CN103809193A - Capture system for improving weak GNSS (global navigation satellite system) signal processing gain - Google Patents

Abstract

The invention provides a capture system for improving weak GNSS (global navigation satellite system) signal processing gain, and aims to provide a processing gain capture system capable of increasing the GNSS processing gain and avoiding related loss of integral operation. The technical scheme includes that an integral extension unit (8) comprising a data storage module (11) and a series combination addition module (12) is arranged between a parallel correlation operation unit (7) and a peak value judgment unit (9), the parallel correlation operation unit (7) is used for performing parallel correlation operation for received signals from a radio frequency processing unit (2) and local spreading codes from a local pseudo-code generator (1), transmitting operation processing results into the integral extension unit (8) for extending integrals, transmitting integral extension results into the peak value judgment unit (9) and comparing the integral extension results with a related peak value judgment threshold set by a threshold circuit, and the peak value judgment unit judges whether capture is finished or not by threshold comparison to capture signals.

Description

Improve the capture systems of Weak GNSS signal processing gain

Technical field

The present invention is about the navigation communications field, faint global navigation satellite system GNSS signal acquisition system.

Technical background

Weak GNSS signal capture technique is one of core technology realizing weak signal GNSS navigation, is also one of the Research Challenges in Global Navigation Satellite System (GNSS) field.For satellite navigation signals, under near condition spacious earth's surface, the intensity of satellite navigation signals is in-130dBm left and right, and its carrier-to-noise ratio is approximately 45dB-Hz, and in the time having the covering of buildings or vegetation, signal intensity can decay.Conventionally the signal that carrier-to-noise ratio is greater than to 45dB-Hz is considered as strong signal, and the signal that is less than 28dB-Hz is considered as to feeble signal.For GNSS commercial satellite signal, the significantly decline of signal power makes receiver complete location by detection signal.The decay of signal energy is the subject matter that high sensitivity satellite navigation receiver faces.

Spread spectrum communication system is owing to having expanded signal spectrum at transmitting terminal, reduced information in receiving end despreading, and the benefit that such system is brought is greatly to have improved anti-jamming margin.Theoretical analysis shows, the interference free performance of various spread spectrum systems is relevant with the spread-spectrum signal bandwidth ratio after information spread spectrum.Generally spread-spectrum signal bandwidth W is called to processing gain GP with the ratio of inromation bandwidth △ F, it has shown the degree that spread spectrum system signal to noise ratio (S/N ratio) is improved.In addition, some other performance of spread spectrum system is also mostly relevant with GP.Therefore, processing gain is an important performance indexes of spread spectrum system.Anti-jamming margin MJ is directly proportional to spread processing gain G P, and after spread processing gain improves, anti-jamming margin improves greatly, and even signal also can proper communication under certain noise is fallen into oblivion.Common spread spectrum device always by the bandwidth expansion of user profile (information to be transmitted) to even thousand times of decades of times, hundreds of times, to improve as much as possible processing gain.

Global Navigation Satellite System (GNSS) take GPS, GALILEO, GLONASS as representative is all take direct sequence spread spectrum skill as basis.Signal capture is a process of pseudo-code and Doppler frequency deviation being carried out to two-dimensional search, carries out related operation by the pseudo-code under different Doppler frequency deviations, realizes Time and Frequency Synchronization.Under feeble signal level, often need to adopt longer integral time to increase processing gain, and adopt parallel correlator structure to optimize capture time.Because code Doppler can cause the relative sliding that receives signal and local pseudo-code, cause long-time integration computing to occur associated loss.The existing proportionate relationship of utilizing between carrier wave and code Doppler of having researched and proposed, carries out a yard Doppler shift compensation according to the frequency interval of carrier wave frequency deviation search, with the phase slip that reduces to be caused by code Doppler shift in integral process.

In the prior art, still have yard Doppler's residual error after Doppler effect correction, be subject to the restriction of carrier wave frequency search step-length, carrier wave frequency deviation step-size in search is larger, and code Doppler residual error is larger.Code Doppler residual error can cause that code phase slides equally, thereby limit the further increase of feeble signal level lower integral time: in the time that pseudo-code phase slides past a chip, integral energy can not run up on same code phase, cause extending integral time and not reach the object that improves processing gain.

