Abstract: In traditional vehicular networks， most of the information transmissions were conducted by mobile cellular networks. One of the shortcomings of transmissions with cellular networks is the very long delay time， and consequently it is not applicable to realtime alarm information.However， in broadband wireless networks， the endtoend delay of alarm information delivered through multihop broadcast transmission can be greatly decreased. According to the characteristics of vehicular networks， a transmitteroriented AMBP(alternating multihop broadcast protocol)was proposed on the basis of geographical position. In the protocol， the next hop relaying node was selected by a vehicle and the alternate transmission threshold value was calculated with the neighbor information that was kept in its neighbor vehicle table. Finally， different transmission policies were taken by the proposed AMBP based on the relationships between packet size and the transmission threshold value. Experimental results showed that packet loss rate， transmission delay， and delay jitter can be successfully reduced by the proposed AMBP， which demonstrates that it is more suitable for distributed vehicular communication environment.

Key words: distributed vehicular networks, multihop transmission, relaying nodes, alarm information, broadcast protocol