  Dedicated short-range communication (DSRC) enables vehicular communication
using periodic broadcast messages. We propose to use these periodic broadcasts
to perform inter-vehicle ranging. Motivated by this scenario, we study the
general problem of precise range estimation between pairs of moving vehicles
using periodic broadcasts. Each vehicle has its own independent and
unsynchronized clock, which can exhibit significant drift between consecutive
periodic broadcast transmissions. As a consequence, both the clock offsets and
drifts need to be taken into account in addition to the vehicle motion to
accurately estimate the vehicle ranges. We develop a range estimation algorithm
using local polynomial smoothing of the vehicle motion. The proposed algorithm
can be applied to networks with arbitrary number of vehicles and requires no
additional message exchanges apart from the periodic broadcasts. We validate
our algorithm on experimental data and show that the performance of the
proposed approach is close to that obtained using unicast round-trip time
ranging. In particular, we are able to achieve sub-meter ranging accuracies in
vehicular scenarios. Our scheme requires additional timestamp information to be
transmitted as part of the broadcast messages, and we develop a novel timestamp
compression algorithm to minimize the resulting overhead.