Summary of the invention

In order to overcome during feeble signal catches, code Doppler frequency deviation has limited integral time, cause the limited problem of processing gain, the invention provides one can increase GNSS capture systems processing gain, and can avoid the Weak GNSS signal processing gain capture systems of integral operation associated loss.

Above-mentioned purpose of the present invention can realize by following measures, the invention provides a kind of capture systems that improves Weak GNSS signal processing gain, comprise: local pn code generator 1, RF processing unit 2, tapped delay wire module 3, multiplier 4, Parallel correlation unit 7, peak value judging module 9 and related operation unit 10, is characterized in that: between Parallel correlation unit 7 and peak value judging module 9, be provided with the expansion integral unit 8 being made up of data memory module 11 tandem compound summation module 12; Parallel correlation arithmetic element 7 is carried out Parallel correlation computing to the reception signal from RF processing unit 2 with from the local spreading code of local pseudo-code generator 1, calculation process result is sent into expansion integral unit 8 and expand integration, and expansion integral result is sent into peak value decision unit 9 compare with the relevant peaks decision threshold of threshold circuit setting, peak value decision unit 9 is by thresholding comparison, the judgement whether completing is caught in execution, and settling signal is caught.

The present invention has following beneficial effect than prior art.The present invention is by the expansion integral unit 8 arranging between Parallel correlation unit 7 and peak value judging module 9, can be with less hardware resource consumption expense, increase the processing gain of GNSS capture systems, with respect to traditional GNSS capture technique, there is following clear superiority aspect feeble signal fast Acquisition realizing:

The first, utilize described expansion Integral Technology, can effectively reduce phase slip that yard Doppler causes to the related operation restriction of integral time, break through upper limit integral time of traditional GNSS capture systems, thereby improve acquisition sensitivity.

The second, the present invention realizes simply, only need in traditional capture systems, increase expansion integral unit (8), and remaining circuit is not needed to redesign; From the angle of complexity and resource overhead, when this algorithm is realized on programmable gate array chip (FPGA), only need to consume a small amount of adder logic and storer.

The maximum integral time of having limited traditional related operation due to code Doppler frequency deviation.On the basis of traditional related operation, the present invention utilizes expansion integral unit to realize increase integral time, thereby has solved the limited problem of processing gain.Resource consumption of the present invention is few, only need in traditional capture systems, increase expansion integral unit 8, need not redesign remaining circuit.

Accompanying drawing explanation

Fig. 1 is the capture systems circuit theory schematic diagram that the present invention improves Weak GNSS signal processing gain.

Fig. 2 is that Fig. 1 expands integral unit 8 inner structure schematic diagram.

Fig. 3 is M × N data matrix storage schematic diagram in Fig. 1 data memory module 11.

Fig. 4 is the principle of work schematic diagram that Fig. 1 expands integral unit 8.

Fig. 5 is that Fig. 4 expands integral principle schematic diagram.

Embodiment

Below in conjunction with drawings and Examples, invention is further illustrated.

Consult Fig. 1, Fig. 2.In embodiment described below, the capture systems that improves Weak GNSS signal processing gain, comprising: local pn code generator 1, RF processing unit 2, tapped delay wire module 3, multiplier 4, coherent integration module 5, non-coherent integration module 6, Parallel correlation unit 7, expansion integral unit 8, peak value judging module 9 and related operation unit 10.Wherein related operation unit 10 comprises and is connected on coherent integration module 5 and the non-coherent integration module 6 on circuit between multiplier 4 output terminals and expansion integral unit 8; Exhibition integral unit 8 as shown in Figure 2 data memory module 11 tandem compound summation module 12 forms, and is connected between Parallel correlation unit 7 and peak value judging module 9.In above-mentioned expansion integral unit 8, data memory module (11) is by the N correlations computing Output rusults from Parallel correlation arithmetic element 7M bar branch road, be stored in successively N independently storage space, obtain one as shown in Figure 3, renewal frequency is the data matrix of M × N of NT, and its element representation is D _i,j, 1≤i≤M, 1≤j≤N, i, j represent j correlated results D of i article of branch road output _i,j.Combination summation module (12) is by the element D of M × N data matrix in data memory module (11) _i,jcombine addition according to the operation steps below providing, complete N expansion integration of M phase place, export M expansion integral result.

