Telit Wireless Solutions ME910C1 Series Istruzioni per l'installazione e il funzionamento

LE910Cx/ME910C1/ML865C

1/NE910C1/A-GPS

Application Note

80529NT11738A Rev. 3 –2021-09-27

Telit Technical Documentation

 
 LE910Cx/ME910C1/ML856C1/NE910C1 A-GPS Application Note 
 
 
 
80529NT11738A Rev. 3 Page 2of 22 2021-09-27 
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CONTENTS 
CONTENTS 2 
APPLICABILITY TABLE 4 
1. INTRODUCTION 5 
 Scope 5 
 Audience 5 
 Contact Information, Support 5 
 Symbol Conventions 6 
 Related Documents 6 
2. BACKGROUND INFORMATION 7 
 GPS- Global Positioning System 7 
 GNSS - Global Navigation Satellite System 8 
 Time to First Fix (TTFF) 8 
3. GNSS SOLUTION 10 
 Standalone GNSS 10 
 A-GPS - Secure User Plane Location (SUPL) 11 
3.2.1. MS-Based mode 12 
4. PRODUCT AND SAFETY INFORMATION 16 
 Copyrights and Other Notices 16 
4.1.1. Copyrights 16 
4.1.2. Computer Software Copyrights 16 
 Usage and Disclosure Restrictions 17 
4.2.1. License Agreements 17 
4.2.2. Copyrighted Materials 17 
4.2.3. High Risk Materials 17 
4.2.4. Trademarks 18 
4.2.5. Third Party Rights 18 
4.2.6. Waiver of Liability 18 
 Safety Recommendations 19 
5. GLOSSARY 20 

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6. DOCUMENT HISTORY 21

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APPLICABILITY TABLE

PRODUCTS

ME910C1 Series

NE910C1 Series

ML865C1 Series

LE910C1/C4 Series

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1. INTRODUCTION

Scope

This document provides guidelines for using the Assisted GPS (A-GPS) functionality

provided by Telit's ME910 family of modules. This document also includes information on

the Secure User Plane Location (SUPL) standard created by the OMA standardization

body.

Audience

This document is intended for Telit customers, who need to develop applications that use

the Location Service (LCS).

Contact Information, Support

For general contact, technical support services, technical questions and report of

documentation errors contact Telit Technical Support at:

•

•

•

•

•

Alternatively, use:

https://www.telit.com/contact-us

For detailed information about where you can buy the Telit modules or for

recommendations on accessories and components visit:

https://www.telit.com

Our aim is to make this guide as helpful as possible. Keep us informed of your comments

and suggestions for improvements.

Telit appreciates the user feedback on our information.

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Symbol Conventions

Danger: This information MUST be followed or catastrophic

equipment failure or personal injury may occur.

Warning: Alerts the user on important steps about the module

integration.

Note/Tip: Provides advice and suggestions that may be useful when

integrating the module.

Electro-static Discharge: Notifies the user to take proper grounding

precautions before handling the product.

Table 1: Symbol Conventions

All dates are in ISO 8601 format, that is YYYY-MM-DD.

Related Documents

•[1] ME910C1 Quick Start Guide, 80529NT11661A

•[2] ME910C1/NE910C1/ML865C1 AT Commands Reference Guide,

80529ST10815A

•[3] LE910Cx AT Command Reference Guide 80502ST10950A

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2. BACKGROUND INFORMATION

GPS- Global Positioning System

The GPS system is based on a constellation of 24 satellites that are evenly spread across

six circular orbital planes with a height of around 20200 km. Orbits in this height are

referred to as medium earth orbit (MEO).

Each satellite has an atomic clock and follows a known orbit: GPS receivers use the time

information regularly transmitted by the satellites and the time elapsed for receiving this

signal from each satellite to compute their positions.

Note: The detailed description of the GPS system is beyond the scope

of this document.

Figure 1: ECEF Coordinate System

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As shown in the above figure, Telit GPS receivers defaults to the geodetic reference

(datum) WGS-84, an ECEF (Earth Centered, Earth Fixed) coordinate system that consists

in an ellipsoid approximating the total mass of the Earth.

WGS-84 provides a worldwide common grid system that can be translated into local

coordinate systems or map datums. Many different reference ellipsoids are used around

the world: a specific reference is chosen to minimize the local differences between the

geoid and the ellipsoid separation or other mapping distortions. Local map datums are

the best fit to the local shape of the earth and are not universally applicable.

GNSS - Global Navigation Satellite System

In addition to the GPS constellation, other satellite navigation systems are currently in

operation or under development. The working principles of these systems are similar to

those of the GPS systems described in the previous section.

When the system has global coverage, it is referred to as Global Navigation Satellite

System (GNSS).

Galileo (European Union), BeiDou (China), GPS (USA), and GLONASS (Russia) are the

GNSSs currently in operation, although Galileo and Beidou are not yet fully operational.

Furthermore, additional regional navigation and augmentation systems are under

development (QZSS, NAVIC, and so on).

Time to First Fix (TTFF)

One of the parameters characterizing the performance of a GNSS receiver is the Time to

First Fix (TTFF). TTFF indicates the time required for a GNSS device to get and process

adequate satellite signals and data to provide accurate positional information (a “fix”).

To provide an accurate position, GNSS receivers use the following data sets:

•Satellite signals

•Timing information (for example, GPS time)

•Almanac data

•Ephemeris data

When a GNSS device is switched off for an extended time, the acquired information can

expire and, when it is switched on again, it will take longer to re-acquire these data sets,

resulting in a longer "Time to First Fix". One way to speed up the TTFF is to use the

Assisted-GPS (A-GPS) Positioning Technique.

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A-GPS is based on the use of a data connection (for example, a cellular network) to

provide predicted satellite information from an A-GPS server to the GNSS receiver. With

the help of this data, the receiver is usually able to achieve a positional fix faster than

using live data only. Although the term “A-GPS” is commonly used, the server-based data

can also refer to other constellations (for example, GLONASS predictions).

A "cold" start is when the GNSS receiver must receive all data before starting navigation,

which can take several minutes.

A "warm" start is when the GNSS has most of the data it needs in memory and will start

quickly, within a minute or less.

A “hot” start is when the receiver has all the data from the satellites (time, almanac,

ephemeris) and only needs to calculate the positional solution. The fix is usually acquired

in few seconds.

In other words, using A-GPS allows the device to start in a condition similar to “warm”

and “hot”, thus shortening the TTFF.

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3. GNSS SOLUTION

Standalone GNSS

Standalone (or autonomous) GNSS mode is a feature that allows the GNSS receiver

installed on the cellular module to perform First Fixing without the use of network data.

The GNSS receiver estimates position directly from satellites (GPS, GLONASS, and so on)

in line of sight.

To set up the GNSS receiver in standalone mode, follow the steps outlined below.

Although modern cellular modules integrate a GNSS receiver rather than a GPS receiver,

the AT commands still refer to GPS for legacy reasons.

1. To start from a known GNSS setting, switch on/off the module and restore the

default GNSS parameters.

AT$GPSRST

2. Delete the GPS information stored in NVM. It is the history buffer interfacing the

GPS receiver to the module.

AT$GPSNVRAM=15,0

Note: This step is optional and should be performed only if the buffer

needs to be cleaned.

3. Verify that no GNSS information is available after history buffer cleaning.

AT$GPSACP

$GPSACP

4. Start the GNSS receiver in standalone mode.

AT$GPSP=1

5. To enable unsolicited messages of GNSS data in NMEA format, refer to [2]. In this

example, only RMC sentence is enabled:

AT$GPSNMUN=3,0,0,0,0,1,0

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