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Topology Management and TSCH Scheduling for Low-Latency Convergecast in In-Vehicle WSNs
Abstract
Intra-vehicle Wireless Sensor Networks (WSNs) require reliable and real-time data delivery. The Time-Slotted Channel Hopping (TSCH) mode of the IEEE 802.15.4 standard provides a reliable solution for low-power networks through guaranteed medium access and channel diversity. However, satisfying the stringent requirements of dense in-vehicle networks demands for special consideration in network formation and TSCH scheduling. This paper targets convergecast in dense in-vehicle WSNs in which all nodes can potentially directly reach the sink node. A cross-layer Low-Latency Topology management and TSCH scheduling (LLTT) technique is proposed that provides a very high timeslot utilization for the TSCH schedule and minimizes communication latency. Two techniques, namely grouped retransmission and periodic aggregation, are also exploited to increase the performance of the TSCH communications. The experimental results show that LLTT reduces the end-to-end communication latency compared to other approaches, while keeping the communications reliable by using dedicated links and grouped retransmissions.
... Farias et al. [10] proposed a queue-based algorithm for the path computation element to increase the reliability in industrial scenarios. The authors in [11] proposed a cross-layer low-latency topology management and TSCH scheduling technique that provides a very high timeslot utilization to minimize communication latency. The works in [10], [11] does not concern itself with throughput -a challenge we aim to handle in the paper. ...
... The authors in [11] proposed a cross-layer low-latency topology management and TSCH scheduling technique that provides a very high timeslot utilization to minimize communication latency. The works in [10], [11] does not concern itself with throughput -a challenge we aim to handle in the paper. Other centralized scheduling approaches in IIoT-TSCH networks worth mentioning are [12], which maximizes the energy efficiency, and [13] addressing latency issues. ...
... In the scheduling algorithms described above [10][11][12][13][14][15][16][17], the notion of fairness fails to exist. Several works in the literature have addressed fairness in the wireless networks domain [20][21][22]. ...
Time-Slotted Channel Hopping (TSCH) mode in the IEEE 802.15.4-2015 standard provides ultra-high reliability and ultra-low power consumption to sensor devices. The key feature of TSCH is the scheduling of time slots and frequencies, which falls outside the current standards. In this paper, we focus on throughput maximizing and max-min fair scheduling problems in a centralized TSCH networks. At first, a polynomial time algorithm for the throughput maximizing scheduling problem is proposed. We proceed to investigate and deliberate on some instances of the problem with their combinatorial properties. Secondly, a novel auction based scheduling algorithm that uses a first-price sealed-bid auction mechanism is presented for the throughput maximizing problem. Simulation results show that the proposed algorithm obtains a close throughput performance to the optimal one obtained through CPLEX with a much lower complexity. Moreover, we propose a novel heuristic for the max-min fair scheduling problem and demonstrate its performance through extensive simulations in terms of the total throughput and fairness varying the number of nodes, frequencies and antennas. Simulation results indicate the effectiveness of the proposed algorithm and its close performance to the optimal solution.
... Despite its effectiveness, tracking node mobility introduces significant overhead, and dynamic adaptation to the traffic pattern is not considered. A cross-layer approach optimizing topology and TSCH schedule is presented in [15] to minimize latency. While achieving high timeslot utilization, power consumption remains a concern. ...
... min a∈A c(s, a)subject to (5), (9), (13),(15) ...
The Industrial Internet of Things (IIoT) demands adaptable Networked Embedded Systems (NES) for optimal performance. Combined with recent advances in Artificial Intelligence (AI), tailored solutions can be developed to meet specific application requirements. This study introduces HRL-TSCH, an approach rooted in Hierarchical Reinforcement Learning (HRL), to devise Time Slotted Channel Hopping (TSCH) schedules provisioning IIoT demand. HRL-TSCH employs dual policies: one at a higher level for TSCH schedule link management, and another at a lower level for timeslot and channel assignments. The proposed RL agents address a multi-objective problem, optimizing throughput, power efficiency, and network delay based on predefined application requirements. Simulation experiments demonstrate HRL-TSCH’s superiority over existing state-of-art approaches, effectively achieving an optimal balance between throughput, power consumption, and delay, thereby enhancing IIoT network performance.
... 15.4e time-slotted channel hopping (TSCH) [2], a MAC protocol for low-power and lossy network (LLN), is H. Kim one of those examples. It has been designed to satisfy the growing demand for more reliable and energy-efficient LLNs in emerging Internet of Things (IoT) applications such as industrial IoT [3]- [8], in-vehicle IoT [9], [10], environmental monitoring [11]- [14], home IoT [15], and health IoT [16]- [18]. TSCH brings the benefits of time-slotted communication to LLN, and its channel hopping allows the network to become more robust to external interference or multi-path fading through frequency diversity. ...
... Attempts have been made to aggregate application layer payloads from multiple nodes into a single frame in order to increase throughput, taking advantage of the fact that packet sizes in TSCH networks are typically short [9], [30], [40]- [42]. However, aggregation size is limited to a single frame and is applicable only for the same application-layer destination whereas ASAP is a link-layer solution that allows aggregating larger number of frames and slots. ...
Time-slotted communication is used in countless protocols and systems. IEEE 802.15.4e time-slotted channel hopping (TSCH) is one of those examples which has shown remarkable performances in the literature. However, time-slotted systems have one fundamental drawback: a slot is predefined to be sufficiently long enough to accommodate one exchange of a maximum-sized packet and an acknowledgment. If most packets in the system are far smaller than the maximum, a significant amount of residue time within each slot is wasted, leading to corresponding loss in effective data rate. To address this fundamental challenge, we propose utility-based adaptation of slot-size and aggregation of packets (ASAP) which reduces wasted time in slotted systems to improve throughput and latency. ASAP consists of two orthogonal approaches: slot-length adaptation (SLA) dynamically adapts time-slot length to actual packet size distribution, and utility-based packet aggregation (UPA) transmits aggregated packets in multiple consecutive slots to maximize slot utility. We case-study ASAP in the context of TSCH. We implement ASAP on real embedded devices, and evaluate on large-scale testbeds using state-of-the-art schedulers to demonstrate a 2.21x improvement in throughput as well as a 78.7% reduction in latency.
... In [56], the authors study how to efficiently build a wireless network topology to gather data from onboard sensors in a car, where all nodes see each other, which permits a star topology. However, some links can be of poor quality. ...
... connexes sur l'utilisation de réseaux sans-fil à l'intérieur d'un pack batterie de véhicule électrique D'autres ont déjà commencé à étudier cette possibilité. Alonso et al.[76] ont évalué les performances de différentes antennes à l'intérieur d'une enceinte batterie, et recommandent d'utiliser des antennes PIFA dans la bande des 2,4GHz.La chaîne de traction, et en particulier le moteur du véhicule, émet des rayonnements électromagnétiques, mais qui se trouvent en dessous des 100kHz[75], et ne devraient donc pas interférer avec le réseau sans-fil.Dans[56], les auteurs étudient un réseau sans fil à bord d'un véhicule, où tous les noeuds sont à portée les uns des autres, et préconisent d'utiliser une topologie en arbre à 2 niveaux (en plus du noeud racine), afin d'utiliser les chemins les plus fiables. Ils suggèrent aussi d'utiliser un mécanisme d'agrégation des données aux noeuds intermédiaires.b.3 performance d'un réseau iot dans un pack batterie de véhicule électriqueAfin de connaître précisément la qualité moyenne des liens réseau avec la technologie choisie à l'intérieur d'un pack batterie, mais aussi de connaître l'impact de la position et des potentielles interférences avec d'autres utilisateurs de la bande des 2,4GHz, de nombreux tests ont été réalisés. ...
