Duty Cycling Research Articles

A Sub-60- $\mu \text{A}$ Multimodal Smart Biosensing SoC With >80-dB SNR, 35- $\mu \text{A}$ Photoplethysmography Signal Chain

A sub-60- $\mu \text{A}$ multimodal analog front-end and ultralow energy biosensing CMOS SoC is presented. A 35- $\mu \text{A}$ photoplethysmography (PPG) signal chain that consumes five times lower power than state of the art has been demonstrated. An SNR of >80 dBFS was achieved using circuit and system techniques that enable sub-1% analog duty cycling. Input signal-aware, on-the-fly, real-time data path adaptation algorithms implemented on an external microcontroller and synchronized by an ultralow power on-chip FSM along with a 1.3- $\mu \text{W}$ , 14-b, 1-kSPS SAR ADC further lower system energy. A programmable, asynchronous reset capacitive amplifier (PARCA) with noise efficiency factor (NEF) of 4.8 and $dx$ / $dt$ analog feature extractor demonstrates energy efficient electrocardiogram (ECG) capture. A wearable platform using this SoC that simultaneously captures ECG plus PPG and wirelessly transmits the heart rate using Bluetooth low energy every 2 s to a smartphone lasts for greater than five days from a 250-mAhr battery.

SleepTalker: A ULV 802.15.4a IR-UWB Transmitter SoC in 28-nm FDSOI Achieving 14 pJ/b at 27 Mb/s With Channel Selection Based on Adaptive FBB and Digitally Programmable Pulse Shaping

Achieving wireless communications at 5–30 Mb/s in energy-harvesting Internet-of-Things (IoT) applications requires energy efficiencies better than 100 pJ/b. Impulse-radio ultrawideband (UWB) communications offer an efficient way to achieve high data rate at ultralow power for short-range links. We propose a digital UWB transmitter (TX) system-on-chip (SoC) designed for ultralow voltage in 28-nm FDSOI CMOS. It features a PLL-free architecture, which exploits the duty-cycling nature of impulse radio through aggressive duty cycling within the pulse modulation time slot for high energy efficiency and minimum jitter accumulation. Wide-range on-chip adaptive forward back biasing is used for threshold voltage reduction, PVT compensation, and tuning of both the carrier frequency and the output power. To ensure spectral compliance with output power regulations without the use of bulky and expensive off-chip filters, a programmable pulse-shaping functionality is integrated in the digital power amplifier based on a 7–9-GS/s, 5-b current DAC. Operated at 0.55 V, it achieves a record energy efficiency of 14 pJ/b for the TX alone and 24 pJ/b for the complete SoC with embedded power management. The TX SoC occupies a core area of 0.93 mm2.

Network Coded Cooperative Communication in a Real-Time Wireless Hospital Sensor Network.

The paper presents a network coded cooperative communication (NC-CC) enabled wireless hospital sensor network architecture for monitoring health as well as postural activities of a patient. A wearable device, referred as a smartband is interfaced with pulse rate, body temperature sensors and an accelerometer along with wireless protocol services, such as Bluetooth and Radio-Frequency transceiver and Wi-Fi. The energy efficiency of wearable device is improved by embedding a linear acceleration based transmission duty cycling algorithm (NC-DRDC). The real-time demonstration is carried-out in a hospital environment to evaluate the performance characteristics, such as power spectral density, energy consumption, signal to noise ratio, packet delivery ratio and transmission offset. The resource sharing and energy efficiency features of network coding technique are improved by proposing an algorithm referred as network coding based dynamic retransmit/rebroadcast decision control (LA-TDC). From the experimental results, it is observed that the proposed LA-TDC algorithm reduces network traffic and end-to-end delay by an average of 27.8% and 21.6%, respectively than traditional network coded wireless transmission. The wireless architecture is deployed in a hospital environment and results are then successfully validated.

A Self-Adaptive Sleep/Wake-Up Scheduling Approach for Wireless Sensor Networks.

Sleep/wake-up scheduling is one of the fundamental problems in wireless sensor networks, since the energy of sensor nodes is limited and they are usually unrechargeable. The purpose of sleep/wake-up scheduling is to save the energy of each node by keeping nodes in sleep mode as long as possible (without sacrificing packet delivery efficiency) and thereby maximizing their lifetime. In this paper, a self-adaptive sleep/wake-up scheduling approach is proposed. Unlike most existing studies that use the duty cycling technique, which incurs a tradeoff between packet delivery delay and energy saving, the proposed approach, which does not us duty cycling, avoids such a tradeoff. The proposed approach, based on the reinforcement learning technique, enables each node to autonomously decide its own operation mode (sleep, listen, or transmission) in each time slot in a decentralized manner. Simulation results demonstrate the good performance of the proposed approach in various circumstances.

