CN103499825B - Method for rapidly capturing BDS weak signals of high-orbit spacecraft - Google Patents

Abstract

The invention discloses a method for rapidly capturing BDS weak signals of a high-orbit spacecraft. The method includes the steps that NH code phases are removed through 2ms data overlapping and accumulation and autocorrelation of NH codes, weak signal capturing is finished by the cooperation of 20ms coherent accumulation with multiple times of incoherent accumulation, a parallel code phase search strategy based on FFT/IFFT is adopted, and therefore capturing speed is improved. By the adoption of the method, the problem that coherent accumulation time can not be prolonged because the NH code phases of the BDS signals are unknown can be solved, capturing sensitivity of the BDS signals is high, the capturing speed of the BDS signals is high, and the method can be widely applied to a BDS navigation receiver which is used for executing a high-orbit task, a moon exploration return task and other spaceflight tasks, and has wide popularization and application prospect.

Description

A kind of high rail spacecraft BDS weak signal quick capturing method

Technical field

The present invention relates to a kind of high rail spacecraft BDS(triones navigation system) weak signal fast Capture Technique, can be used for exchanging the satellite navigation signals being shaped with the secondary codings such as NH code (Neumann-Hoffman code) and carry out weak signal fast Acquisition, belong to satellite application field.

Background technology

High rail spacecraft all plays an important role in recent years in land and overocean communications, aerological sounding, educational applications, live telecast, disaster early warning etc., particularly geostationary orbit spacecraft, with the stationary characteristic over the ground of its uniqueness, become communication, meteorology, scouting, time service and follow the tracks of and the important track resources of the earth satellite such as data relay and scientific research.The quantity of China to high rail spacecraft demand increases year by year, and the independent navigation of high rail spacecraft has become the space flight new technology of China in the urgent need to development.

GPS (Global Position System) relies on its global, round-the-clock, continuous and high-precision feature, plays an important role in national defence, national security, economic security and social life.China just has the BDS (triones navigation system) of Global coverage ability in early implementation construction, expect the year two thousand twenty and possess basic service ability.High rail spacecraft use navigation neceiver to become the focus of all kinds of engineer applied.

Because high rail spacecraft orbit height is higher than navigation constellation, receiver needs to receive the navigation satellite signal from earth opposite.The earth block and the increase of signal propagation distance causes the factors such as received power reduction, will cause using conventional receiver technology to there is the shortcomings such as visible star number reduces, the navigation signal duration is short, received signal power is faint.

Solving and receiving the faint basic ideas of pilot signal power is adopt multicycle signal energy accumulation, by the Cumulative sum (coherent accumulation, non-coherent accumulation) to multiple 1ms correlation, brings signal to noise ratio (S/N ratio) to promote.But there is NH code in BDS, will in acquisition procedure, the problem causing coherent accumulation length limited because NH code phase is unknown; If only adopt non-coherent accumulation process, now need data to be processed by huger than data during coherent accumulation, reduce acquisition speed simultaneously, thus cause high rail to receive the difficulty of BDS signal.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of high rail spacecraft BDS weak signal quick capturing method is provided, the present invention can overcome because NH code phase is unknown and limit the problem that coherent accumulation length causes efficiently promoting accumulated process gain, can be used for designing the BDS navigation neceiver with higher acquisition sensitivity level, practical.

Technical solution of the present invention is:

A kind of high rail spacecraft BDS weak signal quick capturing method, comprises step as follows:

(1) obtain the 1ms data under local values of Doppler frequency shift, by its zero padding to 2ms, and FFT conversion is carried out to these data, after getting conjugation, obtain data 1;

(2) carry out continuous print 2ms data buffer storage respectively after the intermediate-freuqncy signal of reception being carried out digital sample, namely 1ms and 2ms carries out buffer memory, and 2ms and 3ms carries out buffer memory, and buffer memory 20 groups, obtains data 2 successively;

(3) the 2ms data of often organizing in the data 2 obtained in step (2) be multiplied with a chip of 20 bit NH codes successively respectively, described NH code is 0,0,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,1,0, obtain 20 groups to be multiplied with NH code after data 3;