The traction battery of an electric vehicle is a key component. It is also a sensitive system for which the voltage and temperature of the cells it is made of must be kept in a given working range. This is the role of the Battery Management System (BMS). The BMS is made of subsystems, called Cells Sensor Units (CSU), which supervise the cells and report their state to a central component named Master Control Unit (MCU). Moreover, they are in charge of performing battery cells balancing, as cells do not have exactly equal capacity, and imbalance between them may appear with usage over time, when they are wired in series. In current BMS implementations, this periodic communication is performed through wires. In this work, we have studied the possibility to replace this wired communication with a wireless medium, by using standardized protocol stack of the Internet of Things (IoT).After evaluating different communication protocols, we have chosen to base our work on IEEE Std. 802.15.4-2015 Time Slotted Channel Hopping (TSCH). We first have tested this protocol within an battery pack environment, through experimentation, using actual wireless capable nodes. Thus, we were able to determine that the radio links quality is high, that the car's engine electromagnetic emissions should not interfere with the wireless communication, and that most of the problems would come from other users of the 2.4GHz band, and Wi-Fi in particular. We then have sought to determine what the most adapted topology and scheduling management strategies for such a scenario are. To this end, we have proposed two algorithms for centralized network management, based on the Linear Programming and Simple Descent techniques, in order to optimize the topology and slotframe. Considering that many parameters are involved in this optimization work, we have therefore evaluated our algorithms under various setups, and used the results to determine what the best values for these algorithms parameters are. Moreover, we have proposed a routing protocol, which makes use of these algorithms in an iterative way to compute the best possible topology and slotframe, and which allows to propagate the decisions of the centralized network manager to the nodes. This protocol, heavily inspired by the Routing Protocol for Low-Power and Lossy Networks (RPL), relies on periodic messages and asynchronous events to keep the wireless nodes up-to-date with the latest network manager decision. Finally, we have tested this solution with a network of objects in a vehicular environment.
... Therefore, to reduce the power consumption, the nodes could be put into sleep mode. The issue is how to design the schedule for each node so that the overall WSN power consumption is minimized [12]. Moreover, the scheduling algorithm may interleave the transmissions without or less error. ...
Wireless Sensor Networks (WSNs) have been broadly applied in many fields such as industry, agriculture, event detection & monitoring, time critical applications and research to facilitate the gathering and distribution of information. The WSNs consist of many low cost sensor nodes. Each sensor node consists of a microprocessors and radio transceivers and can only be equipped with limited resources like power, bandwidth etc. Fuzzy logic is a recent approach to tackle few of the important decision making aspects of WSNs. Fuzzy sets provides a robust mathematical solutions for dealing with real-world problems and non-statistical uncertainty. The paper reviews few fuzzy set based solutions for WSNs applications.
... Tavakoli et al. proposed a cross-layer low-latency topology management and TSCH scheduling technique, which employs LQI as the quality metric directly. Experimental results show that it reduces the end-to-end communication latency compared to other approaches while keeping communications reliable [33]. ...
Multichannel communication has great potential in environments with unknown interference patterns. However, existing link quality metrics and models are generally established and verified under a single-channel scenario, which does not consider the impacts of radio interference and channel change. Therefore, it is hard to directly judge whether these metrics and models are still valid under a multichannel scenario. This paper empirically analyzes the applicability of popular link quality metrics and models in multiple channels with different interference levels. Results show that the link quality estimation (LQE) capability of traditional metrics will be affected by the interference level of the channel, which makes the conclusions obtained under a single-channel scenario no longer valid. Meanwhile, traditional LQE models are basically not adaptive to radio interference and channel change. They are only valid for channels with similar interference under which they are modeled. If these models are directly used under a multichannel scenario, the link quality will be overestimated inevitably. In other words, traditional LQE metrics and models cannot be directly used in the multichannel scenario. It is necessary to deeply analyze the statistical characteristics of popular link quality metrics in multiple typical channels and design channel and interference adaptive metrics and models to support effective multichannel communication.
... A star topology may be used to connect all sensor nodes. However, the high density of sensor nodes can lead to high network interference and latency in a contention-based MAC protocol [173]. The TSCH protocol provides both time and frequency diversity for transmissions boosting the network reliability [55]. ...
p> Wireless Sensor Networks (WSNs), which are enablers of the Internet of Things (IoT) technology, are typically used en-masse in widely physically distributed applications to monitor the dynamic conditions of the environment. They collect raw sensor data that is processed centralised. With the current traditional techniques of state-of-art WSNs programmed for specific tasks, it is hard to react to any dynamic change in the conditions of the environment beyond the scope of the intended task. To solve this problem, a synergy between Software-Defined Networking (SDN) and WSNs has been proposed. This paper aims to present the current status of Software-Defined Wireless Sensor Network (SDWSN) proposals and introduce the readers to the emerging research topic that combines Machine Learning (ML) and SDWSN concepts, also called ML-SDWSNs. ML-SDWSN grants an intelligent, centralised and resource-aware architecture to achieve improved network performance and solve the challenges currently found in the practical implementation of SDWSNs. This survey provides helpful information and insights to the scientific and industrial communities, and professional organisations interested in SDWSNs, mainly the current state-of-art, ML techniques, and open issues.</p
... Centralized approaches. One approach for interference mitigation consists in collecting information at the network coordinator, who then derives a corresponding mitigation strategy [7,31,32,34,40,44,47,49,53]. To handle internal interference, the network coordinator (e.g. the root node of the RPL tree in a LLN) first collects connectivity information about all nodes in the network. ...
... A star topology may be used to connect all sensor nodes. However, the high density of sensor nodes can lead to high network interference and latency in a contention-based MAC protocol [173]. The TSCH protocol provides both time and frequency diversity for transmissions boosting the network reliability [55]. ...
Wireless Sensor Network (WSN), which are enablers of the Internet of Things (IoT) technology, are typically used en-masse in widely physically distributed applications to monitor the dynamic conditions of the environment. They collect raw sensor data that is processed centralised. With the current traditional techniques of state-of-art WSN programmed for specific tasks, it is hard to react to any dynamic change in the conditions of the environment beyond the scope of the intended task. To solve this problem, a synergy between Software-Defined Networking (SDN) and WSN has been proposed. This paper aims to present the current status of Software-Defined Wireless Sensor Network (SDWSN) proposals and introduce the readers to the emerging research topic that combines Machine Learning (ML) and SDWSN concepts, also called ML-SDWSNs. ML-SDWSN grants an intelligent, centralised and resource-aware architecture to achieve improved network performance and solve the challenges currently found in the practical implementation of SDWSNs. This survey provides helpful information and insights to the scientific and industrial communities, and professional organisations interested in SDWSN, mainly the current state-of-art, ML techniques, and open issues.
... Both AMUS and LaDiS take into account that children should be scheduled before their parents in order to benefit from packet aggregation. The authors of LLTT [18] acknowledge this as well, but propose a practical periodic aggregation at the network layer instead. They also use shared time slots in order to boost the performance of LLTT. ...
The Industrial Internet of Things (IoT) has gained a lot of momentum thanks to the introduction of Time Slotted Channel Hopping (TSCH) in IEEE 802.15.4. At last, we can enjoy collision-free, low-latency wireless communication in challenging environments. Nevertheless, the fixed size of time slots in TSCH provides an opportunity for further enhancements. In this paper, we propose an enhanced centralized TSCH scheduling (ECTS) algorithm with simple packet aggregation while collecting data over a tree topology. Having in mind that the payload of a sensor node is rather short, we attempt to put more than one payload in one packet. Thus, we occupy just one cell to forward them. We investigated the schedule compactness of ECTS in Matlab, and we evaluated its operation, after implementing it in Contiki-NG, using Cooja. Our results show that ECTS with packet aggregation outperforms TASA in terms of slotframe duration and imposes fairness among the nodes in terms of latency. A validation exercise using real motes confirms its successful operation in real deployments.
... Both AMUS and LaDiS take into account that children should be scheduled before their parents in order to benefit from packet aggregation. The authors of LLTT [18] acknowledge this as well, but propose a practical periodic aggregation at the network layer instead. They also use shared time slots in order to boost the performance of LLTT. ...
