| 1. |
- Markdahl, Johan, et al.
(författare)
-
Towards Almost Global Synchronization on the Stiefel Manifold
- 2018
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Ingår i: 2018 IEEE Conference on Decision and Control (CDC), Miami Beach, FL, USA, Dec. 17-19, 2018. - Miami Beach, Florida : IEEE. ; , s. 496-501
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Konferensbidrag (refereegranskat)abstract
- The Kuramoto model evolves on the circle, i.e., the 1-sphere S1. A graph G is referred to as S1 -synchronizing if the Kuramoto model on G synchronizes almost globally. This paper generalizes the Kuramoto model and the concept of synchronizing graphs to the Stiefel manifold St (p, n). Previous work on generalizations of the Kuramoto model have largely been influenced by results and techniques that pertain to the original model. It was recently shown that all connected graphs are Sn -synchronizing for all n ≥ 2. However, that does not hold for n = 1. Previous results on generalized models may thus have been overly conservative. The n-sphere is a special case of the Stiefel manifold, namely St(1, n+1). As such, it is natural to ask for the extent to which the results on Sn can be extended to the Stiefel manifold. This paper shows that all connected graphs are St(p, n) -synchronizing provided the pair (p, n) satisfies p ≤ [2n/3]-1. © Copyright 2019 IEEE - All rights reserved.
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| 2. |
- Bernard, Florian, et al.
(författare)
-
HiPPI : Higher-order projected power iterations for scalable multi-matching
- 2019
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Ingår i: IEEE International Conference on (ICCV) Computer Vision. - New York : Institute of Electrical and Electronics Engineers (IEEE). - 1550-5499. ; 2019-October, s. 10283-10292
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Tidskriftsartikel (refereegranskat)abstract
- The matching of multiple objects (e.g. shapes or images) is a fundamental problem in vision and graphics. In order to robustly handle ambiguities, noise and repetitive patterns in challenging real-world settings, it is essential to take geometric consistency between points into account. Computationally, the multi-matching problem is difficult. It can be phrased as simultaneously solving multiple (NP-hard) quadratic assignment problems (QAPs) that are coupled via cycle-consistency constraints. The main limitations of existing multi-matching methods are that they either ignore geometric consistency and thus have limited robustness, or they are restricted to small-scale problems due to their (relatively) high computational cost. We address these shortcomings by introducing a Higher-order Projected Power Iteration method, which is (i) efficient and scales to tens of thousands of points, (ii) straightforward to implement, (iii) able to incorporate geometric consistency, (iv) guarantees cycle-consistent multi-matchings, and (iv) comes with theoretical convergence guarantees. Experimentally we show that our approach is superior to existing methods. © 2019 IEEE.
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| 3. |
- Bernard, Florian, et al.
(författare)
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Sparse Quadratic Optimisation over the Stiefel Manifold with Application to Permutation Synchronisation
- 2021
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Ingår i: Advances in Neural Information Processing Systems. - Maryland Heights, MO : Morgan Kaufmann Publishers. - 9781713845393 ; , s. 25256-25266
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Konferensbidrag (refereegranskat)abstract
- We address the non-convex optimisation problem of finding a sparse matrix on the Stiefel manifold (matrices with mutually orthogonal columns of unit length) that maximises (or minimises) a quadratic objective function. Optimisation problems on the Stiefel manifold occur for example in spectral relaxations of various combinatorial problems, such as graph matching, clustering, or permutation synchronisation. Although sparsity is a desirable property in such settings, it is mostly neglected in spectral formulations since existing solvers, e.g. based on eigenvalue decomposition, are unable to account for sparsity while at the same time maintaining global optimality guarantees. We fill this gap and propose a simple yet effective sparsity-promoting modification of the Orthogonal Iteration algorithm for finding the dominant eigenspace of a matrix. By doing so, we can guarantee that our method finds a Stiefel matrix that is globally optimal with respect to the quadratic objective function, while in addition being sparse. As a motivating application we consider the task of permutation synchronisation, which can be understood as a constrained clustering problem that has particular relevance for matching multiple images or 3D shapes in computer vision, computer graphics, and beyond. We demonstrate that the proposed approach outperforms previous methods in this domain. © 2021 Neural information processing systems foundation. All rights reserved.
