Xuemin (Sherman) Shen

University of Waterloo, Ватерлоо, Ontario, Canada

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Publications (124)120.33 Total impact

  • Fangqin Liu, Tom H. Luan, Xuemin Sherman Shen, Chuang Lin
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    ABSTRACT: The packet loss burstiness over wireless channels is commonly acknowledged as a key impacting factor on the performance of networking protocols. An accurate evaluation of the packet loss burstiness, which reveals the characteristics and performance of the wireless channels, is crucial to the design of wireless systems and the quality-of-service provisioning to end users. In this paper, a simple yet accurate analytical framework is developed to dimension the packet loss burstiness over generic wireless channels. In specific, we first propose a novel and effective metric to characterize the packet loss burstiness, which is shown to be more compact, effective, and accurate than the metrics proposed in existing literature for the same purpose. With this metric, we then develop an analytical framework and derive the closed-form solutions of the packet loss performance, including the packet loss rate and the loss-burst/loss-gap length distributions. Lastly, as an example to show how the derived results can be applied to the design of wireless systems, we apply the analytical results to devise an adaptive packetization scheme. The proposed packetization scheme adaptively adjusts the packet length of transmissions based on the prediction of the packet loss rate and loss-burst/loss-gap lengths of the wireless channel. Via extensive simulations, we show that with the proposed packetization scheme, the channel throughput can be enhanced by more than 10% than the traditional scheme.Copyright © 2012 John Wiley & Sons, Ltd.
    Wireless Communications and Mobile Computing 08/2014; 14(12):1160-1175. · 1.29 Impact Factor
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    Rong Jiang, Rongxing Lu, Jun Luo, Chengzhe Lai, Xuemin Sherman Shen
    Security and Communication Networks 08/2014; · 0.43 Impact Factor
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    ABSTRACT: This paper investigates energy efficient uplink communications for battery-constrained mobile terminals (MTs). We consider a heterogeneous wireless medium where MTs communicate with base stations (BSs) and access points (APs) of different networks with overlapped coverage. Unlike the existing research, we develop a joint bandwidth and power allocation framework that maximizes energy efficiency for a set of MTs, in different service areas, with best effort service and multi-homing capabilities. The problem formulation captures the heterogeneity of the medium, in terms of different service areas, channel conditions, available resources at BSs/APs of different networks, and different available maximum power at the MTs. In addition, the framework is implemented in a decentralized manner which is desirable in a case that different networks are operated by different service providers. Simulation results are presented to demonstrate the performance of the proposed framework.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
  • 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 06/2014; 13(6):3281-3292. · 2.76 Impact Factor
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    ABSTRACT: Millimeter wave (mmWave) communication is a promising technology to support high-rate (e.g., multi-Gbps) multimedia applications because of its large available bandwidth. Multipacket reception is one of the important capabilities of mmWave networks to capture a few packets simultaneously. This capability has the potential to improve medium access control layer performance. Because of the severe propagation loss in mmWave band, traditional backoff mechanisms in carrier sensing multiple access/collision avoidance (CSMA/CA) designed for narrowband systems can result not only in unfairness but also in significant throughput reduction. This paper proposes a novel backoff mechanism in CSMA/CA by giving a higher transmission probability to the node with a transmission failure than that with a transmission success, aiming to improve the system throughput. The transmission probability is adjusted by changing the contention window size according to the congestion status of each node and the whole network. The analysis demonstrates the effectiveness of the proposed backoff mechanism on reducing transmission collisions and increasing network throughput. Extensive simulations show that the proposed backoff mechanism can efficiently utilize network resources and significantly improve the network performance on system throughput and fairness. Copyright © 2014 John Wiley & Sons, Ltd.
    Wireless Communications and Mobile Computing 06/2014; · 1.29 Impact Factor
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    ABSTRACT: Carrier Aggregation is considered as a key revolution in Long Term Evolution-Advanced systems to meet the explosively increasing aspiration for high data rates. Unlike extensive simulative evaluations on CA in literature, current theoretical analysis on CA is not convincing due to lack of effective interference modeling. In this paper, we exploit the theory of stochastic geometry to provide tractable statistical interference modeling for downlink CA in LTE-A systems. Our objective is to demonstrate the benefits of CA by comparing the user performance between the legacy LTE users and LTE-A users. Specifically, we first model the distributions of base stations and users into Poisson Point Processes. Then, the user service probability and subchannel usage in each carrier are calculated for LTE and LTE-A users, respectively. The obtained probabilities are applied to derive the user SINR distribution and ergodic rates. To better clarify the impact of system/user parameters on the investigated performance, a special case is presented where the network is interference-limited and the channel fast fading is considered as Rayleigh fading. Finally, simulation results validate our analytical model and demonstrate that LTE-A users can achieve significantly better SINR and ergodic-rate performance than LTE users when the cell is not heavily loaded.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