The Industrial Internet of Things (IoT) has gained a lot of momentum thanks to the introduction of Time Slotted Channel Hopping (TSCH) in IEEE 802.15.4. At last, we can enjoy collision-free, low-latency wireless communication in challenging environments. Nevertheless, the fixed size of time slots in TSCH provides an opportunity for further enhancements. In this paper, we propose an enhanced centralized TSCH scheduling (ECTS) algorithm with simple packet aggregation while collecting data over a tree topology. Having in mind that the payload of a sensor node is rather short, we attempt to put more than one payload in one packet. Thus, we occupy just one cell to forward them. We investigated the schedule compactness of ECTS in Matlab, and we evaluated its operation, after implementing it in Contiki-NG, using Cooja. Our results show that ECTS with packet aggregation outperforms TASA in terms of slotframe duration and imposes fairness among the nodes in terms of latency. A validation exercise using real motes confirms its successful operation in real deployments.
... Although the solutions proposed in these studies can optimize the latency and channels in the convergecast operation, the system performance is still degraded remarkably by interference, such as noise or other devices that affect the connectivity and induce low reliability on the ISM channels. Some techniques have been directly applied to improve the convergecast reliability, such as allowing retransmissions [20], [21] or constructing multiple routing choices [22]. Nevertheless, these methods might only enhance the convergecast reliability to some extent but generally can not maximize the reliability under stringent latency constraints. ...
The performance of data aggregation in industrial wireless communications can be degraded by environmental interference on Industrial Scientific Medical (ISM) channels. In this paper, the opportunistic spectrum access capability of cognitive radio (CR) was applied to enable devices to share primary channels with the aim of enhancing the transmission performance of the WirelessHART network. We considered a linear convergecast network, where the packets generated at each device were routed to the gateway (GW) through the aid of neighboring devices. The solar-powered cognitive access points (CAPs) were deployed to improve the successful transmission probability of the packets among field devices by opportunistically allocating the primary channels to the devices for data transmissions. In this paper, we formulate the scheduling problem of long-term throughput maximization as a framework of a Markov decision process by considering the constraints of the minimum delay, the number of required ISM channels, and the harvested energy at the CAPs. Then, we propose a deep reinforcement learning-based scheduling scheme to optimally assign multiple ISM and primary channels to the field devices in each superframe to maximize the received packets at the GW. The simulation results confirmed the superiority of the proposed scheme compared to existing methods.
... Many distributed TSCH scheduling algorithms are proposed based on the basic 6top random cell selection [20,21]. In essence, Karaagac et al. [22] presented an overview of how 6TiSCH architecture and an experimental study that represents the deterministic behavior in 6TiSCH networks. ...
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 neighbourhood. 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.
... In [20], the authors study how to efficiently build a wireless network topology to gather data from onboard sensors in a car, where all nodes see each other, which permits star topology. However, some links can be of poor quality. ...
The Battery Management System of an Electric Vehicle is a system designed to ensure safe operation of the battery pack, and report its state to other systems. It is a distributed system, and the communication between its sub-modules is performed through wired buses. In this article, we study the opportunity to use a wireless technology named IEEE Std 802.15.4 Time Slotted Channel Hopping, a standardized protocol for low power and lossy networks. We first describe the real-world experiments we did to measure the link quality, at Medium Access Control layer, for wireless nodes placed inside an EV battery pack. Then, we propose two topology management and scheduling strategies using techniques named Linear Programming and Simple Descent, based on the results obtained in the experiments. Their goal is to achieve efficient data transfer while complying to the battery management constraints.
... Centralized and M. Angurala, M. Bala and Sukhvinder Singh Bamber Egyptian Informatics Journal xxx (xxxx) xxx distributed techniques consider conditions such as failures in the medium access, collisions in the wireless medium, traffic and many more. R. Tavakoli et al. [26] proposed Time-Slotted Channel Hopping (TSCH) and cross layer Low-Latency topology management to provide high timeslot utilization for the TSCH schedule with minimum latency. M. Vecchio et al. [27] proposed an integrated optimization framework by means of topology design to improve the convergence speed of a distributed consensus algorithm. ...
In this contemporary era, recent developments have seen proliferation of methods on improving energy utilization for wireless sensor networks. Although the proposed methods can mitigate the problem of rapid battery depletion to some extent, the lifespan of sensor nodes is still a biggest constraint. Many studies conducted so far have shown continuous network functions with the help of external harvesting techniques. However, these provide low output because of the limitation on the energy capturing devices. Therefore, energy limitation strongly restricts the usage of wireless sensor nodes. This paper aims to provide high recharging rates and better energy efficiency by proposing a three-step mechanism, which is an extension of our existing proposed work J-ERLB (Joint Energy Replenishment and Load Balancing). In a three-step mechanism, topology selection followed by recharging and load balancing are combined together to prolong the lifetime of sensor nodes. Topology selection is performed by implementing J-ERLB on various topologies like ring, star, and cluster. Further, taking advantage of Unmanned Aerial vehicle (UAV) we focus on data collection and high-rate recharging. We have implemented System on Chip (SoC) integrated chip on UAV to achieve goal of perpetual network operations. Finally, the effectiveness of proposed mechanism is tested by comparing its numerical outcomes with existing J-ERLB and J-MERDG (Joint Mobile Energy Replenishment and Data Gathering) techniques. The overall throughput for 3SM is doubled in comparison with the existing techniques, whereas the average remaining energy shows 6 times better savings for the proposed solution in comparison to the existing J-ERLB and J-MERDG when varying data rates is applied.
... They make a central node schedule slotframes for all nodes according to global information on traffic load and conflict relation among nodes. LLTT [33] also builds a fixed TSCH network to reduce end-to-end latency. However, these schemes assume fixed routing topology and constant traffic load, which does not hold in the real world. ...
... In [17], a clustering algorithm based on Prim's minimum-spanning-tree was proposed, which is not suitable for crossroads in urban road environments. In [18], a periodic clustering method that uses effectively available bandwidth was proposed to reduce the delay caused by clustering. However, this method is only suitable for the cluster mechanism of static network nodes, not for dynamic vehicle networks [19]. ...
The cellular vehicle-to-everything (C-V2X) networks support diverse kinds of services such as traffic management, road safety, and sharing data. However, the safety issues cannot be ignored in the process of information transmission. In this paper, a joint clustering and blockchain scheme is proposed for real-time information security transmission to prevent some vehicles from sending malicious messages to disrupt the traffic order at the crossroads in C-V2X networks. In this scheme, the dynamic stability of the cluster is maintained by updating the trust value of the vehicle nodes, which can improve the real-time and accuracy of the information transmission. The modified Webster algorithm is presented to divert the traffic flow so as to reduce the traffic jams at the crossroads. Meanwhile, the blockchain technology is utilized to establish a vehicle trust management mechanism in C-V2X, which can avoid malicious tampering of vehicle information during information sharing and ensure the safety of vehicle information communication. The simulation results of the Veins simulation platform are provided to demonstrate the effectiveness of the proposed algorithm and verify that the proposed scheme can guarantee the security of real-time information transmission.
... Due to its harmonious features with the native protocol, WCAN chances in succeeding and predominating the I2V communication are strong. Likewise, the compatibility between heterogeneous IVNCSs with wireless sensor networks is expected to reduce wiring [71]. ...
The in-vehicular networked control system is among the most critical embedded processes. The controller area
network (CAN) has prevailed intra-vehicle communication for decades. Meanwhile, requirements of future transportation
systems are expected to emphasise the in-vehicle communication complexity, which endangers the reliability/safety of the
intelligent navigation. At first, this study reviews the recent solutions proposed to overcome the CAN expanding complexity.
Challenges that tomorrow's intelligent vehicles may raise for CAN reliability are investigated. The comprehensive coverage of
current research efforts to remove the impact of these challenges is presented. Further, the in-vehicle system reliability of future
automated vehicles is also related to the fault diagnosis performances. Hence, different classes of system-level diagnosis
strategies are compared relatively to the requirements of automotive embedded networks. Furthermore, to thoroughly cover
CAN reliability engineering issues, focus is given to the automotive validation techniques. The hardware in the loop, real-time
analysis and computer-aided-design tools intervene in various phases along the in-vehicular network life cycle. Parameters that
stand behind the efficiency and accuracy of these techniques in validating the new generation of vehicles are analysed. The
authors finally draw some deductive predictions about the future directions related to the reliability of the intelligent
transportation system in-vehicular communication.
