Ai-Chun Pang

National Taiwan University, T’ai-pei, Taipei, Taiwan

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Publications (97)61.15 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: With the explosive growth in mobile data traffic, femtocell technology is regarded as the most effective way to enhance the mobile service quality and system capacity of cellular networks. However, the major problem with femtocell deployment is finding an appropriate access control mode that mobile operators and users are willing to adopt. Among the various kinds of access control modes, the hybrid access mode is considered the most promising because it allows femtocells to give preferential access to femtocell owners, while other public users can only access femtocells with certain restrictions. Because all femtocell owners are selfish, how to provide sufficient incentives so that they will share their femtocell resources is a challenging issue. To address the problem, we propose an economic framework for mobile operator and femtocell users based on game theoretical analysis. We also exploit the concept of revenue sharing, which provides a positive cycle to sustain the femtocell service. In the framework, a femtocell game is formulated where the femtocell owners determine the proportion of femtocell resources they will share with public users, while the operator maximizes its benefit by setting the ratio of the revenue distributed to femtocell owners. We analyze the existence and uniqueness of the Nash Equilibrium of the game. The results of extensive simulations show that the proposed framework maximizes the operator’s benefit and satisfies the users’ service requirements.
    IEEE Transactions on Computers 11/2015; 64(11):1-1. DOI:10.1109/TC.2015.2394453 · 1.66 Impact Factor
  • Ya-Ju Yu · Ai-Chun Pang · Pi-Cheng Hsiu · Yuguang Fang
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    ABSTRACT: Mobile devices have increasingly been used to run multimedia applications which are extremely downlink-intensive. The conventional rate adaptive and/or margin adaptive approach for radio resource allocation may result in unnecessary energy consumption on mobile devices, which will not be energy efficient for mobile multimedia applications. In this paper, we develop an energy adaptive approach and design an energy-efficient downlink resource allocation scheme to support multimedia applications. The objective is to minimize the total energy consumption of mobile devices for data reception while meeting the data rate requirements at mobile devices and the transmit power constraint at the base station. We show that the optimization problem is $mathcal {NP}$ -hard and then propose an efficient algorithm that has a provable performance guarantee under a certain condition. We have conducted extensive simulations to evaluate the efficacy of the proposed algorithm and our results provide useful insights into the design of energy-efficient resource allocation for wireless systems.
    IEEE Transactions on Mobile Computing 09/2015; 14(9):1833-1846. DOI:10.1109/TMC.2014.2369016 · 2.54 Impact Factor
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    Computer Communications 03/2015; 58(1). DOI:10.1016/j.comcom.2015.02.001 · 1.70 Impact Factor
  • IEEE Transactions on Emerging Topics in Computing 01/2015; DOI:10.1109/TETC.2015.2433936
  • Computer Communications 01/2015; · 1.70 Impact Factor
  • Te-Chuan Chiu · Ya-Ju Yu · Ai-Chun Pang · Tei-Wei Kuo
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    ABSTRACT: With the rapid growth of mobile data traffic, operators are expected to densely deploy base stations to meet user demands. Recent researches have indicated that the densely deployed base stations lead to the significant increase of the operational expenses of operators due to the electricity bills to maintain their operation, and thus the profit of operators is greatly decreased. Different from the past works in dynamically switching on/off base stations for energy saving, we propose to consider the benefits of users in service fee discounts as a joint optimization process in cutting down the energy consumption of base stations to maximize the total profit of operators. The optimization problem is formulated and shown being NP-hard. We then propose a profit-aware algorithm to switch off base stations, as needed, with the adjustment of the data rates provided to the users who are willing to receive discounts. The simulation results show that the proposed algorithm can significantly increase the total profit of operators and introduce a win-win situation to both users and operators.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
  • Te-Chuan Chiu · Che-Wei Pai · Yuan-Yao Shih · Ai-Chun Pang
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    ABSTRACT: Thanks to the recent advance on power engineering and wireless communications, the smart grid technology has emerged and users are now capable of deploying renewable energy generators and storage devices at their homes. On the other side, due to the rise of environmental consciousness, electric companies are eager to replace traditional generators with renewable energy. One of the most efficient ways is to provide an electricity buyback scheme for electric companies to encourage users to generate more renewable energy at their homes. Different from the previous works, we consider dynamic pricing with renewable energy buyback as our target scenario. We formulate the dynamic pricing problem as a convex optimization problem and propose a day-ahead time-dependent pricing scheme. The goal of our developed framework is to achieve the maximum benefits for both users and electric companies. To the best of our knowledge, this is one of the very first works to tackle the time-dependent problem with taking the environmental benefit of renewable energy into consideration for smart grid. The numerical results show that our framework can significantly reduce the peak time loading and efficiently balance the system energy provision.
