CN108549096B - Method and device for error correction and decoding of GPS navigation message - Google Patents
Method and device for error correction and decoding of GPS navigation message Download PDFInfo
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- H03M13/05—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words using block codes, i.e. a predetermined number of check bits joined to a predetermined number of information bits
- H03M13/11—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words using block codes, i.e. a predetermined number of check bits joined to a predetermined number of information bits using multiple parity bits
- H03M13/1102—Codes on graphs and decoding on graphs, e.g. low-density parity check [LDPC] codes
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Abstract
A method and apparatus for error correction decoding of GPS navigation message, said method comprises according to tracking the integral value of the channel and noise channel, confirm the signal to noise ratio of the received signal, when the signal to noise ratio is smaller than or equal to the threshold value, decode and is invalid; when the signal-to-noise ratio is larger than the threshold value, then: and (3) carrying out error correction decoding on the GPS navigation message: determining a hard decision sequence and a confidence sequence according to the integral value of the tracking channel, and rearranging the hard decision sequence and the confidence sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; determining and outputting a decoding sequence according to the rearrangement hard decision sequence, the rearrangement confidence sequence and the error position condition; and parity check is carried out on the decoding sequence, if the parity check is correct, the decoding sequence is output, and if the parity check is wrong, the decoding is invalid. The invention improves the decoding sensitivity of the navigation message, reduces the bit error rate, and is particularly suitable for the design of a GPS receiver under low signal-to-noise ratio.
Description
Technical Field
The invention relates to the technical field of satellite navigation, in particular to a method and a device for error correction decoding of a GPS navigation message.
Background
The accuracy of the navigation message is very important for realizing quick positioning, speed measurement and time service of the GPS receiver. In the prior art, a receiver performs parity check on data bits extracted from a tracking loop to obtain a navigation message value. The parity check method using the Hamming code can only detect bit errors in the navigation message transmission process, and does not fully utilize the error correction capability of the Hamming code. Under the condition of low signal-to-noise ratio, the probability of errors in the navigation message is greatly improved, and at the moment, a large number of messages cannot be discarded through verification, so that the subsequent processing of the receiver is not facilitated.
Disclosure of Invention
Technical problem to be solved
The present invention is directed to a method and an apparatus for decoding and correcting an error of a GPS navigation message, so as to solve at least one of the above technical problems.
(II) technical scheme
In one aspect of the present invention, a method for decoding an error correction of a GPS navigation message is provided, which includes:
determining a real-time signal-to-noise ratio of a received signal according to an integral value of a tracking channel and a noise channel of a receiver, and when the signal-to-noise ratio is smaller than or equal to a threshold value, decoding is invalid; when the signal-to-noise ratio is larger than a threshold value, the following steps are carried out:
carrying out error correction decoding on the GPS navigation message: determining a hard decision sequence and a confidence sequence according to the integral value of the tracking channel, rearranging the hard decision sequence and the confidence sequence, and determining a rearranged hard decision sequence and a rearranged confidence sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; determining and outputting a decoding sequence according to the rearrangement hard decision sequence, the rearrangement confidence sequence and the error position condition; and
and performing parity check on the decoding sequence, outputting the decoding sequence if the parity check is correct, and invalidating the decoding if the parity check is wrong.
In some embodiments of the present invention, determining a hard decision sequence and a confidence sequence from the integration values of the tracking channels refers to: after the receiver realizes bit synchronization and frame synchronization, integral values in 32 tracking channels are continuously extracted from the 29 th bit starting edge of each GPS navigation message to form a receiving sequence, the symbols of the receiving sequence are judged to determine a hard decision sequence, and the absolute value of the receiving sequence is taken to obtain a confidence sequence.
In some embodiments of the present invention, rearranging the hard decision sequence and the confidence sequence to determine a rearranged hard decision sequence and a rearranged confidence sequence comprises the sub-steps of:
removing the 32 th bit of the hard decision sequence, keeping the order of the former 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged hard decision sequence; and
and removing the 32 th bit of the confidence sequence, keeping the order of the first 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged confidence sequence.
