Connected and automated vehicles (CAVs) have the potential to address a number of safety, mobility, and sustainability issues of our current transportation systems. Cooperative longitudinal motion control is one of the key CAV technologies that allows vehicles to be driven in a cooperative manner to achieve system-wide benefits. In this paper, we provide a literature survey on the progress accomplished by researchers worldwide regarding cooperative longitudinal motion control systems of multiple CAVs. Specifically, the architecture of various cooperative CAV systems is reviewed to answer how cooperative longitudinal motion control can work with the help of multiple system modules. Next, different operational concepts of cooperative longitudinal motion control applications are reviewed to answer where they can be implemented in today's transportation systems . Different cooperative longitudinal motion control methodologies and their major characteristics are then described to answer what the critical design issues are . This paper concludes by describing an overall landscape of cooperative longitudinal motion control of CAVs, as well as pointing out opportunities and challenges in the future research and experimental implementations.

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A Survey on Cooperative Longitudinal Motion Control of Multiple Connected and Automated Vehicles

In a platoon of connected vehicles, time headway plays an important role in both traffic capacity and road safety. It is desirable to maintain a lower time headway while satisfying string stability in a platoon, since this leads to a higher traffic capacity and guarantees the disturbance attenuation ability. In this paper, we study a multiple-predecessor following strategy to reduce time headway via vehicle-to-vehicle (V2V) communication. We first introduce a new definition of desired inter-vehicle distances based on the constant time headway (CTH) policy, which is suitable for general communication topologies. By exploiting lower-triangular structures in a time headway matrix and an information topology matrix, we derive a set of necessary and sufficient conditions on feedback gains for internal asymptotic stability. Further, by analyzing the stable region of feedback gains, a necessary and sufficient condition on time headway is also obtained for the string stability specification. It is proved that a platoon can be asymptotically stable and string stable when the time headway is lower bounded. Moreover, this bound can be reduced by increasing the number of predecessors. These results explicitly highlight the benefits of V2V communication on reducing time headway for platooning of connected vehicles.

Reducing time headway for platooning of connected vehicles via V2V communication

Cooperative driving systems may increase the utilization of road infrastructure resources through coordinated control and platooning of individual vehicles with the potential of enhancing both traffic safety and efficiency. Vehicle cooperative driving is essentially a hybrid system that is a combination of discrete events, i.e., the transition of discrete cooperative maneuvering modes, such as vehicle merging and platoon splitting, as well as continuous vehicle dynamics. In this paper, a novel hybrid system consisting of the discrete cooperative maneuver switch and the continuous vehicle motion control is introduced into a multi-vehicle cooperative control system with a distributed control structure, leading each automated vehicle to conduct path planning and motion control separately. The primary novelty of this paper lies in that it presents a control algorithm combining artificial potential field (APF) approach with model predictive control (MPC), and using the optimizer of the MPC controller to replace the gradient-descending method in the traditional APF approach. Such a method can accomplish both path planning and motion control synchronously. Second, based on hybrid automata, a cooperative maneuver switching model consisting of a system state set and a discrete maneuver transition rule is established for two discrete maneuvers in the cooperative driving system, i.e., single-vehicle cruising and multiple-vehicle platooning. Simulations in several typical traffic scenarios demonstrate the effectiveness of the proposed method.

Path Planning and Cooperative Control for Automated Vehicle Platoon Using Hybrid Automata

In a platoon control system, a fixed and symmetrical topology is quite rare because of adverse communication environments and continuously moving vehicles. This paper presents a distributed adaptive sliding mode control scheme for more realistic vehicular platooning. In this scheme, adaptive mechanism is adopted to handle platoon parametric uncertainties, while a structural decomposition method deals with the coupling of interaction topology. A numerical algorithm based on linear matrix inequality is developed to place the poles of the sliding motion dynamics in the required area to balance quickness and smoothness. The proposed scheme allows the nodes to interact with each other via different types of topologies, e.g., either asymmetrical or symmetrical, either fixed or switching. Different from existing techniques, it does not require the exact values of each entity in the topological matrix, and only needs to know the bounds of its eigenvalues. The effectiveness of this proposed methodology is validated by bench tests under several conditions.

