VII Probe Message Processes Roy Sumner

Probe Messages Intent of probes What a probe message contains How they are generated How they are transmitted How they can be managed

Intent of Probe Messages Use vehicles as probes to generate data for applications and users – an SAE development Vehicles collect data, its upload to an RSE then forwarded to the VII network Users subscribe to this data Certain users can actively manage the way probe data is collected Key constraints are: –ensure privacy –accommodate technological changes

Content of Probe Messages

HeaderSnapshot1Snapshot2Snapshot3Snapshot4 LatLongTimeACIDACMLength LatLongTimeWipersBrakesTemp … Header Probe message Snapshot Probe Message Structure # snapshots

Probe Message Header Application class identifier (ACID) Application Context Mark Length of Message Length of Message including headers Recently added position/time of transmission

Position and Time Seconds since last Probe Message sent Universal Time Coordinated (UTC) Time Precision Positioning Precision Longitude of center of vehicle Latitude of center of vehicle Heading Vehicle Speed Heading Precision Speed Precision Altitude Precision Altitude Vehicle Type

Vehicle Status Elements Vehicle Exterior Lights? Wipers Brake Applied Stability Control (Event) Traction Control (Event) Anti-Lock Brakes (Event) Sun Sensor Rain Sensor Air Temperature Front Wheel Angle Rate of Change in Steering Wheel (Event) Wheel that Exceeded Vertical Acceleration Threshold (Event) Vertical Acceleration Value (Event) Longitudinal Acceleration Lateral Acceleration Obstacle Distance Obstacle Direction Yaw Rate 100% Brake Boost Applied (Event)

Weather Status Elements – J2735 Wipers – off intermittent low high and sweeps per minute Stability Control - on Traction Control - on Anti-Lock Brakes - on Sun Sensor 0-7, 0= Dark, 1=Minimal Sun 7=Maximum Rain Sensor - on Air Temperature -127 to +127°C

How Snapshots are generated

Snapshot are Generated: Definition: a snapshot is a collection of all vehicle status elements at one place and time Three methods of snapshot collection: –Periodically – at intervals between RSEs – subject of current discussion –When events occur –When the vehicle starts & stops Vehicles have a limited snapshot buffer (currently 30) Snapshots includes all available vehicle status elements plus time, location, speed, & heading Currently only one snapshot format

Periodic Snapshot Generation Default state is intended to evenly distribute snapshots At low speed snapshots (<20mph) every 6 seconds – settings can be changed At high speeds (>60mph) every 30 seconds Between 20 and 60 mph linearly spread SpeedRSE Spacing Time between snapshots (<20mph1 miles6 secs 20-60Linearly spread (>60mph10 miles30secs

Snapshot can be Generated: By distance if set at the upstream RSU: SpeedDistance between snapshots ≤ S1D1 >S1 & < S2linear extrapolation >S2D2

Event Snapshot Generation Event snapshots are produced when a vehicle status element threshold is exceeded or when a device is activated or the value varies Examples: –Traction control turns on (icy conditions) –Wheel vertical acceleration exceeds threshold (potholes)

Starts & Stops Snapshot Generation A start is when the vehicle speed exceeds a threshold (default = 10 mph) A stop is when there is no movement for some threshold stop time (default = 5s) and no other stops have occurred within a threshold time (default = 15s) Snapshots are not generated between stops and starts

Snapshot Temporary ID Generated by the OBE Independent of MAC address Allows short term vehicle trajectories to be known Recalculated after: –120 seconds or –1km Whichever comes last

How Probe Messages are Transmitted

Probe Message Queues Enhanced GPS Vehicle systems Location and time Vehicle status elements Snapshot # 2 Snapshot # 1 Snapshot # 4 Snapshot # 3 Snapshot # 6 Snapshot # 5 ….. Snapshot # 30

Probe Message Queues Header – this is a probe message Snapshot # 2 Snapshot # 17 Snapshot # 4 Snapshot # 5 Header – this is a probe message Snapshot # 1 Snapshot # 3 Snapshot # 6 Snapshot # 5 To the RSE Snapshots reordered as follows: 1. Events 2. Stops & starts 3. Periodic – oldest data removed as new data arrives – Note – likely to be modified

How Probe Messages can be Managed

Probe Management Concept Instruct OBE to generate more snapshots Message structure: –Temporary Snapshot Interval - time between snapshots –Probe Management Conclusion - management duration one of: a time – seconds a distance - meters out of range of current RSU after a threshold time (default = 5s) a new RSU that supports probe management is detected –Number of Managed Fields these are the vehicle status elements and their thresholds that can be changed to generate more snapshots. –Time between Probe Message Transmissions

Probe Management Examples Collect snapshots every second – mapping Reduce vertical acceleration threshold – roughness measurement Snapshot on heading changes >45° - turning movements – comparison of snapshot IDs gives turning movements Report 1 sec snapshot every 4 secs – adaptive control

Current Status Probe message has been balloted at SAE as part of J2735 Thresholds need definition Management message development is beginning