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| 4. |
- Bernard, Florian, et al.
(författare)
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Synchronisation of partial multi-matchings via non-negative factorisations
- 2019
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Ingår i: Pattern Recognition. - Amsterdam : Elsevier. - 0031-3203 .- 1873-5142. ; 92, s. 146-155
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study permutation synchronisation for the challenging case of partial permutations, which plays an important role for the problem of matching multiple objects (e.g. images or shapes). The term synchronisation refers to the property that the set of pairwise matchings is cycle-consistent, i.e. in the full matching case all compositions of pairwise matchings over cycles must be equal to the identity. Motivated by clustering and matrix factorisation perspectives of cycle-consistency, we derive an algo- rithm to tackle the permutation synchronisation problem based on non-negative factorisations. In order to deal with the inherent non-convexity of the permutation synchronisation problem, we use an initialisation procedure based on a novel rotation scheme applied to the solution of the spectral relaxation. Moreover, this rotation scheme facilitates a convenient Euclidean projection to obtain a binary solution after solving our relaxed problem. In contrast to state-of-the-art methods, our approach is guaranteed to produce cycle-consistent results. We experimentally demonstrate the efficacy of our method and show that it achieves better results compared to existing methods. © 2019 Elsevier Ltd
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| 5. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Injection Molding and Appearance of Cellulose-Reinforced Composites
- 2019
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Ingår i: Polymer Engineering and Science. - : John Wiley and Sons Inc.. - 0032-3888 .- 1548-2634. ; 60:1, s. 5-12
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Tidskriftsartikel (refereegranskat)abstract
- Composite materials based on an ethylene-acrylic acid (EAA) copolymer and 20 wt% cellulose fibers were compounded by two runs in a twin-screw extruder. The composite material with cellulose fibers (CF) and a reference of unfilled EAA were injection molded into plaques using three different temperature profiles with end zone temperatures of 170°C, 200°C, and 230°C. The injection molded samples were then characterized in terms of their mechanical properties, thermal properties, appearance (color and gloss), and surface topography. The higher processing temperatures resulted in a clear discoloration of the composites, but there was no deterioration in the mechanical performance. The addition of cellulose typically gave a tensile modulus three times higher than that of the unfilled EAA, but the strength and strain at rupture were reduced when fibers were added. The processing temperature had no significant influence on the mechanical properties of the composites. Gloss measurements revealed negligible differences between the samples molded at the different melt temperatures but the surface smoothness was somewhat higher when the melt temperature was increased. In general, addition of the cellulose to the EAA reduced the gloss level and the surface smoothness.
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| 6. |
- Gao, Maolin, et al.
(författare)
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Isometric multi-shape matching
- 2021
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Ingår i: Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition. - Washington, DC : IEEE. - 9781665445092 ; , s. 14178-14188
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Konferensbidrag (refereegranskat)abstract
- Finding correspondences between shapes is a fundamental problem in computer vision and graphics, which is relevant for many applications, including 3D reconstruction, object tracking, and style transfer. The vast majority of correspondence methods aim to find a solution between pairs of shapes, even if multiple instances of the same class are available. While isometries are often studied in shape correspondence problems, they have not been considered explicitly in the multi-matching setting. This paper closes this gap by proposing a novel optimisation formulation for isometric multi-shape matching. We present a suitable optimisation algorithm for solving our formulation and provide a convergence and complexity analysis. Our algorithm obtains multi-matchings that are by construction provably cycle-consistent. We demonstrate the superior performance of our method on various datasets and set the new state-ofthe-art in isometric multi-shape matching. © 2021 IEEE
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| 7. |
- Markdahl, J., et al.
