P. Krishnamurthy

NTNU Samfunnsforskning, Nidaros, Sør-Trøndelag, Norway

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Publications (60)15.65 Total impact

  • P. Krishnamurthy, M. Weiss, D. Tipper
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    ABSTRACT: Dynamic spectrum access (DSA), where the permission to use slices of radio spectrum is dynamically shifted (in time an in different geographical areas) across various communications services and applications, has been an area of interest from technical and public policy perspectives over the last decade. The underlying belief is that this will increase spectrum utilization, especially since many spectrum bands are relatively unused, ultimately leading to the creation of new and innovative services that exploit the increase in spectrum availability. Determining whether a slice of spectrum, allocated or licensed to a primary user, is available for use by a secondary user at a certain time and in a certain geographic area is a challenging task. This requires “context information” which is critical to the operation of DSA. Such context information can be obtained in several ways, with different costs, and different quality/usefulness of the information. In this paper, we describe the challenges in obtaining this context information, the potential for the integration of various sources of context information, and the potential for reuse of such information for related and unrelated purposes such as localization and enforcement of spectrum sharing. Since some of the infrastructure for obtaining finegrained context information is likely to be expensive, the reuse of this infrastructure/information and integration of information from less expensive sources are likely to be essential for the economical and technological viability of DSA.
    Information Reuse and Integration (IRI), 2013 IEEE 14th International Conference on; 01/2013
  • Conference Proceeding: Wireless network virtualization
    Xin Wang, P. Krishnamurthy, D. Tipper
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    ABSTRACT: Virtualization of wired networks and end computing systems has become one of the leading trends in networked ICT systems. In contrast relatively little virtualization has occurred in infrastructure based wireless networks, but the idea of virtualizing wireless access is gaining attention as it has the potential to improve spectrum utilization and perhaps create new services. In this paper we survey the state of the current research in virtualizing wireless networks. We define and describe possible architectures, the issues, hurdles and trends towards implementation of wireless network virtualization.
    Computing, Networking and Communications (ICNC), 2013 International Conference on; 01/2013
  • Kunjie Xu, D. Tipper, P. Krishnamurthy, Yi Qian
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    ABSTRACT: Multihop wireless networks can be subjected to nonstationary phenomena due to a dynamic network topology and time varying traffic. However, the simulation techniques used to study multihop wireless networks focus on the steady-state performance even though transient or nonstationary periods will often occur. Moreover, the majority of the simulators suffer from poor scalability. In this paper, we develop an efficient performance modeling technique for analyzing the time varying queueing behavior of multihop wireless networks. The one-hop packet transmission (service) time is assumed to be deterministic, which could be achieved by contention-free transmission, or approximated in sparse or lightly loaded multihop wireless networks. Our model is a hybrid of time varying adjacency matrix and fluid flow based differential equations, which represent dynamic topology changes and nonstationary network queues, respectively. Numerical experiments show that the hybrid fluid based model can provide reasonably accurate results much more efficiently than standard simulators. Also an example application of the modeling technique is given showing the nonstationary network performance as a function of node mobility, traffic load and wireless link quality.
    Computing, Networking and Communications (ICNC), 2013 International Conference on; 01/2013
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    Tae-Hoon Kim, D. Tipper, P. Krishnamurthy
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    ABSTRACT: Heterogeneous conditions can occur in multi-hop wireless networks due to a variety of factors such as variations in transmission power and signal propagation environments. Directed links can occur when the environment and/or the nodes are heterogeneous. In this paper, we examine the network connectivity for heterogeneous multi-hop wireless networks and propose an algorithm to identify the connectivity of the network. We follow this with a numerical study of the connectivity in random topologies. Lastly, we propose two schemes for constructing additional links to enhance the connectivity of the network. Our proposed schemes identify the links to be improved or created via a cluster based approach.
    Communications (ICC), 2011 IEEE International Conference on; 07/2011
