CN105759288B - The Big Dipper B1I weak signal catching methods of feature based sequence - Google Patents
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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
- G01S19/246—Acquisition or tracking or demodulation of signals transmitted by the system involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
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Abstract
The present invention proposes a kind of Big Dipper B1I weak signal catching methods of feature based sequence, and for solving, capture rate present in existing Big Dipper B1I weak signal catching methods is low and the technical problem of capture ability difference；Include the following steps：1 sets characteristic sequence length, obtains characteristic sequence storehouse；2 read Big Dipper B1I digital medium-frequency signals；3 will read data carries out parity packet by millisecond；4 carry out NH demodulation using characteristic sequence, and will add up per group demodulation data block；5 odd even zero paddings；The local reproduction signal of 6 generations, carries out related operation；7 compare the size of peak value in correlated results, extract detected value；8 thresholdings judge, if less than step 9 is performed if thresholding, otherwise terminate；9 cycle criterions, if cycle-index is less than 20, read the data of delay 1ms, perform step 4, otherwise terminate.The acquisition performance of the present invention is high and acquisition speed is fast, the capture available for Big Dipper B1I weak signals.
Description
Technical field
The invention belongs to technical field of satellite navigation, is related to a kind of catching method of satellite-signal, and in particular to Yi Zhongji
In the Big Dipper B1I weak signal catching methods of characteristic sequence, suitable for the capture of Big Dipper B1I weak signals.
Technical background
Satellite navigation positioning is most widely used navigator fix mode in modern society, at present the navigation of four large satellites of the whole world
System has the GPS in the U.S., GLONASS, the Galileo of European Union and the Beidou satellite navigation system in China of Russia.China
No. two satellite navigation systems of the Big Dipper built, to provide the comprehensive worldwide navigation positioning service in sea, land and sky as target,
21 Beidou navigation satellites have been succeeded in sending up at present, have constantly been strided forward to the networking of Big Dipper system global.
Big Dipper B1I signal broadcast D1 navigation messages, D1 navigation messages speed are 50bps, and it is 1kbps's to be modulated with speed
Secondary coding, its secondary coding use Neumann-Hoffman codes (abbreviation NH codes).One information bit width of D1 navigation messages is
20 milliseconds, the ranging code cycle be 1 millisecond, using 20 bits NH codes (00000100110101001110) and navigation information code and
Ranging code synchronous modulation.Every 1 bit navigation information code corresponds to a NH code cycle for this, and every 1 bit NH codes correspond to a ranging
In the code cycle, this causes have bit saltus step may in every 1 millisecond of navigation data.
Capture, is search satellites in view, and roughly determines the carrier frequency of satellite-signal and the process of ranging code phase.
It need to be realized using the correlation feature of ranging code, locally reproduction signal progress is related to receiver for the satellite-signal that will be inputted
Computing, operation result peak value and thresholding are compared, and to determine whether to capture satellite, and are determined according to peak value position
Carrier frequency and ranging code phase.But in the complex environments such as jungle, interior, tunnel, signal energy is due to multipath reflection, obstacle
Thing the factor such as blocks and can seriously undermine, and such weak signal can not be captured by directly carrying out relevant treatment.Need to extend at this time
The related operation time, accumulates correlation result to reach sufficiently large storage gain, to capture satellite-signal.
The method of traditional capture weak signal mainly has coherent integration method and non-coherent integration method.Coherent integration method is will be more
The correlation result in a continuous ranging code cycle corresponds to position and adds up, to improve signal gain, but since navigation information code is jumped
Become, there is a situation where that accumulated value is cancelled out each other, storage gain decay, limits integration duration.Non-coherent integration method, correlation is transported
It is added after calculating result modulus, eliminating the saltus step of navigation information code with this influences, but noise has been carried out square operation during modulus,
New noise is introduced, weakens output signal-to-noise ratio, brings Square loss.For Big Dipper B1I signals, there are navigation information code saltus step
Simultaneously as the presence of secondary coding, each millisecond has a possibility of bit saltus step, and the above method is directly using can bring bigger
Gain loss, therefore cannot be directly used to the capture of Big Dipper B1I weak signals.
