Create a Multihop Communication Link

STK Pro, STK Premium (Air), STK Premium (Space), 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.

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.

This lesson requires an Internet connection and STK 12.8 or newer.

Capabilities covered

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

  • STK Pro
  • Communications

Problem statement

You require a quick and simple way to simulate and analyze multihop communications. A ship passing through the Panama Canal Zone needs to transmit data to a ship located in the Strait of Hormuz using two geosynchronous satellites. The entire communication system is analog. Surface units are using K-Band (18-24 GHz) communications. Satellite to satellite communications are via S-Band (2-4 GHz). The ship transiting the Panama Canal can target its phased array communication antennas at the satellite. Satellite to satellite communications are also targeted via small parabolic or Gaussian antennas. Satellite to surface antennas are fixed and boresighted away from the ships. The ship transiting the Straight of Hormuz can target its parabolic receive antenna at the satellite. You are looking for an opportunity during which you can pass data.

Solution

Use the STK software's Communications capability to model a scenario that analyzes a multihop communication link from a ship transiting the Panama Canal Zone to a ship transiting the Strait of Hormuz. Apply the STK application's radio frequency environmental features to obtain realistic communications analysis.

What you will learn

Upon completion of this tutorial, you will understand:

  • How to model communications involving analog transponders
  • How to activate rain and atmospheric absorption models
  • How to generate a custom bent pipe report using the Chain object and the Report & Graph Manager

Using a starter scenario (*vdf file)

To speed things up and allow you to focus on the portion of this exercise that teaches you build a multihop communication system in the STK application, a partially created scenario has been provided for you.

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

Saving a VDF as a Scenario file

When you save a scenario in the STK application, it will save in the format in which it originated. In other words, if you open a VDF, the default save format will be a VDF (.vdf). The same is true for a scenario file (*.sc). If you want to save a VDF as a SC file (or vice-versa), you must change the file format when you are performing the Save As procedure.

  1. Open the File menu.
  2. Select Save As....
  3. Select the STK User folder in the navigation pane.
  4. Select Comm_MultiHopLink ().
  5. Click Open.
  6. Open the Save as type drop-down list.
  7. Select Scenario Files (*.sc).
  8. Click Save.
  9. Click Yesto Replace existing file.

Save often!

Building a communications link

In the Object Browser, you can see multiple Sensor objects. The Sensor objects are simulating servo motors and are being used to point a steerable antenna at a specific target or boresight an antenna in a specific area. You will attach a Transmitter or Receiver object to a specified Sensor object, which will point the embedded antenna at a target. Prior to beginning the scenario, you can get an overall feel of where each object is located and where the different sensors point.

You'll build the communication link starting where the transmission begins and follow the transmission until it reaches its destination.

Configuring the terrain atmospheric models to your scenario

You will configure your scenario to include the ITU-R rain model and the ITU-R atmospheric absorption model.

Loading the ITU-R rain model

You will use the ITU-R rain model for your analysis.

  1. Right-click on Comm_MultiHopLink () in the Object Browser.
  2. Select Properties ().
  3. Select the RF - Environment page when the Properties Browser opens.
  4. Select the Rain, Cloud & Fog tab.
  5. Select the Use check box in the Rain Model panel.
  6. Click the Rain Loss Model Component Selector ().
  7. Select the newest ITU-R (International Telecommunication Union) model (e.g. ITU-R- P618-13) in the Rain Loss Models list when the Select Component dialog box opens.
  8. Click OK to close the Select Component dialog box.
  9. Click Apply to accept the changes and keep the Properties Browser open.

Loading the ITU-R atmospheric absorption model

You will use the ITU-R atmospheric absorption model.

  1. Select the Atmospheric Absorption tab.
  2. Select the Use check box.
  3. Click the Atmospheric Absorption Model Component Selector ().
  4. Select the newest ITU-R (International Telecommunication Union) model (e.g. ITU-R- P676-13) in the Atmospheric Absorption Models list when the Select Component dialog box opens.
  5. Click OK to close the Select Component dialog box.
  6. Click OK to accept your changes and to close the Properties Browser.

Building the transmission uplink from the Canal Zone

A communications link exists between Canal_Transit () and Geo_West (). Canal_Transit () is transmitting on a frequency of 20 GHz with a power of 30 dBW. Canal_Transit () is employing a phased array transmit antenna. Geo_West () is using a 4.6 meter diameter fixed boresight parabolic receiver antenna.

