Communications Part 5: Introduction to Modeling Propagation Loss in an Urban Environment

STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this training by contacting AGI Support at support@agi.com or 1-800-924-7244.

This lesson requires STK 12.5 or newer to complete it in its entirety.

Capabilities covered

This lesson covers the following STK Capabilities:

  • STK Pro
  • Communications
  • Urban Propagation Extension (UProp)

Problem

You need to compute diffraction losses in an urban environment and apply them to a link budget. Luckily, urban propagation determines the impact of buildings, terrain, and ground reflections on your communications. You want to assess the effects of urban propagation to plan for link outages and asset redundancy. You are interested in how hand-held communication devices will be affected by buildings and structures. You need to analyze communications from a central location in a city to determine carrier to noise ratio throughout the city.

Solution

You will use a combination of STK, STK Communications capability, STK Coverage capability, and the Urban Propagation Wireless InSite Model to create communications coverage in an urban test zone looking for dead zones throughout the city.

If you are new to STK, review the following Level 1 - Beginner tutorials first: Part 1: Build Scenarios and Part 2: Objects and Properties.

What you will learn

Upon completion of this tutorial, you will understand the following:

  • How to use Urban Propagation for STK Communications.
  • How to display C/N Contours in the 3D Graphics window.

Video guidance

Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).

Using the starter scenario (*.vdf file)

To speed things up and enable you to focus on this lesson's main goal, you will use a partially created scenario. The partially created scenario is saved as a visual data file (VDF) in your STK install.

Retrieving the starter scenario

  1. Launch STK ().
  2. Click Open a Scenario () in the Welcome to STK dialog box.
  3. Go to <STK install folder>\Data\Resources\stktraining\VDFs\.
  4. Select STK_Communications.vdf.
  5. Click Open.

Visual data files versus Scenario files

You must make sure that you save your work in STK as a scenario file (.sc) and not a visual data file (.vdf) by selecting Save As from the STK File menu. A VDF is a compressed version of an STK scenario, which makes them great for sending your work in STK to others. However, you want to use a scenario file while working with STK on your machine.

If you open a VDF file, STK keeps it as a VDF and does not automatically convert it to a scenario file. This means, STK does not change the file type of your scenario when you launch your scenario. You need to convert the VDF to a Scenario file using Save As.

Saving a VDF file as a Scenario file

Use Save As from the STK File menu to convert the VDF file that you opened into a scenario file.

  1. Open the File menu.
  2. Select Save As.
  3. Select the STK User folder on the left side of the Save As window.
  4. Click New Folder.
  5. Rename New Folder to match the title of the scenario.
  6. Open the folder you just created.
  7. Enter the name of the folder into File name field.
  8. Open the Save as type drop-down menu.
  9. Select Scenario Files (*.sc).
  10. Click Save.

Enhancing situational awareness

In this scenario, you will analyze communications between a central location in a city and grid throughout the city.

  1. Select the check box for the following objects in the Object Browser:
    • Skopje_Extents ()
    • Skopje_CommSite ()
  2. Click Save (). Save often during this lesson!

Changing the analysis period

Since you are analyzing a grid with no moving objects, you can narrow your analysis period to 1 second. This is a trick you can do in STK to shorten your computation time.

  1. Right-click on your Scenario object () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Time page when the Properties Browser opens.
  4. Set the following in the Analysis Period frame:
    5. Option Value
    Start: 1 Aug 2022 06:00:00.000 UTCG
    Stop: +1sec
  5. Click Apply to accept your change and to keep the Properties Browser open.

Using analytical terrain

You will use a local terrain file for analysis and visualization.

  1. Select the Basic - Terrain page. You can see that Use terrain server for analysis is turned off.
  2. Select the Use check box for SRTM_Skopje.pdtt in the Custom Analysis Terrain Sources frame.
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Introduction to Urban Propagation Wireless InSite model

The Urban Propagation Wireless InSite model offers a selection of a deterministic model and four empirical models for calculating path loss between two locations in an urban environment. The deterministic model, Triple Path Geodesic, was developed by Remcom as a derivative of their Wireless InSite 3D propagation loss module, Wireless InSite.