In order to reduce the influence that secondary coding captures weak signal, being typically employed on the basis of traditional catching method increases
The demodulating process of NH codes is realized, specially circulation repeatedly travels through all possible combinations of the length for the NH code sequences of 20 bits
Related operation is carried out, the peak value chosen in all correlation results carries out prize judgment.But such method is traveling through 20 bits
It can increase calculation amount during all combinations of NH code sequences, cause acquisition speed to reduce.Such as Chinese patent application, Shen Qing Publication
Number CN102928853A, entitled " a kind of method for capturing Big Dipper D1 satellite navigation system weak signals ", discloses one kind
The method for capturing Big Dipper D1 satellite navigation system weak signals.This method first carries out weak signal ranging code phase, Doppler's frequency
Rate two-dimensional search, then carries out coherent integration and collects 20 coherent integration results, choose a kind of NH sequences, tied with 20 integrations
Fruit is multiplied one by one, and carries out non-coherent integration, repeats the above steps, and is finished until 20 kinds of NH secondary codings sequences travel through, will most
Big value carries out thresholding and judges to determine whether to capture signal, in the case of reaching there are NH secondary codings, obtains higher place
The effect that reason gain reaches.Though the invention can peel off NH secondary codings, all of the NH code sequences that searching loop length is 20 are needed
Combination demodulates to realize, computationally intensive, capture processing time length.
The content of the invention
It is an object of the invention to overcome above-mentioned the shortcomings of the prior art, it is proposed that a kind of north of feature based sequence
Struggle against B1I weak signal catching methods, for solve capture rate present in existing Big Dipper B1I weak signal catching methods it is low and capture
The technical problem of energy force difference.
The basic ideas that the present invention realizes are：The concept in linear generating space is expanded into NH codes, is chosen certain in NH codes
The characteristic sequence of length, fast and effectively carries out NH demodulation, eliminates limitation of the NH code polarity saltus steps to integration duration, to determine
The phase of satellite-signal NH codes is determined while signal ranging code phase and Doppler frequency shift.And it will be carried out per 1ms navigation datas
Parity packet computing, avoids related operation duration Nepit from inverting with this, and the data block after can NH be demodulated is directly cumulative right
Odd even zero padding is carried out afterwards, is carried out parallel related operation using Fast Fourier Transform (FFT), is reduced operand, improves arithmetic speed.
According to above technical thought, realize the technical solution that the object of the invention uses, include the following steps：
Step 1, the characteristic length k of NH codes in Big Dipper B1I signals is calculated, and characteristic sequence is set according to this feature length k
Length is K, and from NH codes successively intercepted length be K 20 characteristic sequences, composition characteristic sequence library CK, wherein k≤K≤
20, wherein the step of realizing for calculating the characteristic length k of NH codes in Big Dipper B1I signals is：
Step 1a) input secondary coding sequence specific value；
Step 1b) sequence length NsRepresent, k represents longest continuous 1 or 0 number in the sequence；
Step 1c) be k with length subsequence obtain a NsThe Metzler matrix of × k is often capable that one is moved to left on the basis of lastrow
Position；
Step 1d) calculating matrix M Correlation series, check in matrix M whether there is identical row, if any
Two rows are identical, then k values are increased by 1, repeat step (1c) structure Metzler matrix, is identical until not having any two row in matrix M
, obtain the characteristic length k=7 of the NH code sequences；
Step 2, Big Dipper B1I digital medium-frequency signals are inputted, read any N milliseconds of data from the digital medium-frequency signal, N >=
K+20；
Step 3, parity packet is carried out by millisecond to the data of the reading, respectively obtains the odd number for including N number of data block
Group Sodd={ D1,D2,...,Di,...,DNAnd even number set Seven={ E1,E2,...,Ei,...,EN, wherein DiRepresent odd number group
In i-th of data block, EiRepresent i-th of data block in even number set, the data volume of 0.5ms is included in each data block；
Step 4, carry out NH demodulation and demodulating data block adds up：
Step 4a) from the odd number group SoddWith even number set SevenIn j-th of data BOB(beginning of block), respectively sequentially extract K number
According to block, wherein j is labelled amount, is recorded in every group from which data BOB(beginning of block) extraction data block；
Step 4b) every group of K extracted data block be multiplied by characteristic sequence storehouse CKIn first characteristic sequence respective value,
Obtain K odd number group demodulating data block and K even number set demodulating data block；
Step 4c) K demodulating data block in every group is corresponded into position add up, obtain odd data block and even data
Block：
Wherein SoIt is the odd data that corresponding position is added up after the K data block extracted in odd number group carries out NH demodulation
Block, SeIt is the even data block that corresponding position is added up after the K data block extracted in even number set carries out NH demodulation, CK1(n) table
Show CKIn n-th NH code in first characteristic sequence；
Step 5, to the SoAnd SeCarry out odd even zero padding respectively, when obtaining the odd number block of a length of 1ms and when a length of 1ms
Even numbered blocks；
Step 6, when will be described the odd number block of a length of 1ms and when a length of 1ms even numbered blocks respectively with local reproduction signal into
Parallel related operation of the row based on Fast Fourier Transform (FFT), obtains odd number group matrix of consequence and even number set matrix of consequence；
Step 7, compare the size of peak value in odd number group matrix of consequence and even number set matrix of consequence, extract big peak value as inspection
Measured value；
Step 8, judge whether the detected value has reached detection threshold, if detected value has reached the detection threshold of setting,
Then acquisition success, otherwise performs step 9；
Step 9, if cycle-index is less than 20 times, data, that is, j of delay 1ms adds 1, performs step (4), otherwise judges to catch
Obtain failure.
