Multipath Exploitation in Through-Wall Radar Imaging Via Point Spread Functions

Abstract

Due to several sources of multipath in through-wall radar sensing, such as walls, floors, and ceilings, there could exist multipath ghosts associated with a few genuine targets in the synthetic aperture beamformed image. The multipath ghosts are false positives and therefore confusable with genuine targets. Here, we develop a multipath exploitation technique using point spread functions, which associate and map back the multipath ghosts to their genuine targets, thereby increasing the effective signal-to-clutter ratio (SCR) at the genuine target locations. To do so, we first develop a multipath model advocating the Householder transformation, which permits modeling multiple reflections at multiple walls, and also allows for unconventional room/building geometries. Second, closed-form solutions of the multipath ghost locations assuming free space propagation are derived. Third, a nonlinear least squares optimization is formulated and initialized with these free space solutions to localize the multipath ghosts in through-wall radar sensing. The exploitation approach is general and does not require a priori assumptions on the number of targets. The free space multipath ghost locations and exploitation technique derived here may be used as is for multipath exploitation in urban canyons via synthetic aperture radar. Analytical expressions quantifying the SCR gain after multipath exploitation are derived. The analysis is validated with experimental EM results using finite-difference time-domain simulations.

Multipath Exploitation in Non-LOS Urban Synthetic Aperture Radar

“…In [14], exploitation of single bounce multipath (ghost) targets in the presence of the target LOS paths was analyzed in the SAR domain for through-the-wall sensing. The objective here unlike [5]- [12] is to reduce false positives and improve the SCR at the target location by association and mapping of the multipath [14], [15].…”

“…In other words, is an element of indexed appropriately. For subsequent operations on the matrices , we normalize them as (15) where, denotes the absolute value that we allow to operate on matrices elementwise as well. A simple thresholding operation is now employed with threshold parameter given by,…”

“…We see that four multipath trajectories now intersect at the target location. For the image domain algorithm, the focus locations of the combination multipath are required, which are obtained from techniques used in [15]. After computing the focused locations of combination multipath, exploiting them is straightforward from the image domain exploitation technique presented here.…”

Multipath removal by online blind deconvolution in through-the-wall-imaging

“…Earlier works considered the problem of multipath elimination by assuming a perfect knowledge of the reflective geometry of the scene. For example, Setlur et al [3,4] have developed multi-path signal models to associate the multi-path ghosts to the true target locations, thereby improving the radar system performance by reducing false positives in the original SAR image. Chang [5] proposed a physics based approach to multi-path exploitation where the imaging kernel of the back-projection method is designed to focus on specific propagation paths of interest.…”

Blind multi-path elimination by sparse inversion in Through-The-Wall-Imaging

“…In [3] and [4], multi-path signal models are derived to associate and map the multi-path ghosts to the true target locations, thereby improving the radar system performance by reducing false positives in the original SAR image. A physics based approach to multi-path exploitation is proposed in [5] where the imaging kernel of the back-projection method is designed to focus specific propagation paths of interest.…”