Browsing by Author "Tovar, Eduardo"
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- Active Flow Control for Aerospace Operations by means of a Dense Wireless Sensor and Actuator NetworkPublication . Robles, Ramiro; Loureiro, João; Tovar, Eduardo; Viana, Júlio; Cintra, João; Rocha, AndréThis paper presents the design of an active flow control (AFC) system for commercial aircraft based on a dense wired/wireless sensor and actuator network. The goal is to track gradients of pressure across the surface of the fuselage of commercial aircraft. This collected information will be used to activate a set of actuators that will attempt to reduce the skin drag effect produced by the separation between laminar and turbulent flows. This will be translated into increased lift-off forces, higher speeds, longer ranges and reduced fuel consumption. The paper describes the architecture of the system in the context of the European research project DEWI (dependable embedded wireless infrastructure) using the concept of the DEWI Bubble. A simulator architecture is also proposed to model each process of the AFC system and the DEWI Bubble. To the best of our knowledge this is the first approach towards the use of wireless sensor technologies in the field of active flow control.
- Active Flow Control using Dense Wireless Sensor and Actuator NetworksPublication . Robles, Ramiro; Viana, Júlio; Loureiro, João; Cintra, João; Rocha, André; Tovar, EduardoThis paper describes the design of an active flow control (AFC) system for aeronautics applications based on dense wireless sensor and actuator networks (WSANs). The objective of this AFC system is to track gradients of pressure (or wall shear stress) across the surface of the fuselage of commercial aircraft. This collected information is used to activate a set of actuators that will attempt to reduce the skin drag effect produced by the separation between laminar and turbulent flows. This is expected to be translated into increased lift-off forces, higher vehicle speeds, longer ranges and reduced fuel consumption. The paper describes the architecture of the system in the context of the European research project DEWI (dependable embedded wireless infrastructure) using the concept of the DEWI Bubble and its three-tier architecture especially designed to ensure dependability and interoperability in industrial WSANs. A system-level simulator is also proposed to model each process of the AFC system and the aeronautics DEWI Bubble infrastructure, highlighting the interactions between the network simulation and the results of the computational fluid dynamics (CFD) simulation. The key element in the proposed solution is a polygonal patch of wired sensors and actuators. This patch is provided with a wireless link to a central coordinator or access point conveniently located in the aircraft to maximize coverage to a network of distributed patches. A trade-off between scalability, size of the patches, fluid speed/viscosity, sampling sensor and actuator rates in space and time, and the capacity/delay characteristic of the wireless inter-patch and the wireline intra-patch communication technologies is also here discussed. The hybrid wireless/wired sensor and actuator network achieves great flexibility, scalability, manageability, troubleshooting, and modularity as compared to a solution exclusively based on wireline or wireless components. The final details of the prototype and results in a wind tunnel test-bed are here described, demonstrating the validity of the concept and the use of wireless technologies for aeronautical applications (flexible architecture and innovative services). Future issues regarding security, safety and trustiness of the AFC system are also briefly introduced in the context of the spin-off European project SCOTT (secure connected trusted things).
- AdaptC: programming adaptation policies for WSN applicationsPublication . Gaur, Shashank; Almeida, Luis; Tovar, EduardoEvolution in both hardware and software technologies has enabled Wireless Sensor Networks(WSNs) to target a multiplicity of domains. Programming for such advanced WSNs remains a challenging process for users, especially as the WSN may need to make changes as per outcomes from different scenarios during execution. Usually, various adaptation policies are written while programming such applications to enable changes. However it is difficult for the programmer to anticipate changes for new scenarios. It also becomes difficult to reuse these adaptation policies. In this paper, we propose AdaptC, an abstraction for such adaptation policies that facilitates re-usability and expansion across various WSNs. We also present concepts for the design and implementation of AdaptC. We evaluate the abstraction for multiple use cases and compare it against existing work.
- Adding local priority-based dispatching mechanisms to P-NET networks: a fixed priority approachPublication . Tovar, Eduardo; Vasques, Francisco; Burns, AlanIn this paper we address the real-time capabilities of P-NET, which is a multi-master fieldbus standard based on a virtual token passing scheme. We show how P-NET’s medium access control (MAC) protocol is able to guarantee a bounded access time to message requests. We then propose a model for implementing fixed prioritybased dispatching mechanisms at each master’s application level. In this way, we diminish the impact of the first-come-first-served (FCFS) policy that P-NET uses at the data link layer. The proposed model rises several issues well known within the real-time systems community: message release jitter; pre-run-time schedulability analysis in non pre-emptive contexts; non-independence of tasks at the application level. We identify these issues in the proposed model and show how results available for priority-based task dispatching can be adapted to encompass priority-based message dispatching in P-NET networks.
- An Exact Schedulability Test for Global FP Using State Space PruningPublication . Burmyakov, Artem; Bini, Enrico; Tovar, EduardoWe propose an exact schedulability test for sporadic realtime tasks with constrained deadlines, scheduled by Global Fixed Priority (GFP). Our test is faster and less memory consuming than other state-of-the-art exact tests. We achieve such results by employing a set of techniques that cut down the state space of the analysis, which extend the prior work by Bonifaci and Marchetti-Spaccamela. Our test is implemented in C++ code, and it is publicly available.
