CN101614804A - Bit synchronous method of gps navigation message data and device under the weak signal - Google Patents

Abstract

Bit synchronous method of gps navigation message data and device under a kind of weak signal, method of the present invention comprises: the GPS receiver enters into gps satellite signal trapped state and collection and acquisition and waits to catch the gps satellite signal data; The maximum likelihood of the bit boundary of calculating in single navigation message data bit; Calculate the maximum likelihood of the navigation message data bit boundary under the preseting length; According to the border and the data value of the judicious navigation message data bit of aforementioned calculation result, and judge that whether signal outputs to the gps signal tracking module to carry out the auxiliary of following function, up to auxiliary following function is arranged, carries out bit synchronous operation.The present invention can be fast and accurately obtain the exact position of the phase overturn of gps navigation message data under the faint situation of gps satellite signal, thereby make the GPS receiver enter tracking mode smoothly to realize positioning function.

Description

Bit synchronous method of gps navigation message data and device under the weak signal

Technical field

The present invention relates to GPS (GPS) positioning and navigation field, more particularly, relate to a kind of gps satellite positioning and navigation receiver realizes bit synchronous method of gps navigation message data and use under the faint situation of gps satellite signal device that is used for.

Background technology

The GPS location technology is to utilize high aerial gps satellite, launches the carrier frequency radio distance-measuring signal of L-band earthward, is received continuously in real time by receiver user on the ground, calculates the position at receiver antenna place thus.The space segment of gps system is made up of gps satellite, is called satellite constellation.The distribution setting of satellite constellation will guarantee that the earth takes up an official post where to put at any time and can observe four satellites simultaneously at least.

When gps satellite when user's visual field rises, the receiver user on ground can capture the signal by the selected satellite to be measured of certain satellite altitude cutoff angle, and can follow the tracks of the operation of these satellites; To received gps signal, carry out conversion, amplification and the processing of data,, separate and translate the navigation message that gps satellite sends so that measure the travel-time of gps signal from the satellite to the receiving antenna, calculate the three-dimensional position of receiver in real time, even three-dimensional velocity and time.

The GPS receiver is mainly realized navigation locating function by four main functions.These functions comprise catches the gps satellite signal of sky, catch after finishing the gps satellite signal that has captured is followed the tracks of, be to obtain the navigation message information of modulating in the gps satellite signal then, according to the textual information after the demodulation and temporal information in order to carry out the position calculation at receiver user place, final navigation and the positioning function of realizing.

Realize in the link of positioning function at the GPS receiver, the demodulation of the navigation message data of gps satellite signal is an important link, no matter how success of the Base-Band Processing of GPS receiver, how outstanding the acquisition sensitivity of GPS receiver and tracking sensitivity be, when correct demodulation gps satellite navigation message data, all can't export the locating information of locating information or even output error.And the key of correct demodulation navigation message information is exactly to realize the bit synchronization process of navigation message data, accurately and fast the data boundary of location navigation telegraph text data.

In the GPS of routine receiver, the gps satellite capturing function of receiver can obtain the essential informations such as carrier frequency C/A sign indicating number initial phase of gps satellite signal, utilize these information, the GPS receiver can be correct the tracking mode that enters gps satellite, under tracking mode, obtain the bit flipping of navigation message data then.But under faint gps satellite signal situation, the accurate judgement of being carried out the navigation message data by the signal trace function of GPS receiver is very difficult, and this makes the overall sensitivity of conventional GPS receiver be limited in the demodulation of navigation message data.

Summary of the invention

The objective of the invention is to overcome the problem that above-mentioned prior art exists, provide a kind of under faint gps satellite signal situation, the GPS receiver realizes that the navigation message data bit can draw bit synchronous method of gps navigation message data and device under the weak signal of numerical value of the navigation message data bit position of optimal estimation and data synchronously.

Method of the present invention be at the GPS receiver when catching gps satellite signal, the mode that adopts data ordering and navigation message data maximum likelihood to approach, obtain the data boundary of gps signal navigation message data fast and accurately, thereby realize that GPS receiver correct completion bit under the situation of weak signal is synchronous.