In some embodiments of the present invention, determining the syndrome from the reordered hard decision sequence comprises the sub-steps of:
extracting bit values of 1 st, 3 rd, 4 th, 5 th, 7 th, 8 th, 12 th, 13 th, 14 th, 15 th, 16 th, 19 th, 20 th, 22 th, 25 th and 30 th of the rearranged hard decision sequence, and calculating modulo 2 sum of the bit values to obtain a 1 st bit value of the syndrome; and
and circularly moving the rearranged hard decision sequence by 1, 2, 3 and 4 bits to the left, extracting bit values of 1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 16, 19, 20, 22, 25 and 30 of the rearranged hard decision sequence, calculating modulo 2 of the bit values, and obtaining bit values of 2, 3, 4 and 5 of the syndrome, thereby determining the syndrome.
In some embodiments of the present invention, before the determining the error bit by the table lookup, the method further comprises the steps of:
looking up a table in a shift value table according to the syndrome to obtain a corresponding shift value N;
adding the shift value to two error positions P1 and P2 corresponding to each error pattern number in the error pattern position table respectively to obtain two corrected error positions Pm1 ═ mod (P1+ N), Pm2 ═ mod (P2+ N); and
and constructing a corrected error pattern position table, wherein the corrected error pattern position table comprises 16 corrected error positions corresponding to the syndromes.
In some embodiments of the present invention, determining and outputting a decoded sequence based on the reordered hard decision sequence, the reordered confidence sequence, and the error location condition comprises the substeps of:
extracting values at corresponding positions of the rearrangement confidence sequence according to each error position condition, adding and summing to obtain 16 added values in total;
according to the error position condition corresponding to the maximum value in the 16 added values, performing modulo 2 sum on the bit value at the corresponding position and 1 in the rearranged hard decision sequence, and determining the rearranged hard decision sequence after error correction, wherein the rest positions are unchanged; and
and shifting the 27 th bit, 28 th bit and 29 th bit in the rearranged hard decision sequence after error correction to the 30 th bit and 31 th bit, and deleting the 32 nd bit value of the hard decision sequence before the final complement of the sequence to determine the decoding sequence.
In some embodiments of the present invention, parity checking the coded sequence refers to: performing modulo-2 summation on 32 bit values of the decoding sequence, and checking if the 32 modulo-2 summation values are added to be 0; if the 32 modulo-2 sums add to 1, the check is false.
In another aspect of the present invention, there is also provided a GPS navigation message error correction decoding apparatus, including:
the preprocessing module is used for determining the real-time signal-to-noise ratio of a received signal according to the integral values of a tracking channel and a noise channel of the receiver, and when the signal-to-noise ratio is smaller than or equal to a threshold value, decoding is invalid; when the signal-to-noise ratio is larger than a threshold value, outputting the integral value of the tracking channel to an error correction decoding module;
the error correction decoding module is used for determining a hard decision sequence and a confidence coefficient sequence according to the integral value of the tracking channel, rearranging the hard decision sequence and the confidence coefficient sequence and determining a rearranged hard decision sequence and a rearranged confidence coefficient sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; determining and outputting a decoding sequence according to the rearrangement hard decision sequence, the rearrangement confidence sequence and the error position condition; and
and the parity check module is used for carrying out parity check on the decoding sequence, outputting the decoding sequence if the parity check is correct, and invalidating the decoding if the parity check is wrong.
