MODESA: An optimized multichannel slot assignment for raw data convergecast in wireless sensor networks

International audienceIn aerospace applications, wireless sensor networks (WSNs) collect data from sensor nodes towards a sink in a multi-hop convergecast structure. The throughput requirement of these applications is difficult to meet with a single wireless channel. That is why, in this paper, we focus on a multichannel time slot assignment that minimizes the data gathering cycle. We first formalize the problem as a linear program and compute the optimal time needed for a raw data convergecast in various multichannel topologies. These optimal times apply to sinks equipped with one or several radio interfaces. We then propose our algorithm called MODESA and prove its optimality in various multichannel topologies. We evaluate its performances in terms of number of slots, maximum buffer size and number of active/sleep switches per node. Furthermore, we present variants of MODESA achieving a load balancing between the channels used

Delay Optimized Time Slot Assignment for Data Gathering Applications in Wireless Sensor Networks

International audienceWireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in confined environments such as mines or nuclear power plants because of their simplicity of deployment and low cost. In these application domains, WSNs are used to gather data from sensor nodes towards a sink in a multi-hop convergecast structure. In this paper, we focus on a traffic-aware time slot assignment minimizing the schedule length for tree topologies and for two special deployments (i.e. linear and multi-linear) representative of unusual environments. We formalize the problem as a linear program and provide results on the optimal number of slots. We then propose a delay optimized algorithm with two heuristics that minimize on the one hand the energy consumption and on the other hand the storage capacity as secondary criteria

Multichannel access for bandwidth improvement in IEEE 802.15.4 wireless sensor networks

International audienceIn this paper, we propose a new multichannel allocation protocol for ZigBee/IEEE 802.15.4 networks. The main goal is to improve the global throughput which is basically insufficient to satisfy high bandwidth requirements for applications like monitoring or traffic control. The solution is based on the availability of multiple channels on current low- cost, low-energy radio transceivers, such as TI/Chipcon CC2420, which can be easily tuned dynamically to different frequencies. This possibility can be exploited to increase the number of simultaneous transmissions on adjacent links. The allocation of the different channels is centralized and distributed by the coordinator thanks to a function designed to compute the channel offset between two successive children routers. In the nodes, the switching process between the transmission and the reception channels is triggered starting from the PHY primitive available on the transceiver. The evaluation shows that the proposed protocol improves the global throughput by a factor between 2 and 5, depending on the scenario, compared to the single-channel solution or a random channel allocation

An Adaptive Strategy for an Optimized Collision-Free Slot Assignment in Multichannel Wireless Sensor Networks

International audienceConvergecast is the transmission paradigm used by data gathering applications in wireless sensor networks (WSNs). For efficiency reasons, a collision-free slotted medium access is typically used: time slots are assigned to non-conflicting transmitters. Furthermore, in any slot, only the transmitters and the corresponding receivers are awake, the other nodes sleeping in order to save energy. Since a multichannel network increases the throughput available to the application and reduces interference, multichannel slot assignment is an emerging research domain in WSNs. First, we focus on a multichannel time slot assignment that minimizes the data gathering delays. We compute the optimal time needed for a raw data convergecast in various multichannel topologies. Then, we focus on how to adapt such an assignment to dynamic demands of transmissions (e.g., alarms, temporary additional application needs and retransmissions). We formalize the problem using linear programming, and we propose an incremental technique that operates on an optimized primary schedule to provide bonus slots to meet new transmission needs. We propose AMSA, an Adaptive Multichannel Slot Assignment algorithm, which takes advantage of bandwidth spatial reuse, and we evaluate its performances in terms of the number of slots required, slot reuse, throughput and the number of radio state switches

DiSCA: a Distributed Scheduling for Convergecast in Multichannel Wireless Sensor Networks

International audience—The new IEEE 802.15.4e standard does not specify how the schedule of medium accesses followed by wireless sensors is built. That is why, we propose a distributed interference-aware joint channel and time slot assignment, called DiSCA, for a traffic-aware convergecast in multichannel wireless sensor networks (WSNs). Unlike most previous studies, we consider two cases of transmissions: without acknowledgment and with immediate acknowledgment. We provide the minimum bound on the number of time slots needed for a convergecast with a sink equipped with multiple radio interfaces. Simulations results show that DiSCA is close to the optimal in terms of the number of slots and outperforms TMCP

Installer un Ordonnancement dans un Réseau 6TiSCH Contraint Multi-Saut en utilisant CoAP (Version Etendue)

Scheduling in a IEEE802.15.4e TSCH (6TiSCH) low-power wireless network can be done in a centralized or distributed way. When using centralized scheduling, a scheduler installs a communication schedule into the network. This can be done in a standards-based way usingCoAP. In this report, we compute the number of packets and the latency this takes, on real-world examples. The result is that the cost is very high using today's standards, much higher than when using an ad-hoc solution such as OCARI. We conclude by making recommendations to drastically reduce the number of messages and improve the efficiency of the standardized approach.Dans ce rapport de recherche, nous montrons comment installer un ordonnancement d'activités des noeuds dans un réseau contraint radio multi-sauts IEEE802.15.4e TSCH en utilisant le standard CoAP. A travers un exemple illustratif simple, nous calculons le nombre de messages véhiculés dans l'ensemble du réseau pour différentes méthodes compatibles avec ces standards existants. Nous notons que l'utilisation des standards existants se traduit par un coût très important en terme de nombre de messages et en latence. Ce coût est bien superieur à celuid'une solution ad-hoc comme OCARI. Nous concluons en faisant différentes recommandations pour réduire ce nombre de messages et donc améliorer l'efficacité des protocoles standardisés

