of Telematics at the University of Lübeck, Germany
- Since Februar 2008 Professor for Communicationsystems and Distributed Systems at the University of Applied Sciences Lübeck
- Since December 2013 Head of Center of Excellence CoSA
- Since 2016 Member of University of Lübeck at the Institute of Telematics
- ANSim: Have a look at the new Web Site of ANSim http://www.ansim.info/- A simple to use Ad-Hoc Network Simulator, developed for my PhD Thesis.
An overview of the courses is available at the web pages of the study programs.
Courses at International University in Bruchsal
- Introduction to C Programming (MICT) - Programming Styles / Part: Procedural Programming (BSc)
- Networking and Distributed Systems / Assistant (BSc)
- Software Engineering / Assistant (MICT)
- Web Applications with Java and XML (BSc)
- Web Programming (MICT)
- Advanced Networking / Wireless Networks (MICT)
- Wireless Networks (MICT)
- Enterprise Information Systems I (MBA)
- Information Systems (BBA)
- Operating Systems (BSc)
- Cryptographic Techniques / Practical Part: Applications (BSc)
Courses at University of Lübeck
- Operating- and Communications Systems (BSc, MSc and Diplom)
- Operating Systems (BSc and Diplom)
- Computernetworks (BSc and Diplom)
- Mobile Communications (MSc and Diplom)
- Security in Networks and Distributed Systems (BSc, MSc and Diplom)
- Wireless Sensor Networks (MSc and Diplom)
- Access to the course material is available at my old homepage
Courses at Lübeck University of Applied Sciences
- Principles of Communications (Bachelor ISE)
- Communication Networks (Bachelor KIM)
- Digital Transmission (Bachelor KIM)
- System Design Projecte (Bachelor KIM)
- Communications Engineering (Master AIT)
- Studyprojects (Master AIT)
- Wireless Networks in Automation Systems (Master AIT)
see also Google Scholar profile Horst Hellbrück
|||Java 5.0 - Das Tiger-Release , Carl-Hanser-Verlag, 2004. [bib]|
|||Analytische und simulationsbasierte Verfahren zur Konnektivitätsbestimmung und -verbesserung von Ad-Hoc-Netzen , Shaker-Verlag, 2004. [bib] [pdf] [abstract]|
Konnektivitï¿½t und Verbindungsdauer sind wichtige Kenngrï¿½ï¿½en, um die Qualitï¿½t von Ad-Hoc-Netzen zu bewerten. In der vorliegenden Arbeit befassen wir uns mit diesen Kenngrï¿½ï¿½en. Wir fï¿½hren ausgehend von den praktischen Anforderungen der Anwendungen eines Ad--Hoc--Netzes eine alternative Definition der Konnektivitï¿½t ein. Unter Konnektivitï¿½t verstehen wir die Wahrscheinlichkeit, dass ein Pfad zwischen zwei zufï¿½llig ausgewï¿½hlten Knoten existiert. Ein Vergleich mit den bisherigen Definitionen der Konnektivitï¿½t aus der Graphentheorie und die Anwendbarkeit der Definition auf existierende funktionierende Netze bestï¿½tigen die Praxistauglichkeit unserer gewï¿½hlten Definition. Mit Hilfe eines einfachen ï¿½bertragungsmodells berechnen und simulieren wir Konnektivitï¿½t in Ad-Hoc-Netzen, wobei wir die in anderen Arbeiten vernachlï¿½ssigten Randeffekte berï¿½cksichtigen. Die zum Erreichen der Konnektivitï¿½t notwendige Anzahl von direkten Nachbarn fï¿½r quadratische oder kreisfï¿½rmige Flï¿½chen ist unabhï¿½ngig von der Grï¿½ï¿½e des statischen Ad-Hoc-Netzes. Auf Netzwerke mit beweglichen Knoten lassen sich die statischen Ergebnisse direkt ï¿½bertragen, wenn die Bewegung der Knoten in der gleichen rï¿½umlichen Knotenverteilung wie im statischen Fall resultiert. Die verallgemeinerten Ergebnisse aus den Berechnungen und Simulationen mittels unseres Simulators ANSim lassen sich zur Analyse eines bis dato unbekannten Szenarios unkompliziert einsetzen und liefern gute Abschï¿½tzungen der Konnektivitï¿½t und mï¿½glichen Verbindungsdauer. Wir untersuchen den Einsatz beweglicher Infrastrukturknoten, die fï¿½r eine Erhï¿½hung der Konnektivitï¿½t innerhalb des Ad-Hoc-Netzes sorgen und mit Hilfe eines Algorithmus zur dynamischen Ortswahl platziert werden. Bewegliche Infrastrukturknoten erreichen eine deutliche Verbesserung und zeigen eine grï¿½ï¿½ere Steigerung der Konnektivitï¿½t als statisch platzierte Infrastrukturknoten. Zum Austausch der Positionsinformationen entwickeln wir ein eigens optimiertes MILE-Protokoll basierend auf dem DREAM-Positionsdienst. Eine prototypische Implementierung im Netzwerksimulator ns2 bestï¿½tigt die Ergebnisse der beweglichen Infrastrukturknoten. Das MILE-Protokoll benï¿½tigt nur einen sehr geringen Anteil der Bandbreite verglichen mit dem AODV-Routing-Protokoll trotz dessen optimierten reaktiven Funktionsprinzips.
|||Brachialis Pulse Wave Measurements with Ultra-Wide Band and Continuous Wave Radar, Photoplethysmography and Ultrasonic Doppler Sensors , In Sensors Multidisciplinary Digital Publishing Institute (MDPI), volume 21, 2021. [bib] [abstract]|
The measurement and analysis of the arterial pulse wave provides information about the state of vascular health. When measuring blood pressure according to Riva-Rocci, the systolic and diastolic blood pressure is measured non-invasively with an inflatable pressure cuff on the upper arm. Today’s blood pressure monitors analyze the pulse wave in reference to the rising or falling cuff pressure. With the help of additional pulse wave analysis, one can determine the pulse rate and the heart rate variability. In this paper, we investigated the concept, the construction, and the limitations of ultrawideband (UWB) radar and continuous wave (CW) radar, which provide continuous and non-invasive pulse wave measurements. We integrated the sensors into a complete measurement system. We measured the pulse wave of the cuff pressure, the radar sensor (both UWB and CW), the optical sensor, and ultrasonic Doppler as a reference. We discussed the results and the sensor characteristics. The main conclusion was that the resolution of the pulse radar was too low, even with a maximum bandwidth of 10 GHz, to measure pulse waves reliably. The continuous wave radar provides promising results for a phantom if adjusted properly with phase shifts and frequency. In the future, we intend to develop a CW radar solution with frequency adaption.
|||MAMPI-UWB—Multipath-Assisted Device-Free Localization with Magnitude and Phase Information with UWB Transceivers , In Sensors Multidisciplinary Digital Publishing Institute, volume 20, 2020. [bib] [abstract]|
In this paper, we propose a multipath-assisted device-free localization (DFL) system that includes magnitude and phase information (MAMPI). The DFL system employs ultra-wideband (UWB) channel impulse response (CIR) measurements, enabling the extraction of several multipath components (MPCs) and thereby benefits from multipath propagation. We propose a radio propagation model that calculates the effect on the received signal based on the position of a person within a target area. Additionally, we propose a validated error model for the measurements and explain the creation of different feature vectors and extraction of the MPCs from Decawave DW1000 CIR measurements. We evaluate the system via simulations of the position error probability and a measurement setup in an indoor scenario. We compare the performance of MAMPI to a conventional DFL system based on four sensor nodes that measures radio signal strength values. The combination of the magnitude and phase differences for the feature vectors results in a position error probability that is comparable to a conventional system but requires only two sensor nodes.
|||Contact-Free Biosignal Acquisition via Capacitive and Ultrasonic Sensors , In IEEE Access Institute of Electrical and Electronics Engineers (IEEE), volume 8, 2020. [bib]|
|||IoTiSS: Internet of Things in Smart Streetlighting , In ITG-Fachbericht-Mobilkommunikation VDE VERLAG GmbH, 2019. [bib] [abstract]|
In the Internet of Things (IoT), sensors measure data and transfer their measurements to servers on the Internet. Street lamps cover a large area, are in the proximity of buildings and sensors and thereby provide an ideal gateway for the IoT. In this paper, we introduce a system consisting of a transport network of street lamps operating in the 868MHz ISM-band and a sensor network operating at 2.4GHz ISM-band. Therefore, each street lamp contains at least two radio frequency equipped modules that communicate with each other via a local short-range wired bus system. We set up the nodes with the Contiki-NG operating system and an open protocol stack with state-of-the-art protocols for our applications. This solution serves as an open architecture for the IoT which is portable and flexible. The first results of our testbed and simulation show the functionality of the system. In the future, optimization and further test are required to ensure the scalability of the system..
|||A new localization algorithm based on neural networks , In Proceedings of the 3rd KuVS/GI Expert Talk on Localization, 2018. [bib] [pdf] [abstract]|
Indoor localization plays a major role in a wide range of applications. To determine the location of a tag, localization algorithm is required. In the past, machine learning algorithms were difficult to implement in consumer hardware, but with the advent of tensor processing units, even smartphones are capable to use artificial intelligence to solve complex problems. In this paper, we investigate a machine learning algorithm based on neural networks and compare the result to a linear least squares estimator. We design and evaluate different neural networks. Based on our observation, the neural network delivers poor performance compared to the linear least squares estimator.
|||Drahtlose Robuste Adaptive Industrielle Systeme , In ITG-Fachbericht-Mobilkommunikation VDE VERLAG GmbH, 2018. [bib] [abstract]|
Die industrielle Fertigung wandelt sich mit der Digitalisierung. Fertigungsstücke werden individuell durch Industrie 4.0-Technologien; sie sind jederzeit und überall erfassbar. Fertigungsprozesse werden digitalisiert und bilden Struktur und Verhalten einer Fertigungs- und Produktionsstrasse ab, womit sich wichtige Erkenntnisse zum Ablauf gewinnen lassen. Dies setzt eine Vernetzung der Fertigungsstücke voraus, welche die klassische Automatisierung ergänzt. Drahtlose Sensoren sind an Fertigungsstücke gekoppelt und bilden großflächige und dichte Sensornetze. Messgrößen der Sensoren sind beispielsweise Ort, Zeit, Temperatur, Beschleunigung, Geräusch oder Luftfeuchte, welche nach Anforderung der Datenanalyse ausgewählt und ausgewertet werden. Derartige Sensornetze stellen neue Herausforderungen und Forschungsfragen an Industrie 4.0-Anwendungen. Das Projekt DRAISE hat das Ziel, produktionsrelevante Daten in Industrieanlagen zuverlässig zu erfassen und entsprechend aufzubereiten. Hierfür werden Transportwagen einer Fertigung drahtlos vernetzt und Temperatur, Erschütterung, Position und Zeit erfasst. Zusätzlich interagieren die Mitarbeiter in der Produktion über eine definierte Mensch-Maschine-Schnittstelle mit dem System. Zur Minimierung der Auswirkungen durch andere, drahtlose Systeme werden Time Division Multiple Access (TDMA)-basierende Protokolle für die Single-Hop- und Multi-Hop-Kommunikation entwickelt. Die Kommunikation wird durch Lokalisierungskomponenten ergänzt, welche mit einem System auf Basis von Ultra-Wide-Band (UWB) implementiert ist. Für die angestrebte, zuverlässige und robuste Kommunikation werden zukünftig Frequenzsprungverfahren und Spectrum Sensing die entwickelten Protokolle erweitern. Ein großflächig und produktiv eingesetzter Demonstrator dient der ständigen Leistungsbewertung des Systems.
|||Towards Intrinsic Molecular Communication Using Isotopic Isomerism , In Open Journal of Internet Of Things (OJIOT) RonPub, volume 4, 2018. [bib] [pdf] [abstract]|
In this paper we introduce a new approach for molecular communication (MC). The proposed method uses isotopomers as symbols in a communication scenario, and we name this approach isotopic molecular communication (IMC). We propose a modulation scheme based on isotopic isomerism, where symbols are encoded via isotopes in molecules. This can be advantageous in applications where the communication has to be independent from chemical molecular concentration. Application scenarios include nano communications with isotopes in a macroscopic environment, i.e. encoding freshwater flow of rivers or drinking water utilities, or medical applications where blood carries isotopomers used for communication in a human or animal body. We simulate the capacity of communication in the sense of symbols per second and maximum symbol rate for different applications. We provide estimations for the symbol rate per distance and we demonstrate the feasibility to identify isotopes reliably. In summary, this isotopic molecular communication is a new paradigm for data transfer independent from molecular concentrations and chemical reactions, and can provide higher throughput than ordinary molecular communications.
|||UWB-based Single Reference Point Positioning System , In ITG-Fachbericht-Mobilkommunikation VDE VERLAG GmbH, 2017. [bib] [abstract]|
Indoor positioning enables new applications, for instance monitoring of goods in smart factories. For such applications, indoor positioning requires cost-effective solutions with high accuracy. State-of-the-art positioning systems are expensive due to high infrastructure and maintenance costs. In this paper we suggest an accurate UWB-based single reference point positioning system using multiple antennas. We compare lateration and hyperbolic lateration as positioning methods and present efficient algorithms for UWB-based single reference point positioning systems. We present theoretical limits based on the Cramer-Rao lower bound and derive an error estimation as well as evaluation results. Our measurements indicate that decimeter accuracy is possible.
|||Memory Efficient Forwarding Information Base for Content-Centric Networking , In International Journal of Computer Networks & Communications (IJCNC), volume 9, 2017. [bib] [pdf] [abstract]|
Content-Centric Networking (CCN) is a new paradigm for the future Internet where content is addressed by hierarchically organized names with the goal to replace TCP/IP networks. Unlike IP addresses, names have arbitrary length and are larger than the four bytes of IPv4 addresses. One important data structure in CCN is the Forwarding Information Base (FIB) where prefixes of names are stored together with the forwarding face. Long prefixes create problems for memory constrained Internet of Things (IoT) devices. In this work, we derive requirements for a FIB in the IoT and survey possible solutions. We investigate, design and compare memory-efficient solutions for the FIB based on hashes and Bloom-Filters. For large number of prefixes and an equal distribution of prefixes to faces we recommend a FIB implementation based on Bloom-Filters. In all other cases, we recommend an implementation of the FIB with hashes.
|||Survey of challenges and towards a unified architecture for location systems , In Journal of Network and Computer Applications, volume 67, 2016. [bib] [pdf] [abstract]|
Abstract Localization is a key aspect of emergent applications in the medical, industrial and consumer field. In this article we survey state of the art, identify current challenges and issues for localization systems and suggest a unified layered architecture. The analysis reveals that challenges cannot be addressed in an isolated manner for example, energy consumption is tied to the choice of algorithm and employed hardware. To separate various challenges and investigate them independently, we propose the concept of position providers. Position providers in the lower layers allow abstraction of positioning methods, positioning algorithms and positioning hardware. Thereby, a position provider encapsulates methods, algorithms and hardware. Furthermore, we suggest a classification of position providers inspired by related work. We propose a unified architecture for location systems which uses positioning and integration layers as main building blocks.