    2014 ICC - 2014 IEEE International Conference on Communication Workshop (ICC); 06/2014
  • Yuan-Yao Shih · Ai-Chun Pang · Pi-Cheng Hsiu
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    ABSTRACT: With the increasing sophistication and maturity of biomedical sensors and the significant advances on low-power circuits and wireless communications technologies, wireless body area networks (WBANs) have emerged recently to provide pervasive health monitoring for humans. In WBANs, smart phones can serve as data sinks to forward the sensing data to back-end servers. Due to the battery concern of smart phones and the postural changes of humans, temporary disconnection between sensors and their associated smart phones may frequently happen in WBANs. In this case, the sensing data would be lost when the limited memory space of sensors overflows. To prevent excessive data loss, this paper proposes a scheme to parasitize the data on existing public Wi-Fi networks, once the links from sensors to the smart phones become unavailable. Specifically, an optimization problem to maximize the time during which data loss can be avoided by exploiting the data parasitizing scheme is formulated, where a decision set of the packets' size and sending timing to public Wi-Fi networks needs to be determined. We develop an offline algorithm to obtain an optimal decision set and present an efficient online algorithm for practical implementations. The feasibility of the proposed scheme and the efficacy of the algorithms are demonstrated through prototype implementations on a WBAN testbed with biomedical sensor devices for real-world experiments.
    2014 IFIP Networking Conference; 06/2014
  • Shyh-En Lin · Wan-Ping Tsai · Meng-Hsun Tsai · Ai-Chun Pang
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    ABSTRACT: Human mobility models strongly affect the performance in Mobile Ad Hoc Network (MANET). In order to get a more precise estimation of routing performance, it is crucial to construct a more realistic human mobility model. There are three properties investigated in literature which represent the patterns of human mobility. This paper analyzes real human traces and introduces a new property that the inter-hub movement of a human is not straight. We then construct a new random human mobility model called Irregular Orbit Levy-walk (IROL), and verify its ability to capture all of the four properties simultaneously. To investigate the feasibility of IROL, we measure routing performance of real traces, IROL, and other models in MANET on two data sets. In both data sets, IROL describes the real traces the best in terms of throughput and receive rate.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
  • Ya-Ju Yu · Ai-Chun Pang · Pi-Cheng Hsiu · Yuguang Fang
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    ABSTRACT: Mobile users have become increasingly addicted to multimedia applications which are extremely downlink-intensive. We observed that conventional objectives, like rate adaptive and margin adaptive, adopted for radio resource allocation may lead to unnecessary energy consumption of mobile devices, which is adverse to the development of mobile multimedia applications. This paper presents an alternative objective, called energy adaptive, and formulates the energy-efficient downlink resource allocation problem. The objective is to minimize the total energy consumption of mobile devices for data reception while satisfying users' data rate requirements and base station's available transmit power. We prove that the target problem is NP-hard and propose an efficient heuristic algorithm to solve the problem. The results of simulations conducted to evaluate the efficacy of the proposed algorithm agree with our observation on the conventional objectives, as well as providing some useful insights into the design of energy-efficient downlink resource allocation for wireless systems.
