Blind-Spot Vehicle Distance Estimation Using High-Frequency FMCW Radar and Passive Metal Reflector

This paper proposes a method for estimating inter-vehicle distances in blind-spot environments by combining high-frequency radar with passive metal sheets. Specifically, the approach utilizes the directional radiation pattern of a 60 GHz frequency-modulated continuous-wave (FMCW) radar and the reflective boundary conditions provided by strategically placed passive metal sheets. By analyzing reflection characteristics derived from varying beam angles and applying discrete Fourier transform (DFT), the system enables the detection of vehicles that are visually occluded and cannot be identified by conventional sensors such as cameras, LiDAR, or millimeter-wave radar. The method was validated using three vehicles, including the radar-mounted ego vehicle, by varying the distance between the two vehicles ahead and adjusting the radar’s emission angle. Experimental results demonstrated successful detection of inter-vehicle distances in non-line-of-sight scenarios with an accuracy within 0.15 m. Furthermore, to validate real-world applicability, real-time inter-vehicle distance measurements were conducted using dynamic vehicles and guardrails as passive reflectors. The system achieved detection accuracy within 0.26 meters under practical conditions. This technique enhances environmental awareness for next-generation mobility platforms by enabling indirect yet precise perception in occluded conditions. Moreover, it has potential for mitigating chain-reaction collisions caused by delayed recognition or reaction by elderly drivers, contributing significantly to traffic safety.