Browsing by Author "Chen, Wen-Tsuen"

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A Framework for Simultaneous Message Broadcasting Using CDMA-Based Visible Light Communications
(2015-12-01)
Chen, Yan-Ann
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Chang, Yi-Ting
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Tseng, Yu-Chee
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Chen, Wen-Tsuen
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資訊工程學系
Internet of Things applications are fast growing recently. One of the things that has a lot of potential is the lighting equipment since it is widely used in our daily life. Recently, the technology of visible light communication (VLC) has been widely discussed. VLC has several advantages, such as freedom of license, line-of-sight security, and less health concern compared with radio-based systems. In addition, the rapid progress of light emitting diode (LED) technology by solid-sate lighting allows VLC to be easily deployed and integrated with the existing lighting infrastructure at low costs. However, VLC, when integrated with lighting infrastructure, is usually for one-way communication and is highly sensitive to external interfering light. Thus, transmitting or broadcasting multiple messages simultaneously over a visible light channel without any preprocessing may result in serious collisions. In this paper, we propose a framework to tackle these problems by optical code division multiple access (CDMA) for VLC. With our approach, a VLC receiver can enter an environment without any prior configuration and can be designed with simple hardware. Even a mobile device with a high-resolution photodiode sensor can be used as a receiver. We demonstrate an application of indoor positioning by querying the location service provider on the Internet with the IDs decoded from the received light signals. The prototyping results reveal some communication properties of CDMA-based VLC and its potential for indoor positioning applications.
A Load-Balanced Guiding Navigation Protocol in Wireless Sensor Networks
(2008)
Chen, Wen-Tsuen
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Chen, Po-Yu
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Wu, Cheng-Han
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Huang, Chi-Fu
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資訊工程學系
One of the major applications of wireless sensor networks is guiding navigation service with its goal to assist moving objects in leaving a hazardous region safely and quickly. In this paper, we propose a distributed guiding navigation protocol that can guide moving objects to multiple exits with load balancing among multiple navigation paths to the exits. With the assistances of sensor nodes, moving objects are guided to different navigation paths so that they can move to exits as soon as possible without causing congestion. In some traditional navigation algorithms, a sensor may select a wrong guiding direction when an information-updating packet has not flooded through the whole network. Hence, the guiding direction of the sensor may oscillate in a short time and guided objects will confuse with this phenomenon, called direction oscillation problem. This problem will be eliminated in our proposed protocol. Simulation results indicate that our protocol can guide moving objects to exits in shorter time and solve the direction oscillation problem effectively.
A Simple and Efficient Data Forwarding Mechanism In Wireless Relay Networks
(2009)
Chen, Wen-Tsuen
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Lin, Tzu-Ming
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Tsao, Shiao-Li
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資訊工程學系
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Department of Computer Science
Wireless relay network Is a low-cost solution for extending the service coverage and increasing the throughput of the conventional single-hop wireless network. By deploying a relay network, a base station (BS) can provide services to subscriber stations (SSs) through relay links. The functionality of a relay station (RS) is simpler than a BS, and RSs only forward packets between SSs, RSs and the BS without too much packet processing. However, current solutions require a RS to store and process the packet before it can determine the destination, and thus introduce extra processing and buffering overheads on the RS. This study proposes a simple and efficient forwarding scheme which multiplexes bursts to the SSs attached to the same access RS. By applying the proposed end-to-end burst switching mechanism, the RS merely checks the frame header and can decide the final destination without packet processing. The experiment results demonstrate the superior performance of the proposed scheme than other approaches.
acPad: Enhancing Channel Utilization for 802.11ac Using Packet Padding
(2017-01-01)
Lin, Chi-Han
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Chen, Yi-Ting
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Lin, Kate Ching-Ju
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Chen, Wen-Tsuen
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資訊工程學系
Multi-User Multiple Input Multiple Output (MU-MIMO) enables a multi-antenna access point (AP) to serve multiple users simultaneously, and has been adopted as the IEEE 802.11ac standard. While several PHY-MAC designs have recently been proposed to improve the throughput performance of a MU-MIMO WLAN, they, however, usually assume that all the concurrent streams are of roughly equal length. In reality, users usually have frames with heterogeneous lengths even after aggregation, leading to different lengths of transmission time. Hence, the concurrent transmission opportunities might not always be fully utilized when some streams finish earlier than the others in a transmission opportunity (TXOP). To resolve this inefficiency, this paper presents acPad, a PHY-MAC design that adds additional frames to fill up the idle channel time and better utilize the spatial multiplexing gain. Our acPad identifies proper users as the padding so as to improve the padding gain, while preventing this padding from harming all the ongoing streams. Our evaluation via large-scale trace-driven simulations demonstrates that acPad improves the throughput by up to 2.83x, or by 1.36x on average, as compared to the conventional 802.11ac.
