阅读说明：本技术 一种北斗星基增强单频定位卫星筛选的方法 (Method for screening Beidou satellite-based enhanced single-frequency positioning satellite ) 是由 熊帅 邵搏 张键 戴凯阳 原彬 雷哲哲 李平力 于 2020-12-06 设计创作，主要内容包括：本发明提供了一种北斗星基增强单频定位卫星筛选的方法,利用BDSBAS用户接收机接收的GPS L1C/A频点伪距、载波观测值,GPS L1C/A基本导航电文,BDSBAS B1单频增强电文进行可用定位卫星筛选,既严格遵守国际民航相关标准要求,又考虑BDSBAS系统特点,满足了用户高精度位置解算和高完好性保障的需求。本发明符合国际民航组织标准要求的增强卫星筛选方法,具有可操作性,在BDSBAS用户接收机导航定位算法设计、测试等工程应用中具有实际价值,可满足用户高精度导航定位精度与高完好性保障需求。(The invention provides a method for screening a Beidou satellite-based enhanced single-frequency positioning satellite, which utilizes a GPS L1C/A frequency point pseudo-range and a carrier observation value received by a BDSBAS user receiver, a GPS L1C/A basic navigation message and a BDSBAS B1 single-frequency enhanced message to screen an available positioning satellite, strictly complies with the requirements of international civil aviation related standards, considers the characteristics of a BDSBAS system, and meets the requirements of high-precision position resolving and high integrity guarantee of a user. The enhanced satellite screening method meeting the international civil aviation organization standard requirement has operability, has practical value in engineering application such as design and test of BDSBAS user receiver navigation positioning algorithm, and can meet the requirements of users on high-precision navigation positioning precision and high integrity guarantee.)

1. A method for screening a Beidou satellite-based enhanced single-frequency positioning satellite is characterized by comprising the following steps:

step 1: resolving time t, and acquiring all satellite PRN numbers, GPS L1C/A basic navigation messages and BDSBAS B1C enhanced messages observed by a user receiver at the resolving time t;

step 2: judging whether the PRN number of the user observation satellite is circulated, and entering the step 3 if the PRN number is not circulated; otherwise, judging the health state of the next satellite and entering the step 13;

and step 3: determining whether satellite UDREI is equal to 14 or 15;

resolving the enhanced message B1C to obtain the UDREI value of the satellite, and if the UDREI value is equal to 14 or equal to 15, entering the step 12; otherwise, UDREI is not equal to 14 nor 15, then step 4 is entered;

and 4, step 4: judging the service level of the user;

if the user service level is any one of LPV, LP or LNAV/VNAV, entering step 6, and setting corresponding information overtime time limit according to the UDREI comparison table and the message information content overtime table; otherwise, entering step 5;

and 5: setting corresponding information overtime time limit according to the En Route, Terminal, user service level of LNAV level, UDREI comparison table and message information content overtime table, and entering step 7;

step 6: judging whether the satellite UDREI is less than or equal to 12, and if the satellite UDREI is less than or equal to 12, entering a step 7; otherwise, the satellite UDREI is larger than 12, and the step 12 is entered;

and 7: ephemeris data age matching;

matching the IOD in the enhanced electric text of the satellite B1C with the IODE in the L1C/A basic navigation text, if the searched IODE and IOD are equal in value, the matching is successful, and selecting one group closest to the resolving moment t from several groups of successfully matched L1C/A basic navigation texts for subsequent calculation, and entering step 8; otherwise, if the matching is not successful, the step 12 is entered;

and 8: judging the correction number and UDREI overtime;

judging whether the slow change correction number, the fast change correction number and the UDREI are overtime, and entering the step 12 if any one of the slow change correction number, the fast change correction number and the UDREI is overtime; otherwise, the time is not overtime, and the step 9 is entered;

and step 9: searching the grid points of the ionized layer;

calculating the ionospheric puncture point of the user according to an RTCA DO-229E specified algorithm, searching effective ionospheric lattice points around the puncture point, if the value of the IGP GIVE parameter is less than 15 and is not overtime, the IGP is effective, and entering the step 10;

step 10: judging whether the number of the searched effective IGPs is more than or equal to 3, if so, entering a step 11, otherwise, entering a step 12;

step 11: setting the satellite health bit flag to be 0, enabling the satellite to be available, and entering the step 2;

step 12: setting the satellite health bit flag to be 1, and entering step 2 if the satellite is unhealthy and unavailable;

step 13: entering BDSBAS user navigation positioning subsequent processing.

