GPS Reception and Interference

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

Required Capability Install: This lesson requires an additional capability installation for STK Terrain Integrated Rough Earth Model (TIREM). The TIREM install is included in the STK Pro software download, but requires a separate install process. Read the Readme.htm found in the STK install folder for installation instructions. You can obtain the necessary install by visiting http://support.agi.com/downloads or calling AGI support.

This lesson requires an internet connection and version 12.9 of the STK software or newer to complete in its entirety. If you have an earlier version of the STK software, you can complete a legacy version of this lesson.

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.

Capabilities covered

This lesson covers the following capabilities of the Ansys Systems Tool Kit® (STK®) digital mission engineering software:

  • STK Pro
  • Communications
  • Aviator
  • Terrain Integrated Rough Earth Model (TIREM)

Problem statement

Engineers and technicians require tools to create simulations and analyze results to plan future missions before spending time and money fielding assets to perform on-site analysis. You are simulating a future training mission where a light aircraft will fly a search pattern over mountainous terrain. You need to determine how well the aircraft receives GPS transmissions. Although illegal to purchase and use in the United States, GPS jammers pose a threat to your test. You want to know how these jammers could affect your communications so you can confidently plan future missions when there is a possibility of GPS interference in the rescue area of operations. A team of engineers will drive to an area centrally located under the aircraft's search pattern to determine if one of these devices will affect the aircraft's reception of the GPS signal.

Solution

Use the STK Pro software and a local, analytical terrain file to design the mountainous training area where the test will take place. Use the Communications capability to build the satellite GPS transmitters, the aircraft's GPS receiver, and measure interference against the GPS signal. Then, use the Aviator capability to create a search pattern for a light aircraft built to specifications. Then, use the Terrain Integrated Rough Earth Model (TIREM) capability to predict radio frequency propagation loss over irregular terrain. Combine these models to understand how the jammer will affect communications in your scenario.

What you will learn

Upon completion of this tutorial, you will be able to:

  • Design GPS satellite transmitters, which use GPS Global Antenna Patterns
  • Design a GPS receiver, which uses a GPS Fixed Reception Pattern Antenna (FRPA)
  • Use radio frequency environmental models and system noise temperature calculations
  • Use the Aviator capability to design a simple search pattern for a small aircraft
  • Determine GPS reception in the target area
  • Create a small GPS interference source
  • Use the TIREM capability to predict radio frequency propagation loss over irregular terrain
  • Analyze GPS jamming

Creating a new scenario

First, you must create a new STK scenario, then build from there.

  1. Launch the STK application ().
  2. Click Create a Scenario in the Welcome to STK dialog box.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name GPS_Analysis
    Location Default
    Start Default date, use 19:00:00.000 UTCG
    Stop + 4 hrs
  4. Click OK when you finish
  5. Click Save () when the scenario loads.

    6. The STK software automatically creates a folder with the same name as your scenario for you.

  6. Verify the scenario name and location in the Save As dialog box.
  7. Click Save.

Save () often during this tutorial!

Disabling streaming terrain

You're using a local terrain file for analysis. Turn off Terrain Server.

  1. Right-click on GPS_Analysis () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Terrain page when the Properties Browser opens.
  4. Clear the Use terrain server for analysis check box in the Terrain Server panel.
  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling the scenario's RF environment

A number of environmental factors can affect the performance of a communications link. Since you're modeling the downlink portion of a satellite transmission, you'll enable rain and atmospheric absorption models at the scenario level. The scenario's RF Environment properties enable you to apply various models to your analyses. When enabled, the models will affect all RF phenomena in the scenario.

  1. Select the RF - Environment page.
  2. Select the Rain, Cloud & Fog tab.
  3. Select the Use check box in the Rain Model panel.
  4. Confirm you are using the default ITU-R rain loss model.

    5. When enabled, the STK software uses the rain model to estimate the amount of degradation (or fading) of the signal when passing through rain.

  5. Select the Atmospheric Absorption tab.
  6. Select the Use check box.
  7. Confirm you are using the default ITU-R atmospheric absorption model.
  8. Click OK to confirm your selections and to close the Properties Browser.

