  Co-channel coexistence between Dedicated Short-Range Communications (DSRC)
and Wi-Fi needs thorough study. The reason is that although the 5.850-5.925 GHz
(5.9 GHz) band has been reserved for DSRC so far, the U.S. government is moving
swiftly on opening the band to be shared with Wi-Fi. However, most prior work
lacks sufficient scientific rigor by relying on performance metrics such as
packet delivery rate (PDR) and packet delay that cannot accurately measure
performance of a vehicular network that primarily uses broadcast in
dissemination of packets. Precise analysis of such broadcast operation is
essential for rigorous investigation of DSRC-Wi-Fi coexistence because most
safety-critical applications of DSRC operate based on broadcast. This paper
proposes a new metric that can more accurately characterize the performance of
a broadcast-based DSRC network. The new metric is used to (i) characterize
coexistence of DSRC with IEEE 802.11ac-based Wi-Fi and (ii) suggest selection
of key medium access control (MAC) parameters for DSRC: inter-broadcast
interval (IBI) and contention window (CW).
