Peng-Jun Wan

Illinois Institute of Technology, Chicago, Illinois, United States

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Publications (173)70.34 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We are in an age where people are paying increasing attention to energy conservation around the world. The heating and air-conditioning systems of buildings introduce one of the largest chunks of energy expenses. In this article, we make a key observation that after a meeting or a class ends in a room, the indoor temperature will not immediately increase to the outdoor temperature. We call this phenomenon thermal inertia. Thus, if we arrange subsequent meetings in the same room rather than in a room that has not been used for some time, we can take advantage of such undissipated cool or heated air and conserve energy. Though many existing energy conservation solutions for buildings can intelligently turn off facilities when people are absent, we believe that understanding thermal inertia can lead system designs to go beyond on-and-off-based solutions to a wider realm. We propose a framework for exploring thermal inertia in room management. Our framework contains two components. (1) The energy-temperature correlation model captures the relation between indoor temperature change and energy consumption. (2) The energy-aware scheduling algorithms: given information for the relation between energy and temperature change, energy-aware scheduling algorithms arrange meetings not only based on common restrictions, such as meeting time and room capacity requirement, but also energy consumptions. We identify the interface between these components so further works towards same on direction can make efforts on individual components. We develop a system to verify our framework. First, it has a wireless sensor network to collect indoor, outdoor temperature and electricity expenses of the heating or air-conditioning devices. Second, we build an energy-temperature correlation model for the energy expenses and the corresponding room temperature. Third, we develop room scheduling algorithms. In detail, we first extend the current sensor hardware so that it can record the electricity expenses in re-heating or re-cooling a room. As the sensor network needs to work unattendedly, we develop a hardware board for long-range communications so that the Imote2 can send data to a remote server without a computer relay close by. An efficient two-tiered sensor network is developed with our extended Imote2 and TelosB sensors. We apply laws of thermodynamics and build a correlation model of the energy needed to re-cool a room to a target temperature. Such model requires parameter calibration and uses the data collected from the sensor network for model refinement. Armed with the energy-temperature correlation model, we develop an optimal algorithm for a specified case, and we further develop two fast heuristics for different practical scenarios. Our demo system is validated with real deployment of a sensor network for data collection and thermodynamics model calibration. We conduct a comprehensive evaluation with synthetic room and meeting configurations, as well as real class schedules and classroom topologies of The Hong Kong Polytechnic University, academic calendar year of Spring 2011. We observe 20% energy savings as compared with the current schedules.
    ACM Transactions on Sensor Networks (TOSN). 11/2013; 10(1).
  • Chao Ma, Fahad Al-dhelaan, Peng-Jun Wan
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    ABSTRACT: This paper addresses the joint selection and power assignment of a largest number of given links which can communicate successfully at the same time under the physical interference model. For this optimization problem, we present a constant-approximation algorithm with improved performance over existing approximation algorithms. In addition, both the algorithm design and analysis are applicable to arbitrary path-loss exponent and arbitrary dimension of the deployment space.
    Proceedings of the 8th international conference on Wireless Algorithms, Systems, and Applications; 08/2013
  • Chao Ma, Fahad Al-dhelaan, Peng-Jun Wan
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    ABSTRACT: This paper studies the problem of selecting a maximum independent set of links with a fixed monotone and sublinear power assignment under the physical interference model. The best-known approximation bound for this problem is a very large constant. In this paper, we present an approximation algorithm for this problem, which not only has a much smaller approximation bound but also produces an independent set of links with a stronger property, i.e., strong independence.
    Proceedings of the 8th international conference on Wireless Algorithms, Systems, and Applications; 08/2013
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    ABSTRACT: Static greedy link schedulings have much simpler implementation than dynamic greedy link schedulings such as Longest-queue-first (LQF) link scheduling. However, its stability performance in multi-channel multi-radio (MC-MR) wireless networks is largely under-explored. In this paper, we present a stability subregion with closed form of a static greedy link scheduling in MC-MR wireless networks under the 802.11 interference model. By adopting some special static link orderings, the stability subregion is within a constant factor of the stable capacity region of the network. We also obtain constant lower bounds on the throughput efficiency ratios of the static greedy link schedulings in some special static link orderings.
