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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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

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

EPO SET

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.

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Data

SV available

bitmask(Hbytes)

*** ***

Byte offset 16[LSB]~19[MSB] 20~23 24~27

Example 09 00 00 00

Data

SV available

bitmask(Lbytes)

Byte offset 4[LSB]~7[MSB]

Example DF 5D 94 67

***

0~2

SVID

3

FE

***

12~15

***

8~11

***

18~31

Figure 4: Galileo EPO Header

You can parse the data from Figure 5: BDS EPO Header as follows.

⚫ SVID is FF for BDS. ⚫ SV available bitmask: 3F FF BF FC 3F FF. ⚫ Total available SVs: 41. ⚫ Available SVs: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,

32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46.

Data

SV available

bitmask(Hbytes)

*** ***

Byte offset 16[LSB]~19[MSB] 20~23 24~27

Example FF 3F 00 00

Data

SV available

bitmask(Lbytes)

Byte offset 4[LSB]~7[MSB]

Example FF 3F FC BF

***

0~2

SVID

3

FF

***

12~15

***

8~11

***

18~31

Figure 5: BDS EPO Header

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2.2.3. EPO File Format – GPS + GLONASS

GPS EPO SET

SAT data

1

31 32 65 66

2 87 88

1

31 32 65 66

2 87 88

1

31 32 65 66

2 87 88

GLONASS EPO SET

Figure 6: EPO File Format – GPS + GLONASS

The basic unit of an EPO file is SAT Data, and the size of SAT Data is 72 bytes. In GPS + GLONASS EPO files, one EPO SET contains 56 SAT Data, so the EPO SET data size is 4032 bytes. Each EPO file contains several EPO SETs. The file size must be a multiple of 4032 bytes. An EPO SET is valid for 6 hours. Therefore, there will be 4 EPO SETs for one day.

2.3. EPO File Types

The EPO data can be downloaded in the form of files. You can select the most suitable file type to download based on the availability of a data connection and storage space of your application. See Table

3: Download URL of EPO Files and Table 5: EPO File Types to decide on the file type to be downloaded.

Table 5: EPO File Types

EPO Type

GNSS Type

Description

Unified QEPO

GPS only

6-hour prediction orbit (ephemeris). Single file containing the latest available GPS EPO data.

Unified QEPO

GPS + GLONASS

6-hour prediction orbit (ephemeris). Single file containing the latest available GPS + GLONASS EPO data.

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2.4. Recommended Download Procedures of EPO Files

Set daily timer to check

EPO effectiveness

Daily timer expires

Position fixed

Download EPO file(s) for

backup

Back up prepared EPO

files

Power on GNSS

receiver

Will EPO files expire

today?

1)

Have valid EPO

files?

3)

Download unified QEPO

files

Verify downloaded

data

EPO aiding with backup

file

Position fixed

Verify downloaded

data

2)

Yes

No

Yes

Figure 7: Recommended Download Procedures of EPO Files

EPO Type

GNSS Type

Description

Unified QEPO

BDS/Galileo only

6-hour prediction orbit (ephemeris). Single file containing the latest available BDS/Galileo EPO data.

EPO

GPS only

3–14 days of prediction orbit (ephemeris). Split into 5 files, each containing 3-day information.

EPO

Galileo only

3- or 7-day prediction orbit (ephemeris).

EPO

BDS only

3-day prediction orbit (ephemeris).

EPO

GPS + GLONASS

3–14 days of prediction orbit (ephemeris). Split in 5 files, each containing 3-day information.

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1. 1) You must know the current UTC time to download valid EPO files.

2. 2) Send $PAIR470 to check if the data are correct.

3. 3) If the device is powered off for a long time, EPO files stored in flash may expire.

2.5. EPO File Validity Period

EPO file validity period is related to the current UTC time. The EPO file validity period can be obtained from the last segment of the EPO file. See Figure 1: EPO File Format – GPS Only or the sample of how to calculate EPO file validity period (GPS_Hour + 6). It is necessary to download the EPO file 12 hours in advance. The following codes show the conversion between UTC time and GPS time.

void utc_to_gpstime(kal_uint32 year, //Input year kal_uint8 mon, //Input month: 1~12 kal_uint8 day, //Input day: 1~31 kal_uint8 hour, //Input hour: 0~23 kal_uint8 min, //Input minute: 0~59 kal_uint8 sec, //Input second: 0~59 kal_int32* wn, //Output GPS week number double* tow) //Output GPS time of week { kal_int32 iYearsElapsed; //Elapsed years since 1980 kal_int32 iDaysElapsed; //Elapsed days since Jan 5/Jan 6, 1980 kal_int32 iLeapDays; //Leap days since Jan 5/Jan 6, 1980 kal_int32 i; //Number of days at the start of each month (ignore leap years). kal_uint16 doy[12] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};

iYearsElapsed = year - 1980; i = 0; iLeapDays = 0; while (i <= iYearsElapsed) { if ((i % 100) == 20) { if ((i % 400) == 20) { iLeapDays++; } }

