Low signal-to-noise ratio spread spectrum signal capturing method with variable symbol rate
阅读说明：本技术 一种符号速率可变的低信噪比扩频信号捕获方法 (Low signal-to-noise ratio spread spectrum signal capturing method with variable symbol rate ) 是由 韩小娟 杨克元 张宗攀 王健欢 石伟 于 2020-06-16 设计创作，主要内容包括：一种符号速率可变的低信噪比扩频信号捕获方法,(1)对AD采样后的数据进行正交下变频；(2)进行累加降速；(3)将累加降速后的数据由串行转成并行；同时确定最小频率区间个数,对本地伪码速率进行修正,并对产生的本地伪码进行存储；(4)读出数据与伪码实现相关运算；将相关运算后的数据串行划分成不同的频率区间；(5)对相关运算后的数据进行累加降速；(6)进行二次变频再累加,之后进行乒乓缓存；(7)读取数据进行FFT运算；当一个频率区间数据处理完成后,判断应用场景要求的最低载噪比是否高于预设的阈值,若高于,则直接根据FFT运算结果进行捕获结果判决,否则,先进行非相干累加,然后根据非相干累加结果进行捕获结果判决。(A low signal-to-noise ratio spread spectrum signal capture method with variable symbol rate, (1) data after AD sampling is subjected to orthogonal down-conversion; (2) performing accumulation speed reduction; (3) converting the accumulated data subjected to speed reduction from serial to parallel; meanwhile, determining the number of minimum frequency intervals, correcting the rate of the local pseudo code, and storing the generated local pseudo code; (4) the read data and the pseudo code realize the correlation operation; serially dividing the data after the correlation operation into different frequency intervals; (5) accumulating and reducing the speed of the data after the correlation operation; (6) performing secondary frequency conversion and accumulation, and then performing ping-pong cache; (7) reading data and performing FFT operation; and after the data processing of one frequency interval is finished, judging whether the lowest carrier-to-noise ratio required by the application scene is higher than a preset threshold value, if so, directly judging a capturing result according to an FFT (fast Fourier transform) operation result, otherwise, firstly carrying out incoherent accumulation, and then judging the capturing result according to the incoherent accumulation result.)
1. A method for acquiring a spread spectrum signal with a variable symbol rate and a low signal-to-noise ratio, the method comprising:
(1) carrying out orthogonal down-conversion on the AD sampled data, and moving the data to a baseband;
(2) accumulating and reducing the speed of the baseband data after the down-conversion according to the bandwidth of the input spread spectrum signal;
(3) sequentially storing the accumulated data subjected to speed reduction into a cache region, and converting the accumulated data subjected to speed reduction from serial to parallel; meanwhile, the number of minimum frequency intervals is determined according to the Doppler frequency offset range and the signal-to-noise ratio, the local pseudo code rate is corrected according to the central frequency point of each frequency interval, and the generated local pseudo code is stored in a storage area;
(4) reading out data and pseudo codes from the cache region and the storage region, and multiplying corresponding bits to realize related operation; serially dividing the data after the correlation operation into different frequency intervals according to the number of the frequency intervals determined in the step (3);
(5) sequentially aiming at each frequency interval, accumulating and reducing the speed of the data after the correlation operation;
(6) performing secondary frequency conversion and re-accumulation on the data accumulated in the step (5), and then performing ping-pong cache by adopting two storage areas, wherein one of the two storage areas is in a writing state, the other storage area is in a reading state, and the depths of the storage areas are consistent; marking the frequency interval obtained after the secondary frequency conversion as a small frequency interval;
(7) reading data from the storage area in the step (6) and performing FFT operation; and after the data processing of one frequency interval is finished, judging whether the lowest carrier-to-noise ratio required by the application scene is higher than a preset threshold value, if so, directly judging a capturing result according to an FFT (fast Fourier transform) operation result, otherwise, firstly carrying out incoherent accumulation, and then judging the capturing result according to the incoherent accumulation result.
2. The method of claim 1, wherein: the width of the buffer area in the step (3) is m, and the depth of the buffer area is expressed as
K is a modulation data rate, M is the number of modulation data participating in capture obtained according to a signal-to-noise ratio and the modulation data rate, clk is a processing clock of AD sampling, N is the number of points of accumulated speed reduction, and g is the reciprocal of data sliding precision when data symbols are removed by using an ergodic method.
