Vehicular Platoon Control Research Articles

Co-Design of Consensus-Based Approach and Reliable Communication Protocol for Vehicular Platoon Control

Automated and coordinated vehicle platoon driving is challenging as the complexity of vehicle control and the presence of unreliable wireless inter-vehicle communication. This subject has an interdisciplinary nature, involving control theories, vehicle dynamics, and communication. Due to the constant interaction between control logic and communication topology, a co-design approach for the controller and for reliable communication protocol becomes necessary. This paper describes the AddP-CACC - a consensus-based solution to vehicle platoons. The proposed solution turns the communication topology into a design parameter that dynamically reconfigures the controller. In addition, the controller automatically compensates for outdated information caused by network losses and delays. AddP-CACC was implemented in the PLEXE tool and was compared with other related works. Simulation results have shown the robustness and performance of the proposed solution in various scenarios that would include realistic propagation conditions with interference caused by other vehicles. The results have also evidenced the ability of the proposed solution to maintain a stable vehicular platoon by using different communication topologies, different vehicle flows, even in the presence of strong interferences, delays, and fading conditions.

Model Predictive Control for Connected Vehicle Platoon Under Switching Communication Topology

Vehicular platoon control can effectively achieve group consensus, improve vehicular running safety and increase road capacity. However, some constraints exist in practical situations due to the limitations of traffic environment in time-varying metrics (time-delay, packet-dropout or interruption) in wireless communication systems. In this work, a distributed model predictive control (MPC) algorithm is proposed for connected vehicle platoon with a focus on switching communication topologies and control strategy under abnormal communications. Firstly, the predecessor-leader following is selected as the basic communication topology, by which the switching communication topology and the desired vehicle spacing policy are established. Secondly, the platoon control algorithm of connected vehicles is established and a set of constraints is analyzed. Thirdly, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{ L}}_{2} $ </tex-math></inline-formula> -norm string stability criterion and the asymptotic stability criterion are considered within the proposed MPC. Finally, a co-simulation platform for connected vehicle platoon is developed based on Prescan/Matlab/V2X communication simulator. In addition, the platoon control algorithm is tested in three traffic scenarios including normal communication, leading vehicle with abnormal communication and following vehicle with abnormal communication. The experiments demonstrate that the communication topologies in different communication environments can be switched well in real time through the proposed platoon control algorithm. In addition, the string stability, the consistency of vehicle spacing, speed and acceleration are proven to be guaranteed simultaneously.

Adaptive Event-Triggered Platoon Control Under Unreliable Communication Links

The application of inter-vehicle wireless communication offers significant advantages in terms of improving traffic efficiency and safety while also suffering from unreliable communication links. This paper deals with the problem of event-triggered vehicular platoon control with communication time delay and package dropout, aiming to achieve a suitable trade-off between communication utilization and vehicle following performance. A disturbance based platoon model with communication time delay, package dropout and event-triggered scheme is established. Subsequently, the criterion for co-designing the event-trigger parameters and CACC controller parameters is derived by adopting the parameter space approach with the requirements to ensure individual vehicle internal stability, following accuracy and platoon string stability. To achieve a superior trade-off between communication resource utilization and following performance under unreliable communication condition, the adaptive event-triggered threshold is designed for the varying failure probability. The effectiveness of the proposed adaptive CACC strategy is verified using numerical simulations of a six-vehicle platoon during the FTP 72 drive cycle. The comparison results of three different scenarios show that the adaptive event-triggered scheme guarantees the following performance even when failure probability is 0.4.

Distributed Adaptive Event-Triggered Control and Stability Analysis for Vehicular Platoon

This paper is concerned with the stability of the vehicular platoon consisting of a leader and multiple cooperative autonomous driving followers. The objective of the platoon control is to ensure all vehicles traveling at the same speed while maintaining a safety spacing. To achieve the objective, a novel control framework consisting of the distributed adaptive event-triggered observer and the car-following control protocol is proposed for the vehicular platoon control. The condition that only few following vehicles can access the information of the leader is considered. In order to design controllers while avoid using any global information, such as the system matrix and the state of the leader, a distributed event-triggered observer is proposed, such that each vehicle can observe the dynamics of the leader. Based on this observer, both collision avoidance and limited communication source of each vehicle are simultaneously considered in the design of the observer. It is shown that under the proposed control framework, the platoon can achieve asymptotical stable, meanwhile, the amount of transmission data and communication cost among vehicles can be reduced. Finally, numerical simulations are presented to show the applicability of the obtained results.

