International audience

Smart mobility aims to enhance the passenger experience by optimizing transportation modes while minimizing environmental impact. In this context, Urbanloop, a pioneering urban transportation system utilizing autonomous pod vehicles on dedicated rail circuits (loops), provides a low-energy, low-carbon, and personalized travel experience, free from intermediate stops or transfers. This innovative system not only sets a world record for the lowest energy consumption per kilometer per passenger but also successfully completed its first passenger deployment during the 2024 Olympic Games. Since the efficient monitoring and management of pod movements require stable, high-performance, and continuous communication, 5G emerges as a key enabler in meeting these demands. In this paper, we first introduce the core principles of the Urbanloop system and then examine the necessity of 5G integration by analyzing how communication QoS impacts system safety and performance. Using Veins-Simu5G, we evaluate the effects of packet loss and latency under various communication and mobility scenarios, and the related impacts on safety distance and pod deployment density. Finally, we validate our simulation findings through preliminary real-world testing with the OAIBOX platform, built upon the OpenAirInterface framework, confirming the practical relevance of our results for future deployments.

As time-sensitive networks must guarantee the end-to-end delay requirement of data flows, the worst-case delay (WCD) analysis is mandatory. To date, several analytical approaches have been proposed for WCD analysis, mainly in two classes: network-calculus approaches (NC), and real-time scheduling-oriented approaches such as response-time analysis (RTA), and compositional performance analysis (CPA). In spite of advances in WCD analysis techniques, the computation of the exact worst-case delay faces combinatorial explosion issues, therefore several approaches have been developed to provide an upper bound with more or less pessimism. Nevertheless, reducing pessimism remains challenging, and each approach differs from others in specific scenarios. In this context, this paper provides a comprehensive comparative study that analyzes the results of WCD calculation approaches under the Non-preemptive Fixed Priority Scheduling Policy. To further reduce the pessimism, we propose a new algorithm BWE (Blocking-Waived Estimation) built for switched network architectures upon RTA, which further investigates the relationship between blocking time and transmission time of the flow of interest (e.g., virtual link in AFDX) in adjacent hops. As illustrated in an example network architecture, the result produced by BWE is generally less pessimistic (the WCD is reduced by at maximum 34.34%) compared to the state-of-the-art RTA/CPA calculation results.

A number of V2X (Vehicle-to-Everything) messages are standardized by the European Telecommunication Standardization Institute (ETSI), such as CAM (Cooperative Awareness Message) and CPM (Collective Perception Message).Since road safety and traffic efficiency are on the basis of the assumption that correct and accurate V2V messages are shared, ensuring the trustworthiness of these V2X messages becomes an essential task in IoV (Internet of Vehicles) security.However, containing safety-related information makes V2X messages susceptible to malicious insider attacks from compromised vehicles after the PKI (Public Key Infrastructure) authentication step (Farran and Khoury, 2023), such as Ghost Vehicles (GV) (Gyawali and Qian, 2019), passively or actively reaching a 'ghost' state in terms of communication, position, etc.By integrating CPS (Collective Perception Service) in the Veins simulator, our work aims to propose a trust assessment model in IoV against several types of CAM-and CPM-based GV to increase security.The simulation results provide a preliminary analysis of the feasibility of the proposed model and show the effectiveness in terms of assessing V2X messages' trustworthiness.

Real-time networks are used by distributed embedded systems of increasing complexity. This leads to a need for precise design and configuration techniques for these networks.This paper presents an approach for the iterative configuration of a real-time network and the associated distributed real-time control application that is to be deployed on it.The approach consists in combining network modeling and Component-Based Software Engineering techniques to automatically calculate the model of the data streams that will be exchanged over the network.The paper explains how to calculate the parameters used in data stream models from the specification of the application architecture and behavior. A single specification is used to generate both the data stream models and the infrastructure code of the application, thus providing guarantee of consistency between the behavior of the actual system and the network configuration. The use of this approach is demonstrated on an example which uses a TSN network.

Crowdsourcing technology enables complex tasks to be solved with the aid of a group of workers in the Internet of Things (IoT). On the one hand, crucial sensing data can be collected and processed to enhance smart IoT applications. On the other hand, crowdsourcing IoT (Crowd-IoT) is still facing threats due to the diverse quality of crowdsourced data, and especially the misbehavior of malicious workers. In this paper, we propose a Stochastic Bayesian Game (SBG) to address the Byzantine Altruistic Rational (BAR) based misbehavior, where workers’ behavioral types can be deduced reasonably and the requestor can perform optimal actions accordingly by taking the long-term gain into consideration. To validate and evaluate the performance of the proposed model, we simulate various scenarios and conduct a comparison with other approaches. The numerical results show the effectiveness and feasibility of our proposed solution.

Heterogeneous robots equipped with multi-modal sensors (e.g., UAV, wheeled and legged terrestrial robots) provide rich and complementary functions that may help human operators to accomplish complex tasks in unknown environments. However, seamlessly integrating heterogeneous agents and making them interact and collaborate still arise challenging issues. In this paper, we define a ROS 2 based software architecture that allows to build incarnated heterogeneous multi-agent systems (HMAS) in a generic way. We showcase its effectiveness through a scenario integrating aerial drones, quadruped robots, and human operators (see https://youtu.be/iOtCCticGuk). In addition, agent spatial awareness in unknown outdoor environments is a critical step for realizing autonomous individual movements, interactions, and collaborations. Through intensive experimental measurements, RTK-GPS is shown to be a suitable solution for achieving the required locating accuracy.

