1-D Coordinate Based on Local Information for MAC and Routing Issues in WSNs

More and more critical Wireless Sensor Networks (WSNs) applications are emerging. Those applications need reliability and respect of time constraints. The underlying mechanisms such as MAC and routing must handle such requirements. Our approach to the time constraint problem is to bound the hop-count between a node and the sink and the time it takes to do a hop so the end-to-end delay can be bounded and the communications are thus real-time. For reliability purpose we propose to select forwarder nodes depending on how they are connected in the direction of the sink. In order to be able to do so we need a coordinate (or a metric) that gives information on hop-count, that allows to strongly differentiate nodes and gives information on the connectivity of each node keeping in mind the intrinsic constraints of WSWs such as energy consumption, autonomy, etc. Due to the efficiency and scalability of greedy routing in WSNs and the financial cost of GPS chips, Virtual Coordinate Systems (VCSs) for WSNs have been proposed. A category of VCSs is based on the hop-count from the sink, this scheme leads to many nodes having the same coordinate. The main advantage of this system is that the hops number of a packet from a source to the sink is known. Nevertheless, it does not allow to differentiate the nodes with the same hop-count. In this report we propose a novel hop-count-based VCS which aims at classifying the nodes having the same hop-count depending on their connectivity and at differentiating nodes in a 2-hop neighborhood. Those properties make the coordinates, which also can be viewed as a local identifier, a very powerful metric which can be used in WSNs mechanisms.Comment: (2011

RTXP : A Localized Real-Time Mac-Routing Protocol for Wireless Sensor Networks

Protocols developed during the last years for Wireless Sensor Networks (WSNs) are mainly focused on energy efficiency and autonomous mechanisms (e.g. self-organization, self-configuration, etc). Nevertheless, with new WSN applications, appear new QoS requirements such as time constraints. Real-time applications require the packets to be delivered before a known time bound which depends on the application requirements. We particularly focus on applications which consist in alarms sent to the sink node. We propose Real-Time X-layer Protocol (RTXP), a real-time communication protocol. To the best of our knowledge, RTXP is the first MAC and routing real-time communication protocol that is not centralized, but instead relies only on local information. The solution is cross-layer (X-layer) because it allows to control the delays due to MAC and Routing layers interactions. RTXP uses a suited hop-count-based Virtual Coordinate System which allows deterministic medium access and forwarder selection. In this paper we describe the protocol mechanisms. We give theoretical bound on the end-to-end delay and the capacity of the protocol. Intensive simulation results confirm the theoretical predictions and allow to compare with a real-time centralized solution. RTXP is also simulated under harsh radio channel, in this case the radio link introduces probabilistic behavior. Nevertheless, we show that RTXP it performs better than a non-deterministic solution. It thus advocates for the usefulness of designing real-time (deterministic) protocols even for highly unreliable networks such as WSNs

Modeling Local Broadcast Behavior of Wireless Sensor Networks with Timed Automata for Model Checking of WCTT

International audienceWireless Sensor Networks (WSNs) are usually deployed in order to monitor parameters of an area. When an event occurs in the network an alarm is sent to a special node called the sink. In critical real-time applications, when an event is detected, the Worst Case Traversal Time (WCTT) of the message must be bounded. Although real-time protocols for WSNs have been proposed, they are rarely formally verified. The model checking of WSNs is a challenging problem for several reasons. First, WSNs are usually large scale so it induces state space explosion during the verification. Moreover, wireless communications produce a local broadcast behavior which means that a packet is received only by nodes which are in the radio range of the sender. Finally, the radio link is probabilistic. The modeling of those aspects of the wireless link is not straightforward and it has to be done in a way that mitigate the state space explosion problem. In this paper we particularly focus on the modeling of the local broadcast behavior with Timed Automata (TA). We use TA because they have sufficient expressiveness and analysis power in order to check time properties of protocols, as shown in the paper. Three ways of modeling local broadcast with synchronizations of TA are presented. We compare them and show that they produce different state space sizes and execution times during the model checking process. We run several model checking on a simple WSN protocol and we conclude that one model mitigate the state explosion problem better than the others. In the future, the next step will be to enhance this model with the probabilistic aspect of radio communications and to show it remains the best one

