CN105759288A - Feature sequence-based Beidou B1I weak signal acquisition method - Google Patents
Feature sequence-based Beidou B1I weak signal acquisition method Download PDFInfo
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Abstract
The invention provides a feature sequence-based Beidou B1I weak signal acquisition method, so as to solve technical problems that the existing Beidou B1I weak signal acquisition method is low in acquisition efficiency and poor in acquisition ability. The method comprises the following steps: 1, a feature sequence length is set, and a feature sequence library is acquired; 2, Beidou B1I digital intermediate frequency signals are read; 3, parity grouping is carried out on the read data according to milliseconds; 4, the feature sequence is used for NH demodulation, and groups of demodulation data blocks are accumulated; 5, parity zero padding is carried out; 6, local replication signals are generated for correlation operation; 7, the peak values in correlation results are compared, and a detection value is extracted; 8, a threshold is judged, if the detection value is lower than the threshold, the step 9 is carried out, or, the process is over; and 9, circulation is judged, if the circulation times are lower than 20, data with 1ms delay are read, the step 4 is carried out, or, the process is over. The method of the invention can be used for acquiring Beidou B1I weak signals and is high in acquisition performance and quick in acquisition speed.
Description
Technical field
The invention belongs to technical field of satellite navigation, relate to the catching method of a kind of satellite-signal, be specifically related to the Big Dipper B1I weak signal catching method of a kind of feature based sequence, it is adaptable to catching of Big Dipper B1I weak signal.
Technical background
Satellite navigation location is most widely used navigator fix mode in modern society, and global four large satellite navigation system have the Beidou satellite navigation system of the GPS of the U.S., Muscovite GLONASS, the Galileo of European Union and China at present.No. two satellite navigation systems of the Big Dipper that China is building, to provide the omnibearing worldwide navigation positioning service in sea, land and sky for target, have succeeded in sending up 21 Beidou navigation satellites at present, have constantly strided forward to Big Dipper system global networking.
Big Dipper B1I signal broadcast D1 navigation message, D1 navigation message speed is 50bps, and is modulated with the secondary coding that speed is 1kbps, and its secondary coding adopts Neumann-Hoffman code (being called for short NH code).One information bit width of D1 navigation message is 20 milliseconds, and the ranging code cycle is 1 millisecond, adopts NH code (00000100110101001110) and navigation information code and the ranging code synchronous modulation of 20 bits.For this every 1 bit navigation information code corresponding NH code cycle, in every 1 bit NH code corresponding ranging code cycle, this makes have bit saltus step to be likely in every 1 millisecond of navigation data.
Catch, be search satellites in view, and determine the carrier frequency of satellite-signal and the process of ranging code phase place roughly.The dependency feature that need to utilize ranging code realizes, the satellite-signal being about to input carries out related operation with receiver this locality reproduction signal, operation result peak value and thresholding are compared, to determine whether to capture satellite, and determines carrier frequency and ranging code phase place according to peak value position.But in the complex environments such as jungle, indoor, tunnel, signal energy can seriously undermine due to factors such as multipath reflection, barrier block, is made directly relevant treatment and cannot capture this type of weak signal.Now need to extend the related operation time, correlation result is accumulated and reaches sufficiently large storage gain, to capture satellite-signal.
Traditional method catching weak signal mainly has coherent integration method and non-coherent integration method.Coherent integration method is to be added up the correlation result correspondence position in multiple continuous print ranging code cycles, improves signal gain, but due to navigation information code saltus step, there is the situation that accumulated value is cancelled out each other, and storage gain is decayed, and limits integration duration.Non-coherent integration method, will be added after correlation result delivery, eliminates navigation information code saltus step impact with this, but in delivery process, noise has been carried out square operation, introduce new noise, weakens output signal-to-noise ratio, bring Square loss.For Big Dipper B1I signal, exist navigation information code saltus step simultaneously as the existence of secondary coding, each millisecond has the possibility of bit saltus step, and said method directly use can bring bigger gain loss, therefore cannot be directly used to catching of Big Dipper B1I weak signal.
