Specifications

IntroductionGPS and Assisted GPS
13Operating Manual 1171.5248.12 ─ 15
uploaded almanac. The user only needs to specify time and location; all other configu-
rations are done automatically by the R&S Signal Generator. This assures the calculation
of a realistic scenario with an optimal 4-satellite constellation i.e. minimum Position Dilu-
tion of Precision (PDOP).
The generic workflow is described in chapter 2.8.3, "Generating GPS Signal with Flexible
Simulation Time (Localization Mode Auto SV Selection)", on page 20.
2.4.4 Signal generation with projection of the ephemeris navigation data
The R&S Signal Generators employs a special algorithm for projection of the ephemeris
navigation data that allows the generation of a valid navigation message without limitation
in the simulation time. The ephemerides are automatically updated and the limitation
problem of maximum allowed time span of two hours between the simulation time and
the TOE (Time of Ephemeris) is already solved.
Any moment between the TOA and the TOA + 3.5 days can be selected as start simu-
lation time. While testing a GPS receiver with enabled Almanac protocol check, the max-
imum value of the simulation time will be limited by the fact, that the almanac files are
valid for period not longer than 3.5 days.
The generic workflow is described in chapter 2.8.3, "Generating GPS Signal with Flexible
Simulation Time (Localization Mode Auto SV Selection)", on page 20.
2.4.5 Satellite handover
The special signal generation localization mode "Auto SV Selection and Update" is pro-
vided for the generation of a valid GPS signal over long period of time. In this mode, the
R&S Signal Generator constantly calculates the localization signal based on two criteria,
the optimal 4-satellite constellation with minimum PDOP and the satellite's visibility
respecting the Satellite Elevation Mask. While the PDOP is a system parameter that is
calculated by the R&S Signal Generator and displayed in real-time, the satellite's visibility
is a configurable parameter that can be adjust by the user to simulate satellites with
different elevations.
Depending on the current satellite's conditions and the used number of satellites, a
sophisticated algorithm decides how often the PDOP and the satellite's visibility have to
be proved and at which moment of time the satellite's constellation has to be changed.
Satellites that do not fulfill the criteria for minimum PDOP and sufficient visibility are
exchanged dynamic and on-the-fly and the process is called satellite handover. Infor-
mation about the expected time of the next upcoming handover is provided by the param-
eter Get Next Handover Time.
The generic workflow is described in chapter 2.8.4, "Generating GPS Signal with Satellite
Handover (Localization Mode Auto SV Selection and Update)", on page 21.
Functional Overview Option GPS (R&S-K44)