Formal Verification of Real-Time Wireless Sensor Networks Protocols with Realistic Radio Links

International audienceMany critical applications which rely on Wireless Sensor Networks (WSNs) are proposed. Forest fire detection, land- slide detection and intrusion detection are some examples. Critical applications require correct behavior, reliability, and the respect of time constraints. Otherwise, if they fail, con- sequences on human life and the environment could be catas- trophic. For this reason, the WSN protocols used in these applications must be formally verified. Unfortunately the radio link is unreliable, it is thus difficult to give hard guar- antees on the temporal behavior of the protocols (on wired systems the link error probability is very low [7], so they are considered reliable). Indeed, a message may experience a very high number of retransmissions. The temporal guaran- tee has thus to be given with a probability that it is achieved. This probability must meet the requirements of the applica- tion. Network protocols have been successfully verified on a given network topology without taking into account unre- liable links. Nevertheless, the probabilistic nature of radio links may change the topology (links which appear and dis- appear). Thus instead of a single topology we have a set of possible topologies, each topology having a probability to exist. In this paper, we propose a method that produces the set of topologies, checks the property on every topology, and gives the probability that the property is verified. This technique is independent from the verification technique, i.e. each topology can be verified using any formal method which can give a "yes" or "no" answer to the question: "Does the model of the protocol respect the property?". In this paper we apply this method on f-MAC [23] pro- tocol. F-MAC is a real-time medium access protocol for WSNs. We use UPPAAL model checker [10] as verification tool. We perform simulations to observe the difference be- tween average and worst case behaviors

On the Reliability of Wireless Sensor Networks Communications

International audienceMore and more Wireless Sensor Networks (WSNs) applica- tions and protocols are proposed. Notably, critical applications, which must meet time and reliability requirements. Works on the real-time ca- pability of WSNs have been proposed [1]. In this paper we propose to study the achievable reliability of WSNs, tacking into account the prob- abilistic nature of the radio link. We define the reliability of a WSN to be the probability that an end-to-end communication is successful (i.e. the packet is received by the sink). We propose a theoretical framework inspired by a reference model [5]. We use the framework to derive the reliability of two types of routing schemes: unicast-based and broadcast- based. We show that in the case of broadcast-based, the sink is a relia- bility bottleneck of the network. We also discuss the impact of the MAC scheme on the reliability

Proposition et vérification formelle de protocoles de communications temps-réel pour les réseaux de capteurs sans fil