Technical Field

The invention relates to the field of Satellite navigation enhancement, in particular to a single-frequency enhanced positioning Satellite screening method in Beidou Satellite-Based Augmentation System (BDSBAS) user positioning solution.

Background

The BDSBAS is a Satellite-Based Augmentation System (SBAS) which is independently built according to international standards in China, and integrity monitoring of a Global Navigation Satellite System (GNSS) which passes through the upper part of China is realized through monitoring stations distributed in China.

The BDSBAS broadcasts a single-frequency slow-varying correction number (broadcast by messages MT24 and MT 25), a fast-varying correction number (broadcast by messages MT 2-5), ionosphere grid correction information (GIVD broadcast by messages MT18 and MT 26), user differential distance error indexes (UDREI broadcast by messages MT 2-MT 6) and related information of a degradation parameter (broadcast by messages MT7, MT10, MT27 and MT 28) through a B1C frequency point of a Geosynchronous geostationary Earth satellite (GEO), so that differential enhancement of a GPS system is realized, and service performance enhancement meets the index requirements of a class I international civil aviation Vertical guided APproach (APV-I).

TABLE 1 UDREI COMPARATIVE TABLE

The BDSBAS user receiver simultaneously receives pseudo-range and carrier observed values of a frequency point L1C/A of a GPS system, L1C/A basic navigation messages and BDSBAS B1C enhanced messages, carries out enhanced positioning calculation to obtain self position information and protection level information, and achieves navigation positioning service of guaranteeing high integrity of users. BDSBAS B1C enhanced message enhanced GPS system PRN number 1 through 37 satellites whose orbits, clock error fast/slow varying corrections, ionospheric corrections, UDREI integrity information have corresponding timeout periods according to ICAO SARPs specifications, as shown in tables 2 and 3.

Table 2 message information content time-out table

TABLE 3 fast-change correction number degradation factor user timeout table

The BDSBAS user needs to strictly screen observable satellites according to different grades of self service and the maximum overtime time limit of each information in the process of enhanced positioning calculation so as to ensure that the obtained positioning result and protection and information are real and reliable, otherwise, serious potential safety hazard occurs. The user service level is divided into two major categories, namely, air Route (En Route), Terminal area (Terminal), Lateral Navigation (LNAV), horizontal/Vertical Navigation (LNAV/VNAV), location beacon Performance (LP), and location beacon Performance with Vertical guidance (LPV).

At present, a BDSBAS system is in a construction stage, related user terminals are also in a development test state, and a specific method for user side enhanced satellite screening according to international civil aviation standard requirements for the BDSBAS system is not disclosed.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for screening a Beidou satellite-based enhanced single-frequency positioning satellite, which utilizes a GPS L1C/A frequency point pseudo-range and a carrier observed value received by a BDSBAS user receiver, a GPS L1C/A basic navigation message and a BDSBAS B1 single-frequency enhanced message to screen an available positioning satellite, strictly complies with the requirements of the relevant standard of international civil aviation, considers the characteristics of a BDSBAS system, and meets the requirements of high-precision position resolving and high integrity guarantee of a user. The invention provides a user single-frequency positioning satellite screening method which strictly meets the requirements of international civil aviation organization standards and aims at the specific conditions of a BDSBAS system, so as to meet the requirements of design, test, application and the like of a BDSBAS system user receiver.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps:

step 1: resolving time t, and acquiring all satellite PRN numbers, GPS L1C/A basic navigation messages and BDSBAS B1C enhanced messages observed by a user receiver at the resolving time t;

step 2: judging whether the PRN number of the user observation satellite is circulated, and entering the step 3 if the PRN number is not circulated; otherwise, judging the health state of the next satellite and entering the step 13;

and step 3: determining whether satellite UDREI is equal to 14 or 15;

resolving the enhanced message B1C to obtain the UDREI value of the satellite, and if the UDREI value is equal to 14 or equal to 15, entering the step 12; otherwise, UDREI is not equal to 14 nor 15, then step 4 is entered;

and 4, step 4: judging the service level of the user;

if the user service level is any one of LPV, LP or LNAV/VNAV, entering step 6, and setting corresponding information overtime time limit according to the UDREI comparison table and the message information content overtime table; otherwise, entering step 5;

and 5: setting corresponding information overtime time limit according to the En Route, Terminal, user service level of LNAV level, UDREI comparison table and message information content overtime table, and entering step 7;

step 6: judging whether the satellite UDREI is less than or equal to 12, and if the satellite UDREI is less than or equal to 12, entering a step 7; otherwise, the satellite UDREI is larger than 12, and the step 12 is entered;