Smart grid substation automation and protection applications are time-critical, since any real time constraint violation may result in disastrous consequences. However, meeting real time requirements in Substation Communication Networks (SCN) is a challenging issue. To address the various real time requirements, the IEC 61850 standard specifies several application protocols that were based on Ethernet but is recently moving to TSN (Time Sensitive Networking). This raises the following question: is TSN always relevant for SCN? This paper attempts to answer this question through a comparison of traditional switched Ethernet and the Time Aware Shaper (TAS) mechanism associated with the TSN standard. We highlight the difficulty in answering the question simulating scenarios in which TAS is relevant and others in which it is not. We conclude by making some recommendations for using the TAS of TSN in SCN.

The IEEE 802.1 TSN working group published a set of standards which adds new functionalities to switched Ethernet networks. These new functionalities notably aim at making the design of deterministic Ethernet networks possible, enabling their use for real-time applications. This determinism comes however at the cost of a greatly increased complexity in configuration effort, especially for largescale networks. In addition, this new complexity also affects the network simulation tools that are commonly used when designing such networks. As most of the existing ones only partially support new TSN functionalities, one has often to combine several simulators for achieving a reliable TSN network design. In this paper, we propose a model-based approach which aims at assisting the design of TSN networks. Modeling allows the creation of a formal representation of the network which can then be used to automatically generate configurations. This approach has been successfully implemented as a TSN configuration software called MoBACT, that enables the use of multiple simulation/emulation tools during the design phase by generating configurations for different targets for easing crosscheck of simulation results. Since each generated configuration is derived from the same representation of the network, our approach guarantees the consistency of the different configurations generated for each tool.

Preventing the negative effects caused by misbehaving of nodes or malicious intrusions is an essential task in trust management (TM) for the Internet of Things (IoT). Although many TM models have been proposed and developed, the majority of these approaches assign nodes trust scores by means of a single static evaluation mechanism without taking into consideration the heterogeneity of IoT nodes and network segments, and the challenges posed by context awareness and scalability. Thus, an applicable TM model is needed to overcome these limitations. In this paper, a phase-based dynamic TM (PDTM) model is proposed. This model enables nodes’ trust scores to be calculated diversely and dynamically in terms of phases. Finally, numerical results show the effectiveness and the accuracy of the proposed model, and resilience against various types of trust-related attacks (TRA).

Long Range Wide Area Network (LoRaWAN) introduces the Adaptive Data rate (ADR) mechanism [1] aiming to maximize both battery life of the end-devices and overall network capacity. ADR performs adaptive tuning of radio configurations of the nodes by adjusting bandwidth, spreading factor, coding rate and transmission power parameters whenever the signal quality changes. The ADR algorithm was established for stable radio channel environments and is not efficient when conditions dramatically change (e.g. mobility). So, we have previously proposed an Enhanced-ADR (E-ADR) [2] that deals with mobile nodes in case of predefined mobility patterns. However, several Internet of Thing (IoT) applications, such as smart cattle ranching in smart farms [3], require sensors travelling with unknown or undefined trajectories. So, this paper extends E-ADR to unknown mobility patterns. This extension, called VHMM-based E-ADR, is based on a Variable order Hidden Markov Model (VHMM) to predict the node trajectory. It has been implemented on Waspmote SX1272 hardware platform. Experimental results show its high efficiency in terms of the packet loss rate (PLR) and the power consumption.

IEC 61850 has become the reference standard for Substation Automation Systems (SAS) in smart power grids. Current IEC 61850 compliant SAS use Ethernet technology for both Event-Triggered (ET) and Time-Triggered (TT) traffic to transport highly critical messages requiring low-latency guarantees. However the real-time guarantee is often achieved by over-provisioning network resources. In this paper we study the potentials of using Time-Sensitive Networking (TSN) in SAS. TSN adds real-time enhancement to the existing IEEE 802.1Q standard by providing several new traffic shapers. If TT traffic can be guaranteed by scheduling its transmission at the right time using TSN time-aware shaper, it is not the case for ET traffic. The paper contribution is twofold: proposing a first mapping of the IEC 61850 protocols to the TSN traffic classes, based on the analysis of both TSN and IEC 61850 protocols; and developing an exact worst-case delay (WCD) analysis for ET traffic. The tightness of the developed WCD analysis has be shown by simulations.

IEC 61850 has become the reference standard for Substation Automation Systems (SAS) in smart power grids. Switched Ethernet is used for machine to machine communication within SAS. In order to meet stringent real-time constraints, the IEC 61850 application layer protocols can be mapped into different IEEE802.1Q priorities according to their real-time constraints and application criticality. However, the delay evaluation to guarantee real-time requirements can be difficult to perform, especially for lower priority but still real-time constrained traffic. In fact, most existing end-to-end worst-case delay analyses provide upper-bounds, leading to some pessimism and consequently network resource over-provision. In this paper, we present a new method for determining a tight worst-case delay. This method is based on the study of flow characteristics from a given network path. As a flow is interfered by other concurrent flows on its path, their relative offsets with the considered flow greatly impact on its delay. Studying all combinations to find the actual worst-case delay results in high complexity. We show that this complexity can be reduced by only analysing local worst-case delay at each switch in stead of the whole path where the change at each switch would need re-analysing the already analysed switches. An algorithm is also proposed to perform the analysis. An illustrating example shows that our method can reduce the pessimism as it provides the tight worst-case delay instead of the upper-bound of the worst-case delay.

