Yuki Horita

Effect of Decentralized Congestion Control on Cooperative Systems

Vehicular cooperative systems are expected to provide a promising solution for enhancing active safety of vehicles. It requires stable and secure wireless communications for mutual information exchange among vehicles. In order to realize stable and secure communications, packet loss due to collisions need to be suppressed and communication apparatus should be ensured to perform proper cryptographic verification of packets. Because the hardware constraints in cooperative systems allow only a limited rate for cryptographic processing of packets, congestion control acts as a key technology to solve these challenges. This paper proposes a congestion control algorithm for vehicular cooperative systems to control the packet reception rate at a communication apparatus of a vehicle. The proposed algorithm is evaluated quantitatively by network simulation. The results show that the proposed algorithm can stabilize the packet reception rate by controlling the packet transmission rate on surrounding vehicles in a decentralized manner.

Symmetric key distribution for car-to-car/infrastructure communication systems

Services such as sending a pre-crash sensing warning and traffic condition warning are expected to be provided in car-to-car/infrastructure (C2X) communication systems. Maintaining message integrity is essential for these services because wrong messages may cause collision accidents and congestion. A message authentication code (MAC) generated by using a symmetric key is used to authenticate a message. The sender and receiver of a message must possess the same symmetric key before initiating communications. In the mentioned warning services, the sender of a message cannot know who receives the message, because the message is broadcast. Moreover, it is difficult for a road-side unit (RSU) to distribute a key to an onboard unit (OBU) because an OBU cannot always communicate with a RSU. Therefore, key distribution is a problem in C2X communication systems. We thus propose a protocol for key distribution. In the protocol, all OBUs and RSUs that exist in a certain area possess the same key. An OBU obtains the keys for the area in which the OBU is present and for the area to which the OBU will go next. The protocol enables a vehicle to verify message integrity by using a symmetric key in C2X communication systems.