Below introduce in detail the technical scheme that realizes the object of the invention:

The bit synchronous method of gps navigation message data under a kind of weak signal is to realize that by the GPS receiver navigation message data are bit synchronous, it is characterized in that may further comprise the steps:

First step, GPS receiver enter into gps satellite signal trapped state and collection and acquisition and wait to catch the gps satellite signal data;

Second step, the maximum likelihood of the bit boundary of calculating in single navigation message data bit;

Third step, the maximum likelihood of the navigation message data bit boundary under the calculating preseting length;

The 4th step, according to the maximum likelihood that calculates the navigation message data bit boundary that obtains, the border of judicious navigation message data bit and data value, and judge whether signal outputs to the gps signal tracking module to carry out the auxiliary of following function, up to auxiliary following function is arranged, carry out bit synchronous operation.

The bit synchronous device of gps navigation message data under a kind of weak signal is to be made of the module that places the GPS receiver, it is characterized in that comprising:

The gps signal data acquisition module is in order to gather gps satellite signal data pending and that calculate;

The gps signal trapping module is in order to catch gps satellite signal from described gps signal data acquisition module;

Gps signal data bit synchronization module calculates and judgement synchronously in order to the gps satellite signal data of gathering in the described gps signal data acquisition module are carried out the gps navigation message data bit;

The gps signal tracking module is in order to follow the tracks of the gps satellite signal that described gps signal trapping module and gps signal data bit synchronization module have captured, to realize follow-up bit synchronization positioning function.

Beneficial effect of the present invention:

The method of the invention is to be under the gps satellite trapped state and can to carry out at the GPS receiver, the GPS receiver system need not to enter the GPS tracking mode, the inventive method need obtain the gps satellite signal data before carrying out simultaneously, and data length requires according to the GPS receiver performance and arithmetic capability is set.

The method of the invention is in the navigation message data boundary maximum likelihood situation of calculating under the preseting length, be under the condition of weak output signal, carry out when two and two are above in order to the gps signal data length that calculates navigation message data boundary maximum likelihood, by surpassing the data computation of several navigation message data bit, the calculating of navigation message data boundary will be more accurate.

The method of the invention is after calculating the maximum likelihood that obtains the navigation message data bit boundary, can determine the possible bit boundary of navigation message data, the operating result of catching that cooperates the GPS receiver simultaneously, directly the assistant GPS receiver is finished the tracking operation of gps satellite signal, finishes the demodulation operation of navigation message data simultaneously.

The method of the invention is when realizing, and is very little to GPS receiver system demand, the convenient realization.In the gps satellite signal processing procedure, break away from conventional dependence GPS receiver tracking functional module and realize the bit synchronous mode of navigation message data, can catch operation with gps satellite in GPS receiver acquisition function phases carries out simultaneously, finish the bit synchronous operation of navigation message data more fast, simultaneously finished the navigation message data bit synchronously after, can with the capturing function assistant GPS receiver system tracking mode that enters gps satellite simultaneously.

Simultaneously the method for the invention when realizing owing to be to be in acquisition phase at the GPS receiver to carry out, can set length as required in order to the gps signal data of calculating the navigation message data bit boundary, like this under the faint situation of gps satellite signal, can accurately finish the detection of navigation message data bit boundary and determining of navigation message data value equally fast, the quick more and accurate exact position that obtains the phase overturn of gps navigation message data, thus make the GPS receiver enter tracking mode smoothly to realize positioning function.

For further specifying above-mentioned purpose of the present invention, design feature and effect, the present invention is described in detail below with reference to accompanying drawing.

Description of drawings

Fig. 1 is the flow chart of steps of the method for the invention.

Fig. 2 is to gps navigation message data bit data in synchronization processing module figure in the typical GPS receiver.

Fig. 3 is single gps navigation message data bit boundary maximum likelihood calculating chart.