Les RCsF sont des réseaux ad hoc, sans fil, large échelle déployés pour mesurer des paramètres de l'environnement et remonter les informations à un ou plusieurs emplacements (nommés puits). Les éléments qui composent le réseau sont de petits équipements électroniques qui ont de faibles capacités en termes de mémoire et de calcul ; et fonctionnent sur batterie. Ces caractéristiques font que les protocoles développés, dans la littérature scientifique de ces dernières années, visent principalement à auto-organiser le réseau et à réduire la consommation d'énergie. Avec l'apparition d'applications critiques pour les réseaux de capteurs sans fil, de nouveau besoins émergent, comme le respect de bornes temporelles et de fiabilité. En effet, les applications critiques sont des applications dont dépendent des vies humaines ou l'environnement, un mauvais fonctionnement peut donc avoir des conséquences catastrophiques. Nous nous intéressons spécifiquement aux applications de détection d'événements et à la remontée d'alarmes (détection de feu de forêt, d'intrusion, etc), ces applications ont des contraintes temporelles strictes. D'une part, dans la littérature, on trouve peu de protocoles qui permettent d'assurer des délais de bout en bout bornés. Parmi les propositions, on trouve des protocoles qui permettent effectivement de respecter des contraintes temporelles mais qui ne prennent pas en compte les spécificités des RCsF (énergie, large échelle, etc). D'autres propositions prennent en compte ces aspects, mais ne permettent pas de garantir des bornes temporelles. D'autre part, les applications critiques nécessitent un niveau de confiance très élevé, dans ce contexte les tests et simulations ne suffisent pas, il faut être capable de fournir des preuves formelles du respect des spécifications. A notre connaissance cet aspect est très peu étudié pour les RcsF. Nos contributions sont donc de deux types : * Nous proposons un protocole de remontée d'alarmes, en temps borné, X-layer (MAC/routage, nommé RTXP) basé sur un système de coordonnées virtuelles originales permettant de discriminer le 2-voisinage. L'exploitation de ces coordonnées permet d'introduire du déterminisme et de construire un gradient visant à contraindre le nombre maximum de sauts depuis toute source vers le puits. Nous proposons par ailleurs un mécanisme d'agrégation temps-réel des alarmes remontées pour lutter contre les tempêtes de détection qui entraînent congestion et collision, et donc limitent la fiabilité du système. * Nous proposons une méthodologie de vérification formelle basée sur les techniques de Model Checking. Cette méthodologie se déroule en trois points, qui visent à modéliser de manière efficace la nature diffusante des réseaux sans fil, vérifier les RCsF en prenant en compte la non-fiabilité du lien radio et permettre le passage à l'échelle de la vérification en mixant Network Calculus et Model Checking. Nous appliquons ensuite cette méthodologie pour vérifier RTXP.Wireless Sensor Networks (WSNs) are ad hoc wireless large scale networks deployed in order to monitor physical parameters of the environment and report the measurements to one or more nodes of the network (called sinks). The small electronic devices which compose the network have low computing and memory capacities and run on batteries, researches in this field have thus focused mostly on self-organization and energy consumption reduction aspects. Nevertheless, critical applications for WSNs are emerging and require more than those aspects, they have real-time and reliability requirements. Critical applications are applications on which depend human lives and the environment, a failure of a critical application can thus have dramatic consequences. We are especially interested in anomaly detection applications (forest fire detection, landslide detection, intrusion detection, etc), which require bounded end to end delays and high delivery ratio. Few WSNs protocols of the literature allow to bound end to end delays. Among the proposed solutions, some allow to effectively bound the end to end delays, but do not take into account the characteristics of WSNs (limited energy, large scale, etc). Others, take into account those aspects, but do not give strict guaranties on the end to end delays. Moreover, critical applications require a very high confidence level, simulations and tests are not sufficient in this context, formal proofs of compliance with the specifications of the application have to be provided. The application of formal methods to WSNs is still an open problem. Our contributions are thus twofold : * We propose a real-time cross-layer protocol for WSNs (named RTXP) based on a virtual coordinate system which allows to discriminate nodes in a 2-hop neighborhood. Thanks to these coordinates it is possible to introduce determinism in the accesses to the medium and to bound the hop-count, this allows to bound the end to end delay. Besides, we propose a real-time aggregation scheme to mitigate the alarm storm problem which causes collisions and congestion and thus limit the network lifetime. * We propose a formal verification methodology based on the Model Checking technique. This methodology is composed of three elements, (1) an efficient modeling of the broadcast nature of wireless networks, (2) a verification technique which takes into account the unreliability of the wireless link and (3) a verification technique which mixes Network Calculus and Model Checking in order to be both scalable and exhaustive. We apply this methodology in order to formally verify our proposition, RTXP.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

A study of a coronal hole associated with a large filament eruption

We report the results of a detailed study of an equatorial coronal hole and a dimming region related to the eruptions of a nearby large filament and subsequent coronal mass ejections (CMEs). The dynamic eruptions of the filament and the associated CMEs are probably related to the magnetic reconnection involving the magnetic field lines at the filament footpoints. During the starting processes of the filament eruption, we observed several newly emerged small magnetic flux concentrations close to the filament footpoints. Disturbance increase in the prominence body was observed during the pre-eruption processes. After the filament eruption, we observed evacuated filament material from the filament channel towards the coronal hole. Thus, all the region is perturbed and EUV loops and bright points are observed before and after the eruptions. Additionally, after the CME, we observed the disappearance of the dimming region and the coronal hole, followed by photospheric magnetic diffusion. We discussed a possible magnetic reconnection scenario and MHD waves involved during these processes.National Science Foundation/[1212096]/NSF/Estados UnidosNational Aeronautics and Space Administration/[NNX14AJ53G]/NASA/Estados UnidosUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones Espaciales (CINESPA

