A Temperature-Compensated BLE Beacon and 802.15.4-to-BLE Translator on a Crystal-Free Mote

International audienceCrystal-free radios have the potential to revolutionize the IoT: due to their single-chip nature, they are both very cheap (no external components required) and very small (the size of a grain of rice). The Single-Chip Micro Mote (SCμM) is a 2×3×0.3 mm3 crystal-free chip that can communicate with off-the-shelf transceivers over Bluetooth Low Energy (BLE) or IEEE 802.15.4. Setting its communication frequency is challenging because the crystal-free chip can rely only on internal oscillating circuits, which are very susceptible to temperature. Without compensation, a SCμM chip can no longer communicate with an off-the-shelf BLE receiver if the temperature changes by more than 1.25 °C. This paper introduces a two-step temperature compensation method, allowing SCμM to successfully send BLE frames over a 20 °C temperature range. After performing initial calibration during optical bootloading, we use an open-loop linear model to estimate the ambient temperature and continuously tune the mote’s local oscillator (LO) frequency as the temperature changes. We show how the mote can use the intermediate frequency of 802.15.4 frames it receives from nearby off-the-shelf transceivers as a frequency reference to adjust its LO frequency. This compensation method enables SCμM to operate as a tiny BLE beacon, a BLE temperature sensor (for retail or medical applications), or a 802.15.4-to-BLE translation device

Industrial IoT with Crystal-Free Mote-on-Chip

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QuickCal: Assisted Calibration for Crystal-Free Micro-Motes

International audienceThe Single Chip Micro Mote (SCµM) is a crystal-free single-chip mote that brings us one step closer to the Smart Dust vision, in particular as it can communicate with off-the-shelf IEEE802.15.4 and Bluetooth Low Energy devices. However, before it can be part of such networks, the crystal-free SCµM chip needs to be able to accurately tune its communication frequency to synchronize to the network. This is a challenge since its on-board RC and LC-based resonating circuits have a drift rate that can be 3 orders of magnitude worse than crystal-based oscillators typically used in today's radios. This article introduces QuickCal, a solution that allows a SCµM chip to self-calibrate against off-the-shelf devices dedicated to assisting with its calibration. We show that a SCµM chip can self-calibrate against this QuickCal Box in fewer than 3 min. We further validate that, once it has self-calibrated, a SCµM chip can reliably communicate with off-the-shelf IEEE802.15.4 devices. Finally, we demonstrate a heterogeneous network-composed of a SCµM chip and an OpenMote device-implementing a full 6TiSCH Industrial IoT protocol stack, which uses time synchronization and channel hopping. This is the first time that a crystal-free radio is participating in a channel-hopping enabled TSCH network

Accurate 3D Lighthouse Localization of a Low-Power Crystal-Free Single-Chip Mote

International audienceWe present a system for centimeter-precision 3 dimensional localization of a 2×3×0.3 mm3, 5 mg, wireless system-on-chip by utilizing a temporally-structured infrared illumination scheme generated by a set of base stations. This 3D localization system builds on previous work by adding a second lighthouse station to enable 3D localization and using the integrated wireless radio, making the localization system fully wireless. We demonstrate 3D tracking with mean absolute errors of 1.54 cm, 1.50 cm,and 5.1 cm for the X, Y, and Z dimensions. This is the first time such a lighthouse localization system has been able to localize amonolithic single-chip wireless system

Efficient and Interference-Resilient Wireless Connectivity for IoT Applications

With the coming of age of the Internet of Things (IoT), demand on ultra-low power (ULP) and low-cost radios will continue to boost tremendously. The Bluetooth-Low-energy (BLE) standard provides a low power solution to connect IoT nodes with mobile devices, however, the power of maintaining a connection with a reasonable latency remains the limiting factor in defining the lifetime of event-driven BLE devices. BLE radio power consumption is in the milliwatt range and can be duty cycled for average powers around 30μW, but at the expense of long latency. Furthermore, wireless transceivers traditionally perform local oscillator (LO) calibration using an external crystal oscillator (XTAL) that adds significant size and cost to a system. Removing the XTAL enables a true single-chip radio, but an alternate means for calibrating the LO is required. Innovations in both the system architecture and circuits implementation are essential for the design of truly ubiquitous receivers for IoT applications. This research presents two porotypes as back-channel BLE receivers, which have lower power consumption while still being robust in the presents of interference and able to receive back-channel message from BLE compliant transmitters. In addition, the first crystal-less transmitter with symmetric over-the-air clock recovery compliant with the BLE standard using a GFSK-Modulated BLE Packet is presented.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162942/1/abdulalg_1.pd

