CN116366092A

CN116366092A - Doppler capturing method, device and storage medium

Info

Publication number: CN116366092A
Application number: CN202211708043.6A
Authority: CN
Inventors: 梁珍; 朱晓晴; 杨春景; 尚佳栋; 任鹏; 张文婧
Original assignee: Beijing Institute of Remote Sensing Equipment
Current assignee: Beijing Institute of Remote Sensing Equipment
Priority date: 2022-12-29
Filing date: 2022-12-29
Publication date: 2023-06-30

Abstract

The invention provides a Doppler capturing method, a Doppler capturing device and a storage medium, which are used for realizing the successful Doppler capturing under the scene without a synchronous sequence, thereby providing a data basis for the demodulation of a subsequent communication system. The method comprises the following steps: preprocessing the received signal to obtain an initial target signal; sampling the initial target signal to obtain a first target signal; performing first coarse acquisition on a first target signal; when the first coarse acquisition is determined to be successful, sampling an initial target signal to obtain a second target signal; performing second coarse capturing on the second target signal; when the second coarse capturing is determined to be successful, determining the chip offset of the first coarse capturing and the second coarse capturing according to the final correlation peak in the first coarse capturing and the final correlation peak in the second coarse capturing respectively; determining a chip offset difference value according to the chip offset of the two coarse acquisitions; and if the difference value is smaller than the preset threshold value, ending the coarse capturing, and if the difference value is not smaller than the preset threshold value, re-performing the second coarse capturing.

Description

Doppler capturing method, device and storage medium

Technical Field

The present invention relates to the field of wireless communications technologies, and in particular, to a doppler capturing method, a device and a storage medium.

Background

The Doppler effect refers to the difference between the received signal and the transmitted signal caused by the distance between the receiving and transmitting devices, the relative motion of the receiving and transmitting devices in the propagation process, and the crystal oscillator error of the receiving and transmitting clock can cause code offset of the received signal, on one hand, the first point of the information data is not the first point of the receiving end sampling, and on the other hand, the received data has corresponding broadening relative to the transmitted data. In order to compensate the influence of the frequency offset, code offset and other conditions generated by the relative motion on the modulation signal and realize the synchronization under a high-dynamic large-frequency-offset spread spectrum system, the conventional algorithm is an FFT-based acquisition algorithm, and the FFT-based acquisition algorithm is easy to realize by hardware. It converts the time domain correlation calculation of the received signal with the local PN code into multiplication on the frequency domain by using the circular shift correlation theorem. The FFT capturing algorithm greatly reduces capturing time through FFT fast operation, so that capturing results are more accurate. The FFT acquisition algorithm utilizes the synchronization sequence of all 0 or all 1 in the frame format to accumulate signal energy and extract frequency and code phase information from the signal energy. However, when there is no all-0 or all-1 synchronization sequence in the frame format, the conventional acquisition algorithm cannot directly acquire the frequency offset and the code phase, so as to affect demodulation of the communication system. Therefore, how to solve the problem that the capturing of frequency offset and code phase cannot be directly realized in the scene without a synchronous sequence under the spread spectrum system is still lack of effective means.

Disclosure of Invention

The invention provides a Doppler capturing method, a Doppler capturing device and a storage medium, which are used for realizing the successful Doppler capturing in a scene without a synchronous sequence under a spread spectrum system, thereby providing a data base for the demodulation of a subsequent communication system.

In a first aspect, the present invention provides a doppler acquisition method, including:

preprocessing the received signal to obtain an initial target signal;

sampling the initial target signal to obtain a first target signal;

performing first coarse acquisition on a first target signal;

when the first coarse acquisition is determined to be successful, sampling an initial target signal to obtain a second target signal;

performing a second coarse acquisition on a second target signal;

when the second coarse acquisition is determined to be successful, determining the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition according to the final correlation peak in the first coarse acquisition and the final correlation peak in the second coarse acquisition respectively;

determining a chip offset difference value according to the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition;

and ending the second coarse acquisition if the chip offset difference value is smaller than a preset threshold value, and carrying out the second coarse acquisition again if the chip offset difference value is not smaller than the preset threshold value.

