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Provably-Correct Safety Protocol for Cooperative Platooning

Sebastian Mair, Matthias Althoff

TL;DR

This work proposes a safety protocol that can be applied to arbitrary controllers in platooning to prevent collisions in a provably correct manner while still realizing a small distance to the preceding vehicle.

Abstract

Cooperative Adaptive Cruise Control (CACC) is a well-studied technology for forming string-stable vehicle platoons. Ensuring collision avoidance is particularly difficult in CACC due to the small desired inter-vehicle spacing. We propose a safety protocol preventing collisions in a provably-correct manner while still maintaining a small distance to the preceding vehicle, by utilizing communicated braking capabilities. In addition, the safety of the protocol is ensured despite possible communication failures. While our concept can be applied to any CACC system, we particularly consider a class of CACCs, where the platoon vehicles successively agree on a consensus behavior. Our safety protocol is evaluated on various scenarios using the CommonRoad benchmark suite.

Provably-Correct Safety Protocol for Cooperative Platooning

TL;DR

This work proposes a safety protocol that can be applied to arbitrary controllers in platooning to prevent collisions in a provably correct manner while still realizing a small distance to the preceding vehicle.

Abstract

Cooperative Adaptive Cruise Control (CACC) is a well-studied technology for forming string-stable vehicle platoons. Ensuring collision avoidance is particularly difficult in CACC due to the small desired inter-vehicle spacing. We propose a safety protocol preventing collisions in a provably-correct manner while still maintaining a small distance to the preceding vehicle, by utilizing communicated braking capabilities. In addition, the safety of the protocol is ensured despite possible communication failures. While our concept can be applied to any CACC system, we particularly consider a class of CACCs, where the platoon vehicles successively agree on a consensus behavior. Our safety protocol is evaluated on various scenarios using the CommonRoad benchmark suite.
Paper Structure (28 sections, 8 theorems, 20 equations, 5 figures, 2 tables, 3 algorithms)

This paper contains 28 sections, 8 theorems, 20 equations, 5 figures, 2 tables, 3 algorithms.

Table of Contents

  1. INTRODUCTION
  2. Related Work
  3. Correct-by-construction Controllers
  4. Online Verification
  5. Contributions
  6. Preliminaries
  7. General System Description
  8. Platoon Vehicle Description
  9. Consensus-based CACCs
  10. SAFETY SPECIFICATION
  11. SOLUTION CONCEPT
  12. Monotone Dynamics
  13. Safety Verification
  14. Overall Algorithm
  15. Recapturing Controller
  16. ...and 13 more sections

Key Result

Theorem 1

For any input trajectories $\underline{a}_d(\cdot)$, $a_d(\cdot)$ and $\overline{a}_d(\cdot)$, that fulfill the conditions it holds that Proof: We show the first inequality in eq:monotonicity, and the proof for the second one works analogously. For brevity, we write $\underline{s}(t)$ and $\underline{v}(t)$ for the position and velocity of $\underline{\boldsymbol{\xi}}(t; \undertilde{x} ,\unde

Figures (5)

  • Figure 1: Overview of our safety protocol for vehicle $i$, including communication (dashed).
  • Figure 2: Overview of the procedure for safely changing the braking capability of $i$, including communication (dashed).
  • Figure 3: Activity diagram showing the simplified procedure for safely changing the braking capability of $i$. Block $1$ to $3$ correspond to the blocks in Alg. \ref{['alg:update-a-min']}, and the functionality of block $4$ is integrated into the other blocks here for the sake of a better understanding.
  • Figure 4: (a) Occupancies. The safe distance drops as soon as coupling is done at the very beginning. (b) Effective accelerations and $a_{\text{min}}^{(i)}$ (dashed) for each platoon vehicle $i$, and road incline angle $\alpha$ (red) from the perspective of $2$. Activations of the fail-safe controller are shown for vehicle $1$ (dotted).
  • Figure 5: (a) CommonRoad. (b) Occupancies. (c) Effective accelerations and $a_{\text{dec}}^{(i)}$ (dashed). After vehicle $1$ leaves the platoon, the consensus acceleration limit decreases again.

Theorems & Definitions (9)

  • Theorem 1: Monotonicity in the Position Domain
  • Corollary 1: Bounds of Reachable Position
  • Remark 1: $t_{\text{accept}}$ is reset when the candidate is deleted
  • Lemma 1: Candidate is not greater than braking limit
  • Lemma 2: Braking limit changes are restricted
  • Lemma 3: Increasing sent braking limit gives time reset
  • Theorem 2: Braking Limit Invariance
  • Theorem 3: Ego Braking Limit Update
  • Theorem 4: Leader Braking Limit Update