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Networking and robotics are increasingly coming together to meet the requirements of applications that only advances in both fields can enable. This paper explores one of these joint applications, namely, using a robotic platform such as an Unmanned Aerial System (UAS) to wirelessly retrieve data produced by the devices of a sensor network. For energy conservation purposes devices operate according to a set duty cycle, or are endowed with wake-up radio transceivers allowing them to transmit and receive data only when needed. We define two simple UAS-aided data collection strategies depending on whether the devices use duty cycling or can be woken up by the visiting UAS. The performance of the two strategies is evaluated by using GreenCastalia, an open source simulator extended to model duty cycles, wake-up radio capabilities and the mobility of the UAS. We compare the two strategies with respect to the amount of data the UAS can collect in its visit, the energy consumption of the devices and the corresponding network lifetime. Our results show the key role of low-cost, low-energy consumption wake-up receivers in providing ways of collecting all data from the sensing devices while consuming a negligible fraction of the energy required to devices operating with a duty cycle. As a result, the lifetime of wake-up radio-based networks is orders of magnitude higher than that afforded to networks with duty cycling: Many decades vs. the very few years of networks with extremely low duty cycles.

Wake-up radios (WuRs) are usually designed as a secondary near-zero power radio receiver used to trigger the main radio when a new communication is started over the air. Despite the tight relation with the main radio functions, it is usually implemented with separate hardware, firmware, and it is far from being integrated in the most diffused standard wireless protocols for sensors networks and for the Internet of Things (IoT). In this work, we want to check in-deep the coexistence between the Bluetooth Low Energy (BLE), which is one of the most used low-power short-range wireless standards for mobile and wearable communication, and a wake-up facility implemented in the same band. We focus on the analysis of the limits, advantages and drawbacks of adding this interesting feature in the BLE standard, and we discuss about the improvements in terms of power saving and latency of the communication. We target IoT applications and scenarios with a high density of BLE devices, analyzing the standard protocol and how WuRs can enhance its performance. Two common communication schemes will help us to show the limits and to define a design methodology for the application. Simulation results will show the trade-offs of the communication performance and the difference from a normal usage of the BLE. Finally, considerations about the usability of BLE with WuRs and guidelines will be provided as concluding remarks.

International audience; Body Area Networks (BAN) have received significant attention in recent years and have found a wide range of applications, including wearable devices for fitness and health tracking, and mobile communications. Battery lifetime continues to be the main bottleneck in these small form factor devices, thus low power design and advanced power management techniques are required to sustain the increasing demands on power. As radio transceivers are typically the most power hungry subsystem in a wearable sensors device, optimizations to reduce the communication power consumption, such as using adaptive power management coupled with ultra-low power receivers have been widely investigated. In this work, we focus on the design of a novel wearable wake-up radio consuming only few nW during listening mode, significantly reducing the overall power consumption of communication, which enables aggressive power management techniques. We propose the co-design of an ad-hoc wearable antenna which directly matches the impedance of the analog frontend in order to improve the performance in terms of sensitivity and directivity in BAN context. Our novel wake up radio consumes only 400nW while providing short-range communication, and features on board addressing capability to further reduce the power due to false wake ups. Using in-field measurements, we evaluate the benefits of the ad-hoc antenna compared to state-of-the-art off-the-shelf solutions in terms of range, sensitivity and addressing capability. We quantify energy savings and estimate the lifetime prolongation of the sensor node by integrating our wake-up radio in a wearable system.

Wireless sensor networks (WSNs) are today widely employed in real world applications. However, their lifetime is still challenging and the most critical limitation for the success of this technology. In fact, wireless sensors nodes, which are the backbone of the network, are typically powered by limited energy storage devices (i.e. small batteries or supercaps) and their short lifetime is a critical issue. To overcome this limitation a major research effort focuses on reducing power consumption, especially of communication, as the radio transceiver is one of the highest power consumers. A critical energy-efficiency issue in WSN transceivers is idle listening. Wake-up radio receivers are very effective in minimizing idle listening. This fact has resulted in a significant number of wake-up radio receiver architectures proposed in last decade. In this work we present an advanced design and implementation of an advanced wake-up radio that is capable of both processing the received data (i.e. for addressing) and retransmitting data or wake up messages to the neighbours when necessary. With these features it can be possible to further enhance the energy efficiency of the communication and allowing ultra-low power multi-hop communication. Experimental results demonstrate the functionality as well as the power and range of the proposed design which is ready for future energy efficient and pure-asynchronous MAC protocols.

