CN102520423B - Rapid capturing method for Circuit for rapidly capturing long period pseudo random spread spectrum code of satellite navigation receiver and capturing method thereof - Google Patents

Abstract

The invention discloses a circuit for rapidly capturing a long period pseudo random spread spectrum code of a satellite navigation receiver and a capturing method thereof. The circuit comprises: a data preprocessing module, a sampling data control module, a frequency mixing module, a local spread spectrum code generation module and a single capturing engine. The single capturing engine comprises: a local spread spectrum code memory, a first stage coherent integral module, a first stage coherent data memory, a second stage coherent integral module, a third stage incoherent integral module and a threshold control comparison module. An output terminal of the data preprocessing module is connected with an input terminal of the frequency mixing module through the sampling data control module. The output terminal of the frequency mixing module is connected with one input terminal of the first stage coherent integral module. The local spread spectrum code generation module is connected with another input terminal of the first stage coherent integral module. The circuit of the invention has the following characteristics that: integral gain is high; an anti-electromagnetism interference ability is strong; a capturing sensitivity is high; capturing precision is high; a capturing false alarm rate is low; a capturing speed is fast; reliability is high. And there are many other characteristics.

Description

The quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver

Technical field

The present invention relates to a kind of fast Acquisition circuit and catching method thereof of long period pseudo random spread spectrum code of satellite navigation receiver.

Background technology

At present there are " Big Dipper " and the Galileo of European Union of the GPS of the U.S., Muscovite GLONASS (Global Navigation Satellite System), China in built and non-geo satellite system that building in the world, and Japanese and India has also proposed navigational satellite system plan separately.

Satellite navigation location can catching by civilian C/A code and military P (Y) yard, this dual mode is realized, C/A code code length is short, the time that realization is caught is shorter, catching because its code length is very long of P code, the time that realization is caught is longer, and generally catching of P code is to utilize the guiding of C/A code to complete.At first the user captures the C/A code, then utilize the precise time information be modulated at the navigation message on the C/A code and provide to complete catching the P code, the advantage of this mode is: both utilized the high characteristics of P code bearing accuracy, avoided again the long shortcoming of P code capture time.But there is very large defective in this mode when being used for more strongly disturbing application scenarios is arranged, because the cycle of C/A code is short, bit rate is low, therefore is easy to be disturbed, and under strongly disturbing channel condition, is difficult to guide by the C/A code capture the P code.Therefore the satellite navigation and location system of P code Direct Acquisition technology in noisy electromagnetic environment has great significance.

But the bit rate of P code is up to 10.23MHz, in the time of 1ms, error will increase the hunting zone of 20460 code phases, this makes the hunting zone of code phase in the Direct Acquisition of P code very large, then considers the sampling rate more than 4 times, needs data volume to be processed huge especially.And the cycle of P code reaches a couple of days, and causing is aperiodic in essence in acquisition procedure, and this has brought very large difficulty also for the Direct Acquisition of P code, realizes having increased difficulty also just for simultaneously the hardware of P code Direct Acquisition.Direct Acquisition for the P code has carried out a large amount of research both at home and abroad, and existing achievement in research mainly comprises XFAST algorithm, the direct method of average, the overlapping method of average, makes FFT and segmented matched filter method etc. based on the part correlation of going here and there and being correlated with.The XFAST algorithm accelerated the search speed of code phase, yet when PN code overlap-add can make the synchronous code phase place, the signal-to-noise ratio degradation of gained relevant peaks caused the acquisition performance variation by with local PN code overlap-add; Directly the method for average has identical basic thought with the overlapping method of average, be about to receive the every S of a signal sampling point addition, local PN code is done same the processing, adopts FFT and IFFT to realize spectrum correlation, compares related operation FFT used with the XFAST algorithm and counts and greatly reduce, saved hardware resource, yet during the synchronous code phase place, the relevant peaks signal-to-noise ratio degradation is larger than XFAST, must adopt repeatedly cumulative technology to compensate, cause mean acquisition time elongated.When carrier wave frequency deviation is larger, in order to overcome it to the impact of relevant peaks, the XFAST algorithm, directly the method for average and the overlapping method of average all must adopt frequency domain frequency sweep or time domain sweep frequency technique, thisly must make mean acquisition time become greatly at frequency deviation and code phase two-dimensional search one by one.Compare with the segmented matched filter method, have larger anti-carrier wave frequency deviation ability based on the part correlation of going here and there and being correlated with as FFT, and carry out simultaneously the search of carrier doppler frequency deviation in the searching code phase place, be conducive to improve acquisition speed.

