DSRC and IEEE 802.11ac Adjacent Channel Interference Assessment for the 5.9 GHz Band

The 5.9 GHz spectrum band is proposed for vehicular communications using Dedicated Short Range Communications (DSRC), but this band may need to be shared with unlicensed Wi-Fi devices. A recent Federal Communications Commission (FCC)'s Notice of Proposed Rulemaking (NPRM) outlines two interference mitigation techniques for spectrum coexistence: Detect and Vacate and Re-channelization. A major technical challenge of Re-channelization is that DSRC may experience harmful or a reduced functionality because of adjacent channel interference from Wi-Fi transmitters. We therefore conducted Wi-Fi/DSRC adjacent channel interference experiments to evaluate the significance of Wi-Fi signals adjacent to DSRC transmissions. Our measurements show a significant degradation of DSRC performance from 802.11ac adjacent channel interference only for certain scenarios where the distances between the Wi-Fi transmitter to DSRC receiver is 15 m or below and the distances between the DSRC transmitter to receiver is 300m or higher. However, there is no severe effect when the DSRC transmit power is at the standard 33 dBm level, even considering the recommended fading margin of 5-10 dB.