CN110927749B - Rapid frame synchronization method for GPS navigation message - Google Patents
Rapid frame synchronization method for GPS navigation message Download PDFInfo
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- CN110927749B CN110927749B CN201911220781.4A CN201911220781A CN110927749B CN 110927749 B CN110927749 B CN 110927749B CN 201911220781 A CN201911220781 A CN 201911220781A CN 110927749 B CN110927749 B CN 110927749B
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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
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- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
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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 rapid frame synchronization method of a GPS navigation message, belonging to the technical field of satellite navigation. The method comprises the steps of receiving and collecting GPS navigation messages, calculating the intra-week seconds and subframe numbers of the navigation messages to be received currently, reconstructing conversion words in each subframe, calculating the current predicted page number by using a local clock, reproducing the navigation messages locally, searching in the neighborhood range counted by the local clock when the navigation signals are unlocked, and the like. The method can utilize the local time counting and the navigation message received before, can quickly realize the frame synchronization processing of the navigation signal, and can accelerate the positioning speed of the navigation receiver.
Description
Technical Field
The invention belongs to the technical field of satellite navigation, and particularly relates to a rapid frame synchronization method for a GPS navigation message, which can be used for frame synchronization processing of the navigation message.
Background
Navigation messages are modulated on navigation signals transmitted by a global navigation satellite system (GPS). The message contains system time, ephemeris parameters, clock correction parameters, ionosphere delay parameters, troposphere delay parameters and almanac information of the satellite. By receiving the parameters, the user receiver can realize the calculation of the self position, speed, time and other information.
The navigation messages of the GPS satellite navigation system are arranged into a data stream D (t) in the form of frames and subframes, each satellite sends the navigation messages frame by frame, the continuity of time information is marked, and the effective time of the navigation messages can reach 2-3 hours generally. Each frame of navigation message is 1500 bits long, 30s in total, and is composed of 5 subframes in sequence. Each subframe is 300 bits long, and is 6s in total, and consists of 10 words in turn. Each word is 30 bits long with the highest bit being transmitted first and each word ending with a 6-bit parity check code. Each bit in the navigation message is 20ms long, and the C/A code repeats 20 periods. The first two words of each sub-frame are respectively a telemetry word (TLW) and a conversion word (HOW), and the last eight words constitute a data block. The navigation information contained in different sub-frames has different emphasis points. The data block in the 1 st subframe is generally referred to as a first data block, and mainly contains information including: the week number, the user ranging precision, the clock correction parameter, the IODC and the like; the data blocks in the 2 nd and 3 rd sub-frames are generally called second data blocks, and the main information comprises 16 Keplerian orbit parameters representing the satellite orbit and perturbation parameters; the data blocks in the 4 th and 5 th sub-frames are the third data blocks, and the main contents of the third data blocks include almanac information and health status of all satellites. Under the condition of not updating the satellite orbit parameters, the contents in the first and second data blocks are not updated; the third data block adopts a paging transmission mode, wherein the 4 th sub-frame and the 5 th sub-frame in one main frame are called one page, and the total page is 25 pages. Therefore, 750s are needed for 12.5min after the whole set of navigation messages is sent.
After the GPS navigation receiver captures and tracks satellite signals, firstly carrying out bit synchronization and frame synchronization to finish the analysis of navigation messages; and then, the emission time is calculated by utilizing the code NCO, the carrier NCO, the bit synchronization result and the frame synchronization result which are output by tracking. And finally, calculating the position, time and speed information of the user receiver by using the transmitting time. In the whole receiving process, the time consumption of frame synchronization is long, and shortening the frame synchronization time is very important for improving the positioning speed of a receiver.
The conventional frame synchronization method mainly judges the frame synchronization state by searching information such as a frame header in a TLW, an intra-week second count in a HOW, CRC (cyclic redundancy check) and the like. Because one frame length of the GPS is 6 seconds and only one TLW and HOW exist in one subframe, once missing, it is necessary to wait at least 6 seconds until receiving the TLW and HOW information of the next subframe again. Especially, when the navigation receiver is applied in scenes such as urban canyons, the signal intensity change is large, the lock losing time of a single satellite signal is long, and the error rate of received messages is increased. Chinese patent publication No. CN 106571862a discloses a method for fast frame synchronization of a GPS receiver, which can effectively shorten the frame synchronization time of other satellites only after the frame synchronization of the first satellite signal, but the frame synchronization time of the first satellite is still not shortened, and the navigation message information collected before can not be effectively utilized to assist the fast frame synchronization of the navigation signal.