The Triple Path Geodesic model is a rapid urban propagation model that uses the buildings' 3D geometry data to define an urban environment. The 3D geometry data is used to compute wedge diffractions. The Triple Path Geodesic model produces higher fidelity results than empirical models but at greatly reduced computation times compared to full physics-based models.

Enabling the Urban Propagation Wireless InSite model

  1. Select the RF - Environment page.
  2. Select the Urban & Terrestrial tab.
  3. Select the Use check box.
  4. Click the Urban Terrestrial Propagation Loss Model ellipsis ().
  5. Select Urban Propagation Wireless InSite () in the Urban Terrestrial Propagation Loss Models list, once the Select Component dialog box opens.
  6. Click OK to close the Select Component dialog box.
  7. Ensure TPGEODESIC is set for the Calculation Method:.

TPGEODESIC Calculation method

The deterministic model, which is the default, is the preferred model. It produces higher fidelity results than empirical models. Triple Path Geodesic returns the no data value unless it meets this restriction: transmitter and receiver must be outside of buildings and above ground. The TPGEODESIC model provides good general coverage of cityscapes between any pair of antennas not located underground or indoors.

Using an Urban Geometry Data file

The shapefiles for STK’s Urban Propagation capability must have polygon features to represent building footprints and an elevation attribute to represent elevations of the buildings. You should limit the shapefile to a maximum range of three square kilometers. The shapefile may contain holes in its building polygons (e.g., courtyards, shafts, and plazas) but those holes are not recognized either analytically or graphically by the Urban Propagation Extension.

  1. Click the File: ellipsis () in the Urban Geometry Data frame.
  2. Browse to the Urban building Geometry Data File (typically: <STK install folder>\Data\Resources\stktraining\samples) in the Select File dialog box.
  3. Select Skopje.shp.
  4. Click Open.

Determining the building height data attribute

You can use the data attribute in the Urban Geometry Data file to provide the building height. 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. When HeightAboveTerrain is used, the calculation determines a building height relative to terrain.

  1. Open the Data Attribute shortcut menu in the Building Height frame.
  2. Select ZV2.
  3. Open the Reference Method shortcut menu.
  4. Select Height Above Terrain.

Enabling Terrain Data

You loaded analytical terrain into your scenario. Select this check box to incorporate the effect of terrain in your urban propagation analysis.

  1. Select the Use Terrain Data check box.
  2. Click OK to accept your changes and to close the Properties Browser.
  3. Click Reset () in the Animation toolbar.

Visualizing the Skopje shapefile in the 3D Graphics window

Although not required, for situational awareness, view the Skopje shapefile in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Click Properties () in the 3D Window Defaults toolbar.
  3. Select the Details page.
  4. Click Add in the Shapefiles frame.
  5. Browse to the Skopje.shp file (typically: <STK install folder>\Data\Resources\stktraining\samples) in the Select Shapefile dialog box.
  6. Select Skopje.shp.
  7. Click Open.

Configuring the Skopje shapefile

  1. Click More... in the Shapefiles frame.
  2. Expand the Height Reference: shortcut menu in the Attributes frame when the Shapefile Details dialog box opens.
  3. Select Terrain.
  4. Open the Top Height: shortcut menu.
  5. Select Field.
  6. Open the Field Name: shortcut menu.
  7. Select ZV2.
  8. Click OK to close the Shapefile Details dialog box.
  9. Click OK to close the Properties Browser.

Visualizing the terrain in the 3D Graphics window

Display the SRTM_Skopje.pdtt and the Skopje shapefile in the 3D Graphics window by zooming to Skopje_Extents ().

  1. Select the SRTM_Skopje.pdtt check box in Globe Manager.
  2. Bring the 3D Graphics window to the front.
  3. Right-click on Skopje_Extents () in the Object Browser.
  4. Select Zoom To in the shortcut menu.
  5. Use your mouse to zoom in and view the Skopje shapefile and surrounding terrain.

SKOPJE SHAPE FILE

Inserting a Transmitter object to the Skopje Communications Site

The communications site is located approximately in the center of the Skopje shapefile. You can place both the transmitter and receiver at that location.