Stability and Formation Error of Homogeneous Vehicular Platoons With Communication Time Delays

The problem of decentralized control of vehicular platoon is addressed, subject to non-uniform time-varying delays in the communication links among the vehicles. Our control goal is to drive the vehicles to reach a specified line formation, while moving forward according to the platoon leader speed. The control law in each vehicle is computed only by local relative information regarding its neighboring vehicles. The first result shows that communication delays cause steady-state formation error, whose value can be analytically calculated from the system data, and may lead to instability, if the delays values surpass a threshold. Hence, in the light of this finding, we present a decentralized control law to compensate for the delay effect, providing zero steady-state formation error. The paper is concluded by showing simulated experiments over six different communication topologies illustrating the applicability of our proposal.

Centralized and decentralized distributed control of longitudinal vehicular platoons with non‐uniform communication topology

AbstractIn this paper, the distributed control of a longitudinal platoon of vehicles with non‐uniform communication topology is studied. In the case of non‐uniform communication topology, some eigenvalues of the network's matrix may be complex which complicates the stability analysis of the platoon. Most previous studies on vehicular platooning focus mainly on uniform topologies such as uni‐directional, bi‐directional, and multi predecessors following. Since all eigenvalues of these topologies are real, the stability analysis can be performed in a straightforward manner. A third‐order linear differential model is employed to describe the upper‐level dynamics of each vehicle. The 3 N‐order closed‐loop dynamics of the platoon are decoupled to individual third‐order dynamics by presenting a new approach. Two new centralized and decentralized control protocols are introduced to perform the stability analysis of the closed‐loop dynamics. A constant time headway strategy is employed to adjust the inter‐vehicle spacing. Simulation results with different scenarios are presented to illustrate the effectiveness of the proposed approaches.

Adaptive Sliding Mode Control of Vehicular Platoons With Prescribed Tracking Performance

This paper investigates a vehicular platoon control problem with prescribed tracking performance in the presence of actuator saturation, uncertain parameters, and unknown disturbances. Two adaptive sliding mode control schemes based on leader–predecessor and leader–bidirectional information flows are presented to ensure string stability and strong string stability, respectively, with a prescribed tracking performance. The actuator saturation nonlinearity is addressed by approximating it with a smooth hyperbolic tangent function. The effects of uncertain parameters and exogenous disturbances are dealt with by introducing a set of adaptation laws. The effectiveness of the proposed control schemes is demonstrated via numerical simulation results.

Deep Learning for Reliable Mobile Edge Analytics in Intelligent Transportation Systems: An Overview

Intelligent transportation systems (ITSs) will be a major component of tomorrow's smart cities. However, realizing the true potential of ITSs requires ultralow latency and reliable data analytics solutions that combine, in real time, a heterogeneous mix of data stemming from the ITS network and its environment. Such data analytics capabilities cannot be provided by conventional cloud-centric data processing techniques whose communication and computing latency can be high. Instead, edge-centric solutions that are tailored to the unique ITS environment must be developed. In this article, an edge analytics architecture for ITSs is introduced in which data is processed at the vehicle or roadside smart sensor level to overcome the ITS's latency and reliability challenges. With a higher capability of passengers' mobile devices and intravehicle processors, such a distributed edge computing architecture leverages deep-learning techniques for reliable mobile sensing in ITSs. In this context, the ITS mobile edge analytics challenges pertaining to heterogeneous data, autonomous control, vehicular platoon control, and cyberphysical security are investigated. Then, different deep-learning solutions for such challenges are revealed. The discussed deep-learning solutions enable ITS edge analytics by endowing the ITS devices with powerful computer vision and signal processing functions. Preliminary results show that the introduced edge analytics architecture, coupled with the power of deep-learning algorithms, provides a reliable, secure, and truly smart transportation environment.

