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Wake-up radio is an emerging technology with the ambitious goal of reducing the communication power consumption in smart sensor networks and Internet of Things. This reduction in power consumption will enable a new generation of applications which could achieve a longer lifetime than is achievable today. Wake up radios are required to work with a low power budget and should exhibit low latency coupled with high sensitivity and addressing capabilities. Typically they are combined with existing radio transceiver and power management techniques to reduce the overall communication power while maintaining the same communication performance. This paper presents a dual band (2.4GHz and 868MHz) wake up radio with the above mentioned characteristics. The dual band solution is exploited to increase the flexibility of the wake up radio, allowing interoperability with the two most common frequencies used in Wireless Sensors Networks and Internet of Things. Simulation results present a system able to exploit the two bands with sensitivity as low as −53dBm at 868MHz and −45dBm at 2450MHz. Experimental results on power consumption demonstrate the low power consumption of the proposed solution with only 1.276μW of power consumption in listening mode. The addressing is performed by an ultra low power on board PIC microcontroller with 40nW of power consumption when the wake up radio is in listening mode and only 70 μW when the data are received and parsed.

Wireless body area networks (WBANs) have the huge potential to enhance people's lives. They are already present in many application domains, for instance sport and fitness, but they are wide spreading in particular in health and rehabilitation. However, there are still challenging issues that limit their wide diffusion in real life: primarily, the limited lifetime due to the batteries that usually supply the devices. This limitation affects usability and force the data processing to be simple to match the power constraints. This work tries to address the energy limitation by enabling both efficient and complex signal-processing applications and extension of lifetime. We present a power management strategy combining an ultra-low power wake up radio with context awareness. The context aware power manager based on activity recognition decides which nodes must be activated exploiting a nano-power wake up radio and power management policies. Result shows that by using both approaches it is possible to extend battery life of sensor nodes from few hours to an entire week.

A self-sustainable wireless sensor node for the monitoring radiation in contaminated and poorly accessible areas is presented. The node is designed to work in collaboration with an unmanned aerial vehicle used for two essential mission steps: air-deploying the wireless sensor nodes at suitable locations and acquiring data logs via ultra-low power, short-range radio communication in fly-by mode, after a wake-up routine. The system allows for the use of off-the-shelf components for defining mission, drop-zone and trajectory, for compressing data, and for communication management. The node is equipped with a low-power nuclear radiation sensor and it was designed and implemented with self-sustainability in mind as it will be deployed in hazardous, inaccessible areas. To this end, the proposed node uses a combination of complementary techniques: a low-power microcontroller with non-volatile memory, energy harvesting, adaptive power management and duty cycling, and a nano-watt wake-up radio. Experimental results show the power consumption efficiency of the solution, which achieves 70uW in sleep mode and 500uW in active mode. Finally, simulations based on actual field measurements confirm the solution's self-sustainability and illustrate the impact of different sampling rates and that of the wake-up radio.

Wearable technologies are ooding the consumer market, and have massively entered the market of electronic con-sumers and people are now surrounded by an increasing number of "smart" objects to wear. The main issue that limits the success of these devices is limited battery life-time. Energy-neutral operation, which does not require bat-tery recharging or replacement (similar to automatic quartz watches) is highly desirable in this context. In this paper, we present the first energy-neutral wearable device, equipped with an ultra low power camera and an electrophoretic dis-play (EPD) which is supplied by a solar energy harvester. The novel design includes several hardware and software op-timizations to achieve energy neutrality. In particular, we implemented innovative methods for displaying gray-scale images to obtain up to 9 gray-scale levels using a black-and-white display. This reduces by 43.7% the energy consump-tion in comparison to the state of art. Moreover, we imple-mented aggressive power management for the camera acqui-sition which saves up to 91.4% of energy to acquire an image. Experimental results, with different scenarios, demonstrate advanced functionality and the energy neutrality of the sys-tem that can acquire and display up to 54 images per hour in indoor scenario.

Wearable technology is gaining popularity, with people wearing everything "smart" from clothing to glasses and watches. Nowadays wearables are battery-powered and a critical issue is the limited lifetime. So most devices have to be recharged every few days or even hours and thus they miss the expectations for a truly unobtrusive user experience. This paper presents InfiniTIME, a novel sensor-rich smart bracelet powered by small photovoltaic cells, designed to achieve energy neutrality even with modest indoor light levels. Experimental characterization of the fully operational prototype demonstrates a wide range of energy optimization techniques used to achieve the neutrality target. Simulations using energy intake measurements from various deployment scenarios confirm that the InfiniTIME achieves energy neutrality with indoor lighting levels in an office for several realistic application scenarios featuring data acquisition from the on-board camera and multiple sensors, visualization and radio connectivity.

