Xuemin (Sherman) Shen

University of Waterloo, Waterloo, Ontario, Canada

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Publications (91)57.58 Total impact

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    ABSTRACT: With the proliferation of smart grid research, the Advanced Metering Infrastructure (AMI) has become the first ubiquitous and fixed computing platform. However, due to the unique characteristics of AMI, such as complex network structure, resource-constrained smart meter, and privacy-sensitive data, it is an especially challenging issue to make AMI secure. Energy theft is one of the most important concerns related to the smart grid implementation. It is estimated that utility companies lose more than $25 billion every year due to energy theft around the world. To address this challenge, in this paper, we discuss the background of AMI and identify major security requirements that AMI should meet. Specifically, an attack tree based threat model is first presented to illustrate the energy-theft behaviors in AMI. Then, we summarize the current AMI energy-theft detection schemes into three categories, i.e., classification-based, state estimation-based, and game theory-based ones, and make extensive comparisons and discussions on them. In order to provide a deep understanding of security vulnerabilities and solutions in AMI and shed light on future research directions, we also explore some open challenges and potential solutions for energy-theft detection.
    Tsinghua Science & Technology 04/2014; 19(2):105-120.
  • Hao Liang, Amit Kumar Tamang, Weihua Zhuang, Xuemin Sherman Shen
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    ABSTRACT: Rising concerns about the efficiency, reliability, economics, and sustainability in electricity production and distribution have been driving an evolution of the traditional electric power grid toward smart grid. A key enabler of the smart grid is the two-way communications throughout the power system, based on which an advanced information system can make optimal decisions on power system operation. Due to the expected deep penetration of renewable energy sources, energy storage devices, demand side management (DSM) tools, and electric vehicles (EVs) in the future smart grid, there exist significant technical challenges on power system planning and operation. Specifically, efficient stochastic information management schemes should be developed to address the randomness in renewable power generation, buffering effect of energy storage devices, consumer behavior patterns in the context of DSM, and high mobility of EVs. In this paper, we provide a comprehensive literature survey on the stochastic information management schemes for the smart grid. We start this survey with an introduction to the smart grid system architecture and the technical challenges in information management. Various component-level modeling techniques are presented to characterize the sources of randomness in the smart grid. Built upon the component-level models, we further explore the system-level stochastic information management schemes for smart grid planning and operation. Future research directions and open research issues are identified.
    IEEE Communications Surveys &amp Tutorials 01/2014; 16(3):1746-1770. · 4.82 Impact Factor
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    ABSTRACT: In this paper, we study the resource allocation in a device-to-device (D2D) communication underlaying green cellular network, where the base station (BS) is powered by sustainable energy. Our objective is to enhance the network sustainability and efficiency by introducing power control and cooperative communication. Specifically, we propose optimal power adaptation schemes to maximize the network efficiency under two practical power constraints. We then take the dynamics of the charging and discharging processes of the energy buffer into consideration to ensure the network sustainability. To this end, the energy buffer is modeled as a G/D/1 queue where the input energy has a general distribution. Power allocation schemes are proposed based on the statistics of the energy buffer to enhance the network efficiency and sustainability. Both theoretical analysis and numerical results demonstrate that our proposed power allocation schemes can improve the network throughput drastically while maintaining the network sustainability at a certain level.
    IEEE Transactions on Wireless Communications 01/2014; 13(2):1129-1139. · 2.42 Impact Factor
  • Younghyun Kim, Haneul Ko, Sangheon Pack, Xuemin Sherman Shen
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    ABSTRACT: In this paper, we propose a vehicular passenger mobility-aware bandwidth allocation (V-MBA) scheme in mobile hotspots. The V-MBA scheme consists of both call admission control and bandwidth adjustment functions to lower handoff vehicle service dropping probability and efficiently utilize resource of base station. Specifically, a handoff priority scheme with guard bandwidth is employed to protect handoff vehicle service. Also, bandwidth is dynamically assigned to each vehicle by exploiting vehicular passenger movement pattern that includes getting on and off events at a station. We evaluate the V-MBA scheme by developing a continuous-time Markov chain model. Simulation results demonstrate that the V-MBA scheme can guarantee low new vehicle service blocking probability and handoff vehicle service dropping probability through flexible bandwidth allocation.
