CN102707296A - Satellite selecting method for single-constellation satellite navigation system - Google Patents

Abstract

The invention relates to a satellite selecting method for a single-constellation satellite navigation system, belonging to the field of satellite navigation. In the method, the needed visible satellites in the minimum number can be selected, located and resolved one by one through the analysis on the geometrical configuration characteristics of the optimal visible satellite combination and in accordance with the distribution characteristics of the elevation values and the azimuth values of visible satellites together with the tetrahedral volume; the problem that too many matrix multiplications and matrix inversions exist in the traditional satellite selecting method can be effectively solved, the calculation quantity is reduced and the processing speed of a receiver is increased; and the operation is easy, the satellite selecting principle is simple and the operation is fast. The method is suitable for all kinds of global navigation satellite systems and can meet the requirements of high-dynamic users on real-time property.

Description

A kind of satellite selection method that is used for single constellation satellite navigation system

Technical field

The present invention relates to a kind of satellite selection method that is used for single constellation satellite navigation system, belong to the satellite navigation field.

Background technology

Satellite navigation positioning calculation precision depends on the pseudo range observed quantity sum of errors geometric dilution of precision GDOP of satellite, and GDOP is distributed by the satellite geometry that is used for positioning calculation to determine.Utilize the satellite of single constellation to position four visual satellites of user of minimum needs, confirm three-dimensional position and necessary minimum four observed quantities of receiver clock correction so that the user to be provided.The problem that the present invention will solve is exactly few visible star of how selecting fast that geometric distributions is more excellent, number is tried one's best.Traditional satellite selection method is in visible star, to find out all four stars combinations; The tetrahedron volume that GDOP value through calculating all combinations or user form to the terminal point of the vector of unit length of four stars is therefrom selected the maximum four stars combination of GDOP value minimum or tetrahedron volume as the final star result that selects.

Suppose constantly in a certain observation; The user can observe n (n >=a 4) satellite of certain satellite navigation system simultaneously; A kind of traditional satellite selection method is that all four stars of traversal make up pairing GDOP value in n satellite, and selects one group of GDOP value minimum as the final star result that selects.Because the tetrahedron volume that GDOP and user form to the terminal point of the vector of unit length of four stars is inversely proportional to; Therefore another kind of traditional satellite selection method is that all four stars of traversal make up pairing tetrahedron volume in n satellite, and selects tetrahedron volume maximum a group as the final star result that selects.If four satellites selecting corresponding position coordinates under solid (ECEF) coordinate system of ground heart is (x _i, y _i, z _i) (i=1,2,3,4), user's corresponding position coordinates under the ECEF coordinate system is (x _u, y _u, z _u), then the computing formula of GDOP is following:

$\mathrm{GDOP}=\sqrt{\mathrm{trace}{\left(H^{T}H\right)}^{-1}}---\left(1\right)$

The user is following to the computing formula of the tetrahedron volume V that the terminal point of the vector of unit length of four stars is formed:

$V=\frac{1}{6}\left|H\right|---\left(2\right)$

Wherein, $H=\left[\begin{array}{cccc}{a}_{x1}& a_{y1}& a_{z1}& 1\\ a_{x2}& a_{y2}& {\mathrm{<figure-callout\; id="2"\; label="a\; z"\; filenames="DEST\_PATH\_HDA00001752952500022.png"\; state="\{\{state\}\}">a</figure-callout>}}_z& 1\\ a_{x3}& a_{y3}& {\mathrm{<figure-callout\; id="3"\; label="a\; z"\; filenames="DEST\_PATH\_HDA00001752952500022.png"\; state="\{\{state\}\}">a</figure-callout>}}_z& 1\\ a_{x4}& a_{y4}& {\mathrm{<figure-callout\; id="4"\; label="a\; z"\; filenames="DEST\_PATH\_HDA00001752952500022.png"\; state="\{\{state\}\}">a</figure-callout>}}_z& 1\end{array}\right],$ $a_{\mathrm{Xi}}=\frac{x_i-x_u}{r_i},$ $a_{\mathrm{Yi}}=\frac{y_i-y_u}{r_i},$ $a_{\mathrm{Zi}}=\frac{z_i-z_u}{r_i}$

