CN101819278A - Signal acquisition method of GPS receiver - Google Patents

Abstract

The invention discloses a signal acquisition method of a GPS receiver, and the method comprises the following steps: Step 1: searching order of Doppler frequency shift is set; Step 2: the GPS receiver receives an intermediate frequency digital signal, and rough acquisition is carried out on the signal, thus obtaining rough Doppler frequency shift and a C/A code phase; and Step 3: fine acquisition is carried out on the signal after the rough acquisition, thus obtaining fine Doppler frequency shift; in the method, through the rough acquisition of the intermediate frequency digital signal and according to motion characteristics of a carrier, frequencies which are more likely to occur in the Doppler frequency shift are firstly searched, and the order-jump search of the Doppler frequency shift reduces the Doppler frequency shift search times, reduces the search calculation and enhances the acquisition speed; and the fine acquisition of the intermediate frequency digital signal shortens the Doppler frequency shift search step size, and the fine Doppler frequency shift obtained by adopting conic fitting has the advantages of high speed, high precision, accurate acquisition results, easy operation and insensitivity to jump of navigation data bits.

Description

A kind of signal acquisition methods of GPS receiver

Technical field

The present invention relates to a kind of signal acquisition methods of GPS receiver, belong to signal capture technical field in the satellite navigation.

Background technology

Development along with infotech, satellite navigation system GPS (globel positionsystem) has appearred the seventies at twentieth century, can cheapness be easily the whole world Anywhere, whenever, high precision and continuous information such as position, speed, course, attitude and time are provided.Satellite navigation will change in the air, the system of sea and land transportation control and dispatching system; for the development of communications and transportation provides bigger space; help the economy and the security of sea, land and sky, world transportations, as be used for the gps satellite navigational system of Caribbean screen, the GPS navigation system that is used for passenger plane, following big aircraft and will adopt Beidou satellite navigation system.Therefore satellite navigation is of great importance for the development of country and even world economy, international exchanges and cooperation, helps promoting global economical integration.

Along with influence and the effect of global navigation satellite positioning system in national economy and national defense construction increases day by day, its great strategic importance that has particularly, cause the great attention of China, and carried out relevant research in succession, set up profound research and development base, satellite navigation location.

The major equipment of gps satellite navigation is the GPS receiver, and the gordian technique that the GPS receiver relates to mainly contains the catching of signal, the tracking of high dynamic signal, hi-Fix and resolves etc.Wherein, signal capture is the important component part of GPS receiver, is the prerequisite of signal trace and demodulation navigation data bits.Existing signal capture technology has that the code phase serial is caught, the Doppler shift serial is caught, and these algorithm operation quantities are big, and time-consuming length is unfavorable for the catching fast of signal, location etc.James Bao-yenTsui.Fundamentals of Global Positioning System Receivers:a software approach[M] .New York:John Wiley﹠amp; Sons Inc., 2000. disclose a kind of code phase parallel capture algorithm based on FFT (Fast FourierTransformation), its algorithm is realized principle as shown in Figure 1, code phase parallel capture algorithm computing based on FFT is very fast relatively, but because in specific implementation process, common algorithm needs a large amount of Fourier transforms to calculate, and is also more time-consuming.

Summary of the invention

The objective of the invention is to propose a kind of signal acquisition methods of GPS receiver, reached the capture time weak point, caught the accurate effect of result in order to address the above problem.

The signal acquisition methods of a kind of GPS receiver of the present invention comprises following step:

Step 1: the search-order of setting Doppler shift;

According to the motion conditions of satellite and carrier, set the search-order of Doppler shift, comprise n Doppler shift in the search-order, step-size in search is q, unit is kHz;

Step 2: the GPS receiver receives digital intermediate frequency signal, and signal is slightly caught, and obtains thick Doppler shift and C/A code phase;

Specifically comprise following step:

(1) according to the Doppler shift search-order of setting, local carrier oscillator and C/A code generator produce the intermediate-freuqncy signal under the current Doppler shift, intermediate-freuqncy signal is carried out related operation with the digital intermediate frequency signal that receives, obtain the correlation of first each C/A code phase of Doppler shift place, maximal value is peak value P in the correlation ₀, peak value P ₀Corresponding C/A code phase is N ₀