    IEEE Transactions on Wireless Communications 01/2014; 13(6):3281-3292. · 2.42 Impact Factor
  • Ning Lu, Xuemin Sherman Shen
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    ABSTRACT: The capacity scaling law of wireless networks has been considered as one of the most fundamental issues. In this survey, we aim at providing a comprehensive overview of the development in the area of scaling laws for throughput capacity and delay in wireless networks. We begin with background information on the notion of throughput capacity of random networks. Based on the benchmark random network model, we then elaborate the advanced strategies adopted to improve the throughput capacity, and other factors that affect the scaling laws. We also present the fundamental tradeoffs between throughput capacity and delay under a variety of mobility models. In addition, the capacity and delay for hybrid wireless networks are surveyed, in which there are at least two types of nodes functioning differently, e.g., normal nodes and infrastructure nodes. Finally, recent studies on scaling law for throughput capacity and delay in emerging vehicular networks are introduced.
    IEEE Communications Surveys &amp Tutorials 01/2014; 16(2):642-657. · 4.82 Impact Factor
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    ABSTRACT: Dynamic spectrum access (DSA) can be leveraged by introducing external spectrum sensing for secondary users (SUs) to overcome the hidden primary users (PUs) problem and improve spectrum utilization. In this paper, we investigate the DSA networks with external sensors, i.e., external sensing agents, to utilize spectrum access opportunities located in cellular frequency bands. Considering the diversity of SUs' demands and the secondary bandwidths discovered by external sensors, it is critical to manage the detected spectrum resources in an efficient way. To this end, we formulate the resource management problem in the DSA networks as a dynamic resource demand-supply matching problem, and propose a cooperative matching solution. Specifically, spectrum access opportunities are classified into two types by the resource block size: massive sized blocks and small sized blocks. For the former type, SUs are encouraged to share the whole time-frequency block via forming coalitional groups with a "wholesale" sharing approach. For the latter type, the resource "aggregation" sharing approach is proposed to meet the time-frequency demand of individual SUs. To further reduce the delay in the spectrum allocation and compress the matching process, we develop a distributed fast spectrum sharing (DFSS) algorithm, which can deal with both two aforementioned types of resource sharing cases. Simulation results show that the DFSS algorithm can adapt to the dynamic spectrum variations in the DSA networks and the average utilization of detected spectrum access opportunities reaches nearly 90%.
    IEEE Transactions on Wireless Communications 01/2014; 13(2):1047-1057. · 2.42 Impact Factor
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    ABSTRACT: There is a growing interest in the use of renewable energy sources to power wireless networks in order to mitigate the detrimental effects of conventional energy production or to enable deployment in off-grid locations. However, renewable energy sources, such as solar and wind, are by nature unstable in their availability and capacity. The dynamics of energy supply hence impose new challenges for network planning and resource management. In this paper, the sustainable performance of a wireless mesh network powered by renewable energy sources is studied. To address the intermittently available capacity of the energy supply, adaptive resource management and admission control schemes are proposed. Specifically, the goal is to maximize the energy sustainability of the network, or equivalently, to minimize the failure probability that the mesh access points (APs) deplete their energy and go out of service due to the unreliable energy supply. To this end, the energy buffer of a mesh AP is modeled as a G/G/1(/N) queue with arbitrary patterns of energy charging and discharging. Diffusion approximation is applied to analyze the transient evolution of the queue length and the energy depletion duration. Based on the analysis, an adaptive resource management scheme is proposed to balance traffic loads across the mesh network according to the energy adequacy at different mesh APs. A distributed admission control strategy to guarantee high resource utilization and to improve energy sustainability is presented. By considering the first and second order statistics of the energy charging and discharging processes at each mesh AP, it is demonstrated that the proposed schemes outperform some existing state-of-the-art solutions.
    IEEE Journal on Selected Areas in Communications 01/2014; 32(2):345-355. · 3.12 Impact Factor
  • Xinsheng Zhou, Liang-Liang Xie, Xuemin Sherman Shen
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    ABSTRACT: In two-way relay channels, two terminal nodes exchange information with the help of a relay node. Designing practical coding schemes for such channels is challenging, especially when messages are encoded into multiple streams and a destination node receives signals from multiple nodes. In this paper, we prove an achievable region for half-duplex three-phase two-way relay channels. Furthermore, we propose low-density parity-check (LDPC) codes for such channels where two source codewords are encoded by systematic LDPC codes at the relay node. To analyze the performance of the codes, discretized density evolution is derived for the joint decoder at terminal nodes. Based on the discretized density evolution, degree distributions are optimized by iterative linear programming in 3 steps. The length of the obtained optimized codes is 26% longer than the theoretic one.
