Quectel LC26G, LC76G, LC86G Application Note

LC26G&LC76G&LC86G Series

AGNSS Application Note

GNSS Module Series

Version: 1.0
Date: 2022-10-10
Status: Released

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About the Document

Revision History

Document Information

Title

LC26G&LC76G&LC86G Series AGNSS Application Note

Subtitle

GNSS Module Series

Document Type

Application Note

Document Status

Released

Revision

Date

Description

-

2022-07-11

Creation of the document

1.0

2022-10-10

First official release

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Contents

About the Document ................................................................................................................................... 3

Contents ....................................................................................................................................................... 4

Table Index ................................................................................................................................................... 6

Figure Index ................................................................................................................................................. 7

1 Introduction .......................................................................................................................................... 8

1.1. Differences Between Host EPO and Flash EPO ...................................................................... 8

1.2. AGNSS Requirements ............................................................................................................... 9

2 Download EPO Files .......................................................................................................................... 10

2.1. Get EPO Files from Server ...................................................................................................... 10

2.2. EPO File Format ...................................................................................................................... 11

2.2.1. EPO File Format – GPS Only ........................................................................................ 12

2.2.2. EPO File Format – BDS/Galileo Only ............................................................................ 13

2.2.3. EPO File Format – GPS + GLONASS ........................................................................... 15

2.3. EPO File Types ........................................................................................................................ 15

2.4. Recommended Download Procedures of EPO Files .............................................................. 16

2.5. EPO File Validity Period .......................................................................................................... 17

3 AGNSS Implementation ..................................................................................................................... 19

3.1. AGNSS with Flash EPO .......................................................................................................... 19

3.1.1. Binary Protocol ............................................................................................................... 19

3.1.2. EPO Data Transfer Protocol .......................................................................................... 21

3.1.2.1 Pseudo Code for EPO Data Transfer Protocol ...................................................... 21

3.1.3. AGNSS Procedure with Flash EPO ............................................................................... 25

3.2. AGNSS with Host EPO ............................................................................................................ 26

3.2.1. Recommended Sequence for Host EPO ....................................................................... 26

3.2.2. Sample Code to Send EPO ........................................................................................... 27

4 AGNSS Related Messages ................................................................................................................ 30

4.1. PAIR470 PAIR_EPO_GET_STATUS ..................................................................................... 30

4.2. PAIR471 PAIR_EPO_SET_DATA .......................................................................................... 31

4.3. PAIR472 PAIR_EPO_ERASE_FLASH_DATA ....................................................................... 32

4.4. PAIR590 PAIR_TIME_SET_REF_UTC .................................................................................. 33

4.5. PAIR600 PAIR_LOC_SET_REF ............................................................................................. 34

5 Download EPO Data with QGNSS .................................................................................................... 36

5.1. Download Flash EPO with QGNSS ......................................................................................... 36

5.2. Download Host EPO with QGNSS .......................................................................................... 37

6 AGNSS Implementation Example ..................................................................................................... 39

6.1. Flash EPO Implementation...................................................................................................... 39

6.2. Host EPO Implementation ....................................................................................................... 40

7 Appendix A References ..................................................................................................................... 42

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8 Appendix B Special Characters ....................................................................................................... 44

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Table Index

Table 1: Differences Between Flash EPO and Host EPO ........................................................................... 8

Table 2: AGNSS Related Commands .......................................................................................................... 9

Table 3: Download URL of EPO Files ........................................................................................................ 10

Table 4: EPO Data SVID Range ................................................................................................................ 11

Table 5: EPO File Types ............................................................................................................................ 15

Table 6: Description of Binary Protocol Fields ........................................................................................... 20

Table 7: Start of EPO Binary Format ......................................................................................................... 20

Table 8: EPO Data Binary Format ............................................................................................................. 20

Table 9: End of EPO Binary Format .......................................................................................................... 20

Table 10: Related Document ..................................................................................................................... 42

Table 11: Terms and Abbreviations ........................................................................................................... 42

Table 12: Special Characters ..................................................................................................................... 44

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Figure Index

Figure 1: EPO File Format – GPS Only ..................................................................................................... 12

Figure 2: Format of Several Segments of EPO Files ................................................................................ 12

Figure 3: EPO File Format – BDS/Galileo Only ......................................................................................... 13

Figure 4: Galileo EPO Header ................................................................................................................... 14

Figure 5: BDS EPO Header ....................................................................................................................... 14

Figure 6: EPO File Format – GPS + GLONASS ........................................................................................ 15

Figure 7: Recommended Download Procedures of EPO Files ................................................................. 16

Figure 8: Binary Protocol Structure ............................................................................................................ 19

Figure 9: AGNSS Procedure with Flash EPO ............................................................................................ 25

Figure 10: Suggested Sequence for Host EPO ......................................................................................... 27

Figure 11: QGNSS Interface for Setting Flash EPO .................................................................................. 36

Figure 12: Download Flash EPO File ......................................................................................................... 37

Figure 13: QGNSS Interface for Setting Host EPO ................................................................................... 38

Figure 14: Download Host EPO File .......................................................................................................... 38

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1 Introduction

EPO (Extended Prediction Orbit) is an AGNSS feature implemented by the chipset supplier, which should
improve the TTFF duration of the GNSS receivers. This document mainly describes the EPO file
downloading process, AGNSS implementation, EPO related PAIR commands and how to download EPO
data through the QGNSS tool. Please be aware that AGNSS can’t improve the TTFF duration in cases
where the signal level is too low (either due to poor RF design, or signal reception quality).

