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Integration of Steerable Smart Antennas to IETF 6TiSCH Protocol for High Reliability Wireless IoT Networks
Abstract
Steerable directional antennas are increasingly utilised to improve the overall performance of the traditional wireless sensor networks. Steerable directional antenna based networking solutions increase the network capacity by providing a longer range of transmission and reduced interference as compared to networking solutions with omni-directional antennas. However, the use of smart antennas requires complex algorithms and such algorithms may not be easily leveraged in low power Internet of Things (IoT) networks. This study presents mechanisms for integrating low complexity smart antenna solutions into IETF 6TiSCH protocol with the aim of creating scalable and reliable industrial IoT networks. The solution defines extensions to MAC layer and scheduling mechanisms of IETF 6TiSCH protocol to enable its seamless integration with low complexity steerable smart antennas. The results of this study show that smart antenna enabled 6TiSCH protocol stack outperforms the legacy 6TiSCH stack in terms of data delivery performance especially in high density scenarios.<br
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This paper proposes a Medium Access Control (MAC) protocol using directional antennas in wireless ad-hoc networks, which achieves frame-collision reduction, freezing-state duration reduction, and deafness-problem mitigation simultaneously. The idea of the proposed protocol is that Pulse/Tone exchange is applied to the Opportunistic Directional MAC protocol (OPDMAC). By applying the Pulse/Tone exchange prior to Request to Send/Clear to Send (RTS/CTS) handshake, RTS-to-RTS frame collisions are reduced dramatically. Additionally, RTS-to-DATA frame collisions in the OPDMAC are changed to Pulse signal-to-DATA frame overlaps in the proposed protocol. This change makes the DATA-frame transmissions in success because the Pulse signal-to-DATA frame overlaps are regarded as a deafness problem. On that basis, the deafness-problem mitigation can be obtained in the proposed protocol by adaptive transmission-direction switching, which follows the OPDMAC technique. The freezing-state durations can be also reduced by the transmission-direction switching. As a result, the proposed protocol provides high network throughput compared with conventional protocols. Simulation results show the validity and effectiveness of the proposed protocol.
IETF 6TiSCH standard aims to create reliable, deterministic and low power networks by scheduling bandwidth resources in time and frequency domains. The main emphasis of 6TiSCH protocol is that it creates Internet of Things (IoT) networks with a deterministic and controllable delay. However, many of its benefits are tied to the ability of the 6TiSCH scheduler to optimally distribute radio resources among wireless nodes which may not be possible where the number of frequency resources are limited and several other wireless technologies share the same frequency band (e.g. WiFi, Bluetooth and IEEE 802.15.4). Here, the integration of a low complexity directional antenna system with IETF 6TiSCH protocol is investigated with the aim of creating a 6TiSCH solution with higher spatial reuse. 6TiSCH nodes equipped with such smart directional antennas can schedule bandwidth resources not only in time and frequency domain but also in spatial (space) domain.
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 this paper, we have introduced low-profile electronically steerable parasitic array radiator (ESPAR) antenna that can successfully be used to estimate direction-of-arrival (DoA) of incoming signals in wireless sensor network (WSN) applications, in which the height of the complete antenna has to be low. The proposed antenna is over 3 times lower than high-profile ESPAR antenna designs currently available in the literature for DoA estimation, can provide 8 unique main beam directions and relies on simplified beam steering, which makes it applicable to simple and inexpensive WSN nodes. Measurements using our fabricated ESPAR antenna prototype indicate that relying solely on received signal strength (RSS) values recorded at the antenna output port it is possible to achieve accurate DoA estimation results with error levels similar to those available for high-profile ESPAR antennas relying on the similar energy-efficient simplified beam steering concept and having 12 unique main beam directions. As a consequence, the overall time required for DoA estimation using the proposed antenna can be reduced by 33%.