LoRa is becoming an attractive low cost and low power WAN solution for many real-world IoT applications. LoRa has been designed for static end-devices to individually use the optimal configuration through an adaptive data rate mechanism (ADR), thanks to the possibility to choose a set of LoRa physical layer transmission parameters. However a large class of IoT applications (e.g. connected farm) also includes mobile nodes with specific mobility patterns. For those applications, the current ADR control algorithm may not be efficient when the radio channel attenuation rapidly changes because of the node mobility. This paper contributes to enhance the ADR mechanism by taking into account the position of the mobile devices and their trajectories in order to have a dynamic allocation. The Enhanced-ADR (E-ADR) minimizes the transmission time and energy consumption as well as packet loss for mobile devices. The testbed-based experiments show that E-ADR improves the quality of service (QoS) of the overall networks.

SDN is a promising solution for vehicular networks challenges. Distributing the SDN control plane achieved more scalability and performance. However, synchronization between different controllers of network state generates extra-delay that is not suitable with delay-sensitive applications in vehicular networks like emergency services. In this paper, we investigate the e2e (end-to-end) delay in variable density vehicular scenarios with variable number of controllers. Our experiments prove the benefits of using multi-controllers in terms of delay but also the need of the deployment of the effective number according to the vehicular network density.

The idea of leveraging Software Defined Networking (SDN) in vehicular networks has drawn a lot of attention in the last years. SDN flexibility and programmability brought promising solutions for VANET challenges, namely Quality of Services (QoS) and scalability which are the main characteristics of Internet of Vehicles (IoV). Such networks are characterized by fast topological changes due to their variable dynamicity and density. In fact, SDN decouples control plane and data plane, providing programmability to configure the network. However, based on a single controller, SDN is criticized for not supporting scalability and for decreasing the overall network Quality of service. Using multiple controllers becomes the tendency of recent works to meet the need of large networks. Throughout this paper, we survey the proposed SDN-based architectures for vehicular networks. Considering the control plane impact, centralized or distributed, the QoS improvements brought by theses architectures are studied and criticized in order to derive the suitability of each proposal to resolve the IoV challenges and meet its requirements for the various applications.

In cyber-physical systems, mobile actuators can enhance system's flexibility and scalability, but at the same time incurs complex couplings in the scheduling and controlling of the actuators. In this paper, we propose a novel event-driven method aiming at satisfying a required level of control accuracy and saving energy consumption of the actuators, while guaranteeing a bounded action delay. We formulate a joint-design problem of both actuator scheduling and output control. To solve this problem, we propose a two-step optimization method. In the first step, the problem of actuator scheduling and action time allocation is decomposed into two subproblems. They are solved iteratively by utilizing the solution of one in the other. The convergence of this iterative algorithm is proved. In the second step, an online method is proposed to estimate the error and adjust the outputs of the actuators accordingly. Through simulations and experiments, we demonstrate the effectiveness of the proposed method.

Wireless sensor and actuator networks (WSANs) are emerging as a new generation of wireless sensor networks. Due to the coupling between the sensing areas of the sensors and the action areas of the actuators, the efficient coordination among the nodes is a great challenge. In this paper, we address the problem of distributed node coordination in WSANs aiming at meeting the user's requirements on the states of the points of interest (POIs) in a real-time and energy-efficient manner. The node coordination problem is formulated as a nonlinear program. To solve it efficiently, the problem is divided into two correlated subproblems: 1) the sensor-actuator (S-A) coordination and 2) the actuator-actuator (A-A) coordination. In the S-A coordination, a distributed federated Kalman filter-based estimation approach is applied for the actuators to collaborate with their ambient sensors to estimate the states of the POIs. In the A-A coordination, a distributed Lagrange-based control method is designed for the actuators to optimally adjust their outputs, based on the estimated results from the S-A coordination. The convergence of the proposed method is proved rigorously. As the proposed node coordination scheme is distributed, we find the optimal solution while avoiding high computational complexity. The simulation results also show that the proposed distributed approach is an efficient and practically applicable method with reasonable complexity.

The diversity of IoT applications implies the requirement of reliable yet efficient MAC solutions for supporting transmissions for various traffic patterns. In this paper, we propose GoMacH, an efficient MAC protocol that provides high reliability and throughput for handling various traffic loads in IoT. GoMacH seamlessly integrates several outstanding techniques. It adopts the phase-lock scheme to achieve low-power, duty-cycled communication. It also utilizes a dynamic slots allocation scheme for providing accurate and instantaneous throughput boost. Furthermore, like in TSCH, GoMacH spreads its communications onto IEEE 802.15.4's 16 channels, leading to high reliability. GoMacH has been implemented in open source on RIOT OS, and has also been seamlessly integrated into IETF's 6LoWPAN/RPL/UDP stack. Experimental results on SAMR21-xpro test-beds verify the practicality of GoMacH and its capabilities for consistently providing high throughput, high delivery ratio, and low radio duty-cycle.

