CN102571294A - Cyclic redundancy check codes (CRC)-based method for correcting satellite navigation message errors - Google Patents
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Abstract
The invention relates to a cyclic redundancy check codes (CRC)-based method for correcting satellite navigation message errors, and belongs to the technical field of satellite navigation. The method comprises the following steps of: constructing a CRC check module, then constructing a CRC error correcting code table, performing error pattern detection according to the CRC error correcting code table, and performing error correction on correctable error patterns obtained by detection. By the method, whether the message is error can be checked, and 1bit error patterns in the error navigation message can also be corrected; compared with the application condition that the CRC error correction is not used, the method has the advantages of effectively reducing the frame error rate of the navigation message, improving the continuity of positioning under weak signal conditions and improving the positioning performance; and the method is suitable for a random satellite navigation system using the CRC as navigation message check errors.
Description
Technical field
(Cyclic Redundancy Check codes, CRC) method of correction satellite navigation message mistake belongs to the satellite navigation technical field to the present invention relates to a kind of use CRC.
Background technology
Along with the application that with the gps system is the representative satellite navigation system is constantly expanded; New being applied on positioning accuracy and the reliability proposed requirements at the higher level; The U.S. has implemented the GPS updating program under this background; Successively designed three the novel civil signal of GPS L2C, L5, L1C towards different application, new signal has adopted many new technology at aspects such as pseudo-code design, modulation system, error correction coding and message formats.The principle that the Big Dipper COMPASS satellite navigation system of the Galileo satellite navigation system in Europe and China is also distinguished according to service designed the civil signal of a plurality of different purposes, and Muscovite GLONASS satellite navigation system is carried out the technology experiment of L3 OC signal on the K-1 satellite from beginning in 2011.
The novel navigation message of gps system is greatly improved with traditional navigation message in design; An important improvement is the variation of text error detection coding, and novel text generally adopts the stronger CRC CRC of error detecing capability to replace the Hamming code of GPS NAV text.GPS L2C, L5 have adopted CNAV text (IS-GPS-200E, IS-GPS-705A), and text frame length 300 bits adopt the CRC-24 check code, and its coding generator polynomial is:
g(x)＝x
24+x
23+x
18+x
17+x
14+x
11+x
10+x
7+x
6+x
5+x
4+x
3+x+1；
The L1C signal adopts CNAV-2 text (IS-GPS-800A), and text comprises 3 sub-frame, and subframe 1 is used for synchronously, subframe 2 frame lengths 600 bits, and subframe 3 frame lengths 274 bits, subframe 2,3 all adopts CRC-24 as check code.The Galileo satellite navigation system in Europe comprises text (European GNSS (Galileo) the Open Service Signal In Space Interface Control Document of F/NAV, two kinds of forms of I/NAV; 2010), F/NAV form text frame length 244 bits adopt the CRC-24 check code; Be applied to the E5a navigation signal; I/NAV form text frame length 120 bits adopt the CRC-24 verification, are applied to E5b and E1b navigation signal.Similar error detection coding scheme has also been adopted in the civil navigation message design of China's Big Dipper COMPASS satellite navigation system and Russian GLONASS system.
The purpose of the error detection coding in the navigation message is the correctness of inspection navigation message, reduces wrong text to location influence, in case conventional treatment principle is to detect that text makes a mistake then wrong text is abandoned.When navigation receives when being in weak signal environment or high dynamic platform, the probability that the mistake in the text takes place can be very big, and the discard processing of mistake text can cause available text very few, thus the continuity of influence location even can't locate.According to Coding Theory; The CRC coding belongs to the shorten cyclic codes in the linear block codes; But both can also error correction of error detection; Its error-detection error-correction performance determines by minimum Hamming distance, and the minimum Hamming distance of CRC is by generator polynomial and code word size decision, when minimum Hamming code uses CRC can correct one or more mistakes (the CRC error correction applications expansion in [Yang Jie 2005] wireless transmission) in the code word during apart from d >=3; Use the FER of CRC error correction can effectively reduction navigation message, improve the satellite fix performance.
Summary of the invention
The objective of the invention is to propose a kind of satellite navigation message error correction method based on the CRC error detection coding structure in the navigation message in order to overcome the problem that existing satellite navigation receiver navigation message FER in weak signal environment is high, locate poor continuity.
The present invention realizes through following technical proposals:
A kind of satellite navigation message error correction method based on the CRC coding comprises the steps:
According to the CRC in satellite navigation message standard coding generator polynomial g (x):
g(x)＝x
24+x
23+x
18+x
17+x
14+x
11+x
10+x
7+x
6+x
5+x
4+x
3+x+1，
According to the error detection principles of construction CRC check module of CRC, the effect of CRC check module is the verification remainder and structure CRC error correction code table that is used to calculate navigation message.
