Using the Scalable Network Modeling Interface to Analyze Communications Network Performance

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.

Capabilities covered

This lesson covers the following STK Capabilities:

• STK Pro
• Communications

What you will learn

In the following tutorial, you will analyze communication network performance between a convoy and a UAV relay as the convoy traverses a valley road.

• You will use STK and STK's Communications capability to:
  • Model the dynamic positions of each asset
  • Consider their antenna pointing
  • Compute link budget information between the UAV and the ground vehicle radio operator
• You will use the Scalable Network Modeling Interface to analyze network performance throughout the mission.

This tutorial guides you through creating STK objects that are then imported into the Scalable Network Modeling Interface. An alternative method, which is not part of this tutorial, is to import wireless interfaces from the Scalable Network Modeling Interface configuration directly into the Scalable Network Modeling Interface. To learn more about importing wireless interfaces, see Importing a Scalable Network Modeling Interface Configuration File.

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.

Defining the physical layer using STK

High-fidelity modeling of the physical layer is one of STK's strengths. STK is a physics-based software geometry engine that accurately models the time-dynamic position and orientation of vehicles, the characteristics and pointing of sensors and communications assets, and the spatial relationships (e.g., line of sight) between objects.

Creating a scenario

1. Launch STK ().
2. Click the Create a Scenario () button.
3. Enter the following in the STK: New Scenario Wizard:

Option	Value
Name	ScalableNetworkInterface
Start	1 Mar 2010 08:00:00.000 UTCG
Stop	1 Mar 2010 08:40:00.000 UTCG

4. When you finish, click OK.
5. When the scenario loads, click Save (). A folder with the same name as your scenario is created for you.
6. In the Save As window, verify the scenario name and location and click Save.

Updating the animation start time

There is a 25-second start time difference between each ground vehicle that will be added to this scenario. To see all ground vehicles at the start of animation, change the Animation Start time.

1. Open ScalableNetworkInterface's () properties ().
2. Select the Basic - Time page.
3. Set the Animation's Start Time to 1 Mar 2010 08:01:15.000 UTCG.
4. Click OK to accept the changes and close the Properties Browser.
5. Click Reset () in the Animation Toolbar.

Adding terrain and imagery to your scenario

To add the sample terrain file and imagery for enhanced 3D visualization:

1. Bring the 3D Graphics window to the front.
2. In the 3D Graphics window toolbar, click the Globe Manager () icon. Globe Manager is docked below the Object Browser.
3. In the Hierarchy toolbar, click Add Terrain/Imagery () .
4. Select Add Terrain/Imagery ().
5. When the Globe Manager: Open Terrain and Imagery Data window opens, ensure Local Files is selected.
6. Go to <STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial.
7. Select SWalesHiRes.pdtt and Scalable.pdttx.
8. Click Add.
9. When the Use Terrain for Analysis window appears, click Yes.
10. In the Globe Manager, right-click SWalesHiRes.pdtt and select Zoom to to view the terrain and imagery in the 3D Graphics window.

Populating the scenario

To model the mission, populate the scenario with the following objects:

To save steps when defining vehicle routes, this tutorial uses the StkExternal propagator, which enables you to import the position and velocity for a vehicle directly from an ephemeris file.

Inserting an Aircraft object to model the UAV

1. Using the Insert STK Objects Tool (), insert an Aircraft () object using the Insert Default method
2. Rename the Aircraft () UAV.
3. Right-click UAV () and select Properties ().
4. On the Basic - Route page, change the Propagtor to StkExternal.
5. Click the ellipsis button () beside the Filename field.
6. Browse to <STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial.
7. Select UAV.e.
8. Click Open.
9. Click Apply and keep UAV's Properties Browser open.

Setting the attitude

Override the default attitude settings and use a previously generated attitude file.

1. Select the Basic - Attitude page.
2. Select the Override Basic & Target Pointing Attitude for specified times check box in the Precomputed section.
3. Click the ellipsis button () beside the File field.
4. Go to <STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial.
5. Select UAV.a.
6. Click Open.