Using low duty-cycle is the most common technique to extend the system lifetime in WSNs. However, it also implies limited throughput and long delay and the penalty is even higher under variable traffic patterns. In this paper, we present iQueue-MAC, a hybrid CSMA/TDMA MAC that adapts to variable/bursty traffic. With light load, iQueue-MAC uses a contention-based CSMA mechanism that provides low delay with scattered transmissions. When traffic increases, detected by a forming backlog in the sender, iQueue-MAC changes to a contention-free TDMA mechanism allocating transmission slots. Thus, iQueue-MAC mitigates packet buffering and reduces packet delay, combining the best of TDMA and CSMA. In this paper we also show how iQueue-MAC can operate in both single and multi channel modes. We implemented it on SIM32W108 chips together with other reference WSN protocols for comparison. iQueue-MAC exhibits similar figures during light traffic. However, with bursty traffic its throughput can be five times that of CoSenS and Ri-MAC-MC and its delay 20 times lower. Finally, iQueue-MAC is able to effectively use multiple channels, duplicating its throughput when compared to single channel operation.

The size of target will induce a degradation of tracking performance, which has been neglected for simplicity in most previous studies. In multiple target tracking, occlusions will be caused by target size effect, one target can become a moving obstacle blocking the direct channel between the anchor and another target. In this paper, the data association problem in multiple target tracking is investigated. To reduce the computational complexity of traditional Joint Probabilistic Data Association (JPDA) algorithm, a modified JPDA algorithm is proposed to execute data association in multiple target tracking by utilizing the information of occlusion conditions, which is identified by a three-step algorithm. Simulation results show that the proposed algorithm is with good tracking performance and low computational complexity.

Wireless charging is a promising technology for provisioning dynamic power supply in wireless rechargeable sensor networks (WRSNs). The charging equipment can be carried by some mobile nodes to enhance the charging flexibility. With such mobile chargers (MCs), the charging process should simultaneously address the MC scheduling, the moving and charging time allocation, while saving the total energy consumption of MCs. However, the efficient solutions that jointly solve those challenges are generally lacking in the literature. First, we investigate the multi-MC coordination problem that minimizing the energy expenditure of MCs while guaranteeing the perpetual operation of WRSNs, and formulate this problem as a mixed-integer linear program (MILP). Second, to solve this problem efficiently, we propose a novel decentralized method which is based on Benders decomposition. The multi-MC coordination problem is then decomposed into a master problem (MP) and a slave problem (SP), with the MP for MC scheduling and the SP for MC moving and charging time allocation. The MP is being solved by the base station (BS), while the SP is further decomposed into several sub-SPs and being solved by the MCs in parallel. The BS and MCs coordinate themselves to decide an optimal charging strategy. The convergence of proposed method is analyzed theoretically. Simulation results demonstrate the effectiveness and scalability of the proposed method.

Wireless sensor networks (WSN) are inherently multi - constrained. They need to preserve energy while offering reliable and timely data reporting for a non-negligible number of scenarios. This is particularly true when a node should decide which forwarder has to be chosen for routing a packet. Nevertheless, solving multi-constrained routing problems is NP-complete. Most approaches involve transforming the problem into a single constrained problem using a cost function, although this may lead to suboptimal solutions. Some other solutions are based on heuristics. However, their high implementation complexity prevents their online use. Hence, they are not suitable for highly dynamic WSNs. In this paper we make use of Operator Calculus (OC) methods on graphs to solve path selection in the presence of multiple constraints. OC has lower resolution time complexity compared to other techniques. Based on OC, we develop a distributed algorithm for path selection in a graph. We develop a new routing protocol which makes use of this algorithm: the Operator Calculus based Routing Protocol (OCRP). In OCRP, a node selects the set of eligible next hops based on the given constraints and the distance to the destination. It then sends the packet to all eligible next hops. The protocol is implemented in Contiki OS and emulated for TelosB motes using Cooja. We compare its performance against tree and directional flooding routing and show the advantages of our technique.

Many WSN industrial applications impose requirements in terms of end to end delay. However, the end to end delay estimation in WSNs is not a simple task because of the high dynamic of networks, the use of duty-cycled MAC protocols as well as the impact of the routing protocols. Markov-based modelling is an interesting approach to deal with this problem aiming to provide an analytical model useful for understanding protocol's behavior and to estimate the end to end delay, among other performance parameters. However, existing Markov-based analytic models abstract the reality simplifying the analysis and thus resulting models are not accurate enough for estimating the end to end delay. Furthermore, establishing an accurate Markov model using classic approaches is very difficult considering the highly dynamic behavior of the sensor nodes. In this paper, we propose a novel approach to obtain the Markov chain model of sensor nodes by means of Process Mining techniques through the code execution trace. End to end delay is then computed based on this Markov chain. Experimentations were done using IoT-LAB testbed platform. Comparisons in terms of delay are presented for two different metrics of the RPL protocol (hop count and ETX).

In the current protocol stack for Internet of Things in general and wireless sensor network in particular, many devices rely on the Contiki MAC protocol at their MAC layer. This protocol is widely used and enabled by default for several industrial environments and time sensitive monitoring and control applications. However, few work exists regarding the performance of this protocol because it lacks of an underlying theoretical model for analysing its performance. In this paper, we propose a novel approach relying on process mining technique that aims to obtain a Markov chain model for networks running the Contiki MAC protocol. In particular, we present a comprehensive specification of the protocol and a Markov chain model obtained through the analysis and instrumentation of its reference implementation. We used the obtained Markov chain to analyze and estimate the end to end delay distribution for a multi-hops transmission with static routing. The approach can also be extended to a wide range of protocols.