$r_i=\sqrt{{(x_i-x_u)}^2+{(y_i-y_u)}^2+{(z_i-z_u)}^2},(i=\mathrm{1,2,3,4})$

Can find out from formula (1) and formula (2); Traditional satellite selection method need carry out the calculating of

inferior GDOP value or tetrahedron volume V; With GPS is example; The gps satellite that the user can observe simultaneously can reach 6-12, that is to say that traditional satellite selection method need carry out the calculating of 15-495 GDOP value or tetrahedron volume V.And each calculating all relates to matrix multiplication, matrix inversion or the computing of matrix determinant.Though it is optimum that traditional satellite selection method selects the star result, corresponding bearing accuracy is best, and its operand is big, and the computing time that needs is longer, especially for high dynamic subscriber, is unfavorable for its requirement to real-time.Therefore, under the situation of sacrificing a spot of bearing accuracy, it is very significant can finding the little quick satellite selection method of a kind of calculated amount.

Summary of the invention

The objective of the invention is for reducing the calculated amount of receiver positioning calculation, the time of accelerating the receiver cold start-up, alleviate the burden of receiver user processor, a kind of satellite selection method that is applicable to single constellation satellite navigation system is proposed.The present invention is a kind of optimization to traditional satellite selection method, can under the prerequisite of sacrificing a small amount of bearing accuracy, select the required minimal number visible satellite of positioning calculation fast.

A kind of satellite selection method that is used for single constellation satellite navigation system; Through analyzing the geometric configuration characteristics of best visible star combination, according to the distribution characteristics of each visible elevation angle value and azimuth value and combine the tetrahedron volume to select the required minimal number visible satellite of positioning calculation one by one.Specifically realize through following steps:

Step 1, according to the number of satellite and the layout of different GPS constellations, the GDOP threshold value of selected combinations of satellites is set; According to the receiver present position visual field of satellite in the satellite navigation system is provided with the height cutoff angle, the open degree in the visual field is inversely proportional to the height cutoff angle, and promptly the visual field is open more, and the height cutoff angle is transferred lowly more, and the visual field is narrow more, and elevation angle needs suitably to improve.

Step 2, reject the non-healthy star in the satellite navigation system according to the correlation parameter that characterizes the satellite health situation in the satellite ephemeris; Calculate the position coordinates of each healthy satellite under the ECEF coordinate system, and in healthy satellite, obtain visible star sum n according to the height cutoff angle that step 1 is provided with.

Step 3, the visible coordinate conversion of star under the ECEF coordinate system arrived customer-centric; Be in the coordinate system (ENU coordinate system) of three of coordinate systems with its east orientation, north orientation and zenith direction respectively; And carry out unitization, write down its position coordinates on the unit sphere that with user is the centre of sphere.

Step 4, in the ENU coordinate system, calculate the elevation angle and the position angle of each visible star, and select the maximum satellite of elevation angle as first the satellite S1 that selects the star result.

Step 5, the visible star sum of basis are judged; If n≤6; Then traversal Samsung combination in the visible star of residue, select the maximum Samsung combination conduct of the tetrahedron volume corresponding with S1 combination back select the star result second and third, four star S2, S3, S4, change step 9 then over to; If n＞6 change step 6 over to.

Step 6, calculate each visible star in position and the distance of S1 between position corresponding on the unit sphere corresponding on the unit sphere, second satellite S2 of star result selected in the visible star conduct of chosen distance maximum.

Step 7, choose the 3rd satellite S3.

Step 7.1, the elevation angle of elevation angle of removing the visible star beyond fixed S1, the S2 and S2 is poor, take out the satellite of the absolute value of difference less than α.In order to make corresponding tetrahedron volume big as far as possible, S3 and S2 should be in the sustained height angular regions, and promptly α is more little good more, is generally less than 30 ° in the practical implementation.

Step 7.2, the position angle of the satellite that step 7.1 is obtained and the position angle of S2 are poor.If the absolute value of difference then differs from this absolute value greater than 180 ° again with 240 °; If the absolute value of difference differs from this absolute value less than 180 ° again with 120 °.

