The Experts below are selected from a list of 717 Experts worldwide ranked by ideXlab platform

Sneha Kumar Kasera - One of the best experts on this subject based on the ideXlab platform.

  • On fast and accurate detection of unauthorized wireless access points using Clock Skews,” in Mobicom 2008
    2012
    Co-Authors: Suman Jana, Sneha Kumar Kasera
    Abstract:

    We explore the use of Clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using Clock Skews is to overcome one of the major limitations of existing solutions- the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the Clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) timestamps sent out in the beacon/probe response frames. We use two different methods for this purpose- one based on linear programming and the other based on least square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF timestamp data from several APs in two different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that Clock Skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received timestamp of the frames and show that with this enhancement our methodology can find Clock Skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, and NTP synchronization on Clock Skews. Our results indicate that the use of Clock Skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks

  • on fast and accurate detection of unauthorized wireless access points using Clock Skews
    IEEE Transactions on Mobile Computing, 2010
    Co-Authors: Suman Jana, Sneha Kumar Kasera
    Abstract:

    We explore the use of Clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using Clock Skews is to overcome one of the major limitations of existing solutions - the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the Clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) time stamps sent out in the beacon/probe response frames. We use two different methods for this purpose - one based on linear programming and the other based on least-square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF time stamp data from several APs in three different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that Clock Skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received time stamp of the frames and show that with this enhancement, our methodology can find Clock Skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, Clock source selection, and NTP synchronization on Clock Skews. Our results indicate that the use of Clock Skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks.

  • on fast and accurate detection of unauthorized wireless access points using Clock Skews
    ACM IEEE International Conference on Mobile Computing and Networking, 2008
    Co-Authors: Suman Jana, Sneha Kumar Kasera
    Abstract:

    We explore the use of Clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using Clock Skews is to overcome one of the major limitations of existing solutions - the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the Clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) timestamps sent out in the beacon/probe response frames. We use two different methods for this purpose - one based on linear programming and the other based on least square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF timestamp data from several APs in two different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that Clock Skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received timestamp of the frames and show that with this enhancement our methodology can find Clock Skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, and NTP synchronization on Clock Skews. Our results indicate that the use of Clock Skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks.

Allejan Van Der Veen - One of the best experts on this subject based on the ideXlab platform.

  • JOINT LOCALIZATION AND Clock SYNCHRONIZATION FOR WIRELESS SENSOR NETWORKS
    2016
    Co-Authors: Sundeep Prabhakar Chepuri, Geert Leus, Allejan Van Der Veen
    Abstract:

    A fully-asynchronous network with one target sensor and a few anchors (nodes with known locations) is considered. Lo-calization and synchronization are traditionally treated as two separate problems. In this paper, localization and synchro-nization is studied under a unified framework. We present a new model in which time-stamps obtained either via two-way communication between the nodes or with a broadcast based protocol can be used in a simple estimator based on least-squares (LS) to jointly estimate the position of the tar-get node as well as all the unknown Clock-Skews and Clock-offsets. The Cramér-Rao lower bound (CRLB) is derived for the considered problem and is used as a benchmark to analyze the performance of the proposed estimator. Index Terms — Clock synchronization, Clock-skew, Clock-offset, localization, wireless sensor networks

  • Joint Ranging and Synchronization for an Anchorless Network of Mobile Nodes
    2015
    Co-Authors: Raj Thilak Rajan, Student Member, Allejan Van Der Veen
    Abstract:

    Abstract—Synchronization and localization are critical chal-lenges for the coherent functioning of a wireless network, which are conventionally solved independently. Recently, various esti-mators have been proposed for pairwise synchronization between immobile nodes, based on time stamp exchanges via two-way communication. In this paper, we consider a network of mobile nodes for which a novel joint time-range model is presented, treating both unsynchronized Clocks and the pairwise distances as a polynomial functions of true time. For a pair of nodes, a least squares solution is proposed for estimating the pairwise range parameters between the nodes, in addition to estimating the Clock offsets and Clock Skews. Extending these pairwise solutions to network-wide ranging and Clock synchronization, we present a central data fusion based global least squares algorithm. A unique solution is nonexistent without a constraint on the cost function e.g., a Clock reference node. Ergo, a constrained framework is proposed and a new Constrained Cramér–Rao Bound (CCRB) is derived for the joint time-range model. In addition, to alleviate the need for a single Clock reference, various Clock constraints are presented and their benefits are investigated using the proposed solutions. Simulations are conducted and the algorithms are shown to approach the theoretical limits. Index Terms—Joint estimation, relative position, sum constraint, nullspace constraint, virtual Clock. I

