Ibtissem Ben Makhlouf

A Benchmark Suite for Hybrid Systems Reachability Analysis

Since about two decades, formal methods for continuous and hybrid systems enjoy increasing interest in the research community. A wide range of analysis techniques were developed and implemented in powerful tools. However, the lack of appropriate benchmarks make the testing, evaluation and comparison of those tools difficult. To support these processes and to ease exchange and repeatability, we present a manifold benchmark suite for the reachability analysis of hybrid systems. Detailed model descriptions, classification schemes, and experimental evaluations help to find the right models for a given purpose.

An Evaluation of Two Recent Reachability Analysis Tools for Hybrid Systems

Abstract The hybrid systems community is still struggling to provide practically applicable verification tools. Recently, two new tools, PHAVer and Hsolver, were introduced which promise to be a further step in this direction. We evaluate and compare both tools with the help of several benchmark examples. The results show that both have their strengths and weaknesses, and that there still is no all-purpose reachability analysis tool for hybrid systems.

Current Challenges in the Verification of Hybrid Systems

Latest developments brought interesting theoretical results and powerful tools for the reachability analysis of hybrid systems. However, there are still challenging problems to be solved in order to make those technologies applicable to large-scale applications in industrial context. To support this development, in this paper we give a brief overview of available algorithms and tools, and point out some of their individual characteristics regarding various properties which are crucial for the verification of hybrid systems. We present exemplary evaluations on three benchmarks to motivate the need for further development and discuss some of the main challenges for future research in this area.

HyPro: A C++ Library of State Set Representations for Hybrid Systems Reachability Analysis

In this tool paper we introduce HyPro, our free and open-source C++ programming library, which offers implementations for the most prominent state set representations used by flowpipe-construction-based reachability analysis techniques for hybrid systems.

A testing platform for cooperative vehicle platoon controllers

This paper presents a hardware implementation of a platoon of four 1:14 scaled trucks. For this experiment, each truck was equipped with sensors for the measurement of specific variables required for the control of the platoon. These variables were transmitted via WLAN to an MPC555 processor in which the controller as well as the incoming data were processed. Graphical User Interfaces (GUIs) have been developed to monitor the dynamic behavior of the system under full communication as well as under disturbances and to modify the parameters of the system online. To test the platform a cascade control structure has been proposed.

Safety Verification of a Controlled Cooperative Platoon Under Loss of Communication Using Zonotopes

Abstract This paper investigates the safety properties of a networked platoon of vehicles. The vehicles exchange information via a communication network that is subject to failure of single nodes or a complete loss of communication. An LMI-based controller is applied to maintain short distances between the vehicles. The system is modeled as a hybrid automaton, in which the continuous part represents the dynamical behavior of the platoon and the discrete part are spontaneous events related to the switching communication topology. For safety assessment, a reachability analysis of linear hybrid systems with uncertain inputs is applied. It consists of computing an approximation of the reachable set using zonotopes. In this paper, we propose a recursive scheme for the computation of the reachable set for hybrid systems with arbitrary transitions. We consider, as a study case, the worst case scenario corresponding to the transition from a fully functioning communication between the vehicles to a total loss of communication. We use the results of the verification to determine the minimum safe distances between the vehicles guaranteeing collision-free drive under network disturbances.

A platoon of vehicles approaching an intersection: A testing platform for safe intersections

Intersections are one of the most complex driving scenarios for an autonomous vehicle. When a platoon of autonomous vehicles following a leader approaches the intersection, the platoon should change its highway mode to other modes in order to cross the intersection safely. Therefore, the position, velocity and acceleration of the vehicles inside the platoon should be available. Furthermore, information about the position and velocity of other vehicles in the intersection area should be known too. The platoon controller should use all these information to decide which mode will be adopted. In fact, the platoon has to decide whether to stop, to pass or to split the platoon while crossing the intersection. This paper proposes a scaled testing platform of four electronically coupled vehicles equipped with a positioning system and an intersection management system. We tested different scenarios related to different crossing modes of the platoon. The experiments showed that we can change the platoon mode from a highway mode to an intersection drive efficiently.

Safety Verification of a Cooperative Vehicle Platoon with Uncertain Inputs Using Zonotopes

Abstract This paper presents an approach to safety verification of a controlled cooperative platoon of vehicles. To guarantee collision free operation, spacing errors must not exceed critical bounds. Our approach is based on the reachability analysis of linear systems subject to uncertain inputs. The reachable sets are represented by zonotopes. We propose an accurate approximation of the contribution of the uncertain inputs to the whole reachable set. This approach reduces the propagation of the over-approximation error and leads to tight approximation sets.

Safety Assessment of Networked Vehicle Platoon Controllers – Practical Experiences With Available Tools

Abstract Vehicle platoons are usually modelled as continuous dynamic systems. But the parameters of the embedded controllers require particular adaptation depending on the quality and changes commonly occurring in communication networks. These changes may lead to delays or in extreme cases to loss of information. Hence, these changes trigger the jump from one continuous state to another and may be considered as discrete events arising, in general, spontaneously. In this work, we use the formalism of hybrid automata to carry out a safety analysis of controlled vehicle platoons. We are interested in the safety verification of a platoon of vehicles, which communicate with each other via a wireless network. Our aim is to check, if a collision could take place within the platoon under a predefined control law including mode switches. In this paper, we report on results for the non-switching case and for pre-defined switching times. In addition, using different verification tools for this case study allows for the assessment of the performance of these tools and their limitations.

Reachability analysis for managing platoons at intersections

In this work we address the management of a platoon of vehicles passing an intersection. In such a situation we have to decide under which conditions the platoon can pass the intersection in its entirety while avoiding collisions. If this cannot be assured, the platoon should be stopped at the intersection line or possibly split. For this purpose a decision about the vehicle from which the platoon should be divided in two sub-platoons must be taken. In this case, the part ahead can drive safely through the intersection, while the second part must wait at the stop line for a permission to pass. The decision is made based on the results of reachability analysis of hybrid systems. The dynamics of the controlled platoon and the vehicle on the other side of the intersection is modeled as a linear time invariant system with uncertain input. For the computation of reachable sets we use our method based on zonotopes as approximation sets. We show how decisions to manage the platoon at the intersection under safety guarantees can be supported by the results of the reachability analysis and information about the intersection infrastructure.