Influence of Driving Behaviors on the Stability in Car Following

Car following is the most common phenomenon in single-lane traffic. However, the propagation of the small perturbation of the velocity of the leading car will affect traffic flow. Driving behaviors play an important role in the determination of the qualitative dynamics of vehicles in the car-following process. Under different traffic environments, driving behaviors depend on the level of perceived risk, acceleration and deceleration habits, and reaction characteristics of the driver. The desired safety margin (DSM) model can directly describe the driving behaviors in the car-following process by using the parameters of the risk perception of drivers, sensitivity coefficient of acceleration and deceleration, and response time. In this paper, we investigate the influence of the accepted risk level, response time, and sensitivity factor on the traffic flow via the DSM model. The stability criterion of the simplified DSM model is derived via linear stability theory. Analytical results indicate that a backward propagating of perturbation would enlarge or shrink with the change of three driving behavior parameters of accepted risk level, sensitivity coefficient of acceleration or deceleration, and response time. Results show that careful driving can improve the stability of traffic flow and that system stability can be maintained by adjusting the acceleration and deceleration control parameters, increasing DSM, or decreasing response time for the adaptive cruise control or vehicular platoon control system. The results can provide reasonable values of driving behavior parameters for the stability of the primitive DSM model using the simplified DSM model. Furthermore, we analyze the influence of interval DSMs, and the acceleration and deceleration sensitivity of the primitive DSM model on the stability of traffic flow through numerical simulations. Results imply that the lower limit of the DSM influences traffic flow more significantly than the upper limit of the DSM. Moreover, the increase in deceleration sensitivity has a more important influence on the stability of traffic flow than the increase in acceleration sensitivity. The numerical simulation results are in good agreement with the analytical results and the relevant experimental results of previous studies.

Robust Control of Heterogeneous Vehicular Platoon with Non-Ideal Communication

The application of wireless communication to platooning brings such challenges as information delay and varieties of interaction topologies. To compensate for the information delay, a state predictor based control strategy is proposed, which transmits the future information of nodes instead of current values. Based on the closed loop dynamics of platoon with state predictor and feedback controller, a decoupling strategy is presented to analysis and design the platoon control system with lower order by adopting the eigenvalue decomposition of topological matrix. A numerical method based on LMI (Linear Matrix Inequality) is provided to find the required robust performance controller. Moreover, the influence of information delay on performance is studied theoretically and it is found that the tolerable maximum delay is determined by the maximum topological eigenvalue. The effectiveness of the proposed strategy is validated by several comparative simulations under various conditions with other methods.

Event-Driven Connected Vehicular Platoon Control With Mixed Time-Varying Delay

In this research, connected vehicular platoon control is investigated with mixed time-varying delay. An event-driven information interaction method for connected vehicular platoon system is built, which considered the combined effect of communication-actuator time-varying delay and event-driven mechanism. The new standard for asymptotically stable and criterion for the controller gains and the trigger parameters are obtained based on Lyapunov method. The derived controller is offset by new conditions, which are used to ensure the vehicular platoon system that can achieve string stability. Finally, the effectiveness and advantage of the proposed algorithm are demonstrated by numerical simulations and experiments results with electric experimental cars.

Formation control of longitudinal vehicular platoons under generic network topology with heterogeneous time delays

The problem of third-order consensus of homogeneous vehicular platoons in the presence of communication and parasitic delays is investigated. The communication topology of vehicular networks is assumed to be directed and generic. Therefore, a number of eigenvalues of the network’s matrix are complex, entangling the stability analysis of the closed-loop dynamics. By considering both communication and parasitic delays, a new linear centralized consensus protocol is designed for each vehicle. It will be shown that the closed-loop dynamics of vehicular networks with generic topology is in the form of linear systems with multiple delays. By presenting a new approach, the resultant linear time delay system is decoupled to individual third- and sixth-order dynamical equations. By performing the stability analysis of the new equations, it will be proven that the control parameters are independent of the network’s topology. Therefore, the control design and stability analysis will be significantly simplified compared with previous studies. To find the stable regions of time delay, the cluster treatment characteristic root method is employed. Simulation results are provided to show the effectiveness of the proposed approach.

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

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.

Stable Longitudinal Control of Heterogeneous Vehicular Platoon With Disturbances and Information Delays

This paper presents a robust control method for heterogeneous vehicle platoon subject to varying road slopes, aerodynamic drag, and wireless communication delay. First, a heterogeneous vehicle platoon is built, including parameter uncertainty, equivalent communication delay, network-induced delay caused by discrete data in sensor and wireless communication, and external disturbance (i.e., road slope and wind). Second, a Lyapunov–Krasovskii functional-based $H_\infty $ controller is designed to generate the state-feedback control which could ensure inner-vehicle stability and string stability of platoon simultaneously. Third, $\mathcal {L}_{2} $ string stability is proposed to ensure the platoon stability that guarantees the perturbations that do not grow unbounded as they propagate through the platoon. Simulation results indicate the proposed robust controller achieves tracking of desired inter-vehicle spacing and string stable of platoon while comparing with the regular string stability controller.