|||Iterative approach for anchor configuration of positioning systems , In ICT Express, volume 2, 2016. [bib] [pdf] [abstract]|
With anchor positions and measurements of distances between an object and anchors, positioning algorithms calculate the position of an object, e.g. via lateration. Positioning systems require calibration and configuration prior to operation. In the past, approaches employed reference nodes with GPS or other reference location systems to determine anchor positions. In this article, we propose an approach to determine anchor positions without prior knowledge. We evaluate our approach with simulations and real data based on the Decawave DW1000 radio and show that the error is proportional to the mean error of the distance estimation.
|||Reflection and transmission of ultra-wideband pulses for detection of vascular pressure variation and spatial resolution within soft tissues , In Biomedical Physics & Engineering Express, volume 2, 2016. [bib] [pdf] [abstract]|
Ultra-wideband signals have a variety of applications. An upcoming medical application is the detection of the heart rate of patients. However, current UWB systems provide poor resolution and are only able to detect vessels with a large diameter, e.g. the aorta. The detection and quantification of vascular dilation of thinner vessels is essential to develop wearable ultra-wideband based devices for real-time detection of cardiovascular conditions of the extremities. The reflection and transmission processes of those signals within inhomogeneous bodies are complex and their prediction is challenging. In this paper, we present an experimental setup (UWB system; phantom) for the detection of vascular dilation within soft tissues. Furthermore, we suggest a theoretical simulation model for the prediction of the reflection of ultra-wideband pulses and compare these simulated predictions to results of measurements within the phantom. The results verify that we are able to identify vascular dilation within the simulation model and the experimental setup, depending on the depth of the vessel (20 mm, 40 mm, 60 mm).
|||Receiving more than data - a signal model, theory and implementation of a cognitive IEEE 802.15.4 receiver , In EAI Endorsed Trans. Cognitive Communications, volume 2, 2016. [bib] [pdf] [abstract]|
Standard medium access schemes sense the channel immediately prior transmission, but are blind during the transmission. Therefore, standard transceivers have limited cognitive capabilities which are important for operation in heterogeneous radio environments. Specifically, mobile interferers move gradually into the reception range before actually causing collisions. These gradual interferences cannot yet be detected, and upcoming collisions cannot be predicted. We present a theoretical analysis of the received and demodulated signal. This analysis and the derived signal model verifies that the received signal contains more than transmitted data exclusively. Enhanced signal processing extracts signal components of an interference at the receiver and enables advanced interference detection to provide information about approaching mobile interferers. Our theoretical analysis is evaluated by simulations and experiments with an IEEE 802.15.4 transmitter and an extended cognitive receiver.
|||Cooperative Sensing Protocols and Evaluation via IEEE 802.15.4 Devices , In Special Issue of Self Optimized Radio Technologies (Journal of Physical Communication) Elsevier Science Publishers B. V., volume 19, 2016. [bib] [pdf] [abstract]|
Spectrum Sensing is one of the important tasks for wireless devices. By sensing the spectrum, wireless devices sense their radio environment and perform spectrum access accordingly to reduce collisions. Due to radio propagation effects and inherent noise in the measurements, performance of todays wireless technologies with individual spectrum sensing cannot solve the hidden node problem. Cooperative sensing is seen as a way to improve the performance of wireless devices improving the radio bandwidth utilization and minimizing interference among wireless devices. To the best of our knowledge, this is the first work which provides protocols for cooperative sensing and presents experimental results with IEEEź802.15.4 devices. We present and implement protocols and applications for primary, secondary and cooperative users with a dedicated control channel. Thereby, the secondary user receiver serves as a first cooperative node in the system which reduces collisions between primary and secondary users. We evaluate the system performance with receiver sensing and additional cooperative nodes. We also propose a mechanism to extend the protocol for multiple secondary users sharing the same control channel. Based on the evaluations, we also provide recommendations for usage of cooperative sensing with focus on IEEE 802.15.4.
|||Entwicklung einer kompakten Sensorplattform für prototypischen Einsatz in der Medizintechnik , In ImpulsE (submitted), volume 20, 2015. [bib]|
|||FULFILL - Framework zur Visualisierung, Speicherung und Filterung von Lokalisierungs-Messdaten , In ImpulsE, volume 18, 2014. [bib]|
|||Neugestaltung des Labors Kommunikationsnetze , In ImpulsE, volume 17, 2013. [bib] [abstract]|
Das Labor Kommunikationsnetze am Fachbereich Elektrotechnik und Informatik wurde in den vergangenen Jahren in einem kontinuierlichen Prozess neu gestaltet, um Studierenden die Konfiguration moderner Netzinfrastrukturen zu vermitteln und entsprechende Versuche durchzuführen. Das Labor kann dabei für eine Reihe von Lehrveranstaltungen zu Rechnernetzen inklusive der Themenbereiche Netzsicherheit und mobile Netze eingesetzt werden. Ausserdem bildet es eine hervorragende Basis für verschiedene Forschungsaktivitäten.
|||Höhenbestimmung mittels Luftdrucksensoren und differentieller Messung für Indoor-Anwendungen , In ImpulsE, volume 17, 2013. [bib]|
|||Transparent Integration of Non-IP WSN into IP Based Networks , In International Conference on Distributed Computing in Sensor Systems and Workshops IEEE Computer Society, 2012. [bib] [abstract]|
Embedded devices connected to the Internet will start an increasing growth of the Internet in near future. Wireless Sensor Networks (WSN) will play a major role in that growth. In the past several solutions were proposed to make sensor networks IP capable. Today there are IPv6-Stacks available including web servers running on sensor nodes. However, a gateway is always needed to convert the routing protocols and MAC-Layer Protocols including compression of IP packets to run on these devices. The overhead using IPv6 on the nodes is very high in respect of code size and message overhead. Therefore, in our approach we design and implement a system based on simple protocols target for sensor network nodes and a flexible gateway working in a hybrid fashion for our sensor network testbed. We successfully integrated this non-IP WSN in the Internet and our testbed is productive available from any computer connected to the Internet for reference. In this paper we present the architecture of our solution and present the implementation details of a standard WSN application that can be used for evaluation.
|||Software Defined Radio - Flexible Plattform fuer Forschung und Lehre , In ImpulsE, volume 16, 2012. [bib] [pdf]|
|||Verborgenes Rechencluster im neuen Studienarbeitsraum der Elektrotechnik und Informatik , In Impulse, volume 16, 2012. [bib] [pdf]|
|||Methods for Improving the Flow of Traffic , In missing journal Birkhäuser Verlag, 2011. [bib] [pdf]|
|||Hovering Data Clouds for Organic Computing , In missing journal Birkhäuser Verlag, volume , 2011. [bib] [abstract]|
As part of our project AutoNomos, we have investigated traffic information and management systems that motivate the usage of new methods and tools inspired by Organic Computing paradigms. Current traffic monitoring and management approaches with stationary infrastructure lack flexibility with respect to system deployment and have difficulties with detecting unpredictable events (e.g., accidents). One goal of AutoNomos is the development of a distributed and selforganising traffic information and management system without a centralised infrastructure. Our system relies on a GPS-based navigation system and a wireless radio interface; vehicles can gather information about the current position on the road network and form a vehicular ad-hoc network (VANET) to share information about traffic phenomena. In this article, we introduce Hovering Data Clouds (HDCs) as a tool to collect, aggregate and disseminate application-specific data. HDCs evolve in a self-organising manner at locations of relevant data in the system. Although their data is hosted on the nodes, HDCs exist independent of the individual carriers. While HDCs float between physical carriers, their corresponding HDC messages are disseminated in the network by a new effective transport protocol named AutoCast, designed according to Organic Computing paradigms. Finally, we demonstrate that HDCs detect traffic phenomena reliably and propagate them robustly within the network.
|||Cooperative Virtual Memory for Sensor Nodes , Chapter in Real-World Wireless Sensor Networks Springer Berlin / Heidelberg (Pedro Marron, Thiemo Voigt, Peter Corke, Luca Mottola, eds.), volume 6511, 2010. [bib] [pdf] [abstract]|
Wireless sensor networks (WSN) have unique challenges and constraints. Sensor nodes e.g. have tough memory limitations. However, the latest advances in WSN research direct for an implementation of lightweight versions of Internet protocols like IPv6, TCP, and HTTP on sensor nodes. These protocols have challenging requirements. Especially, memory consumption of these protocols is often higher than the physical RAM that microcontrollers have integrated. Therefore, we suggest an approach for virtual memory providing more memory than the available RAM. As microcontrollers do not include a memory management unit the usage of memory is implemented in cooperative fashion based on the C standard library function malloc and free. We suggest an underlying file system and a hardware abstraction layer to support various external or internal memory devices like Flash or EEPROM. In this work in progress we present an API, some implementation details and preliminary results including future work.
|||Empowered by Wireless Communication: Distributed Methods for Self-Organizing Traffic Collectives , In ACM Transactions on Autonomous and Adaptive Systems, 2009. [bib]|
|||AutoCast: A General-Purpose Data Dissemination Protocol and its Application in Vehicular Networks , In Ad Hoc & Sensor Wireless Networks journal (AHSWN), volume 6, 2008. [bib] [abstract]|
For today's mobile applications in ubiquitous/pervasive environments, the classical client-server approach with tightly-coupled components does not suit anymore. Instead, new ways of information passing between such mobile components have to be searched: components will often have no dedicated communication partner, but rather send data into a certain direction in order to inform all participants in a specific area about an event or a status. This process is called data dissemination. In this paper we introduce a new data dissemination protocol named AutoCast. Unlike other approaches, AutoCast is flexible enough to support a broad variety of different types of mobile applications. The paper presents the major design decisions taken forAutoCast and the protocol features in detail. A thorough evaluation shows the effectiveness and efficiency of the new protocol.
|||Hovering Data Clouds: A Decentralized and Self-Organizing Information System , Chapter in Proceedings of International Workshop on Self-Organizing Systems, Passau, Germany, 2006. [bib] [abstract]|
With ever-increasing numbers of cars, traffic congestion on the roads is a very serious economic and environmental problem for our modern society. Existing technologies for traffic monitoring and management require stationary infrastructure. These approaches lack flexibility with respect to system deployment and unpredictable events (e.g., accidents). Moreover, the delivery of traffic reports from radio stations is imprecise and often outdated. In the project AutoNomos we aim at developing a decentralized system for traffic monitoring and managing, based on vehicular ad-hoc networks (VANETs). Our objective is to design a system for traffic forecasting that can deliver faster and more appropriate reactions to unpredictable events. In our design, cars collect traffic information, extract the relevant data, and generate traffic reports. A key concept are so-called Hovering Data Clouds (HDCs), which are based on the insight that many crucial structures in traffic (e.g., traffic jams) lead an existence that is independent of the individual cars they are composed of. The result is an elegant, robust and self-organizing distributed information system. In this paper we demonstrate first experimental results.
|||Praxiserfahrungen mit MarathonNet - Ein mobiles Sensornetz im Sport , In PIK - Praxis der Informationsverarbeitung und Kommunikation, volume 29, 2006. [bib] [pdf] [abstract]|
Das Forschungsgebiet der Sensornetze sieht massiv verteilte Anwendungen mit einer Vernetzung von hunderten oder tausenden von kleinen meist batteriebetriebenen autarken Endgerï¿½ten vor. Aufgrund der zurzeit noch teuren Hardware und des hohen Aufwands von Feldversuchen basieren die Ergebnisse heutzutage weitestgehend auf Simulationen. Der ï¿½bergang von der Simulation zum praktischen Einsatz wird von Forschern zunehmend als eine neue Herausforderung gesehen. Unser Projekt MarathonNet hat das Ziel, in einem attraktiven Anwendungsfeld neu entwickelte Verfahren unter praxisrelevanten Umstï¿½nden zu testen. Wir prï¿½sentieren in diesem Artikel unsere ersten Erfahrungen beim ï¿½bergang von der virtuellen Welt der Simulation hin zur Ableitung der Anforderungen an die Hardware und Software und berichten von den Ergebnissen beim ersten Einsatz wï¿½hrend eines Marathons.
|||MINE and MILE: Improving Connectivity in Mobile Ad-Hoc Networks , In Mobile Computing and Communications Review MCCR, volume 8, 2004. [bib] [pdf] [abstract]|
Ad-Hoc networks are useful where infrastructure networks cannot be deployed or are not cost effective, like temporary deployment in a conference or in case of emergency. However, the nature of ad-hoc networks and especially the mobility of nodes make it difficult to achieve a certain minimum connectivity, which is an indispensable property for many applications. The question we are interested in is: How can connectivity in ad-hoc networks be improved? In this paper, we suggest to introduce dedicated mobile nodes whose only purpose is to maintain the network. These Mobile Infrastructure NodEs (MINEs) move to positions where they are useful to (re-)create links between normal nodes. We introduce into the MINE concept and then present and analyze several information exploitation and movement strategies these infrastructure nodes could follow in order to efficiently complete their job. These strategies are based on a location exchange protocol which we call Mobile Infrastructure Location Exchange (MILE). Simulations compare the different strategies and show the usefulness of the approach, and they argue for the efficiency of the MILE protocol.
|||Differential Ultrasonic Detection of Small Objects for Underwater Applications , In Global Oceans 2020, 2020. [bib] [abstract]|
Exploration of natural and artificial underwater structures is an actual field in development and research projects. Acoustic detection methods are well known and can be used to create seabed and subbottom profiles. The systems have limitations for detection of small objects, especially in presence of large acoustic reflectors. The detection of flat buried objects like unexploded ordnance (UXO) is very difficult with acoustic systems. This work presents a simple setup that utilizes three unfocused transceivers to detect small acoustic disturbances in presence of large acoustic reflectors. We suggest a differential ultrasonic receiver to eliminate equal signal components of two overlapping receivers to detect small objects. Furthermore, we present a differential single-receiver system and an evaluation of different algorithms for data visualization and compare with the frequently applied envelope in single receiver systems. It is possible to detect small objects with the diameter of $6 unitmm$ located in the water-sediment interface with the differential receiver setup.
|||MAMPI – Multipath-assisted Device-free Localization with Magnitude and Phase Information , In International Conference on Localization and GNSS, 2020. [bib] [abstract]|
Narrowband radio-frequency (RF)-based device-free localization (DFL) systems suffer from multipath propagation. Therefore, we propose multipath-assisted device-free localization with magnitude and phase information (MAMPI), a DFL system that employs ultra-wideband (UWB) channel impulse response (CIR) measurements between a transmitter and receiver and thereby benefits from multipath propagation. We implement a model that includes raytracing, diffraction, and inaccuracies of measurements in a validated error model. The multipath-assisted DFL system creates feature vectors at any position based on magnitude and phase measurements of each multipath component (MPC) of the CIR. We evaluate our new approach with a position error probability based on the propagation model including errors, as well as a distance metric of the feature vector of the positions. We compare the performance of the system with a line-of-sight solution with four instead of two nodes and variants of magnitude-only and phase-only approaches. By combining the magnitude and phase measurements of a multipath-assisted DFL system, we achieve a position error probability that is similar to the conventional DFL system.