    2013 IEEE Globecom Workshops (GC Wkshps); 12/2013
  • Yeong-Sheng Chen · Tang-Te Lo · Chiu-Hua Lee · Ai-Chun Pang
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    ABSTRACT: To achieve location privacy for Location-Based Services (LBS) in the Vehicular Ad-hoc Network (VANET) environment, many pseudonym changing mechanisms have been proposed in the literature. Although some exiting mechanisms, such as AGE, SLOW, SPOT and can achieve high security level, yet much overhead is incurred due to a large number of pseudonym changes. While performing pseudonym changes, the services from the location server will be interrupted and the routing has to be reestablished, causing communication overheads. In light of this observation, this study proposes efficient pseudonym changing schemes to minimize the number of pseudonym changes while still achieving high location privacy protection level. Criteria for performing pseudonym changing are proposed by considering the age of pseudonyms, the speed, and the moving direction of the vehicles. Thus, four mechanisms AS, AD, SD and ADS are developed by using the combination of these three factors. Simulations have been carried out with the SUMO simulator. Compared with other existing pseudonym changing approaches, simulation results show that the proposed mechanisms have better performance in the sense of achieving high protection rate with less number of pseudonym changes, and, in particular, ADS always has the best performance.
    2013 International Conference on Connected Vehicles and Expo (ICCVE); 12/2013
  • Ya-Ju Yu · Ching-Chih Chuang · Hsin-Peng Lin · Ai-Chun Pang
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    ABSTRACT: Recently, large-scale data centers are widely built to support various kinds of cloud services, which are mostly delivered by multicast. Even with multicast, cloud services may still generate a large amount of data traffic in some bottleneck links and, even worse, cause network congestion. Thus, how to reduce the redundancy of data transmissions to mitigate network congestion is essential. In addition to wired transmissions, modern data centers adopt wireless links to augment network capacity. Under the coexisting scenario of wired and wireless links, this paper studies multicast data delivery problem. Specifically, a multicast tree problem is defined, and the objective is to minimize the total multicast data traffic. We prove the problem is NP-hard and propose an efficient heuristic algorithm to solve the problem. A series of experiment results shows that our proposed algorithm is very effective, compared with an optimal solution designed for traditional wired data centers.
    38th Annual IEEE Conference on Local Computer Networks (LCN 2013); 10/2013
  • Wei-Te Wong · Ai-Chun Pang · Miao-Ru Hsu
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    ABSTRACT: The next-generation cellular networks are envisioned to operate with heterogeneous wireless networks. Under such scenario, user device is required to periodically perform sensing for available RATs and switch between the one that best fits its current usage scenario. Such requirement may be highly energy-consuming; hence, efficient RAT selection mechanism is necessary to help user device select the best available RAT for its data transmission. In this paper, we propose a mechanism to make accurate RAT access recommendations to user devices by the Support Vector Machine tool, which can reduce unnecessary energy consumption due to periodic sensing. Simulation results demonstrate that our proposed methodology is highly accurate and capable of maintaining the average number of sensings as low as possible.
    Proceedings of the 2013 Research in Adaptive and Convergent Systems; 10/2013
  • Yuan-Yao Shih · Wei-Ho Chung · Pi-Cheng Hsiu · Ai-Chun Pang
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    ABSTRACT: ZigBee is a specification formalized by the IEEE 802.15.4 standard for low-power low-cost low-data-rate wireless personal area networks. In ZigBee networks, a tree topology is often used to construct a wireless sensor network for data delivery applications. However, delivery failures constantly occur in ZigBee wireless applications due to node movements and network topology changes. The conventional route reconstruction method is designed to mitigate the effects of topology changes, but it consumes a large amount of resources. In this paper, we exploit the regularity in node mobility patterns to reduce the frequency of route reconstructions and ensure that the transmission of data to mobile nodes is efficient. To increase the data delivery ratio and mitigate the effects of packet loss caused by the node mobility, we propose a ZigBee node deployment and tree construction framework. In particular, the framework considers the regularity in mobility patterns during the construction of the routing tree and deployment of nodes. It also includes an overhearing mechanism for mobile nodes to further improve the data delivery ratio. We present details of the proposed algorithms for node deployment and tree construction in the framework. The effectiveness of network topologies constructed under the framework is demonstrated through comprehensive ns-2 simulations based on two real-world scenarios. The results show that our approach can construct ZigBee tree topologies with a high data delivery ratio and low routing overhead.
