Browsing by Author "Wang, You-Chiun"

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A Cross-Layer Framework for Overhead Reduction, Traffic Scheduling, and Burst Allocation in IEEE 802.16 OFDMA Networks
(2011-05-01)
Liang, Jia-Ming
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Chen, Jen-Jee
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Wang, You-Chiun
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Tseng, Yu-Chee
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資訊工程學系
IEEE 802.16 orthogonal frequency-division multiple access (OFDMA) downlink subframes have a special 2-D channel-time structure. Allocation resources from such a 2-D structure incur extra control overheads that hurt network performance. Existing solutions try to improve network performance by designing either the scheduler in the medium access control layer or the burst allocator in the physical layer, but the efficiency of overhead reduction is limited. In this paper, we point out the necessity of "codesigning" both the scheduler and the burst allocator to efficiently reduce overheads and improve network performance. Under the partial-usage-of-subcarriers model, we propose a cross-layer framework that covers overhead reduction, real-time and non-real-time traffic scheduling, and burst allocation. The framework includes a two-tier priority-based scheduler and a bucket-based burst allocator, which is more complete and efficient than prior studies. Both the scheduler and the burst allocator are tightly coupled together to solve the problem of arranging resources to data traffic. Given available space and bucket design from the burst allocator, the scheduler can well utilize the frame resource, reduce real-time traffic delays, and maintain fairness. On the other hand, with priority knowledge and resource assignment from the scheduler, the burst allocator can efficiently arrange downlink bursts to satisfy traffic requirements with low complexity. Through analysis, the cross-layer framework is validated to give an upper bound to overheads and achieve high network performance. Extensive simulation results verify that the cross-layer framework significantly increases network throughput, maintains long-term fairness, alleviates real-time traffic delays, and enhances frame utilization.
A lightweight, self-adaptive lock gate designation scheme for data collection in long-thin wireless sensor networks
(2013-01-01)
Wang, You-Chiun
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Chuang, Che-Hsi
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Tseng, Yu-Chee
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Shen, Chien-Chung
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資訊工程學系
Constrained by the physical environments, the long-thin topology has recently been promoted for many practical deployments of wireless sensor networks (WSNs). In general, a long-thin topology is composed of a number of long branches of sensor nodes, where along a branch each sensor node has only one potential parent node toward the sink node. Although data aggregation may alleviate excessive packet contention, the maximum payload size of a packet and the dynamically changing traffic loads may severely affect the amount of sensor readings that may be collected along a long branch of sensor nodes. In addition, many practical applications of long-thin WSNs demand the exact sensor readings at each location along the deployment areas for monitoring and analysis purposes, so sensor readings may not be aggregated when they are collected. This paper proposes a lightweight, self-adaptive scheme that designates multiple collection nodes, termed lock gates, along a long-thin network to collect sensor readings sent from their respective upstream sensor nodes. The self-adaptive lock gate designation scheme balances between the responsiveness and the congestion of data collection while mitigating the funneling effect. The scheme also dynamically adapts the designation of lock gates to accommodate the time-varying sensor reading generation rates of different sensor nodes. A testbed of 100 Jennic sensor nodes is developed to demonstrate the effectiveness of the proposed lock gate designation scheme. Copyright (c) 2011 John Wiley & Sons, Ltd.
A request control scheme for data recovery in DVB-IPDC systems with spatial and temporal packet loss
(2013-07-01)
Yang, Wen-Hsin
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Wang, You-Chiun
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Tseng, Yu-Chee
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Lin, Bao-Shuh Paul
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資訊工程學系
Recently, digital video broadcasting-handheld (DVB-H) and IP datacast over DVB-H (DVB-IPDC) have been developed to support broadcasting services. DVB-H is designed to support digital video broadcast for handheld devices, whereas DVB-IPDC can integrate with an IP-relay network to complement the data loss problem in DVB-H. Assuming that WiMAX networks are adopted to support DVB-IPDC, this paper points out two critical problems: group packet loss (GPL) and broadcast data handover (BDH). GPL occurs when there is a burst of retransmission requests for the same pieces of data with high spatial or temporal correlation. BDH happens when some devices that made the above requests handover to new serving cells. To solve these problems, we propose lazy wait and group acknowledgement schemes to alleviate duplicate requests by exploiting their spatial and temporal correlations. This not only reduces the requests submitted by neighboring devices in both space and time domains but also avoids handovering devices from sending duplicate requests in new cells. Through mathematical analysis, we show how to adaptively adjust the timers of lazy wait and group acknowledgement based on channel quality. Simulation results prove that our schemes can efficiently reduce retransmission requests and retransmission packets, thus alleviating congestion in the IP-relay network. Copyright (c) 2011 John Wiley & Sons, Ltd.
