How to Model Propagation Loss in an Urban Environment

In the following tutorial, you will analyze communications between a patrol vehicle and a command post in a city environment. The analysis will include:

The following frequency and STK object settings are recommended or required for analysis with the Urban Propagation Wireless InSite Real Time 2.5 model:

The sample shapefile, Skopje.shp, used in this tutorial is provided by East View Cartographic (EVC).

Note: Licenses required for this tutorial are STK/Communications, Urban Propagation Extension for STK/Communications, STK Professional Edition, and STK/Coverage. An STK/Terrain, Imagery and Maps (STK/TIM) license is not required for this tutorial, but is required to include Bing Maps in the scenario.

Create a Scenario

Create a scenario for the following analysis period:

Start Time: 19 Oct 2009 15:10:00.000 UTCG
Stop Time: 19 Oct 2009 15:12:00.000 UTCG

Add Terrain to your Scenario

Terrain added to the scenario properties will be used by the Urban Propagation Extension for analysis. For more information on using terrain in your analysis, see Terrain. To add the sample terrain file to the scenario:

  1. Go to the Scenario's Basic->Terrain properties page.
  2. Click Add, select AGI Terrain File (pdtt) as the file type, and browse to <STK install area>\Help\STK\samples\SRTM_Skopje.pdtt.
  3. Make sure that Use is enabled for the terrain file and click Apply. The SRTM_Skopje.pdtt terrain file will be used in the urban analysis.
  4. Go to the Scenario's 3D Graphics->Global Attributes properties page and select Draw On Terrain when Available. Click OK.
  5. Add the terrain file to the 3D Graphics window:
    1. Select the 3D Graphics window.
    2. Click to open the Globe Manager window.
    3. From the Globe Manager toolbar, click to display the Open Terrain and Imagery Data window.
    4. Browse to <STK install area>\Help\STK\samples\.
    5. Select SRTM_Skopje.pdtt and click Open. The file will be displayed in the Globe Manager window.

Apply the Urban Propagation Model

  1. Go to the Scenario's RF->Environment properties page. Under Atmospheric Absorption Model, make the following selections and click OK.
    1. Select Use and browse to Urban Propagation WIRT 2.5 and click OK.
    2. Keep TPGEODESIC as the Calculation Method. TPGEODESIC, which is the triple path compute option, produces higher fidelity results than the other options, which are empirical models.
    3. Browse to the urban building geometry data file, <STK install area>\Help\STK\samples\Skopje.shp. An urban building geometry data file is a polygon shapefile with a *.shp extension.
    4. The Projection/Horizontal Datum field indicates if the WGS84 coordinate system is specified in latitude/longitude coordinates or UTM coordinates. Keep the default value of Lat/Lon WGS84.
    5. The Building Height Data Attribute list contains all the columns in the data file. You will need to know which column contains the height attribute. In the Skopje.shp file, the ZV2 column contains the height attribute, so select ZV2.
    6. There are two Building Height Reference Methods for calculating the building height reference. Since terrain is included in the scenario, select HeightAboveTerrain.
    7. The building height attribute can be specified in feet or meters. Keep Meters as the Building Height Unit.
    8. Leave the Override Geometry Tile Origin disabled.
    9. Enable Use Terrain Data and click OK.
  3. Save the scenario.

Add Objects to the Scenario

Populate the scenario with the following objects:

Skopje Facility

To model the transmitter at the command post, create a facility object and attach a transmitter to it:

  1. Select Insert Facility From City Database from the Insert menu. Search for and add Skopje.
  2. Go to the Skopje Facility's Basic->Position properties page, change Height Above Ground to .001 km and set Use terrain data. Click OK.
  3. Add a default transmitter to the Skopje facility.
  4. The maximum frequency that is valid with the Urban Propagation model is 7 GHz. The default frequency for a transmitter is 14.5 GHz, so go to the Transmitter's Basic->Definition properties page and change Frequency to 7 GHz. In addition, change the EIRP value to 3 dBW.
  5. Go to the Transmitter's Constraints->Basic properties page, clear Line of Sight and click OK.