Disclosure of Invention
In view of the above, the present invention provides a method for fast frame synchronization of a GPS navigation message, which can reproduce a currently received navigation message by using a local clock and a previously received navigation message, and can solve the problem of fast frame synchronization in a navigation receiver.
In order to achieve the purpose, the invention adopts the technical scheme that:
a rapid frame synchronization method of a GPS navigation message comprises the following steps:
(1) receiving and collecting a GPS navigation message, performing CRC (cyclic redundancy check) on the navigation message, and storing the navigation message of 1-3 subframes and the navigation message of 4-5 subframes separately, wherein words 3-10 of the 4-5 subframes are stored according to page numbers of the subframes, and each page number corresponds to a group of storage information;
(2) calculating the intra-week seconds and the subframe number of the navigation message to be received currently by using the whole second counting of the local clock; the calculation mode of the subframe number is as follows:
frame_id=[t/6]%5+1；
the seconds in the week are calculated as:
tow=[t/6]；
wherein, frame _ id is the subframe number; tow is seconds in the week; t is local clock count in seconds; [] Represents rounding down; % is remainder taking operation;
(3) reconstructing the conversion word in each subframe, putting the intra-week seconds and the subframe number calculated in the step (2) into the reconstructed conversion word, and ensuring that the 29 th bit and the 30 th bit of the reconstructed conversion word are all zero;
(4) calculating a current predicted page number using a local clock;
(5) reproducing the navigation message locally; in the reproduced navigation message, telemetry words of each subframe are 30-bit telemetry word information after CRC check in the received navigation message, conversion words of each subframe are conversion words reconstructed in the step (3), words 3-10 of 1-3 subframes are word 3-10 parts of 1-3 subframes after CRC check in the received navigation message, and words 3-10 of 4-5 subframes are stored information which is stored in the step (1) and corresponds to the page number calculated in the step (4);
(6) when the navigation signal is unlocked, searching in a neighborhood range of the local clock count t; and at each search position, carrying out exclusive or operation on the navigation message which is locally reproduced and the navigation message which is currently received, is subjected to bit synchronization and has a word length, and if the calculation result is all zero or all 1, completing the frame synchronization of the navigation message.
Further, the specific manner of the step (3) is as follows:
(301) converting the intra-week seconds calculated in the step (2) into a binary number of 17 bits, and taking the binary number as an initial value d of the first 17 bits of the converted word after reconstruction1~d17；
(302) According to the passing throughBit 30D of the telemetry word after CRC check30' determining initial value d of 18, 19 bits of reconstructed converted word18、d19If D is30Is' 1, then d18、d19For negation of 18, 19 bits in the conversion word in the received navigation message, if D30If' is 0, then d18、d19Converting the values of 18 and 19 bits in the words in the received navigation message;
(303) converting the subframe number calculated in the step (2) into a binary number of 3 bits, and taking the binary number as an initial value d of 20, 21 and 22 bits of the converted word after reconstruction20~d22；
(304) Setting initial value d of 23, 24 bits of reconstructed conversion word23、d24And (3) calculating the final value of 25-30 bits of the reconstructed conversion word by a CRC (Cyclic redundancy check) formula, wherein the final value is all 0:
D25=D29’^d1^d2^d3^d5^d6 ^d10^d11^d12^d13^d14^d17^d18^d20^d23；
D26=D30’^d2^d3^d4^d6^d7 ^d11^d12^d13^d14^d15^d18^d19^d21^d24；
D27=D29’^d1^d3^d4^d5^d7 ^d8^d12^d13^d14^d15^d16^d19^d20^d22；
D28=D30’^d2^d4^d5^d6^d8 ^d9^d13^d14^d15^d16^d17^d20^d21^d23；
D29=D30’^d1^d3^d5^d6^d7 ^d9^d10^d14^d15^d16^d17^d18^d21^d22^d24；
D30=D29’^d3^d5^d6^d8^d9 ^d10^d11^d13^d15^d19^d22^d23^d24；
in the formula, D29' is the 29 th bit value of the telemetry word after CRC check, and is exclusive OR operation;
(305) according to D29And D30Is reset d23、d24The value of (c): d24=D29、d23=D29^D30；
(306) Determining the final value of 1-24 bits of the reconstructed conversion word:
Di=D30’^di，i=1…24；
the reconstruction of the converted word is completed.