|||Development of an Electro Impedance Tomography-based Platform for Measurement of burial Depth of Cables in Subsea Sediments , In Oceans 2019, 2019. [bib] [abstract]|
Cables buried in the seabed are objects of interests especially as companies have to verify that the buried depth of the cables is in the expected range, typically $1~m$. Although several measurement systems have been designed in the past, there is no solution available that provides an accuracy of $pm10~cm$ for this purpose. In our approach we suggest to model and measure the electrical field and electrical impedance to determine the depth of a sea cable. In the first step we develop an electrical static field model for analytic investigations. We validate the model by a simulation tool and provide results for critical environmental parameters that affect our measurement accuracy.
|||On the Effective Length of Channel Impulse Responses in UWB Single Anchor Localization , In International Conference on Localization and GNSS, 2019. [bib] [abstract]|
Recently, single anchor localization evolves as a new research topic that exploits multipath propagation for calculation of tag positions. With a combination of movement information and particle filters, they provide a precision that is similar to multi-anchor systems. However, a systematic approach to the design and implementation of such systems is not yet available. The combination of theory and mathematical modeling for channel impulse responses is still an open research question that we address in this paper. Therefore, we propose a new representation of a channel impulse response targeted for single anchor localization systems. Based on this representation, we model the relationship between tag positions and channel impulse responses and evaluate the statistic properties of channel impulse responses in this application. In this paper, we introduce a new metric for the assessment of anchor positions, the effective length of CIRs. By the shortest effective length of a set of CIRs, we identify the best anchor position, since it indicates the position where requirements for the measurement of the channel impulse response are lowest.
|||eNAV - Enhanced Co-Existence of IEEE802.15.4 and IEEE 802.11 , In IEEE Symposium on Local and Metropolitan Area Networks, 2019. [bib] [abstract]|
In the future, the Internet of Things will become increasingly important in a Smart City, for example. Today, however, established radio standards in license-free bands show that radios in heterogeneous networks interfere with each other. This includes radio standards in particular in the license-free 2.4 GHz ISM band. In this publication, we investigate IEEE 802.15.4 and IEEE 802.11 and show how radios in heterogeneous networks coordinate their actions in order to share radio resources. With the Extended Network Allocation mechanism, we demonstrate that IEEE 802.15.4 frame losses are reduced by a maximum of 50 percent even if strong interference occurs. We also show the design and implementation of an Extended Network Allocation enabled Gateway for the Internet of Things and provide a detailed description. For evaluation, we conduct measurements in a realworld application and environment.
|||IKARion: Enhancing a Learning Platform with Intelligent Feedback to Improve Team Collaboration and Interaction in Small Groups , In Proceedings of the 18th International Conference on Information Technology Based Higher Education and Training, 2019. [bib] [abstract]|
Due to a high number of participants and limited human tutoring capacities, close supervision and human guidance is hardly possible in large online courses. Thus, the aim of the IKARion project is to develop methods for intelligent and automated diagnosis and intervention in online learning environments. In this paper, we present our distributed and autonomous feedback system aiming to improve team collaboration and interaction by means of interventions. The feedback system detects and diagnoses existing and emerging problems within the groups based on their interaction patterns. Based on principles of pedagogy and educational psychology, analysis metrics and appropriate measures are provided for different types of feedback including mirroring for exploratory and informative prompts providing appropriate information about progress and actual state for the teamwork, and guiding prompts aiming to modify the interaction and collaboration of a team or an individual student. The distributed feedback system consists of three essential components: Moodle-based learning management system along with various prompts implemented as Moodle plugins, Learning Analytics Backend, and Rule-based Intervention System based on an expert system. We describe, on an architectural level, the distributed feedback system and its components. As a result, we show measurements of two long term experiments carried out in two online courses at university level with a duration of one semester each. We conclude the paper with an outlook on future work.
|||Analysis of Types, Positioning and Appearance of Visualizations in Online Teaching Environments to Improve Learning Experiences , In International Conference on Applied Human Factors and Ergonomics, 2019. [bib] [abstract]|
In this paper we investigate different visualizations of learners’ data related to collaborative online learning in terms of suitability and attractiveness to students. Furthermore, we analyze whether positioning and color appearance of these data visualizations might have an effect on learners’ behavior. To that end, we conducted an online study (n=120) as well as an eye tracking study (n=20) to compare different types of visualizations. Results show that students prefer classical data visualizations like bar charts. Visualizations placed in the sidebar of a two column web interface get less attention than visualizations in the header of the main content area. Color schemes do not seem to influence the perception of visualizations. We discuss possible explanations and implications for designing data visualizations in learning environments.
|||Minimizing Indoor Localization Errors for Non-Line-of-Sight Propagation , In International Conference on Localization and GNSS, 2018. [bib] [abstract]|
Indoor Localization becomes more important, as it provides additional context for many applications for example in the Internet of Things (IoT). Time-of-flight measurements, as a basis for distance estimation, are susceptible for non-line-of-sight (NLOS) propagation, resulting in large distance errors. Standard least squares solutions to estimate the targets location do not account for NLOS propagation which results in large scale errors. We investigate the difference between L1- and L2-minimization and present a new framework based on a modified RANSAC approach. Additionally, we investigate a Support Vector Machine (SVM) to detect NLOS measurements.We present simulation and measurement results and evaluate our approach. We show that our framework delivers better performance in presence of NLOS propagation compared to plain L1- or L2-minimization.
|||RF-Based Safety-Critical Hybrid Localization , In The Ninth International Conference on Indoor Positioning and Indoor Navigation (IPIN), 2018. [bib] [abstract]|
In safety-critical environments, e.g. paint or machine shops, precise knowledge of positions of persons is important. If an emergency is detected, e.g. a fire or an intruder in the safety-critical area of heavy machinery, emergency shutdown procedures are activated. This requires fine-grained localization with a tag-based localization system, where the person carries a tag. Without a person carrying a tag, precise localization and detection is difficult. In this paper, we propose a RF-based hybrid localization system for safety-critical localization that consists of two major components: a tag-based and device-free subsystem. The device-free subsystem provides coarse-grained localization and monitors a gate area, serving as an entrance towards the safety-critical area where fine-grained localization is required. We propose an architecture of the system, discuss our setup and evaluate typical use cases. Our preliminary evaluation demonstrates that our system detects the correct state of the hybrid localization system with an accuracy of 90%.
|||Listen and Talk in IEEE 802.15.4 with Dual Radio , In 2018 Advances in Wireless and Optical Communications (RTUWO) (RTUWO'18), 2018. [bib] [abstract]|
In wireless sensor networks, the license-free 2.4 GHz industrial medical and scientific band is increasingly popular. The popularity of this license-free band results in growing heterogeneous wireless networks in which the channel state detection becomes difficult. In this paper, we present a novel solution to enable Listen and Talk with an IEEE 802.15.4 dual radio transceiver sensor node, to provide a channel state detection. In contrast, to Listen before Talk or Clear Channel Assessment, our approach named Advanced Clear Channel Assessment talks and listens, which means checking the channel state during transmission. We show that Advanced Clear Channel Assessment increases the channel busy detection compared to Clear Channel Assessment by a factor of six. Furthermore, we provide a novel metric to compare detection algorithms for channel state based on threshold levels.
|||TriClock – Clock Synchronization compensating Drift, Offset and Propagation Delay , In IEEE International Conference on Communications, 2018. [bib] [abstract]|
In wireless sensor networks (WSN) precise clock synchronization is still a challenge e.g. for synchronized medium access control (MAC). State of the art solutions require many messages or neglect clock drifts or propagation delay. In multi-hop networks synchronization errors increase with the number of hops because numerous messages increase latency. The latency and clock drift reduces synchronization accuracy. Finally, propagation delay introduces additional synchronization offsets. We introduce a novel synchronization protocol that requires a single message to compensate both clock offset and clock drift and one additional message to account for propagation delay. With this minimal amount of messages, an efficient multi-hop synchronization is practicable. We implement our approach on a DWM1000 hardware and evaluate the protocol in single-hop and multi-hop configuration. In our preliminary experiments, we achieved a synchronization accuracy of 0.46 ns in a single-hop configuration within 3.6 ms and 6 ns in a multi-hop configuration for 5 hops within 11 ms which is appropriate for MAC and time-division multiple access (TDMA) implementations.
|||Sundew: Design and Evaluation of a Model-based Device-free Localization System , In The Ninth International Conference on Indoor Positioning and Indoor Navigation (IPIN), 2018. [bib] [abstract]|
The state-of-the-art in device-free localization systems based on RF-measurements is fingerprinting. Fingerprinting requires reference measurements called fingerprints that are recorded during a training phase. Especially in device-free localization systems, recording of reference measurements for fingerprinting is a tedious, costly, and error-prone task. In this paper, we propose Sundew, a model-based device-free localization system that does not need fingerprinting in the sense of reference measurements but is able to calculate signal strength values at any position and compare it to actual measurements after a simple calibration phase. Sundew — as any device-free localization system — requires a metric for comparison of feature vectors. In this paper, we investigate the influence of nine different distance metrics on the positioning accuracy. Simulations and measurements show that our suggested model-based device-free localization system works best with the L 1 distance metric. Sundew estimates 90% of positions in a 2.5m x 2.5m grid correctly, independent of the orientation of the person in the target area.
|||A Model-based Approach for Self-healing IoT Systems , In Proceedings of the 7th International Conference on Sensor Networks (SENSORNETS) , 2018. [bib] [abstract]|
IoT systems become more and more important in our daily life. They will perform monitoring and control tasks which are often safety-critical. Therefore, it is obviously important that IoT systems work reliably, i.e., fulfill their specification. Even if something unexpected happens, it is required that the system moves back into a correct state which we name self-healing. In this paper, we present our idea for a model-based approach for self-healing IoT systems. Based on a formal specification of the system’s properties, we derive monitors which observe the system behavior and trigger healing actions when necessary. In IoT systems, the placement of such systems becomes important due to the increased unreliability of single devices. The paper outlines basic ideas where to place monitors and how to assign monitoring tasks to IoT devices.
|||Autonome Unterwasserfahrzeuge und Kommunikationssysteme , In MST 2018 - Multisensortechnologie: Low-Cost Sensoren im Verbund Deutsche Hydrographische Gesellschaft, volume 92, 2018. [bib] [pdf] [abstract]|
Jedes moderne geodätische Messinstrument ist ein Multisensorsystem, nicht jedes kann aber als Low-Cost System bezeichnet werden. Dieser Band bietet einen Überblick zu Multisensorsystemen, Beiträge zu mathematischen Modellen zur Sensorfusion sowie zu Kommunikations-, Kalibrier- und Synchronisationsaspekten. Klassische Anwendungen wie Gleisaufnahme, Straßenerfassung sowie Überwachungsaufgaben werden beschrieben. Weitere Anwendungen finden Unterwasser, bei Verkehrsbetrieben und in der kinematischen Ingenieurvermessung statt. Ein Schwerpunkt liegt auf der Positionsbestimmung für Fußgänger und Fahrzeuge.
|||Unterwasserkommunikation, Systemvernetzung & autonome Kommunikation im Projekt BOSS , In Hydrographie 2018 - Trend zu unbemannten Messsystemen Deutsche Hydrographische Gesellschaft, volume 91, 2018. [bib] [pdf] [abstract]|
Mit unbemannten hydrographischen Erfassungssystemen, die meist ferngesteuert, zum Teil autonom oder im Verbund arbeiten, werden neue Anwendungsfelder erschlossen. Es stellt sich die Frage: Wie anwendungsreif und wirtschaftlich sind unbemannte Systeme und wie wirkt sich dies auf das Leistungsspektrum der Hydrographie aus? Dieser Band vermittelt Grundlagen zu Datenerfassungsmethoden mit integrierten Multisensorsystemen und gibt einen aktuellen Überblick über Anwendungen im Binnenbereich sowie Projekte im Hochsee- und Küstenbereich. Der Stand der Technik und die neuesten Entwicklungen werden vorgestellt.
|||Name-Centric Services for the Internet of Things , In 3rd International Conference on Networked Systems (NetSys), 2017. [bib] [abstract]|
Today, we see the development of the Internet of Things (IoT). Latest IoT devices are embedded, single-board computers (SBC) equipped with Ethernet and WiFi. Those SBCs are run an operating system and have network interfaces and use standard Internet protocols like IP, TCP, and so on. Compared to the envisioned devices for the future IoT these SBCs are still large and connected to a steady power supply. The next step in evolution towards the future IoT will be smaller, microcontroller driven devices which will operate for years on small batteries. Such small devices communicating via lowpower radios and also equipped with sensors are known as wireless sensor nodes. Ad-hoc networks formed by multiple wireless sensor nodes are so called wireless sensor networks (WSN).
|||Optical Underwater Distance Estimation , In Oceans MTS/IEEE, 2017. [bib] [abstract]|
Data communication with high data rate and precise underwater positioning with an accuracy of several centimeters is a problem. Precise positioning is important for autonomous operation and helps conserve energy which is important for many tasks. State-of-the-art acoustic communication faces difficulties underwater, e.g. multipath fading or variation of propagation speed. In this work, we propose optical distance estimation, which is the foundation for positioning. We combine the Beer-Lambert law and the inverse-square-law to model the channel of the medium. We investigate different wavelengths and employ curve fitting based on the Levenberg-Marquardt algorithm to determine the unknown coefficients of the model e.g. absorption. Our evaluation shows promising results and distance estimation of up to 25~m is possible. In stream water we determined the mean error for the optical distance estimation of 0.04m.
|||DRAISE - Drahtlose, Roboste Adaptive, Industrielle Systeme , In Zukunft der Netze 2017, Postersession, 2017. [bib]|
|||Wireless Underwater Communication via Analog OFDM Modulated Light , In Proceedings of the International Conference on Underwater Networks & Systems ACM, 2017. [bib] [pdf] [abstract]|
Short range wireless high data rate underwater communication systems become increasingly important. We provide the implementation, the setup and measurement results of the bit rate of our optical wireless underwater communication system in the Baltic Sea. In contrast to state of the art, our approach uses low frequency analog OFDM modulated light. This solution increases robustness, flexibility, and range. Furthermore, it decreases power requirements. Even with up to a 30 degree angular displacement of the transmitter the system works very well at a 6 m distance, and with a moderate power consumption of 7 W.
|||S-TDoA - Sequential Time Difference of Arrival - A Scalable and Synchronization Free Approach for Positioning , In IEEE Wireless Communications and Networking Conference, 2016. [bib] [abstract]|
In the past various solutions for localization evolved to productive usage for wireless applications. These solutions are robust, precise and energy efficient. However, scalability, complexity and flexibility are still open issues. Especially, supported number of objects or update rates for localization are still limiting factors for the usage of the systems. In this work we suggest an approach called S-TDoA which stands for sequential Time Difference of Arrival that supports unlimited number of objects and high update rates. The key concept is a sequential triggering of anchors that send periodic messages. Tags determine their position by listening to the anchor messages and measuring time intervals. Additionally, this approach enhances security because tags are not visible as they do not send messages. We implement and evaluate S-TDoA in a localization system based on UWB-RF- Chips. The preliminary results demonstrate the advantages of our implementation regarding scalability and update rates as well as privacy.