    IEEE Transactions on Vehicular Technology 07/2013; 62(6):2763-2779. DOI:10.1109/TVT.2013.2245693 · 1.98 Impact Factor
  • Chien-Han Chai · Yuan-Yao Shih · Ai-Chun Pang
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    ABSTRACT: With the explosive growth of mobile data traffic, the femtocell technology is one of the proper solutions to enhance mobile service quality and system capacity for cellular networks. However, one of the key problems for femtocell deployment is to find appropriate access control in which mobile operators and users are willing to be involved. Among all kinds of access control modes, the hybrid access mode is considered as the most promising one, which allows femtocells to provide preferential access to femtocell owners and subscribers while other public users can access femtocells with certain restriction. Since all femtocell owners are selfish, how to provide enough incentives to the owners for sharing their femtocell resources is challenging. In this paper, we construct an economic framework for mobile operator and femtocell users by a game theoretical analysis and introduce the concept of profit sharing to provide a positive cycle to sustain the femtocell service. In this framework, a femtocell game is formulated, where the femtocell owners determine the proportion of femtocell resources shared with public users while the operator can maximize its own benefit by determining the ratio of revenue distribution to femtocell owners. The existence of the Nash equilibrium of the game is analyzed. Extensive simulations are conducted to show that the profit of the operator can be maximized while the service requirements of users can be maintained by the proposed framework.
    INFOCOM, 2013 Proceedings IEEE; 04/2013
  • Hsin-Chun Wu · Shuo-Cheng Hu · Ai-Chun Pang
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    ABSTRACT: Cognitive radio (CR) network is proposed to solve the utilization of radio spectrum resource. Spectrum trading has been an interesting topic in CR networks. In this paper, we formulate the problem as a game between multiple primary users (PUs) and multiple secondary users (SUs). We model the dynamic behavior of SUs using the theory of evolutionary game and the competition among PUs using a non-cooperative game. An evolution algorithm is presented to achieve the evolutionary equilibrium for a SU. For a PU, an iterative algorithm for strategy adaption to achieve Nash equilibrium is presented. We also introduce the idea of giving discount to the SUs which can provide help for the PU in broadcasting information. The numerical results show that our proposed model can achieve the optimal equilibrium point and the payoffs of both PUs and SUs are higher than those in the ordinary pricing-based game.
    Advances in Intelligent Systems and Applications - Volume 1, 01/2013: pages 581-590;
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    Ya-Ju Yu · Pi-Cheng Hsiu · Ai-Chun Pang
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    ABSTRACT: Layer-based video coding, together with adaptive modulation and coding, is a promising technique for providing real-time video multicast services on heterogeneous mobile devices. With the rapid growth of data communications for emerging applications, reducing the energy consumption of mobile devices is a major challenge. This paper addresses the problem of resource allocation for video multicast in fourth-generation wireless systems, with the objective of minimizing the total energy consumption for data reception. First, we consider the problem when scalable video coding is applied. We prove that the problem is NP-hard and propose a 2-approximation algorithm to solve it. Then, we investigate the problem under multiple description coding, and show that it is also NP-hard and cannot be approximated in polynomial time with a ratio better than 2, unless P=NP. To solve this case, we develop a pseudo-polynomial time 2 approximation algorithm. The results of simulations conducted to compare the proposed algorithms with a brute-force optimal algorithm and a conventional approach are very encouraging.