In one embodiment, the coarse capture is performed according to the following procedure:

segmenting the total duration of the first target signal based on the preset duration to obtain a plurality of target signals with preset durations;

and translating the target signals of each section of preset duration according to a first preset translation mode to obtain a preset number of translation target signals corresponding to each section of target signals.

According to the initial spread spectrum code and the translation target signals of the target signals, determining the correlation value between the initial spread spectrum code and the translation target signals in the time domain;

differential coherent accumulation is carried out on the correlation value of the initial spread spectrum code and the translation target signal in the time domain, so that a positive correlation peak and a negative correlation peak of the first target signal in each translation mode are obtained;

determining a final correlation peak according to the positive correlation peak and the negative correlation peak of the first target signal in each translation mode; and judging whether the coarse capturing is successful according to the following flow:

judging whether the peak value of the final correlation peak is larger than a coarse acquisition judgment threshold;

if yes, determining that the coarse capturing is successful;

if not, determining that the coarse acquisition fails.

In one embodiment, after ending the second coarse capture, further comprising:

determining carrier Doppler compensation quantity and synchronous head change according to the final correlation peak in the coarse acquisition;

Compensating the first target signal and the second target signal according to the carrier Doppler compensation quantity to obtain an input signal;

based on the second coarse captured chip offset and a second preset translation mode, translating an input signal to obtain a first translation signal, a second translation signal and a third translation signal respectively;

determining a first synchronization head and a second synchronization head according to the synchronization head change;

based on the initial spreading code, respectively determining a first spreading code and a second spreading code according to the first synchronization head and the second synchronization head;

multiplying the first translation signal, the second translation signal and the third translation signal with the first spreading code and the second spreading code respectively, and then performing coherent accumulation to obtain corresponding spreading sequences;

performing Fast Fourier Transform (FFT) on each spread spectrum sequence;

taking the square of each sequence after FFT;

determining the maximum of the squares of all sequence modes;

judging whether the maximum value is larger than a judgment threshold;

if yes, the fine capture is successful;

if not, the fine capture fails.

In one embodiment, the preprocessing of the received signal to obtain the initial target signal specifically includes:

down-converting the received signal, the baseband signal obtained after down-converting is represented by the following expression: y (t) =ad (t) c (t- τ) cos (ω) ₀ +ω _d )t+n(t)；

Sampling the baseband signal to obtain a sampling signal;

carrying out low-pass filtering on the sampling signal to obtain an initial target signal;

wherein y (t) is a baseband signal, A is signal amplitude, d (t) is modulation data information, c (t-tau) is an initial spreading code, omega ₀ For carrier frequency omega _d For Doppler shift, n (t) is additive Gaussian white noise.

In one embodiment, determining a correlation value between the initial spreading code and the shift target signal in the time domain according to the initial spreading code and the shift target signal of the plurality of segments of target signals specifically includes:

and carrying out time-frequency two-dimensional full parallel search on different translation target signals of each section of target signals, and determining the correlation value between the initial spread spectrum code and the translation target signals in the time domain.

In one embodiment, the correlation value of the initial spreading code and the shifted target signal in the time domain is determined by the following formula:

wherein y (m) is the m element in the sequence, c (m-N) is the initial spread spectrum code, N bits are shifted right by taking the m element as a reference, N is the number of points of time domain discrete signals, k is the number of frequency domain signals, the value range of k is more than or equal to 0 and less than or equal to N-1, e ^-2πjkn/N 、e ^-2πjkm/N And e ^2πjk(m-n)/N For a set of orthogonal bases in the N-dimensional complex space, Z (N) is a convolution operation result of the initial spreading code and the target signal in the time domain, Z (k) is a correlation value in the frequency domain, Y (k) is a received signal in the frequency domain, and C (k) is an initial spreading code signal in the frequency domain.

