Joint Detection of Human and Object Motion Using Harmonic Micro-Doppler Radar and Harmonic Tags

We present a new method for jointly detecting the motion of moving people and tagged objects using harmonic micro-Doppler radar and passive harmonic tags. Wirelessly measuring the motion of people and held objects is important for applications, including sensing in living spaces and industrial monitoring. A significant challenge in discriminating the motion of objects from that of people is the relatively low signal power generated by the radar return from a held object relative to the clutter return power. We overcome this limitation by using harmonic tags that generate a response at a harmonic of the incident radar signal. The radar emits a continuous-wave (CW) signal at a fundamental frequency of 2.5 GHz, which scatters off the person and is collected by a 2.5 GHz receiver. The harmonic tag collects the 2.5 GHz signal and generates a harmonic response at 5 GHz, which is collected by a 5 GHz receiver on the radar. Frequency modulation on the 5 GHz signal is thus generated only by the motion of the tag, while the 2.5 GHz modulation is predominantly due to the motion of the person. The fundamental and harmonic received signals can thus be processed separately for direct joint detection of the dynamic motion of people and held objects.