CN117938199A - Spread spectrum signal three-level capturing method, system, equipment and medium - Google Patents
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Abstract
A spread spectrum signal three-stage capturing method, system, device and medium, the method includes: modeling a received spread spectrum signal, determining a search range of a local receiver frequency and a first-stage acquisition frequency search step length, setting a code phase search step length of the local receiver, carrying out first-stage acquisition on the spread spectrum signal according to the search range of the local receiver frequency and the first-stage acquisition frequency search step length to obtain an accurate value of the code phase dimension and a rough frequency estimated value obtained by the first-stage acquisition, carrying out second-stage acquisition on the spread spectrum signal to obtain a more accurate frequency estimated value of the second-stage acquisition, and carrying out third-stage acquisition on the spread spectrum signal to obtain an accurate frequency estimated value of the third-stage acquisition; the system, the device and the medium are used for realizing a spread spectrum signal three-level capturing method; the invention has the advantages of high signal capturing precision, short capturing time, low hardware resource requirement and high signal capturing integrity.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a spread spectrum signal three-level capturing method, a system, equipment and a medium.
Background
With the continuous development of mobile communications, there is an increasing demand for instant messaging, and one of the key technologies that has to be mentioned is capturing of a spread spectrum signal, where when the spread spectrum signal arrives at a receiver, there is a phase shift of the spread spectrum code and a doppler frequency shift generated by a relative motion between a transmitter and a receiver, so that, in order to track and demodulate a received signal to obtain transmitted bit information, it is first required to determine the frequency and the phase of the spread spectrum code of the received signal, so as to ensure that a local receiver can copy a carrier signal and a spread spectrum code signal synchronous with the received signal, so as to facilitate subsequent tracking and signal demodulation.
Common spread spectrum signal capturing methods include a time domain serial capturing algorithm, a parallel frequency searching capturing algorithm, a parallel code phase searching capturing algorithm and the like; the time domain serial capturing algorithm shows the transformation of signals in each step of flow in the capturing process in the simplest and most clear way, but the serial violent searching way brings about the problem of long capturing time; the parallel frequency search acquisition algorithm can realize parallel processing of all frequency bands in a frequency domain while determining one code phase through Fourier transformation, and reduces the acquired search dimension to the code phase dimension, but the method has the problem that a large amount of Fourier transformation needs to be performed in one accumulation time, has higher requirements on hardware resources, and particularly causes more load on hardware under the condition of using long spread spectrum codes.
The invention patent application with publication number of CN116094543A discloses a high-precision spread spectrum signal capturing method, which comprises the following steps: data sampling is carried out on the received signals; carrying out compensation correction of carrier frequency on the sampled data; performing pseudo code phase correlation despreading on the frequency-corrected sampling data to obtain correlation integral data; calculating according to the related integral data to obtain self-adaptive detection threshold, related integral peak value and side peak information; performing interpolation correction on the pseudo code phase and the carrier frequency; comparing the corrected correlation integral peak value with a self-adaptive detection threshold to detect whether the received signal is successfully captured, and calculating to obtain a received signal to noise ratio, a spread spectrum code phase and a carrier Doppler frequency shift; however, the method is only used for sampling and processing the signal once, so that the signal capturing precision is low, the calculated amount of the method is large, and the requirement on hardware resources is high.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a three-stage capturing method, a system, equipment and a medium for a spread spectrum signal.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
A method for three-level acquisition of spread spectrum signals, comprising the steps of:
step 1, modeling a received spread spectrum signal;
step 2, combining the spread spectrum signal model established in the step 1 to determine the searching range of the local receiver frequency and the searching step length of the first-stage capturing frequency;
Step 3, setting a code phase searching step length of the local receiver, and carrying out first-stage capturing on the spread spectrum signal according to the searching range of the frequency of the local receiver and the first-stage capturing frequency searching step length determined in the step 2 to obtain a precise value of the code phase dimension and a rough frequency estimated value obtained by the first-stage capturing;
step4, on the basis of the first-stage capturing in the step 3, carrying out second-stage capturing on the spread spectrum signal to obtain a more accurate frequency estimation value of the second-stage capturing;
And 5, performing third-stage capturing on the spread spectrum signal on the basis of the second-stage capturing in the step 4 to obtain an accurate frequency estimation value of the third-stage capturing.