Surviving the Hair Dryer: Continuous Calibration of a Crystal-Free Mote-on-Chip

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Energy aware optimization for low power radio technologies

The explosive growth of IoT is pushing the market towards cheap, very low power devices with a strong focus on miniaturization, for applications such as in-body sensors, personal health monitoring and microrobots. Proposing procedures for energy efficiency in IoT is a difficult task, as it is a rapidly growing market comprised of many and very diverse product categories using technologies that are not stable, evolving at a high pace. The research in this field proposes solutions that go from physical layer optimization up to the network layer, and the sensor network designer has to select the techniques that are best for its application specific architecture and radio technology used. This work is focused on exploring new techniques for enhancing the energy efficiency and user experience of IoT networks. We divide the proposed techniques in frame and chip level optimization techniques, respectively. While the frame level techniques are meant to improve the performance of existing radio technologies, the chip level techniques aim at replacing them with crystal-free architectures. The identified frame level techniques are the use of preamble authentication and packet fragmentation, advisable for Low Power Wide Area Networks (LPWANs), a technology that offers the lowest energy consumption per provided service, but is vulnerable in front of energy exhaustion attacks and does not perform well in dense networks. The use of authenticated preambles between the sensors and gateways becomes a defence mechanism against the battery draining intended by attackers. We show experimentally that this approach is able to reduce with 91% the effect of an exhaustion attack, increasing the device's lifetime from less than 0.24 years to 2.6 years. The experiments were conducted using Loadsensing sensor nodes, commercially used for critical infrastructure control and monitoring. Even if exemplified on LoRaWAN, the use of preamble authentication is extensible to any wireless protocol. The use of packet fragmentation despite the packet fits the frame, is shown to reduce the probability of collisions while the number of users in the duty-cycle restricted network increases. Using custom-made Matlab simulations, important goodput improvement was obtained with fragmentation, with higher impact in slower and denser networks. Using NS3 simulations, we showed that combining packet fragmentation with group NACK can increase the network reliability, while reducing the energy consumed for retransmissions, at the cost of adding small headers to each fragment. It is a strategy that proves to be effective in dense duty-cycle restricted networks only, where the headers overhead is negligible compared to the network traffic. As a chip level technique, we consider using radios for communication that do not use external frequency references such as crystal oscillators. This would enable having all sensor's elements on a single piece of silicon, rendering it even ten times more energy efficient due to the compactness of the chip. The immediate consequence is the loss of communication accuracy and ability to easily switch communication channels. In this sense, we propose a sequence of frequency synchronization algorithms and phases that have to be respected by a crystal-free device so that it can be able to join a network by finding the beacon channel, synthesize all communication channels and then maintain their accuracy against temperature change. The proposed algorithms need no additional network overhead, as they are using the existing network signaling. The evaluation is made in simulations and experimentally on a prototype implementation of an IEEE802.15.4 crystal-free radio. While in simulations we are able to change to another communication channel with very good frequency accuracy, the results obtained experimentally show an initial accuracy slightly above 40ppm, which will be later corrected by the chip to be below 40 ppm.El crecimiento significativo de la IoT está empujando al mercado hacia el desarrollo de dispositivos de bajo coste, de muy bajo consumo energético y con un fuerte enfoque en la miniaturización, para aplicaciones que requieran sensores corporales, monitoreo de salud personal y micro-robots. La investigación en el campo de la eficiencia energética en la IoT propone soluciones que van desde la optimización de la capa física hasta la capa de red. Este trabajo se centra en explorar nuevas técnicas para mejorar la eficiencia energética y la experiencia del usuario de las redes IoT. Dividimos las técnicas propuestas en técnicas de optimización de nivel de trama de red y chip, respectivamente. Si bien las técnicas de nivel de trama están destinadas a mejorar el rendimiento de las tecnologías de radio existentes, las técnicas de nivel de chip tienen como objetivo reemplazarlas por arquitecturas que no requieren de cristales. Las técnicas de nivel de trama desarrolladas en este trabajo son el uso de autenticación de preámbulos y fragmentación de paquetes, aconsejables para redes LPWAN, una tecnología que ofrece un menor consumo de energía por servicio prestado, pero es vulnerable frente a los ataques de agotamiento de energía y no escalan frente la densificación. El uso de preámbulos autenticados entre los sensores y las pasarelas de enlace se convierte en un mecanismo de defensa contra el agotamiento del batería previsto por los atacantes. Demostramos experimentalmente que este enfoque puede reducir con un 91% el efecto de un ataque de agotamiento, aumentando la vida útil del dispositivo de menos de 0.24 años a 2.6 años. Los experimentos se llevaron a cabo utilizando nodos sensores de detección de carga, utilizados comercialmente para el control y monitoreo de infrastructura crítica. Aunque la técnica se ejemplifica en el estándar LoRaWAN, el uso de autenticación de preámbulo es extensible a cualquier protocolo inalámbrico. En esta tesis se muestra también que el uso de la fragmentación de paquetes a pesar de que el paquete se ajuste a la trama, reduce la probabilidad de colisiones mientras aumenta el número de usuarios en una red con restricciones de ciclos de transmisión. Mediante el uso de simulaciones en Matlab, se obtiene una mejora importante en el rendimiento de la red con la fragmentación, con un mayor impacto en redes más lentas y densas. Usando simulaciones NS3, demostramos que combinar la fragmentación de paquetes con el NACK en grupo se puede aumentar la confiabilidad de la red, al tiempo que se reduce la energía consumida para las retransmisiones, a costa de agregar pequeños encabezados a cada fragmento. Como técnica de nivel de chip, consideramos el uso de radios para la comunicación que no usan referencias de frecuencia externas como los osciladores basados en un cristal. Esto permitiría tener todos los elementos del sensor en una sola pieza de silicio, lo que lo hace incluso diez veces más eficiente energéticamente debido a la integración del chip. La consecuencia inmediata, en el uso de osciladores digitales en vez de cristales, es la pérdida de precisión de la comunicación y la capacidad de cambiar fácilmente los canales de comunicación. En este sentido, proponemos una secuencia de algoritmos y fases de sincronización de frecuencia que deben ser respetados por un dispositivo sin cristales para que pueda unirse a una red al encontrar el canal de baliza, sintetizar todos los canales de comunicación y luego mantener su precisión contra el cambio de temperatura. Los algoritmos propuestos no necesitan una sobrecarga de red adicional, ya que están utilizando la señalización de red existente. La evaluación se realiza en simulaciones y experimentalmente en una implementación prototipo de una radio sin cristal IEEE802.15.4. Los resultados obtenidos experimentalmente muestran una precisión inicial ligeramente superior a 40 ppm, que luego será corregida por el chip para que sea inferior a 40 ppm.Postprint (published version