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    ABSTRACT: The inherent channel characteristics of impulse-based UWB networks affect the MAC layer performance significantly. Most previous studies on evaluating MAC protocols are based on prolonged simulations and do not account for the multiple access interference due to multipath delay spread. In this work, we develop CTU, an analytical framework for Capturing the Throughput dependencies in UWB networks, while taking into account the PHY layer effects. The key attributes of CTU are: 1) It is modular; it can be easily modified to provide a basis for evaluating a wide range of MAC protocols for impulse-based UWB networks. The only requirements are that the MAC protocol under study be based on time-hopping and the modulation scheme be pulse position modulation; these are common design decisions in UWB networks. 2) It considers the channel characteristics in addition to MAC layer effects; CTU correlates probabilistically the multipath delay profile of the channel with the packet error rate. We employ CTU to evaluate the performance of different generic medium access procedure. We compare the results with those from extensive simulations and show the high accuracy of CTU. We use CTU to assess the impact of various system parameters on the MAC layer performance; we make several interesting observations that are discussed in depth.
    IEEE Transactions on Mobile Computing 06/2011; · 2.40 Impact Factor
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    ABSTRACT: In this paper, we develop a performance modeling technique for analyzing the time varying network layer queueing behavior of multihop wireless networks with constant bit rate traffic. Our approach is a hybrid of fluid flow queueing modeling and a time varying connectivity matrix. Network queues are modeled using fluid-flow based differential equation models which are solved using numerical methods, while node mobility is modeled using deterministic or stochastic modeling of adjacency matrix elements. Numerical and simulation experiments show that the new approach can provide reasonably accurate results with significant improvements in the computation time compared to standard simulation tools.
    Performance Computing and Communications Conference (IPCCC), 2010 IEEE 29th International; 01/2011
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    A. Aksu, P. Krishnamurthy, D. Tipper, O. Ercetin
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    ABSTRACT: Recent work on cooperative communications has demonstrated benefits in terms of improving the reliability of links through diversity and/or increasing the reach of a link compared to a single transmitter transmitting to a single receiver (single-input single-output or SISO). In one form of cooperative transmissions, multiple nodes can act as virtual antenna elements and provide such benefits using space-time coding. In a multi-hop sensor network, a source node can make use of its neighbors as relays with itself to reach an intermediate node, which will use its neighbors and so on to reach the destination. For the same reliability of a link as SISO, the number of hops between a source and destination may be reduced using cooperative transmissions. However, the presence of malicious or compromised nodes in the network impacts the use of cooperative transmissions. Using more relays can increase the reach of a link, but if one or more relays are malicious, the transmission may fail. In this paper, we analyze this problem to understand the conditions under which cooperative transmissions may fare better or worse than SISO transmissions.
    Collaborative Computing: Networking, Applications and Worksharing (CollaborateCom), 2010 6th International Conference on; 11/2010 · 1.11 Impact Factor
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    ABSTRACT: In order to effectively deploy survivability techniques to improve the resilience of mobile ad hoc networks, one must be able to identify all the weak points of the network topology. The weak or critical points of the topology are those links and nodes whose failure results in partitioning of the network. Here we propose a new algorithm based on results from algebraic graph theory, that can find the critical points in the network for single and multiple failure cases. Utilizing this algorithm we present numerical results that examine how the number of critical points varies with nodal density. Secondly, we propose three localized topological control schemes to improve the network connectivity around critical points to lessen their importance and improve the network resilience. Numerical studies to evaluate the proposed schemes under node and link failure network conditions are presented.
    Design of Reliable Communication Networks, 2009. DRCN 2009. 7th International Workshop on; 11/2009
  • K. Panyim, T. Hayajneh, P. Krishnamurthy, D. Tipper
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    ABSTRACT: Jamming attacks are considered one of the most devastating attacks as they are difficult to prevent and sometimes hard to detect. In this paper we consider the impact of the placement and range of limited-range jammers on ad hoc networks. Limited range jammers are more difficult to detect as they use transmission powers similar to that of regular nodes (or perhaps even smaller transmit powers). The attacker can locate his jammer(s) randomly in the network. Alternatively, jammers can be placed at strategic locations. For instance, intuitively, this can be nodes with the highest traffic inputs/outputs (discovered by sensing the traffic flow in the network). Using OPNET, we perform extensive simulations to show how significant such strategically placed attacks can be compared to random placement of limited-range jammers on both TCP and UDP traffic.
    Local Computer Networks, 2009. LCN 2009. IEEE 34th Conference on; 11/2009
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    Chih-Kuang Lin, V. Zadorozhny, P. Krishnamurthy