A Vehicular Wireless Sensor Network for CO(2) Monitoring
(2009-01-01)
Hu, Shu-Chiung
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Wang, You-Chiun
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Huang, Chiuan-Yu
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Tseng, Yu-Chee
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資訊工程學系
Micro-climate monitoring usually requires deploying a large number of measurement tools. By adopting vehicular wireless sensor networks (VSNs), we can use fewer tools to achieve fine-grained monitoring. This work proposes a VSN architecture to realize micro-climate monitoring based on GSM short messages and availability of GPS receivers on vehicles. We demonstrate our prototype of a Zig Bee-based car network to monitor the concentration of carbon dioxide (CO(2)) gas in areas of interest. The reported data are sent to a server, which is integrated with Google Maps as our user interface. Since mobility of these vehicles is not controllable and sending short messages incurs charges, we also design an on-demand approach to adjust vehicles' reporting rates to balance between the micro-climate accuracy and the communication cost.
A Vehicular Wireless Sensor Network for CO2 Monitoring
(2009-01-01)
Hu, Shu-Chiung
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Wang, You-Chiun
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Huang, Chiuan-Yu
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Tseng, Yu-Chee
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資訊工程學系
Micro-climate monitoring usually requires deploying a large number of measurement tools. By adopting vehicular wireless sensor networks (VSNs), we can use fewer tools to achieve fine-grained monitoring. This work proposes a VSN architecture to realize micro-climate monitoring based on GSM short messages and availability of GPS receivers on vehicles. We demonstrate our prototype of a Zig Bee-based car network to monitor the concentration of carbon dioxide (CO2) gas in areas of interest. The reported data are sent to a server, which is integrated with Google Maps as our user interface. Since mobility of these vehicles is not controllable and sending short messages incurs charges, we also design an on-demand approach to adjust vehicles' reporting rates to balance between the micro-climate accuracy and the communication cost.
Algorithms, Protocols and Future Applications of Wireless Sensor Networks
(2010-12-01)
Wang, You-Chiun
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Ohtsuki, Tomoaki
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Vasilakos, Athanasios (Thanos)
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Sabharwal, Ashutosh
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Chen, Yuh-Shyan
Compression and storage schemes in a sensor network with spatial and temporal coding techniques
(2008)
Wang, You-Chiun
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Hsieh, Yao-Yu
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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 provide a convenient manner to monitor the physical environments. How to extend the network lifetime by reducing the amount of message transmissions is a critical issue. In this paper, we propose a multi-resolution compression and storage (MCS) framework to compress and preserve sensing data in a wireless sensor network. Our MCS framework adopts spatial and temporal compression schemes to reduce the amount of message transmissions, so the network lifetime can he prolonged and the network congestion can be alleviated. In addition, we also develop a storage mechanism to maintain sensing data in sensor nodes, so that users can query more detailed data when necessary. Our proposed methods consider the hardware limitations of sensor nodes. We also implement a prototyping system on the MICAz Mote platform.
Distributed deployment schemes for mobile wireless sensor networks to ensure multilevel coverage
(2008-09-01)
Wang, You-Chiun
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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
One of the key research issues in wireless sensor networks (WSNs) is how sensors can efficiently be deployed to cover an area. In this paper, we solve the k-coverage sensor deployment problem to achieve multilevel (k) coverage of the area of interest I. We consider two subproblems: the k-coverage placement problem and the distributed dispatch problem. The placement problem asks how the minimum number of sensors required and their locations in I can be determined to guarantee that I is k-covered and the network is connected, while the dispatch problem asks how mobile sensors can be scheduled to move to the designated locations according to the result computed by the placement strategy if they are not in the current positions such that the energy consumption due to movement is minimized. Our solutions to the placement problem consider both the binary and probabilistic sensing models and allow an arbitrary relationship between the communication distance and the sensing distance of sensors, thereby relaxing the limitations of existing results. For the dispatch problem, we propose a competition-based scheme and a pattern-based scheme. The competition-based scheme allows mobile sensors to bid for their closest locations, while the pattern-based scheme allows sensors to derive the target locations on their own. Our proposed schemes are efficient in terms of the number of sensors required and are distributed in nature. Simulation results are presented to verify their effectiveness.
