Case Study for reduced priority management frames – Vehicular Safety Communication

1. Case Study for reduced priority management frames – Vehicular Safety Communication Kenney – Toyota/VSC3

2. DSRC – Dedicated Short Range Communication • An FCC-endorsed vehicular communication technology based on 802.11 in the 5.9 GHz band • 75 MHz allocated in the US (7 x 10 MHz channels w/ 5 MHz guard) • 30 MHz pledged in Europe • Japan is pursuing similar technology Kenney – Toyota/VSC3

3. Applications • Primary applications are safety – collision prevention and mitigation • Secondary applications include • Mobility (traffic, navigation, in-vehicle signage, eco-driving) • Tolling • Commercial (retail advertisements, Internet access) Kenney – Toyota/VSC3

4. Example Safety Applications • Vehicle-to-vehicle communication (V2V) • Forward Collision Warning • Emergency Electronic Brake Lights • Do Not Pass Warning • Blind Spot Warning • Intersection Collision Avoidance • Vehicle-to/from-Roadside Infrastructure (V2I) • Intersection Collision Avoidance based on intersection messages: • Geographic Intersection Description (GID) • Signal Phase And Timing (SPAT) Kenney – Toyota/VSC3

5. REAR-END COLLISION EEBL ALERTS DRIVER WIRELESS MESSAGE STOPPED ENOUGH DISTANCE TO STOP Emergency Electronic Brake Lights WITHOUT EEBL WITH EEBL Kenney – Toyota/VSC3

6. Safety Apps IEEE 802.11& 802.11p SAE J2735 message IEEE 1609.3 Layer 3/4 V2V Safety Communication • Relies primarily on frequent broadcasts by each vehicle of important state info, including: • Position • Speed, acceleration, heading • Brake and stability status • Vehicle size • Recent path history • Predicted path • Special event flags • GPS corrections • See SAE J2735 Message Set Dictionary standard IEEE 1609.4channel switching Kenney – Toyota/VSC3

7. 802.11p Communication • Outside the context of a BSS • No BSS setup • No beacon, probe, authentication, association, … • Management frames most likely in DSRC are: • Vendor Specific Action frame (will be used for a variety of purposes, including advertising services on other DSRC channels) • Timing Advertisement frame (defined in 802.11p) • Management frames generally of lower importance than data frames. Would like to be able to send with lower priority. Kenney – Toyota/VSC3

8. Performance Concerns • Packet delivery rate in dense, fast-moving traffic • Example: • 3 kbit safety message • 10 messages per vehicle per second • 20 vehicles per lane per km • Communication range +- 500 meters • 10 MHz channel, 6 Mbps OFDM • 10 lanes x 20 Veh/lane/km x 30 kbit/veh/sec x 1 km = 6 Mbps • Realistic traffic saturates channel. High collision rate. Kenney – Toyota/VSC3

9. Access Priority • Channel dominated by vehicle safety messages (data frames) • Most vehicle safety messages are routine • Occasional event content raises importance • Sender not always aware when content is critical for collision avoidance • Channel is shared with other traffic, including management frames (VSA, TA) • 802.11 requirement to map management frames to AC-VO conflicts with goals of vehicular safety communication. Kenney – Toyota/VSC3