The spread spectrum signal modeling in the step 1 specifically comprises the following steps:
si(t)＝d(t)·c(t-τ)·sin[2π(fIF+fd)t+θi]+n
Wherein d (t) represents the transmitted data code, c (t) represents the spreading code, τ represents the phase of the spreading code, f IF represents the signal intermediate frequency, f d represents the Doppler shift, θ i represents the phase of the received signal, and n represents the mean of 0 and the variance of 0 Is a gaussian white noise of (c).
The step2 specifically comprises the following steps:
Step 2.1, the frequency of the local carrier signal is denoted as f IF, the code phase is 0, the frequency difference between the local carrier signal and the received signal is denoted as f d, the existing code phase difference is τ, and the maximum doppler shift is denoted as f max, the frequency range of the received signal is: [ f IF-fd,fIF+fd ], the search range of the local receiver frequency;
Step 2.2, selecting the period duration of the spreading code c 1 (T) with the longest length as the coherent accumulation time T coh1 during the first-stage capturing, thereby obtaining the search step length during the first-stage capturing as follows: Δf 1＝1/Tcoh1; meanwhile, the search range of the local receiver frequency determined in the step 2.1 is divided into ：fIF-fd、fIF-fd+Λf1、fIF-fd+Λf2、......、fIF+fd, according to the search step length and respectively recorded as a frequency point 1, a frequency point 2, a frequency point 3, a frequency point n.
The step 3 specifically comprises the following steps:
Step 3.1, setting the code phase searching step length of the local receiver to be 0.5 chip;
Step 3.2, setting a local carrier frequency value according to the frequency points divided in the step 2.2, and mixing a received signal with a local carrier to realize down-conversion; performing fast Fourier transform on the mixed signal, and transforming the mixed signal from a time domain to a frequency domain, and marking the mixed signal as FFT [ s (n) ];
Step 3.3, the local spreading code is recorded as c 1 (t), the fast Fourier transform is carried out on c 1 (t), conjugation processing is carried out on the signal transformed to the frequency domain, and the signal after conjugation processing is recorded as FFT * [ c (n) ];
Step 3.4, multiplying the FFT [ s (n) ] obtained in step 3.2 with the FFT * [ c (n) ] obtained in step 3.3, and then performing inverse fast Fourier transform to obtain a time domain result R (n):
Wherein d (N) represents a data bit, f e、θe represents a frequency difference and a phase difference between a received signal and a local carrier, N represents a code length of a local spreading code c 1 (t) in step 3.3, and R b represents a duration of a single chip of the local spreading code c 1 (t);
step 3.5, performing differential coherent integration on the time domain result R (n) obtained in step 3.4, specifically:
Step 3.5.1, since the time domain result R (n) in step 3.4 is accumulated on the basis of a set of spreading codes c 1 (t), the next following time domain result R (n+1) can be expressed as:
wherein d (n+1) represents a data bit;
Step 3.5.2, conjugate multiplying the accumulated result of the local spreading code c 1 (t) before and after, and marking the result obtained by conjugate multiplying as E (n):
step 3.5.3, cut off this step, only despread spreading code c 1 (t), spreading code c 2 (t) still exists, d (n) d (n+1) in E (n) and two data bits multiplied by d '(n) d' (n+1) in spreading code c 2 (t) are in one-to-one correspondence, and the result after differential accumulation can be expressed as E dfc (n):
Wherein N dfc represents the number of coherent integration values subjected to differential accumulation; it can be obtained that the control of the frequency searching step length is realized by adjusting the length N of the spread spectrum code;
Step 3.6, traversing the frequency points divided in step 2.2 one by one, repeating the steps 3.2 to 3.5 by using local carriers corresponding to different frequency values, combining all the results to obtain a two-dimensional matrix in code phase dimension and frequency dimension, and searching the code phase corresponding to the maximum differential coherence accumulation value E dfcMAX-1 (n) And coarse frequency bin value/>Wherein code phase/>Namely the accurate value, the rough frequency point value/>, of the code phase dimensionI.e. the rough estimate obtained by the first-order capture.
