Takahiro Fujiwara | Hakodate National College of Technology (original) (raw)

Papers by Takahiro Fujiwara

This paper proposes an ad-hoc routing protocol using unicast-based route discovery in a hybrid wi... more This paper proposes an ad-hoc routing protocol using unicast-based route discovery in a hybrid wireless network, ECCA, which combines ad-hoc networking scheme with a centralized hierarchical network. The network aims to collect damage assessment information in disaster circumstances, maintaining connections between a base station (BS) and nodes by way of multihopping. In the event that a direct link between BS and a node disconnects, the node switches the mode from a cellular to an ad-hoc mode in order to access BS via neighboring nodes. A routing protocol proposed in this paper builds a route by way of monitoring neighbors' communications instead of broadcasting a route request packet. Experiments show that approximately 90% of nodes can discover a route within a few hops, even if only 20% of nodes are able to access BS directly. Even in a low node density, the network is capable of transferring data within three hops.

A number of institutes have addressed for wide technical subjects to mitigate damage in a large n... more A number of institutes have addressed for wide technical subjects to mitigate damage in a large natural and man-made disaster. Several systems have been proposed and developed for damage assessment. We have to consider exploiting multimodal information in order to mitigate damage and conduct disaster restoration quickly and smoothly. This paper describes a system to collect damage assessment information, using hybrid wireless network enhanced with ad hoc networking. Experimental system showed that it is feasible to collect alarm information within one minute from sensors installed in residences and/or lifeline facilities. Computer simulation indicates that the hybrid wireless network is capable of maintaining connections with 90 % of terminals even in the aftermath of a disaster. In addition, we discuss a scheme for information integration.

2000 Asia-Pacific Microwave Conference. Proceedings (Cat. No.00TH8522)

A wireless data acquisition system is investigated for monitoring and control of city lifeline in... more A wireless data acquisition system is investigated for monitoring and control of city lifeline in disaster situations. This paper describes an experimental system consisting of a 2.1 GHz TDM and 2.4 GHz hybrid TD-CDMA systems and experimental results obtained to date. The system was able to collect the urgent data (2B/terminal) from some 260 k household terminals in 51.7 s and the additional detailed data (32 B/terminal) from some 65 k (=260k/4) household terminals in 2.8 min.

Smart Structures and Systems

Quick, accurate damage monitoring is strongly required for damage assessment in the aftermath of ... more Quick, accurate damage monitoring is strongly required for damage assessment in the aftermath of a large natural disaster. Wireless sensor networks are promising technologies to acquire damage information in a citywide area. The wireless sensor networks, however, would be faced with difficulty to collect data in real-time and to expand the scalability of the networks. This paper discusses a scheme of network architecture to cove a whole city in multi-tier heterogeneous networks, which consist of wireless sensor networks, access networks and a backbone network. We first review previous studies for citywide damage monitoring, and then discuss the feature of multi-tier heterogeneous networks to cover a citywide area.

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2017

Regarding Structural Health Monitoring (SHM) for seismic acceleration, Wireless Sensor Networks (... more Regarding Structural Health Monitoring (SHM) for seismic acceleration, Wireless Sensor Networks (WSN) is a promising tool for low-cost monitoring. Compressed sensing and transmission schemes have been drawing attention to achieve effective data collection in WSN. Especially, SHM systems installing massive nodes of WSN require efficient data transmission due to restricted communications capability. The dominant frequency band of seismic acceleration is occupied within 100 Hz or less. In addition, the response motions on upper floors of a structure are activated at a natural frequency, resulting in induced shaking at the specified narrow band. Focusing on the vibration characteristics of structures, we introduce data compression techniques for seismic acceleration monitoring in order to reduce the amount of transmission data. We carry out a compressed sensing and transmission scheme by band pass filtering for seismic acceleration data. The algorithm executes the discrete Fourier transform for the frequency domain and band path filtering for the compressed transmission. Assuming that the compressed data is transmitted through computer networks, restoration of the data is performed by the inverse Fourier transform in the receiving node. This paper discusses the evaluation of the compressed sensing for seismic acceleration by way of an average error. The results present the average error was 0.06 or less for the horizontal acceleration, in conditions where the acceleration was compressed into 1/32. Especially, the average error on the 4th floor achieved a small error of 0.02. Those results indicate that compressed sensing and transmission technique is effective to reduce the amount of data with maintaining the small average error.