Ground Vehicle

  1. Add a default ground vehicle and open up its properties.
  2. On the Ground Vehicle's Basic->Route properties page, add the following route points. Note that we set the altitude to adhere to the recommendation that all objects that travel over terrain be at least one meter above ground.

  3. Latitude Longitude Altitude
    42.00004 deg 21.41604 deg 0.001 km
    41.99817 deg 21.42527 deg 0.001 km
    42.00037 deg 21.42708 deg 0.001 km
    41.99896 deg 21.42978 deg 0.001 km
    41.99930 deg 21.43370 deg 0.001 km

  4. Under Altitude Reference, select Terrain and set the following:
  6. Go to the Ground Vehicle's Constraints->Basic properties page, clear Line of Sight, and click OK.
  7. Add a default receiver to the ground vehicle.
  8. Go to the Receiver's Constraints->Basic properties page, clear Line of Sight, and click OK.

Locate the Shapefile in the 3D Graphics Window

Creating an Area Target that has the same size and shape and is in the same location as the shapefile will enable you to quickly find the shapefile in the 3D Graphics window. The Area Target is also used for coverage analysis later in this tutorial. To create the Area Target:

  1. Go the Scenario's RF->Environment properties page to get the Terrain Extent values.
  2. Create an Area Target and use the Terrain Extent values to define the boundaries of the Area Target, as shown below:
  3. Latitude Longitude
    41.9904 deg 21.4157 deg
    41.9904 deg 21.4357 deg
    42.0044 deg 21.4357 deg
    42.0044 deg 21.4157 deg
  4. To view the shapefile in the 3D Graphics window, right-click AreaTarget1 and select Zoom To.

Display the Results in the 3D Graphics Window

Make the following changes to the 3D Graphics window and properties:

  1. Click Microsoft Bing Maps () and select Aerial to display the roads through Skopje.

  2. Note: An STK/TIM license and an Internet connection are required to use Microsoft Bing Maps.

  3. You now want to check the position of the facility and the route for the ground vehicle. The Urban Propagation extension does not include the inside of buildings in its analysis, so make sure that the facility is not located in a building. Also, make sure that the ground vehicle will stay on the road when the scenario is animated. To make changes, use the 3D Object Editor to move the facility or change the ground vehicle's route.
  4. Click the down arrow on View From/To () and select GroundVehicle->GroundVehicle1 so that you can follow it when you animate the scenario.
  5. Change the time step to 0.1 sec and animate the scenario. The ground vehicle should stay on the roads as it goes through town. If the ground vehicle does not stay on the road, use the 3D Object Editor to modify its route. Note that the ground vehicle passes in front of the facility.
  6. Save the scenario.

Generate a Link Budget Report

A Link Budget report can provide an overview of the quantities of the Communications parameters throughout the mission. To generate the report:

  1. Right-click the Transmitter object and select Access Tool from the menu.
  2. Under Associated Objects, select Receiver1 under GroundVehicle and click Compute.
  3. Click the Access Report to confirm that there is access between the transmitter and the receiver.
  4. Minimize the report and click Report & Graph Manager....
  5. Select Link Budget - Detailed under Installed Styles and click Generate....
  6. Change the step size for the report to 1.0 sec.
  7. Animate the scenario and observe the access link between the ground vehicle and the command post. During animation, the Line of Sight graphical line will go through buildings; however, be aware that this is only a geometric rendering and not does reflect a communications link.
  8. Look at the report to determine if a communications parameter requires additional tweaking because of its potential impact on communications between the ground vehicle and the command post. The next procedure provides an example of determining the impact of one constraint on communications.

Create an Access Report with a BER Constraint

To determine the impact of the Bit Error Rate (BER) constraint on communications, do the following to generate a simple Access report that will show when communication is and is not possible between the ground vehicle and the command post:

  1. Go to the Transmitter's Constraints->Comm properties page.
  2. Select Max and set the maximum Bit Error Rate to 1e-6 and click OK.
  3. Animate the scenario and observe that there is a time when there is no access between the two objects.
  4. Go to the Report & Graph Manager and generate the Gaps report for Access to view the exact amount of time when there is no access between the two objects.

Compute Object Coverage

Note: An STK/Coverage license is required for the rest of the tutorial.