The step4 specifically comprises the following steps:
Step 4.1, using the rough frequency value obtained in step 3.6 The frequency search range for the second level acquisition is set as follows: /(I)
Step 4.2, selecting the period length of the spreading code c 2 (T) as the coherent accumulation time T coh2, so that the search step length of the second-stage acquisition is Δf 2＝1/Tcoh2, and the frequency points of the frequency dimension search are divided into Respectively marking a frequency point 1, frequency points 2 and … … and a frequency point n;
Step 4.3, setting the frequency value of the local carrier wave as the value of the frequency point 1 in the step 4.2, mixing the received signal with the local carrier wave to realize down-conversion, and carrying out fast Fourier transform on the down-converted signal to convert the signal into a frequency domain;
step 4.4, code phase obtained by step 3.6 Adjusting the spread spectrum code c 2 (t) to realize code alignment, and despreading and accumulating the signals after down-conversion in the step 4.3 to obtain a time domain signal R (n);
step 4.5, performing differential coherent integration on the time domain signal R (n) obtained in step 4.4 in the same manner as in step 3.5;
Step 4.6, traversing the frequency points divided in step 4.2 one by one, using the local carrier wave heavy load corresponding to each frequency value in steps 4.3 to 4.5, obtaining the accumulated value corresponding to each frequency point after scanning is completed, and searching the frequency point value corresponding to the maximum differential coherent accumulated value E dfcMAX-2 (n) Frequency bin value/>Namely a more accurate estimated value obtained by the second-stage capture.
The step 5 specifically comprises the following steps:
The third level acquisition is the same as the second level acquisition, the only difference is that the third level acquisition uses a frame synchronization header sequence of a spread spectrum signal, and the second level acquisition uses a spread spectrum code; according to the frame synchronization header sequence of the spread spectrum signal, the spread spectrum signal is captured in a third level in the same way as in the step 4, and finally the frequency point value corresponding to the maximum coherent accumulation value, namely the optimal Doppler frequency shift estimated value, is obtained Optimal Doppler Shift estimation/>The accurate estimated value obtained by the third-stage capturing is obtained.
A spread spectrum signal three-level acquisition system comprising:
The spread spectrum signal modeling module is used for modeling the received spread spectrum signal;
The frequency search range acquisition module is used for determining a search range of the frequency of the local receiver and a first-stage acquisition frequency search step length;
The first-stage acquisition module of the spread spectrum signal is used for carrying out first-stage acquisition on the spread spectrum signal to obtain a precise value of the code phase dimension and a rough frequency estimated value obtained by the first-stage acquisition;
The second-stage capturing module of the spread spectrum signal is used for carrying out second-stage capturing on the spread spectrum signal to obtain a more accurate frequency estimation value of the second-stage capturing;
And the spread spectrum signal third-stage capturing module is used for carrying out third-stage capturing on the spread spectrum signal to obtain an accurate frequency estimation value of the third-stage capturing.
A spread spectrum signal three-level acquisition device comprising:
the memory stores a computer program of the spread spectrum signal three-level capturing method and is equipment readable by a computer;
And the processor is used for realizing the spread spectrum signal three-level capturing method when executing the computer program.
A computer readable storage medium having stored therein a computer program which when executed by a processor is capable of implementing the spread spectrum signal three level acquisition method.
Compared with the prior art, the invention has the beneficial effects that:
1. The method has the advantages of high signal capturing precision by modeling the received spread spectrum signal and capturing the spread spectrum signal by gradually reducing the searching step length in a three-stage capturing mode.
