Ai-Chun Pang

National Tsing Hua University, Hsinchu, Taiwan, Taiwan

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Publications (78)45.31 Total impact

  • 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
  • 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; 01/2013
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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 01/2013; 62(6):2763-2779. · 2.06 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.
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    ABSTRACT: Data center plays an important role in cloud computing. Cloud computing provides novel perspectives in Internet technologies and raises issues in the architecture, protocol, and implementation of existing networks and data centers. Although various cloud-based data center architectures have been proposed in recent years, some challenging issues, e.g., congestion control, load balancing and energy efficiency, still need to be addressed. In this paper, we present the designs of network architecture for data center servers, and then analyze and compare several promising solutions to tackle those challenging problems.
    Wireless Personal Multimedia Communications (WPMC), 2012 15th International Symposium on; 01/2012
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    ABSTRACT: ZigBee, a unique communication standard designed for low-rate 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, the cluster tree is especially suitable for wireless sensor networks because of its support for power saving operations and light-weight routing. However, the restricted routing paths caused by the cluster tree would form transmission bottlenecks such that it is difficult to guarantee quality of service (QoS) for critical packet deliveries in mission-critical networks. To address the problem, we propose a QoS-oriented framework with an analytical model to provide stochastic QoS guarantees for urgent information deliveries in ZigBee cluster-tree networks. Through analysis and simulations, we demonstrate the efficacy of the proposed framework.
    Communications (ICC), 2012 IEEE International Conference on; 01/2012
  • Source
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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 01/2012; 23:513-520. · 1.80 Impact Factor
  • Wei-Te Wong, Ya-Ju Yu, Ai-Chun Pang
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    ABSTRACT: Given the explosive growth of mobile subscribers, network operators have to densely deploy base stations to serve the exponentially increasing access demands. Nevertheless, recent researches have pointed out that base station operation has been identified as a significant portion of total system energy consumption and 90% of the traffic is carried by only 40% of base stations even under peak traffic demand. Therefore, switching off underutilized base stations for saving power is an important issue with the increasing awareness of environmental responsibility and economical concerns of network operators. This paper targets the problem of dynamic base station operation, with an objective to minimize total power consumption of all base stations. We prove this problem is NP-hard and cannot be approximated in polynomial time with a ratio better than 3/2. Then, we propose a distributed algorithm to tackle it. The simulation results show that our proposed algorithm can significantly reduce the network power consumption.
    Global Communications Conference (GLOBECOM), 2012 IEEE; 01/2012
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    Y. Yu, P. Hsiu, A. 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 01/2012; · 2.40 Impact Factor
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    ABSTRACT: Wireless charging technology is considered as one of the promising solutions to solve the energy limitation problem for large-scale wireless sensor networks. Obviously, charger deployment is a critical issue since the number of chargers would be limited by the network construction budget, which makes the full-coverage deployment of chargers infeasible. In many of the applications targeted by large-scale wireless sensor networks, end-devices are usually equipped by the human and their movement follows some degree of regularity. Therefore in this paper, we utilize this property to deploy chargers with partial coverage, with an objective to maximize the survival rate of end-devices. We prove this problem is NP-hard, and propose an algorithm to tackle it. The simulation results show that our proposed algorithm can significantly increase the survival rate of end-devices. To our knowledge, this is one of very first works that consider charger deployment with partial coverage in wireless rechargeable sensor networks.
    Network Operations and Management Symposium (APNOMS), 2012 14th Asia-Pacific; 01/2012
  • Yung-Feng Lu, Chin-Fu Kuo, Ai-Chun Pang
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    ABSTRACT: Wireless Sensor Networks (WSN) have recently been in the limelight for many domains. The characteristics of sensor networks have imposed various restrictions on their system designs. Since sensor nodes usually are developed by low-cost hardware, one major challenge in the development of many sensor-network applications is to provide high-security features with limited resources. In this paper, we propose a half-key scheme based on the well-known random key pre-distribution scheme and DDHV-D deployment knowledge to provide resource-efficient key management in wireless sensor networks 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.