(författare)
-
High-dimensional Kuramoto models on Stiefel manifolds synchronize complex networks almost globally
- 2020
-
Ingår i: Automatica. - Amsterdam : Elsevier. - 0005-1098 .- 1873-2836. ; 113
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Tidskriftsartikel (refereegranskat)abstract
- The Kuramoto model of coupled phase oscillators is often used to describe synchronization phenomena in nature. Some applications, e.g., quantum synchronization and rigid-body attitude synchronization, involve high-dimensional Kuramoto models where each oscillator lives on the n-sphere or SO(n). These manifolds are special cases of the compact, real Stiefel manifold St(p,n). Using tools from optimization and control theory, we prove that the generalized Kuramoto model on St(p,n) converges to a synchronized state for any connected graph and from almost all initial conditions provided (p,n) satisfies p≤2/3n−1 and all oscillator frequencies are equal. This result could not have been predicted based on knowledge of the Kuramoto model in complex networks over the circle. In that case, almost global synchronization is graph dependent; it applies if the network is acyclic or sufficiently dense. This paper hence identifies a property that distinguishes many high-dimensional generalizations of the Kuramoto models from the original model. © 2019 Elsevier Ltd
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| 8. |
- Moggi, E., et al.
(författare)
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Sound over-approximation of probabilities
- 2020
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Ingår i: Acta Cybernetica. - Szeged : University of Szeged, Institute of Informatics. - 0324-721X. ; 24:3, s. 269-285
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Tidskriftsartikel (refereegranskat)abstract
- Safety analysis of high confidence systems requires guaranteed bounds on the probabilities of events of interest. Establishing the correctness of algorithms that aim to compute such bounds is challenging. We address this problem in three steps. First, we use monadic transition systems (MTS) in the category of sets as a framework for modeling discrete time systems. MTS can capture different types of system behaviors, but we focus on a combination of non-deterministic and probabilistic behaviors that often arises when modeling complex systems. Second, we use the category of posets and monotonic maps as a setting to define and compare approximations. In particular, for the MTS of interest, we consider approximations of their configurations based on complete lattices. Third, by restricting to finite lattices, we obtain algorithms that compute over-approximations, i.e., bounds from above within some partial order of approximants, of the system configuration after n steps. Interestingly, finite lattices of “interval probabilities” may fail to accurately approximate configurations that are both non-deterministic and probabilistic, even for deterministic (and continuous) system dynamics. However, better choices of finite lattices are available. © 2020 University of Szeged, Institute of Informatics. All rights reserved.
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| 9. |
- Sidorenko, Galina, 1985-
(författare)
-
Cooperative Automated Driving for Enhanced Safety and Ethical Decision-Making
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Advances in technologies for vehicular communication enable new applications for Cooperative Intelligent Transportation Systems (C-ITS). Communicating vehicles share information and cooperate, which allows for improved safety, fuel economy, and traffic efficiency. Platooning – a coordinated string of vehicles with small Inter-Vehicle Distances (IVDs) – comprises one such C-ITS application. Any C-ITS application must comply with high safety requirements to pass standardization and be commercially deployed. Moreover, trusted solutions should be guaranteed even for critical scenarios or rare edge cases. This thesis presents two sets of contributions related to cooperative automated driving. Firstly, it provides conditions ensuring safe platooning or vehicle following. Secondly, it introduces an ethical framework to guide autonomous decision-making in scenarios involving imminent collisions. In the first set of contributions, we consider emergency braking scenarios for vehicles driving in a platoon or following each other. In such scenarios, the lead vehicle suddenly brakes. This requires swift responses from followers to prevent rear-end collisions. Here, Vehicle-to-Everything (V2X) communication has the potential to significantly reduce reaction times by allowing the lead vehicle to notify followers of the emergency braking. The presented safety analysis yields computationally efficient methods and algorithms for calculating minimum IVDs for rear-end collision avoidance. The IVDs are computed for closed-loop and open-loop configurations. The open-loop configuration implies followers drive with a constant velocity until the onset of braking, whereas in the closed-loop configuration, a controller is used under some restrictions. In addition, a centralized approach for optimization of IVDs in platoon formations is carried out. Such an approach allows for improved fuel consumption and road utilization. An analytical comparison shows that our proposed Vehicle-to-Vehicle (V2V) communication-based solution is superior to classic automated systems, such as automatic emergency braking system, which utilizes only onboard sensors. Wireless communication provides intentions to vehicles almost immediately, which allows for smaller IVDs while guaranteeing the same level of safety.In the second set of contributions, an ethical framework to guide autonomous decision-making is presented. Even though collisions resulting from edge cases are unlikely, it is essential to address them in motion planning logic for autonomous vehicles. Decisions made in such situations should always prioritize ethical considerations, such as saving human lives. Adhering to ethical principles in the development and deployment of autonomous vehicles is essential for fostering public understanding and acceptance. The thesis presents a framework of ethical V2X communication, where V2X is acknowledged as an essential means for enabling autonomous vehicles to perform coordinated actions to meet certain ethical criteria. The presented framework demonstrates how the risk or harm resulting from unavoidable collisions can be mitigated or redistributed under ethical considerations through cooperation between vehicles. Overall, the presented thesis highlights the importance of C-ITS and, specifically, V2X communication in managing emergency scenarios. V2X communication enables faster response times and facilitates cooperative maneuvers, which helps preventing rear-end collisions or mitigating their consequences under ethical considerations. Future work directions include an extension of the obtained results by considering more advanced models of vehicles, environment, and communication settings; and applying the proposed frameworks to more complicated traffic scenarios.
