IEEE 1609.4 DSRC multi-channel operations and its implications on vehicle safety communications

This paper provides an overview of IEEE 1609.4, a work in progress standard for multi-channel operations over the 5.9 GHz Dedicated Short Range Communications (DSRC) spectrum. In the U.S., the DSRC spectrum is organized into several channels. IEEE 1609.4 defines a time-division scheme for DSRC radios to alternately switch within these channels to support different applications concurrently. We describe the main features of IEEE 1609.4 in detail and discuss the main concerns with the original protocol design. In particular, we focus on those issues that can have a significant impact on vehicle safety communications. While IEEE 1609.4 is currently being updated and revised, this paper is intended to contribute to the technical discussions, and to bring attention to the most relevant and critical issues. This paper also contains results from software simulations conducted to study vehicle safety communications under stressful but realistic conditions. These results confirm concerns for the currently proposed scheme and provide a motivation for updating and revising the standard.