ECE6110 -PhysicalModel - MeasurementBased Physical Layer...

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Unformatted text preview: MeasurementBased Physical Layer Modeling for Wireless Network Simulations Dheeraj Reddy 1 George F. Riley 2 1 Intel Research Hillsboro, OR { } 2 College of Engineering Department of ECE Georgia Institute of Technology Atlanta, GA 30332-0250 { riley } Abstract Simulation methods have become an integral part of almost all aspects of networking research and particularly in the area of wireless networks. Any new protocol or methodology that is proposed for wireless networks almost always will be demonstrated using simula-tions. However, there is little evidence that existing models of physical layer signal propagation and signal strength calculations produce realistic or meaningful results. Indeed, there have been a number of empirical studies that have shown little predictability in measured signal strength and packet receipt probability for deployed networks. Common assumptions used in simulation models about the behavior of the wireless signal have been shown to often be invalid. These prior works motivated us to design a stochastic model for wireless signal propagation in our GTNetS simulator. Our model is based on a detailed empirical measurement study and uses random variations to produce more realistic behavior for wireless packet transmissions and reception modeling. I. INTRODUCTION AND RELATED WORK Network simulations have been used extensively to evaluate the performance of wireless networks. With the advent of Wireless Ad-Hoc networks and Sensor networks, simulation has become a virtual necessity because of the scale and complexity of a given network. There are several popular network simulators [1], [2], [3], [4], [5] used in the research community as well as the industry. Almost all of them include protocol models of the IEEE 802.11 specifications in considerable detail. However, most of these have fairly theoretical models of wireless PHY layer. In fact, many simulators provide a simple free space model in which the signal loss is a function of the inverse square of the distance (1 /r 2 ) . The two such models which are most prevalent are the Friis free-space model and the Two-ray ground reflection model. The Friis free space model assumes a flat ideal terrain without any obstacles. It ignores fading and shadowing effects. The Two-ray ground reflection model , on the other hand, considers both the direct and the ground-reflected propagation paths between the transmitter and the receiver. The latter has been shown to be reasonably accurate in the case of predicting signal-strengths over distances of several kilometers when the transmitter power is large and the transmitter is mounted at a large elevation. In contrast, wireless links in WLANs use low power transmitters and the distances involved are hardly more than a couple of hundred meters. Recently, shadowing models [6] have also been incorporated into some simulators [1]. These models account for obstruc-tions in indoor scenarios and outdoor shadowing via a...
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This note was uploaded on 10/18/2010 for the course ECE 6110 taught by Professor Staff during the Fall '08 term at Georgia Institute of Technology.

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ECE6110 -PhysicalModel - MeasurementBased Physical Layer...

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