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| 10. |
- Sidorenko, Galina, 1985-, et al.
(författare)
-
Emergency braking with ACC : how much does V2V communication help
- 2022
-
Ingår i: IEEE Networking Letters. - Piscataway, NJ : IEEE. - 2576-3156. ; 4:3, s. 157-161
-
Tidskriftsartikel (refereegranskat)abstract
- This paper provides a safety analysis for emergency braking scenarios involving consecutive vehicles which utilize adaptive cruise control (ACC) with a constant-distance policy together with vehicle-to-vehicle (V2V) communication. We identify analytically, how the minimum safe inter-vehicle distance(IVD) that allows avoiding rear-end collision can be shortened with the use of electronic emergency brake lights and derive the explicit dependency of such IVDs on V2V communication time delay. We further show how these results can be used to compute probabilities of safe braking in the presence of packet losses.
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| 11. |
- Sidorenko, Galina, 1985-, et al.
(författare)
-
Ethical V2X : Cooperative Driving as the only Ethical Path to Multi-Vehicle Safety
- 2023
-
Ingår i: 2023 IEEE 98th Vehicular Technology Conference (VTC2023-Fall). - : IEEE. - 9798350329285 - 9798350329292
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Konferensbidrag (refereegranskat)abstract
- We argue that an information exchange between vehicles via the vehicular communications is the foundation for ethical driving. In other words - autonomous vehicles must be cooperative to be able to resolve ethical dilemmas in a multi-vehicle scenario. We show this by exploring the minimal setting of a longitudinal driving in a formation of three vehicles. © 2023 IEEE.
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| 12. |
- Sidorenko, Galina, 1985-, et al.
(författare)
-
Safety of Automatic Emergency Braking in Platooning
- 2022
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Ingår i: IEEE Transactions on Vehicular Technology. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 71:3, s. 2319-2332
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Tidskriftsartikel (refereegranskat)abstract
- A platoon comprises a string of consecutive highly automated vehicles traveling together. Platooning allows for increased road utilization and reduced fuel consumption due to short inter-vehicular distances. Safety in terms of guaranteeing no rear-end collisions is of utmost importance for platooning systems to be deployed in practice. We compare how safely emergency braking can be handled by emerging V2V communications on the one hand and by radar-based measurements of existing AEBS on the other. We show that even under conservative assumptions on the V2V communications, such an approach significantly outperforms AEBS with an ideal radar sensor in terms of allowed inter-vehicle distances and response times. Furthermore, we design two emergency braking strategies for platooning based on V2V communications. The first braking strategy assumes centralized coordination by the leading vehicle and exploits necessary optimal conditions of a constrained optimization problem, whereas the second -- the more conservative solution -- assumes only local information and is distributed in nature. Both strategies are also compared with the AEBS.
