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Wireless communication circuits often dominate the power consumption of Internet of Things (IoT) devices such as small battery-powered commercial wearables or low-power-wide-area-network (LPWAN) environmental sensors for infrastructure. More specifically, a large fraction of this power comes from node-to-hub or node-to-node networking requirements, especially when such devices communicate with low-to-medium average throughput. To reduce this power, instead of duty-cycling the main receiver, employing an auxiliary wake-up receiver (WuRX) that monitors the RF spectrum for a pre-defined wake-up signature either continuously or in duty-cycle fashion has been proved to be an effective solution. In this thesis, WuRX designs targeting ultra-low-power and high sensitivity for different usage scenarios are investigated. First, a WuRX for emerging LPWAN applications targeting to be used with the always-on WuRX communication protocol is presented. This design explores architecture-level and circuit-level techniques to operate with near-zero power consumption while achieving high sensitivity. Moreover, an active and a passive envelope detector (ED) that employ pseudo-balun architectures are also proposed, which further improve sensitivity and enable operation at a higher frequency band. On the other hand, WuRXs for commercial applications targeting to be used primarily with the duty-cycled WuRX communication protocol while being compatible with well-established wireless standards are also presented. First, a Bluetooth Low Energy (BLE) WuRX achieves low power, high sensitivity, interference-resiliency, and standard-compatibility through a combination of communication and circuit techniques, including high-Q filtering by a bank of FBAR resonators and a frequency-hopped mixer-first RF front-end that responds to a 4-dimensional (4-D) wake-up signature. This work is then further enhanced to achieve higher sensitivity while maintaining comparable interference-resiliency and power without the off-chip FBAR filters for a fully integrated solution. More importantly, this enhanced design is the first dual-mode WuRX compatible with both BLE and Wi-Fi transmitters, thanks to a carefully architected frequency plan that supports BLE advertisement channel hopping or a proposed subcarrier-based within-channel Wi-Fi frequency hopping scheme. As a result, the presented WuRX designs could potentially help enable new wireless IoT applications, particularly those that have low-to-medium average throughput requirements.

Low-power wireless technology is a part and parcel of our daily life, shaping the way in which we behave, interact, and more generally live. The ubiquity of cheap, tiny, battery-powered devices augmented with sensing, actuation, and wireless communication capabilities has given rise to a ``smart" society, where people, machines, and objects are seamlessly interconnected, among themselves and with the environment. Behind the scenes, low-power wireless protocols are what enables and rules all interactions, organising these embedded devices into wireless networks, and orchestrating their communications. The recent years have witnessed a persistent increase in the pervasiveness and impact of low-power wireless. After having spawned a wide spectrum of powerful applications in the consumer domain, low-power wireless solutions are extending their influence over the industrial context, where their adoption as part of feedback control loops is envisioned to revolutionise the production process, paving the way for the Fourth Industrial Revolution. However, as the scale and relevance of low-power wireless systems continue to grow, so do the challenges posed to the communication substrates, required to satisfy ever more strict requirements in terms of reliability, responsiveness, and energy consumption. Harmonising these conflicting demands is far beyond what is enabled by current network stacks and control architectures; the need to timely bridge this gap has spurred a new wave of interest in low-power wireless networking, and directly motivated our work. In this thesis, we take on this challenge with a main conceptual and technical tool: concurrent transmissions (CTX), a technique that, by enforcing nodes to transmit concurrently, has been shown to unlock unprecedented fast, reliable, and energy efficient multi-hop communications in low-power wireless networks, opening new opportunities for protocol design. We first direct our research endeavour towards industrial applications, focusing on the popular IEEE 802.15.4 narrowband PHY layer, and advance the state of the art along two different directions: interference resilience and aperiodic wireless control. We tackle radio-frequency noise by extensively analysing, for the first time, the dependability of CTX under different types, intensities, and distributions of reproducible interference patterns, and by devising techniques to push it further. Specifically, we concentrate on CRYSTAL, a recently proposed communication protocol that relies on CTX to rapidly and dependably collect aperiodic traffic. By integrating channel hopping and noise detection in the protocol operation, we provide a novel communication stack capable of supporting aperiodic transmissions with near-perfect reliability and a per-mille radio duty cycle despite harsh external interference. These results lay the ground towards the exploitation of CTX for aperiodic wireless control; we explore this research direction by co-designing the Wireless Control Bus (WCB), our second contribution. WCB is a clean-slate CTX-based communication stack tailored to event-triggered control (ETC), an aperiodic control strategy holding the capability to significantly improve the efficiency of wireless control systems, but whose real-world impact has been hampered by the lack of appropriate networking support. Operating in conjunction with ETC, WCB timely and dynamically adapts the network operation to the control demands, unlocking an order-of-magnitude reduction in energy costs w.r.t. traditional periodic approaches while retaining the same control performance, therefore unleashing and concretely demonstrating the true ETC potential for the first time. Nevertheless, low-power wireless communications are rapidly evolving, and new radios striking novel trade-offs are emerging. Among these, in the second part of the thesis we focus on ultra-wideband (UWB). By providing hitherto missing networking primitives for multi-hop dissemination and collection over UWB, we shed light on the communication potentialities opened up by the high data throughput, clock precision, and noise resilience offered by this technology. Specifically, as a third contribution, we demonstrate that CTX not only can be successfully exploited for multi-hop UWB communications but, once embodied in a full-fledged system, provide reliability and energy performance akin to narrowband. Furthermore, the higher data rate and clock resolution of UWB chips unlock up to 80% latency reduction w.r.t. narrowband CTX, along with orders-of-magnitude improvements in network-wide time synchronization. These results showcase how UWB CTX could significantly benefit a multitude of applications, notably including low-power wireless control. With WEAVER, our last contribution, we make an additional step towards this direction, by supporting the key functionality of data collection with an ultra-fast convergecast stack for UWB. Challenging the internal mechanics of CTX, WEAVER interleaves data and acknowledgements flows in a single, self-terminating network-wide flood, enabling the concurrent collection of different packets from multiple senders with unprecedented latency, reliability, and energy efficiency. Overall, this thesis pushes forward the applicability and performance of low-power wireless, by contributing techniques and protocols to enhance the dependability, timeliness, energy efficiency, and interference resilience of this technology. Our research is characterized by a strong experimental slant, where the design of the systems we propose meets the reality of testbed experiments and evaluation. Via our open-source implementations, researchers and practitioners can directly use, extend, and build upon our contributions, fostering future work and research on the topic.

