CCR: Cost‐aware cell relocation in 6TiSCH networks

In the context of industrial applications, ensuring medium access control is a fundamental challenge. Industrial IoT devices are resource-constrained and must guarantee reliable communication while reducing energy consumption. The IEEE 802.15.4e standard proposed time-slotted channel hopping (TSCH) to meet the requirements of the industrial Internet of Things. TSCH relies on time synchronization and channel hopping to improve performance and reduce energy consumption. Despite these characteristics, configuring an efficient schedule under varying traffic conditions and interference scenarios remains a challenging problem. The exploitation of reinforcement learning (RL) techniques offers a promising approach to address this challenge. AI enables TSCH to dynamically adapt its scheduling based on real-time network conditions, making decisions that optimize key performance criteria such as energy efficiency, reliability, and latency. By learning from the environment, reinforcement learning can reconfigure schedules to mitigate interference scenarios and meet traffic demands. In this work, we compare various reinforcement learning (RL) algorithms in the context of the TSCH environment. In particular, we evaluate the deep Q-network (DQN), double deep Q-network (DDQN), and prioritized DQN (PER-DQN). We focus on the convergence speed of these algorithms and their capacity to adapt the schedule. Our results show that the PER-DQN algorithm improves the packet delivery ratio and achieves faster convergence compared to DQN and DDQN, demonstrating its effectiveness for dynamic TSCH scheduling in Industrial IoT environments. These quantifiable improvements highlight the potential of prioritized experience replay to enhance reliability and efficiency under varying network conditions.

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.

Wireless Sensor Nnetworks (WSNs) are becoming increasingly widespread owing to the introduction of the Internet of Things (IoT) and the networks' comparatively low cost and usability. WSNs are usually battery-powered, owing to their low power consumption, which however limits their computational performance. The lifetime of a WSN strongly depends on its communication-related power consumption. Time Slotted Channel Hopping (TSCH) solves the problem of power consumption by featuring both time-division and frequency- division multiplexing in the system's Media Access Control (MAC) layer. In this paper, Pruning-based Coloring Scheduling (PRCOS) is proposed, which is an algorithm for TSCH scheduling that accounts for the power consumption to extend the system's lifetime. Using mathematical analysis, we show that the proposed algorithm decreases the transfer time and energy consumption by factors of 0.43 and 0.57, respectively, compared with existing algorithms.

The IEEE 802.15.4-2015 TSCH (Time Slotted Channel Hopping) standard provides high-reliability, deterministic delay, and energy efficiency with the channel hopping and the TDMA. The standard does not specify the scheduling method, which is an essential part of the solution. One of the representative studies in TSCH scheduling is Orchestra. It is an autonomous scheduling method with minimal overhead that does not require a negotiation process between nodes. However, with high traffic load, performance of the Orchestra is greatly degraded because of its fixed schedule. If a node has children, continuous collisions occur in the slot of the node. We propose a novel algorithm called SRCA (Slot Reallocation for Collision Avoidance), as a solution for this problem. The SRCA autonomously updates the schedule. When a child requests a slot reallocation, the parent allocates a new slot with a low probability of collision. Another algorithm called SJCA (Slot reJection for Collision Avoidance) is further proposed in this work. It improves the SRCA to operate in an environment with interference where a sending node can disturb a transmission from a hidden node. In the SJCA, a node determines whether a collision due to interference will occur in the slot newly allocated by the parent. If so, it rejects the slot and requests again. We compare the performance of the SRCA and the SJCA against the Orchestra and e-TSCH-Orch through simulations. It is confirmed that the SJCA is robust to interference. In most cases, the SJCA shows better performance of PAR (Packet Acknowledgement Ratio), PLR (Packet Loss Rate), and latency than others. It is also verified that the SJCA provides high-reliability and low latency compared to existing technologies.

IWSNs (Industrial Wireless Sensor Networks) have become the next step in the evolution of WSN (Wireless Sensor Networks) due to the nature and demands of modern industry. With this type of network, flexible and scalable architectures can be created that simultaneously support traffic sources with different characteristics. Due to the great diversity of application scenarios, there is a need to implement additional capabilities that can guarantee an adequate level of reliability and that can adapt to the dynamic behavior of the applications in use. The use of SDNs (Software Defined Networks) extends the possibilities of control over the network and enables its deployment at an industrial level. The signaling traffic exchanged between nodes and controller is heavy and must occupy the same channel as the data traffic. This difficulty can be overcome with the segmentation of the traffic into flows, and correct scheduling at the MAC (Medium Access Control) level, known as slices. This article proposes the integration in the SDN controller of a traffic manager, a routing process in charge of assigning different routes according to the different flows, as well as the introduction of the Time Slotted Channel Hopping (TSCH) Scheduler. In addition, the TSCH (Time Slotted Channel Hopping) is incorporated in the SDN-WISE framework (Software Defined Networking solution for Wireless Sensor Networks), and this protocol has been modified to send the TSCH schedule. These elements are jointly responsible for scheduling and segmenting the traffic that will be sent to the nodes through a single packet from the controller and its performance has been evaluated through simulation and a testbed. The results obtained show how flexibility, adaptability, and determinism increase thanks to the joint use of the routing process and the TSCH Scheduler, which makes it possible to create a slicing by flows, which have different quality of service requirements. This in turn helps guarantee their QoS characteristics, increase the PDR (Packet Delivery Ratio) for the flow with the highest priority, maintain the DMR (Deadline Miss Ratio), and increase the network lifetime.