Nodes in wireless sensor networks (WSNs) typically have limited power supply and networks are often expected to be functional for extended periods. Therefore, the minimization of energy consumption and the maximization of network lifetime are key objectives in WSN. This paper proposes an overlay, energy optimized, sensor network to extend the functional lifetime of an energy-intensive sensor network application. The overlay network consists of additional nodes that exploit recent advances in energy harvesting and wake-up radio technologies, coupled with an application specific, complementary, ultra-low power sensor. The experimental results and simulations demonstrate that this approach can ensure survivability of energy-inefficient sensor networks. Simulating applications using energy-intensive video cameras and air quality sensors, combined with the proposed overlayed ultra-low power sensor network, demonstrates that this approach can increase functional lifetime toward perpetual operation and is suitable for WSN applications in which complementarity exists between the required energy-intensive sensors and low-cost sensors that can be used as triggers.

A high-sensitivity fully passive 868-MHz wake-up radio (WUR) front-end for wireless sensor network nodes is presented. The front-end does not have an external power source and extracts the entire energy from the radio-frequency (RF) signal received at the antenna. A high-efficiency differential RF-to-DC converter rectifies the incident RF signal and drives the circuit blocks including a low-power comparator and reference generators; and at the same time detects the envelope of the on-off keying (OOK) wake-up signal. The front-end is designed and simulated 0.13μm CMOS and achieves a sensitivity of -33 dBm for a 100 kbps wake-up signal.

In power-limited wireless devices such as wireless sensor networks, wearable components, and Internet of Things devices energy efficiency is a critical concern. These devices are usually battery operated and have a radio transceiver that is typically their most power-hungry block. Wake-up radio schemes can be used to achieve a reasonable balance among energy consumption, range, data receiving capabilities and response time. In this paper, a high-sensitivity low power wake-up radio receiver (WUR) for wireless sensor networks is presented. The wake-up radio is comprised of a fully passive differential RF-to-DC converter that rectifies the incident RF signal, a low-power comparator and an ultra low power microcontroller to detects the envelope of the on-off keying (OOK) wake-up data used as address. We designed and implemented a novel low power tunable wake up radio with addressing capability, a minimal power consumption of only 196nW and a maximum sensitivity of -55dBm and minimal wake up time of 130μs without addressing and around 1,6ms with 2byte addressing at 10Kbit/s data rate. The flexibility of the solution makes the wake up radio suitable for both power constrained low range application (such as Body Area Network) or applications with long range needs. The wake up radio can work also at different frequencies and the addressing capability directly on board helps reduce false positives. Experimental on field results demonstrate the low power of the solution, the high sensitivity and the functionality.

Hydrogen fuel cells are considered one of the most promising alternatives to batteries, because of their higher energy density and they are not affected by issues related to self-discharge. Fuel cells are very attractive for devices with long lifetime requirements. Unfortunately, fuel cells suffer from slow dynamic response to load changes and require active gas flow control. These issues have not been previously addressed for portable systems and small scale fuel-cells. This work presents a hybrid hydrogen micro fuel cell/ Li-Ion battery power unit for embedded systems and wireless sensor networks which tackles these issues. The power system is microcontroller-based and it provides a driver circuits to control the hydrogen flow closing and opening an electro-valve certified for hydrogen gas. We first describe the fuel cell implementation we characterize its power delivery capability. Next, we present the architecture of the developed prototype for the power unit and the fuel flow control system. Finally an evaluation of the performance during Li-Ion battery recharges is presented. The behaviour of hybrid system is examined and tested and the experimental results show the high efficiency (around 85%) of the proposed solution. A 1000mAh Li-Ion battery is re-charged with 11liters of hydrogen in around 2 hours.

Scarce energy budget of battery-powered wireless sensor nodes calls for cautious power management not to compromise performance of the system. To reduce both energy consumption and delay in energy-hungry wireless sensor networks for latency-restricted surveillance scenarios, this paper proposes a multimodal two-tier architecture with wake-up radio receivers. In video surveillance applications, using information from distributed low-power pyroelectric infrared (PIR) sensors which detect human presence limits the activity of cameras and reduces their energy consumption. PIR sensors transmit the information about the event to camera nodes using wake-up radio receivers. We show the benefits of wake-up receivers over duty-cycling in terms of overcoming energy consumption vs. latency trade- off (proved with two orders of magnitude lower latency – only 9 ms). At the same time, the power consumption of the camera node including a wake- up receiver is comparable with the one having only duty-cycled main transceiver with 1% duty cycle (about 32 mW for 25 activations per hour).

Wearable electronics is increasingly attracting researchers and manufacturers for the application opportunities it opens. Chip makers are responding to the hot wearable-computer trend with new components, microcontrollers and sensors. The most critical challenge is the autonomy of the systems. Even if battery management can help in extending the lifetime, the trade-off between features given by a multisensory platforms and autonomy can determine if a platform will win or not in the marketplace. In this paper we present a bracelet device, which attempts to maximize the capability of sensors on board, while still keeping the energy consumption low. Aggressive power management and an accurate selection of the sensors are addressed in this paper to demonstrate the effectiveness of our design.

Proceedings of the 2016 Design, Automation & Test in Europe Conference & Exhibition (DATE), ISBN:978-3-9815370-7-9, ISBN:3-9815370-7-6