Browsing by Author "Li, Zhiwu"
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- Dual Mode for Vehicular Platoon Safety: Simulation and Formal VerificationPublication . Karoui, Oussama; Khalgui, Mohamed; Koubâa, Anis; Guerfala, Emna; Li, Zhiwu; Tovar, EduardoIn order to cope with uncertainties in a platoon, this paper proposes a reconfigurable multi-agent architecture to address the platoon safety problem by handling two modes: the normal mode and the degraded mode. At this stage of research, the normal mode is characterized by the interaction between agents over a Vehicle-to-Vehicle (V2V) communication network while the degraded mode simply involves sensors for a local perception. The switching from the normal mode to the degraded one is triggered when the communication quality is considered not fully reliable. A PID (Proportional Integral Derivative) controller is proposed to regulate the inter-vehicle distance and orientation. Two models are proposed in this paper: in the first one, the management operations such as splitting and joining are set up while the second is mainly modeled to assess the implemented controller quality. In this paper, the safety of a platoon is represented by the quality of tracking and the inter-vehicle distance. The mentioned features are assessed for both modes through a formal verification using the Uppaal software. We prove the efficiency of the proposed platoon model for several situations such as merging, following or leaving the platoon by verifying different properties using the model checking. The evaluation of the second model, simulated by the Webots software, proves the impact of the number of vehicles on the platoon performance and the vehicle tracking quality. We conclude that when the platoon reaches a certain number of vehicles, the safety criterion is no more reliable.
- Multi-agent Adaptive Architecture for Flexible Distributed Real-time SystemsPublication . Chniter, Hamza; Li, Yonghui; Khalgui, Mohamed; Koubaa, Anis; Li, Zhiwu; Jarray, FethiRecent critical embedded systems become more and more complex and usually react to their environment that requires to amend their behaviors by applying run-time reconfiguration scenarios. A system is defined in this paper as a set of networked devices, where each of which has its own operating system, a processor to execute related periodic software tasks, and a local battery. A reconfiguration is any operation allowing the addition-removal-update of tasks to adapt the device and the whole system to its environment. It may be a reaction to a fault or even optimization of the system functional behavior. Nevertheless, such scenario can cause the violation of real-time or energy constraints, which is considered as a critical run-time problem. We propose a multi-agent adaptive architecture to handle dynamic reconfigurations and ensure the correct execution of the concurrent real-time distributed tasks under energy constraints. The proposed architecture integrates a centralized scheduler agent (ScA) which is the common decision making element for the scheduling problem. It is able to carry out the required run-time solutions based on operation research techniques and mathematical tools for the system's feasibility. This architecture assigns also a reconfiguration agent (RA p ) to each device p to control and handle the local reconfiguration scenarios under the instructions of ScA. A token-based protocol is defined in this case for the coordination between the different distributed agents in order to guarantee the whole system's feasibility under energy constraints.
- On Feasibility of Multichannel Reconfigurable Wireless Sensor Networks Under Real-Time and Energy ConstraintsPublication . Ben Aissa, Yousra; Bachir, Abdelmalik; Khalgui, Mohamed; Koubaa, Anis; Li, Zhiwu; Qu, TingThis paper deals with the medium between two reconfigurable sensor nodes characterized by radio interfaces that support multiple channels for exchanging real-time messages under energy constraints. These constraints are violated if the consumed energy in transmission is higher than the remaining quantity of energy. A reconfiguration, i.e., any addition or removal of tasks in devices and consequently of messages on the medium, can cause the violation of real-time or energy constraints at run time. To achieve a feasible scheduling in time (i.e., message deadlines will be respected) and energy (i.e., there is available energy) on the medium, we propose new dynamic solutions: Balance, Dilute, and a Combination of them to manage any addition or removal of messages. The proposed approach utilizes the energy harvesting techniques and the PowerControl algorithm to reduce the nonharvested consumed energy. The proposed strategies achieve significant improvement over existing methods and provide the highest percentage of adding messages, with a lower average in response time and energy consumption. They reach a percentage of success in adding the highest priority messages while meeting deadlines up to 85%.
- Performance Evaluation of Vehicular Platoons using WebotsPublication . Karoui, Oussama; Guerfala, Emna; Koubâa, Anis; Khalgui, Mohamed; Tovar, Eduardo; Wu, Naiqi; Al-Ahmari, Abdulrahman; Li, ZhiwuSafety issue of vehicular platoons remains a critical challenge and is still open for investigation. In this study, the authors propose an accurate simulation model for vehicular platoons, taking into consideration of the kinematics and dynamics aspects of the platoon and its physical constraints. A hybrid controller formed by two different longitudinal and lateral proportional–integral–derivative controllers and two operation modes at the same time is developed and simulated using Webots. By this study, the aim is to deeply study the performance of the platoon and reveal its weakness in real scenarios. The latter includes normal/degraded operating modes, different speeds, full brake scenarios and various global positioning system accuracies. Results show the efficiency of the platoon controller even in the predefined degraded mode.
- System and method for operating a follower vehicle in a vehicle platoonPublication . Li, Zhiwu; Karoui, Oussama; Koubaa, Anis; Khalgui, Mohamed; Guerfala, Emna; Tovar, Eduardo; Wu, NaiqiA method for operating a follower vehicle in a vehicle platoon includes determining, during operation, whether the follower vehicle is operating in a normal state or an abnormal state based on an operation condition of a component of the follower vehicle, or a communication between the follower vehicle and a preceding vehicle in the vehicle platoon. The method further includes selecting a first control mode if the follower vehicle is in the normal state and a second control mode if the follower vehicle is in the abnormal state so as to control movement of the follower vehicle using the selected control mode. In the first control mode, the follower vehicle uses communication data received from the preceding vehicle in the vehicle platoon to control its movement. In the second control mode, the follower vehicle uses data obtained by one or more of its sensors to control its movement.