(4) coherent accumulation is carried out to 20 groups of 2ms data that step (3) obtains in data 3, obtains the coherent accumulation value that length is 2ms, and carry out FFT operation obtain data 4;

(5) respectively data 4 are multiplied with data 1 successively contraposition, obtain data 5, IFFT conversion is carried out to data 5 again and obtains data 6;

(6) repeatedly non-coherent accumulation is carried out to data 6, obtain 1 group of data 7;

(7) Nai Man-Pierre's Si criterion is utilized to carry out detection threshold judgement to data 7, judge whether successfully lock-on signal, if successful lock-on signal enters step (9), otherwise judge whether 20 NH code phases have been searched for, if do not have search to complete, enter step (8), if searched for the local values of Doppler frequency shift of change to enter step (1);

(8) to NH code ring shift chip of 20 bits, enter step (2), repeat step (2) ~ (7);

(9) end is caught.

The present invention's beneficial effect is compared with prior art:

(1) when the present invention is directed to coherent accumulation, the unknown of NH code phase causes carrying out long-time accumulation problem, adopts and accumulates the overlap of 2ms data, eliminate this impact, extends the coherent accumulation time to 20ms, thus improves the acquisition sensitivity of BDS signal.

(2) present invention employs the mode of overlapping accumulated value being carried out to non-coherent accumulation, improve processing gain further.

(3) the present invention adopts and to walk abreast code phase fast search based on FFT/IFFT, greatly in engineering must improve acquisition speed, reduces the resource loss brought 20msNH code auto-correlation computation.

Accompanying drawing explanation

Fig. 1 is the inventive method process flow diagram;

Fig. 2 is the NH code searching principle schematic of 2ms data overlap of the present invention accumulation;

Fig. 3 the present invention is that input signal is multiplied with NH code schematic diagram;

Fig. 4 the present invention is NH code auto-correlation schematic diagram;

Fig. 5 the present invention is 2ms data overlap accumulated process schematic flow sheet.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is further described in detail.

One provided by the invention high rail BDS weak signal quick capturing method, can be used for design and there is weak signal processing power BDS navigation neceiver, the present invention removes NH code phase by the accumulation of 2ms data overlap, complete the weak signal acquisition procedure that 20ms coherent accumulation coordinates several times non-coherent accumulation, and adopt the parallel code phase search strategy based on FFT/IFFT, improve acquisition speed.

As shown in Figure 1, concrete steps of the present invention are as follows:

(1) obtain the 1ms data under local values of Doppler frequency shift, by its zero padding to 2ms, and FFT conversion is carried out to these data, after getting conjugation, obtain data 1;

(2) carry out continuous print 2ms data buffer storage respectively after the intermediate-freuqncy signal of reception being carried out digital sample, namely 1ms and 2ms carries out buffer memory, and 2ms and 3ms carries out buffer memory, and buffer memory 20 groups, obtains data 2 successively;

(3) the 2ms data of often organizing in the data 2 obtained in step (2) be multiplied with a chip of 20 bit NH codes successively respectively, described NH code is 0,0,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,1,0, obtain 20 groups to be multiplied with NH code after data 3;

(4) the 20 groups of 2ms data obtained in data 3 step (3) carry out coherent accumulation (such as: the 1st group of 2ms data and the 2nd group of 2ms accumulate, result after accumulation is accumulated with the data of the 3rd group of 2ms again, until 20 groups of 2ms data coherency accumulations terminate), obtain the coherent accumulation value that length is 2ms, and carry out FFT operation obtain data 4;

(5) respectively data 4 are multiplied with data 1 successively contraposition, obtain data 5, IFFT conversion is carried out to data 5 again and obtains data 6;

(6) repeatedly non-coherent accumulation is carried out to data 6, obtain 1 group of data 7; Number of times data 6 being carried out to non-coherent accumulation is relevant with acquisition sensitivity, and the acquisition sensitivity of requirement is higher, and it is more to carry out incoherent accumulative number of times;

(7) Nai Man-Pierre's Si criterion is utilized to carry out detection threshold judgement to data 7, judge whether successfully lock-on signal, if successful lock-on signal enters step (9), otherwise judge whether 20 NH code phases have been searched for, if do not have search to complete, enter step (8), if searched for the local values of Doppler frequency shift of change to enter step (1);

(8) to NH code ring shift chip of 20 bits, enter step (2), repeat step (2) ~ (7);

(9) end is caught.