Fig. 4 is a navigation message data bit boundary maximum likelihood calculating chart under the preseting length.

Fig. 5 is the navigation message data structure diagram of gps satellite signal modulation.

Embodiment

Be elaborated below in conjunction with the embodiment of accompanying drawing to the bit synchronous method of gps navigation message data under the weak signal of the present invention.

Referring to Fig. 5, Fig. 5 is the navigation message data structure diagram of gps satellite signal modulation, and as shown in Figure 5, the least unit of the navigation message data of gps satellite is position (bit), and its length is 20 milliseconds, takies 20 C/A chips altogether.It is one of 1 millisecond of expression of per 20 standards.So obtain the navigation message data of satellite, what at first need to do is 1 millisecond of border seeking and lock per 20 millisecond of one bit data, is about to 1 millisecond continuous data and is divided into 20 milliseconds data by lattice, and this operation is called bit synchronization.X among Fig. 5 is that 1 frame is 5 subframes; Y is that 1 subframe is 10 words; Z is that 1 word is 10 (bit); W is that the 4th, 5 subframes contain 25 pages.

Referring to Fig. 2, Fig. 2 is to gps navigation message data bit data in synchronization processing module figure in the GPS receiver, in the GPS receiver system as shown in Figure 2, gps navigation message data bit data in synchronization treating apparatus is mainly comprised following four main modular: gps signal data acquisition module 21, in order to gather gps satellite signal data pending and that calculate; Gps signal trapping module 22 is in order to catch gps satellite signal from gps signal data acquisition module 21; Gps signal data bit synchronization module 23 calculates and judgement synchronously in order to the gps satellite signal data of gathering in the gps signal data acquisition module 21 are carried out the gps navigation message data bit; Gps signal tracking module 24 is in order to follow the tracks of gps satellite signal that gps signal trapping module 22 and gps signal data bit synchronization module 23 captured to realize follow-up bit synchronization positioning function.A typical GPS receiver system also comprises other accordingly as functional modules such as position calculation except that the gps signal data processing module, do not contact directly because of having with the method for the invention, so do not give unnecessary details at this.

Referring to Fig. 1, Fig. 1 is the workflow diagram of the bit synchronous method of gps navigation message data under the weak signal of the present invention, promptly is that the GPS receiver is realized the bit synchronous process flow diagram of navigation message data, is described in detail as follows.

S10, the gps signal data acquisition module 21 in the GPS receiver enters into the gps satellite signal trapped state.

S11 waits to catch the gps satellite signal data by 22 collections of gps signal trapping module and acquisition.

S12 carries out the calculating of the maximum likelihood of the bit boundary in single navigation message data bit by gps signal data bit synchronization module 23 with the gps satellite signal data of gathering.

S13 is finished the calculating of the maximum likelihood of the navigation message data bit boundary under the preseting length by gps signal data bit synchronization module 23.

S14 is by the maximum likelihood of gps signal data bit synchronization module 23 according to the navigation message data bit boundary of calculating acquisition, the border of judicious navigation message data bit and data value.

S15 according to the result of acquisition procedure, judges by gps signal data bit synchronization module 23 whether signal outputs to gps signal tracking module 24 to carry out the auxiliary of following function, if not auxiliary following function, flow process is returned S11 again.

S16 if auxiliary following function is arranged, carries out bit synchronous operation.

In process flow diagram shown in Figure 1, calculate when the maximum likelihood of single navigation message data bit boundary, employing be Doppler frequency correction and the pseudo-random code sequence correction of being adopted according to GPS receiver acquisition gps satellite.When setting up signal model simultaneously, what noise model adopted is the additive white Gaussian noise model, calculates by likelihood function, draws the navigation message data bit position of optimal estimation and the numerical value of data.