... Time-synchronized channel hopping (TSCH) is among the most popular standards in the scope of WSAN to support real-time data traffic. Salient features, such as time-division multiple-access (TDMA), centralized scheduling and frequency diversity, have gradually underpinned its adoption in a number of application domains, from factory automation and process control [9] to vehicles [16], paving the way for the Industrial Internet of Things (IIoT) and Industry 4.0 [15]. ...
With the scope of Industry 4.0 and the Industrial Internet of Things (IIoT), wireless technologies have gained momentum in the industrial realm. Wireless standards such as WirelessHART, ISA100.11a, IEEE 802.15.4e and 6TiSCH are among the most popular, given their suitability to support real-time data traffic in wireless sensor and actuator networks (WSAN). Theoretical and empirical studies have covered prioritized packet scheduling in extenso, but only little has been done concerning methods that enhance and/or guarantee real-time performance based on routing decisions. In this work, we propose a greedy heuristic to reduce overlap in shortest-path routing for WSANs with packet transmissions scheduled under the earliest-deadline-first (EDF) policy. We evaluated our approach under varying network configurations and observed remarkable dominance in terms of the number of overlaps, transmission conflicts, and schedulability, regardless of the network workload and connectivity. We further observe that well-known graph network parameters, e.g., vertex degree, density, betweenness centrality, etc., have a special influence on the path overlaps, and thus provide useful insights to improve the real-time performance of the network.
... A tangible advantage of these solutions is the ability to cover larger areas, at the price of an increased communication latency. Multi-hop WSNs often rely on a multi-level tree topology that stems from a root node [45]. As a matter of fact, mesh topologies also exist where routes between nodes are (somehow) arbitrary, but they are less common in practice and will not be analyzed in this work. ...
Reliability, power consumption, and latency are the three main performance indicators of wireless sensor networks. Time slotted channel hopping (TSCH) is a promising technique introduced in the IEEE 802.15.4 standard that performs some steps ahead in the direction of the final dream to meet all the previous requirements at the same time. In this article, a simple and effective mathematical model is presented for TSCH that, starting from measurements performed on a real testbed, permits to characterize both the network and the surrounding environment. To better characterize power consumption, an experimental measurement campaign was purposely performed on OpenMote B devices. The model, which was checked against a real 6TiSCH implementation, can be employed to predict network behaviour when configuration parameters are varied, in such a way to satisfy different application contexts. Results show that, when one of the three above indices is privileged, unavoidably there is a worsening of the others.
... A motivating example is wireless in-vehicle networks. Since TSCH is designed for reliable industrial applications, it is considered as a promising option for communication of various devices (sensors, actuators, and microprocessors) within a vehicle [2]. However, there are many cases (e.g., behind traffic lights or in the parking lots) in which several vehicles are very close to one another in a period of time. ...
Low-power Wireless Sensor Networks (WSNs) play a key role in realization of the Internet-of-Things (IoT). Among others, Time Slotted Channel Hopping (TSCH) is a Medium Access Control (MAC) operational mode of the IEEE 802.15.4 standard developed for communications in short range IoT networks. TSCH provides high level reliability and predictability by its channel hopping mechanism and time division channel access nature. In many applications, a number of TSCH networks may coexist in the same neighborhood. Several vehicles close to one another, each including a TSCH network for its in-vehicle communications, serve as an example. Since such networks are running independent of one another, they are not expected to be synchronized in time, and they are not scheduled to operate in exclusive frequency channels. This may lead to inter-TSCH interferences deteriorating the reliability of the networks, which is an important requirement for many IoT applications. This paper analyzes the impact of multiple asynchronous TSCH networks on one another. An analytical model is developed that estimates the chance of such interferences, and the expectation of the number of affected TSCH channels when a number of them are in the vicinity of one another. The developed model is verified using extensive simulations and realworld experiments. Also, a scalable and fast multi-TSCH coexistence simulator is developed that is used to get insight about coexistence behaviors of any number of TSCH networks with various configurations.
... According to the above analysis and related literatures [12][13][14], some empirical values can be given. In order to minimize the time average power consumption of the system, we can describe the problem as the following optimization problem: ...
In the Industrial Internet of Things (IIoT), it is an urgent task to reduce power loss and enhance energy efficient through reasonable allocation of resources. Inspired by time slot channel frequency hopping, this paper puts forward a dynamic allocation model for time and power resources. Based on the proposed model, a dynamic resource allocation algorithm was designed to reduce energy consumption. In addition, a power and time allocation algorithm was developed to maximize the energy efficiency of the system. The workflows of the two algorithms were introduced in details. Simulation results show that both dynamic resource allocation algorithm could reduce the energy loss of the communication system, while ensuring the stability of the data queue. The research findings help to promote the performance of communication systems in different scenarios of the IIoT.
... To minimize communication delays and make full use of time slots in In-Vehicle WSNs, the authors of [18] proposed a cross-layer low-latency topology management method that adapts an optimized graph isomorphism strategy, then, the schedule generator provides low delivery latency by adopting the selected topology. The work in [19] presented a new network model that considered a multidimensional scheduling space as flow-link-channel-slot tuples. ...
As a key characteristic for industrial wireless sensor networks, deterministic scheduling aims to ensure that real-time data flows arrive at destination devices under deadline constraints by allocating necessary communication resources, such as time slots and channels. Current research on deterministic scheduling mainly focuses on how to obtain a feasible scheduling solution. However, optimizing average transmission delays under deterministic flow deadlines is rarely considered when multiple scheduling solutions exist. To address this issue, in this paper we propose two scheduling algorithms: branch and bound based on link conflict classification, and least conflict degree first. The prior algorithm obtains optimal schedulable ratio by constructing a search tree and adopting necessary conditions of scheduling. The latter algorithm dynamically adjusts the scheduling order of flows to distribute channels in a heuristic manner, and achieves approximate optimal schedulable ratio in a short time with low complexity. Simulation results show that both of the proposed algorithms effectively reduce the average transmission delays of real-time data flows while guaranteeing that all flows are delivered before their deadlines.
... Although these approaches provide theoretically optimal scheduling, in practice, they suffer significant control overhead to update network information for the root node and slow schedule adjustment when topology is changed. For this reason, centralized scheduling methods are more suitable for a static environment where routing topology rarely changes [32]. ...
Although low-power lossy network (LLN), at its early stage, commonly used asynchronous link layer protocols for simple operation on resource-constrained nodes, development of embedded hardware and time synchronization technologies made Time-Slotted Channel Hopping (TSCH) viable in LLN (now part of IEEE 802.15.4e standard). TSCH has the potential to be a link layer solution for LLN due to its resilience to wireless interference (e.g., WiFi) and multi-path fading. However, its slotted operation incurs non-trivial cell scheduling overhead: two nodes should wake up at a time-frequency cell together to exchange a packet. Efficient cell scheduling in dynamic multihop topology in wireless environments has been an open issue, preventing TSCH's wide adoption in practice. This work introduces ALICE, a novel autonomous link-based cell scheduling scheme which allocates a unique cell for each directional link (a pair of nodes and traffic direction) by closely interacting with the routing layer and using only local information, without any additional communication overhead. We implement ALICE on Contiki and evaluate its effectiveness on the IoT-LAB public testbed with 68 nodes. ALICE generally outperforms Orchestra (the state-of-the-art method) and even more so under heavy traffic and high node density, increasing throughput by 2 times with 98.3% reliability and reducing latency by 70%, route changes by 95%, and radio duty cycle by 35%. ALICE can serve as an autonomous scheduling framework, which paves the way for TSCH-based LLN to go on.
... In the literature, a number of applications of 6TiSCH are present. However, most of them only consider monitoring applications [9] [10] [11]. How to use the 6TiSCH networks in control applications remains an unresolved issue. ...
IETF 6TiSCH is emerging as a promised open-standard for industrial internet of things (IIoT). With employing Time Slotted Channel Hopping (TSCH) mode, 6TiSCH can meet critical requirements in the industrial sector such as reliability, determinism and real time. 6TiSCH is currently focusing on monitoring applications. This paper considers its applicability in industrial control, in which sensor and actuator are coexistent in the network. We first investigate applicable wireless sensor-actuator models based on 6TiSCH. Then, an efficient data transmission scheme between sensor and actuator is proposed. Through simulation results, we show that our solution achieves a significant improvement in terms of end-to-end latency and energy consumption compared to the bursty transmission in the 6TiSCH networks.
