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Utilize Wireless InSite's UTD and MWFDTD models for accurate RF predictions over irregular terrains. Import and overlay images, analyze terrain profiles, and run simulations. Enhance results with Z-Scaling and GeoTiff overlays.
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Irregular Terrain Overview • Wireless InSite uses UTD and moving window FDTD (MWFDTD) calculation models on irregular terrains • It is usually assumed that all significant ray paths are in a single vertical plane passing through the Tx and Rx • Remcom’s UTD model includes multiple diffractions and reflections in this plane • More accurate than Longley-Rice and Knife-edge models • Linearizing terrain preprocesses the terrain to remove unneeded points in the terrain profile to improve speed and accuracy of the UTD solution • MWFDTD uses the Finite Difference Time Domain method to solve Maxwell’s equations directly on original terrain profile • A full 3-D model is also available
Propagation over Irregular Terrain Accurate UTD model for irregular terrain Import images and overlay predictions
Simple Irregular Terrain Example • Comparing to Institute of Telecommunication Sciences (ITS) measurements made near Boulder, CO • Measurements were taken from 230 to 9190 MHz • Measurements were made with one receiving location and taken at several heights (1 – 13 meters) • Horizontally polarized antennas • Transmitter was moved to different locations and transmitted at a height of 6.6 meters
Running in Wireless InSite • Import terrain • Import GeoTiffs • Create waveform • Create Antenna • Place transmitters and receivers • Create a study area • Select output • Run calculation • View results
Importing DEM Terrain • USGS DEM data can be downloaded freely on the world wide web • Specify the northeast and southwest corners of area to import • Provide names of input files (e.g. greeley-w.dem) • Select material for the imported terrain
Z-Scaling • Helps visually discern differing elevations in relatively flat terrain • Does not effect calculations • Everything in the project view is scaled when turned on
Z-Scaling Example Normal Scaled
Importing GeoTiff Images • Useful for referencing position of features, transmitters, receivers and output • Specify northeast and southwest corners of area to import
Placing Transmitters and Receiver Points • Transmitters placed by longitude and latitude positions • Used edit position option to place points exactly • Longitude and latitude of transmitters were given in ITS data
Creating Vertical Route of Receivers • Similar to creating a horizontal receiver route • Both control points have the same longitude and latitude coordinates but have different heights above terrain • Best to place first point slightly above terrain
Creating Vertical Plane Study Area • Specify ray spacing, number of reflections, number of diffractions and linearization options • Increasing the allowed terrain error removed more points from the terrain profile
Predicted and Measured Path Loss for Profile R1-10-T2-A at 410 MHz
Predicted and Measured Path Loss for Profile R1-10-T4 at 410 MHz
Predicted and Measured Path Loss for Profile R1-20-T7 at 410 MHz
Creating Vertical Surface of Receivers • Similar to creating route of receivers • Has the parameters of a route of receivers and additional parameters for height and vertical spacing
Irregular Terrain Simulations Using MWFDTD • Apply full wave 2-D Finite Difference Time Domain (FDTD) method for lossy dielectric media • Use pulsed excitation of transmitting antenna • Obtain narrowband results by application of Fourier Transform to time domain FDTD output • Apply FDTD mesh only to portion of propagation path which contains significant pulse energy • Move FDTD mesh along the propagation path with the pulse-Moving Window FDTD (MWFDTD) • Change terrain and foliage in mesh at leading/trailing edges as mesh window moves
Comparison of MWFDTD Predictions to ITS Path Loss Measurements • Set up the project in the same way as the vertical plane calculations • Choose moving window FDTD propagation model in the study area properties window • Can adjust cells per wavelength and size of the moving window
Modeling of Foliage • Foliage is modeled as a collection of randomly oriented scatterers (leaves, branches) • R. H. Lang, A. Schneider, S. Seker, F. J. Altman, “UHF radiowave propagation through forest,” Technical report CECOM-81-0136-4, U. S. Army Communication-Electronics Command, Sept. 1982 • S. A. Torrico, H. L. Bertoni, R. H. Lang, “Modeling tree effects on path loss in a residential environment,” IEEE Trans. Antennas Propagat. vol 46, pp. 872-880, 1998 • Bio-Physical Inputs: size of scatterers, orientations, density, dielectric properties • Yields an effective permittivity for the foliage which is frequency and polarization dependent.
Modeling of Foliage (2) • Wavelength >> Leaves, Branches • Effective complex permittivity determines forward scattered field, incoherently scattered field ignored • Field decays exponentially over short distances • Propagation over large distances via so-called lateral wave (Power 1/R4)
Foliage Materials • Foliage features can be added to a project either manually or by importing geo-referenced foliage information from publicly available databases • Set the foliage properties by choosing the material type • InSite includes a number of common types of foliage • Grass • Dense Deciduous Forest In Leaf: type=biophysical • Sparse Deciduous Forest In Leaf • Dense Deciduous Forest Out of Leaf • Sparse Deciduous Forest Out of Leaf • Dense Pine Forest • Sparse Pine Forest
A flat ground about 1 km in length Two large groves of trees about 250-300 meters across Trees are 20 m tall Sparse foliage material Frequency = 200 MHz Transmitter is 10 m high, vertically polarized Calculate received power on a vertical plane and along horizontal and vertical routes Transmitter MWFDTD Example:Propagation Through Foliage
Trees Trees MWFDTD Example:Propagation Through Foliage (3) • Received power along a horizontal route, 2 m above the ground
