Spatial Multipath Characterization via in Situ Harmonic Transponders

Wireless communication between devices moving in complex environments is prone multipath effects. Thus measuring and characterizing the multipath caused by an environment prior to deploying a system is of interest. Standard approaches nominally require a transmitting source at one end of a link and a separate receiving setup at the other. In this work, we present an alternative in which a passive harmonic transponder is embedded in the environment to be characterized. Harmonic transponders are passive, nonlinear wireless devices that receive an interrogation signal at one frequency $(f)$ and backscatter harmonics (typically, $2 f$ is of interest). Using a remote interrogator (combination of transmitter and receiver), we are able, using an amplitude modulated (AM) interrogation signal, to separately determine the forward link loss at $f$, from the reverse link loss at $2 f$. Using the proposed method, we demonstrate the ability to characterize the multipath, over space, of a high-multipath reverberation chamber.