Adding analytical and visual terrain

An STK terrain inlay (.pdtt) file can be used both for analysis and for visualization in the 3D Graphics window. Use a preinstalled terrain inlay file to your scenario using the Globe Manager.

  1. Bring the 3D Graphics window to the front.
  2. Click Globe Manager () on the 3D Graphics window's Globe Manager toolbar.
  3. Click Add Terrain/Imagery () on the Globe Manager Hierarchy toolbar when Globe Manager opens.
  4. Select Add Terrain/Imagery... () in the drop-down menu.
  5. Click the Path ellipsis () when the Globe Manager: Open Terrain and Imagery Data dialog box opens.
  6. Browse to the install directory at C:\Program Files\STK_ODTK 13\Data\Resources\stktraining\imagery when the Browse For Folder dialog box opens.
  7. Click OK to confirm your selection and to close the Browse For Folder dialog box.
  8. Select the StHelens_Training.pdtt check box.
  9. Click Add.
  10. Click Yes when prompted to use StHelens_Training.pdtt for analysis.

Viewing the inlaid terrain

View the terrain inlay in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on StHelens_Training.pdtt () in the Globe Manager hierarchy.
  3. Select Zoom To () in the shortcut menu.
  4. Use your mouse to move around and zoom in and out to view the terrain in the 3D Graphics window.

Inserting operational GPS satellites

Add the currently operational GPS satellites into your scenario.

Using the Standard Object Database

Use the Standard Object database to add the GPS satellites to your scenario.

  1. Return to the STK application.
  2. Bring the Insert STK Objects tool () to the front.
  3. Select Satellite () in the Select An Object To Be Inserted list.
  4. Select From Standard Object Database () in the Select A Method list.
  5. Click Insert. . ..

Inserting the operational GPS satellites

Search for operational GPS satellites using the AGI Standard Object Data Service.

  1. Clear the Data Sources - Local check box.
  2. Enter GPS in the Name or ID field.
  3. Scroll down in the Data Sources panel and locate Operational Status.
  4. Open the Operational Status drop-down list.
  5. Select Operational.
  6. Click Search.
  7. Select all the satellites in the Results list.
  8. Click Insert.
  9. When all the GPS satellites have propagated, click Close to close the Search Standard Object Data dialog box.

Modeling the GPS satellite transmitters

The STK software's Communications capability simulates the performance of communications systems in the context of their missions. Use the Communicationto model the physical components of your communications system. Start by attaching and modeling the GPS satellites' transmitters.

Inserting a Transmitter object

Attach a Transmitter object to a GPS satellite in your scenario to model characteristics of the transmitter, the antenna it uses, and the environment in which it operates.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Transmitter () object using the Insert Default () method.
  3. Select the first Satellite () object when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Right-click on Transmitter1 () in the Object Browser.
  6. Select Rename in the shortcut menu.
  7. Rename Transmitter1 () GPS_Tx1.

Modeling a GPS satellite transmitter

Use a GPS Satellite Transmitter model with the Transmitter object. This model lets you set up multiple antenna beams, each with its own specs and its own polarization and orientation properties. For this lesson, you are configuring one beam.

  1. Open GPS_Tx1's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Transmitter Model Component Selector ().
  4. Select GPS Satellite Transmitter Model () when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.

Modifying the beam specs

Modify the power parameter of your beam.

  1. Select the Beams tab.
  2. Select the Beam Specs sub-tab.
  3. Enter 27.45 W in the Power field.
  4. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling the GPS global antenna pattern

Modify the antenna parameters for your beam. For this analysis, you will use the GPS global antenna pattern. This antenna type models a GPS satellite antenna operating a global beam on the L1, L2 , or L5 frequency bands and uses a polar coordinate system. You will keep things simple, and model the Block IIR, L1 antenna type.

  1. Select the Antenna sub-tab.
  2. Select the Antenna sub-tab's Model Specs sub-tab.
  3. Ensure GPS Global is selected in the Antenna Model field.
  4. Open the Block Type drop-down list.
  5. Select IIR, L1.

