Dissertations / Theses on the topic 'Wake-Up radio'

With the word of smart, the whole world is running on the smart technologies and smart devices which are fairly constructed by wireless sensors networks. The heart of the WSNs are nodes, which are deployed in different environmental conditions with different applications.‘Power constraint’ is a major challenge faced by all manufacturers of nodes, as all the components of the nodes are running just with a single source battery.The work presented in this thesis is an attempt to reduce the power consumption of WSNsby developing a unique Wake-Up Radio system that is super-efficient in power consumption when one compares it to duty cycling method. This paper presents a simple wake-up radio architecture with easily available Off the shelf components and operating in ISM band.At the transmitting end, a receiver with 125 KHz baseband signal is modulated on an 868MHz frequency carrier and is transmitted with the help of homemade dipole antenna. The wake-up radio receiver is constructed with a receiving antenna of 868 MHz and a network that matches good impedance to reduce the power loss of received signal, followed by a demodulation circuit with HSMS-285C zero bias Schottky diode to retrieve the baseband signal and to increase the sensitivity of the device. Later, the retrieved baseband signal is received by AS3933 low frequency wake-up receiver. The AS933 works like a comparator which compares the incoming address with the stored address to generate wake-up interrupt over node’s microcontroller activating it to perform its function.Measurements were made with the help of AS3933 demo board. The proposed system has a current consumption of 42.74μA including the current consumption of the components deployed in the demo board. In an ideal case, wake-up radio can be constructed without usingAS3933 demo board by using only AS3933 IC that gives current consumption of 2.8μA. The developed prototype has a sensitivity of -40 dBm which resulted in a wake-up distance of 20meters at an output power of -5 dBm from the transmitting antenna. This justifies that the proposed system lowers power consumption in wireless sensor networks when compared to duty cycling.

La consommation des systèmes de communication pour l'IoT peut être réduite grâce à un nouveau paradigme de réception radio. La technique consiste à ajouter un récepteur supplémentaire à chaque noeud IoT, appelé Wake Up Radio (WU-RX). Le rôle du WU-RX est de surveiller le canal de communication et de réveiller le récepteur principal (aussi appelé récepteur de données) lors de la réception d'une demande de communication. Une analyse des implémentations des WU-RX existants montre que les systèmes de l'état de l'art sont suffisamment sensibles par rapport aux récepteurs de données classiques mais manquent de robustesse face aux brouilleurs. Pour améliorer cette caractéristique nous proposons un étage de filtrage accordable `a fréquence intermédiaire qui nous permet de scanner toute la bande FI en cherchant le canal utilisé pour la demande de réveil. Ce filtre a été implémenté en utilisant les principes du traitement numérique de données à temps continu et consiste en un CAN suivi par un processeur numérique à temps continu. Le principe de fonctionnement du CAN est basé sur les modulateurs delta, avec une boucle de retour améliorée qui lui permet la quantification des signaux de fréquence plus élevé pour une consommation énergétique plus faible. Par conséquent, il a une plage de fonctionnement entre 10MHz et 50MHz ; pour un SNDR entre 32dB et 42dB et une consommation de 24uW. Cela se traduit par une figure de mérite entre 3fJ/conv-step et 10fJ/conv-step, une des meilleures pour la gamme de fréquences sélectionnée. Le processeur numérique est constitué d'un filtre IIR suivi par un filtre FIR. L'atténuation hors bande apportée par le filtre IIR permet de réduire le taux d'activité vu par le filtre FIR qui, par conséquent, consomme moins d'énergie. Nous avons montré, en simulation, une réduction de la puissance consommée par le filtre FIR d'un facteur entre 2 et 3. Au total, les deux filtres atteignent plus que 40dB de réjection hors bande, avec une bande passante de 2MHz qui peut être délacée sur toute la bande passante du CAN. Dans un pire cas, le système proposé (CAN et processeur numérique) consomme moins de 100uW, cependant la configuration des signaux à l'entrée peut rendre cette consommation plus faible
Wake-Up Receivers (WU-RX) have been recently proposed as candidates to reduce the communication power budget of wireless networks. Their role is to sense the environment and wake up the main receivers which then handle the bulk data transfer. Existing WU-RXs achieve very high sensitivities for power consumptions below 50uW but severely degrade their performance in the presence of out-of-band blockers. We attempt to tackle this problem by implementing an ultra low power, tunable, intermediate frequency filtering stage. Its specifications are derived from standard WU-RX architectures; it is shown that classic filtering techniques are either not tunable enough or demand a power consumption beyond the total WU-RX budget of 100uW. We thus turn to the use of Continuous Time Digital Signal Processing (CT-DSP) which offers the same level of programmability as standard DSP solutions while providing an excellent scalability of the power consumption with respect to the characteristics of the input signal. A CT-DSP chain can be divided into two parts: the CT-ADC and the CT-DSP itself; the specifications of these two blocks, given the context of this work, are also discussed. The CT-ADC is based on a novel, delta modulator-based architecture which achieves a very low power consumption; its maximum operation frequency was extended by the implementation of a very fast feedback loop. Moreover, the CT nature of the ADC means that it does not do any sampling in time, hence no anti-aliasing filter is required. The proposed ADC requires only 24uW to quantize signals in the [10MHz 50MHz] bandwidth for an SNR between 32dB and 42dB, resulting in a figure of merit of 3-10fJ/conv-step, among the best reported for the selected frequency range. Finally, we present the architecture of the CT-DSP which is divided into two parts: a CT-IIR and a CT-FIR. The CT-IIR is implemented by placing a standard CT-FIR in a feedback loop around the CT-ADC. If designed correctly, the feedback loop can now cancel out certain frequencies from the CT-ADC input (corresponding to those of out-of-band interferers) while boosting the power of the useful signal. The effective amplitude of the CT-ADC input is thus reduced, making it generate a smaller number of tokens, thereby reducing the power consumption of the subsequent CT-FIR by a proportional amount. The CT-DSP consumes around 100uW while achieving more than 40dB of out-of-band rejection; for a bandpass implementation, a 2MHz passband can be shifted over the entire ADC bandwidth

Abstract. The last decade has been really ambitious in new research and development techniques to reduce energy consumption especially in wireless sensor networks (WSNs). Sensor nodes are usually battery-powered and thus have very limited lifetime. Energy efficiency has been the most important aspect to discuss when talking about wireless body area network (WBAN) in particular, since it is the bottleneck of these networks. Medium access control (MAC) protocols hold the vital position to determine the energy efficiency of a WBAN, which is a key design issue for battery operated sensor nodes. The wake-up radio (WUR) based MAC and physical layer (PHY) have been evaluated in this research work in order to contribute to the energy efficient solutions development. WUR is an on-demand approach in which the node is woken up by the wake-up signal (WUS). A WUS switches a node from sleep mode to wake up mode to start signal transmission and reception. The WUS is transmitted or received by a secondary radio transceiver, which operates on very low power. The energy benefit of using WUR is compared with conventional duty-cycling approach. As the protocol defines the nodes in WUR based network do not waste energy on idle listening and are only awakened when there is a request for communication, therefore, energy consumption is extremely low. The performance of WUR based MAC protocol has been evaluated for both physical layer (PHY) and MAC for transmission of WUS and data. The probabilities of miss detection, false alarm and detection error rates are calculated for PHY and the probabilities of collision and successful data transmission for channel access method Aloha is evaluated. The results are obtained to compute and compare the total energy consumption of WUR based network with duty cycling. The results prove that the WUR based networks have significant potential to improve energy efficiency, in comparison to conventional duty cycling approach especially, in the case of low data-reporting rate applications. The duty cycle approach is better than WUR approach when sufficiently low duty cycle is combined with highly frequent communication between the network nodes.

La natura wireless delle tecnologie per IOT si accosta nella maggior parte dei casi allo sviluppo di sistemi alimentati a batteria o comunque con un basso fabbisogno energetico. Infatti, la portabilità e l’affidabilità degli smart objects sono direttamente collegate con la loro autonomia energetica. In alcuni casi risulta impossibile, o comunque non conveniente, alimentare i sistemi con la rete elettrica (si pensi al controllo degli spazi agricoli); alternativamente, è necessario garantire la loro utilizzabilità in mancanza di fonti di energia convenzionali, come per esempio nelle applicazioni di sicurezza e monitoraggio, studiate per funzionare in situazioni critiche. Anche per questo motivo, la ricerca, sia in ambito accademico che industriale, ha compiuto notevoli sforzi nello sviluppare nuove tecnologie orientate al basso consumo energetico: i cosiddetti sistemi (ultra-)low power. Questa tesi, sviluppata presso il Centro di Ricerca sui Sistemi Elettronici “Ercole de Castro” dell’Università di Bologna, si focalizza sul progetto di un sistema di controllo digitale dedicato alla sincronizzazione ed alla gestione di Wake-Up Radio. Nel capitolo 1 si tratta in maniera più specifica le architetture di trasmettitori e ricevitori a basso consumo, introducendo il concetto di Wake-Up Radio. Nel capitolo 2 vengono esposte le caratteristiche e le funzionalità offerte dalle Wake-Up Radio. Nel capitolo 3 si presenta il problema della sincronizzazione nei sistemi wireless ed alcune soluzioni ad esso associate. Nel capitolo 4 viene illustrato il sistema digitale e il suo processo di sintesi. Vengono anche ri-portate le principali prestazioni di interesse. Nel capitolo 5 l’architettura viene ottimizzata per ridurne ulteriormente il consumo. Alla fine dell’elaborato sono presentate le conclusioni di questo lavoro di tesi, cercando di discuterne eventuali sviluppi futuri, cercando di aver contribuito positivamente in questo ambito di ricerca stimolante ed in costante evoluzione.