Wireless Sensor Networks have become a key enabler for Industrial Internet of Things (IoT) applications; however, to adapt to the derived robust communication requirements, deterministic and scheduled medium access should be used, along with other features, such as channel hopping and frequency diversity. Implementing these mechanisms requires a correct synchronization of all devices in the network, a stage in deployment that can lead to non-operational networks. The present article presents an analysis of such situations and possible solutions, including the common current approaches and recommendations, and proposes a new beacon advertising method based on a specific Trickle Timer for the Medium Access Control (MAC) Time-Slotted Channel Hopping (TSCH) layer, decoupling from the timers in the network and routing layers. With this solution, improvements in connection success, time to join, and energy consumption can be obtained for the widely extended IEEE802.15.4e standard.
The so-called Industrial Internet of Things (IIoT) is expected to transform our world, and in depth modernize very different domains such as manufacturing, energy, agriculture, construction industry, and other industrial sectors. The need for low power radio networks first led to low duty cycle approaches where nodes turn off their radio chipset most of the time to save energy. The medium access control (MAC) has thus been largely investigated over the last fifteen years. Unfortunately, classical contention access methods use a random access and are unable to provide guarantees. In the meantime, some dedicated standards have emerged (e.g. IEEE 802.15.4-2006, IEEE 802.15.4-2015), combining Time Division Multiple Access (TDMA) with slow channel hopping in order to enable reliability and energy efficiency. Slow channel hopping allows each node to use different channels for a frame and its possible retransmissions with a low-cost hardware. To provide high-reliability, these protocols rely on a common schedule in order to prevent simultaneously interfering transmissions. In this context, we clearly observe a strong growth of the number of proposals in the last years, denoting a strong interest of the research community for deterministic slow channel hopping scheduling for the IIoT. We categorize here the numerous existing solutions according to their objectives (e.g. high-reliability, mobility support) and approaches. We also identify some open challenges, expected to attract much attention over the next few years.
Synchronized communication has recently emerged as a prime option for low-power critical applications. Solutions such as Glossy or Time Slotted Channel Hopping (TSCH) have demonstrated end-to-end reliability upwards of 99.99%. In this context, the IETF Working Group 6TiSCH is currently standardizing the mechanisms to use TSCH in low-power IPv6 scenarios. This paper identifies a number of challenges when it comes to implementing the 6TiSCH stack. It shows how these challenges can be addressed with practical solutions for locking, queuing, scheduling and other aspects. With this implementation as an enabler, we present an experimental validation and comparison with state-of-the-art MAC protocols. We conduct fine-grained energy profiling, showing
the impact of link-layer security on packet transmission. We evaluate distributed time synchronization in a 340-node testbed, and demonstrate that tight synchronization (hundreds of microseconds) can be achieved at very low cost (0.3% duty cycle, 0.008% channel utilization). We finally compare TSCH against traditional MAC layers: low-power listening (LPL) and CSMA, in terms of reliability, latency and energy. We show
that with proper scheduling, TSCH achieves by far the highest reliability, and outperforms LPL in both energy and latency.
In this letter, a new single-anchor indoor localization concept employing electronically steerable parasitic array radiator (ESPAR) antenna has been proposed. The new concept uses a simple fingerprinting algorithm adopted to work with directional main beam and narrow minimum radiation patterns of ESPAR antenna that scans 360 area around the base station, while the signal strength received from a mobile terminal is being recorded for each configuration. The letter describes the antenna design and necessary fingerprinting algorithm expansion and shows measurements of the proof-of-concept prototype performed within the experimental setup. Localization results obtained from indoor measurements indicate that the proposed concept can provide better results than the similar approach based on a switched-beam antenna introduced by Giorgetti et al. (IEEE Commun. Lett., vol. 13, no. 1, pp. 58-60, Jan. 2009).
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.