Selecting a model

Selecting a model to apply to the UAV.

1. Select the 3D Graphics - Model page.
2. Click the ellipsis button () beside the Model File field.
3. Select rq-1a_predator.glb.
4. Click Open.
5. Click OK to accept the changes and close the Properties Browser.

Viewing the route

1. To view the aircraft's route, right-click UAV in the Object Browser and select Zoom To.
2. Adjust the animation time step to 1.00 sec.
3. Play () through the scenario.

The ephemeris and attitude files used to define the UAV were created using the Aviator propagator. STK's Aviator capability is an advanced propagator that creates a route using a sequence of curves parameterized by readily available performance characteristics of aircraft, including cruise airspeed, climb rate, roll rate, and bank angle. To learn more about modeling an aircraft using Aviator, see Aviator. To learn more about the various aircraft propagators available with STK, see The Aircraft Object.

STK also offers propagators for high-fidelity modeling of ground vehicles, launch vehicles, missiles, satellites, and ships.

Inserting ground vehicles to model the convoy

Use the StkExternal propagator and the default GroundVehicle object to easily create four trucks in the convoy. Define the ground vehicles as follows:

1. Using the Insert STK Objects Tool (), insert a Ground Vehicle () object using the Define Properties method.
2. On the Basic - Route page, change the Propagtor to StkExternal.
3. Click the ellipsis button () beside the Filename field.
4. Browse to <STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial.
5. Select mobile1.e.
6. Click Open.
7. Click OK to accept the changes and close the Properties Browser.
8. Rename the Ground Vehicle () GroundVehicle1.
9. Repeat the steps above three (3) more times to insert GroundVehicle2, GroundVehicle3, and GroundVehicle4.

   Add Object...	Import Ephemeris File ...
   GroundVehicle1	<STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial/mobile1.e
   GroundVehicle2	<STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial/mobile2.e
   GroundVehicle3	<STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial/mobile3.e
   GroundVehicle4	<STK install folder>\Data\Resources\stktraining\samples\ScalableTutorial/mobile4.e

   The ephemeris files for the GroundVehicles were created using the GreatArc propagator. The Great Arc Propagator defines vehicles that follow a point-by-point path over or below the surface of the Earth at a given altitude or depth.

Modeling communications assets

Use antenna objects attached to sensors to model your communications assets.

Tracking the convoy from the UAV

1. Using the Insert STK Objects Tool () insert a Sensor () object using the Insert Default method.
2. Select UAV () on the Select Object window.
3. Click OK.
4. Rename the Sensor () UAVtoGV2.
5. Right-click UAVtoGV2 () and select Properties ().
6. Select the Basic - Pointing page.
7. Change the Pointing Type to Targeted.
8. Move () GroundVehicle2 () from the Available Targets list to the Assigned Targets list.
9. Select the 3D Graphics - Attributes page.
10. Ensure the Translucent Lines check box is selected.
11. Set the Projection Translucency percentage to 100.
12. Click OK to accept the changes, and close the Properties Browser.

Adding an antenna to the UAV

1. Using the Insert STK Objects Tool (), insert an Antenna () object using the Insert Default method.
2. Select UAVtoGV2 () on the Select Object Window.
3. Click OK.
4. Rename the Antenna () UAVtoGV2antenna. The antenna names carry over to the Scalable Network Modeling Interface.
5. Right-click UAVtoGV1antenna () and select Properties ().
6. On the Basic - Definition page, set the following:

   Option	Value
   Type	Parabolic
   Design Frequency	14 GHz
   Diameter	0.762 m
   Efficiency	80 %

7. Select the 3D Graphcs - Attributes page and set the following:

   Option	Value
   Show Volume	Enable
   Gain Scale (per dB)	0.001 km
   Elevation - Resolution	0.1 deg

8. Click OK to accept the changes and close the Properties Browser.

Adding antennas to the convoy

1. Copy UAVtoGV2antenna() to GroundVehicle1 ().
2. Rename the antenna () WiFi1.
3. Right-click WiFi1 () and select Properties ().
4. On the Basic - Definition page, set the following:

   Option	Value
   Type	Dipole
   Design Frequency	2.4 GHz
   Diameter	0.124914 m
   Efficiency	100 %

5. Click OK to accept the changes and close the Properties Browser.
6. Copy WiFi1 to GroundVehicle2, GroundVehicle3, and GroundVehicle4. Rename the antennas as follows:

   Object	Antenna Name
   GroundVehicle2	WiFi2
   GroundVehicle3	WiFi3
   GroundVehicle4	WiFi4

Completing the communications link between the UAV and the convoy

To finish modeling the communications link between the UAV and convoy, use complex transmitter and receiver models. This will give more insight into the performance of the wireless links. The complex model can reference an antenna object. Antenna objects are used in the definitions of Scalable Network Modeling Interface interfaces.

Adding a transmitter to the convoy

1. Using the Insert STK Objects Tool (), insert a Transmitter () object using the Insert Default method.
2. Select GroundVehicle2 () on the Select Object Window.
3. Click OK.
4. Rename the Transmitter () GV2toUAV_Xmtr.
5. Right-click GV2toUAV_Xmtr () and select Properties ().
6. On the Basic - Definition page, click the ellipsis button (Component Selector) () beside the Type field.
7. Select Complex Transmitter Model.
8. Click OK.
9. Select the Model Specs tab and set the following:

   Option	Value
   Frequency	14 GHz
   Power	10 dBW

10. Select the Antenna tab and set the following to link the transmitter to a fixed antenna:

    Option	Value
    Reference Type	Link
    Antenna Name	WiFi2

11. Click OK to accept the changes and close the Properties Browser.

Adding a receiver to the uav

1. Using the Insert STK Objects Tool (), insert a Receiver () object using the Insert Default method.
2. Select UAV () on the Select Object Window.
3. Rename the Receiver () UAVtoGV2_Rcvr.
4. Right-click UAVtoGV2_Rcvr () and select Properties ().
5. On the Basic - Definition page, click the ellipsis button (Component Selector) () beside the Type field
6. Select Complex Receiver Model.
7. Click OK.
8. Select the Model Specs tab and set the following:

   Option	Value
   Auto Track	Disable
   Frequency	14 GHz

9. Select the Antenna tab and set the following to link the receiver to an antenna that is targeted to GroundVehicle2:

   Option	Value
   Reference Type	Link
   Antenna Name	Sensor/UAVtoGV2/Antenna/UAVtoGV2antenna

10. Click OK to accept the changes and close the Properties Browser.

Using the 3D Graphics window to view antenna performance

The antenna characteristics for each asset are defined based on performance specifications, pointing, and body location.

1. Zoom To the UAV.
2. Animate () the scenario.
3. View the following in the 3D Graphics window:
• Antenna gain volume for the UAV receiver tracking the reported location of GroundVehicle2.
• Antenna pitch. The antenna can pitch from nadir to 5 deg off the UAV's XY-plane, where X points in the direction of the vehicle's ECF velocity vector, Z is aligned with the nadir direction, and Y forms a right-handed Cartesian coordinate system with X and Z. This affects communications availability depending on the UAV's current position and attitude.
4. Reset () the scenario.
5. Zoom To GroundVehicle2.
6. Animate () the scenario to view the antenna gain volume for GroundVehicle2.
7. Reset () the scenario.

Performing analysis on the communications links

The dynamic Link Budget is calculated based on each asset's current position, attitude, and (defined) transmitter and receiver parameters. You can display the Link Budget results dynamically in the 3D Graphics window or in a static report.

Displaying communications parameters dynamically

You can dynamically display the receiver gain over the equivalent noise temperature (g/T), the bit energy to noise power spectral density ratio (Eb/No), and Bit Error Rate (BER) for the link between GroundVehicle2 and the UAV over time in the 3D Graphics window.

