Adaptive Multi-Channel Offset Assignment for Reliable IEEE 802.15.4 TSCH Networks

International audienceMore and more IoT applications require low-power operations and high reliability (close to 100%). Unfortunately, radio transmissions are unreliable by nature since they are prone to collision and external interference. The IEEE 802.15.4-2015 TSCH standard has been recently proposed to provide high-reliability through radio channel hopping and by appropriately scheduling all the transmissions. Since some of the radio channels still suffer from external interference, blacklisting techniques consist in detecting bad radio channels, and in privileging the good ones to transmit the packets. MABO-TSCH is a centralized scheduling algorithm which allocates several channel offsets to allow each radio link to apply a localized blacklist. However, such strategy is inefficient for large blacklists. In this study, we propose to allocate the channel offsets dynamically at each timeslot according to the number of parallel transmissions, while still avoiding collisions. We evaluate the performance of our solution relying on a real experimental dataset, highlighting the relevance of dynamic and per timeslot channel offset assignment for environments with high external interference, such as a smart building

High Performance Wireless Sensor-Actuator Networks for Industrial Internet of Things

Wireless Sensor-Actuator Networks (WSANs) enable cost-effective communication for Industrial Internet of Things (IIoT). To achieve predictability and reliability demanded by industrial applications, industrial wireless standards (e.g., WirelessHART) incorporate a set of unique features such as a centralized management architecture, Time Slotted Channel Hopping (TSCH), and conservative channel selection. However, those features also incur significant degradation in performance, efficiency, and agility. To overcome these key limitations of existing industrial wireless technologies, this thesis work develops and empirically evaluates a suite of novel network protocols and algorithms. The primary contributions of this thesis are four-fold. (1) We first build an experimental testbed realizing key features of the WirelessHART protocol stack, and perform a series of empirical studies to uncover the limitations and potential improvements of existing network features. (2) We then investigate the impacts of the industrial WSAN protocol’s channel selection mechanism on routing and real-time performance, and present new channel and link selection strategies that improve route diversity and real-time performance. (3) To further enhance performance, we propose and design conservative channel reuse, a novel approach to support concurrent transmissions in a same wireless channel while maintaining a high degree of reliability. (4) Lastly, to address the limitation of the centralized architecture in handling network dynamics, we develop REACT, a Reliable, Efficient, and Adaptive Control Plane for centralized network management. REACT is designed to reduce the latency and energy cost of network reconfiguration by incorporating a reconfiguration planner to reduce a rescheduling cost, and an update engine providing efficient and reliable mechanisms to support schedule reconfiguration. All the network protocols and algorithms developed in this thesis have been empirically evaluated on the wireless testbed. This thesis represents a step toward next-generation IIoT for industrial automation that demands high-performance and agile wireless communication

Técnica de mapeamento adaptativo de canais para redes sem fio industriais

O uso de redes sem fio em ambientes industriais é uma realidade nos dias atuais devido às suas vantagens como facilidade de instalação, custo de manutenção, entre outras. Porém, com o uso compartilhado do espectro de rádio frequência, o problema de coexistência entre redes sem fio torna-se inevitável. Este trabalho apresenta um sistema para diminuir os problemas ocasionados pela coexistência entre redes e com isso evitar a redu- ção na robustez que problemas deste tipo trazem. É proposto um sistema de mapeamento adaptativo de canais em redes industriais que utilizam a técnica Time Slotted Channel Hopping, onde é realizada a análise do espectro de frequências, e na sequência é realizada a remoção dos canais ocupados do mapa de possíveis canais a serem utilizados nas comunicações. Com o uso deste sistema, são reduzidos os problemas de colisão durante a realização das comunicações, garantindo desta forma a robustez da rede, um dos requisitos básicos quando se trata de redes industriais sem fio. O aumento da robustez da rede consequentemente irá impactar no consumo de energia dos dispositivos da rede, devido a redução da necessidade de retransmissões. Como forma de escolha dos canais a serem evitados, é proposto o uso de técnicas estatísticas utilizadas como mecanismo de seleção, de tal forma que o número de canais removidos é adaptável. É apresentado um estudo de caso do sistema de mapeamento adaptativo de canais em uma rede WirelessHART, onde é realizada uma análise da taxa de falhas de transmissão em situações sem e com o uso do sistema de mapeamento proposto.The use of wireless networks in industrial environments is a reality today due to its advantages such as, ease of installation, maintenance cost, among others. However, with the shared use of radio frequency spectrum, the problem of network coexistence becomes inevitable. This work presents a system to reduce the problems caused by the coexistence between networks and thus avoid the reduction in the robustness that problems of this type brings. An adaptive channel mapping system is proposed in industrial networks using the Time Slotted Channel Hopping technique, where the frequency spectrum analysis is performed and the busy channels are removed from the map of possible channels to be used in communications. This avoids collision problems during communications, thus ensuring network robustness, one of the basic requirements when it comes to industrial wireless networks. Increased network robustness will consequently impact the power consumption of network devices due to the reduced need for retransmissions. As a way of choosing the channels to be avoided, it is proposed to use statistical techniques used as a selection mechanism, so that the number of removed channels is adaptable. A case study of the adaptive channel mapping system in a WirelessHART network is presented, where an analysis of the transmission failure rate in situations without and with the use of the proposed mapping system is performed