Using the Terrain Integrated Rough Earth Model (TIREM)

The main focus of this tutorial is how to make optimal use of the TIREM model.

STK Professional, Communications, and Terrain Integrated Rough Earth Model (TIREM).

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Install TIREM

The TIREM extension for Communications and Radar must be installed on your computer. In order to obtain an installation of the TIREM extension and a demo license, you will need to call 1.610.981.8875 or Email eval@agi.com.

TIREM

The TIREM extension is available for Communications and Radar. The TIREM extension allows STK Communications to predict radio frequency propagation loss over irregular terrain and seawater for ground-based and air-borne transmitters and receivers. The TIREM extension incorporates the commercial TIREM propagation tool, which is the de facto propagation tool for the United States Federal Government. TIREM is used in hundreds of modeling and simulation (M&S) tools and tactical military radios for the Department of Defense.

TIREM predicts median propagation loss from 1 MHz to 40 GHz. The techniques used to calculate these losses include:

  • Free-space spreading
  • Reflection
  • Diffraction
  • Surface-wave
  • Tropospheric-scatter
  • Atmospheric absorption

STK uses the TIREM model as an option for the Atmospheric Absorption Model in RF Link Budget computations.

Best Practices

To make the most efficient use of the TIREM analysis, we recommend the following:

  • For static links, a single time step is all that is required.
  • For dynamic links that interact with terrain, the larger the timestep, the shorter the runtime.
  • The higher the resolution of the terrain file, the longer the runtime.
  • This model only applies when antennas are below 30 km.
  • If you have a combination of static links that interact with terrain and dynamic links that do not, compute the static link losses using TIREM in a single step, change the atmospheric loss model to an appropriate model other than TIREM, and add static losses to the static links. The static loss incurred will be combined with other Pre-Receive losses entered as a Receiver model parameter. The effect on system temperature can be added as a constant temperature value.
  • Do not use .pdtt terrain files when using TIREM near sea-water. The use of .pdtt files will most likely not represent 0.0 MSL for sea-water and thus TIREM will not consider sea-water propagation characteristics.
  • Disable Line-of-sight, Terrain Mask, or Az-El Mask constraints to take advantage of the over-the-horizon analysis capabilities of the TIREM module.

Create a New Scenario

  1. Launch STK ().
  2. From the Welcome to STK window, click Create a Scenario and enter TIREM_Tutorial in the Name field.
  3. Set the Analysis Period Start and Stop times from 1 Jul 2016 16:00:00.00 UTCG to 2 Jul 2016 16:00:00.00 UTCG.
  4. Click OK.

Save Often!

Disable Terrain Server

  1. Open the TIREM_Tutorial () properties ().
  2. Browse to the Basic – Terrain page.
  3. Disable Use terrain server for analysis.
  4. Click Apply.

Set TIREM as the Propagation Loss Model

  1. Select the RF - Environment page.
  2. Click the Atmospheric Absorption tab.
  3. Enable Use.
  4. Select the TIREM model as the Model Type and click OK.
  5. Click OK to accept the changes to the scenario properties.

Use a Local Terrain File for Analysis

Add analytical terrain from a local file. Microsoft Bing Maps can be used for imagery. However, imagery is not required.

  1. Launch the Globe Manager () from the 3D Graphics window toolbar.
  2. Use the Add Terrain/Imagery () option in the Globe Manager to load your terrain file (*.pdtt) both analytically and to the globe in the 3D Graphics window.
  3. Browse to <Install Directory>Help\stktraining\imagery and select PtMugu_ChinaLake.pdtt.
  4. Click Open.
  5. Click Yes when prompted to Use Terrain for Analysis.

Declutter the 3D Graphics Window

Since you're using terrain in the 3D Graphics window, a common user preference is to use Label Declutter. It declutters labels away from the central body and towards the viewer, keeping the labels from being obscured by the terrain.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on the 3D Graphics window and select Properties ().
  3. On the Details page, find the Label Declutter field and check Enable.
  4. Click OK.

Create a Communications Ground Site

Throughout the scenario, all objects using TIREM must be at least one (1) meter in height above the terrain surface.

  1. Insert the following Place () object using the From City Database () method:
    • Bella Vista (California) (Latitude: 35.6 Longitude: -118.3)
  2. Open Bella_Vista's () Properties ().
  3. On the Basic - Position page, set Height Above Ground to 1 m (one meter).
  4. Click OK.

