CN102288975B - Capturing method based on DFT (Discrete Fourier Transformation) optimization - Google Patents

Abstract

The invention belongs to the fields of communication and navigation, and discloses a capturing method based on DFT (Discrete Fourier Transformation) optimization. Specific to the problems of low efficiency, small number of responses and high power consumption existing in the conventional satellite navigation capturing method, the coefficient of DFT is quantified, so that computation of the DFT is optimized; and meanwhile, the points of the DFT are optimized as required, so that a large calculated quantity and a large quantity of storage resources and other resources are saved. During navigation application, the coefficient of the DFT is quantified at a low bit, and the DFT points are cut according to a Doppler deviation search range simultaneously, so that the calculated quantity and calculating points of the DFT are reduced greatly, and storage resources, calculation resources, time, power consumption and the like are saved. The method can be effectively applied to satellite navigation.

Description

A kind of catching method of optimizing based on DFT

Technical field

The invention belongs to communication and navigation field, relate in particular to the catching method that is used for satellite navigation.

Background technology

GPS (GPS, Global Position System) is the accurate global position system of a new generation.The GPS receiver generally includes the catching of signal, signal carrier and sign indicating number locking, navigation message and the extraction of pseudorange and resolving of calculating and locator value to the processing of received signal.What gps system adopted is spread spectrum technic; Before the band spread receiver despread-and-demodulation, must make the spreading code and the carrier wave of receiver local recovery and receive signal Synchronization; Only at code phase and carrier frequency error within the specific limits the time, detuner could operate as normal.Owing to there is the influence of the factors such as time delay, Doppler shift, multipath effect of drift, the electric wave transmission of frequency source; Code phase and carrier wave can have certain uncertainty synchronously; Therefore receiver must at first be caught signal; Code phase and estimating carrier frequencies error be reduced in the certain limit just can offer track loop, carry out signal trace.Catching of navigation satellite signal is the first step and the key that the GPS receiver signal is handled.

In the receiver, in army's sign indicating number receiver and multimode rake receiver, resource, volume and power consumption are a great problems of constraint receiver development especially at present.To this problem, domestic and international many mechanisms and unit have carried out big quantity research.The great majority of catching of satellite-signal are based on the time domain with on the frequency domain and realize that traditional method is on time domain, to utilize the way of serial search that spreading code is caught.At first propose to use FFT to realize the quick capturing method of spreading code at document " Van Nee, Coenen, Davenport.New Fast GPS Code-Acquisition Technique Using FFT; Electronic Letters; 1991, vol.27, NO.2:158-160 "; The multiple sampling plan of FFT is compared and analyze at document " C.Yang.Fast code acquisition with FFT and its sampling schemes; Proc.Institute of Navigation ION-GPS 96; Kansas City; MO, September 1996,1729-173 "; Proposed XFAST at document " Extended Replica Folding for Direct Acquisition of GPS P-Code and Its Performance Analysis; Proceedings of ION GPS 2000.Salt Lake City; Ut:The Institute of Navigation; 2000.2070-2078 " and realized P (Y) yard quick Acquisition Scheme, proposed the sequence blocks searching algorithm at document " Sequential Block Search for Direct Acquisition of Long Codes under Large Uncertainty, Proceedings of the 2001 National Technical Meeting.Long Beach; CA:ION; Jan.2001.408-414 " again, and to utilizing FFT to realize the short period sign indicating number, the catching method of long period sign indicating number and no periodic sign indicating number is classified and concluded.The analysis of the domestic method that long code is directly caught is also a lot, and has much provided corresponding achievement in research in realization, the string of realizing like the large-scale parallel correlator and the sliding correlation detector method of combination, and overlapping averaging method is duplicated in expansion, and the method for PMF-FFT etc.

Because the relative motion that exists between satellite and the receiver will inevitably be introduced Doppler shift in the receiver use.And Doppler shift will cause spreading gain to be decayed, and work is caught in influence, therefore in acquisition procedure, must carry out corresponding compensation and handle, and remove the influence that Doppler shift produced.In order to realize the receiver of low-power consumption, low-resource and miniaturization, special many scholars have proposed numerous optimization methods in the multimode rake receiver in future, but the optimization problem of efficient, resource, power consumption etc. still is the research emphasis of catching.