In one embodiment, differential coherent accumulation is performed on correlation values of an initial spreading code and a translation target signal in a time domain to obtain a positive correlation peak and a negative correlation peak of a first target signal in each translation mode, which specifically includes:

and carrying out accumulation operation on the correlation value of the initial spread spectrum code in the time domain under each translation mode and the corresponding translation target signal in each section of target signal, and determining a positive accumulation result and a negative accumulation result of the first target signal under each translation mode by the following formula:

according to the positive accumulation result and the negative accumulation result of the first target signal in each translation mode, determining a positive correlation peak and a negative correlation peak of the first target signal in each translation mode through the following formulas:

wherein,,

representing the forward accumulation of differential coherent demodulation correlation values, < >>

Represents the negative accumulation of the differential coherent demodulation correlation value, yk represents the kth coherent accumulation result, +.>

The conjugate of the k+1th coherent integration result is represented, L represents the number of coherent integration times, CB represents the correlation peak, V represents the differential coherent demodulation correlation value integration, and E (V) represents the expectation of the differential coherent demodulation correlation value integration.

In a second aspect, the present invention provides a doppler acquisition device comprising:

The preprocessing module is used for preprocessing the received signals to obtain initial target signals;

the sampling module is used for sampling the initial target signal to obtain a first target signal; when the first coarse capturing is successful, sampling the initial target signal to obtain a second target signal;

the coarse capturing module is used for performing first coarse capturing processing on the first target signal and performing second coarse capturing on the second target signal; when the chip offset difference value is not smaller than a preset threshold value, re-performing the second coarse acquisition;

a first determining module, configured to determine a chip offset of the first coarse capturing and a chip offset of the second coarse capturing according to a final correlation peak in the first coarse capturing and a final correlation peak in the second coarse capturing, respectively; determining a chip offset difference value according to the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition;

the first judging module is used for judging whether the chip offset difference value is smaller than a preset threshold value or not;

and the ending module is used for ending the second coarse acquisition when the chip offset difference value is smaller than a preset threshold value.

In one embodiment, the coarse capture module comprises:

The time length segmentation submodule is used for segmenting the total time length of the first target signal based on the preset time length to obtain a plurality of target signals with the preset time length;

the translation sub-module is used for translating each section of target signals with preset time length according to a first preset translation mode to obtain a preset number of translation target signals corresponding to each section of target signals;

the first determining submodule is used for determining the correlation value between the initial spread spectrum code and the translation target signal in the time domain according to the initial spread spectrum code and the translation target signal of the plurality of segments of target signals;

the coherent accumulation sub-module is used for carrying out differential coherent accumulation on the correlation value of the initial spread spectrum code and the translation target signal in the time domain to obtain a positive correlation peak and a negative correlation peak of the first target signal in each translation mode;

the second determining submodule is used for determining a final correlation peak according to the positive correlation peak and the negative correlation peak of the first target signal in each translation mode;

the judging sub-module is used for judging whether the peak value of the final correlation peak is larger than a coarse acquisition judgment threshold; if yes, determining that the coarse capturing is successful; if not, determining that the coarse capturing fails; the method comprises the steps of,

the coarse capturing module is specifically configured to perform, through each sub-module, a first coarse capturing process on a first target signal and perform a second coarse capturing process on a second target signal; and when the chip offset difference value is not smaller than a preset threshold value, re-performing the second coarse acquisition.

In one embodiment, the apparatus further comprises:

the second determining module is used for determining carrier Doppler compensation quantity and synchronous head change according to the final correlation peak in the coarse acquisition;

the compensation module is used for compensating the first target signal and the second target signal according to the carrier Doppler compensation quantity to obtain an input signal;

the translation module is used for translating the input signal based on the second coarse captured chip offset and a second preset translation mode of the preset translation modes to respectively obtain a first translation signal, a second translation signal and a third translation signal;

the third determining module is used for determining the first synchronous head and the second synchronous head according to the change of the synchronous heads;

a fourth determining module, configured to determine, based on the initial spreading code, a first spreading code and a second spreading code according to the first synchronization header and the second synchronization header, respectively;

the operation module is used for multiplying the first translation signal, the second translation signal and the third translation signal with the first spreading code and the second spreading code respectively and then carrying out coherent accumulation to obtain corresponding spreading sequences; performing Fast Fourier Transform (FFT) on each spread spectrum sequence; taking the square of each sequence after FFT; determining the maximum of the squares of all sequence modes;

The second judging module is used for judging whether the maximum value is larger than a judging threshold or not; if yes, the fine capture is successful; if not, the fine capture fails.