Step 7.3; Find out the minimum satellite of absolute value in the difference that step 7.2 obtains; (size of β value has been reacted S3 and the S2 distribution situation at angle, sustained height angular region interior orientation less than β to judge this absolute value; The β value is more little, and S3 and S2 position angle difference absolute value make then that more near 120 ° or 240 ° corresponding tetrahedron volume is big more).If less than, then this star is elected to be the 3rd satellite S3; If be not less than; Then on the basis of α, increase the absolute difference of elevation angle gradually with a fixed step size; Again choose satellite less than new absolute difference; Poor to the satellite aximuth of newly choosing again according to the method for step 7.2 then, up to find make the absolute value of position angle difference less than the satellite of β as the 3rd the satellite S3 that selects the star result.

If when elevation angle difference absolute value is increased to 30 °, also do not select the satellite of the absolute value of position angle difference less than β, when then getting elevation angle difference absolute value and being 30 °, star result's the 3rd satellite S3 selected in difference absolute value minimum satellite conduct in position angle.

Step 8, calculate the tetrahedron volume that all the other visible stars and first three satellite of having selected are formed, select to make the maximum satellite of volume as the 4th the satellite S4 that selects the star result.

Step 9, judge the combination of selected four stars GDOP value whether less than the GDOP threshold value of setting in the step 1.If less than, then select star to finish; If be not less than, then conduct the 5th the satellite S5 that the star result is selected in a satellite conduct with S2, S3, S4 position angle difference absolute value sum maximum a by-election, select star to finish.

Beneficial effect

1, this method realizes a selecting star through the tetrahedron volumetric method of optimizing, and has solved effectively to have a large amount of matrix multiplications and the problem of matrix inversion in traditional satellite selection method, has reduced calculated amount and has promoted the receiver processing speed.

2, this method is easy and simple to handle, selects the star principle simple, compares with traditional most preferably star method, and speed on average improves about ten times.

3, this method is applicable to all GLONASSs, also satisfies the requirement of high dynamic subscriber to real-time simultaneously.

Description of drawings

Fig. 1 for of the present invention be used for single constellation satellite navigation system select the star process flow diagram;

Fig. 2 selects star for Beijing area user in the embodiment carves at a time before, traditional traversal method is selected behind the star and the inventive method is selected the visible star station heart view behind the star;

Fig. 3 compares for the GDOP result that different traditional traversal methods constantly selected star and the inventive method to select star to calculate at a day of Beijing area user in the embodiment;

Fig. 4 selects star and the inventive method to select star to compare spent computing time for Beijing area user in the embodiment in traditional traversal methods of one day difference moment.

Embodiment

For embodiment of the present invention is described better, the present invention is done further detailed description below in conjunction with accompanying drawing and instance.

The present invention provides a kind of quick satellite selection method that is used for single constellation satellite navigation system, and said method flow is as shown in Figure 1.

When utilizing certain GLONASS satellite to position, receiver can observe multi-satellite simultaneously in a certain epoch of observation, will therefrom select the minimal number satellite that can satisfy positioning requirements at present and position and resolve.

1, adopt GPS, GLONASS and GALILEO system in the present embodiment, according to the best combinations of satellites GDOP value of traversal method experiment statistics, the GDOP threshold value that selected combinations of satellites is set is respectively 3,4,4, and it is 5 ° that the height cutoff angle is set.

2, reject the non-healthy star in the satellite navigation system according to the correlation parameter that characterizes the satellite health situation in the satellite ephemeris, calculate the position coordinates of other each satellite under the ECEF coordinate system, and obtain visible star sum n according to the height cutoff angle.

3, the visible coordinate conversion of star under the ECEF coordinate system arrived in the ENU coordinate system, and carry out unitization, write down its position coordinates on the unit sphere that with user is the centre of sphere.If the position coordinates of user under the ECEF coordinate system is (x _u, y _u, z _u), corresponding the earth longitude and latitude is that (B, L), the visible position coordinates of star under the ECEF coordinate system is (x _s, y _s, z _s), the then visible coordinate of star under the ENU coordinate system is:

$\left[\begin{array}{c}{x}_E\\ y_N\\ z_U\end{array}\right]=\left[\begin{array}{ccc}-\sin L& \cos L& 0\\ -\sin B\cos L& -\sin B\sin L& \cos B\\ \cos B\cos L& \cos B\sin L& \sin B\end{array}\right]\left[\begin{array}{c}{x}_s-x_u\\ y_s-y_u\\ z_s-z_u\end{array}\right]---\left(3\right)$