One of the most important requirements for wireless sensor networks (WSNs) is the energy efficiency, since sensors are usually fed by a battery that cannot be replaced or recharged. Radio wake-up - the technology that lets a sensor completely turn off and be reactivated by converting the electromagnetic field of radio waves into energy - is now one of the most emergent strategies in the design of wireless sensor networks. This work presents Scheduled on Demand Radio WakeUp (SORW), a flexible scheduler designed for a wireless sensor network where duty cycling strategy and radio wake-up technology are combined in order to optimize the network lifetime. In particular, it tries to keep sensors sleeping as much as possible, still guaranteeing a minimum number of detections per unit of time. Performances of SORW are provided through the use of OMNet++ simulator and compared to results obtained by other basic approaches. Results show that with SORW it is possible to reach a theoretical lifetime of several years, compared to simpler schedulers that only reach days of activity of the network.

Nei nodi wireless per applicazioni IoT, i ricetrasmettitori (transceiver) a radio-frequenza (RF) sono responsabili della maggior parte del consumo di potenza. Inoltre, se da un lato il picco di potenza assorbita avviene in corrispondenza degli istanti di trasmissione, dall’altro il ricevitore, che deve essere mantenuto sempre attivo anche quando il resto del sistema è in stato di “idle”, consuma una buona frazione dell’energia totale. Al fine di ridurre questo consumo, una particolare tipologia di ricevitori detti di “wake-up” sono tra i principali oggetti di ricerca nell’ambito dell’IoT. Essi hanno prestazioni ridotte e consumo molto basso, poiché devono restare sempre attivi mentre il resto del nodo è in stato di “idle”. Tale Wake-Up Radio (WUR) ha il compito di “ascoltare” il canale e attivare il ricevitore principale ed il microcontrollore solo quando c’è qualche richiesta in arrivo. Una parte integrante del ricevitore Wake-Up è il circuito per la decodifica dei byte trasmessi, che di solito comprendono almeno un codice d’indirizzo, che deve essere estratto e confrontato con l’indirizzo memorizzato nel ricevitore. Soltanto se questo confronto ha esito positivo viene attivato il resto del sistema. L’obiettivo di questo lavoro di tesi è il progetto di un sistema di clock recovery basato su PLL analogico a bassissimo consumo per sistemi Wake-Up Radio di tipo short-range caratterizzati da una bit rate di 1 kbps. Tale sistema deve fornire alla rete di controllo un clock allineato in fase e frequenza con i dati ricevuti. Rispetto ad altri sistemi in cui si deve semplicemente decodificare un indirizzo, la soluzione basata su PLL oggetto di questo studio (poiché implica consumi e tempi di aggancio non trascurabili) è particolarmente adatta per lunghe trasmissioni. Nel progetto di un PLL a basso consumo l’obiettivo consiste nell’ottimizzare il trade-off tra consumo (con correnti nell’ordine del nanowatt) e tempo di aggancio.

L’obiettivo principale nella progettazione di una Wireless sensor Network (WSN) in ambito ultra-low power è la minimizzazione dei consumi energetici, per aumentare la durata della batteria o addirittura rimuoverla, rendendo il sistema autosufficiente. La maggior parte dell’energia in questi sistemi viene consumata dal ricevitore, che rimane acceso aspettando l’inizio di una comunicazione. Gestire le accensioni del ricevitore si rivela la tecnica migliore per abbassare il consumo energetico. Un circuito studiato per la gestione del ricevitore è la Wake-up Radio (WuR). Una Wake-up radio è un circuito con bassi consumi di potenza, dell’ordine dei uW, che analizza il canale radio e attiva il ricevitore principale solo se viene rilevato un segnale di wake-up, che può limitarsi alla semplice presenza di un segnale ad una certa frequenza o può prevedere la presenza di un indirizzo. In questo elaborato è presentata la progettazione di una Wake-up Radio a componenti discreti. In particolare ci si è concentrati sull’implementazione di una rete di indirizzamento utilizzando i componenti più efficienti presenti sul mercato. Per prima cosa si definiscono le specifiche della rete di indirizzamento e le sue possibili implementazioni; seguono poi la selezione dei componenti, la sintesi logica e infine l’analisi dei consumi. Il risultato finale è di un consumo pari a 2,1 uW in stato di riposo e 417 uW in stato di decodifica dell’indirizzo, ricavato con una frequenza di clock pari a 10KHz. Considerando la bit-rate di trasmissione dell’indirizzo di 7kbit/s e un massimo tempo di risveglio di 60ms la potenza media necessaria al funzionamento della rete è di 12 uW, paragonabile a quella ottenuta in altri progetti in letteratura.

Oggetto di studio di questa tesi di laurea è la realizzazione di un firmware dedicato alla sezione logica di controllo di una Wake-up Radio implementata su tag RFID, realizzata attraverso l'utilizzo di un microcontrollore ultra-low power. Per la realizzazione del sistema, si é deciso di utilizzare il microcontrollore Apollo prodotto da Ambiq Micro. Tale dispositivo, basandosi sull'architettura Subthreshold Power Optimized Technology (SPOT) brevettata da Ambiq, utilizza transistori polarizzati in regione di sottosoglia, presentando i migliori valori di consumo dichiarati sul mercato.

Nowadays, Internet of things applications are increasing, and each end-node has more demanding requirements such as energy efficiency and speed. The thesis proposes a heterogeneous elaboration unit for smart power applications, that consists of an ultra-low-power microcontroller coupled with a small (around 1k equivalent gates) soft-core of embedded FPGA. This digital system is implemented in 90-nm BCD technology of STMicroelectronics, and through the analysis presented in this thesis proves to have good performance in terms of power consumption and latency. The idea is to increase the system performance exploiting the embedded FPGA to managing smart power tasks. For the intended applications, a remarkable computational load is not required, it is just required the implementation of simple finite state machines, since they are event-driven applications. In this way, while the microcontroller deals with other system computations such as high-level communications, the eFPGA can efficiently manage smart power applications. An added value of the proposed elaboration unit is that a soft-core approach is applied to the whole digital system including the eFPGA, and hence, it is portable to different technologies. On the other hand, the configurability improvement has a straightforward drawback of about a 20–27% area overhead. The eFPGA usage to manage smart power applications, allows the system to reduce the required energy per task from about 400 to around 800 times compared to a processor implementation. The eFPGA utilization improves also the latency performance of the system reaching from 8 to 145 times less latency in terms of clock cycles. The thesis also introduces the architecture of a nano-watt wake-up radio integrated circuit implemented in 90-nm BCD technology of STMicroelectronics. The wake-up radio is an auxiliary always-on radio for medium-range applications that allows the IoT end-nodes to drastically reduce the power consumption during the node idle-listening communication phase.

