Analyzer: Communications Analysis

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

Note: 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.

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

Capabilities Covered

This lesson covers the following capabilities:

  • STK Core
  • STK Analyzer
  • Coverage
  • Communications

Analyzer

Analyzer is integrated into the STK workflow to help you automate and analyze STK trade studies in order to better understand the design of your system. For purposes of this tutorial, Analyzer will be used to:

  • Perform Trade Studies. Analyzer will allow you to quickly perform “what if” studies so that you can understand how changing various Scenario parameters will impact the Scenario.
  • Optimize Scenario Parameters. Once you understand the key parameters of a Scenario, an optimizer will be employed to drive the Scenario to an optimal configuration.

Tutorial

In this tutorial, you will do the following:

  • Analyze a STK Communications Scenario for trends.
  • Optimize Communications Scenario parameters to meet mission objectives.

This tutorial is designed to teach you how to explore the STK design space in order to optimize your communications scenario. You will learn how to perform Parametric, Carpet Plot and Optimization studies that vary input variables through a range of values and plots one or more output variables.

Energy per Bit to Noise Power Spectral Density Ratio (Eb/No)

The goal of this scenario is to analyze a satellite in geosynchronous orbit (GEO) that will communicate with facilities spanning the contiguous United States (CONUS). Think of the coverage grid points as being locations of communication sites. the Coverage Definition object allows you to use a custom point file which would come in handy should you have actual locations of your communication sites. You need to better understand the requirements for the GEO satellite transmitter. In particular this includes specifying communications parameters for the transmitter. This study will focus on the Eb/No.

To better understand how the GEO satellite transmitter parameters impact coverage capabilities, a series of parametric studies will be run. For each parametric study, a single design parameter will be run through a sweep of values. At each value, coverage statistics will be collected using a Figure of Merit.

Your goal for this problem is to optimally configure the satellite’s transmitter to best provide link closure to all facilities via a high Eb/No. There are a handful of parameters that will impact our study:

  • Power
  • Frequency
  • Data Rate

Another parameter that will be studied is the antenna dish size.

To initiate the analysis, perform a few parametric studies to see how changing each of these parameters impacts the coverage capability. This will be followed by creation of a carpet plot to view how multiple parameters impact coverage. Lastly, an optimization study will be performed to scan through the design space to find a solution that meets requirements.

Starter Scenario

To speed things up and allow you to focus on the portion of this exercise that teaches you Analyzer, a partially created scenario has been provided for you.

Load the Starter Scenario

The STK scenario (VDF) used with this tutorial is located in the STK Data Federate (SDF). To open the scenario:

  1. Ensure that the Welcome dialog is visible in the STK Workspace.
  2. Click Open a Scenario.
  3. Select STK Data Federate from the Location: dropdown.
  4. Navigate to Sites/AGI/documentlibrary/STK 12/Starter Tutorials folder.

Open the VDF

  1. Select Analyzer_Comm_Analysis.vdf.
  2. Click Open .

Save the Starter Scenario as an *.sc File

When you open the scenario, a folder with the same name as the scenario will be created in the default user folder (C:\Documents\STK 12, for example). The scenario will not be saved automatically. When you save a scenario in STK, it will save in the format in which it originated. Therefore, if you open a VDF, the default save format will be a VDF. The same is true for a scenario file (*.sc). To save the VDF as an SC file, change the file format using the Save As procedure:

  1. Open the File menu and select Save As...
  2. Click to browse to your user location.
  3. Open the folder with the same name as the scenario.
  4. Change Save as type: to Scenario Files (*.sc) and click Save .
  5. Click Yes to confirm

2D Graphics Window

Determine Eb/No

In the 2D Graphics window, Geo_Sat’s antenna is boresighted at the geographic center of the contiguous United States (Centroid). The color contours represent the Eb/No dB of the transmission.

Eb/No Legend

  1. In the Object Browser, right click on EbNo_Avg () and select the Report & Graph Manager ().
  2. In the Installed Styles list, select the Grid Stats report and click Generate... .

    3. Grid Stats Report

    The contours are based on the minimum and maximum values in the report.

  3. Close the report and the Report & Graph Manager.

Analyzer Layout

Use the Analyzer Main Form to configure input/output variables available for further analysis. You can first select an object in the scenario tree on the left. When an object is selected, all possible input variable candidates are listed under the Inputs General tab and the Inputs Constraints tab. All output variable candidates are listed under the Outputs Data Providers tab, Outputs Object Coverage tab, Outputs DeckAccess tab or Outputs MissileModelingTools tab.