The random distribution of sensors and the irregularity of routing paths lead to unordered sensory data which are difficult to deal with in Wireless Sensor Networks (WSNs). However, for simplicity, most existing researches ignore those characteristics in the designs of Compressive Sensing based Data Aggregation Schemes (CSDAS). Since conventional sparsification bases (e.g., DCT, Wavelets) are inefficient to deal with unordered data, performances of CSDAS with conventional bases are inevitably constrained. In this work, a novel CSDAS which adopts Treelet transform as a sparse transformation tool is proposed. Our CSDAS is capable to exploit both spatial relevance and temporal smoothness of sensory data. Moreover, our CSDAS contains a novel correlation based clustering strategy which is realized with the localized correlation structure of sensory data returned by Treelets and facilitates energy saving of CSDAS in WSNs. Comparative results show the reconstruction error rate with adopting Treelet transform in CSDAS is about 18% lower than that of conventional ones when the normalized energy consumption is 0.3. Even larger performance gain will be obtained at higher energy consumption level. Meanwhile, simulations results further show that our novel correlation based clustering strategy is of great potential. Specially, there is a gain of roughly 35% for total energy savings with our proposed clustering strategy.

Performance analysis of wireless sensor networks is a difficult task because of the high dynamic of networks and the use of duty-cycled MAC protocols. Markov-based modelling is an interesting approach to deal with this problem. However, existing Markov-based analytic models, being MAC protocol-centric rather than network-centric, work under strong assumptions and do not allow to encompassing important network parameters like radio channel fading and capture effect, or actual implementation optimizations (not always specified in the protocol description). In this paper we propose a novel approach to obtain a Markov chain model for networks running different MAC protocols by means of Process Mining Techniques. We present the main aspects of our approach together with the results obtained for the standard IEEE 802.15.4. The obtained Markov model can be used to evaluate various performance parameters. The approach can also be extended to a wider range of protocols.

The concept of network virtualization was introduced to facilitate flexible service deployment for the future Internet. This recent technology provides a powerful tool to run multiple logical networks on the same physical substrate defined as virtual networks (VNs). Each physical link is split into virtual links and each VN receives a fraction of the available capacity. Bandwidth allocation for multiple VMs aims at sharing the physical links among multiple VNs. It is a critical challenge for both service providers (SPs) and infrastructure providers (InPs). This allocation should take into account the quality of service (QoS) requirements of the flows that are crossing each VN. In this paper, we consider a virtualized network environment where the SP deploys multiple VNs with different links' capacity demands and QoS requirements. Each VN competes with other VNs to receive fractions of physical links managed by multiple InPs. We present a two-layer controller system that adapts to the dynamic change of the workload of each VN. The system uses a prediction-based approach in order to find the optimal request for each VN. The request depends on the estimation of the relationship between the VN performance in terms of packet delays and the actual and past allocations. Then, due to the capacity constraint of the physical link, the system adjusts the offered bandwidth for each of them. Our model offers flexible distributed autonomous control of the bandwidth allocation to maintain the offered QoS to each VN at the desired level in response to the dynamics of the workload. Our mechanism provides an optimum allocation of the physical links by distributing the bandwidth periodically. It also offers the possibility of adjusting the VNs' parameters to take into account the current network behaviour to avoid bottleneck virtual links.

The most critical issue in network virtualization is the dynamic resource allocation of the physical substrate. There is a need to monitor the running virtual routers in order to allow an adaptive change in the resource allocation. In this paper, we focus on the router data plane virtualization and we explore this issue by presenting a new dynamic allocation approach through queuing theory. We consider the problem where multiple instances of virtual routers (VRs) that have some quality of service (QoS) requirements are sharing different physical resources. We propose a novel router architecture that offers a strong isolation between concurrent VRs and provides a dynamic allocation scheme in order to guarantee the provided QoS to each of them. Our approach aims at providing a higher isolation for the concurrent virtual routers sharing the same infrastructure. We propose a dynamic Weighted Fair Queuing (WFQ) scheduler for each physical resource and an algorithm for adjusting the weight of each VR in order to reduce the delay of the packet processing and avoid the bottlenecks. We also propose an admission control mechanism that estimates the current load of the physical node and decides either to accept or reject a creation request of a new VR. Simulation results show that the proposed approach achieves good performance in terms of delay minimization inside the virtual router.

This work contains a routing proposition to be used over a Wireless Sensor Network (WSN) location system based on the IEEE 802.15.4 standard. The technical solution for communication consists of an n-ary tree algorithm for routing using a 16 bit addressing scheme. It is compared to a binary routing scheme originally used on a real system which suffers from coverage, routing and addressing problem. An analysis of the coverage aspects is driven by a geometric study. It includes an analysis of a generated topology for different coverage areas and different routing topologies. The geometric analysis is validated by a simulation work. We observe that the proposed scheme outperforms the existing routing solution in terms of hop-count, delay and association process time. The work puts in evidence that the Connectivity of the network is an important parameter to be considered during the network deployment and for the routing scheme.