(2) obtain the correlation of each code phase at i Doppler shift place, obtain peak value P _iWith peak value P _iCorresponding C/A code phase N _iWherein, i=2,3 ... n;

(3) if P _i/ P ₀〉=S then stops to carry out i+1 the search to n Doppler shift, captures the corresponding satellite-signal of C/A sign indicating number that produces with the C/A code generator, obtains thick Doppler shift f _DopAt i Doppler shift place, corresponding C/A code phase is N _i, forward step 3 to, wherein S is threshold setting, determines f according to Signal-to-Noise _DopUnit is kHz; Otherwise forward step (4) to;

(4) if S＞P _i/ P ₀〉=1, return step (2), calculate the peak value at i+1 Doppler shift place and the C/A code phase of peak value correspondence; Otherwise forward step (5) to;

(5) if P _i/ P ₀＜1, P in addition then ₀=P _i, return step (2), calculate the peak value at i+1 Doppler shift place and the C/A code phase of peak value correspondence;

(6) finish when the search of all Doppler shifts, be not met P _i/ P ₀The P of 〉=S _iValue then shows the corresponding satellite-signal of C/A sign indicating number that does not have in the signal with the generation of C/A code generator, and the C/A sign indicating number sequence of next satellite that the C/A code generator produces is returned step (1), continues search of satellite signals;

Step 3: the signal after slightly catching is carried out meticulous catching, obtain meticulous Doppler shift;

Specifically comprise following step:

I: local C/A sign indicating number generator is a start bit with the C/A code phase that obtains in the step 2, produce the local C/A sign indicating number sequence of T time span, C/A sign indicating number sequence and the digital intermediate frequency signal that receives are multiplied each other, peel off the C/A sign indicating number of digital intermediate frequency signal, then digital intermediate frequency signal becomes the continuous carrier signal;

II:

In the kHz scope, establish step-length

Obtain seven Doppler shift x successively ₁To x ₇, intermediate-freuqncy signal and the continuous carrier that local oscillator under seven Doppler shifts is produced carries out related operation respectively, obtains seven correlation y ₁To y ₇, in seven correlations, choose d correlation, be designated as h successively ₁To h _d, h ₁To h _dCorresponding Doppler shift is e ₁To e _d, 3≤d≤7;

Choosing method is specially:

I: when d=3, establish that maximum correlation value is y in seven correlations _m, corresponding Doppler shift is x _m, get x _M-1And x _M+1And corresponding correlation is y _M-1And y _M+1, wherein, 2≤m≤6;

Ii: when d=4, establish that maximum correlation value is y in seven correlations _m, y _mCorresponding Doppler shift is x _m

1. when m=2, choose correlation y ₁To y ₄And corresponding Doppler shift x ₁To x ₄

2. when m=6, choose correlation y ₄To y ₇And corresponding Doppler shift x ₄To x ₇

3. when 3≤m≤5, get x _M-1And x _M+1And corresponding correlation is y _M-1And y _M+1, choose y _M-2With y _M+2Among higher value and corresponding Doppler shift thereof;

Iii: when d=5, establish that maximum correlation value is y in seven correlations _m, corresponding Doppler shift is x _m,

1. when m=2, choose correlation y ₁To y ₅And corresponding Doppler shift x ₁To x ₅

2. when m=6, choose correlation y ₃To y ₇And corresponding Doppler shift x ₃To x ₇

3. when 3≤m≤5, get x _M-2, x _M-1, x _M+1, x _M+2And corresponding correlation is y _M-2, y _M-1, y _M+1, y _M+2

Iv: when d=6, with y ₁With y ₇Middle smaller value and corresponding Doppler shift thereof remove, and choose all the other six correlations and corresponding Doppler shift thereof;

V: when d=7, choose seven correlations and corresponding Doppler shift thereof;

Set up the model equation of quafric curve:

$h_i={\mathrm{ae}}_i^2+{\mathrm{be}}_i+c---\left(1\right)$

A wherein, b, c is coefficient to be asked, e _iBe Doppler shift, h _iBe e _iCorresponding correlation, i=1,2 ... d, then set up system of equations:

Ax＝B??????????????(2)

Wherein:

$A=\left[\begin{array}{ccc}{e}_1^2& e_1& 1\\ e_2^2& e_2& 1\\ ...& ...& ...\\ e_d^2& e_d& 1\end{array}\right],B=\left[\begin{array}{c}{h}_1\\ h_2\\ ...\\ h_d\end{array}\right],x=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]---\left(3\right)$

Adopt the conic fitting method, separate system of linear equations and get:

x＝(A ^TA) ^-1A ^TB??????(4)

Through type (4) obtains a, b, and c brings formula (1) into, and the position that obtains the maximal value correspondence according to the character of quafric curve is:

$X=-\frac{b}{2a}---\left(5\right)$

X is meticulous Doppler shift; The C/A code phase that obtains in then meticulous Doppler shift X, the step 2 is N _i, finish satellite signal acquisition, stop the search of this satellite Doppler shift, return step 2, enter catching of next satellite.

The invention has the advantages that:

(1) slightly catching digital intermediate frequency signal among the present invention, according to the kinetic characteristic of carrier, at first to search for Doppler shift and those bigger frequencies of possibility occur, the jumping preface search of this Doppler shift reduces the Doppler shift searching times, reduce the search arithmetic amount, improve acquisition speed;

(2) slightly catching digital intermediate frequency signal among the present invention, only need obtain under a certain Doppler shift, the intermediate-freuqncy signal that local carrier oscillator and local C/A code generator produce and the digital intermediate frequency signal of reception need not to calculate relevant time maximal value or relevant average at the correlation peak at each code phase place;

(3) among the present invention the meticulous of digital intermediate frequency signal caught, shorten the Doppler shift step-size in search, adopt the mode of conic fitting to obtain meticulous Doppler shift, the meticulous Doppler shift speed that obtains like this is fast, the precision height, it is accurate to catch the result, easy operating, and also insensitive to the saltus step of navigation data bits;

(4) the present invention not only can apply in the GPS receiver system, also can use in other satellite navigation receiver systems based on CDMA signal format, has good versatility.

Description of drawings

Fig. 1 is a code phase parallel capture algorithm synoptic diagram in the background technology;

Fig. 2 is a method flow diagram of the present invention;

Fig. 3 is a signal capture synoptic diagram of the present invention.

Embodiment

The present invention is described in further detail below in conjunction with drawings and Examples.

The present invention is a kind of signal acquisition methods of GPS receiver, and flow process comprises following step as shown in Figures 2 and 3:

Step 1: the search-order of setting Doppler shift;

According to the motion conditions of satellite and carrier, set the search-order of Doppler shift, comprise n Doppler shift in the search-order, step-size in search is q, unit is kHz.For the carrier that moves on the ground, it is more reasonable that the Doppler shift scope is arranged on [7,7] kHz, and Doppler shift is ± 2, the probability that ± 3kHz occurs is bigger, therefore, at first searches for the digital intermediate frequency signal that these Doppler shifts can capture satellite faster, and the search-order of setting Doppler shift among the present invention is [2,2 ,-3,3 ,-1,1 ,-4,4,0,-5,5 ,-6,6,-7,7], unit is kHz, and step-size in search is 1kHz.For the situation under aerial or other specific environments, the search-order of Doppler shift can have the motion conditions of satellite motion and carrier to determine through deriving.

Step 2: the GPS receiver receives digital intermediate frequency signal, and signal is slightly caught, and obtains thick Doppler shift and C/A code phase;

The GPS receiver receives digital intermediate frequency signal, and then based on the code phase parallel capture algorithm of FFT, of the present invention slightly catching specifically comprises following step:

(1) according to the Doppler shift search-order of setting, local carrier oscillator and C/A code generator produce the intermediate-freuqncy signal under the current Doppler shift, intermediate-freuqncy signal is carried out related operation with the digital intermediate frequency signal that receives, obtain the correlation of first each C/A code phase of Doppler shift place, maximal value is peak value P in the correlation ₀, peak value P ₀Corresponding C/A code phase is N ₀

Described related operation is meant intermediate-freuqncy signal and the digital intermediate frequency signal that receives is multiplied each other at each point, summation then, and the result who obtains is correlation.