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    ABSTRACT: In this paper, cooperative sensing for multi-channel cognitive radio networks (CRNs) is studied, whereby the secondary users (SUs) cooperate with each other to sense the multiple channels owned by the primary users (PUs). The objective is to better protect the primary system while satisfying the SUs' requirement on the expected access time. A general scenario is considered, where the channels present different usage characteristics and the detection performance of individual SUs varies due to the channel conditions between the PUs and SUs. With the dynamics in the channel usage characteristics and the detection capacities, each SU chooses one channel for sensing to minimize the interference to the PUs. The problem is formulated as a nonlinear integer programming problem which is NP-complete in general. To find the solution efficiently, the original problem is transformed into a variant of convex bipartite matching problem by constructing a complete bipartite graph and defining proper weight vectors. Based on the problem transformation, a channel assignment algorithm is proposed for computing in polynomial time the solution in terms of the number of SUs, the number of channels, and the maximum value of weights. Simulation results are presented to validate the performance of the proposed algorithm.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
  • Kai Fan, Jie Li, Hui Li, Xiaohui Liang, Xuemin Sherman Shen, Yintang Yang
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    ABSTRACT: Radio frequency identification (RFID) has been regarded as one of the 10 important technologies in the 21st century. Because of its capability to rapidly and accurately collect and process data in real-time, RFID has been widely applied in many areas, such as Internet of Things and Smart Grid. However, the existing security threats become more severe toward RFID authentication scheme. The traditional security mechanisms cannot be used in RFID directly because of the limitations of processing capability, storage space, and power supply of RFID tags. In this paper, we propose a revocable secure efficient lightweight RFID authentication scheme (RSEL). To achieve authentication efficiency, the key of the tag is chosen to reduce the number of hash computing in the database. Furthermore, the key is stored in the database and updated constantly with the tag to prevent the tracking and synchronization attacks. The valid period of each tag is stored in the database so that RSEL can revoke the expired tag. The correctness of RSEL has been proved using GNY logic. The performance of RSEL in terms of security and efficiency is evaluated. Compared with other existing approaches, RSEL achieves stronger security and higher efficiency. Copyright © 2013 John Wiley & Sons, Ltd.
    Concurrency and Computation Practice and Experience 04/2014; 26(5):1084-1096. · 0.78 Impact Factor
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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.
  • T.H. Luan, L.X. Cai, Jiming Chen, Xuemin Sherman Shen, Fan Bai
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    ABSTRACT: This paper proposes a practical and cost-effective approach to construct a fully distributed roadside communication infrastructure to facilitate the localized content dissemination to vehicles in the urban area. The proposed infrastructure is composed of distributed lightweight low-cost devices called roadside buffers (RSBs), where each RSB has the limited buffer storage and is able to transmit wirelessly the cached contents to fast-moving vehicles. To enable the distributed RSBs working toward the global optimal performance (e.g., minimal average file download delays), we propose a fully distributed algorithm to determine optimally the content replication strategy at RSBs. Specifically, we first develop a generic analytical model to evaluate the download delay of files, given the probability density of file distribution at RSBs. Then, we formulate the RSB content replication process as an optimization problem and devise a fully distributed content replication scheme accordingly to enable vehicles to recommend intelligently the desirable content files to RSBs. The proposed infrastructure is designed to optimize the global network utility, which accounts for the integrated download experience of users and the download demands of files. Using extensive simulations, we validate the effectiveness of the proposed infrastructure and show that the proposed distributed protocol can approach to the optimal performance and can significantly outperform the traditional heuristics.
    IEEE Transactions on Vehicular Technology 03/2014; 63(3):1419-1435. · 2.64 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 03/2014; 13(3):1668-1677. · 2.76 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 02/2014; 13(2):1047-1057. · 2.76 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 02/2014; 32(2):345-355. · 4.14 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 02/2014; 13(2):658-668. · 2.76 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 02/2014; 13(2):1129-1139. · 2.76 Impact Factor
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    ABSTRACT: Distributed energy resources (DERs), which are characterized by small-scale power generation technologies to provide an enhancement of the traditional power system, have been strongly encouraged to be integrated into the smart grid, and numerous trading strategies have recently been proposed to support the energy auction in the emerging smart grid marketing. However, few of them consider the security aspects of energy trading, such as privacy preservation, bid integrity, and pre-filtering ability. In this paper, we propose an efficient searchable encryption scheme for auction (SESA) in emerging smart grid marketing. Specifically, SESA uses a public key encryption with keyword search technique to enable the energy sellers (e.g., DERs) to inquire suitable bids while preserving the privacy of the energy buyers. Additionally, to facilitate the seller to search for detailed information of the bids, we also propose an extension of SESA to support conjunctive keywords search. Security analysis demonstrates that the proposed SESA and its extension can achieve data and keyword privacy, bid integrity and trapdoor unforgeability. Simulation results also show that both SESA and its extension have less computation and communication overhead than the existing searchable encryption approaches. Copyright © 2013 John Wiley & Sons, Ltd.
    Security and Communication Networks 01/2014; 7(1):234-244. · 0.43 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. · 6.49 Impact Factor
  • Jian Qiao, Xuemin Sherman Shen, Jon W. Mark, Yejun He
    IEEE Transactions on Vehicular Technology 01/2014; 64(1):1-1. · 2.64 Impact Factor
  • 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. · 6.49 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

Publication Stats

889 Citations
120.33 Total Impact Points


  • 2003–2014
    • University of Waterloo
      • Department of Electrical & Computer Engineering
      Ватерлоо, Ontario, Canada
  • 2011
    • McMaster University
      • Department of Electrical and Computer Engineering
      Hamilton, Ontario, Canada
  • 2008
    • Georgia State University
      • Department of Computer Science
      Atlanta, Georgia, United States
  • 2007
    • University of Victoria
      • Department of Electrical and Computer Engineering (ECE)
      Victoria, British Columbia, Canada