CN110007325A - A kind of rapid frame synchronization method for star base enhancing L5 signal - Google Patents
A kind of rapid frame synchronization method for star base enhancing L5 signal Download PDFInfo
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- CN110007325A CN110007325A CN201910298729.4A CN201910298729A CN110007325A CN 110007325 A CN110007325 A CN 110007325A CN 201910298729 A CN201910298729 A CN 201910298729A CN 110007325 A CN110007325 A CN 110007325A
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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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- Radar, Positioning & Navigation (AREA)
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Abstract
The present invention provides a kind of rapid frame synchronization method for star base enhancing L5 signal, the data that SBAS L5 receiver is obtained by carrier wave first pass through Manchester decoding, generate the decoding data of first time；Data after Manchester decodes are decoded FEC with Viterbi decoding algorithm, generate original navigation telegraph text data；Position or the offset of frame identification are found in original navigation telegraph text data；According to offset of the frame head in initial data, the epoch count inside receiver is adjusted, the epoch count of one frame start position of navigation message is made to be equal to 0.Inventive algorithm process is simple, and memory space and arithmetic speed get a promotion, and False Rate levels off to 0, can satisfy requirement of engineering.
Description
Technical field
The invention belongs to field of satellite navigation, are related to a kind of frame synchornization method of signal.
Background technique
Currently, Satellite Navigation Technique is widely applied in every field, it has also become the important link in national development,
But due to the limitation of technology and systems, demand is unable to satisfy in certain high-precision applications occasions.Satellite-based augmentation system
It is wide and at low cost that (Satellite-Based Augmentation System, hereinafter referred to as SBAS) possesses precision height, range
Characteristic becomes various countries' satellite navigation and develops important technology direction.
SBAS is to be monitored as a large amount of widely distributed monitoring stations (known to position) to navigation satellite, obtains original measurement
Data Concurrent is sent to master station.Master station calculates a variety of update informations such as ephemeris error, satellite clock correction, ionosphere delay, passes through
Upload station is finally corrected to geostationary orbit (Geostationary Earth Orbit, hereinafter referred to as GEO) satellite
Information distributing improves positioning accuracy to users.
The U.S. issues " IWG satellite-based augmentation system L5 Interface Control File (SBAS ICD) draft " within 2016, increases L5
Signal realizes the tracking of L1 and L5 double frequency, can effectively correct ionosphere delay error, provides corresponding integrity protection, it is ensured that
The availability and continuity of system.
A frame length 250 for SBAS L5 signal text.It is frame identification that one frame, which starts 4 bits, followed by the information of 6 bits
The data area of type number and 216 bits is finally 24 CRC checks.The navigation message frame format of SBAS L5 signal is such as
Shown in Fig. 1.
The frame identification of SBAS L5 signal text uses distributed arrangement.One complete 24 frame identification, according to 0101
1100 0,110 1,001 0,011 1010 sequence is sequentially distributed first four in 6 frames.
Forward error correction (the Forward Error of 1/2 encoding rate is used to the original navigation text of 250bps
Correction, abbreviation FEC), it is generated as the data flow of 500bps.Physical circuit is as shown in Figure 2.Pass through Manchester's code again
(Manchester Encoded) becomes the data flow that rate is 1000bps, after synthesizing with spreading code, is emitted by carrier modulation
It goes out.
But traditional characteristic character match normal plane, to the distributed nature of SBAS L5 text frame identification, there are data bit to need
The deficiency that the amount of asking is big and discrimination is low.
Summary of the invention
For overcome the deficiencies in the prior art, the present invention provides a kind of frame head searching method based on CRC check, can be fast
It is fast accurately to complete frame synchronization.
The technical solution adopted by the present invention to solve the technical problems the following steps are included:
1) data that SBAS L5 receiver is obtained by carrier wave first pass through Manchester decoding, generate the decoding of first time
Data；
2) data after Manchester decodes are decoded FEC with Viterbi decoding algorithm, generate original lead
Navigate telegraph text data；
3) position or the offset of frame identification are found in original navigation telegraph text data；
4) offset according to frame head in initial data adjusts the epoch count inside receiver, makes navigation message one
The epoch count of frame start position is equal to 0.