During the recent years, the research related to Wake-up Radio (WuR) systems has gained noticeable interest. In WuR systems, a node initiating a communication first sends a Wake-up Call (WuC) by means of its Wake-up Transmitter (WuTx), to the Wake-up Receiver (WuRx) of a remote node to activate it in an on-demand manner. Until the reception of the WuC, the node's MCU and main data transceiver are in sleep mode. Hence, WuR drastically reduce the power required by wireless nodes. This thesis provides a complete analysis of several WuR designs vs. conventional MAC protocols for Wireless Sensor Networks (WSN). The research is performed in an incremental fashion and includes hardware, softwar and simulation topics. WuR systems enable energy savings in plenty of different applications, e.g., retrieving information from environmental pollution sensors placed in a city by a mobile collector node, or activating a sleeping wireless AP. They are easy to program in and provide implicit synchronization. However, achieving a good WuRx design may become a challenge because power amplifiers cannot be used for the sake of energy. The system proposed in chapter 2 is a successful WuR system prototype. The so-called SµA-WuRx is less complex than commercial WuR systems, it is cheaper from the monetary point of view, requires several times less energy and allows for up to 15 meters of communication, an adequate value for WuR systems. However, the system can be improved by including several desirable features, such as longer operational ranges and/or addressing mechanisms. The so-called Time-Knocking (TicK) addressing strategy, analyzed in chapter 3, enables energy efficient node addressing by varying the time between WuCs received by a MCU. TicK allows for variable length addresses and multicast. A WuR system may not fit any possible application. Thus, while the SµA-WuRx and TicK efficiently solved many of the requirements of single-hop and data-collector applications, they lack of flexibility. Instead, SCM-WuR systems in chapter 4 feature an outstanding trade-off between hardware complexity, current consumption and operational range, and even enable multi-hop wake-up for long remote sensor measure collection. To contextualize the WuR systems developed, chapter 5 provides an overview of the most important WuR systems as of 2014. Developing a MAC protocol which performs acceptably in a wide range of diverse applications is a very difficult task. Comparatively, SCM-WuR systems perform properly in all the use cases (single and multi-hop) presented in chapter 6. Bluetooth Low Energy, or BLE, appears as a duty-cycled MAC protocol mainly targeting single-hop applications. Because of its clearly defined use cases and its integration with its upper application layers, BLE appears as an extremely energy-efficient protocol that cannot be easily replaced by WuR. Because of all these aspects, the performance of BLE is analyzed in chapter 7. Finally, chapter 8 tries to solve one of the issues affecting WuR systems, that is, the need for extra hardware. While this issue seems difficult to solve for WuRx, the chapter provides ideas to use IEEE 802.11-enabled devices as WuTx.
Durant els últims anys, la investigació relativa als sistemes de Ràdios de Wake-up (de l'anglès Wake-up Radio, WuR) ha experimentat un interès notable. En aquests sistemes, un node inicia la comunicació inal.làmbrica transmetent una Wake-up Call (WuC), per mitjà del seu transmissor de Wake-up (WuTx), dirigida al receptor de Wake-up (WuRx) del node remot. Aquesta WuC activa el node remot, el microcontrolador (MCU) i la ràdio principals del qual han pogut romandre en mode "sleep" fins el moment. Així doncs, els sistemes WuR permeten un estalvi dràstic de l'energia requerida pels nodes sense fils. Aquesta tesi proposa diferents sistemes WuR i els compara amb protocols MAC existents per a xarxes de sensors sense fils (Wireless Sensor Networks, WSN). La investigació es realitza de forma progressiva i inclou hardware, software i simulació. Els sistemes WuR permeten un estalvi energètic notable en moltes aplicacions: recol¿lecció d'informació ambiental, activació remota de punts d'accés wi-fi, etc. Són fàcils de programar en software i comporten una sincronització implícita entre nodes. Malauradament, un consum energètic mínim impossibilita l'ús d'amplificadors de potència, i dissenyar-los esdevé un repte. El sistema presentat en el capítol 2 és un prototip exitós de sistema WuR. De nom SµA-WuR, és més senzill que alternatives comercials, és més econòmic, requereix menys energia i permet distàncies de comunicació WuR majors, de fins a 15 metres. L'estratègia d'adreçament Time-KnocKing, presentada en el capítol 3, permet dotar l'anterior SµA-WuR d'una forma d'especificar el node adreçat, permetent estalvi energètic a nivell de xarxa. TicK opera codificant el temps entre diferents WuC. Depenent del temps entre intervals, es desperten el/s node/s desitjats d'una forma extremadament eficient. Tot i els seus beneficis, hi ha aplicacions no implementables amb el sistema SµA-WuR. Per a aquest motiu, en el capítol 4 es presenta el sistema SCM-WuR, que ofereix un rang d'operació de 40 a 100 metres a canvi d'una mínima complexitat hardware afegida. SCM-WuR cobreix el ventall d'aplicacions del sistema SµA-WuRx, i també les que requereixen multi-hop a nivell WuR. El capítol 5 de la tesi compara els dos sistemes WuR anteriors vers les propostes més importants fins el 2014. El capítol 6 inclou un framework de simulació complet amb les bases per a substituir els sistemes basats en duty-cycling a WuR. Degut a que desenvolupar un protocol MAC que operi acceptablement bé en multitud d'aplicacions esdevé una tasca pràcticament impossible, els sistemes WuR presentats amb anterioritat i modelats en aquest capítol representen una solució versàtil, interessant i molt més eficient des del punt de vista energètic. Bluetooth Low Energy, o Smart, o BLE, representa un cas d'aplicació específica on, degut a la gran integració a nivell d'aplicació, la substitució per sistemes de WuR esdevé difícil Per a aquesta raó, i degut a que es tracta d'un protocol MAC extremadament eficient energèticament, aquesta tesi conté una caracterització completa de BLE en el capítol 7. Finalment, el capítol 8 soluciona un dels inconvenients del sistemes WuR, el disseny de WuTx específics, presentant una estratègia per a transformar qualsevol dispositiu IEEE 802.11 en WuTx.

Il presente lavoro di Tesi è stato incentrato sul dimensionamento di un sistema wireless epidermico abile a monitorare parametri fisiologici. La fase iniziale del lavoro è stata spesa per indagare le varie tipologie di sorgenti utili ad effettuare Energy Harvesting in contesti applicativi biomedicali, ed analizzare lo stato dell’arte in merito ai sistemi miniaturizzati, passivi, interfacciabili alla superficie corporea, configurabili nel settore di ricerca e-skin. Il corpo centrale del lavoro è stato quello di dimensionare un nuovo sistema wireless epidermico, energeticamente autonomo. Tale sistema è stato strutturato in tre catene costitutive. La prima di queste definita di Energy Harvesting e storage, presenta una cella solare, un boost converter –charger per il management della potenza ed una thin film battery come elemento di storage. La seconda catena è configurabile come quella di ricezione, in cui l’elemento cruciale è una Wake-Up Radio (WUR), la cui funzione è quella di abilitare il sistema di misura costituito da Microcontroller e sensore solo quando un Reader comunicherà la corretta sequenza di bit abilitanti alla lettura. La presente scelta ha mostrato vantaggi in termini di ridotti consumi. La terza ed ultima catena del sistema per mezzo di Microcontrollore e Transceiver consentirà di trasmettere via RF il dato letto al Reader. Una interfaccia grafica utente implementata in Matlab è stata ideata per la gestione dei dati. La sezione ultima della Tesi è stata impostata analizzando i possibili sviluppi futuri da seguire, in particolare integrare il sistema completo utilizzando un substrato flessibile così come il Kapton e dotare il sistema di sensoristica per misure biomediche specialistiche per esempio la misura del SpO2.

Abstract This thesis proposes cross-layer approaches which enable to improve energy efficiency of wireless sensor networks and wireless body area networks (WSN & WBAN). The focus is on the physical (PHY) and medium access control (MAC) layers of communication protocol stack and exploiting their interdependencies. In the analysis of the PHY and MAC layers, their relevant characteristics are taken into account, and cross-layer models are developed to study the effect of these layers on energy efficiency. In addition, cross-layer analysis is applied at the network level by addressing hierarchical networks' energy efficiency. The objective is to improve energy efficiency by taking into account that substantial modifications to current standards and techniques are not required to take advantage of the proposed methods. The studied scenarios of WSN take advantage of the wake-up radio (WUR). A generic WUR-based MAC (GWR-MAC) protocol with objective to improve energy efficiency by avoiding idle listening is proposed. First, the proposed cross-layer model is developed at a general level and applied to study the forward error correction (FEC) code rate selection effect on the length of the transmission period and energy efficiency in a star topology network. Then an energy efficiency model for intelligent hierarchical architecture based on GWR-MAC is proposed and performance comparison with a duty-cycle radio (DCR) approach is performed. Interactions between different layers' devices are taken into account, and the WUR and DCR approaches are compared as a function of event frequency. The third cross-layer model focuses on the effect of the FEC code rate and data packet payload length on the energy efficiency of the IEEE Std 802.15.6-based WBANs using IR-UWB PHY. The results acquired by using analytical modelling and simulations with the Matlab software clearly illustrates the potential energy gains that can be achieved with the proposed cross-layer approaches. The developed WUR-based MAC protocol, analytical models and achieved results can be exploited by other researchers in the WSN and WBAN field. The contribution of this thesis is also to stimulate further research on these timely topics and foster development of short-range communication, which has a crucial role in future converging networks such as the Internet of Things
Tiivistelmä Tässä väitöskirjassa ehdotetaan protokollakerrosten välistä tietoa hyödyntäviä (cross-layer) lähestymistapoja, jotka mahdollistavat energiatehokkuuden parantamisen langattomissa sensori- ja kehoverkoissa. Työ kohdistuu fyysisen- ja kanavanhallintakerroksen välisen vuorovaikutuksen tutkimiseen. Fyysisen- ja kanavanhallintakerrosten analyysissä huomioidaan niiden tärkeimmät ominaisuudet ja tutkitaan kerrosten yhteistä energiatehokkuutta. Lisäksi kerrosten välistä analyysiä sovelletaan verkkotasolle tutkimalla hierarkkisen verkon energiatehokkuutta. Tavoitteena on energiatehokkuuden parantamisen mahdollistaminen siten, että merkittäviä muutoksia nykyisiin standardeihin ja tekniikoihin ei tarvitse tehdä hyödyntääkseen ehdotettuja menetelmiä. Tutkitut sensoriverkkoskenaariot hyödyntävät heräteradiota. Väitöskirjassa ehdotetaan geneerinen heräteradiopohjainen kanavanhallintaprotokolla (GWR-MAC), jolla parannetaan energiatehokkuutta vähentämällä turhaa kanavan kuuntelua. Kerrosten välinen malli kehitetään ensin yleisellä tasolla ja sen avulla tutkitaan virheenkorjauskoodisuhteen valinnan vaikutusta lähetysperiodin pituuteen ja energiatehokkuuteen tähtitopologiaan pohjautuvissa sensoriverkoissa. Sitten väitöskirjassa ehdotetaan energiatehokkuusmalli älykkäälle GWR-MAC -protokollaan perustuvalle hierarkkiselle arkkitehtuurille ja sen suorituskykyä vertaillaan toimintajaksoperiaatteella toimivaan lähestymistapaan. Eri kerroksilla olevien laitteiden väliset vuorovaikutukset huomioidaan heräteradio- ja toimintajaksoperiaatteella toimivien verkkojen suorituskykyvertailussa tapahtumatiheyden funktiona. Kolmas malli kohdistuu virheenkorjauskoodisuhteen ja datapaketin hyötykuorman pituuden energiatehokkuusvaikutuksen tutkimiseen IEEE 802.15.6 -standardiin perustuvissa langattomissa kehoverkoissa. Analyyttinen mallinnus ja Matlab-ohjelmiston avulla tuotetut simulointitulokset osoittavat selvästi energiatehokkuushyödyt, jotka saavutetaan ehdotettuja menetelmiä käyttämällä. Kehitetty GWR-MAC -protokolla, analyyttiset mallit ja tulokset ovat hyödynnettävissä sensori- ja kehoverkkotutkijoiden toimesta. Tämän väitöskirjan tavoitteena on myös näiden ajankohtaisten aiheiden jatkotutkimuksen stimulointi sekä lyhyen kantaman viestinnän kehityksen vauhdittaminen, sillä niillä on erittäin merkittävä rooli tulevaisuuden yhteen liittyvissä verkoissa, kuten esineiden ja asioiden Internetissä

