## 2 Materials and Methods
### Determination of the Cardinal Direction
This is an important concept, and if the preceding vehicle meets with an accident, it can be prevented by notifying the following vehicle in advance that the preceding vehicle is dangerous. As vehicles traveling in the reverse direction do not need to recognize information of those moving in the forward direction, the problem of message congestion or contention to disseminate emergency messages may occur less frequently. The zone of relevance (ZOR) and a ring-based approach of vehicle-density-based emergency broadcast (VDEB) have been proposed to solve the dissemination problem of emergency messages while avoiding problems such as the broadcast storm or message contention [32; 33]. However, these solutions are very theoretical and rely on several network simulation tools. In addition, studies on installing a sensor belt section on the road would require selecting the proper section range, and it is not a realistic solution, due to very expensive construction costs [33]. ## 5 Conclusions

This paper presented a topological sequence recognition mechanism for forming a connected car-based subgroup and recognizing the geographical location and relative position according to the dynamic topology changes of the preceding or following vehicles for each vehicle in the subgroup. Further, this paper applied this mechanism to the CMVF system and verified its efficiency by driving on a real road. To prevent accidents, even autonomous vehicles or vehicles with advanced driving assistants can be rendered safe if information can be obtained on the situation of other vehicles in the vicinity. In addition, in the NLOS environment, traffic and road situation information from preceding vehicles is more important. In these cases, there are problems such as the broadcast storm or message congestion in information while disseminating messages. The proposed topological sequence recognition mechanism as a solution can alleviate the problems of message dissemination as each vehicle knows the situation of other vehicles that are in front of and behind it. Furthermore, the proposed mechanism does not disseminate messages to vehicles that are being driven in the reverse direction, because vehicles are aware of the driving directions between one another. In particular, to prevent secondary accidents due to vehicle accidents that have occurred

Figure 2.0 Conceptual illustration of the topological vehicle sequence shown in Figure 2.1

in the front, when the preceding vehicles deliver emergency messages, the proposed mechanism is very effective because the following vehicles are known, and the messages can only be disseminated to the following vehicles. Meanwhile, the CMV client uses a smartphone, and therefore, even if it is not an autonomous vehicle or connected car, the connected car service can be provided using a smartphone of a driver who is driving a non-autonomous vehicle. Even if connected car technology is not fully realized in previously manufactured vehicles, the proposed mechanism can be used by a driver's smartphone itself or applied to the current navigation system. In vehicles that will be manufactured in the future, it is necessary to incorporate the proposed mechanism in the Electronic Control Unit (ECU) or the trip computer of autonomous vehicles for safer autonomous driving. [PERSON], [PERSON], [PERSON] designed the present study; [PERSON], [PERSON] and [PERSON] reviewed the literature, and drafted the manuscript; [PERSON], [PERSON] and [PERSON] performed the system workflow and implementation of the proposed algorithms; [PERSON], [PERSON], [PERSON] and [PERSON] critically revised the manuscript. All authors have read and agreed to the submitted version of the manuscript. This study was supported by the 2020 Academic Research Support Program in Gangneung-Wonju National University and the Basic Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (NRF-2017R1D1A3B03034102). The present research has also been conducted by the Research Grant of Kwangwoon University in 2019.