VEHICULAR AD-HOC
NETWORKS
Many safety applications rely on multi-hop broadcasting
to disseminate safety messages. In most existing multi-hop broadcasting
protocols, one next forwarder is selected through contention among forwarder
candidates based on their different waiting times. In this paper, we first
analyze the latency and collision of the existing protocols, and point out two problems: 1)
unnecessary delay occurs in the contention process due to the lack of
considering the distribution of vehicles and 2) the short difference between
waiting times of forwarder candidates may allow redundant broadcasts to collide with each other.
Secondly, we propose a new multi-hop broadcast protocol called RObust and Fast
Forwarding (ROFF) to mitigate both problems. ROFF solves the
first problem of unnecessary delay by allowing a forwarder candidate to use the
waiting time which is inversely proportional to its forwarding priority.
A lot of safety
applications over vehicular ad-hoc networks (VANET) rely on emergency message dissemination (EMD) through multi-hop broadcast. In EMD, a
certain vehicle (i.e. source) issues an emergency message when a dangerous
situation such as vehicle collision has been detected. Since the emergency message includes
time-sensitive life-critical information, it should be disseminated to all
vehicles in the target region as quickly and reliably as possible. Commonly,
the target region is a road segment that is up to several kilometers long in
the opposite direction of the source.
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