The step 3) finds position or the offset of frame identification using the matched method of characteristic character.
The step 3) the following steps are included:
Step 3.1) obtains 500 original data sequences after Viterbi decoding；
Step 3.2) matches 4 frame identifications of n in 500 original data sequences, terminates to walk if n is greater than 6
It is rapid 3)；
Step 3.3) jumps to step 3.4) if finding n frame identification and offset less than 250, otherwise n value
Add 1 and jumps to step 3.2)；
Step 3.4) carries out CRC check judgement；
Step 3.5) finds frame head if CRC check correctly, otherwise jumps to step 3.3) in remaining initial data
Continue searching frame head；
Step 3.6) calculates position of the frame head in 500 initial data.
The step 4) the following steps are included:
Step 4.1) obtains 2400 data, carries out Manchester decoding and obtains 1200 data；
Step 4.2) carries out Viterbi decoding to 1200 data；
Step 4.3) searches for frame head based on CRC method in 600 data；
Step 4.4) finds frame head and just jumps to step 4.8), otherwise continues searching；
Step 4.5) handles 1200 dislocation positions, carries out VCP decoding；
Step 4.6) finds frame head and just jumps to step 4.8), otherwise jumps to step 4.7)；If it is what is negated for the second time
Data bit searches for then end step 4)；
Step 4.7) handles 2400 data-conversions, repeats above step 4.1)~4.6)；
Step 4.8) completes epoch adjustment, and the epoch of place for starting a frame is counted as 0.
The beneficial effects of the present invention are: algorithm flow is simple, memory space and arithmetic speed get a promotion, False Rate approach
In 0, requirement of engineering can satisfy.
Detailed description of the invention
Fig. 1 is SBAS L5 message format；
Fig. 2 is L5 FEC register value；
Fig. 3 is the frame synchronizing process block diagram of navigation neceiver；
Fig. 4 is the search frame head algorithm flow chart based on CRC check；
Fig. 5 is SBAS L5 frame synchronization Project Realization flow chart.
Specific embodiment
Present invention will be further explained below with reference to the attached drawings and examples, and the present invention includes but are not limited to following implementations
Example.
The frame synchronizing process of SBAS L5 provided by the invention is as shown in figure 3, receiver is needed by the data that carrier wave obtains
4 processes are adjusted by Manchester decoding, Viterbi decoding, frame head search and epoch.
A) Manchester decodes
The data that SBAS L5 receiver is obtained by carrier wave first pass through Manchester decoding, generate the decoding number of first time
According to.The rule execution that Manchester decoding rule is 1 for 0,01 according to general 10.
B) Viterbi decoding
Data after Manchester decodes are decoded FEC with Viterbi decoding algorithm, generate original lead
Navigate telegraph text data.Viterbi decoding uses code rate, and the parameter of generator polynomial G1 (171) G2 (133) is translated to complete software for 1/2
Code.
C) frame head is searched for
Position or the offset of frame identification are found in original navigation message serial data, generally use characteristic character
The method matched.
Traditional characteristic character method is directed to the distributed frame head of SBAS L5, at least needs to obtain initial data i.e. 6 of 6 frames
1500 data of second.In view of the boundary of frame identification, 1504 data are at least needed, could include complete 6 frame identifications.By
In distributed 4 bit frame identifications, many erroneous judgements can be encountered in 1500 original navigation telegraph text data sequences, algorithm
Complexity is substantially improved.
The present invention uses the frame identification searching method based on CRC check, as long as navigation message data sequence is complete there are one
Whole frame can accurately find frame identification.In view of border condition, at least needing data bit is 500.
It is to the omission factor of CRC check, i.e., different in order to ensure CRC check can accurately identify a whole frame data
Data have identical verification to be analyzed.
General for general (n, k) form CRC coding, k are binary sequence length to be encoded, after n is coding
Binary sequence length, then r=n-k is to generate polynomial number.