2. By gradually narrowing the search range to capture signals, the capture time is shortened, and the number of times of Fourier transformation is greatly reduced due to the reduction of the number of search points, so that the requirement on hardware resources is reduced.
3. The frame synchronization head sequence of the spread spectrum signal is used for carrying out third-stage capturing, so that the autocorrelation of the frame synchronization head is involved, the signal frame synchronization is indirectly realized, and the information of a complete frame can be directly obtained in the following signal tracking and other stages, so that the signal capturing integrity is high.
In summary, the method and the device have the advantages of high signal capturing precision, short capturing time, low hardware resource requirement and high signal capturing integrity by modeling the received spread spectrum signal and adopting a three-stage capturing mode to gradually narrow the searching range and capture the spread spectrum signal by gradually narrowing the searching step length.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
FIG. 2 is a schematic flow chart of a three-stage capture method of the present invention.
Fig. 3 is a simulation diagram of a first level capture result according to an embodiment of the present invention.
Fig. 4 is a second stage capture result simulation diagram of an embodiment of the present invention.
Fig. 5 is a third stage capture result simulation diagram of an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
The present invention provides one embodiment.
Setting experimental conditions: generating a group of data to be transmitted by Matlab, inserting an m sequence with the length of 31 into the front end of the data as a frame header sequence, firstly performing primary spreading by using the m sequence with the length of 15, then performing secondary spreading by using a CA code with the length of 1023, setting the code phase offset to 519 and the Doppler frequency offset to-3356 Hz, and then adding noise to the signal to construct a received signal.
Referring to fig. 1 and 2, a method for three-stage acquisition of a spread spectrum signal includes the steps of:
Step 1, modeling a received spread spectrum signal, specifically:
si(t)＝d(t)·c(t-τ)·sin[2π(fIF+fd)t+θi]+n
Wherein d (t) represents the transmitted data code, c (t) represents the spreading code, τ represents the phase of the spreading code, f IF represents the signal intermediate frequency, f d represents the Doppler shift, θ i represents the phase of the received signal, and n represents the mean of 0 and the variance of 0 Is white gaussian noise;
Step 2, combining the spread spectrum signal model established in the step 1 to determine the search range of the local receiver frequency and the first-stage acquisition frequency search step length, wherein the method specifically comprises the following steps:
Step 2.1, the frequency of the local carrier signal is recorded as f IF, the code phase is 0, the frequency difference between the local carrier signal and the received signal is f d, the existing code phase difference is τ, and the maximum Doppler frequency shift is recorded as f max;
step 2.2, in order to reduce the amount of acquisition search operation, a large frequency offset search step is set in the acquisition of this stage, so that the Gold code length of 1023 is selected as the correlation integration time, and the search step of the first stage is In practical use, in order to consider the 3dB attenuation condition, setting Deltaf 1 to be 1KHz; therefore, the frequency points searched in the subsequent frequency dimension are sequentially-20 KHz, -19KHz, -18KHz, … …,19KHz and 20KHz, and are respectively marked as frequency point 1, frequency point 2 and … … and frequency point n;
Step 3, setting a code phase search step length of the local receiver, and performing first-stage acquisition on the spread spectrum signal according to the search range of the frequency of the local receiver and the first-stage acquisition frequency search step length determined in the step 2, so as to obtain a precise value of the code phase dimension and a rough estimated value obtained by the first-stage acquisition, wherein the method specifically comprises the following steps:
Step 3.1, setting the code phase searching step length of a local receiver to be 0.5 chip according to the code phase searching step length setting in signal capturing under the general condition;
Step 3.2, setting the frequency value of the local carrier wave to be-20 KHz, and mixing the received signal with the local carrier wave to realize down-conversion; performing fast fourier transform (fast Fourier transform, FFT) on the mixed signal, transforming the mixed signal from the time domain to the frequency domain, denoted FFT [ s (n) ];
