  In vehicular communications, traffic-related information should be spread
over the network as quickly as possible to maintain a safer transportation
system. This motivates us to develop more efficient information propagation
schemes. In this paper, we propose a novel virtual-MIMO-enabled information
dissemination scheme, in which the vehicles opportunistically form virtual
antenna arrays to boost the transmission range and therefore accelerate
information propagation along the highway. We model the information propagation
process as a renewal reward process and investigate in detail the
\emph{Information Propagation Speed} (IPS) of the proposed scheme. The
corresponding closed-form IPS is derived, which shows that the IPS increases
cubically with the vehicle density but will ultimately converge to a constant
upper bound. Moreover, increased mobility also facilitates the information
spreading by offering more communication opportunities. However, the limited
network density essentially determines the bottleneck in information spreading.
Extensive simulations are carried out to verify our analysis. We also show that
the proposed scheme exhibits a significant IPS gain over its conventional
counterpart.
