Reinhard Exel

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The use of wireless technologies in Factory Automation is attractive due to several advantages (mobility, cost, etc.); however, to satisfy the requirements of industrial applications, they have to be improved in terms of real-time performance. Handover is a particular weakness in cellular wireless systems, e. g., in IEEE 802.11, since it may introduce delay(More)
With the rise of Global Navigation Satellite Systems (GNSSes), accurate outdoor localization has become a widelyused service in our daily lives. Yet, most indoor localization systems are not able to deliver a similar performance due to typical multipath environments causing scattering and diffraction of the received signal. Depending on the amplitudes,(More)
— Clock synchronization protocols for packet-oriented networks, like IEEE 1588, depend on time stamps drawn from a local clock at distinct points in time. Due to the fact that software-generated time stamps suffer from jitter caused by non-deterministic execution times, many implementations for high precision clock synchronization rely on hardware support.(More)
The introduction of wireless networks in the factory floor offers many advantages. Besides a new flexibility for automation, also features like the localisation of wireless devices ease the use of this technology. However, for the application on the factory floor real-time guarantees have to be given, which can be ensured by schemes like TDMA, which is(More)
Time based localisation methods like GPS are widely used for outdoor navigation, whereas indoor navigation is typically performed only on a cell-basis or based on the Received Signal Strength Indicator. Since RSSI is not able to fulfil all current requirements, Time of Arrival and Time Difference of Arrival based approaches have recently gained focus. As(More)
In the recent years, the term wireless factory automation began raising interest. Its probably most appreciated feature, mobility, is yet acknowledged as the key for new applications. Nevertheless, this apparent freedom comes with a palette of requirements, whereof one is localisa-tion. Although locating systems have been an extensive research topic for(More)
Synchronizing clocks in a distributed system is an indeed challenging task. Although there exists a various class of applications, like synchronizing the clock of a PC with the Network Time Protocol, where an accuracy of several milliseconds is sufficient, many applications, such as synchronized test and measurement or localization services in wireless LANs(More)
In distributed systems, clock synchronization performance is hampered by delays and jitter accumulated not only in the network, but also in the timestamping procedures of the devices being synchronized. This is particularly critical in software timestamp-based synchronization where both software- and hardware-related sources contribute to this behavior.(More)