step 3, performing fast Fourier transform (fast Fourier transform, FFT) on the CA code with the local length of 1023, and performing conjugate processing on the signal transformed to the frequency domain, namely FFT * [ c (n) ];
step 3.4, multiplying the FFT [ s (n) ] obtained in step 3.2 with the FFT * [ c (n) ] obtained in step 3.3, and then performing inverse fast Fourier transform (INVERSE FAST Fourier Transform, IFFT) to obtain a time domain result R (n):
Wherein d (N) represents a data bit, f e、θe represents a frequency difference and a phase difference between a received signal and a local carrier, N represents a code length of a local spreading code c 1 (t) in step 3.3, and R b represents a duration of a single chip of the local spreading code c 1 (t);
Step 3.5, performing differential coherent integration on the time domain result R (N) obtained in step 3.4, wherein the number of coherent integration values N dfc =15×31=465 subjected to differential accumulation;
Step 3.6, setting the local frequency value as the frequency point 2 in the step 1.2, namely-19 KHz, and repeating the steps 3.1 to 3.4 until all the frequency points are scanned; drawing all accumulated amplitude values of the current search, as shown in fig. 3, it can be seen from the graph that the code phase corresponding to the maximum differential coherent accumulation value E dfcMAX-1 (n) is 519, the frequency value is-3 kHz, the captured code phase is the same as the set value, the error between the rough frequency capture value and the true value is 356Hz, and the error at the moment is within 1 KHz;
And 4, on the basis of the first-stage capturing in the step 3, carrying out second-stage capturing on the spread spectrum signal to obtain a more accurate estimated value of the second-stage capturing, wherein the method specifically comprises the following steps:
Step 4.1, setting the rough Doppler frequency shift value-3 kHz obtained in the step 3.6 as a central frequency point of second-stage capturing search, wherein the search interval is [ -4KHz, -2KHz ];
the period duration of the m sequence in the step 4.2 is Taking attenuation caused by frequency errors into consideration, setting the search step length of the second-stage capture as 50Hz in the simulation, so that the frequency points of the subsequent frequency dimension search are sequentially-4 KHz, -3.95KHz, -3.90KHz, … …, -2KHz, and are respectively recorded as frequency point 1, frequency points 2 and … … and frequency point n;
step 4.3, setting the frequency value of the local carrier to be-4 KHz, mixing the received signal with the local carrier, and performing FFT conversion to obtain a corresponding frequency domain signal;
Step 4.4, adjusting the local spreading code according to the code phase 519 obtained in step 3.5 to realize code alignment, and despreading and accumulating the signals after down-conversion in step 4.3 to obtain a time domain signal R (n);
Step 4.5: performing differential coherent integration on the time domain accumulation result R (N) obtained in the step 4.4, wherein the number of coherent integration values N dfc =31 in which differential accumulation is performed;
Step 4.6: setting the local frequency value to be-3.95 KHz, and repeating the steps 4.3 to 4.5 until all frequency points are scanned; drawing all accumulated amplitude values of the search, as shown in fig. 4, it can be seen from fig. 4 that the frequency point value corresponding to the maximum differential coherent accumulation value E dfcMAX-2 (n) is-3.35 kHz, namely a more accurate estimated value obtained by second-stage capturing, and the error between the estimated value and the actual frequency offset value is 6Hz until the second-stage capturing is finished;
And 5, on the basis of the second-stage capturing in the step 4, performing third-stage capturing on the spread spectrum signal to obtain an accurate estimated value of the third-stage capturing, wherein the accurate estimated value is specifically as follows:
According to the frame synchronization header sequence of the spread spectrum signal, namely the m sequence with the length of 31, the searching step length is The third-stage capturing is carried out on the spread spectrum signal in the same way as in the step 4, the capturing result is drawn as shown in fig. 5, the frequency offset value corresponding to the peak value can be seen to be-3356 KHz, namely the accurate estimated value obtained by the third-stage capturing, and the third-stage capturing of the spread spectrum signal is completed up to the present; the method and the device have the advantages of high signal capturing precision, short capturing time, low hardware resource requirement and high signal capturing integrity by modeling the received spread spectrum signal and adopting a three-stage capturing mode to gradually narrow the searching range and capture the spread spectrum signal step by step.
