4

Assisted GNSS

GNSS receivers need accurate satellite position data from at least four 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 an external source. This reduces

considerably the time to get fix especially in critical environments when the ephemeris download time could be

very long.

The Teseo-LIV3FL supports three types of assisted GNSS.

4.1

ST-assisted GPS

ST-assisted GPS® (STAGPS) software is able to provide predicted ephemeris to the GNSS engine. It reaches in

less time than the normal 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.

The autonomous solution STAGPS works by using the real past ephemeris downloaded from the sky. It stores in

its internal database to extrapolate the parameter of future ephemeris up to 5 days of forecast. For this 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 actual ephemeris input database is determined by the history of the

device operating in the past periods.

The Teseo-LIV3FL 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 only solution combines the advantage of universal assistance data protocol with lightweight data access. It

needs only about 8 KB biweekly data transfers to maintain fast and accurate GPS performance.

From this uploaded payload called "seed", ST-assisted GPS ™ is able to generate satellite orbit forecasts for up

to 14 days at the customer for the complete GPS constellation and the GLONASS constellation.

A unique feature of ST-assisted GPS is the dual-mode ability to perform seamless fallback from the 14-days

server-based forecast to the 5-days self-sustaining in-field forecast capability depending on usage patterns.

This is very useful to keep the quality of the GNSS experience, if a connected device loses the ability to contact

the server due to coverage or roaming problems or any other wireless connectivity problem.

4.3

Real-time AGPS

Real-time assisted GPS (RT-AGPS) solution is a server based assisted GPS, therefore it requires a network

connection to download assistance data from the server.

RT-AGPS works downloading the real-time ephemeris data by an assistance server. Access to the server is

allowed thanks to the internal password provided by Teseo-LIV3FL to the host processor. The data acquired in

real-time must be provided to Teseo-LIV3FL.

Proprietary NMEA commands are supported on Teseo-LIV3FL to acquire the credential access to the external

server and to inject the data to the Teseo-LIV3FL.

STMicroelectronics partner provides available server solution access for free on Teseo-LIV3FL solution.

Real-time A-GPS allows continuous /real-time satellite position determination.

Teseo-LIV3FL

Assisted GNSS

DS13881 - Rev 4

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