Tohru Asami

Prototype implementation of ambient RF energy harvesting wireless sensor networks

Energy harvesting is a key technique that can be used to overcome the barriers that prevent the real world deployment of wireless sensor networks (WSNs). In particular, solar energy harvesting has been commonly used to overcome this barrier. However, it should be noted that WSNs operating on solar power suffer form energy shortage during nighttimes. Therefore, to solve this problem, we exploit the use of TV broadcasts airwaves as energy sources to power wireless sensor nodes. We measured the output of a rectenna continuously for 7 days; from the results of this measurement, we showed that Radio Frequency (RF) energy can always be harvested. We developed an RF energy harvesting WSN prototype to show the effectiveness of RF energy harvesting for the usage of a WSN. We also proposed a duty cycle determination method for our system, and verified the validity of this method by implementing our system. This RF energy harvesting method is effective in a long period measurement application that do not require high power consumption.

Ambient-RF-energy-harvesting sensor node with capacitor-leakage-aware duty cycle control

In this paper, we present a software control method that maximizes the sensing rate of wireless sensor networks (WSN) that are solely powered by ambient RF power. Different from all other energy harvesting WSN systems, RF powered systems present a new challenge for the energy management. A WSN node repeatedly charges and discharges at short intervals depending on the energy intake. A capacitor is used for an energy storage in the energy harvesting system because of its efficient charge and discharge performance and infinite recharge cycles. When this charging time is too short, the node is more likely to experience an energy shortage. On the contrary, if it is too long, more energy is lost because of the leakage in the capacitor. Therefore, we implemented an adaptive duty cycle control scheme that is optimized for RF energy harvesting. This method maximizes the sensing rate considering the leakage problem, a factor that has never previously been studied in this context. Our control scheme improves efficiency by aggregate evaluation of the operation reliability and leakage reduction.

A battery-less, energy harvesting device for long range scavenging of wireless power from terrestrial TV broadcasts

Use of Japanese Integrated Services Digital Broadcasting Terrestrial (ISDB-T) standard has resulted in broadcast of perpetually on, wireless digital TV signals over the air at wider bandwidths in UHF bands for smart phones & video-on-demand. This paper presents a unique energy harvesting prototype capable of scavenging wireless power from such broadcasts and well capable of powering on electronics operating at 3V from wireless TV signals for limited duty cycle at distance of 6.5km from source.

Energy consumption targets for network systems

Followed by related development activities in Japan, a comprehensive investigation on energy consumption in ITC industry is presented. Photonic network will have more important roles in mobile networks than in fixed networks.

A Calorie Count Application for a Mobile Phone Based on METS Value

This paper shows a methodology of estimating a users everyday energy expenditure using a 3-axis accelerometer of a mobile phone handset. We first infer the users posture based on the acceleration sensor reading and calculate METS value, which is considered as a measure for estimating calorie consumption for daily activities. The experimental result shows that our application is as accurate as a reference device.

Feasibility and potential application of power scavenging from environmental RF signals

In this paper, we presented measurement results of electrical field intensity from broadcasting and mobile communication systems in order to show the feasibility of energy harvesting from RF signals. Experimental results show that RF signal from mobile phone systems are observed at various locations but the strength varies frequently depending on the mobile phone traffic. Radiowave from broadcasting tower, on the other hand, was very stable temporally but the strength depends on the distance from the broadcasting tower. From the measurement results, we believe it is possible to scavenge electric energy from RF signals using a carefully tuned rectifier with high gain directional antenna. However, it is also necessary to compensate instability of enegy supply by tricks in the upper layers such as network protocols and application software.

Compressed sensing method for human activity sensing using mobile phone accelerometers

This paper presents the first complete design to apply the compressed sensing (CS) theory to activity sensor data gathering for smart phones. Today, most of the mobile phones are equipped with multiple sensors, such as cameras, GPS, and accelerometers. By exploiting the sensing features, we capture many different events and share them over the mobile network. One of the most important challenges for such a participatory sensing system is to reduce the battery consumption of the mobile device. We overcome this challenge by reducing the communication data, without introducing intensive computation at mobile terminals. The CS technique consists of very simple matrix operations at the mobile side, and CPU-intensive reconstruction is performed on the resource-rich machine on the network side. Since CS is a lossy compression technique, the reconstructed signal contains errors depending on the degree of sparseness of the original signal. We evaluated the proposed method by using a large amount of real activity data consisting of six basic activities performed by 90 test subjects. We also implemented our method on the iPhone/iPod platform and showed that our method can reduce power consumption by approximately 16% as compared with ZIP compression, while maintaining the error below 10%.

Prototype implementation of wireless sensor network using TV broadcast RF energy harvesting

Energy harvesting is a key technique that can be used to overcome the barriers that prevent the real world deployment of wireless sensor networks. We explored the use of airwaves of TV broadcasts as energy sources to power wireless sensor nodes. We measured the output of a rectenna continuously for 7 days. The experimental results showed that the daily and weekly cycles of TV broadcasts affected the harvested energy output. We developed a Radio Frequency (RF) energy harvesting wireless sensor network prototype to show the effectiveness of RF energy harvesting for the usage of a wireless sensor network. We also proposed a duty cycle determination method for our system, and verified this by implementation.

Designing a Framework for Scalable Coordination of Wireless Sensor Networks, Context Information and Web Services

Context-aware services are one of the key applications in the ubiquitous computing environment where physical and virtual information are seamlessly integrated across the network. However, so far we have found few discussions on architectural styles for such integration of wireless sensor networks and other networks services and objects. Conventional context aware services have been built in an ad-hoc manner, making it difficult to build new applications or evolve existing ones. The objective of this paper is to discuss the architectural requirements from several points of view such as entry barrier, extensibility, interoperability, and scalability. Then we show a service coordination framework based on REST architectural style.

A Communication System with a Fast Handover under a High Speed Mobile Environment

This paper proposes a communication system using Wi- Fi (IEEE802.11g) to link between the Internet and high speed rail systems traveling at around 300km/h. In order to adapt Wi-Fi for high speed mobile communication, we optimized its coverage on a rail track with a developed directional antenna, which has a communication range of around 500m by 10mW. With the antenna, however, a mobile entity had to switch over antennae (a layer 2 handover (L2HO)) every 6 to 7 seconds. Furthermore Mobile IP handovers (a layer 3 handover (L3HO)) had to be appropriately controlled to avoid a simultaneous handover of Layer 2 and 3, which results in a fatal communication disruption. Therefore the designed system in this paper separated a L3HO from a L2HO. As a result, a maximum of 25Mbps with an average of 16Mbps for the UDP throughput and an average L2HO time of 110ms were realized while travelling at 270km/h.