Recently, there has been increasing interest in intelligent transport systems and intelligent connected vehicles. Vehicular ad hoc networks play an important role in these areas. Many time-division multiple access (TDMA)-based protocols have been proposed to obtain lower transmission delay and packet loss rate.However, transmission collisions occur when nodes that belong to the same two-hop set use the same time slot in TDMA-based protocols. Meanwhile, nodes reacquire slots because of the packet loss caused by poor channel conditions, which further lowers the protocol's performance. In this paper, we study TCG-MAC, a combined TDMA and carrier-sense multiple access (CSMA) medium access control (MAC)-layer protocol. Each time frame is divided into two parts: the TDMA period (TP) and the CSMA period (CP). TP is used for application data transmission, and CP is used for the slot requirement. If two or more nodes acquire the same time slot in the CP, game theory is used to improve the slot allocation efficiency. The simulation results demonstrate that TCGMAC performs well in different traffic densities and channel conditions. Trans Emerging Tel Tech. 2019;30:e3730.wileyonlinelibrary.com/journal/ett
In this paper, a test method of the forward collision warning (FCW) function is proposed and the forward collision risk factor is defined. Firstly, the concept of the minimum alarm distance is given according to the road scene and vehicle movement state, and then the calculation equation of the minimum alarm distance is derived by combining kinematics equation and driver's response time. We compare the actual vehicle distance and the minimum alarm distance to determine whether the FCW test is successful. The actual vehicle distance and the minimum alarm distance are used as the parameters to derive the calculation method of the vehicle's FCW risk factor. Finally, the test scenario is deployed in simulation software, and multiple test cases of FCW are established. By observing the simulation process and analyzing the experimental data, we found that the motion rule of the tested vehicle conforms to our theoretical analysis, and the experimental result is similar to the predicted result, so the conclusion is drawn: The FCW test method based on minimum alarm distance has confidence. At the same time, we conduct a comparative experiment on the hazard factor. The hazard factor we propose is applicable to more automatic driving conditions, and can be continuously output in the test process, which is more conducive to analysis. INDEX TERMS Forward collision warning, risk factor, safe distance, simulation scenario test.
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