Determine the Impacts of Power on Coverage

The first study you will perform varies power to determine which value is best. You need to select input and output variables from the main Analyzer window to pass to the Parametric Study tool.

Select the input variable.

  1. Click the Analyzer button on the Analyzer Tool Bar.

    2. Analyzer Tool Bar Analyzer Icon

    Another way of opening Analyzer is to go to the Object Browser, right click on the scenario object (or any object), select the object's Plugins, and click Analyzer.

  2. When Analyzer is open, in the STK Variables list, expand Geo_Sat and then expand Tgt_Centroid.
  3. Select DL_Tx.
  4. In the STK Property Variables field, expand Model (Complex_Transmitter_Model), then ModelSpecs.
  5. Double-click Power. This moves Power to the Analyzer Variables field as an input.

Select the output variables.

  1. In the Object Browser, expand CONUS_Cov and select EbNo_Avg.
  2. In the Data Provider Variables field, expand Overall Value and double-click the following items to move them into the Analyzer Variables field:
    • Minimum
    • Maximum
    • Average

Parametric Study Tool

The Parametric Study Tool runs a Scenario through a sweep of values for some input variable. The resulting data can be plotted to view trends.

  1. In the Analyzer tool bar, select Parametric Study.

    2. Parametric Study Icon

    Analyzer builds a parametric representation of the currently loaded Scenario. This representation is viewed in the Component Tree displayed on the left side of each trade study tool.

  2. When the Parametric Study opens, in the Component Tree, using your left mouse button, drag Power to the Design Variable field on the right.

    3. Design Variable

  3. Set the following Design Variables:
    4. OptionValue
    starting value:300
    ending value:3000
    number of samples:10
    step size:300

  4. In the Component Tree, using your left mouse button, drag Minimum, Maximum, and Average to the Responses field on the right.
  5. In the lower right hand corner of the Parametric Study Tool, click Run... .

Data Explorer

The Data Explorer is a tool used by Trade Study tools to display data while they are being collected from STK. While data is being collected, the Data Explorer displays a progress meter, a halt button, and the data.

Table Page

The Table page displays trade study data in a tabular form. It is the default window that is present for all trade studies. Cells are shaded differently depending on the associated variable's state. Input variables are shown with green text, valid values are displayed with black text, invalid values are displayed with gray text, and modified values are displayed with blue text. From the table it is possible to view and edit all values in your trade study and even to add and remove whole runs.

Table Page

Toolbar

Once the trade study is complete and all data has been collected, the Data Explorer toolbar becomes active.

Data Explorer Tool Bar

Plot Types

Some trade study tools will automatically launch a default plot window when the trade study runs. Other plots can be created from the Add View dropdown menu.

Views

There are multiple views that can be selected to visualize the data seen on the Table Page. You can choose views by clicking on Add View.

  1. Close the 2D Scatter Plot that opened when you ran the trade study.
  2. On the Table Page tool bar, expand Add View.
  3. Select the 2D Line plot.

Dimensions

Use the Dimensions menu option to set which variable is displayed on which axis. In certain plots, you can set other global plot controls based on the plot variables.

  1. Click Dimensions.
  2. Open the x pull down menu and select Power.

    3. The chart now shows Minimum vs Power. Obviously, you could change y to Maximum or Average plots. However, you will add Maximum and Average to the plots results for comparison on one plot.

  3. In the Dimensions tool bar and select the plus (+) button.
  4. Change Series 2 (x) to Power and change (y) to Maximum. This adds Maximum to the plot.
  5. In the Dimensions tool bar and select the plus (+) button.
  6. Change Series 3 (x) to Power and change (y) to Average. This adds Average to the plot.
  7. Click on the plot to close the Dimension menu.

Axes

Use the Axes tab to set options for the axes.

  1. Click Axes.
  2. Select the Ticks tab.
  3. Change the Max # value to 40.
  4. Click on the plot to close the Axes menu.

    5. Custom 2D Line Plot

  5. Close the 2D Line Plot and the Table Page.
  6. When prompted to save, select No .
  7. Return to the Parametric Study Tool.
  8. Increase Power Design Variables by setting the following values:
    9. OptionValue
    starting value:3000
    ending value:30000
    number of samples:10
    step size:3000
  9. Click Run... .
  10. Close the 2D Scatter Plot that opened when you ran the trade study.
  11. On the Table Page tool bar, expand Add View .
  12. Select the 2D Line plot.

    13. This study gives you an understanding of what power to use for the transmitter to give the best overall minimum Eb/No. This tutorial is focusing on Power vs Minimum at 0 dB. Looking at the 2D Line plot, you can see that this is reached with a power level somewhere between 6000 and 9000 watts. You could continue to refine the Parametric Study until you find the desired value. Furthermore, you could enter that value in the Parametric Study Tool's component list under Power Value which is editable and sync that value back to STK.