Coordinate after the unitization is:

${\left[\begin{array}{ccc}{\mathrm{ex}}_E& {\mathrm{ey}}_N& {\mathrm{ez}}_U\end{array}\right]}^T=\frac{{\left[\begin{array}{ccc}{x}_E& y_N& z_U\end{array}\right]}^T}{\sqrt{x_{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="DEST\_PATH\_HDA00001752952500022.png"\; state="\{\{state\}\}">E</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="y\; N"\; filenames="DEST\_PATH\_HDA00001752952500022.png"\; state="\{\{state\}\}">y</figure-callout>}}_N^{}+z_U^2}}---\left(4\right)$

4, in the ENU coordinate system, calculate the elevation angle and the position angle of each visible star.It is thus clear that the computing formula of the elevation angle el of star and position angle az is:

$\mathrm{el}=\arctan \left(\frac{z_U}{\sqrt{x_E^2+y_N^2}}\right)---\left(5\right)$

$\mathrm{az}=\arctan \left(\frac{x_E}{y_N}\right)---\left(6\right)$

Result of calculation is revised, made 0 °≤el≤90 °, 0 °≤az≤360 °.

Because the size of GDOP value and the tetrahedron volume that the user forms to the terminal point of the vector of unit length of four stars are inversely proportional to, volume is big more, and corresponding GDOP value is more little.Desirable maximum volume tetrahedron differs each other by having minimum altitude angle and position angle that the star at 120 ° three stars and maximum height angle forms.Therefore at first select the maximum satellite of elevation angle as first the satellite S1 that selects the star result.

5, judge according to visible star sum; If n≤6; Then traversal Samsung combination in the visible star of residue; Select the maximum Samsung combination of the tetrahedron volume corresponding with S1 combination back as select the star result second and third, four star S2, S3, S4, specifically computing method are seen formula (2), change step 9 then over to; If n＞6 change step 6 over to.

6, calculate each visible star in position and the distance of S1 between position corresponding on the unit sphere corresponding on the unit sphere, second satellite S2 of star result selected in the maximum visible star conduct of chosen distance.Can guarantee that like this tetrahedron top is bigger to the distance of bottom surface.

7, the elevation angle of the elevation angle of all the other visible stars and S2 is poor; In order to make corresponding tetrahedron volume big as far as possible, S3 and S2 should be in the sustained height angular regions, and promptly α is more little good more; Be generally less than 30 ° in the practical implementation; The α value of present embodiment is 15 °, and the absolute value that promptly takes out difference is less than 15 ° satellite, and the position angle of the position angle of these visible stars and S2 is poor.If absolute difference is greater than 180 °, then itself and 240 ° are differed from; If absolute difference is less than 180 °, itself and 120 ° are differed from.Therefrom find out the minimum satellite of absolute value of difference, judge that whether this value is less than β (according to experiment statistics, the β value is taken as 30 ° in the present embodiment).If less than, then selecting this star is the 3rd the satellite S3 that selects the star result; If be not less than; On 15 ° basis, be that step-length increases elevation angle difference absolute value gradually then with 5 °; Again choose satellite less than new absolute difference; Poor to the position angle then, up to find make the absolute value of position angle difference less than the satellite of β as the 3rd the satellite S3 that selects the star result.When elevation angle difference absolute value is increased to 30 °, also do not select the satellite that satisfies condition, star result's the 3rd satellite S3 selected in the minimum satellite conduct of absolute value of then getting the position angle difference.

8, calculate the tetrahedron volume that all the other visible stars and first three satellite of having selected are formed, concrete computing method are seen formula (2), select to make the maximum satellite of volume as the 4th the satellite S4 that selects the star result.

Whether the GDOP value of 9, judging selected four stars combination is less than the GDOP threshold value that is provided with in the step 1.If less than, then select star to finish; If be not less than, then conduct a by-election one with the maximum satellite of selected back three satellite aximuth absolute difference sums as the 5th the satellite S5 that selects the star result, select the star end.