In conjunction with specific engineering construction case, provide technology embodiment and simulation results:

(1) 2ms data overlap accumulative removal NH code phase design

As shown in Figure 2,3, the NH code searching principle of 2ms data overlap accumulation and flow process, be shown in Fig. 2 to the treatment scheme of 2ms data.

Suppose that the phase differential of input signal and NH code sequence is ξ, the result that now continuous print 2ms data are multiplied with NH code is successively: D _k=[(1-ξ) N _k, N _k+1, ξ N _k+2] × N _k+1

By 20 groups of D _kdata are added successively:

$\begin{array}{c}\mathrm{\Σ}{D}_k=(1-\mathrm{\ξ})\×\underset{k=1}{\overset{20}{\mathrm{\Σ}}}{N}_k\×N_{k+1}+\underset{k=1}{\overset{20}{\mathrm{\Σ}}}{N}_{k+1}\×N_{k+1}+\mathrm{\ξ}\×\underset{k=1}{\overset{20}{\mathrm{\Σ}}}{N}_{k+2}\×N_{k+1}\\ =(1-\mathrm{\ξ})\×R_N\left(1\right)+20\×R_N\left(0\right)+\mathrm{\ξ}\×R_N(-1)\end{array}$

R in formula _n() is autocorrelation value corresponding to the different code phase of NH code.As shown in Figure 4, be the autocorrelation function of NH code, known at code phase 1 and-1 place according to Fig. 4, the autocorrelation value of NH code is 0, and the autocorrelation value at code phase 0 place is maximum.Therefore from above formula computing, by the accumulation to 20 groups of 2ms data, middle 1ms can eliminate the impact of NH code phase completely, and Fig. 5 is shown in by concrete schematic diagram.

Adopt which, the middle 1ms data of 2ms accumulation gained are relevant to local 1ms data, find correlation peak, be equivalent to the gain having carried out 20 coherent accumulations.

The content be not described in detail in instructions of the present invention belongs to the known technology of those skilled in the art.

Claims (1)

1. a high rail spacecraft BDS weak signal quick capturing method, is characterized in that step is as follows:

(1) obtain the 1ms data under local values of Doppler frequency shift, by its zero padding to 2ms, and FFT conversion is carried out to these data, after getting conjugation, obtain data 1;

(2) carry out continuous print 2ms data buffer storage respectively after the intermediate-freuqncy signal of reception being carried out digital sample, namely 1ms and 2ms carries out buffer memory, and 2ms and 3ms carries out buffer memory, and buffer memory 20 groups, obtains data 2 successively;

(3) the 2ms data of often organizing in the data 2 obtained in step (2) be multiplied with a chip of 20 bit NH codes successively respectively, described NH code is 0,0,0,0,0,1,0,0,1,1,0,1,0,1,0,0,1,1,1,0, obtain 20 groups to be multiplied with NH code after data 3;

(4) coherent accumulation is carried out to 20 groups of 2ms data that step (3) obtains in data 3, obtains the coherent accumulation value that length is 2ms, and carry out FFT operation obtain data 4;

(5) respectively data 4 are multiplied with data 1 successively contraposition, obtain data 5, IFFT conversion is carried out to data 5 again and obtains data 6;

(6) repeatedly non-coherent accumulation is carried out to data 6, obtain 1 group of data 7;

(7) Nai Man-Pierre's Si criterion is utilized to carry out detection threshold judgement to data 7, judge whether successfully lock-on signal, if successful lock-on signal enters step (9), otherwise judge whether 20 NH code phases have been searched for, if do not have search to complete, enter step (8), if searched for the local values of Doppler frequency shift of change to enter step (1);

(8) to NH code ring shift chip of 20 bits, enter step (2), repeat step (2) ~ (7);

(9) end is caught;

In step (6), the number of times of non-coherent accumulation carries out to data 6 relevant with acquisition sensitivity.