The Wireless Token Ring Protocol (WTRP) is a medium access control protocol for wireless networks in Intelligent Transportation Systems. It supports quality of service in terms of bounded latency and reserved bandwidth. WTRP is efficient in the sense that it reduces the number of retransmissions due to collisions. It is fair in the sense that each station takes a turn to transmit and is forced to give up the right to transmit after transmitting for a specified amount of time. It is a distributed protocol that supports many topologies since not all stations need to be connected to each other or to a central station. It can be used with an admission control agent for bandwidth or latency reservations. WTRP is robust against single node failure. WTRP is designed to recover gracefully from multiple simultaneous faults. It has applications to inter-access point coordination in ITS DSRC, and safety-critical vehicle-to-vehicle networking.

This report describes the design and implementation of a wireless token bus protocol for local area networks. This is the second wireless token passing protocol that has been jointly designed by the PATH program and the faculty and students of the EECS department at UC Berkeley.

The first wireless token bus protocol, designed by Duke Lee and Professor Pravin Varaiya, was successfully implemented to provide the wireless network required by an automated vehicle platoon. The token passing mode of wireless medium access control was chosen to provide the delivery time guarantees required by the safety critical control data transport required by the platoon. This protocol is currently also being used for safe automated vehicle merging maneuvers.

The token bus protocol described in this report represents a significant advance over the first version. The earlier protocol did not permit the wireless radios to dynamically join and leave the network while still maintaining the quality of service for those remaining in the network. This version does. The earlier version also worked only when each wireless radio in the network was within range of every other radio in the network at all times. This version relaxes this requirement. Since mobile wireless LAN’s frequently encounter hidden or exposed terminal configurations, these advances greatly enhance the usefulness of the protocol.