Multimedia Transmission for Emergency Services in VANETs

Emergency warning applications in a vehicular ad hoc network (VANET) requires successful dissemination of warning notification within a geographical area spanning multiple hops. Multimedia transmission provides an accurate overview of the emergency event in the form of an image, an audio or a video. However, the reliable transmission of emergency multimedia messages using multi-hop broadcast techniques suffer from broadcast storm and severe interference from the existing periodic single-hop safety messages. In this paper, we propose an efficient time-slotted multi-hop broadcast protocol for emergency multimedia transmission. To avoid interference with the safety messages already in place, we propose to allocate separate multi-hop time slots for the multimedia messages, and devise a signaling mechanism that ensures a reliable delivery of these multimedia messages. The proposed mechanism can also handle the scenario of lost acknowledgment (ACK) and thus effectively reduce the unnecessary retransmissions of the multimedia messages. Simulation results confirm that the developed protocol substantially outperforms existing schemes in terms of both the number of required multi-hop transmissions and the dissemination delay, while maintaining a high reception rate and a low end-to-end delay for the single-hop safety messages.