Compared with prior art, the present invention have the following advantages that：
1) present invention for the characteristic sequence of K by length with packet data block due to when carrying out NH demodulation, being multiplied come real
It is existing, and the value of K is more than or equal to the characteristic length of NH codes and less than or equal to 20, is repeatedly traveled through with the circulation used in the prior art
Length is compared for 20 NH codes all possible combinations to carry out the method for NH demodulation, reduces the calculation amount in demodulating process, from
And improve acquisition speed.
2) present invention will carry out parity packet per 1ms data, and odd number group and even number set are demodulated and phase respectively
Computing is closed, it is not include bit reversal necessarily to have one group in such odd even group, avoids in the prior art related fortune for a long time
Weakening of the higher bit Overturn ratio to storage gain during calculation, improves signal-detection probability, more efficient completion Big Dipper B1I weak signals
Capture, effectively improves acquisition performance.
3) the characteristic sequence length K set in the present invention, can select different K in its value range according to specific environment
Value, is suitable for the capture of varying strength weak signal, further increases acquisition performance.
Brief description of the drawings
Fig. 1 is the FB(flow block) of the present invention；
Fig. 2 is to the parity packet schematic diagram of data streams read in the present invention；
Fig. 3 is the zero padding schematic diagram of odd data block and even data block in the present invention.
Embodiment
Below in conjunction with the drawings and specific embodiments, the technical solution taken the present invention is further described：
Referring to the drawings 1, implementation steps of the invention are as follows：
Step 1, according to the characteristic length k of NH codes in the Big Dipper B1I signals for calculating gained, it is K to set characteristic sequence length,
And from NH codes successively intercepted length be K 20 characteristic sequences, composition characteristic sequence library CK, wherein k≤K≤20.
The wherein characteristic length k of NH codes and characteristic sequence storehouse CK, it is that the concept in linear generating space is expanded into NH codes
In obtained from, wherein the length in the linear generating space of NH codes is known as characteristic length.For its characteristic length of same sequence
It is definite value, can be used directly after once calculating.For the NH codes used in Big Dipper B1I signals, its characteristic length k=7 is calculated to obtain,
Characteristic length k is obtained by following steps：
Step 1a) input secondary coding sequence specific value, for Big Dipper B1I signals, its NH sequence is
(00000100110101001110)；
Step 1b) sequence length NsRepresent, k represents longest continuous 1 or 0 number in the sequence；
Step 1c) be k with length subsequence obtain a NsThe Metzler matrix of × k is often capable that one is moved to left on the basis of lastrow
Position；
Step 1d) calculating matrix M Correlation series, check in matrix M whether there is identical row, if any
Two rows are identical, then k values are increased by 1, repeat step 1c structure Metzler matrix, are identical until not having any two row in matrix M
, obtain the characteristic length k=7 of the NH code sequences；
Characteristic sequence storehouse is the set of certain amount characteristic sequence, characteristic sequence storehouse CKGenerated by following steps：First
Characteristic sequence length K is set, and k≤K≤20, are then shifted serially the subsequence that intercepted length is K, by 20 sons from NH sequences
Sequence composition characteristic sequence library CK={ CK1,CK2,...,CKi,...,CK20}.Wherein CKIt is characterized feature when sequence length is K
Sequence library, CKiRepresent since i-th of chip of NH codes, length is the subsequence of K, these subsequences are known as the feature sequence of NH codes
Row.Because NH codes sequence length is 20 in Big Dipper B1I signals, by 20 characteristic sequence composition characteristic sequence libraries.