Efficient Packet Recovery Using Prioritized Network Coding in DVB-IPDC Systems
(2012-03-01)
Yang, Wen-Hsin
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Wang, You-Chiun
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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
The DVB-H standard is proposed to disseminate videos to mobile devices. However, packet loss is inevitable due to the broadcasting nature. To deal with this issue, DVB-IPDC suggests incorporating another wireless network for data retransmission. This paper takes a WiMAX network as an example in DVB-IPDC and models its channel as repetitive frames. During each frame, mobile devices sends their recovery requests of lost packets to a WiMAX base station and the base station adopts network coding to broadcast these packets. This paper then formulates a prioritized network coding (PNC) problem that asks how the base station uses at most tau coded packets in each frame such that it can recover the maximum aggregate number of lost packets while minimize the aggregate number of packets discarded due to out of deadlines. We develop a solution using XOR coding, which constructs a weighted bipartite graph to calculate the benefit to broadcast each coded packet. Then, the solution tries to maximize the overall benefit by finding a maximum-weighted tau dominating set. The contribution of this paper is to propose a new PNC problem in DVB-IPDC systems and develop an efficient PNC solution.
Efficient Resource Allocation for Energy Conservation in Uplink Transmissions of IEEE 802.16j Transparent Relay Networks
(2010)
Liang, Jia-Ming
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Wang, You-Chiun
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Chen, Jen-Jee
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Liu, Jui-Hsiang
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Tseng, Yu-Chee
By introducing the relay capability, the IEEE 802.16j standard is developed to improve the WiMAX performance. Under the transparent mode, existing studies aim at improving network throughput by increasing the transmission rates of mobile stations (MSs). However, we show that using higher rates will let MSs consume more energy. In the paper, we define an energy-conserved uplink resource allocation (EURA) problem in 802.16j networks under the transparent mode, which asks how to arrange the uplink resource to 1) satisfy MSs' requests and 2) minimize their energy consumption. Objective 1 is necessary while objective 2 should be achieved when objective 1 is met. The above bi-objective problem is especially important when the network is non-saturated. The EURA problem is NP-hard and we propose a heuristic with two key designs. First, we exploit relay stations to allow more concurrent uplink transmissions to fully use the frame space. Second, we reduce MSs' transmission powers by adjusting their rates and paths. Simulation results show that our heuristic can save up to 80% of MSs' energy as compared with existing work.
Energy-Balanced Dispatch of Mobile Sensors in a Hybrid Wireless Sensor Network
(2010-12-01)
Wang, You-Chiun
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Peng, Wen-Chih
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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
We consider a hybrid wireless sensor network with static and mobile nodes. Static sensors monitor the environment and report events occurring in the sensing field. Mobile sensors are then dispatched to visit these event locations to conduct more advanced analysis. A big challenge is how to schedule these mobile sensors' traveling paths in an energy-balanced way so that their overall lifetime is maximized. We formulate this problem as a multiround sensor dispatch problem and show it to be NP-complete. Then, we propose a centralized and a distributed heuristics to schedule mobile sensors' traveling paths. Our heuristics allow arbitrary numbers of mobile sensors and event locations in each round and have an energy-balanced concept in mind. The centralized heuristic tries to minimize mobile sensors' moving energy while keeping their energy consumption balanced. The distributed heuristic utilizes a grid structure for event locations to bid for mobile sensors. Through simulations, we show the effectiveness of our schemes. This paper contributes in defining a more general multiround sensor dispatch problem and proposing energy-efficient solutions to it.
Energy-efficient network selection with mobility pattern awareness in an integrated WiMAX and WiFi network
(2010-02-01)
Yang, Wen-Hsin
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Wang, You-Chiun
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Tseng, Yu-Chee
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Lin, Bao-Shuh P.