  • joint ranging and synchronization for an anchorless network of mobile nodes
    IEEE Transactions on Signal Processing, 2015
    Co-Authors: Raj Thilak Rajan, Allejan Van Der Veen
    Abstract:

    Synchronization and localization are critical challenges for the coherent functioning of a wireless network, which are conventionally solved independently. Recently, various estimators have been proposed for pairwise synchronization between immobile nodes, based on time stamp exchanges via two-way communication. In this paper, we consider a network of mobile nodes for which a novel joint time-range model is presented, treating both unsynchronized Clocks and the pairwise distances as a polynomial functions of true time. For a pair of nodes, a least squares solution is proposed for estimating the pairwise range parameters between the nodes, in addition to estimating the Clock offsets and Clock Skews. Extending these pairwise solutions to network-wide ranging and Clock synchronization, we present a central data fusion based global least squares algorithm. A unique solution is nonexistent without a constraint on the cost function e.g., a Clock reference node. Ergo, a constrained framework is proposed and a new Constrained Cramer–Rao Bound (CCRB) is derived for the joint time-range model. In addition, to alleviate the need for a single Clock reference, various Clock constraints are presented and their benefits are investigated using the proposed solutions. Simulations are conducted and the algorithms are shown to approach the theoretical limits.

  • joint Clock synchronization and ranging asymmetrical time stamping and passive listening
    IEEE Signal Processing Letters, 2013
    Co-Authors: Sundeep Prabhakar Chepuri, Raj Thilak Rajan, Geert Leus, Allejan Van Der Veen
    Abstract:

    A fully asynchronous network with one sensor and M anchors (nodes with known locations) is considered in this letter. We propose a novel asymmetrical time-stamping and passive listening (ATPL) protocol for joint Clock synchronization and ranging. The ATPL protocol exploits broadcast to not only reduce the number of active transmissions between the nodes, but also to obtain more information. This is used in a simple estimator based on least-squares (LS) to jointly estimate all the unknown Clock-Skews, Clock-offsets, and pairwise distances of the sensor to each anchor. The Cramer-Rao lower bound (CRLB) is derived for the considered problem. The proposed estimator is shown to be asymptotically efficient, meets the CRLB, and also performs better than the available Clock synchronization algorithms.

  • Joint Clock synchronization and ranging: Asymmetrical time-stamping and passive listening
    2013
    Co-Authors: Sundeep Prabhakar Chepuri, Raj Thilak Rajan, Geert Leus, Student Member, Allejan Van Der Veen
    Abstract:

    Abstract—A fully asynchronous network with one sensor and anchors (nodes with known locations) is considered in this letter. We propose a novel asymmetrical time-stamping and passive listening (ATPL) protocol for joint Clock synchronization and ranging. The ATPL protocol exploits broadcast to not only reduce the number of active transmissions between the nodes, but also to obtain more information. This is used in a simple estimator based on least-squares (LS) to jointly estimate all the unknown Clock-Skews, Clock-offsets, and pairwise distances of the sensor to each anchor. The Cramér–Rao lower bound (CRLB) is derived for the considered problem. The proposed estimator is shown to be asymptotically efficient, meets the CRLB, and also performs better than the available Clock synchronization algorithms. Index Terms—Clock synchronization, Clock-offset, Clock-skew, wireless sensor networks. I

Suman Jana - One of the best experts on this subject based on the ideXlab platform.

  • On fast and accurate detection of unauthorized wireless access points using Clock Skews,” in Mobicom 2008
    2012
    Co-Authors: Suman Jana, Sneha Kumar Kasera
    Abstract:

    We explore the use of Clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using Clock Skews is to overcome one of the major limitations of existing solutions- the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the Clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) timestamps sent out in the beacon/probe response frames. We use two different methods for this purpose- one based on linear programming and the other based on least square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF timestamp data from several APs in two different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that Clock Skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received timestamp of the frames and show that with this enhancement our methodology can find Clock Skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, and NTP synchronization on Clock Skews. Our results indicate that the use of Clock Skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks

  • on fast and accurate detection of unauthorized wireless access points using Clock Skews
    IEEE Transactions on Mobile Computing, 2010
    Co-Authors: Suman Jana, Sneha Kumar Kasera
    Abstract:

    We explore the use of Clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using Clock Skews is to overcome one of the major limitations of existing solutions - the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the Clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) time stamps sent out in the beacon/probe response frames. We use two different methods for this purpose - one based on linear programming and the other based on least-square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF time stamp data from several APs in three different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that Clock Skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received time stamp of the frames and show that with this enhancement, our methodology can find Clock Skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, Clock source selection, and NTP synchronization on Clock Skews. Our results indicate that the use of Clock Skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks.

