In this paper, a new MAC protocol, called Reliable Busy Tone Multiple Access with Neighboring Information Table (RBTMA-NIT), is proposed for safety applications in Vehicular ad hoc networks (VANETs). Derived from the conventional busy tone multiple access (BTMA), RBTMA-NIT introduces three mechanisms to reduce the transmission delay of emergency messages: 1) the original emergency message and its copies are assigned two different priorities; 2) a table, called neighboring information table (NIT), is built to reduce the redundant transmissions; and 3) the contention policy is improved by selecting feasible nodes, setting suitable contention window and limiting the transmission time of message on each node. Simulation results demonstrate that the proposed MAC protocol can effectively reduce the covering time during which all nodes in the system have received the emergency message.
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