NOTE

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else if ((i % 4) == 0) { iLeapDays++; } i++; } /* iLeapDays = iYearsElapsed / 4 + 1; */. if ((iYearsElapsed % 100) == 20) { if (((iYearsElapsed % 400) == 20) && (mon <= 2)) { iLeapDays--; } } else if (((iYearsElapsed % 4) == 0) && (mon <= 2)) { iLeapDays--; } iDaysElapsed = iYearsElapsed * 365 + doy[mon - 1] + day + iLeapDays - 6; //Convert time to GPS weeks and seconds. *wn = iDaysElapsed / 7; *tow = (double)(iDaysElapsed % 7) * 86400 + hour * 3600 + min * 60 + sec; }

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3 AGNSS Implementation

This chapter describes the two AGNSS implementation methods: Host EPO and Flash EPO.

⚫ Implement AGNSS with Host EPO

The host sends EPO data to the GNSS receiver through NMEA (ASCII) PAIR commands, such as $PAIR471.

⚫ Implement AGNSS with Flash EPO

The EPO data are downloaded to the flash of GNSS receiver through Binary Protocol.

Flash EPO retains data longer than Host EPO.

3.1. AGNSS with Flash EPO

Flash EPO can store up to 14 days of EPO assistance data in flash, which enables the receiver to use the available data since boot time. The communication protocol of Flash EPO is Binary Protocol. Thus, you need to download assistance data to the GNSS receiver in the binary format specified in this document. See Chapter 3.1.2 EPO Data Transfer Protocol and Chapter 3.1.3 AGNSS Procedure with Flash EPO for details.

3.1.1. Binary Protocol

LengthPreamble MsgID Payload Checksum

The range for checksum calculation

Frame preamble,

fixed as 0x04 0x24

2-byte

Message

2-byte

Message ID

1-byte

Checksum

Tail

Frame tail,

fixed as 0xAA 0x44

Figure 8: Binary Protocol Structure

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Table 6: Description of Binary Protocol Fields

The EPO binary format is divided into start message, EPO data message and end message.

Table 7: Start of EPO Binary Format

Table 8: EPO Data Binary Format

Table 9: End of EPO Binary Format

Field

Length (Byte)

Description

Preamble

2

Fixed as 0x2404. Little-endian.

MsgID

2

Message ID.

Length

2

Payload length. Unit: byte. Default packet size: 72 bytes. Little-endian.

Payload

Variable

Payload data to be transferred.

Checksum

1

The checksum is the 8-bit exclusive OR of all bytes in the message between (but not including) the Preamble and the Checksum.

Tail

2

Fixed as 0x44AA. Little-endian.

Preamble

MsgID

Length

Payload

Checksum

Tail

0x04 0x24

0xB0 0x04

1

‘G’ – GPS ‘R’ – GLONASS ‘E’ – Galileo ‘C’ – BDS

0x**

0xAA 0x44 2 Bytes

2 Bytes

1 Byte

2 Bytes

Preamble

MsgID

Length

Payload

Checksum

Tail

0x04 0x24

0xB1 0x04

72

EPO Data

0x**

0xAA 0x44

2 Bytes

72 Bytes

1 Byte

2 Bytes

Preamble

MsgID

Length

Payload

Checksum

Tail

0x04 0x24

0xB2 0x04

1

‘G’ – GPS ‘R’ – GLONASS

0x**

0xAA 0x44

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3.1.2. EPO Data Transfer Protocol

When transmitting assistance data, the host first sends the start message packet, then splits the EPO data into data packets and sends them, and finally sends the end message packet. The host should follow the EPO Data Transfer Protocol when transferring EPO data to the GNSS receiver.

