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Hiroyuki Morikawa

Bio: Hiroyuki Morikawa is an academic researcher from University of Tokyo. The author has contributed to research in topics: Wireless sensor network & Ubiquitous computing. The author has an hindex of 26, co-authored 267 publications receiving 2614 citations. Previous affiliations of Hiroyuki Morikawa include Kanazawa Institute of Technology & National Institute of Information and Communications Technology.


Papers
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Proceedings ArticleDOI
15 May 2003
TL;DR: A new indoor positioning system called DOLPHIN, which consists of distributed wireless sensor nodes which are capable of sending and receiving RF and ultrasonic signals and enables autonomous positioning of the objects with minimal manual configuration.
Abstract: Determining physical location of indoor objects is one of the key issues in development of context-aware applications in ubiquitous computing environments. This is mainly because context information obtained from sensor networks is meaningful only when the physical location of the context information source is determined. Recently, several indoor location information systems, such as Active Bat and Cricket, have been developed for precise indoor object localization. However, to provide accurate physical location tracking in large-scale space, those systems requires a lot of manual configuration for all the ultrasonic sensor nodes. To reduce configuration costs, we developed a new indoor positioning system called DOLPHIN. The DOLPHIN system consists of distributed wireless sensor nodes which are capable of sending and receiving RF and ultrasonic signals. These nodes are attached to various indoor objects. And using a novel distributed positioning algorithm in the nodes, DOLPHIN enables autonomous positioning of the objects with minimal manual configuration. This paper describes the design and implementation of the DOLPHIN system, and evaluates basic performance through several experiments in an indoor environment.

208 citations

Journal ArticleDOI
TL;DR: A timing delay insertion method is proposed, the offset-CT method, that adds random timing delay before the packets while preventing the timing offset from diverging over the multi-hop network.
Abstract: In this paper, we strive to construct an efficient multi-hop network based on the sub-GHz low-power wide-area technology. Specifically, we investigate the combination of LoRa, a physical-layer standard that can provide several-kilometer outdoor coverage, and concurrent transmission (CT), a recently proposed multi-hop protocol that can significantly improve the network efficiency. The main contributions of this paper are threefold. 1) Since the CT enhances the network efficiency by allowing synchronized packet collisions, the performance of the physical-layer receiver under such packet collisions needs to be carefully examined to ensure the network reliability. We first extensively evaluate the LoRa receiver performance under CT to verify that LoRa is compatible to CT. Specifically, we find that, due to the time-domain and frequency-domain energy spreading effect, LoRa is robust to the packet collisions resulting from CT. 2) We further find the receiver performance under CT can be further improved by introducing timing offsets between the relaying packets. In view of this, we propose a timing delay insertion method, the offset-CT method, that adds random timing delay before the packets while preventing the timing offset from diverging over the multi-hop network. 3) We conduct proof-of-concept experiments to demonstrate the feasibility of CT-based LoRa multi-hop network and the performance improvement brought by the proposed offset-CT method.

146 citations

Proceedings ArticleDOI
22 Sep 2000
TL;DR: In this paper, a burst optical deflection routing protocol is proposed to reduce the blocking probability and increase the performance of burst switching WDM optical networks by using idle optical links as fiber delay lines for contention resolution.
Abstract: Given the significant progress made and the continuing advances expected in the optical networking technology, it becomes attractive to build a future Optical Internet that natively supports bursty IP datagrams. Burst switching WDM optical networks are touted as suitable network architectures for future Optical Internet backbones. However, the lack of optical processing capabilities results in increased burst blocking probability, which in turn leads to very limited network performance. Efficient contention resolution method is therefore necessary. Based on discussions of the state of the art of recent optical technologies, a burst optical deflection routing protocol is proposed. The idea of this approach is to use idle optical links as fiber delay lines for contention resolution. Simulation results show that the proposed protocol is available solution for effectively reducing the blocking probability and increasing the performance of burst switching WDM optical networks.