If you look at the 2D and 3D Graphics windows, you can see the satellite’s sensor boresight contour in the canal zone.

3D Canal Zone boresight

There are many parameters that reflect the quality of a signal, but Bit Error Rate (BER) is typically a good indicator. For this tutorial, we will focus on BER. The lower the BER, the better the quality of the signal.

  1. Select Transmitter () in the Insert STK Objects tool.
  2. Select the Insert Default () method.
  3. Click Insert... .
  4. Select Canal_Transit () in the Select Object dialog box.
  5. Click OK.
  6. Right click on Transmitter1 () in the Object Browser.
  7. Select Rename in the shortcut menu.
  8. Rename Transmitter1 () to UplinkXmtr.

Selecting a Complex Transmitter Model

The Complex Transmitter Model allows you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Open UplinkXmtr'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 when the Select Component dialog box opens.
  5. Click OK to close the Select Component dialog box.
  6. Select the Model Specs tab.
  7. Enter 20 GHz in the Frequency field.
  8. Enter 8 Mb/sec in the Data Rate field.
  9. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling a phased array antenna

The phased array antenna model consists of many radiating elements. Each element is modeled as an isotropic pattern.

  1. Select the Antenna tab.
  2. Click the Antenna Model Component Selector ().
  3. Select Phased Array () in the Antenna Models list when the Select Component dialog box opens.
  4. Click OK to close the Select Component dialog box.
  5. Select the Model Specs sub tab.
  6. Enter 21 GHz in the Design Frequency field.

Configuring the antenna elements

The Element Configuration tab enables you to define the physical aspects of the antenna elements

  1. Select the Element Configuration sub-sub tab.
  2. Enter the following in the Number of Elements panel:
    3. Option Value
    X 7
    Y 7
  3. Click Applyto accept your changes and to keep the Properties Browser open.

Selecting the beam direction provider

The Beam Direction Provider tab enables you to select where the antenna points its beam.

  1. Select the Beam Direction Provider sub-sub tab.
  2. Select the Enabled check box in the Beam Steering panel.
  3. Move () Geo_West () from the objects list to the selected objects list.
  4. Click Apply to accept your changes and to keep the Properties Browser open.

Orienting the antenna

The STK application provides methods to specify the orientation of the antenna coordinate frame relative to the coordinate frame of the parent object. You want to move the antenna to its location on the 3D Graphics model.

  1. Select the Orientation sub-sub tab.
  2. Set the following in the Position Offset panel:
    3. Option Value
    X -42 m
    Y -29 m
    Z 35 m
  3. Click Apply to accept your changes and to keep the Properties Browser open.

You can use these steps when using the STK application to place the object onto the 3D Graphics model in its correct location.

Displaying the antenna pattern in the 3D Graphics window

The 3D Graphics Attributes page for UplinkXmtr () allows you to control the 3D Display of the antenna pattern.

  1. Select the 3D Graphics - Attributes page.
  2. Select the Show Volume check box in the Volume Graphics panel.
  3. Enter the following settings:
    4. Option Value
    Show as wireframe Selected
    Gain Scale (per dB) 0.1 km
    Minimum Displayed Gain -5 dB
  4. Select the Set azimuth and elevation resolution together check box in the Pattern panel.
  5. Click OK to accept your changes and to close the Properties Browser.

You can use these steps later in the lesson to view other antenna patterns if you desire to do so.

Viewing the antenna pattern in the 3D Graphics window

View Canal_Transit's antenna pattern in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right click on Canal_Transit () in the Object Browser.
  3. Select Zoom To.
  4. Use your mouse to zoom out so that you can see the phased array antenna pattern.
  5. Notice that the antenna pattern is located on the ship's superstructure where the actual antenna is located on the ship.

Canal transit's phased array antenna pattern

Configuring an analog transponder

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. Select TgtCanalZone () in the Select Object dialog box.
  3. Click OK to close the Select Object dialog box.
  4. Rename the Receiver1 () to UplinkRcvr.

Using a Complex Receiver Model

The Complex Receiver Model allows you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Open UplinkRcvr'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 when the Select Component dialog box opens.
  5. Click OK to close the Select Component dialog box.
  6. Click Apply to accept your change and to keep the Properties Browser open.

Modeling a parabolic antenna

The Parabolic Antenna Model is an analytical model of a uniformly illuminated antenna.