3.1.2.1 Pseudo Code for EPO Data Transfer Protocol

Pseudo code for the EPO data transfer procedure of GPS + GLONASS, for reference only:

#define GNSS_APP_BINARY_BINARY_PREAMBLE1 (0x04) #define GNSS_APP_BINARY_BINARY_PREAMBLE2 (0x24) #define GNSS_APP_BINARY_BINARY_ENDWORD1 (0xAA) #define GNSS_APP_BINARY_BINARY_ENDWORD2 (0x44)

#define GNSS_APP_BINARY_BINARY_PREAMBLE_SIZE (2) #define GNSS_APP_BINARY_BINARY_CHECKSUM_SIZE (1) #define GNSS_APP_BINARY_BINARY_ENDWORD_SIZE (2) #define GNSS_APP_BINARY_BINARY_CONTROL_SIZE (GNSS_APP_BINARY_BINARY_PREAMBLE_SIZE + \ GNSS_APP_BINARY_BINARY_CHECKSUM_SIZE + \ GNSS_APP_BINARY_BINARY_ENDWORD_SIZE)

#define GNSS_APP_BINARY_BINARY_MESSAGE_ID_SIZE (2) #define GNSS_APP_BINARY_BINARY_PAYLOAD_LENGTH_SIZE (2) #define GNSS_APP_BINARY_BINARY_PAYLOAD_HEADER_SIZE (GNSS_APP_BINARY_BINARY_MESSAGE_ID_SIZE + \ GNSS_APP_BINARY_BINARY_PAYLOAD_LENGTH_SIZE)

#define GNSS_APP_BINARY_BINARY_MAX_DATA_SIZE (512) #define GNSS_APP_BINARY_BINARY_MAX_PAYLOAD_DATA_SIZE (GNSS_APP_BINARY_BINARY_MAX_DATA_SIZE - \ GNSS_APP_BINARY_BINARY_CONTROL_SIZE - \ GNSS_APP_BINARY_BINARY_PAYLOAD_HEADER_SIZE)

typedef enum gnss_app_binary_binary_decode_results { GNSS_APP_BINARY_BINARY_DECODE_SUCCESS = 0,

Preamble

MsgID

Length

Payload

Checksum

Tail

‘E’ – Galileo ‘C’ – BDS

2 Bytes

1 Byte

2 Bytes

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GNSS_APP_BINARY_BINARY_DECODE_WRONG_PARAMETER = -1, GNSS_APP_BINARY_BINARY_DECODE_WRONG_PREAMBLE = -2, GNSS_APP_BINARY_BINARY_DECODE_WRONG_CHECKSUM = -3, GNSS_APP_BINARY_BINARY_DECODE_WRONG_ENDWORD = -4, }gnss_app_binary_binary_decode_results_t; typedef struct gnss_app_binary_binary_payload { uint16_t message_id; uint16_t data_size; /* actual size of data in payload data buffer */ uint8_t data[GNSS_APP_BINARY_BINARY_MAX_PAYLOAD_DATA_SIZE]; }gnss_app_binary_binary_payload_t;

uint8_t gnss_app_binary_calculate_binary_checksum(const gnss_app_binary_binary_payload_t* const payload) { uint8_t checksum = 0; uint8_t* pheader = NULL; uint8_t* pdata = NULL; uint16_t i; if (NULL == payload) { return 0; } /* The checksum is the 8-bit exclusive OR of all bytes in the payload. */ pheader = (uint8_t*)payload; for (i = 0; i < GNSS_APP_BINARY_BINARY_PAYLOAD_HEADER_SIZE; i++) { checksum ^= *pheader; pheader++; } pdata = (uint8_t*)payload->data; for (i = 0; i < payload->data_size; i++) { checksum ^= *pdata; pdata++; } return checksum; }

int16_t gnss_app_binary_encode_binary_packet(uint8_t* const buffer, uint16_t max_buffer_size, const gnss_app_binary_binary_payload_t* const payload) { uint8_t* pbyte; uint16_t required_length; if (NULL == buffer || payload == NULL) { return -1; } required_length = payload->data_size + GNSS_APP_BINARY_BINARY_CONTROL_SIZE +

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GNSS_APP_BINARY_BINARY_PAYLOAD_HEADER_SIZE; if (max_buffer_size < required_length) { return -1; } memset((void*)buffer, 0, max_buffer_size); buffer[0] = GNSS_APP_BINARY_BINARY_PREAMBLE1; buffer[1] = GNSS_APP_BINARY_BINARY_PREAMBLE2; pbyte = &buffer[2]; memcpy(pbyte, payload, GNSS_APP_BINARY_BINARY_PAYLOAD_HEADER_SIZE); pbyte += GNSS_APP_BINARY_BINARY_PAYLOAD_HEADER_SIZE; memcpy(pbyte, payload->data, payload->data_size); pbyte += payload->data_size; *pbyte++ = gnss_app_binary_calculate_binary_checksum(payload); *pbyte++ = GNSS_APP_BINARY_BINARY_ENDWORD1; *pbyte = GNSS_APP_BINARY_BINARY_ENDWORD2; return required_length; }

