In the proposed cooperative sensor system, pedestrians carry a reactive transceiver which is interrogated by a localization and tracking unit in the car. The prototype system applies Round-Trip Time-of-Flight (RTOF) techniques for the determination of the distance between the transponder and the demonstrator vehicle. A smart antenna array integrated into the car is used to determine the Direction-of-Arrival (DoA) of the transponder’s response signal. Knowing the distance and azimuth angle relative to the car, the pedestrian’s position and movement are calculated. These data are used as input for a highly reliable collision warning and collision mitigation system.

The sensor system is capable of addressing a huge number of communication partners within each measurement cycle. Additionally, secure burst identification is ensured for a robust localization and the suppression of unwanted co-channel interference. This is achieved by using pseudo random coded signals with a Time Division Multiple Access (TDMA) method. The distance accuracy was improved by introducing a new mirror technique in combination with an interpolation algorithm. The prototype localization system set up at 2.4 GHz covers a range up to 200m in free field condition. With the current system a distance resolution with centimeter accuracy and an angular measurement accuracy of about 1 degree have been achieved.

Based on this low-cost transponder-based localization system, a preventive vulnerable road user (VRU) protection system has been designed and integrated in a test vehicle. The system is capable to provide a warning to the driver if a crash is likely and to autonomously brake the vehicle if the crash is unavoidable.