Browsing by Author "Wu, Fang-Jing"

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A novel stability-based routing protocol for mobile ad-hoc networks
(2007-04-01)
Tarng, Jenn-Hwan
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Chuag, Bing-Wen
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Wu, Fang-Jing
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資訊工程學系
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電信工程研究所
The dynamics of Mobile Ad-hoc NETworks (MANETs), as a consequence of mobility of mobile hosts, pose a problem in finding stable multi-hop routes for communication between a source and a destination. Traditional ad-hoc routing protocols are proposed to find multi-hop routes based on shortest path routing algorithms, which cannot effectively adapt to time-varying radio links and network topologies of MANETs. In this paper, a novel stability-based ad hoc routing protocol, which is named as Ad-hoc On-demand Stability Vector (AOSV) routing protocol, is proposed to properly and effectively discover stable routes with high data throughput and long lifetime by considering the radio propagation effect on signal strength. Here, a stochastic mobile-to-mobile radio propagation model is proposed to predict path loss as well as received signal strength between adjacent nodes, and the estimation of link/route stability is derived from the prediction of signal strength. With awareness of link and route stabilities, a path finding algorithm is designed to explore the stable route with largest route stability for a source and destination pair. The performance of AOSV protocol is compared with the well-known Ad-hoc On-demand Distance Vector (AODV) routing protocol and other related works. Simulation results indicate that the AOSV routing protocol leads to significant throughput increases up to 70% improvement comparing to AODV, and provides better performance than related works.
A Wireless Human Motion Capturing System for Home Rehabilitation
(2009)
Tseng, Yu-Chee
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Wu, Chin-Hao
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Wu, Fang-Jing
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Huang, Chi-Fu
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King, Chung-Ta
Following the trend of miniature intelligent sensing, wearing small, integrated wireless sensor nodes, such as one with accelerometers and compasses, to capture human body motions may have many applications in medical care and computer animation. In this paper, we demonstrate the use of intelligent sensors to capture human motions for home rehabilitation. We design a game to help a patient to conduct his/her rehabilitation program. For each exercise, the patient is instructed to wear sensors on specified movable body parts. The system will then estimate the quality of the movements and give scores as if it is advised by a therapist. In this way, patients will no longer feel painful and boring as that in traditional rehabilitation, which is typically done in hospitals.
Activity Sense Organs: Energy-efficient Activity Sensing with Adaptive Duty Cycle Control
(2016-01-01)
Wu, Fang-Jing
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Tseng, Yu-Chee
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Peng, Wen-Chih
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資訊工程學系
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Department of Computer Science
Recently, smartphones with built-in sensors are exploited to detect human activities. Since sensing human activities may exhaust energy of a smartphone, this work brings up the concept of "activity sense organs" to the uprising smartphone sensing paradigm. As the human sense organs are the most important sensors to perceive real-world information, this work identifies the most important sensors to perceive a particular human activity based on the "quality of the features" contributed by sensors. To optimize the energy usage of activity sensing, we exploit the importance of sensors to profile the duty-cycles of sensors for activity detection. Specifically, a smartphone will operate in a duty-cycled sensing mode, where sensors in the activity sense organs will collect data at the higher sampling rate than those sensors not in the activity sense organs. We design a knowledge lifecycle to find out the activity sense organs, profile the sensing modes of activity detection, and adjust the sensing mode for real-time activity detection. The experimental results indicate that the activity sense organs provide sufficient information for activity detection.
Cyber-Physical Handshake
(2011-08-01)
Wu, Fang-Jing
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Chu, Feng-I
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
While sensor-enabled devices have greatly enriched human interactions in our daily life, discovering the essential knowledge behind sensing data is a critical issue to connect the cyber world and the physical world. This motivates us to design an innovative sensor-aided social network system, termed cyber-physical handshake. It allows two users to naturally exchange personal information with each other after detecting and authenticating the handshaking patterns between them. This work describes our design of detection and authentication mechanisms to achieve this purpose and our prototype system to facilitate handshake social behavior.