(2) obtain the correlation of each code phase at i Doppler shift place, obtain peak value P _iWith peak value P _iCorresponding C/A code phase N _iWherein, i=2,3 ... n.

(3) if P _i/ P ₀〉=S, wherein S is threshold setting, between determining according to Signal-to-Noise, thresholding is between 1.6-2.0, usually get empirical value 1.8, then stop to carry out i+1 search, capture the corresponding satellite-signal of C/A sign indicating number that produces with the C/A code generator, obtain thick Doppler shift f to n Doppler shift _DopAt i Doppler shift place, corresponding C/A code phase is N _i, f _DopUnit be kHz, forward step 3 to; Otherwise forward step (4) to;

(4) if S＞P _i/ P ₀〉=1, return step (2), calculate the peak value at i+1 Doppler shift place and the C/A code phase of peak value correspondence; Otherwise forward step (5) to;

(5) if P _i/ P ₀＜1, then allow P ₀=P _i, return step (2), calculate the peak value at i+1 Doppler shift place and the C/A code phase of peak value correspondence;

(6) finish when the search of all Doppler shifts, be not met P _i/ P ₀The P of 〉=S _iBe worth, then show the corresponding satellite-signal of C/A sign indicating number that does not have in the signal with the generation of C/A code generator, change the C/A sign indicating number that the C/A code generator produces, make the C/A sign indicating number sequence of next satellite of C/A code generator generation, return step (1), the continuation search of satellite signals;

Step 3: the signal after slightly catching is carried out meticulous catching, obtain meticulous Doppler shift;

Because slightly catch the satellite-signal resolution that obtains be

The carrier frequency of kHz can not satisfy the requirement of carrier tracking loop, so the present invention differs in tens hertz local carrier oscillator frequency and signal(-) carrier frequency by meticulous catching.

The present invention utilizes and slightly catches the C/A code phase that obtains, and shortens the Doppler shift step-size in search and calculates correlation, adopts the method for conic fitting to obtain meticulous carrier frequency, specifically comprises following step:

(1) local C/A sign indicating number generator is a start bit with the C/A code phase that obtains in the step 2, produce the local C/A sign indicating number sequence of T time span, T is 1-5ms, usually get 1ms, C/A sign indicating number sequence and the digital intermediate frequency signal that receives are multiplied each other, peel off the C/A sign indicating number of digital intermediate frequency signal, then digital intermediate frequency signal becomes the continuous carrier signal.

(2) according to slightly catching the Doppler shift f that obtains _Dop, then the digital intermediate frequency signal Doppler shift exists

Within the kHz,

In the kHz scope, establish step-length

KHz obtains seven Doppler shift x successively ₁To x ₇, intermediate-freuqncy signal and the continuous carrier that local carrier oscillator under seven Doppler shifts is produced carries out related operation respectively, obtains seven correlation y ₁To y ₇, in seven correlations, choose d correlation, be designated as h successively ₁To h _d, h ₁To h _dCorresponding Doppler shift is e ₁To e _d, 3≤d≤7.

Choosing method is specially:

I: when d=3, establish that maximum correlation value is y in seven correlations _m, corresponding Doppler shift is x _m, get x _M-1And x _M+1And corresponding correlation is y _M-1And y _M+1, wherein, 2≤m≤6;

Ii: when d=4, establish that maximum correlation value is y in seven correlations _m, y _mCorresponding Doppler shift is x _m

4. when m=2, choose correlation y ₁To y ₄And corresponding Doppler shift x ₁To x ₄

5. when m=6, choose correlation y ₄To y ₇And corresponding Doppler shift x ₄To x ₇

6. when 3≤m≤5, get x _M-1And x _M+1And corresponding correlation is y _M-1And y _M+1, choose y _M-2With y _M+2Among higher value and corresponding Doppler shift thereof;

Iii: when d=5, establish that maximum correlation value is y in seven correlations _m, corresponding Doppler shift is x _m,

4. when m=2, choose correlation y ₁To y ₅And corresponding Doppler shift x ₁To x ₅

5. when m=6, choose correlation y ₃To y ₇And corresponding Doppler shift x ₃To x ₇

6. when 3≤m≤5, get x _M-2, x _M-1, x _M+1, x _M+2And corresponding correlation is y _M-2, y _M-1, y _M+1, y _M+2

Iv: when d=6, with y ₁With y ₇Middle smaller value and corresponding Doppler shift thereof remove, and choose all the other six correlations and corresponding Doppler shift thereof;

V: when d=7, choose seven correlations and corresponding Doppler shift thereof.