Further, the page number page _ id in the step (4) is calculated in the following manner:
page_id=[[[t/6]%125]/5]+1。
further, the radius of the neighborhood in the step (6) is 60 ms.
Adopt above-mentioned technical scheme's beneficial effect to lie in:
1. the method uses the previously received GPS navigation message, uses the local clock to update the TLW telemetry word, the TOW within-week second counting and the CRC check result in the received message to reproduce the navigation message which is possibly received locally, and then matches the message which is received locally and is subjected to bit synchronization with the reproduced navigation message in a certain search window to the navigation message with a word length, thereby quickly completing the frame synchronization of the navigation message.
2. The invention overcomes the defects of slow frame synchronization and incapability of effectively utilizing the navigation message information received before in the prior art, and can achieve the purpose of fast frame synchronization after the navigation signal is locked again.
Drawings
Fig. 1 is a flowchart of a frame synchronization method according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a navigation message in the embodiment of the present invention.
FIG. 3 is a schematic diagram illustrating search determination in an embodiment of the present invention.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
As shown in fig. 1, a method for fast frame synchronization of a GPS navigation message includes the following steps:
(1) receiving and collecting a GPS navigation message, performing CRC (cyclic redundancy check) on the navigation message, and storing the navigation message of 1-3 subframes and the navigation message of 4-5 subframes separately, wherein words 3-10 of the 4-5 subframes are stored according to page numbers of the subframes, and each page number corresponds to a group of storage information;
(2) calculating the intra-week seconds and the subframe number of the navigation message to be received currently by using the whole second counting of the local clock; the calculation mode of the subframe number is as follows:
frame_id=[t/6]%5+1；
the seconds in the week are calculated as:
tow=[t/6]；
wherein, frame _ id is the subframe number; tow is seconds in the week; t is local clock count in seconds; [] Represents rounding down; % is remainder taking operation;
(3) reconstructing the conversion word in each subframe, putting the intra-week seconds and the subframe number calculated in the step (2) into the reconstructed conversion word, and ensuring that the 29 th bit and the 30 th bit of the reconstructed conversion word are all zero;
(4) calculating a current predicted page number using a local clock;
(5) reproducing the navigation message locally; in the reproduced navigation message, telemetry words of each subframe are 30-bit telemetry word information after CRC check in the received navigation message, conversion words of each subframe are conversion words reconstructed in the step (3), words 3-10 of 1-3 subframes are word 3-10 parts of 1-3 subframes after CRC check in the received navigation message, and words 3-10 of 4-5 subframes are stored information which is stored in the step (1) and corresponds to the page number calculated in the step (4);
(6) when the navigation signal is unlocked, searching in a neighborhood range of the local clock count t; and at each search position, carrying out exclusive or operation on the navigation message which is locally reproduced and the navigation message which is currently received, is subjected to bit synchronization and has a word length, and if the calculation result is all zero or all 1, completing the frame synchronization of the navigation message.
Further, the specific manner of the step (3) is as follows:
(301) converting the intra-week seconds calculated in the step (2) into a binary number of 17 bits, and taking the binary number as an initial value d of the first 17 bits of the converted word after reconstruction1~d17；
(302) According to the 30 th bit D of the telemetry word after CRC check30' determining initial value d of 18, 19 bits of reconstructed converted word18、d19If D is30Is' 1, then d18、d19For negation of 18, 19 bits in the conversion word in the received navigation message, if D30If' is 0, then d18、d19Converting the values of 18 and 19 bits in the words in the received navigation message;
(303) converting the subframe number calculated in the step (2) into a binary number of 3 bits, and taking the binary number as an initial value d of 20, 21 and 22 bits of the converted word after reconstruction20~d22；
(304) Setting initial value d of 23, 24 bits of reconstructed conversion word23、d24And (3) calculating the final value of 25-30 bits of the reconstructed conversion word by a CRC (Cyclic redundancy check) formula, wherein the final value is all 0:
D25=D29’^d1^d2^d3^d5^d6 ^d10^d11^d12^d13^d14^d17^d18^d20^d23；
D26=D30’^d2^d3^d4^d6^d7 ^d11^d12^d13^d14^d15^d18^d19^d21^d24；
D27=D29’^d1^d3^d4^d5^d7 ^d8^d12^d13^d14^d15^d16^d19^d20^d22；
D28=D30’^d2^d4^d5^d6^d8 ^d9^d13^d14^d15^d16^d17^d20^d21^d23；
D29=D30’^d1^d3^d5^d6^d7 ^d9^d10^d14^d15^d16^d17^d18^d21^d22^d24；
D30=D29’^d3^d5^d6^d8^d9 ^d10^d11^d13^d15^d19^d22^d23^d24；
in the formula, D29' is the 29 th bit value of the telemetry word after CRC check, and is exclusive OR operation;
(305) according to D29And D30Is reset d23、d24The value of (c): d24=D29、d23=D29^D30；
(306) Determining the final value of 1-24 bits of the reconstructed conversion word:
Di=D30’^di，i=1…24；
the reconstruction of the converted word is completed.