Les réseaux de capteurs sans fil qui conviennent pour vaste domaine d’applications, constituent une solution prometteuse qui répond à toute exigence de surveillance continue. L’autonomie énergétique des nœuds constitue un facteur de vulnérabilité qui influe directement leur longévité et la capacité du réseau à assurer longuement la couverture d’une zone géographique d’intérêt. La gestion de consommation énergétique représente la seule approche pour accroître la durée de vie de ces réseaux et leur conférer une autonomie raisonnable. Des solutions logicielles proposées à travers les protocoles MAC, apportent des améliorations significatives à la minimisation de la dépense énergétique des nœuds. Elles permettent de réduire les périodes d’écoute du canal qui, représente l’opération la plus coûteuse en termes d’énergie dans le fonctionnement des nœuds de capteurs sans fil. Néanmoins, se limiter à ces solutions n’est pas suffisant pour garantir une longévité acceptable. La seule méthode pour optimiser la conservation d’énergie dans les RCSFs est de mettre chaque nœud constamment en mode faible puissance et d’utiliser un mécanisme de télé-réveil à travers des signaux de réveil. Cela implique, l’utilisation de circuits de réveil de faible consommation qui assurent la surveillance de canal et qui déclenchent le réveil des nœuds uniquement à chaque fois qu’événement d’intérêt se produit. Dans ce contexte, une quantité importante de travaux ont proposés l’utilisation d’un mécanisme d’adressage (adresses MAC ou d’autres informations binaires), pour permettre aux nœuds non concernés de retourner rapidement dans son état de sommeil. Cette démarche est intéressante, mais implique toutefois une dépense énergétique non négligeable, liée à la réception et au traitement des informations d’adresse au niveau de tous les nœuds. La solution la plus efficace énergétiquement serait l’utilisation d’une autre forme d’adresse. Cette thèse s’inscrit dans le contexte de minimisation de la consommation énergétique des RCSFs par la mise en œuvre d’un adressage qui permet aux nœuds de recevoir et de traiter les signaux de réveil, sans allumer leur module de communication principal. Il s’agit pour nous de supprimer la dépense énergétique liée à l’allumage du module RF et à la réception de paquets d’adresse, en se tournant vers l’exploitation de la durée des signaux de réveils. Notre solution se repose sur les caractéristiques matérielles du microcontrôleur (IRQ, Timer/Counter) des nœuds de capteurs. Elle permet de réduire les complexités liées aux conditionnements des signaux de réveils. Notre solution est implémentée sur un réseau de petite taille. Elle est évaluée expérimentalement et ses performances énergétiques sont comparées à celles d’un schéma classique de télé-réveil sans mécanisme d’adressage et à celles d’un schéma classique basé sur le duty-cycling
Wireless sensor networks that are suitable for a wide range of applications, represent a promising solution that meets any requirement for continuous monitoring. The energy autonomy of sensor nodes constitutes a vulnerability factor that directly affects their longevity and the capacity of the network to ensure long coverage of the geographical area of interest. Energy consumption management is the only way to increase the lifespan of these networks and to give them a reasonable autonomy. Software solutions proposed through MAC protocols, bring significant improvements to the minimization of the energy expenditure of sensor nodes. They reduce the idle-listening periods which represents the most expensive operation in terms of energy, in the operation of the wireless sensor nodes. However, Focusing lonely on these solutions is not enough to guarantee acceptable longevity. The only way to optimize energy conservation in the WSN is to constantly put each node in low power mode and use a wakeup mechanism through wake-up signals. This involves the use of low-power wake-up circuits that provide channel monitoring, and trigger node wake-up only whenever event of interest occurs. In this context, a significant amount of work has proposed the use of an addressing mechanism (MAC addresses or other binary informations), to allow non-concerned nodes to quickly return to their sleep state. This approach is interesting, but involves a significant energy expenditure, related to address information’s reception and processing at all nodes. The most energy efficient solution would be the use of another type of address. This thesis is part of the context of minimizing the energy consumption of the WSN, using an addressing system that allows sensor nodes to receive and process the wake-up signals, without turning on their main communication module. It is to eliminate the energy expenditure related to the RF module’s activation and the reception of address packets, by exploiting wakeup signals duration. Our solution is based on the hardware characteristics of the microcontroller (IRQ, Timer/Counter) of sensor nodes. It reduces the complexities related to wakeup signals conditioning. Our solution is implemented on a small network. Its evaluations were done experimentally and its energy performance is compared to a conventional wake-up mechanism without addressing,and a conventional scheme based on duty-cycling

Abstract Wireless sensors play a bigger and bigger role in our everyday life and they have become a part of our life in homes, vehicles, traffic, food production and healthcare, monitoring and controlling our activities. Low-cost and resource-efficient solutions are an essential part of this development. The aim of the study was to develop solutions, which improve the energy efficiency of wireless sensor networks yet still fulfil the requirements of monitoring applications. In the study, five new solutions were developed to save energy in wireless sensor networks and all the solutions were studied and verified with test bed implementations. The developed solutions are: 1. Energy-efficient medium access control (MAC), namely revive MAC (R-MAC) for duty-cycling networks with a long sampling interval (many minutes) 2. Wake-up radio solution for on-demand sampling networks, which uses the main radio as the wake-up transmitter 3. Energy-efficient internet of things (IoT) routing solution for wake-up routing with a routing protocol for low-Power and lossy networks (RPL) 4. Energy-efficient IoT compression solution: robust header compression (ROHC) compression with constrained application protocol (CoAP) 5. Data analysis solution based on an energy-efficient sensor node, where filter clogging is forecast from analysis of the vibration data at the node. All the developed solutions were promising and can be utilized in many domain areas. The solutions can be considered as proofs of concept, which need to be developed further for use in final products
Tiivistelmä Langattomat sensoreilla on yhä suurempi osuus jokapäiväisessä arjessa, jossa langattomat sensorit ovat tulleet osaksi kodin, autojen, ruuantuotannon sekä terveyden valvonta- ja seurantajärjestelmiä. Oleellisena osana tätä kehitystä ovat sekä edulliset että energia- ja resurssitehokkaat ratkaisut. Työn päämääränä oli kehittää ratkaisuja, jotka parantavat langattoman sensoriverkon energia tehokkuutta niin, että edelleen täytetään monitorointi sovellutusten asettamat vaatimukset. Työssä kehitettiin viisi uutta ratkaisua säästää energiaa langattomissa sensoriverkoissa ja kaikki ratkaisut tutkittiin ja varmennetiin työssä tehdyillä testi alustoilla. Kehitetyt ratkaisut ovat: 1. Energiatehokas alempi siirtoyhteyskerroksen protokolla (medium access control, MAC), nimittäin heräävä MAC (Revive MAC, R-MAC) jaksoittain toimiville (duty-cycling) verkoille, joissa on pitkät mittausvälit (useita minuutteja). 2. Heräteradioratkaisu (wake-up) pyynnöstä toimiville (on-demand) verkoille, joissa pääradiota käytetään heräte signaalin lähettämiseen. 3. Energiatehokas esineiden internetin (Internet of Things, IoT) reititysratkaisu herätereititykseen käyttäen matalatehoisille ja häviöllisille verkoille suunniteltua reititysprotokollaa (Routing protocol for low-Power and Lossy networks, RPL). 4. Energiatehokas IoT-pakkausratkaisu: varmatoiminen otsakkeen pakkausprotokolla (Robust Header Compression, ROHC) yhdessä rajoitettujen sovellusten protokollan (Constrained Application Protocol, CoAP) kanssa. 5. Energiatehokas sensorilaite perusteinen data prosessointi ratkaisu suodattimen tukkeutumisen ennustamiseen värähtelymittauksia käyttäen. Kaikki kehitetyt ratkaisut olivat lupaavia ja niitä voidaan käyttää useilla sovellutusalueilla. Ratkaisut ovat soveltuvuusselvityksiä (proof of concept), joita pitää kehittää edelleen loppu tuotteiden käyttöön