In order to reduce the impact that weak signal is caught by secondary coding, it is typically employed on the basis of tradition catching method to increase the demodulating process to NH code and realize, it is specially likely the combining of NH code sequence that circulation repeatedly traversal length is 20 bits and carries out related operation, choose the peak value in all correlation result and carry out prize judgment.But this type of method can increase amount of calculation in the process of the traversal 20 bit NH all combinations of code sequence, causes that acquisition speed reduces.Such as Chinese patent application, application publication number CN102928853A, denomination of invention is " a kind of method catching Big Dipper D1 satellite navigation system weak signal ", discloses a kind of method catching Big Dipper D1 satellite navigation system weak signal.First weak signal is carried out ranging code phase place, Doppler frequency two-dimensional search by the method, then carry out coherent integration and collect 20 coherent integration results, choose a kind of NH sequence, it is multiplied one by one with 20 integral results, and carries out non-coherent integration, repeat the above steps, until 20 kinds of NH secondary coding sequence traversals are complete, maximum carries out thresholding judge to determine whether to capture signal, when reaching to exist NH secondary coding, obtain the effect that higher processing gain reaches.Though this invention can peel off NH secondary coding, but all combinations of the NH code sequence needing searching loop length to be 20 realize demodulation, computationally intensive, catch the process time long.
Summary of the invention
It is an object of the invention to the deficiency overcoming above-mentioned prior art to exist, propose the Big Dipper B1I weak signal catching method of a kind of feature based sequence, for solving the technical problem that capture rate is low and capture ability is poor existed in existing Big Dipper B1I weak signal catching method.
The basic ideas that the present invention realizes are: by the conceptual expansion in linear generating space to NH code, choose the characteristic sequence of certain length in NH code, carry out NH demodulation fast and effectively, eliminate the NH code polarity saltus step restriction to integration duration, to determine the phase place of satellite-signal NH code while determining signal ranging code phase place and Doppler frequency shift.And every 1ms navigation data is carried out parity packet computing, avoid related operation duration Nepit to reverse with this, and can then carry out odd even zero padding by directly cumulative for the data block after NH demodulation, utilize fast Fourier transform to carry out parallel related operation, reduce operand, improve arithmetic speed.
According to above technical thought, it is achieved the technical scheme that the object of the invention adopts, comprise the steps:
Step 1, according to the characteristic length k of NH code in the Big Dipper B1I signal of calculating gained, arranging characteristic sequence length is K, and intercepted length is 20 characteristic sequences of K successively from NH code, composition characteristic sequence library CK, wherein k≤K≤20；
Step 2, inputs Big Dipper B1I digital medium-frequency signal, reads any N millisecond data, N >=K+20 from this digital medium-frequency signal；
The data of described reading are carried out parity packet by millisecond, respectively obtain the odd number group S comprising N number of data block by step 3odd={ D1,D2,...,Di,...,DNAnd even number set Seven={ E1,E2,...,Ei,...,EN, wherein DiRepresent i-th data block in odd number group, EiRepresent i-th data block in even number set, each data block comprises the data volume of 0.5ms；
Step 4, carries out NH demodulation and demodulating data block adds up:
Step 4a) from described odd number group SoddWith even number set SevenMiddle jth data block starts, and sequentially extracts respectively K data block, and wherein j is labelled amount, records and often from which data block starts to extract data block in group；
Step 4b) K the data block often organizing extraction is multiplied by characteristic sequence storehouse CKIn the respective value of first characteristic sequence, obtain K odd number group demodulating data block and K even number set demodulating data block；
Step 4c) is added up in K demodulating data block correspondence position in often group, obtain odd data block and even data block:
Wherein SoBeing after K the data block extracted in odd number group carries out NH demodulation, add up the odd data block obtained in corresponding position, SeBeing after K the data block extracted in even number set carries out NH demodulation, add up the even data block obtained in corresponding position, CK1N () represents CKIn n-th NH code in first characteristic sequence；
Step 5, to described SoAnd SeCarry out odd even zero padding respectively, obtain odd number block that duration is 1ms and duration is the even numbered blocks of 1ms；
Step 6, carries out the parallel related operation based on fast Fourier transform with this locality reproduction signal respectively by odd number block and the even numbered blocks that duration is 1ms that described duration is 1ms, obtains odd number group matrix of consequence and even number set matrix of consequence；
Step 7, compares the size of peak value in odd number group matrix of consequence and even number set matrix of consequence, and extracting big peak value is detected value；
Step 8, it is judged that whether described detected value has reached detection threshold, if detected value has reached the detection threshold set, then acquisition success, otherwise performs step 9；
Step 9, if cycle-index is lower than 20 times, then the data and the j that postpone 1ms add 1, perform step (4), otherwise judge to catch unsuccessfully.