FILE* gnss_epo_file = NULL; #define GNSS_MAX_EPO_NUMBER (37) #define GNSS_MAX_RECORD_SIZE (72) static uint32_t gnss_epo_sv_buf[(GNSS_MAX_EPO_NUMBER * GNSS_MAX_RECORD_SIZE) / sizeof(uint32_t)]; int16_t gnss_epo_encode_binary(uint16_t msg_id, char* buffer, uint16_t buffer_size, char* data_input, int32_t data_length) { gnss_app_binary_binary_payload_t payload; int16_t binary_message_length; memset((void*)&payload, 0, sizeof(gnss_app_binary_binary_payload_t)); payload.message_id = msg_id; payload.data_size = (uint16_t)data_length; memcpy(payload.data, data_input, sizeof(uint8_t) * data_length); binary_message_length = gnss_app_binary_encode_binary_packet(buffer, buffer_size, &payload); return binary_message_length; }

void gnss_epo_binary_demo() { gnss_app_binary_data_t data; gnss_app_binary_data_result_t result = { 0 }; uint32_t* epobuf; int32_t i; char buffer[500]; uint16_t length = 0;

int32_t buffer_size = 0;

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uint8_t segment = 0;

uint8_t curr_sys_type = 'G'; //type is the GPS gnss_epo_file = fopen("EPO_GR_3_1.DAT", "rb"); length = gnss_epo_encode_binary(1200, buffer, 512, &curr_sys_type, 1); gnss_app_uart_send_data(buffer, length); memset(&gnss_epo_sv_buf, 0, sizeof(gnss_epo_sv_buf)); while (gnss_epo_read_data(&gnss_epo_sv_buf, 32 * GNSS_MAX_RECORD_SIZE, segment * (32 + 24) * GNSS_MAX_RECORD_SIZE)) { segment++; for (i = 0; i < 32; i++) { epobuf = (uint32_t*)(gnss_epo_sv_buf + ((i * GNSS_MAX_RECORD_SIZE) /

4)); length = gnss_epo_encode_binary(1201, buffer, 512, (char*)epobuf, GNSS_MAX_RECORD_SIZE); gnss_app_uart_send_data(buffer, length); } memset(&gnss_epo_sv_buf, 0, sizeof(gnss_epo_sv_buf)); } length = gnss_epo_encode_binary(1202, buffer, 512, &curr_sys_type, 1);

gnss_app_uart_send_data(buffer, length);

curr_sys_type = 'R'; //type is the GLONASS length = gnss_epo_encode_binary(1200, buffer, 512, &curr_sys_type, 1); gnss_app_uart_send_data(&data, &result); memset(&gnss_epo_sv_buf, 0, sizeof(gnss_epo_sv_buf)); segment = 0; while (gnss_epo_read_data(&gnss_epo_sv_buf, 37 * GNSS_MAX_RECORD_SIZE, (segment * (32 + 24) * GNSS_MAX_RECORD_SIZE) + (32 * GNSS_MAX_RECORD_SIZE))) { segment++; for (i = 0; i < 24; i++) { epobuf = (uint32_t*)(gnss_epo_sv_buf + ((i * GNSS_MAX_RECORD_SIZE) /

4)); length = gnss_epo_encode_binary(1201, buffer, 512, (char*)epobuf, GNSS_MAX_RECORD_SIZE); gnss_app_uart_send_data(buffer, length); } memset(&gnss_epo_sv_buf, 0, sizeof(gnss_epo_sv_buf)); } length = gnss_epo_encode_binary(1202, buffer, 512, &curr_sys_type, 1); gnss_app_uart_send_data(buffer, length); fclose(gnss_epo_file); }

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3.1.3. AGNSS Procedure with Flash EPO

Power on

GNSS

Have an EPO file?

Send Reference Position

Send Reference Time

Position fixed

Download EPO files with

Binary Protocol

Restart GNSS

YES

NO

Has EPO file expired?

NO

Erase EPO fileYES

Verify

downloaded data

Figure 9: AGNSS Procedure with Flash EPO

1. Power on the GNSS module.

2. Check if there are EPO data in the GNSS module flash memory with $PAIR470.

3. If the flash memory contains EPO data, go to the next step to check data validity. Otherwise, download EPO data to the GNSS module and verify the downloaded data, then restart the GNSS module and go to Step 5.

4. Check whether the EPO file in the GNSS module flash memory has expired.

5. If the EPO file is still valid, go to Step 6. Otherwise, erase the expired EPO file with $PAIR472 and download a new EPO file.

6. Send reference time to the GNSS module with $PAIR590.

7. Send reference position to GNSS module with $PAIR600.

8. Wait for the GNSS module to fix position.

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3.2. AGNSS with Host EPO

Host EPO allows for a simpler text-based implementation that enables the receiver to perform a fast start-up where assistance data must be sent to the receiver each time it boots. When using Host EPO, the receiver can only receive one block of assistance data valid for 6 hours.

