Through-the-Wall SAR Auto-Focusing With Low Accuracy Positioning System

This paper analyzes a through-the-wall synthetic aperture radar (SAR) imaging system designed for indoor use with imprecise positioning systems. Due to uncertainties in transceiver positions at scanning timestamps and the defocusing effects caused by multi-medium (air-wall-air) wave propagation, an autofocus algorithm is essential to achieve high-quality SAR imaging for further detection purposes. We propose a fast and accurate autofocus procedure integrated with the back-projection algorithm, outperforming conventional SAR autofocus algorithms (e.g., map drift algorithm, phase gradient algorithm). Furthermore, we present extensive simulated and experimental results for two indoor positioning systems: a stereoscopic camera and a radio frequency localization system based on the off-the-shelf Pulson P440 transceiver. The primary contributions of this paper include a novel SAR autofocus algorithm based on a prominent scatterer located in front of or behind the wall, along with a fast, recursive routine for solving the nonlinear system of equations associated with the 3D localization system.