Summary of the invention

The present invention is in order to solve the bigger problem of efficient, resource and power consumption in the existing satellite navigation catching method, to have proposed a kind of catching method of optimizing based on DFT.

Technical scheme of the present invention is: a kind of catching method of optimizing based on DFT comprises the steps:

S1 carries out related operation to the satellite-signal N point data that receives and the N point data of the pseudo-random code of this locality;

S2 makes N point DFT to the result of each related operation among the step S1, Wherein x (n) is the result of related operation, and X (k) is the frequency-domain result behind the calculating DFT, and detailed process is following: be reduced into the M five equilibrium to N Along ent on the frequency domain complex plane, establish N=M*m, behind the branches such as M, the value on the M five equilibrium

Replace score values such as original N

Be score values such as N

In the interval $\left[\begin{array}{cc}{e}^{-j\frac{2\mathrm{\π}}{(M-\frac{1}{2})*m}}& e^{-j\frac{2\mathrm{\π}}{(M+\frac{1}{2})*m}}\end{array}\right)$ Or $\left(\begin{array}{cc}{e}^{-j\frac{2\mathrm{\π}}{(M-\frac{1}{2})*m}}& e^{-j\frac{2\mathrm{\π}}{(M+\frac{1}{2})*m}}\end{array}\right]$ On value all use the value on the M five equilibrium Replace, calculate N point DFT according to the DFT computing method then, obtain the DFT frequency-domain result;

S3 compares DFT frequency-domain result and preset threshold value, if surpass threshold value; Obtain the Doppler shift value of signal, if do not surpass threshold value, then code phase moves data; Continue step S1; If still come to nothing after all phase searches finish, then change intermediate frequency or sign indicating number sequence, continue search.

Further, also comprise the steps: between said step S2 and the step S3

Calculate DFT and calculate the maximal value of counting

Wherein, f _sBe the sampling rate of the satellite-signal that receives, Δ f is how general row frequency shift (FS) maximal value, then according to the n that counts that calculates _MaxCalculate DFT, the interval of promptly calculating k is [N-n _Max/ 2N-1] and [0 n _Max/ 2-1] the value of X (k).

Beneficial effect of the present invention: the present invention is through providing a kind of a kind of efficient and low-resource optimized Algorithm that proposes based on the algorithm of DFT, and effectively is applied to satellite navigation.Coefficient through to DFT quantizes, and then the calculating of DFT is optimized, and as required DFT is counted simultaneously to be optimized, and has practiced thrift a large amount of storage resources and calculated amount.In navigation application; Except the DFT coefficient is hanged down bit quantization; Also DFT is counted simultaneously and carry out cutting, thereby make calculated amount and the calculating of the DFT minimizing in a large number of counting all, conserve memory resource, computational resource, time and power consumption etc. according to search Doppler shift scope.

Description of drawings

Fig. 1 is the catching method schematic flow sheet of optimizing based on DFT of the present invention.

Fig. 2 is the DFT coefficient synoptic diagram of the bit quantization of the embodiment of the invention.

Embodiment

Below in conjunction with accompanying drawing and concrete embodiment the present invention is done further elaboration.

The method of traditional calculating DFT is to calculate according to formula

, and promptly each frequency domain components all must calculate the product of N Along ent on N input signal and the frequency domain complex plane.Therefore in the receiver acquisition process,, can bring the bigger problem of efficient, resource and power consumption based on the catching method of traditional DFT.