The Internet-of-Things (IoT) has the potential to revolutionize our understanding and real-time awareness about the world around us in order to make our lives simpler, safer, and more efficient. However, IoT growth depends strongly on how cost effective the solutions are. Battery-based systems may suffer from limited lifetimes, which incur regular maintenance, replacement, and downtime costs. Energy-harvesting based systems can suffer from poor dependability when environmental sources supply insufficient power, which leads to poor application quality. Generally, lifetime and dependability both increase when system power consumption is lowered. Thus, to achieve global IoT scale beyond the 10s of billions of devices, dominating factors of system power consumption must be addressed. Many edge IoT devices perform events with relatively low-activity factors, such that their dominant source of power consumption stems from components performing essential functions. Given that these systems communicate wirelessly, they must keep their receivers active in order to hear wireless requests even in these low-activity factor scenarios. This energy inefficient idle listening can easily account for a significant portion of the floor power. Wake-up receivers (WuRXs) are a candidate solution to this challenge by acting as energy-efficient wireless notifiers that wake up a system upon reception of a specific wireless code. However, many of the reported WuRXs require excessive power consumption for desired levels of performance. Further, the real power improvement from wake-up receivers, and other components, in an integrated system is difficult to predict without the context of system architecture, design options, and operational constraints. This limits the ability of designers to realize energy-efficient IoT systems. This dissertation addresses WuRX design challenges in three phases. An analysis and comparison are completed on two conventional WuRX duty-cycling techniques as well as the proposed within-packet duty-cycling mechanism, which was developed to further reduce WuRX power consumption. A variety of critical WuRX digital baseband techniques and architectures are presented with accompanying modeled and measured results. Lastly, the discussed concepts are applied in commercial CMOS on four different wake-up receiver designs achieving state-of-the-art power at near and sub-µW levels, due to the presented duty-cycling methods, along with high-performance in terms of RF sensitivity, wake-up latency, and interference rejection. This dissertation then addresses low-power IoT system design challenges by proposing a system-level modeling framework based on system architecture, design, and operation information to enable fast virtual prototyping and an understanding of trade-offs across a variety of scenarios. Several experiments concerning the integration of wake-up radios into the system context are conducted with this framework to demonstrate examples of the component's impact.