and 7: ephemeris data age (IODE) matching;

matching the IOD in the enhanced electric text of the satellite B1C with the IODE in the L1C/A basic navigation text, if the searched IODE and IOD are equal in value, the matching is successful, and selecting one group closest to the resolving moment t from several groups of successfully matched L1C/A basic navigation texts for subsequent calculation, and entering step 8; otherwise, if the matching is not successful, the step 12 is entered;

and 8: judging the correction number and UDREI overtime;

judging whether the slow change correction number, the fast change correction number and the UDREI are overtime, and entering the step 12 if any one of the slow change correction number, the fast change correction number and the UDREI is overtime; otherwise, the time is not overtime, and the step 9 is entered;

and step 9: an Ionospheric Grid Point (IGP) search;

calculating an Ionospheric Puncture Point (IPP) of a user according to an algorithm specified in an RTCA DO-229E (Minimum Operational Performance Standards for Global Positioning System/Satellite-Based Augmentation System air velocity Equipment) document, searching for an effective ionospheric lattice point (IGP) around the puncture point, wherein if the GIVE parameter value of the IGP is less than 15 and is not overtime, the IGP is effective, and the step 10 is entered;

step 10: judging whether the number of the searched effective IGPs is more than or equal to 3, if so, entering a step 11, otherwise, entering a step 12;

step 11: setting the satellite health bit flag to be 0, enabling the satellite to be available, and entering the step 2;

step 12: the satellite health bit flag is set to 1. The satellite is unhealthy and unavailable, and the step 2 is carried out;

step 13: entering BDSBAS user navigation positioning subsequent processing.

The invention has the beneficial effect that the enhanced satellite screening method which meets the requirements of the international civil aviation organization standard is provided under the condition that the BDSBAS user receiver simultaneously receives the GPS L1C/A basic navigation message and the BDSBAS B1C single-frequency enhanced message. The method has operability, has practical value in engineering application such as design and test of BDSBAS user receiver navigation positioning algorithm, and can meet the requirements of users on high-precision navigation positioning precision and high integrity guarantee.

Drawings

FIG. 1 is a flow chart of a Beidou-based enhanced single-frequency positioning satellite screening method of the invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

The invention relates to a method for screening a Beidou satellite-based enhanced single-frequency positioning satellite, wherein at a resolving moment t, a user receiver receives a pseudo range and a carrier measured value of a GPS L1C/A frequency point, if and only if the pseudo range and the carrier measured value exist simultaneously, the satellite is regarded as visible, and the total number of visible satellites at the moment is recorded as n. The specific steps are shown in fig. 1, and the steps are as follows:

step 1: resolving the moment t, and acquiring an observation satellite and an ephemeris;

resolving time t which is the GPS intra-week second of the current resolving epoch; a user observes satellite PRN numbers, and the satellite PRN numbers are all GPS satellite PRN number sets observed by a receiver at the time t; the GPS L1C/A basic navigation ephemeris is a plurality of groups of basic navigation ephemeris information (each group of ephemeris comprises information such as ephemeris, clock error, IODE and the like) which are stored in the receiver at the time t within the last 5 minutes; the BDSBAS B1C enhances the telegraph text, which is the updated correction number and integrity enhancement information (including the information of fast change correction number, slow change correction number, GIVD, GIVE and the like of UDREI and IGP) at the time of the receiver t. And (5) after the relevant information is obtained, entering the step 2.

Step 2: judging whether the PRN number of the GPS satellite observed by the user is circulated

Arranging GPS satellite PRN numbers observed by a user from small to large, sequentially judging satellite health, and entering step 13 if all observable satellites are judged to be finished; otherwise, the health judgment of the next satellite is carried out, and the step 3 is entered.

And step 3: determining whether satellite UDREI is equal to 14 or 15;

when B1C increases UDREI of the satellite in the text to 14, it indicates that the satellite is not monitored; 15, this indicates that the satellite is not available. If the UDREI is equal to 14 or 15, the satellite cannot be used for subsequent user navigation positioning solution, and the step 12 is entered; otherwise UDREI is neither equal to 14 nor 15 and step 4 is entered.

And 4, step 4: judging the service level of the user;

aiming at different service level requirements of users, each type of enhanced message has different timeout time limits, which are shown in table 1 and table 2. If the user service level requirement is any one of LP, LPV or LNVA/VNAV, setting the overtime time limit of each type of the enhanced message according to the table 1 and the table 2, and entering the step 6; otherwise, the user service level is not LP, LPV or LNVA/VNAV, and step 5 is entered.