To calculate and display the BER constraint levels along the ground vehicle's route:

Clear All Accesses and Constraints

  1. Go to the Analysis menu and remove all accesses.
  2. Go to the Transmitter's Constraints->Comm properties page and clear Max under Bit Error Rate. Click OK.

Define Object Coverage

  1. Right-click Receiver1 and select Coverage Tool.
  2. Assign the transmitter on the Skopje facility as an asset.
  3. Click Define... under Figure of Merit.
  4. On the Specify Figure of Merit window, select Access Constraint as the Type and BitErrorRate as the Constraint.
  5. Change the Time Step to 1 sec and click OK.
  6. Under Graphics, click Contours....
  7. Select Use Contour Levels on Vehicle Track.
  8. For the Add Method, select Explicit and enter the following levels. Remember to click Add each time you enter a level.
  9. 1e-30
    1e-20
    1e-10
    1e-5
    1e-1
    2e-1
  10. Select Use Color Ramp. Select green as the first color and red as the second color for the ramp colors. Click OK to return to the Object Coverage tool.
  11. Select Save Configuration.
  12. Click Apply.
  13. Click Compute.

Display Object Coverage

  1. View the ground vehicle route in the 3D Graphics window. Red indicates a high bit error rate and green indicates a low bit error rate.
  2. Go to the 3D Graphics window. The route should look similar to the following:

Compute Received Isotropic Power for the Entire Region

Now you are going to compute coverage for the entire area that the shapefile covers. A figure of merit will be used to display the quality of the communication links to every part of the city. This will allow you to easily see which routes will provide a favorable communication link with the facility and which routes to avoid.

  1. Create a CoverageDefinition object and set the following properties:
    1. Make Type Custom Regions.
    2. Click Select Regions... and select AreaTarget1.
    3. Click Grid Constraint options… and set Reference Constraint Class to Receiver and select GroundVehicle/Receiver1.
    4. There is always a trade-off between resolution and computational speed with grid resolution. In this case, however, the resolution has to be high enough to resolve the features of the urban environment. Set Point Granularity, Lat/lon to .0001 deg and Point Altitude to Altitude above Terrain and .001 km.
    5. Go to the Basic->Assets properties page and assign the transmitter as an asset.
    6. Go to the Basic->Interval properties page and clear Use Scenario Time Period and set the Stop time to 19 Oct 2009 15:10:01.000 UTC. Setting the interval to one second is adequate for static coverage.
    7. Go to the Basic->Advanced properties page and clear Automatically Recompute Accesses and click OK.
  3. Go to the 3D Graphics window and select View From/To->Area Target->AreaTarget1. The area target should include all the urban data from the shape file, the ground vehicle's route, and the facility. You should also see all of the coverage's grid points in the area target.
  4. Attach a Figure of Merit object to the CoverageDefinition object. On the Figure of Merit's Basic->Definition properties page:
    1. Select Access Constraint as the Type and RcvdIsotropicPower as the Constraint.
    2. Under FOM Value Limits, select Use FOM Value in Limits for Statistics and set the minimum value to -3000 dBW and the maximum value to 0 dBW. Click OK.
  6. Select Compute Accesses from the CoverageDefinition menu.
  7. Generate the Grid Stats report for FigureofMerit1 to determine the minimum and maximum values to use for coverage contours. The report will take a few minutes to generate.
  8. Turn off the grid points since they are no longer needed and the color of the grid points may interfere with the coverage contour colors. To turn off the grid points, go to the Coverage Definition's 2D Graphics->Attributes properties page, and under Static Graphics, clear Show Points.
  9. Go to the FOM's 2D Graphics->Contours properties page, Select Static as the Type, enable Show, and select Smooth Fill as the Style. Set these values for the contour graphics, which are based on the minimum and maximum FOM values in the Value by Grid point report:

  10. Start: -300 dBW
    Stop: -60 dBW
    Step: 4

  11. Click Add Levels and set the Start Color to Red and End Color to Green.
  12. Go to the Figure of Merit's 3D Graphics->Attributes properties page, and under Smooth Contours, change Pixels Per Degree to 100000 and click OK. The rendering will take a few minutes to complete.
  13. Click OK and go back to the 3D Graphics window. Red indicates the least amount of received isotropic power.