The catching method of optimizing based on DFT of the present invention, idiographic flow is as shown in Figure 1, comprises the steps:

S1 carries out related operation to the satellite-signal N point data that receives and the N point data of the pseudo-random code of this locality;

S2 makes N point DFT to the result of each related operation among the step S1,

Wherein x (n) is the result of related operation, and X (k) is the frequency-domain result behind the calculating DFT, and detailed process is following: be reduced into the M five equilibrium to N Along ent on the frequency domain complex plane, establish N=M*m, behind the branches such as M, the value on the M five equilibrium

Replace score values such as original N

Be score values such as N

In the interval $\left[\begin{array}{cc}{e}^{-j\frac{2\mathrm{\π}}{(M-\frac{1}{2})*m}}& e^{-j\frac{2\mathrm{\π}}{(M+\frac{1}{2})*m}}\end{array}\right)$ Or $\left(\begin{array}{cc}{e}^{-j\frac{2\mathrm{\π}}{(M-\frac{1}{2})*m}}& e^{-j\frac{2\mathrm{\π}}{(M+\frac{1}{2})*m}}\end{array}\right]$ On value all use the value on the M five equilibrium

Replace, calculate N point DFT according to the DFT computing method then, obtain the DFT frequency-domain result; The m here can be integer, also can be decimal.

S3 compares DFT frequency-domain result and preset threshold value, if surpass threshold value; Obtain the Doppler shift value of signal, if do not surpass threshold value, then code phase moves data; Continue step S1; If still come to nothing after all phase searches finish, then change intermediate frequency or sign indicating number sequence, continue search.

In order further to reduce calculated amount, between step S2 and step S3, also comprise the steps: to calculate DFT and calculate the maximal value of counting

Wherein, f _sBe the sampling rate of the satellite-signal that receives, Δ f is how general row frequency shift (FS) maximal value, then according to the n that counts that calculates _MaxCalculate DFT, the interval of promptly calculating k is [N-n _Max/ 2 N-1] and [0 n _Max/ 2-1] the value of X (k).Here, DFT conversion frequency domain representation scope is 0 to f _s, search for how general row frequency swing and be-1* Δ f～Δ f.

If the result of related operation is x (n), according to the DFT conversion, then the DFT of sequence x (n) is:

$X\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}x\left(n\right)e^{-j\frac{2\mathrm{\π}}{N}\mathrm{kn}}=X\left(e^{\mathrm{j\ω}}\right){|}_{\mathrm{\ω}=\frac{2\mathrm{\π}}{N}k}.$

Because e ^{J θ}So=cos θ-jsin θ is the DFT coefficient

Be the data on the N Along ent on the unit circle.If circle be divided into M N, usually N is the integral multiple of M, the coefficient of DFT has only M so, but it is constant to import number of data points, through putting the data of circle N five equilibrium under near the data the M five equilibrium among the data of M five equilibrium.Select suitable M, can greatly practice thrift storage resources, calculated amount and the computational resource of DFT.

When getting 8, M waits timesharing, and can be to obtain a more excellent effect.Be that example describes below with M=8.

The present invention gets 8 timesharing such as grade by M and calculates, and can know that according to

of DFT quantizing all coefficients in back all is positioned on the unit circle of complex plane.As shown in Figure 2, be divided into 8 equal portions to a complex plane circumference, to the DFT coefficient carry out 2 bit quantizations can the point on the eight equal parts all expression finish, and coefficient is carried out the later quantization parameter of suitable amplification is [1.5; 1+i, 1.5i ,-1+i ,-1.5;-1-i ,-1.5i, 1-i].According to the quantization parameter of DFT, DFT computing multiplication resources can have been become direct-connected signal (coefficient is ± 1) or several registers and totalizer (coefficient is ± 1.5) by original multiplier, and this will reduce the operand of DFT greatly.Suppose to be now 256 DFT; Carrying out five equilibrium because M gets 8, is that (1.5,0) replace so 240～256 and 1～16 Along ent in original 256 five equilibriums uses the corresponding DFT coefficient of first Along ent in the M=8 Along ent; 17～48 Along ents become (1 with the DFT coefficient of second Along ent of eight equal parts point; I) replace, 49～80 Along ents become (15i) replacement with the 3rd Along ent DFT coefficient of eight equal parts point, and the DFT that remaining coefficient and other are counted by that analogy.

