Defining and Constraining Links
Complex communication systems may present many potential links for a given receiver or transmitter. You must establish criteria for determining which transmitter will communicate with which receiver.
Use the Link Definition page to select among the link criteria, described below, and specify whether the selected criterion is to constrain the receiving or transmitting constellations in the CommSystem.
| Link Criteria | Description |
|---|---|
| MaxElevation | Selects the nonconstraining object that has the highest elevation angle with reference to the constraining object. |
| MinRange | Selects the nonconstraining object with the minimum distance to the constraining object. |
| Maximum RIP | Selects the link with the maximum received isotropic power (RIP). |
| Maximum C/N | Selects the link with the maximum carrier-to-noise ratio. |
| CustomPlugin | Specifies a user-defined selection strategy. Browse to a MATLAB or VBScript script.
For a list of required inputs and outputs, see CommSystem Link Selection Strategy Plugin Points. For information on scripting in STK, see Engine Plugin Scripts. For instructions on the setup and use of plugin points, see Plugin Scripts. To develop a custom script from a sample template, select the appropriate sample plugin script in MATLAB or VBScript, from <STK install folder>\CodeSamples\Extend\PluginScripts. |
The Constraining Constellations will generally, but not always, comprise the objects closest to the Earth. Only one link will be established for each object contained within the constraining constellations. For example, several transmitters may be visible to a receiver on the ground, but only one of them will be selected for a given time. Yet, that same transmitter may also support another link to another receiver.
Different link criteria will sometimes lead to different results. In the following figure, for example, if receiver R3 is constrained by the Min Range criterion, it will be paired with the transmitter closest to it: T3. The Max Elevation Angle constraint will select the transmitter that is most nearly overhead with respect to R3, namely, T4.
Link criteria compared