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2014, 2014

Wireless sensor networks (WSNs) technologies have attracted much attention to collect damage info... more Wireless sensor networks (WSNs) technologies have attracted much attention to collect damage information in a natural disaster. WSNs to monitor temperature or humidity usually collect data once in some seconds or some minutes. Since structural health monitoring (SHM), meanwhile, aims to make a diagnosis for the state of a structure based on detected acceleration, WSNs are a promising technology to collect acceleration data. One concern to employ WSNs in SHM is to detect phenomena at a high sampling rate under energy-aware condition. In this paper, we describe a model for seismic acceleration monitoring, configured with multi-layer networks: WSNs, a wireless distribution system (WDS) and a database server, where the WDS is mainly operating in a wireless local area network (WLAN). Examining the performance in the test bed for the monitoring system, the results showed the system was capable of collecting acceleration at a rate of 100 sampling per second (sps) even in the fashion of intermittent operation, and capable of storing data into a database. We also suggest that the method using intermittent operation with appropriate sampling rate is effective in providing a long time operation for the system by considering in the response motion of a structure.

電子情報通信学会技術研究報告信学技報, Jan 19, 2012

22nd International Conference on Advanced Information Networking and Applications - Workshops (aina workshops 2008), 2008

Several systems for disaster damage mitigation have been studied based on various perspectives. T... more Several systems for disaster damage mitigation have been studied based on various perspectives. Those previous works suggest it is not easy to get an effective method to comprehend damage conditions due to diversity of disaster damage. This paper discusses a scheme for damage assessment information gathering based on macro and micro perspectives. We, especially, take notice of sensor networks, which play a significant role for the micro perspective. Discussion of this paper for damage monitoring is still open-ended, since unexpected circumstances may lurk in a disaster, and technical environments useful for disaster will even more progress. Moreover, integration of the macro and micro perspectives for damage information r should be a significant future work.

Proceedings of the 6th annual workshop on Wireless of the students, by the students, for the students - S3 '14, 2014

Sensor Network technologies are expected to be used in various kinds of application systems. Most... more Sensor Network technologies are expected to be used in various kinds of application systems. Most of them, however, have been developed to work in a dedicated system. It is desired that various types of sensor networks could be operable in a same application system. To meet the requirement, we have studied middleware architecture named CMSAS (Common Middleware in Sensors, Actuators and Storages), which aims to realize virtual communications between various devices such as heterogeneous sensor networks, actuators and storages. In this paper, we propose the concept of CMSAS based on RT middleware, which was developed by National Institute of Advanced Industrial Science and Technology (AIST) to integrate components in robot technologies. We discuss implementation design of CMSAS in wireless sensor networks to collect acceleration data.

2010 IEEE International Conference on Sensor Networks, Ubiquitous, and Trustworthy Computing, 2010

Wireless sensor networks have been studied for several applications. Disaster damage monitoring i... more Wireless sensor networks have been studied for several applications. Disaster damage monitoring is one of the significant applications in sensor networks. If sensors are set up in buildings or on water pipelines, they could detect damage, victims trapped beneath rubble, or water leakage in case of a natural disaster. Since such a monitoring system is required to operate for a long term (e.g. several years) by batteries, power consumption of a node would be a critical issue. To fulfill the requirement, intermittent operation is employed in several medium access control (MAC) protocols in sensor networks. Moreover, those monitoring systems have to deal with several types of information, such as temperature, acceleration, alarm signals and so on, in some cases including image data to comprehend surrounding conditions. Some of them are gathered periodically, and some are in event-driven operation. Due to the diversity of information resources in sensor networks, the monitoring system requires short latency in bidirectional communications to control the process of data transmission dynamically. Considering these conditions, this paper describes a damage monitoring scheme using bidirectional low latency operation on a MAC protocol, which implements a short latency on bidirectional transmission in an active/sleep operation mode. Some fundamental evaluations show that the protocol is capable of achieving the short latency.