- An Explicit GTS allocation algorithm for IEEE 802.15.4Publication . Chen, Jianxin; Ferreira, Luís; Tovar, EduardoThe IEEE 802.15.4 standard provides appealing features to simultaneously support real-time and non realtime traffic, but it is only capable of supporting real-time communications from at most seven devices. Additionally, it cannot guarantee delay bounds lower than the superframe duration. Motivated by this problem, in this paper we propose an Explicit Guaranteed time slot Sharing and Allocation scheme (EGSA) for beacon-enabled IEEE 802.15.4 networks. This scheme is capable of providing tighter delay bounds for real-time communications by splitting the Contention Free access Period (CFP) into smaller mini time slots and by means of a new guaranteed bandwidth allocation scheme for a set of devices with periodic messages. At the same the novel bandwidth allocation scheme can maximize the duration of the CFP for non real-time communications. Performance analysis results show that the EGSA scheme works efficiently and outperforms competitor schemes both in terms of guaranteed delay and bandwidth utilization.
- An implicit GTS allocation mechanism in IEEE 802.15.4 for time-sensitive wireless sensor networks: theory and practicePublication . Koubâa, Anis; Alves, Mário; Tovar, Eduardo; Cunha, AndréTimeliness guarantee is an important feature of the recently standardized IEEE 802.15.4 protocol, turning it quite appealing for Wireless Sensor Network (WSN) applications under timing constraints. When operating in beacon-enabled mode, this protocol allows nodes with real-time requirements to allocate Guaranteed Time Slots (GTS) in the contention-free period. The protocol natively supports explicit GTS allocation, i.e. a node allocates a number of time slots in each superframe for exclusive use. The limitation of this explicit GTS allocation is that GTS resources may quickly disappear, since a maximum of seven GTSs can be allocated in each superframe, preventing other nodes to benefit from guaranteed service. Moreover, the GTS may be underutilized, resulting in wasted bandwidth. To overcome these limitations, this paper proposes i-GAME, an implicit GTS Allocation Mechanism in beacon-enabled IEEE 802.15.4 networks. The allocation is based on implicit GTS allocation requests, taking into account the traffic specifications and the delay requirements of the flows. The i-GAME approach enables the use of one GTS by multiple nodes, still guaranteeing that all their (delay, bandwidth) requirements are satisfied. For that purpose, we propose an admission control algorithm that enables to decide whether to accept a new GTS allocation request or not, based not only on the remaining time slots, but also on the traffic specifications of the flows, their delay requirements and the available bandwidth resources. We show that our approach improves the bandwidth utilization as compared to the native explicit allocation mechanism defined in the IEEE 802.15.4 standard. We also present some practical considerations for the implementation of i-GAME, ensuring backward compatibility with the IEEE 801.5.4 standard with only minor add-ons. Finally, an experimental evaluation on a real system that validates our theoretical analysis and demonstrates the implementation of i-GAME is also presented
- An industrial view on the common academic understanding of mixed-criticality systemsPublication . Esper, Alexandre; Nelissen, Geoffrey; Nélis, Vincent; Tovar, EduardoWith the rapid evolution of commercial hardware platforms, in most application domains, the industry has shown a growing interest in integrating and running independently-developed applications of different “criticalities” in the same multi-core platform, with the objective of improving the performance/cost ratio of the system. Such integrated systems are commonly referred to as mixed-criticality systems (MCS). Most of the MCS-related research published in the state-of-the-art cite the safety-related standards associated to each application domain (e.g. aeronautics, space, railway, automotive). However, those standards are not, in most cases, freely available, and do not always clearly and explicitly specify the requirements for mixed-criticality systems. This paper addresses the important challenge of presenting the relevant information available in some of the safety-related standards, such that the mixed-criticality concept is understood from an industrialist’s perspective. In addition, the paper evaluates state-of-the-art mixed-criticality real-time scheduling models and algorithms against the safety-related standards.
- An Integrated Lateral and Longitudinal Look Ahead Controller for Cooperative Vehicular PlatooningPublication . Vasconcelos Filho, Ênio; Koubaa, Anis; Severino, Ricardo; Tovar, EduardoCooperative Vehicular Platooning (CoVP), has been emerging as a challenging Intelligent Traffic Systems application, promising to bring-about several safety and societal benefits. Relying on V2V communications to control such cooperative and automated actions brings several advantages. In this work, we present a Look Ahead PID controller for CoVP that solely relies upon V2V communications, together with a method to reduce the disturbance propagation in the platoon. The platooning controller also implements a solution to solve the cutting corner problem, keeping the platooning alignment. We evaluate its performance and limitations in realistic simulation scenarios, analyzing the stability and lateral errors of the CoVP, proving that such V2V enabled solutions can be effectively implemented.
- An Intersection Management Protocol for Mixed Autonomous and Legacy VehiclesPublication . Reddy, Radha; Almeida, Luis; Tovar, EduardoAn important element in urban traffic management is the Intersection Management (IM) that deals with traffic lights signaling (either real or virtual). Intersections are vulnerable to traffic congestion and accidents. Therefore, this paper investigates a synchronous intersection management protocol for mixed autonomous and humandriven vehicles in the context of decentralized traffic management.