Prashant Krishnamurthy

University of Pittsburgh, Pittsburgh, Pennsylvania, United States

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Publications (140)

  • Kaveh Pahlavan · Prashant Krishnamurthy · Yishuang Geng
    [Show abstract] [Hide abstract] ABSTRACT: Precise and accurate localization is one of the fundamental scientific and engineering technologies needed for the applications enabling the emergence of the Smart World. Localization techniques became popular with the global positioning system for outdoor applications, and in recent years, this has been followed by Wi-Fi localization for indoor applications. More recently, localization science and technology has progressed into in-body medical applications. Localization technologies have their own specific challenges depending on the application and environment, which are left for scientists and engineers to overcome. This paper presents the relation among different elements of the Smart World and corresponding localization technologies, classifies localization applications enabling smart devices and environments into logical categories, describes the complexity of the technologies used for localization, and introduces some of the open challenges for localization in the Smart World.
    Article · Dec 2015 · IEEE Access
  • Source
    Xin Wang · Prashant Krishnamurthy · David Tipper
    [Show abstract] [Hide abstract] ABSTRACT: Virtualization of wireless networks holds the promise of major gains in resource usage efficiency through spectrum/radio resources sharing. Unlike the case in wired networks, achieving high capacity, providing ef- fective isolation, and customization of the network requires intelligent configuration of wireless resources due to the effects of interference. In this paper, we focus on how to configure the “over-the-air” part of virtual wireless networks to enable simultaneous use of radio resources that overlap geographically. A configuration framework is proposed based on an infrastructure cellular network that employs fractional frequency reuse (FFR) and Multiple-input Multiple-output (MIMO) to combat interference. Multiple scenarios are examined that include various network sizes and base station distances. Five radio resources configuration cases are developed and investigated with each of these scenarios for a number of parameter settings (e.g., transmit power, MIMO degree). From the analysis of capacity data obtained from simulations, we observe some gen- eral trends in the aggregate spectral efficiency, and more importantly, a variety of tradeoffs between service providers (SPs) or virtual network operators. Based on these tradeoffs, we create configuration maps using which, a network resource manager can select specific network configurations (transmit power, MIMO, etc.) to meet the demand and capabilities of SPs and their subscribers.
    Full-text Article · Dec 2015 · Computer Communications
  • Xin Wang · Prashant Krishnamurthy · David Tipper
    Conference Paper · Oct 2015
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    Kunjie Xu · David Tipper · Yi Qian · Prashant Krishnamurthy
    [Show abstract] [Hide abstract] ABSTRACT: The performance of vehicular ad hoc networks (VANETs) is subject to frequent changes due to node mobility, so that nonstationary/transient network behavior always exists. In addition, safety applications in VANETs are very sensitive to the real-time performance of delay and packet delivery ratio. Although there are extensive studies on the steady-state performance analysis of vehicular networks, little work exists on evaluating their time varying behavior. In this paper, we develop a performance model to efficiently estimate the dynamic behavior of VANETs. In this work, vehicle’s transmission queue is modeled using fluid-flow based differential equations which are solved using numerical methods, while network hearing topology is modeled by a time varying adjacency matrix which can be determined from stochastic models, measurements or discrete event simulations. Numerical results illustrate that our performance model is able to promptly respond to the ongoing dynamic conditions of VANETs and provide reasonably accurate performance results.
    Full-text Article · Aug 2015 · IEEE Transactions on Vehicular Technology
  • Source
    Ayman Abdelhamid · Prashant Krishnamurthy · David Tipper
    [Show abstract] [Hide abstract] ABSTRACT: Cellular network virtualization is being considered as a key trend in future mobile networks towards improved resource utilization. However, virtualization scenarios need investigation to understand the considerations which should be taken into account when deploying virtualized wireless networks in practice. Towards this, we address the performance of a virtualized network in the presence of heterogeneous classes of traffic. In previous cellular network virtualization literature, both Realtime (RT) and Non-Realtime (NRT) traffic requests have been included without distinction. Both types are provisioned using the same algorithm for allocation of resources specified by the Network Scheduler [1]. However, different types of traffic have different characteristics [2], e.g., RT requests are delay sensitive but may need fixed bandwidth, and hence should be treated differently, especially when wireless channel conditions are factored into the scheduling. We recognize this difference and in this paper, we propose a new approach to improve scheduling of resources for RT and NRT traffic. In particular, we prioritize the traffic belonging to different virtual slices from all service providers (SP/VEs) at the Network Scheduler before allocating resources to different SP/VEs, i.e., we form a Virtual Prioritized Slice (VPS). The virtual prioritized slice is forwarded to the VPS scheduler to serve all RT requests first. Only after the RT traffic is scheduled, the NRT traffic is provisioned using proportional fairness (PF) scheduling. We show by simulation results that this new VPS approach helps outperform recently proposed resource allocation schemes.