From the examples of the present invention, it is known that:
The existing time domain serial acquisition method needs to search one by one in the code phase dimension and the frequency dimension, so that the method needs to A quadratic addition operation in which/>The number of the search for the frequency band; the parallel code phase search acquisition algorithm realizes the parallel search of the code phase dimension by utilizing the property that the frequency domain multiplication is equivalent to the time domain convolution, and the time-frequency domain interconversion is mainly realized by fast Fourier transform FFT and inverse fast Fourier transform IFFT, so the computation is mainly concentrated on the FFT and the IFFT, and the computation is needed to be carried outPerforming a secondary multiplication and addition operation; the three-level capturing method provided by the invention is based on the realization thought of the parallel code phase search capturing algorithm, and the calculation is compressed to/>The third-level capturing method provided by the invention is different from the parallel code phase search capturing algorithm in that the reasons of the capturing range, the searching step length and the error are reduced step by step and precisely captured step by using the third-level serial capturing, so that the searching number/>, in the frequency bandCompared with the prior parallel code phase search acquisition method, the method has smaller resource consumption in implementation, and the embodiment of the invention proves that the number of the shared search frequency bands is the number of the first-stage frequency band searches, the number of the second-stage frequency band searches and the number of the third-stage frequency band searches,If the same acquisition accuracy is to be achieved in the same Doppler frequency shift range, the number of frequency bands to be searched by the parallel code phase search acquisition algorithm is/>Therefore, the three-level capturing method provided by the invention can not only realize capturing of the spread spectrum signal code phase and the frequency offset value, but also has lower calculated amount under the condition of the same capturing error, and has lower consumption of resources when in hardware implementation.
A spread spectrum signal three-level acquisition system comprising:
The spread spectrum signal modeling module is used for modeling the received spread spectrum signal;
The frequency search range acquisition module is used for determining a search range of the frequency of the local receiver and a first-stage acquisition frequency search step length;
The first-stage acquisition module of the spread spectrum signal is used for carrying out first-stage acquisition on the spread spectrum signal to obtain a precise value of the code phase dimension and a rough frequency estimated value obtained by the first-stage acquisition;
The second-stage capturing module of the spread spectrum signal is used for carrying out second-stage capturing on the spread spectrum signal to obtain a more accurate frequency estimation value of the second-stage capturing;
And the spread spectrum signal third-stage capturing module is used for carrying out third-stage capturing on the spread spectrum signal to obtain an accurate frequency estimation value of the third-stage capturing.
A spread spectrum signal three-level acquisition device comprising:
the memory stores a computer program of the spread spectrum signal three-level capturing method and is equipment readable by a computer;
And the processor is used for realizing the spread spectrum signal three-level capturing method when executing the computer program.
A computer readable storage medium having stored therein a computer program which when executed by a processor is capable of implementing the spread spectrum signal three level acquisition method.
Claims (9)
1. A method for three-level acquisition of a spread spectrum signal, comprising the steps of:
step 1, modeling a received spread spectrum signal;
step 2, combining the spread spectrum signal model established in the step 1 to determine the searching range of the local receiver frequency and the searching step length of the first-stage capturing frequency;
Step 3, setting a code phase searching step length of the local receiver, and carrying out first-stage capturing on the spread spectrum signal according to the searching range of the frequency of the local receiver and the first-stage capturing frequency searching step length determined in the step 2 to obtain a precise value of the code phase dimension and a rough frequency estimated value obtained by the first-stage capturing;
step4, on the basis of the first-stage capturing in the step 3, carrying out second-stage capturing on the spread spectrum signal to obtain a more accurate frequency estimation value of the second-stage capturing;
And 5, performing third-stage capturing on the spread spectrum signal on the basis of the second-stage capturing in the step 4 to obtain an accurate frequency estimation value of the third-stage capturing.
