TESEO-LIV3F datasheet(14/37 Pages) STMICROELECTRONICS

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Assisted GNSS

Teseo-LIV3F

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DS12152 Rev 7

Assisted GNSS

GNSS receivers need accurate satellite position data from at least 4 satellites to produce a

fix.

Accurate satellite data -ephemeris data- is valid for 4hrs only for GPS and 30 min only for

GLONASS.

After that time a receiver must download new ephemeris data.

Ephemeris download can take from dozens of seconds to several minutes, hours or can fail

to download.

Assisted-AGPS is a mechanism to provide ephemeris assistance from external source, this

reduces considerably the time to get fix especially in critical environments when the

ephemeris download time could be very long.

Teseo-LIV3F supports three types of Assisted GNSS.

4.1

ST Assisted GPS

The ST Assisted GPS® (STAGPS) software is able to provide predicted ephemeris to the

GNSS engine in a time frame less than the usual time (about 30 seconds) needed to

download real ephemeris from the sky. This reduces considerably the time to get fix

especially in critical environments when the ephemeris download time could be very long.

STAGPS autonomous solution works using the past real ephemeris (downloaded from the

sky and stored in its internal database) to extrapolate the parameter of future ephemeris (up

to 5 days of prediction). For these reason the STAGPS® autonomous performances (in

terms of position accuracy using predicted ephemeris) are strictly dependent on the real

ephemeris database content. In normal usage of STAGPS® autonomous, the system

automatically uploads the real ephemeris into its database as soon as new ephemeris are

downloaded from the sky. This means that the global content of the real ephemeris input

database is determined by the history of the device running periods in the past.

The Teseo-LIV3F software with STAGPS® capability implements a command interface at

the NMEA level to allow interaction with the STAGPS® library. It supports commands to

enable/disable the STAGPS® functionality or to upload ephemeris and seed into the

STAGPS® working memory. Most of the implemented commands could be used for testing

the STAGPS® performance in different working scenarios.

4.2

Predictive AGNSS

ST-Assisted GPS™ when used in systems with network data access is able to provide full-

constellation long-term prediction taking advantage of an assistance server.

This unique solution combines the advantage of universal assistance data protocol with

lightweight data access, by needing only about 8 KB bi-weekly data transfers to maintain

fast and accurate GPS performance.

Starting from this downloaded payload called "seed" ST-Assisted GPS™ is capable of

generating at the client satellite orbit predictions for up to 14 days, with very high accuracy,

for the complete GPS constellation and GLONASS constellation.

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