An Efficient Automatic Repeat Request Mechanism for Wireless Multihop Relay Networks
(2013-07-01)
Lin, Tzu-Ming
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Chen, Wen-Tsuen
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Tsao, Shiao-Li
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資訊工程學系
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Department of Computer Science
Recently, relay technology has been adopted to enhance the coverage and performance of wireless networks such as Worldwide Interoperability for Microwave Access and Long-Term Evolution Advanced (LTE-A). However, using relays to forward packets may induce more packet losses than traditional single-hop wireless networks because transmissions are conducted through multiple radio links. When there are lost packets, relay stations (RSs) decide whether to retransmit these packets with automatic repeat request (ARQ) strategies. We observe that an improper ARQ strategy increases latency, blocked packets, and workloads on the multihop relay network. This paper proposes a new relay ARQ (RARQ) scheme, providing efficient acknowledgement to reduce packet latency and the number of blocked packets with small workloads. We also propose an analytic model to evaluate the performance of the proposed mechanism. Simulation results have validated the proposed model and demonstrated that our ARQ scheme outperforms conventional approaches.
Channel Holding Time of Packet Sessions in All-IP Cellular Networks
(2014)
Weng, Jeng-Feng
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Ku, Bying-He
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Chen, Jyh-Cheng
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Chen, Wen-Tsuen
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資訊工程學系
In this paper, we analyze the packet session channel holding time for packet-switched cellular networks. Channel holding time depends on mobility which is characterized by cell residence time in this paper. We apply Hyper-Erlang distribution model to investigate the packet session channel holding time in which a session will experience active and idle periods. In terms of new session, handoff session in busy mode, handoff session with new arrival packets in idle mode and handoff session without arrival packet in idle mode, we demonstrate that the effective channel holding time is exponentially distributed if and only if the cell residence time is exponentially distributed. The analytical results provide a new approach to evaluate traffic performance and system design in packet-switched cellular networks.
Decentralized Energy-Conserving and Coverage-Preserving Protocols for Wireless Sensor Networks
(2006-05-01)
Huang, Chi-Fu
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Lo, Li-Chu
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Tseng, Yu-Chee
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Chen, Wen-Tsuen
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資訊工程學系
In this article, we propose several decentralized protocols that schedule sensors' active and sleeping periods to prolong the network lifetime while maintain the sensing field sufficiently covered. The proposed protocols are based on a model similar to that of Yan et al. [ 2003], but improve its results in several senses. First, our approach can significantly reduce the computational complexity incurred, and at the same time achieve better accuracy in determining the coverage of the sensing area. Second, we extend the result such that it can support multilayer coverage of the sensing field. Third, we further enhance it [Yan et al. 2003] by proposing several optimization mechanisms to balance or reduce sensors' energy expenditure.
Distributed Address Assignment with Address Borrowing for ZigBee Networks
(2014-01-01)
Hu, Shu-Chiung
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Lin, Cheng-Kuan
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Tseng, Yu-Chee
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Chen, Wen-Tsuen
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資訊工程學系
ZigBee is a popular communication standard for wireless sensor networks. It suggests a distributed address assignment mechanism (DAAM), which is easy to implement but may restrict the number of children of a router and the depth of the network. Since DAAM is too conservative, the utilization of the 16-bit address pool may become poor, causing the orphan problem. In this paper, we propose a distributed address assignment scheme by allowing a parent to borrow a subtree of address space from a neighbor to alleviate the orphan problem. When a new node tries to associate with a parent router which has no free address, this parent router will inquire its 2hop neighbors for lending a subtree of free address space. We also propose a light-weight routing to support one-to-one routing in this environment.
