Controlling Congestion in Safety-Message Transmissions: A Philosophy for Vehicular DSRC Systems

Dedicated short-range communication (DSRC) is a powerful new technology that allows vehicles to communicate with each other. [DSRC is the U.S. vehicle communication technology operating in the 5.9-GHz Intelligent Transportation Systems (ITS) band; the analogous technology in Europe is called Cooperative ITS, and the band is referred to as ITS G5.] In particular, they exchange safety messages that allow collision threats to be identified and avoided. Channel congestion is a significant challenge because it causes safety messages to be lost and introduces latency in threat modeling at the application layer. This article describes a philosophy of DSRC congestion control, based on maximizing channel throughput via distributed control of the rate at which each vehicle transmits safety messages. It then defines a specific adaptive control algorithm, a weighted version of the LInear MEssage Rate Integrated Control (LIMERIC) algorithm. Weighted-LIMERIC has provable stability, convergence, and weighted fairness attributes. NS-2 simulation results that demonstrate these attributes are also presented.