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Enhancing Vehicle Safety Communication Through Reduced Priority Management Frames

This case study explores the implementation of reduced priority management frames within the Toyota VSC3 Dedicated Short Range Communication (DSRC) system. Focused on advancing vehicular safety communication, the study details technologies endorsed by the FCC, leveraging 802.11 standards in the 5.9 GHz band. Key applications include vehicle-to-vehicle (V2V) communication for collision prevention, emergency braking alerts, and roadside infrastructure messaging. The research highlights challenges in packet delivery rates amidst dense traffic and the importance of prioritizing safety messages over non-critical communication.

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Enhancing Vehicle Safety Communication Through Reduced Priority Management Frames

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  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

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