The present invention compared with prior art, has the advantage that
1) due to the fact that when carrying out NH demodulation, it is multiplied with packet data block by characteristic sequence that length is K and realizes, and the value of K is be more than or equal to the characteristic length of NH code and less than or equal to 20, repeatedly travel through compared with the NH code that length is 20 likely combines the method carrying out NH demodulation with the circulation adopted in prior art, reduce the amount of calculation in demodulating process, thus improve acquisition speed.
2) every 1ms data have been carried out parity packet by the present invention, and odd number group and even number set are demodulated and related operation respectively, necessarily having one group in such odd even group is do not comprise bit reversal, avoid the higher bit Overturn ratio weakening to storage gain during long-time related operation in prior art, improve signal-detection probability, more efficient complete catching of Big Dipper B1I weak signal, effectively improve acquisition performance.
3) the characteristic sequence length K arranged in the present invention, can select different K values according to specific environment in its span, be suitable for catching of varying strength weak signal, further increase acquisition performance.
Accompanying drawing explanation
Fig. 1 is the FB(flow block) of the present invention；
Fig. 2 is the parity packet schematic diagram in the present invention to data streams read；
Fig. 3 is the zero padding schematic diagram of odd data block and even data block in the present invention.
Detailed description of the invention
Below in conjunction with the drawings and specific embodiments, the technical scheme that the present invention is taked is further described:
With reference to accompanying drawing 1, the enforcement step of the present invention is as follows:
Step 1, according to the characteristic length k of NH code in the Big Dipper B1I signal of calculating gained, arranging characteristic sequence length is K, and intercepted length is 20 characteristic sequences of K successively from NH code, composition characteristic sequence library CK, wherein k≤K≤20.
The wherein characteristic length k and characteristic sequence storehouse C of NH codeK, it is the conceptual expansion in linear generating space to NH code will obtain, wherein the length in the linear generating space of NH code is called characteristic length.It is definite value for its characteristic length of same sequence, can directly use after once calculating.For the NH code adopted in Big Dipper B1I signal, calculating its characteristic length k=7, characteristic length k is obtained by following steps:
Step 1a) input the concrete value of secondary coding sequence, for Big Dipper B1I signal, its NH sequence is (00000100110101001110)；
Step 1b) sequence length NsRepresenting, k represents the number of continuous print 1 or 0 the longest in this sequence；
Step 1c) obtain a N with the subsequence that length is ksThe Metzler matrix of × k, each row moves to left one on lastrow basis；
Step 1d) calculate the Correlation series of matrix M, check in matrix M whether have identical row, if it is identical for having any two row, then k value is increased by 1, repeat step 1c and build Metzler matrix, until it is identical for not having any two row in matrix M, obtain the characteristic length k=7 of this NH code sequence；
Characteristic sequence storehouse is the set of some characteristic sequences, characteristic sequence storehouse CKGenerated by following steps: first characteristic sequence length K, k≤K≤20 are set, from NH sequence, then sequentially shift the subsequence that intercepted length is K, 20 sub-sequences form characteristic sequence storehouse CK={ CK1,CK2,...,CKi,...,CK20}.Wherein CKFor the characteristic sequence storehouse that characteristic sequence length is during K, CKiExpression starts from NH code i-th chip, and length is the subsequence of K, and these subsequences are called the characteristic sequence of NH code.Because NH code sequence length is 20 in Big Dipper B1I signal, so by 20 characteristic sequence composition characteristic sequence libraries.
