Multihop Latency Model for Industrial Wireless Sensor Networks Based on Interfering Nodes

Emerging Industry 4.0 applications require ever-increasing amounts of data and new sources of information to more accurately characterize the different processes of a production line. Industrial Internet of Things (IIoT) technologies, and in particular Wireless Sensor Networks (WSNs), allow a large amount of data to be digitized at a low energy cost, thanks to their easy scalability and the creation of meshed networks to cover larger areas. In industry, data acquisition systems must meet certain reliability and robustness requirements, since other systems such as predictive maintenance or the digital twin, which represents a virtual mapping of the system with which to interact without the need to alter the actual installation, may depend on it. Thanks to the IEEE 802.15.4e standard and the use of Time-Slotted Channel Hopping (TSCH) as the medium access mechanism and IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) as the routing protocol, it is possible to deploy WSNs with high reliability, autonomy, and minimal need for re-configuration. One of the drawbacks of this communication architecture is the low efficiency of its deployment process, during which it may take a long time to synchronize and connect all the devices in a network. This paper proposes an analytical model to characterize the process for the creation of downstream routes in RPL, whose transmission of multi-hop messages can present complications in scenarios with a multitude of interfering nodes and resource allocation based on minimal IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH). This type of multi-hop message exchange has a different behaviour than the multicast control messages exchanged during the synchronization phase and the formation of upstream routes, since the number of interfering nodes changes in each retransmission.

Parent and PHY Selection in Slot Bonding IEEE 802.15.4e TSCH Networks

While IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) networks should be equipped to deal with the hard wireless challenges of industrial environments, the sensor networks are often still limited by the characteristics of the used physical (PHY) layer. Therefore, the TSCH community has recently started shifting research efforts to the support of multiple PHY layers, to overcome this limitation. On the one hand, integrating such multi-PHY support implies dealing with the PHY characteristics to fit the resource allocation in the TSCH schedule, and on the other hand, defining policies on how to select the appropriate PHY for each network link. As such, first a heuristic is proposed that is a step towards a distributed PHY and parent selection mechanism for slot bonding multi-PHY TSCH sensor networks. Additionally, a proposal on how this heuristic can be implemented in the IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH) protocol stack and its Routing Protocol for Low-power and Lossy network (RPL) layer is also presented. Slot bonding allows the creation of different-sized bonded slots with a duration adapted to the data rate of each chosen PHY. Afterwards, a TSCH slot bonding implementation is proposed in the latest version of the Contiki-NG Industrial Internet of Things (IIoT) operating system. Subsequently, via extensive simulation results, and by deploying the slot bonding implementation on a real sensor node testbed, it is shown that the computationally efficient parent and PHY selection mechanism approximates the packet delivery ratio (PDR) results of a near-optimal, but computationally complex, centralized scheduler.

Enhanced Wireless Grid Technologies for the Harmonized Devices in Future IoT Systems

The paper proposes the enhanced wireless grid technologies for the future Internet of Things (IoT) systems. The paper shows a realization of the wireless grid by suitably exploiting the existing wireless Smart Utility Networks (SUN) that is standardized by IEEE 802.15.4g/4e task groups and is certified by Wi-SUN alliance. Medium Access Control (MAC) layer functions that is mainly defined by IEEE 802.15.4e standard and IEEE 802.15.10 recommended practice are effectively modified according to the assumed IoT services and satisfy the requirement of harmonized mesh activities by massive radio devices. In order to realize this function, SUN radio devices that exploit Layer 2 Routing (L2R) control scheme in IEEE 802.15.10 are employed to realize the autonomous mesh management function as well as the multiple service supporting function. The performance is evaluated through the experiments by employing the developed SUN devices as well as simulator evaluations. The paper also proposes novel data retransmission schemes by exploiting the data concatenation functions in IEEE 802.15.10 as well as evaluating its performances by computer simulations and experiments. Consequently, this paper confirms that the obtained results through both simulator evaluations and experiments matches to each other.