FDoF: Enhancing Channel Utilization for 802.11ac
(2018-02-01)
Lin, Chi-Han
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Chen, Yi-Ting
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Lin, Kate Ching-Ju
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Chen, Wen-Tsuen
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資訊工程學系
Multi-user multiple input multiple output (MU-MIMO) enables a multi-antenna access point to serve multiple users simultaneously, and has been adopted as the IEEE 802.11ac standard. While several PHY-MAC designs have recently been proposed to improve the throughput performance of a MU-MIMO WLAN, they, however, usually assume that all the concurrent streams are of roughly equal length. In reality, users usually have frames with heterogeneous lengths even after aggregation, leading to different lengths of a transmission time. Hence, the concurrent transmission opportunities might not always be fully utilized when some streams finish earlier than the others in a transmission opportunity. To resolve this inefficiency, this paper presents full degree-of-freedom (FDoF), a PHY-MAC design that exploits a novel power allocation scheme to reduce the idle channel time and further leverages frame padding to better utilize the spatial multiplexing gain. Unlike traditional MIMO power allocation, which aims at maximizing the theoretical sum-rate, FDoF's power allocation explicitly considers heterogeneous frame lengths and minimizes the channel time required to finish concurrent frames, as a result improving the effective throughput. FDoF's padding protocol then identifies proper users to reuse the remaining idle channel time, while preventing this padding from harming all the ongoing streams. Our evaluation via large-scale trace-driven simulations demonstrates that FDoF's improves the throughput by up to 2.83x, or by 1.36x on average, as compared to the conventional 802.11ac. By combining FDoF's power allocation with frame padding, the average throughput gain can be further increased to 1.75x.
Information processing and data management in wireless sensor networks
(2007-12-01)
Tseng, Yu-Chee
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Peng, Wen-Chih
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Leung, Victor C. M.
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Chen, Wen-Tsuen
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Pinotti, M. Cristina
k-Angle Object Coverage Problem in a Wireless Sensor Network
(2012-12-01)
Tseng, Yu-Chee
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Chen, Po-Yu
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Chen, Wen-Tsuen
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資訊工程學系
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Department of Computer Science
One of the fundamental issues in sensor networks is the coverage problem, which reflects how well a field is monitored or tracked by sensors. Various versions of this problem have been studied, such as object, area, barrier, and hole coverage problems. In this paper, we define a new k-angle object coverage problem in a wireless sensor network. Each sensor can only cover a limited angle and range, but can freely rotate to any direction to cover a particular angle. Given a set of sensors and a set of objects at known locations, the goal is to use the least number of sensors to k-angle-cover the largest number of objects such that each object is monitored by at least k sensors satisfying some angle constraint. We propose centralized and distributed polynomial-time algorithms to solve this problem. Simulation results show that our algorithms can be effective in maximizing coverage of objects. A prototype system is developed to demonstrate the usefulness of angle coverage.
Modeling and Analysis of Channel Holding Time and Handoff Rate for Packet Sessions in All-IP Cellular Networks
(2017-04-01)
Ku, Bying-He
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Ren, Yi
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Weng, Jeng-Feng
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Chen, Jyh-Cheng
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Chen, Wen-Tsuen
It is essential to model channel holding time (CHT), cell residence time (CRT), and handoff rate for performance analysis and algorithm evaluation in mobile cellular networks. The problem has been extensively studied in the past for circuit-switched (CS) cellular networks. However, little research has been done on packet-switched (PS) cellular networks. Unlike that a call occupies a dedicated channel during its whole lifetime in CS networks, an active session in PS networks occupies and releases channels iteratively due to discontinuous reception (DRX) mechanism. In this paper, we investigate the key quantities in PS cellular networks. We present a set of comprehensive new models to characterize the quantities and their relationship in PS networks. The models shed light on the relationship between CHT and CRT and handoff rate. The analytical results enable wide applicability in various scenarios and therefore have important theoretical significance. Moreover, the analytical results provide a quick way to evaluate traffic performance and system design in PS cellular networks without wide deployment, which can save cost and time.