Insert a Receiver

  1. Insert a Receiver () object using the Insert Default () method.
  2. Attach the Receiver () object to Bella_Vista.
  3. Rename the Receiver object "BVRcvr."
  4. Open the BVRcvr's () properties ().
  5. On the Basic - Definition page, set the receiver type to Medium Receiver.
  6. On the Model Specs tab, set the Gain to 45 dB.
  7. Select the System Noise Temperature tab.
  8. Enable Compute.
  9. In the Antenna Noise field, enable Compute and then Sun and Atmosphere.
  10. Select the Constraints - Basic page.
  11. Disable the Line of Sight (required when using TIREM).
  12. Click OK.

Communications Vehicle

  1. Insert a Ground Vehicle () object using the Insert Default () method.
  2. Rename the Vehicle object "ATV".
  3. Open the ATV’s () properties ().
  4. In the Altitude Reference field, make the following changes:
    5. Option Value
    Reference: Terrain
    Terrain Granularity: 10 m (meters)
    Interp Method: Terrain Height
  5. Click Insert Point and make the following changes:
    6. Option Value
    Latitude 35 deg
    Longitude -118.3 deg
    Altitude 1 m
  6. Click Insert Point again and make the following changes:
    7. Option Value
    Latitude 36 deg
  7. Click OK.

Export a PropDef (.pg) File for ATV

A PropDef (.pg) file is an ASCII text file (.pg) that contains an element set and path definition for a vehicle.

  1. In the Object Browser, right click on ATV () and select Export Ephemeris/Attitude.
  2. Change the External STK File Type: to PropDef.
  3. Click Export File.
  4. Click Close.

The file is automatically saved in the scenario folder.

Insert a Transmitter

Use a simple transmitter model.

  1. Insert a Transmitter () object using the Insert Default () method.
  2. Attach the Transmitter () object to ATV.
  3. Rename the Transmitter object "ATVXmtr."
  4. Open the ATVXmtr's () properties ().
  5. Select the Constraints - Basic page.
  6. Disable Line of Sight.
  7. Click OK.

Calculate a Ground to Ground Link Budget

STK allows you to determine the times one object can "access," or see, another object. In addition, you can impose constraints on accesses between objects to define what constitutes a valid access. These constraints are defined as properties of the objects whose accesses are being calculated. This capability is used in STK Communications to define communications links.

  1. Right-click BVRcvr () in the Object Browser and select Access ().
  2. In the Access Tool's Associated Objects List, expand ATV ().
  3. Select the ATVXmtr ().
  4. Click Report & Graph Manager () button.
  5. In the Styles section, if required, expand Installed Styles.
  6. Select the Link Budget – Detailed report style and click Generate.
  7. View the Link Budget report and note the Atmospheric Loss (Atmos Loss (dB)).

    8. The number fluctuation in the column is due to the ground vehicle moving in and out of terrain. You'll notice other columns are affected such as Carrier to Noise Ratio (C/N (dB)) and Energy Per Bit to Noise Power Spectral Density Ratio (Eb/No (dB)).

  8. Close the report, Report & Graph Manager and Access Tool.

Create an Aircraft

Simulate a low flying aircraft that is following terrain at 1000 feet AGL (height above ground level). You will use the ground vehicle's PropDef file and apply it to the aircraft. The aircraft will fly 1000 feet AGL using ATV's route.

  1. Insert an Aircraft () object using the Insert Default () method.
  2. Rename the Aircraft () object "TestAcft."
  3. Open the TestAcft's () properties ().
  4. Click the Import from File... button.
  5. Select ATV's ProDef file and click Open.
  6. In the Altitude Reference field, make the following changes:
    7. Option Value
    Reference: Terrain
    Terrain Granularity: 5 km
    Interp Method: Terrain Height
  7. Make the following changes to both waypoints:
    8. Option Value
    Altitude 1000 ft
    Speed 100 mi/hr
  8. Click OK.

Reuse ATV's Transmitter

A simple and smart thing to do when using STK is to reuse objects that are pre-built to required specifications.

  1. In the Object Browser, right click on ATVXmtr () and select Copy ().
  2. Right-click on TestAcft and select Paste ().
  3. Expand TestAcft. STK automatically renames the transmitter object by using a one-up numbering system.
  4. Rename TestAcft's Transmitter object "AcftXmtr."

Calculate an Air to Ground Link Budget

  1. In the Object Browser, right-click on BVRcvr () and select Access ().
  2. In the Access Tool's Associated Objects List, expand TestAcft.
  3. Select AcftXmtr ().
  4. Click Report & Graph Manager button.
  5. From the Report & Graph Manager window, select the Link Budget – Detailed report style and click Generate.
  6. View the Link Budget report and note the Atmos Loss (dB), C/N (dB), and Eb/No (dB).
  7. Keep the report open.

