Shunsuke Saruwatari

A high-density earthquake monitoring system using wireless sensor networks

In this paper we present a high-density earthquake monitoring system using wireless sensor networks. For high-precision monitoring, we developed Pavenet OS, which is a hard-realtime operating system for sensor nodes, and acceleration sensor board. Sensor nodes of the system sample acceleration with less than 0.3 us jitter with Pavenet OS. The system provides earthquake engineering researchers the ability to measure vibrations of structures during earthquakes at less cost and higher node density than previous systems.

Full Duplex Media Access Control for Wireless Multi-Hop Networks

Wireless full-duplexing enables a transmission and a reception on the same frequency channel at the same time, and has the potential to improve the end-to-end throughput of wireless multi-hop networks. In the present paper, we propose a media access control (MAC) protocol for wireless full- duplex and multi-hop networks called Relay Full- Duplex MAC (RFD-MAC). The RFD-MAC is an asynchronous full-duplex MAC protocol, which consists of a primary transmission and a secondary transmission. The RFD-MAC increases the full-duplex links by overhearing frames, which include 1-bit information concerning the existence of a successive frame, and selecting a secondary transmission node using the gathered information. The gathered information is also used to avoid a collision between the primary and secondary transmission. Simulation results reveal that the proposed RFD-MAC improves up to 68%, 49% and 56% of end-to-end throughput compared to CSMA/CA, FD-MAC and MFD-MAC, respectively.

Ubiquitous Structural Monitoring using Wireless Sensor Networks

Ubiquitous structural monitoring (USM) of buildings using wireless sensor networks is one of the most promising emerging technologies for mitigation of seismic hazard. This technology has the potential to change fundamentally the traditional monitoring systems. This paper provides an introduction of wireless sensor network technology for USM, and identifies some of opportunities and associated challenges

A Novel Wireless Wake-Up Mechanism for Energy-Efficient Ubiquitous Networks

Excessive power consumption is a major problem in wireless communication. This is particularly true in ubiquitous computing environments, since wireless devices consume a considerable amount of energy in idle listening. Wake-up wireless communication technology is a promising candidate for reducing power consumption during idle listening. To realize wake-up wireless communication, this paper proposes a novel ID matching mechanism that uses a Bloom filter. This paper describes the design and implementation of a wireless wake-up module that uses this ID matching mechanism. Simulation results reveal that the wake-up module consumes only 12.4 muW while idle listening, and that employing this Bloom-filter-based approach eliminates 99.95 % of power consumption in our application scenarios.

A Prototype of a Multi-core Wireless Sensor Node for Reducing Power Consumption

This paper presents initial experiment results toward realizing a multi-core CPU for wireless sensor nodes. The multi-core CPU reduces power consumption with enabling users to easily manage hard real-time tasks. The results show a sensor node with triple CPUs can eliminate about 76 % of power consumption compared to a single CPU sensor node.

Distributed spectrum sensing utilizing heterogeneous wireless devices and measurement equipment

A suitable spectrum policy is essential to allow efficient use of the radio spectrum. The Japanese government currently employs a Command and Control (C&C) regime, but measures must be taken to speed up governmental decisions. The first step is to obtain spectrum utilization data which can form the basis of such decisions. This paper describes the design, implementation and evaluation of a distributed spectrum sensing system that continually measures spectrum utilization at multiple locations. The system has an architecture that enables it to utilize a wide range of existing wireless devices and measurement equipment, which can be used as sensing nodes to rapidly expand the coverage area. By focusing on the way to easily expand the measurement coverage, our work complements previous spectrum measurements, which have been conducted with high accuracy in the context of cognitive radios.

Preliminary evaluation of simultaneous data and power transmission in the same frequency channel

Combining wireless transmission of data and power signals enables us to use wireless devices without charging batteries. To improve the utilization of wireless resources, a sender could simultaneously transmit data and power signals in the same frequency channel. A disadvantage of simultaneous transmission is that it induces interference between data and power signals. To minimize the effect of interference, we propose a new frequency-sharing system. The proposed system makes two contributions. The first contribution is interference cancellation of the power signal to receive data from the collided signal using a combination of digital and analog interference cancellation techniques. The second contribution is a media access control protocol to receive the transmitted power effectively by varying the sleep time. To evaluate the performance of the proposed system, we built an experimental apparatus using software-defined radio. Evaluations show that it is feasible to transmit data and power simultaneously using the proposed system.

A wireless full-duplex and multi-hop network with collision avoidance using directional antennas

Wireless full-duplexing enables multi-hop wireless networks to increase network performance, such as the end-to-end throughput. However, the combination of wireless full-duplexing and multi-hop communication produces a secondary transmission collision problem due to the increase of transmission opportunities. This paper proposes directional asynchronous full-duplex medium access control (DAFD-MAC) to avoid interference on primary and secondary nodes. DAFD-MAC suppresses the secondary transmission collision problem by sending a data frame with directional antennas and also a Network Allocation Vector (NAV) frame while receiving the data frame. The simulation results show that the proposed DAFD-MAC outperforms carrier sense multiple access/collision avoidance (CSMA/CA), full-duplex MAC (FD-MAC), and multi-hop full-duplex MAC (MFD-MAC).

A multi-channel bulk data collection for structural health monitoring using wireless sensor networks

Data-intensive wireless sensor network applications, such as structural health monitoring and earthquake monitoring, require high throughput bulk data collection. Based on the fact that each node stores the same amount of sensor data, we propose a Maximum-Subtree-First Collection Protocol (MSFCP), which adopts Maximum-Subtree-First scheduling on top of multi-channel block transfer to maximize overall throughput. We present the theoretical analysis that MSFCP can achieve optimal throughput in the ideal propagation environment, and we achieve overall throughput of 135 kbps on the IRIS Mote platform.

A Ubiquitous Power Management System to Balance Energy Savings and Response Time Based on Device- level Usage Prediction

Power conservation has become a serious concern during peoples daily life. Ubiquitous computing technologies clearly provide a potential way to help us realize a more environment-friendly lifestyle. In this paper, we propose a ubiquitous power management system called Gynapse, which uses multi-modal sensors to predict the exact usage of each device, and then switches their power modes based on predicted usage to maximize the total energy saving under the constraint of user required response time. We build a three-level Hierarchical Hidden Markov Model (HHMM) to represent and learn the device level usage patterns from multi-modal sensors. Based on the learned HHMM, we develop our predictive mechanism in Dynamic Bayesian Network (DBN) scheme to precisely predict the usage of each device, with user required response time under consideration. Based on the predicted usage, we follow a four-step process to balance the total energy saving and response time of devices by switching their power modes accordingly. Preliminary results demonstrate that Gynapse has the capability to reduce power consumption while keeping the response time within users requirement, and provides a complementary approach to previous power management systems.