    6. If you look in the Block Type list, you can see antenna types for the other block types.

  6. Enter 80 % in the Efficiency field.
  7. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting right-hand circular polarization

Polarization is a property of an electromagnetic wave that describes the orientation of the electric field vector with reference to the antenna's orientation. Antennas used in GPS systems are right-hand circularly polarized.

  1. Select the Antenna sub-tab's Polarization sub-tab.
  2. Select the Use check box.
  3. Open the Linear drop-down list.
  4. Select Right-hand Circular.
  5. Click Apply to confirm your selection and to keep the Properties Browser open.

Setting the data rate

The transmitter's data rate is a compound dimension with data bits and time as simple dimensions. For public use, the GPS design uses a Coarse/Acquisition pseudo-random noise (PRN) code transmitted at a data rate of 1.023 megabits per second.

  1. Select the transmitter's Model Specs tab.
  2. Enter 1.023 Mb/sec in the Data Rate field.
  3. Click Apply to confirm your change and to keep the Properties Browser open.

Modeling the modulator

The STK software's Communications capability allows you to select from multiple modulators, including user-defined modulators. The GPS Coarse/Acquisition code uses the binary Phase-shift keying (BPSK) modulation technique, which is the default setting. You will also use the Power Spectral Density (PSD) option. The Power Spectral Density option allows the scenario to model the actual spectral shape of the transmitted signal based on the modulation, data rate, etc. PSD is used to determine the Bandwidth Overlap Factor. By using signal PSD, you combine the entire signal including losses in your analysis. The nulls are where the main lobe and side lobes drop to zero.

  1. Select the Modulator tab.
  2. Select the Use Signal PSD check box.
  3. Enter 1 in the Number of Spectrum Nulls field.
  4. Click Apply to confirm your changes and to keep the Properties Browser open.

Notice that setting the number of spectrum null to 1 automatically sets the Bandwidth to 2.046 MHz, which you can see in the Signal Bandwidth panel.

Visualizing the antenna pattern

The Transmitter's object's 3D Graphics Attributes properties allow you to control the 3D display of contour lines and antenna patterns. Volume graphics displays the shape and gain levels of antenna beams.

  1. Select the 3D Graphics – Attributes page.
  2. Select the Show Volume check box in the Volume Graphics panel.
  3. Click Apply to confirm your selection and to keep the Properties Browser open.
  4. Bring the 3D Graphics window to the front.
  5. Right-click on the Satellite () object to which you attached the Transmitter () object in the Object Browser.
  6. Select Zoom To in the shortcut menu.

    7. GPS Transmitter Antenna Pattern

    Blue shows the maximum gain and red shows the minimum gain.

  7. Return to GPS_Tx1's () Properties () when finished.
  8. Clear the Show Volume check box in the Volume Graphics panel.
  9. Click OK to confirm your change and to close the Properties Browser.

Reusing the GPS transmitter

Copy and paste the GPS_Tx1 Transmitter object to the remaining GPS satellites in your scenario.

  1. Select GPS_Tx1 () in the Object Browser.
  2. Click Copy () on the Object Browser toolbar.
  3. Select the next Satellite () object in the Object Browser.
  4. Click Paste () on the Object Browser toolbar.
  5. Using this method, Paste () the transmitter to the remaining GPS satellites.

You only have to copy the transmitter the first time, then paste it onto the remaining satellites. To save time, you can use the Ctrl+C and Ctrl+V keyboard shortcuts to copy and paste your transmitters to the satellites.

Although there is no need to rename the new transmitters in this tutorial (you can just keep the STK numbering), this is one instance where in a real world scenario, matching transmitter names to the satellite can help you when running a report or graph.

Modeling the test area

Use an Area Target object to outline the test area. An Area Target object models a region on the surface of a central body. Using an Area Target object will also simplify creating a flight route for the test aircraft.

Inserting an Area Target object

Insert an Area Target object using the Area Target Wizard.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert an Area Target () object using the Area Target Wizard () method.
  3. Enter Test_Area in the Name field when the Area Target Wizard opens.
  4. Click Insert Point four times.
  5. Set the following in the Points panel in the order shown:
    6. Latitude Longitude
    46.00 deg -123.00 deg
    46.00 deg -122.00 deg
    47.00 deg -122.00 deg
    47.00 deg -123.00 deg
  6. Click OK to confirm your changes and to close the Area Target Wizard.