Further, the page number page _ id in the step (4) is calculated in the following manner:
page_id=[[[t/6]%125]/5]+1。
further, the radius of the neighborhood in the step (6) is 60 ms.
Specifically, the method uses the navigation message collected before and the local clock count to reproduce the navigation message which is currently received, and realizes frame synchronization by comparing the recaptured navigation signal with the reproduced signal within a certain time search range, and the specific implementation mode is as follows:
1) collecting a navigation message of a currently received GPS, and storing messages of 1-3 subframes and navigation messages of 4 th and 5 th subframes separately (the navigation messages after CRC check are stored, wherein the 4 th and 5 th subframes are stored according to page numbers of the navigation messages);
2) and calculating the tow, the subframe number and the word number of the navigation message to be received currently by using the whole second counting of the local clock. In order to simplify the description mode, the navigation message of the whole subframe is reproduced once;
the calculation of the subframe number is as follows:
frame_id=[t/6]%5+1；
the HOW calculation mode in the HOW word is as follows:
tow=[t/6]；
where t is expressed as a local clock count in seconds; [] Represents a round-down operation;
3) for the TLW, only the collected 30-bit TLW information subjected to CRC needs to be used as the navigation message which is currently received, and the first 8 bits are 0x8b (16-system);
4) the structure of HOW is shown in fig. 2. Different information of tow count and frame number in different subframes, and simultaneously, in order to ensure D at tail of HOW29And D30Is all zero, thus D23And D24Nor are they all identical. When the method reproduces the navigation message, the tow and the subframe number calculated by local counting are required to be put into the how to calculate D23、D24To ensure D29、D30Is all zero. The calculation method is as follows:
converting the calculated tow into a binary of 17bitMaking a number to obtain d1~d17；
According to D in reproduction TLW30', when D30' 1 is, d in HOW will be received before18、d19Bit negation; otherwise, the previously received d is maintained18、d19；
According to the previously calculated subframe number, the current local count is converted into subframe number information of 3 bits, and d is obtained20、d21、d22；
Default d23、d24Is all 0, i.e. d23=0、d24=0, then the following CRC check equation is used:
D25=D29’^d1^d2^d3^d5^d6 ^d10^d11^d12^d13^d14^d17^d18^d20^d23；
D26=D30’^d2^d3^d4^d6^d7 ^d11^d12^d13^d14^d15^d18^d19^d21^d24；
D27=D29’^d1^d3^d4^d5^d7 ^d8^d12^d13^d14^d15^d16^d19^d20^d22；
D28=D30’^d2^d4^d5^d6^d8 ^d9^d13^d14^d15^d16^d17^d20^d21^d23；
D29=D30’^d1^d3^d5^d6^d7 ^d9^d10^d14^d15^d16^d17^d18^d21^d22^d24；
D30=D29’^d3^d5^d6^d8^d9 ^d10^d11^d13^d15^d19^d22^d23^d24；
to ensure that the final D29, D30 are all zero, the final D24=D29、d23=D29^D30；
If D in TLW30A value of 1 requires d to be calculated for the previous value1~d24Negation operation, otherwise not to d1~d24Performing any operation to obtain final D1~D24；D25~D30The check bit of (1) is not processed;
namely: di=D30’^di，i=1…24；
D in this HOW word1~D30The reconstruction is done locally.
