CN112698366A - Frame synchronization method for satellite positioning receiver - Google Patents
Frame synchronization method for satellite positioning receiver Download PDFInfo
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- CN112698366A CN112698366A CN202011348066.1A CN202011348066A CN112698366A CN 112698366 A CN112698366 A CN 112698366A CN 202011348066 A CN202011348066 A CN 202011348066A CN 112698366 A CN112698366 A CN 112698366A
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- 238000012545 processing Methods 0.000 claims abstract description 19
- 238000012795 verification Methods 0.000 claims description 7
- 238000006073 displacement reaction Methods 0.000 abstract 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01S19/13—Receivers
- G01S19/35—Constructional details or hardware or software details of the signal processing chain
- G01S19/37—Hardware or software details of the signal processing chain
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Abstract
The invention discloses a frame synchronization method of a satellite positioning receiver, which comprises the steps of carrying out displacement and XOR processing on text data and matched data after in-place synchronization is established, carrying out matching processing on the processed data according to C/N0, and completing frame synchronization establishment after matching is successful. And after frame synchronization, verifying by using the matching data. The shift exclusive-or processing in the invention ensures that each matching is compared only once, can establish frame synchronization under different signal levels, and can eliminate the frame synchronization in time when the frame synchronization is wrong, thereby avoiding the influence of the frame synchronization mistake on the positioning precision.
Description
Technical Field
The invention relates to a method for providing frame synchronization for a positioning receiver of a satellite navigation system, belonging to the technical field of surveying and mapping science and technology.
Background
After the satellite positioning receiver captures the tracking signal, the telegraph text broadcast in the satellite signal is also required to be obtained, so that parameters such as ephemeris and the like are obtained for positioning and resolving. The message can be obtained through demodulation, and the message information can be analyzed according to the message format after bit synchronization and frame synchronization. Frame synchronization is a process for determining the starting position of a text frame, and is an important part in signal information processing links of a satellite positioning receiver.
Frame synchronization usually adopts a method of matching feature data, the feature data usually refers to a frame synchronization header and other fixed data in a text, and the frame synchronization is established after matching is consistent. Due to the strength factor of the locking signal, when the signal is weak, error codes can occur in the demodulated text data, so that complete matching can not be achieved when the characteristic data is matched, and thus frame synchronization cannot be established late. Similarly, due to text errors, the established frame synchronization is wrong with a certain probability, and if the frame synchronization is not checked, the wrong pseudorange always participates in positioning solution, so that a wrong positioning result is generated. Therefore, how to establish frame synchronization more quickly and efficiently and avoid the influence of frame synchronization establishment errors on positioning is an urgent problem to be solved.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a frame synchronization method for a satellite positioning receiver, which can perform frame synchronization on satellite signals with different signal levels, and perform verification after the frame synchronization is established, so as to avoid the influence on positioning caused by the error in establishing the frame synchronization.
The invention is realized by adopting the following technical scheme for solving the technical problem, and specifically comprises the following steps:
step 1, after a satellite positioning receiver captures a signal, waiting for bit synchronization establishment, after the bit synchronization is established, updating text data according to a fixed time interval, and acquiring the text data when the text is updated.
And 2, shifting and XOR processing are carried out on the text data and the matching data, wherein the shifting refers to shifting the data by one bit to the right, the XOR refers to carrying out bit XOR operation on the data before shifting and the shifted data, and the matching data refers to frame header data or other characteristic data used for frame synchronization.
And 3, acquiring the carrier-to-noise ratio C/N0 of the satellite signal needing to establish frame synchronization currently. The threshold value for bit matching is determined according to the carrier-to-noise ratio C/N0 size.
Step 4, matching the processed text data and the matched data, wherein when the number of bits matched is more than or equal to a threshold value, the matching is successful, and the frame synchronization is established; and when the matched bit number is smaller than the threshold value, the processed text data is shifted to the right by one bit, and then matching is carried out until the processed text data is completely shifted to the right.