121 citations

Book ChapterDOI
07 Sep 2004
TL;DR: In this paper, a fully distributed ultrasonic positioning system is proposed to locate various indoor objects with lower initial configuration cost, which enables the deployment of indoor positioning systems beyond laboratory use.
Abstract: Obtaining indoor location information is one of the essential technologies for enriching various ubiquitous computing applications Although many indoor location systems have been proposed until now, wide-area deployments in everyday environments are still extremely rare To deploy indoor locating systems beyond laboratory use, we believe that the initial configuration cost of the system should be reduced This paper describes a fully distributed ultrasonic positioning system which enables us to locate various indoor objects with lower initial configuration cost

118 citations

Journal ArticleDOI
TL;DR: A tree-based SF clustering algorithm (TSCA) to conduct SF allocation in a multihop LoRa network focuses on balancing the airtime between the subnets while ensuring connectivity and uses simulations to show that this approach can significantly increase the network performance compared with other approaches.
Abstract: LoRa is a low-power long-range IoT standard that uses the chirp spread spectrum technique, and we have strived to further extend its coverage by utilizing the direct device-to-device (D2D) links to construct a multi-hop relay network. In LoRa, the spreading factor (SF) is an important parameter, which not only provides great flexibility between the data rate and sensitivity but also presents a new dimension for multiple accesses. Our approach to improving the capacity of a multihop LoRa network is to attempt to off-load the data traffic into several subnets by utilizing this multiple-access dimension. Each subnet rooted at a sink node is allocated a specific SF on the basis of network clustering. This enables packet transmission in parallel with multiple SFs to become feasible. To allow such parallel transmissions, our considerations are: 1) ensuring the connectivity of all subnets; 2) off-loading the traffic according to the number of nodes, data rates, and network topologies of each subnet; and 3) shortening the airtime of each subnet by reducing the hop count. Toward these objectives, we present a tree-based SF clustering algorithm (TSCA) to conduct SF allocation in a multihop LoRa network. The TSCA focuses on balancing the airtime between the subnets while ensuring connectivity. Furthermore, we use simulations to show that our approach can significantly increase the network performance compared with other approaches. We additionally deploy a real-chip experiment to evaluate the feasibility of parallel transmission in practice.

76 citations


Cited by
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Christopher M. Bishop1
01 Jan 2006
TL;DR: Probability distributions of linear models for regression and classification are given in this article, along with a discussion of combining models and combining models in the context of machine learning and classification.
Abstract: Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

10,141 citations

Proceedings Article
01 Jan 1991
TL;DR: It is concluded that properly augmented and power-controlled multiple-cell CDMA (code division multiple access) promises a quantum increase in current cellular capacity.
Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

2,951 citations

Patent
29 Aug 2006
TL;DR: In this paper, a set top box for interacting with broadband media streams, with an adaptive user interface, content-based media processing and/or media metadata processing, and telecommunications integration, is presented.
Abstract: An intelligent electronic appliance preferably includes a user interface, data input and/or output port, and an intelligent processor. A preferred embodiment comprises a set top box for interacting with broadband media streams, with an adaptive user interface, content-based media processing and/or media metadata processing, and telecommunications integration. An adaptive user interface models the user, by observation, feedback, and/or explicit input, and presents a user interface and/or executes functions based on the user model. A content-based media processing system analyzes media content, for example audio and video, to understand the content, for example to generate content-descriptive metadata. A media metadata processing system operates on locally or remotely generated metadata to process the media in accordance with the metadata, which may be, for example, an electronic program guide, MPEG 7 data, and/or automatically generated format. A set top box preferably includes digital trick play effects, and incorporated digital rights management features.

2,644 citations

Journal ArticleDOI
TL;DR: This paper provides an extensive survey of mobile cloud computing research, while highlighting the specific concerns in mobile cloud Computing, and presents a taxonomy based on the key issues in this area, and discusses the different approaches taken to tackle these issues.

1,671 citations

Journal ArticleDOI
TL;DR: A comprehensive survey of numerous IPSs, which include both commercial products and research-oriented solutions are given, and the trade-offs among these systems are outlined from the viewpoint of a user in a PN.
Abstract: Recently, indoor positioning systems (IPSs) have been designed to provide location information of persons and devices. The position information enables location-based protocols for user applications. Personal networks (PNs) are designed to meet the users' needs and interconnect users' devices equipped with different communications technologies in various places to form one network. Location-aware services need to be developed in PNs to offer flexible and adaptive personal services and improve the quality of lives. This paper gives a comprehensive survey of numerous IPSs, which include both commercial products and research-oriented solutions. Evaluation criteria are proposed for assessing these systems, namely security and privacy, cost, performance, robustness, complexity, user preferences, commercial availability, and limitations.We compare the existing IPSs and outline the trade-offs among these systems from the viewpoint of a user in a PN.

1,538 citations