IEEE 802.15.4 protocol stack is the basis of many wireless sensor networks (WSN) and has been proposed for low data rate and low power applications. The standard defines a duty cycle in order to allow devices to achieve efficient energy consumption. Defining the best duty cycle configuration becomes important to extend the network life time. Several works have been done in order to study the behavior of the protocol when considering duty cycle configuration and how this configuration impacts its performance parameters. Usually, the analysis is evaluated by using simulation tools. The objective of this paper is to bring an analysis of the IEEE 802.15.4 duty cycle when considering a real scenario over TinyOS and Telosb motes instead of using a simulation approach. We show through measurement how duty cycle impacts in performance metrics such as average delay and packet drop rate in realistic scenarios.

Duty-cycling technique has been widely adopted in MAC protocols for wireless sensor networks to conserve energy. However, low duty-cycle also leads to limited throughput in most of existing solutions. In this paper, we propose iQueue-MAC to provide immediate yet energy-efficient throughput enhancement for dealing with burst or heavy traffic. Combined with CSMA/CA, iQueue-MAC makes use of queue length of each sensor node and allocates suitable TDMA slots to them for packets transmission. During light traffic period, no extra slots will be allocated; iQueue-MAC acts like other low duty-cycle MACs to conserve power. While in burst or heavy traffic period, iQueue-MAC senses the build up of packet queues and dynamically schedules adequate number of slots for packet transmission. We have implemented iQueue-MAC on STM32W108 chips that offer IEEE 802.15.4 standard communication. We set up several real-world experimental scenarios, including a 46 nodes multi-hop test-bed for simulating a general application, and conducted numerous experiments to evaluate iQueue-MAC, in comparison with other traffic adaptive duty-cycle protocols, such as multi-channel version RI-MAC and CoSenS. Results clearly show that iQueue-MAC outperforms multi-channel version of RI-MAC and CoSenS in terms of packet delay and throughput.

As technology advancements in robotics and wireless communication, tracking mobile targets using mobile sensors has aroused widespread concern in recent years. In this paper, we propose a novel coordinative moving strategy for autonomous mobile sensor networks to guarantee the target can be detected in each observed step while minimizing the amount of moving sensors. The proposed scheme consists of obtaining the current position of the target, which is then used to predict the next time-step location of the target. Once the uncertainty region of the target's position is defined, the proposed method allows the mobile sensors to cover it in an optimal way. Therefore, we can assign each mobile sensor to an optimal location to cover the uncertainty region while minimizing the total traveled distance of sensors. Extensive simulations are given to evaluated performance and demonstrate the efficiency of the proposed strategy.

In this work, we present an empirical support of an analytical approach which employs a frequency domain analysis for estimating end-to-end delay in multi-hop networks. The proposed analytical results of the end-to-end delay distribution are validated through simulation and compared with queueing based analysis by defining two concrete scenarios. Our results demonstrate that an analytical prediction schema is insufficient to provide an adequate estimation of the end-to-end delay distribution function, but it requires to be combined with a simulation method for detailed links and nodes latencies distribution.

IEEE 802.15.4 standard specifies a beacon-enabled mode which provides a synchronization environment using beacon transmissions. However, this mode is designed for single hop networks and its use in multi-hop networks is not straight-forward. The main challenges of using beacon-enabled mode in multi-hop networks are how to efficiently schedule beacon transmissions to avoid direct and indirect beacon collisions and how to make a schedule tolerant to the clock drifts due to the low cost components. In this paper, we present TBoPS, a novel technique for scheduling beacons in the cluster tree topology. TBoPS uses a dedicated period called beacon only period (BOP) to schedule beacons at the beginning of IEEE 802.15.4 super-frame. The advantages of TBoPS is that every beacon-enabled node selects a beacon schedule distributively during association. We analysed the robustness of TBoPS to clock drifts. We also show through simulations that all nodes in the network are synchronized and follow the same super frame structure.

An innovative minimal paths algorithm based on operator calculus in graded semigroup algebras is described. Classical approaches to routing problems invariably require construction of trees and the use of heuristics to prevent combinatorial explosion. The operator calculus approach presented herein, however, allows such explicit tree constructions to be avoided. Moreover, the implicit tree structures underlying the problem are pruned automatically by the inherent properties of the semigroup algebras used in this approach. The operator calculus algorithm proposed here is applied to the problem of precomputed routing in a store-and-forward (S&F) satellite constellation, which provides message communication services by relaying messages between satellites through gateways on the ground. The minimum end-to-end delay paths obtained are compared with the best existing heuristics-based results. The best existing results were obtained from a greedy algorithm designed to explore only a portion of the solution space in order to avoid combinatorial explosion and memory overload. In all test cases, the operator calculus is shown to return paths whose minimum end-to-end delay is either equal to or less than that of the best existing result. In some cases, in which the tree pruning algorithm did not find a solution, the operator calculus does. These results correspond to a one-single constraint case considering the end-to-end delay as the cost of the links, if the case of multi constraints is considered (e.g. bandwidth, rapidity,...) the operator calculus approach can be similarly used.

Data traversing packet networks experience varying delays, resulting in noticeable delay jitters. This significantly degrades overall system performance in a real-time multimedia network. This paper proposes TSJC, a novel traffic shaping algorithm with delay jitter constraints for real-time multimedia networks, on the basis of traditional shaping algorithms and their traffic characteristics. TSJC computes the queuing delay and queuing delay variation on line by monitoring the token bucket states, such as the queue length and token arrival rate. TSJC adaptively configures system parameters based on the queuing delay and time jitter, to provide universally low jitter outputs. Simulations have shown that TSJC can both smooth traffic fluctuation and decrease the delay jitter.