Summary of the invention

The object of the invention is to solve the deficiency of existing long period pseudorandom spread spectrum code capture circuit and method thereof, a kind of fast Acquisition circuit and catching method thereof of novel long period pseudo random spread spectrum code of satellite navigation receiver are provided, the signal-to-noise ratio degradation of relevant peaks when overcoming traditional XFAST algorithm PN code overlap-add and making the synchronous code phase place, acquisition performance is poor; Directly the method for average and the overlapping method of average have been saved hardware resource, but the relevant peaks signal-to-noise ratio degradation is even more serious, must adopt repeatedly cumulative technology to compensate, and mean acquisition time is long; And traditional catching method storage gain is low, poor signal to noise, and anti-electromagnetic interference capability is poor, and acquisition sensitivity is poor, acquisition speed is slow and the shortcoming such as poor reliability.

The objective of the invention is to be achieved through the following technical solutions: the fast Acquisition circuit of long period pseudo random spread spectrum code of satellite navigation receiver, be connected with the output terminal of A/D converter, it comprises data preprocessing module, sampled data control module, frequency mixing module, local spreading code generation module and single capture engine, and single capture engine comprises local spreading code storer, first order coherent integration module, first order coherence data storer, second level coherent integration module, third level non-coherent integration module and thresholding control comparison module; The output terminal of data preprocessing module is connected with the input end of frequency mixing module by the sampled data control module, the output terminal of frequency mixing module is connected with an input end of first order coherent integration module, local spreading code generation module is connected by local spreading code storer another input end with first order coherent integration module, and the output terminal of first order coherent integration module is connected by the input end that first order coherence data storer, second level coherent integration module and third level non-coherent integration module and thresholding are controlled comparison module successively.

The present invention also comprises a sampled data storer, and the sampled data storer is connected with the sampled data control module.

The quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver, it comprises the following steps:

(1) satellite navigation receiver antenna receives satellite navigation signals, and the satellite navigation signals that receives is transferred to the radio frequency down-conversion device carries out down-converted, and the signal after down-converted is converted to digital medium-frequency signal through A/D converter again;

(2) digital medium-frequency signal enters the data preprocessing module of capturing unit, and data preprocessing module is adjusted into the stationary conduit number with digital medium-frequency signal and reaches the fixedly data of bit wide;

(3) data after data preprocessing module is processed enter the sampled data control module and carry out segmentation control processing, and the sampled data control module is divided into Y*Z data block with sampled data, and each data block comprises that X data number of samples is according to being designated as S _i(n), wherein, i=0,1 ..., Y*Z-1, n=0,1 ..., X-1, data block is stored in the sampled data storer;

(4) data transmission to the frequency mixing module after the sampled data control module is processed is carried out down coversion and is gone intermediate frequency process, produces the I/Q orthogonal data, is designated as respectively:

Is _i(n)＝S _i(n)*sin(2π*f _I*m*t _s)，i＝0，1，...，Y*Z-1，n＝0，1，...，X-1；

Qs _i(n)＝S _i(n)*cos(2π*f _I*m*t _s)，i＝0，1，...，Y*Z-1，n＝0，1，...，X-1，

Wherein, f _IBe intermediate frequency carrier frequency, t _sBe the sampling period, which sampled point m is;