Making the area target visible

Earlier in the scenario, you turned off streaming terrain. This affects the view of the Area Target object when using a local terrain file. You need to change your Scenario object's 3D Graphics Global Attributes so you can view the Area Target on the terrain.

  1. Open GPS_Analysis' () Properties ().
  2. Select the 3D Graphics - Global Attributes page when the Properties Browser opens.
  3. Open the On Terrain drop-down list in the Surface Lines panel.
  4. Select On.
  5. Click OK to confirm your selection and to close the Properties Browser.

Decluttering labels

Objects located on the surface of the terrain could be covered by the terrain, which makes them unreadable. You can fix this by making a change to the 3D Graphics Window Details properties.

  1. Bring the 3D Graphics window to the front.
  2. Click Properties () on the 3D Window Defaults toolbar.
  3. Select the Details page when the Properties Browser opens.
  4. Select the Enable check box in the Label Declutter panel.
  5. Click OK to confirm your selection and to close the Properties Browser.

Viewing the test area

View Test_Area in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to Test_Area ().
  3. Zoom out on the 3D Graphics window to view the entire outline of Test_Area.

    4. test area

    Look at the southeastern corner of the test area. This is Mount St. Helens.

  4. Use your mouse to zoom back to the surface and explore the terrain.

Modeling the test aircraft

Your test will use a light aircraft equipped with a GPS receiver to fly search pattern inside of the designated test area. Use the Aviator capability to model the aircraft and its flight path. The Aviator capability models the aircraft's route through a sequence of curves parameterized by well-known performance characteristics of aircraft, including cruise airspeed, climb rate, roll rate, and bank angle.

Inserting an Aircraft object

Insert an Aircraft object using the Insert Default method.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert an Aircraft () object using the Insert Default () method.
  3. Rename Aircraft1 () Test_Acft.

Using the Aviator propagator

Select the Aviator propagator to create the test aircraft's flight route.

  1. Open Test_Acft's () Properties ().
  2. Select the Basic - Route page when the Properties Browser opens.
  3. Open the Propagator drop-down list.
  4. Select Aviator.
  5. Click Apply to confirm your selection and to keep the Properties Browser open.
  6. Click Optimize STK for Aviator when the Flight Path Warning dialog box opens.
  7. Read the information in the Flight Path Warning dialog box.
  8. Click OK to close the Flight Path Warning dialog box.

Selecting the aircraft model

In Aviator, an aircraft model defines the physical characteristics of the aircraft, the aircraft configuration, and the modes of flight — performance models — that define how the aircraft flies in any given situation. You will model a light aircraft using the pre-defined Basic General Aviation model.

  1. Click Select Aircraft () in the Initial Aircraft Setup toolbar.
  2. Select Basic General Aviation () in the User Aircraft Models () list in the Select Aircraft dialog box.

    3. Note that Basic General Aviation () is read only (). Read-only items in the Aviator Catalog Manager cannot be modified. They can be duplicated and then modified when needed.

  3. Click OK to confirm your selection and to close the Select Aircraft dialog box.
  4. Click Apply to confirm your changes and to keep the Properties Browser open.

Inserting the first procedure

Every mission must have at least one phase, and can have as many phases as you desire. You can select a specific set of performance models to use with each phase, allowing you perform one mission with multiple performance characteristics. You will only use one phase in this scenario.

  1. Right-click on Phase 1 () in the Mission List.
  2. Select Insert First Procedure for Phase ... () in the shortcut menu.

Selecting the site type

Each phase is composed sites and procedures. A site defines the location (excluding altitude) of the procedure and the types of procedures that are available to select. The exact relationship between the site location and the procedure is dependent on the specific procedure. A procedure is an action the aircraft performs at, or relative to, a site. Use the STK Area Target site type to define your search area.

  1. Select STK Area Target () in the Select Site Type list in the Site Properties dialog box.
  2. Select Test_Area () in the Link To list.
  3. Click Next >.