2. The method for capturing the spread spectrum signal in three levels according to claim 1, wherein the modeling of the spread spectrum signal in step 1 is specifically:
si(t)＝d(t)·c(t-τ)·sin[2π(fIF+fd)t+θi]+n
Wherein d (t) represents the transmitted data code, c (t) represents the spreading code, τ represents the phase of the spreading code, f IF represents the signal intermediate frequency, f d represents the Doppler shift, θ i represents the phase of the received signal, and n represents the mean of 0 and the variance of 0 Is a gaussian white noise of (c).
3. The method for capturing the spread spectrum signal in three stages according to claim 1, wherein the step2 specifically comprises:
Step 2.1, the frequency of the local carrier signal is denoted as f IF, the code phase is 0, the frequency difference between the local carrier signal and the received signal is denoted as f d, the existing code phase difference is τ, and the maximum doppler shift is denoted as f max, the frequency range of the received signal is: [ f IF-fd,fIF+fd ], the search range of the local receiver frequency;
Step 2.2, selecting the period duration of the spreading code c 1 (T) with the longest length as the coherent accumulation time T coh1 during the first-stage capturing, thereby obtaining the search step length during the first-stage capturing as follows: Δf 1＝1/Tcoh1; meanwhile, the search range of the local receiver frequency determined in the step 2.1 is divided into ：fIF-fd、fIF-fd+Λf1、fIF-fd+Λf2、......、fIF+fd, according to the search step length and respectively recorded as a frequency point 1, a frequency point 2, a frequency point 3, a frequency point n.
4. A method for three-stage acquisition of a spread spectrum signal according to claim 1 or 3, wherein said step3 is specifically:
Step 3.1, setting the code phase searching step length of the local receiver to be 0.5 chip;
Step 3.2, setting a local carrier frequency value according to the frequency points divided in the step 2.2, and mixing a received signal with a local carrier to realize down-conversion; performing fast Fourier transform on the mixed signal, and transforming the mixed signal from a time domain to a frequency domain, and marking the mixed signal as FFT [ s (n) ];
Step 3.3, the local spreading code is recorded as c 1 (t), the fast Fourier transform is carried out on c 1 (t), conjugation processing is carried out on the signal transformed to the frequency domain, and the signal after conjugation processing is recorded as FFT * [ c (n) ];
Step 3.4, multiplying the FFT [ s (n) ] obtained in step 3.2 with the FFT * [ c (n) ] obtained in step 3.3, and then performing inverse fast Fourier transform to obtain a time domain result R (n):
Wherein d (N) represents a data bit, f e、θe represents a frequency difference and a phase difference between a received signal and a local carrier, N represents a code length of a local spreading code c 1 (t) in step 3.3, and R b represents a duration of a single chip of the local spreading code c 1 (t);
step 3.5, performing differential coherent integration on the time domain result R (n) obtained in step 3.4, specifically:
Step 3.5.1, since the time domain result R (n) in step 3.4 is accumulated on the basis of a set of spreading codes c 1 (t), the next following time domain result R (n+1) can be expressed as:
wherein d (n+1) represents a data bit;
Step 3.5.2, conjugate multiplying the accumulated result of the local spreading code c 1 (t) before and after, and marking the result obtained by conjugate multiplying as E (n):
step 3.5.3, cut off this step, only despread spreading code c 1 (t), spreading code c 2 (t) still exists, d (n) d (n+1) in E (n) and two data bits multiplied by d '(n) d' (n+1) in spreading code c 2 (t) are in one-to-one correspondence, and the result after differential accumulation can be expressed as E dfc (n):
Wherein N dfc represents the number of coherent integration values subjected to differential accumulation; it can be obtained that the control of the frequency searching step length is realized by adjusting the length N of the spread spectrum code;
Step 3.6, traversing the frequency points divided in step 2.2 one by one, repeating the steps 3.2 to 3.5 by using local carriers corresponding to different frequency values, combining all the results to obtain a two-dimensional matrix in code phase dimension and frequency dimension, and searching the code phase corresponding to the maximum differential coherence accumulation value E dfcMAX-1 (n) And coarse frequency bin value/>Wherein code phase/>Namely the accurate value, the rough frequency point value/>, of the code phase dimensionI.e. the rough estimate obtained by the first-order capture.