When arranging K value, different length can be selected according to specific environment in its span, to adapt to catching of the weak signal of varying strength.
Step 2, inputs Big Dipper B1I digital medium-frequency signal, reads any N millisecond data, N >=K+20 from this digital medium-frequency signal.
Wherein, the Big Dipper B1I digital medium-frequency signal of input, is the Big Dipper B1I signal adopting receiver to receive, and obtains after radio frequency amplification, down coversion and sampling processing.
The data read are carried out parity packet by millisecond, respectively obtain the odd number group S comprising N number of data block by step 3odd={ D1,D2,...,Di,...,DNAnd even number set Seven={ E1,E2,...,Ei,...,EN, wherein DiRepresent i-th data block in odd number group, EiRepresent i-th data block in even number set, each data block comprises the data volume of 0.5ms.
Wherein the data of reading are carried out parity packet by millisecond, concrete operations are: by the data of reading in units of 1ms, it is a data block in odd number group that the data of every 1ms are divided into two parts, the data of front 0.5ms, and the data of rear 0.5ms are a data block in even number set.Concrete parity packet schematic diagram such as Fig. 2.
The data of every 1ms carry out parity packet can avoid owing to bit reversal is on catching the impact brought.Because for Big Dipper B1I signal, owing to NH code is modulated, every 1ms data have the possibility of bit reversal, and after carrying out 1 millisecond of parity packet, necessarily having one group of data is do not comprise bit reversal.
Step 4, carries out NH demodulation and demodulating data block adds up:
Step 4a) from odd number group SoddWith even number set SevenMiddle jth data block starts, and sequentially extracts respectively K data block, and wherein j is labelled amount, records and often from which data block starts to extract data block in group；
Step 4b) K the data block often organizing extraction is multiplied by characteristic sequence storehouse CKIn the respective value of first characteristic sequence, obtain K odd number group demodulating data block and K even number set demodulating data block；
Step 4c) is added up in K demodulating data block correspondence position in often group, obtain odd data block and even data block:
Wherein SoBeing after K the data block extracted in odd number group carries out NH demodulation, add up the odd data block obtained in corresponding position, SeBeing after K the data block extracted in even number set carries out NH demodulation, add up the even data block obtained in corresponding position, CK1N () represents CKIn n-th NH code in first characteristic sequence；
Wherein labelled amount j, when first time uses, its value meets j+19+K≤N, it is to avoid when needing repeatedly to circulate, extracted data block exceedes the situation reading data volume.
Wherein the process of NH demodulation is particularly as follows: for K data block of extraction from often group, be multiplied by C by the data of wherein nth data blockKIn first characteristic sequence CK1The n-th NH code, obtain demodulating data block, 1≤n≤K.
Step 5, to SoAnd SeCarry out odd even zero padding respectively, obtain odd number block that duration is 1ms and duration is the even numbered blocks of 1ms.
Wherein odd even zero padding carries out as follows, concrete schematic diagram such as Fig. 3:
Step 5a) to odd data block So, after data block, zero padding to duration is the data volume of 1ms；
Step 5b) dual numbers data block Se, before data block, zero padding to duration is the data volume of 1ms；
Step 6, carries out the parallel related operation based on fast Fourier transform with this locality reproduction signal respectively by odd number block and the even numbered blocks that duration is 1ms that duration is 1ms, obtains odd number group matrix of consequence and even number set matrix of consequence, and related operation step is as follows:
Step 6a) utilize the sin function in matlab software and cos function to generate homophase carrier wave and quadrature carrier respectively, wherein local carrier frequency need to step-length fstep, travel through IF-FRE fIFNeighbouring Doppler frequency shift scope [fmin,fmax] in all frequencies, fmin, fmaxThe respectively lower limit of Doppler frequency shift and the upper limit, desirable f herestep=500Hz, fmin=-10KHz, fmax=10KHz, fIFIF-FRE according to input signal is determined；
Step 6b) according to Big Dipper B1I signal ranging code structural generation this locality ranging code, it is multiplied by homophase carrier wave and the quadrature carrier of generation, the homophase carrier wave after being modulated and the quadrature carrier after modulation respectively with local ranging code；
Step 6c) quadrature carrier after the homophase carrier wave after modulation and modulation to be sampled, sample frequency wants consistent with the sample frequency of the satellite-signal read；
Step 6d) using the sampled data of the homophase carrier wave after modulation as real part, using the sampled data of the quadrature carrier after modulation as imaginary part, obtain local reproduction signal.