Implementing Host EPO only requires a few PAIR sentences and the whole data transfer can be performed in NMEA mode. See Chapter 4 AGNSS Related Messages for detailed description of

$PAIR471, $PAIR590 and $PAIR600.

3.2.1. Recommended Sequence for Host EPO

After the module is powered on, it sends an aiding request 1) to notify the expiration of the stored GNSS assistance data when both assistance data and ephemeris are invalid. Therefore, if the module does not report an aiding request, it is recommended to determine whether the assistance data have expired by sending $PAIR470 after the host receives the system startup message. The host sends the assistance data in the sequence shown in Figure 10: Suggested Sequence for Host EPO.

Host EPO procedure:

1. GNSS module starts up;

2. Host sends Reference Time;

3. Host sends Reference Position;

4. Host sends EPO data.

The supplied Reference Time, Reference Position and EPO data must comply with the requirements listed in Chapter 1.2 AGNSS Requirements.

1. 1) The module automatically outputs $PAIR010 messages to indicate the expiration of stored GNSS assistance data. For details about $PAIR010, see document [1] protocol specification.

2. In the current implementation, the host needs to wait for a $PAIR001 packet to be returned before sending another segment of EPO data. For details about $PAIR001, see document [1] protocol

specification.

NOTE

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GNSS Receiver Host

GNSS Module Powers Up

Start up message

Assistance Data (Time)

PAIR001 (ACK)

Assistance Data (Position)

PAIR001 (ACK)

EPO Assistance Data Segment 001

EPO Assistance Data Segment 002

PAIR001 (ACK)

Host needs to wait for ACK packages

Loop

[Repeats until all EPO data are sent]

Host EPO Sequence

Figure 10: Suggested Sequence for Host EPO

3.2.2. Sample Code to Send EPO

The following is the reference code to send one segment EPO data to GNSS chip. It indicates how to construct PAIR messages for GNSS receiver. PAIR messages for Reference Time and Reference Position are not included in this example.

#define GNSS_GLONASS_EPO_BASE_ID (64) #define GNSS_GALILEO_EPO_BASE_ID (100) #define GNSS_BDS_EPO_BASE_ID (200)

#define MNL_SERVICE_MAX_COMMAND_LEN (352) #define EPO_DEMO_RECORD_SIZE (72)

typedef enum{ EPO_DEMO_MODE_GPS, EPO_DEMO_MODE_GLONASS,

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EPO_DEMO_MODE_GALILEO, EPO_DEMO_MODE_BEIDOU }epo_demo_mode_t;

int32_t epo_demo_get_sv_prn(int32_t type, uint8_t *data) { int32_t sv_id, sv_prn = 0;

sv_id = data[3];

switch(type) { case EPO_DEMO_MODE_GPS: sv_prn = sv_id; break; case EPO_DEMO_MODE_GLONASS: sv_prn = sv_id - GNSS_GLONASS_EPO_BASE_ID; break; case EPO_DEMO_MODE_GALILEO: if(sv_id == 255) { sv_prn = 255; } else { sv_prn = sv_id - GNSS_GALILEO_EPO_BASE_ID; } break; case EPO_DEMO_MODE_BDS: if(sv_id == 255) { sv_prn = 255; } else { sv_prn = sv_id - GNSS_BDS_EPO_BASE_ID; } break; default: sv_prn = 0; } return sv_prn; }

void epo_demo_send_data(epo_demo_epo_data_t *data_p, int32_t data_num, int32_t type){

char temp_buffer[MNL_SERVICE_MAX_COMMAND_LEN] = {0}; uint8_t data_buffer[EPO_DEMO_RECORD_SIZE] = {0}; int32_t i; int32_t sv_prn = 0;

for(i = 0; i < data_num; i++) {

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unsigned int *epobuf = (unsigned int *)data_buffer; epo_demo_epo_fread(data_p, data_buffer, EPO_DEMO_RECORD_SIZE); sv_prn = epo_demo_get_sv_prn(type, data_buffer);

sprintf((char *) temp_buffer, "471,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X", (unsigned int)type, (unsigned int)sv_prn, epobuf[0], epobuf[1], epobuf[2], epobuf[3], epobuf[4], epobuf[5], epobuf[6], epobuf[7], epobuf[8], epobuf[9], epobuf[10], epobuf[11], epobuf[12], epobuf[13], epobuf[14], epobuf[15], epobuf[16], epobuf[17]);

gnss_app_send_command_ex(temp_buffer); memset(temp_buffer, 0, MNL_SERVICE_MAX_COMMAND_LEN); } }

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4 AGNSS Related Messages

This chapter outlines AGNSS related PAIR messages (proprietary NMEA messages defined by the chipset supplier). “P” means proprietary message, “AIR” means the command defined by the chipset supplier.