In order only Doppler's frequency band to be searched for, can adjust the DFT coefficient, concentrate on coefficient in the frequency band range that needs and carry out conversion, the parameter of other frequency band is not then calculated, can also save a large amount of calculated amount like this.If sampling rate is f _s, DFT conversion frequency domain representation scope is 0 to f so _sBe ± 10KHZ that computer capacity needs only so if search for how general row scope

Just can calculate maximum calculating counts and is n _Max, count according to this then and just can calculate the DFT of needs.Suppose to adopt the 4ms data to be 256 DFT; Therefore spectral resolution is that corresponding

is when DFT is dispersed in calculating; In order to search for ± the 10KHz signal, calculative counting to therefore only needs 216 o'clock to 255 o'clock, 0 o'clock to 39 o'clock X (k) to get final product.Thereby need not calculate 256 whole DFT.If same only search ± 5KHz only needs calculating 236 to 255 points, 0 o'clock to 19 o'clock DFT to get final product, other frequency computation part principle is the same.Full frequency-domain search if desired, perhaps the hunting zone is very big, causes the calculation procedure number to surpass the mode of FFT, can be applied to FFT to this quantification manner and get on.

Can find out, of the present inventionly quantize, can simplify the calculating of DFT, quantize later as required counting of DFT being optimized simultaneously, can practice thrift a large amount of storage resources and calculated amount through coefficient to DFT.In navigation application; Except the DFT coefficient is quantized; Also DFT is counted simultaneously and carry out cutting according to search Doppler shift scope; Make the calculating of DFT count and calculated amount all reduces, conserve memory resource, computational resource, time and power consumption etc., this method can effectively be applied to satellite navigation.

Those of ordinary skill in the art will appreciate that embodiment described here is in order to help reader understanding's principle of the present invention, should to be understood that protection scope of the present invention is not limited to such special statement and embodiment.Those of ordinary skill in the art can make various other various concrete distortion and combinations that do not break away from essence of the present invention according to these teachings disclosed by the invention, and these distortion and combination are still in protection scope of the present invention.

Claims (4)

1. a catching method of optimizing based on DFT comprises the steps:

S1 carries out related operation to the N point data of the satellite-signal that receives and the N point data of the pseudo-random code of this locality;

S2 makes N point DFT to the result of each related operation among the step S1,

Wherein x (n) is the result of related operation, and X (k) is the frequency-domain result behind the calculating DFT, and detailed process is following: be reduced into the M five equilibrium to N Along ent on the frequency domain complex plane, establish N=M*m, behind the branches such as M, the value on the M five equilibrium

Replace score values such as original N Score values such as N In the interval $\left[\begin{array}{cc}{e}^{-j\frac{2\mathrm{\π}}{(M-\frac{1}{2})*m}}& e^{-j\frac{2\mathrm{\π}}{(M+\frac{1}{2})*m}}\end{array}\right)$ Or $\left(\begin{array}{cc}{e}^{-j\frac{2\mathrm{\π}}{(M-\frac{1}{2})*m}}& e^{-j\frac{2\mathrm{\π}}{(M+\frac{1}{2})*m}}\end{array}\right]$ On value all use the value on the M five equilibrium

Replace, calculate N point DFT according to the DFT computing method then, obtain the DFT frequency-domain result;

S3 compares DFT frequency-domain result and preset threshold value, if surpass threshold value; Obtain the Doppler shift value of signal, if do not surpass threshold value, then code phase moves data; Continue step S1; If still come to nothing after all phase searches finish, then change intermediate frequency or sign indicating number sequence, continue search.

2. the catching method of optimizing based on DFT according to claim 1 is characterized in that, also comprises the steps: between said step S2 and the step S3

Calculate DFT and calculate the maximal value of counting

Wherein, f _sBe the sampling rate of the satellite-signal that receives, Δ f is how general row frequency shift (FS) maximal value, then according to the n that counts that calculates _MaxCalculate DFT, the interval of promptly calculating k is [N-n _Max/ 2N-1] and [0 n _Max/ 2-1] the value of X (k).

3. the catching method of optimizing based on DFT according to claim 1 and 2 is characterized in that described N is the integral multiple of M.

4. the catching method of optimizing based on DFT according to claim 1 and 2 is characterized in that described M is 8.

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