And 5: the user service level is En Route, Terminal, LNAV;

the user service level is any one of En Route, Terminal and LNAV, the overtime time limit of each type of the enhanced message is set according to the table 1 and the table 2, and the step 7 is entered.

Step 6: judging whether the satellite UDREI is less than or equal to 12;

for users with service level requirements such as LP, LP or LNVA/VNAV, in order to ensure the positioning accuracy and integrity requirements, a satellite in B1C enhanced electric text can be used for subsequent navigation positioning solution only if its UDREI is less than or equal to 12. If UDREI is less than or equal to 12, entering step 7; otherwise UDREI is greater than 12 and step 12 is entered.

And 7: matching ephemeris IODE;

the user receiver stores multiple groups of GPS L1C/A frequency point basic navigation message information received within 5 minutes before the resolving time t, and each group of basic messages has respective IODE (ephemeris data age); and comparing the IOD of the satellite in the B1C enhanced message updated at the time t with the IODE in each group of basic navigation messages one by one, and if the IODE and the IOD have equal values, successfully matching. A group of basic navigation messages which are successfully matched with the IODE and are closest to the current resolving moment t are used for calculating the orbit and clock error of the subsequent GPS satellite, and the step 8 is entered; otherwise, if the matching of the messages IODE of any group is not successful, the step 12 is entered.

And 8: judging the correction number and UDREI overtime;

recording the timeout period of the slow-varying correction number in table 1 and table 2 as timeout according to the user service level requirement_lcThe timeout period of the fast-change correction is recorded as timeout_fcThe UDREI timeout period is denoted as timeout_UDREI(ii) a Recording the receiving time of the slowly-changing correction number of the satellite into tow_lcThe receiving time of the fast-changing correction number is recorded as tow_fcThe receiving time of UDREI is recorded as tow_UDREI。

If: t-tow_lc＞timeout_lcThen the satellite is slowThe change number times out;

if: t-timeout_fc＞timeout_fcIf the satellite fast change correction times out;

if: t-timeout_UDREI＞timeout_UDREIThen the satellite UDREI times out.

If and only if the slow change correction number, the fast change correction number and the UDREI of the satellite are not overtime, entering step 9; otherwise, either timeout occurs, and step 12 is entered.

And step 9: ionospheric Grid Point (IGP) search.

According to a method specified in the RTCA-DO229E standard of the International civil aviation organization, the Ionospheric Puncture Points (IPPs) of a user are calculated, and effective available ionospheric grid points are searched in the B1C enhanced broadcast IGP information. Recording the grid point ionosphere vertical delay (GIVD) receiving time as tow_GIVDThe vertical delay timeout period of the grid ionosphere is recorded as timeout_GIVD。

If: if the grid ionospheric vertical delay error index (GIVEI) of the Ionospheric Grid Point (IGP) is equal to 15, the grid point is invalid;

if: t-timeout_GIVD＞timeout_GIVDIf the grid point is invalid, the grid point is invalid;

when either of the above two conditions is satisfied, the IGP is invalid; otherwise, the IGP has a GIVEI less than 15, and the GIVD has not timed out, the IGP is valid.

And entering step 10 after the ionosphere grid point searching and judging is finished.

Step 10: it is determined whether the searched valid IGPs are greater than or equal to 3.

If the number of the searched effective IGPs is more than or equal to 3, entering a step 11; otherwise step 12 is entered.

Step 11: the satellite health flag position is 0.

After the judgment, the satellite health flag bit is set to 0, which indicates that the satellite is healthy, and the satellite health flag bit can be used for subsequent navigation positioning operation and should be reserved, and the step 2 is entered.

Step 12: the satellite health flag position is 1.

After the judgment, the satellite health flag bit is set to 1, which indicates that the satellite is unhealthy and can not be used for subsequent navigation positioning operation, and the satellite health flag bit is removed, and the step 2 is entered.

Step 13: entering BDSBAS user navigation positioning subsequent processing.

After the BDSBAS B1C single-frequency enhanced satellite screening is completed, a subsequent enhanced positioning operation program can be carried out.

Through the steps, the invention particularly describes the enhanced satellite screening method which meets the requirements of the international civil aviation organization standard under the condition that the BDSBAS user receiver simultaneously receives the GPS L1C/A basic navigation message and the BDSBAS B1C single-frequency enhanced message. The method has operability, has practical value in engineering application such as design and test of BDSBAS user receiver navigation positioning algorithm, and can meet the requirements of users on high-precision navigation positioning precision and high integrity guarantee.