WiFi is not commonly used for building IoT nodes since the high power consumption of the WiFi interfaces. WiFi consumes 40 times for power when transmitting and 10 times more than a Bluetooth Low Energy node when receiving. This consumption can be reduced using a technique called Wake Up Radio. This approach consists on having a very low power receiver that is using to indicate when the data receiver (the one that consumes a significant amount of power) should be ready to receive. The usage of the approach makes the WIFi very efficient in terms of bits per Joule and it is WiFi is not commonly used for building IoT nodes due to the high power consumption of the WiFi interfaces. This consumption can be reduced using a technique called Wake Up Radio. This approach consists on having a very low power receiver that is used to indicate when the data receiver (the one that consumes a significant power) should be ready to receive. In this thesis, we designed a WuR system with addressing capabilities and implemented a WuRx based in an extreme low power MCU that is able to decode a predefined address and emit commands to the IoT device who has been set in sleep mode. The WuRx was designed and implemented for two different schemes. The first one is a WuRx aligned with the new emerging standard 802.11ba being developed by the IEEE, which demands the modification of the radio and WiFi interfaces. Additionally, a more compatible WuTx based on legacy devices is proposed for this new approach. The second scheme consists of a Wake-Up Radio system based on Pulse Width Modulation that operates with legacy WiFi devices. Experimental tests allowed to conclude that both solutions can be conveniently used for low power applications with different latency and power consumption requirements. WiFi no es un estándar comúnmente usado en la implementación de dispositivos para redes de IoT debido al alto consumo de energía de sus interfaces. Este consumo puede reducirse usando una técnica llamada Wake Up Radio (WuR), que consiste en un receptor de muy baja potencia que tiene como función indicar a la interfaz de radio principal (alto consumo) que debe estar lista para recibir. En este sentido, hemos diseñado un sistema de WuR con capacidades de direccionamiento e implementamos un Receptor de Wake up (WuRx) basado en una un microcontrolador de extrema baja potencia capaz de decodificar una dirección predefinida y emitir comandos al dispositivo IoT en modo de bajo consumo. Específicamente, el WuRx fue diseñado e implementado en base a dos esquemas diferentes. El primero está alineado con el nuevo estándar 802.11ba, que está siendo desarrollado por el IEEE, pero que requiere la modificación de las interfaces de radio WiFi. Adicionalmente, se propone un Transmisor Wake Up (WuTx) compatible con dispositivos ?legacy? para hacer frente a este nuevo enfoque. El segundo esquema consiste en un sistema de WuR basado en modulación por anchos de pulso que opera con dispositivos WiFi ?legacy?. Las pruebas experimentales permitieron concluir que ambas soluciones pueden usarse convenientemente para aplicaciones de baja potencia con diferentes requisitos de latencia y consumo de energía. WiFi no es un estándar comúnmente usado en la implementación de dispositivos para redes de IoT debido al alto consumo de energía de sus interfaces. Este consumo puede reducirse usando una técnica llamada Wake Up Radio (WuR), que consiste en un receptor de muy baja potencia que tiene como función indicar a la interfaz de radio principal (alto consumo) que debe estar lista para recibir. En este sentido, hemos diseñado un sistema de WuR con capacidades de direccionamiento e implementamos un Receptor de Wake up (WuRx) basado en una un microcontrolador de extrema baja potencia capaz de decodificar una dirección predefinida y emitir comandos al dispositivo IoT en modo de bajo consumo. Específicamente, el WuRx fue diseñado e implementado en base a dos esquemas diferentes. El primero está alineado con el nuevo estándar 802.11ba, que está siendo desarrollado por el IEEE, pero que requiere la modificación de las interfaces de radio WiFi. Adicionalmente, se propone un Transmisor Wake Up (WuTx) compatible con dispositivos ?legacy? para hacer frente a este nuevo enfoque. El segundo esquema consiste en un sistema de WuR basado en modulación por anchos de pulso que opera con dispositivos WiFi ?legacy?. Las pruebas experimentales permitieron concluir que ambas soluciones pueden usarse convenientemente para aplicaciones de baja potencia con diferentes requisitos de latencia y consumo de energía.