GNSS time to first fix - seed time - does it help? WP7702

Hi

The use case is for an SMS only system with GNSS - IP connectivity is not available. The WP does have the time / date. Does anyone know how to optimise in-building TTFF ?

My first thought was to seed the time - does anyone know if this will help? and how to implement it?

Kind regards

John

Hi John,

When WP77 Module is registered to the Network, Modem could get time information by NITZ (Network Identity and Time Zone) from Network. It provides local time and date, time zone and DST offset.
NITZ is optional and NOT implemented by all Mobile Network Operators. That time from Modem can be used by GNSS engine to optimize TTFF. No action required on (Legato) application side.

If position has been already fixed (first fix done), time was acquired from GNSS signals. Module‘s internal RTC will maintained it (coin cell could be required if VBATT is switched off). When GNSS engine is started, time is used like other information available from previous GNSS position fix (last position, ephemeris, …), to optimize TTFF.

Moreover, it is possible to inject time as Aiding data (XTRA service).
Using AT commands:
!GPSXTRATIME Inject
Inject GPS or UTC time into gpsOneXTRA system
Inject the GPS or UTC time into the gpsOneXTRA system.
!GPSXTRATIMEENABLE
Enable gpsOneXTRA time information, and set or report specific
gpsOneXTRA time settings

or Legato API:
le_gnss_InjectUtcTime()
It is mandatory to enable the ‘Extended Ephemeris’ file injection into the GNSS device with le_gnss_EnableExtendedEphemerisFile() before injecting time with this API.

Please refer to https://docs.legato.io/latest/le__gnss__interface_8h.html#aea1811e39dfae1516b08404adfbaec22

Hope it helps!

Best regards

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