Step 6e) this locality reproduction signal is carried out fast Fourier transform, obtain the frequency domain data of local reproduction signal；
Step 6f) data block is carried out fast Fourier transform, obtain the frequency domain data of data block；
Step 6g) this locality is reappeared the frequency domain data being multiplied by data block after the frequency domain data of signal takes complex conjugate, then multiplied result is carried out inverse fast Fourier transform, obtain the correlation result of each data block and local reproduction signal.
Step 7, compares the size of peak value in odd number group matrix of consequence and even number set matrix of consequence, and extracting big peak value is detected value；
Step 8, it is judged that whether detected value has reached detection threshold, if detected value has reached the detection threshold set, then acquisition success, otherwise performs step 9；
Here detection threshold is according to signal intensity and requirements set, and the judgement of signal detection employs in the present invention ratio of peak value and meansigma methods, and arranging detection threshold according to standard empirical is 4.
After acquisition success, according to peak value position in a matrix can obtain Doppler frequency shift and the ranging code phase place of signal.Realize while catching ranging code phase place and carrier frequency, determine satellite-signal NH code phase.
Step 9, if cycle-index is lower than 20 times, then the data and the j that postpone 1ms add 1, perform step 4, otherwise judge to catch unsuccessfully.
The above is only the preferred embodiment of the present invention, it is noted that for those skilled in the art, under the premise without departing from the principles of the invention, and amendment made for the present invention is all in protection scope of the present invention.
Claims (8)
1. a Big Dipper B1I weak signal catching method for feature based sequence, comprises the steps:
(1) according to the characteristic length k of NH code in the Big Dipper B1I signal of calculating gained, arranging characteristic sequence length is K, and intercepted length is 20 characteristic sequences of K successively from NH code, composition characteristic sequence library CK, wherein k≤K≤20；
(2) input Big Dipper B1I digital medium-frequency signal, reads any N millisecond data, N >=K+20 from this digital medium-frequency signal；
(3) data of described reading are carried out parity packet by millisecond, respectively obtain 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 data block in odd number group, EiRepresent i-th data block in even number set, each data block comprises the data volume of 0.5ms；
(4) carry out NH demodulation and demodulating data block add up:
(4a) from described odd number group SoddWith even number set SevenMiddle jth data block starts, and sequentially extracts respectively K data block, and wherein j is labelled amount, records and often from which data block starts to extract data block in group；
(4b) K the data block often organizing extraction is multiplied by characteristic sequence storehouse CKIn the respective value of first characteristic sequence, obtain K odd number group demodulating data block and K even number set demodulating data block；
(4c) is added up in K demodulating data block correspondence position in often group, obtains odd data block and even data block:
Wherein SoBeing after K the data block extracted in odd number group carries out NH demodulation, add up the odd data block obtained in corresponding position, SeBeing after K the data block extracted in even number set carries out NH demodulation, add up the even data block obtained in corresponding position, CK1N () represents CKIn n-th NH code in first characteristic sequence；
(5) to described SoAnd SeCarry out odd even zero padding respectively, obtain odd number block that duration is 1ms and duration is the even numbered blocks of 1ms；
(6) odd number block and the even numbered blocks that duration is 1ms that described duration is 1ms are carried out the parallel related operation based on fast Fourier transform with this locality reproduction signal respectively, obtain odd number group matrix of consequence and even number set matrix of consequence；
(7) comparing the size of peak value in odd number group matrix of consequence and even number set matrix of consequence, extracting big peak value is detected value；
(8) judge whether described detected value has reached detection threshold, if detected value has reached the detection threshold set, then acquisition success, otherwise perform step (9)；
(9) if cycle-index is lower than 20 times, then the data and the j that postpone 1ms add 1, perform step (4), otherwise judge to catch unsuccessfully.