In some embodiments of the present invention, the error correction coding module comprises:
a sequence determining unit, configured to determine a hard decision sequence and a confidence sequence according to the integral values of the tracking channels, and after the receiver achieves bit synchronization and frame synchronization, the error correction decoding module continuously extracts the integral values in 32 tracking channels from the 29 th bit start edge of each GPS navigation message to form a receiving sequence, determines a symbol of the receiving sequence to determine the hard decision sequence, and obtains an absolute value of the receiving sequence to obtain the confidence sequence;
a rearrangement unit, configured to remove the 32 th bit of the hard decision sequence, keep the first 26 bits unchanged, shift the 27 th and 28 th bits to the 29 th, 30 th and 31 th bits, and then form a rearranged hard decision sequence; removing the 32 th bit of the confidence sequence, keeping the order of the first 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged confidence sequence;
a syndrome determining unit, configured to extract bit values of 1 st, 3 rd, 4 th, 5 th, 7 th, 8 th, 12 th, 13 th, 14 th, 15 th, 16 th, 19 th, 20 th, 22 th, 25 th, and 30 th of the rearranged hard decision sequence, and modulo-2 sum the bit values to obtain a 1 st bit value of the syndrome; and circularly moving the rearranged hard decision sequence by 1, 2, 3 and 4 bits to the left, extracting bit values of 1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 16, 19, 20, 22, 25 and 30 of the rearranged hard decision sequence, calculating modulo 2 of the bit values, and obtaining bit values of 2, 3, 4 and 5 of the syndrome, thereby determining the syndrome;
an error pattern position determining unit, configured to look up a table in a shift value table according to the syndrome to obtain a corresponding shift value N; adding the shift value to two error positions P1 and P2 corresponding to each error pattern number in the error pattern position table respectively to obtain two corrected error positions Pm1 ═ mod (P1+ N), Pm2 ═ mod (P2+ N); constructing a corrected error pattern position table, wherein the corrected error pattern position table comprises 16 corrected error positions corresponding to the syndrome; and
a decoding sequence determining unit, configured to extract values at corresponding positions of the rearrangement confidence sequence according to each error position condition, add and sum the values to obtain 16 added values in total; according to the error position condition corresponding to the maximum value in the 16 added values, performing modulo 2 sum on the bit value at the corresponding position and 1 in the rearranged hard decision sequence, and determining the rearranged hard decision sequence after error correction, wherein the rest positions are unchanged; and shifting the 27 th bit, 28 th bit and 29 th bit in the rearranged hard decision sequence after error correction to the 30 th bit and 31 th bit, and deleting the 32 nd bit value of the hard decision sequence before the final complement of the sequence to determine the decoding sequence.
In some embodiments of the present invention, the parity module parity-checks the coded sequence by: the parity check module calculates the modulo-2 sum of the 32 bit values of the decoding sequence, and if the 32 modulo-2 sums are added to be 0, the parity check is error-free; if the 32 modulo-2 sums add to 1, the check is false.
(III) advantageous effects
Compared with the prior art, the method and the device for correcting and decoding the GPS navigation message at least have the following advantages:
1. determining the signal-to-noise ratio of a received signal through the integral values of a tracking channel and a noise channel of a receiver, and when the signal-to-noise ratio is smaller than or equal to a threshold value, decoding is invalid; when the signal-to-noise ratio is larger than the threshold value, the error correction decoding is carried out on the GPS navigation message, the parity check is carried out on the decoding sequence, whether the decoding is effective or not is judged, the decoding sensitivity of the navigation message is improved, the bit error rate is reduced, and the method is particularly suitable for designing a GPS receiver under the low signal-to-noise ratio.
2. A rearrangement method is also adopted to construct Hamming (31, 26) codes with cyclic characteristics, and soft-decision error correction decoding is carried out on the codes based on the syndrome, so that bit errors in the navigation message can be corrected, and the decoding performance is improved.
Drawings
Fig. 1 is a schematic step diagram of a GPS navigation message error correction decoding method according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of the sub-steps of rearranging the hard decision sequence and the confidence sequence in step S2 to determine a rearranged hard decision sequence and a rearranged confidence sequence.
Fig. 3 is a diagram illustrating sub-steps of determining a syndrome according to the rearranged hard decision sequence in step S2.
FIG. 4 is a diagram illustrating the steps before determining the error bits by looking up the table in step S2.
Fig. 5 is a schematic diagram illustrating the sub-steps of determining and outputting a decoding sequence according to the rearranged hard decision sequence, the rearranged confidence sequence and the error location condition in step S2.
Fig. 6 is a schematic structural diagram of a GPS navigation message error correction decoding device according to an embodiment of the present invention.
Fig. 7 is a schematic structural diagram of an error correction decoding module according to an embodiment of the present invention.
FIG. 8 is a performance simulation diagram of an embodiment of the present invention.
