California Partners for Advanced Transportation Technology

This paper describes a medium access control (MAC) protocol to enable multi-channel operation for dedicated short range communication (DSRC). In particular, we focus on the challenge of supporting potentially high-bandwidth commercial or info-tainment communications between vehicle and roadside in hotspots over several service channels, while concurrently enabling time-critical vehicle-vehicle communication for safety in a separate channel. In our architecture, within hotspots, communication is aided by one of the access points in the hotspot. This access point is designated the Coordinating Access Point (CAP). Outside hotspots, communication is for safety and is conducted in an ad-hoc fashion. The CAP protocol design is a variant of IEEE802.11 PCF, modified for multi-channel operation. The design objective is to maximize utilization of the service channel used for non-safety communication while meeting the Quality of Service (QoS) constraints of the safety communications. The performance of 802.11 DCF, PCF, and the CAP extension is quantified by simulation in NS-2. The mobility model represents a 4-lane freeway at maximum vehicular traffic flow derived from the SHIFT traffic simulator. The CAP design is shown to significantly enhance both safety and non-safety communication relative to DCF and PCF only.