Further specify the present invention with concrete numerical value below.

Select for use GPS, GLONASS and GALILEO system to carry out the emulation explanation respectively, wherein GPS considers by 27 stars by 24 stars considerations, GALILEO systems by 32 stars considerations, GLONASS.Ephemeris is with reference to constantly being chosen for 0: 0: 0 on the 1st January of UTC2006, and the user observation place is chosen for Beijing area (latitude: 39 ° of north latitude, longitude: 116 ° of east longitudes).

1, obtain the GDOP experiment statistics of best combinations of satellites according to the traversal method, the GDOP threshold value of GPS, GLONASS and GALILEO system is set at 3,4,4 respectively, and it is 5 ° that the height cutoff angle is set.

2, reject the non-healthy star in the satellite navigation system according to the correlation parameter that characterizes the satellite health situation in the satellite ephemeris, calculate the position coordinates of other each satellite under the ECEF coordinate system.And obtain visible star sum n according to the height cutoff angle.

1) visible star sum n=10 among the GPS, being numbered of all visible stars:

03，13，15，16，19，21，23，25，31，32；

2) visible star sum n=6 among the GLONASS, being numbered of all visible stars:

12，13，14，22，23，24；

3) visible star sum n=9 in the GALILEO system, being numbered of all visible stars:

04，05，06，11，12，13，23，24，25。

3, calculate each visible star position coordinates under the ENU coordinate system, and carry out unitization, write down its position coordinates on the unit sphere that with user is the centre of sphere.

4, calculate the elevation angle and the position angle of each visible star.

1) the corresponding elevation angle of visible star is among the GPS:

61.81，35.96，13.28，59.48，25.50，11.28，55.22，33.24，16.11，64.66；

Corresponding position angle is:

177.87，306.37，91.62，38.16，195.77，65.09，258.94，118.05，172.68，293.47。

2) the corresponding elevation angle of visible star is among the GLONASS:

50.61，69.10，15.90，38.21，80.67，27.15；

Corresponding position angle is:

134.10，338.88，324.75，32.42，263.83，222.59。

3) corresponding elevation angle is in the GALILEO system:

42.75，71.75，33.94，35.50，59.03，32.22，7.08，16.88，11.70；

Corresponding position angle is:

308.61，37.50，96.80，177.15，110.98，49.97，318.78，275.88，231.35。

Select the maximum satellite of elevation angle as first the satellite S1 that selects the star result then.

Selected first the satellite S1 of GPS is: 32;

Selected first the satellite S1 of GLONASS is: 23;

Selected first the satellite S1 of GALILEO system is: 05.

5, judge that according to visible star sum for GPS, n=10＞6 change step 6 over to;

For GLONASS, n=6, the combination of traversal Samsung is calculated corresponding tetrahedron volume according to formula (2) in five stars except that S1, selects corresponding tetrahedron volume maximum three star S2, S3, S4 and is followed successively by: 12,14,24.Change step 9 then over to;

For the GALILEO system, n=9＞6 change step 6 over to.

6, calculate each visible star in position and the distance of S1 between position corresponding on the unit sphere corresponding on the unit sphere.

For GPS, each visible star is followed successively by with the distance of No. 32 stars between position corresponding on the unit sphere in position corresponding on the unit sphere: 0.764,0.512,1.535,0.741,1.153,1.483,0.337,1.313,1.387.No. 15 satellites choosing maximal value 1.535 correspondences are as S2.

For GALILEO, each visible star is followed successively by with the distance of No. 05 star between position corresponding on the unit sphere in position corresponding on the unit sphere: 0.835,0.822,1.135,0.529,0.686,1.281,1.326,1.486.No. 25 satellites choosing maximal value 1.486 correspondences are as S2.

7, the elevation angle of the elevation angle of all the other visible stars and S2 is poor, and take absolute value.

For GPS, its value is followed successively by: 48.53,22.69,46.21,12.23,2.00,41.94,19.96,2.83.Selected value is less than No. 19, No. 21 and No. 31 satellites of 15 ° 12.23,2.00 and 2.83 correspondences, and the position angle that these three satellites are corresponding and the position angle of No. 15 stars are poor, and take absolute value.Its value is followed successively by: 104.15,26.53,81.06.These values differ from itself and 120 °, and take absolute value all less than 180 °, and its value is followed successively by: 15.85,93.47,38.94.Judge minimum value 15.85＜30, choose its No. 19 corresponding satellites as the 3rd the satellite S3 that selects the star result.

