CN102288975A - 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 of receiver local recovery and carrier wave and received signal synchronous, 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.At 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 realize that traditional method is to utilize the way of serial search that spreading code is caught on time domains.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 "; Compare and analyze in the multiple sampling plan of 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 " FFT; Propose 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, 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 " the sequence blocks searching algorithm has been proposed 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 is 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 as 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 must carry out corresponding compensation and handle in acquisition procedure, 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 N point data of the pseudo-random code of the satellite-signal N point data that receives and 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 as follows: N Along ent on the frequency domain complex plane is reduced into the M five equilibrium, establishes 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

Or

On value all use value on the M five equilibrium

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

S4, DFT frequency-domain result and default threshold value are compared, 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 behind the described step S2:

S3 calculates DFT and calculates 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).

Beneficial effect of the present invention: the present invention is by 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.Quantize by the coefficient to DFT, and then the calculating of DFT is optimized, as required DFT being counted simultaneously is optimized, and has saved 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, all reduce conserve memory resource, computational resource, time and power consumption etc. in a large number thereby make the calculated amount of DFT and calculating count 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

The invention will be further elaborated below in conjunction with accompanying drawing and specific embodiment.

The method of traditional calculating DFT is according to formula

Calculate, 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 comprises the steps: as shown in Figure 1

S1 carries out related operation to the N point data of the pseudo-random code of the satellite-signal N point data that receives and 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 as follows: N Along ent on the frequency domain complex plane is reduced into the M five equilibrium, establishes 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

Or

On value all use 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.

S4, DFT frequency-domain result and default threshold value are compared, 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, behind step S2, also comprise 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/ 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-j sin θ is the DFT coefficient

Be the data on the N Along ent on the unit circle.If circle is divided into M＜N, N is the integral multiple of M usually, and the coefficient of DFT has only M so, but it is constant to import number of data points, by the data of circle N five equilibrium being put under near the data the M five equilibrium among the data of M five equilibrium.Select suitable M, can greatly save 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, according to DFT's

Quantizing all coefficients in back as can be known all is positioned on the unit circle of complex plane.As shown in Figure 2, a complex plane circumference has been divided into 8 equal portions, 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 register and totalizer (coefficient is ± 1.5) by original multiplier, and this will reduce the operand of DFT greatly.Suppose to be now 256 DFT, because getting 8, M carries out five equilibrium, so originally 240: 256 in 256 five equilibriums and 1: 16 Along ent are (1.5 with the DFT coefficient of first Along ent correspondence in the M=8 Along ent, 0) replaces, 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 (1.5i) 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, coefficient is concentrated in the frequency band range that needs 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, so spectral resolution is corresponding

When calculating discrete DFT, in order to search for ± the 10KHz signal, calculative count into

Therefore only need 216 o'clock to 255 o'clock, 0 o'clock to 39 o'clock X (k) to get final product.Thereby do not need to 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.

As can be seen, of the present inventionly quantize, can simplify the calculating of DFT, quantize later as required counting of DFT being optimized simultaneously, can save a large amount of storage resources and calculated amount by 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 technology enlightenments 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 pseudo-random code of the N point data of the satellite-signal that receives and 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 as follows: N Along ent on the frequency domain complex plane is reduced into the M five equilibrium, establishes 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

Or

On value all use value on the M five equilibrium Replace, calculate N point DFT according to the DFT computing method then, obtain the DFT frequency-domain result;

S4, the threshold value of crossing the DFT frequency-domain result and presetting relatively, 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 step S3 behind the described step S2, calculates DFT and calculates 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).

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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