This paper capitalizes on two emerging trends, i.e., the growing use of wireless at the edge of industrial control networks and the growing interest to integrate IP into said networks. This is facilitated by recent design contributions from the IEEE and the IETF, where the former developed a highly efficient deterministic time–frequency scheduled medium access control protocol in the form of IEEE 802.15.4e timeslotted channel hopping (TSCH) and the latter IPv6 networking paradigms in the form of 6LoWPAN/ROLL, and scheduling approaches in the form of 6TiSCH. The focus of the present work is on advancing the state-of-the-art of deterministic 6TiSCH schedules toward more flexible but equally reliable distributed approaches. In addition, this paper aims to introduce the first implementation of 6TiSCH networks for factory automation environments: it outlines the challenges faced to overcome the scalability issues inherent to multihop dense low-power networks; the experimental results confirm that the naturally unreliable radio medium can support time-critical and reliable applications. These developments pave the way for wireless industry-grade monitoring approaches.

/pdf/decentralized-traffic-aware-scheduling-in-6tisch-networks-4h2pg31lx7.pdf

Decentralized Traffic Aware Scheduling in 6TiSCH Networks: Design and Experimental Evaluation

Multichannel assignment protocols in wireless sensor networks

Mobile ad hoc networks (MANETs) are becoming increasingly common, and typical network loads considered for MANETs are increasing as applications evolve. This, in turn, increases the importance of bandwidth efficiency while maintaining tight requirements on energy consumption, delay and jitter. Coordinated channel access protocols have been shown to be well suited for highly loaded MANETs under uniform load distributions. However, these protocols are in general not as well suited for non-uniform load distributions as uncoordinated channel access protocols due to the lack of on-demand dynamic channel allocation mechanisms that exist in infrastructure based coordinated protocols. In this paper, we present a lightweight dynamic channel allocation mechanism and a cooperative load balancing strategy that are applicable to cluster based MANETs to address this problem. We present protocols that utilize these mechanisms to improve performance in terms of throughput, energy consumption and inter-packet delay variation (IPDV). Through extensive simulations we show that both dynamic channel allocation and cooperative load balancing improve the bandwidth efficiency under non-uniform load distributions compared to protocols that do not use these mechanisms as well as compared to the IEEE 802.15.4 protocol with GTS mechanism and the IEEE 802.11 uncoordinated protocol.

Cooperative Load Balancing and Dynamic Channel Allocation for Cluster-BasedMobile Ad Hoc Networks

This paper presents a wireless sensor node (WSN) system where an electromagnetic (EM) energy harvester is utilized for charging its rechargeable batteries while the system is operational. The capability and the performance of an in-house low-frequency EM energy harvester for charging rechargeable NiMH batteries were experimentally verified in comparison to a regular battery charger. Furthermore, the power consumption of MicaZ motes, used as the WSN, was evaluated in detail for different operation conditions. The battery voltage and current were experimentally monitored during the operation of the MicaZ sensor node equipped with the EM vibration energy harvester. A compact (24.5 cm3) in-house EM energy harvester provides approximately 65 µA charging current to the batteries when excited by 0.4 g acceleration at 7.4 Hz. It has been shown that the current demand of the MicaZ mote can be compensated for by the energy harvester for a specific low-power operation scenario, with more than a 10-fold increase in the battery lifetime. The presented results demonstrate the autonomous operation of the WSN, with the utilization of a vibration-based energy harvester.

https://www.mdpi.com/1996-1073/7/10/6323/pdf

Powering-up Wireless Sensor Nodes Utilizing Rechargeable Batteries and an Electromagnetic Vibration Energy Harvesting System

Real-time multimedia applications require quality of service (QoS) provisioning in terms of bounds on delay and packet loss along with soft bandwidth guarantees. The shared nature of the wireless communication medium results in interference. Interference combined with the overheads, associated with a medium access control (MAC) protocol, and the implementation of a networking protocol stack limit the available bandwidth in IEEE 802.15.4-based networks and can result in congestion, even if the transmission rates of nodes are well below the maximum bandwidth supported by an underlying communication technology. Congestion degrades the performance of admitted real-time multimedia flow(s). Therefore, in this paper, we experimentally derive the IEEE 802.15.4 channel capacity using an unslotted CSMA-CA MAC protocol. We experimentally derive channel capacity for two cases, that is, when the CSMA-CA protocol is working without ACKs and when it is working with ACKs. Moreover, for both cases, we plot the relationship of offered data load with delay and packet loss rate. Simulation results demonstrate that the parameters that affect the choice of a CSMA-CA MAC layer protocol are end-to-end delay and packet loss requirements of a real-time multimedia flow, data load within the interference range of transmitters along the forwarding path, and length of the forwarding path.