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| 13. |
- Sidorenko, Galina, 1985-
(författare)
-
Safety of Cooperative Automated Driving : Analysis and Optimization
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New cooperative intelligent transportation system (C-ITS) applications become enabled thanks to advances in communication technologies between vehicles(V2V) and with the infrastructure (V2I). Communicating vehicles share information with each other and cooperate, which results in improved safety, fuel economy, and traffic efficiency. An example of a C-ITS application is platooning, which comprises a string of vehicles that travel together with short inter-vehicle distances (IVDs).Any solution related to C-ITS must comply with high safety requirements in order to pass standardization and be commercially deployed. Furthermore, trusted safety levels should be assured even for critical scenarios.This thesis studies the conditions that guarantee safety in emergency braking scenarios for heterogeneous platooning, or string-like, formations of vehicles. In such scenarios, the vehicle at the head of the string emergency brakes and all following vehicles have to automatically react in time to avoid rear-end collisions. The reaction time can be significantly decreased with vehicle-to-vehicle (V2V) communication usage since the leader can explicitly inform other platooning members about the critical braking.The safety analysis conducted in the thesis yields computationally efficient methods and algorithms for calculating minimum inter-vehicle distances that allow avoiding rear-end collisions with a predefined high guarantee. These IVDs are theoretically obtained for an open-loop and a closed-loop configurations. The former implies that follower drives with a constant velocity until braking starts, whereas in the latter, an adaptive cruise control (ACC) with a constant-distance policy serves as a controller. In addition, further optimization of inter-vehicle distances in the platoon is carried out under an assumption of centralized control. Such an approach allows achieving better fuel consumption and road utilization.The performed analytical comparison suggests that our proposed V2V communication based solution is superior to classical automated systems, such as automatic emergency braking system (AEBS), which utilizes only onboard sensors and no communication. Wireless communication, enabling to know the intentions of other vehicles almost immediately, allows for smaller IVDs whilst guaranteeing the same level of safety.Overall, the presented thesis highlights the importance of C-ITS and, specifically, V2V in the prevention of rear-end collisions in emergency scenarios. Future work directions include an extension of the obtained results by considering more advanced models of vehicles, environment, and communication settings; and applying the proposed algorithms of safety guaranteeing to other controllers, such as ACC with a constant time headway policy.
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| 14. |
- Sidorenko, Galina, 1985-, et al.
(författare)
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Towards a Complete Safety Framework for Longitudinal Driving
- 2022
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Ingår i: IEEE Transactions on Intelligent Vehicles. - Piscataway, NJ : IEEE. - 2379-8858 .- 2379-8904. ; 7:4, s. 809-814
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Tidskriftsartikel (refereegranskat)abstract
- Formal models for the safety validation of autonomous vehicles have become increasingly important. To this end, we present a safety framework for longitudinal automated driving. This framework allows calculating minimum safe inter-vehicular distances for arbitrary ego vehicle control policies. We use this framework to enhance the Responsibility-Sensitive Safety (RSS) model and models based on it, which fail to cover situations where the ego vehicle has a higher decelerating capacity than its preceding vehicle. For arbitrary ego vehicle control policies, we show how our framework can be applied by substituting real (possibly computationally intractable) controllers with upper bounding functions. This comprises a general approach for longitudinal safety, where safety guarantees for the upper-bounded system are equivalent to those for the original system but come at the expense of larger inter-vehicular distances.
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| 15. |
- Sidorenko, Galina, 1985-, et al.
(författare)
-
Vehicle-to-Vehicle Communication for Safe and Fuel-Efficient Platooning
- 2020
-
Ingår i: 2020 IEEE Intelligent Vehicles Symposium (IV). - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 9781728166735 ; , s. 795-802
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Konferensbidrag (refereegranskat)abstract
- A platoon consists of a string of vehicles traveling close together. Such tight formation allows for increased road throughput and reduced fuel consumption due to decreased air resistance. Furthermore, sensors and control algorithms can be used to provide a high level of automation. In this context, safety – in terms of no rear-end collisions – is a key property that needs to be assured. We investigate how vehicle-to-vehicle communication can be used to reduce inter-vehicle distances while guaranteeing safety in emergency braking scenarios. An optimization-based modeling scheme is presented that, under certain restrictions, provides an analytical calculation of inter-vehicle distances for safe braking. In contrast to earlier simulation-based approaches, the framework allows for computationally efficient solutions with explicit guarantees. Two approaches for computing braking strategies in emergency scenarios are proposed. The first assumes centralized coordination by the leading vehicle and exploits necessary optimal conditions of a constrained optimization problem, whereas the second – the more conservative solution – assumes only local information and is distributed in nature. We illustrate the usefulness of the approaches through several computational simulations. © 2020 IEEE.
