Time Slotted Channel Hopping Research Articles

Channel Quality Prediction for TSCH Blacklisting in Highly Dynamic Networks: A Self-Supervised Deep Learning Approach

Cross-Technology Interference (CTI) is a severe issue for wireless networks operating in the license-free ISM bands. In particular, CTI can significantly affect the performance of low-power wireless links used in the Internet-of-Things (IoT). The IEEE 802.15.4 standard adopts a channel hopping scheme in its Time-Slotted Channel Hopping (TSCH) mode as a means to mitigating the adverse effect of CTI. However, the indiscriminate procedure by which TSCH nodes hop over different channels can suffer from severe interference in specific channels. Adaptive channel blacklisting is a technique to alleviate this issue by leaving out low-quality channels from the hopping list. To enable an effective blacklisting, especially in highly varying networks, an accurate real-time prediction of the quality of all available channels is of paramount importance. Previous studies rely on the past records of the channels as an indication of their quality in near future. Evidently, such approaches cannot extend to highly dynamic environments. This paper present a self-supervised approach for training deep neural networks capable of predicting the future behaviour of the frequency channels. The trained models can then substitute the quality assessment approaches in blacklisting schemas. Considering in-vehicle wireless networks as a target application, we evaluate this idea using a real-world experimental dataset, consisting of three measurement scenarios inside a moving vehicle. The experimental results show that using the proposed technique for TSCH blacklisting significantly improves the reliability of networks experiencing such highly dynamic interference and performs at least as good as the existing channel assessment methods in low-interference conditions.

Coexistence Analysis of Co-Located BLE and IEEE 802.15.4 TSCH Networks

Bluetooth Low Energy (BLE) and IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) are widely used low-power standard technologies developed for short-range communications in the internet-of-things. In many applications, BLE and TSCH networks may be deployed in the vicinity of one another, which may lead to Cross Technology Interference (CTI) influencing each other's performance. Both technologies utilize channel hopping to alleviate the impact of external interferences. However, having a model to quantitatively estimate the performance of coexisting TSCH and BLE networks and analyze the role of networks' configuration settings is still an open problem. To address this, we provide a probabilistic analysis of collision-free communication of coexisting BLE and TSCH networks. Moreover, a fast coexistence simulation model is developed that computes the ratio of collision-free transmissions. This model is used to investigate how the performance of the coexisting networks may deviate from the results of the probabilistic analysis. It gives the designers a proper estimation of the worst case performance degradation due to such coexistence. It is shown that severity of the impact of coexisting BLE-TSCH networks on one another depends on the setup configurations and the relative timing of the two networks. The results show that these two technologies can coexist well with collision-free ratios of more than 92.58% and 96.29% in the tested configurations for TSCH and BLE, respectively.

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.

A Latin rectangles-based TSCH scheduling and interference mitigation design

The Industrial Internet of Things (IIoT) connects a large number of industrial objects to the Internet that requires a higher level of control in terms of reliability, low power, and delay. IEEE 802.15.4e is the standard of the IIoT and includes time-synchronized channel hopping mechanisms to allow multiple communications. It controls the medium access operations using a time–frequency schedule. However, TSCH (Time Slotted Channel Hopping) specification does not specify how to build an optimized schedule. In this paper, we propose a distributed channel hopping scheme by providing an analytical model for the exploitation of Latin rectangles to avoid interference and collisions. Indeed, Latin rectangles are used to perform the scheduling process, where rows present the channel offsets and columns for slot offsets. Thus, the frequency of communication is derived using Latin rectangles, which prevents the scheduling function of nodes from considering channels already allocated in their neighborhood. Consequently, interference and multi-path fading are mitigated with more reliability and robustness. Markov chain model for the queue on every node is introduced and takes the bulk arrivals and the slot distribution into account. We analyze the efficiency of this algorithm by analytical techniques and extensive simulations for three bulk arrivals: Poisson, Bernoulli, and Geometric.