This article presents a novel centrality-driven gateway designation framework for the improved real-time performance of low-power wireless sensor networks (WSNs) at system design time. We target time-synchronized channel hopping (TSCH) WSNs with centralized network management and multiple gateways with the objective of enhancing traffic schedulability by design . To this aim, we propose a novel network centrality metric termed minimal-overlap centrality that characterizes the overall number of path overlaps between all the active flows in the network when a given node is selected as gateway. The metric is used as a gateway designation criterion to elect as a gateway the node leading to the minimal number of overlaps. The method is then extended to multiple gateways with the aid of the unsupervised learning method of spectral clustering . Concretely, after a given number of clusters are identified, we use the new metric at each cluster to designate as cluster gateway the node with the least overall number of overlaps. Extensive simulations with random topologies under centralized earliest-deadline-first (EDF) scheduling and shortest-path routing suggest our approach is dominant over traditional centrality metrics from social network analysis, namely, eigenvector , closeness , betweenness , and degree . Notably, our approach reduces by up to the worst-case end-to-end deadline misses achieved by classical centrality-driven gateway designation methods.
The wireless sensor network (WSN) can be used in many applications, especially electrical distribution systems (EDS). The power transmitted on the distribution line has a huge impact by environmental changes like temperature, humidity etc., leading to problems like voltage sag, voltage swell, and changes in the power frequency. These effects affect the devices that are driven by power, for large scale industries, the impact is so heavy. To monitor the imbalance in the transmitting power, the sensor nodes are used to monitor the PQ issues. Then the monitored information needs to be transmitted to the monitoring centre; in this flow, communication plays an important role in minimising the cost of the WSN. For monitoring the PQ, first, the sensor nodes are deployed in the appropriate area. Deploying the sensor node anywhere on the sensor node is impossible. Therefore, the node in this article is used on the feed circuit, which is mounted on the insulator for protection from the power supply. Then the bald eagle search (BES) optimisation based ZigBee communication protocol (ZBES) is designed to transmit the retrieved data from the sensor node to the monitoring station. The designed protocol will make the cost efficient and energy saving path to transmit data to the edge node. The performance of the proposed routing protocol is compared with the ZigBee and other routing protocols.
Escalation in the use of Internet-of-Things (IoT) devices gives rise to the number of networks operating in the license-free 2.4 GHz frequency band. This prepares the ground for networks to experience interference from coexisting networks and thus performance degradation. Time Slotted Channel Hopping (TSCH), as an operational medium access mode of the IEEE 802.15.4 technology, was introduced to ensure the reliability of IoT networks when they undergo coexistence. It uses frequency hopping as a protective strategy against long-term packet losses due to interference. However, when several independent TSCH networks coexist, they are prone to interfere with one another. In extreme scenarios, coexisting TSCH networks may block links of one another for an extended duration of time, leading to application failure. In this paper, we propose a novel technique called time hopping to secure the reliability of coexisting TSCH networks. The developed technique synchronously and periodically alters the timing of nodes within a TSCH network to avoid coexisting TSCH networks from getting stuck in extreme coexistence scenarios and long-term continuous collisions. We evaluate the effectiveness of the proposed technique through extensive simulations. The results clearly show that the proposed time hopping technique substantially improves the worst-case inter-network collision ratio, with as much as 50% improvement in some tested scenarios. The implementation of the technique is very simple, with almost no communication or computation overhead for the constrained wireless nodes; it is done and tested on real nodes for proof of concept.
In order for real-time wireless networks (RTWNs) to achieve desired Quality of Service (QoS) for real-time sensing and control, effective packet scheduling algorithms play a critical role, especially in the presence of unexpected disturbances. Most existing solutions in the literature focus either on static or dynamic schedule construction to meet the desired QoS requirements, but have a common assumption that all wireless links are reliable. However, this assumption is not realistic in real-life settings. To address this drawback, this paper introduces a novel reliable dynamic packet scheduling framework, called RD-PaS. RD-PaS can not only construct static schedules to meet both the timing and reliability requirements of end-to-end flows in RTWNs, but also construct new schedules rapidly to handle abruptly increased network traffic induced by unexpected disturbances while minimizing the impact on existing network flows. Through judiciously sharing time slots among tasks, RD-PaS can significantly reduce the number of required time slots to meet the system reliability requirement and improve the network throughput. The functional correctness of the RD-PaS framework has been validated through its implementation and deployment on a real-life RTWN testbed. Extensive simulation-based experiments have also been performed to evaluate the effectiveness of RD-PaS, especially in large-scale network settings.
In IEEE 802.15.4 standard for low-power low-range wireless communications, only one channel is employed for transmission which can result in increased energy consumption, high network delay and poor packet delivery ratio (PDR). In the subsequent IEEE 802.15.4-2015 standard, a Time-slotted Channel Hopping (TSCH) mechanism has been developed which allows for a periodic yet fixed frequency hopping pattern over 16 different channels. Unfortunately, however, most of these channels are susceptible to high-power coexisting Wi-Fi signal interference and to possibly some other ISM-band transmissions. This interference manifests itself in the form of the presence/absence of other devices with either or both static and dynamic channel selection policies. In order to isolate channels with undesirable conditions, blacklisting mechanisms are defined to adapt the channel hopping process. However, the existing solutions which form blacklists unrealistically assume that the statistical model of the external interference remains fixed, and do not vary over time. In this paper, we realistically assume that the impact of external interferes on 802.15.4 may generally follow a non-stationary pattern, and accordingly formulate the adaptive channel hopping problem as a Dynamic Multi-Armed Bernoulli Bandit (Dynamic MABB) process from the machine learning theory. We then propose an online learning algorithm with track-ability properties for computing an adaptive hopping policy. Simulations confirm that when the statistics of the external interference has a switching regime, the proposed solution outperforms the previous schemes in terms of both energy efficiency as well as two important KPIs for TSCH-based networks, i.e., PDR and latency.
Although wireless networks are becoming a fundamental infrastructure for various control applications, they are inherently exposed to network faults such as lossy links and node failures in environments such as mining, outdoor monitoring, and chemical process control. In this paper, we propose a proactive fault-tolerant mechanism to protect the wireless network against temporal faults without any explicit network state information for mission-critical control systems. Specifically, the proposed mechanism optimizes the multiple routing paths, link scheduling, and traffic generation rate such that it meets the control stability demands even if it experiences multiple link faults and node faults. The proactive network relies on a constrained optimization problem, where the objective function is the network robustness, and the main constraints are the set of the traffic demand, link, and routing layer requirements. To analyze the robustness, we propose a novel performance metric called stability margin ratio, based on the network performance and the stability boundary. Our numerical and experimental performance evaluation shows that the traffic generation rate and the delay of wireless networks are found as critical as the network reliability to guarantee the stability of control systems. Furthermore, the proposed proactive network provides more robust performance than practical state-of-the-art solutions while maintaining high energy efficiency.
Conserving energy is probably the most important requirement in wireless sensor networks. In TSCH, this goal is obtained by subdividing time into slots, and by switching the communication interface of Internet of Things devices (frequently referred to as motes) off when, at any given time, neither transmissions nor receptions are scheduled for them. Nevertheless, in this kind of networks a considerable amount of energy may still be wasted due to idle listening. This occurs every time a cell is scheduled for frame reception but no transmissions are performed in the related slot and channel.
The IEEE 802.15.4 and ZigBee applications are widely used specifications for the design of Wireless Sensor Networks (WSNs), Among the different available network topologies, cluster-tree networks are pointed out as the most suitable to implement large-scale WSNs, becoming an attractive solution for monitoring applications. However, cluster-tree networks may suffer from high end-to-end communication delay and also from network congestion. Thus, the selection of efficient network formation schemes and the definition of adequate communication structures are relevant research issues. In this context, this paper proposes an efficient mechanism to improve convergecast traffic in large-scale cluster-tree wireless sensor networks. The main idea combines a network formation process driven by the data generation characteristics of individual nodes and an efficient allocation scheme of the active periods, in order to improve typical convergecast message streams generated by the sensor nodes. Simulation results show that efficient network configuration approaches can significantly reduce end-to-end communication delays and decrease the overall network congestion.