Selecting the procedure type

A procedure is an action the aircraft performs at, or relative to, a site. You can use an Area Target object to define a waypoint at the centroid of the selected area target, or, combined with the Area Target Search procedure, to define a search area. An Area Target Search procedure conducts a search pattern flight — comprised of raster parallel lines — within the selected STK Area Target site.

  1. Select AreaTargetSearch () in the Select Procedure Type list when the Procedure Properties dialog box opens.
  2. Clear the Use Aircraft Default Cruise Altitude check box in the Altitude panel.
  3. Enter 8000 ft in the Altitude field.
  4. Set the following in the Search Options panel:
    5. Option Value
    Max Separation 5 nm
    Course Mode Override
    Centroid True Course 90 deg
  5. Enter 5.00 in the Turn Factor field, located in the Enroute Options panel.

    6. The Turn Factor is the maximum amount — expressed as a multiplier — that the turn radius will be increased to minimize the bank angle required to complete the turn.

  6. Click Finish to confirm your selections and to close the Procedure Properties dialog box.
  7. Click OK to confirm your changes and to close the Properties Browser.

Viewing the aircraft's flight route

View Test_Acft's flight route in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to Test_Area ().
  3. Zoom in or out using your mouse so that you can see Test_Acft's flight route.

    4. Aircraft Flight Route

Aviator calculated a search pattern based on the parameters that you set. The course is defined based on Test_Area's centroid.

Modeling the GPS receiver

The test aircraft is equipped with a GPS receiver, which uses a Fixed Reception Pattern Antenna (FRPA).

Inserting a Receiver object

Insert and attach a Receiver object to the test aircraft.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Receiver () object using the Insert Default () method.
  3. Select Test_Acft () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename Receiver1 () GPS_Rx.

Using a Complex Receiver model

A Complex Receiver model enables you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Open GPS_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 () when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.

Setting the amplifier model specs

Adjust the low noise amplifier (LNA) losses and gain. A low noise amplifier is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio.

  1. Select the Model Specs tab.
  2. Set the following:
    3. Option Value
    Antenna to LNA Line Loss 1 dB
    LNA Gain 20 dB
    LNA to Receiver Line Loss 10 dB
  3. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling a GPS FRPA antenna pattern

The receiver requires a GPS FRPA antenna pattern. A GPS FRPA is a single element, omni-directional antenna designed to receive GPS satellite signals from about five to ten degrees above the horizon and up.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select GPS FRPA () when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling linear polarization

The receiver is linearly polarized with the electrical field aligned with the reference axis. Although it would be optimal for the receiver's antenna polarization to match the transmitter's, it is common to transmit with circular polarization but receive using linear polarization. You will lose power due to the polarization mismatch which will be modeled.

  1. Select the Polarization sub-tab.
  2. Select the Use check box.
  3. Ensure the Polarization is set to Linear, which is the default selection.
  4. Set the Cross-Pol Leakage Threshold to -30 dB.

    5. You only use Cross-Pol Leakage with a Receiver object. Whenever the STK software detects a complete polarization mismatch between the transmitted signal and the received signal under ideal conditions, the cross polarization leakage value is applied to model the less-than-ideal real-world performance.

  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the antenna's orientation

The STK software provides methods to specify the orientation of the antenna coordinate frame relative to the coordinate frame of the parent object. The antenna’s default orientation method is Azimuth Elevation, and the default elevation is 90 degrees, which points the antenna boresite along its parent object's positive Z vector. The positive Z vector of an Aircraft object points to its nadir. You need to point the antenna up along the negative Z vector.

  1. Select the Orientation sub-tab.
  2. Enter -90 deg in the Elevation field.
  3. Click Apply to confirm your change and to keep the Properties Browser open.

Modeling system noise temperature

The Receiver's System Noise Temperature allows you to specify the system's inherent noise characteristics. These can help simulate real-world RF situations more accurately.