License assisted access-WiFi coexistence with TXOP backoff for LTE in unlicensed band

License assisted access (LAA) was proposed as a solution to the challenge of satisfying high throughput requirement in cellular network with limited licensed band. LAA uses long term evolution (LTE) carrier aggregation technique to combine licensed and unlicensed bands, specifically 5 GHz WiFi band, in order to achieve high data rates. However, LAA has several critical concerns for services provision on 5 GHz unlicensed band. In this article, an overview of the techniques concerning the coexistence of LTE and WiFi on the same unlicensed band is presented. We first present several general approaches including power control of LTE evolved Node B (eNB), carrier selection, LTE duty cycling, self clear to send (CTS) and request to send/CTS (RTS/ CTS), and listen before talk (LBT). Then, we focus on LBT techniques for LAA-WiFi coexistence and discuss how LBT based coexistence solutions can dynamically respond to the variations in network load and ensure fair coexistence in a distributed manner. Based on the LBT mechanism, we also present a fairness-aware LAA-WiFi coexisting scheme with TXOP (transmitted in a single transmission opportunity) backoff for LAA eNB. Finally, the performances of various LBT solutions for LAA-WiFi coexistence are evaluated using Markov chain analytical model.

Medium Access for Concurrent Traffic in Wireless Body Area Networks: Protocol Design and Analysis

Wireless body area networks have been deployed to monitor the health condition of patients. In these applications, multiple sensors are required to report real-time data to the sink such that a physician can diagnose accurately, particularly for intensive care patients, which boosts the convergecast traffic load and increases the collision probability. However, the existing protocols cannot effectively operate under such concurrent traffic load. To bridge this gap, we present a novel two-phase receiver-initiated medium access control (MAC) protocol for concurrent traffic based on asynchronous duty cycling, which is called C-MAC. Technically, C-MAC in the first phase employs carrier-sense multiple access with collision avoidance of the IEEE 802.15.6 standard and designs an ordering-based communication algorithm to effectively avoid collisions. Moreover, C-MAC enables sensor nodes to switch to standby mode to avoid idle listening and overhearing in the second phase. Furthermore, theoretically, we explicitly formulate the mathematical expressions of the random delay and energy consumption of C-MAC. Finally, we conduct extensive numerical analysis and simulation to demonstrate the correctness of theoretical results and the better effectiveness and efficiency of C-MAC than that of RI-MAC and A-MAC in terms of transmission delay and energy consumption.

A Mobility-Aware Adaptive Duty Cycling Mechanism for Tracking Objects during Tunnel Excavation.

Tunnel construction workers face many dangers while working under dark conditions, with difficult access and egress, and many potential hazards. To enhance safety at tunnel construction sites, low latency tracking of mobile objects (e.g., heavy-duty equipment) and construction workers is critical for managing the dangerous construction environment. Wireless Sensor Networks (WSNs) are the basis for a widely used technology for monitoring the environment because of their energy-efficiency and scalability. However, their use involves an inherent point-to-point delay caused by duty cycling mechanisms that can result in a significant rise in the delivery latency for tracking mobile objects. To overcome this issue, we proposed a mobility-aware adaptive duty cycling mechanism for the WSNs based on object mobility. For the evaluation, we tested this mechanism for mobile object tracking at a tunnel excavation site. The evaluation results showed that the proposed mechanism could track mobile objects with low latency while they were moving, and could reduce energy consumption by increasing sleep time while the objects were immobile.

Low-power catalytic gas sensing using highly stable silicon carbide microheaters

A robust silicon carbide (SiC) microheater is used for stable low-power catalytic gas sensing at high operating temperatures, where previously developed low-power polycrystalline silicon (polysilicon) microheaters are unstable. The silicon carbide microheater has low power consumption (20 mW to reach 500 °C) and exhibits an order of magnitude lower resistance drift than the polysilicon microheater after continuously heating at 500 °C for 100 h and during temperature increases up to 650 °C. With the deposition of platinum nanoparticle-loaded boron nitride aerogel, the SiC microheater-based catalytic gas sensor detects propane with excellent long-term stability while exhibiting fast response and recovery time (~1 s). The sensitivity is not affected by humidity, nor during 10% duty cycling, which yields a power consumption of only 2 mW with frequent data collection (every 2 s). With a simple change of heater material from silicon to SiC, the microheater and resulting catalytic gas sensor element show significant performance improvement.