Step 5, judging whether the frame synchronization establishment is completed: if the frame synchronization is established, checking the position of the matched data in the text within a set time range, carrying out shift exclusive-or processing on the text data and the matched data during checking, and determining the bit number of the two groups of data matching according to the carrier-to-noise ratio C/N0. And when the matched bit number is more than or equal to the threshold value set by the current level, the check is passed, and the current frame synchronization is kept. And if the check is not passed all the time within the set time range, discarding the current frame synchronization.
Has the advantages that: the message data and the matching data are shifted and subjected to XOR processing through the establishment of bit synchronization, the processed data are subjected to matching processing according to C/N0, and the shift XOR processing enables the comparison to be performed only once in each matching, so that the frame synchronization can be established under different signal levels, and meanwhile, the frame synchronization error can be eliminated in time when the frame synchronization error occurs, and the influence of the frame synchronization error on the positioning precision is avoided.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without limiting the invention.
FIG. 1 is a flow chart of the method steps of the present invention;
fig. 2 is a flow chart of a frame synchronization establishment matching process.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An embodiment of the present invention provides a frame synchronization method for a positioning receiver, and referring to fig. 1, fig. 1 is a schematic diagram of steps of a frame synchronization method for a satellite receiver provided by the present invention, and a specific implementation manner is as follows:
after the receiver bit synchronization is established, the message data is updated at regular intervals, for example, the B1I D1 code, and the message data is updated at 600ms intervals, that is, 30 bits are updated each time. Reading 30-bit text data, shifting the text data to the right by one bit, performing bit XOR operation on the text data before shifting and the text data after shifting, shifting the matching data to the right by one bit, and performing bit XOR operation on the matching data before shifting and the matching data after shifting. Taking the B1I D1 code as an example, the frame sync code pre (whose value is 11100010010 in binary representation) is right-shifted by 1 bit to obtain 1110001001 (in binary representation), and the shifted data is xor-ed before the shift to obtain 0010011001 (in binary representation).
And acquiring the carrier-to-noise ratio C/N0 of the satellite signal required to establish frame synchronization currently. The threshold value for bit matching is determined according to the carrier-to-noise ratio C/N0 size. The threshold set at each signal level is obtained from empirical values or actual measurements, and for example, the B1I D1 code may be divided into the following segments: C/N0 is more than or equal to 36dBHz, and the threshold value is = 10; C/N0 is more than or equal to 33dBHz and less than 36dBHz, and the threshold value = 9; C/N0 is more than or equal to 30dBHz and less than 33dBHz, and the threshold value = 8; C/N0 is more than or equal to 27dBHz and less than 30dBHz, and the threshold value = 7; C/N0 < 27dBHz, threshold = 6.
Matching the processed text data and the matched data as shown in fig. 2, wherein the matching is successful when the number of bits matched is more than or equal to the threshold value, and the frame synchronization is established; and when the matched bit number is smaller than the threshold value, the processed text data is shifted to the right by one bit, and then matching is carried out until the processed text data is completely shifted to the right. For example, code B1I D1: assuming that a certain satellite contains frame synchronization codes when the message data is updated for a certain time, C/N0=39dBHz, and when the processed message data is not shifted to the right, the number of matched and consistent bits is not equal to 10; shifting the processed text by one bit to the right, and continuing matching; if the processed text is shifted to the right by six bits, the number of the matched bits is equal to 10, and at the moment, the matching is successful, and the frame synchronization is established. After the frame synchronization is established, the text data is verified according to the position of the matched data in the text within a set time range. Taking the B1I D1 code as an example, a frame message is repeated every 6s for 6s, and the frame sync code is repeated every 6s, and a time range of 30s is set for verification when the message data is updated to the frame sync code position. During verification, the text data and the matching data are shifted and subjected to exclusive OR processing. Taking the B1I D1 code as an example, the text data is 30 bits obtained when the text data is updated, the text data is shifted to the right by one bit, and the data before shifting and the data after shifting are subjected to bit exclusive or operation. The matching data is right-shifted by one bit using a frame sync code pre (whose value is represented as 11100010010 in binary), and the shifted data is exclusive-or' ed before the shift to 0010011001 (represented in binary).