When setting K values, different length can be selected according to specific environment in its value range, to adapt to varying strength
Weak signal capture.
Step 2, Big Dipper B1I digital medium-frequency signals are inputted, read any N milliseconds of data from the digital medium-frequency signal, N >=
K+20。
Wherein, the Big Dipper B1I digital medium-frequency signals of input, are the Big Dipper B1I signals received using receiver, by penetrating
Obtained after frequency amplification, down coversion and sampling processing.
Step 3, parity packet is carried out by millisecond to the data of reading, respectively obtains the odd number group S comprising N number of data blockodd
={ D1,D2,...,Di,...,DNAnd even number set Seven={ E1,E2,...,Ei,...,EN, wherein DiRepresent i-th in odd number group
A data block, EiRepresent i-th of data block in even number set, the data volume of 0.5ms is included in each data block.
The data of reading are wherein subjected to parity packet by millisecond, concrete operations are：By the data of reading using 1ms to be single
The data of every 1ms are divided into two parts by position, and the data of preceding 0.5ms are a data block in odd number group, the data of rear 0.5ms
For a data block in even number set.Specific parity packet schematic diagram such as Fig. 2.
The data of every 1ms are carried out parity packet can avoid due to the bit reversal influence next to capture zone.Because for
Big Dipper B1I signals, since NH codes are modulated, there is the possibility of bit reversal per 1ms data, inevitable after carrying out 1 millisecond of parity packet
There is one group of data not comprising bit reversal.
Step 4, carry out NH demodulation and demodulating data block adds up：
Step 4a) from odd number group SoddWith even number set SevenIn j-th of data BOB(beginning of block), respectively sequentially extract K data
Block, wherein j are labelled amount, are recorded in every group from which data BOB(beginning of block) extraction data block；
Step 4b) every group of K extracted data block be multiplied by characteristic sequence storehouse CKIn first characteristic sequence respective value,
Obtain K odd number group demodulating data block and K even number set demodulating data block；
Step 4c) K demodulating data block in every group is corresponded into position add up, obtain odd data block and even data
Block：
Wherein SoIt is the odd data that corresponding position is added up after the K data block extracted in odd number group carries out NH demodulation
Block, SeIt is the even data block that corresponding position is added up after the K data block extracted in even number set carries out NH demodulation, CK1(n) table
Show CKIn n-th NH code in first characteristic sequence；
Wherein labelled amount j, its value meets j+19+K≤N when using for the first time, when avoiding the need for repeatedly being circulated, institute
Extract data block and exceed the situation for reading data volume.
Wherein NH demodulation process be specially：, will wherein nth data block for the K data block extracted from every group
Data be multiplied by CKIn first characteristic sequence CK1N-th of NH code, obtain demodulating data block, 1≤n≤K.
Step 5, to SoAnd SeRespectively carry out odd even zero padding, when obtaining the odd number block of a length of 1ms and when a length of 1ms even number
Block.
Wherein odd even zero padding carries out as follows, specific schematic diagram such as Fig. 3：
Step 5a) to odd data block So, behind data block zero padding to when a length of 1ms data volume；
Step 5b) dual numbers data block Se, before data block zero padding to when a length of 1ms data volume；
Step 6, by when a length of 1ms odd number block and when a length of 1ms even numbered blocks carry out base with local reproduction signal respectively
In the parallel related operation of Fast Fourier Transform (FFT), odd number group matrix of consequence and even number set matrix of consequence, related operation step are obtained
It is rapid as follows：
Step 6a) utilize matlab softwares in sin functions and cos functions generate same phase carrier wave and quadrature carrier respectively,
Wherein local carrier frequency need to be with step-length fstep, traversal IF frequency fIFNeighbouring Doppler frequency shift scope [fmin,fmax] in institute
There are frequency, fmin, fmaxThe respectively lower and upper limit of Doppler frequency shift, can use f herestep=500Hz, fmin=-10KHz,
fmax=10KHz, fIFDetermined according to the IF frequency of input signal；
Step 6b) according to Big Dipper B1I signal ranging code structural generations local ranging code, life is multiplied by respectively with local ranging code
Into same phase carrier wave and quadrature carrier, obtain modulated same phase carrier wave and modulated quadrature carrier；
Step 6c) modulated same phase carrier wave and modulated quadrature carrier are sampled, sample frequency will and be read
Satellite-signal sample frequency it is consistent；
Step 6d) using the sampled data of modulated same phase carrier wave as real part, by the sampling of modulated quadrature carrier
Data obtain local reproduction signal as imaginary part.