Local pn code generator 1 is sent local spread-spectrum pseudo code into Parallel correlation unit 7, carries out, after the copying of 1:M, receiving signal respectively carry out multiplying with M road, and this multiplying can realize by XOR.RF processing unit 2 is sent baseband I, Q signal into the M road tapped delay line circuit that the tapped delay wire module 3 in Parallel correlation unit 7 forms, and obtains the needed M of Parallel correlation computing road and receives signal; Local pn code generator 1 completes local spread-spectrum pseudo code by the multiplier 4 in related operation unit 10 and receives the related operation of signal, the integration T.T. T≤T of related operation unit 10 ₀, T ₀for Doppler shift causes the time that receives relative sliding between signal and local pseudo-code and reach 1/2 chip, T ₀can be according to the absolute value of the maximum carrier doppler frequency displacement of system

calculate:

in formula, R _cfor GNSS bit rate, f _cfor carrier frequency.Shown in Fig. 2, expand in the data memory module 11 that data that integral unit 8 exports 1～M related operation unit 10 deposit in, the output of N correlations computing is stored in successively N independently storage space by data memory module 11, the element of M × N data matrix in data memory module 11 is combined addition by combination summation module 12, completes N expansion integration of M phase place; Threshold circuit in peak value decision unit 9, by the expansion integral result obtaining and thresholding comparison, obtains being greater than the code phase corresponding to relevant peaks of thresholding, and settling signal is caught.

Consult Fig. 3.In M × N of NT data matrix, the p article of branch road expansion integration D that combination summation module 12 is exported _p(N) be:

$D_p\left(N\right)=\max \left\{G_p^{+}\left(N\right){\∪G}_p^{-}\left(N\right)\right\}$

And there is 1≤p≤M; In formula, D _p(N) be p article of branch road expansion integration, ∪, for set join operator, max{} is illustrated in set all elements and gets the maximum, gathers

(N) and (N), while representing respectively code Doppler for just (+) and bear (-), expand the possible combination addition result of integration, its set N time

(N) and

(N) element number is 2 ^n-1, N is natural number.

(N) and

(N) can be obtained by following recursion step:

(1) in the time of N=1, $G_p^{+}\left(1\right)=\left\{D_{p,1}\right\},G_p^{-}\left(1\right)=\left\{D_{p,1}\right\};$

(2) in the time of N > 1, right

1≤i≤2 ^(N-1)-1, set

(N) in, 2i-1 and 2i element are respectively

with

in like manner, right

1≤i≤2 ^(N-1)-1, set

(N) in, 2i-1 and 2i element are respectively

with

with

represent respectively set

with

in i element, 1≤i≤2 ^(N-1)-1

Fig. 4 has further described the principle of work of expansion integral unit 8.The time interval T of adjacent legs _d=aT _c, T _ca chip time, 0 < a≤0.5.Wherein P-2, P-1, P and P+1 represent respectively four adjacent legs of parallel correlator.The processing gain of catching for maximizing Weak GNSS signal, related operation time T should be got maximum of T ₀.Suppose carrier doppler frequency displacement

and (zero moment) P branch road reception signal aligns with local pseudo-code in the time that integration is initial, (T in the time of related operation unit 10 first integral result of output ₀moment), P branch road receives signal 1/2 chip that will relatively with local pseudo-code stagger, and (P-1) branch road receives signal and will align with local pseudo-code, integral energy will continue accumulation at (P-1) branch road afterwards.By that analogy, to 2T ₀in the moment, (P-2) branch road will align with local pseudo-code, and integral energy will continue accumulation at (P-2) branch road ... therefore,, from maximizing the angle of integration gross energy, N the expansion integral result of branch road P is

As the above analysis, for $f_d\&Element;[-f_d^{\max },f_d^{\max }],$ Expansion integration is added and is formed by the element combinations of M × N data matrix different lines in memory module 11.N time expansion integration has 2 ⁿ-a kind of array mode.

Consult Fig. 4, Fig. 5.Grid chart can be easy to expand to the situation of N > 4, but from the angle of resource consumption and performance boost compromise, suggestion expansion integral number of times N is no more than 6 times.From t=0, expansion integration can advance along different paths in grid, selects different D _i,jcombine cumulative.Consider that correlation integral time Doppler shift can not undergo mutation, do not have the problem of Doppler shift flip-flop sign, path only has Liang Tiao branch (to indicate f on each node _dexcept=0 path), as shown in the direction of arrow in Fig. 5.Its implication is: work as f _dwhen < 0, current resident node D _i,jnext integral node be D _{i, j+1}and D _{i-1, j+1}; Work as f _dwhen > 0, D _i,jnext integral node be D _{i, j+1}and D _{i+1, j+1}.

