  In a Vehicular Ad-hoc Network (VANET), the performance of the communication
protocol is influenced heavily by the vehicular density dynamics. However, most
of the previous works on VANET performance modeling paid little attention to
vehicle distribution, or simply assumed homogeneous car distribution. It is
obvious that vehicles are distributed non-homogeneously along a road segment
due to traffic signals and speed limits at different portions of the road, as
well as vehicle interactions that are significant on busy streets. In light of
the inadequacy, we present in this paper an original methodology to study the
broadcasting performance of 802.11p VANETs with practical vehicle distribution
in urban environments. Firstly, we adopt the empirically verified stochastic
traffic models, which incorporates the effect of urban settings (such as
traffic lights and vehicle interactions) on car distribution and generates
practical vehicular density profiles. Corresponding 802.11p protocol and
performance models are then developed. When coupled with the traffic models,
they can predict broadcasting efficiency, delay, as well as throughput
performance of 802.11p VANETs based on the knowledge of car density at each
location on the road. Extensive simulation is conducted to verify the accuracy
of the developed mathematical models with the consideration of vehicle
interaction. In general, our results demonstrate the applicability of the
proposed methodology on modeling protocol performance in practical signalized
road networks, and shed insights into the design and development of future
communication protocols and networking functions for VANETs.