Channel Condition Based Dynamic Beacon Interval for Faster Formation of 6TiSCH Network

Industrial applications of Internet of Things (IoT) demand high reliability, deterministic latency, and high scalability with energy efficiency to the communication and networking protocols. 6TiSCH is a time slotted channel hopping (TSCH) medium access control (MAC) protocol running under the IPv6 enabled higher layer protocols for industrial IoT (IIoT). In this paper, we theoretically analyze the network formation protocol in 6TiSCH network. Analysis reveals that the performance of the 6TiSCH network degrades when a pledge (new node) joins as it increases channel congestion by allowing to transmit beacon message. On the other hand, beacon transmission is essential to expand or reorganize the present network topology. To overcome this performance tradeoff, a channel condition based dynamic beacon interval (C2DBI) scheme is proposed in which beacon transmission interval varies with channel congestion status during network formation. Channel congestion status is estimated by each joined node in distributed manner, and subsequently changes its beacon generation interval to best fit with present condition. Finally the performance of C2DBI is compared with the minimal configuration standard and few other benchmark protocols. Analytical, simulation and real testbed results show that the proposed scheme outperforms the state of the art protocols in terms of joining time and energy consumption during network formation.

TSCH and RPL Joining Time Model for Industrial Wireless Sensor Networks.

Wireless sensor networks (WSNs) play a key role in the ecosystem of the Industrial Internet of Things (IIoT) and the definition of today’s Industry 4.0. These WSNs have the ability to sensor large amounts of data, thanks to their easy scalability. WSNs allow the deployment of a large number of self-configuring nodes and the ability to automatically reorganize in case of any change in the topology. This huge sensorization capacity, together with its interoperability with IP-based networks, allows the systems of Industry 4.0 to be equipped with a powerful tool with which to digitalize a huge amount of variables in the different industrial processes. The IEEE 802.15.4e standard, together with the access mechanism to the Time Slotted Channel Hopping medium (TSCH) and the dynamic Routing Protocol for Low-Power and Lossy Networks (RPL), allow deployment of networks with the high levels of robustness and reliability necessary in industrial scenarios. However, these configurations have some disadvantages in the deployment and synchronization phases of the networks, since the time it takes to synchronize the nodes is penalized compared to other solutions in which access to the medium is done randomly and without channel hopping. This article proposes an analytical model to characterize the behavior of this type of network, based on TSCH and RPL during the phases of deployment along with synchronization and connection to the RPL network. Through this model, validated by simulation and real tests, it is possible to parameterize different configurations of a WSN network based on TSCH and RPL.

Thorough Performance Evaluation & Analysis of the 6TiSCH Minimal Scheduling Function (MSF)

IEEE Std 802.15.4-2015 Time Slotted Channel Hopping (TSCH) is the de facto Medium Access Control (MAC) mechanism for industrial applications. It renders communications more resilient to interference by spreading them over the time (time-slotted) and the frequency (channel-hopping) domains. The 6TiSCH architecture bases itself on this new MAC layer to enable high reliability communication in Wireless Sensor Networks (WSNs). In particular, it manages the construction of a distributed communication schedule that continuously adapts to changes in the network. In this paper, we first provide a thorough description of the 6TiSCH architecture, the 6TiSCH Operation Sublayer (6top), and the Minimal Scheduling Function (MSF). We then study its behavior and reactivity from low to high traffic rates by employing the Python-based 6TiSCH simulator. Our performance evaluation results demonstrate that the convergence pattern of MSF is the root cause of the majority of packet losses observed in the network. We also show that MSF is prone to over-provisioning of the network resources, especially in the case of varying traffic load. We propose a mathematical model to predict the convergence pattern of MSF. Finally we investigate the impact of varying parameters on the behavior of the scheduling function.

OSCAR: An Optimized Scheduling Cell Allocation Algorithm for Convergecast in IEEE 802.15.4e TSCH Networks.

Today’s wireless sensor networks expect to receive increasingly more data from different sources. The Time Slotted Channel Hopping (TSCH) protocol defined in the IEEE 802.15.4-2015 version of the IEEE 802.15.4 standard plays a crucial role in reducing latency and minimizing energy consumption. In the case of convergecast traffic, nodes close to the root have consistently heavy traffic and suffer from severe network congestion problems. In this paper, we propose OSCAR, an novel autonomous scheduling TSCH cell allocation algorithm based on Orchestra. This new design differs from Orchestra by allocating slots according to the location of the node relative to the root. The goal of this algorithm is to allocate slots to nodes according to their needs. This algorithm manages the number of timeslots allocated to each node using the value of the rank described by the RPL routing protocol. The goal is that the closer the node is to the root, the more slots it gets in order to maximize the transmission opportunities. To avoid overconsumption, OSCAR sets up a mechanism to adjust the radio duty cycle of each node by reducing the slots allocated to inactive nodes regardless of their position in the network. We implement OSCAR on Contiki-ng and evaluate its performance by both simulations and experimentation. The performance assessment of OSCAR shows that it outperforms Orchestra on the average latency and reliability, without significantly increasing the average duty cycle, especially when the traffic load is high.

