GNSS Research

Research into satellite navigation, aka SatNav or Global Navigation Satellite Systems (GNSS) and related technologies.
Example systems: GPS, GLONASS, Galileo, BeiDou.

Assisted GNSS (A-GNSS)

Also known as Assisted GPS (A-GPS). Greatly improves the Time To First Fix (TTFF) by downloading almanac and ephemeris data via mobile broadband or WiFi, instead of waiting for the slow download via the GNSS signal.


SUPL (Secure User Plane Location) is the most common protocol used to retrieve the current almanac and ephemeris data.
There are no free software SUPL servers that we know off. Android uses Google's servers ( by default. Most carriers also default to on their APN. GrapheneOS runs a proxy to Google at


PSDS (Predicted Satellite Data Service) is the generic name for a server that provides long-term (usually weekly) forecasts of satellite positions. It allows fast TTFF for several days even without an internet connection.
The data format is vendor specific. There are implementations from:
  • Qualcomm, known as gpsOneXTRA or just XTRA. Serving XTRA Assist Data files. Servers:,, or
  • Broadcom, which downloads 3 files.

Updated by dl lud 23 days ago · 5 revisions

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