  1. Select the Antenna tab.
  2. Select the Model Specs sub tab.
  3. Click the Antenna Model Component Selector ().
  4. Select the Parabolic () in the Antenna Models list when the Select Component dialog box opens.
  5. Click OK to close the Select Component dialog box.
  6. Enter 21 GHz in the Design Frequency field.
  7. Enter 4.6 m in the Diameter field.
  8. Click Apply to accept your changes and to keep the Properties Browser open.

Adding additional gains and losses

During communications analyses, it is often necessary to model gains and losses that affect performance but are not defined using built-in analytical models.

  1. Select the Additional Gains and Losses tab.
  2. Click Add in the Pre-Receive Gains/Losses panel.
  3. Enter 2 dB in the Gain cell.
  4. Click Add in the Pre-Demodulation Gains/Losses panel.
  5. Enter 2 dB in the Gain cell.
  6. Click OK to accept your changes and to close the Properties Browser.

Inserting Geo West's transmitter

Attach a Transmitter object to Geo_West's sensor.

  1. Insert a Transmitter () object using the Insert Default () method.
  2. Select Tgt_Geo_East () in the Select Object dialog box.
  3. Click OK to close the Select Object dialog box.
  4. Rename Transmitter2 () to Geo_West_ReXmtr.

Using a Complex Retransmitter Model

The Complex Retransmitter Model allows you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Open Geo_West_ReXmtr 's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Transmitter Model Component Selector ().
  4. Select Complex Re-Transmitter Model () in the Transmitter Models list when the Select Component dialog box opens.
  5. Click OK to close the Select Component dialog box.
  6. Select the Model Specs tab.
  7. Set the following parameters:
    8. Option Value
    Sat. Power 20 dBW
    Sat. Flux Density -120 dBW/m^2
    • Sat. Power or Saturation Output Power is the RF Power output of the transmitter as measured at the input to the antenna when the amplifier is at its saturated state.
    • Sat. Flux Density or Saturation Flux Density (SDF) is the amplifier's saturation point by the input flux density in dBW/m2. This represents the per carrier flux density for systems supporting multiple carriers per transmitter. A lower SFD value makes the input of the transponder more sensitive and requires less uplink power from the uplink station. Increasing the sensitivity in the transponder allows the introduction of more noise into the system, due to the higher sensitivity.
  8. Click Apply to accept your changes and to keep the Properties Browser open.

Selecting a Gaussian Antenna Model

The Gaussian Antenna Model uses an analytical model of a Gaussian beam. The model is similar to a parabolic antenna.

  1. Select the Antenna tab.
  2. Keep the Gaussian Antenna Model type.
  3. Enter 3 GHz in the Design Frequency field.
  4. Enter 2 m in the the Diameter field.
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the transfer function frequency coefficients

Frequency coefficients specify the transmitted frequency as a function of the received frequency. They can only be entered in polynomial form. The coefficient order displays in the left column of the table and updates automatically as coefficients are added or removed. Input and output units are in Hz. The default coefficients of -7.0e+08 and 1.0 are used to model a 700 MHz down conversion. The transmitter is transmitting on a frequency of 4 GHz.

  1. Select the Transfer Functions tab.
  2. Change the Index 0 Coefficient to -1.6e+010.
  3. Click OK to accept your changes and to close the Properties Browser.

Inserting Geo_East's receiver

Continue the link by attaching a Receiver object to Geo_East. You can somewhat simplify this process by reusing UplinkRcvr.

  1. Select UplinkRcvr () in the Object Browser.
  2. Click Copy () in the Object Browser toolbar.
  3. Select Tgt_Geo_West () in the Object Browser.
  4. Click Paste () in the Object Browser toolbar.
  5. Rename UplinkRcvr1 () to Geo_East_Rcvr.

Updating Geo East Receiver's properties

You need to make a couple of changes to Geo_East_Rcvr's properties.

  1. Open Geo_East_Rcvr's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Select the Antenna tab.
  4. Set the Design Frequency to 3 GHz.
  5. Enter 2 m in the Diameter field.
  6. Click OK to accept your changes and to close the Properties Browser.

Completing Geo East's transponder

Geo_East will retransmit the data to Hormuz_Transit.

  1. Copy () Geo_West_ReXmtr () and paste () it to TgtHormuz () in the Object Browser.
  2. Rename Geo_West_ReXmtr1 () to Geo_East_ReXmtr.

Changing the antenna properties

Configure a Parabolic antenna model for the Geo_East_ReXmt transmitter.