Time Slotted Channel Hopping and ContikiMAC for IPv6 Multicast-Enabled Wireless Sensor Networks.

Smart buildings benefit from IEEE 802.15.4e time slotted channel hopping (TSCH) medium access for creating reliable and power aware wireless sensor and actuator networks (WSANs). As in these networks, sensors are supposed to communicate to each other and with actuators, IPv6 multicast forwarding is seen as a valuable means to reduce traffic. A promising approach to multicast, based on the Routing Protocol for Low Power and Lossy Networks (RPL) is Bidirectional Multicast RPL Forwarding (BMRF). This paper aimed to analyze the performance of BMRF over TSCH. The authors investigated how an adequate TSCH scheduler can help to achieve a requested quality of service (QoS). A theoretical model for the delay and energy consumption of BMRF over TSCH is presented. Next, BMRF’s link layer (LL) unicast and LL broadcast forwarding modes were analyzed on restricted and realistic topologies. On topologies with increased interference, BMRF’s LL broadcast on top of TSCH causes high energy consumption, mainly because of the amount of energy needed to run the schedule, but it significantly improves packet delivery ratio and delay compared to ContikiMAC under the same conditions. In most cases, the LL unicast was found to outperform the LL broadcast, but the latter can be beneficial to certain applications, especially those sensitive to delays.

Performance evaluation of AODV over CSMA and TSCH

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.

Performance comparison of IEEE 802.15.4 and IEEE 802.15.4e based MAC algorithm in wireless body sensor networks

One of the potential applications of Wireless Sensor Network for improving the lifestyle of human beings is Wireless Body Sensor Network (WBSN). A dedicated health monitoring system is referred to as the Ubiquitous Health Monitoring (UHM) system consisting of the Internet of Things (IoT) based access points which are made available in a cloud-based server. So, ZigBee based IEEE 802.15.4 technology is extensively used in the implementation of Medium Access Control (MAC) and Physical (PHY) layers. Hence, a comparison is provided in terms of the features of the modified IEEE 802.15.4e standard. An algorithmic approach for the MAC layer helped in regulated power consumption of the sensor node by controlling the transmission power for the packets. This is initiated in the algorithm by categorizing the packets as Delay sensitive and Delay insensitive. By regulating the channel access strategy using Medium Access Control (MAC) layer, the energy consumption of the transceiver reduces, thus improving the energy consumption of the communication system and lifetime of the sensor network. For better throughput using IEEE 802.15.4e, the performance of Deterministic and Synchronous Multi-channel Extension (DSME) is found to be trustworthy than Time Slotted Channel Hopping (TSCH).

Distributed Channel Ranking Scheduling Function for Dense Industrial 6TiSCH Networks.

The Industrial Internet of Things (IIoT) is considered a key enabler for Industry 4.0. Modern wireless industrial protocols such as the IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) deliver high reliability to fulfill the requirements in IIoT by following strict schedules computed in a Scheduling Function (SF) to avoid collisions and to provide determinism. The standard does not define how such schedules are built. The SF plays an essential role in 6TiSCH networks since it dictates when and where the nodes are communicating according to the application requirements, thus directly influencing the reliability of the network. Moreover, typical industrial environments consist of heavy machinery and complementary wireless communication systems that can create interference. Hence, we propose a distributed SF, namely the Channel Ranking Scheduling Function (CRSF), for IIoT networks supporting IPv6 over the IEEE 802.15.4e TSCH mode. CRSF computes the number of cells required for each node using a buffer-based bandwidth allocation mechanism with a Kalman filtering technique to avoid sudden allocation/deallocation of cells. CRSF also ranks channel quality using Exponential Weighted Moving Averages (EWMAs) based on the Received Signal Strength Indicator (RSSI), Background Noise (BN) level measurements, and the Packet Delivery Rate (PDR) metrics to select the best available channel to communicate. We compare the performance of CRSF with Orchestra and the Minimal Scheduling Function (MSF), in scenarios resembling industrial environmental characteristics. Performance is evaluated in terms of PDR, end-to-end latency, Radio Duty Cycle (RDC), and the elapsed time of first packet arrival. Results show that CRSF achieves high PDR and low RDC across all scenarios with periodic and burst traffic patterns at the cost of increased end-to-end latency. Moreover, CRSF delivers the first packet earlier than Orchestra and MSF in all scenarios. We conclude that CRSF is a viable option for IIoT networks with a large number of nodes and interference. The main contributions of our paper are threefold: (i) a bandwidth allocation mechanism that uses Kalman filtering techniques to effectively calculate the number of cells required for a given time, (ii) a channel ranking mechanism that combines metrics such as the PDR, RSSI, and BN to select channels with the best performance, and (iii) a new Key Performance Indicator (KPI) that measures the elapsed time from network formation until the first packet reception at the root.