Detailed Description
In the prior art, a receiver can only detect bit errors in the navigation message transmission process by using a Hamming code parity check method, but does not fully utilize the error correction capability of the Hamming code, so that the error probability is greatly improved, a large number of messages cannot be discarded through check, and the subsequent processing of the receiver is not facilitated. In view of the above, the present invention provides a method and an apparatus for decoding a GPS navigation message with error correction, wherein a syndrome obtained by performing parity check on data bits is used to perform soft-decision decoding on the GPS navigation message, so that bit errors occurring in the navigation message can be corrected, the navigation message decoding sensitivity is improved, the bit error rate is reduced, and the method and the apparatus are suitable for designing a GPS receiver with a low signal-to-noise ratio.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
In one aspect of the embodiments of the present invention, a method for decoding an error correction of a GPS navigation message is provided, and fig. 1 is a schematic diagram of steps of the method for decoding an error correction of a GPS navigation message according to the embodiments of the present invention, as shown in fig. 1, the method includes the steps of:
s1, determining the real-time signal-to-noise ratio of the received signal according to the integral values of the tracking channel and the noise channel of the receiver, and stopping the operation of the GPS navigation message error correction decoding method when the signal-to-noise ratio is less than or equal to a threshold value (which can be selected according to actual requirements) and the decoding is invalid; and when the signal-to-noise ratio is larger than the threshold value, performing the steps S2 and S3. Generally, the threshold value is determined by the error correction decoding simulation performance of the GPS navigation message error correction decoding method.
S2, carrying out error correction decoding on the GPS navigation message: determining a hard decision sequence and a confidence sequence according to the integral value of the tracking channel, rearranging the hard decision sequence and the confidence sequence, and determining a rearranged hard decision sequence and a rearranged confidence sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; and determining and outputting a decoding sequence according to the rearranged hard decision sequence, the rearranged confidence sequence and the error position condition.
Wherein, determining a hard decision sequence and a confidence sequence according to the integrated value of the tracking channel refers to: after the receiver realizes bit synchronization and frame synchronization, integral values in 32 tracking channels are continuously extracted from the 29 th bit starting edge of each GPS navigation message to form a receiving sequence, the symbols of the receiving sequence are judged to determine a hard decision sequence, and the absolute value of the receiving sequence is taken to obtain a confidence sequence.
For example, the integration duration of each integration value of the tracking channel is 20ms, which is the duration of 1 bit of data in the GPS. After the receiver realizes bit synchronization and frame synchronization, starting from the 29 th bit start edge of each navigation telegraph, continuously extracting integral values in 32 tracking channels to form a receiving sequence r ═ r0，rl，...，r31]Judging the sign to obtain a hard decision sequence v ═ v0，vl，...，v31]：
vi＝sgn(ri)(i＝0，1，...，31)
Obtaining an absolute value of a received sequence r and then obtaining a confidence sequence l ═ l0，l1，...，l31]：
li＝|ri|(i＝0，1，...，31)
Fig. 2 is a schematic diagram of the sub-steps of rearranging the hard decision sequence and the confidence sequence in step S2 to determine a rearranged hard decision sequence and a rearranged confidence sequence, as shown in fig. 2, the sub-steps are as follows:
s201, removing the 32 th bit of the hard decision sequence, keeping the order of the former 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged hard decision sequencev′＝[v′0，v′1，...，v′26，v′27，v′28，v′29，v′30]＝[v0，v1，...，v28，v29，v30，v26，v27]；
S202, similar to the configuration of the rearranged hard decision sequence, removing the 32 th bit of the confidence sequence, keeping the order of the first 26 bits unchanged, and moving the 27 th and 28 th bits to the 29 th, 30 th and 31 th bits to form the rearranged confidence sequence:
l′＝[l′0，l′1，...，l′26，l′27，l′28，l′29，l′30]＝[l0，l1，...，l28，l29，l30，l26，l27]。
in addition, fig. 3 is a schematic diagram of sub-steps of determining a syndrome according to the rearranged hard decision sequence in step S2, as shown in fig. 3, the sub-steps include:
s211, extracting bit values of 1 st, 3 rd, 4 th, 5 th, 7 th, 8 th, 12 th, 13 th, 14 th, 15 th, 16 th, 19 th, 20 th, 22 th, 25 th and 30 th of the rearranged hard decision sequence, and solving modulo 2 sum to obtain a 1 st bit value of the syndrome;
s212, after circularly moving the rearranged hard decision sequence by 1, 2, 3, and 4 bits to the left, extracting bit values of 1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 16, 19, 20, 22, 25, and 30 of the rearranged hard decision sequence, modulo 2 thereof and obtaining bit values of 2, 3, 4, and 5 of the syndrome, thereby determining the syndrome:
for example, when the syndrome data of 5 bits are not all 0, it indicates that there is an error bit in the rearranged hard decision sequence. The error pattern position table (see table 1 for details) stores the error position conditions of all 16 error patterns when the syndrome is 10100 and the rearranged hard decision sequence contains 1 or 2 errors.