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| 16. |
- Thunberg, Johan, 1982-
(författare)
-
Consensus and Pursuit-Evasion in Nonlinear Multi-Agent Systems
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Within the field of multi-agent systems theory, we study the problems of consensus and pursuit-evasion. In our study of the consensus problem, we first provide some theoretical results and then consider the problem of consensus on SO(3) or attitude synchronization.In Chapter 2, for agents with states in R^m, we present two theorems along the lines of Lyapunov’s second method that, under different conditions, guarantee asymptotic state consensus in multi-agent systems where the interconnection topologies are switching. The first theorem is formulated by using the states of the agents in the multi-agent system, whereas the second theorem is formulated by using the pairwise states for pairs of agents in the multi-agent system.In Chapter 3, the problem of consensus on SO(3) for a multi-agent system with directed and switching interconnection topologies is addressed. We provide two different types of kinematic control laws for a broad class of local representations of SO(3). The first control law consists of a weighted sum of pairwise differences between positions of neighboring agents, expressed as coordinates in a local representation. The structure of the control law is well known in the consensus community for being used in systems of agents in the Euclidean space, and here we show that the same type of control law can be used in the context of consensus on SO(3). In a later part of this chapter, based on the kinematic control laws, we introduce torque control laws for a system of rigid bodies in space and show that the system reaches consensus when these control laws are used.Chapter 4 addresses the problem of consensus on SO(3) for networks of uncalibrated cameras. Under the assumption that each agent uses a camera in order to measure its rotation, we prove convergence to the consensus set for two types of kinematic control laws, where only conjugate rotation matrices are available for the agents. In these conjugate rotations, the rotation matrix can be seen as distorted by the (unknown) intrinsic parameters of the camera. For the conjugate rotations we introduce distorted versions of well known local parameterizations of SO(3) and show consensus by using control laws that are similar to the ones in Chapter 3, with the difference that the distorted local representations are used instead. In Chapter 5, we study the output consensus problem for homogeneous systems of agents with linear continuous time-invariant dynamics. We derive control laws that solve the problem, while minimizing a cost functional of the control signal. Instead of considering a fixed communication topology for the system, we derive the optimal control law without any restrictions on the topology. We show that for all linear output controllable homogeneous systems, the optimal control law uses only relative information but requires the connectivity graph to be complete and in general requires measurements of the state errors. We identify cases where the optimal control law is only based on output errors.In Chapter 6, we address the multi-pursuer version of the visibility pursuit-evasion problem in polygonal environments. By discretizing the problem and applying a Mixed Integer Linear Programming (MILP) framework, we are able to address problems requiring so called recontamination and also impose additional constraints, such as connectivity between the pursuers. The proposed MILP formulation is less conservative than solutions based on graph discretizations of the environment, but still somewhat more conservative than the original underlying problem. It is well known that MILPs, as well as multi-pursuer pursuit-evasion problems, are NP-hard. Therefore we apply an iterative Receding Horizon Control (RHC) scheme, where a number of smaller MILPs are solved over shorter planning horizons. The proposed approach is illustrated by a number of solved examples.
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| 17. |
- Thunberg, Johan, 1982-, et al.
(författare)
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Cooperative Vehicles versus Non-Cooperative Traffic Light : Safe and Efficient Passing
- 2023
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Ingår i: Computers. - Basel. - 2073-431X. ; 12:8
-
Tidskriftsartikel (refereegranskat)abstract
- Connected and automated vehicles (CAVs) will be a key component of future cooperative intelligent transportation systems (C-ITS). Since the adoption of C-ITS is not foreseen to happen instantly, not all of its elements are going to be connected at the early deployment stages. We consider a scenario where vehicles approaching a traffic light are connected to each other, but the traffic light itself is not cooperative. Information about indented trajectories such as decisions on how and when to accelerate, decelerate and stop, is communicated among the vehicles involved. We provide an optimization-based procedure for efficient and safe passing of traffic lights (or other temporary road blockage) using vehicle-to-vehicle communication (V2V). We locally optimize objectives that promote efficiency such as less deceleration and larger minimum velocity, while maintaining safety in terms of no collisions. The procedure is computationally efficient as it mainly involves a gradient decent algorithm for one single parameter. © 2023 by the authors.