    Edit and Sync to STK

  13. Close the 2D Line Plot and the Table Page.
  14. When prompted to save, select No .
  15. Close the Parametric Study Tool.
  16. Return to Analyzer.

Determine the Impacts of Frequency on Coverage

Power is not the only transmitter parameter that will impact your coverage. Frequency also has an impact. To determine how much, run another Parametric Study.

Select the input variable.

  1. In the STK Variables list, expand Geo_Sat and then expand Tgt_Centroid.
  2. Select DL_Tx.
  3. In the STK Property Variables field, expand Model (Complex_Transmitter_Model) and then ModelSpecs.
  4. Double-click Frequency. This moves Frequency to the Analyzer Variables field as an input.
  5. In the Analyzer tool bar select Parametric Study.
  6. In the Component Tree, using your left mouse button, drag Frequency to the Design Variable field on the right.
  7. Set the following Design Variables:
    8. OptionValue
    starting value:10
    ending value:20
    number of samples:11
    step size:1
  8. In the Component Tree, using your left mouse button, drag Minimum, Maximum and Average to the Responses field on the right.
  9. In the lower right hand corner of the Parametric Study Tool, click Run... .
  10. Close the 2D Scatter Plot that opened when you ran the trade study.
  11. On the Table Page tool bar, expand Add View.
  12. Select the 2D Line plot.

Dimensions

  1. Click Dimensions.
  2. Open the x pull down menu and select Frequency.

    3. The chart now shows Minimum vs Frequency. Obviously, you could change y to Maximum or Average plots. However, you will add Maximum and Average to the plots results for comparison on one plot.

  3. In the Dimensions tool bar and select the plus (+) button.
  4. Change Series 2 (x) to Frequency and change (y) to Maximum. This adds Maximum to the plot.
  5. In the Dimensions tool bar and select the plus (+) button.
  6. Change Series 3 (x) to Frequency and change (y) to Average. This adds Average to the plot.
  7. Click on the plot to close the Dimension menu.

    8. This study gives you an understanding of what frequency band to use for the transmitter which provides the best overall minimum Eb/No. Eb/No decreases with frequency due to an increase in propagation loss and decrease in Gaussian Antenna gain (the default antenna type you are using on the transmitter). You can see that frequencies < 13 GHz will assure you of an Eb/No > 0 for all of CONUS.

    Custom 2D Line Plot

  8. Close the 2D Line plot and the Table Page.
  9. When prompted to save, select No .
  10. Close the Parametric Study Tool.
  11. Return to Analyzer.

Determine the Impacts of Data Rate on Coverage

The next parameter impacting coverage is the data rate of the transmitter. For this study, you will vary the data rate from 10 to 20 Mb/sec (megabits per second).

Select the input variable.

  1. In the STK Variables list, expand Geo_Sat and then expand Tgt_Centroid.
  2. Select DL_Tx.
  3. In the STK Property Variables field, expand Modulator.
  4. Double-click DataRate. This moves DataRate to the Analyzer Variables field as an input.
  5. In the Analyzer tool bar select Parametric Study.
  6. In the Component Tree, using your left mouse button, drag DataRate to the Design Variable field on the right.
  7. Set the following Design Variables:
    8. OptionValue
    starting value:10e+06
    ending value:20e+06
    number of samples:11
    step size:1e+06
  8. In the Component Tree, using your left mouse button, drag Minimum, Maximum and Average to the Responses field on the right.
  9. In the lower right hand corner of the Parametric Study Tool, click Run... .
  10. Close the 2D Scatter Plot that opened when you ran the trade study.
  11. On the Table Page tool bar, expand Add View and select the 2D Line plot.

Dimensions

  1. Click Dimensions.
  2. Open the x pull down menu and select DataRate.

    3. The chart now shows Minimum vs DataRate. Obviously, you could change y to Maximum or Average plots. However, you will add Maximum and Average to the plots results for comparison on one plot.

  3. In the Dimensions tool bar and select the plus (+) button.
  4. Change Series 2 (x) to DataRate and change (y) to Maximum. This adds Maximum to the plot.
  5. In the Dimensions tool bar and select the plus (+) button.
  6. Change Series 3 (x) to DataRate and change (y) to Average. This adds Average to the plot.
  7. Click on the plot to close the Dimension menu.

Data Rate Change

Coverage decreases with increased data rate. Decreasing the data rate equivalently decreases the bandwidth and increases the Eb/No.