    IEEE Transactions on Wireless Communications 01/2014; 13(3):1668-1677. · 2.42 Impact Factor
  • Xiaoxia Zhang, Xuemin Sherman Shen, Liang-Liang Xie
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    ABSTRACT: This paper considers an LTE-Advanced cooperative cellular network where a Type II relay station (RS) is deployed to enhance the cell-edge throughput and to extend the coverage area. To better exploit the existing resources, the RS and the eNodeB (eNB) transmit in the same channel (In-Band) with decode-and-forward relaying strategy. For such a network, this paper proposes joint Orthogonal Frequency Division Multiplexing (OFDM) subcarrier and power allocation schemes to optimize the downlink multi-user transmission efficiency. Firstly, an optimal power dividing method between eNB and RS is proposed to maximize the achievable rate on each subcarrier. Based on this result, we show that the optimal joint resource allocation scheme for maximizing the overall throughput is to allocate each subcarrier to the user with the best channel quality and to distribute power in a water-filling manner. Since QoS provision is one of the major design objectives in cellular networks, we further formulate a lexicographical optimization problem to maximize the minimum rate of all users while improving the overall throughput. A sufficient condition for optimality is derived. Due to the complexity of searching for the optimal solution, we propose an efficient, low-complexity suboptimal joint resource allocation algorithm, which outperforms the existing suboptimal algorithms that simplify the joint design into separate allocation. Both theoretical and numerical analyses demonstrate that our proposed scheme can drastically improve the fairness as well as the overall throughput.
    IEEE Transactions on Wireless Communications 01/2014; 13(2):658-668. · 2.42 Impact Factor
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    Rong Jiang, Rongxing Lu, Chengzhe Lai, Jun Luo, Xuemin(Sherman) Shen
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    ABSTRACT: Supervisory Control And Data Acquisition (SCADA) systems are vital for operation and control of critical infrastructures in smart grid. Availability is one of the most important security objectives in SCADA communications, unavailability of which may further undermine the power delivery, and a reliable key management is essential to address this problem. In this paper, in order to simultaneously resolve the transmission security and availability in SCADA group communications, we propose a robust and efficient group key management scheme, called LiSH, which is characterized by developing a secure self-healing mechanism with t-revocation capability using one-way function to protect current session keys from being attacked by intruders. Detailed security analysis shows that the proposed LiSH scheme is secure in terms of collusion-free, and t-wise forward and backward security. In addition, performance evaluation also demonstrates its efficiency in terms of low storage and communication overheads.
    Proc. IEEE Globe Communication Conference (Globecom), Atlanta, GA USA; 12/2013
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    ABSTRACT: Vehicular networks consist of highly mobile vehicles communications, where connectivity is intermittent. Due to the distributed and highly dynamic nature of vehicular network, to minimize the end-­to-­end delay and the network traffic at the same time in data forwarding is very hard. Heuristic algorithms utilizing either contact-­level or social-­level scale of vehicular mobility have only one-­sided view of the network and therefore are not optimal. In this paper, by analyzing three large sets of Global Positioning System (GPS) trace of more than ten thousand public vehicles, we find that pairwise contacts have strong temporal correlation. Furthermore, the contact graph of vehicles presents complex structure when aggregating the underlying contacts. In understanding the impact of both levels of mobility to the data forwarding, we propose an innovative scheme, named ZOOM, for fast opportunistic forwarding in vehicular networks, which automatically choose the most appropriate mobility information when deciding next data-­relays in order to minimize the end-­to-­end delay while reducing the network traffic. Extensive trace-­driven simulations demonstrate the efficacy of ZOOM design. On average, ZOOM can improve 30% performance gain comparing to the state-­of-­art algorithms.
    INFOCOM 2013; 01/2013
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    Mohamed M.E.A. Mahmoud, Xuemin (Sherman) Shen
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    ABSTRACT: In multihop cellular networks, the mobile nodes usually relay others' packets for enhancing the network performance and deployment. However, selfish nodes usually do not cooperate but make use of the cooperative nodes to relay their packets, which has a negative effect on the network fairness and performance. In this paper, we propose a fair and efficient incentive mechanism to stimulate the node cooperation. Our mechanism applies a fair charging policy by charging the source and destination nodes when both of them benefit from the communication. To implement this charging policy efficiently, hashing operations are used in the ACK packets to reduce the number of public-key-cryptography operations. Moreover, reducing the overhead of the payment checks is essential for the efficient implementation of the incentive mechanism due to the large number of payment transactions. Instead of generating a check per message, a small-size check can be generated per route, and a check submission scheme is proposed to reduce the number of submitted checks and protect against collusion attacks. Extensive analysis and simulations demonstrate that our mechanism can secure the payment and significantly reduce the checks' overhead, and the fair charging policy can be implemented almost computationally free by using hashing operations.