1.1. Differences Between Host EPO and Flash EPO

Both methods (Host EPO and Flash EPO) help the GNSS receiver to shorten the TTFF duration, but their
differences make each of them suitable for different applications.

Host EPO (also called Real Time AGNSS) allows the receiver to store data in the internal RAM. Up to 6
hours of assistance data are sent to the receiver through NMEA PAIR commands listed in Chapter 4

AGNSS Related Messages. For Host EPO, there is no data retention after the GNSS receiver reboots,

and the data should be re-downloaded.

Flash EPO, on the other hand, allows the receiver to store in the flash for 3, 7 or 14 days’ assistance data
which are sent to the receiver through Binary Protocol defined by the chipset supplier. Flash EPO enables
the receiver to reuse all assistance information stored in flash before the information expires. See Chapter

2.5 EPO File Validity Period for the validity period of EPO files.

Table 1: Differences Between Flash EPO and Host EPO

The maximum flash memory EPO data retention period is 14 days for GPS-only and GPS + GLONASS

Type

Flash EPO

Host EPO

Storage Space

Flash

RAM

Storage Capacity

3, 7 and 14 days’ assistance data

6-hour assistance data

Protocol

Binary

NMEA (ASCII)

NOTE

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EPO files, 7 days for Galileo EPO files and 3 days for BDS EPO files. If 30-day GPS-only or GPS +
GLONASS EPO files are sent, only the first 14 days of EPO data will be stored.

1.2. AGNSS Requirements

The host needs to provide the Reference Time, Reference Position and EPO data to the GNSS receiver.
The information provided by the host must meet the following requirements so that the GNSS receiver
can make better use of EPO:

⚫ The Reference Time should be accurate within 3 seconds and must be specified in UTC time.
⚫ The Reference Position should be accurate within 30 km from the receiver’s actual position. Keep in

mind that if the receiver’s view of the sky is limited, the accuracy of the Reference Position needs to
be increased.

⚫ The EPO data should be valid.

Wrong (out of boundaries) reference time and position will extend the TTFF duration.

The receiver can benefit from any of the assistance data to improve the TTFF. All assistance data
(Reference Time, Reference Position and EPO data) are useful but none of them are mandatory. If some
of them are not available or have expired, it is recommended to avoid using them.

The host can provide the Reference Time, Reference Position and EPO data to the GNSS receiver
through the messages listed in the following table. See Chapter 4 AGNSS Related Messages for a
detailed description of these messages.

Table 2: AGNSS Related Commands

Packet Type

Data Content

$PAIR471

GPS/GLONASS/Galileo/BDS EPO data for a single satellite.

$PAIR590

Reference UTC Time.

$PAIR600

Reference Position.

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2 Download EPO Files

Quectel does not provide any Service Level Agreement for the EPO files. You are expected to download
the EPO data to your own server and share the files to end devices to ensure EPO data availability.

2.1. Get EPO Files from Server

Table 3: Download URL of EPO Files

The following is a complete URL sample:
http://wpepodownload.mediatek.com/QGPS.DAT?vendor=AAA&project=BBB&device_id=CCC

⚫ The query string starts with “?” and is separated by “&”.
⚫ The values of “vendor” and “project” (AAA and BBB in the example) are issued by Quectel. Contact

EPO Type

GNSS Type

EPO File URL

File Name

Unified QEPO

GPS only

http://wpepodownload.mediatek.co
m/QGPS.DAT?vendorinfo

Single name: QGPS.DAT

Unified QEPO

GPS + GLONASS

http://wpepodownload.mediatek.co
m/QG_R.DAT?vendorinfo

Single name: QG_R.DAT

Unified QEPO

BDS only

http://wpepodownload.mediatek.co
m/QBD2.DAT?vendorinfo

Single name: QBD2.DAT

Unified QEPO

Galileo only

http://wpepodownload.mediatek.co
m/QGA.DAT?vendorinfo

Single name: QGA.DAT

EPO

GPS only

http://wpepodownload.mediatek.co
m/EPO_GPS_3_X.DAT?vendorinfo

X = 1–10

EPO_GPS_3_1.DAT to
EPO_GPS_3_10.DAT

EPO

GPS + GLONASS

http://wpepodownload.mediatek.co
m/EPO_GR_3_X.DAT?vendorinfo

X = 1–10

EPO_GR_3_1.DAT to
EPO_GR_3_10.DAT

EPO

BDS only

http://wpepodownload.mediatek.co
m/EPO_BDS_3.DAT?vendorinfo

EPO_BDS_3.DAT

EPO

Galileo only

http://wpepodownload.mediatek.co
m/EPO_GAL_X.DAT?vendorinfo

X = 3 or 7

EPO_GAL_3.DAT or
EPO_GAL_7.DAT

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Quectel Technical Support to get the value.