Pair Auction and Matching for Resource Allocation in Full-Duplex Cellular Systems
(2020-04-01)
Chao, Cheng-Chih
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Wang, Chih-Yu
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Lee, Chia-Han
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Wei, Hung-Yu
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Chen, Wen-Tsuen
Full-duplex techniques improve spectral efficiency in cellular networks by allowing a transceiver to simultaneously transmit and receive data with the same radio resource. To minimize self-interference and inter-node interference due to the deployment of full-duplex radio, users have to feed back their measurements of interference to allow the base station to effectively allocate resources and form transmission pairs. Considering that the interference measurements are private information, users may not report the true values and may try to gain their own benefits. To solve this problem, we propose a strategy-proof resource allocation mechanism for full-duplex cellular networks. The proposed scheme, which is based on auction and matching theories, guarantees that users report true values of their channel quality and utilities, and therefore guarantees the correctness of feedback information and the efficiency of resource allocation. Moreover, the proposed matching-based mechanism is theoretically proved to be stable and Pareto efficient. Simulation results confirm that, compared to a centralized scheme with non-truthful information from users, the proposed scheme can achieve an 11% gain.
Providing Group Tour Guide by RFIDs and Wireless Sensor Networks
(2009-06-01)
Chen, Po-Yu
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Chen, Wen-Tsuen
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Tseng, Yu-Chee
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Huang, Chi-Fu
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資訊工程學系
This paper proposes a new application framework for group tour guiding services based on RFIDs and wireless sensor networks. We consider a sensing field mixed with multiple independent tourist groups, each with a leader and several members. Members of a group will follow the moving path of their leader, but may occasionally roam around randomly on their own interests. Sensor nodes have to track leaders' locations and maintain guiding paths from members to leaders. A member may inquire where his/her leader is, and a leader may "recall" his/her members. We propose a feasible solution to such an application by using existing technologies and off-the-shelf components. A group guiding protocol is presented. The design enables reliable group guiding at low-cost and low traffic load. Our prototyping system is reported and system performance is discussed.
Strengthening Modern Electronics Industry Through the National Program for Intelligent Electronics in Taiwan
(2013-01-01)
Chen, Wen-Tsuen
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Lin, Youn-Long
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Lee, Chen-Yi
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Chiang, Jeng-Long
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Chang, Meng-Fan
Taiwan's semiconductor industry has had a profound influence on both domestic economics and the global IT industry. To enhance its competitiveness and expand its global impact, the Taiwan government commenced the National Program for Intelligent Electronics (NPIE) in 2011 to promote technological innovation of medical electronics, green electronics, vehicular (car) electronics, conventional computer, communication, and consumer electronics, the so-called "MG+4C" applications. The government allocated a budget of $430 million over 5 years to facilitate technology development, advanced research, talent cultivation, industry promotion, and international collaboration. By coordinating with government agencies, research institutions, universities, and corporations, the NPIE develops an integrated framework of academia and industry in Taiwan. It also emphasizes the enhancement of product verification, regulations, and participation in international alliances and standards. By transferring academic results to industry in emerging MG+4C applications, it is expected that the NPIE will contribute to the global semiconductor community, energize Taiwan's IC industry, and create innovative products and intelligent systems for better life and better environment.
Traffic-Aware Sensor Grouping for IEEE 802.11ah Networks: Regression Based Analysis and Design
(2019-03-01)
Chang, Tung-Chun
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Lin, Chi-Han
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Lin, Kate Ching-Ju
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Chen, Wen-Tsuen
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資訊工程學系
Traditional IEEE 802.11 network is designed for the use of small scale local wireless networks. However, the emergence of the Internet of Things (loT) has changed the scene of wireless communications. Thus, recently, the IEEE task group ah (TGah) has been dedicated to the standardization of a new protocol, called IEEE 802.11ah, which is customized for this type of large-scale networks. IEEE 802.11ah adopts a grouping-based MAC protocol to reduce the contention overhead for each group of devices. However, most existing designs simply randomly partition devices into groups, and less attention has been paid to the problem of forming efficient groups. Therefore, in this paper, we argue that the performance of grouping is closely related to heterogeneity in traffic demands of devices, and propose a traffic-aware grouping algorithm to improve channel utilization. Since channel utilization of a group closely depends on the collision probability, we further derive a regression-based analytical model to estimate the contention success probability with consideration of sensors' heterogeneous traffic demands. The evaluation via NS-3 simulations shows that the proposed regression-based model is quite accurate even when clients have diverse traffic demands, and our traffic-aware grouping outperforms other baseline approaches, especially when the network is nearly saturated.