Vana Jelicic

Benefits of Wake-Up Radio in Energy-Efficient Multimodal Surveillance Wireless Sensor Network

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 versus latency tradeoff (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).

Design, Implementation, and Performance Evaluation of a Flexible Low-Latency Nanowatt Wake-Up Radio Receiver

Wireless sensor networks (WSNs) have received significant attention in recent years and have found a wide range of applications, including structural and environmental monitoring, mobile health, home automation, Internet of Things, and others. As these systems are generally battery operated, major research efforts focus on reducing power consumption, especially for communication, as the radio transceiver is one of the most power-hungry components of a WSN. Moreover, with the advent of energy-neutral systems, the emphasis has shifted toward research in microwatt (or even nanowatt) communication protocols or systems. A significant number of wake-up radio receiver (WUR) architectures have been proposed to reduce the communication power of WSN nodes. In this work, we present an optimized ultra-low power (nanowatt) wake-up receiver for use in WSNs, designed with low-cost off-the-shelf components. The wake-up receiver achieves power consumption of 152 nW (with -32 dBm sensitivity), sensitivity up to -55 dBm (with maximum power of 1,2 μW), latency from 8 μs, tunable frequency, and short commands communication. In addition, a low power solution, which includes addressing capability directly in the wake-up receiver, is proposed. Experimental results and simulations demonstrate low power consumption, functionality, and benefits of the design optimization compared with other solutions, as well as the benefits of addressing false positive (FP) outcomes reduction.

Reducing power consumption of image transmission over IEEE 802.15.4/ZigBee sensor network

Reduction of power consumption and networks autonomy prolongation are crucial for a WSN. This is typically performed with low duty cycle of sensor nodes. A special challenge in WSNs is transmission of a large amount of data, like images and video, that is becoming more and more required in various applications. This paper presents a study of fragmented image transmission with IEEE 802.15.4/ZigBee protocol where power consumption is reduced by maximal frame filling and disabling MAC acknowledgment with implementation of control field on APL layer. Protocol modification by implementing transmission control on APL layer is necessary in order to achieve successful image transmission, even for the original protocol. Disabling MAC acknowledgment enables communication power reduction of around 7.6%. Another advantage is active time shortening of 1.6%, which prolongs networks lifetime.

Wireless sensor node modelling for energy efficiency analysis in data-intensive periodic monitoring

Data-intensive wireless sensor applications, such as remote visual inspection using high-resolution video sensors, require a special design approach in order to save energy and prolong lifetime of a battery-powered wireless sensor node. This study is motivated by searching for the most efficient communication protocol for high-resolution image transmission in environmental monitoring sensor networks, where data should be transmitted periodically, but relatively rarely (usually once or twice per day). Some previous publications propose ZigBee or Wi-Fi as suitable candidates for data-intensive wireless transmission, but the literature lacks a systematic study that would provide a guidance for designing such systems. We construct a measurement-based model of a wireless sensor node with emphasis on the communication unit. We measured the energy consumption of commercially available wireless ZigBee and Wi-Fi modules, as well as the influence of the interface bandwidth limitation that reduces their energy efficiency. The model includes real-world communication channel properties that at high bit-rates reduce the communication range and increase the energy consumption due to a higher susceptibility to noise.Our results show that in scenarios when the node sends up to 64kB of data per session once per day, the estimated lifetime of a ZigBee node is up to 10% longer than of a Wi-Fi node. However, when the amount of data per session increases, the Wi-Fi wins due to its higher energy efficiency during data transfer. When the data amount reaches 10MB, the lifetime of a Wi-Fi node using UDP protocol is 5 times longer than that of a ZigBee node. On the other hand, the Wi-Fi node lifetime decreases with increasing number of sessions per day, because the connection establishment with the access point is very energy consuming. As a result, when 5 sessions per day are required the ZigBee node can offer 40% longer lifetime than the Wi-Fi node when 10kB of data is transmitted per session.