In one embodiment, the preprocessing module includes:

the frequency conversion submodule is used for carrying out frequency down conversion on the received signals, and the baseband signals obtained after the frequency down conversion are represented by the following expression: y (t) =ad (t) c (t- τ) cos (ω) ₀ +ω _d )t+n(t)；

The sampling submodule is used for sampling the baseband signal to obtain a sampling signal;

the filtering sub-module is used for carrying out low-pass filtering on the sampling signal to obtain an initial target signal;

In one embodiment, the first determining submodule is specifically configured to perform time-frequency two-dimensional full parallel search on different translation target signals of each segment of target signals, and determine a correlation value between an initial spreading code and the translation target signals in a time domain.

In one embodiment, the first determining submodule is specifically configured to determine a correlation value between the initial spreading code and the translation target signal in the time domain according to the following formula:

Wherein y (m) is the m element in the sequence, c (m-N) is the initial spread spectrum code, N bits are shifted right by taking the m element as a reference, N is the number of points of time domain discrete signals, k is the number of frequency domain signals, the value range of k is more than or equal to 0 and less than or equal to N-1, e ^-2πjkn/N 、e ^-2πjkm/N And e ^2πjk(m-n)/N Is one of N-dimensional complex spaceThe group orthogonal basis, Z (n) is the convolution operation result of the initial spreading code and the target signal in the time domain, Z (k) is the correlation value in the frequency domain, Y (k) is the received signal in the frequency domain, and C (k) is the initial spreading code signal in the frequency domain.

In one embodiment, the coherent accumulation sub-module includes:

the operation unit is used for carrying out accumulation operation on the correlation value between the initial spread spectrum code in the time domain under each translation mode and the corresponding translation target signal in each section of target signal, and determining the positive accumulation result and the negative accumulation result of the first target signal under each translation mode through the following formula:

and determining a positive correlation peak and a negative correlation peak of the first target signal in each translation mode according to the positive accumulation result and the negative accumulation result of the first target signal in each translation mode by the following formula:

wherein,,

representing the forward accumulation of differential coherent demodulation correlation values, < > >

Indicating negative accumulation of differential coherent demodulation correlation values, y _k Represents the kth coherent accumulation result, +.>

Represents the conjugate of the k+1th coherent accumulation result, L represents the phaseThe number of dry accumulations, CB, represents the correlation peak, V represents the differential coherent demodulation correlation value accumulation, and E (V) represents the expectation of the differential coherent demodulation correlation value accumulation.

In a third aspect, the invention provides a computing device comprising at least one processor and at least one memory, wherein the memory stores a computer program which, when executed by the processor, causes the processor to perform the steps of a doppler acquisition method as provided in the first aspect.

In a fourth aspect, a computer readable medium is provided, characterized in that it stores a computer program executable by a terminal device, which when run on the terminal device causes the terminal device to perform the steps of a doppler acquisition method provided in the first aspect.

The invention provides a Doppler capturing method, a Doppler capturing device and a storage medium, which are used for carrying out low-pass filtering on a baseband waveform after carrying out down-conversion on a received signal to a baseband, and carrying out coarse capturing on a preprocessed digital baseband signal, thereby realizing capturing of frequency offset and code phase under the condition of no all 0 or all 1 synchronous sequences. Further, by using the correlation value between the spread spectrum code and the target signal, the peak-to-average ratio calculation is performed on the obtained result after coherent accumulation, and the result is compared with a threshold value, so as to determine whether the signal is captured. On the basis, the synchronization sequence obtained by coarse acquisition estimation is used for judging fine acquisition, frequency offset and code phase of signals are further corrected, and follow-up processing such as tracking, demodulation, frame synchronization and decoding is performed on the signals after acquisition is completed, so that the signals are demodulated. Therefore, the acquisition can be successfully completed under the condition that the synchronous sequence is not in the data link frame format through the processing, so that the data with small residual frequency offset is obtained, and a data base is provided for a communication system, and the receiver is helped to carry out correct demodulation subsequently.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation on the invention. In the drawings:

fig. 1 is a flow chart of a doppler capturing method according to an embodiment of the present invention;

fig. 2 is a schematic flow chart of coarse capturing in a doppler capturing method according to an embodiment of the present invention;

fig. 3 is a schematic flow chart of fine acquisition in a doppler acquisition method according to an embodiment of the present invention;

fig. 4 is a schematic diagram of a doppler capturing device according to an embodiment of the present invention.

Detailed Description

The terms first, second and the like in the description and in the claims and in the above-described figures are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments described herein may be implemented in other sequences than those illustrated or otherwise described herein. Reference herein to "a plurality of" or "a number" means two or more than two. "and/or", describes an association relationship of an association object, and indicates that there may be three relationships, for example, a and/or B, and may indicate: a exists alone, A and B exist together, and B exists alone.

The preferred embodiments of the present invention will be described below with reference to the accompanying drawings of the specification, it being understood that the preferred embodiments described herein are for illustration and explanation only, and not for limitation of the present invention, and embodiments of the present invention and features of the embodiments may be combined with each other without conflict.

The following describes in detail the technical solutions provided by the embodiments of the present specification with reference to the accompanying drawings.

Example 1

An embodiment of the present invention provides a doppler capturing method, as shown in a flow chart of the doppler capturing method provided in fig. 1 according to the embodiment of the present invention, including:

s11, preprocessing the received signals to obtain initial target signals.

In specific implementation, the received signal is preprocessed in a scene without all 0 or all 1 synchronization sequences in the frame format, so as to obtain a processed digital baseband signal.

In one embodiment, the step S11 specifically includes:

step one, down-converting the received signal, wherein the baseband signal obtained after down-conversion is represented by the following expression: y (t) =ad (t) c (t- τ) cos (ω) ₀ +ω _d )t+n(t)；

Wherein y (t) is a baseband signal, A is signal amplitude, d (t) is modulation data information, c (t-tau) is a spreading code, omega ₀ For carrier frequency omega _d For Doppler shift, n (t) is additive Gaussian white noise;

step two, sampling the baseband signal to obtain a sampling signal;

and step three, carrying out low-pass filtering on the sampling signal to obtain an initial target signal.

In specific implementation, the received signal is down-converted to baseband, the baseband signal obtained after down-conversion can be represented by the expression, y (n) is obtained by sampling the baseband signal, y (n) is subjected to low-pass filtering, high-frequency components and out-of-band noise are filtered, and the obtained digital baseband signal after the processing is the initial target signal.

S12, sampling the initial target signal to obtain a first target signal.

And (3) sampling according to the initial target signal obtained in the step S11, and obtaining a first target signal serving as input data of first coarse capturing.

It should be noted that, the first target signal, the second target signal, or any target signal may be obtained by sampling the initial target signal.

S13, performing first coarse acquisition on the first target signal.

And (3) performing a first coarse acquisition process on the first target signal obtained in the step S12.

Step one, segmenting the total duration of a first target signal based on preset duration to obtain a plurality of target signals with preset duration.

Dividing the first target signal into a plurality of small segments according to a preset time length based on the total time length, wherein the preset time length can be determined according to an empirical value, actual scene requirements and the like.

And secondly, translating each section of target signals with preset time length according to a first preset translation mode to obtain a preset number of translation target signals corresponding to each section of target signals.

Specifically, the preset number is determined according to a preset translation mode, different translation modes correspond to different frequency offsets, and each section of target signal obtained in the step one is translated according to the preset translation mode, namely, different frequency offsets are set for each section of target signal. For example, if the preset translation modes are respectively 1, 2..k bits to the left, 1,2 … k bits to the right, and 0 bits to the right, and 2k+1 kinds are total, each segment of target signal is translated according to the preset translation modes, and each segment of target signal is translated to obtain 2k+1 kinds of translated target signals with different frequency offsets.