Given length is the information sequence m of ki(i=1~k) can be expressed as following multinomial:
M (x)=mk+mk-1x+mk-2x2+…m1xk-1 (1)
Generator polynomial g (x) is represented by following multinomial:
Multinomial m (x) xrDivided by generator polynomial g (x), it is as follows to obtain residue R (x):
R (x)=pr+pr-1x+pr-2x2+…p1xr-1 (3)
Then p1p2…prConstitute cyclic redundancy check sequence.
For k data to be encoded sequence, will there is 2kThe different expression formula of kind, and for r generator polynomial most multilist
Show 2rA different residue.So will theoretically have 2k/2r=2k-rA different data sequence shares a residue, there is erroneous judgement
Probability.The numerical value of k-r is bigger, and the data sequence judged by accident is more, but the probability judged by accident is only related with the value of r
It is 1/2r。
Form of the L5 navigation message using (250,226), generator polynomial are as follows:
Wherein,
So it is 1/2 that the search of L5 frame head, which generates the probability of false judgment,24, level off to 0, fully meet engineering actual demand.
The detailed process for searching for frame head is as shown in Figure 4.
Step 1: 500 original data sequences after obtaining Viterbi decoding.
Step 2: matching 4 frame identifications of n in 500 data sequences, if n is greater than 6, jump to step 7.
Step 3: jumping to step 4 if finding n frame identification and offset less than 250, otherwise n+1 and jump
To step 2.
Step 4: carrying out CRC check judgement.
Step 5: finding frame head if CRC check correctly, otherwise jump to step 3 and continue to search in remaining initial data
Rope frame head
Step 6: calculating position of the frame head in 500 initial data.
Step 7: terminating.
D) epoch is adjusted.
According to offset of the frame head in initial data, the epoch count inside receiver is adjusted.Make one frame of navigation message
The epoch count of initial position is equal to 0.
Navigation neceiver tracking algorithm generally uses section's Stas phase discriminator.Because of its 180 degree to I and Q signal
Phasing back is insensitive, so navigation data bits are it is possible that reversion.The bit stream for inputting viterbi decoder originates G0G1
The inconsistent phenomenon for setting uncertain generation causes decoding result incorrect.
In view of two kinds of uncertainties that navigation message data in practical engineering application occur, point four kinds of situations is needed to come successively
Search for frame head.(1) the nonreversible Viterbi decoding G0G1 of data bit does not generate dislocation；(2) the nonreversible Viterbi decoding of data bit
G0G1 generates dislocation；(3) data bit reversal Viterbi decoding G0G1 does not generate dislocation；(4) data bit reversal Viterbi decoding
G0G1 generates dislocation.
In view of the boundary alignment characteristic of data storage in the data bit-loss and engineering in decoding, 2400 data are chosen
To complete frame synchronization.Ideally there are 600 data, the minimum greater than 500 behind Manchester and Viterbi decoding
Data demand.
Project Realization detailed process is as shown in figure 5, steps are as follows:
Step 1: obtaining 2400 data, carry out Manchester decoding and obtain 1200 data；
Step 2: Viterbi decoding is carried out to 1200 data；
Step 3: frame head being searched for based on CRC method in 600 data；
Step 4: finding frame head and just jump to step 8, otherwise continue searching；
Step 5: 1200 dislocation positions being handled, VCP decoding is carried out；
Step 6: finding frame head and just jump to step 8, otherwise jump to step 7.It is searched if it is the data bit negated for the second time
Rope jumps to step 9；
Step 7: 2400 data-conversions being handled, the above 1-6 step is repeated；
Step 8: completing epoch adjustment, it is 0 that the epoch of place for starting a frame, which counts,；
Step 9: terminating.
Implementation result:
Frame synchornization method described in the invention programs realization with C language in 6657 platform of TI DSP.Following table
Lattice were measured to the key modules time in frame synchronizing process.
6 frame synchronization are run, time statistics is as shown in table 1 below:
Time consumed by 16 frame synchronization of table (unit is nanosecond)
It is as shown in table 2 that Key Functions or functional module in frame synchronization do time statistics:
2 Key Functions of table and module time measurement (unit is nanosecond)
It is as shown in table 3 to the time statistical result of decoding function after frame synchronization:
Decoding function time measurement after 3 frame synchronization of table (unit is nanosecond)
Pass through the comparative analysis of table 1, table 2, table 3:
(1) telegraph text data of simulation source SBAS L5 signal is received, frame synchronization all successes demonstrate this patent frame synchronization
Accuracy and realizability.
