GPS Satellites: Time-Dependent Transmitter Locations

GPS satellites are time-dependent satellites. These satellites should be analyzed over time.

ProMan offers the possibility to define time (UTC time) and a location on the globe (coordinates of a location in an arbitrary UTM zone, based on WGS 84 coordinate datum) - and then the location of the satellites relative to this location is computed by ProMan automatically.

In contrary to geostationary satellites for moving satellites, their position cannot be given by longitude and height over equator but have to compute for a given time based on their ephemeris data (orbital data). You have to provide the GPS orbit data information. This can be done through one of the following methods:
Almanac datasets
The data can be downloaded either from USCG or Celestrak1 and is weekly updated.
TLE datasets
Data is updated weekly.

After downloading the dataset for the week of interest, you can compute the time-dependent locations of the GPS satellites for all locations on the globe.

Creation

Click Project > Edit Project Parameter and click the Sites tab to get an overview of the currently considered sites.


Figure 1. The Edit Project Parameter dialog, Sites tab.
New satellites can be added as follows:
  • Clicking on the Add button on the Sites tab of the Edit Project Parameters dialog
  • Using a mouse tool which can be activated via
    • the menu Project > Sites > Site: New
    • The icon in the Project toolbar.
      Note: The mouse tool can only be used if the project dialog is not displayed. If the Project dialog is displayed, new transmitters can only be entered via the Transmitter tab of the Edit Project Parameter dialog.
  • Select the type of transmitter by one of the following methods:
    • Specify the name of the Almanac or TLE file.
    • Select the file by clicking on the Change button.


Figure 2. The Transmitter type dialog, set to GPS Satellites (Almanac Definitions).

Based on the orbit data (for example, given in the TLE-set) and the given time instance the satellite location(s) relative to the UTM zone (in which the geographic database used for the simulation is defined) will be computed. Accordingly, two new dimensions have been incorporated in the radio planning tool: satellite dimension and time dimension. Each defined time instance will lead to a specific site including the available satellites for the given time and location (for example, above the horizon or a defined minimum elevation angle).

Based on this moving satellite extension it is possible to compute the LOS areas and the received signal power for the defined satellites over time, which will be for example useful for the analysis of GPS performance.

In the next dialog, the reference point and the reference time (GMT) can be defined. By default, the center of the loaded (building) database is taken as a reference point (including the UTM zone which can be defined with the WallMan application). On the right side of this dialog, the time instance (GMT) and a minimum elevation angle can be specified (satellites below this elevation will not be converted).


Figure 3. The GPS Satellites dialog - Almanac properties.


Figure 4. The GPS Satellites dialog - TLE properties.

All the converted satellites are displayed together with their coordinates in the Sites tab of the Edit Project Parameters dialog. By adding further sites, it is also possible to simulate various time instances and therefore to investigate the system availability over time. Each defined time instance will lead to an individual site (including the available satellites). All defined sites are listed on the Sites tab.

For each defined satellite object the wave propagation can be predicted, for example, the LOS / NLOS areas, received power, path loss, field strength, and channel profiles.


Figure 5. The Edit Project Parameter dialog - Sites tab.


Figure 6. The Site dialog for time instances.

Application

To simulate various time instances and, therefore, to investigate the system availability over time the user has to define multiple sites with individual time settings. Each defined time instance will lead to an individual site (including the available satellites).
Note: When importing GPS satellite time-dependent locations using Almanac datasets, the site number is appended to the transmitter name.
1 http://www.celestrak.com/GPS/almanac/Yuma/