Load balancing and energy conservation techniques are one of the significant constraints in the design of in software defined wireless sensor network (SD-WSN). Usually, clustering method helps the network in the minimum utilization of energy that results in enhancing network lifetime. Moreover, various nodes in the multi-hop network that are near to the base station drain their battery very quickly thus lead to creating hot spot problem in a network. To overcome such constraints, this paper proposes a multilayer clustering architecture for selection of forwarding node, rotation of cluster head, and inter and intra-cluster routing communication. The proposed scheme efficiently tackle the rotation of forwarder node by incorporating routing table (table list) at each node. Moreover, the rotation is performed by the consideration of two threshold levels of the residual energy of a node. Also, the exploitation of decision maker node, forwarder node, backup forwarder node, and non-forwarder node enhancing the routing strategy in a network. The performance of the proposed scheme is tested and evaluated by C programming language. The results show that the proposed scheme successful achieve better results than TLPER and EADUC in energy consumption per node, end-to-end communication, hop count in cluster formation.
Emerging Industrial Internet of Things applications, such as smart factories, require reliable communication and robustness against interference from colocated wireless systems. To address these challenges, frequency-hopping spread spectrum has been used by different protocols, including IEEE802.15.4-2015 TSCH. Frequency-hopping spread spectrum can be improved with the aid of blacklists to avoid bad frequencies. The quality of channels in most environments shows significant spatial-temporal variation, which limits the effectiveness of simple blacklisting schemes. In this article, we propose an enhanced blacklisting solution to improve the TSCH protocol. The proposed algorithms work in a distributed fashion, where each pair of receiver/transmitter nodes negotiates a local blacklist, based on the estimation of packet delivery ratio. We model the channel quality estimation as a multiarmed bandit problem and show that it is possible to create blacklists that provide results close to optimal without any separate learning phase. The proposed algorithms are implemented in OpenWSN and evaluated through simulations in 2 different scenarios with about 40 motes and experiments using an indoor testbed with 40 TelosB motes.
Time-Slotted Channel Hopping (TSCH) is a part of an emerging IEEE 802.15.4e standard to enable deterministic low-power mesh networking. It promises to pave the way to the future Internet of (Important) things by offering high reliability and low latency for wireless industrial applications. Nonetheless, the standard only provides a framework but it does not mandate a specific scheduling mechanism. In this paper, we propose a centralized Adaptive MUlti-hop Scheduling method (AMUS) based on the latest TSCH MAC. AMUS first enables sequential multi-hop scheduling to provide low latency guarantee for time critical applications. Secondly, the novel tentative cell allocation method allocates additional resources to vulnerable links such that possible MAC retransmissions can be accommodated within the same slotframe, hence significantly reducing the delay caused by interference or collisions. Last but not least, the battery power of the node can be further conserved by adopting the proposed End-of-Q notification mechanism. Preliminary simulation results have confirmed that AMUS outperforms other popular scheduling algorithms in the literature.
Time slotted operation is a well-proven approach to achieve highly reliable low-power networking through scheduling and channel hopping. It is, however, difficult to apply time slotting to dynamic networks as envisioned in the Internet of Things. Commonly, these applications do not have pre-defined periodic traffic patterns and nodes can be added or removed dynamically.
This paper addresses the challenge of bringing TSCH (Time Slotted Channel Hopping MAC) to such dynamic networks. We focus on low-power IPv6 and RPL networks, and introduce Orchestra. In Orchestra, nodes autonomously compute their own, local schedules. They maintain multiple schedules, each allocated to a particular traffic plane (application, routing, MAC), and updated automatically as the topology evolves. Orchestra (re)computes local schedules without signaling overhead, and does not require any central or distributed scheduler. Instead, it relies on the existing network stack information to maintain the schedules. This scheme allows Orchestra to build non-deterministic networks while exploiting the robustness of TSCH.
We demonstrate the practicality of Orchestra and quantify its benefits through extensive evaluation in two testbeds, on two hardware platforms. Orchestra reduces, or even eliminates, network contention. In long running experiments of up to 72~h we show that Orchestra achieves end-to-end delivery ratios of over 99.99%. Compared to RPL in asynchronous low-power listening networks, Orchestra improves reliability by two orders of magnitude, while achieving a similar latency-energy balance.
This article considers the data aggregation scheduling problem, where a collision-free schedule is determined in a distributed way to route the aggregated data from all the sensor nodes to the base station within the least time duration. The algorithm proposed in this article (Distributed algorithm for Integrated tree Construction and data Aggregation (DICA)) intertwines the tree formation and node scheduling to reduce the time latency. Furthermore, while forming the aggregation tree, DICA maximizes the available choices for parent selection at every node, where a parent may have the same, lower, or higher hop count to the base station.
The correctness of the DICA is formally proven, and upper bounds for time and communication overhead are derived. Its performance is evaluated through simulation and compared with six delay-aware aggregation algorithms. The results show that DICA outperforms competing schemes. The article also presents a general hardware-in-the-loop framework (DAF) for validating data aggregation schemes on Wireless Sensor Networks (WSNs). The framework factors in practical issues such as clock synchronization and the sensor node hardware. DICA is implemented and validated using this framework on a test bed of sensor motes that runs TinyOS 2.x, and it is compared with a distributed protocol (DAS) that is also implemented using the proposed framework.
Wireless Sensor Networks (WSNs) play a vital role in today's real world applications. The effectiveness of WSNs purely depends on the data collection scheme. Numerous data collection schemes such as multipath, chain, tree, cluster and hybrid topologies are available in literature for collecting data in WSNs. However, the existing data collection schemes fail to provide a guaranteed reliable network in terms of mobility, traffic, and end-to-end connection. In this paper, a Velocity Energy-efficient and Link-aware Cluster-Tree (VELCT) scheme for data collection in WSNs is proposed which would effectively mitigate the problems of coverage distance, mobility, delay, traffic, tree intensity, and end-to-end connection. The proposed VELCT constructs the Data Collection Tree (DCT) based on the cluster head location. The data collection node in the DCT does not participate in sensing on this particular round, however, it simply collects the data packet from the cluster head and delivers it to the sink. The designed VELCT scheme minimizes the energy exploitation, reduces the end-to-end delay and traffic in cluster head in WSNs by effective usage of the DCT. The strength of the VELCT algorithm is to construct a simple tree structure, thereby reducing the energy consumption of the cluster head and avoids frequent cluster formation. It also maintains the cluster for a considerable amount of time. Simulation results have demonstrated that VELCT provides better QoS in terms of energy consumption, throughput, end-to-end delay, and network lifetime for mobility-based WSNs.
Energy savings optimization becomes one of the major concerns in the wireless sensor network (WSN) routing protocol design, due to the fact that most sensor nodes are equipped with the limited nonrechargeable battery power. In this paper, we focus on minimizing energy consumption and maximizing network lifetime for data relay in one-dimensional (1-D) queue network. Following the principle of opportunistic routing theory, multihop relay decision to optimize the network energy efficiency is made based on the differences among sensor nodes, in terms of both their distance to sink and the residual energy of each other. Specifically, an Energy Saving via Opportunistic Routing (ENS_OR) algorithm is designed to ensure minimum power cost during data relay and protect the nodes with relatively low residual energy. Extensive simulations and real testbed results show that the proposed solution ENS_OR can significantly improve the network performance on energy saving and wireless connectivity in comparison with other existing WSN routing schemes.
Modern vehicles incorporate dozens of sensors to provide vital sensor data to electronic control units, typically through physical wires, which increase the weight, maintenance, and cost of cars. Wireless sensor networks have been contemplated for replacing the current physical wires with wireless links, although existing networks are all single-hop, presumably because cars are small enough to be covered by lowpower communication, and multihop networking requires organizational overhead. In contradiction with previous works, we experimentally investigate the use of multihop wireless communication to support intra-car sensor networking. Extensive tests, run under various vehicular environments, indicate the potential for significant reliability, robustness, and energy usage improvements over existing single-hop approaches. Our implementation is based on the Collection Tree Protocol, a state-of-the-art multihop data collection protocol.