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    ABSTRACT: We propose a novel framework that combines probabilistic transmission with Latin squares characteristics to tune channel access, meeting various demands in network performance (Energy vs. Delay). The proposed technique is decentralized, scalable, and has low overhead. We develop an analytical model to estimate the network performance and validate the benefits of the proposed framework via simulation-based experiments.
    Sensor Technologies and Applications, 2009. SENSORCOMM '09. Third International Conference on; 07/2009
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    T. Hayajneh, P. Krishnamurthy, D. Tipper, Taehoon Kim
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    ABSTRACT: Detecting malicious packet dropping is important in ad hoc networks to combat a variety of security attacks such as blackhole, greyhole, and wormhole attacks. We consider the detection of malicious packet drops in the presence of collisions and channel errors and describe a method to distinguish between these types. We present a simple analytical model for packet loss that helps a monitoring node to detect malicious packet dropping attacks. The model is analyzed and evaluated using simulations. The results show that it is possible to detect malicious packet drops in the presence of collisions and channel errors.
    Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
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    Chih-Kuang Lin, V. Zadorozhny, P. Krishnamurthy
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    ABSTRACT: We introduce a distributed grid-based scheduling access scheme that mitigates high data loss in data intensive sensor networks. Our approach alleviates transmission collisions by applying virtual grids and adopting Latin Squares Characteristic to time slot assignments. We demonstrate that our technique efficiently handles sensor mobility with acceptable data loss and low overhead.
    Mobile Data Management, 2008. MDM '08. 9th International Conference on; 05/2008
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    ABSTRACT: The inherent channel characteristics of impulse-based UWB networks affect the MAC layer performance significantly. Previous studies on evaluating MAC protocols are based on prolonged simulations, and do not account for the multiple-access interference that arises due to multipath delay spread. In this work, we develop CTU, an analytical framework that captures the performance of MAC protocols, while taking into account the underlying PHY layer effects. The key attributes that make CTU novel are: (a) It is modular and therefore flexible; it can be easily modified to provide a basis for characterizing and evaluating a wide range of MAC protocols designed for impulse-based UWB networks. The only requirements are that the MAC protocol under study be based on time-hopping, and the modulation scheme be pulse position modulation; these are common design decisions in most impulse based UWB networks, (b) It considers the channel characteristics in addition to MAC layer effects; in particular, CTU correlates probabilistically the multipath delay profile of the channel with the packet error rate. We employ CTU to evaluate the performance of a generic medium access procedure. We compare the results with those from extensive simulations and show the high accuracy of CTU. We use CTU to assess the impact of various system parameters on the MAC layer performance; we make several interesting observations that are discussed in depth.
    INFOCOM 2008. The 27th Conference on Computer Communications. IEEE; 05/2008
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    N. Swangmuang, P. Krishnamurthy
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    ABSTRACT: Analytical models to evaluate and predict "precision" performance of indoor positioning systems based on location fingerprinting are lacking. Such models can be used to improve the design of positioning systems, for example by eliminating some fingerprints and reducing the size of the location fingerprint database. In this paper, we develop a new analytical model that employs proximity graphs for predicting performance of indoor positioning systems based on location fingerprinting. The model allows computation of an approximate probability distribution of error distance given a location fingerprint database based on received signal strength and its associated statistics. The performance results from the simulation and the analytical model are found to be congruent. This model also allows us to perform analysis of the internal structure of location fingerprints. We employ the analysis of the internal structure to identify and eliminate unnecessary location fingerprints stored in the database, thereby saving on computation while performing location estimation.
    Pervasive Computing and Communications, 2008. PerCom 2008. Sixth Annual IEEE International Conference on; 04/2008
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    Chih-Kuang Lin, V. Zadorozhny, P. Krishnamurthy
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    ABSTRACT: In this paper, we introduce novel probabilistic transmission protocols for data intensive wireless sensor networks. The protocols combine a randomized transmission scheme with scheduling based on heuristics to alleviate network performance degradation due to excessive collisions and retransmissions. In particular, by utilizing local information about sensor neighbors, our protocols minimize collisions in areas with high channel contention. The simulation results of our hybrid techniques show improved performance of data delivery and reduced energy consumption compared to carrier-sensing based IEEE 802.15.4 CAP mode and time-division based DRAND.