(2) 1200 Manchester decodings are about the half of 2400 Manchester decoding times.But when 2400
When the first abandon occurs in Manchester decoding, the time can extend to 425US from 280US.
In (3) six frame synchronizing process, frame head, time-consuming about 30MS are most preferably found twice.Worst is to find frame 4 times
Head, about time-consuming 60MS.
(4) 600 Viterbis are about the half of 1200 Viterbi time.
(5) Viterbi decoding is time-consuming longest process in frame synchronization.
Pass through the above comparative analysis, it can be seen that in place of advantage of the invention:
(1) frame synchornization method proposed by the present invention based on CRC only needs 2400 texts that can complete frame synchronization,
Than 6000 traditional initial data, fast 3.5 seconds realization frame synchronization.
(2) present invention proposes the frame synchornization method of SBAS L5 signal, compared with the frame head matching algorithm of 6 characters, algorithm stream
Journey is simpler, and there are about 2 times of promotions for memory space and arithmetic speed.
(3) present invention proposes the frame synchornization method of SBAS L5 signal, and the probability of erroneous judgement is 1/224 to level off to 0, meets
Requirement of engineering.
Claims (4)
1. a kind of rapid frame synchronization method for star base enhancing L5 signal, it is characterised in that the following steps are included:
1) data that SBAS L5 receiver is obtained by carrier wave first pass through Manchester decoding, generate the decoding number of first time
According to；
2) data after Manchester decodes are decoded FEC with Viterbi decoding algorithm, generate original navigation electricity
Literary data；
3) position or the offset of frame identification are found in original navigation telegraph text data；
4) offset according to frame head in initial data adjusts the epoch count inside receiver, plays one frame of navigation message
The epoch count of beginning position is equal to 0.
2. the rapid frame synchronization method according to claim 1 for star base enhancing L5 signal, it is characterised in that: described
Step 3) finds position or the offset of frame identification using the matched method of characteristic character.
3. the rapid frame synchronization method according to claim 1 for star base enhancing L5 signal, it is characterised in that: described
Step 3) the following steps are included:
Step 3.1) obtains 500 original data sequences after Viterbi decoding；
Step 3.2) matches 4 frame identifications of n in 500 original data sequences, the end step 3 if n is greater than 6)；
Step 3.3) jumps to step 3.4) if finding n frame identification and offset less than 250, and otherwise n value adds 1 simultaneously
Jump to step 3.2)；
Step 3.4) carries out CRC check judgement；
Step 3.5) finds frame head if CRC check correctly, otherwise jumps to step 3.3) and continues in remaining initial data
Search for frame head；
Step 3.6) calculates position of the frame head in 500 initial data.
4. the rapid frame synchronization method according to claim 1 for star base enhancing L5 signal, it is characterised in that: described
Step 4) the following steps are included:
Step 4.1) obtains 2400 data, carries out Manchester decoding and obtains 1200 data；
Step 4.2) carries out Viterbi decoding to 1200 data；
Step 4.3) searches for frame head based on CRC method in 600 data；
Step 4.4) finds frame head and just jumps to step 4.8), otherwise continues searching；
Step 4.5) handles 1200 dislocation positions, carries out VCP decoding；
Step 4.6) finds frame head and just jumps to step 4.8), otherwise jumps to step 4.7)；If it is the data negated for the second time
Then end step 4 is searched in position)；
Step 4.7) handles 2400 data-conversions, repeats above step 4.1)~4.6)；
Step 4.8) completes epoch adjustment, and the epoch of place for starting a frame is counted as 0.
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| CN115499093A (en) * | 2022-08-01 | 2022-12-20 | 北京北方联星科技有限公司 | SBAS signal non-decoding frame synchronization method based on FEC coding |
| CN115499093B (en) * | 2022-08-01 | 2024-05-24 | 北京北方联星科技有限公司 | SBAS signal non-decoding frame synchronization method based on FEC coding |
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