|||Impact of Altitude Difference for Local Positioning Systems and Compensation with Two-Stage Filters , In 2016 International Conference on Localization and GNSS, 2016. [bib] [abstract]|
In range-based positioning systems, an altitude difference between tag and reference plane causes errors in two- and three-dimensional positioning. We analyze how these errors reduce accuracy of Local Positioning Systems (LPS) and show how compensation of the altitude difference improves performance of positioning. In this paper, we consider the availability of additional altitude information and transform the three-dimensional positioning problem into a two-dimensional problem. We provide algorithms for time-based positioning systems with a two-stage estimator for Two-Way Ranging and Time Difference of Arrival and incorporate additional altitude information. We simulate our approach for altitude difference compensation and provide an evaluation based on a Ultra-Wideband (UWB) radio with ranging capability and a barometric sensor for additional altitude information. A comparison is then made between our approach and standard solutions such as the Extended Kalman filter and the Unscented Kalman filter. Finally, the successful decrease in the positioning error for two- and three-dimensional positioning system, using the system disclosed herein, is illustrated. Based on our analysis, we derive practical solutions to deal with altitude differences for positioning systems.
|||Introduction, Discussion and Evaluation of Recursive Bayesian Filters for Linear and Nonlinear Filtering Problems in Indoor Localization , In The Seventh International Conference on Indoor Positioning and Indoor Navigation, 2016. [bib] [abstract]|
Linear and nonlinear filtering for state estimation (e.g. position estimation or sensor fusion) for indoor positioning and navigation applications is a challenging task. Sensor fusion becomes more important with cost-effective sensors being readily available. However, state estimation with recursive Bayesian filters for sensor fusion and filtering are difficult to apply. We present an overview for the general Bayesian filter and derive the most commonly used recursive Bayesian filters, namely the Kalman, extended Kalman and the unscented Kalman filter along with the particle filter. The later Kalman filters are extension of the original Kalman filter, which are able to solve nonlinear filtering problems. The particle filter is also able to solve nonlinear filtering problems. We evaluate the recursive Bayesian filters for linear and nonlinear filtering problems for sensor fusion from relative dead reckoning positioning data and absolute positioning data from an UWB positioning system. We discuss and evaluate performance and computational complexity and provide recommendations for the use case of the recursive Bayesian filters.
|||QRPos: Indoor Positioning System for Self-Balancing Robots based on QR Codes , In The Seventh International Conference on Indoor Positioning and Indoor Navigation, 2016. [bib]|
|||Investigation of Anomaly-based Passive Localization with Received Signal Strength for IEEE 802.15.4 , In The Seventh International Conference on Indoor Positioning and Indoor Navigation, 2016. [bib] [abstract]|
Localization has important applications, for instance intrusion detection and elderly care. Such applications benefit from Device-free passive (DfP) localization systems, which employ received signal strength measurements (RSSM) to detect and track entities that neither participate actively in the localization process nor emit signals actively. RSSMs include received signal strength indicator (RSSI), energy detection (ED) and link quality indicator (LQI) measurements. This paper compares different packet-based RSSMs for DfP localization and presents detection results of a DfP anomaly-based detection system employed by IEEE 802.15.4 compliant devices. Furthermore, we investigate techniques for anomaly detection with continuous RSSI measurements.
|||Testbed for Development of Networked Autonomous Underwater Vehicles , In Oceans'16 MTS/IEEE Shanghai, 2016. [bib] [abstract]|
Development of underwater vehicles is a complex and challenging task. Especially the integration of components like sensors and actuators in a control loop is difﬁcult and costly and requires many experiments. One of the difﬁculties is the lack of debugging facilities underwater. In this paper, we suggest a distributed system architecture and a testbed concept for the development of networked autonomous underwater vehicles. Our approach is based on standard Ethernet and TCP/IP enabling use of industrial hardware like single board computers and switches. Furthermore, we suggest a mesh network with a layer 2 ad-hoc routing for wireless interconnection of underwater vehicles and infrastructure like base stations. The suggested mesh network integrates WiFi for communication on the surface and under- water electrical ﬁeld communication. To support the integration process of sensors and actuators we suggest external components for our testbed. We implement an external component including a remotely operated underwater vehicle. This remotely operated underwater vehicle serves as a carrier for sensors and allows the implementation of a control loop in underwater environments. We set up a testbed and present an evaluation of the ad-hoc routing and a dedicated control application with the remotely operated vehicle in a water tub.
|||Design of Expert Systems for Autonomous Underwater Vehicle Control , In Oceans'16 MTS/IEEE Monterey, CA, USA, 2016. [bib] [abstract]|
The development process of an intelligent autonomous underwater vehicle (AUV) is based on experiential knowledge leading to uncertainty in the software development for the intelligent AUV control. In this work we suggest an expert system to implement the AUV control software because expert systems handle uncertainty during the development process better than conventional, procedural programming languages. Furthermore, we provide design principles for the system architecture and the expert system. Finally, we present preliminary evaluation results on our designated computer hardware for the AUV we develop in a joint research project.
|||Architecture and Message Processing for Name-Centric Services in Wireless Sensor Networks , In 2016 Advances in Wireless and Optical Communications (RTUWO) (RTUWO2016), 2016. [bib] [abstract]|
Name-centric approaches provide maximum flexibility for applications, as a result, the future of Internet services is heading towards the increased importance of name-centric approaches. However, for the Internet of Things to become more name-centric, implementations of resource-constrained devices are required. Although there have been advances in the Internet of Things, such as CoAP and DPWS (Devices Profile for Web Services), these are not considered name-centric. A key to successful name-centric solutions for wireless sensor networks, is efficient handling and processing of names. In this paper we address architectural level communication and implementation for resource constraint devices. Finally, we evaluate the processing times and memory consumption of our implementation.
|||Embedded Multibeam Sonar Feature Extraction for Online AUV Control , In Oceans'16 MTS/IEEE Shanghai, 2016. [bib] [abstract]|
For development of an intelligent unmanned au- tonomous underwater vehicle (AUV), sensor data needs to be processed online for navigation and mission planning. In this work, we suggest a complete workﬂow and a processing chain to retrieve multibeam sonar data for AUV control. Our approach is based on the well-known image processing library OpenCV which provides sophisticated image recognition algorithms. We implement a processing chain for feature extraction on multibeam sonar acoustic image which retrieves contours of objects and coordinate points of the contours. Coordinate points are discrete data which can be easily processed further with additional algorithms. E.g. size of objects can be determined with the coordinate points or an expert system can classify objects with help of the coordinate points. Our solution will be embedded in an online control of an AUV. We evaluate the performance of our feature extraction approach using pre-recorded sonar data.
|||A Flexible and Modular Platform for Development of Short-range Underwater Communication , In Proceedings of the 11th ACM International Conference on Underwater Networks & Systems ACM, 2016. [bib] [pdf] [abstract]|
The development process of short-range underwater communication systems consists of different phases. Each phase comprises a multitude of specific requirements to the development platform. Typically, the utilized hardware and software is custom-built for each phase and wireless technology. Thus, the available platforms are usually not flexible and only usable for a single development phase or a single wireless technology. Furthermore, the modification and adaption between the phases and technologies are costly and time-consuming. Platforms providing the flexibility to switch between phases or even wireless technologies are either expensive or are not suitable to be integrated into underwater equipment. We developed a flexible and modular platform consisting of a controller and different front ends. The platform is capable of performing complex tasks during all development phases. To achieve high performance with more complex modulation schemes, we combine an embedded Linux processor with a field programmable gate array (FPGA) for computational demanding tasks. We show that our platform is capable of supporting the development of short-range underwater communication systems using a variety of wireless underwater communication technologies.
|||Indoor Localization based on Bi-Phase Measurements for Wireless Sensor Networks , In 2015 IEEE Wireless Communications and Networking Conference (WCNC): - Track 3: Mobile and Wireless Networks (IEEE WCNC 2015 - Track 3- Mobile and Wireless Networks), 2015. [bib] [abstract]|
Indoor localization is important for medical and industrial application as well as for wireless emergency and security systems. For such applications an accuracy within a few meters is desired. Available radio based systems within that accuracy are neither cost effective nor easy to deploy. In this work, we suggest an approach called biphase measurement based on phase measurements with two frequencies to determine the location of a tag. We design and build a complete indoor positioning system based on bi-phase measurements with easy to deploy wireless sensor nodes. The wireless sensor nodes shape anchors and tags and communicate results to a location engine of the indoor positioning system. Our implementation comprises lowcost IEEE802.15.4 radio chips with built-in support for phase measurements unit for both, anchor and tags. We compute the position of the tag based on distance estimation retrieved with bi-phase measurements. We evaluate our indoor positioning system providing first measurement results for accuracy and precision and discuss trade-off between scalability, real-time and accuracy.
|||Integrating Expert System CLIPS into DUNE for AUV Control , In Oceans'15 MTS/IEEE Genova, 2015. [bib] [abstract]|
In this paper, we motivate the need for a flexible and robust system architecture for autonomous underwater vehicles. We present a novel concept for integrating the expert system CLIPS into an AUV navigation environment DUNE. Our approach provides complete tool support for automatic source code generation and therefore allows fast and target-oriented development of control software for AUVs. We present the design of the architecture comprised of DUNE and CLIPS. In an application example we describe each step of the software development with implementation details. We show the benefits of such an expert system for a flexible AUV control. For evaluation we measure the execution time of the system and the number of fired rules of our expert system. By that we demonstrate that the approach is suited for embedded hardware of an AUV.
|||Receiving more than Data - A Signal Model and Theory of a Cognitive IEEE 802.15.4 Receiver , In Proceedings of the 10th International Conference on Cognitive Radio Oriented Wireless Networks (CROWNCOM), 2015. [bib] [abstract]|
In standard medium access, transmitters perform spectrum sensing. Information about concurrent interferers is gained mainly during this sensing period.Especially during transmission respectively reception there is a blind gap where transmitter and receiver have limited capabilities to detect interferer. Standard radio receiver devices for IEEE 802.15.4 provide solely data output and no cognitive capabilities. Particularly mobile interferer create problems when moving gradually into reception range. First, they create small interference before actually causing collision later, when approaching. However, small interference is not yet detectable by today?s transceivers. As a solution, we provide a signal model and an architecture for an extended cognitive IEEE 802.15.4 receiver as a basis for advanced signal processing for interference detection. The results of our theoretical analysis verify that the received signal contains signal marks of the interferer and therefore holds more information than transmitted data. Our theory is evaluated by simulations and experiments with a pair of IEEE 802.15.4 transmitter and an extended cognitive receiver.
|||Simulation and Evaluation of an Optical Channel Model for Underwater Communication , In Proceedings of the International Conference on UnderWater Networks and Systems 2015, 2015. [bib] [abstract]|
Underwater communication gains increasing importance with rising need for autonomous underwater vehicles (AUV) and underwater infrastructure. Many applications require only a short range link up to a few meters, but high data rates up to several megabit per second. Optical communication is a promising solution for these applications. However, the performance of underwater optical communication is highly dependent on water conditions. Previous implementations rarely provide theoretical background on design decisions and rely on experimental results to verify range and data rates. We propose a model that enables an evaluation of range and signal strength dependent on the most important components of seawater. Furthermore, we implement a prototype based on simulation results and validate the model with measurement data.
|||Interference Detection on Reception for IEEE 802.15.4 Transmissions , In Proceedings of the 21th European Wireless Conference, 2015. [bib] [abstract]|
With the increasing number of wireless devices and competing technologies in overlapping frequency bands an improved spectrum sensing is needed. Todays IEEE 802.15.4 transceiver perform spectrum sensing before transmission. They cannot detect and classify interference during transmission and reception reliably as there is a blind gap during transmission. Strong interference can be detected if bit errors occur. However, the transmission time is a long time interval compared to spectrum/carrier sensing before. In a crowded 2.4GHz ISM band with mobile interfering sources transceivers need continuous spectrum awareness to improve coexistence. In our approach we extend the physical layer (PHY) of a traditional receiver with additional signal processing. We perform signal analysis with Fourier transform of a demodulated signal to detect interferer during reception before bit errors or collisions occur. We implement our algorithm with a software defined radio as an extension of the physical layer (PHY) of an IEEE 802.15.4 transceiver. We evaluate our approach with measurements and detect mobile interferers in a real world environment. We discuss the design space of solutions as a trade-off between the quality of interference detection and the time for detection.
|||Wireless Medical Sensors - Context, Robustness and Safety , In 49th annual conference of the German Society for Biomedical Engineering (BMT 2015), 2015. [bib]|
|||Performance Evaluation of Cooperative Sensing via IEEE 802.15.4 Radio , In Wireless Communications and Networking Conference, IEEE (WCNC 2015), 2015. [bib] [abstract]|
Spectrum Sensing is one of the important tasks for the wireless devices but due to fading, shadowing and noise the performance of individual spectrum sensing devices is not ideal. Cooperative Sensing is seen as a way to improve the performance of individual spectrum sensing devices resultantly improving the efficient utilization of radio bandwidth and minimizing the interference among wireless devices. State of the art are extensive simulations and analysis on cooperative sensing although there are also number of performance evaluations of various fusion rules of cooperative sensing using software defined radios and FPGAs. The limitation of previous work is that they do not address the question how we can improve the overall performance of real systems with cooperative sensing. To the best of our knowledge, this is the first experimental work which presents cooperative sensing protocols with standard radios and evaluates the system performance using cooperative sensing. With IEEE 802.15.4 equipped radio devices we model primary, secondary and cooperating users. We implement cooperative sensing protocols, setup a scenario, perform measurements and compare system performance with and without cooperative sensing. All the experiments are automated with the wisebed testbed software. The evaluation results of cooperative sensing protocols indicate new challenges for optimization and provide awareness to the problem of improving the overall system performance
|||Accurate Radio Distance Estimation by Phase Measurements with Multiple Frequencies , In The Fifth International Conference on Indoor Positioning and Indoor Navigation 2014 (IPIN 2014), 2014. [bib] [abstract]|
Indoor localization is beneficial for logistics, industrial applications and for several consumer applications. In the area of logistics, e.g. warehouses, localization accuracy within a few meters is desired. Available radio based systems within that accuracy are neither cost effective nor easy to deploy. Distance estimations are one possible method for localization. In this work, we propose phase measurements between two wireless sensor nodes for distance estimation. We introduce a mathematical model to estimate distances from phase measurements with multiple frequencies and provide a systematic analysis of possible sources of errors. Additionally, we derive requirements, e.g. resolution and speed for a phase measurement unit to reach certain accuracy. To proof our theoretical results, we present evaluation results based on our implementation. Our implementation comprises a low cost IEEE 802.15.4 hardware with a built-in phase measurement unit. We implement the developed algorithm for distance estimation in our wireless sensor network and use two wireless sensor nodes to perform a phase measurement. The contribution of the paper comprises a new model for phase measurements to estimate distances and a preliminary evaluation with our hardware.
|||A Solution for the Naming Problem for Name-Centric Services , In 12th International Conference on Wired & Wireless Internet Communications (WWIC 2014), 2014. [bib] [abstract]|
In recent past name-centric or content-centric networking (CCN) has gained substantial attention in the networking community. In a further development step name-centric service architecture enables the flexible placement and distribution of services in the network especially in a heterogeneous environment of wired and wireless (sensor) networks. However, the problem of structuring and creating hierarchies for names in name-centric networks is not solved yet. E.g. there is no configuration of service names in name-centric service WSN, no concept of unsolicited names or link-local names in CCN. In IP networks, DHCP or IPv6 auto- configuration is available, but no equivalent technique exists for CCN. We analyze the naming problem in the software development life cycle for name-centric services in WSN and propose a structure, hierarchy, and configuration mechanism for names. The paper introduces the overall concept and preliminary steps of implementation.