Towards Secure & Green Advanced Metering Infrastructure (AMI)

ABSTRACT This paper deals with the design issues of a secure and green Advanced Metering Infrastructure (AMI). The first part of the paper suggests enhancing the reliability of AMI system using wireless ad hoc Network technology. The suggested Advanced Metering Infrastructure consists of various types of wireless nodes we called Green Wireless Router (GWR). Here, we propose that GWRs can harvest the energy needed for its work from the surrounding environment, especially solar energy. Such suggestion permits to install GWRs in any place without considering the power supply availability and hence, extensive area is covered by the AMI. The different network traffic patterns generated from running a customized AMI simulation model were used in an experimental network based mainly on UBICOM IP2022 network processor platform (as the implementation of the intended GWR)with the aim of measuring its power consumption under different realistic circumstances. In order to decrease the power consumption of the suggested GWR and to extend the life time of the batteries, a two power management schemes we called Controlled Duty Cycling(CDC) and Event Driven Duty Cycling were suggested and implemented. The second part of the paper suggests a GWR security model to protect it against different internal and external threats. The suggested GWR security model must respond to many objectives, it should ensure that the administrative information exchanged is correct and undiscoverable (information authenticity and privacy), the source is who he claims to be (message integrity and source authentication) and the system is robust and available (using Cooperative Intrusion Detection System).

The Study of Traffic-Aware ContikiMAC

MAC (Medium Access Control) is an important protocol for wireless sensor networks (WSN) to ensure the efficiency of communication. The ContikiMAC is the default radio duty cycling (RDC) mechanism in Contiki, which is an open source real-time operating system for WSN. ContikiMAC is more energy-efficient than other MAC protocols, but it is not well adapted to variable traffic loads because it’s duty-cycling is based on static wake-up frequency. In this paper, we propose a traffic-aware ContikiMAC which can automatically adjusting the duty cycle according to the traffic load of the network. The simulation results indicate that the traffic-aware ContikiMAC has greatly improved the network in the performance of power consumption, latency and packet loss.

Wi-Fi Coexistence with Duty Cycled LTE-U

Coexistence of Wi-Fi and LTE-Unlicensed (LTE-U) technologies has drawn significant concern in industry. In this paper, we investigate the Wi-Fi performance in the presence of duty cycle based LTE-U transmission on the same channel. More specifically, one LTE-U cell and one Wi-Fi basic service set (BSS) coexist by allowing LTE-U devices to transmit their signals only in predetermined duty cycles. Wi-Fi stations, on the other hand, simply contend the shared channel using the distributed coordination function (DCF) protocol without cooperation with the LTE-U system or prior knowledge about the duty cycle period or duty cycle of LTE-U transmission. We define the fairness of the above scheme as the difference between Wi-Fi performance loss ratio (considering a defined reference performance) and the LTE-U duty cycle (or function of LTE-U duty cycle). Depending on the interference to noise ratio (INR) being above or below −62 dbm, we classify the LTE-U interference as strong or weak and establish mathematical models accordingly. The average throughput and average service time of Wi-Fi are both formulated as functions of Wi-Fi and LTE-U system parameters using probability theory. Lastly, we use the Monte Carlo analysis to demonstrate the fairness of Wi-Fi and LTE-U air time sharing.

Aggregated Packet Transmission in Duty-Cycled WSNs: Modeling and Performance Evaluation

Duty cycling (DC) is a popular technique for energy conservation in wireless sensor networks (WSNs) that allows nodes to wake up and sleep periodically. Typically, a single-packet transmission (SPT) occurs per cycle, leading to possibly long delay. With aggregated packet transmission (APT), nodes transmit a batch of packets in a single cycle. The potential benefits brought by an APT scheme include shorter delay, higher throughput, and higher energy efficiency. In the literature, different analytical models have been proposed to evaluate the performance of SPT schemes. However, no analytical models for the APT mode on synchronous DC medium access control (MAC) mechanisms exist. In this paper, we first develop a 3-D discrete-time Markov chain (DTMC) model to evaluate the performance of an APT scheme with packet retransmission enabled. The proposed model captures the dynamics of the state of the queue of nodes and the retransmission status and the evolution of the number of active nodes in the network, i.e., nodes with a nonempty queue. We then study the number of retransmissions needed to transmit a packet successfully. Based on the observations, we develop another less-complex DTMC model with infinite retransmissions, which embodies only two dimensions. Furthermore, we extend the 3-D model into a 4-D model by considering error-prone channel conditions. The proposed models are adopted to determine packet delay, throughput, packet loss, energy consumption, and energy efficiency. Furthermore, the analytical models are validated through discrete-event-based simulations. Numerical results show that an APT scheme achieves substantially better performance than its SPT counterpart in terms of delay, throughput, packet loss, and energy efficiency and that the developed analytical models reveal precisely the behavior of the APT scheme.