  1. Select the System Noise Temperature tab.
  2. Select the Compute option.
  3. Enter 4.8 dB in the Noise Figure field in the LNA panel.
  4. Select the Compute option in the Antenna Noise panel.
  5. Select the following check boxes:
    • Earth
    • Sun
    • Atmosphere
    • Rain
    • Cosmic Background
  6. Click Apply to confirm your changes and to keep the Properties Browser open.

Using a Terrain Mask constraint

The test aircraft is flying over a mountainous area, and you'll need to account for any line-of-sight access blockages between the GPS satellite transmitters and the aircraft-mounted GPS receiver. Since are using analytical terrain, you can add a Terrain Mask constraint to the Receiver object to model the terrain blockages.

  1. Select the Constraints - Active page.
  2. Click Add new constraints () in the Active Constraints toolbar.
  3. Type terrain in the Search field in the Select Constraints to Add dialog box.
  4. Select Terrain Mask in the Constraint Name list.
  5. Click Add.
  6. Click Close to close the Select Constraints to Add dialog box.
  7. Click Apply to confirm your selection and to keep the Properties Browser open.

Visualizing the antenna pattern

Set the volume graphics and view the antenna pattern in the 3D Graphics window.

  1. Select the 3D Graphics - Attributes page.
  2. Select the Show Volume check box in the Volume Graphics panel.
  3. Click Apply to confirm your selection and to keep the Properties Browser open.
  4. Bring the 3D Graphics window to the front.
  5. Zoom to Test_Acft ().

    6. Receiver Antenna Pattern

  6. Return to GPS_Rx's () Properties () when finished.
  7. Clear the Show Volume check box in the Volume Graphics panel.
  8. Click OK to confirm your changes and to close the Properties Browser.

Determining GPS reception quality

Determine the signal quality between the GPS transmitters and the GPS receiver. A link budget reports the values that determine the GPS reception. For the purposes of this scenario, you will focus on one column in the link budget: C/No (dB * Hz). The carrier to noise density ratio (C/No) where C is the carrier power and No is equal to kT (Boltzmann's constant × system temperature) is the noise density. It is equivalent to C/N with a normalized Bandwidth (B=1). In this instance, the compound dimension being used is Spectral Density and the Base Dimension is Bandwidth × Ratio. The Bandwidth is in Hertz (Hz).

Computing access

Before you can generate a link budget, you must first compute the accesses between the aircraft-mounted GPS receiver and the GPS satellite transmitters using the Access tool.

  1. Right-click on GPS_Rx () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select all of the Satellite () objects in the associated objects list when the Access tool opens.
  4. Right-click on one of the Satellite () objects.
  5. Select Expand All in the shortcut menu.
  6. Right-click on one of the Transmitter () object.
  7. Select Select All Transmitters in the shortcut menu.
  8. Click .

Be patient. This could take a couple of minutes.

Creating a link budget report

Generate a Link Budget - Detailed report using the Report & Graph Manager.

  1. Click Report & Graph Manager....
  2. Select all of the Access () objects in the Object Type list when the Report & Graph Manager opens.
  3. Select the Specify Time Properties option in the Time Properties panel.
  4. Set the following time property options:
    5. Option Value
    Use step size / time bound Selected
    Step size: 60 sec
  5. Select the Link Budget - Detailed () report in the Installed Styles () folder in the Styles list.
  6. Click Generate....

Reviewing the Link Budget - Detailed report

Review the report. How is the reception between your GPS receiver and the satellite transmitters based on C/No (dB*Hz) of greater than or equal to 35? Keep in mind you're going to see fluctuations due to RF environment, location of the satellites (overhead, low on the horizon), distance, etc. Any fields in the report where it says "Data Unavailable" means there was no access between the GPS receiver and the GPS transmitter on that satellite.

  1. Browse to the C/No (dB * Hz) column.
  2. Scroll down through the report.
  3. View other data based on settings:
    • Atmos Loss (dB)
    • Rain Loss (dB)
    • Tatmos (K)
    • Train (K)
    • Tsun (K)
    • Tearth (K)
    • Tcosmic (K)
    • Tantenna (K)
  4. Close the Link Budget - Detailed report, the Report & Graph Manager, and the Access tool.

Modeling the test team's location

The test team is deploying a small, portable GPS jammer near the center of the test area.