Data Gathering by Mobile Mules in a Spatially Separated Wireless Sensor Network
(2009)
Wu, Fang-Jing
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Huang, Chi-Fu
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
While wireless sensor networks (WSNs) are typically targeted at large-scale deployment, due to many practical or inevitable reasons, a WSN may not always remain connected. In this paper we consider the possibility that a WSN may be spatially separated into multiple subnetworks. Data gathering, which is a fundamental mission of WSN, thus may rely on a mobile mule ("mule" for short) to conduct data gathering by visiting each subnetwork. This leads to the problem of minimizing the path length traversed by the mobile mule. We show that minimizing the path length, which may reflect the data gathering latency and the energy consumption of the mule is a generalization of the traveling salesman problem and is NP-complete. Some heuristics based on geometrical properties of node deployment are proposed. Our simulation results show that these heuristics perform very close to optimal solutions in most practical cases.
Demo Abstract: My Tai-Chi Book: A Virtual-Physical Social Network Platform
(2010-01-01)
Wu, Fang-Jing
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Huang, Chen-Shao
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
While social networks on Web platforms have attracted a lot of interests, including more natural and physical inputs into such systems to enhance human interaction is desirable. Using body-area sensor networks (BSNs) to capture human motions opens up an opportunity toward this goal. These motivate us to design a novel virtual-physical social network platform 1 with typical social network functions and capable of receiving various inputs from remote BSNs. Through our platform, users can share conventional messages and images as well as sensory data in several interesting ways. We demonstrate a Tai-Chi exercise social network and some testing results.
Distributed Wake-up Scheduling for Data Collection in Tree-Based Wireless Sensor Networks
(2009-11-01)
Wu, Fang-Jing
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
In a multi-hop wireless network, a conventional way of defining interference neighbors is to prohibit a node from using the same slot/code as those of its 1-hop and 2-hop neighbors. However, for data collection in a wireless sensor network, since the set of communication nodes is limited and the transmission directions are toward the sink, we show that a less strict set of interference neighbors can be defined. Based on this observation, we develop an efficient distributed wake-up scheduling scheme for data collection in a sensor network that achieves both energy conservation and low reporting latency.
Energy-conserving data gathering by mobile mules in a spatially separated wireless sensor network
(2013-10-25)
Wu, Fang-Jing
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
This paper considers a spatially separated wireless sensor network, which consists of a number of isolated subnetworks that could be far away from each other in distance. We address the issue of using mobile mules to collect data from these sensor nodes. In such an environment, both data-collection latency and network lifetime are critical issues. We model this problem as a bi-objective problem, called energy-constrained mule traveling salesman problem (EM-TSP), which aims at minimizing the traversal paths of mobile mules such that at least one node in each subnetwork is visited by a mule and the maximum energy consumption among all sensor nodes does not exceed a pre-defined threshold. Interestingly, the traversal problem turns out to be a generalization of the classical traveling salesman problem (TSP), an NP-complete problem. With some geometrical properties of the network, we propose some efficient heuristics for EM-TSP. We then extend our heuristics to multiple mobile mules. Extensive simulation results have been conducted, which show that our proposed solutions usually give much better solutions than most TSP-like approximations. Copyright (c) 2011 John Wiley & Sons, Ltd.
From wireless sensor networks towards cyber physical systems
(2011-08-01)
Wu, Fang-Jing
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Kao, Yu-Fen
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
In the past two decades, a lot of research activities have been dedicated to the fields of mobile ad hoc network (MANET) and wireless sensor networks (WSN). More recently, the cyber physical system (CPS) has emerged as a promising direction to enrich the interactions between physical and virtual worlds. In this article, we first review some research activities in WSN, including networking issues and coverage and deployment issues. Then, we review some CPS platforms and systems that have been developed recently, including health care, navigation, rescue, intelligent transportation, social networking, and gaming applications. Through these reviews, we hope to demonstrate how CPS applications exploit the physical information collected by WSNs to bridge real and cyber spaces and identify important research challenges related to CPS designs. (C) 2011 Elsevier B.V. All rights reserved.