Fog Assisted 6TiSCH Tri-Layer Network Architecture for Adaptive Scheduling and Energy-Efficient Offloading Using Rank-Based Q-Learning in Smart Industries

The smart industry is a significant realization of the internet of things. IPv6 over time-slotted channel hopping (6TiSCH) is the new standard that has emerged as a promising technology for industrial communications. The demanding issues of smart industries include scalability, latency, and energy efficiency. Existing studies have presented scheduling schemes for 6TiSCH-based industries. However, these works are not suitable for practical scenarios where emergencies frequently occur. Hence, this study aims to improve scalability, latency, and energy efficiency in 6TiSCH-based smart industries for practical scenarios. A new fog assisted 6TiSCH Tri-Layer architecture is designed with a network layer, smart communication layer, and cloud layer. Scalability and latency are realized by fog computing in the smart communication layer. The rough set-based root selection (R2S) algorithm improves the network layer’s energy efficiency by constructing an R2S and destination-oriented direct acyclic graph. Emergency cognizant distributed adaptive scheduling minimizes the latency for data transmission through fuzzy Bayesian learning-based parent selection and multiobjective gravitational search algorithm-based channel selection. In the fog layer, the rank-based Q-learning algorithm performs offloading to manage the energy consumption among fog nodes. Industrial data are stored in the cloud layer where they can be accessed by end users. The performance is evaluated by modeling the tri-layer 6TiSCH network in network simulator-3.26. Experiments show that the proposed work achieves satisfactory results in terms of energy consumption, latency, end-to-end delay, response time, and transmission efficiency.

Enhancing SDN WISE with Slicing Over TSCH.

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.

A Theoretical Association Time Model for IEEE 802.15.4 TSCH Networks

The Time Slotted Channel Hopping (TSCH) mode of the standard IEEE 802.15.4 provides Medium Access Control (MAC) for most Low power and Lossy Network (LLN) applications in the Internet of Things (IoT). TSCH uses a synchronized schedule with frequency diversity to allow flexible, reliable and resilient communication. The standard defines an association algorithm to allow nodes to autonomously form the network. The time required to create the network can be long, which consumes valuable energy given that nodes keep their radios on when trying to associate. In this letter, we propose a theoretical model to estimate the time required for a node to associate to one single synchronizer. This model extends and complements earlier mathematical models. Its results comply with outcomes from extensive simulation studies. This makes the proposed model a valuable tool to further investigate the time needed to form TSCH-based LLN networks.

ODeSe: On-Demand Selection for multi-path RPL networks

The Internet of Things (IoT) has become ubiquitous due to its flexibility, ease-of-use, and reduced cost. As a consequence, the industry is adopting these systems in its transformation into Industry 4.0. However, the strict Quality of Service (QoS) requirements of the industry are not met with the default best-effort provisions of the IoT. Most industrial applications require strict guarantees in terms of end-to-end network reliability and latency. For instance, consecutive packet losses can lead to communication disruptions in supply chain systems. Therefore, adaptations are being made to fulfill these requirements with the IEEE Std 802.15.4-2015 Time slotted Channel Hopping (TSCH) link-layer standard and the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) standard at the Internet Engineering Task Force (IETF). However, even by employing such industrial protocols, it is still difficult to achieve the expected QoS levels. Considering that RPL constructs and maintains a single-path from a source to a destination if there are potential issues on this path (e.g., queue overflow, variable wireless link quality) packets may suffer unexpected delays and even drops. If we consider a multi-path implementation where each node can replicate a packet into several paths, the transmission reliability improves since each packet copy is used to forward the packet information. However, uncontrolled replication can lead to network flooding, resulting in excessive power consumption. In this article, we present On-Demand Selection (ODeSe), a novel multi-path routing algorithm, which improves our previous work, the Common Ancestor (CA) algorithms, by selecting the most suitable upward forwarders. Moreover, we use the Packet Automatic Repeat reQuest, Replication and Elimination, and Overhearing (PAREO) functions in order to improve network reliability and availability. In order to control the number of relay nodes during a transmission, ODeSe forces each node of the same relay level to select the same Preferred Parent (PP) and the same Alternative Parent (AP). Thus, we address the trade-off between the total number of traversed nodes in the network and high reliability. Using the Cooja network simulator running the Contiki OS, we compare ODeSe against single-path RPL and multi-path RPL with different alternative parent selection algorithms. The results demonstrate that ODeSe outperforms single-path RPL in terms of reliability, and multi-path RPL in terms of energy consumption while maintaining a 99.14% packet delivery ratio.