Lower TestAcft's Altitude

TestAcft will fly at a lower altitude. In order not to intersect with terrain, you need to increase terrain granularity.

  1. Open TestAcft's () properties ().
  2. On Basic - Route page, change Altitude Reference - Granularity to 1 km.
  3. Change Altitude for both waypoints to 500 ft.
  4. Click OK.

Re-calculate the Air to Ground Link Budget

  1. Return to the Link Budget - Detailed report and scroll to the Atmos Loss (dB) column.
  2. Refresh the report and note the new loses.

    3. Since TestAcft is flying at a lower altitude, the atmospheric loses increase.

  3. Close the report, Report & Graph Manager and Access Tool.

Create a Sounding Rocket

  1. Insert a Missile () object using the Insert Default () method.
  2. Rename the Missile object "Rocket".
  3. Open Rocket's () properties ().
  4. On the Basic - Trajectory page, make the following changes:
    5. Option Value
    Launch Latitude - Geodetic 35.5 deg
    Launch Longitude -119 deg
    Launch Altitude .3 km
    Change Fixed Delta V to: Fixed Apogee Alt 150 km
    Impact Latitude - Geodetic 35.5 deg
    Impact Longitude -116 deg
    Impact Altitude 10 ft
  5. Click OK.

Reuse the TestAcft's Transmitter

  1. In the Object Browser, right click on AcftXmtr () and select Copy ().
  2. Right-click on Rocket and select Paste ().
  3. Rename Rocket's Transmitter object RocketXmtr.

Calculate a Ground to High Altitude Link Budget

  1. In the Object Browser, right-click on BVRcvr () and select Access ().
  2. In the Access Tool's Associated Objects List, expand Rocket.
  3. Select RocketXmtr ().
  4. Click Report & Graph Manager button.
  5. From the Installed Styles list, select the Link Budget – Detailed report style and click Generate.
  6. View the Link Budget report and note the Atmos Loss (dB), C/N (dB), and Eb/No (dB).

    7. Note that the atmospheric loss values approach zero as the altitude of the Missile increases and Line of Sight remains. As BVRcvr loses Line of Sight with the Missile over the horizon, the atmospheric losses increases. Atmospheric loss will be computed above 30 km, however, the TIREM model does not apply above 30 km.

  7. Close the report, Report & Graph Manager and Access Tool.

Create an Analog Transponder

STK Communications models an analog transponder as a combination of a receiver and a retransmitter. In an analog transponder, the transmitted signal is essentially a reflection of the received signal, with the added possibility of frequency translation or power amplification.

  1. Insert a Receiver () object using the Insert Default () method.
  2. Attach the Receiver () object to TestAcft.
  3. Rename the Receiver object "ULRcvr."
  4. Open ULRcvr's properties ().
  5. Browse to the Constraints - Basic page.
  6. Disable Line of Sight.
  7. Click OK.
  8. Insert a Transmitter () object using the Insert Default () method.
  9. Attach the Transmitter () object to TestAcft.
  10. Rename the Transmitter () object "ReXmtr."
  11. Open ReXmtr's properties ().
  12. On the Basic - Definition page, change the Type: to Simple Re-Transmitter Model.
  13. Browse to the Constraints - Basic page.
  14. Disable Line of Sight.
  15. Click OK.

Create a Chain

ATV will transmit data to Bella_Vista using TestAcft's transponder. To do this in STK, you will need to use a Chain object.

  1. Insert a Chain () object using the Insert Default () method.
  2. Rename the Chain object "ATVtoBV."
  3. Open ATVtoBV's () properties ().
  4. The Assigned Objects need to be entered in the order that the data flows. Move the Available Objects to the Assigned Objects list in the following order:
    • ATVXmtr ()
    • ULRcvr ()
    • ReXmtr ()
    • BVRcvr ()
  5. Click OK.

Create a Bent Pipe Link Budget

  1. In the Object Browser, right click on ATVtoBV ().
  2. Select the Report & Graph Manager () in the menu.
  3. In Styles - Installed Styles, select the report named Bent Pipe Comm Link.
  4. Click Generate.

The report contains link performance data for the uplink (first line), downlink (second line), and the combined link (third line). Degradation in downlink and composite link performance can readily be perceived. At times you will see degraded link performance between ATV and Bella_Vista. This degraded link performance is due to the increasing distance between ATV and TestAcft and terrain between ATV and TestAcft and terrain between TestAcft and Bella_Vista.

SAVE YOUR WORK!

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