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EDAM - The Effective Directivity Antenna Model

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EDAM is a model for the way environmental effects alter the effective gain of a directional antenna. It is well understood that the environment effects radio propagation, and a great variety of path loss and fading models attempt to capture these effects. What is less appreciated is that these effects interact with the directional effects of antennas (e.g. by attenuating lobes or creating good non-straight-line paths) so that considering antenna gain and propagation loss as orthogonal components of signal loss leads to incorrect results.

Rather than attempting to model every propagation path and antenna lobe in a specific environment, EDAM provides a randomized model which tends to produce directional effects similar in kind and quantity to those measured in actual environments. EDAM is parameterized by a small number of constants which characterize a type of environment: We provide fitted ranges of values for open outdoor, urban outdoor, line-of-sight indoor, and non-line-of-sight indoor environments, but you can measure and supply constants which more accurately describe your environment if you so choose.

Understanding Directionality Error

Variation in directional effect on signal strength for an 18dBi patch antenna.  "Reference" indicates the expected value.
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Variation in directional effect on signal strength for an 18dBi patch antenna. "Reference" indicates the expected value.

We distinguish between two concepts here: By directional gain, we mean the effect of the antenna itself on signal strength (or reception) as a function of the direction relative to the antenna. By effective directivity, we mean the variation in signal strength (or reception) as a function of the direction relative to the antenna between two specific points in a real environment. The difference is that effective directivity includes, in addition to the antenna itself, all aspects of the environment which cause the path loss to vary as a function of the antenna's orientation. In a world where antenna effects and propagation loss were orthogonal issues (and this is the world assumed in most simulators and analysis) effective directivity and directional gain would be identical.

The picture at right shows the effective directivity of a patch panel antenna measured in several environments along with an estimate of the true gain, labeled "Reference." The difference between the measured values and the reference line is the error in the traditional orthogonal model. EDAM generates stochastic models of this error which are statistically similar to what is actually observed.

How EDAM works

EDAM process schematic
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EDAM process schematic

The basic principles of EDAM are quite simple. We find that the error, or offset between the gain and the effective directivity are generally consistent between adjacent angles and are strongly correlated with both the type of environment and gain of the antenna. The offset is estimated by dividing the azimuth into contiguous partitions, each of which is modeled by a random variable where the distribution is determined by the environment and the antenna model. The number of partitions, as well as the parameters of the distributions, are empirically fitted.

The EDAM algorithms (illustrated somewhat ambiguously at right) are roughly as follows:

  • At the beginning of each random trial (Algorithm a):
  1. Produce a partition of the azimuth at every node.
  2. For each node, for each partition, do:
    1. Compute a random offset drawing from the appropriate distribution
  • For each signal (Algorithm b):
  1. Estimate effective directivity (at both the sender and receiver) as the directional gain less the direction-specific offset.
  2. Use effective directivity estimate rather than simple gain, in addition to appropriate fading and path-loss models, to estimate the received signal strength.
  • As with any stochastic simulation, multiple repeated trials are necessary!

Implementations

There are currently two implementations of EDAM: The first is as a patch for the QualNet simulator, version 4.5.1. This is a cleaned-up version of the code used in "The Impact of Directional Antenna Models on Simulation Accuracy" below. It has consequently been somewhat tested, but the algorithmic logic is entangled with QualNet's processing. The second is a pure Ruby implementation, which is less heavily tested but much clearer.

  • QualNet Patch: qualnet-4.5.1-edam-0.1.patch in Caleb's QualNet Hacks
  • Ruby script: EDAM_in_Ruby. Note that this implementation is intended for computing a single signal strength estimate, so the notion of maintaining offset estimates between samples in the course of a simulation is lost.

About Us

EDAM was developed by Eric Anderson and Caleb Phillips. The original QualNet implementation was done by Gary Yee. The faculty advisors are Douglas Sicker and Dirk Grunwald.