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資訊工程學系
To provide wireless Internet access, WiFi networks have been deployed in many regions such as buildings and campuses. However, WiFi networks are still insufficient to support ubiquitous wireless service due to their narrow coverage. One possibility to resolve this deficiency is to integrate WiFi networks with the wide-range WiMAX networks. Under such an integrated WiMAX and WiFi network, flow to conduct energy-efficient handovers is a critical issue. In this paper, we propose a handover scheme with geographic mobility awareness (HGMA), which considers the historical handover patterns of mobile devices. HGMA can conserve the energy of handovering devices from three aspects. First, it prevents mobile devices from triggering unnecessary handovers according to their received signal strength and moving speeds. Second, it contains a handover candidate selection method for mobile devices to intelligently select a subset of WiFi access points or WiMAX relay stations to be scanned. Therefore, mobile devices can reduce their network scanning and thus save their energy. Third, HGMA prefers mobile devices staying in their original WiMAX or WiFi networks. This can prevent mobile devices from consuming too much energy on interface switching. In addition, HGMA prefers the low-tier WiFi network over the WiMAX network and guarantees the bandwidth requirements of handovering devices. Simulation results show that HGMA can save about 59-80% of energy consumption of a handover operation, make mobile devices to associate with WiFi networks with 16-62% more probabilities, and increase about 20-61% of QoS satisfaction ratio to handovering devices. Copyright (C) 2009 John Wiley & Sons, Ltd.
Energy-efficient uplink resource allocation for IEEE 802.16j transparent-relay networks
(2011-11-10)
Liang, Jia-Ming
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Wang, You-Chiun
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Chen, Jen-Jee
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Liu, Jui-Hsiang
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Tseng, Yu-Chee
The IEEE 802.16j standard is defined to enhance WiMAX networks with relay capacity. Under the transparent mode, existing studies only target improving network throughput by increasing the transmission rates of mobile stations (MSs) and maximizing concurrent transmissions. However, using a higher transmission rate or allowing more concurrent transmissions could harm MSs in terms of their energy consumption, especially when they are battery-powered. In this paper, we consider the energy-conserved resource allocation problem in the uplink direction of an IEEE 802.16j network under the transparent mode. This problem asks how to arrange the frame usage with satisfying MSs' demands as the constraint and minimizing their total energy consumption as the objective. We prove this problem to be NP-complete and develop two energy-efficient heuristics, called demand-first allocation (DFA) and energy-first allocation (EFA) schemes. These heuristics employ a gradient-like search method to approximate the optimal solution. Specifically, DFA tries to satisfy MSs' demands first by using as less frame space as possible. Then, with the remaining frame space. DFA tries to save MSs' energy by lowering their transmission rates or adjusting their transmission paths. Viewed from a different perspective. EFA first allocates the frame space to MSs to consume the least energy. Since the total allocation may exceed the frame space. EFA then exploits spatial reuse and rate adjustment to pack all demands into one frame. simulation results show that our heuristics can approximate the ideal performance bounds and save up to 90% of MSs' energy as compared to existing results. (C) 2011 Elsevier B.V. All rights reserved.
Exploiting Spectral Reuse in Routing, Resource Allocation, and Scheduling for IEEE 802.16 Mesh Networks
(2009-01-01)
Chen, Lien-Wu
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Tseng, Yu-Chee
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Wang, You-Chiun
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Wang, Da-Wei
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Wu, Jan-Jan
The IEEE 802.16 standard for wireless metropolitan area networks (WMANs) is defined to meet the need for wide-range broadband wireless access at low cost. The objective of this paper is to study how to exploit spectral reuse in resource allocation in an IEEE 802.16 mesh network, which includes routing tree construction (RTC), bandwidth allocation, time-slot assignment, and bandwidth guarantee of real-time flows. The proposed spectral reuse framework covers bandwidth allocation at the application layer, RTC and resource sharing at the medium access control: (MAC) layer, and channel reuse at the physical layer. To the best of our knowledge, this is the first paper that formally quantifies spectral reuse in IEEE 802.16 mesh networks and exploits spectral efficiency under an integrated framework. Simulation results show that the proposed schemes significantly improve the throughput of IEEE 802.16 mesh networks.
