The broadcast-based geocast enables efficient data dissemination to vehicles within a given geographical region. When dealing with broadcast, unnecessary retransmissions must be suppressed by controlling the packet forwarding to avoid the broadcast storm problem. However, most of existing broadcast suppression methods do not work in urban environments since buildings block the communication between two vehicles. Moreover, geocast protocols need to be adapted to requirements inside or outside the geocast region. In this paper, we propose Urban Geocast based on Adaptive Delay (UGAD) protocol which adopts delay-based broadcast suppression scheme for urban environments. UGAD makes vehicles at intersections rebroadcast quickly by assigning them preferential delay values. Furthermore, vehicles use two different forwarding modes as parameters in order to fulfill the requirements of geocast. This develops the packet arrival ratio within a given geocast region, while reducing redundant rebroadcasts. Simulation results in an urban scenario show that UGAD achieves high packet arrival ratio as well as low packet rebroadcast ratio compared with existing methods.
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