Mobility management algorithms and applications for mobile sensor networks
(2012-01-01)
Wang, You-Chiun
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Wu, Fang-Jing
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
Wireless sensor networks (WSNs) offer a convenient way to monitor physical environments. In the past, WSNs are all considered static to continuously collect information from the environment. Today, by introducing intentional mobility to WSNs, we can further improve the network capability on many aspects, such as automatic node deployment, flexible topology adjustment, and rapid event reaction. In this paper, we survey recent progress in mobile WSNs and compare works in this field in terms of their models and mobility management methodologies. The discussion includes three aspects. Firstly, we discuss mobility management of mobile sensors for the purposes of forming a better WSN, enhancing network coverage and connectivity, and relocating some sensors. Secondly, we introduce path-planning methods for data ferries to relay data between isolated sensors and to extend a WSN's lifetime. Finally, we review some existing platforms and discuss several interesting applications of mobile WSNs. Copyright (C) 2010 John Wiley & Sons, Ltd.
Non-Location-Based Mobile Sensor Relocation in a Hybrid Static-Mobile Wireless Sensor Network
(2009)
Wu, Fang-Jing
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Hsu, Hsiu-Chi
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Tseng, Yu-Chee
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Huang, Chi-Fu
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資訊工程學系
An inherent concern for a wireless sensor network (WSN) is the unbalanced energy consumption problem, where sensors closer to the sink are more likely to exhaust their energy faster than other nodes. To mitigate this problem, this paper considers including some resource-rich mobile nodes, called mobile data-pumps, to conduct data relaying from static sensors to the sink. The network thus becomes a two-tier network, with the original static sensors at the low tier and data-pumps at both low and high tiers. We propose a novel distributed navigation protocol that does not rely on any location information of sensor nodes to relocate data-pumps to meet both goals of connectivity and load balance. The main idea is a concept called virtual Voronoi cells, which can help data-pumps to locally balance their loads using the underlaying low-tier topology and thus significantly balance energy consumption of sensors. Simulation results are presented to verify the effectiveness of our result.
Opportunistic data collection for disconnected wireless sensor networks by mobile mules
(2013-05-01)
Tseng, Yu-Chee
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Wu, Fang-Jing
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Lai, Wan-Ting
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資訊工程學系
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Department of Computer Science
This paper considers a field with a number of isolated wireless sensor networks served by some mobile mules and base stations (BSs). Sensing data needs to be carried by mobile mules to BSs via opportunistic contact between them. Also, such contact may not be frequent. Thus there are four types of communications in this environment: (i) inter-node communications within a WSN, (ii) opportunistic WSN-to-mule communications, (iii) opportunistic mule-to-mule communications, and (iv) opportunistic mule-to-BS communications. In such disconnected WSNs, since sensors' memory spaces are limited and data collection from isolated WSNs to mules and then to BSs relies on opportunistic communications in the sense that contact between these entities is occasional, storing and collecting higher-priority data is necessary. Therefore, there are two critical issues to be addressed: the data storage management in each isolated WSN and opportunistic data collection between these entities. We address the storage management problem by modeling the limited memory spaces of a WSN's sensor nodes as a distributed storage system. Assuming that there is a sink in the WSN that will be visited by mobile mules occasionally, we address three issues: (i) how to buffer sensory data to reduce data loss due to a shortage of storage spaces, (ii) if dropping of data is inevitable, how to avoid higher-priority data from being dropped, and (iii) how to manage the data nearby the sink to facilitate the downloading jobs of mules when the downloading time is unpredictable. We propose a Distributed Storage Management (DSM) strategy based on a novel shuffling mechanism similar to heap sort. It allows nodes to exchange sensory data with neighbors efficiently in a distributed manner. For the opportunistic data collection problem, based on a utility model, we then develop an Opportunistic Data Exchange (ODE) strategy to guide two mules to exchange data that would lead to a higher reward. To the best of our knowledge, this is the first work addressing distributed storage strategy for isolated WSNs with opportunistic communications using mobile mules. We conduct extensive simulations to investigate the merit of DSM and ODE. The simulation results indicate that the level of data importance collected by our DSM is very close to a global optimization and our ODE could facilitate delivery of important data to BSs through mules. We also implement these strategies in a real sensor platform, which demonstrates that the simple and light-weight protocols can achieve our goals. (C) 2013 Elsevier B.V. All rights reserved.