For the GALILEO system, its value is followed successively by: 31.04,22.24,23.80,47.33,20.52,4.62,5.17.Selected value is less than No. 23 and No. 24 satellites of 15 ° 4.62 and 5.17 correspondences, and the position angle that these two satellites are corresponding and the position angle of No. 25 stars are poor, and take absolute value.Its value is followed successively by: 87.43,44.52.These two values are all less than 180 °, itself and 120 ° are differed from, and take absolute value, and its value is followed successively by: 32.57,75.48.These two values are all greater than 30 °; On 15 ° basis, be the restriction that step-length increases elevation angle difference absolute value gradually then with 5 °; The satellite of elevation angle difference absolute value between 15 °-20 ° do not exist; Continue to choose No. 06, No. 11 and No. 13 satellites of 22.24,23.80 and 20.52 correspondences of elevation angle difference absolute value between 20 °-25 °, the position angle that these three satellites are corresponding and the position angle of No. 25 satellites are poor, and take absolute value.Its value is followed successively by: 134.55,54.20,181.38.Differ from 120 ° or 240 ° respectively based on its value size, and take absolute value, its value is followed successively by: 14.55,65.8,58.62.Judge minimum value 14.55＜30, choose its No. 06 corresponding satellite as the 3rd the satellite S3 that selects the star result.

8, calculate the tetrahedron volume that all the other visible stars and first three satellite of having selected are formed, select to make the maximum satellite of volume as the 4th the satellite S4 that selects the star result.For GPS, S4 is No. 13 satellites.For GALILEO, S4 is No. 23 satellites.

9, judge whether needs by-election satellite according to the GDOP threshold value that is provided with in the step 1.

For GPS, therefore corresponding GDOP=4.004＞3 of having selected of four stars combination need elect satellite additional member.Calculate other visible star and back three satellite aximuth absolute difference sums of having selected, choose and make that the maximum satellite of this value is No. 16 satellites.Therefore, for the final star result that selects of GPS be: 13,15,16,19,32.

For GLONASS, therefore corresponding GDOP=3.561＜4 of having selected of four stars combination need not elect satellite additional member, and the star result that selects that it is final is: 12,14,23,24.

For the GALILEO system, therefore corresponding GDOP=2.474＜4 of having selected of four stars combination need not elect satellite additional member, and the star result that selects that it is final is: 05,06,23,25.

Shown in Figure 2 for before selecting star, traditional traversal method is selected behind the star and the inventive method is selected the visible star station heart view behind the star.The center of circle representes that elevation angle is 90 ° position among the figure, and circle from the inside to surface representes that respectively elevation angle is the position of 45 ° and 0 °.Can find out that by figure the method for the invention and traditional traversal method select the star the possibility of result inconsistent, the inventive method is selected five stars at most for use, minimumly selects four stars for use, is far smaller than the satellite number that selects star preceding.

Fig. 3 has shown respectively that with Fig. 4 the Beijing area user GDOP result that different traditional traversal methods constantly selected star and the inventive method to select star to calculate at a day compares and spent result of calculation compares.Can find out that by Fig. 3 the GDOP result that the inventive method selects star to calculate is similar with traditional traversal method result of calculation.Can not satisfy accuracy requirement to some constantly optimum corresponding GDOP value of four stars, the present invention adopts the method for a star of by-election to reduce GDOP value, so some moment the inventive method result of calculation even travel through method result of calculation less than tradition.Can find out that by Fig. 4 the inventive method selects the spent time of star to be far smaller than traditional traversal method consumed time, selects star speed on average to improve about 10 times.

Single constellation star choosing method for satellite navigation system of the present invention can be used for any GLONASS; Under the prerequisite of sacrificing a small amount of bearing accuracy; Solved effectively and had a large amount of matrix multiplications and the problem of matrix inversion in traditional satellite selection method; Reduced calculated amount and promoted the receiver processing speed, also satisfied the requirement of high dynamic subscriber simultaneously real-time.

