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Decreasing the Artificial Attenuation of the RCSIM Radio Channel Simulation

Software

Abigail SnyderResearch Alliance in Math and Science

Computational Sciences and EngineeringMentor: Jim Nutaro, PhD

August 13, 2008Oak Ridge, Tennessee

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Outline Introduction Background Research Objective Implementation Results Conclusions Future Research

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IntroductionOak Ridge National Laboratory is currently improving the accuracy of the radio channel simulation software RCSIM by reformulating the scattering junctions that it uses to propagate a simulated radio wave

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Background Radio waves naturally experience path loss

(attenuation) as they move outward from signal source

Certain level of artificial attenuation in computer simulations of radio wave propagation

Goal to increase overall accuracy of RCSIM software in part by decreasing artificial attenuation

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Background Radio waves (all waves) propagate in the

shape of a sphere Using Transmission Line Matrix method

(TLM) signal is propagated forward and backward along set geometry at scattering junctions to specific number of neighboring nodes (based on geometry chosen) according to:

2/(Number of Directions)*(State of Node)-InputoppN

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Background Three geometries for scattering junction

were compared to the original rectilinear scheme:– tetrahedral– cubic-close packed– octahedral

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Background Ideally, the more directions (the more

neighboring nodes) to a displaced node, the more sphere-like propagation will be

Sphere-like propagation is denoted by lack (or at least decrease from rectilinear scheme) of directional dependencies in propagation

From Nutaro: An Event Driven Simplified TLM Method for Predicting Path-Loss

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Background

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Research ObjectiveFind a geometry that will improve the overall accuracy of the RCSIM radio channel simulation software by decreasing the artificial attenuation from geometry by more closely mirroring the sphere shape of actual radio wave propagation

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Implementation

Determine schemes to find neighboring nodes to displaced node for each geometry

Marshmallows = Science

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Implementation Build free-space simulators for each

geometry using C++ Choose points for each direction from the

displacement (100, 110, 111) Compare maximum states for each data point

to determine error values

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Results

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ResultsRectilinear

-50

0

50

100

150

200

250

300

350

400

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

Distance

1/St

ate

= 1/

v

Direction 100 Direction 110 Direction 111Linear (Direction 100) Linear (Direction 110) Linear (Direction 111)

Tetrahedral

-100

0

100

200

300

400

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

Distance

1/St

ate

= 1/

v

Direction 100 Direction 110 Direction 111Linear (Direction 100) Linear (Direction 110) Linear (Direction 111)

Cubic Close Packed

-200

20406080

100120140

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

Distance

1/St

ate

= 1/

v

Direction 100 Direction 110 Direction 111Linear (Direction 100) Linear (Direction 110) Linear (Direction 111)

Octahedral

0

50

100

150

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

Distance

1/St

ate

= 1/

v

Direction 100 Direciton 110 Direction 111Linear (Direction 100) Linear (Direciton 110) Linear (Direction 111)

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Conclusions Error value for the tetrahedral scheme is

better than rectilinear scheme, but directional dependencies too great for practical use

Error value for octahedral scheme is best, though experiences inaccuracies in111 direction as edge is approached

Error for cubic-close packed scheme is close enough to octahedral to make it possible to implement as well, but inconsistent data presents problems

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Conclusions Goal was to determine scheme for scattering

junctions that would more closely imitate sphere of wave propagation than current rectilinear scheme

Initially believed would be cubic-close packed scheme since has most directions/neighboring nodes using TLM method (12 compared to six for rectilinear, four for tetrahedral and eight for octahedral)

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Conclusions In reality, the octahedral scheme provided

better results This is most likely because octahedral

scheme provides most directions while still maintaining a square, computer-friendly geometry

Regular Grid Cubic-Close Packed Grid

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Future Research

Implement the octahedral scheme into RCSIM software to determine the overall improvement to results

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Acknowledgments

The Research Alliance in Math and Science program is sponsored by the Office of Advanced Scientific Computing Research, U.S. Department of Energy.

The work was performed at the Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC under Contract No. De-AC05-00OR22725. This work has been authored by a contractor of the U.S. Government, accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.Thanks to Jim Nutaro, Kara Kruse and Richard Ward for their roles as mentors. Thanks to Debbie McCoy and Jacki Isaacs.

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Questions

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QUESTIONS?