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Positioning Application: What is a Pseudorange Ramp and how do I apply them in a scenario?

  • PosApp (SimGEN, SimREPLAYplus)
  • A Pseudorange Ramp (PR Ramp) is a way of applying a controlled offset to a satellite's pseudorange
  • It is an 'undeclared' error, i.e. it is simulated on the RF signal only and NOT reported in the navigation message
  • The change in pseudorange affects the satellite signal code and carrier phase equally
    • SimGEN users can view this using the 'Quick-look data' feature
    • Using 'Signal' Keywords = "Pseudorange" & "Pseudorange Carrier"
  • There are three ways of applying a PR Ramp
        1. Use the PR Ramp toolbar button. See Figure 1
        2. Prepare a User Actions file. See Figure 2
        3. Use remote command = PR_RAMP
  • Method 1 and 3 allow the user to interactively apply PR Ramps during the scenario run
  • Method 2 allows the user to plan, in advance, the PR Ramps that they will need during the scenario run
    • Method 3 can also support this, as long as the user's remote system has the ability to work from pre-defined instructions
  • This article concentrates on methods 1 and 2.
  • For more information on remote control please refer to the SimREMOTE manual, DGP00792AAA

     Figure 1

                                      Figure 2



  1. Click the toolbar button before or during a scenario run
  2. The control window shown in Figure 3 is displayed.
  3. If existing ramps are in progress or waiting to be actioned, they will be shown here
  4. Use the buttons at the bottom of the window to take action.
        - For the purpose of this article we will use "New" to add a new PR Ramp

                                        Figure 3
  5. "Tx Type" = Select the satellite constellation using
  6. "Tx ID" = Select the satellite ID using
  7. "Start time"  = Enable if you want the ramp to start at some later time into the scenario run or leave disabled to apply the ramp immediately
  8. "Start state" = Important if you are applying many ramps to the same 'Tx ID' in the same 'Tx Type'
        - "Reset" = Cancel any existing ramp effect and start afresh with the new ramp
        - "Hold" = Apply the new ramp on top of the current ramp that is in effect, even if the current ramp is not yet completed
  9. "Pseudorange change" = Specify the magnitude of the PR Ramp offset using
  10. "Ramp up time" = How long it will take to achieve the full "Pseudorange change", i.e. PR Ramp Rate
        - This needs to be carefully controlled as each simulator has a signal velocity dynamic limit
        - If the dynamic limit is exceeded the maximum value is used and the ramp will take longer than planned to reach the full PR offset
  11. "Hold time" = How long the satellite pseudorange is held at the full "Pseudorange change" offset
  12. "Ramp down time" = equivalent to "Ramp up time", to return the satellite signal to its normal pseudorange

    a) PR Ramps created using the above method are lost when the scenario ends (unless User Actions Recording is in use, menu [Options-->User Actions Recording]).
    b) Create a User Actions File to repeatedly user PR Ramps in a scenario



  1. Go to the scenario tree [Options-->User actions file]
  2. Double-click to open the editor. See Figure 4

                                                                                            Figure 4
  3. Select 'Command type' = "PR ramp"
  4. The settings are identical to the definitions given for the PR Ramp Toolbar Button above.
  5. The one exception is "Action time" vs. "Start time"
        - In this instance use 'Action time' to schedule when the PR Ramp should happen
        - Do not use 'Start time' as it will conflict with 'Action time'
        - You MUST specify an action time. You cannot apply an 'immediate' PR Ramp from User Actions
  6. Create a time-ordered list of scheduled PR Ramps. See Figure 6

                                                                             Figure 5
  • In PosApp 6.04, the user has the capability to use the "Rate" instead of the "Ramp up time" or the "Ramp down time" with the "Pseudorange change". While before, the user could define the duration of the specific event, i.e. "Ramp up time" or "Ramp down time", now he can define the rate of change of the ramp in m/s (Figure 6).
                                                                                       Figure 6

Further details on the PR Ramp feature and how to use User Actions files, refer to the SimGEN manual, DGP00686AAA

Product : SimREPLAYplus,SimGEN,PosApp,Pseudorange