TABLE 1
Note: x indicates that there is only one error location in this case.
The table of shift values (see table 2 for details) contains the shift values corresponding to all syndromes, and is used to calculate the error positions of 16 error patterns corresponding to different syndromes.
TABLE 2
Fig. 4 is a schematic diagram of the step before determining the error bit by looking up the table in step S2, as shown in fig. 4, further including the following steps:
s221, looking up a table in a shift value table according to the syndrome to obtain a corresponding shift value N;
s222, adding the shift value to two error positions P1 and P2 corresponding to each error pattern number in the error pattern position table to obtain two corrected error positions Pm1 ═ mod (P1+ N), Pm2 ═ mod (P2+ N);
s223, constructing a corrected error pattern position table, wherein the corrected error pattern position table comprises 16 corrected error positions corresponding to the syndromes.
Fig. 5 is a schematic diagram illustrating the sub-steps of determining and outputting a decoding sequence according to the rearranged hard decision sequence, the rearranged confidence sequence and the error location condition in step S2, where the sub-steps include:
s231, extracting values at corresponding positions of the rearrangement confidence sequence according to each error position condition, adding and summing to obtain 16 added values:
s232, according to the error position condition corresponding to the maximum value in the 16 added values, performing modulo 2 sum on the bit value and 1 at the corresponding position in the rearranged hard decision sequence, keeping the rest positions unchanged, and determining the rearranged hard decision sequence c after error correction;
s233, shifting the 27 th, 28 th and 29 th bits of the rearranged hard decision sequence after error correction to the positions after the 30 th and 31 th bits, and determining the 32 nd bit value deleted by the hard decision sequence before the final complement of the sequence, thereby determining the decoded sequence c'.
And S3, performing parity check on the decoding sequence, outputting the decoding sequence if the parity check is correct, and invalidating the decoding if the parity check is correct.
Performing parity check on the decoded sequence: performing modulo-2 summation on 32 bit values of the decoding sequence, and checking if the 32 modulo-2 summation values are added to be 0; if the 32 modulo-2 sums add to 1, the check is false.
In another aspect of the embodiment of the present invention, a device for error correction decoding of a GPS navigation message is further provided, and fig. 6 is a schematic structural diagram of the device for error correction decoding of a GPS navigation message according to the embodiment of the present invention, as shown in fig. 6, the device includes a preprocessing module 1, an error correction decoding module 2, and a parity check module 3.
The preprocessing module 1 is used for determining a real-time signal-to-noise ratio of a received signal according to an integral value of a tracking channel and a noise channel of a receiver, and when the signal-to-noise ratio is smaller than or equal to a threshold value, decoding is invalid; when the signal-to-noise ratio is larger than a threshold value, outputting the integral value of the tracking channel to an error correction decoding module 2;
the error correction decoding module 2 is configured to determine a hard decision sequence and a confidence sequence according to the integral value of the tracking channel, rearrange the hard decision sequence and the confidence sequence, and determine a rearranged hard decision sequence and a rearranged confidence sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; and determining and outputting a decoding sequence according to the rearranged hard decision sequence, the rearranged confidence sequence and the error position condition.
Fig. 7 is a schematic structural diagram of an error correction decoding module according to an embodiment of the present invention, and as shown in fig. 7, in some embodiments of the present invention, the error correction decoding module 2 includes a sequence determining unit 21, a rearranging unit 22, a syndrome determining unit 23, an error pattern position determining unit 24, and a decoded sequence determining unit 25.