1. Right-click GV2toUAV_Xmtr under GroundVehicle2 and select Access... ().
2. Select UAVtoGV2_Rcvr under UAV in the Associated Objects list.
3. Click 3D Graphics Displays....
4. Click Add...
5. Select Link Budget - BER.
6. Click OK to close the Add a Data Display window.
7. Click OK to close the 3D Graphics Data Display window.
8. Minimize the Access window and animate () the scenario to view the dynamic display.
9. Reset () the scenario.

Generating a static link budget report

Display the same data in a static report to determine the quality of the link between the UAV and the convoy.

1. Restore the Access window.
2. Click Report & Graph Manager ....
3. Make sure that GroundVehicle-GroundVehicle2-Transmitter-GV2toUAV_Xmtr-To-Aircraft-UAV-Receiver-UAVtoGV2_Rcvr is highlighted in the window showing available links.
4. Double-click Link Budget- Detailed under Installed Styles.
5. Notice in the Link Budget report that the BER remains negligible throughout the analysis.
6. Change the Current Scenario Time to 1 Mar 2010 08:01:25 in the Animation toolbar to display the results in the 3D Graphics window. Notice the large angle between the direction of the link and the antenna boresight on the ground vehicle.

You can also create an STK custom graph to illustrate the same problem area. The following graph shows the Link Information BER data provider over time. For more information on creating custom reports and graphs, see Generating Reports & Graphs.

 

7. Minimize the report. It will be used later in the tutorial.
8. Close the Report & Graph Manager and Access windows.

Displaying the Scalable Network Modeling Interface toolbar and Launching the Scalable Network Modeling Interface Scenario Explorer

Now that the physical objects are fully defined using STK, we can map those objects into the Scalable Network Modeling Interface simulation using the Scalable Network Modeling Interface.

1. Select Toolbars->Scalable Network Modeling Interface from the View menu to display the toolbar.

The Scalable Network Modeling Interface toolbar enables you to access and interact with the Scalable Network Modeling Interface.



These same Scalable Network Modeling Interface functions are also available from the Utilities menu.

2. Click to launch the Scalable Network Modeling Interface Scenario Explorer. It is very similar to the Scalable Network Modeling Interface application GUI. The Scalable Network Modeling Interface Scenario Explorer contains an object tree and a properties pane.

Configure your scenario in the Scalable Network Modeling Interface

Define your scenario configuration.

1. In the object tree, expand the Scenario Configuration folder.
2. Select General->General Settings.
3. In the properties pane, notice that the Simulation Time of 2400S is inherited from the STK Scenario Analysis time. Also, notice that the Simulation Time is bolded. All values that are user-defined or inherited from STK are bolded.
4. Select Channel Properties and expand Number of Channels
5. A second channel needs to be defined for communication between GroundVehicle2 and the UAV. Change the following channel properties:

   Option	Value
   Number of Channels	2
   Channel Frequency [1]	14 GHz

6. In the object tree, expand Hierarchy.
7. Verify that there is one node for each STK parent object in the STK scenario.
8. Richt-click the following nodes one at a time, select Add - Wireless Network Interface, and then define the following interfaces between STK antennas:



Node	Interface Name	Instance Name
UAV	UAVtoGV2	UAVtoGV2/UAVtoGV2antenna
GroundVehicle2	GV2toUAV	WiFi2
GroundVehicle1	GV1_Wifi	WiFi1
GroundVehicle2	GV2_Wifi	WiFi2
GroundVehicle3	GV3_Wifi	WiFi3
GroundVehicle4	GV4_Wifi	WiFi4

Creating connections between Scalable Network Modeling Interfaces

Defining your connections

Now that you have defined the interfaces between STK antennas, you can define your connections.

1. Define the following connections by right-clicking Connections and making the proper selection.



Connection Type	Name	Parameters
Wireless Subnet	Convoy	Move the following Available Interfaces to Selected Interfaces: GroundVehicle1/GV1_Wifi GroundVehicle2/GV2_Wifi GroundVehicle3/GV3_Wifi GroundVehicle4/GV4_Wifi Keep the default values for all other parameters.
Wireless Subnet	GV2toUAV	Move the following Available Interfaces to Selected Interfaces: UAV/UAVtoGV2 GroundVehicle2/GV2toUAV Keep the default values for all other parameters.
Application	n/a	Source: GroundVehicle4 Destination: UAV Application: CBR

The Convoy and GV2toUAV are located under Connections - Wireless Subnets in the object tree.