Branch road P is realized to expansion integration N time, need to this branch road the correlated results on (N-1) road before and after it.Therefore, in the time that the pseudo-code cycle is greater than M, the degree of depth of data memory module 11 should expand to M+2 (N-1), for the related operation result of each (N-1) road code phase before and after the code phase of store M road, if this result does not exist, fill in zero in the relevant position of storage space.

Below take gps signal L1 frequency range as example, carrier frequency f _c=1575.42MHz, bit rate R _c=10.23MHz, carrier doppler frequency deviation f _d=2kHz.Be 1ms when the coherent integration time, for guaranteeing that the correlated performance loss that carrier wave frequency deviation causes is less than 1dB, tradition GPS capture systems generally adopts the frequency deviation step-size in search of 500Hz, and the proportionate relationship between frequency deviation compensates code Doppler frequency deviation according to carrier wave frequency deviation and code, can calculate on integral time of related operation and be limited to $T_0=1/(2f_d^{\max }{R}_c/f_c)=308\mathrm{ms},$ Wherein $f_d^{\max }=250\mathrm{Hz}$ For the half of carrier wave frequency deviation scouting interval.

Without loss of generality, establish the degree of parallelism M=100 of Parallel correlation unit 7, concrete treatment step is as follows:

RF processing unit 2 is sent into baseband I, Q signal in Parallel correlation unit 7 and is formed 100 road tapped delay line circuit by tapped delay wire module 3, obtains needed 100 tunnels of Parallel correlation computing and receives signal.The time interval T of adjacent legs _d=T _c2=12R _c.Local pn code generator 1 is sent local spread-spectrum pseudo code into Parallel correlation unit 7, carries out after the copying of 1:100, and Yu100 road receives signal and carries out multiplying respectively.Related operation unit 10 completes local spread-spectrum pseudo code and receives the related operation of signal.The integration T.T. T of related operation unit 10 gets maximum of T ₀=308ms.Expansion integral unit 8 deposits the data of the output of 100 related operation unit 10 in data memory module 11, the output of 3 correlations computings is stored in successively 3 independently storage spaces by data memory module 11, obtain the data matrix of 100 × 3, its update cycle is NT=924ms.

Consider that the pseudo-code cycle is much larger than M=100, the degree of depth of data memory module 11 expands to M+2 (N-1)=104, for storing the related operation result of 100 each (N-1)=2 road, code phases front and back, road code phases.Because data memory module 11 is take NT=924ms as the cycle, so the related operation result of N-1=2 road code phase can obtain in the upper once update cycle before current 100 road code phases, and retained.Catch initial a period of time, in data memory module 11,2 (N-1)=4 storage unit of expansion should extend this as 0.The element of 104 × 3 data matrixes in data memory module 11 is combined addition by combination summation module 12.Take branch road p as example, 1≤p≤100, have

$D_p\left(N\right)=\max \left\{\begin{array}{c}{D}_{p,1}+D_{p,2}+D_{p,3}\\ D_{p,1}+D_{p,2}+D_{p-\mathrm{1,3}},D_{p,1}+D_{p-\mathrm{1,2}}+D_{p-\mathrm{1,3}},D_{p,1}+D_{p-\mathrm{1,2}}+D_{p-\mathrm{2,3}}\\ D_{p,1}+D_{p,2}+D_{p+\mathrm{1,3}},D_{p,1}+D_{p+\mathrm{1,2}}+D_{p+\mathrm{1,3}},D_{p,1}+D_{p+\mathrm{1,2}}+D_{p+\mathrm{2,3}}\end{array}\right\}$

The expansion integral result that peak value decision unit 9 obtains step 5 and thresholding comparison, obtain being greater than the code phase corresponding to relevant peaks of thresholding, thereby settling signal is caught.The present invention does not limit threshold circuit specific implementation.

Above the embodiment of the present invention is described in detail, has applied embodiment herein the present invention is set forth, the explanation of above embodiment is just for helping to understand method and apparatus of the present invention; , for one of ordinary skill in the art, according to thought of the present invention, all will change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention meanwhile.