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
We have witnessed the Fixed Internet emerging with virtually every computer being connected today; we are currently witnessing the emergence of the Mobile Internet with the exponential explosion of smart phones, tablets and net-books. However, both will be dwarfed by the anticipated emergence of the Internet of Things (IoT), in which everyday objects are able to connect to the Internet, tweet or be queried. Whilst the impact onto economies and societies around the world is undisputed, the technologies facilitating such a ubiquitous connectivity have struggled so far and only recently commenced to take shape. To this end, this paper introduces in a timely manner and for the first time the wireless communications stack the industry believes to meet the important criteria of power-efficiency, reliability and Internet connectivity. Industrial applications have been the early adopters of this stack, which has become the de-facto standard, thereby bootstrapping early IoT developments with already thousands of wireless nodes deployed. Corroborated throughout this paper and by emerging industry alliances, we believe that a standardized approach, using latest developments in the IEEE 802.15.4 and IETF working groups, is the only way forward. We introduce and relate key embodiments of the power-efficient IEEE 802.15.4-2006 PHY layer, the power-saving and reliable IEEE 802.15.4e MAC layer, the IETF 6LoWPAN adaptation layer enabling universal Internet connectivity, the IETF ROLL routing protocol enabling availability, and finally the IETF CoAP enabling seamless transport and support of Internet applications. The protocol stack proposed in the present work converges towards the standardized notations of the ISO/OSI and TCP/IP stacks. What thus seemed impossible some years back, i.e., building a clearly defined, standards-compliant and Internet-compliant stack given the extreme restrictions of IoT networks, is commencing to become reality.
The demand for wireless bandwidth in indoor environments such as homes and offices continues to increase rapidly. Although wireless technologies such as MIMO can reach link throughputs of 100s of Mbps (802.11n) for a single link, the question of how we can deliver high throughput to a large number of densely-packed devices remains an open problem. Directional antennas have been shown to be an effective way to increase spatial reuse, but past work has focused largely on outdoor environments where the interactions between wireless links can usually be ignored. This assumption is not acceptable in dense indoor wireless networks since indoor deployments need to deal with rich scattering and multipath effects. In this paper we introduce DIRC, a wireless network design whose access points use phased array antennas to achieve high throughput in dense, indoor environments. The core of DIRC is an algorithm that increases spatial reuse and maximizes overall network capacity by optimizing the orientations of a network of directional antennas. We implemented DIRC and evaluated it on a nine node network in an enterprise setting. Our results show that DIRC improves overall network capacity in indoor environments, while being flexible enough to adapt to node mobility and changing traffic workloads.
The use of directional antennas for wireless communications brings several benefits, such as increased communication range and reduced interference. One example of directional antennas are electronically switched directional (ESD) antennas that can easily be integrated into Wireless Sensor Networks (WSNs) due to their small size and low cost. However, current literature questions the benefits of using ESD antennas in WSNs due to the increased likelihood of hidden terminals and increased power consumption. This is mainly because earlier studies have used directionality for transmissions but not for reception.
In this article, we introduce novel cross-layer optimizations to fully utilize the benefits of using directional antennas. We modify the Medium Access Control (MAC) , routing, and neighbor discovery mechanisms to support directional communication. We focus on convergecast investigating a large number of different network topologies. Our experimental results, both in simulation and with real nodes, show when the traffic is dense, networks with directional antennas can significantly outperform networks with omnidirectional ones in terms of packet delivery rate, energy consumption, and energy per received packet.
Various legacy and emerging industrial applications require closed-loop control over multiple hops. Existing multi-hop wireless technologies do not completely fulfill the stringent requirements of closed-loop control. This paper proposes a novel wireless solution, termed as GALLOP, for closed-loop control over multi-hop networks. GALLOP adopts a pragmatic approach for tackling the peculiarities of closed-loop control. Key aspects of GALLOP design include control-aware multi-hop scheduling for cyclic information exchange with very low and deterministic latency, cooperative transmissions for very high reliability and low-overhead signaling mechanism for scalable operation in large-scale networks. GALLOP has been specifically designed for control loops closed over the whole multi-hop network with dynamics on the order of few milliseconds. Performance evaluation through hardware implementation on a Bluetooth 5 testbed and system-level simulations demonstrate the viability of GALLOP in providing high-performance connectivity as required by closed-loop control applications.