  1. Close the 2D Line Plot and the Table Page.
  2. When prompted to save, select No .
  3. Close the Parametric Study Tool.
  4. Return to Analyzer.

Determine the Impacts of Antenna Size on Coverage

The next parameter you will examine is the size of the antenna dish for the transmitter. Although this isn't part of the transmitter's optimization, it's an interesting study. For this study, vary the dish size from 0.5 to 2 m (meters).

Select the input variable.

  1. In the STK Variables list, expand Geo_Sat and then expand Tgt_Centroid.
  2. Select DL_Tx.
  3. In the STK Property Variables field, expand Antenna and then ModelSpec.
  4. Double-click Diameter. This moves Diameter to the Analyzer Variables field as an input.
  5. In the Analyzer tool bar select Parametric Study.
  6. In the Component Tree, using your left mouse button, drag Diameter to the Design Variable field on the right.
  7. Set the following Design Variables:
    8. OptionValue
    starting value:0.5
    ending value:2
    number of samples:16
    step size:0.1
  8. In the Component Tree, using your left mouse button, drag Minimum, Maximum and Average to the Responses field on the right.
  9. In the lower right hand corner of the Parametric Study Tool, click Run... .
  10. Close the 2D Scatter Plot that opened when you ran the trade study.
  11. On the Table Page tool bar, expand Add View and select the 2D Line plot.

Dimensions

  1. Click Dimensions.
  2. Open the x pull down menu and select Diameter.

    3. The chart now shows Minimum vs Diameter. Obviously, you could change y to Maximum or Average plots. However, you will add Maximum and Average to the plots results for comparison on one plot.

  3. In the Dimensions tool bar and select the plus (+) button.
  4. Change Series 2 (x) to Diameter and change (y) to Maximum. This adds Maximum to the plot.
  5. In the Dimensions tool bar and select the plus (+) button.
  6. Change Series 3 (x) to Diameter and change (y) to Average. This adds Average to the plot.
  7. Click on the plot to close the Dimension menu.

    8. Antenna Size Change

    Notice that while the maximum and for the most part average Eb/No values rise with increasing antenna size, the minimum value decreases. The maximum coverage value increases with increasing antenna diameter, however you do see diminishing returns. The reason for this is that as antenna size increases, the gain increases while the Beamwidth decreases. Locations farthest from the antenna boresight see their Eb/No values drop as the Beamwidth decreases. Take a closer look at the average coverage.

  8. Close the 2D Line Plot.

Looking Closer at the Average

  1. On the Table Page expand Add View and select 2D Line Plot.
  2. Expand Dimensions and make the following changes:
    3. OptionValue
    xDiameter
    yAverage
  3. Select Axes.
  4. Select the Ticks tab and change Max # to 20.
  5. Click the 2D Line Plot.

    6. Eb/No vs Antenna Size (Average)

    The average Eb/No value reaches a peak value at an antenna diameter of about 1.5 m (meters) and then the average Eb/No values begin to decrease.

  6. Close the 2D Line Plot and the Table Page.
  7. When prompted to save, click No .
  8. Close the Parametric Study Tool.
  9. Return to Analyzer.

Determine if Power and Frequency Impact One Another

You have determined that power and frequency have significant impacts on coverage capability while data rate has less of an influence. Power has an increasingly positive impact. Frequency has a negative influence. This leads to the following question:

How do frequency and power affect one another?

You can answer the question by performing a 2-dimensional parametric study called a Carpet Plot.

Carpet Plot Tool

A Carpet Plot is a means of displaying data dependent on two variables in a format that makes interpretation easier than normal multiple curve plots. A Carpet Plot can be thought of as a multi-dimensional Parametric Study.

  1. In the Analyzer tool bar select Carpet Plot.

    2. Carpet Plot Icon

    Setting the design variables is similar to using the Parametric Study Tool except you now have two variables instead of one.

  2. In the Component Tree, using your left mouse button, drag Frequency to the first Design Variable field on the right and Power to the second Design Variable field.
  3. Set the following Frequency Design Variables:
    4. OptionValue
    From10
    To20
    Num Steps5
    Step Size2.5
  4. Set the following Power Design Variables:
    5. OptionValue
    From3000
    To30000
    Num Steps6
    Step Size5000

    If you are wondering why this tutorial uses large step sizes, it's due to keeping the tutorial time under an hour. These settings will require a total of thirty runs to obtain every variable combination. On your own, you can set the frequencies and power to change at smaller step sizes to make the trade study more realistic. Be patient. Depending on your settings, you could end up running hundreds of runs.