  • on fast and accurate detection of unauthorized wireless access points using Clock Skews
    ACM IEEE International Conference on Mobile Computing and Networking, 2008
    Co-Authors: Suman Jana, Sneha Kumar Kasera
    Abstract:

    We explore the use of Clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using Clock Skews is to overcome one of the major limitations of existing solutions - the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the Clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) timestamps sent out in the beacon/probe response frames. We use two different methods for this purpose - one based on linear programming and the other based on least square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF timestamp data from several APs in two different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that Clock Skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received timestamp of the frames and show that with this enhancement our methodology can find Clock Skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, and NTP synchronization on Clock Skews. Our results indicate that the use of Clock Skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks.

Eby G Friedman - One of the best experts on this subject based on the ideXlab platform.

  • optimal Clock skew scheduling tolerant to process variations
    Design Automation Conference, 1996
    Co-Authors: Josè Luis Neves, Eby G Friedman
    Abstract:

    A methodology is presented in this paper for determining an optimal set of Clock path delays for designing high performance VLSI/ULSI-based Clock distribution networks. This methodology emphasizes the use of non-zero Clock skew to reduce the system-wide minimum Clock period. Although choosing (or scheduling) Clock skew values has been previously recognized as an optimization technique for reducing the minimum Clock period, difficulty in controlling the delays of the Clock paths due to process parameter variations has limited its effectiveness. In this paper the minimum Clock period is reduced using intentional Clock skew by calculating a permissible Clock skew range for each local data path while incorporating process dependent delay values of the Clock signal paths. Graph-based algorithms are presented for determining the minimum Clock period and for selecting a range of process tolerant Clock Skews for each local data path in the circuit, respectively. These algorithms have been demonstrated on the ISCAS-89 suite of circuits. Furthermore, examples of Clock distribution networks with intentional Clock skew are shown to tolerate worst case Clock skew variations of up to 30% without causing circuit failure while increasing the system-wide maximum Clock frequency by up to 20% over zero skew-based systems.

  • minimizing power dissipation in non zero skew based Clock distribution networks
    International Symposium on Circuits and Systems, 1995
    Co-Authors: Jose L. Neves, Eby G Friedman
    Abstract:

    A methodology is presented in this paper for synthesizing low power Clock distribution networks. The Clock distribution networks are designed with localized non-zero Clock skew so as to improve circuit performance and reliability. Each branch of the Clock tree is assigned a delay value that is emulated by one or more CMOS inverters, each designed such that the output load appears as being predominantly capacitive. A design technique is presented for selecting the size and number of inverters within each branch such that the total power dissipated within the Clock distribution network is minimized. The power dissipation model considers both dynamic and short circuit power components. Simulation results exhibit reductions of up to 25% in total power dissipation within the Clock distribution network, while accurately implementing the desired Clock Skews.

Geert Leus - One of the best experts on this subject based on the ideXlab platform.

  • JOINT LOCALIZATION AND Clock SYNCHRONIZATION FOR WIRELESS SENSOR NETWORKS
    2016
    Co-Authors: Sundeep Prabhakar Chepuri, Geert Leus, Allejan Van Der Veen
    Abstract:

    A fully-asynchronous network with one target sensor and a few anchors (nodes with known locations) is considered. Lo-calization and synchronization are traditionally treated as two separate problems. In this paper, localization and synchro-nization is studied under a unified framework. We present a new model in which time-stamps obtained either via two-way communication between the nodes or with a broadcast based protocol can be used in a simple estimator based on least-squares (LS) to jointly estimate the position of the tar-get node as well as all the unknown Clock-Skews and Clock-offsets. The Cramér-Rao lower bound (CRLB) is derived for the considered problem and is used as a benchmark to analyze the performance of the proposed estimator. Index Terms — Clock synchronization, Clock-skew, Clock-offset, localization, wireless sensor networks

  • Robust time-based localization for asynchronous networks
    2016
    Co-Authors: Yiyin Wang, Geert Leus, Student Member, Senior Member
    Abstract:

