An Ultra-Low-Cost Early Warning Sensor for Pedestrians

In this work, we present a low-cost wearable sensor that alerts pedestrian users of vehicles approaching from behind to avoid potential collisions. It uses a custom IQ Doppler radar board at 10.5 GHz on low-cost FR4 substrate to differentiate incoming vehicles' positive Doppler shift from the receding environment's negative shift. A second signal processing board with a microcontroller and accelerometer, also on FR4, performs Fourier analysis on the I and Q components to identify incoming vehicles. Using the onboard accelerometer, the module determines the user's instantaneous state of the gait and adjusts detection thresholds in real time to dynamically account for the complex movements of the pedestrian. The sensor correctly detects approaching vehicles in the presence of other stationary and receding objects at average distances of 27.6 and 28.2 meters for walking and jogging, respectively.