Decentralized Congestion Control Protocols for V2V Communications and Their Challenging Issues

Vehicular industries have made constant efforts in developing cooperative vehicular systems to satisfy the needs for reducing car accidents and increasing traffic safety. In recent years, to satisfy these requirements, wireless communication-based vehicular ad hoc network (VANET) has been emerging as one of the promising solutions. Several research efforts have been conducted for developing the cooperative collision warning (CCW) application using vehicular safety communication. To realize CCW, however, the existing technical challenges, such as the decentralized congestion control (DCC) of periodic beacon broadcasts and reliable emergency message dissemination in congested situation, should be solved. In this paper, we present the existing MAC protocols for DCC in vehicular safety communications and point out their limitations and technical challenges. The question about how to solve these problems is also discussed in this paper.