According to the text frame length N that stipulates in the satellite navigation message standard, 1 different bit error pattern data of structure N kind are sent N kind 1 bit error pattern data into the CRC check module in the step 1 successively, obtain N different CRC check remainder S
i, i representes the sequence number of 1 bit error pattern data, i=1 ... N.The verification remainder S of i kind 1 bit error pattern data
iWith errors present P
iForm i clauses and subclauses in the error correction code table, N the clauses and subclauses that the different 1 bit error pattern data of N kind are produced deposit CRC error correction code table in order in.
The concrete characteristic of 1 bit error pattern data is: a string length is the 2 system bit streams of N, and 1 " 1 " and N-1 " 0 " is arranged in N bit, and wherein " 1 " representative makes a mistake, and " 0 " representative does not make a mistake.Its building method is: i bit of i kind 1 bit error pattern data is 1, and other is 0, errors present P
i=i.
The concrete characteristic of CRC error correction code table is: code table has N clauses and subclauses, and each clauses and subclauses comprises 1 errors present and 1 verification remainder, the errors present P in the 1st to N clauses and subclauses
iOrder according to from 1 to N increases progressively.
The CRC check module that the satellite navigation message that receives is sent in the step 1 is carried out the verification computing,, carry out follow-up positioning calculation computing if verification remainder S=0 thinks that then text is correct; If verification remainder S ≠ 0 thinks that then text makes a mistake, carry out the search of CRC error correction code table and whether can correct with the misjudgment pattern.
Concrete judgment principle is: with the verification remainder S of N clauses and subclauses in the verification remainder S of current text and the CRC error correction code table in the step 2
iCarry out order relatively, if find S
i=S thinks that then error pattern can correct, and keeps and S
iErrors present P in same clauses and subclauses
iOtherwise think that error pattern can not correct, current text carries out discard processing.
Concrete grammar is: the errors present P that obtains according to step 3
i, with navigation message P
iIndividual bit overturns, thereby corrects 1 bit mistake.
So far, the process of using CRC to correct the navigation message mistake finishes.
Beneficial effect
A kind of satellite navigation message error correction method that the present invention proposes based on the CRC coding; Not only can check whether mistake of text; Can also correct a mistake 1 bit error pattern in the navigation message; The applicable cases of CRC error correction is not used in contrast, can effectively reduce the FER of navigation message, improves the continuity of the location under the weak signal conditions and improves positioning performance.
Description of drawings
Fig. 1 is that typical satellite navigation receiver is handled block diagram in the prior art;
Fig. 2 is the GPS CNAV navigation message frame assumption diagram in the embodiment;
Fig. 3 is a satellite navigation message error correction flow chart of the present invention;
Fig. 4 is the comparison diagram that in the embodiment GPS CNAV text is used FER before and after the CRC error correction.
Embodiment
Technical scheme of the present invention is described further objects and advantages of the present invention in order better to explain below in conjunction with accompanying drawing and embodiment.In this embodiment, will use GPS CNAV text to describe as an example.
Typical satellite navigation receiver structure is as shown in Figure 1; Satellite-signal obtains navigation message through despreading, demodulation, decoding; Navigation message uses the CRC check sign indicating number to check the correctness of text, thinks that when the verification remainder is 0 text is correct, carries out follow-up positioning calculation computing; When the verification remainder is not 0, think the text mistake, the mistake text carries out discard processing.
The navigation message that the L2C of gps system, L5 signal use is the CNAV text, and frame format is as shown in Figure 2, frame length 300 bits, and wherein end 24 bits are CRC check sign indicating numbers, its generator polynomial is: g (x)=x
24+ x
23+ x
18+ x
17+ x
14+ x
11+ x
10+ x
7+ x
6+ x
5+ x
4+ x
3+ x+1.The CNAV text is under the condition of 300 bits at frame length, obtains minimum Hamming distance d=6 through computer search, and a corresponding code polynomial is m (x)=x
54+ x
45+ x
43+ x
30+ x
6+ 1, can detect maximum 5 bit mistakes or correct 2 bit mistakes according to the character CRC-24 of block code.In typical satellite navigation system, be p=10 through the text error rate behind the error-correcting decoding
-3～10
-5, get p=10
-3The probability that 1 bit mistake then takes place in 1 frame text is FER
1bit=300 * 10
-3* (1-10
-3)
299=0.2224, the probability that 2 bit mistakes take place is FER
2bit=300 * 299 * (10
-3)
2* (1-10
-3)
298/ 2=0.0333 shows that probability that 1 bit mistake takes place much larger than the probability that 2 bit mistakes take place, can select to correct 1 bit or 2 bit mistakes when error correction, and the difference of the two is the resource and the complexity that need, and present embodiment selects to correct 1 bit mistake.