When in above-mentioned flow process S12, calculating the maximum likelihood of single navigation message data bit boundary, according to single navigation message data layout, as shown in Figure 3, for the navigation message data bit of a standard, comprised 20 basic correlation units, can be expressed as for the energy of each elementary cell:

D _i=Ad _i+ n _iFormula 1

In the formula, D _iBe the energy value of i basic correlation unit, A is the gps signal energy value that receives, d _iBe the data value of i basic correlation unit modulation, d _iBe 1 or-1.n _iIt is the noise power value of i basic correlation unit.

When calculating gps navigation message data boundary maximum likelihood, suppose that a is the possible data border of current calculating, b is real data boundary, then has:

$B_a=\frac{1}{\sqrt{20}}\underset{i=a}{\overset{a+19}{\mathrm{\Σ}}}{D}_i$ Formula 2

B is real data boundary, and formula 1 substitution formula 2 can be got following formula:

$\underset{i=a}{\overset{a+19}{\mathrm{\Σ}}}{D}_i=\{\underset{j=a}{\overset{b}{\mathrm{\Σ}}}A{d}_j+\underset{j=b+1}{\overset{a+19}{\mathrm{\Σ}}}A{d}_{j+1}\}+\underset{i=a}{\overset{a+19}{\mathrm{\Σ}}}{n}_i$ Formula 3

According to formula 3, if a is a correct bit boundary or when just in time being the data bit of two adjacent same symbols, B _aThen will be maximal value, otherwise since different data symbol positions, B _aWill diminish.Under the normal condition, this is very easy to be judged, but under weak gps signal situation, the noise B that will seriously decay _aValue, therefore when data bit is estimated, the mode of using maximum likelihood to approach.Suppose B _aBe normal distribution, n _iBe additive white Gaussian noise (noise model adopt be the additive white Gaussian noise model), d _iBe the data value of equiblibrium mass distribution, the maximum likelihood of the bit boundary of gps signal data and data value can obtain by finding the solution maximal value so.Just have:

$\begin{array}{c}\mathrm{Max}\\ {\left\{d\right\}}_1^N\end{array}f\left(S\right|{\left\{d\right\}}_1^N,b)$ Formula 4

F (S|{d} in the formula ₁ ^N, b) be the maximum likelihood function of S, setting A is the expectation energy value of gps signal data, then has:

p _{1, a}=| B _a-Ad ₁| ² Formula 5

P in the formula _{1, a}It then is the weighting function of this single navigation data bits.

After having calculated the weighting function of single navigation data bits, in above-mentioned flow process S13, begin to calculate the maximum likelihood of the navigation message data bit boundary of preseting length.Referring to Fig. 4, Fig. 4 is a navigation message data bit boundary maximum likelihood calculating chart under the preseting length, hypothesis is calculated the data ( data 1,2,3,4,5) of 5 gps data bit lengths altogether among the figure, under the bit boundary of each supposition, two kinds of possible data values 1 and-1 is arranged all.Calculate gained according to aforementioned single navigation message data bit maximum likelihood, can get under the situation of multidata position:

p _{N, a}=| B _{N, a}-Ad _n| ² Formula 6

N is the current data bits that calculates in the formula.And calculate p successively by the political reform combination of navigation message data value shown in Figure 4 _{N, a}After, calculating the pairing a of gained minimum value is the boundary value of navigation message data bit.So far, the measuring and calculating of navigation message data boundary is finished.

The device of aforementioned calculation and operating process and use is the exemplary embodiment of the method for the invention and device, the above implementation method and the device of use only are to be used for illustrating purpose of the present invention, and be not as limitation of the invention, for one of ordinary skill in the art, on the basis of above-mentioned implementation method and device, multiple variation can be done, purpose of the present invention can be realized equally.But this variation obviously should be in the protection domain of claims of the present invention.

Claims (4)

1, the bit synchronous method of gps navigation message data under a kind of weak signal is to realize that by the GPS receiver navigation message data are bit synchronous, it is characterized in that may further comprise the steps:

First step, GPS receiver enter into gps satellite signal trapped state and collection and acquisition and wait to catch the gps satellite signal data;

Second step, the maximum likelihood of the bit boundary of calculating in single navigation message data bit;

Third step, the maximum likelihood of the navigation message data bit boundary under the calculating preseting length;

The 4th step, according to the maximum likelihood that calculates the navigation message data bit boundary that obtains, the border of judicious navigation message data bit and data value, and judge whether signal outputs to the gps signal tracking module to carry out the auxiliary of following function, up to auxiliary following function is arranged, carry out bit synchronous operation.