  1. Zoom to Skopje_CommSite ().
  2. Select Transmitter () in the Insert STK Objects Tool.
  3. Select the Insert Default () method.
  4. Click Insert...
  5. Select Skopje_CommSite () in the Select Object dialog box.
  6. Click OK.
  7. Right-click on Transmitter1 () in the Object Browser.
  8. Select Rename.
  9. Rename Transmitter1 () to TwoWay_Tx.

Using a complex transmitter model

You will use a complex transmitter model for your analysis. When using the Urban Propagation Wireless InSite model, your frequency cannot go below 100 MHz. There is no upper limit restriction; however, above 7 GHz, predictions can become more sensitive to the finer resolution building details that may not be present in the shapefile or in the model's internal, simplified geometry.

  1. Open TwoWay_Tx's () properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Transmitter Model Component Selector ().
  4. Select Complex Transmitter Model () in the Transmitter Models list, once the Select Component dialog box opens.
  5. Click OK to accept your selection and to close the Select Component dialog box.
  6. Select the Model Specs tab.
  7. Set the following:
    8. Option Value
    Frequency: 450 MHz
    Power 4 W
    Data Rate: 10 Mb/sec
  8. Click Apply to accept your changes and to keep the Properties Browser open.

Using a dipole antenna for the transmitter

Your transmitter uses a dipole antenna.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select Dipole () in the Antenna Models list, once the Select Component dialog box opens.
  5. Click OK to accept your change and to close the Select Component dialog box.
  6. Set the following:
    7. Option Value
    Design Frequency: 450 MHz
    Length: 0.32 m
    Efficiency: 80 %
  7. Click Apply to accept your changes and to keep the Properties Browser open.

Adjusting the antenna height

For your analysis, place the antenna 6 feet above the terrain. Provided that both transmitter and receiver are above ground, there is no height restriction. However, prediction fidelity declines if both the transmitter and receiver are on or close to the ground (less than one meter). This is because ground conditions that are important to the analysis (e.g., ground cancellation) are not included.

  1. Select the Orientation sub-tab.
  2. Enter -6 ft in the Z: field in the Position Offset frame.
  3. Click Applyto accept your changes and to keep the Properties Browser open.

Disabling the line of sight and Az-El Mask constraints

You should not enable STK Line of Sight and Az-El Mask constraints. The Triple Path Geodesic model of the Urban Propagation Extension employs a higher-fidelity algorithm to simulate RF propagation in an urban environment than a simple line-of-sight prediction. In particular, the model has the capability to make signal attenuation predictions in situations with an obscured line-of-sight transmission. It does so by considering three of the most significant paths of diffracted energy around buildings and over terrain. Thus, the use of Line of Sight and Az-El/terrain mask constraints is not appropriate when using the Triple Path Geodesic model.

  1. Select the Constraints - Basic page.
  2. Clear the Line of Sight check box.
  3. Click OK to accept your changes and to close the Properties Browser.

Inserting a Receiver object to the Skopje Communications Site

Attach a Receiver () object to Skopje_CommSite.

  1. Insert a Receiver () object using the Insert Default () method.
  2. Select Skopje_CommSite () in the Select Object dialog box.
  3. Click OK to close the Select Object dialog box.
  4. Rename Receiver1 () to TwoWay_Rx.

Using a complex receiver model

You will use a complex receiver model for your analysis.

  1. Open TwoWay_Rx's () properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Receiver Model Component Selector ().
  4. Select Complex Receiver Model () in the Receiver Models list, once the Select Component dialog box opens.
  5. Click OK to accept your selection and to close the Select Component dialog box.

Using a dipole antenna for the receiver

Your receiver uses a dipole antenna.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select Dipole () in the Antenna Models list, once the Select Component dialog box opens.
  5. Click OK to accept your change and to close the Select Component dialog box.
  6. Set the following:
    7. Option Value
    Design Frequency: 450 MHz
    Length: 0.32 m
    Efficiency: 80 %
  7. Click Apply to accept your changes and to keep the Properties Browser open.

Adjusting the antenna height

Place the antenna 6 feet above the terrain.