    INFOCOM, 2013 Proceedings IEEE; 01/2013
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    ABSTRACT: Maximizing the wireless network capacity under physical interference model is notoriously hard due to the nonlocality and the additive nature of the wireless interference under the physical interference model. This problem has been extensively studied recently with the achievable approximation bounds progressively improved from the linear factor to logarithmic factor. It has been a major open problem whether there exists a constant-approximation approximation algorithm for maximizing the wireless network capacity under the physical interference model. In this paper, we improve the status quo for the case of linear transmission power assignment, which is widely adopted due to its advantage of energy conservation. By exploring and exploiting the rich nature of the wireless interference with the linear power assignment, we develop constant-approximation algorithms for maximizing the wireless network capacity with linear transmission power assignment under the physical interference model, in both the unidirectional mode and the bidirectional mode.
    INFOCOM, 2013 Proceedings IEEE; 01/2013
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    ABSTRACT: For wireless link scheduling in multi-channel multi-radio wireless networks aiming at maximizing (concurrent) multi-flow, constant-approximation algorithms have recently been developed in [11]. However, the running time of those algorithms grows quickly with the number of radios per node (at least in the sixth order) and the number of channels (at least in the cubic order). Such poor scalability stems intrinsically from the exploding size of the fine-grained network representation upon which those algorithms are built. In this paper, we introduce a new structure, termed as concise conflict graph, on the node-level links directly. Such structure succinctly captures the essential advantage of multiple radios and multiple channels. By exploring and exploiting the rich structural properties of the concise conflict graphs, we are able to develop fast and scalable link scheduling algorithms for either minimizing the communication latency or maximizing the (concurrent) multi-flow. These algorithms have running time growing linearly in both the number of radios per node and the number of channels, while not sacrificing the approximation bounds.
    INFOCOM, 2013 Proceedings IEEE; 01/2013
  • Yu Cheng, Hongkun Li, Peng-Jun Wan
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    ABSTRACT: A wide range of next generation wireless networks are based on the multiradio multichannel (MR-MC) network model. A full exploration of the MR-MC wireless network capacity incurs challenging cooperative networking issues including transmission cooperation, resource allocation cooperation, and cross-layer protocol cooperation. In this article, rather than focus on protocol designs for specific cooperative networking issues, we present a generic theoretical framework that could guide the protocol or algorithm development to approach the maximum network capacity. Based on our multidimensional conflict graph (MDCG) tool, we could achieve a cross-layer linear programming framework to study the optimal cooperative networking in two complementary aspects: optimal network dimensioning and throughputoptimal control. While certain NP-hard computing issues hindered the MR-MC network optimization for a long time, the MDCG-based framework can readily generate simple polynomial and distributed algorithms with guaranteed capacity region.
    IEEE Wireless Communications 01/2012; 19(2):66-73. · 3.74 Impact Factor
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    ABSTRACT: Longest-queue-first (LQF) link scheduling is a greedy link scheduling in multihop wireless networks. Its stability performance in single-channel single-radio (SC-SR) wireless networks has been well studied recently. However, its stability performance in multi-channel multi-radio (MC-MR)wireless networks is largely under-explored. In this paper, we present a stability subregion with closed form of the LQF scheduling in MC-MR wireless networks, which is within a constant factor of the network stability region. We also obtain constant lower bounds on the efficiency ratio of the LQF scheduling in MC-MR wireless networks under the 802.11 interference model or the protocol interference model.