(5) the local spread spectrum code sequence that is produced by local spreading code generation module deposits local spreading code storer according to the mode of fragmented storage, and data are designated as: p _i(n), i=0,1 ..., Y*Z-1, n=0,1 ... X-1;

(6) I/Q data and local spread spectrum code sequence are transferred to first order coherent integration module and carry out the segmentation related operation, finish successively the Y*Z section, the data after the first order coherent integration of every section are respectively:

${\mathrm{It}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}{\mathrm{Is}}_i\left(x\right)*p_i\left(x\right),i=\mathrm{0,1},...,Y*Z-1,$

${\mathrm{Qt}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}Q{s}_i\left(x\right)*p_i\left(x\right),i=\mathrm{0,1},...,Y*Z-1,$

Each Y*Z of I/Q two-way related data after first order coherent integration is deposited in first order coherence data storer;

(7) total Y*Z of the value that in first order coherent integration result, phase differential is identical, wherein Z organizes altogether, every group of Y data, every Y data are taken out and transferred to second level coherent integration module and do second level coherent integration from first order coherence data storer, its method is to estimate by the fast Fourier transformation operation power spectrum that Y orders, the value of power spectrum output is the result of coherent accumulation, realizes the two-stage coherent integration:

(It2 _Y*i，It2 _Y*i+1，...，It2 _Y*(i+1)-1)＝fft(It1 _Y*i，It1 _Y*i+1，...，It1 _Y*(i+1)-1)，i＝0，1，...，Z-1，

(Qt2 _Y*i，Qt2 _Y*i+1，...，Qt2 _Y*(i+1)-1)＝fft(Qt1 _Y*i，Qt1 _Y*i+1，...，Qt1 _Y*(i+1)-1)，i＝0，1，...，Z-1；

(8) data transmission to third level non-coherent integration module is carried out third level non-coherent integration, and the I/Q data are asked modular arithmetic, and every Z identical data of Doppler are carried out noncoherent accumulation, obtains altogether Y accumulated value:

${\mathrm{Dt}3}_i=\underset{j=0}{\overset{Z-1}{\mathrm{\Σ}}}[{\left({\mathrm{It}2}_{Y*j+i}\right)}^2+{\left({\mathrm{Qt}2}_{Y*j+i}\right)}^2],i=\mathrm{0,1},...,Y-1;$

(9) data are controlled comparison module through thresholding, complete the calculating of threshold value, thresholding is controlled and is divided into thresholding pattern and maximal value pattern, under the thresholding pattern, and accumulated value and the thresholding of third level non-coherent integration module output is compared, find out maximal value and corresponding phase differential and Doppler's valuation thereof, if find to exist the spectral line that surpasses thresholding, explanation captures code, otherwise adjusts local spreading code generation module, carry out next round and catch, repeating step (6) is to step (9); Under the maximal value pattern, calculated specific Time And Frequency uncertainty, find out maximal value wherein.

Local spreading code storer of the present invention is for table tennis buffer, in order to simultaneously this storer is carried out read/write access.

First order coherent integration of the present invention be calculated as calculated off-line.

In thresholding pattern of the present invention, the calculating of threshold value is to do on average with the correlation of a segment encode sheet nearest before current result of calculation and Doppler frequency lattice, as decision threshold.

In thresholding pattern of the present invention, if find to exist the spectral line that surpasses thresholding during threshold judgement, continue the correlation of the several phase places of calculated for subsequent and Doppler frequency lattice, the correlation several times that goes out greater than correlation and the subsequent calculations of threshold value more for the first time, of getting maximum wherein.

The invention has the beneficial effects as follows:

(1) sampling two-stage coherent integration processing mode, reduced the non-coherent integration loss to greatest extent, improved storage gain, namely improved receiving sensitivity.

(2) increased data preprocessing module, the input data are carried out anti-interference process, wide Bit data is processed, again data bit is reduced to enter trapping module after anti-interference, reduce resource loss, and can be applied to multiple radio frequency scheme, increased the reusability of subsequent captured engine.

