Multi-hop transmission scheme compatible with single-hop periodic broadcast in vehicle-to-vehicle communications

Decentralized time division multiple access (D-TDMA) is an autonomous slotted protocol originally designed for the single-hop periodic broadcast of safety messages. With the arrival of new ITS applications based on multiple wireless link transmissions, however, the introduction of new mechanisms is essential to share the time domain between single-hop periodic broadcast (safety messages) and multi-hop transmission. Because the scarce 10 MHz-band is going to be used as one communication channel in Japan, a highly reliable medium access control (MAC) scheme is required to handle both safety and multi-hop messages. We propose the multi-hop transmission scheme compatible with single-hop periodic broadcast. In our solution, each terminal that transmits a multi-hop packet first starts a slot reservation procedure to avoid packet collisions with safety messages and thus maintain as high a delivery rate as possible. Then, the transmitting nodes use the D-TDMA structure to check the reception of the multi-hop packet at the relay side. If any failure is detected, the packet is retransmitted as soon as possible. Concerning the routing algorithm, we assume that messages are routed to the destination along the road having the best vehicular traffic and that the road information is provided by D-TDMA. Computer simulations were conducted for an urban environment in which vehicles are moving. The simulation results show that our scheme maintains the delivery rate of safety messages and can recover multi-hop packets in the case of transmission failure.