3. The method of claim 2, wherein: converting the accumulated speed-reduced data from serial to parallel by the following method:
the order of writing data into the cache region is BRAM _1, the first address of BRAM _2 … … BRAM _ m, the second address of BRAM _1, BRAM _2 … … BRAM _ m, the … …, BRAM _1, BRAM _2 … … BRAM _ m
when reading, data corresponding to one address of BRAM _1 and BRAM _2 … … BRAM _ m is read at one time;
BRAM _1 … … BRAM _ m is a storage space corresponding to one address of the cache region.
4. The method of claim 1, wherein: the number of the frequency intervals in the step (3) needs to meet the requirement
Wherein the one-time accumulation time of the capture operation is TlDoppler frequency range of-Fd～FdAt a radio frequency of FsPseudo code rate of fc。
5. The method of claim 1, wherein: the pseudo code rate after being corrected in the step (3) is
Wherein, the central frequency point of the frequency interval is FqAt a radio frequency of FsPseudo code rate of fc。
6. The method of claim 1, wherein: when the frequency interval is divided in the step (4), 1 correlation operation results in m are accumulated to realize speed reduction, m1 is determined by a sampling clock and a Doppler interval, and according to a sampling theorem, the accumulated data rate is required to be greater than 2 times of the maximum Doppler frequency offset and is recorded asAt the data rate A, according to the frequency interval number obtained in the step (3), carrying out orthogonal frequency conversion on the received signal by using the central frequency point of each interval, wherein the central frequency point FqAnd (4) the pseudo code rate correction quantity in the step (3) is in one-to-one correspondence.
7. The method of claim 1, wherein: the data rate accumulated in step (5)
Wherein, A is the data rate after the correlation accumulation in the step (4), J is the accumulation number, and the Doppler frequency range is-Fd～FdAnd Q is the number of frequency intervals.
8. The method of claim 1, wherein: the reading in the step (7) is realized by the following modes:
reading M × g data corresponding to one small frequency interval, performing FFT operation, reading M × g data from the initial address +1, repeating the operation for g times, reading data corresponding to the next small frequency interval, and repeating the operation for g times until the data corresponding to all the small frequency intervals are completely read;
m is the number of modulation data participating in the capture operation; g is the reciprocal of the data sliding precision when the data symbols are removed by the traversal method.
9. The method of claim 1, wherein: the FFT operation in the step (7) is realized by the following steps:
firstly, g sampling points corresponding to each data symbol are accumulated to obtain M partial accumulation results, and then the partial accumulation results are accumulated again according to the polarity of modulation data, wherein the M modulation data have 2 in total due to the symmetry of 0 and 1(M-1)And (4) carrying out polarity combination, and taking the maximum value of results under different polarity combinations as an FFT operation result.
10. The method of claim 9, wherein: the judgment of the capturing result in the step (7) is specifically as follows:
after all code phase searching corresponding to a certain frequency interval is completed, judging whether the acquisition is successful or not, judging whether all frequency intervals are searched or not, if not, switching the frequency intervals, and continuing the acquisition operation; and (4) if all frequency intervals are searched, judging whether the maximum value is larger than a threshold, namely whether the acquisition is successful, if the acquisition is successful, continuing the tracking, and if the acquisition is not successful, restarting from the step (3).
11. The method of claim 1, wherein: calculating a capture time after step (7), said capture time comprising a data buffering time and a capture computation time, said data buffering time being
in the formula, clk is the processing clock of AD sampling, k is the modulation data rate, M is the number of modulation data participating in capture obtained according to the signal-to-noise ratio and the modulation data rate, g is the reciprocal of the data sliding precision when data symbols are removed by using the traversal method, fcH is the pseudo code rate, H is the pseudo code period, Q is the number of frequency intervals in step (4), J is the accumulated number in step (5), m is the buffer width, m1 is the accumulated number in step (4), t is the sliding precision of the pseudo code phase, and D is the secondary time in step (6)The number of the small frequency intervals after frequency conversion.
Technical Field
The invention belongs to the field of communication, and relates to a low signal-to-noise ratio spread spectrum signal acquisition method with variable symbol rate.
Background
The Direct Sequence Spread Spectrum (DSSS) communication system has the advantages of interference resistance, multipath fading resistance, high ranging precision, code division multiple access support, strong concealment and the like. The technology is widely adopted in aerospace measurement and control communication, and the functions of distance measurement, speed measurement, remote control, remote measurement and the like are organically combined together. The incoherent data bit modulation direct sequence spread spectrum is a signal form widely applied to telemetering and remote control signals in space measurement and control communication.