(3) after the data of the certain phase differential of every search, just upgrade one section sampled data, carry out the new time difference and frequency difference and calculate, in the dynamic application scenarios of height or fast-changing channel circumstance, frequency difference and the actual value calculated are more approaching, have guaranteed the normal operation of follow-up carrier track.

(4) second level coherent integration adopts FFT (Fast Fourier Transform (FFT)) algorithm to complete, and the operand of FFT is O (Nlog2N+N), than the operand O (N of direct time-domain computing ³) much smaller, save to greatest extent computing time and system resource, and can find simultaneously phase differential and carrier doppler off-set value.

(5) judging threshold is the mean value of the correlation of front nearest a period of time of current result of calculation and Doppler frequency lattice, in the dynamic application scenarios of height or fast-changing channel circumstance, guaranteed that the judging threshold that calculates is real-time, has effectively improved acquisition probability.

(6) when the correlation computations result occurring greater than threshold value, continue the correlation of the several phase places of calculated for subsequent and Doppler frequency lattice, the correlation several times that goes out greater than correlation and the subsequent calculations of threshold value more for the first time, find out a maximum correlation, the phase differential that this correlation is corresponding and Doppler frequency are poor to be only the most accurately, effectively reduces false-alarm probability.

(7) support simultaneously thresholding pattern and maximal value pattern, tackle respectively at signal conditioning good environment and the poor environment of signal conditioning, can reduce capture time in the good environment of signal conditioning, can improve acquisition sensitivity in the poor environment of signal conditioning.

(8) support a plurality of capture engines of exampleization, can be in capturing unit a plurality of capture engines of exampleization, process in the mode of streamline, improved acquisition speed and capture rate.

Description of drawings

Fig. 1 is capture circuit composition frame chart of the present invention;

Fig. 2 is that first order coherent integration is calculated schematic block diagram;

Fig. 3 is that 8 FFT calculate schematic diagram.

Embodiment

further describe technical scheme of the present invention below in conjunction with accompanying drawing: as shown in Figure 1, the fast Acquisition circuit of long period pseudo random spread spectrum code of satellite navigation receiver, be connected with the output terminal of A/D converter, it comprises data preprocessing module, the sampled data control module, frequency mixing module, local spreading code generation module and single capture engine, single capture engine comprises local spreading code storer, first order coherent integration module, first order coherence data storer, second level coherent integration module, third level non-coherent integration module and thresholding are controlled comparison module, it also comprises a sampled data storer, the sampled data storer is connected with the sampled data control module.The output terminal of data preprocessing module is connected with the input end of frequency mixing module by the sampled data control module, the output terminal of frequency mixing module is connected with an input end of first order coherent integration module, local spreading code generation module is connected by local spreading code storer another input end with first order coherent integration module, and the output terminal of first order coherent integration module is connected by the input end that first order coherence data storer, second level coherent integration module and third level non-coherent integration module and thresholding are controlled comparison module successively.

The quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver, it comprises the following steps:

(1) satellite navigation receiver antenna receives satellite navigation signals, and the satellite navigation signals that receives is transferred to the radio frequency down-conversion device carries out down-converted, and the signal after down-converted is converted to digital medium-frequency signal through A/D converter again;

(2) digital medium-frequency signal enters the data preprocessing module of capturing unit, and data preprocessing module is adjusted into the stationary conduit number with digital medium-frequency signal and reaches the fixedly data of bit wide;

(3) data after data preprocessing module is processed enter the sampled data control module and carry out segmentation control processing, and the sampled data control module is divided into Y*Z data block with sampled data, and each data block comprises that X data number of samples is according to being designated as S _i(n), wherein, i=0,1 ..., Y*Z-1, n=0,1 ..., X-1, data block is stored in the sampled data storer;

(4) data transmission to the frequency mixing module after the sampled data control module is processed is carried out down coversion and is gone intermediate frequency process, produces the I/Q orthogonal data, is designated as respectively:

Is _i(n)＝S _i(n)*sin(2π*f _I*m*t _s)，i＝0，1，...，Y*Z-1，n＝0，1，...，X-1；

Qs _i(n)＝S _i(n)*cos(2π*f _I*m*t _s)，i＝0，1，...，Y*Z-1，n＝0，1，...，X-1，

Wherein, f _IBe intermediate frequency carrier frequency, t _sBe the sampling period, which sampled point m is;

(5) the local spread spectrum code sequence that is produced by local spreading code generation module deposits local spreading code storer according to the mode of fragmented storage, and data are designated as: p _i(n), i=0,1 ..., Y*Z-1, n=0,1 ... X-1; Local spreading code storer is table tennis buffer, supports storer is carried out read-write operation simultaneously;

(6) I/Q data and local spread spectrum code sequence are transferred to first order coherent integration module and carry out the segmentation related operation, finish successively the Y*Z section, the data after the first order coherent integration of every section are respectively:

${\mathrm{It}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}{\mathrm{Is}}_i\left(x\right)*p_i\left(x\right),i=\mathrm{0,1},...,Y*Z-1,$

${\mathrm{Qt}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}Q{s}_i\left(x\right)*p_i\left(x\right),i=\mathrm{0,1},...,Y*Z-1,$

As shown in Figure 2, each Y*Z of the I/Q two-way related data after first order coherent integration is deposited in first order coherence data storer, first order coherent integration be calculated as calculated off-line, improved the speed of computing;

(7) total Y*Z of the value that in first order coherent integration result, phase differential is identical, wherein Z organizes altogether, every group of Y data, every Y data are taken out and transferred to second level coherent integration module and do second level coherent integration from first order coherence data storer, its method is to estimate by Fast Fourier Transform (FFT) (FFT) the computing power spectrum that Y orders, the value of power spectrum output is the result of coherent accumulation, realizes the two-stage coherent integration:

(It2 _Y*i，It2 _Y*i+1，...，It2 _Y*(i+1)-1)＝fft(It1 _Y*i，It1 _Y*i+1，...，It1 _Y*(i+1)-1)，i＝0，1，...，Z-1，

(Qt2 _Y*i，Qt2 _Y*i+1，...，Qt2 _Y*(i+1)-1)＝fft(Qt1 _Y*i，Qt1 _Y*i+1，...，Qt1 _Y*(i+1)-1)，i＝0，1，...，Z-1；

As shown in Figure 3, be that 8 FFT calculate schematic diagram;

(8) data transmission to third level non-coherent integration module is carried out third level non-coherent integration, and the I/Q data are asked modular arithmetic, and every Z identical data of Doppler are carried out noncoherent accumulation, obtains altogether Y accumulated value:

${\mathrm{Dt}3}_i=\underset{j=0}{\overset{Z-1}{\mathrm{\Σ}}}[{\left({\mathrm{It}2}_{Y*j+i}\right)}^2+{\left({\mathrm{Qt}2}_{Y*j+i}\right)}^2],i=\mathrm{0,1},...,Y-1;$

(9) data are controlled comparison module through thresholding, complete the calculating of threshold value, the calculating that thresholding is controlled the threshold value of comparison module is divided into thresholding pattern and maximal value pattern: under the thresholding pattern, accumulated value and the thresholding of the output of third level non-coherent integration module are compared, find out maximal value and corresponding phase differential and Doppler's valuation thereof, if find to exist the spectral line that surpasses thresholding, explanation captures code, otherwise adjust local spreading code generation module, carry out next round and catch, repeating step (6) is to step (9); Under the maximal value pattern, calculated specific Time And Frequency uncertainty, find out maximal value wherein.