Claims (5)

1. satellite selection method that is used for single constellation satellite navigation system is characterized in that: may further comprise the steps:

Step 1, according to the number of satellite and the layout of different GPS constellations, the GDOP threshold value of selected combinations of satellites is set; According to the receiver present position visual field of satellite in the satellite navigation system is provided with the height cutoff angle;

Step 2, reject the non-healthy star in the satellite navigation system based on the relevant parameter that characterizes the satellite health situation in the satellite ephemeris; Calculate the position coordinates of each healthy satellite under the body-fixed coordinate system of the earth's core, and in healthy satellite, obtain visible star sum n based on the height angle of cut-off that step 1 is provided with;

Step 3, the visible coordinate conversion of star under the body-fixed coordinate system of the earth's core arrived customer-centric; Be in the ENU coordinate system of three of coordinate systems with its east orientation, north orientation and zenith direction respectively; And unitization, write down its position coordinates on the unit sphere that with user is the centre of sphere;

Step 4, in the ENU coordinate system, calculate the elevation angle and the position angle of each visible star, and select the maximum satellite of elevation angle as first the satellite S1 that selects the star result;

Step 5, the visible star sum of basis are judged; If n≤6; Then traversal Samsung combination in the visible star of residue, select the maximum Samsung combination conduct of the tetrahedron volume corresponding with S1 combination back select the star result second and third, four star S2, S3, S4, change step 9 then over to; If n＞6 change step 6 over to;

Step 6, calculate each visible star in position and the distance of S1 between position corresponding on the unit sphere corresponding on the unit sphere, second satellite S2 of star result selected in the visible star conduct of chosen distance maximum;

Step 7, choose the 3rd satellite S3;

Step 7.1, the elevation angle of elevation angle of removing the visible star beyond fixed S1, the S2 and S2 is poor, take out the satellite of the absolute value of difference less than α;

Step 7.2, the position angle of the satellite that step 7.1 is obtained and the position angle of S2 are poor; If the absolute value of difference then differs from this absolute value greater than 180 ° again with 240 °; If the absolute value of difference differs from this absolute value less than 180 ° again with 120 °;

Step 7.3 is found out the minimum satellite of absolute value in the difference that step 7.2 obtains, and judges that whether this absolute value is less than β; If less than, then this star is elected to be the 3rd satellite S3; If be not less than; Then on the basis of α, increase the absolute difference of elevation angle gradually with a fixed step size; Again choose satellite less than new absolute difference; Poor to the satellite aximuth of newly choosing again according to the method for step 7.2 then, up to find make the absolute value of position angle difference less than the satellite of β as the 3rd the satellite S3 that selects the star result;

If when elevation angle difference absolute value is increased to 30 °, also do not select the satellite of the absolute value of position angle difference less than β, when then getting elevation angle difference absolute value and being 30 °, star result's the 3rd satellite S3 selected in difference absolute value minimum satellite conduct in position angle;

Step 8, calculate all the other visible stars and the tetrahedron volume that first three the satellite S1 that has selected, S2, S3 form, select to make the maximum satellite of volume as the 4th the satellite S4 that selects the star result;

Step 9, judge the combination of selected four stars GDOP value whether less than the GDOP threshold value of setting in the step 1; If less than, then select star to finish; If be not less than, then conduct the 5th the satellite S5 that the star result is selected in a satellite conduct with S2, S3, S4 position angle difference absolute value sum maximum a by-election, select star to finish.

2. a kind of satellite selection method that is used for single constellation satellite navigation system according to claim 1 is characterized in that: the open degree in the visual field is inversely proportional to the height cutoff angle.

3. a kind of satellite selection method that is used for single constellation satellite navigation system according to claim 1 is characterized in that: α is generally less than 30 ° in the practical implementation.

4. a kind of satellite selection method that is used for single constellation satellite navigation system according to claim 1 is characterized in that: the size of β value satisfies makes S3 and S2 position angle difference absolute value near 120 ° or 240 °, and as a kind of embodiment, the β value is taken as 30 °.

5. a kind of satellite selection method that is used for single constellation satellite navigation system according to claim 1 is characterized in that: be applicable to all GLONASSs.

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