The application link you created is named CBR: GroundVehicle4 - UAV and is located under Connections - Applications.

Setting up the GV2toUAV wireless subnet

Set up the GV2toUAV wireless subnet so that it can only transmit and receive on the second channel and that the Radio Type and MAC Protocol are appropriate for the large range of the link between the GroundVehicle and the UAV.

1. Set the following parameters for the GV2toUAV wireless subnet:

Layer	Parameter	Value
Physical Layer	Listenable Channel Mask Listening Channel Mask Radio Type Data Rate Reception Threshold (dBm)	01 (only 14 GHz is selected) 01 (only 14 GHz is selected) Abstract 100 Mbps -181
MAC Layer	MAC Protocol	Generic MAC
Network Layer	Schedulers and Queues - Number of IP Output Queues	1
Routing Protocol	Routing Protocol IPv4	AODV

2. Ensure the Assign IP address to interfaces to match network IP box is checked. If you do not select this check box, the interface will not run.

Setting up the Convoy wireless subnet

1. Set the following parameters for the Convoy wireless subnet:

Layer	Parameter	Value
Physical Layer	Listenable Channel Mask Listening Channel Mask Radio Type TransmissionPower at 1 Mbps TransmissionPower at 2 Mbps TransmissionPower at 6 Mbps TransmissionPower at 11 Mbps	10 (only 2.4 GHz is selected) 10 (only 2.4 GHz is selected) 802.11b Radio 45 Mbps 45 Mbps 45 Mbps 45 Mbps
Network Layer	Schedulers and Queues - Number of IP Output Queues	1
Routing Protocol	Routing Protocol IPv4	AODV

2. Ensure the Assign IP address to interfaces to match network IP box is checked. If you do not select this check box, the interface will not run.

Setting up the CBR application

1. For the CBR application, change the following parameters:

Parameter	Value
Items to Send	360
Start Time	790 seconds
End Time	1150 seconds

The Start and End Time settings enable you to focus on the section of the route where BER drops significantly, as indicated by the Link Budget report.

The Items to Send value of 360 in combination with the 360 sec time period between Start Time and End Time force the application to send one packet per second.

Run a Scalable Network Modeling Interface experiment

1. Click to run a Scalable Network Modeling Interface experiment.

The status of the run is displayed in the progress bar. Scalable Network Modeling Interface Experiment files and optionally, an STK VDF file, are saved to the folder specified on the Scalable Network Modeling Interface preferences page, and the Stat File Viewer that shows the .stat file generated by the experiment is displayed. The statistical categories are listed in the object tree.

2. If the Stat File Viewer does not display, click to display the Scalable Network Modeling Interface Command-line Output Log, which lists all messages generated by the Scalable Network Modeling Interface Experiment run.
3. Correct any errors listed in the log.
4. Rerun the Scalable Network Modeling Interface experiment.

Discussing the details of the network simulation is beyond the scope of this tutorial. This tutorial only highlights selected results.

5. Look at the statistics for the following categories:

   Category	Result
   Transport-> UDP	As you can see from the results, the UAV did not receive all 360 packets sent from GroundVehicle4.
   Network->AODV for IPv4	These statistics show the number of times that the application tried to find a route from GroundVehicle4 to the UAV, the number of times there was no route available, and the number of packets dropped. Look at all the statistics in this category to determine if there are any network problems.
   Number of Data Packets Dropped for no route	The statistics show that most of the packets made it through the network because the application could find a route from GroundVehicle4 to the UAV.
   Application->CBR Server	The First Packet Received statistics show that there was around a 100 msec delay before the first packet was received.

6. Close the Stat File Viewer.
7. Save your scenario.