  5. In the Component Tree, using your left mouse button, drag Minimum to the Responses field on the right.
  6. In the lower right hand corner of the Carpet Plot Tool, click Run... .

    7. Carpet Plot

    Using the Carpet Plot you can determine combinations of frequency and power desired for your requirement which is an Eb/No of 0 dB.

  7. Close the Carpet Plot and the Table Page.
  8. When prompted to save, select No .
  9. Close the Carpet Plot Tool.
  10. Return to Analyzer.

Optimize Transmitter Parameters

You now know that transmitter parameters have a large impact on coverage capabilities. In order to optimize these parameters, you can either guess at values, or employ an optimization tool. Although you can clearly see trends from the previous studies, guessing at values will be difficult because you are dealing with multiple parameters at the same time and the trends you have studied thus far assume only one or two parameters are changed at a time.

To solve more complex problems, an optimization tool can be a very useful guide. An optimizer is an automated tool that makes mathematical calculations about a design problem and incrementally attempts to find an optimal solution. The algorithm you will employ here is an optimizer. The selected algorithm will compute derivatives about an initial point in the design space and compute a search direction. This process will repeat until no more progress can be achieved on the objective function.

An optimizer will be used in this problem to minimize the power requirement for the transmitter while maintaining a minimum coverage capability of 0 dB for the coverage area.

Optimization Tool

The Optimization Tool is a collection of optimization algorithms that can be used within Analyzer. Currently over 30 algorithms are available including gradient based optimizers, genetic algorithms, multi-objective algorithms, and other heuristic search methods (see Algorithm Comparison Chart). A common graphical user interface is provided to define optimization problems. An algorithm selection wizard is also provided to make it easy to choose algorithms that will work best for the problem at hand.

  1. In the Analyzer tool bar select the Optimization Tool.

    2. Optimization Tool Icon

    The objective is to minimize the value for power by changing frequency, data rate, and power all while maintaining a minimum Eb/No value of as close to 0 to 10 dB as possible.

  2. In the Component Tree, using your left mouse button, drag Power to the Objective field on the right.
  3. Ensure the Goal field is set to Minimize.
  4. In the Component Tree, using your left mouse button, drag Minimum to the Constraint field on the right.
  5. Set the Lower Bound to 0 (zero) and the upper bound to 10 (ten).
  6. In the Component Tree, using your left mouse button, drag Power, Frequency, and DataRate to the Variable field on the right.
  7. Make the following changes:
    8. OptionLower BoundUpper Bound
    Power30030000
    Frequency1020
    DataRate10e620e6
  8. Set Algorithm to Design Explorer.

    9. Design Explorer is an advanced optimization algorithm that was developed to efficiently solve difficult real-world design problems. Design Explorer can effectively solve difficult optimization problems where engineering analyses take long time to run, their responses are noisy and highly non-linear, and engineering simulations may fail. Design Explorer automatically creates approximation models of objectives and constraints and uses them to perform optimization runs with different starting points to find global optimum. Design Explorer solves general constrained optimization problems with continuous design variables.

  9. In the lower right hand corner of the Optimization Tool, click Run .

    10. The optimizer will display a history of steps as it progresses. By default only the objective definition will be displayed.

    The above process can be repeated to add plots for frequency and data rate.

  10. Close the 2D Scatter Plot
  11. When the optimization study is complete, the View Output button on the Optimization Tool panel will contain the convergence history of the process. Select the Best Design tab which will contain the optimized values. These values are also displayed in the Value column for the design variables in the Optimization Tool. See images below.

  12. Click the Sync to STK button to push these parameters to the scenario.

    13. Optimization Parameters

    The optimizer was able to drive power to its lower bound of 300 W while at the same time attaining the goal of between 0 and 10 dB of minimum Eeb/Nn for all time.

    1. Recompute the Coverage analysis
      1. Right click on CONUS_Cov
      2. Extend the CoverageDefinition menu
      3. Select Compute Access
    2. Regenerate the Grid Stats Report
      1. In the Installed Styles list, select the Grid Stats report and click Generate... .
      2. In the Object Browser, right click on EbNo_Avg () and select the Report & Graph Manager ().

    If you create a final Grid Stats Report you obtain the following:

    Final Grid Stats Report

    You can compare your 2D Graphics view with the original legend:

    The legend is enabled on the Figure of Merit - 2D Graphics - Static page)

    Final 2D Graphics Window View

When You Finish

  1. Close the Table Page, the Optimization Tool, Analyzer, the Report & Graph Manager, and any open reports.
  2. Save your work.
  3. Close the scenario.
  4. Close STK.