Inserting a Place object

Insert a Place object to simulate the location of the test team.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Place () object using the Insert Default () method.
  3. Rename Place1 () Test_Team.

Setting test team's location

The test team is deployed in a clearing at the end of a dirt road, very near the test area's centroid. Their jammer will be placed atop a 2-meter antenna.

  1. Open Test_Team's () Properties ().
  2. Select the Basic - Position page when the Properties Browser opens.
  3. Set the following in the Position panel:
    4. Option Value
    Latitude 46.4995 deg
    Longitude -122.4944 deg
    Height Above Ground 2 m

    Height Above Ground raises the Test_Team Place object two meters above the surface of the terrain. When you attach a Transmitter object to Test_Team, the Transmitter object's antenna will also be raised two meters above the terrain's surface.

  4. Click OK to confirm your changes and to close the Properties Browser.

Viewing the test team's location

View the test team's location in the 3D Graphics window. This is where the GPS jammer will be deployed. Look at its location compared to the test aircraft's flight route.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to Test_Team ().
  3. Use your mouse to view the area where the GPS jammer will be deployed and its location relative to the test aircraft.

    4. Test Team and Aircraft

Determining the range from the test team to the test aircraft

The jammer's manufacturer claims its maximum effective radius is 400 meters. Determine how far the test aircraft will be from test team during the test using an AER report, which reports azimuth, elevation, and range values for the relative position vector between the base object and the target object, during access intervals.

  1. Right-click on Test_Team () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select Test_Acft () in the Associated Objects list when the Access tool opens.
  4. Click .
  5. Click AER... in the Reports panel.
  6. Scroll down to the Statistics at the bottom of the AER report.
  7. Note the minimum and maximum range of the Test_Acft () from Test_Team ().

    8. The aircraft never gets closer than approximately one to two kilometers from the test team. This is well outside the manufacturer's claimed radius of 400 meters.

  8. Close () the AER report when finished.
  9. Click Close to close the Access tool.

Modeling the portable jammer

Model the test team's jammer with a new Transmitter object.

Attaching a Transmitter object to Test_Team

Attach a Transmitter object to Test_Team.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Transmitter () object using the Insert Default () method.
  3. Select Test_Team () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename Transmitter2 () Jammer.

Configuring the GPS jammer

Use a Complex Transmitter Model for the jammer.

  1. Open Jammer’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 in the Select Component dialog box.
  5. Click OK to confirm your selection and to close the Select Component dialog box.

Setting the model specs

Model the jammer's frequency and power. Most small, portable GPS jammers have similar specifications.

  1. Select the Model Specs tab.
  2. Set the following options:
    3. Option Value
    Frequency 1.57542 GHz
    Power 35 W
  3. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling a dipole antenna pattern

For this analysis, you will use a dipole antenna pattern. Dipole antennas are modeled analytically using modeling equations that can be found in standard antenna texts.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select Dipole () when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Set the following options:
    7. Option Value
    Design Frequency 1.57542 GHz
    Length 7 in
    Efficiency 80 %
  7. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling vertical polarization

Set the antenna's polarization to vertical.

  1. Select the Polarization sub-tab.
  2. Select the Use check box.
  3. Open the Linear drop-down list.
  4. Select Vertical.
  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Modeling the jammer's modulation

Model the jammer's modulator. The Narrowband Uniform analytical modulator models narrowband jammers.

  1. Select the Modulator tab.
  2. Open the Name drop-down list.
  3. Select Narrowband Uniform.
  4. Click Apply to confirm your selection and to keep the Properties Browser open.

Preparing the jammer's transmitter for TIREM

Disable the Line-of-sight, Terrain Mask, and Az-El Mask constraints to take advantage of the over-the-horizon analysis functionality of TIREM.

  1. Select the Constraints - Active page.
  2. Clear the Enable check box for Line Of Sight in the Active Constraints list.
  3. Click Apply to confirm your change and to keep the Properties Browser open.