The traditional acquisition method of spread spectrum signals only relates to acquisition of spread spectrum code words, and does not consider the influence of non-coherent data modulation on the acquisition; or the acquisition of non-coherent spread spectrum signals when the doppler frequency offset is small, only involving a high signal-to-noise ratio. Some of the publications available at present relate to a method for capturing a spread spectrum signal with a variable data rate, for example, document 1, "a method for capturing an incoherent spread spectrum signal with a variable data rate" (author: gujie), a method for combining a segment matched filtering and an incoherent accumulation of a received signal, a method for eliminating the influence of data bit flipping on the capturing performance, and a method for correcting doppler frequency offset by frequency search. The length of matched filtering is half of the modulation data period, the searching step diameter during Doppler correction is related to the modulation data rate, and the method is not suitable for the condition of low signal-to-noise ratio and large Doppler, because under the condition of low signal-to-noise ratio, half data symbols are accumulated and then subjected to incoherent accumulation, and great square loss exists; when the modulation data rate is low, the frequency interval of the correction Doppler frequency offset is correspondingly low, a plurality of intervals need to be divided under large Doppler, and the capture time is correspondingly prolonged. Document 2 research on acquisition algorithm of spread spectrum signal under high dynamic low signal-to-noise ratio (author: the section) proposes a method for rapidly acquiring spread spectrum signal under high dynamic low signal-to-noise ratio based on secondary acquisition, without considering influence of non-coherent data modulation on acquisition.
Disclosure of Invention
The technical problem solved by the invention is as follows: overcomes the defects of the prior art, provides a spread spectrum signal acquisition method with variable symbol rate and low signal-to-noise ratio,
the technical scheme of the invention is as follows: a method for acquiring spread spectrum signals with low signal-to-noise ratio and variable symbol rate is realized by the following steps:
(1) carrying out orthogonal down-conversion on the AD sampled data, and moving the data to a baseband;
(2) accumulating and reducing the speed of the baseband data after the down-conversion according to the bandwidth of the input spread spectrum signal;
(3) sequentially storing the accumulated data subjected to speed reduction into a cache region, and converting the accumulated data subjected to speed reduction from serial to parallel; meanwhile, the number of minimum frequency intervals is determined according to the Doppler frequency offset range and the signal-to-noise ratio, the local pseudo code rate is corrected according to the central frequency point of each frequency interval, and the generated local pseudo code is stored in a storage area;
(4) reading out data and pseudo codes from the cache region and the storage region, and multiplying corresponding bits to realize related operation; serially dividing the data after the correlation operation into different frequency intervals according to the number of the frequency intervals determined in the step (3);
(5) sequentially aiming at each frequency interval, accumulating and reducing the speed of the data after the correlation operation;
(6) performing secondary frequency conversion and re-accumulation on the data accumulated in the step (5), and then performing ping-pong cache by adopting two storage areas, wherein one of the two storage areas is in a writing state, the other storage area is in a reading state, and the depths of the storage areas are consistent; marking the frequency interval obtained after the secondary frequency conversion as a small frequency interval;
(7) reading data from the storage area in the step (6) and performing FFT operation; and after the data processing of one frequency interval is finished, judging whether the lowest carrier-to-noise ratio required by the application scene is higher than a preset threshold value, if so, directly judging a capturing result according to an FFT (fast Fourier transform) operation result, otherwise, firstly carrying out incoherent accumulation, and then judging the capturing result according to the incoherent accumulation result.
Preferably, the width of the buffer in step (3) is m, and the depth of the buffer is expressed as m
K is a modulation data rate, M is the number of modulation data participating in capture obtained according to a signal-to-noise ratio and the modulation data rate, clk is a processing clock of AD sampling, N is the number of points of accumulated speed reduction, and g is the reciprocal of data sliding precision when data symbols are removed by using an ergodic method.
Preferably, the accumulated speed-reduced data is converted from serial to parallel by the following method:
the order of writing data into the cache region is BRAM _1, the first address of BRAM _2 … … BRAM _ m, the second address of BRAM _1, BRAM _2 … … BRAM _ m, the … …, BRAM _1, BRAM _2 … … BRAM _ m
when reading, data corresponding to one address of BRAM _1 and BRAM _2 … … BRAM _ m is read at one time;
BRAM _1 … … BRAM _ m is a storage space corresponding to one address of the cache region.