The IETF IPv6 over the TSCH mode of IEEE802.15.4e (6TiSCH) working group has standardized a set of protocols to enable low power industrial-grade IPv6 networks. 6TiSCH proposes a protocol stack rooted in the Time Slotted Channel Hopping (TSCH) mode of the IEEE802.15.4-2015 standard, supports multi-hop topologies with the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) routing protocol, and is IPv6-ready through 6LoWPAN. 6TiSCH has defined the missing control plane protocols to match link-layer resources to the routing topology and application communication needs. 6TiSCH has also defined a secure light-weight join processes combining link-layer security features (through Counter with CBC-MAC (CCM*)) with a secure joining procedure using the Constrained Application Protocol (CoAP). This tutorial provides a comprehensive overview of the 6TiSCH architecture and protocol suite, including the 6TiSCH Operation Sublayer (6top), the 6top Protocol (6P), and how it uses 6LoWPAN, IP-in-IP encapsulation, and RPL. This document is meant to be used both as a primer, and as a reference. It is tailored to the advanced researcher and engineer implementing and building upon IETF 6TiSCH specifications.
The industrial Internet of Things (IIoT) is expected to revolutionize the current industry. The capillary introduction of sensors and actuators for real-time monitoring and remote control and their seamless integration into existing information systems will represent a technological breakthrough. The definition of wireless communication standards will play a crucial role in reducing deployment costs and minimizing the time for installation. The new IPv6 over the TSCH mode of IEEE802.15.4e communication stack, 6TiSCH, represents the current leading standardization effort that aims at achieving both reliable and timed wireless communication and integration within IPv6 communication networks for industrial systems. In this paper, the network formation dynamics of 6TiSCH networks are assessed, considering the current guidelines for the so-called minimal configuration, a static initial configuration to guarantee control communication during network bootstrap. It is shown that the minimal configuration might lead to long network formation and suboptimal performance of the routing algorithm which may result into a disconnected network. In order to overcome this issue, a dynamic resource management algorithm to be executed during network bootstrap is proposed. Simulation and experimental results show that the proposed solution allows to minimize the network formation time and also helps in optimizing routing operations leading to the discovery of better routes.
We consider IPv6-enabled networks that run on top of the time-slotted channel hopping mode of IEEE802.15.4 (6TiSCH). The ongoing discussions in the standardization community concern the network formation process and the definition of a bootstrapping protocol by which a new mote is admitted into the network. Because the bootstrapping traffic uses the same shared slots as the network broadcasts, the key to the optimal performance of the network formation process lays in the optimization of the network broadcasting strategy. The problem boils down to the issue of stabilizing slotted Aloha. To do so, we adapt a broadcast algorithm to the specifics of 6TiSCH networks. By simulation, we evaluate the optimal broadcast transmission probability in the network. We answer the open questions in the IETF 6TiSCH standardization community that concern the performance of the network formation process for the optimal values of transmission probability. As the main contribution of the letter, we provide network administrators with a set of values that allow the formation of dense networks.
Neighbor discovery, one of the most fundamental bootstrapping networking primitives, is particularly challenging in decentralized wireless networks where devices have directional antennas. In this paper, we study the following fundamental problem, which we term oblivious neighbor discovery: How can neighbor nodes with heterogeneous antenna configurations discover each other within a bounded delay in a fully decentralised manner without any prior coordination or synchronisation? We establish a theoretical framework on the oblivious neighbor discovery and the performance bound of any neighbor discovery algorithm achieving oblivious discovery. Guided by the theoretical results, we then devise an oblivious neighbor discovery algorithm, which achieves guaranteed oblivious discovery with order-minimal worst case discovery delay in the asynchronous and heterogeneous environment. We further demonstrate how our algorithm can be configured to achieve a desired tradeoff between average and worst case performance.
