  Millimeter wave sensing has recently attracted a lot of attention given its
environmental robust nature. In situations where visual sensors like cameras
fail to perform, mmwave radars can be used to achieve reliable performance.
However, because of the poor scattering performance and lack of texture in
millimeter waves, radars can not be used in several situations that require
precise identification of objects. In this paper, we take insight from camera
fiducials which are very easily identifiable by the camera, and present
R-fiducial tags, which smartly augment the current infrastructure to enable a
myriad of applications with mmwave radars. R-fiducial acts as a fiducial for
mmwave sensing, similar to camera fiducials, and can be reliably identified by
a mmwave radar. We identify a precise list of requirements that a millimeter
wave fiducial has to follow and show how R-fiducial achieves all of them.
R-fiducial uses a novel spread-spectrum modulation technique that provides low
latency with high reliability. Our evaluations show that R-fiducial can be
reliably detected upto 25m and upto 120 degrees field of view with a latency of
the order of milliseconds. We also conduct experiments and case studies in
adverse and low visibility conditions to showcase the applicability of
R-fiducial in a wide range of applications.