|||Underwater Electric Field Communication , In Proceedings of the International Conference on Underwater Networks & Systems ACM, 2014. [bib] [pdf] [abstract]|
Underwater communications receive more attention with rising need for autonomous underwater vehicles (AUV) and underwater infrastructure. Numerous applications e.g. video streams often require only a short-range wireless transmission up to several meters in seawater with high data rates up to several megabit per second. Radio transmission in high frequency band offers high data rates but due to extreme attenuation the range is limited to less than one meter. Therefore, we suggest to set up an electrical field by two electrodes forming a dipole for transmission and reception in the MF Band (medium frequency band between 100 kHz and 10 MHz). Analytic calculations and simulations verify the concept. In the second step, we measure the transmission channel with different transmitter and receiver geometries. We show that the achievable transmission range of our approach is scalable with the separation distance between the electrodes. In a first practical evaluation with software defined radios we realized a communication link with digital modulation and a data rate of two megabit per second with signal frequency of 2 MHz for several meters.
|||Experimental Evaluation & Optimization of a UWB Localization System for Medical Applications , In 48th annual conference of the German Society for Biomedical Engineering (BMT 2014), 2014. [bib]|
|||Evaluation of Radio Based, Optical and Barometric Localization for Indoor Altitude Estimation in Medical Applications , In The Fifth International Conference on Indoor Positioning and Indoor Navigation, 2014. [bib] [abstract]|
The advances of electronics provide options for improved monitoring of patients in clinical environment.Medical applications like blood pressure monitoring require precise and wireless altitude measurement in indoor environment. An error of only a few centimeters may lead to mistreatment of patients.Furthermore, user requirements like small form factor, usability and robust operation are important in the medical field.Existing evaluations of indoor localization systems focus on accuracy analysis of x- and y-coordinates and not on the z-coordinate (altitude). In this paper, we define evaluation criteria for altitude estimation in medical applications. We compare an Ultra-Wide-Band indoor localization system, an optical Microsoft Kinect camera system and our own development of a wireless barometric sensor against these criteria. We present a comparative measurement setup, results and a final evaluation of the three systems in an indoor environment.
|||Wiseman - A Management and Deployment Approach for WSN Testbed Software , In 2013 IEEE INFOCOM Student Poster Session (INFOCOM'2013 Student Posters), 2013. [bib] [pdf] [abstract]|
Wireless Sensor Networks (WSNs) are an emerging technology. Today research in this field focuses on WSN testbeds to evaluate algorithms under realistic conditions. Numerous WSN testbed platforms allow remote deployment of WSN code and control of WSN experiments. However, one major aspect for testbeds was not addressed until now, namely the deployment and management of the testbed software itself. By deployment we mean installation and configuration of software. Once deployed on the testbed machines executables or services need maintenance and management. During testbed lifetime, periodic redeployment of testbed software is necessary due to new software versions, configuration changes, or an extension of the testbed. In this work, we present Wiseman a management and deployment approach and an implementation of Wiseman for the Wisebed WSN testbed software.
|||Name-Centric Service Architecture for Cyber-Physical Systems (Short Paper) , In Service-Oriented Computing and Applications (SOCA), 2013 6th IEEE International Conference on, 2013. [bib] [abstract]|
The goal of Service-Oriented Architectures (SOA) is to enable easy cooperation of a large number of computers and orchestration of services that are connected via a network. However, SOA for wireless senor networks (WSN) and cyber-physical systems (CPS) is still a challenging task. Consequently, for design and development of large CPS like WSNs connected to clouds, SOA has not yet evolved as an integral technology. One of the limiting issues is service registration and discovery. In large CPS discovery of services is tedious, mostly due to the fact that services are often semantically bound to a region or an application function while SOA forces service endpoints to be based on addresses of nodes. Also, today, SOA technologies are not used for service composition within sensor nodes and between sensor nodes, and even worse, different methods exist for service access in a WSN and in the backend. Therefore, service development differs largely in WSN and cloud. To overcome this limitation, we suggest a name-centric service architecture for cyber-physical systems. Our architecture is based on (a) using URNs instead of URLs to provide a service-centric architecture instead of service- or location-centric networking, (b) using the well-known CCNx protocol as a basis for our architecture which supports location and access transparency, and (c) employing CCN-WSN as the resource-efficient lightweight implementation for WSNs to build a name-based service bus for CPS. We evaluate the architecture by implementing an example application for facility management.
|||CCN-WSN - a lightweight, flexible Content-Centric Networking Protocol for Wireless Sensor Networks , In 2013 IEEE Eighth International Conference on Intelligent Sensors, Sensor Networks and Information Processing (IEEE ISSNIP 2013), 2013. [bib] [abstract]|
In future Internet research, content centric networking (CCN) is a new promising approach. CCNx has been introduced recently as an open source protocol suite for CCN and implementation base for practical research. In wireless sensor networks (WSNs) research, data or content centric approaches like in-network processing and data aggregation are important. While the principle of CCN is a suitable approach in WSNs, the CCNx protocol suite designed for PCs is not applicable to resource-constrained WSNs. Additionally, gateways necessary between CCNx and WSN are difficult to implement. Therefore, we design, implement and evaluate a lightweight variant of a CCN protocol specifically for WSNs called CCN-WSN. Key concepts of CCNx protocol are integrated but a variety of aspects are revised to meet the memory and computational constraints of sensor nodes and communication patterns in WSNs. E.g. the message format is simplified and some fields are omitted completely. Instead, we propose a flexible naming strategy which extends the functionality of content names to add small amount of data in interest messages. For performance evaluation a challenging time-synchronization application was implemented with CCN-WSN to demonstrate the flexibility of the approach and a comparison with a reference protocol for data dissemination called AutoCast is presented.
|||Short Paper: Collaboration Between VANET Applications Based on Open Standards , In 2013 IEEE Vehicular Networking Conference (VNC) (IEEE VNC 2013), 2013. [bib] [abstract]|
As of today, there is a variety of self-contained vehicular ad hoc network (VANET) applications. In many scenarios, they could complement each other if they would allow for interoperability. However, since they often use different data formats and do not share a common, machine-readable and platform-independent definition of terms and semantics, they cannot mutually understand and reuse each other's data. Consequently, in this paper we propose a VANET Ontology (VO) for defining the semantics of VANET relevant terms and a common VANET Data Representation (VDR) to facilitate interoperability between arbitrary VANET applications.
|||Precise Indoor Altitude Estimation based on differential barometric Sensing for wireless Medical Applications , In Body Sensor Networks Conference 2013 (BSN2013), 2013. [bib] [abstract]|
Some medical applications require precise information of position and orientation of a patient as changes affect pressure condition inside the body. In this paper we focus on altitude estimation, where altitude is a distance, in vertical direction, between a reference and a point of a human body. We suggest equipping wireless sensor nodes with high resolution pressuresensors to calculate the altitude with the barometric formula. We implement a body sensor network based on IEEE 802.15.4 and synchronization mechanism with a reference. Pressure variations due to environmental effects are compensated by cancellation with this differential measurement setup. We demonstrate the need for differential measurements and show with a series of measurements that environmental pressure variations have no significant effect on the proposed altitude estimation. Compared to existing systems, our solution is cost effective, easy to deploy and provides a flexible tradeoff between precision and location lag by adjusting a filter constant.
|||Performance Evaluation Metric for Cooperative Sensing in Heterogeneous Radio Environments , In European Wireless Conference, IEEE, 2013. [bib] [abstract]|
Spectrum sensing is a major task for wireless devices in order to improve coexistence among them in heterogeneous radio environments. Wireless communication includes at least two partners: transmitter and receiver. Therefore, cooperation between partners can improve the performance of spectrum sensing by reducing effort, improving sensing result or a combination of both. An optimal cooperative sensing scheme is a first step to achieve complete awareness of the radio environment for wireless devices. To the best of our knowledge, this is the first theoretical work performed in order to understand the problem of developing optimal cooperative sensing schemes for heterogeneous radio environments for multiple users and single channel. We analyze the problem and perform analytical work which results in a cooperative sensing model. The model comprises sensing schedule, data fusion rules, PU's traffic pattern, and detection performance of the sensing device. A new performance evaluation metric is introduced for optimum spectrum sensing in heterogeneous radio environments. An evaluation of available exemplary cooperative sensing schemes shows that none provides optimality in all scenarios.
|||Non-Invasive Cognitive Radio for Firm Real Time Sensor Applications in heterogeneous Radio Environments , In Proceedings of the Sixth International Conference on Sensor Technologies and Applications (SENSORCOMM), 2012. [bib] [pdf] [abstract]|
Some applications in Sensor Networks need firm real-time support in order to work properly. The difference to hard real-time systems is that this type of application can withstand minor violations of the maximum delay and minimum throughput if these violations are limited. Many standards like IEEE 802.15.4 provide standardized means to ensure delay and bandwidth constraints which work well when there are no interferers in the same frequency band. However, in a heterogeneous environment today these approaches fail when the interference is not aware of the IEEE 802.15.4 traffic. Switching the channel is one option to avoid this kind of interference. We suggest a new non-invasive cognitive radio protocol approach where all participants follow simple rules to enable firm real-time conditions in decentralized design. As a demonstrator we use a three-fold pendulum with firm real-time signal delay constraints of 5ms. The contributions of the paper comprise evaluation results by real measurements with the demonstrator system.
|||API for Data Dissemination Protocols - Evaluation with AutoCast , In The Third World Congress on Nature and Biologically Inspired Computing (NaBIC 2011) IEEE, 2011. [bib] [pdf] [abstract]|
In the past various protocols inspired by nature and biology have been proposed to disseminate or transfer data in mobile or static ad-hoc networks. Many of them are designed for usage in wireless sensor networks or vehicular ad-hoc networks. Recently, we have developed and designed a general purpose data dissemination protocol called AutoCast in this field that we evaluated in detail by simulations. When we started to use AutoCast in real applications, we found out that the description of AutoCast is incomplete, as we provided the algorithms of AutoCast in details but did neither provide nor describe a suitable Application Programming Interface (API) and AutoCast was closely coupled to the application. The focus of this article is twofold. First, we propose an appropriate API to encapsulate data dissemination protocols like AutoCast and we specify the service interface of AutoCast in detail. This API can serve as a reference model for other nature and biologically inspired data dissemination approaches and applications. Second, we evaluate two applications based on our API with AutoCast in the field of wireless sensor networks and vehicular ad-hoc networks to illustrate the usage of the API and demonstrate the flexibility of this approach.
|||GAAP - Generic Android Application Programming , In Proceedings of WWW/Internet 2011 (Bebo White, Pedro Isaías, Flávia Maria Santoro, eds.), 2011. [bib] [pdf] [abstract]|
Today, smartphones are one of the fastest growing markets in the world where Android is receiving more and more attention. In the beginning when users of smartphones use Internet applications with generic WWW-Browsers recently there is a trend that they are been replaced by special applications. For each service in the Internet e.g. Android users need to download, install and maintain individual applications. However, there are too many service providers that have their own application that need to be updated regularly because new functionality is added. Many users lose control of this administrative process which bears additionally security risks. In this paper, we suggest a generic android application programming (GAAP) comparable to a middleware where the application logic and presentation layer is placed on the server. By this approach users do not need to update their installed application. Additionally, we suggest using android-like syntax and message format for layout and GUI following the KISS-principle (Keep it simple and stupid). For evaluation purpose we developed an application providing typical GUI elements for users to demonstrate the effectiveness of GAAP approach.
|||CSOR - Carrier Sensing On Reception , In Proceedings of the 4th International Conference on Cognitive Radio and Advanced Spectrum Management (CogART), 2011. [bib] [pdf] [abstract]|
Since the 1990s the number of wireless devices increases and new areas of applications evolved. Therefore, frequency spectrum has become a scarce resource with no free frequencies left all over the world and interference between transmissions sharing the same frequency band is started to become one of the major problems in wireless transmission. The ISM bands become crowded with various standards sharing the same frequency band. One solution to the problem is to use frequency bands that are rarely used by the licensed users like TV channels, where in some region specific channels are not used at all. As a result, we need to develop adaptive systems that search for unused spectrum, use it as long as the band is free and shift to other frequency bands if there is a risk to interfere with a primary user. Such systems being aware of their radio environment are called Cognitive Radios. To search for unused frequencies and detect primary users approaches that listen before talk or efficient carrier/spectrum sensing algorithms have been presented in the past. These mechanisms are incomplete and one of the drawbacks of today's wireless transmissions is that communication partners do not detect interference reliable during an ongoing transmission. In this paper we suggest a cross layer approach Carrier Sense on Reception (CSOR) that extends the functionality of the physical layer of a transceiver to be able to detect interference while receiving data. We introduce the idea, describe the concept and give first evaluation results as a proof of concept based on real measurements.
|||Poster Abstract: Real-World G-Lab: Integrating Wireless Sensor Networks with the Future Internet , In TridentCom 2010: The 6th International ICST Conference on Testbeds and Research Infrastructures for the Development of Networks & Communities, 2010. [bib] [pdf] [abstract]|
Today's Internet is approaching architectural limits that are set up by its legacy architecture. It is based on technologies and algorithms that were developed about 30 years ago. Thus intensive research is done in the field of new protocols and algorithms fulfilling the needs of the Future Internet. We believe that wireless sensor networks (WSNs), sensor-equipped devices such as cellphones and other embedded systems will have a vital part in this context, providing a way to obtain information about the real world. All of these new devices will produce a huge amount of data by sensing and interacting with their environment. At present, complex low-level sensor node programming and algorithm knowledge is necessary to access sensor data, and only a few mature techniques exist to integrate heterogeneous WSNs with the Internet. The goal of Real-World G-Lab, which is part of the German-Lab (G-Lab) project, is to overcome these obstacles by working on the different levels of protocols, services and applications. We will enable developers to write applications that rely on sensor data input, without knowledge of the underlying hardware platform and the network communication algorithms. This implies that sensors are able to participate in the Future Internet as peer hosts. This enables new fields of applications but likewise opens a set of new challenges in the context of efficient request processing by WSNs. Efficiency here means the optimization of query-latency, energy efficiency and general service-guarantees regarding the access to sensor nodes. Beyond this we need the ability to scale to a large amount of requests from the Internet while maintaining low latencies. We will verify our concepts and applications inside the controllable environment of the G-LAB research network, by adding several outdoor WSN deployments to the experimental facility of the G-LAB project. In summary, Real-World G-LAB will contribute to the integration of resource-constrained (wireless) sensor devices into the Future Internet by investigating several key challenges, ranging from low-level energy efficiency to improved high-level application development.