Preferably, the number of frequency intervals in the step (3) needs to satisfy
Wherein the one-time accumulation time of the capture operation is TlDoppler frequency range of-Fd～FdAt a radio frequency of FsPseudo code rate of fc。
Preferably, the pseudo code rate after the modification in the step (3) is
Wherein, the central frequency point of the frequency interval is FqAt a radio frequency of FsPseudo code rate of fc。
Preferably, when the frequency interval is divided in the step (4), 1 correlation operation results are accumulated every m to realize speed reduction, m1 is determined by the sampling clock and the doppler interval, and the accumulated number is determined according to the sampling theoremThe data rate is greater than 2 times the maximum Doppler frequency offset, and is recorded asAt the data rate A, according to the frequency interval number obtained in the step (3), carrying out orthogonal frequency conversion on the received signal by using the central frequency point of each interval, wherein the central frequency point FqAnd (4) the pseudo code rate correction quantity in the step (3) is in one-to-one correspondence.
Preferably, the data rate accumulated in step (5)
Wherein, A is the data rate after the correlation accumulation in the step (4), J is the accumulation number, and the Doppler frequency range is-Fd～FdAnd Q is the number of frequency intervals.
Preferably, the reading in step (7) is realized by:
reading M × g data corresponding to one small frequency interval, performing FFT operation, reading M × g data from the initial address +1, repeating the operation for g times, reading data corresponding to the next small frequency interval, and repeating the operation for g times until the data corresponding to all the small frequency intervals are completely read;
m is the number of modulation data participating in the capture operation; g is the reciprocal of the data sliding precision when the data symbols are removed by the traversal method.
Preferably, the FFT operation in step (7) is implemented by:
firstly, g sampling points corresponding to each data symbol are accumulated to obtain M partial accumulation results, and then the partial accumulation results are accumulated again according to the polarity of modulation data, wherein the M modulation data have 2 in total due to the symmetry of 0 and 1(M-1)And (4) carrying out polarity combination, and taking the maximum value of results under different polarity combinations as an FFT operation result.
Preferably, the judgment of the capturing result in the step (7) is specifically as follows:
after all code phase searching corresponding to a certain frequency interval is completed, judging whether the acquisition is successful or not, judging whether all frequency intervals are searched or not, if not, switching the frequency intervals, and continuing the acquisition operation; and (4) if all frequency intervals are searched, judging whether the maximum value is larger than a threshold, namely whether the acquisition is successful, if the acquisition is successful, continuing the tracking, and if the acquisition is not successful, restarting from the step (3).
Preferably, after the step (7), calculating a capture time, wherein the capture time comprises a data buffering time and a capture operation time, and the data buffering time isOne clock cycle, one round of capture operation time isOne clock cycle;
in the formula, clk is the processing clock of AD sampling, k is the modulation data rate, M is the number of modulation data participating in capture obtained according to the signal-to-noise ratio and the modulation data rate, g is the reciprocal of the data sliding precision when data symbols are removed by using the traversal method, fcAnd (3) determining the pseudo code rate, H being the pseudo code period, Q being the number of frequency intervals in the step (4), J being the accumulated number in the step (5), m being the buffer width, m1 being the accumulated number in the step (4), t being the sliding precision of the pseudo code phase, and D being the number of small frequency intervals after twice frequency conversion in the step (6).
Compared with the prior art, the invention has the beneficial effects that:
the method adopts a data polarity traversal method to eliminate the influence of modulation data on capturing, divides a plurality of Doppler frequency intervals, corrects the local pseudo code rate by using the central frequency point of each interval, and ensures that the slip of the local pseudo code relative to a received signal in one accumulation time of capturing operation under low signal-to-noise ratio is not more than half a chip; the FFT results of a plurality of times are subjected to incoherent accumulation, the acquisition of the spread spectrum signals under low signal-to-noise ratio is realized, the incoherent accumulation times can be selected according to the signal-to-noise ratio requirement of the input signals, and the acquisition structure is flexible.
Drawings
FIG. 1 is a schematic diagram of the capture of the method of the present invention.
Fig. 2 is an acquisition control flow.
Detailed Description
The invention is further illustrated by the following examples.