4.1. PAIR470 PAIR_EPO_GET_STATUS

Queries the status of EPO data stored on the GNSS chip.

Type:

Command

Synopsis:

$PAIR470,<System_ID>*<Checksum><CR><LF>

Parameter:

Result: Returns $PAIR001 message and the query result.

Query result message format:

$PAIR470,<System_ID>,<Set>,<FWN>,<FTOW>,<LWN>,<LTOW>,<FCWN>,<FCTOW>,<LCWN>,<LC TOW>*<Checksum><CR><LF>

Field

Format

Unit

Description

<System_ID>

Numeric

-

GNSS system ID. 0 = GPS 1 = GLONASS 2 = Galileo 3 = BDS

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Parameter included in the result:

Example:

$PAIR470,0*25 $PAIR001,470,0*38 $PAIR470,0,1,2098,194400,2098,216000,2098,194400,2098,216000*38

4.2. PAIR471 PAIR_EPO_SET_DATA

Sends the packet containing EPO data for a single satellite.

Type:

Input

Field

Format

Unit

Description

<System_ID>

Numeric

-

GNSS system ID. 0 = GPS 1 = GLONASS 2 = Galileo 3 = BDS

<Set>

Numeric

-

Total number of EPO data sets stored in GNSS chip.

<FWN>

Numeric

-

GPS week number of the first set of EPO data stored in flash.

<FTOW>

Numeric

-

GPS TOW of the first set of EPO data stored in flash.

<LWN>

Numeric

-

GPS week number of the last set of EPO data stored in flash.

<LTOW>

Numeric

-

GPS TOW of the last set of EPO data stored in flash.

<FCWN>

Numeric

-

GPS week number of the first set of EPO data that are currently being used.

<FCTOW>

Numeric

-

GPS TOW of the first set of EPO data that are currently being used.

<LCWN>

Numeric

-

GPS week number of the last set of EPO data that are currently being used.

<LCTOW>

Numeric

-

GPS TOW of the last set of EPO data that are currently being used.

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Synopsis:

$PAIR471,<System_ID>,<SV_ID>,<W[0]>,...,<W[17]>*<Checksum><CR><LF>

Parameter:

Result: Returns $PAIR001 message.

Example:

$PAIR471,1,16,56056272,F2BC0244,4F19AE34,F95C534D,FAE67014,4F19AF6B,F96749BD,9F341F2 D,6F4EA9F,77DB4710,66ADAC2,9ADF3B01,8CC8B19C,29D2D20C,FC5B2E94,1000001C,11005000,7 48B45F4*0A $PAIR001,471,0*39

4.3. PAIR472 PAIR_EPO_ERASE_FLASH_DATA

Erases the EPO data stored in the flash memory.

Type:

Command

Field

Format

Unit

Description

<System_ID>

Numeric

-

GNSS system ID. 0 = GPS 1 = GLONASS 2 = Galileo 3 = BDS

<SV_ID>

Hexadecimal

-

PRN number of the satellite whose EPO data are being sent. GPS Range: 1–32. GLONASS Range: 1–24. Galileo Range: 1–30. BDS Range: 1–37. Special 255: BDS IONO data. Special 254: Galileo IONO data.

<W[0]>–<W[17]>

-

18 words (LSB-first) of one EPO segment data (total 72 bytes).

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Synopsis:

$PAIR472*<Checksum><CR><LF>

Parameter:

None

Result: Returns $PAIR001 message.

Example:

$PAIR472*3B $PAIR001,472,0*3A

4.4. PAIR590 PAIR_TIME_SET_REF_UTC

Sends reference UTC time to GNSS chip for TTFF improvments. Local time should be avoided due to time-zone offset. To achieve a faster TTFF, the reference time should be accurate within 3 seconds and must be specified in UTC time.

Type:

Set

Synopsis:

$PAIR590,<YYYY>,<MM>,<DD>,<hh>,<mm>,<ss>*<Checksum><CR><LF>

Parameter:

Field

Format

Unit

Description

<YYYY>

Numeric

-

UTC year. Minimum value: 1980.

<MM>

Numeric

-

UTC month. Range: 1–12.

<DD>

Numeric

-

UTC day. Range: 1–31.

<hh>

Numeric

-

UTC hours. Range: 0–23.

<mm>

Numeric

-

UTC minutes. Range: 0–59.

<ss>

Numeric

-

UTC seconds. Range: 0–59.