    01/2012;
  • Yu Cheng, Hongkun Li, Peng-Jun Wan, Xinbing Wang
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    ABSTRACT: This paper presents a theoretical analysis of the maximum throughput of a wireless mesh backhaul network that is achievable over a practical carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol. We resort to the multicommodity flow (MCF) formulation augmented with the conflict-graph constraints, whereas we use a novel approach to take into account the collision overhead in the distributed CSMA/CA MAC. Such overhead due to random access has been ignored by existing MCF-based capacity studies, which assume impractical centralized scheduling and result in aggressive capacity planning, which is unachievable over the CSMA/CA MAC. This paper makes the following three main contributions: 1) we develop a generic method of integrating the CSMA/CA MAC analysis with the MCF formulation for optimal network capacity analysis, which readily generates an upper bound of the network throughput; 2) we define a new concept of CSMA/CA clique and theoretically study its relationship to a CSMA/CA area in terms of throughput; and 3) using the CSMA/CA clique as a tool, we derive a lower bound of the network throughput achievable over the CSMA/CA MAC by clique-based MCF formulation. NS-2 simulation results are presented to demonstrate the tightness of the upper and lower bounds that are newly developed, compared to those based on the MCF formulation assuming a slotted system and centralized scheduling.
    IEEE Transactions on Vehicular Technology 01/2012; 61(7):3151-3165. · 2.06 Impact Factor
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    ABSTRACT: Data aggregation, as a primitive communication task in wireless networks, can reduce the communication complexity. However, in-network aggregation usually brings an unavoidable security defect. Some malicious nodes may control a large percentage of the whole network data and compel the network misbehave in an arbitrary manner. Thus, locating the malicious nodes to prevent them from further disaster is a practical challenge for data aggregation schemes. Based on the grouping and localization techniques, we propose a novel integrated protocol to locate malicious nodes. The proposed protocol does not rely on any special hardware and requests only incomplete information of the network from the security schemes. We also conduct simulation study to evaluate the proposed protocol.
    Proceedings - IEEE INFOCOM 01/2012;
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    ABSTRACT: We address a new and general maximal lifetime problem in sensor-target surveillance. We assume that each sensor can watch at most k targets (k ≥ 1) and each target should be watched by ft sensors (h ≥ 1) at any time. The problem is to schedule sensors to watch targets and forward the sensed data to a base station such that the lifetime of the surveillance network is maximized. This general problem includes the existing ones as its special cases (k = 1 and h = 1 in and k = 1 and h ≥ 2 in). It is also important in practice because some sensors can monitor multiple or all targets within their surveillance ranges and multisensor fusion (i.e., watching a target by multiple sensors) gives better surveillance results. The problem involves several subproblems and one of them is a new matching problem called (k, h)-matching. The (k, h)-matching problem is a generalized version of the classic bipartite matching problem (when k = h = 1, (k, h)-matching becomes bipartite matching). We design an efficient (k, h)-matching algorithm to solve the (k, h)-matching problem and then solve the general maximal lifetime problem. As a byproduct of this study, the (k, h)-matching problem and the proposed (k, h)-matching algorithm can potentially be applied to other problems in computer science and operations research.
    IEEE Transactions on Parallel and Distributed Systems 11/2011; · 1.80 Impact Factor
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    ABSTRACT: Link scheduling is a fundamental design issue in multihop wireless networks. All existing link scheduling algorithms require the precise information of the positions, and/or communication/interference radii of all nodes. For practical networks, it is not only difficult or expensive to obtain these parameters, but also often impossible to get their precise values. The link scheduling determined by the imprecise values of these parameters may fail to guarantee the same approximation bounds of the link scheduling determined by precise values. Therefore, the existing link scheduling algorithms lack performance robustness. In this paper, we propose a robust link scheduling, which can be easily computed with only the information on whether a given pair of links have conflict or not and therefore is robust. In addition, our link scheduling does not compromise the approximation bound and indeed sometimes can achieve better approximation bound. Particularly, under the 802.11 interference model, its approximation bound is 16 in general and 6 with uniform interference radii, an improvement over the respective best-known approximation bounds 23 and 7.