    IEEE Transactions on Mobile Computing 10/2012; 11(99-PP):1 - 1. DOI:10.1109/TMC.2011.186 · 2.54 Impact Factor
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    ABSTRACT: ZigBee, a unique communication standard designed for low-rate wireless personal area networks, has extremely low complexity, cost, and power consumption for wireless connectivity in inexpensive, portable, and mobile devices. Among the well-known ZigBee topologies, ZigBee cluster-tree is especially suitable for low-power and low-cost wireless sensor networks because it supports power saving operations and light-weight routing. In a constructed wireless sensor network, the information about some area of interest may require further investigation such that more traffic will be generated. However, the restricted routing of a ZigBee cluster-tree network may not be able to provide sufficient bandwidth for the increased traffic load, so the additional information may not be delivered successfully. In this paper, we present an adoptive-parent-based framework for a ZigBee cluster-tree network to increase bandwidth utilization without generating any extra message exchange. To optimize the throughput in the framework, we model the process as a vertex-constraint maximum flow problem, and develop a distributed algorithm that is fully compatible with the ZigBee standard. The optimality and convergence property of the algorithm are proved theoretically. Finally, the results of simulation experiments demonstrate the significant performance improvement achieved by the proposed framework and algorithm over existing approaches.
    IEEE Transactions on Parallel and Distributed Systems 03/2012; 23(3):513-520. DOI:10.1109/TPDS.2011.192 · 2.17 Impact Factor
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    Yung-Feng Lu · Chin-Fu Kuo · Ai-Chun Pang
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    ABSTRACT: Wireless Embedded Systems (WEBs) has attracted significant interest in recent years, for instance, Wireless Sensor Networks (WSN), have recently been in the limelight for many domains. The characteristics of WEBs have imposed various restrictions on their system designs. Since embedded systems usually are developed by low-cost hardware, one major challenge in the development of many WEBs applications is to provide high-security features with limited resources. In this paper, we propose a novel key establishment scheme, named half-key scheme that based on the well-known random key pre-distribution scheme and DDHV-D deployment knowledge to provide resource-efficient key management in WEBs with reduced memory space requirements and better security enforcement. The capability of the proposed approach is evaluated by an analytical model and a series of experiments.
    ACM SIGAPP Applied Computing Review 03/2012; 12(1):50-59. DOI:10.1145/2188379.2188384
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    ABSTRACT: IEEE 802.16e is a mobile version of Worldwide Interoperability for Microwave Access (WiMAX) that plays an important role in the evolution towards 4G. In this study, we focus on multimedia performance measurement for the purpose of a more realistic mobile WiMAX network test. This study aims to make a contribution in better understanding the mobile WiMAX performance for multimedia applications. For that purpose, we employ Voice over Internet Protocol (VoIP) and video streaming to test the network performance, where two distinct evaluation systems are used, professional and user-friendly. Our test results show that the mobile WiMAX network can support well the bandwidth-intense and delay-sensitive multimedia application. We find that the VoIP quality at the cell center is perfect, where the value of Perceptual Evaluation of Speech Quality exceeds 4. At the cell edge, the quality is degraded but still adequate. We also observe that the downlink of mobile WiMAX network can support video streaming up to 4 Mbps with the Mean Opinion Score (MOS) value of 4.5. On the uplink, the bitrate of 1 Mbps is supported with MOS 4.5 at the cell center and with MOS 3.2 at the cell edge, respectively. Our experiments further indicate that a smooth playback of YouTube 480P video is consistently provided. Finally, the handover case has very limited impact to the overall quality degradation of both VoIP and video streaming.
    EURASIP Journal on Wireless Communications and Networking 02/2012; 2012(1). DOI:10.1186/1687-1499-2012-53 · 0.72 Impact Factor

Publication Stats

628 Citations
61.15 Total Impact Points


  • 2004–2015
    • National Taiwan University
      • Department of Computer Science and Information Engineering
      T’ai-pei, Taipei, Taiwan
  • 2012–2014
    • Academia Sinica
      • Research Center for Information Technology Innovation
      T’ai-pei, Taipei, Taiwan
  • 2005–2007
    • National Tsing Hua University
      Hsin-chu-hsien, Taiwan, Taiwan
  • 2003
    • Quanta Computer Inc.
      Taoyuan City, Taiwan, Taiwan
  • 2001
    • National Chiao Tung University
      • Institute of Computer Science and Engineering
      Hsin-chu-hsien, Taiwan, Taiwan