    Full-text Conference Paper · Jun 2015
  • Konstantinos Pelechrinis · Prashant Krishnamurthy
    [Show abstract] [Hide abstract] ABSTRACT: Location-based social networks (LBSNs) have recently attracted a lot of attention due to the number of novel services they can offer. Prior work on analysis of LBSNs has mainly focused on the social part of these systems. Even though it is important to know how different the structure of the social graph of an LBSN is as compared to the friendship-based social networks (SNs), it raises the interesting question of what kinds of linkages exist between locations and friendships. The main problem we are investigating is to identify such connections between the social and the spatial planes of an LBSN. In particular, in this paper we focus on answering the following general question “What are the bonds between the social and spatial information in an LBSN and what are the metrics that can reveal them?” In order to tackle this problem, we employ the idea of affiliation networks. Analyzing a dataset from a specific LBSN (Gowalla), we make two main interesting observations; (i) the social network exhibits signs of homophily with regards to the “places/venues” visited by the users, and (ii) the “nature” of the visited venues that are common to users is powerful and informative in revealing the social/spatial linkages. We further show that the “entropy” of a venue can be used to better connect spatial information with the existing social relations. The entropy records the diversity of a venue and requires only location history of users (it does not need temporal history). Finally, we provide a simple application of our findings for predicting existing friendship relations based on users’ historic spatial information. We show that even with simple unsupervised or supervised learning models we can achieve significant improvement in prediction when we consider features that capture the “nature” of the venue as compared to the case where only apparent properties of the location history are used (e.g., number of common visits).
    Article · Jun 2015 · Computer Communications
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    Tae-Hoon Kim · David Tipper · Prashant Krishnamurthy
    [Show abstract] [Hide abstract] ABSTRACT: In a multi-hop wireless network, connectivity is determined by the link that is established by the receiving signal strength computed by subtracting the path loss from the transmission power. Two path loss models are commonly used in research, namely two-ray ground and shadow fading, which determine the receiving signal strength and affect the link quality. Link quality is one of the key factors that affect network performance. In general, network performance improves with better link quality in a wireless network. In this study, we measure the network connectivity and performance in a shadow fading path loss model, and our observation shows that both are severely degraded in this path loss model. To improve network performance, we propose power control schemes utilizing link quality to identify the set of nodes required to adjust the transmission power in order to improve the network throughput in both homogeneous and heterogeneous multi-hop wireless networks. Numerical studies to evaluate the proposed schemes are presented and compared.
    Full-text Article · Mar 2015
  • Prashant Krishnamurthy · Vladimir I. Zadorozhny
    Article · Mar 2015 · Information Systems
  • Anh Le · Konstantinos Pelechrinis · Prashant Krishnamurthy
    [Show abstract] [Hide abstract] ABSTRACT: Identifying and understanding the emerging patterns in user activity is an important step in designing and developing features for online social networks. With the explosive growth of user-generated data in such networks, the recorded user activities are no more sparse snapshots but are close to a live reflection of real life. This allows us to extract patterns which are tied to the time and space context of real life activity from such recorded data. In this work, we analyze two rich datasets obtained from two major location-based social networks (Foursquare and Gowalla) and show how users change their activity patterns depending on the country they currently reside on. We also compare activity patterns between foreign users from different countries and local users. The detailed results may not automatically generalize but this kind of analysis can be repeated on different datasets and the outcomes of such analyses can benefit social and behavioral scientists as well as designers of online social media.
    Article · Jun 2014