Low-Power and Lossy Networks (LLNs) are a class of network in which
both the routers and their interconnect are constrained. LLN routers
typically operate with constraints on processing power, memory, and
energy (battery power). Their interconnects are characterized by
high loss rates, low data rates, and instability. LLNs are comprised
of anything from a few dozen to thousands of routers. Supported
traffic flows include point-to-point (between devices inside the
LLN), point-to-multipoint (from a central control point to a subset
of devices inside the LLN), and multipoint-to-point (from devices
inside the LLN towards a central control point). This document
specifies the IPv6 Routing Protocol for Low-Power and Lossy Networks
(RPL), which provides a mechanism whereby multipoint-to-point traffic
from devices inside the LLN towards a central control point as well
as point-to-multipoint traffic from the central control point to the
devices inside the LLN are supp
The Time Synchronized Channel Hopping (TSCH) protocol is part of the newly defined IEEE 802.15.4e standard and represents the latest generation of highly reliable low-power MAC protocols. With implementation details left open, we conceive here a novel Traffic Aware Scheduling Algorithm (TASA) by extending the theoretically well-established graph theory methods of matching and coloring by means of an innovative approach based on network topology and traffic load. TASA is able to support emerging industrial applications requiring low latency at low duty cycle and power consumption. Preliminary simulation results have also been reported to highlight the effectiveness of the proposed algorithm.
We present an algorithm for graph isomorphism and subgraph isomorphism suited for dealing with large graphs. A first version of the algorithm has been presented in a previous paper, where we examined its performance for the isomorphism of small and medium size graphs. The algorithm is improved here to reduce its spatial complexity and to achieve a better performance on large graphs; its features are analyzed in detail with special reference to time and memory requirements. The results of a testing performed on a publicly available database of synthetically generated graphs and on graphs relative to a real application dealing with technical drawings are presented, confirming the effectiveness of the approach, especially when working with large graphs.
IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) aims to improve communication reliability in Wireless Sensor Networks (WSNs) by reducing the impact of the medium access contention, multipath fading, and blocking of wireless links. While TSCH outperforms single-channel communications, cross-technology interference on the license-free ISM bands may affect the performance of TSCH-based WSNs. For applications such as in-vehicle networks for which interference is dynamic over time, it leads to non-guaranteed reliability of the communications over time. This article proposes an Enhanced version of the TSCH protocol together with a Distributed Channel Sensing technique (ETSCH+DCS) that dynamically detects good quality channels to be used for communication. The quality of channels is extracted using a combination of a central and a distributed channel-quality estimation technique. The central technique uses Non-Intrusive Channel-quality Estimation (NICE) technique that proactively performs energy detections in the idle part of each timeslot at the coordinator of the network. NICE enables ETSCH to follow dynamic interference, while it does not reduce throughput of the network. The distributed channel quality estimation technique is executed by all the nodes in the network, based on their communication history, to detect interference sources that are hidden from the coordinator. We did two sets of lab experiments with controlled interferers and a number of simulations using real-world interference datasets to evaluate ETSCH. Experimental and simulation results show that ETSCH improves reliability of network communications, compared to basic TSCH and the state-of-the-art solution. In some experimental scenarios NICE itself has been able to increase the average packet reception ratio by 22% and shorten the length of burst packet losses by half, compared to the plain TSCH protocol. Further experiments show that DCS can reduce the effect of hidden interference (which is not detectable by NICE) on the packet reception ratio of the affected links by 50%.
In this paper, an advanced distributed energy-efficient clustering (ADEEC) protocol was proposed with the aim of balancing energy consumption across the nodes to achieve longer network lifetime for In-Vehicle Wireless Sensor Networks (IVWSNs). The algorithm changes the cluster head selection probability based on residual energy and location distribution of nodes. Then node associate with the cluster head with least communication cost and high residual energy. Simulation results show that ADEEC achieves longer stability period, network lifetime, and throughput than the other classical clustering algorithms.
For the development of reliable intra-vehicle low power wireless communication protocols, realistic wireless channel models are required. In this article, we present measurements taken in two different vehicles (compact passenger cars), one with a petrol and the other with an electric engine, with the aim to develop such channel models. We measured the received signal strength indicator (RSSI) and packet delivery ratio (PDR) values for several channel and communication settings, e.g. varying IEEE 802.15.4 channels, transmit power levels, packet sizes and different levels of Wi-Fi interference. We observed several unique characteristics of the wireless channel behaviour, resulting in separate zones inside the vehicle with similar behaviour, effects due to different types of engines and observed the impact of charging the electric car.
As the complexity of vehicular distributed systems increases rapidly, several hundreds of devices (sensors, actuators, etc.) are being placed in a modern automotive system. With the increase in wiring cables connecting these devices, the weight of a car increases significantly, which degrades the fuel efficiency in driving. In order to reduce the weight of a car, wireless communication has been introduced to replace wiring cables between some devices. However, the extra energy consumption for packet transmissions by wireless devices requires frequent maintenance, e.g., recharging of batteries. In this paper, we propose an intra-vehicle network routing algorithm to simultaneously minimize the wiring weight and the transmit power for wireless communication. Experimental results show that the proposed method can effectively minimize the wiring weight and the transmit power for wireless communication.
The IEEE 802.15.4e MAC amendment has been proposed to meet the requirements of industrial applications. Using slotted medium access with channel hopping, the MAC layer orchestrates the medium accesses of nodes according to a given schedule. Nevertheless, this amendment does not specify how this schedule is computed. The purpose of this paper is to propose a distributed joint time slot and channel assignment, called Wave, for data gathering in low-power lossy networks. This schedule targets minimised data convergecast delays by reducing the total number of slots in the schedule. Moreover, Wave ensures the absence of conflicting transmissions in the schedule provided. In such a schedule, a node is awake only during its transmission slots and those of its children in the convergecast routing graph. Thus, energy efficiency is ensured. In this paper, we present Wave with its properties (e.g. support of heterogeneous traffic, support of a sink equipped with multiple interfaces, worst case delays and buffer size) and compare it with a centralised scheduling algorithm like TMCP and a distributed one like DeTAS. Simulation results show the good performance of Wave compared with TMCP. Because in an industrial environment, several routing graphs can coexist, we study how Wave supports this coexistence. Copyright
In smart factory applications, sensors, actuators, field devices, and supervision systems often require a high degree of reliability and timeliness in information exchange. The quality of service provided by the underlying industrial communication network is a key requisite for quality of control. In this context, the WirelessHART, ISA100.11a, and IEEE802.15.4e time-slotted channel hopping standards contribute novel protocols to support quasi-deterministic services, based on wireless short-range communication technologies. The recently created IETF 6TiSCH working group binds IPv6 to this market. Within the 6TiSCH architecture, the 6top sublayer manages the way communication resources are scheduled in time and frequency. The on-the-fly (OTF) bandwidth reservation module plays a complementary role; it is a distributed approach for adapting the scheduled bandwidth to network requirements. This paper first describes the OTF module and its interactions with the 6top sublayer. It then presents the simulation results of the OTF, drawn from a realistic 50-sensor mote multi-hop network that models a small industrial plant. Results show that the OTF can attain an end-to-end latency of the order of a second, with over 99% end-to-end reliability. The first real-world OTF implementation in OpenWSN is presented to demonstrate that it can easily be added within the 6TiSCH architecture.
Efficient data structures and algorithms can be the key to designing practical programs. Most of this book addresses the traditional model of a computer as pictured below; some memory together with a single processor that can perform basic arithmetic operations (e.g., add, subtract, multiply, divide), make logical tests (e.g., test if a value is less than zero), and follow flow of control accordingly (e.g., goto instructions). The processor may include a few special registers that can be manipulated faster than normal memory, but the bulk of memory is uniform in the sense that access to all locations of memory is equally fast, from which comes the name Random Access Memory (RAM). Of course, computers in practice are much more complicated, with cache memory, secondary storage, multiple processors, etc. However, design methodology based on the RAM model has traditionally served well in more complex models.