A sequence determining unit 21, configured to determine a hard decision sequence and a confidence sequence according to the integrated values of the tracking channels, and after the receiver achieves bit synchronization and frame synchronization, the error correction decoding module 2 continuously extracts the integrated values in 32 tracking channels from the 29 th bit start edge of each GPS navigation message to form a receiving sequence, determines a symbol of the receiving sequence to determine the hard decision sequence, and obtains an absolute value of the receiving sequence to obtain the confidence sequence;
a rearrangement unit 22, configured to remove the 32 th bit of the hard decision sequence, keep the first 26 bits unchanged, shift the 27 th and 28 th bits to the 29 th, 30 th and 31 th bits, and then form a rearranged hard decision sequence; removing the 32 th bit of the confidence sequence, keeping the order of the first 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged confidence sequence;
a syndrome determining unit 23, configured to extract bit values of 1 st, 3 rd, 4 th, 5 th, 7 th, 8 th, 12 th, 13 th, 14 th, 15 th, 16 th, 19 th, 20 th, 22 th, 25 th, and 30 th of the rearranged hard decision sequence, and modulo-2 sum the bit values to obtain a 1 st bit value of the syndrome; and circularly moving the rearranged hard decision sequence by 1, 2, 3 and 4 bits to the left, extracting bit values of 1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 16, 19, 20, 22, 25 and 30 of the rearranged hard decision sequence, calculating modulo 2 of the bit values, and obtaining bit values of 2, 3, 4 and 5 of the syndrome, thereby determining the syndrome;
an error pattern position determining unit 24, configured to look up a table in a shift value table according to the syndrome to obtain a corresponding shift value N; adding the shift value to two error positions P1 and P2 corresponding to each error pattern number in the error pattern position table respectively to obtain two corrected error positions Pm1 ═ mod (P1+ N), Pm2 ═ mod (P2+ N); constructing a corrected error pattern position table, wherein the corrected error pattern position table comprises 16 corrected error positions corresponding to the syndrome;
a decoding sequence determining unit 25, configured to extract values at corresponding positions of the rearrangement confidence sequence according to each error position condition, add and sum the extracted values to obtain 16 added values in total; according to the error position condition corresponding to the maximum value in the 16 added values, performing modulo 2 sum on the bit value at the corresponding position and 1 in the rearranged hard decision sequence, and determining the rearranged hard decision sequence after error correction, wherein the rest positions are unchanged; and shifting the 27 th bit, 28 th bit and 29 th bit in the rearranged hard decision sequence after error correction to the 30 th bit and 31 th bit, and deleting the 32 nd bit value of the hard decision sequence before the final complement of the sequence to determine the decoding sequence.
And finally, the parity check module 3 is used for carrying out parity check on the decoding sequence, outputting the decoding sequence if the parity check is correct, and invalidating the decoding if the parity check is wrong.
The parity check module 3 performs parity check on the coding sequence by: the parity check module 3 calculates a modulo-2 sum of 32 bit values of the decoded sequence, and if the 32 modulo-2 sums are added to be 0, the check is error-free; if the 32 modulo-2 sums add to 1, the check is false.
Fig. 8 is a performance simulation diagram of the embodiment of the present invention, and as shown in fig. 8, the error rate after decoding by using the decoding algorithm of the present invention is greatly reduced compared with the original error rate.
In summary, the method and the device for error correction and decoding of the GPS navigation message determine the signal-to-noise ratio of the received signal through the integral values of the tracking channel and the noise channel of the receiver, and when the signal-to-noise ratio is smaller than or equal to the threshold value, the decoding is invalid; when the signal-to-noise ratio is larger than the threshold value, the error correction decoding is carried out on the GPS navigation message, the parity check is carried out on the decoding sequence, whether the decoding is effective or not is judged, the decoding sensitivity of the navigation message is improved, the bit error rate is reduced, and the method is particularly suitable for designing a GPS receiver under the low signal-to-noise ratio.
Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about".
Furthermore, "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.