    INFOCOM, 2011 Proceedings IEEE; 05/2011
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    ABSTRACT: Longest Queue First (LQF) is a well-known link scheduling strategy in multihop wireless networks. Its throughput efficiency ratio was shown to be exactly the local pooling factor (LPF) of the multihop wireless network in a recent seminar work by Joo et al.. Under the 802.11 interference model with uniform interference radii, the LPF of a multihop wireless network was known to be at least 1/6. However, little is known about the LPF of a multihop wireless network under the 802.11 interference model with arbitrary interference radii or under the protocol interference model. In this paper, we derive constant lower bounds on LPFs of these multihop wireless networks. Specifically, under the 802.11 interference model with arbitrary interference radii, the LPF is at least 1/16. Under the protocol interference model, if the communication radius of each node is at most c times its interference radius for some c <; 1, then the LPF is at least 1/ (2 ⌈π/ arcsin 1-c/2⌈ - 1)).
    INFOCOM, 2011 Proceedings IEEE; 05/2011
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    ABSTRACT: Link scheduling is a fundamental problem in multihop wireless networks because the capacities of the communication links in multihop wireless networks, rather than being fixed, vary with the underlying link schedule subject to the wireless interference constraint. The majority of algorithmic works on link scheduling in multihop wireless networks assume binary interference models such as the 802.11 interference model and the protocol interference model, which often put severe restrictions on interference constraints for practical applicability of the link schedules. On the other hand, while the physical interference model is much more realistic, the link scheduling problem under physical interference model is notoriously hard to resolve and been studied only recently by a few works. This paper conducts a full-scale algorithmic study of link scheduling for maximizing throughput capacity or minimizing the communication latency in multihop wireless networks under the physical interference model. We build a unified algorithmic framework and develop approximation algorithms for link scheduling with or without power control.
    INFOCOM, 2011 Proceedings IEEE; 05/2011
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    Peng-Jun Wan, Xiaohua Xu, O. Frieder
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    ABSTRACT: Shortest link scheduling (SLS) in multihop wireless networks under physical interference model is notoriously hard to resolve and been studied only recently by a few works. Most of the obtained approximation bounds grow linearly with the number of links, and many are only valid with single-hop wireless networks, and some claimed approximation bounds are even false. This paper conducts a rigorous algorithmic study of SLS with power control under the physical interference model. We develop a polynomial O (βlnα)-approximation algorithm for SLS, where α is the independence number and β is the power diversity.
    Mobile Ad-hoc and Sensor Networks (MSN), 2010 Sixth International Conference on; 01/2011
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    Minming Li, Peng-Jun Wan, F. Frances Yao
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    ABSTRACT: Connected dominating set (CDS) in unit disk graphs has a wide range of applications in wireless ad hoc networks. A number of approximation algorithms for constructing a small CDS in unit disk graphs have been proposed in the literature. The majority of these algorithms follow a general two-phased approach. The first phase constructs a dominating set, and the second phase selects additional nodes to interconnect the nodes in the dominating set. In the performance analyses of these two-phased algorithms, the relation between the independence number α and the connected domination number γ c of a unit-disk graph plays the key role. The best-known relation between them is . In this paper, we prove that α≤3.4306γ c +4.8185. This relation leads to tighter upper bounds on the approximation ratios of two approximation algorithms proposed in the literature.
    Algorithmica 01/2011; 61:1000-1021. · 0.49 Impact Factor
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    Peng-Jun Wan, Lixin Wang
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    ABSTRACT: Consider a random multihop wireless network represented by a Poisson point process over a unit-area disk with mean n. Let øn denote its critical transmission radius for its greedy forward routing. Recently, asymptotic bounds on øn have been progressively improved. However, the precise asymptotic probability distribution of øn remains open. In this paper, we settle this open problem. Specifically, let σ = 2π/3 - √3/2. Then for any constant c, the asymptotic probability of equation is proved to be exactly exp (-(1/σ/π-1/3-π/2σ)e-c).
    INFOCOM 2011. 30th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 10-15 April 2011, Shanghai, China; 01/2011
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    ABSTRACT: In multi-hop wireless networks, the use of virtual backbone can greatly simplify routing, broadcasting, as well as energy/bandwidth saving. However, constructing a virtual backbone is costly and time-consuming because of the inevitable transmission interference during the process of the construction. In the literature, most of virtual backbone construction algorithms did not take the interference issue into consideration. To the best of our knowledge, our proposed algorithm is the first fully-distributed, interference-aware virtual backbone construction algorithm that has a proven bound on the construction latency. Besides, our proposed algorithm can be applied to the leader election problem, and such application results in a fully-distributed and interference-aware leader election algorithm of time complexity O(n log n) (where n is the number of nodes). This new leader election algorithm is practical in wireless networks because interference has already been dealt with; is also results in the fastest interference-aware leader election algorithm to the best of our knowledge.