The demand for reliable and energy-efficient low-power wireless network protocols is growing up steadily with the flourish of the emerging Internet of Things (IoT) applications. The Time Slotted Channel Hopping (TSCH), part of the IEEE 802.15.4 standard, represents the latest generation of low-power and highly reliable MAC protocols. It orchestrates the medium access according to a time-frequency communication schedule. Several scheduling algorithms have been introduced for TSCH. In contrast to centralized and distributed scheduling approaches, autonomous scheduling does not occur any signaling overhead and appears as a promising approach. In this study, we review autonomous TSCH scheduling algorithms, including static and recently proposed adaptive algorithms. Then, we investigate, on a real-world testbed, the performance of representative static autonomous scheduling schemes for TSCH protocol. Experimental results show that they suffer from high number of queued packets and buffers overflow, which increase the network delay and decreases the delivery ratio. Finally, we qualitatively compare and discuss the performance of recent adaptive autonomous TSCH scheduling algorithms, showing that research on adaptive autonomous TSCH scheduling still has open issues.

Autonomous and traffic-aware scheduling for TSCH networks

The IPv6 over IEEE 802.15.4e TSCH mode (6TiSCH) network is intended to provide reliable and delay bounded communication in multi-hop and scalable Industrial Internet of Things (IIoT). The IEEE 802.15.4e Time Slotted Channel Hopping (TSCH) link layer protocol allows the nodes to change their physical channel after each transmission to eliminate interference and multi-path fading on the channels. However, due to this feature, new nodes (aka pledges) take more time to join the 6TiSCH network, resulting in significant energy consumption and inefficient data transmission, which makes the communication unreliable. Therefore, the formation of 6TiSCH network has gained immense interest among the researchers. To date, numerous solutions have been offered by various researchers in order to speed up the formation of 6TiSCH networks. This article briefly discusses about the 6TiSCH network and its formation process, followed by a detailed survey on the works that considered 6TiSCH network formation. We also perform theoretical analysis and real testbed experiments for a better understanding of the existing works related to 6TiSCH network formation. This article is concluded after summarizing the research challenges in 6TiSCH network formation and providing a few open issues in this domain of work.

ReSF: Recurrent Low-Latency Scheduling in IEEE 802.15.4e TSCH networks

AODV (Ad hoc On‐Demand Distance Vector) is a well‐known routing protocol for wireless networks. Recently, Time Slotted Channel Hopping (TSCH) was proposed as a MAC layer protocol, specified in the IEEE 802.15.4e standard. As MAC layer protocols can impact the performance of protocols in the layers above, we examine the performance of AODV over TSCH and compare it with CSMA. We investigate using different metrics, such as latency, packet delivery rate, and energy consumption. We implemented AODV, as defined by the RFC 3561, using the embedded systems operational system Contiki‐NG, a well established platform for Low power and Lossy Networks (LLNs), and the Internet of things (IoT). Our results, running on the Cooja platform, show that TSCH can greatly improve the performance of AODV, achieving a packet delivery rate of almost 100%. Moreover, our results also show that TSCH consumes less energy than CSMA.

The IEEE 802.15.4-2015 standard defines a number of Medium Access Control (MAC) layer protocols for low power wireless communications, which are desirable for energy-constrained Internet of Things (IoT) devices. Originally defined in the IEEE 802.15.4e amendment, the Time Slotted Channel Hopping (TSCH) has recently been attracting attention from the research community due to its reduced contention (time scheduling) and robustness against fading (channel hopping). However, it requires a certain level of synchronization between the nodes, which can increase the energy consumption. In this work, we implement the Guard Beacon (GB) strategy, aiming at reducing the guard time usually implemented to compensate for imperfect synchronization. Moreover, besides presenting a realistic energy consumption model for a Contiki Operating System-based TSCH network, we show through analytical and practical results that, without the proposed scheme, the power consumption can be more than 13% higher.

The Industrial Internet of Things (IIoT) uses reliable wireless network solutions such as Time-Slotted Channel Hopping (TSCH) to integrate cyber-physical systems with industrial environments via the IPv6 over TSCH (6TiSCH) protocol stack. The quality of 6TiSCH radio links affects the network performance significantly in terms of energy consumption, latency, and reliability. Therefore, accurate link quality estimation (LQE) is an important feature influencing the design and optimization of higher-layer protocols. Indeed, accurate link quality estimation helps predict link failure and avoid packet loss, which ensures good routes and better quality of service. This paper surveys and discusses existing link quality estimators used in 6TiSCH networks and proposes a taxonomy that captures the fundamental differences among them. Besides, comparisons between different LQE solutions are performed to provide a comprehensive view of the state-of-the-art and useful insights. The paper ends by highlighting open problems in this active area of research.

A Latin rectangles-based TSCH scheduling and interference mitigation design

Evaluating and Modeling IEEE 802.15.4 TSCH Resilience against Wi-Fi Interference in New-Generation Highly-Dependable Wireless Sensor Networks

IEEE standardized a highly efficient, low power, reliable, deterministic and time–frequency enabled medium access control protocol, IEEE 802.15.4e time slotted channel hopping (TSCH) as an amendment to the medium access control (MAC) protocol defined by the IEEE 802.15.4 standard. Once a communication schedule is built, the IEEE 802.15.4e TSCH is able to execute such a communication schedule. IEEE 802.15.4e TSCH standard lea ves out of scope defining how that communication schedule is built, updated and maintained. In order to fill this gap, we introduce such a scheduling algorithm, called as DIVA. DIVA is specifically designed for IEEE 8092.15.4e TSCH networks. It is a totally distributed scheduling algorithm for divergecast traffic where divergecast means that traffic flows in all directions in contrast to convergecast where traffic flows from leave nodes to root. In order to gain more comprehension about DIVA, we conducted extensive simulations. We also compared DIVA with Berkeley’s Aloha-based algorithm.