    Abstract—Time-based localization approaches attract a lot of interest due to their high accuracy and potentially low cost for wireless sensor networks (WSNs). However, time-based local-ization is tightly coupled with Clock synchronization. Thus, the reliability of timestamps in time-based localization becomes an important yet challenging task to deal with. In this paper, we propose robust time-based localization strategies to locate a target node with the help of anchors (nodes with known positions) in asynchronous networks. Two kinds of asynchronous networks are considered: one only with Clock offsets, labeled quasi-synchronous networks, whereas the other with not only Clock offsets but also Clock Skews, labeled fully asynchronous networks. A novel ranging protocol is developed for both networks, namely asymmetric trip ranging (ATR), to reduce the communication load and explore the broadcast property of WSNs. Regardless of the reliability of the timestamp report from the target node, closed-form least-squares (LS) estimators are derived to accurately estimate the target node position. As a result, we counter the uncertainties caused by the target node by ignoring the timestamps from this node. Further-more, in order to simplify the estimator in fully asynchronous networks, localization and synchronization are decoupled. A simple yet efficient method is proposed to first Calibrate the Clock Skews of the anchors, and then Estimate the Node Position (CCS-ENP). Finally, Cramér-Rao bounds (CRBs) and simulation results corroborate the efficiency of our localization schemes. Index Terms—Clock offset, Clock skew, least-squares, localiza-tion, synchronization, two-way ranging. I

  • joint Clock synchronization and ranging asymmetrical time stamping and passive listening
    IEEE Signal Processing Letters, 2013
    Co-Authors: Sundeep Prabhakar Chepuri, Raj Thilak Rajan, Geert Leus, Allejan Van Der Veen
    Abstract:

    A fully asynchronous network with one sensor and M anchors (nodes with known locations) is considered in this letter. We propose a novel asymmetrical time-stamping and passive listening (ATPL) protocol for joint Clock synchronization and ranging. The ATPL protocol exploits broadcast to not only reduce the number of active transmissions between the nodes, but also to obtain more information. This is used in a simple estimator based on least-squares (LS) to jointly estimate all the unknown Clock-Skews, Clock-offsets, and pairwise distances of the sensor to each anchor. The Cramer-Rao lower bound (CRLB) is derived for the considered problem. The proposed estimator is shown to be asymptotically efficient, meets the CRLB, and also performs better than the available Clock synchronization algorithms.

  • Joint Clock synchronization and ranging: Asymmetrical time-stamping and passive listening
    2013
    Co-Authors: Sundeep Prabhakar Chepuri, Raj Thilak Rajan, Geert Leus, Student Member, Allejan Van Der Veen
    Abstract:

    Abstract—A fully asynchronous network with one sensor and anchors (nodes with known locations) is considered in this letter. We propose a novel asymmetrical time-stamping and passive listening (ATPL) protocol for joint Clock synchronization and ranging. The ATPL protocol exploits broadcast to not only reduce the number of active transmissions between the nodes, but also to obtain more information. This is used in a simple estimator based on least-squares (LS) to jointly estimate all the unknown Clock-Skews, Clock-offsets, and pairwise distances of the sensor to each anchor. The Cramér–Rao lower bound (CRLB) is derived for the considered problem. The proposed estimator is shown to be asymptotically efficient, meets the CRLB, and also performs better than the available Clock synchronization algorithms. Index Terms—Clock synchronization, Clock-offset, Clock-skew, wireless sensor networks. I

  • robust time based localization for asynchronous networks
    IEEE Transactions on Signal Processing, 2011
    Co-Authors: Yiyin Wang, Geert Leus
    Abstract:

    Time-based localization approaches attract a lot of interest due to their high accuracy and potentially low cost for wireless sensor networks (WSNs). However, time-based localization is tightly coupled with Clock synchronization. Thus, the reliability of timestamps in time-based localization becomes an important yet challenging task to deal with. In this paper, we propose robust time-based localization strategies to locate a target node with the help of anchors (nodes with known positions) in asynchronous networks. Two kinds of asynchronous networks are considered: one only with Clock offsets, labeled quasi-synchronous networks, whereas the other with not only Clock offsets but also Clock Skews, labeled fully asynchronous networks. A novel ranging protocol is developed for both networks, namely asymmetric trip ranging (ATR), to reduce the communication load and explore the broadcast property of WSNs. Regardless of the reliability of the timestamp report from the target node, closed-form least-squares (LS) estimators are derived to accurately estimate the target node position. As a result, we counter the uncertainties caused by the target node by ignoring the timestamps from this node. Furthermore, in order to simplify the estimator in fully asynchronous networks, localization and synchronization are decoupled. A simple yet efficient method is proposed to first Calibrate the Clock Skews of the anchors, and then Estimate the Node Position (CCS-ENP). Finally, Cramer-Rao bounds (CRBs) and simulation results corroborate the efficiency of our localization schemes.