Grâce au confort d’utilisation qu’elles procurent, les technologies sans fil se retrouvent aujourd’hui dans un vaste panel d’applications. Ainsi le nombre d’éléments de transmission/réception radio se multiplie. Aujourd’hui pour réduire les consommations des éléments radio, il faut les rendre davantage efficaces notamment pour la partie réception. En effet, pour les communications asynchrones, les récepteurs consomment inutilement de l’énergie à attendre qu’une transmission soit faite. Dans l’objectif de réduire ce gaspillage d’énergie, des nouveaux standards ont vu le jour tel que le Zigbee et le Bluetooth Low Energy. Les performances en consommation procurées par ces deux standards résident sur leur fonction périodique à très faible rapport cyclique. Une nouvelle solution émergente pour réduire drastiquement la consommation des récepteurs en les rendant plus efficaces est l’utilisation de récepteur d’activation. Les récepteurs d’activation ou récepteur de réveil sont des récepteurs simples ce qui leur permet d’atteindre une ultra basse consommation uniquement en charge de guetter l’arrivée d’une trame et de réveiller le récepteur principal, placé en veille au préalable, pour traitement de cette dernière. Le récepteur d’activation proposé ici a été réalisé dans la technologie CMOS 160 nm de NXP. Il offre une sensibilité de -54 dBm, pour une consommation moyenne de 35 μA, prodiguant une portée de 70m à 433,92 MHz pour une puissance de 10 dBm émis. Ce récepteur ASK se distingue des autres récepteurs d’activation par le système de calibration breveté avec ajustement automatique la tension de référence requise pour la démodulation. Ce système rend le circuit robuste au problème d’offset DC et ne consomme aucun courant lorsque le circuit est en écoute. Le récepteur d’activation reconnaît un code de Manchester de 24 bits à 25 kbps, programmable grâce à une interface SPI
Wireless technologies are now widespread due to the easiness of use they provide. Consequently, the number of radio devices increases. Despite of the efforts to reduce radio circuits power consumption as they are more and more numerous, now they must achieve ultra-low power consumption. Today, radio devices are made more efficient to reduce their power consumption especially for the receiving part. Indeed, for asynchronous communication, a lot of energy is wasted by the receiver waiting for a transmission. In order to avoid this waste, new standards have been created such as Zigbee and Bluetooth Low Energy. Due to periodic operation with ultra-low duty cycle, they provide ultra-low power consumption. Another solution to drastically reduce the power consumption has emerged, wake-up receiver. Wake-up receivers are based in simple architecture to provide ultra-low power consumption, they are only in charge to wait for a frame and when it occurs, wake-up the main receiver put in standby mode before that. The proposed wake-up receiver has been designed in NXP CMOS technology 160 μm. It provides a-54 dBm sensitivity, consuming 35 μA which allows a 70m range considering a 10 dBm emitter at 433,92 MHz. This wake-up receiver operates with ASK modulation, compared to others it provides a smart patented calibration system to get the necessary reference voltage for demodulation. This mechanism provide DC offset robustness and does not drain any current while the wake-up receiver is operating. To wake up the main receiver a 24 bits programmable Manchester code is required. This code at 25 kbps is programmable by the use of an SPI interface

La sécurité des circuits intégrés pour l’IoT est généralement incompatible avec la faible consommation énergétique attendue de ces circuits. Cette thèse a donc pour but de proposer de nouvelles manières de concilier sécurité et efficacité énergétique pour les circuits intégrés.Dans un premier temps, la sécurisation d’un mécanisme de gestion de l’énergie est étudiée. Les radios de réveil permettent de gérer la sortie de veille d’objets connectés, en réveillant un tel objet lors de la réception d’un code de réveil spécifique, mais elles sont vulnérables aux attaques par déni de sommeil, qui consistent à réveiller constamment l’objet en répétant un même code de réveil de sorte à vider sa batterie. Une nouvelle manière de générer des codes de réveils est proposée, qui permet de contrer efficacement ces attaques avec un coût négligeable en énergie.Dans un second temps, l’efficacité énergétique des contre-mesures contre les attaques matérielles est améliorée à travers deux approches différentes. Une nouvelle contre-mesure mixte, ayant une consommation énergétique plus faible que les protections mixtes existantes, est proposée ; elle consiste en un lissage algorithmique de la consommation offrant une détection intrinsèque des fautes. L’implémentation adaptative de contre-mesures matérielles est également proposée ; elle consiste à moduler le niveau de protection fourni par ces contre-mesures au cours du fonctionnement d’un algorithme protégé, afin d’optimiser la sécurité et la consommation énergétique. Une évaluation de la sécurité des contre-mesures montre qu’elles fournissent une protection efficace contre les attaques matérielles existantes
The goal of this work is to propose new methods that provide both a high security and a high energy efficiency for integrated circuits for the IoT.On the one side, we study the security of a mechanism dedicated to energy management. Wake-up radios trigger the wake-up of integrated circuits upon receipt of specific wake-up tokens, but they are vulnerable to denial-of-sleep attacks, during which an attacker replays such a token indefinitely to wake-up a circuit and deplete its battery. We propose a new method to generate unpredictable wake-up tokens at each wake-up, which efficiently prevents these attacks at the cost of a negligible energy overhead.On the other side, we improve on the energy efficiency of hardware countermeasures against fault and side-channel attacks, with two different approaches. First, we present a new combined countermeasure, which increases by four times the power consumption compared to an unprotected implementation, introduces no performance overhead, and requires less than 8 bits of randomness. Therefore, it has a lower energy overhead than existing combined protections. It consists in an algorithm-level power balancing that inherently detects faults. Then, we propose an adaptive implementation of hardware countermeasures, which consists in applying or removing these countermeasures on demand, during the execution of the protected algorithm, in order to tune the security level and the energy consumption. A security evaluation of all the proposed countermeasures indicates that they provide an efficient protection against existing hardware attacks

This work presents design and full implementation of a fast switchable and band-tunable 5 - 7.5 GHz low noise amplifier (LNA) in a 45nm CMOS SOI technology. The target application are wake-up receivers that employ aggressive duty cycling. Based on a cascode topology, the LNA utilizes a transformer for its 50 input matching as well as a balun with a capacitor bank to realize 8 digitally selectable bands. According to measurement results, the fabricated LNA exhibits a voltage gain of 18 - 21 dB while drawing a current of merely 2.2mA from a 1V supply. At all the 8 bands from 5 to 7.5 GHz, the input reflection coefficient lies below -8 dB, and the noise figure ranges from 7.8 to 6.2 dB. The LNA is able to settle in less than 9.5 ns

O presente documento foi realizado no âmbito da unidade curricular Estágio /Projeto/ Dissertação, do Mestrado em Engenharia Eletrotécnica (MEE), ramo Sistemas Industriais, leccionada no Departamento de Engenharia Eletrotécnica (DEE), do Instituto Superior de Engenharia de Coimbra (ISEC). O estágio foi realizado na ENEIDA Wireless & Sensors, empresa sedeada no edifício ‘E’ do Instituto Pedro Nunes (IPN) em Coimbra. O trabalho realizado no âmbito do referido estágio consistiu no desenvolvimento de soluções baseadas em wake-up radio, para aplicação em projetos, desenvolvidos pela empresa, que empreguem redes de sensores sem fios. Uma ideia promissora para otimizar o consumo de energia de dispositivos de comunicação móvel compreende o uso de uma unidade recetora de ultra-baixo consumo, que seja capaz de controlar o transceiver principal de forma a reduzir o consumo de energia global do sistema. A unidade wake-up receiver (WuRx) está à escuta e liga as interfaces de comunicação somente quando há uma solicitação externa. Caso contrário, todos os componentes do sistema de comunicação estão completamente desligados. Especialmente no domínio dos recursos limitados e uso embutido, as tecnologias wake-up radio permitem ultrapassar as limitações inerentes aos paradigmas de comunicação em ambientes adversos. Neste documento descrevem-se as atividades desenvolvidas ao longo do estágio, salientando-se as metodologias adotadas, os testes realizados, o hardware e as ferramentas utilizadas, os problemas encontrados e as soluções propostas.

In the energy-limited wireless sensor node applications, wake-up radios are required to reduce the average power consumption of the node. Energy-detecting receivers are the best fit for such low power operations. This thesis presents the energy-detecting receiver design; challenges; techniques to enhance sensitivity, selectivity; and multi-access operation. Self-mixers instead of the conventional envelope detectors are proposed and proved to be optimal for signal detection. A fully integrated wake-up receiver uses the self-mixer and time-encoded baseband signal processing to provide a sensitivity of -79.1dBm at 434MHz with 420pW of power, providing an 8dB better sensitivity at 10dB lower power consumption compared to the SoA. A novel approach using narrowband interferers as local oscillators will be presented to further enhance sensitivity and selectivity, effectively operating the energy-detector receiver as a direct down-conversion receiver. Additionally, a clockless continuous-time analog correlator will be introduced to enhance the selectivity to wide-band AM interferers. The architecture uses pulse-position-encoded analog signal processing with VCOs as integrators and pulse-controlled relaxation delays; it operates as a code-domain matched filter to de-spread asynchronous wake-up codes. This code-domain matched filtering also provides code-division multiple access (CDMA) for simultaneous wakeups. Additional enhancement in the link can be achieved using directional antennas, providing spatial gain and selectivity. Certain applications can leverage a nearby reflector similar to a Yagi antenna to enhance the directivity. A low power directional backscatter tag is proposed, it uses multiple antennas acting as a reflectarray by configuring constant phase gradients depending on the direction of arrival (DoA) of the signal. Thus, instead of harvesting energy, the same energy and the surrounding environment can be leveraged to enhance functionality (e.g. interferer as LO, using a backscatter tag on a wall) for low power operation. Innovations spanning both system and circuit architectures that leverage the ambient energy and environment to enable power-efficient solutions for next-generation wake-up radios are presented in this work.

