Collision Avoidance at Intersections in the Presence of Failures

Vladimir Savic, Elad M. Schiller and Marina Papatriantalou,

Computer Science and Engineering

Chalmers University of Technology

Motivation

• V2V enables better awareness of the surroundings,

• distant objects out of the sensing horizon

• V2V is prone to failures, delays and uncertainty of the participating nodes

• A fault-tolerant and affordable implementations are needed

The Intersection Crossing (IC) Problem

• Once a vehicle enters the capture area, there are no guarantees that it can avoid collision with another vehicle coming from a conflicting direction. Capture Area (CA)

Intersection

The Intersection Crossing (IC) Problem

• [safety] No two vehicles from conflicting directions are allowed to enter their the capture area

• [liveness] Eventually, all vehicles can cross the intersection

Capture Area (CA)

Intersection

Existing Solutions

Capture Area (CA)

Intersection

• Current proposals assume that the failure occurrences can be characterize, e.g., via a distribution• a bounded delay w.h.p.

• Such assumptions do not take into account abnormal behavior.• Once an unexpected failure

occurs, neither safety nor liveness is guaranteed

The Challenge

Capture Area (CA)

Intersection

• Communication fairness: a packet that is sent infernally often, is received infernally often

• No bound on the communication delay other than the assumption that it is an unknown finite number.

Our Contribution

• We propose a solution to the intersection crossing (IC) problem with V2V communication.

• We handle any finite number of packet failures.

• We provide:

• Numerical simulations

• An analysis based on a time diagram

• According to our results, based on a real data set, the crossing delay is only slightly increased even in the presence of highly correlated failures.

The System

• We consider two fully autonomous cars (C1, C2), equipped with V2V, GPS and IMU, aiming to cross a road intersection.

Capture Area (CA)

Intersection

The Protocol

We define the following V2V messages:

•MSGHB: periodic heart-beat (HB)

•MSGENTER: indication that car plans to enter the intersection

•MSGEXIT: indication that car plans to exit the intersection

Capture Area (CA)

Intersection

The Protocol

• Makes sure that both vehicles are aware of each other.

• Lets one of the vehicles cross the intersection after this decision was acknowledged by the other vehicle.

• Inform the other vehicle that the road is open after the first crossing.

Time Diagrams: No Failures

Time Diagrams: Fails to Receive Once

Time Diagrams: 3 Consecutive Packet Fails

Numerical simulations

• To analyze the delay caused by communication failures, we use the real measurements available in [1].

• Two scenarios:

• open-field (without any obstacles), and

• harsh (with many obstacles, such as tunnels and bridges)

[1] F. Bai, H. Krishnan, “Reliability analysis of DSRC wireless communication for vehicle safety applications,” in Proc. of IEEE Intelligent Transp. Systems Conf., Sept 2006.

Open-field (without any obstacles)

Harsh (many obstacles, e.g., tunnels, bridges)

Conclusions

• We proposed a technique for dealing with communication failures

• Using this technique, we device a fault-tolerant algorithm for intersection crossing

• We analyzed time diagrams and provided the numerical results in realistic situations that show that both safety and liveness are satisfied

Contact information

This presentation is based on a talked the Vladimir Savic gave in Intelligent Vehicles Symposium 2017: 1005-1012 with the title `Distributed algorithm for collision avoidance at road intersections in the presence of communication failures’

Contact person: Elad Michael Schiller

elad@chalmers.se

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