Distributed Adaptive Sliding Mode Control of Vehicular Platoon With Uncertain Interaction Topology

Connected autonomous vehicles are considered as mitigators
of issues such as traffic congestion, road safety, inefficient fuel
consumption and pollutant emissions that current road transportation
system suffers from. Connected autonomous vehicles
utilise communication systems to enhance the performance of
autonomous vehicles and consequently improve transportation by
enabling cooperative functionalities, namely, cooperative sensing
and cooperative manoeuvring. The former refers to the ability to
share and fuse information gathered from vehicle sensors and road
infrastructures to create a better understanding of the surrounding
environment while the latter enables groups of vehicles to drive in
a co-ordinated way which ultimately results in a safer and more efficient
driving environment. However, there is a gap in understanding
howand to what extent connectivity can contribute to improving the
efficiency, safety and performance of autonomous vehicles. Therefore,
the aim of this paper is to investigate the potential benefits
that can be achieved from connected autonomous vehicles through
analysing five use-cases: (i) vehicle platooning, (ii) lane changing,
(iii) intersection management, (iv) energy management and (v) road
friction estimation. The current paper highlights that although connectivity
can enhance the performance of autonomous vehicles and
contribute to the improvement of current transportation system performance,
the level of achievable benefits depends on factors such
as the penetration rate of connected vehicles, traffic scenarios and
the way of augmenting off-board information into vehicle control
systems.

Towards connected autonomous driving: review of use-cases

The advances in distributed intervehicle communication networks have stimulated a fruitful line of research in cooperative adaptive cruise control (CACC). In CACC, individual vehicles, grouped into platoons, must automatically adjust their own speed using on-board sensors and communication with the preceding vehicle so as to maintain a safe intervehicle distance. However, a crucial limitation of the state of the art of this control scheme is that the string stability of the platoon can be proven only when the vehicles in the platoon have identical driveline dynamics and perfect engine performance (homogeneous platoon), and possibly an ideal communication channel. This paper proposes a novel CACC strategy that overcomes the homogeneity assumption and that is able to adapt its action and achieve string stability even for uncertain heterogeneous platoons. Furthermore, in order to handle the inevitable communication losses, we formulate an extended average dwell-time framework and design an adaptive switched control strategy, which activates an augmented CACC or an augmented adaptive cruise control strategy depending on communication reliability. Stability is proven analytically and simulations are conducted to validate the theoretical analysis.

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An Adaptive Switched Control Approach to Heterogeneous Platooning With Intervehicle Communication Losses

Grouping individual vehicles into platoons with a defined inter-vehicle spacing policy has been proven to greatly improve road throughput and reduce vehicles' energy consumption. The emerging interest in distributed inter-vehicle communication networks has provided new tools for further improvements of the performance of this platoon-based driving pattern. A leading control strategy of such vehicular cyber-physical systems is Cooperative Adaptive Cruise Control (CACC). However, a crucial limitation of the state-of-the-art is that string stability can be proven only when the vehicles in the platoon have identical driveline dynamics (homogeneous platoons). In this paper, we present a novel CACC strategy that overcomes the homogeneity assumption and that is able to adapt its action and achieve string stability even with uncertain heterogeneous platoons. Considering a one-vehicle look-ahead topology, we propose a Model Reference Adaptive Control augmentation: the control objective is to augment a baseline CACC, proven to be string stable in the homogeneous scenario, with an adaptive control term that compensates for each vehicle's unknown driveline dynamics. Asymptotic convergence of the heterogeneous platoon to a string stable platoon is shown analytically for an appropriately designed reference model. Simulations of the proposed CACC strategy are conducted to validate the theoretical analysis.

Adaptive control of interconnected networked systems with application to heterogeneous platooning

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Youssef Abou Harfouch

Papers

An Adaptive Switched Control Approach to Heterogeneous Platooning With Intervehicle Communication Losses

Adaptive control of interconnected networked systems with application to heterogeneous platooning

An Adaptive Approach to Cooperative Longitudinal Platooning of Heterogeneous Vehicles with Communication Losses