As shown in fig. 1, on the basis of a partial correlation FFT algorithm, in the FFT operation process, the influence of modulation data on acquisition is eliminated by using a traversal method, and acquisition of a spread spectrum signal under a low signal-to-noise ratio and a large dynamic condition can be realized, which specifically includes the following steps:
(1) down conversion: carrying out quadrature down-conversion on the AD sampled data, moving the data to a baseband, and assuming that the frequency of an intermediate frequency signal of the AD sampling is f and a processing clock is clk, the frequency of a local carrier is Wc ═ f-clk;
(2) accumulating and reducing the speed: and performing N-point accumulation speed reduction on the baseband data after the down conversion according to the bandwidth of the input spread spectrum signal, wherein the accumulated data rate is clk/N. The purpose of the cumulative slowdown is to reduce the amount of subsequent data storage. N satisfies the sampling theorem.
(3) Data storage: and sequentially storing the accumulated data subjected to speed reduction into a buffer area, wherein the width of the buffer area is determined according to the requirement of capture time, and the depth is determined according to the modulation data rate and the signal-to-noise ratio. Assuming that the width of the buffer is M (the value range is 40-100), the modulation data rate is k, and the number of modulation data participating in capture obtained according to the signal-to-noise ratio and the modulation data rate is M, the depth of the buffer can be expressed as M
(4) And generating and storing a spread spectrum code word: when the data is stored, corresponding storage operation needs to be carried out on the local pseudo code. To achieve a certain capture probability, the lower the signal-to-noise ratio of the input signal, the longer the data accumulation time. Under the condition of low signal-to-noise ratio and large Doppler frequency offset, if the pseudo code rate participating in the correlation operation is the nominal code rate, the relative sliding of the local pseudo code and the received signal can exceed half a chip within the accumulation time of the capturing operation once, and the capturing result is seriously influenced. Therefore, before the local pseudo code is generated, the number of frequency intervals needs to be calculated according to the Doppler frequency offset range and the signal-to-noise ratio, and the local pseudo code rate needs to be corrected according to the central frequency point of each frequency interval.
Assuming that the one-time accumulation time of the capture operation is TlDoppler frequency range of-Fd～FdAt a radio frequency of FsPseudo code rate of fcTo ensure that the code phase slip is less than half a chip in one accumulation time of the acquisition operation, the number Q of frequency intervals needs to satisfyAssuming that the center frequency point of the frequency interval is FqThen the modified pseudo code rate is
In order to realize the correlation accumulation of the local pseudo code and the received signal, the pseudo code also needs to be stored after being generated, and the width of the storage interval is the same as that of the received signal. Since the phase of the local code needs to be shifted during the capturing operation, the local pseudo code needs to store one more data amount corresponding to one code period compared with the received signal. Assuming the pseudo code period is H, the depth of the pseudo code storage space is
(5) Dividing a frequency interval: in order to prevent the code phase shift within one accumulation time of the capture operation from exceeding half a chip, it is necessary to correlate the code phase shift according to the number of frequency intervals in step 4The calculated data is divided into a plurality of frequency intervals, and particularly, the data and code words are read from a received signal storage area and a local pseudo code storage area, and corresponding bits are multiplied to realize related calculation. In order to reduce the number of multipliers in the operation process, it is necessary to accumulate 1 in m correlation operation results to implement speed reduction processing, m1 is determined by a sampling clock and a doppler interval, and the accumulated data rate needs to be greater than 2 times of the maximum doppler frequency offset, which is recorded as
(6) And (3) secondary accumulation: in order to reduce the resource utilization rate, namely, reduce the number of FFT operation points, the frequency-converted data is accumulated and reduced in speed, and the accumulated number J is determined by the coverage range of each frequency interval and the modulation data rate. From step 4, the coverage of each frequency interval isNamely, it isAccumulated data rate by the sampling theorem
(7) Secondary frequency conversion and tertiary accumulation: in order to complete the acquisition of the spread spectrum signal modulated with data of different rates, the data after twice accumulation needs to be subjected to twice frequency conversion and then accumulated. Assuming that the modulation data rate is k, the sliding precision of the data symbols by the traversal method is 1/g of the data symbol width, so the data rate after the three-time accumulation can be set to be the minimum value C ═ g × k, where the minimum data rate corresponds to the minimum FFT point number. After the accumulated data rate is determined, the accumulated point number and the number between cells after the secondary frequency conversion are correspondingly determined:
(8) three cumulative data accesses: in order to save the capture time, the data accumulated for three times is subjected to ping-pong cache by using two storage areas, and one storage area is in a write state while the other storage area is in a read state. Under different modulation data rates, the depths of the storage areas are consistent, so that the same FFT operation module is convenient to call. An address of the storage area stores an accumulation result, the depth is related to the number M of the modulation data participating in the capture operation and the number D of intervals of the secondary frequency conversion, which can be expressed as [ M + g + (g-1) ] D, and sampling points of each small frequency interval are sequentially stored in the storage area. When reading data, firstly reading M × g data corresponding to one interval, performing FFT operation, reading M × g data from the initial address +1, repeating the operation for g times, reading data corresponding to the next small frequency interval, and repeating the operation for g times until the data corresponding to all the small frequency intervals are completely read. The purpose of reading data in this way is to achieve the demodulation of data symbols by means of data sliding.