  1. Open Geo_East_ReXmtr's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Select the Antenna tab.
  4. Select the Model Specs sub-tab.
  5. Click the Antenna Model Component Selector ().
  6. Select Parabolic () in the Antenna Models list when the Select Component dialog box opens.
  7. Click OK to close the Select Component dialog box.
  8. Enter 21 GHz in the Design Frequency field.
  9. Enter 4.6 m in the Diameter field.
  10. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the transfer function frequency coefficients

The downlink frequency is 18 GHz.

  1. Select the Transfer Functions tab.
  2. Change the Index 0 Coefficient to 1.4e+10.
  3. Click OK to accept your changes and to close the Properties Browser.

Creating a downlink receiver

Hormuz_Transit's receiver completes the link.

  1. Select Geo_East_Rcvr () in the Object Browser.
  2. Click Copy () in the Object Browser toolbar.
  3. Select TgtEastSat () in the Object Browser.
  4. Click Paste () in the Object Browser toolbar.
  5. Rename Geo_East_Rcvr1 () to DownlinkRcvr.

Change the antenna properties

Configure DownlinkRcvr's design frequency and antenna diameter.

  1. Open DownlinkRcvr's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Select the Antenna tab.
  4. Enter 21 GHz in the Design Frequency field.
  5. Enter 3 m in the Diameter field.
  6. Click OK to accept your changes and to close the Properties Browser.

Creating a Chain object

A Chain Objectmodels a list of objects in order of access.

Adding a new Chain object

Create a Chain () object that starts at UplinkXmtr () and ends at DownlinkRcvr ().

  1. Insert a Chain () object using the Insert Default () method.
  2. Rename Chain1 () to AnalogLink.

Define the start and end objects

Start by choosing the start object and end object in your chain.

  1. Open AnalogLink's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Start Object ellipsis ().
  4. Select UplinkXmtr () in the Select Object dialog box.
  5. Click OK to close the Select Object dialog box.
  6. Click the End Object ellipsis ().
  7. Select DownlinkRcvr () in the Select Object dialog box.
  8. Click OK to close the Select Object dialog box.

Create the Chain object's connections

After you choose the start and end objects in your chain, you need to build the chain's connections. It doesn't matter in which order you place the connections in the Connections list. What matters is the From Object must be able to access the To Object.

Building the first connection

Build your first connection from UplinkXmtr to UplinkRcvr.

  1. Click Add in the Connections panel.
  2. Click the From Object ellipsis ().
  3. Select UplinkXmtr () in the Select Object dialog box.
  4. Click OK to close the Select Object dialog box.
  5. Click the To Object ellipsis ().
  6. Select UplinkRcvr () in the Select Object dialog box.
  7. Click OK to close the Select Object dialog box.

Building the second connection

Extend the connection from UplinkRcvr to Geo_West_ReXmtr.

  1. Click Extend.
  2. Click the To Object ellipsis ().
  3. Select Geo_West_ReXmtr () in the Select Object dialog box.
  4. Click OK to close the Select Object dialog box.

Building the third connection

Extend the connection from Geo_West_ReXmtr to Geo_East_Rcvr.

  1. Click Extend.
  2. Click the To Object ellipsis ().
  3. Select Geo_East_Rcvr () in the Select Object dialog box.
  4. Click OK to close the Select Object dialog box.

Building the fourth connection

Extend the connection from Geo_East_Rcvr to Geo_East_ReXmtr.

  1. Click Extend.
  2. Click the To Object ellipsis ().
  3. Select Geo_East_ReXmtr () in the Select Object dialog box.
  4. Click OK to close the Select Object dialog box.

Building the fifth and final connection

Finally, extend the connection from Geo_East_ReXmtr to DownlinkRcvr.

  1. Click Extend.
  2. Click the To Object ellipsis ().
  3. Select DownlinkRcvr () in the Select Object dialog box.
  4. Click OK to close the Select Object dialog box.
  5. Click OK to accept your changes and to close the Properties Browser.

Viewing the link in the 2D Graphics window

You can see the completed link from Canal_Transit to Hormuz_Transit in the 2D Graphics window.

  1. Bring the 2D Graphics window to the front.
  2. Zoom out so that you can see the Panama Canal, both satellites and the Strait of Hormuz.

2D Completed Link

You can now see the completed link.

Creating a custom Bent Pipe report

By default, the STK application only handles two links in reports. This means you will have to create a unique report that will model the full communication link from Canal_Transit to Hormuz_Transit. You need to show the BER total for all three links by customizing the Bent Pipe Comm Link report in the Report & Graph Manager.