Sampled-data vehicular platoon control with communication delay

This article investigates sampled-data vehicular platoon control with communication delay. A new sampled-data control method is established, in which the effect of the communication delay is involved. First, a linearized vehicle longitudinal dynamic model is obtained using the exact feedback-linearization technique. Then, under the leader–predecessor following communication strategy, considering communication delay, a platoon control law is proposed based on sampled state information, which allows the weights of state errors to vary along the platoon. Complemented by additional string stability conditions, a useful string-stable platoon controller design algorithm is proposed. Finally, the effectiveness of platoon controller design methodology is demonstrated by numerical examples.

Provably Safe Cruise Control of Vehicular Platoons

We synthesize performance-aware safe cruise control policies for longitudinal motion of platoons of autonomous vehicles. Using set-invariance theories, we guarantee infinite-time collision avoidance in the presence of bounded additive disturbances, while ensuring that the length and the cruise speed of the platoon are bounded within specified ranges. We propose (i) a centralized control policy, and (ii) a distributed control policy, where each vehicle's control decision depends solely on its relative kinematics with respect to the platoon leader. Numerical examples are included.

Stable control of a heterogeneous platoon of vehicles with switched interaction topology, time-varying communication delay and lag of actuator

This paper is devoted to the study of longitudinal control of heterogeneous vehicular platoons with constant spacing policy between successive vehicles. In order to provide a more precise model, communication delays are assumed to be non-uniform and time-varying. A linear control based on relative measurements by considering communication delay and lag is used as the upper level control of each vehicle. In a vehicular platoon, the time-varying communication topology may be a source of instability of the closed-loop dynamics. Therefore, to perform the stability analysis using common Lyapunov function, three new methods based on Lyapunov–Razumikhin and Lyapunov–Krasovskii theorems are introduced. The results of these methods prove the global asymptotic stability of the resultant switched linear time-varying delay systems. A comparison between the proposed methods indicates that the Krasovskii-based approach is more robust against communication delay and lag than the Razumikhin-based approaches. Several simulation studies are provided to show the effectiveness of the proposed methods.

Decoupled robust control of vehicular platoon with identical controller and rigid information flow

Platoon driving has potential to significantly benefit road traffic. This study presents a decoupled robust control strategy for a vehicular platoon with identical feedback controller and rigid information topology. The node dynamics of vehicle with a lower-level controller is assumed to be covered by a multiplicative uncertainty model. The vehicular platoon control system is skillfully decomposed into an uncertain part and a diagonal system by applying linear transformation and eigenvalue decomposition on information flow graph. Then the requirements of robust stability and distance tracking error are equivalent to the H-infinity norm of decoupled sub-systems. Comparative simulations with a non-robust controller and different communication topologies are conducted to demonstrate the robust stability and distance tracking performances of the proposed method.

Robust control of heterogeneous vehicular platoon with uncertain dynamics and communication delay

Platoon formation of highway vehicles has the potential to significantly enhance road safety, improve highway utility, and increase traffic efficiency. However, various uncertainties and disturbances that are present in real-world driving conditions make the implementation of vehicular platoon a challenging problem. This study presents an H-infinity control method for a platoon of heterogeneous vehicles with uncertain vehicle dynamics and uniform communication delay. The requirements of string stability, robustness and tracking performance are systematically measured by the H-infinity norm, and explicitly satisfied by casting into the linear fractional transformation format. A delay-dependent linear matrix inequality is derived to numerically solve the distributed controllers for each vehicle. The performances of the controlled platoon are theoretically analysed by using a delay-dependent Lyapunov function which includes a linear quadratic function of states during the delay period. Simulations with a platoon of heterogeneous vehicles are conducted to demonstrate the effectiveness of the proposed method under random parameters and external disturbances.

Communication Scheduling and Control of a Platoon of Vehicles in VANETs

This paper is concerned with the problem of vehicular platoon control in vehicular ad hoc networks subject to capacity limitation and random packet dropouts. By introducing binary sequences as the basis of network access scheduling and modeling random packet dropouts as independent Bernoulli processes, we derive a closed-form methodology for vehicular platoon control. In particular, an interesting framework for network access scheduling and platoon control codesign is established based on a set of priority rules for network access control. The resulting platoon control and scheduling algorithm can resolve network access conflicts in vehicular ad hoc networks and guarantee string stability and zero steady-state spacing errors. The effectiveness of the method is demonstrated by numerical simulations and experiments with laboratory-scale Arduino cars.