Uhrensynchronisation in einem lokalen Funknetzwerk

The research group Cooperative Autonomous Systems of the Institute for Autonomous intelligent systems (AiS.CAS) of the GMD - German national research center for information technology, in cooperation with the institute for distributed systems of the University of Magdeburg, develops a common platform for autonomous mobile systems which allows these systems to reach a common goal in a cooperative effort. To achieve this, these systems have to interact with their own environment. From this, we derive some real-time constraints: These interactions have to be timed exactly in the case the systems have to interact with their environment, in the case these are observations of the environment, we must be able to establish a timely order. In both cases, the system needs a global time allowing to perform these functions. Since the systems are mobile, the communication between the autonomous systems has to be wireless to preserve the mobility. Thus, a wireless LAN is used. This diploma thesis develops a time synchronization protocol which can be used on a wireless network. This protocol copes with the inherent properties of a wireless LAN that distinguish it from a classical wired LAN. This protocol is analyzed in detail, so that we can guarantee the provided precision of the synchronized clocks under any specified circumstances. These circumstances comprise up to a configurable upper limit for messages losses which is crucial for the wireless medium. Besides the theoretical development and analyzation of the protocol, which is suited for a wireless LAN of the standard lEEE 802.11, this diploma thesis implements this protocol in a device driver under Windows NT, using wireless LAN network interface cards ,,WaveLAN/IEEE" of Lucent Technologies, Inc. With the help of this implementation and a measurement environment specifically designed for this purpose, this implementation has been evaluated in detail, confirming the theoretical results.