    IEEE Transactions on Communications 01/2011; · 1.75 Impact Factor
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    Peng-Jun Wan, Chao Ma, ShaoJie Tang, Boliu Xu
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    ABSTRACT: This paper addresses the joint selection and power assignment of a largest set of given links which can communicate successfully at the same time under the physical interference model in the duplex (i.e. bidirectional) mode. For the special setting in which all nodes have unlimited maximum transmission power, Halldorsson and Mitra [5] developed an approximation algorithm with a huge constant approximation bound. For the general setting in which all nodes have bounded maximum transmission power, the existence of constant approximation algorithm remains open. In this paper, we resolve this open problem by developing an approximation algorithm which not only works for the general setting of bounded maximum transmission power, but also has a much smaller constant approximation bound.
    Wireless Algorithms, Systems, and Applications - 6th International Conference, WASA 2011, Chengdu, China, August 11-13, 2011. Proceedings; 01/2011
  • Peng-Jun Wan, XiaoHua Xu, Zhu Wang
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    ABSTRACT: One of the most fundamental task of wireless networks is to provide coverage of a set of targets. Suppose that all nodes and targets lie in a plane, and all nodes have circular coverage ranges of arbitrary radii. The problem Minimum Wireless Cover (MWC) seeks the fewest nodes to cover the targets. If all nodes are associated with some positive prices, the problem Cheapest Wireless Cover (CWC) seeks a cheapest set of nodes to cover the targets. If all nodes have bounded lives, the problem Max-Life Wireless Cover (MLWC) seeks wireless coverage schedule of maximum life subject to the life constraints of individual nodes. In this paper, we present a polynomial time approximation scheme (PTAS) for MWC, and two randomized 2O(log* n)-approximation algorithms for CWC and MLWC respectively, where n is the number of nodes, and log* n is the iterated logarithm of n with base 2.
    Proceedings of the 12th ACM Interational Symposium on Mobile Ad Hoc Networking and Computing, MobiHoc 2011, Paris, France, May 16-20, 2011; 01/2011

Publication Stats

3k Citations
70.34 Total Impact Points

Institutions

  • 1997–2013
    • Illinois Institute of Technology
      • • Department of Computer Science
      • • Center for Electrochemical Science and Engineering
      Chicago, Illinois, United States
  • 2011
    • National Tsing Hua University
      • Department of Electrical Engineering
      Hsinchu, Taiwan, Taiwan
    • Hong Kong Baptist University
      • Department of Computer Science
      Kowloon, Hong Kong
  • 2007–2010
    • The University of Hong Kong
      • Department of Computer Science
      Hong Kong, Hong Kong
  • 2009
    • Rutgers, The State University of New Jersey
      • Department of Computer Science
      New Brunswick, NJ, United States
    • University of Illinois at Chicago
      • Department of Computer Science
      Chicago, Illinois, United States
  • 2006–2008
    • City University of Hong Kong
      • Department of Computer Science
      Chiu-lung, Kowloon City, Hong Kong
    • National Chiao Tung University
      • Department of Computer Science
      Hsinchu, Taiwan, Taiwan
  • 2005
    • Wuhan University
      Wu-han-shih, Hubei, China
  • 1997–2005
    • University of Minnesota Duluth
      • Department of Computer Science
      Duluth, MN, United States
  • 2000
    • Pace University
      • Program in Computer Science
      New York City, NY, United States
    • University of Illinois, Urbana-Champaign
      • Department of Computer Science
      Urbana, IL, United States
  • 1993
    • Northeast Institute of Geography and Agroecology
      • Institute of Applied Mathematics
      Peping, Beijing, China