Using the TIREM capability

Recall that you enabled both rain and atmospheric absorption models at the scenario level to predict your link budget between the GPS satellites' transmitters and the aircraft's GPS receiver. The jamming device needs to take into account how terrain will affect its performance. The Terrain Integrated Rough Earth Model capability adds fidelity to the calculation and dynamic modeling of point-to-point line-of-sight effects for link performance in communications. It does this by taking into account the effect of irregular terrain and non-line-of-sight effects. The maximum height for these models is 30 km. You can set this RF Environment setting at the object level.

  1. Select the RF - Environment page.
  2. Select the Atmospheric Absorption Tab.
  3. Select the Use check box.
  4. Click the Atmospheric Absorption Model Component Selector ().
  5. Select the newest TIREM () component when the Select Component dialog box opens.
  6. Click OK to confirm your selection and to close the Select Component dialog box.
  7. Click OK to confirm your changes and to close the Properties Browser.

Adding receiver interference sources

You can add interference sources to a GPS receiver's properties. Then, you can assess their impact on the performance of the receiver.

  1. Open GPS_Rx's () Properties ().
  2. Select the Basic - Definition page.
  3. Select the Interference tab.
  4. Select the Use check box.
  5. Select Test_Team/Jammer () in the Available Emitters list.
  6. Move () Test_Team/Jammer () to the Assigned Emitters list.
  7. Click OK to confirm your selection and to close the Properties Browser.

Your link budgets will be automatically recomputed. Be patient. This can take a couple of minutes.

Checking for interference

You can check for interference using a pre-built report.

Generating a Link Budget - Interference report

Generate a Link Budget - Interference report. You can view all the transmitters on one report.

  1. Right-click on GPS_Rx () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Open the Object Type drop-down list in the Report & Graph Manager.
  4. Select Access.
  5. Select all of the Access () objects in the Object Type list, except Place-Test_Team-To-Aircraft-Test_Acft ().
  6. Select the Specify Time Properties option in the Time Properties panel.
  7. Set the following time properties options:
    8. Option Value
    Use step size / time bound Selected
    Step size 60 sec
  8. Select the Link Budget - Interference () report in the Installed Styles folder () in the Styles list.
  9. Click Generate....

Reviewing the report

Review the report to identify the extent of the interference.

  1. Scroll to the right and locate the C/No (dB*Hz) and C/(No+Io) (dB*Hz) columns in your generated report.

    2. The C/(No+Io) (dB*Hz) column measures interference. This is the carrier to noise-plus-interference density ratio (C/(No+Io)), where C is the carrier power, No is kT (Boltzmann's constant × system temperature), and Io is the interference power spectral density.

  2. Scroll down through the report to see how the portable jamming transmitter is affecting the aircraft's GPS reception.

    3. Column One: No Interference / Column Two: Interference

Scrolling through the report, you can see that the jammer is definitely affecting GPS reception, despite the manufacturer's claims.

Saving your work

Clean up and close out your scenario.

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

Summary

This tutorial demonstrated a link budget that focused on a specific value: C/No (dB * Hz). Representational averages were used for both rain and atmospheric absorption losses. GPS Transmitters and the aircraft's GPS receiver were built to model authentic civilian hardware. When the C/No (dB * Hz) value was equal to or greater than 35, GPS reception was good. Actual web specifications for illegal hand-held GPS jammers lead consumers to think they have a very limited jam radius. The jammer specifications used in this scenario stated that the jammer had a jamming radius of up to 400 meters. As you can see, the jammer reached out much further than that when targeting C/No (dB * Hz). You can verify this by matching Access range times against successful interference periods (C/No (dB*Hz) versus C/(No+Io) (dB*Hz)). You also took into account the effect terrain had on the jammer using TIREM.This tutorial is an excellent example of applying real-world hardware specifications and environmental factors into an STK scenario to obtain a better understanding of what the engineering team should expect to see during an actual test.

On your own

You can use this setup to perform additional analyses:

  • Match the Antenna Type to the different GPS block types, and rerun the link budget analysis.
  • Match the receiver's polarization to the transmitter's polarization, and rerun the link budget analysis.
  • Place two or three jammers in different locations through the test area, and analyze interference.
  • Place a jammer on the aircraft and a GPS receiver on the ground, and analyze interference.