  1. Select the Orientation sub-tab.
  2. Enter -6 ft in the Z: field in the Position Offset frame.
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Disabling the line of sight constraint

Turn off the line of sight constraint.

  1. Select the Constraints - Basic page.
  2. Clear the Line of Sight check box.
  3. Click OK to accept your changes and to close the Properties Browser.

Inserting a Coverage Definition to analyze the transmitter broadcast

You will determine how well your transmitter can broadcast within the extents of the Skopje shapefile. You will do this by restricting your coverage grid to the Skopje_Extents Area Target object.

  1. Insert a Coverage Definition () object using the Insert Default () method.
  2. Open CoverageDefinition1's () properties ().
  3. Select the Basic - Grid page when the Properties Browser opens.

Adjusting the grid area of interest

Place your coverage grid inside Skopje_Extents ().

  1. Open the Type drop-down menu in the Grid Area of Interest frame.
  2. Select Custom Regions.
  3. Select Area Targets in the drop-down menu below Custom Regions.
  4. Move () Skopje_Extents () from the Area Targets list to the Selected Regions list.

Defining your grid

You are confining your grid to a small geographical area. Therefore, you will use Distance for the grid spacing.

  1. Select Distance from the drop-down menu in the Point Granularity frame.
  2. Enter 100 ft in the Distance field.

Adding a grid constraint

You will use TwoWay_Rx () as the grid constraint.

  1. Click Grid Constraint Options...
  2. Open the Reference Constraint Class drop-down menu in the Grid Constraint Options dialog box.
  3. Select Receiver.
  4. Select Skopje_CommSite/TwoWay_Rx in the Use Object Instance list.
  5. Click OK to close the Grid Constraints Options dialog box.

Adjusting the grid point altitude

You are analyzing communications from your transmitter to your receiver which is constrained to each grid point inside Skopje_Extents (). Place your grid points at an altitude of 6 feet above the terrain.

  1. Open the Point Altitude drop-down menu.
  2. Select Altitude above Terrain.
  3. Enter 6 ft in the Altitude above Terrain field.
  4. Click Apply to accept your changes and to keep the Properties Browser open.

Selecting assets

Select TwoWay_Tx () as your asset.

  1. Select the Basic - Assets page.
  2. Expand () Skopje_CommSite () in the Assets list.
  3. Select TwoWay_Tx ().
  4. Click Assign.
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the 3D Graphics fill options

Tell STK to display the Figure Of Merit at altitude in the 3D Graphics window.

  1. Select the 3D Graphics - Attributes page.
  2. Select the Show at Altitude check box in the Fill Options frame.
  3. Click OK to accept your changes and to close the Properties Browser.

Computing accesses using your Coverage Definition object

The Compute Accesses tool enables you to compute accesses between the grid points and the assigned assets.

  1. Select CoverageDefinition1 () in the Object Browser.
  2. Open the Coverage Definition menu.
  3. Select Compute Accesses in the shortcut menu.

Inserting a Coverage Figure of Merit object

The Coverage Figure of Merit () object enables you to analyze coverage in various directions over time, using several attitude-dependent figures of merit.

  1. Insert a Figure Of Merit () object using the Insert Default () method.
  2. Select CoverageDefinition1 () in the Select Object dialog box.
  3. Click OK to close the the Select Object dialog box.

Determining access constraints

You are interested in analyzing carrier to noise ratio (C/N). Access Constraints is perfect for this analysis. Access Constraints measures the value of various constraint parameters used to define visibility within STK.

  1. Open FigureOfMerit1's () properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Open the Type drop-down menu in the Definition frame.
  4. Select Access Constraint.
  5. Set the following:
    6. Option Value
    Constraints: C/N
    Compute: Maximum
    Time Step: 1 sec
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Generating grid stats report

The Grid Stats report provides minimum, maximum and average values.

  1. Right-click on FigureOfMerit1 () in the Object Browser.
  2. Select Report & Graph Manager () in the shortcut menu.
  3. Select Grid Stats () in the Installed Styles list, once the Report & Graph Manager opens.
  4. Click Generate....
  5. Scroll to the bottom of the Grid Stats report.
  6. Look at the Maximum (dB) value in the report (e.g., approximately 91 dB). You will use this value to create contours in your 2D and 3D Graphics windows.
  7. Close the Grid Stats report and the Report & Graph Manager.