The number of sensor nodes in the vehicle has increased significantly due to the increasing of different vehicular applications. Since, the wired architecture is not scalable and flexible because of the internal structure of the vehicle, therefore, there is an increasing level of appeal to design a system in which the wired connections to the sensor nodes are replaced with wireless links. Design a wireless sensor network inside the vehicle is more challenging to other networks, e.g., wireless, sensor and computer networks, because of the complex environment inside the vehicle. In this paper, we design a wireless sensor network for intra-vehicular communications. Firstly, we discuss about the link design between a base station and a sensor node and then we design a network scenario inside the vehicle for reliable communication. Finally, the performance is evaluated in terms of network reliability. The simulation results assist to design a robust system for intra-vehicular communications.
The performance of wireless sensor networks (WSN) is prone to adverse influences from a number of factors such as the interference from co-located wireless systems utilising the same spectral space. Channel hopping technique was proposed to mitigate the problem via periodic change of the operating frequency, and has been adopted in the form of time slotted channel hopping (TSCH) by IEEE 802.15.4e standard. This paper proposes adaptive slotted channel hopping (A-TSCH), an enhanced version of the TSCH aided by blacklisting technique. Complete design and implementation specifics are provided; and the results of experiments are analysed to show its advantages over existing TSCH. The main finding of this work is that A-TSCH can significantly improve the reliability of channel hopping scheme and thus provide better protection from interference for wireless sensor networks.
The emerging IEEE802.15.4e standard and IETF RPL routing protocol are core to the organization of multi-hop Low-power and Lossy Networks. They provide key functionalities useful for a really viable Internet of Things. However, several open issues still remain and require research efforts to be solved. Among others, the design of effective scheduling schemes in such systems is one of the major problems; in fact, there are no specifications about how schedules should be realized. Trying to fill this gap, this paper presents a new Decentralized Traffic-Aware Scheduling algorithm, which is able to construct optimum multi-hop schedules in a distributed fashion. Its effectiveness has been proved by using simulation results and comparing it with a centralized scheme. The reported performance results encourage the use of the developed scheduling technique, since it allows a very efficient queue management, and thus it minimizes packet discards due to buffer overflows, while at the same time minimizing the network duty cycle.
Convergecast, in which data from a set of source devices is delivered to a single data sink, is a critical functionality in networks deployed for industrial monitoring and control. We address the latency-optimal link scheduling problem for convergecast in networks operating according to the recent WirelessHART standard. When there is no restriction on the number of channels, we present a latency-optimal scheduling policy in which each routing node is required to buffer at most one packet at any point in time. For networks with a limited number of channels, we first establish a lower bound on the number of channels for latency-optimal convergecast and a lower bound on latency for convergecast using a fixed number of channels, and then present a heuristic scheme for channel-constrained latency-optimal convergecast scheduling. Simulation results confirm that, at much modest computational cost, our heuristic scheme can construct convergecast schedules with latency close to that of the optimal schedules.
In wireless sensor networks (WSNs) nodes often operate unattended in a collaborative manner to perform some tasks. In many applications, the network is deployed in harsh environments such as battlefield where the nodes are susceptible to damage. In addition, nodes may fail due to energy depletion and breakdown in the onboard electronics. The failure of nodes may leave some areas uncovered and degrade the fidelity of the collected data. However, the most serious consequence is when the network gets partitioned into disjoint segments. Losing network connectivity has a very negative effect on the applications since it prevents data exchange and hinders coordination among some nodes. Therefore, restoring the overall network connectivity is very crucial. Given the resource-constrained setup, the recovery should impose the least overhead and performance impact. This paper focuses on network topology management techniques for tolerating/handling node failures in WSNs. Two broad categories based on reactive and proactive methods have been identified for classifying the existing techniques. Considering these categories, a thorough analysis and comparison of all the recent works have been provided. Finally, the paper is concluded by outlining open issues that warrant additional research.
Data structures and algorithms are presented at the college level in a highly accessible format that presents material with one-page displays in a way that will appeal to both teachers and students. The thirteen chapters cover: Models of Computation, Lists, Induction and Recursion, Trees, Algorithm Design, Hashing, Heaps, Balanced Trees, Sets Over a Small Universe, Graphs, Strings, Discrete Fourier Transform, Parallel Computation. Key features: Complicated concepts are expressed clearly in a single page with minimal notation and without the "clutter" of the syntax of a particular programming language; algorithms are presented with self-explanatory "pseudo-code." * Chapters 1-4 focus on elementary concepts, the exposition unfolding at a slower pace. Sample exercises with solutions are provided. Sections that may be skipped for an introductory course are starred. Requires only some basic mathematics background and some computer programming experience. * Chapters 5-13 progress at a faster pace. The material is suitable for undergraduates or first-year graduates who need only review Chapters 1 -4. * This book may be used for a one-semester introductory course (based on Chapters 1-4 and portions of the chapters on algorithm design, hashing, and graph algorithms) and for a one-semester advanced course that starts at Chapter 5. A year-long course may be based on the entire book. * Sorting, often perceived as rather technical, is not treated as a separate chapter, but is used in many examples (including bubble sort, merge sort, tree sort, heap sort, quick sort, and several parallel algorithms). Also, lower bounds on sorting by comparisons are included with the presentation of heaps in the context of lower bounds for comparison-based structures. * Chapter 13 on parallel models of computation is something of a mini-book itself, and a good way to end a course. Although it is not clear what parallel
Topology management protocols play an important role in WSNs, managing the sleep transitions of the nodes to make data transmissions occur in an energy-efficient way, thus prolonging network lifetime. However, classical topology management protocols are not suitable for real-time WSNs, as they may introduce unbounded delays. In a previous work, we presented a static topology management protocol specifically designed for real-time WSNs which is able to provide bounded delay and routing fidelity. This paper extends such work, presenting a dynamic topology management protocol that surpasses the static approach introducing support for event-driven data transmissions and node joining at runtime and providing a novel adaptive technique for energy balancing among nodes to further increase network lifetime. This paper provides a detailed description of the dynamic protocol and simulation results on network lifetime and routing performance with comparative assessments.
We consider the problem of link scheduling in a sensor network employing a TDMA MAC protocol. Our algorithm consists of two phases. The first phase involves edge-coloring: an assignment of a color to each edge in the network such that no two edges incident on the same node are assigned the same color. Our main result for the first phase is a distributed edge-coloring algorithm that needs at most (Δ+1) colors, where Δ is the maximum degree of the network. To our knowledge, this is the first distributed algorithm that can edge-color a graph using at most (Δ+1) colors. The second phase uses the edge-coloring solution for link scheduling. We map each color to a unique timeslot and attempt to assign a direction of transmission along each edge such that the hidden terminal problem is avoided; an important result we obtain is a characterization of network topologies for which such an assignment exists. Next, we consider topologies for which a feasible transmission assignment does not exist for all edges, and obtain such an assignment using additional timeslots. Finally, we show that reversing the direction of transmission along every edge leads to another feasible direction of transmission. Using both the transmission assignments, we obtain a TDMA MAC schedule which enables two-way communication between every pair of adjacent sensor nodes. For acyclic topologies, we prove that at most 2(Δ+1) timeslots are required. Results for general topologies are demonstrated using simulations; for sparse graphs, we show that the number of timeslots required is around 2(Δ+1). We show that the message and time complexity of our algorithm is O(nΔ2+n2m), where n is the number of nodes and m is the number of edges in the network. Through simulations, we demonstrate that the energy consumption of our solution increases linearly with Δ. We also propose extensions to account for non-ideal radio characteristics.
In this article we provide a comprehensive review of the existing literature on techniques and protocols for in-network aggregation in wireless sensor networks. We first define suitable criteria to classify existing solutions, and then describe them by separately addressing the different layers of the protocol stack while highlighting the role of a cross-layer design approach, which is likely to be needed for optimal performance. Throughout the article we identify and discuss open issues, and propose directions for future research in the area
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