Our background in aerospace pays off for this DLR spin-off. Not only the anti-collision system TCAS used in aircrafts inspired us for a technology transfer into the railway domain. In particular positioning accuracy and availability requirements for the train collision avoidance application were challenging as they cannot be solved in a simple way with the help of Global Navigation Satellite Systems (GNSS). Our deep understanding of the GNSS architecture, the algorithms and error sources, and about extensions such as SBAS/GBAS is necessary to understand and solve the problems when using GNSS under railway operational conditions in specific railway environments. Likewise the cooperative direct train-to-train communication system required an exhaustive knowledge of the propagation conditions in typical railway environments under high load. For safety-of-life applications such as the collision avoidance, a particular robust and reliable positioning as well as communication is essential, and thus was the focus of the research led to the technolgoy. Of course the ongoing developments on Galileo and its services are closely monitored.