International audience; Named Data Networking (NDN) is a promising architecture that aims to natively satisfy emerging applications such as the Internet of Things (IoT). Therefore, enabling NDN in realworld IoT deployments is becoming essential in order to benefit from Information Centric Networking (ICN) features. To design realistic NDN-based communication solutions for IoT, revisiting mainstream technologies such as low-power wireless standards may be the key. In this paper, we explore NDN forwarding over IEEE 802.15.4 following two steps. First, we mathematically model a broadcast-based forwarding strategy for NDN over constrained networks with the IEEE 802.15.4 technology in mind. The model estimates the number of frames transmitted and the mean round-trip time per request, under content popularity considerations. Second, based on mathematical and experimental observations of the broadcast-based forwarding at network level, we elaborate Named-Data Carrier-Sense Multiple Access (ND-CSMA), an adaptation of the Carrier-Sense Multiple Access (CSMA) algorithm used in IEEE 802.15.4. Results show that adaptations such as ND-CSMA may be reasonably envisioned to improve NDN efficiency with current IoT technologies.

Global navigation satellite systems (GNSS) have radically changed business, industry, and society, shaping the way we transport, navigate, and generally live every day. After all these years, however, GNSS location information remains only valuable outdoors, leaving indoor environments where people dwell most of the time without proper localization support. Many technologies and systems have approached this problem including optical, inertial, ultrasonic, and radio-frequency (RF), to name a few; yet the problem remains. In this thesis, inspired by the indisputable success of GNSS and the re-emergence of ultra-wideband (UWB) radios to the forefront of technology, we aim to change the state of affairs in RF localization by proposing novel clean-slate UWB ranging and localization schemes based on concurrent transmissions. These are generally considered harmful for communication but become a rich source of localization information when combined with knowledge of the channel impulse response (CIR). Our first novel contribution lies in the concept of concurrent ranging, which allows mobile nodes to simultaneously measure the distance to multiple devices?hereafter, called responders?removing the need for the wasteful long packet exchanges traditionally used for ranging and localization. Different from conventional schemes, which spread responder transmissions over time, we force responders to transmit concurrently and let their signals ?fuse? in the wireless channel; the resulting impulse response, as measured by commercial UWB radios, contains all the necessary timing information to extract the desired distance to all responders. This first contribution, however, also serves us to realize the many challenges ahead to unlock the real power of concurrent transmissions for localization. We address these challenges along the way, starting with Chorus, our second contribution. Chorus exploits an anchor infrastructure that transmits packets concurrently. Mobile nodes listen for these transmissions and measure from the CIR the time difference of arrival (TDoA) of the concurrent signals, privately computing their own position at a high rate using hyperbolic localization. This reverse TDoA scheme, although simple in concept, is extremely powerful in that it enables passive self-localization of infinitely many targets at once, a feature largely missing in the RF literature. In Chorus, we address the difficult challenges to reliably detect and identify the signal from the different responders. Yet, the limited transmission precision of commercial UWB transceivers constrains the many benefits of Chorus. In this context, we i) contribute a model to ascertain the impact of the transmission uncertainty on concurrent transmissions, and ii) address the issue with a compensation mechanism that fine-tunes the local oscillator frequency of responders while they prepare to transmit, allowing us to simultaneously tackle the impact of clock drift on distance estimation. We demonstrate in our evaluation that with this compensation mechanism we can schedule transmissions with < 1 ns error, removing the need to share timestamps to precisely measure distance. We rebuild concurrent ranging around this mechanism, obtaining decimeter-level ranging and localization at a fraction of the cost of conventional schemes. These results turn concurrent ranging into an immediately applicable technique that new systems can now exploit, benefiting from a different set of trade-offs hitherto unavailable. Further, the TX compensation mechanism can be directly applied to Chorus, similarly making fast and accurate passive self-localization a tangible reality. We continue our endeavor with a systematic characterization of the conditions under which UWB concurrent transmissions succeed to provide reliable ranging and communication across different complex channels. The results we put forth empower developers to fully exploit concurrent transmissions in their designs, potentially inspiring a new wave of ranging, and also communication, primitives that can bring to UWB the same striking benefits found in low-power narrowband radios. The thesis is completed by looking at other challenges preventing the wide adoption of UWB localization systems, namely, large-scale operation, energy efficiency, and the complexity to install anchor deployments. We tackle these aspects in the last part of the thesis with three additional contributions. First, we propose Talla, a TDoA system that provides seamless large-scale localization for many tags across cells of time-synchronized anchors. Secondly, we fuse UWB ranging with odometry information and build an uncertainty model that only triggers new UWB estimates if and when needed, reducing consumption and channel utilization while satisfying the application-specific demands in terms of accuracy. And thirdly, we build state-of-the-art mechanisms to automatically compute the positions of all anchors deployed across large areas based on ranging information, facilitating anchor network deployment for the many UWB-based real-time location systems (RTLS) to come. Overall, this thesis changes the landscape of UWB localization with a new set of potentially disruptive schemes and systems that exploit the peculiar benefits of concurrent transmissions and that consequently redefine the trade-offs of the technology.