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    [Show abstract] [Hide abstract] ABSTRACT: One of the most crucial functionalities of cognitive radio networks is spectrum sensing. Completing this task in an accurate manner requires opportunistic spectrum access. Traditionally, sensing has been performed through energy detection by each individual secondary user. In order to increase accuracy, individual measurements are aggregated using different fusion functions. However, even though collaborative spectrum sensing can increase accuracy under benign settings, it is prone to falsification attacks, where malicious secondary users report fake sensings. Previous studies have designed trust (reputation) based systems to contain the effect of the adversaries, ignoring to a large extent the wireless channel irregularities when performing the computation. In this paper, we decouple the reasons behind a false sensing report and propose the Decoupling Trust and Capability Spectrum Sensing System (DTCS3). DTCS3 is a collaborative spectrum sensing system that takes into account both a secondary sensor node’s trust and its capability to sense the channel. Through thorough evaluations that consider a large variety of attack strategies, we show that by accounting for wireless induced effects while calculating the reporting trust of a secondary user, we can significantly improve the performance of a collaborative spectrum sensing system as compared to existing schemes in the literature. In particular, the true positive/negative rates can be improved by as much as 36%, while DTCS3 is able to track and respond to dynamic changes in the adversaries behavior.
    Full-text Conference Paper · Apr 2014
  • [Show abstract] [Hide abstract] ABSTRACT: The deployment of wireless networks for Internet connectivity has been rapid during the last decade. Following this trend, enterprises utilize multiple access points (APs) in order to provide wireless connectivity to authorized users within its premises. However, wireless networks are extremely vulnerable to PHY/MAC layer attacks such as jamming. A jammer transmits electromagnetic energy on the medium in order to either block the access to any legitimate transmitter or cause collisions at the receiver (or both). One of the most advanced jamming models is that of reactive jamming. A reactive jammer does not constantly transmit energy on the air, but only jams when a legitimate (target) packet is on the medium, aiming at its collision at the receiver. Previous studies have shown that reactive jamming is one of the most difficult attack models to detect. In this work, we propose a scheme that performs both detection and localization of a reactive jammer in an enterprise WiFi network. In brief, a reactive jammer can virtually increase the interference range of the target AP and thus increase the busy times of nearby APs that use the same frequency. By quantifying this effect we are able to accurately detect the presence of a reactive jammer and perform a coarse grain localization of the jammer. Our simulation results show that our scheme can achieve high true positives and low false positives simultaneously. In addition, our coarse grain localization scheme exhibits error on the order of the AP coverage area.
    Article · Dec 2013 · Computer Networks
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    Ke Zhang · Konstantinos Pelechrinis · Prashant Krishnamurthy
    [Show abstract] [Hide abstract] ABSTRACT: The proliferation of location-based social networks (LBSNs) has offered many conveniences to their participants, such as place recommendation, tracking of friends, monetary rewards from venues visited and a cheap way of advertisement for local businesses. However, users can misuse the offered features and the major threat for the service providers is that of fake check-ins. Users can easily manipulate the localization module of the underlying application and declare their presence in a counterfeit location. The incentives for these behaviors can be both earning monetary rewards as well as virtual rewards. Therefore, while fake check-ins driven from the former motive can cause monetary losses, those aiming in virtual rewards are also harmful. In particular, they can significantly degrade the services offered from the LBSN providers or third parties that make use of these data. In this paper, we propose and analyze a honeypot venue-based solution to tag users who are generating fake spatial information.
    Full-text Article · Nov 2013 · ACM SIGMOBILE Mobile Computing and Communications Review
  • Xin Wang · Prashant Krishnamurthy · David Tipper
    [Show abstract] [Hide abstract] ABSTRACT: Virtualizing wireless networks has the potential to improve resource usage efficiency (system capacity) through spectrum sharing while allowing for isolation between users and customization of applications {9}. In most work related to wireless network virtualization, the sharing of spectrum is considered at the level of chunks of frequency that do not interfere. Such spectrum sharing, where service provider SPA can use the spectrum allocated to SPB when SPB does not use it, results in multiplexing gains improving the resource usage (see for example, [12]). We argue that sharing radio resources that are a function of geography and signal strength, rather than slices of spectrum is also possible. When we consider sharing of radio resources, the transmit power, the interference, and the usage scenario (capabilities/needs of devices) become important in determining what can be shared. In this paper, the potential gain from sharing such radio resources while using MIMO for combating interference and exploiting spatial degrees of freedom is investigated in a two service provider collaboration scenario. The metric used is the capacity of the system (with a large cell and a small cell) as a function of separation distance, transmit power, cell range, and various MIMO settings. We show that radio resource sharing is feasible, but it has implications on isolation between users of different SPs and MIMO settings are an important factor.