    Proceedings of the 2011 ACM Symposium on Research in Applied Computation; 11/2011
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    ABSTRACT: The IEEE 802.15.4 standard is designed to achieve low-power transmissions in low-rate and short-distance wireless personal area networks (WPANs). For the sake of reducing the control overheads, the modified CSMA/CA protocol used by 802.15.4 does not have the hidden device protection mechanism, such as RTS/CTS mechanism. Previous studies indicated that the probability of any two devices in an infrastructure network unheard of each other is around 41%. Therefore, the hidden device problem (HDP) results in inefficient data transmission and serious power consumption issues in WPAN. In this paper, we propose a cross-layer detection and allocation (CL-DNA) scheme to solve the HDP in IEEE 802.15.4 without the cost of extra control overhead in data transmissions. The proposed scheme detects relationships of hidden devices based on the overlapped signals and then allocates the hidden devices into distinct subperiods for transmissions. Simulation results validated by mathematical analysis show that the proposed scheme significantly improves the goodput with the reduction in power consumption.
    IEEE Sensors Journal 03/2011; · 1.48 Impact Factor
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    ABSTRACT: Scalable video coding with adaptive modulation and coding is a promising technique to provide real-time multicast services for heterogeneous mobile devices. Nevertheless, as the rapid growth of data communication for emerging applications, energy consumption is an critical challenge of mobile devices. This paper targets the problem of resource allocation for scalable video multicast with adaptive modulation-coding schemes in next generation cellular wireless networks, with an objective to minimize the total energy consumption of all mobile devices for reception. We show the NP-hardness of the target problem and propose a 2-approximation algorithm. Extensive simulations are conducted to compare the proposed algorithm with a brute-force optimal algorithm and a conventional approach, which provides some useful insights into power-aware scalable video multicast in 4G wireless systems.
    Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE; 01/2011
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    ABSTRACT: Zigbee, formalized by the IEEE 802.15.4 standard, is a specification for wireless personal area networks with low power, low cost, and a low data rate. In Zigbee, tree topology is commonly practiced to form wireless sensor networks and perform data delivery applications. In Zigbee wireless applications, data delivery failures occur constantly due to the node movements and topology changes of networks. To tackle the topology changes, conventional route reconstruction often involves huge resource consumption. In this paper, we utilize the regularity of mobility patterns to reduce the frequency of route reconstructions and achieve higher efficiency in sending data to mobile nodes. To increase the data delivery ratio, we introduce the metric of mobility-robustness in a tree topology, and propose tree construction with an objective to maximize the mobility-robustness of the constructed tree. We develop an efficient algorithm for effective tree construction. The effectiveness of network topologies constructed using this mobility-robustness metric is demonstrated by NS2 simulations against a real-world scenario.
    Proceedings of IEEE International Conference on Communications, ICC 2011, Kyoto, Japan, 5-9 June, 2011; 01/2011
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    ABSTRACT: In order to decrease the overhead of the dynamic routing mechanisms in large networks, the hierarchical routing protocols have been proposed in the early 80's. The routing complexity and the routing table size are the two most important functional blocks in a dynamic route guidance system. Although various algorithms exist for finding the best routing policy on a hierarchical network, hardly exists any work in studying and evaluating the aforementioned measures of routing complexity and routing table size for a hierarchical network. In this paper, by applying the random geometry theory, we can generalize the mathematical framework from the previous work which discussed the worst-case deterministic models. Our proposed new framework can carry out the averages of the routing complexity and the routing table size, which can be specified as the functions of the hierarchical network parameters such as the number of the hierarchical levels and the subscriber densities (cluster-population) for each hierarchical level. After establishing the relationship between the structure of a hierarchical network and these two crucial network performance measures (routing complexity and routing table size), we present a novel cluster-population optimization method for hierarchical networks and the associated statistical analysis.
    Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE; 01/2010
