DADC: A Novel Duty-cycling Scheme for IEEE 802.15.4 Cluster-tree-based IoT Applications

The IEEE 802.15.4 standard is one of the widely adopted specifications for realizing different applications of the Internet of Things. It defines several physical layer options and Medium Access Control (MAC) sub-layer for devices with low-power operating at low data rates. As devices implementing this standard are primarily battery-powered, minimizing their power consumption is a significant concern. Duty-cycling is one such power conserving mechanism that allows a device to schedule its active and inactive radio periods effectively, thus preventing energy drain due to idle listening. The standard specifies two parameters, beacon order and superframe order, which define the active and inactive period of a device. However, it does not specify a duty-cycling scheme to adapt these parameters for varying network conditions. Existing works in this direction are either based on superframe occupation ratio or buffer/queue length of devices. In this article, the particular limitations of both the approaches mentioned above are presented. Later, a novel duty-cycling mechanism based on MAC parameters is proposed. Also, we analyze the role of synchronization schemes in achieving efficient duty-cycles in synchronized cluster-tree network topologies. A Markov model has also been developed for the MAC protocol to estimate the delay and energy consumption during frame transmission.

Connected coverage with rapid forwarding in energy harvesting wireless sensor networks for critical rare events

<p>To ensure event detection and subsequent rapid forwarding of notification messages, wireless sensor networks deployed to detect critically important rarely occurring events must maintain both sensing coverage and low latency network connectivity at all times. Maintaining coverage for extended periods is relatively straight forward as passive sensing components tend to consume little energy. Maintenance of network connectivity, however, requires sensing devices constantly supply power to their transceivers, significantly reducing the longevity of the sensor network. Energy harvesting can extend the operational life of sensing devices with always on transceivers, potentially to the point where they can operate year round. In addition, over populating the sensing area with more devices than are required to provide complete sensing cover introduces the possibility of self-organisation where sensing devices agree amongst themselves which will remain active and which will be allowed to sleep. Few algorithms have been proposed to address both coverage and forwarding; those that do are either unconcerned with rapid propagation or have not been optimised to handle the constant changes in topology observed in duty cycling networks. This thesis first analyses the energy consumption profiles of commercially available wireless sensing devices then presents mechanisms by which these devices can both maintain sensing coverage and rapidly forward event detection messages delayed only by the inherent latencies found in wireless multi-hop networks. These individual contributions form the basis of a combined algorithm for Coverage Preservation with Rapid Forwarding (CPRF). Through evaluations including live deployment, CPRF is shown to deliver perfect coverage maintenance and low latency message propagation whilst allowing stored-charge conservation via collaborative duty cycling in energy harvesting networks.</p>

Connected coverage with rapid forwarding in energy harvesting wireless sensor networks for critical rare events

<p>To ensure event detection and subsequent rapid forwarding of notification messages, wireless sensor networks deployed to detect critically important rarely occurring events must maintain both sensing coverage and low latency network connectivity at all times. Maintaining coverage for extended periods is relatively straight forward as passive sensing components tend to consume little energy. Maintenance of network connectivity, however, requires sensing devices constantly supply power to their transceivers, significantly reducing the longevity of the sensor network. Energy harvesting can extend the operational life of sensing devices with always on transceivers, potentially to the point where they can operate year round. In addition, over populating the sensing area with more devices than are required to provide complete sensing cover introduces the possibility of self-organisation where sensing devices agree amongst themselves which will remain active and which will be allowed to sleep. Few algorithms have been proposed to address both coverage and forwarding; those that do are either unconcerned with rapid propagation or have not been optimised to handle the constant changes in topology observed in duty cycling networks. This thesis first analyses the energy consumption profiles of commercially available wireless sensing devices then presents mechanisms by which these devices can both maintain sensing coverage and rapidly forward event detection messages delayed only by the inherent latencies found in wireless multi-hop networks. These individual contributions form the basis of a combined algorithm for Coverage Preservation with Rapid Forwarding (CPRF). Through evaluations including live deployment, CPRF is shown to deliver perfect coverage maintenance and low latency message propagation whilst allowing stored-charge conservation via collaborative duty cycling in energy harvesting networks.</p>

Self-configuring asynchronous sleeping in heterogeneous networks

Nowadays, the heterogeneous wireless nano-network topology becomes a need for diverse applications based on heterogeneous networks composed of regions of different node densities. In Wireless Nano-networks (WNNs), nodes are of nano-metric size and can be potentially dense in terms of neighbouring nodes. Nano-nodes have limited resources in terms of processing, energy and memory capabilities. In nano-network(s), even in a communication range limited to tens of centimeters, thousands of neighbours can be found. We proposed a fine-grained duty-cycling method (sleeping mechanism), appropriate to nanonodes, which aims to reduce the number of receptions seen by a node during data packet routing. The present study reveals the usefulness of implementing the sleeping mechanism in heterogeneous networks, as well as configuring a dynamic awaken duration for nodes based on a density estimation algorithm. We also proposed an algorithm that helps in increasing the reliability of the packet received by the destination node.

PRIB-CDS: An Energy Efficient Low Duty Cycle Broadcasting Scheme for Wireless Sensor Network

Low duty cycling is a widely adapted technique to conserve energy in the most used Medium Access Control (MAC) protocols in Wireless Sensor Networks (WSN). But such low duty cycle-based MAC protocols perform poorly under broadcast traffic as they suffer from redundant retransmission and maximization of relay nodes problems. Addressing these issues is critical, as the advent of IoT and ubiquitous computing applications has increased the demand for broadcast support. Our previous work, Preamble based Receiver Initiated Broadcasting MAC (PRIB-MAC) performed well in most parameters under broadcast traffic, but it had scope for improvement in reducing the number of transmissions. In this paper, we propose the PRIB-Connected Dominating Set (PRIB-CDS), built on top of PRIB-MAC with the addition of dynamic forwarding technique by forming a forwarding set with the help of Greedy algorithm. The simulation results of our proposed PRIB-CDS algorithm shows that it has reduced the number of transmissions significantly as it reduces forwarding nodes and balances the energy between the nodes to avoid re-broadcasting the data.

A Pipeline-TDC-Based CMOS Temperature Sensor with a 48 fJ·K2 Resolution FoM

An energy-efficient temperature sensor is important for temperature monitoring in Biomedical Internet-of-things (BIoT) applications. This article presents a time-domain temperature sensor with a pipeline time-to-digital converter (TDC). A programmable-gain time amplifier (PGTA) with high linearity and wide linear range is proposed to improve the resolution of the sensor and to reduce the chip area. The conversion time of the sensor is reduced by the fast TDC that only needs ~26 ns/conversion, which means the sensor is suitable for BIoT applications that commonly use duty cycling mode. Fabricated in a 40 nm standard CMOS technology, the sensor consumes 7.6 μA at a 0.6 V supply and achieves a resolution of 90 mK and a sensitivity of 0.62%/°C in a 1.3 μs conversion time. This translates into a resolution figure-of-merit of 48 fJ·K2. The sensor achieves an inaccuracy of 0.39 °C from −20 °C to 80 °C after two-point calibration. Duty cycling the sensor results in an even lower average power: ~18.6 nW at 10 conversions/s.