|||Designing a Decentralized Traffic Information System -- AutoNomos , In Proceedings of the 16. ITG/GI - Fachtagung Kommunikation in Verteilten Systemen (KiVS), 2009. [bib] [abstract]|
We propose a decentralized traffic information system - AutoNomos - that is based on a thorough investigation of the properties of traffic and recommends a hierarchical data aggregation and forwarding for providing individualized information and support to road users. Our approach differs from work in the field by consequently applying local rules and local decentralized data processing, which turns out to be a key property of robust and scalable computing systems. We present a flexible VANET middleware that assists the application development by providing generic functionality for traffic applications. We discuss the architectural design of the overall system and provide solutions of important design concepts demonstrating the innovation of the approach.
|||Fast Prototyping for VANET Applications with PDAs , In Proceedings of the 1st International Conference on Wireless Communication Society, Vehicular Technology, Information Theory and Aerospace & Electronic Systems Technology (Wireless VITAE), 2009. [bib] [abstract]|
Today Vehicular Ad-Hoc Networks (VANETS) are a promising field for increasing comfort and safety on the road. They have the potential to connect cars with each other and thereby extract information about road conditions or dangers that drivers can't ldquoseerdquo, e.g., the end of a traffic jam behind a curve. In this article we will focus on the practical aspects of VANETs and provide an elegant and simple way to build application prototypes with the help of PDAs equipped with GPS and IEEE 802.11 wireless radio. So far, most research focused on communication aspects of VANETs. We will address the issue of how VANET applications can be implemented quickly as prototypes and propose an architecture for implementation including an interface to navigation software. The main advantage is that we can evaluate user acceptance with our approach additionally. We will show advantages and evaluation by implementing a small demo application that can be extended and be used in the future for further evaluation of protocols and complete applications covering the entire system including the user behavior.
|||FRED -- An Application for a Real-Life Large Scale Multihop Ad Hoc Network , In Proceedings of the 5th Annual IEEE/IFIP Conference on Wireless On Demand Network Systems and Services (WONS'08), 2008. [bib] [pdf]|
|||Evaluating Ad Hoc Networks with FRED , In The 9th ACM International Symposium on Mobile Ad Hoc Networking and Computing (ACM Mobihoc 2008), Demo Session, 2008. [bib]|
|||TraCI: An Interface for Coupling Road Traffic and Network Simulators , In Proceedings of 11th Communications and Networking Simulation Symposium (CNS'08), 2008. [bib]|
|||Practical Experiences on Mobile Inter-Body-Area-Networking , In BodyNets '07: Proceedings of the Second International Conference on Body Area Networks, 2007. [bib]|
|||AutoCast: An Adaptive Data Dissemination Protocol for Traffic Information Systems , In Proceedings of the 66th IEEE Vehicular Technology Conference Fall 2007 (VTC2007-Fall), 2007. [bib] [pdf] [abstract]|
Protocols and applications that rely on unicast and multicast communication are well accepted and still gain more and more popularity. However, these communication paradigms are not optimal for a class of wireless applications where communication partners neither establish specific relationships nor need roles like client and server between each other before data exchange. Applications we have in mind deal with up to several thousands of peers as autonomous wireless network nodes. Nodes communicate events like traffic accidents in a local region or information of common interest to a larger group of network nodes. Intermediate nodes forward or rather gossip information like in a social communication model, comparable to the news of the big fire of Rome in neronian times travelling through Europe and finally reaching villages in rural areas. The challenge of such a concept is to find efficient local rules, which balance communication with respect to bandwidth usage, latency of data, and data delivery ratio. We introduce the promising application AutoNomos - a decentralized traffic information system - which is well suited for the evaluation of such a data dissemination protocol. Next, we present our new approach called AutoCast that is well optimized and self-adaptable towards various dynamic topologies. We compare AutoCast against the theoretical optimum and existing data dissemination protocols. Finally, simulations will demonstrate the efficiency of the approach.
|||NIDES: Ein Verfahren zur Multihop-Distanzschätzung mittels Nachbarschaftsanalyse , In Proceedings of the 15. ITG/GI - Fachtagung Kommunikation in Verteilten Systemen (KiVS), 2007. [bib] [pdf] [abstract]|
Die Bestimmung räumlicher Entfernungen zwischen einzelnen Knoten ist ein wichtiger Aspekt in drahtlosen Sensornetzwerken. In diesem Beitrag präsentieren wir ein neuartiges Verfahren zur Abstandsschätzung, welches auf dem Vergleich von Nachbarschaftslisten basiert. Es nutzt die Tatsache aus, dass zwei dicht zusammen liegende Knoten mehr gemeinsame Nachbarn haben als solche, die weiter voneinander entfernt liegen. Das Verfahren bietet zwei besondere Vorteile gegenüber anderen Ansätzen. Zum einen kommt es gänzlich ohne zusätzliche Hardware aus und zum anderen basiert es nicht auf der Messung physikalischer Größen, wie etwa der Funksignalstärke, welche durch Umwelteinflüsse oft stark verfälscht werden. Wir erläutern die grundlegende Funktionsweise dieses Schätzverfahrens zwischen direkt benachbarten Knoten und präsentieren anschließend ausführliche Untersuchungen zur Anwendung dieser Technik über mehrere Hops hinweg. Anhand von Simulationsergebnissen demonstrieren wir, dass diese Art der Abstandsschätzung auch im Multihopfall zuverlässige Ergebnisse liefert.
|||Radio Propagation-Aware Distance Estimation Based on Neighborhood Comparison , In Proceedings of the 4th European conference on Wireless Sensor Networks (EWSN), 2007. [bib] [pdf] [abstract]|
Distance estimation is important for localization and a multitude of other tasks in wireless sensor networks. We propose a new scheme for distance estimation based on the comparison of neighborhood lists. It is inspired by the observation that distant nodes have fewer neighbors in common than close ones. Other than many distance estimation schemes, it relies neither on special hardware nor on unreliable measurements of physical wireless communication properties like RSSI. Additionally the approach benefits from message exchange by other protocols and requires a single additional message exchange for distance estimation. We will show that the approach is universally applicable and works with arbitrary radio hardware. We discuss related work and present the new approach in detail including its mathematical foundations. We demonstrate the performance of our approach by presenting various simulation results.
|||MarathonNet: Adding Value to large scale Sport Events - A Connectivity Analysis , In Proceedings of the International Conference on Integrated Internet Ad hoc and Sensor Networks (InterSense), 2006. [bib] [pdf] [abstract]|
The project MarathonNet develops wireless sensor networks for monitoring runners during marathon events. The application requires a high degree of connectivity in order to provide actual data for runners and spectators. Depending on the distribution of the runners on the track, the communication range and the number of base stations network partitions might occur that reduce connectivity. To investigate these dependencies in detail we conducted various simulations on connectivity. In this paper we first introduce the application scenario and discuss the impact of the different parameters and their interrelations. We then present the simulation results and discuss their consequences for the application design.
|||FABRIC: Towards Data Type-Centric Middleware Synthesis , In Proceedings of the 2006 International Conference on Distributed Computing (DCOSS 06), 2006. [bib]|
|||Increasing Connectivity of Ad-Hoc Networks , In 13. Fachtagung Kommunikation in Verteilten Systemen KiVS 2003 (GI-Edition), 2003. [bib] [abstract]|
Mobile Ad-Hoc networks are built spontaneously from mobile devices communicating via wireless interfaces. The idea is that some of the devices act as relay stations in such a way that two stations, which are not in direct range, can communicate with each other over this new multi-hop connection. However, the nature of Ad-Hoc networks and especially the mobility of nodes makes it difficult to achieve a certain minimum connectivity, which is an indispensable property for reliable communication. With our simulation tool ANSim (Ad-Hoc Network Simulator), we have already shown that with randomly moving nodes (a realistic assumption) one needs many mobile devices to achieve an acceptable connectivity. In this paper, we therefore investigate the idea of introducing it mobile robots to such a network, whose only function is to act as a relay station thus not to fulfil any application-specific task. The robots have to find out the optimal position in the network, i.e., the place where they can best support application-oriented devices in their work. In this first approach we assume that the robots have full knowledge of the positions of all other devices. We simulate their behaviour in this situation. The results indicate that further work on this idea will be worthwhile.
|||Towards Analysis and Simulation of Ad-Hoc Networks , In Proceedings of the 2002 International Conference on Wireless Networks (ICWN02), 2002. [bib] [pdf] [abstract]|
In order to determine whether the deployment of Ad-Hoc networks in a certain region or field of application is feasible or reasonable, analytic considerations as well as simulations are helpful. At first we introduce the underlying basic model. In the process of the paper we show that a thorough analytic approach is difficult and complex, and demonstrate the limitation of the analysis. Therefore we introduce a simulation tool for such networks and present some first investigation results. It performs in a simple manner the investigation of different Ad-Hoc scenarios by entering some fundamental input parameters.
|||Modeling the Magnitude and Phase of Multipath UWB Signals for the Use in Passive Localization , In 16th Workshop on Positioning, Navigation and Communication, 2019. [bib] [abstract]|
Radio-frequency (RF)-based device-free localization (DFL) systems measure RF parameters such as the received signal strength or channel state information to detect and track objects within a certain area. However, the change of the RF signal caused by the object is superimposed with various changes of the RF signal due to multipath propagation, especially in indoor environments. In this paper, we develop a model for ultra-wideband (UWB) channel impulse response (CIR) measurements for application in DFL systems. The model predicts received signal parameters in a setup with a transmitter and a receiver node, a person and multipath propagation. Different from other approaches, the RF hardware, and the model provides both magnitude and phase information for individual multipath components. We evaluate the new model with real measurements that have been conducted with a Decawave DW1000 radio chip. For the magnitudes, we achieved a correlation factor from 0.78 to 0.87 and maximum mean and standard deviation errors of 1.7 dB and 2.2 dB respectively. For the phase, we achieved correlation factor from 0.6 to 0.81 and maximum mean and standard deviation errors of 0.32 dB and 0.47 dB respectively, showing that the prediction of our proposed model for the magnitude and phase fits well to our measurements.
|||Evaluation of time-based ranging methods: Does the choice matter? , In 14th Workshop on Positioning, Navigation and Communication, 2017. [bib] [abstract]|
Positioning is useful in a number of applications, for instance smart home, smart factory and health care applications. Time-based ranging methods for positioning are the state-of-the-art but require precise timestamping. Sophisticated ranging methods compensate sources of errors, for instance clock drift caused by a crystal or an asymmetrical measuring principle, to provide precise timestamping. So far, no comprehensive study of different time-based ranging methods using the same hardware and the same evaluation setup was carried out. Consequently, we discuss, implement and evaluate five time-based ranging methods, including Two-Way Ranging, Double Two-Way Ranging, Asymmetrical Double-Sided Two-Way Ranging, Symmetrical Double-Sided Two-Way Ranging and Burst Mode Symmetric Double-Sided Two-Way Ranging. We evaluate accuracy, precision, robustness and run time for the ranging methods and answer the question if the choice of the time-based ranging method matters.
|||Weighted Online Calibration for Odometry of Mobile Robots , In IEEE ICC Workshop on Advances in Network Localization and Navigation (ANLN), 2017. [bib]|
|||Anomaly-based Device-free Localization with Particle Filtering , In Workshop on Dependable Wireless Communications and Localization for the IoT, 2017. [bib] [abstract]|
In the Internet of Things (IoT), devices, e.g. sensors or actuators, transmit packets to transfer data. For the IoT localization information is crucial, as it provides additional context for the data. We envision that devices in the IoT know their position and on receipt of a packet, the received signal strength is measured. This measurement is used to build a device-free localization (DFL) system to improve the dependability of the IoT system. DFL systems are able to detect and track persons within a target area that neither wear a device nor participate actively in the process of localization. This work presents an anomaly-based DFL system that measures if a person affects the radio frequency (RF) propagation and determines the position with a particle filter. In our 65m 2 indoor testbed, we employ eight IEEE 802.15.4 compliant wireless transceivers and estimate the position of a person with a median localization error of 1.4m.
|||Modeling Received Signal Strength and Multipath Propagation Effects of Moving Persons , In 14th Workshop on Positioning, Navigation and Communication, 2017. [bib] [abstract]|
Device-free localization (DFL) systems detect and track persons without devices that participate in the localization process. A person moving within a target area affects the electromagnetic field that is measured by received signal strength (RSS) values. Consequently for DFL systems modeling of RSS is important and still an open issue. In this paper, we develop a simple model for prediction of RSS values in a setup with transmitter and receiver devices, a person and multipath propagation. We design and implement the model as a superposition of both, knife-edge diffraction to account for the change made by the person, and, propagation effects such as multipath propagation that result in reflection and path loss including the antenna characteristics. We evaluate our model in comparison with real measurements in various setups with and without multipath propagation. We achieve an accuracy that is close to our hardware limitations, which is the resolution of the measured RSS values of the receiver.
|||Comparison of wired and wireless synchronization with clock drift compensation suited for U-TDoA localization , In 13th Workshop on Positioning, Navigation and Communication, 2016. [bib] [abstract]|
Indoor localization with Uplink Time Difference of Arrival (U-TDoA) provides good scalability, high updates rates and high accuracy. However, clock errors lead to localization errors and synchronization is important. In this paper, we design and implement wired and wireless synchronization and provide a comparison between them. We design and implement a wireless synchronization with clock drift compensation. For wired and wireless synchronization, we discuss reasons for clock deviation that lead to localization errors. We evaluate both approaches in a U-TDoA measurement setup. Finally, we provide recommendations for wired and wireless synchronization.
|||Mobile Robot Seamless Localization with Localization Optimized QR Codes , In 12th Workshop on Positioning, Navigation and Communication, 2015. [bib] [abstract]|
Indoor navigation is a prerequisite for new emerging applications for autonomous mobile robots. Additionally to the location of a robot, the orientation is important for these applications. Furthermore, a solution to this localization problem should be inexpensive and easy extensible for new areas of a building. We propose inexpensive optical landmarks based on localization optimized Quick Response (QR) code for localization of the landmark within an image to reduce computational cost. We further specify the error correction level, border, and size of the QR code for optimal localization. The proposed QR code combines GPS coordinates and local coordinates which allows seamless integration of our approach. We perform image processing to estimate the distance and orientation of a mobile robot with respect to the localization optimized QR code. To evaluate our approach we implemented the approach in an Android application and measured the performance in experiments. Additionally, we suggest a method to retrieve more accurate GPS information based on the measured orientation and distances. Our implementation achieves update rates of up to 3 Hz and an accuracy of 1 cm
|||Tool Chain for Application Development with Name-Centric Services , In The 12th IEEE International Workshop on Managing Ubiquitous Communications and Services, 2015 (MUCS'15), 2015. [bib] [abstract]|
Regarding service oriented architectures various tool chains evolved in the last decades. However, in terms of content-centric approaches tools and middleware are in an early stage. Especially tool support for name-centric services in future heterogeneous networks is not available. Future networks will cover future Internet, wireless sensor networks and cyber-physical systems. Existing content-centric networking provides powerful, flexible, but heavyweight APIs to the developers but does not cover middleware and tool chains for services. Therefore, we implement a solution for application development with name-centric services based on an existing content-centric networking protocol. We design a lightweight service description based on JSON which is short and can be easily understood. We implement a complete tool chain for automatic code generation for server and client applications. We demonstrate the workflow, the convenience for the application developer and the effectiveness of our approach in a convincing application example. A first evaluation of the code generation reveals a prediction of logical lines of code and illustrates the complexity of the problem that is now solved automatically. Our approach is proven to simplify and advance the application development process for name-centric services.