The Internet of Things (IoT) is entering the daily operation of many industries; applications include but are not limited to smart cities, smart grids, smart homes, physical security, e-health, asset management, and logistics. For example, the concept of smart city is emerging in multiple continents, where enhanced street lighting controls, infrastructure monitoring, public safety and surveillance, physical security, gunshot detection, meter reading, and transportation analysis and optimization systems are being deployed on a city-wide scale. A related and cost-effective user-level IoT application is the support of IoT-enabled smart buildings. Commercial space has substantial requirements in terms of comfort, usability, security, and energy management. IoT-based systems can support these requirements in an organic manner. In particular, Power over Ethernet (PoE), as part of an IoT-based solution, offers disruptive opportunities in revolutionizing the in-building connectivity of a large swath of devices. However, a number of deployment-limiting issues currently impact the scope of IoT utilization, including lack of comprehensive end-to-end standards, fragmented cybersecurity solutions, and a relative dearth of fully-developed vertical applications. This article reviews some of the technical opportunities offered and the technical challenges faced by the IoT in the smart building arena.
Several studies have highlighted that the IEEE 802.15.4 standard presents a number of limitations such as low reliability, unbounded packet delays and no protection against interference/fading, that prevent its adoption in applications with stringent requirements in terms of reliability and latency. Recently, the IEEE has released the 802.15.4e amendment that introduces a number of enhancements/modifications to the MAC layer of the original standard in order to overcome such limitations. In this paper we provide a clear and structured overview of all the new 802.15.4e mechanisms. After a general introduction to the 802.15.4e standard, we describe the details of the main 802.15.4e MAC behavior modes, namely Time Slotted Channel Hopping (TSCH), Deterministic and Synchronous Multi-channel Extension (DSME), and Low Latency Deterministic Network (LLDN). For each of them, we provide a detailed description and highlight the main features and possible application domains. Also, we survey the current literature and summarize open research issues.
Electronically Switched Directional (ESD) antennas allow software-based control of the direction of maximum antenna gain. ESD antennas are feasible for wireless sensor network. Existing studies with these antennas focus only on controllable directional transmissions. These studies demonstrate reduced contention and increased range of communication with no energy penalty. Unlike existing literature, in this chapter we experimentally explore controllable antenna directionality at both sender and receiver. One key outcome of our experiments is that directional transmissions and receptions together considerably reduce channel contention. As a result, we can significantly reduce intra-path interference.
By radiating the power in the direction of choice, electronically-switched directional (ESD) antennas can reduce network contention and avoid packet loss. There exists some ESD antennas for wireless sensor networks, but so far researchers have mainly evaluated their directionality. There are no studies regarding the link dynamics of ESD antennas, in particular not for indoor deployments and other scenarios where nodes are not necessarily in line of sight. Our long-term experiments confirm that previous findings that have demonstrated the dependence of angle-of-arrival on channel frequency also hold for directional transmissions with ESD antennas. This is important for the design of protocols for wireless sensor networks with ESD antennas: the best antenna direction, i.e., the direction that leads to the highest packet reception rate and signal strength at the receiver, is not stable but varies over time and with the selected IEEE 802.15.4 channel. As this requires protocols to incorporate some form of adaptation, we present an intentionally simple and yet efficient mechanism for selecting the best antenna direction at run-time with an energy overhead below 2 standard omni-directional transmissions.
Interference from colocated networks operating over the same frequency range, becomes an increasingly severe problem as the number of networks overlapping geographically increases. Our experiments show that such interference is indeed a major problem, causing up to 58% packet loss to a multihop 802.15.4 sensor network competing for radio spectrum with a WiFi network. We present interference estimators that can be efficiently implemented on resource constrained motes using off-the-shelf radios and outline distributed algorithms that use these estimators to dynamically switch frequencies as interference is detected. Lastly, we evaluate the proposed algorithms in the context of a real-life application that downloads large amounts of data over multihop network paths. Our results show that the proposed approach successfully detects interference from competing WiFi channels and selects non-overlapping 802.15.4 channels. As a result, the proposed solution reduces end-to-end loss rate from 22%-58% to < 1%.
A performance analysis of the network formation process in ieee 802.15.4e tsch wireless sensor/actuator networks
- D De Guglielmo
- A Seghetti
- G Anastasi
- M Conti
D. De Guglielmo, A. Seghetti, G. Anastasi, and M. Conti, "A performance analysis of the network formation process in ieee 802.15.4e
tsch wireless sensor/actuator networks," in 2014 IEEE Symposium on
Computers and Communications (ISCC), June 2014, pp. 1-6.