Step 6e) Fast Fourier Transform (FFT) is carried out to local reproduction signal, obtain the frequency domain data of local reproduction signal；
Step 6f) Fast Fourier Transform (FFT) is carried out to data block, obtain the frequency domain data of data block；
Step 6g) frequency domain data of local reproduction signal is taken to the frequency domain data that data block is multiplied by after complex conjugate, then will
Multiplied result carries out inverse fast Fourier transform, obtains each data block and the correlation result of local reproduction signal.
Step 7, compare the size of peak value in odd number group matrix of consequence and even number set matrix of consequence, extract big peak value as inspection
Measured value；
Step 8, judge whether detected value has reached detection threshold, if detected value has reached the detection threshold of setting, catch
Succeed, otherwise perform step 9；
Here detection threshold is set according to signal strength and demand, and the judgement in the present invention to signal detection has used peak value
With the ratio of average value, it is 4 to set detection threshold according to standard empirical.
After acquisition success, according to peak value position in a matrix can obtain the Doppler frequency shift and ranging code phase of signal
Position.Realize and determine satellite-signal NH code phases while ranging code phase and carrier frequency is captured.
Step 9, if cycle-index is less than 20 times, data, that is, j of delay 1ms adds 1, performs step 4, otherwise judges capture
Failure.
The above is only the preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art
For member, without departing from the principle of the present invention, modification made for the present invention is within the scope of the present invention.
Claims (7)
1. a kind of Big Dipper B1I weak signal catching methods of feature based sequence, include the following steps：
(1) the characteristic length k of NH codes in Big Dipper B1I signals is calculated, and it is K to set characteristic sequence length according to this feature length k,
And from NH codes successively intercepted length be K 20 characteristic sequences, composition characteristic sequence library CK, wherein k≤K≤20, it is fallen into a trap
The step of realizing of the characteristic length k of NH codes is in calculation Big Dipper B1I signals：
(1a) inputs the specific value of secondary coding sequence；
(1b) sequence length NsRepresent, k represents longest continuous 1 or 0 number in the sequence；
(1c) obtains a N with the subsequence that length is ksThe Metzler matrix of × k is often capable that one is moved to left on the basis of lastrow；
The Correlation series of (1d) calculating matrix M, check in matrix M whether there is identical row, if any two row is
Identical, then k values are increased by 1, repeat step (1c) structure Metzler matrix, is identical until not having any two row in matrix M, obtains
To the characteristic length k=7 of the NH code sequences；
(2) Big Dipper B1I digital medium-frequency signals are inputted, any N milliseconds of data, N >=K+20 are read from the digital medium-frequency signal；
(3) parity packet is carried out by millisecond to the data of the reading, respectively obtains the odd number group S comprising N number of data blockodd=
{D1,D2,...,Di,...,DNAnd even number set Seven={ E1,E2,...,Ei,...,EN, wherein DiRepresent in odd number group i-th
Data block, EiRepresent i-th of data block in even number set, the data volume of 0.5ms is included in each data block；
(4) carry out NH demodulation and demodulating data block adds up：
(4a) is from the odd number group SoddWith even number set SevenIn j-th of data BOB(beginning of block), respectively sequentially extract K data block, its
Middle j is labelled amount, is recorded in every group from which data BOB(beginning of block) extraction data block；
Every group of K extracted data block is multiplied by characteristic sequence storehouse C by (4b)KIn first characteristic sequence respective value, obtain K
Odd number group demodulating data block and K even number set demodulating data block；
K demodulating data block in every group is corresponded to position and added up by (4c), obtains odd data block and even data block：
Wherein SoIt is the odd data block that corresponding position is added up after the K data block extracted in odd number group carries out NH demodulation, Se
It is the even data block that corresponding position is added up after the K data block extracted in even number set carries out NH demodulation, CK1(n) C is representedK
In n-th NH code in first characteristic sequence；
(5) to the SoAnd SeRespectively carry out odd even zero padding, when obtaining the odd number block of a length of 1ms and when a length of 1ms even numbered blocks；
(6) when will be described the odd number block of a length of 1ms and when a length of 1ms even numbered blocks carried out respectively with local reproduction signal based on fast
The parallel related operation of fast Fourier transformation, obtains odd number group matrix of consequence and even number set matrix of consequence；
(7) size of peak value in odd number group matrix of consequence and even number set matrix of consequence is compared, it is detected value to extract big peak value；
(8) judge whether the detected value has reached detection threshold, if detected value has reached the detection threshold of setting, be captured as
Work(, otherwise performs step (9)；
(9) if cycle-index is less than 20 times, data, that is, j of delay 1ms adds 1, performs step (4), otherwise judges capture failure.