And thirdly, determining the correlation value of the initial spread spectrum code and the translation target signal in the time domain according to the initial spread spectrum code and the translation target signals of the plurality of segments of target signals.

In the implementation, according to the initial spread spectrum code and the translation target signals of the plurality of segments of target signals obtained in the second step, determining the correlation value of the initial spread spectrum code and each translation target signal in the time domain, wherein the spread spectrum code can be calculated by using a local pseudo code.

In the implementation, time-frequency two-dimensional full parallel search is performed on each segment of target signal under different frequency offsets, namely each translation target signal, namely convolution of an initial spread spectrum code on a time domain and each translation target signal is changed into a frequency domain to be multiplied after FFT, so that a correlation value of the initial spread spectrum code on the frequency domain and each translation target signal is obtained, and then the correlation value of the frequency domain is subjected to Fourier inverse transformation to obtain the correlation value of the frequency domain in the time domain.

And fourthly, performing differential coherent accumulation on correlation values of the initial spread spectrum code and the translation target signal in a time domain to obtain a positive correlation peak and a negative correlation peak of the first target signal in each translation mode.

The coherent accumulation is to accumulate the correlation value in a certain time length, namely, accumulate the correlation value between the initial spread spectrum code and the shift target signal in each small preset time length. However, coherent accumulation has certain limitations that can lead to weak signals not being acquired and being affected by residual doppler. And carrying out coherent accumulation on correlation values of a plurality of segments of target signals shifted by the same frequency offset through differential coherent accumulation, and calculating to obtain a positive correlation peak and a negative correlation peak of the first target signal in each shifting mode. The differential coherent accumulation is to multiply the conjugate of the current-segment coherent accumulation result and the last-segment coherent accumulation result.

step 1, performing accumulation operation on correlation values of an initial spreading code in a time domain and corresponding translation target signals in each section of target signals in each translation mode, and determining a positive accumulation result and a negative accumulation result of a first target signal in each translation mode through the following formula:

step 2, determining a positive correlation peak and a negative correlation peak of the first target signal in each translation mode according to a positive accumulation result and a negative accumulation result of the first target signal in each translation mode by the following formula:

wherein,,

Specifically, when the frame format of the communication system contains a synchronization sequence, the capturing can be successfully completed by adopting a general capturing algorithm, and when no special synchronization sequence exists, the maximum influence on capturing is that a correlation peak cannot be obtained directly through coherent accumulation, so that capturing failure is caused. Therefore, firstly coherently accumulating correlation values of the initial spread spectrum code in the time domain and the corresponding shift target signals of all segments of target signals under the same frequency offset, for example, setting the total time length of the first target signal as L, segmenting according to the procedure of the step one in the coarse capturing step, namely dividing the first target signal with the total time length of L into N small segments, shifting each segment of target signal according to the first preset shift mode if M different frequency offsets exist in the first preset shift mode, obtaining M segments of shift target signals after shifting each segment of target signal, obtaining correlation values of each segment of shift target signal and the spread spectrum code through operation, accumulating correlation values of N segments of shift target signals with the same shift frequency offset, and taking the mode through calculation, and obtaining a formula

And->

Solving positive accumulation and negative accumulation of differential coherent demodulation correlation values under M different frequency offsets, and passing through the formula +.>

And obtaining positive correlation peaks and negative correlation peaks under different frequency deviations.

And fifthly, determining a final correlation peak according to the positive correlation peak and the negative correlation peak of the first target signal in each translation mode.

In specific implementation, the correlation values of the same frequency offset of a plurality of segments of target signals are subjected to coherent accumulation, two results of positive accumulation and negative accumulation are obtained in each accumulation, the peak values of the positive correlation peak and the negative correlation peak are compared, the larger correlation peak is determined to be the correlation peak of the frequency offset, the peak values of the correlation peaks of different frequency offsets are compared, and the final correlation peak with the largest correlation peak is determined as the final correlation peak in the coarse capturing process.