EcoSense: A Hardware Approach to On-Demand Sensing in the Internet of Things

An Internet of Things system typically contains a large number of low-cost devices that are mainly powered by batteries and designed to operate for a relatively long period of time. Due to the stagnated battery technology, energy efficiency will still be a burning issue for future IoT systems. To achieve better energy efficiency, we propose an innovative sensor architecture called EcoSense. Unlike traditional software-based approaches (e.g., duty cycling or adaptive sampling techniques), EcoSense provides a hardware-based on-demand sensing mechanism that effectively eliminates the energy waste caused by a sensor working in sleep or standby mode. When desired events are not present, an EcoSense sensor is completely turned off to save energy (i.e., drawing zero current). When desired events occur, an on-demand connection module will harvest energy from the events and reactivate the sensor. We implemented light- and RF-driven EcoSense sensors, and evaluated their performance in realworld experiments. Experimental results show that the EcoSense technique is able to immediately detect lights and RF signals, and offers reasonable reaction distances.

Range extension cooperative MAC to attack energy hole in duty-cycled multi-hop WSNs

Effective techniques for extending lifetime in multi-hop wireless sensor networks include duty cycling and, more recently introduced, cooperative transmission (CT) range extension. However, a scalable MAC protocol has not been presented that combines both. An On-demand Scheduling Cooperative MAC protocol (OSC-MAC) is proposed to address the energy hole problem in multi-hop wireless sensor networks (WSNs). By combining an on-demand strategy and sensor cooperation intended to extend range, OSC-MAC tackles the spatio-temporal challenges for performing CT in multi-hop WSNs: cooperating nodes are neither on the same duty cycle nor are they necessarily in the same collision domain. We use orthogonal and pipelined duty-cycle scheduling, in part to reduce traffic contention, and devise a reservation-based wake-up scheme to bring cooperating nodes into temporary synchrony to support CT range extension. The efficacy of OSC-MAC is demonstrated using extensive NS-2 simulations for different network scenarios without and with mobility. Compared with existing MAC protocols, simulation results show that while we explicitly account for the overhead of CT and practical failures of control packets in dense traffic, OSC-MAC still gives 80–200 % lifetime improvement.

Wireless sensor node demonstrating indoor-light energy harvesting and voltage-triggered duty cycling

We demonstrate a wireless sensor node (WSN) that operates purely on harvested ambient indoor light energy and regulates its duty cycle via voltage-triggered sensing and transmission. The extremely low-power light found in indoor environments can be considered at first sight as unsuitable for high-power load demands characteristic of radios [1], but by leveraging spectrum-tailored solar cells, trickle charging a high-power energy reservoir, and implementing triggered duty cycling, we show that these power demands can be consistently met. All energy harvesting and storage components are fabricated in our labs.

Modeling and performance analysis for a receiver-initiated MAC protocol in wireless sensor networks

Energy efficiency is a very important requirement in designing a MAC protocol for wireless sensor networks using battery-operated sensor nodes. We proposed a new energy-efficient MAC protocol, RIX-MAC, based on asynchronous duty cycling and receiver-initiated scheme. In this article, we analyze the performance such as throughput, delay, and energy consumption of RIX-MAC with modeling and simulation. For mathematical analysis, we first use the Markov chain model and determine the transmission and state probabilities and set the equations to solve throughput and delay. We also calculate the energy consumption by separating a cycle period into TX and RX durations. Our analysis results are validated by comparing with the simulation results obtained by NS-2.