/pdf/contiki-based-ieee-802-15-4-channel-capacity-estimation-and-4cqknj6mdd.pdf

Contiki-Based IEEE 802.15.4 Channel Capacity Estimation and Suitability of Its CSMA-CA MAC Layer Protocol for Real-Time Multimedia Applications

This paper presents the throughput results obtained from a Wireless Sensor Network testbed, with single and multiple sources in different network deployments and routing architectures. The experimental testbed deployed at IIT Madras consisted of commercially available Crossbow TelosB and MicaZ nodes and a custom-built sensor node based on the DigiNet Xbee chip, with all nodes implementing the Zigbee standard. The networks were deployed in uniform grid topologies in three different deployments with up to 228 nodes. The main aim of the experiments is to analyze the throughput and packet delivery ratio observed with single and multiple sources. The experimental results show that delivery ratio reduces with increase in data rate due to collisions and help characterise the network capacity limits.

Testbed based throughput analysis in a Wireless Sensor Network

Designing a multi-hop wireless network is a challenge mainly because of high bit error rates and the inherent broadcast nature of the medium creating interference. To improve the capacity, protocols based on spatial reuse of frequencies with multiple orthogonal channels have been introduced. This is particularly useful in complete wireless environments such as wireless mesh networks and wireless sensor networks (WSN). Based on initial testbed experiments on WSN testbeds, we show that there is a gap between reality and simulation models due to overheads in implementing these protocols. In order to support QoS guarantees in critical paths for such networks, we present a generic channel allocation scheme based on k-distance coloring problem, for multiple channel networks. The scheme is designed keeping in mind the real time deployment issues in wireless networks. We report the results from experiments conducted using a IEEE 802.15.4 based testbed consisting of Xbow MicaZ nodes and results obtained using the OMNET4 simulation environment.

Capacity analysis of multi-hop wireless sensor networks using multiple transmission channels: A case study using IEEE 802.15.4 based networks

This paper presents an implementation based study of multi-channel medium access control protocols in hardware constrained wireless sensor network(WSN) nodes with 802.15.4 radio. In the network architecture presented, each sensor node has a single radio transceiver that can be tuned to any of the available sixteen non-overlapping channels. The simplest way to select data channel is to use a common channel signaling between the nodes. We have conducted experiments to verify whether control channel congestion can occur in case of 802.15.4 radios using MicaZ and TelosB motes. The throughput results show the per-node throughput does not decline as significantly with increasing number of senders, with the proposed multi-channel protocol.

Performance of a multi-channel MAC protocol based on IEEE 802.15.4 radio

To improve the capacity of multi-hop wireless networks, protocols based on spatial reuse of frequencies with multiple orthogonal channels have been studied earlier. This paper focuses on the design, implementation and analysis of multiple-channel based wireless sensor networks (WSN). The objectives of the paper are two-fold. The first objective is to identify the sensor node bottlenecks in implementing multi-channel MAC protocols. In particular, a control channel based MAC protocol is implemented and analyzed. The analysis shows the gap between reality and simulation models due to system overheads in implementing these protocols. The second objective is to understand the capacity limits of multi-hop paths in a WSN with multiple channels. A generic channel allocation scheme based on k-distance coloring technique is developed. The protocols and mechanisms were implemented on a testbed consisting of Crossbow MicaZ and TelosB motes using IEEE 802.15.4 compliant radios. Throughput and delivery ratio measurements from the testbed are reported. Some of these measurements are incorporated in a discrete-event simulator model, based on OMNET++ 4.0 with Mobility Framework, for more detailed throughput analysis. The results show that it is possible to achieve 90 % delivery ratio over paths consisting of as many as 18 hops, in a 10 × 10 grid topology using 16 channels.

Throughput analysis of multiple channel based wireless sensor networks

Target tracking is an important application of Wireless Sensor Networks (WSN). This paper presents the design of a WSN testbed that used a custom-built wireless sensor node, specifically designed for target tracking. The sensor node consists of a Digi Xbee device, a Passive Infrared (PIR) and MaxSonar ultrasonic ranging sensors. Appropriate multi-channel MAC protocols were designed and implemented. The experiments were conducted with up to 20 sensor nodes in indoor and outdoor environments, with a human target moving at pedestrian speeds. We found that directional sensing, inter-sensor interference, sensing and processing delays are significant in determining the target location. This work highlights some of the practical difficulties in realizing such systems in practice. The experiments show that the ultra-sonic ranging sensor does indeed provide improved target tracking information when compared to the PIR sensor.

P. Gireesan Namboothiri

Papers

Testbed based throughput analysis in a Wireless Sensor Network

Capacity analysis of multi-hop wireless sensor networks using multiple transmission channels: A case study using IEEE 802.15.4 based networks

Performance of a multi-channel MAC protocol based on IEEE 802.15.4 radio

Throughput analysis of multiple channel based wireless sensor networks

A testbed for distributed target tracking with directional sensors