Ehsan Nourbakhsh

University of Texas at Dallas, Richardson, Texas, United States

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Publications (11)0 Total impact

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    ABSTRACT: Repeatability, isolation and accuracy are the most desired factors while testing wireless devices. However, they cannot be guaranteed by traditional drive tests. Channel emulators play a major role in filling these gaps in testing. In this pa-per we present an efficient channel emulator which is better than existing commercial products in terms of cost, remote access, support for complex network topologies and scala-bility. We present the hardware and software architecture of our channel emulator and describe the experiments we conducted to evaluate its performance against a commercial channel emulator.
    Proceedings of ACM MSWiM, Montreal, Canada; 09/2014
  • Ehsan Nourbakhsh · Ravi Prakash
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    ABSTRACT: Deployment of Smart Grid networks throughout cities introduces a realistic scenario for a large scale sensor network. Smart Meters create a wireless mesh network for receiving commands and sending metering reports back to provider company. The challenges of reliable and timely communication call for a fresh review of the well studied topic of Wireless Sensor Networks (WSN). We provide a centralized MAC solution for data collection, ATR-MAC, that relaxes requirements in general purpose WSNs, but emphasizes on difficulties a Smart Metering deployment will face. ATR-MAC considers variable reuse distances for minimizing propagation delay. It also increases efficiency of collection deadline instead of energy efficiency, a common concern of general-purpose WSN MAC protocols. We provide time and buffer size analysis of our algorithm, prove its correctness and show experimental results using implementation on a testbed.
    Proceedings of the 16th ACM international conference on Modeling, analysis & simulation of wireless and mobile systems; 11/2013
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    Ravi Prakash · Ehsan Nourbakhsh
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    ABSTRACT: In several sensing applications the parameter being sensed exhibits a high spatial correlation. For example, if the temperature of a region is being monitored, there are distinct hot and cold spots. The area close to the hot spots is usually warmer than average, with a temperature gradient between the hot and cold spots. We exploit this correlation of sensor data to form a forest of logical trees, with the trees collectively spanning all the sensor nodes. The root of a tree corresponds to a sensor reporting the local peak value. The tree nodes represent the value gradient: each node's sensed value is smaller than that of its parent, and greater than that of its children. GrAFS provides a mechanism to maintain some information at the local peaks and the sink. Using this information the sink can answer several queries either directly, or by probing the region of the sensor field that holds the answer. Thus, queries can be answered in a time and/or bandwidth efficient manner. The GrAFS approach to data aggregation can easily adapt to changes in the spatial distribution of sensed values, and also cope with message losses and sensor node failures. Implementation on MICA2 motes and simulation experiments conducted using TinyOS quantify the performance of GrAFS.
    International Conference on Parallel Processing, ICPP 2011, Taipei, Taiwan, September 13-16, 2011; 01/2011
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    ABSTRACT: This article discusses lessons learned from use of our publicly available wireless networking testbed, assert[1]. In [1] we discussed the design and implementation phase of a testbed based on a set of propositions. By opening the testbed to users not familiar with underlying architecture of assert, we put these propositions to the test. While fidelity of the testbed is a major challenge for developers, users assume the fidelity as a given and look for ease of use comparable with a simulator. We list the main demands by users of our testbed and the way we addressed these demands during an enhancement phase.
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    ABSTRACT: As wireless networks become a critical part of home, business and industrial infrastructure, researchers will meet these demands by providing new networking technologies. However, these technologies must be tested before they can be released for mainstream use. We identify the key design considerations for a wireless networking testbed as a) accuracy b) controllability c) mobility d) repeatability e) cost effectiveness f) data collection g) resource sharing h) multi-nodal capability i) scalability. In this paper we portray how we have used coaxial cables and our custom hardware of RF switches and programmable attenuators to create Advanced wireleSS Environment Research Testbed (assert), addressing the above requirements. assert supports various types of wireless devices, providing researchers in academia and industry with the necessary experimentation tools to validate their designed protocols and devices.
    Testbeds and Research Infrastructures. Development of Networks and Communities - 6th International ICST Conference, TridentCom 2010, Berlin, Germany, May 18-20, 2010, Revised Selected Papers; 01/2010
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    ABSTRACT: Software simulation has often been used to evaluate proposed protocols for wireless devices. Simulation allows for rapid development and testing, but does not provide a realistic RF environment. To compensate for this, field experiments are performed. However, problems encountered during field experiments can be difficult to locate and correcting problems on-site can be time-consuming. Emulations attempt to provide the advantages of simulation and field experiments without the suffering the disadvantages of both. This demo provides an overview of the hardware, software, and emulation capabilities of ASSERT, an emulation testbed.
    Proceedings of the 7th ACM Conference on Embedded Networked Sensor Systems; 11/2009
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    R. Prakash · E. Nourbakhsh · K. Sahu
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    ABSTRACT: Application-specific data aggregation can play a significant role in energy-efficient operation of wireless sensor networks. Existing aggregation techniques rely heavily on the routing protocol to build shortest paths to route node measurements to the base station and are limited in the types of supported queries. We propose an aggregation scheme that utilizes the inherent information gradients present in the network. The query is directed to the source of information, resulting in better load sharing in the network. We support a variety of queries ranging from simple maximum, minimum or average of the readings of sensor nodes to more complex quantile queries such as k highest values or k<sup>th</sup> highest value through a generic query algorithm. The query algorithm shifts the computation to the querying agent, thus eliminating any in-network aggregation.
    Communication, Control, and Computing, 2009. Allerton 2009. 47th Annual Allerton Conference on; 11/2009
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    R. Burchfield · E. Nourbakhsh · J. Dix · K. Sahu · S. Venkatesan · R. Prakash
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    ABSTRACT: Most researchers conduct wireless networking experiments in their laboratory or similar indoor environments. Such environments are veritable RF jungles, especially when we consider the ISM bands. In this paper we examine and test several common explicit and implicit assumptions that researchers tend to make about the wireless environment. Although these assumptions are acknowledged by most researchers, the extent of their impact is often underestimated. We find that because the environment is always in flux, it is almost impossible to reproduce the results of an experiment. Hence, there is a high risk of misinterpreting the data obtained from such experiments. Through this paper we try to caution experimenters against such risky assumptions when they venture into the RF jungle. After a successful proof-of-concept experiment, we advocate the use of wireless networking testbeds that provide experimenters better control over the RF environment by using coaxial cables, programmable attenuators and power dividers/combiners.
    Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
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    ABSTRACT: Software simulation has often been used to evaluate pro-posed protocols for wireless devices. Simulation allows for rapid development and testing, but does not provide a real-istic RF environment. To compensate for this, field experi-ments are performed. However, problems encountered dur-ing field experiments can be difficult to locate and correct-ing problems on-site can be time-consuming. Emulations attempt to provide the advantages of simulation and field ex-periments without the suffering the disadvantages of both. This demo provides an overview of the hardware, software, and emulation capabilities of ASSERT, an emulation testbed.
  • Proceedings of the 7th International Conference on Embedded Networked Sensor Systems, SenSys 2009, Berkeley, California, USA, November 4-6, 2009; 01/2009
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    Proceedings of IEEE International Conference on Communications, ICC 2009, Dresden, Germany, 14-18 June 2009; 01/2009