Defining static graphics for the Figure Of Merit

The Static page enables you to define static graphics for a Figure Of Merit object.

  1. Return to FigureOfMerit1's () properties ().
  2. Select the 2D Graphics - Static page.

Adjusting Translucency

Have the Graphics windows display the points as filled polygons and set the translucency.

  1. Select the Filled Area button in the Show Points As frame.
  2. Enter 25.00 in the % Translucency field.

Adding levels

You can specify how levels of coverage quality display in both the 2D and 3D Graphics windows. You are not interested in any areas where the C/N is below five (5) dB. You will round down your maximum C/N dB value to 90 dB.

  1. Select the Show Contours option in the Display Metric frame.
  2. Set the following Level Adding values:
    3. Option Value
    Start: 5 dB
    Stop: 90 dB
    Step: 5 dB
  3. Click Add Levels.

Adjusting the levels' attributes

Using the Color Ramp enables you to apply a spectrum pattern with selected start and end colors.

  1. Ensure the Color Method is set to Color Ramp.
  2. Open the Start Color drop-down menu.
  3. Select red.
  4. Open the End Color drop-down menu.
  5. Select blue.

Using contour interpolation

You will use Natural Neighbor, which applies color smoothly over all points in the grid to differentiate contour levels.

  1. Select the Natural Neighbor option in the Contour Interpolation (points must be filled) frame.
  2. Click Apply to accept your changes and to keep the Properties Browser open.

Displaying contour legends

The Legend provides you with a convenient way to interpret contour data displayed in the 2D and 3D Graphics windows.

  1. Click Legend... in the Levels frame.
  2. Click Layout... when the Static Legend for FigureOfMerit1 opens.
  3. Select the Show at Pixel Location check box in the 2D Graphics Window frame.
  4. Select the Show at Pixel Location check box in the 3D Graphics Window frame.
  5. Type Carrier to Noise Ratio (dB) in the Title field in the Text Options frame.
  6. Enter 0 in the Number Of Decimal Digits field.
  7. Enter 50 in the Color Square Width (pixels) field in the Range Color options frame.
  8. Click OK to close the Figure of Merit Legend Layout dialog box.
  9. Close () the Static Legend for FigureOfMerit1.
  10. Click OK to close FigureOfMerit1's () properties ().

Viewing the contours in the 3D Graphics window

You can view the contours in both the 2D and 3D Graphics windows. You will use the 3D Graphics window. The view is a great way to brief anyone located at the city intersection on where anyone else with a hand held receiver can expect to have communications with you. Areas on the map with no color are below the 5 dB C/N cutoff.

C/N CONTOURS

Summary

This tutorial introduced you to Urban Propagation Wireless InSite Model capabilities using wide-area coverage. A meticulously built shapefile was used to simulate structures inside an urban environment. Using RF Environment, you loaded the shapefile analytically using the Urban Propagation Wireless InSite model. You placed a complex transmitter and receiver model at a central location in the city. Next, you built a coverage definition object and confined the coverage grid to the shapefile's extents. You placed the receiver's constraints at each grid point and selected the transmitter as the asset. You set your figure of merit to access constraint, focusing on carrier to noise ratio, and determined where your ratios would fall below five (5) dB using color contours inside your graphics window.

Save your work

  1. Close any open reports, properties and the Report & Graph Manager.
  2. Save () your work.

On your own

Find specifications for a drone hand held transmitter and update the Transmitter object's properties while keeping the transmitter in the same central location. Raise the receiver to 400 feet in the Coverage Definition setup, which is the typical allowed maximum altitude for recreational pilots. Compute coverage at that altitude. You could create a flight route using an Aircraft object and perform single object coverage at altitude or simply create a link budget. You can move the transmitter to a different location, raise its antenna height and keep the receiver at six (6) feet and perform coverage. There are many variations that you can apply to make this STK capability so interesting.