IEEE 802.15.4 is considered as the de facto standard for wireless sensor networks (WSN). However, the increased probability of collision at heavy load caused by the inherent behavior of CSMA/CA degrades the performance of WSN in terms of throughput and energy consumption. This led some to propose other MAC layer solutions to tackle these problems. Most of them are TDMA-based which provides deterministic medium access. This makes them not scalable in general for large scale WSN. Contrary to that trend, we retain CSMA/CA's simplicity and good scalability properties and propose CoSenS, a collecting and sending burst scheme, that is implemented on the top of CSMA/CA. The idea of CoSenS is that a router does not retransmit packets as they arrive. Instead, it collects data from its children and other neighbor routers during a period of time that we call waiting period (WP), queue them until the expiration of that period and then sends them into a burst during a period of time that we call transmission period (TP). Simulation results show that this scheme greatly enhances throughput, end to end delay and transmission success rate (reliability). In addition, the scheme exhibits a nice property of self-adaptability of transmission periods between neighbor routers.

The deployment strategy for achieving differentiated coverage and probabilistic connectivity in wireless sensor networks is studied in this paper. A novel solution based on elitist non-dominated sorting genetic algorithm (NSGA-II) is proposed. Simulation results show that NSGA-II based strategy can meet the desired coverage requirements and maintain connectivity in a probabilistic manner with a relatively small number of sensors. In addition, for the applications in which the coverage requirement varies in some subareas, a local genetic operation is more time efficient and needs less variation in the original disposal than a renewed global optimization.

A two-hop neighborhood information-based routing protocol is proposed for real-time wireless sensor networks. The approach of mapping packet deadline to a velocity is adopted as that in SPEED; however, our routing decision is made based on the novel two-hop velocity integrated with energy balancing mechanism. Initiative drop control is embedded to enhance energy utilization efficiency, while reducing packet deadline miss ratio. Simulation and comparison show that the new protocol has led to lower packet deadline miss ratio and higher energy efficiency than two existing popular schemes. The result has also indicated a promising direction in supporting real-time quality-of-service for wireless sensor networks.

In this paper, we study the problem of scheduling a set of control tasks. We distinguish three different situations of states of controlled plants: not activated, steady state situation and transient situation. The infinite-horizon and finite-horizon cost functions are respectively used to represent the performance of each control task in last two situations. We propose a scheduling architecture in which, according to the plant state situation, the task handler switches between these two types of performance criterion to determine an on-line (m,k)-constraint based control task scheduling strategy, so that the overall control performance is maintained at a high level in each situation subject to the task schedulability. The approach is exemplified on a set of controllers for different plants.

In this paper, a family of linear congruence sequences with interesting cross-correlation properties is investigated for potential applications in defining new multiple access protocols for distributed wireless systems. One can show that for any finite subset of the sequences with rate sum not exceeding a certain level, there cannot have enough collisions to completely block any particular user no matter how they are shifted with respect to one another. The user un-suppressibility and service guarantee can be exploited in many applications such as wireless sensor or impulse radio systems. To enhance the system's allowable rate sum while possessing the non-blocking property, new protocol sequences are designed. Besides, the throughput shift-invariant property is obtained.

This paper presents a new QoS guarantee scheme called R-(m,k)-firm (Relaxed-(m,k)-firm) which provides the guarantee on transmission delay of at least m out of any k consecutive packets (m/spl les/k). It has several advantages: (1) during network congestion, packets are dropped according to the (m,k) model rather than uncontrollably as the case of TD and RED, avoiding thus undesirable long consecutive packet drops; (2) it allows to admit more real-time flows than the traditional over-provisioning approach. A new mechanism, called DLB (double leaks bucket) is also proposed for dropping a proportion of packets of a flow or of aggregated-flows in case of network congestion while still guaranteeing the R-(m,k)-firm constraint. The sufficient condition for this guarantee is given for configuring the DLB parameters. It is easy to implement DLB in the actual IntServ and Diffserv architectures (by simply replacing the actual leaky, bucket by DLB) for providing respectively per flow and per class (m,k) guarantee, or event per flow R-(m,k)-firm guarantee in Diffserv.

Comparing with hard real-time approach, (m,k)-firm constraint and its related scheduling policies are considered as an efficient way to increase the admission rate of real-time streams to a network thanks to the possibility to drop until k-m out of any k consecutive processing requirements, reducing thus the workload. Although it is interesting for probabilistic (m,k)-firm guarantee, we show however in this paper that for deterministic (m,k)-firm guarantee, reducing the workload by a factor of m/k does not contribute to reducing the resource requirement in general. So the relaxed (m,k)-firm constraint is proposed. The sufficient schedulability condition under non preemptive fixed priority scheduling is derived and its practical interest in terms of the resource requirement reduction is demonstrated.

The$(m, k)$-firm model has recently drawn a lot of attention. It provides a flexible real-time system with graceful degradation of the quality of service (QoS), thus achieving the fault tolerance in case of system overload. In this paper, we focus on the distance-based priority (DBP) algorithm as it presents the interesting feature of dynamically assigning the priorities according to the system's current state (QoS-aware scheduling). However, DBP cannot readily be used for systems requiring a deterministic$(m, k)$-firm guarantee since the schedulability analysis was not done in the original proposition. In this paper, a sufficient schedulability condition is given to deterministically guarantee a set of periodic or sporadic activities (jobs) sharing a common non-preemptive server. This condition is applied to two case studies showing its practical usefulness for both bandwidth dimensioning of the communication system providing graceful degradation of QoS and the task scheduling in an in-vehicle embedded system allowing fault tolerance.