References

The EDAM Model

Journal:

Eric Anderson, Caleb Phillips, Douglas Sicker, Dirk Grunwald - Modeling Environmental Effects on Directionality in Wireless Networks
Mathematical and Computer Modeling , @2010
Bibtex
Author : Eric Anderson, Caleb Phillips, Douglas Sicker, Dirk Grunwald
Title : Modeling Environmental Effects on Directionality in Wireless Networks
In : Mathematical and Computer Modeling -
Adress :
Date : @2010
Abstract

Workshop:

Eric Anderson, Caleb Phillips, Douglas Sicker, Dirk Grunwald - Modeling Environmental Effects on Directionality in Wireless Networks
5th International workshop on Wireless Network Measurements (WiNMee) , June, 2009
Bibtex
Author : Eric Anderson, Caleb Phillips, Douglas Sicker, Dirk Grunwald
Title : Modeling Environmental Effects on Directionality in Wireless Networks
In : 5th International workshop on Wireless Network Measurements (WiNMee) -
Adress :
Date : June 2009

Technical report:

Eric W. Anderson, Caleb T. Phillips, Dirk Grunwald, Douglas Sicker - Modeling Environmental Effects on Directionality in Wireless Networks
Tech Report, Department of Computer Science, University of Colorado at Boulder (CU-CS-1044-08), July, 2008
Bibtex
Author : Eric W. Anderson, Caleb T. Phillips, Dirk Grunwald, Douglas Sicker
Title : Modeling Environmental Effects on Directionality in Wireless Networks
In : Tech Report, Department of Computer Science, University of Colorado at Boulder -
Adress :
Date : July 2008
Abstract

Evaluation of EDAM as a simulation tool

Conference:

Eric Anderson, Gary Yee, Caleb Phillips, Dirk Grunwald, Douglas Sicker - The Impact of Directional Antenna Models on Simulation Accuracy
7th Intl. Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt) , June, 2009
Bibtex
Author : Eric Anderson, Gary Yee, Caleb Phillips, Dirk Grunwald, Douglas Sicker
Title : The Impact of Directional Antenna Models on Simulation Accuracy
In : 7th Intl. Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt) -
Adress :
Date : June 2009
Abstract

Related work by others

Modeling Environmental Effects

Greenstein, L. J., Erceg, V. - Gain reductions due to scatter on wireless paths with directional antennas
Communications Letters, IEEE 3(6):169--171, 1999
Bibtex
Author : Greenstein, L. J., Erceg, V.
Title : Gain reductions due to scatter on wireless paths with directional antennas
In : Communications Letters, IEEE -
Adress :
Date : 1999
Abstract

Using Directional Antennas in Challenging Environments

Marc Blanco, Ravi Kokku, Kishore Ramachandran, Sampath Rangarajan, Karthik Sundaresan - On the Effectiveness of Switched Beam Antennas in Indoor Environments
Passive and Active Network Measurement 4979/2008:122 -- 131, 2008
Bibtex
Author : Marc Blanco, Ravi Kokku, Kishore Ramachandran, Sampath Rangarajan, Karthik Sundaresan
Title : On the Effectiveness of Switched Beam Antennas in Indoor Environments
In : Passive and Active Network Measurement -
Adress :
Date : 2008
Abstract

Xi Liu, Anmol Sheth, Michael Kaminski, Konstantina Papagiannaki, Srinivasan Seshan, Peter Steenkiste - DIRC: Increasing Indoor Wireless Capacity Using Directional Antennas
Proc. SIGCOMM 2009 pp. 171 -- 182, Barcelona, Spain, August, 2009
Bibtex
Author : Xi Liu, Anmol Sheth, Michael Kaminski, Konstantina Papagiannaki, Srinivasan Seshan, Peter Steenkiste
Title : DIRC: Increasing Indoor Wireless Capacity Using Directional Antennas
In : Proc. SIGCOMM 2009 -
Adress : Barcelona, Spain
Date : August 2009