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| 18. |
- Thunberg, Johan, 1982-, et al.
(författare)
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Efficiently Bounding the Probabilities of Vehicle Collision at Intelligent Intersections
- 2021
-
Ingår i: IEEE Open Journal of Intelligent Transportation Systems. - New York, NY : IEEE. - 2687-7813. ; 2, s. 47-59
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Tidskriftsartikel (refereegranskat)abstract
- Intelligent intersections have the potential to serve as an integral part of tomorrow’s traffic infrastructure. Wireless communication is key to enabling such technology. We consider a scenario where two flows of vehicles are to traverse an intelligent intersection. We investigate safety in emergency braking scenarios, where one of the vehicles in a flow suddenly decides to emergency brake and emergency braking messages are broadcast to affected vehicles. We provide a framework for computing lower bounds on probabilities for safe braking – collisions between vehicles are to be avoided. If we require that a crash or collision, for example, occurs at most once in a million scenarios, our approach allows for computation of lower bounds on the time-varying (or distance-varying) packet loss probabilities to ensure this. One of the benefits of the proposed framework is that the computational time is reduced; eliminating, for example, the need for time-consuming Monte Carlo simulations.
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| 19. |
- Thunberg, Johan, 1982-, et al.
(författare)
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Non-negative Spherical Relaxations for Universe-Free Multi-matching and Clustering
- 2023
-
Ingår i: Image Analysis. - Cham : Springer. - 9783031314377 - 9783031314384 ; , s. 260-277
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Konferensbidrag (refereegranskat)abstract
- We propose a novel non-negative spherical relaxation for optimization problems over binary matrices with injectivity constraints, which in particular has applications in multi-matching and clustering. We relax respective binary matrix constraints to the (high-dimensional) non-negative sphere. To optimize our relaxed problem, we use a conditional power iteration method to iteratively improve the objective function, while at same time sweeping over a continuous scalar parameter that is (indirectly) related to the universe size (or number of clusters). Opposed to existing procedures that require to fix the integer universe size before optimization, our method automatically adjusts the analogous continuous parameter. Furthermore, while our approach shares similarities with spectral multi-matching and spectral clustering, our formulation has the strong advantage that we do not rely on additional post-processing procedures to obtain binary results. Our method shows compelling results in various multi-matching and clustering settings, even when compared to methods that use the ground truth universe size (or number of clusters). © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.
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| 20. |
- Thunberg, Johan, 1982-, et al.
(författare)
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Unreliable V2X communication in cooperative driving : Safety times for emergency braking
- 2021
-
Ingår i: IEEE Access. - Piscataway, NJ : IEEE. - 2169-3536. ; 9, s. 148024-148036
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Tidskriftsartikel (refereegranskat)abstract
- Cooperative driving is a promising paradigm to improve traffic efficiency and safety. In congested traffic scenarios, such cooperation allows for safe maneuvering and driving with small inter-vehicle spatial gaps. The vehicles involved coordinate their movements in real-time and continuously update each other about their maneuver execution status by means of Vehicle-to-Everything (V2X) communication. However, unreliable V2X communication increases the Age of Information (AoI) of vehicles' status updates, posing a challenge in situations where emergency braking is required during cooperative maneuvering. To address the interplay between unreliable V2X communication and the resulting impact on traffic safety, we introduce a so-called safety time function, specifically designed for cooperative driving use-cases. The safety time function provides the time available for a vehicle to react to an unexpected event of another vehicle - such as emergency braking to avoid a collision. We provide a computationally efficient algorithm for the computation of safety time functions, which allows for efficient and safe cooperative maneuver planning - even in dense traffic scenarios with many vehicles involved. We show the applicability of our proposed safety time function based on the assessed communication quality for IEEE 802.11p-based V2X communication to meet safety constraints in dense vehicular traffic. © 2021 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.
