| Summary: | 碩士 === 國立成功大學 === 電腦與通信工程研究所 === 101 === It is a widely discussed issue that how to broadcast important safety message in short time in VANET. Broadcast, generally speaking, has no feedback mechanism so that it usually causes collision problem. Reliable broadcast can effectively reduce the collision probability, but it wastes time on procedures, especially for broadcasting emergency safety message. In this paper, it will build AdvB, advanced broadcast which is a new type of broadcast mechanism, by combining the concept of DCF and multi-channel operation in DSRC to decrease collision probability so that it can increases transmission efficiency, plus number of receivers, reduce latency, etc. There is a probability to decide whether to rebroadcast to others for one vehicle after receiving safety message, and it also decides the channel and backoff to broadcast randomly. After finishing broadcasting in control channel the vehicles will return to the original state. The others in service channels have to announce receivers to switch to control channel to listen to safety message, and then those transmitters change to control channel to broadcast safety message. This method can inform other vehicles in different channels to increase receivers. Backoff comes from DCF mechanism. It can decide the transmission priorities by different value of backoff in a vehicle group so that it can reduce broadcast probability and let more vehicles receive safety message successfully.
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