5) Words 3 to 10 of the navigation message of 1 to 3 subframes can be directly used as the navigation message which is subjected to CRC. TLW and HOW in the 4 th-5 th sub-frame navigation messages are also constructed by using 2) -4), but words 3-10 need to be reconstructed according to the page number, and because 1) the satellite almanac information of the 4 th and 5 th sub-frames is stored according to the page number of the navigation messages, only the local clock is used for calculating the currently predicted page number.
The prediction of page number is as follows:
calculating frame _ id = [ t/6]%5+ 1;
judging whether the frame _ id is between 4 and 5, if so, continuing to execute subsequent operations, otherwise, directly exiting;
page_id=[[[t/6]%125]/5]+1。
and selecting the navigation message in words 3-10 corresponding to the 4 th or 5 th subframe according to the frame _ id and the page _ id, and directly using the navigation message as a locally reproduced navigation message.
6) Determining a search range according to the lock losing time of the navigation signal and the counting precision of the local clock, wherein a search window of +/-60 ms (+/-3 navigation messages) can meet most application scenes. The whole calculation process is shown in fig. 3. Because the GPS navigation message adopts a BPSK modulation mode, the navigation message is likely to be completely inverted when being received, so that the navigation message with the word length after the current received bit synchronization is utilized to carry out XOR operation with the locally reproduced navigation message, the calculation result is all zero or all 1 is correct, namely, the frame synchronization of the navigation message is proved to be completed.
Firstly, locally storing navigation messages passing CRC check, wherein the navigation messages of 4-5 subframes are stored according to pages; then, estimating tow, frame _ id and page _ id in the navigation message which should be received currently by using local time counting, and calculating d in HOW by CRC (cyclic redundancy check)23、d24To ensure D in HOW29、D30Is all zero; then splicing the words 3-10 in the previously stored navigation message and the reproduced TLW and HOW according to the frame _ id and the page _ id to obtain a navigation message which is locally received; then determining a search window according to the time of losing lock of the navigation signal; and finally, according to local time counting, carrying out exclusive OR operation on the navigation message with the word length which passes through bit synchronization after lock losing recapture and the navigation message reproduced locally in a certain search window, and quickly realizing frame synchronization of the navigation message according to a calculation result.
In the prior art, in the frame synchronization process after the navigation signal is lost and recaptured, the previously received navigation message can not be effectively utilized, so that the frame synchronization process of the navigation message is slow. The invention provides a rapid frame synchronization method of a GPS navigation message, which utilizes local time counting and the navigation message received before to rapidly realize the frame synchronization of the navigation message.
Specifically, in the state that the receiver signal is unlocked for a long time, the GPS receiver can only reuse the frame header, TLW, and HOW to perform frame synchronization detection again. The method can reproduce the navigation message which is possibly received locally by utilizing the GPS navigation message which is received before and updating TLW, TOW counting and CRC (cyclic redundancy check) results in the message by utilizing the local clock, and then matches the message which is received locally and is subjected to bit synchronization with the reproduced signal to the navigation message with a word length in a certain window time according to the navigation message, thereby quickly completing the frame synchronization of the navigation message.
In the method, a receiver updates the TOW count and the subframe number in the HOW through a local clock by using the previously received complete navigation message, then updates the TLW and the HOW in the message through CRC check, reproduces the first two words in one subframe navigation message which can be locally received, and then updates the rest 8 words in the reproduced message according to the subframe number and the page number. In the time period that the navigation message is not updated, the navigation message locally received at any moment can be reproduced by adopting the mode.
The invention fully utilizes the previously received message information and the local clock, and can dynamically adjust the size of the search window according to the length of the signal lock losing time, thereby not only ensuring the validity of frame synchronization, but also shortening the frame synchronization time, and realizing the frame synchronization of the navigation message at any moment.