    Advanced Information Networking and Applications Workshops, 2007, AINAW '07. 21st International Conference on; 06/2007
  • V. Zadorozhny, P. Krishnamurthy
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    ABSTRACT: Data Intensive Mobile Sensor Networks (DIMSNs) introduce a promising but still under-utilized technology. Meanwhile, there is a growing confidence that certain applications (Killer Apps) have a potential to create a sustained market for this technology. For example, a large team of cooperative mobile robots can be considered as a wireless sensornet composed of a number of mobile nodes most of which are powerconstrained. Such mobile robots can be deployed in conjunction with stationary sensor nodes to acquire and process data for surveillance and tracking, environmental monitoring for highly sensitive areas, or execute search and rescue operations. This example illustrates conceptual attractiveness of the DIMSN systems that generates interesting and appealing research challenges (e.g., intelligent mobile agents, semantically enriched and contextaware wireless services, smart network monitoring infrastructures). However, while providing excellent funding opportunities, those challenges often underestimate the GRAND DETERRENTS that make moves towards practical data-intensive mobile sensornets extremely difficult.
    Mobile Data Management, 2006. MDM 2006. 7th International Conference on; 06/2006
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    P. Keeratiwintakorn, P. Krishnamurthy
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    ABSTRACT: Due to broadcast nature of wireless radio transmission, security services are of paramount importance to protect information exchanged in a wireless network. However, providing security services increases the computation and hence energy consumption due to cryptographic algorithms. Energy tends to be a very limited resource for wireless devices operating on battery. Thus, energy efficient security services are necessary to operate limited wireless devices securely. In this paper, we propose Tunable Security Model (TSM) to minimize energy consumption while providing security services such that the user's security level requirement is satisfied. From our experiments in IEEE 802.11 wireless networks, it is shown that using TSM can save up to 8% energy for low-level security, and up to 43% energy for high-level security.
    Wireless Pervasive Computing, 2006 1st International Symposium on; 02/2006
  • V. Zadorozhny, D. Sharma, P. Krishnamurthy, A. Labrinidis
    01/2005;
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    P. Prasithsangaree, P. Krishnamurthy
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    ABSTRACT: Energy sayings are extremely important in wireless networks where devices operate using battery power. Security in wireless networks is also becoming crucial with the deployment of wireless local area networks in hot spot areas, organizations, hospitals and so on. Security protocols depend on energy consuming operations that occur in the cryptographic primitives used in the protocols. It has been observed that different cryptographic algorithms consume different amounts of energy. Also, the amount of energy consumed can depend on the key size, the number of cryptographic operational rounds, and packet or frame size. At the same time, the strength of a security protocol also depends on the key sizes and ciphers used to build it. We apply these results to protocols in wireless local area networks and study the tradeoffs between the security strengths of these protocols and the amount of energy consumed. For the analysis, we use distributions of packet sizes based on packets collected in home and campus wireless local area networks and measurements of the number of CPU cycles taken for cryptographic computation.
    Vehicular Technology Conference, 2004. VTC2004-Fall. 2004 IEEE 60th; 10/2004
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    K. Kaemarungsi, P. Krishnamurthy
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    ABSTRACT: Indoor positioning systems that make use of received signal strength based location fingerprints and existing wireless local area network infrastructure have recently been the focus for supporting location-based services in indoor and campus areas. A knowledge and understanding of the properties of the location fingerprint can assist in improving design of algorithms and deployment of position location systems. However, most existing research work ignores the radio signal properties. This paper investigates the properties of the received signal strength reported by IEEE 802.11b wireless network interface cards. Analyses of the data are performed to understand the underlying features of location fingerprints. The performance of an indoor positioning system in terms of its precision is compared using measured data and a Gaussian model to see how closely a Gaussian model may fit the measured data.
    Mobile and Ubiquitous Systems: Networking and Services, 2004. MOBIQUITOUS 2004. The First Annual International Conference on; 09/2004

Publication Stats

1k Citations
320 Downloads
3k Views
15.65 Total Impact Points

Institutions

  • 2009
    • NTNU Samfunnsforskning
      Nidaros, Sør-Trøndelag, Norway
  • 2000–2008
    • University of Pittsburgh
      • Telecommunications
      Pittsburgh, Pennsylvania, United States
  • 2006
    • King Mongkut's Institute of Technology Ladkrabang
      • Department of Electrical Engineering
      Bangkok, Bangkok, Thailand
  • 1999
    • University of Oulu
      Uleoborg, Oulu, Finland
  • 1997
    • Worcester Polytechnic Institute
      Worcester, Massachusetts, United States