2. the Big Dipper B1I weak signal catching method of a kind of feature based sequence according to claim 1, it is characterised in that the characteristic length k of the NH code described in step (1), is calculated according to following steps:
(1a) the concrete value of secondary coding sequence is inputted；
(1b) sequence length NsRepresenting, k represents the number of continuous print 1 or 0 the longest in this sequence；
(1c) N is obtained with the subsequence that length is ksThe Metzler matrix of × k, each row moves to left one on lastrow basis；
(1d) Correlation series of matrix M is calculated, check in matrix M whether have identical row, if it is identical for having any two row, then k value is increased by 1, repeat step (1c) and build Metzler matrix, until it is identical for not having any two row in matrix M, obtain the characteristic length k=7 of this NH code sequence.
3. the Big Dipper B1I weak signal catching method of a kind of feature based sequence according to claim 1, it is characterized in that, described in step (1) intercepted length is K 20 characteristic sequence, refer to successively from the t chip of NH code sequence, the subsequence that length is K intercepted, wherein t=1,2, ..., 20.
4. the Big Dipper B1I weak signal catching method of a kind of feature based sequence according to claim 1 is characterized in that, parity packet described in step (3) is: by the data that read in units of 1ms, the data of every 1ms are divided into two parts, the data of front 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.
5. the Big Dipper B1I weak signal catching method of a kind of feature based sequence according to claim 1, it is characterised in that labelled amount j described in step (4a), first time need to ensure that its value meets j+19+K≤N when using.
6. the Big Dipper B1I weak signal catching method of a kind 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 the respective value of first characteristic sequence, concretely comprise the following steps: for K the data block extracted from often group, the data of wherein nth data block are multiplied by CKIn first characteristic sequence CK1The n-th NH code, obtain demodulating data block, wherein 1≤n≤K.
7. the Big Dipper B1I weak signal catching method of a kind of feature based sequence according to claim 1, it is characterised in that the odd even zero padding described in step (5), carries out as follows:
(5a) to odd data block, after data block, zero padding to duration is the data volume of 1ms；
(5b) dual numbers data block, before data block, zero padding to duration is the data volume of 1ms.
8. the Big Dipper B1I weak signal catching method of a kind of feature based sequence according to claim 1, it is characterized in that, described in step (6) with this locality reappear signal carry out the parallel related operation based on fast Fourier transform, as follows generate:
(6a) utilizing the sin function in matlab software and cos function to generate homophase carrier wave and quadrature carrier respectively, wherein local carrier frequency need to step-length fstep, travel through IF-FRE fIFNeighbouring Doppler frequency shift scope [fmin,fmax] in all frequencies, fmin, fmaxThe respectively lower limit of Doppler frequency shift and the upper limit；
(6b) according to Big Dipper B1I signal ranging code structural generation this locality ranging code, homophase carrier wave and the quadrature carrier of generation, the homophase carrier wave after being modulated and the quadrature carrier after modulation it are multiplied by respectively with local ranging code；
(6c) quadrature carrier after the homophase carrier wave after modulation and modulation being sampled, sample frequency wants consistent with the sample frequency of the satellite-signal read；
(6d) using the sampled data of the homophase carrier wave after modulation as real part, using the sampled data of the quadrature carrier after modulation as imaginary part, local reproduction signal is obtained.
(6e) this locality is reappeared signal and carry out fast Fourier transform, obtain the frequency domain data of local reproduction signal；
(6f) data block is carried out fast Fourier transform, obtain the frequency domain data of data block；
(6g) this locality is reappeared the frequency domain data being multiplied by data block after the frequency domain data of signal takes complex conjugate, then multiplied result is carried out inverse fast Fourier transform, obtain the correlation result of each data block and local reproduction signal.
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