In ultra-low power Wireless Sensor Networks (WSNs) sensor nodes need to interact, depending on the application, even at a rapid pace while preserving battery life. Wireless communication brings thereby quite the burden as the radio transceiver requires a relative huge amount of power during both transmission or reception phases. In WSNs with on demand communication, the sensor nodes are required to maintain responsiveness and to act the sooner they receive a request, reducing the overall latency of the network. The aspect is more challenging in asynchronous WSN as the receiver possesses no information about the packet arrival time. In a purely on-demand communication, duty-cycling shows little to almost no improvement. The receiving node, in such scheme, is expected to last for years while also being accessible to other peers. Here arises the utility of an external ultra-low power radio receiver known as Wake-up Receiver (WuRx). Its essential task is to remain as the only part of the system running while the rest of the systems enters the lowest power mode (i.e., sleep state). Once a request signal is received, it notifies the host processor and other peripherals for an incoming communication. With the sensor node being in sleep state (WuRx active only), substantial power levels can be achieved. If the WuRx is able to interact rapidly, the added latency remains negligible. As crucial performance figures, the sensitivity and bit rate are immediately affected by the extreme low-power budget at diifferent magnitudes, depending mainly on the incorporated architecture. This thesis focuses on the design of a feature-balanced WuRx. The passive radio frequency architecture (PRF) relies on passive detection while consuming zero power to extract On-Off-Keying (OOK) modulated envelopes. The featured sensitivity, however, is reduced compared to more complex architectures. A WuRx based on PRF architecture can effectively enable short-range applications. The sensitivity can vary with respect to several parameters including the total generated noise, circuit technology and topology. Two variants of the PRF WuRxs are introduced with the baseband amplifier being the main change. The first revision employs a high performance amplifier with reduced average energy consumption, thanks to a novel power gating control. The second variant focuses on employing an ultra-low power baseband amplifier as it is expected to be in a continuous active state. This thesis also brings the necessary analysis on the passive front-end with the intention to enhance the overall WuRx sensitivity. Proof of concepts are embedded in sensor node boards and feature -61 dBm and -64 dBm of sensitivity for the first and the second variant, respectively, at a packet-error-rate (PER) of 1% whilst demanding a similar power of 7.2 µW during packet listening. During packet decoding, the first variant demands a 150 µW of power, caused greatly by the baseband amplifier. The achieved latency is less than 30 ms and the bit rate is 4 kbit/s, Manchester encoding. For long-range applications, a higher sensitivityWuRx is proposed based on Tuned-RF (TRF) architecture. By embedding a low-noise amplifier (LNA) in the receiver chain, very weak radio signal can be detected. TheWuRx emphasizes higher sensitivity of -90 dBm. The design of the LNA prioritized the highest gain and lowest bias current by sacrifcing the linearity that poses little impact on signal integrity for the OOK modulated signals. The total active power consumption of the TRF WuRx is 1.38 mW. In this work, a fast sampling approach based on power gating protocol allows a drastic reduction in energy consumption on average. By being able to sample in matter of few microseconds, the WuRx is able to detect the presence of a packet and return to sleep state right after packet decoding. Being power-gated dropped the average power consumption to 2.8 µW at a packet detection latency of 32 ms for less than 2 s of interval time between communication requests. The proposed solutions are able to decode a minimum length of 16-bit pattern and operate in the license-free ISM band 868 MHz. This thesis also includes the analysis and implementation of low-power front-end building blocks that are employed by the proposed WuRx.:1 Introduction 1.1 Motivation 1.2 Wake-up Receiver Design Requirements 1.2.1 Energy Consumption 1.2.2 Network Coverage and Robustness 1.2.3 Wake-up Packet Addressing 1.2.4 WuPt Detection Latency 1.2.5 Hosting System, Form-factor and Fabrication Technology 1.3 Thesis Organisation 2 Wireless Sensor Networks 2.1 Radio Communication 2.1.1 Electromagnetic Spectrum 2.1.2 Link Budget Analysis 2.2 Asynchronous Radio Receiver Duty-cycle Control 2.2.1 B-MAC and X-MAC Protocols 2.2.2 Energy and Latency Analysis 2.3 Power Supply Requirements 2.3.1 Low Self-discharge Battery 2.3.2 Energy Harvester 2.4 Summary 3 State-of-the-Art of Wake-up Receivers 3.1 Wake-up Receiver Architectural Analysis 3.1.1 Passive RF Detector 3.1.2 Classical Radio Architectures 3.2 Wake-up Receiver Back-end Stages 3.2.1 Baseband Amplifiers 3.2.2 Analog to Digital Conversion 3.2.3 Wake-up Packet Decoder 3.3 Power Consumption Reduction at Circuit Level 3.3.1 Power Gating 3.3.2 Interference Rejection and Filtering 3.4 Summary 4 Proposal of Novel Wake-up Receivers 4.1 Ultra-low Power On-demand Communication in Wireless Sensor Networks: Challenges and Requirements 4.2 Passive RF Wake-up Receiver 4.3 Power-gated Tuned-RF Wake-up Receiver 5 Low-power RF Front-end 5.1 Narrow-band Low-noise Amplifier (LNA) 5.1.1 Topology 5.1.2 Voltage Gain 5.1.3 Stability 5.1.4 Noise Figure 5.1.5 Linearity 5.2 Envelope Detector 5.2.1 Theory of Square-law Detection and Sensitivity Analysis 5.2.2 Single-Diode Envelope Detector 5.2.3 Voltage Multiplier Envelope Detector 5.3 Hardware Assessment 5.3.1 LNA 5.3.2 Envelope Detector 5.4 Summary 6 Passive RF Wake-up Receiver 6.1 Circuit Implementation 6.1.1 Address Decoder 6.1.2 Envelope Detector 6.1.3 Power-gated Baseband Amplifier 6.1.4 Ultra Low-power Baseband Amplifier 6.2 Experimental Results 6.2.1 Wireless Sensor Node 6.2.2 Measurements 6.3 Summary 7 Power-gated Tuned-RF Wake-up Receiver 7.1 Power-gating Protocol 7.2 Circuit Design 7.2.1 Radio Front-end 7.2.2 Data Slicer 7.2.3 Digital Baseband 7.3 Performance Evaluation 7.4 Summary 8 Conclusion 8.1 Performance Summary 8.2 Future Perspective 8.3 Applications A Two-tone Simulation Setup B Diode Models and Simulation Setup C Preamble Detection C Code Implementation Bibliography Publications
In drahtlosen Sensornetzwerken (WSNs) mit extrem geringem Stromverbrauch müssen Sensorknoten je nach Anwendung kurze Latenzzeiten erreichen ohne die Batterielebensdauer zu beeinträchtigen. Die drahtlose Kommunikation bringt dabei eine ziemliche Belastung mit sich, da der Funktransceiver sowohl während der Sende- als auch der Empfangsphase relativ viel Strom benötigt. Einige marktfähige Funktransceiver benötigen durchschnittlich ca. 10 mA im Empfangsmodus sowie 30 mA im Sendemodus. Deshalb wird heutzutage das sogenannte Duty-Cycling mit bestimmten Sende-, Empfangs- und langen Schlafzeitintervallen eingeführt. Während der Schlafphase ist der Empfänger nicht ansprechbar. Was wiederum zu einer massiven Erhöhung der Latenzzeit führen kann. In vielen Anwendungen und insbesondere im Rahmen der Digitalisierung von Prozessen wird mittlerweile die Fähigkeit On-Demand mit sehr kurzen Latenzzeiten zu kommunizieren verlangt. Diese Anforderung steht in einem Wiederspruch zum genannten Duty-cycle Betrieb. Um dieses Dilemma zu lösen wird im Rahmen dieser Doktorarbeit ein Funkempfänger mit extrem geringen Stromverbrauch untersucht und entwickelt. Mit Hilfe des extrem niedrigen Stromverbrauches kann der Funkempfänger ständig empfangsbereit sein. Er wird zum Hauptempfänger mit dem hohen Stromverbrauch zugeschaltet, so dass nur nach Aufforderung der Hauptempfänger aktiv sein wird. Dieser Empfänger wird Wake-up Empfänger (WuRx) genannt. Seine wesentliche Aufgabe besteht darin, als einziger Teil des Gesamtknotens aktiv zu sein, während der Rest in den Modus mit dem niedrigsten Stromverbrauch versetzt wird. Sobald ein Anforderungssignal empfangen wird, weckt er den Haupt-Prozessor und andere Peripheriegeräte über eine eingehende Kommunikation. Somit ist der Aufweckempfänger essenziell für die Zuverlässigkeit der drahtlosen Kommunikation. Sein Stromverbrauch sollte im µA Bereich sein. Seine Empfangsbereitschaft hängt entscheidend von seiner Empfindlichkeit sowie Bitrate ab. Eine Verbesserung der Empfindlichkeit und Erhöhung der Bitrate würden zwangsläufig zu einer Erhöhung des Stromverbrauches führen. Im Rahmen dieser Doktorarbeit werden unterschiedliche Architekturen von Aufweckempfängern untersucht und umgesetzt. Zusammenhänge zwischen Empfindlichkeit, Bitrate und Stromverbrauch wurden analysiert und mögliche Grenzen gezeigt. Ein wesentliches Augenmerk war dabei, Off-the-Shelf Komponenten zu verwenden. Im Rahmen dieser Doktorabeit wurden in Abhängigkeit von der zu erreichenden Reichweite und Häufigkeit der Kommunikation zwei wesentliche Architekturen mit geeigneten Empfindlichkeiten und extrem geringem Stromverbrauch entwickelt. Für kurze Reichweiten wurde eine passive Hochfrequenzarchitektur (PRF Architektur) basierend auf einer passiven Erkennung von OOK-modulierten (On-Off-Keying) Signalen mittels Hüllkurvenbildung entwickelt. Die erreichte Empfindlichkeit von ca. -64 dBm stellt eine wesentliche Verbesserung gegenüber dem Stand der Technik und Forschung mit einer Empfindlichkeit von ca. -52 dBm dar. Die Empfindlichkeit kann in Bezug auf verschiedene Parameter variieren, einschließlich des insgesamt erzeugten Rauschens, der Schaltungstechnologie und der Topologie. Zwei Varianten der PRF WuRxs wurden realisiert, wobei der Basisbandverstärker die Hauptänderung darstellt. Die erste Version verwendet einen Hochleistungsverstärker mit reduziertem durchschnittlichen Energieverbrauch dank einer neuartigen Leistungssteuerung. Die zweite Variante konzentriert sich auf die Verwendung eines Basisbandverstärkers mit extrem geringer Leistung, da erwartet wird, dass er sich in einem kontinuierlichen aktiven Zustand befindet. Diese Arbeit bringt auch die notwendige Analyse des passiven Front-Ends mit der Absicht, die allgemeine WuRx-Empfindlichkeit zu verbessern. Nachweise der Wirksamkeit sind in Sensorknotenmodulen eingebettet und verfügen über -61 dBm und -64 dBm Empfindlichkeit für die erste bzw. die zweite Variante bei einer Paketfehlerrate (PER) von 1 %, während beim Abhören von Paketen eine ähnliche Leistung von 7.2 µW gefordert wird. Während der Paketdecodierung erfordert die erste Variante eine Leistung von 150 µW, die stark durch den Basisbandverstärker verursacht wird. Die erreichte Latenz beträgt weniger als 30 ms und die Bitrate beträgt 4 kbit/s mit einer Manchester-Codierung. Für Anwendungen mit großer Reichweite wird ein WuRx mit höherer Empfindlichkeit vorgeschlagen. Dieser basiert auf einer TunedRF (TRF) -Architektur. Dabei werden sehr schwache Funksignale durch einen rauscharmen Verstärker (LNA) erkannt und verstärkt. Der WuRx erreicht eine bessere Empfindlichkeit von ca. –90 dBm. Dabei wurde das Augenmerk auf die höchste Verstärkung verbunden mit dem niedrigsten Vorspannungsstrom gelegt. Der LNA wird dann im nicht-linearen Bereich betrieben. Dieser Betriebsmodus beeinflusst nur im geringeren Maße die Signalintegrität der OOK-modulierten Signale. Der gesamte Leistungsverbrauch des TRF WuRx beträgt 1.38 mW. Um den Gesamtleistungsverbrauch im µW Bereich zu reduzieren, wird im Rahmen dieser Arbeit das sogenannte Power-Gating-Protokoll eingeführt. Dabei wird das Funkkanal zyklisch abgetastet. Der WuRx kann innerhalb von wenigen Mikrosekunden das Vorhandensein eines Pakets erkennen und direkt nach der Paketdecodierung in den Ruhezustand zurückkehren. Durch diesen Ansatz konnte der durchschnittliche Stromverbrauch bei einer Paketerkennungslatenz von ca. 32 ms innerhalb einer Abtastrate von 2 s auf 2.8 µW reduziert werden. Die vorgeschlagenen Lösungen können eine Mindestlänge von 16-Bit-Mustern decodieren und im lizenzfreien ISM-Band 868 MHz arbeiten.:1 Introduction 1.1 Motivation 1.2 Wake-up Receiver Design Requirements 1.2.1 Energy Consumption 1.2.2 Network Coverage and Robustness 1.2.3 Wake-up Packet Addressing 1.2.4 WuPt Detection Latency 1.2.5 Hosting System, Form-factor and Fabrication Technology 1.3 Thesis Organisation 2 Wireless Sensor Networks 2.1 Radio Communication 2.1.1 Electromagnetic Spectrum 2.1.2 Link Budget Analysis 2.2 Asynchronous Radio Receiver Duty-cycle Control 2.2.1 B-MAC and X-MAC Protocols 2.2.2 Energy and Latency Analysis 2.3 Power Supply Requirements 2.3.1 Low Self-discharge Battery 2.3.2 Energy Harvester 2.4 Summary 3 State-of-the-Art of Wake-up Receivers 3.1 Wake-up Receiver Architectural Analysis 3.1.1 Passive RF Detector 3.1.2 Classical Radio Architectures 3.2 Wake-up Receiver Back-end Stages 3.2.1 Baseband Amplifiers 3.2.2 Analog to Digital Conversion 3.2.3 Wake-up Packet Decoder 3.3 Power Consumption Reduction at Circuit Level 3.3.1 Power Gating 3.3.2 Interference Rejection and Filtering 3.4 Summary 4 Proposal of Novel Wake-up Receivers 4.1 Ultra-low Power On-demand Communication in Wireless Sensor Networks: Challenges and Requirements 4.2 Passive RF Wake-up Receiver 4.3 Power-gated Tuned-RF Wake-up Receiver 5 Low-power RF Front-end 5.1 Narrow-band Low-noise Amplifier (LNA) 5.1.1 Topology 5.1.2 Voltage Gain 5.1.3 Stability 5.1.4 Noise Figure 5.1.5 Linearity 5.2 Envelope Detector 5.2.1 Theory of Square-law Detection and Sensitivity Analysis 5.2.2 Single-Diode Envelope Detector 5.2.3 Voltage Multiplier Envelope Detector 5.3 Hardware Assessment 5.3.1 LNA 5.3.2 Envelope Detector 5.4 Summary 6 Passive RF Wake-up Receiver 6.1 Circuit Implementation 6.1.1 Address Decoder 6.1.2 Envelope Detector 6.1.3 Power-gated Baseband Amplifier 6.1.4 Ultra Low-power Baseband Amplifier 6.2 Experimental Results 6.2.1 Wireless Sensor Node 6.2.2 Measurements 6.3 Summary 7 Power-gated Tuned-RF Wake-up Receiver 7.1 Power-gating Protocol 7.2 Circuit Design 7.2.1 Radio Front-end 7.2.2 Data Slicer 7.2.3 Digital Baseband 7.3 Performance Evaluation 7.4 Summary 8 Conclusion 8.1 Performance Summary 8.2 Future Perspective 8.3 Applications A Two-tone Simulation Setup B Diode Models and Simulation Setup C Preamble Detection C Code Implementation Bibliography Publications