Set up the model equation of quafric curve:

$h_i={\mathrm{ae}}_i^2+{\mathrm{be}}_i+c---\left(1\right)$

A wherein, b, c is coefficient to be asked, x _iBe Doppler shift, y _iBe x _iCorresponding correlation, i=1,2 ... d, then can set up system of equations:

Ax＝B????????????????????(2)

Wherein:

$A=\left[\begin{array}{ccc}{e}_1^2& e_1& 1\\ e_2^2& e_2& 1\\ ...& ...& ...\\ e_d^2& e_d& 1\end{array}\right],B=\left[\begin{array}{c}{h}_1\\ h_2\\ ...\\ h_d\end{array}\right],x=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]---\left(3\right)$

Adopt the conic fitting method, separate this system of linear equations and get:

x＝(A ^TA) ^-1ATB???????????(4)

Through type (4) obtains a, b, and c brings formula (1) into, and the position that gets the maximal value correspondence according to the character of quafric curve is:

$X=-\frac{b}{2a}---\left(5\right)$

X is meticulous Doppler shift, the meticulous Doppler shift X and the code phase N that then obtain _i, stop the search of this satellite Doppler shift, return step 2, enter catching of next satellite.

Utilize actual acquisition to obtain and many groups signal that signal simulator produces carries out simulating, verifying, the present invention catches time-consuming about 5s, and Doppler shift and C/A phase acquisition precision are higher, can satisfy the requirement of carrier tracking loop.

Embodiment 1:

The satellite-signal of search PRN5 satellite, the intermediate frequency of establishing digital intermediate frequency signal is 4.123968MHz, sample frequency is 16.367667MHz, Doppler shift step-size in search 1kHz when catching, according to step 1, establishing the Doppler shift search-order is [2,2 ,-3,3 ,-1,1 ,-4,4,0 ,-5,5 ,-6,6,-7,7], unit is kHz.

Obtain by step 2, when Doppler shift 2kHz, peak value 3705 is more outstanding, compares with first peak value 1531, and ratio is greater than thresholding 1.8, then can determine to contain in the signal signal of PRN5 satellite, and slightly catching the Doppler shift that obtains is 2kHz, and corresponding code phase is 13001, and the Doppler shift of back then need not to continue search, for the correlation of clear explanation, list correlation such as table 1 at other several Doppler shifts places.

Table 1PRN5 star is at the correlation peak and the code phase at each Doppler shift place

Doppler shift	??-2	??2	??-3	??3	??-1	??1	??-4	??4
									Peak value	??1531	??3705	??1464	??3340	??1549	??3606	??1291	??1228
The C/A code phase	??10584	??13001	??4783	??12999	??5139	??12998	??7723	??1738
									Doppler shift	??0	??-5	??5	??-6	??6	??-7	??7
Peak value	??1153	??1479	??1178	??1323	??1172	??1463	??1254
									The C/A code phase	??2873	??4356	??91	??13470	??2242	??1680	??12600

According to step 3, calculate the 2kHz left and right sides 6 correlations of 250Hz at interval, tabulation as 2.

The correlation that the meticulous Doppler's frequency meter of table 2 is calculated

Doppler shift	??1.25	??1.5	??1.75	??2	??2.25	??2.5	??2.75
								Correlation	??3729	??4481	??3986	??3705	??3568	??3412	??3385

As seen from the above table, selecting Doppler shift [1.25,1.5,1.75] kHz is independent variable x _i, corresponding correlation peak [3729,4481,3986] is dependent variable y _i, through curve fitting, the meticulous Doppler shift of gained is 1525Hz, so far, the Doppler shift that has obtained digital intermediate frequency signal is 1525Hz and C/A code phase 13001, stops the search of this satellite Doppler shift, enters catching of next satellite.

