All posts filed under: Publications

Synchronization with phase rate correction

Synchronization algorithms based on the theory of pulse-coupled oscillators are evaluated on programmable radios. It is experimentally demonstrated that the stochastic nature of coupling is a key ingredient for convergence to synchrony. We propose a distributed algorithm for automatic phase rate equalization and show that synchronization precisions below one microsecond are possible.

Achieving consensus in networks with disturbances

The problem of finding a consensus in a group of people occurs in many social contexts. In a similar way, distributed algorithms for consensus play an important role in networked computing and communication systems if centralized decision making is difficult or impossible. Each entity in such a system processes only local information obtained from its neighbors and ideally performs only simple computations. Despite this simplicity, the process of consensus building should be robust against different types of disturbance, such as faulty entities, noise, and communication errors. A research team with members from Klagenfurt and Genoa has now analyzed the robustness of a special class of consensus algorithms, namely binary consensus, in which all entities must eventually agree on one out of two possible values. The motivation for their study is as follows: Some binary consensus algorithms that work well in noiseless and error-free networks—such as the well-known Gacs-Kurdyumov-Levin algorithm—show convergence problems in networks with disturbances. In turn, some other algorithms that are inferior in noiseless and error-free networks may actually improve their performance with the …

Collaborative mapping with mobile robot teams

New packages for the Robot Operating System (ROS) are available for autonomous exploration of unknown environments using collaborating mobile robots equipped with cameras. The software offers wireless ad hoc communications between robots, merging of maps from different robots, and coordinated selection of exploration frontiers. A prototype with four robots was built that demonstrates its functionality in an indoor environment.

Wireless technologies for small UAV systems

Small unmanned aerial vehicles (UAVs) are more and more used in civil applications, for example, in disaster situations to provide rescue teams with up-to-date aerial photos. The wireless communications to UAVs and between UAVs is an important building block in such systems. Researchers from U Klagenfurt, U Toronto, ETH Zürich, and the German Aerospace Center discuss the state-of-the-art on wireless communications for UAV systems along with directions for research and development in the May issue of the IEEE Communications Magazine. “We evaluated the suitability of today’s wireless technologies for their use in UAV systems,” Torsten Andre, a PhD student with Christian Bettstetter, explains. “To do so, we took a top-down approach, starting from the application and deriving communication requirements for the wireless network on a search and rescue mission.” Measurements of experimental aerial networks were analyzed with respect to the requirements including achievable transmission delay and throughput. Publication T. Andre, K. Hummel, A. Schoellig, E. Yanmaz, M. Asadpour, C. Bettstetter, P. Grippa, H. Hellwagner, S. Sand, S. Zhang. Application-Driven Design of Aerial Communication Networks. IEEE …

Programmable radio boards (WARP)

Pulse-coupled oscillator synchronization on FPGA radios

The mathematical modeling of pulse-coupled biological oscillators offers a fully decentralized and scalable approach for time synchronization. There is a broad spectrum of work on pulse-coupled oscillators in physics, biology, neuroscience, and other disciplines. The communications engineering community has been interested to transfer these results to the synchronization of nodes in wireless networks. A one-to-one transfer is infeasible due to the differences between wireless and biological communications. Several extensions and modifications are required with respect to delays, noise, multihop communications, and sync words.

A relay selection protocol for cooperative wireless networks

The key idea behind cooperation in wireless networks is that devices help each other to communicate messages properly over the air. When a transmitter sends messages to a receiver, adjacent devices can overhear these messages. If the direct transmission to the receiver fails, one of those devices can retransmit (“relay”) its message copy to the receiver. It was shown that such relaying can outperform standard communication techniques. In practice, however, coordination protocols among the involved devices are needed, in particular solutions for relay selection and medium access control. Helmut Adam, Evsen Yanmaz, Christian Bettstetter, and Wilfried Elmenreich have been working on this challenge for four years. They specified and evaluated the COREMAC protocol targeted for low-budget and energy-constrained off-the-shelf hardware. The protocol located at the Medium Access Control (MAC) layer integrates radio resource reservation, relay selection, and packet flow. “We believe that cooperative relaying will not be implemented in practice until protocols supporting the physical layer to exploit the benefits of relaying are designed and properly specified,” researcher Adam says. Bettstetter adds: “The challenge of …

Wirtschaftsblatt: Smart network for factory halls

Metal parts in factory halls disturb wireless communications. ICT researchers from Klagenfurt invented a new transmission technique and are now looking for partners for implementation. Although the need for fast and reliable data transmission via WLAN increases in production halls, the technology is still limited. Mobile machinery, forklifts, and robots disturb the radio link between transmitter and receiver. Wolfgang Rössler reports. Read online: Publication Nikolaj Marchenko, Torsten Andre, Günther Brandner, Wasif Masood, and Christian Bettstetter. An Experimental Study of Selective Cooperative Relaying in Industrial Wireless Sensor Networks. IEEE Transactions on Industrial Informatics, vol. 10, no. 3, pp. 1806-1816, August 2014.