A kind of 2. Big Dipper B1I weak signal catching methods of feature based sequence according to claim 1, it is characterised in that
20 characteristic sequences that intercepted length described in step (1) is K, refer to successively since t-th of chip of NH code sequences, cut
The length taken be K subsequence, wherein t=1,2 ... ..., 20.
3. a kind of Big Dipper B1I weak signals catching method of feature based sequence according to claim 1 is it is characterized in that, step
Suddenly the parity packet described in (3) is：By read data in units of 1ms, the data of every 1ms are divided into two parts, it is preceding
The data of 0.5ms are a data block in odd number group, and the data of rear 0.5ms are a data block in even number set.
A kind of 4. Big Dipper B1I weak signal catching methods of feature based sequence according to claim 1, it is characterised in that
Labelled amount j described in step (4a), need to ensure that its value meets j+19+K≤N when using for the first time.
A kind of 5. Big Dipper B1I weak signal catching methods of feature based sequence according to claim 1, it is characterised in that
K data block described in step (4b) is multiplied by characteristic sequence storehouse CKIn first characteristic sequence respective value, concretely comprise the following steps：
For the K data block extracted from every group, the data of wherein nth data block are multiplied by CKIn first characteristic sequence CK1's
N-th of NH code, obtains demodulating data block, wherein 1≤n≤K.
A kind of 6. Big Dipper B1I weak signal catching methods of feature based sequence according to claim 1, it is characterised in that
Odd even zero padding described in step (5), carries out as follows：
(5a) to odd data block, behind data block zero padding to when a length of 1ms data volume；
(5b) dual numbers data block, before data block zero padding to when a length of 1ms data volume.
A kind of 7. Big Dipper B1I weak signal catching methods of feature based sequence according to claim 1, it is characterised in that
The parallel related operation based on Fast Fourier Transform (FFT) is carried out with local reproduction signal described in step (6), as follows
Generation：
(6a) generates same phase carrier wave and quadrature carrier respectively using the sin functions in matlab softwares and cos functions, wherein locally
Carrier frequency need to be with step-length fstep, traversal IF frequency fIFNeighbouring Doppler frequency shift scope [fmin,fmax] in all frequencies,
fmin, fmaxThe respectively lower and upper limit of Doppler frequency shift；
(6b) is multiplied by the same of generation respectively according to Big Dipper B1I signal ranging code structural generations local ranging code with local ranging code
Phase carrier wave and quadrature carrier, obtain modulated same phase carrier wave and modulated quadrature carrier；
(6c) samples modulated same phase carrier wave and modulated quadrature carrier, the satellite letter that sample frequency will and be read
Number sample frequency it is consistent；
(6d) makees the sampled data of modulated quadrature carrier using the sampled data of modulated same phase carrier wave as real part
For imaginary part, local reproduction signal is obtained；
(6e) carries out Fast Fourier Transform (FFT) to local reproduction signal, obtains the frequency domain data of local reproduction signal；
(6f) carries out Fast Fourier Transform (FFT) to data block, obtains the frequency domain data of data block；
The frequency domain data of local reproduction signal is taken the frequency domain data that data block is multiplied by after complex conjugate by (6g), then by multiplied result
Inverse fast Fourier transform is carried out, obtains each data block and the correlation result of local reproduction signal.
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| CN107991695A (en) * | 2017-11-07 | 2018-05-04 | 南京航空航天大学 | Big Dipper weak signal catching method based on zero padding algorithm and differential coherence algorithm |
| CN110108307A (en) * | 2019-05-17 | 2019-08-09 | 北京邮电大学 | A kind of terrible imaging method of adjustable orthogonalization depth |
| CN112987041B (en) * | 2019-12-13 | 2024-05-14 | 深圳开阳电子股份有限公司 | Bit synchronization method and device under weak signal and computer storage medium |
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