Range-Free Mobile Actor Relocation in a Two-Tiered Wireless Sensor and Actor Network
(2016-05)
Wu, Fang-Jing
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Hsu, Hsiu-Chi
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Shen, Chien-Chung
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Tseng, Yu-Chee
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資訊工程學系
Two-tiered wireless sensor and actor networks (WSANs) have been proposed to enhance network capabilities, where a set of resource-rich mobile nodes (termed actors) form a connected backbone to relay sensing data from static sensors to the sink and sometimes are requested by sensors to perform a particular action. Such a two-tiered WSAN facilitates scalability and can efficiently reduce the energy consumption incurred by conventional hop-by-hop relaying via only sensors. However, relocating actors to achieve both connectivity and load balance is a challenge, especially when there is no location information of the nodes. Connectivity ensures that the actors are connected, whereas load balance ensures that actors collect and originate a similar amount of sensory data from the sensors. In this article, we formulate the Connected and Balanced Mobile Actor Relocation (CBMAR) optimization problem to address both connectivity and load balance and prove that the problem is NP-hard. We thus propose a dual-mode distributed actor relocation protocol that does not rely on any location information of nodes to relocate actors. The idea is to locally form virtual Voronoi cells of actors (termed covering cells) based on the lower-tiered topology, where each actor locally recruits its own sensor members to form its own covering cell. By maintaining the covering cell, each actor locally relocates itself toward a sensor along the lower-tiered topology. Extensive simulation results show that the protocol can achieve both objectives of connectivity and load balance with low moving and communication overheads.
The Privacy Exposure Problem in Mobile Location-based Services
(2016-01-01)
Wu, Fang-Jing
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Brust, Matthias R.
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Chen, Yan-Ann
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Luo, Tie
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資訊工程學系
Mobile location-based services (LBSs) empowered by mobile crowdsourcing provide users with context-aware intelligent services based on user locations. As smartphones are capable of collecting and disseminating massive user location-embedded sensing information, privacy preservation for mobile users has become a crucial issue. This paper proposes a metric called privacy exposure to quantify the notion of privacy, which is subjective and qualitative in nature, in order to support mobile LBSs to evaluate the effectiveness of privacy-preserving solutions. This metric incorporates activity coverage and activity uniformity to address two primary privacy threats, namely activity hotspot disclosure and activity transition disclosure. In addition, we propose an algorithm to minimize privacy exposure for mobile LBSs. We evaluate the proposed metric and the privacy-preserving sensing algorithm via extensive simulations. Moreover, we have also implemented the algorithm in an Android-based mobile system and conducted real-world experiments. Both our simulations and experimental results demonstrate that (1) the proposed metric can properly quantify the privacy exposure level of human activities in the spatial domain and (2) the proposed algorithm can effectively cloak users' activity hotspots and transitions at both high and low user-mobility levels.
Traffic-Attracted Mobile Relay Deployment in a Wireless Ad Hoc Network
(2012)
Wu, Fang-Jing
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Hsu, Hsiu-Chi
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
This paper considers an ad hoc network, where a set of energy-rich mobile nodes, termed mobile relays, are used to facilitate relaying packets so as to mitigate the energy consumption of static nodes. Existing work has focused on link-level relaying behaviors. In this work, we show how to achieve route-level relaying by overhearing route control and data packets. This allows mobile relays to redirect the traffic of static nodes and thus reduce their energy consumption. As the relocation of mobile relays needs to dynamically adjust the current traffic condition, a dynamic relocation scheme of mobile relays needs to be designed. In this paper, we refer to the mobile relay deployment (MRD) problem and design a distributed protocol for mobile relays. In our protocol, mobile relays do not necessarily participate in the routing discovery process, so static nodes can quickly switch back to their original routing paths without reconstruction efforts once mobile relays leave their communication ranges. Simulations by QualNet are presented to evaluate the performance of our protocol as compared to link-level relaying.