A kind of satellite navigation message error correction method based on the CRC coding, as shown in Figure 3, the concrete steps that the CNAV text uses CRC to correct a mistake are:
With the i kind (i=1,2 ..., 300) and 1 bit error pattern data send into the CRC check resume module in the step 1, obtain the verification remainder S of i kind 1 bit error pattern data
i, with verification remainder S
iWith errors present P
i=i forms 1 clauses and subclauses, deposits 300 clauses and subclauses in CRC error correction code table by wrong position order from small to large, and the error correcting code list structure of CNAV text is as shown in table 1.
The CRC error correcting code list structure of table 1CNAV text
| Errors present P i | Verification remainder S i |
| 1 | S 1 |
| 2 | S 2 |
| 3 | S 3 |
| ... | ... |
| 299 | S 299 |
| 300 | S 300 |
Concrete judgment principle is: 300 clauses and subclauses in the sequential search error correction code table, relatively S
iWith the S of current text, if find S
i=S thinks that then error pattern can correct, and keeps and S
iCorresponding errors present P
i, S for example
25=S, P
25=25, its implication is that the 25th bit of current text makes a mistake; If in 300 clauses and subclauses, do not find S
i=S thinks that then error pattern can not correct, and current text carries out discard processing.
Concrete grammar is: obtain error bit position P according to step 3
i, correct 1 bit mistake in the current text, the text after the error correction carries out follow-up positioning calculation to be handled.For example step 3 obtains P
25=25, then the 25th bit with current text overturns, and promptly obtains the navigation message after the error correction
So far, the process of using CRC to correct the navigation message mistake finishes.
Be the performance of concrete analysis CRC error correction method, used software emulation CNAV text CRC error correction procedure, text frame length 300 bits of emulation; Error detection coding is CRC-24; Fig. 4 is the simulation CRC code correction result who carries out according to embodiment, and transverse axis is represented the text error rate BER, and the longitudinal axis is represented text FER FER; Curve A representes not use the navigation message FER of CRC code correction; Curve B representes to adopt the navigation message FER behind the CRC code correction, as can be seen from the figure uses the CRC code correction to effectively reduce the FER of navigation message, and concrete FER improves performance data such as table 2.
FER improved after table 2 used the CRC error correction
| The error rate | FER before the error correction | FER after the |
| 1×10 -2 | 0.95 | 0.80 |
| 1×10 -3 | 0.26 | 0.037 |
| 1×10 -4 | 2.9×10 -2 | 4.4×10 -4 |
| 1×10 -5 | 2.9×10 -3 | 4.5×10 -6 |
| 1×10 -6 | 2.9×10 -4 | 4.5×10 -8 |
| 1×10 -7 | 2.9×10 -5 | 4.5×10 -10 |
The inventive method is applicable to GPS of America global position system L2C, the used CNAV navigation message of L5 signal; The CNAV-2 navigation message that the L1C signal is used; F/NAV, I/NAV navigation message that european galileo Galileo global position system is used; The used navigation message of China's Big Dipper COMPASS global position system, the navigation message that the Russian GLONASS global position system is used.
The inventive method is not limited to specific gps satellite navigation system, but is applicable to the satellite navigation system of any use CRC as the navigation message check code.
Though described execution mode of the present invention in conjunction with accompanying drawing, to those skilled in the art, under the prerequisite that does not break away from the principle of the invention, can also make some distortion and improvement, these also should be regarded as belonging to protection scope of the present invention.
Claims (5)
1. the satellite navigation message error correction method based on the CRC coding is characterized in that: comprise the steps:
Step 1, structure CRC check module;
According to the CRC in satellite navigation message standard coding generator polynomial g (x):
g(x)＝x
24+x
23+x
18+x
17+x
14+x
11+x
10+x
7+x
6+x
5+x
4+x
3+x+1，
Error detection principles of construction CRC check module according to CRC;
Step 2, structure CRC error correction code table;
According to the text frame length N that stipulates in the satellite navigation message standard, 1 different bit error pattern data of structure N kind are sent N kind 1 bit error pattern data into the CRC check module in the step 1 successively, obtain N different CRC check remainder S
i, i representes the sequence number of 1 bit error pattern data, i=1 ... N; The verification remainder S of i kind 1 bit error pattern data
iWith errors present P
iForm i clauses and subclauses in the error correction code table, N the clauses and subclauses that the different 1 bit error pattern data of N kind are produced deposit CRC error correction code table in order in;
The building method of 1 bit error pattern data is: i bit of i kind 1 bit error pattern data is 1, and other is 0, errors present P
i=i;
The concrete characteristic of CRC error correction code table is: code table has N clauses and subclauses, and each clauses and subclauses comprises 1 errors present and a verification remainder, the errors present P in the 1st to N clauses and subclauses
iOrder according to from 1 to N increases progressively;
Step 3, error pattern detects;
The CRC check module that the satellite navigation message that receives is sent in the step 1 is carried out the verification computing,, carry out follow-up positioning calculation computing if verification remainder S=0 thinks that then text is correct; If verification remainder S ≠ 0 thinks that then text makes a mistake, carry out the search of CRC error correction code table and whether can correct with the misjudgment pattern;
Step 4 is carried out error correction to the correctable error pattern that obtains after step 3 verification;
So far, the process of using CRC to correct the navigation message mistake finishes.