博士
國立臺灣科技大學
電機工程系
99
Energy efficiency is an important challenge for resource constrained wireless sensor networks. Most research use Media Access Control (MAC) and wake-up radio (WUR) to achieve energy efficiency. As MAC can’t eliminate the idle listening and currently proposed WURs focus on low power hardware design with low sensitivity and short radio range, it means current WURs will increase the deployment density and installation and maintenance cost, and won’t be suitable to wireless sensor networks. This thesis proposes an event-driven WUR design and a spreading code algorithm in order to eliminate the idle listening, improve sensitivity, and enhance the radio range. Our design decreases the deployment density and installation and maintenance cost, and is more suitable to wireless sensor networks. The other method to achieve energy efficiency is improving the throughput of WUR. As improving the throughput is achieved by reducing the symbol error rate, which can reduce wake-up signal’s retransmissions, and avoid waking up high power data radios, and therefore increase the node lifetime. As current proposed WURs focus on hardware design and don’t take software design into account, and therefore reduce the throughput. This will increase symbol error rate, retransmissions, and effectively reduce the node lifetime. This thesis proposes a block orthogonal code algorithm in order to improve the throughput and power consumption. Most of the published wake-up radios propose low energy design at the expense of reduced radio range, which means that they require an increased deployment density of sensor networks. In this thesis, we introduce a design of a high sensitivity 916.5 MHz wake-up radio using low data rate and forward error correction (FEC). It improves the sensitivity, up to − 122 dBm at a data rate 370 bit / s. It achieves up to 13 dB of coding gain with symbol error rate (SER) 10−2, and up to 4 times the range of the data radio, rendering it more suitable to sensor networks. Our design can receive wake-up signal reliably from any IEEE 802.15.4 transmitter and achieves a low packet error rate (PER) 0.0159 at SNR 4 dB. Furthermore, our design encodes the node ID into a wake-up signal to avoid waking up the undesired nodes. In terms of improving the throughput of wake-up radios, we propose the use of a block orthogonal code to reduce the symbol error rate, and therefore improve the throughput of wake-up radios used in sensor networks. Currently proposed wake-up radios that use, for example, on-off keying modulation focus on integrated circuit design for low power operation. They do not take error correction coding into account and therefore increase the error rates and reduce the node lifetime. We develop a system model to evaluate the throughput of our proposed scheme. We implement a simulation of this model and show that our approach significantly improves the throughput of these radios. When compared with on-off keying modulation using 8B10B encoding we can achieve up to a factor of 10 improvement in the radio’s throughput without any additional hardware or energy consumption.