    Conference Paper · Nov 2013
  • Korporn Panyim · Prashant Krishnamurthy · Anh Le
    [Show abstract] [Hide abstract] ABSTRACT: Key pre-distribution in nodes is often employed to address the problems of security with a single secret key and management with pair-wise secret keys in ad hoc and sensor networks. Sensor nodes can establish secure links with their neighbors through shared key predistributed before node deployment. At the ends of the spectrum of key pre-distribution schemes are random and deployment based key pre-distribution. Random key pre-distribution suffers from a smaller probability of sharing keys with neighbors. Deployment based key pre-distribution has a near 100% probability of sharing keys with immediate neighbors but not with nodes that are further away. When a network is jammed and jamming coping techniques (such as increase in power, use of directional antennas, and spatial retreats) are used, the nodes that are new neighbors due to changes in physical connectivity may or may not share keys with a given node. In this paper, we examine the impact of increasing transmission power to cope with jamming on secure connectivity (provided by different key predistribution schemes) in ad hoc and sensor networks.
    Conference Paper · Nov 2013
  • Korporn Panyim · Prashant Krishnamurthy · Anh Le
    [Show abstract] [Hide abstract] ABSTRACT: One of the first steps to provide security for sensor networks is to pre-distribute cryptographic keys among sensor nodes for bootstrapping security. Each node can use stored keys to establish secure links with surrounding neighbors once deployed in the sensor field. Jamming attacks can force a network to perform different coping techniques to avoid jamming in order to continue data transmission tasks. Performing such techniques may cause change in secure connectivity of the network. In this paper, we study the impact of jamming attacks on secure connectivity (provided by different key predistribution schemes) when the network uses directional antennas to cope with jamming. Directional transmissions can perhaps create more links to nodes that are further away (within the beamforming direction). However, a node may also lose some links to nearby nodes that are not within the main beam or strong side beam.We investigate changes in secure connectivity (provided by different key predistribution schemes) when nodes transmit with directional antennas to cope with jamming attacks.
    Conference Paper · Nov 2013
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    Prashant Krishnamurthy · Martin BH Weiss · David Tipper
    [Show abstract] [Hide abstract] 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 fine-grained 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.
    Full-text Conference Paper · Aug 2013
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    Tae-Hoon Kim · David Tipper · Prashant Krishnamurthy
    [Show abstract] [Hide abstract] ABSTRACT: Maintaining connectivity is essential in multi-hop wireless networks since the network topology cannot be pre-determined due to mobility and environmental effects. To maintain the connectivity, a critical point in the network topology should be identified where the critical point is the link or node that partitions the network when it fails. In this paper, we propose a new critical point identification algorithm and also present numerical results that compare the critical points of the network and H-hop sub-network illustrating how effectively sub-network information can detect the network-wide critical points. Then, we propose two localized topological control resilient schemes that can be applied to both global and local H-hop sub-network critical points to improve the network connectivity and the network resilience. Numerical studies to evaluate the proposed schemes under node and link failure network conditions show that our proposed resilient schemes increase the probability of the network being connected in variety of link and node failure conditions.
    Full-text Article · Jun 2013
  • Prashant Krishnamurthy · Konstantinos Pelechrinis
    Article · Jun 2013
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    Xin Wang · Prashant Krishnamurthy · David Tipper
    [Show abstract] [Hide abstract] 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.
    Full-text Conference Paper · May 2013
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    Xin Wang · Prashant Krishnamurthy · David Tipper
    [Show abstract] [Hide abstract] 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 oc-curred 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.
    Full-text Conference Paper · Jan 2013

Publication Stats

3k Citations

Institutions

  • 2000-2013
    • University of Pittsburgh
      • • School of Information Sciences
      • • Telecommunications
      Pittsburgh, Pennsylvania, United States
  • 2012
    • Trinity College Dublin
      Dublin, Leinster, Ireland
  • 2009
    • Norwegian University of Science and Technology
      Nidaros, Sør-Trøndelag, Norway
  • 1999
    • University of Oulu
      • Centre for Wireless Communications (CWC)
      Uleoborg, Oulu, Finland
  • 1998
    • Worcester Polytechnic Institute
      • Department of Electrical and Computer Engineering
      Worcester, Massachusetts, United States