Irregular Terrain and Foliage Applications

1. Irregular Terrain and Foliage Applications

2. 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

3. Propagation over Irregular Terrain Accurate UTD model for irregular terrain Import images and overlay predictions

4. 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

5. 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

6. 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

7. 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

8. Z-Scaling Example Normal Scaled

9. Importing GeoTiff Images • Useful for referencing position of features, transmitters, receivers and output • Specify northeast and southwest corners of area to import

10. Terrain with GeoTIFF Overlay

11. 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

12. 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

13. Project with Transmitters and Receivers

14. Project with Transmitters and Receivers (2)

15. Project with Transmitters and Receivers (3)

16. 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

17. Graph of Original Terrain Profile and Linearized Profile

18. Predicted and Measured Path Loss for Profile R1-10-T2-A at 410 MHz

19. Predicted and Measured Path Loss for Profile R1-10-T4 at 410 MHz

20. Predicted and Measured Path Loss for Profile R1-20-T7 at 410 MHz

21. Terrain ExamplePredicting Path Loss vs. Receiver Height

22. Terrain ExampleVertical Plane Coverage

23. 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

24. Viewing Vertical Surface Output

25. 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

26. Illustration of MWFDTD Method

27. 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

28. Terrain profile R1-010-T5-O

29. R1-010-T4-O Results

30. 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.

31. 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)

32. 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

33. Change Foliage Properties Using the Biophysical Parameters

34. Change Foliage Properties by Setting Attenuation

35. 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

36. MWFDTD Example:Propagation Through Foliage (2)

37. Trees Trees MWFDTD Example:Propagation Through Foliage (3) • Received power along a horizontal route, 2 m above the ground

38. Foliage Cover on Irregular Terrain