The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element from another or the order of manufacture, and the use of the ordinal numbers is only used to distinguish one element having a certain name from another element having a same name.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A method for error correction decoding of GPS navigation messages comprises the following steps:
determining a real-time signal-to-noise ratio of a received signal according to an integral value of a tracking channel and a noise channel of a receiver, and when the signal-to-noise ratio is smaller than or equal to a threshold value, decoding is invalid; when the signal-to-noise ratio is larger than a threshold value, the following steps are carried out:
carrying out error correction decoding on the GPS navigation message: determining a hard decision sequence and a confidence sequence according to the integral value of the tracking channel, rearranging the hard decision sequence and the confidence sequence, and determining a rearranged hard decision sequence and a rearranged confidence sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; determining and outputting a decoding sequence according to the rearrangement hard decision sequence, the rearrangement confidence sequence and the error position condition; and
performing parity check on the decoding sequence, outputting the decoding sequence if the parity check is correct, and invalidating the decoding if the parity check is wrong;
wherein, rearranging the hard decision sequence and the confidence sequence to determine a rearranged hard decision sequence and a rearranged confidence sequence comprises the following substeps:
removing the 32 th bit of the hard decision sequence, keeping the order of the former 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged hard decision sequence; and
and removing the 32 th bit of the confidence sequence, keeping the order of the first 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged confidence sequence.
2. The method of claim 1, wherein determining a hard decision sequence and confidence sequence from the integration values of the tracking channels refers to: after the receiver realizes bit synchronization and frame synchronization, integral values in 32 tracking channels are continuously extracted from the 29 th bit starting edge of each GPS navigation message to form a receiving sequence, the symbols of the receiving sequence are judged to determine a hard decision sequence, and the absolute value of the receiving sequence is taken to obtain a confidence sequence.
3. The method of claim 1, wherein determining the syndrome from the reordered hard decision sequence comprises the sub-steps of:
extracting bit values of 1 st, 3 rd, 4 th, 5 th, 7 th, 8 th, 12 th, 13 th, 14 th, 15 th, 16 th, 19 th, 20 th, 22 th, 25 th and 30 th of the rearranged hard decision sequence, and calculating modulo 2 sum of the bit values to obtain a 1 st bit value of the syndrome; and
and circularly moving the rearranged hard decision sequence by 1, 2, 3 and 4 bits to the left, extracting bit values of 1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 16, 19, 20, 22, 25 and 30 of the rearranged hard decision sequence, calculating modulo 2 of the bit values, and obtaining bit values of 2, 3, 4 and 5 of the syndrome, thereby determining the syndrome.
4. The method of claim 3, wherein before determining the error bits from the table lookup, further comprising the steps of:
looking up a table in a shift value table according to the syndrome to obtain a corresponding shift value N;
adding the shift value to two error positions P1 and P2 corresponding to each error pattern number in the error pattern position table respectively to obtain two corrected error positions Pm1 ═ mod (P1+ N), Pm2 ═ mod (P2+ N); and
and constructing a corrected error pattern position table, wherein the corrected error pattern position table comprises 16 corrected error positions corresponding to the syndromes.
5. The method of claim 1, wherein determining and outputting a decoding sequence based on the reordered hard decision sequence, the reordered confidence sequence, and the error location case comprises the sub-steps of:
extracting values at corresponding positions of the rearrangement confidence sequence according to each error position condition, adding and summing to obtain 16 added values in total;
according to the error position condition corresponding to the maximum value in the 16 added values, performing modulo 2 sum on the bit value at the corresponding position and 1 in the rearranged hard decision sequence, and determining the rearranged hard decision sequence after error correction, wherein the rest positions are unchanged; and
and shifting the 27 th bit, 28 th bit and 29 th bit in the rearranged hard decision sequence after error correction to the 30 th bit and 31 th bit, and deleting the 32 nd bit value of the hard decision sequence before the final complement of the sequence to determine the decoding sequence.
6. The method of claim 1, wherein parity checking the coded sequence refers to: performing modulo-2 summation on 32 bit values of the decoding sequence, and checking if the 32 modulo-2 summation values are added to be 0; if the 32 modulo-2 sums add to 1, the check is false.