2. a kind of satellite navigation message error correction method according to claim 1 based on the CRC coding; It is characterized in that: the described 1 bit error pattern data of step 2 are that length is the 2 system bit streams of N; 1 " 1 " and N-1 " 0 " is arranged in N bit; Wherein " 1 " representative makes a mistake, and " 0 " representative does not make a mistake.
3. a kind of satellite navigation message error correction method based on the CRC coding according to claim 1 is characterized in that: the method for step 3 described search CRC error correction code table and misjudgment pattern is: with the verification remainder S of N clauses and subclauses in the verification remainder S of current text and the CRC error correction code table in the step 2
iCarry out order relatively, if find S
i=S thinks that then error pattern can correct, and keeps and S
iErrors present P in same clauses and subclauses
iOtherwise think that error pattern can not correct, current text carries out discard processing.
4. a kind of satellite navigation message error correction method based on CRC coding according to claim 1, it is characterized in that: the concrete grammar that said step 4 pair correctable error pattern is carried out error correction is: the errors present P that obtains according to step 3
i, with navigation message P
iIndividual bit overturns, thereby corrects 1 bit mistake.
5. a kind of method of using the CRC coding to correct the satellite navigation message mistake according to claim 1 is characterized in that: said method is applicable to the satellite navigation system of any use CRC as the navigation message check code.
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| CN105450281A (en) * | 2016-01-27 | 2016-03-30 | 中国人民解放军国防科学技术大学 | System and method for diversity reception of multiple identical user receiver inbound signals |
| CN103746773B (en) * | 2013-12-31 | 2017-02-15 | 深圳信息职业技术学院 | Method and system for correcting errors of decoded data by using UMTS (Universal Mobile Telecommunications System) receiver |
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| CN108549096A (en) * | 2018-04-17 | 2018-09-18 | 中国科学院微电子研究所 | Method and device for error correction and decoding of GPS navigation message |
| CN111030710A (en) * | 2019-12-02 | 2020-04-17 | 北京北方联星科技有限公司 | Method for adaptively improving decoding speed of Galileo navigation system E5 signal |
| CN112564858A (en) * | 2020-11-05 | 2021-03-26 | 山东中科泰岳电子科技有限公司 | CRC error correction method and system for satellite navigation |
| CN117452455A (en) * | 2023-12-26 | 2024-01-26 | 中国人民解放军国防科技大学 | Method for designing text decoding module of navigation receiver for embedded test |
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| WO2017092617A1 (en) * | 2015-11-30 | 2017-06-08 | 华为技术有限公司 | Error estimation method, base station and terminal |
| CN105450281A (en) * | 2016-01-27 | 2016-03-30 | 中国人民解放军国防科学技术大学 | System and method for diversity reception of multiple identical user receiver inbound signals |
| CN105450281B (en) * | 2016-01-27 | 2018-11-02 | 中国人民解放军国防科学技术大学 | A kind of system and method to more parts of same subscriber machine check-in signal diversity receptions |
| CN108549096A (en) * | 2018-04-17 | 2018-09-18 | 中国科学院微电子研究所 | Method and device for error correction and decoding of GPS navigation message |
| CN111030710A (en) * | 2019-12-02 | 2020-04-17 | 北京北方联星科技有限公司 | Method for adaptively improving decoding speed of Galileo navigation system E5 signal |
| CN112564858A (en) * | 2020-11-05 | 2021-03-26 | 山东中科泰岳电子科技有限公司 | CRC error correction method and system for satellite navigation |
| CN112564858B (en) * | 2020-11-05 | 2022-08-09 | 山东中科泰岳电子科技有限公司 | CRC error correction method and system for satellite navigation |
| CN117452455A (en) * | 2023-12-26 | 2024-01-26 | 中国人民解放军国防科技大学 | Method for designing text decoding module of navigation receiver for embedded test |
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Application publication date: 20120711 |