Embodiment 2:

The satellite-signal of search PRN8 satellite, the intermediate frequency of establishing digital intermediate frequency signal is 4.123968MHz, sample frequency is 16.367667MHz, Doppler shift step-size in search 1kHz when catching, according to step 1, establishing the Doppler shift search-order is [2,2 ,-3,3 ,-1,1 ,-4,4,0 ,-5,5 ,-6,6,-7,7], unit is kHz.Pass through step 2, table 3 is satellite PRN8 correlations at each Doppler shift place, each peakedness ratio is more approaching, there is not outstanding spike, peak-peak is 1585, minimum peak is 1255, do not satisfy big peak value with than the ratio of small leak greater than the condition of setting thresholding 1.8, then do not contain the signal of PRN8 satellite in the digital intermediate frequency signal.

Table 3PRN8 star is at the correlation peak and the code phase at each Doppler shift place

Doppler shift	??-2	??2	??-3	??3	??-1	??1	??-4	??4
									Peak value	??1418	??1255	??1427	??1524	??1389	??1377	??1373	??1585
The C/A code phase	??7422	??10400	??2791	??328	??3802	??14903	??677	??11500
									Doppler shift	??0	??-5	??5	??-6	??6	??-7	??7
Peak value	??1384	??1456	??1568	??1479	??1369	??1479
									The C/A code phase	??2255	??12990	??13635	??11214	??7145	??3188

Claims (6)

1. the signal acquisition methods of a GPS receiver is characterized in that, comprises following step:

Step 1: the search-order of setting Doppler shift;

According to the motion conditions of satellite and carrier, set the search-order of Doppler shift, comprise n Doppler shift in the search-order, step-size in search is q, unit is kHz;

Step 2: the GPS receiver receives digital intermediate frequency signal, and signal is slightly caught, and obtains thick Doppler shift and C/A code phase;

Specifically comprise following step:

(1) according to the Doppler shift search-order of setting, local carrier oscillator and C/A code generator produce the intermediate-freuqncy signal under the current Doppler shift, intermediate-freuqncy signal is carried out related operation with the digital intermediate frequency signal that receives, obtain the correlation of first each C/A code phase of Doppler shift place, maximal value is peak value P in the correlation ₀, peak value P ₀Corresponding C/A code phase is N ₀

(2) obtain the correlation of each code phase at i Doppler shift place, obtain peak value P _iWith peak value P _iCorresponding C/A code phase N _iWherein, i=2,3 ... n;

(3) if P _i/ P ₀〉=S then stops to carry out i+1 the search to n Doppler shift, captures the corresponding satellite-signal of C/A sign indicating number that produces with the C/A code generator, obtains thick Doppler shift f _DopAt i Doppler shift place, corresponding C/A code phase is N _i, forward step 3 to, wherein S is threshold setting, determines f according to Signal-to-Noise _DopUnit is kHz; Otherwise forward step (4) to;

(4) if S＞P _i/ P ₀〉=1, return step (2), calculate the peak value at i+1 Doppler shift place and the C/A code phase of peak value correspondence; Otherwise forward step (5) to;

(5) if P _i/ P ₀＜1, P in addition then ₀=P _i, return step (2), calculate the peak value at i+1 Doppler shift place and the C/A code phase of peak value correspondence;

(6) finish when the search of all Doppler shifts, be not met P _i/ P ₀The P of 〉=S _iValue then shows the corresponding satellite-signal of C/A sign indicating number that does not have in the signal with the generation of C/A code generator, and the C/A sign indicating number sequence of next satellite that the C/A code generator produces is returned step (1), continues search of satellite signals;

Step 3: the signal after slightly catching is carried out meticulous catching, obtain meticulous Doppler shift;

Specifically comprise following step:

I: local C/A sign indicating number generator is a start bit with the C/A code phase that obtains in the step 2, produce the local C/A sign indicating number sequence of T time span, C/A sign indicating number sequence and the digital intermediate frequency signal that receives are multiplied each other, peel off the C/A sign indicating number of digital intermediate frequency signal, then digital intermediate frequency signal becomes the continuous carrier signal;