Exploring load-balance to dispatch mobile sensors in wireless sensor networks
(2007)
Wang, You-Chiun
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Peng, Wen-Chih
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Chang, Min-Hsien
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Tseng, Yu-Chee
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資訊工程學系
In this paper, a hybrid sensor network consisting of static and mobile sensors is considered, where static sensors are used to detect events, and mobile sensors can move to event locations to conduct more advanced analysis. By exploring the load balance concept, we propose a CentralSD algorithm to efficiently dispatch mobile sensors. Our algorithm is general in that the numbers of mobile sensors and events can be arbitrary. When mobile sensors are more than event locations, we transform the dispatch problem to a maximum-matching problem in a weighted bipartite graph. When there are fewer mobile sensors than event locations, we propose an efficient clustering scheme to group event locations so that the maximum-matching approach can still be applied. To reduce message cost, we also develop a distributed GridSD algorithm. Simulation results are presented to verify the effectiveness of the proposed algorithms.
iMouse: An integrated mobile surveillance and wireless sensor system
(2007-06-01)
Tseng, Yu-Chee
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Wang, You-Chiun
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Cheng, Kai-Yang
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Hsieh, Yao-Yu
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資訊工程學系
With their environment-sensing capability, wireless sensor networks can enrich human life in applications such as healthcare, building monitoring, and home security. The iMouse system integrates WSN technologies into surveillance technologies to support intelligent mobile surveillance services. The authors suggest several ways to improve or extend iMouse. One option is to facilitate mobile sensor navigation by, for example, integrating localization schemes to guide mobile sensors instead of using color tapes. A second option is to exploit coordination among mobile sensors, especially when they're on the road.
iPower: an energy conservation system for intelligent buildings by wireless sensor networks
(2009)
Yeh, Lun-Wu
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Wang, You-Chiun
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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) provide a convenient way to monitor the physical environment. Exploiting the context-aware capability of WSN to achieve energy conservation in intelligent buildings is an attractive direction. We thus propose an iPower (intelligent and personalised energy conservation system by WSNs) system which combines WSNs and appliance control devices to provide personalised energy conservation services. A WSN is deployed in each room to monitor the usage of electric appliances and to help determine if there are electric appliances that can be turned off for energy conservation. The iPower system is quite intelligent and can adapt to personal need by automatically adjusting electric appliances to satisfy users' requirements. The design and implementation details of iPower are reported in this paper.
Measuring air quality in city areas by vehicular wireless sensor networks
(2011-11-01)
Hu, Shu-Chiung
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Wang, You-Chiun
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Huang, Chiuan-Yu
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Tseng, Yu-Chee
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資訊工程學系
This paper considers a micro-climate monitoring scenario, which usually requires deploying a large number of sensor nodes to capture environmental information. By exploiting vehicular sensor networks (VSNs), it is possible to equip fewer nodes on cars to achieve fine-grained monitoring. Specifically, when a car is moving, it could conduct measurements at different locations, thus collecting lots of sensing data. To achieve this goal, this paper proposes a VSN architecture to collect and measure air quality for microclimate monitoring in city areas, where nodes' mobility may be uncontrollable (such as taxis). In the proposed VSN architecture, we address two network-related issues: (1) how to adaptively adjust the reporting rates of mobile nodes to satisfy a target monitoring quality with less communication overhead and (2) how to exploit opportunistic communications to reduce message transmissions. We propose algorithms to solve these two issues and verify their performances by simulations. In addition, we also develop a ZigBee-based prototype to monitor the concentration of carbon dioxide (CO(2)) gas in city areas. (C) 2011 Elsevier Inc. 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.
Multiresolution Spatial and Temporal Coding in a Wireless Sensor Network for Long-Term Monitoring Applications
(2009-06-01)
Wang, You-Chiun
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Hsieh, Yao-Yu
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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 many WSN (wireless sensor network) applications, such as [1], [2], [3], the targets are to provide long-term monitoring of environments. In such applications, energy is a primary concern because sensor nodes have to regularly report data to the sink and need to continuously work for a very long time so that users may periodically request a rough overview of the monitored environment. On the other hand, users may occasionally query more in-depth data of certain areas to analyze abnormal events. These requirements motivate us to propose a multiresolution compression and query (MRCQ) framework to support in-network data compression and data storage in WSNs from both space and time domains. Our MRCQ framework can organize sensor nodes hierarchically and establish multiresolution summaries of sensing data inside the network, through spatial and temporal compressions. In the space domain, only lower resolution summaries are sent to the sink; the other higher resolution summaries are stored in the network and can be obtained via queries. In the time domain, historical data stored in sensor nodes exhibit a finer resolution for more recent data, and a coarser resolution for older data. Our methods consider the hardware limitations of sensor nodes. So, the result is expected to save sensors' energy significantly, and thus, can support long-term monitoring WSN applications. A prototyping system is developed to verify its feasibility. Simulation results also show the efficiency of MRCQ compared to existing work.