Low-Power Gas Sensing Using Single Walled Carbon Nano Tubes in Wearable Devices

Air quality monitoring is gaining importance in public health due to the increasing level of the pollution in cities. In addition, people are more concerned about their personal exposure and they are interested to know the concentration levels of the pollutants, which surround them. In recent years, a wearable technology can be useful for continuous air quality monitoring when people are moving in urban and industrial environments. As wearable systems are usually battery-powered and gas sensors are power-hungry, energy-efficient design and power management are required. In this paper, we present a two-stage gas sensing concept where novel multiple-single-walled carbon nanotubes (SWCNT) are proposed as detectors for an energy-hungry metal-oxide (MOX)-semiconductor gas sensor. We simulate the system performance combining the low power consumption of SWCNT gas sensors and the more mature MOX sensor to achieve an energy-efficient wearable device able to monitor the air quality continuously while achieving long lifetime. We perform the simulations using measured power consumptions for two event-driven scenarios to evaluate the power consumption reduction and lifetime extension in a wearable mobile context. Our results show that the proposed approach prolongs node lifetimes by 30 times compared with adaptive duty-cycling with only MOX gas sensors. We also propose that the nanotube recovery time issue can be overcome by using four single nanotubes on the same chip, which results in an extension of lifetime.

Energy-efficient atmospheric CO concentration sensing with on-demand operating MOX gas sensor

Collaborative mobile air-pollution monitoring, employing context aware sampling scheduling, requires on-demand sensing of gas concentration. If MOX gas sensors are used, their energy consumption can be reduced by on-demand heating, with a risk to compromise the sensing repeatability. We experimentally investigate response of MiCS-5525 CO MOX sensor to intermittent heating sequences consisting of a train of short rectangular pulses. We analyse stability of response, energy consumption and sensitivity at low concentrations, for various combinations of pulse waveform period and duty-cycle. We obtained stable readings for the heating sequences consuming 200-300 mJ, saving over 30% of energy per reading.

Evaluation of MOX gas sensor transient response for low-power operation

Metal-Oxide Semiconductor gas sensors are small in size and affordable, which makes them appropriate for implementation in battery-powered wearable sensing devices. However, their big flaw is the need to be heated to a certain temperature to react with the gas from the atmosphere, which consumes energy and drains the battery of the sensing device. In this paper we experimentally evaluate the possibilities to determine changes in gas concentration from the very beginning of the sensors response. Our experiments in controlled conditions show that the increment of CO concentration could be determined in the first 65 ms of sensor heating, while the sensing layer is still in its transient state. That indicates the possibility of more than 30 times energy savings compared to the experiments where the CO concentration is determined after the sensing layer reaches stable state.

From single point of measurement to distributed sensing in long-term glacier monitoring

Glacial environment monitoring is a key task in understanding natural phenomena related to global warming. For the last 30 years, Automatic Weather Stations (AWSs) have been spreading among the meteorological and geophysical community, and are on the way to become a de facto standard to perform long-lasting unattended data acquisitions in single localized points of interest. Sensor Networks (SNs), on the other hand, promise the possibility to perform measurements with a higher spatial density and lower cost. Designing and developing a SN for glacial environment face particular challenges for embedded electronics and sensor systems, which is why SNs are still under research and development in this field. This paper surveys the AWSs and SNs for glacial monitoring applications and compares their characteristics.

Towards Internet of Things for event-driven low-power gas sensing using carbon nanotubes

One of most important applications of sensing devices under the Internet of Things paradigm is air quality monitoring, which is particularly useful in urban and industrial environments where air pollution is an increasing public health problem. As these sensing systems are usually battery-powered and gas sensors are power-hungry, energy-efficient design and power management are required to extend the devices lifetime. In this paper, we present a two-stage concept where a novel low-power carbon nanotube is used as a gas detector for an energy-consuming metal-oxide (MOX) semiconductor gas sensor. We propose a design of a heterogeneous sensor node where we exploit the low-power nanotube gas sensor and the more accurate MOX sensor. This work performs energy consumption simulations for three event-driven scenarios to evaluate the power consumption reduction, as well as the limitations of carbon nanotubes. Our results show the benefits of the proposed approach over the scenarios with adaptive duty-cycling with only MOX gas sensors, proved with 20%-35% node lifetime prolongation. The delay introduced due to the nanotube recovery time can be overcome by radio duty-cycled activity for detecting alarm messages from the neighbour nodes.

Enhancing performance of wireless sensor networks in glacial environments using wake-up receivers

Development of radio telemetry enabled long-term monitoring of hard-to-reach and harsh environments. This paper compares two WSN deployment projects for gathering sensor data in glacier monitoring application — GlacsWeb and PermaSense, in terms of system design and wireless communication. We discuss the potential benefits of energy-efficient event detection using wake-up receivers together with duty-cycled communication. We show that adding a WURx would increase the average power consumption of Dozer protocol for 10%, but it would reduce the delay from 2 minutes to several milliseconds. Besides for event detection, WURx could be used for synchronizing the beginning of the TDMA communication, which would eliminate the need for clock drift compensation, making the protocol simpler and lighter.