  We perform an extensive study of cooperative awareness in vehicular
communication based on periodic message exchange. We start by analyzing
measurements collected on four test sites across Europe. To measure cooperative
awareness, we use three metrics: 1) neighborhood awareness ratio; 2) ratio of
neighbors above range; and 3) packet delivery rate. Using the collected data,
we define a simple model for calculating neighborhood awareness given packet
delivery ratio for a given environment. Finally, we perform realistic,
large-scale simulations to explore the achievable performance of cooperative
awareness under realistic transmit power and transmit rate constraints. Our
measurements and simulation results show that: i) above a certain threshold,
there is little benefit in increasing cooperative message rate to improve the
awareness; higher transmit power and fewer messages transmissions are a better
approach, since message delivery is dominated by shadowing. ii) the efficacy of
cooperative awareness varies greatly in different environments on both large
scale (e.g., 90\% awareness is achievable up to 200~m in urban and over 500~m
in highway) and small scale (e.g., vehicles in nearby streets can have
significantly different awareness); iii) V2V and V2I communication have
distinct awareness patterns; iv) each location has a distinct transmit power
that achieves high awareness; and v) achieving high awareness levels results in
increased reception of potentially unwanted messages; therefore, a balance
needs to be found between awareness and interference, depending on the specific
context. We hope our results will serve as a starting point for designing more
effective periodic message exchange services for cooperative awareness.
