  In next-generation vehicular environments, precise localization is crucial
for facilitating advanced applications such as autonomous driving. As
automation levels escalate, the demand rises for enhanced accuracy,
reliability, energy efficiency, update rate, and reduced latency in position
information delivery. In this paper, we propose the exploitation of
backscattering from retro-directive antenna arrays (RAAs) to address these
imperatives. We introduce and discuss two RAA-based architectures designed for
various applications, including network localization and navigation. These
architectures enable swift and simple angle-of-arrival estimation by using
signals backscattered from RAAs. They also leverage multiple antennas to
capitalize on multiple-input-multiple-output (MIMO) gains, thereby addressing
the challenges posed by the inherent path loss in backscatter communication,
especially when operating at high frequencies. Consequently, angle-based
localization becomes achievable with remarkably low latency, ideal for mobile
and vehicular applications. This paper introduces ad-hoc signalling and
processing schemes for this purpose, and their performance is analytically
investigated. Numerical results underscore the potential of these schemes,
offering precise and ultra-low-latency localization with low complexity and
ultra-low energy consumption devices.