The data that data preprocessing module produces A/D converter are adjusted into the stationary conduit number and reach the fixedly data of bit wide, when the front end scheme changes, have guaranteed the independence of back capture engine module, have increased the reusability of capture engine.First, for different radio frequencies, the dynamic range of adjusting due to inner AGC (automatic gain control) is different, the analog if signal amplitude of output also can be different, will cause like this through after the A/D conversion, the bit bit wide of valid data is inconsistent, and data preprocessing module can judge selection to the active data bit according to the output of different radio frequency, data is issued the capture engine of back after being adjusted into stationary conduit number and bit wide again.Second, for the multisystem multi-frequency-point satellite navigation (for example: GPS L1/L2/L5, the Big Dipper two generations B1/B3, GLONASS and Galineo etc.), the capturing unit outside may connect a plurality of radio-frequency modules, data preprocessing module can be converted to the data input of a plurality of radio-frequency modules the data of stationary conduit number, guarantees the independence of back capture engine module.The 3rd, for different A/D schemes, the digital bit bit wide of output may be inconsistent, data preprocessing module can be according to different A/D schemes, the valid data bit is analyzed judgement, then MSB (high order bit) is intercepted, be converted to the fixedly data of bit wide.The 4th, for anti-interference satellite navigation receiver, anti-interference mode commonly used is many array-element antenna of use self-adaptation system, namely forms zero by the directional diagram of adjusting array in the direction of disturbing and falls into, stop undesired signal to enter receiver, thereby reach jamproof purpose; Need to increase the anti-interference process module in Base-Band Processing, anti-interference process generally needs outside A/D to have higher dynamic range, and namely the A/D bit wide needs very wide; At this moment the anti-interference process module can be put in data preprocessing module, after removing undesired signal, reduce the A/D data bit width, again data are sent into afterwards the capture engine of back, in this way, not only the independence of capture engine can be guaranteed, the hardware resource consumption of capture engine can also be reduced.

The sampled data control module is carried out segmentation with the pretreated data of data and is controlled processing, then data are stored in the sampled data storer.Be filled with and start first order coherent integration etc. data, then sampled data being read successively from the sampled data storer with system clock speed, sending into first order coherent integration module and make related operation.The another one effect of this module is that after the data of the certain phase differential of every search, this module is just controlled and re-started data sampling, uses new sampled data to catch calculating.This mode can guarantee that when high dynamic scene, the phase of calculating, frequency difference and actual value are more approaching, can work normally to guarantee follow-up carrier track.When Doppler shift is very fast, avoid occurring and successfully catching, but situation about can not follow the tracks of.

Sampled data enters frequency mixing module, carries out down coversion and goes intermediate frequency process, produces the I/Q orthogonal data, is designated as respectively:

Is _i(n), i=0 wherein, 1 ..., Y*Z-1; N=0,1 ..., X-1;

Qs _i(n), i=0 wherein, 1 ..., Y*Z-1; N=0,1 ..., X-1;

: Is _i(n)=S _i(n) * sin (2 π * f _I* m*t _s), Qs _i(n)=S _i(n) * cos (2 π * f _I* m*t _s)

Wherein, f _IBe intermediate frequency carrier frequency, t _sBe the sampling period, which sampled point m is.

IQ orthogonal data and local spread spectrum code sequence are transferred to first order coherent integration module carry out the segmentation related operation, finish successively the Y*Z section, the data after the first order coherent integration of every section are respectively:

${\mathrm{It}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}{\mathrm{Is}}_i\left(x\right)*p_i\left(x\right),i=\mathrm{0,1},...,Y*Z-1;$

${\mathrm{Qt}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}Q{s}_i\left(x\right)*p_i\left(x\right),i=\mathrm{0,1},...,Y*Z-1;$

Each Y*Z of I/Q two-way related data after first order coherent integration is deposited in first order coherence data storer, first order coherent integration be calculated as calculated off-line, improved the speed of computing.Total Y*Z of the value that in first order coherent integration result, phase differential is identical, wherein Z organizes altogether, every group of Y data, every Y data are taken out and transferred to second level coherent integration module and do second level coherent integration from first order coherence data storer, its method is to estimate by the Fast Fourier Transform (FFT) FFT power spectrum that Y orders, the value of power spectrum output is the result of coherent accumulation, has so just realized the two-stage coherent integration:

(It2 _Y*i，It2 _Y*i+1，...，It2 _Y*(i+1)-1)＝fft(It1 _Y*i，It1 _Y*i+1，...，It1 _Y*(i+1)-1)，i＝0，1，...，Z-1；

(Qt2 _Y*i，Qt2 _Y*i+1，...，Qt2 _Y*(i+1)-1)＝fft(Qt1 _Y*i，Qt1 _Y*i+1，...，Qt1 _Y*(i+1)-1)，i＝0，1，...，Z-1；。

Data transmission to third level non-coherent integration module is carried out third level non-coherent integration, and the I/Q data are asked modular arithmetic, and every Z identical data of Doppler are carried out noncoherent accumulation, obtains altogether Y accumulated value:

${\mathrm{Dt}3}_i=\underset{j=0}{\overset{Z-1}{\mathrm{\Σ}}}[{\left({\mathrm{It}2}_{Y*j+i}\right)}^2+{\left({\mathrm{Qt}2}_{Y*j+i}\right)}^2],i=\mathrm{0,1},...,Y-1.$

Need carry out thresholding after third level non-coherent integration non-coherent integration is completed calculates and compares, thresholding is controlled and is divided into thresholding pattern and maximal value pattern: the thresholding pattern comprises that thresholding calculates and thresholding compares two steps: (1) thresholding calculates: threshold value is chosen for average+M times of variance, the M value can be configured by software, and its default value is 8.When calculating decision threshold, be to do on average with the correlation of a segment encode sheet nearest before current result of calculation and Doppler frequency lattice, as decision threshold.In the dynamic application scenarios of height or fast-changing channel circumstance, can guarantee farthest that like this decision threshold that calculates is fresh, real-time, can effectively improve acquisition probability.(2) thresholding relatively: accumulated value and the thresholding of the output of third level non-coherent integration module are compared, find out point and corresponding phase differential and Doppler's valuation thereof over threshold value.If the discovery existence over the spectral line of thresholding, does not judge phase place and Doppler frequency and successfully finds out at once.But the correlation of the continuation several phase places of calculated for subsequent and Doppler frequency lattice, the correlation several times that goes out greater than correlation and the subsequent calculations of threshold value more for the first time, find out wherein maximum one, the phase differential that this correlation is corresponding and Doppler frequency are poor to be only the most accurately.This mode can effectively reduce false-alarm probability.If do not find the point over thresholding, need adjust local spreading code generation module, carry out next round and catch.

The maximal value pattern: calculated specific Time And Frequency uncertainty, found out maximal value wherein, we get code and the Doppler valuation of this maximal value for correctly catching.This pattern using has effectively improved acquisition sensitivity in the low signal-to-noise ratio environment under the condition of sacrificing certain capture time.

Claims (5)

1. the quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver, it is characterized in that: it comprises the following steps:

(1) satellite navigation receiver antenna receives satellite navigation signals, and the satellite navigation signals that receives is transferred to the radio frequency down-conversion device carries out down-converted, and the signal after down-converted is converted to digital medium-frequency signal through A/D converter again;

(2) digital medium-frequency signal enters the data preprocessing module of capturing unit, and data preprocessing module is adjusted into the stationary conduit number with digital medium-frequency signal and reaches the fixedly data of bit wide;

(3) data after data preprocessing module is processed enter the sampled data control module and carry out segmentation control processing, and the sampled data control module is divided into Y*Z data block with sampled data, and each data block comprises that X data number of samples is according to being designated as S _i(n), wherein, i=0,1 ..., Y*Z-1, n=0,1 ..., X-1, data block is stored in the sampled data storer;

(4) data transmission to the frequency mixing module after the sampled data control module is processed is carried out down coversion and is gone intermediate frequency process, produces the I/Q orthogonal data, is designated as respectively:

Is _i(n)=S _i(n)*sin(2π*f _I*m*t _s),i=0,1,...,Y*Z-1，n=0,1,...,X-1；

Qs _i(n)=S _i(n)*cos(2π*f _I*m*t _s)，i=0,1，...,Y*Z-1，n=0,1，...,X-1，

Wherein, f _IBe intermediate frequency carrier frequency, t _sBe the sampling period, which sampled point m is;

(5) the local spread spectrum code sequence that is produced by local spreading code generation module deposits local spreading code storer according to the mode of fragmented storage, and data are designated as: p _i(n), i=0,1 ..., Y*Z-1, n=0,1 ... X-1;

(6) I/Q data and local spread spectrum code sequence are transferred to first order coherent integration module and carry out the segmentation related operation, finish successively the Y*Z section, the data after the first order coherent integration of every section are respectively:

${\mathrm{It}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}{\mathrm{Is}}_i\left(x\right)*p_i\left(x\right),$ i=0,1，...,Y*Z-1，

${\mathrm{Qt}1}_i=\underset{x=0}{\overset{X-1}{\mathrm{\Σ}}}{\mathrm{Qs}}_i\left(x\right)*p_i\left(x\right),$ i=0,1，...,Y*Z-1，

Each Y*Z of I/Q two-way related data after first order coherent integration is deposited in first order coherence data storer;

(7) total Y*Z of the value that in first order coherent integration result, phase differential is identical, wherein Z organizes altogether, every group of Y data, every Y data are taken out and transferred to second level coherent integration module and do second level coherent integration from first order coherence data storer, its method is to estimate by the fast Fourier transformation operation power spectrum that Y orders, the value of power spectrum output is the result of coherent accumulation, realizes the two-stage coherent integration:

(It2 _Y*i,It2 _Y*i+1，...,It2 _Y*(i+1)-1)=fft(It1 _Y*i,It1 _Y*i+1，...,It1 _Y*(i+1)-1)，i＝0,1，...,Z-1，

(Qt2 _Y*i,Qt2 _Y*i+1，...,Qt2 _Y*(i+1)-1)=fft(Qt1 _Y*i,Qt1 _Y*i+1，...,Qt1 _Y*(i+1)-1)，i=0,1，...,Z-1；

(8) data transmission to third level non-coherent integration module is carried out third level non-coherent integration, and the I/Q data are asked modular arithmetic, and every Z identical data of Doppler are carried out noncoherent accumulation, obtains altogether Y accumulated value:

I=0,1 ..., Y-1;

(9) data are controlled comparison module through thresholding, complete the calculating of threshold value, thresholding is controlled and is divided into thresholding pattern and maximal value pattern, under the thresholding pattern, and accumulated value and the thresholding of third level non-coherent integration module output is compared, find out maximal value and corresponding phase differential and Doppler's valuation thereof, if find to exist the spectral line that surpasses thresholding, explanation captures code, otherwise adjusts local spreading code generation module, carry out next round and catch, repeating step (6) is to step (9); Under the maximal value pattern, calculated specific Time And Frequency uncertainty, find out maximal value wherein.

2. the quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver according to claim 1 is characterized in that: described local spreading code storer is for table tennis buffer, in order to simultaneously this storer is carried out read/write access.

3. the quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver according to claim 1 is characterized in that: described first order coherent integration be calculated as calculated off-line.

4. the quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver according to claim 1, it is characterized in that: in described thresholding pattern, the calculating of threshold value is to do on average with the correlation of a segment encode sheet nearest before current result of calculation and Doppler frequency lattice, as decision threshold.

5. the quick capturing method of long period pseudo random spread spectrum code of satellite navigation receiver according to claim 1, it is characterized in that: in described thresholding pattern, if find to exist the spectral line that surpasses thresholding during threshold judgement, continue the correlation of the several phase places of calculated for subsequent and Doppler frequency lattice, the correlation several times that goes out greater than correlation and the subsequent calculations of threshold value is more for the first time got wherein maximum one.

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