Enabling Named Data Networking (NDN) in realworld Internet of Things (IoT) deployments becomes essential to benefit from Information Centric Networking (ICN) features in current IoT systems. To design realistic NDN-based communication solutions for IoT, revisiting mainstream technologies such as low-power wireless standards may be the key. In this paper, we explore the NDN forwarding over IEEE 802.15.4 by modeling a broadcast-based forwarding strategy. Based on the observations, we adapt the Carrier-Sense Multiple Access (CSMA) algorithm of 802.15.4 to improve NDN wireless forwarding while reducing broadcast effects in terms of packet redundancy, round-trip time and energy consumption.

We deploy two low-power wireless networks, one in a Smart Agriculture setting (a peach orchard), one in a Smart Building. Both networks use out-of-the-box SmartMesh IP technology to gather sensor values, as well as extensive network statistics. This article presents an in-depth analysis of the performance of both networks, and compares them. Nodes in both exhibit end-to-end reliability of 100%, with an expected lifetime between 4 and 8 years. We show how – contrary to popular belief – wireless links are symmetrical. Thanks to the use of Time Slotted Channel Hopping (TSCH), the network topology is stable, with at most 15 link changes on average per day in the network. We conclude that TSCH as implemented by SmartMesh IP is a perfectly suitable IoT solution for Smart Agriculture and Smart Building applications. Fil: Brun Laguna, Keoma. Institut National de Recherche en Informatique et en Automatique; Francia Fil: Diedrichs, Ana Laura. Universidad Tecnológica Nacional. Facultad Regional de Mendoza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina Fil: Dujovne, Diego. Universidad Diego Portales; Chile Fil: Taffernaberry, Juan Carlos. Universidad Tecnológica Nacional; Argentina Fil: Léone, Rémy. Institut National de Recherche en Informatique et en Automatique; Francia Fil: Vilajosana, Xavier. Institut National de Recherche en Informatique et en Automatique; Francia Fil: Watteyne, Thomas. Institut National de Recherche en Informatique et en Automatique; Francia

Recent standardization efforts on low-power wireless communication technologies, including time-slotted channel hopping (TSCH) and DASH7 Alliance Mode (D7AM), are starting to change industrial sensing applications, enabling networks to scale up to thousands of nodes whilst achieving high reliability. Past technologies, such as ZigBee, rooted in IEEE 802.15.4, and ISO 18000-7, rooted in frame-slotted ALOHA (FSA), are based on contention medium access control (MAC) layers and have very poor performance in dense networks, thus preventing the Internet of Things (IoT) paradigm from really taking off. Industrial sensing applications, such as those being deployed in oil refineries, have stringent requirements on data reliability and are being built using new standards. Despite the benefits of these new technologies, industrial shifts are not happening due to the enormous technology development and adoption costs and the fact that new standards are not well-known and completely understood. In this article, we provide a deep analysis of TSCH and D7AM, outlining operational and implementation details with the aim of facilitating the adoption of these technologies to sensor application developers. info:eu-repo/semantics/publishedVersion

We present a system that leverages physical layer features to combat Cross-Technology Interference (CTI) in low-power wireless networks. Our system incorporates: (i) a lightweight interference detection mechanism for low-power radios that recognizes the type of interference in the received signal, (ii) a lightweight error detection mechanism to estimate and characterize error patterns within interfered packets, and (iii) a CTI-aware protocol that dynamically adapts transmission and recovery mode to the current interference patterns. We implement a prototype of our system for the lowpower IEEE 802.15.4 in software defined radios (SDR). Our early results of the system components demonstrate that we can achieve a high accuracy in error detection and interference type identification. Moreover, we observed a significant performance improvement compared to the standard 802.15.4 systems without interference-awareness.

Low-power wireless networks must leverage radio duty cycling to reduce energy consumption, but duty cycling drastically increases the risk of radio collisions, resulting in power-expensive retransmissions or data loss. We present Strawman, a contention resolution mechanism designed for low-power duty-cycled networks that experience traffic bursts. Strawman efficiently resolves network contention, mitigates the hidden terminal problem, and has zero overhead unless activated to resolve data collisions. Our testbed experiments show that Strawman instantaneously provides increased network capacity when needed, allocates the available bandwidth evenly among contenders, and increases energy efficiency in multihop collection networks compared to the traditionally used random backoff.