Mina Rady

Réseaux sans-fil agiles utilisant plusieurs couches physique: Cette thèse contribue au domaine émergent des réseaux sans-fil agiles utilisant plusieurs couches physiques. Traditionnellement, les réseaux sans-fil industriels n'emploient qu'une seule interface radio, à l'instar des implémentations de la pile protocolaire réseau IETF 6TiSCH qui s'appuient sur la radio IEEE 802.15.4 O-QPSK opérant dans la bande de fréquence à 2,4 GHz. Des progrès dans l'intégration de plusieurs schémas de modulation/codage au sein d'un même circuit radio et capable d'opérer dans différentes bandes de fréquence permettent aujourd'hui l'exploitation au sein d'un même réseau d'une diversité de configurations radios. Nous utilisons le terme "PHY'' pour désigner toute combinaison de : modulation, bande de fréquence et schéma de codage. Dans cette recherche, nous soutenons que la combinaison de PHY longue portée et courte portée peut offrir des performances de bout en bout de réseau équilibrées qu'aucun PHY unique n'atteint. Nous démontrons comment un ensemble de PHY courte et longue portée peut être intégré sous une architecture 6TiSCH généralisée ("g6TiSCH'') et nous évaluons expérimentalement ses performances dans un banc d'essai de 36 nœuds à Inria-Paris. De plus, nous montrons, expérimentalement, comment un slotframe TSCH peut adapter la durée du slot, slot par slot, en fonction du débit du PHY utilisé ("6DYN''). Enfin, nous concevons et évaluons, par simulation, une fonction d'objectif pour RPL qui optimise la durée de vie du réseau ("Life-OF''). Nous démontrons comment Life-OF combine divers PHYs pour augmenter la durée de vie du réseau de jusqu'à 470% par rapport à la fonction d'objectif MRHOF du staandard IETF actuel.

In 1794, French Engineer Claude Chappe coordinated the deployment of a network of dozens of optical semaphores. These formed “strings” that were hundreds of kilometers long, allowing for nationwide telegraphy. The Chappe telegraph inspired future developments of long-range telecommunications using electrical telegraphs and, later, digital telecommunication. Long-range wireless networks are used today for the Internet of Things (IoT), including industrial, agricultural, and urban applications. The long-range radio technology used today offers approximately 10 km of range. Long-range IoT solutions use “star” topology: all devices need to be within range of a gateway device. This limits the area covered by one such network to roughly a disk of a 10 km radius. In this article, we demonstrate a 103 km low-power wireless multi-hop network by combining long-range IoT radio technology with Claude Chappe’s vision. We placed 11 battery-powered devices at the former locations of the Chappe telegraph towers, hanging under helium balloons. We ran a proprietary protocol stack on these devices so they formed a 10-hop multi-hop network: devices forwarded the frames from the “previous” device in the chain. This is, to our knowledge, the longest low power multi-hop wireless network built to date, demonstrating the potential of combining long-range radio technology with multi-hop technology.

In this article, we propose a routing mechanism based on the RPL protocol in a wireless network that is equipped with a mix of short‐range and long‐range radios. We introduce Life‐OF, an objective function for RPL which uses a combination of metrics and the diverse physical layers to boost the network's lifetime. We evaluate the performance of Life‐OF compared to the classical MRHOF objective function in simulations. Two key performance indicators (KPIs) are reported: network lifetime and network latency. Results demonstrate that MRHOF tends to converge to a pure long‐range network, leading to short network lifetime. However, Life‐OF improves network lifetime by continuously adapting the routing topology to favor routing over nodes with longest remaining lifetime. Life‐OF combines diverse radios and balances power consumption in the network. This way, nodes switch between using their short‐range radio to improve their own battery lifetime and using their long‐range radio to avoid routers that are close to depletion. Results show that using Life‐OF improves the lifetime of the network by up to 470% that of MRHOF, while maintaining similar latency.

Wireless networks traditionally use a single physical layer for communication: some use high bit-rate short-range radios, others low bit-rate long-range radios. This article introduces g6TiSCH, a generalization of the standards-based IETF 6TiSCH protocol stack. g6TiSCH allows nodes equipped with multiple radios to dynamically switch between them on a link-by-link basis, as a function of link-quality. This approach results in a dynamic trade-off between latency and power consumption. We evaluate the performance of the approach experimentally on an indoor office testbed of 36 OpenMote B boards. Each OpenMote B can communicate using FSK 868 MHz, O-QPSK 2.4 GHz or OFDM 868 MHz, a combination of long-range and short-range physical layers. We measure network formation time, end-to-end reliability, end-to-end latency, and battery lifetime. We compare the performance of g6TiSCH against that of a traditional 6TiSCH stack running on each of the three physical layers. Results show that g6TiSCH yields lower latency and network formation time than any of the individual PHYs, while maintaining a similar battery lifetime.

New radio chips implement different physical layers, allowing firmware to change modulation, datarate and frequency dynamically. This technological development is an opportunity for industrial low-power wireless networks to offer even higher determinism, including latency predictability. This article introduces 6DYN, an extension to the IETF 6TiSCH standards-based protocol stack. In a 6DYN network, nodes switch physical layer dynamically on a link-by-link basis, in order to exploit the diversity offered by this new technology agility. To offer low latency and high network capacity, 6DYN uses heterogeneous slot durations: the length of a slot in the 6TiSCH schedule depends on the physical layer used. This article shows how reserved bits in 6TiSCH headers can be used to standardize 6DYN and details its implementation in OpenWSN, a reference implementation of 6TiSCH.

Low-power wireless applications require different trade-off points between latency, reliability, data rate and power consumption. Given such a set of constraints, which physical layer should I be using? We study this question in the context of 6TiSCH, a state-of-the-art recently standardized protocol stack developed for harsh industrial applications. Specifically, we augment OpenWSN, the reference 6TiSCH open-source implementation, to support one of three physical layers from the IEEE802.15.4g standard: FSK 868 MHz which offers long range, OFDM 868 MHz which offers high data rate, and O-QPSK 2.4 GHz which offers more balanced performance. We run the resulting firmware on the 42-mote OpenTestbed deployed in an office environment, once for each physical layer. Performance results show that, indeed, no physical layer outperforms the other for all metrics. This article argues for combining the physical layers, rather than choosing one, in a generalized 6TiSCH architecture in which technology-agile radio chips (of which there are now many) are driven by a protocol stack which chooses the most appropriate physical layer on a frame-by-frame basis.