Specifically, according to correlation peaks of different frequency offsets in a first preset translation mode, a final correlation peak is determined by the following formula:

wherein V is the correlation peak of each frequency offset in the first preset translation mode.

In this embodiment, whether or not the rough capturing is successful is determined according to the following procedure:

if yes, determining that the coarse capturing is successful;

if not, determining that the coarse acquisition fails.

Specifically, the correlation value of the initial spread spectrum code and the target signal in the obtained time domain is utilized, the peak-to-average ratio calculation is carried out on the obtained result after coherent accumulation, and the comparison is carried out on the obtained result with a threshold value, so that whether the signal is captured or not can be judged. And comparing the peak value of the final correlation peak with a coarse acquisition judgment threshold, if the correlation peak value is larger than the threshold value, successfully acquiring, and if the correlation peak value is not larger than the threshold value, failing to acquire.

It should be noted that if the coarse capturing is judged to fail, the initial target signal is sampled again to obtain another target signal, the coarse capturing is performed on the other target signal, and the steps are repeated until the coarse capturing is successful.

Thus, if it is determined that the first coarse acquisition fails, sampling and coarse acquisition are repeated until the first coarse acquisition is successful.

And S14, when the first coarse acquisition is successful, sampling the initial target signal to obtain a second target signal.

S15, performing second coarse acquisition on the second target signal.

Specifically, when the first coarse capturing is successful, sampling the received signal again to obtain a second target signal, performing the second coarse capturing on the second target signal, and if the second coarse capturing is judged to fail, repeating the sampling and the coarse capturing until the second coarse capturing is successful, wherein the first coarse capturing is the same as the first coarse capturing.

It should be noted that, the flow of performing the second coarse capturing for the second target signal is the same as the flow of performing the first coarse capturing for the first target in the above step S13, and the implementation of the step S15 may refer to the implementation of the above step S13, which is not repeated here.

S16, when the second coarse capturing is determined to be successful, determining the chip offset of the first coarse capturing and the chip offset of the second coarse capturing according to the final correlation peak in the first coarse capturing and the final correlation peak in the second coarse capturing respectively.

If the second coarse capturing is judged to be successful, the chip offset of the first coarse capturing and the chip offset of the second coarse capturing are respectively determined according to the final correlation peak obtained by the two coarse capturing.

S17, determining a chip offset difference value according to the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition.

S18, if the chip offset difference value is smaller than a preset threshold value, ending the second coarse acquisition, and if the chip offset difference value is not smaller than the preset threshold value, carrying out the second coarse acquisition again.

Ending the second coarse acquisition when the chip offset difference value of the two acquisitions is smaller than a preset threshold value; and if the chip offset difference value of the two acquisitions is not smaller than a preset threshold value, re-performing the second coarse acquisition. The preset threshold value can be determined according to experience, actual scene requirements and the like.

After the second coarse acquisition is finished, the acquisition of the frequency offset and the code phase of the signal can be realized under the condition that no all 0 or all 1 synchronous sequence exists. On the basis, the synchronization sequence obtained by coarse acquisition estimation is used for judging fine acquisition, and the frequency offset and the code phase of the signal can be further corrected through fine acquisition processing.

In one embodiment, after ending the second coarse capture, further comprising:

and step one, determining the carrier Doppler compensation quantity and the synchronous head change according to the final correlation peak in the coarse acquisition.

And obtaining the frequency offset of the signal according to the final correlation peak in the second coarse acquisition, namely the carrier Doppler compensation quantity. If the final correlation peak is a positive correlation peak, the synchronization head change is determined to be a positive change, and if the final correlation peak is a negative correlation peak, the synchronization head change is determined to be a negative change, for example, if the positive correlation peak in the kth coherent accumulation result is larger, the synchronization head is determined to be 1 at the moment, and if the negative correlation peak is larger, the synchronization head is determined to be-1 at the moment.