Matching the two groups of data after the shift XOR, wherein the matching is successful when the number of matched bits is more than or equal to the threshold value, the check is passed, and the current frame synchronization is kept; and if the check is not passed all the time within the set time range, discarding the current frame synchronization. For example, code B1I D1: assuming that after a certain frame synchronization is established, when the telegraph text data is updated to the position of a frame synchronization code for the first time, C/N0=36dBHz, the number of matched bits is 9, the threshold requirement is not met, and the checking is continued; when the text data is updated to the frame synchronization code position for the second time, C/N0=36dBHz, the matching bit number is 10, and the verification is passed, so that the current frame synchronization is maintained. And setting the time range to be 30s, and discarding the current frame synchronization reestablishment if the verification is not passed all the time within 30 s.
In the embodiment, the text data and the matching data are shifted and subjected to exclusive-or processing through the establishment of the bit synchronization, the processed data are subjected to matching processing according to the C/N0, and the shifting exclusive-or processing enables comparison to be performed only once in each matching, so that the frame synchronization can be established under different signal levels, and meanwhile, the frame synchronization can be eliminated in time when the frame synchronization is wrong, and the influence of the frame synchronization mistake on the positioning precision is avoided.
The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A method for frame synchronization of a satellite positioning receiver, comprising the steps of:
after a satellite positioning receiver captures a satellite signal, waiting for bit synchronization establishment, updating the message data at fixed time intervals after the bit synchronization is established, and acquiring the message data when the message data is updated;
shifting and XOR processing are carried out on the acquired text data and the matching data, wherein the matching data is characteristic data used for frame synchronization;
acquiring a carrier-to-noise ratio C/N0 of a satellite signal needing to establish frame synchronization at present, and determining a threshold value during bit matching according to the carrier-to-noise ratio C/N0;
matching the text data after the shifting and the XOR processing with the matching data to obtain a matching bit number, judging and shifting the text data according to the matching bit number and the threshold value to complete the frame synchronization establishment, performing frame synchronization verification if the frame synchronization is established, and returning to obtain the text data again and shifting and XOR processing the text data if the frame synchronization is not established;
performing frame synchronization check, namely shifting and XOR processing on the text data and the matched data to obtain the carrier-to-noise ratio of the current signal, judging to obtain a threshold, matching the two groups of data after XOR shifting, successfully matching when the number of matched bits is greater than or equal to the threshold, passing the check and keeping the current frame synchronization; and if the check is not passed all the time within the set time range, discarding the current frame synchronization.
2. The method of claim 1, wherein the step of obtaining the text data comprises: and after the receiver establishes the in-place synchronization, the latest message data is acquired when the message data is updated according to a fixed time interval.
3. The method as claimed in claim 1, wherein the shifting and xor processing are performed on the obtained text data and the matching data, wherein the shifting is performed by shifting the text data and the matching data by one bit to the right, and the xor processing is performed by performing a bit xor operation on the data before shifting and the data after shifting.
4. The method for frame synchronization of a satellite positioning receiver according to claim 1, wherein said determining and shifting the text data according to the number of matching bits and the threshold value comprises the steps of: when the number of bits which are matched consistently is larger than or equal to the threshold value, the matching is successful, and the frame synchronization is established; and when the matched bit number is smaller than the threshold value, the processed text data is shifted to the right by one bit, and then matching is carried out until the processed text data is completely shifted to the right.
5. The method for frame synchronization of a satellite positioning receiver of claim 1, further comprising the step of frame synchronization checking: checking the position of the matching data in the text within a set time range; wherein, the verification specifically comprises: firstly, carrying out shift XOR processing on text data and matching data to obtain a carrier-to-noise ratio C/N0 of a current check satellite signal, determining a threshold value during bit matching according to the size of the carrier-to-noise ratio C/N0, matching two groups of data subjected to shift XOR, successfully matching when the number of bits matched is more than or equal to the threshold value, passing the check, and keeping the synchronization of the current frame; and if the check is not passed all the time within the set time range, discarding the current frame synchronization.
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| CN114567924A (en) * | 2022-02-14 | 2022-05-31 | 北京瑞迪时空信息技术有限公司 | Frame synchronization method based on terrestrial positioning system receiver, electronic device and medium |
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