Slot Bonding for Adaptive Modulations in IEEE 802.15.4e TSCH Networks

The numerous applications of industrial automation have always posed many challenges for wireless connectivity. In the last decade, IEEE 802.15.4e time-slotted channel hopping (TSCH) networks have provided high reliability and low-power operation in such challenging industrial environments. Typically, TSCH networks employ one modulation at the physical layer and are thus limited by the characteristics of the chosen modulation in terms of, among others, data rate, reliability and energy efficiency. To tackle these limitations and to improve network performance and flexibility in those challenging industrial environments, this work explores the simultaneous use of multiple modulations in a TSCH network. Traditionally, TSCH relies on fixed-duration slots, large enough to send a packet of any size given the fixed data rate. In order to avoid wasting airtime when simultaneously using modulations with different data rates, we propose the concept of slot bonding. This allows the creation of different-sized bonded slots with a duration adapted to the data rate of each chosen modulation. To analyze the proposed slot bonding technique, we formally describe the TSCH slot bonding problem in terms of optimizing the packet delivery ratio while minimizing radio on time, with the inclusion of parent selection and interference avoidance. Afterward, we propose a genetic algorithm that allows us to implement the problem and find solutions heuristically. Finally, we provide insights into preferred parent selection and modulation configurations by using this heuristic approach during extensive simulation experimentation in which the scalability advantage of slot bonding over longer fixed-duration slots is also shown.

Design and Performance Evaluation of a Hysteresis-Free On-the-Fly Scheduling Function for 6TiSCH

This article presents the design and performance evaluation of a hysteresis-free on-the-fly (HF-OTF) scheduling function for the Internet protocol version 6 over the time slotted channel hopping (TSCH) mode of IEEE 802.15.4 based Internet-of-Things (IoT) networks. The proposed HF-OTF scheduling function tackles the problem of determining the amount of network resources (i.e., timeslots and frequency channels) a node needs to request from its preferred parent node. Unlike the conventional OTF scheduling function, the proposed algorithm can determine the required bandwidth without the configuration of a hysteresis quantum. The performance evaluation of HF-OTF scheduling function shows that, under bursty traffic in a TSCH-based IoT mesh network, the proposed HF-OTF outperforms the conventional on-the-fly (OTF) and the enhanced OTF (E-OTF) with optimal hysteresis quantum settings. Specifically, the HF-OTF achieves an end-to-end packet delivery ratio 23% and 34% higher than that of the E-OTF and the conventional OTF, respectively. For the end-to-end latency performance metric, the HF-OTF exhibits an end-to-end latency that is 4% and 24% lower than that of the E-OTF and conventional OTF, respectively.

Channel assignment in TSCH-based wireless sensor networks using fuzzy logic

Recent advances in wireless sensor networks, especially in industry (IWSN), have brought important improvements to deploy a sensor network in such environments. However, there is a high interference level, noise, shadowing, and multipath fading, caused by machines, several metallic objects, which affect the link quality. Some mechanisms have been proposed to deal with these effects, such as frequency hopping and channel blacklisting, or rather, denylisting. However, there are still open issues, such as an appropriate method for managing both mechanisms to avoid similar or adjacent channels in simultaneous transmissions. In addition to denylisting with low quality channels, this paper proposes a greylist with uncertain quality channels, and a whitelist, or rather, allowlist, with good quality channels. A fuzzy logic method to classify them and insert the channels into the appropriate list is used. The mechanism was compared to the channel hopping approach employed on the time slotted channel hopping (TSCH) protocol with and without channel offset management in tree topology networks. The evaluations were made through simulations using a realistic channel model for IWSN, and the results demonstrate that the proposed approach presented better performance in terms of packet delivery rate and determinism. In the studied examples, the network with 53 devices and with the triple channel list approach presented 8% better in terms of packet delivery rate in the application layer than the blind approach (without link quality estimation) of TSCH with channel offset management (no collision), and from 51 to 59% better than approaches without the channel offset management.

Slot Reallocation and Rejection for Collision Avoidance in Autonomous TSCH Networks

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.