A Distributed Joint Channel and Time Slot Assignment for Convergecast in Wireless Sensor Networks

International audienceIn this work, we study raw convergecast in multichannel wireless sensor networks (WSNs) where the sink may be equipped with multiple radio interfaces. We propose Wave, a simple and practical distributed joint channel and time slot assignment. We evaluate the number of slots needed to complete the convergecast by simulation and compare it to the optimal schedule and to a centralized solution

The Cost of Installing a 6TiSCH Schedule

International audienceScheduling in an IEEE802.15.4e TSCH (6TiSCH) low-power wireless mesh network can be done in a centralized or distributed way. When using centralized scheduling, a scheduler computes a communication schedule, which then needs to be installed into the network. This can be done using standards such CoAP and CoMI, or using a custom protocol such as OCARI. In this paper, we compute the number of messages installing and updating the schedule takes, using both approaches, on a realistic example scenario. The cost of using today's standards is high. In some cases, a standards-based solution requires approximately 4 times more messages to be transmitted in the network, than when using a custom protocol. This paper makes three simple recommended changes to the standards which, when integrated, reduce the cost of a standards based solution by 18% to 74%. Since they are still being developed, these recommendations can easily be integrated into the standards

Wave : un Algorithme d'Ordonnancement Distribué pour la Collecte de Données dans les R\'eseaux IEEE 802.15.4e (Version Etendue)

Wireless NetworksWireless sensor networks (WSNs) play a major role in industrial environments for data gathering (convergecast). Among the industrial requirements, we can name a few like 1) determinism and bounded convergecast latencies, 2) throughput and 3) robustness against interferences.The classical IEEE 802.15.4 that has been designed for low power lossy networks (LLNs) partially meets these requirements. That is why the IEEE~802.15.4e MAC amendmenthas been proposed recently. This amendment combines a slotted medium access with a channel hopping (i.e. Time Slotted Channel Hopping TSCH). The MAC layer orchestrates the medium accesses of nodes according to a given schedule. Nevertheless, this amendment does not specify how this schedule is computed. The purpose of this paper is to propose a distributed joint time slot and channel assignment, called Wave for data gathering in LLNs. This schedule targets minimized data convergecast delays by reducing the number of slots assigned to nodes. Moreover, Wave ensures the absence of conflicting transmissions in the schedule provided. In such a schedule, a node is awake only during its slots and the slots of its children in the convergecast routing graph. Thus, energy efficiency is ensured. In this paper, we describe in details the functioning of Wave, highlighting its features (e.g. support of heterogeneous traffic, support of a sink equipped with multiple interfaces) and properties in terms of worst case delays and buffer size. We discuss its features with regard to a centralized scheduling algorithm like TMCP and a distributed one like DeTAS. Simulation results show the good performance of Wave compared to TMCP. Since in an industrial environment, several routing graphs can coexist, we study how Wave supports this coexistence.Les réseaux de capteurs sans fil jouent un rôle majeur pour la collecte de données dans les environnements industriels.Parmi les exigences industrielles visées, nous pouvons citer 1) le déterminisme et les latences de collecte bornées supérieurement, 2) le débit et 3) la robustesse vis-à-vis des interférences.La norme IEEE 802.15.4 classique, qui a été conçue pour les réseaux avec pertes et contraintes énergétiques (ou Low power Lossy Networks, LLNs), ne répond que partiellement à ces exigences. C'est pourquoi l'amendement IEEE~802.15.4e a été proposé récemment.Cet amendement propose un mode d'utilisation TSCH (Time Slotted Channel Hopping) combinant l'accès au médium par slots temporels et le saut de fréquence.La couche MAC orchestre les accès au médium des noeuds du réseau selon un ordonnancement donné. Néanmoins, l'amendement ne spécifie pas comment cet ordonnancement est calculé.Le propos de ce papier est d'offrir un algorithme distribué d'assignation conjointe de fr\équences et de slots temporels pour la collecte dans les LLNs, dénommé Wave.Cet ordonnancement vise à minimiser le temps de collecte en r\éduisant le nombre de slots temporels assignés à l'ensemble des noeuds du réseau.De plus, Wave assure l'absence de transmissions conflictelles dans l'ordonnancement fourni.Dans un tel ordonnancement, un noeud est réveillé uniquement pendant ses slots de transmissions et ceux de ses enfants dans le graphe de routage de la collecte.Ainsi, l'efficacité énergétique est assurée.Dans ce papier, nous décrivons en détails le fonctionnement de Wave, mettant en exergue ses caractéristiques (support du trafic hétérogène, support d'un puits de données avec de multiples interfaces de communication) et ses propriétés en termee de d\élais et de la taille des buffers.Nous discutons ses caract\éristiques en regard d'un algorithme d'ordonnancement centralisé tel que TMCP et d'un algorithme distribué tel que DeTAS.Les résultats de simulations démontrent une meilleure performance de Wave par rapport à TMCP.Enfin, puisque dans un environnement industriel plusieurs graphes de routage peuvent cohabiter, nous étudions comment Wave assure cette coexistence

Building an IEEE 802.15.4e TSCH network

International audience—Most wireless sensor networks that are currently deployed use a technology based on the IEEE 802.15.4 standard. However, this standard does not meet all requirements of industrial applications in terms of latency, throughput and robustness. That is why the IEEE 802.15.4e amendment has been designed, including the Time Slotted Channel Hopping (TSCH) mode. In this paper, we focus on how to build a TSCH network and evaluate the time needed to form the network, using the NS3 simulator. A new beacon advertising algorithm is proposed for TSCH networks. A comparative performance evaluation with solutions already published is done