II:

In the kHz scope, establish step-length

Obtain seven Doppler shift x successively ₁To x ₇, intermediate-freuqncy signal and the continuous carrier that local oscillator under seven Doppler shifts is produced carries out related operation respectively, obtains seven correlation y ₁To y ₇, in seven correlations, choose d correlation, be designated as h successively ₁To h _d, h ₁To h _dCorresponding Doppler shift is e ₁To e _d, 3≤d≤7;

Choosing method is specially:

I: when d=3, establish that maximum correlation value is y in seven correlations _m, corresponding Doppler shift is x _m, get x _M-1And x _M+1And corresponding correlation is y _M-1And y _M+1, wherein, 2≤m≤6;

Ii: when d=4, establish that maximum correlation value is y in seven correlations _m, y _mCorresponding Doppler shift is x _m

1. when m=2, choose correlation y ₁To y ₄And corresponding Doppler shift x ₁To x ₄

2. when m=6, choose correlation y ₄To y ₇And corresponding Doppler shift x ₄To x ₇

3. when 3≤m≤5, get x _M-1And x _M+1And corresponding correlation is y _M-1And y _M+1, choose y _M-2With y _M+2Among higher value and corresponding Doppler shift thereof;

Iii: when d=5, establish that maximum correlation value is y in seven correlations _m, corresponding Doppler shift is x _m,

1. when m=2, choose correlation y ₁To y ₅And corresponding Doppler shift x ₁To x ₅

2. when m=6, choose correlation y ₃To y ₇And corresponding Doppler shift x ₃To x ₇

3. when 3≤m≤5, get x _M-2, x _M-1, x _M+1, x _M+2And corresponding correlation is y _M-2, y _M-1, y _M+1, y _M+2

Iv: when d=6, with y ₁With y ₇Middle smaller value and corresponding Doppler shift thereof remove, and choose all the other six correlations and corresponding Doppler shift thereof;

V: when d=7, choose seven correlations and corresponding Doppler shift thereof;

Set up the model equation of quafric curve:

$h_i={\mathrm{ae}}_i^2+{\mathrm{be}}_i+c---\left(1\right)$

A wherein, b, c is coefficient to be asked, e _iBe Doppler shift, h _iBe e _iCorresponding correlation, i=1,2 ... d, then set up system of equations:

Ax＝B????(2)

Wherein:

$A=\left[\begin{array}{ccc}{e}_1^2& e_1& 1\\ e_2^2& e_2& 1\\ ...& ...& ...\\ e_d^2& e_d& 1\end{array}\right],B=\left[\begin{array}{c}{h}_1\\ h_2\\ ...\\ h_d\end{array}\right],x=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]---\left(3\right)$

Adopt the conic fitting method, separate system of linear equations and get:

x＝(A ^TA) ^-1A ^TB????(4)

Through type (4) obtains a, b, and c brings formula (1) into, and the position that obtains the maximal value correspondence according to the character of quafric curve is:

$X=-\frac{b}{2a}---\left(5\right)$

X is meticulous Doppler shift; The C/A code phase that obtains in then meticulous Doppler shift X, the step 2 is N _i, finish satellite signal acquisition, stop the search of this satellite Doppler shift, return step 2, enter catching of next satellite.

2. the signal acquisition methods of a kind of GPS receiver according to claim 1 is characterized in that, the search-order of Doppler shift is [2,2 ,-3,3 ,-1,1 ,-4,4,0 ,-5,5 ,-6,6 ,-7,7], and unit is kHz, and step-size in search is 1kHz.

3. the signal acquisition methods of a kind of GPS receiver according to claim 1 is characterized in that, threshold setting S value is between the 1.6-2.0.

4. the signal acquisition methods of a kind of GPS receiver according to claim 3 is characterized in that, threshold setting S value is 1.8.

5. the signal acquisition methods of a kind of GPS receiver according to claim 1 is characterized in that, in the step 3, time span T is 1-5ms.

6. the signal acquisition methods of a kind of GPS receiver according to claim 5 is characterized in that, in the step 3, time span T is 1ms.

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