|||VaSili - A Simulation Runtime Environment for Applications in Vehicular Ad-Hoc Networks , In 2015 IEEE 12th Consumer Communications and Networking Conference (CCNC): CCNC 2015 Workshops - VENITS (CCNC 2015 - CCNC 2015 Workshops - VENITS), 2015. [bib]|
|||Integrated Low-Power SDR enabling Cognitive IEEE 802.15.4 Sensor Nodes , In Proceedings of the 8th Karlsruhe Workshop on Software Radios, 2014. [bib] [abstract]|
The number of mobile devices with radio transceivers is increasing. However, standard wireless sensor nodes have limited spectrum awareness in order to avoid col- lisions with other concurrent transmissions in dense spectrum. E.g. IEEE 802.15.4 standard performs carrier sensing before start of the transmission. Spectrum sensing or awareness during the transmission is not provided. These low power devices have only limited capabilities in order to detect and forecast upcoming collisions. In this work, wireless sensor nodes are equipped with additional piggybacked hardware and supplementary signal processing capabilities. An additional RF-frontend and small-size SDR hardware enable sensor nodes to perform cognitive radio functionality. Although the sensor nodes transmit data fully com- pliant to IEEE 802.15.4 the supplementary hardware enhances spectrum awareness significantly even during transmission. A previously published cognitive radio scheme was implemented to demonstrate the signal processing capabilities of the SDR hardware. Additionally, power consumption and battery lifetime were evaluate and calculated.
|||Software Defined Transceiver for Underwater Communication , In Proceedings of the European Workshop on Testbed based Wireless Research, 2014. [bib] [abstract]|
New applications for autonomous underwater vehicles require underwater wireless communication with data rates up to several megabit per second and a transmission range up to several meter. Regular radio transceivers achieve a poor performance in seawater. Therefore, our project evaluates and implements new approaches for optical, acoustic and electric underwater communication. The goal is to implement a flexible software defined transceiver consisting of a FPGA with exchangeable communication modules.
|||Efficient Data Aggregation with CCNx in Wireless Sensor Networks , In 19th EUNICE Workshop on Advances in Communication Networking (EUNICE 2013), 2013. [bib] [abstract]|
CCNx is the reference implementation for a content centric networking (CCN) protocol developed by the Palo Alto Research Center CCNx group. It serves also as reference for our CCN-WSN, a CCNx implementation for wireless sensor networks (WSN). Efficient data aggregation with CCN-WSN is a challenge. In order to collect data from source in the network data sinks have to poll data sources with interests and exclude fields in interests are necessary bloating the interest messages. We solve the problem by introducing three building blocks in CCN-WSN: unicast faces for packet filtering and ``link'' abstraction, a forwarding service for creating network overlay structures used by applications and an intra-node protocol providing an API for applications to interact with the forwarding service. For evaluation purpose we implement an application using a forwarding service implementing a tree topology to collect data in the WSN.
|||A Reusable and Extendable Testbed for Implementation and Evaluation of Cooperative Sensing , In The 8th ACM International Workshop on Performance Monitoring, Measurement and Evaluation of Heterogeneous Wireless and Wired Networks PM2HW2N'13, 2013. [bib] [abstract]|
Cooperative sensing has been identi?ed as a potential improvement for cognitive radios to perceive their radio environment. In the past, algorithms have been developed by analysis and simulations exclusively. With cheaper hardware experimental platforms have been used for evaluation purpose recently. Simulations lack realistic propagation models for radio transmission but are reproducible compared to experimental evaluation done by hand. The effects of reduced detection probability and false alarms are not realistic in these simulations. In this paper, we suggest a reusable and extendable automated testbed software and instructions for deployment of own testbeds. Primary users as well as secondary users with cooperating cognitive radios can be flexibly deployed in the testbed within seconds. The advantage is that a series of even long lasting measurements including automatic logging of results can be easily repeated. Results can be assessed on the fly during the ongoing evaluation by accessing debug output remotely. The testbed supports stationary, portable, and in the future mobile radio devices for flexible scenarios as well as monitoring devices for debugging. The testbed and the radio devices are validated by deploying primary and secondary user in a small scenario whose outcome was analyzed beforehand. The results are as predicted and show the usefulness of this approach.
|||Non-Invasive Cognition driven Spectrum Access in Medical Application via Baseband Processing , In Proceedings of the 7th Karlsruhe Workshop on Software Radios, 2012. [bib] [abstract]|
In the field of medical applications there are special regulations and requirements as many devices are sensitive to interference by other equipment. Although wireless links are susceptible to interference they are potential technologies enabling mobile and wireless applications substituting cables in all medical areas like operating room, intensive care unit or ambient assistant living. With continuous increase of these devices equipped with radio interfaces a non-homogenous radio environment with dense occupancy will form. We propose an approach with high sensitivity for non-invasive cognition of radio environment by fusion of two baseband processing blocks. First, we detect and identify interference by concurrent radio links non-invasively during reception. Second, we minimize invasive channel switching by continually probing and classification of available channels based on adapted probabilities. We use GNU Radio a Software Defined Radio platform to implement this system to provide a non-invasive continuous cognition of the radio environment and minimize the invasive utilization of occupied channels. In this paper we present preliminary studies, the overall idea, the approach and first implementation results.
|||Using and Operating Wireless Sensor Network Testbeds with WISEBED , In Proceedings of the 10th IEEE IFIP Annual Mediterranean Ad Hoc Networking Workshop, 2011. [bib] [pdf] [abstract]|
Current surveys and forecast predict that the number of wireless devices is going to increase tremendously. These wireless devices can be computers of all kinds, notebooks, netbooks, Smartphones and sensor nodes that evolve into realworld scenarios forming a "Real-World-Internet" in the future. In our work we focus on the Future Internet with small battery driven devices forming the "Internet of Things". In recent networking research, testbeds gain more and more attention, especially in the context of Future Internet and wireless sensor networks (WSNs). This development stems from the fact that simulations and even emulations are not considered sufficient for the deployment of new technologies as they often lack realism. Experimental research on testbeds is a promising alternative that can help to close the gap. The deployment of testbeds is challenging and user and operator requirements need to be considered carefully. Therefore, the goal is to design an architecture that allows operators of WSN testbeds to offer numerous users access to their testbeds in a standardized flexible way that matches these requirements. In this paper we first identify some of the requirements, then introduce the architecture and general concepts of our WISEBED approach and show how this architecture meets the requirements of both groups. We give an overview of existing WISEBED compatible WSN testbeds that can be used for experimentation today. Main focus in this paper compared to previous work is to address the perspective of both users and operators on how to experiment or respectively operate a WSN testbed based on WISEBED technology.
|||SAFH - Smooth Adaptive Frequency Hopping , In International Workshop on Cross-Layer Design (IWCLD 2011), 2011. [bib] [pdf] [abstract]|
Wireless systems based on WLAN (802.11), ZigBee (802.15.4) and Bluetooth (802.15.1) are continuously deployed in new applications covering consumer, industry or medical fields. Especially, Bluetooth is recommended by the Health-Care-Organization for medical applications as frequency hopping is considered as a robust scheme. However dealing with frequency-dynamic sources of interference in the 2.4GHz ISM band is important due to the increase of wireless devices. Adaptive frequency hopping (AFH) suggested by the Bluetooth standard and implemented in many of todays products identifies and avoids using bad channels. It is a good and established coexistence mechanism in the presence of frequency-static sources of interference such as WLANs when the 2.4GHz band is not crowded. However, AFH is facing problems in a crowded 2.4GHz band, especially when the interference is dynamic. We developed a cross-layer algorithm SAFH (Smooth Adaptive Frequency Hopping) that is inspired by entropy maximization and the conventional Bluetooth AFH. SAFH assigns usage probabilities to all channels based on an exponential smoothing filter for frame error rates to estimate and predict the channel conditions. The application layer can adapt SAFH by parameter settings in a cross-layer approach. SAFH achieves low average frame error rate and responds fast to changing channel conditions if required from the application. Simulative Evaluation in the presence of different types of interference (802.11b, 802.15.4 and 802.15.1) shows that our algorithm outperforms conventional frequency hopping and AFH. Additionally, SAFH works smoothly and stable exploiting frequency diversity compared to previous approaches like entropy-maximization based adaptive frequency hopping and Utility Based Adaptive Frequency Hopping (UBAFH).
|||RoombaNet - Testbed for Mobile Networks , In Proceedings of the Workshops der wissenschaftlichen Konferenz Kommunikation in verteilten Systemen 2011 (WowKiVS 2011) Electronic Communications of the EASST (Tiziana Margaria, Julia Padberg, Gabriele Taentzer, eds.), volume 37, 2011. [bib] [abstract]|
The design and deployment of wireless networks needs careful planning including various tools for analysis, simulation and evaluation. Therefore, development of software to support deployment of wireless networks has been subject of intensive research for several years. In particular the evaluation of the influence of mobility remains a challenging task. For deployment of mobile communication networks operators perform simulations and measurements during the planning process with large efforts. In the past the research community based their decisions on development of new protocols on simulations exclusively. While network simulators provide fast investigation of huge and also mobile networks they rely on theoretical models which are often considered as inaccurate and too optimistic. Therefore, more and more real wireless network environments called testbeds are established worldwide most of them with static nodes. Testbeds dedicated towards mobile networks remain a challenge as the effort to build such a network increases with mobility. The work here presents an approach for a fully automated real-world mobile network testbed where nodes are piggybacked on mobile robots. The platform with up to 30 mobile nodes and additional 30 static nodes can emulate various scenarios especially suited for pedestrian scenarios or for slow car movements. In this paper we introduce this testbed which is integrated into the larger Real-World GLab Internet testbed facility. We provide first details of the hardware and software components and provide first evaluations as well as present application examples.
|||Limitations of Frequency Hopping in 2.4 GHz ISM-Band for Medical Applications Due to Interference , In Proceedings of the Workshop Consumer eHealth Platforms, Services and Applications (CeHPSA) IEEE CCNC 2011 Conference Proceedings, 2011. [bib] [pdf] [abstract]|
In the past a number of wireless standards evolved in industry and the consumer market that operate in the unlicensed ISM (Industrial, Scientific, Medical) Bands especially in the 2.4GHz range. Today these products are well engineered and standardized, so that more and more medical applications consider wireless transmission based on these standards. Especially in the clinical environment radio links will substitute cables and further enable new fields of applications. Also personal healthcare and ambient assisted living are emerging fields for the future. However, in contrast to many consumer applications medical applications need to guarantee interoperability, ensure coexistence with other applications and have very high requirements for robustness, safety and security. There is an upcoming need for investigation if existing radio standards are prepared for the usage in medical applications regarding reliability and interoperability. In this work we will focus on Frequency Hopping and Bluetooth as one of the technologies that has been designed for robustness and coexistence and evaluate the underlying principles by a comprehensive analysis, simulation and measurements. To the best of our knowledge this comprehensive investigation for robustness of wireless transmission based on Frequency Hopping in a heterogeneous mix of interference from standards like WLAN, IEEE 802.15.4, Bluetooth and proprietary systems in health care environment has not been performed yet. We will conclude the paper by an outlook for further improvement of wireless transmission based on Frequency Hopping suited to the needs of medical applications.
|||EZgate - A Flexible Gateway for the Internet of Things , In Proceedings of the Workshops der wissenschaftlichen Konferenz Kommunikation in verteilten Systemen 2011 (WowKiVS 2011) Electronic Communications of the EASST (Tiziana Margaria, Julia Padberg, Gabriele Taentzer, eds.), volume 37, 2011. [bib] [abstract]|
Two years ago a survey of the wireless world research forum predicted that in the year 2017 there will be seven trillion wireless devices for seven billion humans which is equivalent to 1000 devices per human being on the average. The future will show if this incredible number will be reached but for sure we will see an increasing number of wireless devices forming the Internet of the future. The new evolving ``Internet of Things'' is one of the challenging research topics today. With many wireless resource constraints devices, smart gateways integrating these small battery-powered devices into the future Internet will play a major role for the success of the Internet of Things. These gateways will work as a communication endpoint or proxy enabling transparent services including mechanisms for semantic service discovery, Quality of Service (QoS), and performance enhancing proxies (PEPs). In this work we will introduce a fully operable TCP/IP-Stack EZgate written in Java that allows designing and implementing such gateways for wireless networks in a flexible and fast approach and compare it with related work. We will demonstrate how the protocols in this stack can be assembled in a flexible manner, creating various types of gateways and can be easily extended to implement cross layer techniques. Finally, we evaluate the performance of the implementation for delay and throughput performance to show that EZgate is suitable for use in a productive environment.
|||Middleware for Smart Gateways Connecting Sensornets to the Internet , In MidSens'10: The fifth international workshop on Middleware Tools, Services and Run-Time Support for Sensor Networks, 2010. [bib] [pdf] [abstract]|
There is an increasing trend to integrate sensor networks into the Internet, eventually resulting in an Internet of Things. Recent efforts of porting IPv6 to sensor networks turn sensor nodes into equitable Internet peers and RESTful Web Services on sensor nodes allow a distribution of the application logic among sensor nodes and more powerful Internet nodes. The touching point between a sensor network and the Internet is the gateway which translates between the link-layer protocols used in the Internet (Ethernet, Wi-Fi) and sensor networks (IEEE 802.15.4). So far, the functionality of those gateways was fixed and simple. We propose to turn these gateways into smart gateways by enabling them to execute application code. As only the gateway has full knowledge of and control over both the sensor network and the Internet, smart gateways can act as performance-enhancing proxies and intelligent caches to preserve the limited resources of the sensor network. Also, the smart gateway can perform application-specific protocol conversion between highly optimized but non-standard protocols in the sensor network and standardized, but less efficient protocols in the Internet. In this paper we present the design of a middleware for smart gateways that allows the execution of application code on the gateway by offering simplified interfaces to the sensor network and the Internet. We also report preliminary performance results for key functions of the middleware.
|||Effective Movement Classification for Context Awareness in Medical Applications Networking , In First International Workshop on Medical Applications Networking, 2009. [bib] [abstract]|
Today new medical applications evolve from large stationary devices to small and smart mobile systems that will enable e.g. more efficient post operative health care. These mobile systems that benefit from ongoing miniaturization and energy savings in hardware will allow continuous monitoring of patients accompanying and supporting therapy and detect emergency situations. Additionally to vital data, the physiological load or the context of patients are important to analyze and understand recorded data of mobile patients. Current approaches for movement classification aim to detect very specific movement patterns and are dependent on precise sensor placements and are thus not suited for everyday usage. Therefore, we developed a movement detection and classification algorithm that can be easily integrated in existing embedded devices. Using data from a single accelerometer embedded into the device, the algorithm can classify between different movement patterns -- the ''context'' -- of the monitored person. We will describe the hardware and the algorithm and will provide first evaluation results demonstrating the effectiveness of this approach for providing context awareness in mobile medical applications in real-time.