5. The method for three-stage acquisition of a spread spectrum signal according to claim 1 or 4, wherein the step4 is specifically:
Step 4.1, using the rough frequency value obtained in step 3.6 The frequency search range for the second level acquisition is set as follows: /(I)
Step 4.2, selecting the period length of the spreading code c 2 (T) as the coherent accumulation time T coh2, so that the search step length of the second-stage acquisition is Δf 2＝1/Tcoh2, and the frequency points of the frequency dimension search are divided into Respectively marking a frequency point 1, frequency points 2 and … … and a frequency point n;
Step 4.3, setting the frequency value of the local carrier wave as the value of the frequency point 1 in the step 4.2, mixing the received signal with the local carrier wave to realize down-conversion, and carrying out fast Fourier transform on the down-converted signal to convert the signal into a frequency domain;
step 4.4, code phase obtained by step 3.6 Adjusting the spread spectrum code c 2 (t) to realize code alignment, and despreading and accumulating the signals after down-conversion in the step 4.3 to obtain a time domain signal R (n);
step 4.5, performing differential coherent integration on the time domain signal R (n) obtained in step 4.4 in the same manner as in step 3.5;
Step 4.6, traversing the frequency points divided in step 4.2 one by one, using the local carrier wave heavy load corresponding to each frequency value in steps 4.3 to 4.5, obtaining the accumulated value corresponding to each frequency point after scanning is completed, and searching the frequency point value corresponding to the maximum differential coherent accumulated value E dfcMAX-2 (n) Frequency bin value/>Namely a more accurate estimated value obtained by the second-stage capture.
6. The method for capturing the spread spectrum signal in three stages according to claim 1, wherein the step 5 specifically comprises:
The third level acquisition is the same as the second level acquisition, the only difference is that the third level acquisition uses a frame synchronization header sequence of a spread spectrum signal, and the second level acquisition uses a spread spectrum code; according to the frame synchronization header sequence of the spread spectrum signal, the spread spectrum signal is captured in a third level in the same way as in the step 4, and finally the frequency point value corresponding to the maximum coherent accumulation value, namely the optimal Doppler frequency shift estimated value, is obtained Optimal Doppler Shift estimation/>The accurate estimated value obtained by the third-stage capturing is obtained.
7. A system for implementing a spread spectrum signal three-level acquisition method as claimed in claims 1-6, comprising:
The spread spectrum signal modeling module is used for modeling the received spread spectrum signal;
The frequency search range acquisition module is used for determining a search range of the frequency of the local receiver and a first-stage acquisition frequency search step length;
The first-stage acquisition module of the spread spectrum signal is used for carrying out first-stage acquisition on the spread spectrum signal to obtain a precise value of the code phase dimension and a rough frequency estimated value obtained by the first-stage acquisition;
The second-stage capturing module of the spread spectrum signal is used for carrying out second-stage capturing on the spread spectrum signal to obtain a more accurate frequency estimation value of the second-stage capturing;
And the spread spectrum signal third-stage capturing module is used for carrying out third-stage capturing on the spread spectrum signal to obtain an accurate frequency estimation value of the third-stage capturing.
8. A spread spectrum signal three-level acquisition device comprising:
A memory storing a computer program of a spread spectrum signal three-level acquisition method as claimed in any one of claims 1 to 6, a computer readable device;
A processor for implementing a spread spectrum signal three-level acquisition method as claimed in claims 1-6 when executing said computer program.
9. A computer readable storage medium having a computer program stored therein, wherein the computer program, when executed by a processor, is capable of implementing a spread spectrum signal three-level acquisition method as claimed in claims 1-6.
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