    IEEE Transactions on Mobile Computing 01/2012; 11:753-766. · 2.40 Impact Factor
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    Rongxing Lu, Xiaodong Lin, Xiaohui Liang, Xuemin (Sherman) Shen
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    ABSTRACT: In this paper, to achieve a vehicle user's privacy preservation while improving the key update efficiency of location-based services (LBSs) in vehicular ad hoc networks (VANETs), we propose a dynamic privacy-preserving key management scheme called DIKE. Specifically, in the proposed DIKE scheme, we first introduce a privacy-preserving authentication technique that not only provides the vehicle user's anonymous authentication but enables double-registration detection as well. We then present efficient LBS session key update procedures: 1) We divide the session of an LBS into several time slots so that each time slot holds a different session key; when no vehicle user departs from the service session, each joined user can use a one-way hash function to autonomously update the new session key for achieving forward secrecy. 2) We also integrate a novel dynamic threshold technique in traditional vehicle-to-vehicle (V-2-V) and vehicle-to-infrastructure (V-2-I) communications to achieve the session key's backward secrecy, i.e., when a vehicle user departs from the service session, more than a threshold number of joined users can cooperatively update the new session key. Performance evaluations via extensive simulations demonstrate the efficiency and effectiveness of the proposed DIKE scheme in terms of low key update delay and fast key update ratio.
    IEEE Transactions on Intelligent Transportation Systems 01/2012; 13:127-139. · 3.06 Impact Factor
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    Rongxing Lu, Xiaodong Lin, Haojin Zhu, Xiaohui Liang, Xuemin (Sherman) Shen
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    ABSTRACT: Injecting false data attack is a well known serious threat to wireless sensor network, for which an adversary reports bogus information to sink causing error decision at upper level and energy waste in en-route nodes. In this paper, we propose a novel bandwidth-efficient cooperative authentication (BECAN) scheme for filtering injected false data. Based on the random graph characteristics of sensor node deployment and the cooperative bit-compressed authentication technique, the proposed BECAN scheme can save energy by early detecting and filtering the majority of injected false data with minor extra overheads at the en-route nodes. In addition, only a very small fraction of injected false data needs to be checked by the sink, which thus largely reduces the burden of the sink. Both theoretical and simulation results are given to demonstrate the effectiveness of the proposed scheme in terms of high filtering probability and energy saving.
    IEEE Transactions on Parallel and Distributed Systems 01/2012; 23:32-43. · 1.80 Impact Factor
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    Bong Jun Choi, Hao Liang, Xuemin (Sherman) Shen, Weihua Zhuang
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    ABSTRACT: In this paper, we propose a distributed asynchronous clock synchronization (DCS) protocol for Delay Tolerant Networks (DTNs). Different from existing clock synchronization protocols, the proposed DCS protocol can achieve global clock synchronization among mobile nodes within the network over asynchronous and intermittent connections with long delays. Convergence of the clock values can be reached by compensating for clock errors using mutual relative clock information that is propagated in the network by contacted nodes. The level of clock accuracy is depreciated with respect to time in order to account for long delays between contact opportunities. Mathematical analysis and simulation results for various network scenarios are presented to demonstrate the convergence and performance of the DCS protocol. It is shown that the DCS protocol can achieve faster clock convergence speed and, as a result, reduces energy cost by half for neighbor discovery.