Ultra-low power IoT applications: from transducers to wireless protocols

This dissertation aims to explore Internet of Things (IoT) sensor nodes in various application scenarios with different design requirements. The research provides a comprehensive exploration of all the IoT layers composing an advanced device, from transducers to on-board processing, through low power hardware schemes and wireless protocols for wide area networks. Nowadays, spreading and massive utilization of wireless sensor nodes pushes research and industries to overcome the main limitations of such constrained devices, aiming to make them easily deployable at a lower cost. Significant challenges involve the battery lifetime that directly affects the device operativity and the wireless communication bandwidth. Factors that commonly contrast the system scalability and the energy per bit, as well as the maximum coverage. This thesis aims to serve as a reference and guideline document for future IoT projects, where results are structured following a conventional development pipeline. They usually consider communication standards and sensing as project requirements and low power operation as a necessity. A detailed overview of five leading IoT wireless protocols, together with custom solutions to overcome the throughput limitations and decrease the power consumption, are some of the topic discussed. Low power hardware engineering in multiple applications is also introduced, especially focusing on improving the trade-off between energy, functionality, and on-board processing capabilities. To enhance these features and to provide a bottom-top overview of an IoT sensor node, an innovative and low-cost transducer for structural health monitoring is presented. Lastly, the high-performance computing at the extreme edge of the IoT framework is addressed, with special attention to image processing algorithms running on state of the art RISC-V architecture. As a specific deployment scenario, an OpenCV-based stack, together with a convolutional neural network, is assessed on the octa-core PULP SoC

A Crystal-Free Single-Chip Micro Mote with Integrated 802.15.4 Compatible Transceiver, sub-mW BLE Compatible Beacon Transmitter, and Cortex M0

International audienceWe present an 802.15.4 compatible transceiver that operates without any off-chip frequency reference. With integrated Cortex-M0, the chip can also transmit BLE beacons with only three external connections (power, ground, and antenna). The RF transmitter operates with >10% system efficiency at-10 dBm output power from a regulated supply. The entire chip, including the microprocessor, can operate below 1 mW peak power when transmitting. The analog receiver power consumption is 1.03 mW from a 1.5V battery