2, the bit synchronous method of gps navigation message data under the weak signal as claimed in claim 1 is characterized in that:

The maximum likelihood that calculates in described second step in single navigation message data bit boundary is that the navigation message data bit of a standard has comprised a plurality of basic correlation units according to single navigation message data layout, for the energy of each elementary cell is:

D _i=Ad _i+ n _iFormula 1

In the formula, D _iBe the energy value of i basic correlation unit, A is the gps signal energy value that receives, d _iBe the data value of i basic correlation unit modulation, d _iBe 1 or-1.n _iIt is the noise power value of i basic correlation unit;

When calculating gps navigation message data boundary maximum likelihood, establishing a is the possible data border of current calculating, and b is real data boundary, then has:

$B_a=\frac{1}{\sqrt{20}}\underset{i=a}{\overset{a+19}{\mathrm{\Σ}}}{D}_i$ Formula 2

Above-mentioned formula 1 substitution formula 2 can be got following formula:

$\underset{i=a}{\overset{a+19}{\mathrm{\Σ}}}{D}_i=\{\underset{j=a}{\overset{b}{\mathrm{\Σ}}}{\mathrm{Ad}}_j+\underset{j=b+1}{\overset{a+19}{\mathrm{\Σ}}}{\mathrm{Ad}}_{j+1}\}+\underset{i=a}{\overset{a+19}{\mathrm{\Σ}}}{n}_i$ Formula 3

When data bit was estimated, the mode of using maximum likelihood to approach was established B _aBe normal distribution, n _iBe additive white Gaussian noise, d _iBe the data value of equiblibrium mass distribution, then the maximum likelihood of the bit boundary of gps signal data and data value can obtain by finding the solution maximal value:

$\begin{array}{c}\mathrm{Max}\\ {\left\{d\right\}}_1^N\end{array}f\left(S\right|{\left\{d\right\}}_1^N,b)$ Formula 4

F (S|{d} in the formula ₁ ^N, b) be the maximum likelihood function of S, setting A is the expectation energy value of gps signal data, then has:

p _{1, a}=| B _a-Ad ₁| ²Formula 5

P in the formula _{1, a}It then is the weighting function of this single navigation data bits.

3, the bit synchronous method of gps navigation message data under the weak signal as claimed in claim 1 or 2 is characterized in that:

Calculate the maximum likelihood of the navigation message data bit boundary under the preseting length in the described third step

If calculate the data of n gps data bit length altogether, under the bit boundary of each supposition, two kinds of possible data values 1 and-1 are arranged all, calculate gained according to described single navigation message data bit maximum likelihood, can get under the situation of a plurality of data bit:

p _{N, a}=| B _{N, a}-Ad _n| ²Formula 6

N is the current data bits that calculates in the formula, and a is possible data boundary, calculates p successively according to the political reform combination of navigation message data value _{N, a}After, calculating the pairing a of gained minimum value is the boundary value of navigation message data bit.

4, the bit synchronous device of gps navigation message data under a kind of weak signal is to be made of the module that places the GPS receiver, it is characterized in that comprising:

The gps signal data acquisition module is in order to gather gps satellite signal data pending and that calculate;

The gps signal trapping module is in order to catch gps satellite signal from described gps signal data acquisition module;

Gps signal data bit synchronization module calculates and judgement synchronously in order to the gps satellite signal data of gathering in the described gps signal data acquisition module are carried out the gps navigation message data bit;

The gps signal tracking module is in order to follow the tracks of the gps satellite signal that described gps signal trapping module and gps signal data bit synchronization module have captured, to realize follow-up bit synchronization positioning function.

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