|||VANET Simulation Environment with Feedback Loop and its Application to Traffic Light Assistance , In Proceedings of the 3rd IEEE Workshop on Automotive Networking and Applications, 2008. [bib] [abstract]|
Traffic applications, in which vehicles are equipped with a radio interface and communicate directly with each other and the road traffic infrastructure are a promising field for ad-hoc network technology. Vehicular applications reach from entertainment to traffic information systems, including safety aspects where warning messages can inform drivers about dangerous situations in advance. As performance tests of the real system are very expensive and not comprehensive, today's evaluations are based on analysis and simulation via traffic simulators. In order to investigate the impact of traffic information systems there are two options: First, traffic simulators can be extended by application code and a simplified model for wireless communication. Second, existing network simulators can be coupled with existing traffic simulators. We favour the second approach in this work as we believe that the wireless communication characteristics influence the data transfer significantly and an oversimplified transmission model can lead to flawed results. In this paper we describe the feedback loop built by the Traffic Control Interface (TraCI) to outline its versatility. We explain its use to determine possible energy consumption reduction when traffic lights send their phase schedules to vehicles.
|||FlowerNet - How to design a user friendly Sensor Network , In Proceedings of The Seventh Annual Mediterranean Ad Hoc Networking Workshop (Med-Hoc-Net 2008), 2008. [bib]|
|||GRAPE - Gradient based Routing for All PurposE , In Proceedings of the Third International Workshop on Heterogeneous Multi-Hop Wireless and Mobile Networks 2007 (IEEE MHWMN'07), Pisa, Italien, 2007. [bib] [abstract]|
Routing within wireless mobile multi-hop networks is a challenging task. Therefore, in the past several routing protocols have been developed with various extensions and adoptions to certain specific scenarios. The consensus of the discussion about routing is that depending on all aspects of their application reaching from number of nodes, mobility, to the data traffic profile of the application developers can choose an optimal routing protocol. In the meantime some routing protocols have evolved as standard choice like AODV, DSR, OLSR, TBRPF. With the advent of sensor networks, requirements like scalability and resource consumption are added to the research domain. This resulted in additional extremely specialized routing algorithms or special extensions to existing protocols. So is there really a need and room for another routing protocol? We are convinced that a really simple, efficient, scalable protocol that allows for mobility and is suited for various performance classes of devices does not exist. We propose GRAPE as a completely new approach for routing in wireless multi-hop networks and present performance results based on simulations and measurements that demonstrate the potential of the routing approach.
|||Data-type centric Middleware Synthesis for wireless Sensor Network Application Development , In Proceedings of the Fifth Annual Mediterranean Ad Hoc Networking Workshop (Med-Hoc-Net 2006), 2006. [bib] [abstract]|
Writing applications for wireless sensor networks presents a complex domain, that requires expertise from various fields. Existing middleware frameworks alleviate this problem by hiding low-level networking aspects but are either not comprehensive or not flexible enough. Our system called FABRIC addresses this problem by proposing a data type-centric middleware synthesis framework for heterogeneous devices. While hiding networking aspects and complexity of distributed systems, it still offers the required flexibility because data handling can be differentiated on a per-type basis. This approach especially addresses the unique requirements of resource constrained devices. In addition, FABRIC supports a clear separation between application and framework development, thus supporting a less error-prone development process.
|||Ansätze zur Analyse und Simulation von Ad-Hoc Netzwerken , In Proceedings of the 1st German Workshop on Mobile Ad-Hoc Networks (GI-Edition), 2002. [bib] [pdf]|
|||Verfahren zur kontaktlosen Messung wenigstens eines Vitalparameters eines Patienten , Offenlegungsschrift, DE102020103911.5, 2020. [bib]|
|||Suitable Path Loss Model for LoRa networks in suburban areas , (T. M. Buzug et. al., ed.), 2019. [bib] [abstract]|
Network planning requires a suffficiently accurate model of the path loss of signals. This paper is analyzing the suitability of the Okumura, ECC-33 and COST231 model for the LoRaWAN technology. Since the frequency band is different than Wifi and LTE, the results will differ. Therefore, a measurement in an area of Luebeck is performed and compared to the predictions of the different models. The most suitable model is then used and extended by a loss per building factor. This factor is determined by a series of measurements performed in front of and behind a building. The COST231 and Okumura models show the best prediction, while the Okumura model underestimates the path loss and the COST231 overestimates it.
|||Understanding and Prediction of Ultra-Wide Band Channel Impulse Response Measurements , Technical report, Technische Universität Braunschweig, 2019. [bib] [pdf] [abstract]|
Recently, ultra-wide band transceiver systems have provided data transfer, timestamps and channel impulse response measurements to the user. The interpretation of the timestamps and the channel impulse response, however, is difficult and not intuitive. In simple scenarios, line of sight and non-line of sight pulses can be distinguished easily, which simplifies the reconstruction. For more complex scenarios, the interpretation remains difficult and is still an unsolved problem. In this paper, we investigate the channel impulse response measurements of the DecaWave DW1000 ultra-wide band transceiver and model the expected results for simple scenarios based on information provided from the transceiver data sheet. We will show that we are able to predict the measurement results of the transceiver with acceptable accuracy by applying the model above in experiments.
|||A Practical Toolbox for Getting Started with mmWave FMCW Radar Sensors , Technical report, Technische Universität Braunschweig, 2019. [bib] [pdf] [abstract]|
In this paper, we sum up our experience gathered working with mmWave FMCW radar sensors for localization problems. We give a glimpse of the foundations of radar that is necessary to understand the benefit and advantages of this technology. Moreover, we introduce our open-source software toolbox pymmw based on Python for Texas Instruments IWR1443 ES2.0 EVM sensors to provide students and researchers easy access to those radar sensors. In doing so, one can jump right into sensing with mmWave FMCW radar from a practical point of view and start doing experiments and developing own applications. Finally, pymmw is used for data acquisition of a scene illuminated by three virtual radars in three different states of occupancy showing the potential of mmWave FMCW radar for indoor and distance-based localization applications.
|||Phase Error Correction for IEEE 802.11 Channel State Information , (T. M. Buzug et. al., ed.), 2019. [bib] [abstract]|
Channel State Information (CSI) capture is a new technology, which measures the phase and magnitude of WLAN signals. In this paper, we investigate the accuracy and predictability of CSI phase measurements for potential use in geometric localization. We determine known sources of linear and non-linear error. The known sources of error are then correct for by utilizing a curve fitting method. An ideal mathematical model is created and compared to the corrected phase results. The conclusion is that the phase correction method was effective in some cases, however, the results were inconsistent with additional unaccounted sources of error.
|||Improvements to UWB Channel Impulse Response Measurements for Indoor Localization , (T. M. Buzug et. al., ed.), 2019. [bib] [abstract]|
This paper proposes two methods to improve the accuracy of UWB channel impulse response (CIR) measurements. Improving the accuracy of UWB CIR measurements results in an improvement of the overall accuracy of an indoor localization system. Two methods are analyzed, both with the idea of combining a series of CIR measurements to yield higher accuracy than a single measurement. We evaluated both methods by gathering data at different positions within a room. These methods reduced the error by an average of 7% and 4% respectively. The results indicate that utilizing these techniques will improve the accuracy of localization.
|||Investigation of the Message Delay in Wireless Sensor Networks , (T. M. Buzug et. al., ed.), 2019. [bib] [abstract]|
Wireless sensor networks (WSN) can be implemented across entire cities to connect devices and sensors with each other. The example used in this paper to represent a WSN is that street lamps (nodes) build a transport network, which will be investigated to find the message delay. Furthermore, each street lamp is connected to a garbage can (sensor) via a second network. So that, a garbage-can sends data to a street lamp and the street lamp forwards the data through the transport network until the destination receives the message. Each hop of the message occurs a delay which sums up to a multi-hop delay. In this paper, we simulate the transport network by using Contiki-NG with Cooja and calculate the delay of a message with an algorithm. The algorithm finds the routing path of the received message and saves the calculated multihop delay. Our results demonstrate that the delay of the messages becomes smaller if the throughput to the nodes decreases. For the garbage bin example, the delay would not be a problem, however, keep in mind that a delay of 1s is too much for many applications.
|||Recurrent Neural Network for Sequence Classification of mmWave Radar Data , (T. M. Buzug et. al., ed.), 2019. [bib] [abstract]|
This paper unveils the potential and utilization of Recurrent Neural Network (RNN) in radar applications for sequence classification. We focus on human activity recognition, which inputs are multichannel time series signals acquired by a frequency modulated continuous wave (FMCW) millimeter wave (mmWave) radar. We designed a proof of concept implementation for a system where a mmWave radar records the movement of a human body. The proposed RNN predicts and classifies the direction the human is heading. Such systems are valuable in numerous applications ranging from security and safety applications like detection and assessment of human activity at airports to patient monitoring in hospitals. Applied to the dataset recorded by the mmWave radar the implemented RNN provides satisfying classification results.
|||Proceedings of the 4th KuVS/GI Expert Talk on Localization , Technical report, Technische Universität Braunschweig, 2019. [bib] [pdf]|
|||Impact of the antenna orientation for distance estimation , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf] [abstract]|
Indoor localization is important for a wide range of use cases including industrial, medical and scientific applications. The location accuracy is affected by the localization algorithm and the quality of the measurements as input for the algorithm. Many indoor localization systems employ ultra-wideband distance measurements, as they offer high accuracy and are cost effective. One of the methods for distance measurement is twoway ranging. This paper investigates the impact of the antenna orientation on the distance measurement based on symmetrical double-sided two-way ranging. We show that up to 0.25m of the measurement error is attributed to the orientation of the antennas. We provide explanations and suggest solutions to reduce the effect.
|||Lessons learned: Indoor Ultra-Wideband localization systems for an industrial IoT application , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf] [abstract]|
Since ultra-wideband (UWB) transceivers are available for wireless sensor networks, the usage in research and industry increased. Research efforts resulted in methods, measurement results, and solutions under laboratory conditions for a variety of indoor localization problems provided to the community. In this paper, we present an indoor positioning system (IPS) that is installed in a $mathbf1500 m^2$ real world production facility. In this real-world application, we faced some challenges that research has not addressed yet. For instance, challenges are receiving UWB signals from other floors in a multistory building through windows and multipath effects at walls like reflexions. We present solutions to increase the availability of such large-scale IPS, give a performance evaluation and recommendation for a modified NMEA sentence named iNMEA for IPS receivers.
|||Comparison of Antenna Types and Frequency Bands for Radio-based Device-free Localization , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf] [abstract]|
Radio-based device-free localization systems measure effects on radio signals e.g. signal strength variations to locate objects or persons in a target area. Such systems detect and track persons that do not participate in the localization process. Models for calculating the radio signal propagation are key for the performance in device-free localization systems. Received signal strength (RSS) is simple to measure. However, it is susceptible to changes in the environment and multipath propagation. In this paper, we compare PCB antennas to a circularly polarized cloverleaf antenna and measurements in the 2.4 GHz with measurements to the 868MHz ISM band. We investigate especially if a circularly polarized cloverleaf antenna is resilient against multipath propagation. Our preliminary results demonstrate that our model is suitable to the 868MHz band and the use of the 868MHz band increases the area where a person affects the RSS. The use of a circularly polarized cloverleaf antenna does not help to avoid multipath propagation.
|||Proceedings of the 3rd KuVS/GI Expert Talk on Localization , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf]|
|||S-TDoA (Sequential Time Difference of Arrival)-Verfahren zur Positionsermittlung von bewegbaren Objekten durch sequentielle Ankunftszeitdifferenzbestimmung von periodischen Signalen , EP Patent App. EP20,170,157,702 Google Patents, 2017. [bib] [pdf]|
|||Evaluation of Bluetooth Positioning for Medical Device Tracking , GRIN (T. M. Buzug et. al., ed.), 2017. [bib]|
|||A syntactic approach to wreck pattern recognition in sonar images , GRIN (T. M. Buzug et. al., ed.), 2017. [bib]|
|||Investigation of Anomaly-based Passive Localization with IEEE 802.15.4 , Technical report, RWTH Aachen University, 2016. [bib] [pdf]|
|||Proceedings of the 2nd KuVS Expert Talk on Localization , Technical report, RWTH Aachen University Department of Computer Science of RWTH Aachen University (Mathias Pelka, Grigori Goronzy, Jó Agila Bitsch Link, Horst Hellbrück, Klaus Wehrle, eds.), 2016. [bib] [pdf]|
|||Comparison and Performance Evaluation of Indoor Localization Algorithms based on an Error Model for an Optical System , GRIN (T. M. Buzug et. al., ed.), 2015. [bib]|
|||Proceedings of the 1st KuVS Expert Talk on Localization , Technical report, RWTH Aachen University Department of Computer Science of RWTH Aachen University (Mathias Pelka, Jó Agila Bitsch Link, Horst Hellbrück, Klaus Wehrle, eds.), 2015. [bib] [pdf]|
|||Localization of Heart Reference Point of a Lying Patient with Microsoft Kinect Sensor , GRIN (T. M. Buzug et. al., ed.), 2014. [bib]|
|||Organic Computing Concepts in Protocol Design for Ad-Hoc Networks , Technical report, CoSA Research Group, 2009. [bib] [pdf] [abstract]|
With the change from wired to wireless technologies the complexity of computer networks increases significantly. Distributed applications built on top of these wireless networks must be well designed to work in this difficult and changing environment. Especially the ad-hoc wireless communication between devices with wireless transceivers based on ad-hoc structures is still an open research field. Protocols designed in the past based on simulations solely using simple transmission models and graph theoretic assumptions fail to work reliably in real field tests. Therefore, organic computing systems that have lifelike properties including self-adaptation and self-organization are a promising approach for new protocols in wireless Adhoc networks. In this paper we introduce the idea of organic computing and demonstrate how research in this field can inspire protocol design. For use in wireless ad-hoc networks we extract general organic computing principles that guide designing robust, efficient but simple protocols. Finally we will present three exemplary protocols that have been built with these principles including a summarized evaluation.
|||Supporting WSN Application Development Using Data type-centric Middleware Synthesis , Technical report, 5. GI/ITG KuVS Fachgespräch Drahtlose Sensornetze, 2006. [bib] [pdf] [abstract]|
Writing applications for wireless sensor networks presents a complex domain that requires expertise from various fields. Existing middleware frameworks alleviate this problem by hiding low-level networking aspects but are neither comprehensive nor flexible enough. Our system called Fabric addresses this problem by proposing a data type-centric middleware synthesis framework for heterogeneous devices. While hiding networking aspects and complexity of distributed systems, it still offers the required flexibility because data handling can be differentiated on a per-type basis. This approach especially addresses the unique requirements of resource constrained devices. In addition, Fabric supports a clear separation between application and framework development, thus supporting a less error-prone development process.
|||Basic Analysis and Simulation of Ad-Hoc Networks , Technical report, International University Bruchsal, 2001. [bib] [pdf] [abstract]|
In order to determine whether the deployment of Ad-Hoc networks in a certain region or field of application is feasible or reasonable, analytic considerations as well as simulations are helpful. In this technical report we present a simulation tool for such networks. It performs in a simple manner the investigation of different Ad-Hoc scenarios by entering some fundamental input parameters. At first we introduce the underlying basic model. In the process of the report we show that a thorough analytic approach is difficult and complex, and show the limitation of the analysis. Therefore we introduce our simulation tool.