  1. Right-click on AnalogLink () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Right-click on the Bent Pipe Comm Link () report in the Installed Styles list when the Report & Graph Manager opens.
  4. Select Duplicate ().

Selecting the data providers and elements

You create a new line in the report for additional data providers.

  1. Select the Content page when the Properties Browser opens.
  2. Select Link Information-BER2 in the Report Contents list.
  3. Click New Line.
  4. Select Line 3 in the Report Contents list.
  5. Expand the Link Information () data provider in the Data Providers list.
  6. Add the following data provider elements to Line 3 in the Report Contents list in the order shown:
    • Xmtr Power3 ()
    • Xmtr Gain3 ()
    • EIRP3 ()
    • Prop Loss3 ()
    • Rcvd. Frequency3 ()
    • Rcvd. Iso Power3 ()
    • Flux Density3 ()
    • g/T3 ()
    • C/No3 ()
    • Bandwidth3 ()
    • C/N3 ()
    • Eb/No3 ()
    • BER 3 ()

Changing the report values to scientific notation

Changing the BER to scientific notation allows you to look at the significant digits and the exponent of 10, which is what is shown on the other two lines.

  1. Select Link Information - BER3 in the Report Contents list.
  2. Click Options....
  3. Open the Notation drop-down list when the Options: Section 1, Line 3, Link Information-BER3 dialog box opens.
  4. Select Scientific (e).
  5. Click OK to close the Options: Section 1, Line 3, Link Information-BER3 dialog box.

Adding a line for the composite values

Add a new line that will show the composite values of the entire communications link.

  1. Select Line 4 in the Report Contents window.
  2. Click Remove.
  3. Select Link Information-BER3.
  4. Click New Line.
  5. You are still using the Link Information () data provider.
  6. Select Line 4.
  7. Add the following data provider elements to Line 4 in the Report Contents list in the order shown:
    • IBO3 ()
    • OBO3 ()
    • C/No Tot.3 ()
    • C/N Tot.3 ()
    • Eb/No Tot.3 ()
    • BER Tot.3 ()

Setting the report value to scientific notation

Changing the BER to scientific notation allows you to look at the significant digits and the exponent of 10.

  1. Select Link Information - BER Tot.3 in the Report Contents list.
  2. Click Options....
  3. Open the Notation: shortcut menu when the Options: Section 1, Line 3, Link Information-BER3 dialog box opens.
  4. Select Scientific (e).
  5. Click OK to close the Options: Section 1, Line 3, Link Information-BER3 dialog box.
  6. Click OK to accept your changes and to close the Properties Browser.

Renaming and generating the custom Bent Pipe report

Your custom report has been moved to the My Styles () folder. Rename and then generate the report.

  1. Expand () the My Styles () folder in the Styles list.
  2. Right click on Bent Pipe Comm Link ().
  3. Select Rename in the shortcut menu.
  4. Rename Bent Pipe Comm Link () to Analog Link.
  5. Click Generate... .

    6. Look at the first four lines in the report. The report contains link performance data for the uplink from Canal_Transit () to Geo_West () (first line), the link from Geo_West () to Geo_East () (second line), the link from Geo_East () to Hormuz_Transit () (third line), and the combined link (fourth line). Degradation in retransmitted signal and the composite link performance can readily be perceived by comparing BER1, BER2, BER3 to BER Tot.3.

    Notice the received frequencies for all the links to see how the transfer functions worked.

  6. In order to have a successful transmission, you are looking for a BER Tot. 3 of 1.0e-10 or lower. While looking at the composite BERs scroll through the report.
    • Are there any fluctuations in the values?
    • What is the time window when data can be transmitted successfully across the link?
  7. Close the report and the Report & Graph Manager.

Saving your work

You can clean up and finish your scenario.

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

Summary

In this tutorial, you learned how to create a multihop analog transmission from a ship passing through the Panama Canal to a ship located in the Persian Gulf via two geosynchronous orbiting satellites. The ship traveling through the Panama Canal deployed a phased array antenna and transmitted on a frequency of 20 GHz to a satellite named Geo West. The analog transponder on Geo West retransmitted the signal using a Gaussian antenna on a frequency of 4 GHz to a satellite named Geo East. The analog transponder on Geo East retransmitted the signal using a parabolic antenna on a frequency of 18 GHz to the ship in the Persian Gulf. You created a custom bent pipe report to determine the time window during which you could be certain of transmitting information.

On your own

You can adjust power and data rates to see what effect the different combinations have on the custom bent pipe report. For instance, you could decrease power and data rate.