SARS-CoV-2 recombinant proteins stimulate distinct cellular and humoral immune response profiles in samples from COVID-19 convalescent patients

OBJECTIVES: In this preliminary study we investigated cellular and humoral immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in blood samples from 14 recovered coronavirus disease 2019 (COVID-19) patients and compared them to those in samples from 12 uninfected/unvaccinated volunteers. METHODS: Cellular immunity was assessed by intracellular detection of IFN-γ in CD3+ T lymphocytes after stimulation with SARS-CoV-2 spike (S1), nucleocapsid (NC), or receptor-binding domain (RBD) recombinant proteins or overlapping peptide pools covering the sequence of SARS-CoV-2 spike, membrane and nucleocapsid regions. The humoral response was examined by ELISAs and/or chemiluminescence assays for the presence of serum IgG antibodies directed to SARS-CoV-2 proteins. RESULTS: We observed differences between humoral and cellular immune profiles in response to stimulation with the same proteins. Assays of IgG antibodies directed to SARS-CoV-2 NC, RBD and S1/S2 recombinant proteins were able to differentiate convalescent from uninfected/unvaccinated groups. Cellular immune responses to SARS-CoV-2 protein stimuli did not exhibit a specific response, as T cells from both individuals with no history of contact with SARS-CoV-2 and from recovered donors were able to produce IFN-γ. CONCLUSIONS: Determination of the cellular immune response to stimulation with a pool of SARS-CoV-2 peptides but not with SARS-CoV-2 proteins is able to distinguish convalescent individuals from unexposed individuals. Regarding the humoral immune response, the screening for serum IgG antibodies directed to SARS-CoV-2 proteins has been shown to be specific for the response of recovered individuals

Study of Probabilistic Worst Case Inter-Beacon Delays Under Realistic Vehicular Mobility Conditions

International audienceRoad safety applications are one of the main incentives to deploy vehicular networks. These applications rely on periodic message exchange among vehicles (known as beaconing). The beacon messages contain information about the environment which is used to perceive dangerous situations and alert the drivers. The inter-beacon delay is the time between two consecutive beacons received from a car. It is an essential parameter because, if this delay exceeds the application requirement , the application cannot accurately predict dangerous situations and alert the drivers on time. The worst case inter-beacon delay has thus to be bounded according to the application requirements. Unfortunately, a tight and strict bound is in fact very difficult to obtain for a real network because of the randomness of the collisions among beacons coming from: the unpredictable mobility patterns, random interferences, randomness of the MAC layer backoff, etc. In this paper, we propose to provide a probabilistic worst-case of the inter-beacon delay under realistic mobility using Extreme Value Theory (EVT). EVT provides statistical tools which allow to make predictions on extreme deviations from the average of a parameter. These statistical predictions can be made based on data gathered from simulation or experimentation. We first introduce the EVT technique. Then we discuss its application to the study of inter-beacon delays. Finally, we apply EVT on the results of extensive vehicular network simulation using a realistic mobility trace: the Cologne trace

Proposition and formal verification of real-time wireless sensor networks protocols

