  Automotive synthetic aperture radar (SAR) can achieve a significant angular
resolution enhancement for detecting static objects, which is essential for
automated driving. Obtaining high resolution SAR images requires precise ego
vehicle velocity estimation. A small velocity estimation error can result in a
focused SAR image with objects at offset angles. In this paper, we consider an
automotive SAR system that produces SAR images of static objects based on ego
vehicle velocity estimation from the radar return signal without the overhead
in complexity and cost of using an auxiliary global navigation satellite system
(GNSS) and inertial measurement unit (IMU). We derive a novel analytical
approximation for the automotive SAR angle estimation error variance when the
velocity is estimated by the radar. The developed analytical analysis closely
predicts the true SAR angle estimation variance, and also provides insights on
the effects of the radar parameters and the environment condition on the
automotive SAR angle estimation error. We evaluate via the analytical analysis
and simulation tests the radar settings and environment condition in which the
automotive SAR attains a significant performance gain over the angular
resolution of the short aperture physical antenna array. We show that, perhaps
surprisingly, when the velocity is estimated by the radar the performance
advantage of automotive SAR is realized only in limited conditions. Hence since
its implementation comes with an increase in computation and system complexity
as well as an increase in the detection delay it should be used carefully and
selectively.
