TY - JOUR A1 - Schindelhauer, Christian A1 - Volbert, Klaus A1 - Ziegler, Martin T1 - Geometric spanners with applications in wireless networks JF - Computational Geometry: Theory and Applications N2 - In this paper we investigate the relations between spanners, weak spanners, and power spanners in for any dimension and apply our results to topology control in wireless networks. For , a c-spanner is a subgraph of the complete Euclidean graph satisfying the condition that between any two vertices there exists a path of length at most c-times their Euclidean distance. Based on this ability to approximate the complete Euclidean graph, sparse spanners have found many applications, e.g., in FPTAS, geometric searching, and radio networks. In a weak c-spanner, this path may be arbitrarily long, but must remain within a disk or sphere of radius c-times the Euclidean distance between the vertices. Finally in a c-power spanner, the total energy consumed on such a path, where the energy is given by the sum of the squares of the edge lengths on this path, must be at most c-times the square of the Euclidean distance of the direct edge or communication link. While it is known that any c-spanner is also both a weak -spanner and a -power spanner for appropriate , depending only on c but not on the graph under consideration, we show that the converse is not true: there exists a family of -power spanners that are not weak C-spanners and also a family of weak -spanners that are not C-spanners for any fixed C. However a main result of this paper reveals that any weak c-spanner is also a C-power spanner for an appropriate constant C. We further generalize the latter notion by considering -power spanners where the sum of the δth powers of the lengths has to be bounded; so ()-power spanners coincide with the usual power spanners and ()-power spanners are classical spanners. Interestingly, these ()-power spanners form a strict hierarchy where the above results still hold for any some even hold for while counter-examples exist for . We show that every self-similar curve of fractal dimension is not a -power spanner for any fixed C, in general. Finally, we consider the sparsified Yao-graph (SparsY-graph or YY) that is a well-known sparse topology for wireless networks. We prove that all SparsY-graphs are weak c-spanners for a constant c and hence they allow us to approximate energy-optimal wireless networks by a constant factor. Y1 - 2007 U6 - https://doi.org/10.1016/j.comgeo.2006.02.001 VL - 36 IS - 3 SP - 197 EP - 214 ER - TY - CHAP A1 - Thelen, Simon A1 - Volbert, Klaus A1 - Nunes, Danilo Weber T1 - A Survey on Algorithmic Problems in Wireless Systems T2 - Proceedings of the 12th International Conference on Sensor Networks (SENSORNETS), Vol 1, Feb 23, 2023 - Feb 24, 2023, Lisbon, Portugal N2 - Considering the ongoing growth of Wireless Sensor Networks (WSNs) and the challenges they pose due to their hardware limitations as well as the intrinsic complexity of their interactions, specialized algorithms have the potential to help solving these challenges. We present a survey on recent developments regarding algorithmic problems which have applications in wireless systems and WSNs in particular. Focusing on the intersection between WSNs and algorithms, we give an overview of recent results inside this intersection, concerning topics such as routing, interference minimization, latency reduction, localization among others. Progress on solving these problems could be potentially beneficial for the industry as a whole by increasing network throughput, reducing latency or making systems more energy-efficient. We summarize and structure these recent developments and list interesting open problems to be investigated in future works. KW - Algorithms KW - WSNs KW - Survey KW - Network Construction KW - Routing KW - Interference KW - Localization KW - Charging KW - Latency Y1 - 2023 SN - 978-989-758-635-4 U6 - https://doi.org/10.5220/0011791200003399 SP - 101 EP - 111 PB - SCITEPRESS - Science and Technology Publications ER - TY - CHAP A1 - Nunes, Danilo Weber A1 - Volbert, Klaus T1 - A Wireless Low-power System for Digital Identification of Examinees (Including Covid-19 Checks) T2 - Proceedings of the 11th International Conference on Sensor Networks (SENSORNETS), 07.02.2022 - 08.02.2022 N2 - Indoor localization has been, for the past decade, a subject under intense development. There is, however, no currently available solution that covers all possible scenarios. Received Signal Strength Indicator (RSSI) based methods, although the most widely researched, still suffer from problems due to environment noise. In this paper, we present a system using Bluetooth Low Energy (BLE) beacons attached to the desks to localize students in exam rooms and, at the same time, automatically register them for the given exam. By using Kalman Filters (KFs) and discretizing the location task, the presented solution is capable of achieving 100% accuracy within a distance of 45cm from the center of the desk. As the pandemic gets more controlled, with our lives slowly transitioning back to normal, there are still sanitary measures being applied. An example being the necessity to show a certification of vaccination or previous disease. Those certifications need to be manually checked for everyone entering the university’s building, which requires time and staff. With that in mind, the automatic check for Covid certificates feature is also built into our system. KW - Indoor Navigation KW - Indoor Localisation KW - Low-power Devices KW - Internet of Things KW - RSSI KW - BLE Beacons Y1 - 2022 SN - 978-989-758-551-7 U6 - https://doi.org/10.5220/0010912800003118 SP - 51 EP - 59 PB - SCITEPRESS - Science and Technology Publications ER - TY - CHAP A1 - Thelen, Simon A1 - Eder, Friedrich A1 - Melzer, Matthias A1 - Nunes, Danilo Weber A1 - Stadler, Michael A1 - Rechenauer, Christian A1 - Obergrießer, Mathias A1 - Jubeh, Ruben A1 - Volbert, Klaus A1 - Dünnweber, Jan T1 - A Slim Digital Twin For A Smart City And Its Residents T2 - SOICT '23: Proceedings of the 12th International Symposium on Information and Communication Technology, 2023, Hi Chi Minh, Vietnam N2 - In the engineering domain, representing real-world objects using a body of data, called a digital twin, which is frequently updated by “live” measurements, has shown various advantages over tradi- tional modelling and simulation techniques. Consequently, urban planners have a strong interest in digital twin technology, since it provides them with a laboratory for experimenting with data before making far-reaching decisions. Realizing these decisions involves the work of professionals in the architecture, engineering and construction (AEC) domain who nowadays collaborate via the methodology of building information modeling (BIM). At the same time, the citizen plays an integral role both in the data acquisition phase, while also being a beneficiary of the improved resource management strategies. In this paper, we present a prototype for a “digital energy twin” platform we designed in cooperation with the city of Regensburg. We show how our extensible platform de- sign can satisfy the various requirements of multiple user groups through a series of data processing solutions and visualizations, in- dicating valuable design and implementation guidelines for future projects. In particular, we focus on two example use cases concern- ing building electricity monitoring and BIM. By implementing a flexible data processing architecture we can involve citizens in the data acquisition process, meeting the demands of modern users regarding maximum transparency in the handling of their data. KW - smart city KW - AI KW - digital twin KW - artificial intelligence KW - urban planning KW - BIM KW - portal system Y1 - 2023 SN - 979-8-4007-0891-6 U6 - https://doi.org/10.1145/3628797.3628936 SP - 8 EP - 15 PB - ACM ER -