7. An apparatus for error correction decoding of a GPS navigation message, comprising:
the preprocessing module is used for determining the real-time signal-to-noise ratio of a received signal according to the integral values of a tracking channel and a noise channel of the receiver, and when the signal-to-noise ratio is smaller than or equal to a threshold value, decoding is invalid; when the signal-to-noise ratio is larger than a threshold value, outputting the integral value of the tracking channel to an error correction decoding module;
the error correction decoding module is used for determining a hard decision sequence and a confidence coefficient sequence according to the integral value of the tracking channel, rearranging the hard decision sequence and the confidence coefficient sequence and determining a rearranged hard decision sequence and a rearranged confidence coefficient sequence; determining a syndrome according to the rearranged hard decision sequence, and looking up a table to determine the error position condition; determining and outputting a decoding sequence according to the rearrangement hard decision sequence, the rearrangement confidence sequence and the error position condition; and
the parity check module is used for carrying out parity check on the decoding sequence, outputting the decoding sequence if the parity check is correct, and invalidating the decoding if the parity check is wrong;
a rearrangement unit, configured to remove the 32 th bit of the hard decision sequence, keep the first 26 bits unchanged, shift the 27 th and 28 th bits to the 29 th, 30 th and 31 th bits, and then form a rearranged hard decision sequence; and removing the 32 th bit of the confidence sequence, keeping the order of the first 26 bits unchanged, and moving the 27 th bit and the 28 th bit to the 29 th bit, the 30 th bit and the 31 th bit to form a rearranged confidence sequence.
8. The apparatus of claim 7, wherein the error correction coding module comprises:
a sequence determining unit, configured to determine a hard decision sequence and a confidence sequence according to the integral values of the tracking channels, and after the receiver achieves bit synchronization and frame synchronization, the error correction decoding module continuously extracts the integral values in 32 tracking channels from the 29 th bit start edge of each GPS navigation message to form a receiving sequence, determines a symbol of the receiving sequence to determine the hard decision sequence, and obtains an absolute value of the receiving sequence to obtain the confidence sequence;
a syndrome determining unit, configured to extract bit values of 1 st, 3 rd, 4 th, 5 th, 7 th, 8 th, 12 th, 13 th, 14 th, 15 th, 16 th, 19 th, 20 th, 22 th, 25 th, and 30 th of the rearranged hard decision sequence, and modulo-2 sum the bit values to obtain a 1 st bit value of the syndrome; and circularly moving the rearranged hard decision sequence by 1, 2, 3 and 4 bits to the left, extracting bit values of 1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 16, 19, 20, 22, 25 and 30 of the rearranged hard decision sequence, calculating modulo 2 of the bit values, and obtaining bit values of 2, 3, 4 and 5 of the syndrome, thereby determining the syndrome;
an error pattern position determining unit, configured to look up a table in a shift value table according to the syndrome to obtain a corresponding shift value N; adding the shift value to two error positions P1 and P2 corresponding to each error pattern number in the error pattern position table respectively to obtain two corrected error positions Pm1 ═ mod (P1+ N), Pm2 ═ mod (P2+ N); constructing a corrected error pattern position table, wherein the corrected error pattern position table comprises 16 corrected error positions corresponding to the syndrome; and
a decoding sequence determining unit, configured to extract values at corresponding positions of the rearrangement confidence sequence according to each error position condition, add and sum the values to obtain 16 added values in total; according to the error position condition corresponding to the maximum value in the 16 added values, performing modulo 2 sum on the bit value at the corresponding position and 1 in the rearranged hard decision sequence, and determining the rearranged hard decision sequence after error correction, wherein the rest positions are unchanged; and shifting the 27 th bit, 28 th bit and 29 th bit in the rearranged hard decision sequence after error correction to the 30 th bit and 31 th bit, and deleting the 32 nd bit value of the hard decision sequence before the final complement of the sequence to determine the decoding sequence.
9. The apparatus of claim 7, wherein the parity module parity-checks the coded sequence by: the parity check module calculates the modulo-2 sum of the 32 bit values of the decoding sequence, and if the 32 modulo-2 sums are added to be 0, the parity check is error-free; if the 32 modulo-2 sums add to 1, the check is false.
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