Jan. 2010

Kenney – Toyota/VSC3

Slide 1

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

Case Study for reduced priority management frames – Vehicular Safety Communication

Date: 2010-1-18

Author(s):

Name Affiliation Address Phone email

John KenneyVSC3 and Toyota

InfoTechnology Center

574-272-1403 johnkenney@alumni.nd.edu

Jan. 2010

Kenney – Toyota/VSC3

Slide 2

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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

Jan. 2010

Kenney – Toyota/VSC3

Slide 3

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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)

helloR

Buy Gas, getFree Traffic Data

Free Video withHappy Meal

Service ChannelService Channel

RED LIGHT VIOLATION

Control (Safety) Channel

helloR

Buy Gas, getFree Traffic Data

Free Video withHappy Meal

Service ChannelService Channel

RED LIGHT VIOLATION

Control (Safety) Channel

Jan. 2010

Kenney – Toyota/VSC3

Slide 4

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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)

Jan. 2010

Kenney – Toyota/VSC3

Slide 5

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

Emergency Electronic Brake Lights

WITHEEBL

WITHOUTEEBL

WIRELESS

MESSAGE

STOPPEDEEBL ALERTS DRIVER

REAR-END COLLISION

ENOUGH DISTANCE

TO STOP

Jan. 2010

Kenney – Toyota/VSC3

Slide 6

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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

Safety Apps

IEEE 802.11& 802.11p

SAE J2735 message

IEEE 1609.3 Layer 3/4

IEEE 1609.4channel switching

Jan. 2010

Kenney – Toyota/VSC3

Slide 7

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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.

Jan. 2010

Kenney – Toyota/VSC3

Slide 8

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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.

Jan. 2010

Kenney – Toyota/VSC3

Slide 9

doc.: IEEE 802.11 11-10-0095-00-00ae

Submission

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.