For supporting applications with different timing constraints, a PLC (power line communication) system must provide differentiated QoS (quality of service). In this paper a traffic dispatching policy is specified and implemented which guarantees both required periodic data update and short end-to-end delay of aperiodic data request services. This policy is compared with the classic dual-priority one showing its good performance.

The X-by-Wire systems in cars can only be accepted if they provide at least the same dependability than the traditional ones. In this paper we propose a new approach to evaluate the impact of the EMI perturbations on the dependability of an X-by-Wire architecture. The considered X-by-Wire architecture is distributed around a TDMA-like communication protocol. So a perturbation causes the loss of a communication cycle with a certain probability. The vehicle level failure is then defined as the consecutive loss of a certain number of communication cycles. Its reliability is modeled as that of the well-known consecutive-k-out-of-n:F systems. A case study, together with the EMI perturbations collected on the roads in France, is used to illustrate our approach.

The use of networks for communications between the electronic control units (ECU) of a vehicle in production cars dates from the beginning of the 1990s. The specific requirements of the different car domains have led to the development of a large number of automotive networks such as Local Interconnect Network, J1850, CAN, TTP/C, FlexRay, media-oriented system transport, IDB1394, etc. This paper first introduces the context of in-vehicle embedded systems and, in particular, the requirements imposed on the communication systems. Then, a comprehensive review of the most widely used automotive networks, as well as the emerging ones, is given. Next, the current efforts of the automotive industry on middleware technologies, which may be of great help in mastering the heterogeneity, are reviewed. Finally, we highlight future trends in the development of automotive communication systems.

We propose a trade-off between hard and soft real-time guarantees to maintain an acceptable QoS guarantee in overload condition and maximize efficiently the utilization of network resources. The key of our solution is that many real-time applications are loss-tolerant, but the loss profile must be well defined since successive packet losses are not suitable. We use the concept of (m,k)-firm timing constraints to define a novel guaranteed loss-tolerant QoS. Therefore, we extend the basic WFQ algorithm to take into account the firm timing constraints to provide lower delay guarantees without violating bandwidth fairness or misusing network resources. The proposal is called (m,k)-WFQ. Using network calculus formalism, analytic study gives the deterministic delay bound provided by the (m,k)-WFQ algorithm for upper bounded arrival curve traffic. Theoretical results and simulations show a noticeable improvement on delay guarantee made by (m,k)-WFQ compared to standard WFQ algorithm without much degrading bandwidth fairness.

A CPN based IEC FB model and its application are introduced in this paper. The model not only can analyze the internal procedure of IEC FB, especially the parameter's status propagation and the mode's switch, but also can be integrated into modeling IEC FB application. The latter is explained with an FB application, FB based boiler water level control system.

Steer-by-wire systems must meet not only reliability but also real-time requirements. This paper presents an integrated approach for evaluating both the temporal performance and the behavioral reliability of steer-by-wire systems taking into account the delay variation introduced by network transmission errors. The considered temporal performance is the quality of service perceived by the user, i.e. the vehicle stability. Tests in vehicles and simulations have been realized to estimate the maximum tolerable response time of the system, and to evaluate the impact of this delay on the quality of service. We quantify then the worst case response time of the system for a generic architecture based on TDMA protocol but independent of the communication network (could actually be TTP/C or FlexRay), and apply these generic results to a case study. We further define the notion of "behavioral reliability" as the probability that "the worst case response time is less than a threshold". In our case study this behavioral reliability is evaluated and linked to the Safety Integrity Levels defined in IEC61508-1 standard. Based on this behavioral reliability concept, the final objective of our work is to propose a new dependability analysis method for X-by-Wire systems by taking into account both dynamic performance, fault-tolerance mechanisms and static redundancy of the system.

Presents a modeling and validation method that is suited to manufacturing applications. The validation technique is relevant to performance evaluation by discrete event simulation techniques (the OPNET tool). We propose an object-oriented approach for the modeling of these kinds of applications and identify the different classes of software and hardware components required by such an application. The specification of a software tool implementing the method is based on these classes. This tool provides two specific editors: the "Expert Editor" for the specification of new classes and the "Architecture Editor" for the modeling of an information system. The "Architecture Editor" verifies that the edited model is correct (at the component and architecture levels). As the simulation support is by OPNET, the tool integrates an OPNET model generator. More generally, this approach leads to the specification of a UML profile.

In this paper we deal with a queueing model based on TDM schemes. Many results concerning this kind of model can be found in literature, but a large part of these results only concerns particular cases. Our main concern is to provide a general solution for the exact message sojourn time in the queue that should be available whatever the storage capacity may be. First, the probability distribution function as well as the Laplace transform of the message sojourn time in the buffer are derived, assuming Poisson fixed-length message arrivals, multiple output and finite buffer capacity. Second, taking advantage of these results, we provide the expected value of the message sojourn time and compare our results with those obtained by many authors. The formulas stated here are available for various particular cases especially for unlimited buffer capacity. Finally, we point out that the work done is directly usable for performance evaluation of many communication systems such as real-time networks, multiplexers and ATM links. Therefore, our results are both of theoretical and practical interests.>