Claims (10)

1. one kind is improved the capture systems of Weak GNSS signal processing gain, comprise: local pn code generator (1), RF processing unit (2), tapped delay wire module (3), multiplier (4), Parallel correlation unit (7), peak value judging module (9) and related operation unit (10), is characterized in that: between Parallel correlation unit (7) and peak value judging module (9), be provided with the expansion integral unit (8) being made up of data memory module (11) tandem compound summation module (12); Parallel correlation arithmetic element (7) is carried out Parallel correlation computing to the reception signal from RF processing unit (2) with from the local spreading code of local pseudo-code generator (1), calculation process result is sent into expansion integral unit (8) and expand integration, and the relevant peaks decision threshold that expansion integral result is sent into peak value decision unit (9) and threshold circuit setting is compared, peak value decision unit (9) is by thresholding comparison, the judgement whether completing is caught in execution, and settling signal is caught.

2. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, is characterized in that: related operation unit (10) comprise and are connected on coherent integration module (5) and the non-coherent integration module (6) on circuit between multiplier (4) output terminal and expansion integral unit (8).

3. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, it is characterized in that: in expansion integral unit (8), data memory module (11) will be from the N correlations computing Output rusults of Parallel correlation arithmetic element (7) M bar branch road, be stored in successively N independently storage space, obtain one and have M × N data matrix that M input, renewal frequency are NT, its matrix element is expressed as D _i,j, 1≤i≤M, 1≤j≤N, i, j represent j correlated results of i article of branch road output.

4. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, it is characterized in that: combination summation module (12) is added the element combinations of M × N data matrix in data memory module (11), complete N expansion integration of M phase place, export M expansion integral result.

5. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, it is characterized in that: local pn code generator (1) is sent local spread-spectrum pseudo code into Parallel correlation unit (7), carry out after the copying of 1:M, receive signal with M road respectively and carry out multiplying.

6. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, it is characterized in that: RF processing unit (2) is sent into baseband I, Q signal the M road tapped delay line circuit of tapped delay wire module (3) composition in Parallel correlation unit (7), obtains the needed M of Parallel correlation computing road and receives signal.

7. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, it is characterized in that: local pn code generator (1) completes local spread-spectrum pseudo code by the multiplier (4) in related operation unit (10) and receives the related operation of signal, the integration T.T. T≤T of related operation unit (10) ₀, T ₀for Doppler shift causes the time that receives relative sliding between signal and local pseudo-code and reach 1/2 chip, T ₀according to the absolute value of the maximum carrier doppler frequency displacement of system

calculate:

in formula, R _cfor GNSS bit rate, f _cfor carrier frequency.

8. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 1, it is characterized in that: expansion integral unit (8) deposits the data of 1～M related operation unit (10) output in data memory module (11) in, the output of N correlations computing is stored in successively N independently storage space by data memory module (11), the element of M × N data matrix in data memory module (11) is combined addition by combination summation module (12), completes N expansion integration of M phase place.

9. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 8, is characterized in that: in the M × N data matrix take NT as the update cycle, and p article of branch road expansion integration D of combination summation module (12) output _p(N) be:

$D_p\left(N\right)=\max \left\{G_p^{+}\left(N\right){\&cup;G}_p^{-}\left(N\right)\right\}$

And there is 1≤p≤M; In formula, D _p(N) be p article of branch road expansion integration, ∪, for set join operator, max{} is illustrated in set all elements and gets the maximum, gathers

(N) and

(N), while representing respectively code Doppler for just (+) and bear (-), expand the combination addition result of integration, its set N time (N) and

(N) element number is 2 ^n-1, N is natural number.

10. the capture systems of raising Weak GNSS signal processing gain as claimed in claim 9, is characterized in that:

(N) and

(N) obtained by following recursion step:

(1) in the time of N=1, $G_p^{+}\left(1\right)=\left\{D_{p,1}\right\},G_p^{-}\left(1\right)=\left\{D_{p,1}\right\};$

(2) in the time of N > 1, right

1≤i≤2 ^(N-1)-1, set

(N) in, 2i-1 and 2i element are respectively

with in like manner, right

1≤i≤2 ^(N-1)-1, set

(N) in, 2i-1 and 2i element are respectively

with

with represent respectively set

with in i element, 1≤i≤2 ^(N-1)-1.

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