This paper proposes a networking scheme to operate in wireless networks enhanced with ad hoc netw... more This paper proposes a networking scheme to operate in wireless networks enhanced with ad hoc networking for emergency communications. The access protocol aims to maintain connections between a base station (BS) and terminals by way of multihopping in natural disaster or emergencies, and to provide accessibility to subscribers. In the event that a link between BS and a terminal operating in cellular mode is disconnected, the terminal switches to ad hoc mode to build a route to BS via multihopping. The proposed route discovery scheme is capable of building the route without route request used by other ad hoc protocols. A Markov model is employed to analyze the performances of the network. The simulation results show that 90% of terminals in a cell can retrieve access to BS within three hops, where only 20% of terminals can reach the BS directly. The average throughput of the networks is improved from 20% to 40% within three hops.

Electronics and Communications in Japan (Part I: Communications), 2005

The communications environment is currently well organized. Still, it is not easy to handle requi... more The communications environment is currently well organized. Still, it is not easy to handle requirements for urgent communications in a disaster. In a large-scale disaster, it is highly probable that communications functions will be hampered, making access to communication links itself difficult. There is a need for studies directed at assuring robustness and reliability in the emergency communications system. This paper proposes an access protocol for wireless networks in which the centralized control hierarchical network and the horizontal connection ad hoc network are combined. The routing method in which a terminal that cannot directly communicate with the base station (BS) sends urgent data to the BS through neighboring terminals, and an access control protocol for multihopping, are described. In the proposed scheme, the terminal monitors communications in neighboring nodes and dynamically generates a route based on the number of hops to the BS. Evaluations show that the percentage of terminals that can reach the BS by multihopping involving a few hops is significantly improved. It is also shown that the terminal knows the number of hops to the BS in the proposed method, which makes it possible to predict the throughput and the delay time, which is a property suited to urgent communications.

Vehicular Technology, IEEE Conference, 2000

An application of CDMA technique to a dedicated data collection system for monitoring and control... more An application of CDMA technique to a dedicated data collection system for monitoring and control of city lifelines is considered. This paper describes the system configuration of a 2.4 GHz experimental system in which CDMA is combined with polling technique to access 256 household terminals. Results of preliminary experiments are also presented

Natural Disasters - Multifaceted Aspects in Management and Impact Assessment, 2013

... We obtain the probability (p k ) using equation (2) in conditions of k ≤ K-1 and 0 1 k K k p ... more ... We obtain the probability (p k ) using equation (2) in conditions of k ≤ K-1 and 0 1 k K k p = = ∑ . In the ... [7] T.Fujiwara Y.Shimazaki, H.Toyoshima, S.Ito, M.Sugiura, M.Atsumi, T.Watanabe, S.Mizushina, A TD-CDMA Data Collection System for City Lifeline Monitoring, Proc. ...

Ad Hoc Networks, 2005

This paper describes an ad hoc networking scheme and routing protocol for emergency communication... more This paper describes an ad hoc networking scheme and routing protocol for emergency communications. The objective of the network is to collect damage assessment information quickly and stably in a disaster. The network is configured with a hybrid wireless network, combining ad hoc networks and a cellular network to maintain connectivity between a base station (BS) and nodes even in a disaster. In the event that a direct link between the BS and a node is disconnected due to damage or obstacles, the node switches to the ad hoc mode, and accesses the BS via neighboring nodes by multihopping. The routing protocol proposed in this paper discovers and builds a route by way of monitoring neighborsÕ communications instead of broadcasting a route request packet. The network employs a dedicated medium access control protocol based on TDM (Time Division Multiplexing) for multihopping in ad hoc networks to maintain accessibility and to perform a short delay. Experiments showed that approximately 90% of nodes are capable of reaching the BS within a few hops, even in conditions where only 20% of nodes maintain direct connections to the BS. In addition, the results showed that it is feasible for the network to operate in a short delay for delivering a packet to the BS. However, throughput is not retrieved sufficiently due to the restriction of the access protocol, whereas reachability does improve sufficiently. Therefore, the network is suitable for collecting damage assessment information and transmitting urgent traffic quickly and stably, while the data is restricted to a small amount.