  We present a general framework for improving and extending GNSS-based
positioning by leveraging opportunistic measurements from legacy terrestrial
radio signals. The proposed approach requires only that participating nodes
collect and share reception timestamps of incoming packets and/or other
reference signals transmitted by other fixed or mobile nodes, with no need of
inter-node synchronization. The envisioned scheme couples the idea of
cooperative GNSS augmentation with recent pioneering work in the field of
time-based localization in asynchronous networks. In this contribution we
present the fundamental principles of the proposed approach and discuss the
system-level aspects that make it particularly appealing and timely for
Cooperative ITS applications, with the goal of motivating further research and
experimentation in this direction.