Les RCsF sont des réseaux ad hoc, sans fil, large échelle déployés pour mesurer des paramètres de l'environnement et remonter les informations à un ou plusieurs emplacements (nommés puits). Les éléments qui composent le réseau sont de petits équipements électroniques qui ont de faibles capacités en termes de mémoire et de calcul ; et fonctionnent sur batterie. Ces caractéristiques font que les protocoles développés, dans la littérature scientifique de ces dernières années, visent principalement à auto-organiser le réseau et à réduire la consommation d'énergie. Avec l'apparition d'applications critiques pour les réseaux de capteurs sans fil, de nouveau besoins émergent, comme le respect de bornes temporelles et de fiabilité. En effet, les applications critiques sont des applications dont dépendent des vies humaines ou l'environnement, un mauvais fonctionnement peut donc avoir des conséquences catastrophiques. Nous nous intéressons spécifiquement aux applications de détection d'événements et à la remontée d'alarmes (détection de feu de forêt, d'intrusion, etc), ces applications ont des contraintes temporelles strictes. D'une part, dans la littérature, on trouve peu de protocoles qui permettent d'assurer des délais de bout en bout bornés. Parmi les propositions, on trouve des protocoles qui permettent effectivement de respecter des contraintes temporelles mais qui ne prennent pas en compte les spécificités des RCsF (énergie, large échelle, etc). D'autres propositions prennent en compte ces aspects, mais ne permettent pas de garantir des bornes temporelles. D'autre part, les applications critiques nécessitent un niveau de confiance très élevé, dans ce contexte les tests et simulations ne suffisent pas, il faut être capable de fournir des preuves formelles du respect des spécifications. A notre connaissance cet aspect est très peu étudié pour les RcsF. Nos contributions sont donc de deux types : * Nous proposons un protocole de remontée d'alarmes, en temps borné, X-layer (MAC/routage, nommé RTXP) basé sur un système de coordonnées virtuelles originales permettant de discriminer le 2-voisinage. L'exploitation de ces coordonnées permet d'introduire du déterminisme et de construire un gradient visant à contraindre le nombre maximum de sauts depuis toute source vers le puits. Nous proposons par ailleurs un mécanisme d'agrégation temps-réel des alarmes remontées pour lutter contre les tempêtes de détection qui entraînent congestion et collision, et donc limitent la fiabilité du système. * Nous proposons une méthodologie de vérification formelle basée sur les techniques de Model Checking. Cette méthodologie se déroule en trois points, qui visent à modéliser de manière efficace la nature diffusante des réseaux sans fil, vérifier les RCsF en prenant en compte la non-fiabilité du lien radio et permettre le passage à l'échelle de la vérification en mixant Network Calculus et Model Checking. Nous appliquons ensuite cette méthodologie pour vérifier RTXP.Wireless Sensor Networks (WSNs) are ad hoc wireless large scale networks deployed in order to monitor physical parameters of the environment and report the measurements to one or more nodes of the network (called sinks). The small electronic devices which compose the network have low computing and memory capacities and run on batteries, researches in this field have thus focused mostly on self-organization and energy consumption reduction aspects. Nevertheless, critical applications for WSNs are emerging and require more than those aspects, they have real-time and reliability requirements. Critical applications are applications on which depend human lives and the environment, a failure of a critical application can thus have dramatic consequences. We are especially interested in anomaly detection applications (forest fire detection, landslide detection, intrusion detection, etc), which require bounded end to end delays and high delivery ratio. Few WSNs protocols of the literature allow to bound end to end delays. Among the proposed solutions, some allow to effectively bound the end to end delays, but do not take into account the characteristics of WSNs (limited energy, large scale, etc). Others, take into account those aspects, but do not give strict guaranties on the end to end delays. Moreover, critical applications require a very high confidence level, simulations and tests are not sufficient in this context, formal proofs of compliance with the specifications of the application have to be provided. The application of formal methods to WSNs is still an open problem. Our contributions are thus twofold : * We propose a real-time cross-layer protocol for WSNs (named RTXP) based on a virtual coordinate system which allows to discriminate nodes in a 2-hop neighborhood. Thanks to these coordinates it is possible to introduce determinism in the accesses to the medium and to bound the hop-count, this allows to bound the end to end delay. Besides, we propose a real-time aggregation scheme to mitigate the alarm storm problem which causes collisions and congestion and thus limit the network lifetime. * We propose a formal verification methodology based on the Model Checking technique. This methodology is composed of three elements, (1) an efficient modeling of the broadcast nature of wireless networks, (2) a verification technique which takes into account the unreliability of the wireless link and (3) a verification technique which mixes Network Calculus and Model Checking in order to be both scalable and exhaustive. We apply this methodology in order to formally verify our proposition, RTXP