The world is going towards the Internet of Things (IoT) where trillions of objects that are common in our lives will be enhanced and revolutionized by adding them computational and networking capabilities. Examples are cars, street lamps, industrial machinery, electrical appliances. The corner- stone of Internet of Things research is Wireless Sensor Networks (WSNs). These networks are made of hundreds of low-cost, low-complexity devices endowed with sensors to monitor the surrounding environment or objects. Typically these devices (also called sensors, nodes or motes) are battery-powered, therefore they can operate for a limited amount of time (i.e., days) before running out of energy. This is the main challenge that applications of Wireless Sensor Networks have to face. Since one of the major power consumers in a node is the radio transceiver, a lot of research effort has been put into finding solutions that keep the radio in a low-power state as much as possible, while not harming the communication capability. While this approach brings the network lifetime, i.e. the time before battery-operated nodes die having depleted their energy, to years or more, it introduces significant latency, as the energy reduction comes at the cost of not being able to reach nodes in deep sleep for long period of times. The most promising solution to this problem is the wake-up radio, an additional ultra-low power transceiver used for the sole purpose of triggering the activation of the high power, high bandwidth radio. Wake-up radio enabled IoT systems maintain always on their wake up radio, which has a negligible energy consumption, in this way optimizing both energy and latency performance metrics. Most of the research so far focused on the design of wake-up receivers, while a limited amount of communication protocols that take advantage of this radio has been proposed. Moreover, almost all of these protocols have been evaluated only through simulations. In this thesis we set to start filling this gap. We first evaluate the range performance of an ultra-low power wake-up receiver integrated into a state- of-the-art Wireless Sensor Network mote, the MagoNode++. Based on the results of this evaluation we deploy an outdoor testbed made of MagoNode++ motes. The testbed allows to validate in a real-world scenario our implementation of CTP-WUR, an extension of the widely used Collection Tree Protocol (CTP) for wake-up radio-enabled Wireless Sensor Networks. The comparison between CTP-WUR and CTP demonstrates that wake-up radios can effectively reduce the power consumption and obtain, at the same time, end-to-end latencies in the order of milliseconds, enabling new time critical applications. Based on the results and on the insights gained dur- ing the testbed evaluation a new version of CTP-WUR is presented that improves its performance across all the metrics taken into consideration: end-to-end packet latency, energy consumption and Packet Delivery Ratio.

The vision of Internet of Things (IoT) promises to reshape society by creating a future where we will be surrounded by a smart environment that is constantly aware of the users and has the ability to adapt to any changes. In the IoT, a huge variety of smart devices is interconnected to form a network of distributed agents that continuously share and process information. This communication paradigm has been recognized as one of the key enablers of the rapidly emerging applications that make up the fabric of the IoT. These networks, often called wireless sensor networks (WSNs), are characterized by the low cost of their components, their pervasive connectivity, and their self-organization features, which allow them to cooperate with other IoT elements to create large-scale heterogeneous information systems. However, a number of considerable challenges is arising when considering the design of large-scale WSNs. In particular, these networks are made up by embedded devices that suffer from severe power constraints and limited resources. The advent of low-power sensor nodes coupled with intelligent software and hardware technologies has led to the era of green wireless networks. From the hardware perspective, green sensor nodes are endowed with energy scavenging capabilities to overcome energy-related limitations. They are also endowed with low-power triggering techniques, i.e., wake-up radios, to eliminate idle listening-induced communication costs. Green wireless networks are considered a fundamental vehicle for enabling all those critical IoT applications where devices, for different reasons, do not carry batteries, and that therefore only harvest energy and store it for future use. These networks are considered to have the potential of infinite lifetime since they do not depend on batteries, or on any other limited power sources. Wake-up radios, coupled with energy provisioning techniques, further assist on overcoming the physical constraints of traditional WSNs. In addition, they are particularly important in green WSNs scenarios in which it is difficult to achieve energy neutrality due to limited harvesting rates. In this PhD thesis we set to investigate how different data forwarding mechanisms can make the most of these green wireless networks-enabling technologies, namely, energy harvesting and wake-up radios. Specifically, we present a number of cross-layer routing approaches with different forwarding design choices and study their consequences on network performance. Among the most promising protocol design techniques, the past decade has shown the increasingly intensive adoption of techniques based on various forms of machine learning to increase and optimize the performance of WSNs. However, learning techniques can suffer from high computational costs as nodes drain a considerable percentage of their energy budget to run sophisticated software procedures, predict accurate information and determine optimal decision. This thesis addresses also the problem of local computational requirements of learning-based data forwarding strategies by investigating their impact on the performance of the network. Results indicate that local computation can be a major source of energy consumption; it’s impact on network performance should not be neglected.

Tese de doutoramento em Engenharia Física, no ramo de Instrumentação, apresentada ao Departamento de Física da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
A energia é um recurso limitado em redes de sensores sem fios, pelo que uma gestão eficiente da energia disponível é crucial para aumentar o seu tempo de vida operacional. Assim, a gestão de energia em redes de sensores sem fios tem estado focada no desenvolvimento de mecanismos de activação sincronizada de nós “adormecidos” e de tecnologias de captação de energia do meio envolvente. O objectivo deste trabalho consistiu em explorar estas duas abordagens para criar condições de disponibilidade contínua de energia nos nós de redes sem fios: em primeiro lugar, explorando tecnologias de captação de energia de importantes fontes no meio envolvente: luz solar, diferenciais térmicos e campos electromagnéticos, e, também, cultivando métodos e tecnologias de despertar por radiofrequência (wake-up radio) como forma mais adequada de gerir as oportunidades de operação dos nós de uma rede, poupando energia no tempo restante. São apresentados estudos e soluções realizadas no âmbito industrial, bem como os métodos e resultados da análise realizada para a sua validação. Assim, conseguiu-se: • Uma solução baseada na captação de energia solar, com uma eficiência superior a 70% (desde a saída do painel fotovoltaico), capaz de suportar sensores e repetidores numa rede, acumulando energia correspondente a autonomias de 16 e 40 horas, respectivamente, numa aplicação de diagnóstico de seccionadores de alta-tensão em subestações de distribuição de electricidade; • Uma solução de captação de energia de diferenciais térmicos, para suportar sensores de diagnóstico do estado de funcionamento de purgadores, em linhas industriais de distribuição de vapor, permitindo uma disponibilidade permanente de energia, mesmo para diferenças de temperatura de uns meros 20 °C; • Uma solução de captação de energia de campos magnéticos gerados por correntes eléctricas intensas, para aplicação em sensores sem fios a utilizar em redes de distribuição de electricidade, que, nas circunstâncias dos trabalhos propostos, amplamente demonstrou a viabilidade do conceito e foi industrialmente incorporado numa unidade sem fios para a monitorização de correntes eléctricas e o diagnóstico do estado de fusíveis em postos de transformação; • Duas soluções de despertar por radiofrequência, sem prejuízo da latência de comunicação: (i) despertar colectivo, sincronizado para todos os nós da rede no volume de alcance-rádio do emissor, que se revelou eficaz até aos 37 metros, no interior, consumindo 7 µA e (ii) despertar selectivo, individualizando o nó a activar, com um alcance de 33 metros, igualmente no interior, consumindo 5 µA — em campo aberto, o alcance foi de 10 metros. Em suma: as soluções industriais realizadas no âmbito deste trabalho demonstram a viabilidade de suportar a alimentação em potência de nós de redes sem fios operando em diferentes regimes e dependendo de diversas fontes de energia, em natureza e potência disponível, que, no nosso entender constitui condição necessária ao sucesso industrial das redes de objectos sem fios.
Energy is a limited resource in wireless sensor networks, and so, efficient management of available energy is crucial to increase their operational lifetime. Thus, power management in wireless sensor networks has been focused on developing synchronized activation mechanisms of "asleep" nodes and on technologies for energy harvesting from the environment. The purpose of this study was to explore these two approaches to create conditions of continuous availability of energy in wireless nodes: first, by exploiting important energy sources in the environment: sunlight, thermal differences, and electromagnetic fields, as much as integrating methods and technologies addressing wake-up radio capabilities, as the most appropriate means to determine opportunities for nodes in a network to operate, thus saving energy in the remaining time. Both studies and industry-led solutions are presented, as well as methods and results obtained for validation. Thus, the following results were achieved: • A solution based on solar energy harvesting, with an efficiency over 70% (from the output of the photovoltaic panel) able to support sensors and repeaters in a network, by accumulating energy corresponding to an autonomy of 16 and 40 hours, respectively, which is used for the diagnosis of high-voltage circuit breakers, in electricity distribution substations; • An energy harvesting solution from thermal difference, in order to support sensors for the condition monitoring and diagnosis of steam traps across large-scale plants of process industries, thus allowing continuous availability of energy, even for temperature differences of a mere 20 °C; • An energy harvesting solution from magnetic fields generated by intense electrical currents, for use in wireless sensors in distribution electricity grids, which, in the circumstances of the proposed work, thoroughly demonstrated the concept's feasibility and, thereby, integrated a wireless sensor for the continuous monitoring of electric currents and the condition diagnosis of fuses in secondary distribution substations; • Two wake-up radio solutions, with no effect on communication latency: (i) collective awakening synchronizing all nodes within range of the radio transmitter, which proved effective up to 37 meters’ distance, in indoors condition, consuming 7 µA, and (ii) selective awakening, thus activating each individual node in a network, within a range of 33 meters, also indoors, consuming 5 µA — in open field, the range was reduced to 10 meters. In short: industrial solutions carried out under this study have demonstrated the feasibility of fully supporting the power supply of nodes in wireless networks operating in different regimes and depending on various energy sources, in nature and available power, which, in our view, is mandatory for the industrial success of wireless object networks.
FCT - SFRH/BDE/51607/2011