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Result: Returns $PAIR001 message.

Example:

$PAIR590,2019,2,10,9,0,58*0B $PAIR001,590,0*37

This command needs to be sent every time after GNSS module reboots.

4.5. PAIR600 PAIR_LOC_SET_REF

Sends reference position to GNSS chip for faster TTFF.

Type:

Set

Synopsis:

$PAIR600,<Lat>,<Lon>,<Height>,<AccMaj>,<AccMin>,<Bear>,<AccVert>*<Checksum><CR><LF>

Parameter:

Field

Format

Unit

Description

<Lat>

Numeric

Degree

Reference latitude. Range: -90 to 90. Minus: south; plus: north. It is recommended to express this value in floating point with 6 decimal points.

<Lon>

Numeric

Degree

Reference longitude. Range: -180 to 180. Minus: west; plus: east. It is recommended to express this value in floating point with 6 decimal points.

Numeric

Meter

Reference height.

Numeric

Meter

Semi-major RMS accuracy.

Numeric

Meter

Semi-minor RMS accuracy.

<Bear>

Numeric

Degree

Bearing.

NOTE

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Result: Returns $PAIR001 message.

Example:

$PAIR600,24.772816,121.022636,175.0,50.0,50.0,0.0,100.0*06 $PAIR001,600,0*3D

This command needs to be sent every time after GNSS module reboots.

Field

Format

Unit

Description

Numeric

Meter

Vertical RMS accuracy.

NOTE

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5 Download EPO Data with QGNSS

This chapter describes how to download EPO data through QGNSS. Contact Quectel Technical Support for details on QGNSS.

5.1. Download Flash EPO with QGNSS

Steps to download Flash EPO with the QGNSS tool:

1. Run the QGNSS tool.

2. In the main interface, click “AGNSS” → “Assistant GNSS Offline” as shown below.

Figure 11: QGNSS Interface for Setting Flash EPO

3. Download EPO file to the module. a) Click the “Connect” button to connect to the FTP server. b) Select EPO file. c) Click the “Download selected file” button to download the EPO file to computer. d) Select Satellites type.

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e) Click the “…” button to select EPO file. f) Click “Download” button to download the EPO file to module.

Figure 12: Download Flash EPO File

5.2. Download Host EPO with QGNSS

Steps to download Host EPO with the QGNSS tool:

1. Run the QGNSS tool.

2. In the main interface, click “AGNSS” → “Assistant GNSS Online” as shown below.

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Figure 13: QGNSS Interface for Setting Host EPO

3. Configure parameters: a) Check “Use Current Position” to use current position. b) Check “Use Current UTC” to use current time. c) Click “Transfer” to download host EPO file.

Figure 14: Download Host EPO File

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6 AGNSS Implementation Example

This chapter gives examples of how to download EPO files to the module.

6.1. Flash EPO Implementation

Blue: Sent data Red: ACK information

//Host sends $PAIR472*3B to erase the EPO data stored in the flash memory:

$PAIR472*3B

//Module returns a $PAIR001 message:

$PAIR001,472,0*3A

//Host sends EPO start message in hexadecimal format:

04 24 B0 04 01 00 47 F2 AA 44

//Module returns an ACK message:

04 24 E8 03 04 00 B0 04 00 00 5B AA 44

//Host sends EPO data in hexadecimal format:

04 24 B1 04 48 00 00 A9 05 01 CD 00 80 B6 73 DE ……. FD AA 44

//Module returns an ACK message:

04 24 E8 03 04 00 B1 04 00 00 5A AA 44

……

//Host sends EPO data in hexadecimal format:

04 24 B1 04 48 00 42 A9 05 20 AF 3F 80 B7 71 CE……. FD AA 44

//Module returns an ACK message:

04 24 E8 03 04 00 B1 04 00 00 5A AA 44

//Host sends EPO end data in hexadecimal format:

04 24 B2 04 01 00 52 E5 AA 44

//Module returns an ACK message:

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04 24 E8 03 04 00 B2 04 00 00 59 AA 44

//Host queries the EPO data status stored in the GPS chip:

$PAIR470,0*25

//Module returns $PAIR001 and $PAIR470 messages:

$PAIR001,470,0*38 $PAIR470,0,12,2208,86400,2208,345600,0,0,0,0*34

6.2. Host EPO Implementation

Blue: Sent data Red: ACK information

//Host sends the power-on GNSS system command $PAIR002:

$PAIR002*38

//Module returns $PAIR001:

$PAIR001,002,0*39

//Module outputs $PAIR010 messages automatically:

$PAIR010,1,-1*16 $PAIR010,2,-1*15

//Host sends the reference UTC time command $PAIR590:

$PAIR590,2022,05,01,07,10,27*33

//Module returns a $PAIR001 message:

$PAIR001,590,0*37

//Host sends the reference position information command $PAIR600:

$PAIR600,31.822203,117.115219,175.0,50.0,50.0,0.0,100.0*0F

//Module returns a $PAIR001 message:

$PAIR001,600,0*3D

//Host sends EPO data:

$PAIR471,0,1,105A906,B58000F9,248DE73,F3A00478,F2FD36BA,248DE5E,F844379B,84C21659,6F1 8FEA,124FCF96,103EC82,A6034274,7D15B64A,2F4E5561,24984FBC,1000001C,1100000,1D33F8D3 *3F

//Module returns a $PAIR001 message:

$PAIR001,471,0*39

GNSS Module Series

//Host sends EPO data:

$PAIR471,0,2,205A906,803F5B,24811C6,F67D3826,F4A80421,2481133,7110470,85A4863A,6F1BED3 ,1C59F758,D76D644,A60354C6,7166D3CC,2052969A,C611DBC7,1000001C,0,B41D7D61*08

//Module returns a $PAIR001 message:

$PAIR001,471,0*39

……

//Host sends EPO data:

$PAIR471,0,E,E05A906,EC80019B,2482E2A,950E550,B55D902,248D1E5,708F5C8,83F256C6,6F175 E1,E620A86A,7E544E8,A6039859,22C26DDF,21DDAAB5,7D32DCE7,1000001C,2210000,4941D2A5* 7D

//Module returns a $PAIR001 message:

$PAIR001,471,0*39

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7 Appendix A References

Document Name

[1] Quectel_LC26G&LC76G&LC86G_Series_Protocol Specification

Abbreviation

Description

ACK

Acknowledgement

AGNSS

Assisted GNSS (Global Navigation Satellite System)

EPO

Extended Prediction Orbit

GLONASS

Global Navigation Satellite System (Russia)

GNSS

Global Navigation Satellite System

GPS

Global Positioning System

IMEI

International Mobile Equipment Identity

IONO

Ionospheric

MNL

MTK Navigation Lib

PRN

Pseudo Random Noise

RAM

Random Access Memory

SV

Space Vehicle

SVID

Space Vehicle Identification

TOW

Time of Week

Table 10: Related Document

Table 11: Terms and Abbreviations

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TTFF

Time to First Fix

UART

Universal Asynchronous Receiver/Transmitter

UTC

Coordinated Universal Time

URL

Uniform Resource Locator

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8 Appendix B Special Characters

Table 12: Special Characters

Special Character

Definition

<CR>

Carriage return character.

<LF>

Line feed character.

<...>

Parameter name. Angle brackets do not appear in the message.

[...]

Optional field of a message. Square brackets do not appear in the message.

{…}

Repeated field of a message. Curly brackets do not appear in the message.

Underline

Default setting of a parameter.

Quectel LC26G, LC76G, LC86G Application Note

Specifications and Main Features

Frequently Asked Questions

User Manual

About the Document

Contents

Table Index

Figure Index

1 Introduction

1.1. Differences Between Host EPO and Flash EPO

1.2. AGNSS Requirements

2 Download EPO Files

2.1. Get EPO Files from Server

2.2. EPO File Format

2.2.1. EPO File Format – GPS Only

2.2.2. EPO File Format – BDS/Galileo Only

2.2.3. EPO File Format – GPS + GLONASS

2.3. EPO File Types

2.4. Recommended Download Procedures of EPO Files

2.5. EPO File Validity Period

3 AGNSS Implementation

3.1. AGNSS with Flash EPO

3.1.1. Binary Protocol

3.1.2. EPO Data Transfer Protocol

3.1.2.1 Pseudo Code for EPO Data Transfer Protocol

3.1.3. AGNSS Procedure with Flash EPO

3.2. AGNSS with Host EPO

3.2.1. Recommended Sequence for Host EPO

3.2.2. Sample Code to Send EPO

4 AGNSS Related Messages

4.1. PAIR470 PAIR_EPO_GET_STATUS

4.2. PAIR471 PAIR_EPO_SET_DATA

4.3. PAIR472 PAIR_EPO_ERASE_FLASH_DATA

4.4. PAIR590 PAIR_TIME_SET_REF_UTC

4.5. PAIR600 PAIR_LOC_SET_REF

5 Download EPO Data with QGNSS

5.1. Download Flash EPO with QGNSS

5.2. Download Host EPO with QGNSS

6 AGNSS Implementation Example

6.1. Flash EPO Implementation

6.2. Host EPO Implementation

7 Appendix A References

8 Appendix B Special Characters