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    ABSTRACT: Layer-encoded multimedia multicasting (LMM) has emerged in recent years to support heterogeneous subscriber stations with diverse computing and networking capabilities. With the advance of broadband wireless access technologies, wireless relay networks (WRNs) are expected to provide significant improvement on throughput and extension of coverage for next-generation wireless systems. In this paper, we study a radio resource allocation problem with the consideration of wireless interferences for LMM over WRNs. The problem is formally formulated, and the objective of the problem is to maximize the system utility where the utility is defined as user satisfaction. The NP-hardness of the problem is demonstrated, and then a heuristic algorithm is proposed. A series of experiments are conducted to demonstrate the capability of our proposed algorithm.
    Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE; 01/2010
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    Chi-Yao Hong, Ai-Chun Pang, Pi-Cheng Hsiu
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    ABSTRACT: The emerging wireless relay networks (WRNs) are expected to provide significant improvement on throughput and extension of coverage area for next-generation wireless systems. We study an optimization problem for multihop link scheduling with bandwidth and delay guarantees over WRNs. Our optimization problem is investigated under a more general interference model with a generic objective. The objective can be based on various kinds of performance indexes (e.g., throughput, fairness, and capacity), which can be determined by service providers. Through our theoretical analysis, the intractability and inapproximability of the optimization problem are shown. Due to the intractable computational complexity, we present efficient algorithms to provide a reasonable small approximation factor against any optimal solution even for a worst-case input. Furthermore, some experimental results indicate that our algorithms yield near-optimal performance in the average case.
    IEEE Transactions on Mobile Computing 01/2010; 9:1732-1748. · 2.40 Impact Factor
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    ABSTRACT: The IEEE 802.15.4 standard is able to achieve low-power transmissions in low-rate and short-distance wireless personal area networks (WPANs). Due to the constitutional design of the sensor node and the transmission architecture (client-server model), any data communication between two sensor nodes will involve the coordinator. One shortcoming of redundant channel-access steps will result in excessive contention overheads and, thus, the decrease of channel utilization. This paper proposes an adaptive contention control strategy (ACCS) to solve the problem of transmission efficiency in IEEE 802.15.4. ACCS can be implemented in the IEEE 802.15.4 medium access control (MAC) protocol standard adding no new message type. An analytic model and a simulation model are developed to evaluate the performance of IEEE 802.15.4 and ACCS. The simulation results demonstrate that the proposed scheme significantly improves the goodput, the average queuing delay, the average MAC delay, and the energy consumption.
    IEEE Transactions on Vehicular Technology 12/2009; · 2.06 Impact Factor
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    Chi-Yao Hong, Ai-Chun Pang
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    ABSTRACT: The emerging wireless relay networks (WRNs) are expected to provide significant improvement on throughput and extension of coverage area for next-generation wireless systems. We study an optimization problem for multi-hop link scheduling with bandwidth and delay guarantees over WRNs. Our optimization problem is investigated under a general interference model with a generic objective. The objective can be based on various kinds of performance indexes (e.g., throughput, fairness and capacity) determined by service providers. We present efficient algorithms for maximizing the objective function. The experimental results indicate that our presented algorithms yield near-optimal performance.
    INFOCOM 2009, IEEE; 05/2009
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    ABSTRACT: With the popularity of VoIP, Push-To-Talk (PTT) services over the IP networks have gained their momentum. This research aims at essential design issues for the quality of service of PTT services. We explore the relationship between the speech quality and system design issues. MOS (Mean Opinion Score), which is raised by the ITU-T (International Telecommunication Union) as one of the most common benchmarks, is studied under factors in system designs and implementations. In particular, we focus on the analysis of packet delay, jitter, and packet loss for PTT services. Experiments are designed and executed with the considerations of PTT characteristics. Our goal is to provide more understanding of MOS versus PTT and deliver insights in future PTT system designs.
    Wireless Communications and Networking Conference, 2009. WCNC 2009. IEEE; 05/2009

Publication Stats

427 Citations
45.31 Total Impact Points

Institutions

  • 2007–2010
    • National Tsing Hua University
      • Department of Computer Science
      Hsinchu, Taiwan, Taiwan
  • 2004–2009
    • National Taiwan University
      • Department of Computer Science and Information Engineering
      Taipei, Taipei, Taiwan
  • 2008
    • National University of Kaohsiung
      Kao-hsiung-shih, Kaohsiung, Taiwan
  • 2000–2005
    • National Chiao Tung University
      • Institute of Computer Science and Engineering
      Hsinchu, Taiwan, Taiwan
  • 2003
    • Quanta Computer Inc.
      Taoyuan City, Taiwan, Taiwan