  Broadcast routing has become an important research field for vehicular ad-hoc
networks (VANETs) recently. However, the packet delivery rate is generally low
in existing VANET broadcast routing protocols. Therefore, the design of an
appropriate broadcast protocol based on the features of VANET has become a
crucial part of the development of VANET. This paper analyzes the disadvantage
of existing broadcast routing protocols in VANETs, and proposes an improved
algorithm (namely ODAM-C) based on the ODAM (Optimized Dissemination of Alarm
Messages) protocol. The ODAM-C algorithm improves the packet delivery rate by
two mechanisms based on the forwarding features of ODAM. The first
distance-based mechanism reduces the possibility of packet loss by considering
the angles between source nodes, forwarding nodes and receiving nodes. The
second mechanism increases the redundancy of forwarding nodes to guarantee the
packet success delivery ratio. We show by analysis and simulations that the
proposed algorithm can improve packet delivery rate for vehicular networks
compared against two widely-used existing protocols.