(9) FFT operation: by the formula
The resolution of the FFT result is W/(M × g) (g × k)/(M × g) (k/M), where C is the data rate after three times of accumulation, M is the number of modulated data involved in the acquisition operation, g is the inverse of the data sliding accuracy when data symbols are removed by the traversal method, and k is the modulated data rate. In order to achieve 90% capture probability, the FFT output signal-to-noise ratio is required to be more than or equal to 17dB, and the capture algorithm can adapt to the carrier-to-noise ratio
(10) Incoherent accumulation: and after the FFT result is subjected to modular squaring, storing the result into a buffer area, and after new FFT operation is finished, performing modular squaring on the result and accumulating the result with data in the buffer area, wherein in order to avoid the influence of square loss, the signal-to-noise ratio after each FFT operation needs to be more than 10 dB. One non-coherent accumulation can improve the acquisition signal-to-noise ratio by 3 dB.
(11) And (4) judging a capture result: the acquisition decision module controls the whole acquisition flow, the acquisition control flow chart is shown in fig. 2, after the acquisition flow is started, data and local pseudo codes are respectively cached according to the step 3 and the step 4, relevant accumulation is carried out after the caching of the data and the local pseudo codes is finished, the frequency interval is divided according to the step 5, subsequent acquisition operation is started, after all code phases corresponding to one frequency interval are searched, whether acquisition is successful or not is judged, and if acquisition is successful, tracking operation is started. And comparing the obtained maximum value with a dynamic threshold during judgment, wherein the dynamic threshold can be set to be U times of the average value of each frame of FFT operation result. If the maximum value is larger than the threshold and the new maximum value is larger than the maximum value obtained previously, judging that the previous acquisition result is wrong, resetting the tracking module and restarting tracking; if the maximum value is not updated, the previous acquisition result is correct, and the tracking is continued.
After all code phase searching corresponding to a certain frequency interval is completed, judging whether the acquisition is successful or not, judging whether all frequency intervals are searched or not, if not, switching the frequency intervals, and continuing the acquisition operation; if all frequency intervals are searched, whether the maximum value is larger than a threshold or not is judged, namely whether the acquisition is successful or not, if the acquisition is successful, the tracking is continued, and if the acquisition is not successful, the acquisition module is reset, and the acquisition is restarted.
(12) And (3) calculating the capture time: in the capture algorithm, the subsequent capture operation can be performed only after the data cache region and the pseudo code cache region in the step 3 and the step 4 are full of data, so the capture time is divided into two parts: the data caching time and the capturing operation time, because two caching areas are arranged before the FFT operation to perform ping-pong caching on the data, namely the data is cached while the FFT operation is performed, and the FFT operation time is less than the data caching time, the FFT operation can be omitted when the capturing time is calculated.
(1) From steps 3, 4, data caching needsOne clock cycle;
(2) from steps 5, 6, 7, 8, one clock cycle can be output
(3) If the input signal-to-noise ratio is low and non-coherent accumulation is required, the acquisition time is doubled on the basis of the above time, for example, when two times of non-coherent accumulation are performed: time 2, three times incoherent addition, time 3 … ….
Therefore, the method for capturing the spread spectrum signal with the variable symbol rate and the low signal-to-noise ratio eliminates the influence of modulation data on capturing by using a traversal method in the FFT operation process on the basis of a part of related FFT algorithms. The acquisition of spread spectrum signals with different Doppler ranges and different modulation data rates can be realized by setting different acquisition parameters; dividing a plurality of Doppler frequency intervals, correcting the speed of the local pseudo code by using a central frequency point of each interval to ensure large Doppler frequency offset, wherein the sliding of the local pseudo code relative to a received signal in one accumulation time of capturing operation under low signal-to-noise ratio is not more than half a chip, and eliminating the influence of large Doppler on the capturing operation performance; the FFT results are subjected to incoherent accumulation for a plurality of times under low signal-to-noise ratio, the incoherent accumulation times can be selected according to the signal-to-noise ratio requirement of the input signal, and the acquisition structure is flexible.