    IEEE Transactions on Parallel and Distributed Systems 01/2012; 23:491-504. · 1.80 Impact Factor
  • Mehrdad Dianati, Xuemin (Sherman) Shen, Kshirasagar Naik
    07/2011: pages 147 - 176; , ISBN: 9781119973584
  • Lifei Wei, Haojin Zhu, Zhenfu Cao, Xuemin (Sherman) Shen
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    ABSTRACT: Delay/Disruption tolerant networks (DTNs) are wireless ad-hoc networks, where end-to-end connectivity can not be guaranteed and communications rely on the assumption that the nodes are willing to store-carry-and-forward bundles in an opportunistic way. However, this assumption would be easily violated due to the selfish nodes which are unwilling to consume precious wireless resources by serving as bundle relays. Incentive issue in DTNs is extraordinarily challenging due to the unique network characteristics. To tackle this issue, in this paper, we propose MobiID, a novel user-centric and social-aware reputation based incentive scheme for DTNs. Different from conventional reputation schemes which rely on neighboring nodes to monitor the traffic and keep track of each other’s reputation, MobiID allows a node to manage its reputation evidence and show to demonstrate its reputation whenever necessary. We also define the concepts of self-check and community-check to speed up reputation establishment and allow nodes to form consensus views towards targets in the same community, which is based on our social metric by forwarding willingness. Performance simulation are given to demonstrate the security, effectiveness and efficiency of the proposed scheme. KeywordsSelfish–Reputation based incentive–Cooperating stimulation–Security–Delay/Disruption tolerant networks
    07/2011: pages 177-190;
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    Jian Qiao, Lin X. Cai, Xuemin (Sherman) Shen, Jon W. Mark
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    ABSTRACT: Millimeter-wave (mmWave) communications is a promising enabling technology for high rate (Giga-bit) multimedia applications. However, because of the high propagation loss at 60 GHz band, mmWave signal power degrades significantly over distance. Therefore, a traffic flow being transmitted over multiple short hops can attain higher throughput than that over a single long hop. In this paper, we first design a hop selection metric for the piconet controller (PNC) to select appropriate relay hops for a traffic flow, aiming to improve the flow throughput and balance the traffic loads across the network. We then propose a multi-hop concurrent transmission (MHCT) scheme to exploit the spatial capacity of mmWave WPANs by allowing nodes to transmit concurrently in communication links without causing harmful interference. The analysis of concurrent transmission probability and time division multiplexing demonstrates that the MHCT scheme is capable of improving the time slot utilization. Extensive simulations are conducted to validate the analytical results and demonstrate that the proposed MHCT scheme can improve the average traffic flow throughput and network throughput.
    IEEE Transactions on Wireless Communications 01/2011; 10:3824-3833. · 2.42 Impact Factor
  • Jiming Chen, Chengqun Wang, Youxian Sun, Xuemin (Sherman) Shen
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    ABSTRACT: In this paper, we propose a new approach for localization in wireless sensor networks based on semi-supervised Laplacian regularized least squares algorithm. We consider two kinds of localization data: signal strength and pair-wise distance between nodes. When nodes are close within their physical location space, their localization data vectors should be similar. We first propose a solution using the alignment criterion to learn an appropriate kernel function in terms of the similarities between anchors, and the kernel function is used to measure the similarity between pair-wise sensor nodes in the networks. We then propose a semi-supervised learning algorithm based upon manifold regularization to obtain the locations of the non-anchors. We evaluate our algorithm under various network topology, transmission range and signal noise, and analyze its performance. We also compare our approach with several existing approaches, and demonstrate the high efficiency of our proposed algorithm in terms of location estimation error.
    Computer Networks. 01/2011; 55:2481-2491.
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    Ruonan Zhang, Lin Cai, Jianping Pan, Xuemin (Sherman) Shen
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    ABSTRACT: Video streaming over wireless links is a challenging issue due to the stringent Quality-of-Service (QoS) requirements of video traffic, the limited wireless channel bandwidth and the broadcast nature of wireless medium. As contention-based or reservation-based (i.e., contention-free) medium access control (MAC) protocols in existing wireless link-layer standards cannot efficiently support multimedia applications such as video streaming, a hybrid approach has been proposed, which uses both contention and reservation-based channel access mechanisms to transmit packets for each video source. Using this content-aware resource management approach, each video source reserves well below its peak data rate, and uses contention-based media access to transmit the remainder of the packets. In this paper, we first propose two conflict avoidance strategies and two buffering architectures for video streaming over ad hoc networks. Considering the interactions of reservation and contention, we develop the analytical model for the saturated traffic case and then extend it to derive tight performance bounds for the unsaturated case. Using the MAC protocols specified in the WiMedia ECMA-368 standard as an example, extensive simulations have been conducted to validate the analysis. Real video traces have been used to examine the video streaming performance. The analytical and simulation results demonstrate the effectiveness and efficiency of the hybrid resource management approach, and also reveal the impact of the conflict avoidance strategy and buffering design on the video performance.
    Ad Hoc Networks. 01/2011; 9:623-634.

Publication Stats

442 Citations
57.58 Total Impact Points


  • 2003–2012
    • University of Waterloo
      • Department of Electrical & Computer Engineering
      Waterloo, Ontario, Canada
  • 2011
    • McMaster University
      • Department of Electrical and Computer Engineering
      Hamilton, Ontario, Canada
  • 2010
    • Tsinghua University
      • Department of Computer Science and Technology
      Beijing, Beijing Shi, China
  • 2009
    • University of Manitoba
      • Department of Computer Science
      Winnipeg, Manitoba, Canada
  • 2008
    • Georgia State University
      Atlanta, Georgia, United States