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| 21. |
- Thunberg, Johan, 1982-, et al.
(författare)
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Vehicle-to-Vehicle Communications for Platooning : Safety Analysis
- 2019
-
Ingår i: IEEE Networking Letters. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 2576-3156. ; 1:4, s. 168-172
-
Tidskriftsartikel (refereegranskat)abstract
- Vehicle-to-vehicle (V2V) communication is the key technology enabling platooning. This paper proposes an analytical framework that combines the characteristics of V2V communication (packet loss probabilities and packet transmission delays) with the physical mobility characteristics of vehicles (speed, distance between vehicles and their brake capacities). First, we present the feasible region of communications delays which guarantees safe emergency braking in platooning scenarios. Second, we derive a bound on the probability of safe braking. The presented framework is applied to understand the performance of the state-of-the-art V2V communication protocol for platooning.
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| 22. |
- Yue, Zuogong, et al.
(författare)
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Dynamic network reconstruction from heterogeneous datasets
- 2021
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Ingår i: Automatica. - Amsterdam : Elsevier. - 0005-1098 .- 1873-2836. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- Performing multiple experiments is common when learning internal mechanisms of complex systems. These experiments can include perturbations of parameters or external disturbances. A challenging problem is to efficiently incorporate all collected data simultaneously to infer the underlying dynamic network. This paper addresses the reconstruction of dynamic networks from heterogeneous datasets under the assumption that the underlying networks share the same Boolean structure across all experiments. Parametric models are derived for dynamical structure functions, which describe causal interactions between measured variables. Multiple datasets are integrated into one regression problem with additional demands on group sparsity to assure network sparsity and structure consistency. To acquire structured group sparsity, we propose a sampling-based method, together with extended versions of l1-methods and sparse Bayesian learning. The performance of the proposed methods is benchmarked in numerical simulation. In summary, this paper presents efficient methods on network reconstruction from multiple experiments, and reveals practical experience that could guide applications. © 2020 Elsevier Ltd.
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| 23. |
- Yue, Zuogong, et al.
(författare)
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Network Stability, Realisation and Random Model Generation
- 2019
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Ingår i: 2019 IEEE 58th Conference on Decision and Control (CDC). - New York, NY : IEEE. - 9781728113982 - 9781728113975 - 9781728113999 ; , s. 4539-4544
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Konferensbidrag (refereegranskat)abstract
- Dynamical structure functions (DSFs) provide means for modelling networked dynamical systems and exploring interactive structures thereof. There have been several studies on methods/algorithms for reconstructing (Boolean) networks from time-series data. However, there are no methods currently available for random generation of DSF models with complex network structures for benchmarking. In particular, it may be desirable to generate stable DSF models or require the presence of feedback structures while keeping topology and dynamics random up to these constraints. This work provides procedures to obtain such models. On the path of doing so, we first study essential properties and concepts of DSF models, including realisation and stability. Then, the paper suggests model generation algorithms, whose implementations are now publicly available. © 2019 IEEE.
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| 24. |
- Yue, Zuogong, et al.
(författare)
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System Aliasing in Dynamic Network Reconstruction : Issues on Low Sampling Frequencies
- 2021
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Ingår i: IEEE Transactions on Automatic Control. - Piscataway : IEEE. - 0018-9286 .- 1558-2523. ; 66:12, s. 5788-5801
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Tidskriftsartikel (refereegranskat)abstract
- Network reconstruction of dynamical continuous-time (CT) systems is motivated by applications in many fields. Due to experimental limitations, especially in biology, data can be sampled at low frequencies, leading to significant challenges in network inference. We introduce the concept of "system aliasing" and characterize the minimal sampling frequency that allows reconstruction of CT systems from low sampled data. A test criterion is also proposed to detect the presence of system aliasing. With no system aliasing, the paper provides an algorithm to reconstruct dynamic networks from full-state measurements in the presence of noise. With system aliasing, we add additional prior information such as sparsity to overcome the lack of identifiability. This paper opens new directions in modelling of network systems where samples have significant costs. Such tools are essential to process available data in applications subject to experimental limitations. © 2020, IEEE
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