Claims (4)
1. A rapid frame synchronization method of a GPS navigation message is characterized by comprising the following steps:
(1) receiving and collecting a GPS navigation message, performing CRC (cyclic redundancy check) on the navigation message, and storing the navigation message of 1-3 subframes and the navigation message of 4-5 subframes separately, wherein words 3-10 of the 4-5 subframes are stored according to page numbers of the subframes, and each page number corresponds to a group of storage information;
(2) calculating the intra-week seconds and the subframe number of the navigation message to be received currently by using the whole second counting of the local clock; the calculation mode of the subframe number is as follows:
frame_id=[t/6]%5+1；
the seconds in the week are calculated as:
tow=[t/6]；
wherein, frame _ id is the subframe number; tow is seconds in the week; t is local clock count in seconds; [] Represents rounding down; % is remainder taking operation;
(3) reconstructing the conversion word in each subframe, putting the intra-week seconds and the subframe number calculated in the step (2) into the reconstructed conversion word, and ensuring that the 29 th bit and the 30 th bit of the reconstructed conversion word are all zero;
(4) calculating a current predicted page number using a local clock;
(5) reproducing the navigation message locally; in the reproduced navigation message, telemetry words of each subframe are 30-bit telemetry word information after CRC check in the received navigation message, conversion words of each subframe are conversion words reconstructed in the step (3), words 3-10 of 1-3 subframes are word 3-10 parts of 1-3 subframes after CRC check in the received navigation message, and words 3-10 of 4-5 subframes are stored information which is stored in the step (1) and corresponds to the page number calculated in the step (4);
(6) when the navigation signal is unlocked, searching in a neighborhood range of the local clock count t; and at each search position, carrying out exclusive or operation on the navigation message which is locally reproduced and the navigation message which is currently received, is subjected to bit synchronization and has a word length, and if the calculation result is all zero or all 1, completing the frame synchronization of the navigation message.
2. The method for fast frame synchronization of GPS navigation messages according to claim 1, wherein the specific manner of step (3) is as follows:
(301) converting the intra-week seconds calculated in the step (2) into a binary number of 17 bits, and taking the binary number as an initial value d of the first 17 bits of the converted word after reconstruction1~d17；
(302) According to the 30 th bit D of the telemetry word after CRC check30' determining initial value d of 18, 19 bits of reconstructed converted word18、d19If D is30Is' 1, then d18、d19For negation of 18, 19 bits in the conversion word in the received navigation message, if D30If' is 0, then d18、d19Converting the values of 18 and 19 bits in the words in the received navigation message;
(303) converting the subframe number calculated in the step (2) into a binary number of 3 bits, and taking the binary number as 20 and 2 of the converted word after reconstruction1. Initial value d of 22 bits20~d22；
(304) Setting initial value d of 23, 24 bits of reconstructed conversion word23、d24And (3) calculating the final value of 25-30 bits of the reconstructed conversion word by a CRC (Cyclic redundancy check) formula, wherein the final value is all 0:
D25=D29’^d1^d2^d3^d5^d6 ^d10^d11^d12^d13^d14^d17^d18^d20^d23；
D26=D30’^d2^d3^d4^d6^d7 ^d11^d12^d13^d14^d15^d18^d19^d21^d24；
D27=D29’^d1^d3^d4^d5^d7 ^d8^d12^d13^d14^d15^d16^d19^d20^d22；
D28=D30’^d2^d4^d5^d6^d8 ^d9^d13^d14^d15^d16^d17^d20^d21^d23；
D29=D30’^d1^d3^d5^d6^d7 ^d9^d10^d14^d15^d16^d17^d18^d21^d22^d24；
D30=D29’^d3^d5^d6^d8^d9 ^d10^d11^d13^d15^d19^d22^d23^d24；
in the formula, D29' is the 29 th bit value of the telemetry word after CRC check, and is exclusive OR operation;
(305) according to D29And D30Is reset d23、d24The value of (c): d24=D29、d23=D29^D30；
(306) Determining the final value of 1-24 bits of the reconstructed conversion word:
Di=D30’^di，i=1， …， 24；
the reconstruction of the converted word is completed.
3. The method for fast frame synchronization of a GPS navigation message according to claim 1, wherein the page number page _ id in the step (4) is calculated by:
page_id=[[[t/6]%125]/5]+1。
4. the method for fast frame synchronization of GPS navigation message according to claim 1, wherein the radius of the neighborhood in step (6) is 60 ms.
Priority Applications (1)
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| CN112073151B (en) * | 2020-09-07 | 2023-02-17 | 中电科思仪科技股份有限公司 | Telemetry PCM decoding and frame synchronization method based on FPGA |
| CN114710829B (en) * | 2022-06-06 | 2022-08-05 | 希诺麦田技术（深圳）有限公司 | GPS frame timing synchronization method, equipment and system of ad hoc network device |
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