In this project the radio itself is used as a sensor, the angle of arrival and time-of-flight is used to gauge the position of the transponder.
I found some publications that I think originate from this project over at the TUM website.
There is also a press release from BMW, from which the following is taken:
"In their AMULETT project, researchers investigated the possibilities of Car-2-X Communication with the aim of improving pedestrian safety. To this end they linked up autonomous on-board systems for driving environment assessment with communication between the car and a transponder carried by a pedestrian or cyclist for their own safety. By means of this cooperative sensor technology, the vehicle exchanges data with the “Amulett”, an active RFID-like (Radio Frequency Identification) element, which could in future be integrated into a schoolbag, a mobile phone or a walking stick, for example.
In detail it works as follows: upon receiving an interrogation impulse from the vehicle, the transponder transmits an identification message. This enables its position to be fixed and, even more importantly, identifies its carrier as a vulnerable road user. It works even if the carrier is not within sight of the driver at the time of danger, for example if the pedestrian is obscured by a parked car or a hedge. The Amulett identifies itself through a code that is frequently changed at random to prevent the carrier being linked to a specific transponder. “In this way we ensure that the user remains anonymous – in compliance with data protection laws – without compromising the prediction of the sensor data,” explains Dr Ralph Rasshofer, AMULETT Project Manager for BMW Group Research and Technology."