A Self-adaptive Duty Cycle Receiver Reservation MAC Protocol for Power Efficient Wireless Sensor Networks

Objectives: In Wireless Sensor Networks nodes are deployed into hazardous environments with limited battery source. The nodes must operate with utmost power efficiency to continue performing critical tasks. Methods/Statistical Analysis: In order to be power efficient, the underlying MAC protocol of the network has to be designed to expend minimal energy during the functioning of the nodes. Most of the MAC protocols achieve energy efficiency by controlling the duty cycle. Selfadaptive duty cycle along with receiver reservation provides a viable means to reduce energy expenditure of the nodes. Findings: In this paper, we propose a receiver reservation MAC protocol that utilizes self-adaptive duty cycling which bring better power efficiency in WSN. The sleep interval of the nodes is regulated based on the self-adaptive factor. This factor is determined based on the packets received at the node in current and previous transmission cycles. Application/ Improvements: Receiver reservation helps the network to avoid collisions and back offs. The self-adaptive nature of the MAC protocol enables the nodes to tune their duty cycle based on the data transmitted in the network.

Full On-Device Stay Points Detection in Smartphones for Location-Based Mobile Applications.

The tracking of frequently visited places, also known as stay points, is a critical feature in location-aware mobile applications as a way to adapt the information and services provided to smartphones users according to their moving patterns. Location based applications usually employ the GPS receiver along with Wi-Fi hot-spots and cellular cell tower mechanisms for estimating user location. Typically, fine-grained GPS location data are collected by the smartphone and transferred to dedicated servers for trajectory analysis and stay points detection. Such Mobile Cloud Computing approach has been successfully employed for extending smartphone’s battery lifetime by exchanging computation costs, assuming that on-device stay points detection is prohibitive. In this article, we propose and validate the feasibility of having an alternative event-driven mechanism for stay points detection that is executed fully on-device, and that provides higher energy savings by avoiding communication costs. Our solution is encapsulated in a sensing middleware for Android smartphones, where a stream of GPS location updates is collected in the background, supporting duty cycling schemes, and incrementally analyzed following an event-driven paradigm for stay points detection. To evaluate the performance of the proposed middleware, real world experiments were conducted under different stress levels, validating its power efficiency when compared against a Mobile Cloud Computing oriented solution.

BMRF: Bidirectional Multicast RPL Forwarding

Nowadays, the transition of Wireless Sensor Networks (WSNs) to Internet Protocol version 6 (IPv6), in particular to IPv6 over Low power Wireless Personal Area Networks (6LoWPAN), is evident [1]. However, in most commonly used implementations, not all IPv6 features are available. For example, current implementations are not very optimized for multicast, despite the many benefits multicast can offer with respect to the number of radio transmissions and the amount of consumed energy.In this paper we present Bidirectional Multicast RPL Forwarding (BMRF), a new multicast protocol that combines the best features of the Routing Protocol for Low Power and Lossy Networks (RPL) multicast on the one hand and of Stateless Multicast RPL Forwarding (SMRF) on the other hand. The main features are bidirectionality and the ability to offer a choice between Link Layer broadcast and Link Layer unicast for which the threshold to decide for a mote, which link layer mode to choose, is mainly based on its number of interested children and the duty cycling rate. An implementation of BMRF is realized in Contiki. Our measurements show that BMRF, when using the optimal configuration, results in less radio transmissions, and less energy consumption, and higher packet delivery ratio compared to SMRF, often at the cost of a higher end-to-end delay.

A Low Duty Cycle MAC Protocol for Directional Wireless Sensor Networks

Directional communication in wireless sensor networks minimizes interference and thereby increases reliability and throughput of the network. Hence, directional wireless sensor networks (DWSNs) are fastly attracting the interests of researchers and industry experts around the globe. However, in DWSNs the conventional medium access control protocols face some new challenges including the synchronization among the nodes, directional hidden terminal and deafness problems, etc. For taking the advantages of spatial reusability and increased coverage from directional communications, a low duty cycle directional Medium Access control protocol for mobility based DWSNs, termed as DCD-MAC, is developed in this paper. To reduce energy consumption due to idle listening, duty cycling is extensively used in WSNs. In DCD-MAC, each pair of parent and child sensor nodes performs synchronization with each other before data communication. The nodes in the network schedule their time of data transmissions in such a way that the number of collisions occurred during transmissions from multiple nodes is minimized. The sensor nodes are kept active only when the nodes need to communicate with each other. The DCD-MAC exploits localized information of mobile nodes in a distributed manner and thus it gives weighted fair access of transmission slots to the nodes. As a final point, we have studied the performance of our proposed protocol through extensive simulations in NS-3 and the results show that the DCD-MAC gives better reliability, throughput, end-to-end delay, network lifetime and overhead comparing to the related directional MAC protocols.