⚫ The value of “device_id” (CCC in the example) contains two parts – one is assigned by Quectel and

the other by the customer. For example: if CCC = XXX_YYY, the value XXX is provided by Quectel
and you can contact Quectel Technical Support to get the value, while YYY can be assigned by
yourself and it must be a unique value, such as IMEI. Each device must have a unique ID.

There will be up to 10 files as the GPS-only or GPS + GLONASS EPO files may include a maximum of 30
days of predictions. Slices of 30-day EPO:
_1 for days 1 to 3,
_2 for days 4 to 6,
...
_10 for days 28 to 30.

2.2. EPO File Format

This chapter mainly illustrates the format of the EPO files.

The SVID numbers of EPO files for different constellations are shown below.

Table 4: EPO Data SVID Range

GNSS Type

PRN

EPO Data SVID

GPS

1–32

1–32

GLONASS

1–24

65–88

Galileo

1–36

101–136

BDS

1–54,
55–63

201–254,
190–198

NOTE

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2.2.1. EPO File Format – GPS Only

Day7 ...Day1 Day2

SV1 SV2 SV32SV31

...

Segment Segment1

UTC 0:00-6:00

Segment2 Segment3 Segment4

6:00-12:00 12:00-18:00 18:00-24:00

EPO Format (1 day)

...EPO Format (1 Segment)

EPO Format (1 SV)

SVID

3

GPS_Hour

...

8~11

64~67

Day29 Day30

...

4~70[LSB]~2[MSB]

...

CheckSum

68~71

Data

Byte offset

...

...

Data

Byte offset

Figure 1: EPO File Format – GPS Only

GPS_Secs = GPS_Hour × 3600
GPS_Week Number = GPS_Secs / 604800
GPS TOW = GPS_Secs % 604800

An EPO file contains GPS Time (GPS_Week, GPS_Hour and GPS_Secs). The maximum unit in GPS
Time is GPS week which starts at approximately midnight of January 5th to 6th, 1980.

The following figure illustrates the format of several segments of EPO files.

1 3 4 5 6 7 82 9 11 12 13 14 15 1610 17 19 20 21 22 23 2418 25 27 28 29 30 31 3226

1 3 4 5 6 7 82 9 11 12 13 14 15 1610 17 19 20 21 22 23 2418 25 27 28 29 30 31 3226

1 3 4 5 6 7 82 9 11 12 13 14 15 1610 17 19 20 21 22 23 2418 25 27 28 29 30 31 3226

EPO SET

EPO SET

EPO SET

SAT data

SAT data

Figure 2: Format of Several Segments of EPO Files

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The basic unit of an EPO file is SAT Data and the size of each SAT Data is 72 bytes. One EPO SET
contains 32 SAT Data, so the data size of an EPO SET is 2304 bytes. Each EPO file contains several
EPO SETs and thus the file size must be a multiple of 2304 bytes. An EPO SET is valid for 6 hours.
Therefore, there will be 4 EPO SETs for one day.

2.2.2. EPO File Format – BDS/Galileo Only

Galileo EPO data consist of the 72-byte header and 3- or 7- day fundamental EPO data. BDS EPO data
consist of the 72-byte header and 3-day EPO data only. The EPO format for both has no fixed size.

Day7Day1 Day2

SV SV SVSV

...

Segment Segment1

UTC 0:00-6:00

Segment2 Segment3 Segment4

6:00-12:00 12:00-18:00 18:00-24:00

EPO Format (1 day)

...EPO Format (1 Segment)

EPO Format (1 SV)

SVID

3

GPS_Hour

0[LSB]~2[MSB]

...

4~7

...

8~11

...

64~67

CheckSum

68~71

Data

Byte offset

...

...

Data

Byte offset

Header

72 bytes

Day3

Figure 3: EPO File Format – BDS/Galileo Only

The 72-byte header contains the SV available bitmask that can be used for calculating the available
satellite ID. When the SV available bitmask position is 1, it indicates that the satellite is available, and the
number of the bit indicates the satellite ID.

For example, you can parse the data from Figure 4: Galileo EPO Header as follows.

⚫ SVID is FE for Galileo.
⚫ SV available bitmask: 09 67 94 5D DF.
⚫ Total available SVs: 22.
⚫ Available SVs: 1, 2, 3, 4, 5, 7, 8, 9, 11, 12, 13, 15, 19, 21, 24, 25, 26, 27, 30, 31, 33, 36.