This paper focuses on a network design for cooperative active safety systems (CASS). A Medium Access Control (MAC) protocol design is proposed for a vehicle to send safety message to other vehicles. A quality of service (QoS) model for safety messages is developed that is consistent with the active safety systems literature. The QoS target involves having each message being received with high probability within its specified lifetime by each vehicle within its specified range. The protocol design is based on the rapid re-broadcast of each message multiple times within its lifetime. Six different design variations are proposed. Equations are derived and a simulation tool is developed for assessing the performance of the designs. Design performance is dependent on the number of re-broadcasts, power, modulation, coding, and vehicular traffic volumes. The evaluation focuses on vehicles that are driving on a 4- to 8-lane freeway using 802.11a radio running over a 20 MHz channel in the DSRC spectrum. Results indicate that under certain assumptions regarding the loss probability tolerated by safety applications, the design is able to transport safety messages in vehicular ad-hoc networks.
['Qing Xu', 'Tony Mak', 'Jeff Ko', 'Raja Sengupta']
Medium Access Control Protocol Design for Vehicle-Vehicle Safety Messages