Step two, compensating the first target signal and the second target signal according to the carrier Doppler compensation quantity to obtain an input signal;

in the specific implementation, the target signal which is finally subjected to the first coarse capturing and the target signal which is finally subjected to the second coarse capturing are demodulated according to the captured carrier Doppler compensation quantity.

Thirdly, translating an input signal based on the second coarse captured chip offset and a second preset translation mode to respectively obtain a first translation signal, a second translation signal and a third translation signal;

based on different second preset translation modes, translating the input signal according to the different second preset translation modes on the basis of the second coarse captured chip offset to respectively obtain a first translation signal, a second translation signal and a third translation signal, wherein each second preset translation mode can determine an optimal scheme through multiple experiments, and can also determine through empirical values, actual requirements and the like. For example, if the second preset translation mode is determined to be one-bit-advanced translation, one-bit-in-situ translation and one-bit-delayed translation, the input signal is translated according to 3 different preset translation modes, that is, one-bit-advanced translation is performed before the chip offset obtained by coarse acquisition, one-bit-delayed translation is performed after the chip offset obtained by coarse acquisition, and one-bit-offset-bit-shifted translation is performed after the chip offset obtained by coarse acquisition.

Step four, determining a first synchronous head and a second synchronous head according to the change of the synchronous heads;

in the specific implementation, the first position of the synchronous head obtained by the first or second coarse acquisition judgment is uncertain when the differential operation is carried out, so that the synchronous head is divided into two cases, namely, the first position is 1 and the first position is-1, and the two cases are respectively operated to obtain two synchronous heads.

And fifthly, based on the initial spreading codes, respectively determining the first spreading codes and the second spreading codes according to the first synchronous head and the second synchronous head.

Specifically, after differential operation of the synchronization head obtained through coarse acquisition judgment, the synchronization head and the known spreading code are subjected to Cronecker product, namely, the two synchronization heads obtained in the fourth step are respectively subjected to spreading treatment with the initial spreading code to obtain a first spreading code and a second spreading code of fine acquisition.

And step six, multiplying the first translation signal, the second translation signal and the third translation signal with the first spreading code and the second spreading code respectively, and then performing coherent accumulation to obtain corresponding spreading sequences.

And multiplying the processed three paths of input data with two fine acquisition spread spectrum codes respectively, and then performing coherent accumulation to obtain six sequences.

Step seven, performing fast Fourier transform FFT for each spread spectrum sequence;

step eight, square each sequence after FFT is modulo;

step nine, determining the maximum value in the squares of all sequence modes;

step ten, judging whether the maximum value is larger than a judgment threshold;

if yes, the fine capture is successful;

if not, the fine capture fails.

In specific implementation, the six sequences obtained in the steps are subjected to FFT, the square of the modulus is taken, the maximum value is found, and the maximum value is compared with a fine acquisition judgment threshold, so that the fine acquisition process is completed. And carrying out follow-up processing such as tracking, demodulation, frame synchronization, decoding and the like on the captured signals, and demodulating the signals.

The embodiment of the invention provides a Doppler capturing method, which is characterized in that a received signal is down-converted to a baseband, a baseband waveform is subjected to low-pass filtering to remove noise and high-frequency components, and a processed digital baseband signal is subjected to coarse capturing processing, so that capturing of frequency offset and code phase is realized under the condition of no all 0 or all 1 synchronous sequence. Further, by using the correlation value between the spread spectrum code and the target signal, the peak-to-average ratio calculation is performed on the obtained result after coherent accumulation, and the result is compared with a threshold value, so as to determine whether the signal is captured. On the basis, the synchronization sequence obtained by coarse acquisition estimation is used for judging fine acquisition, frequency offset and code phase of signals are further corrected, and follow-up processing such as tracking, demodulation, frame synchronization and decoding is performed on the signals after acquisition is completed, so that the signals are demodulated. Therefore, the acquisition can be successfully completed under the condition that the synchronous sequence is not in the data link frame format through the processing, so that the data with small residual frequency offset is obtained, and further, a data base is provided for a communication system, and the receiver is helped to carry out correct demodulation subsequently.

Example two

The present embodiment is also provided on the basis of the first embodiment for better understanding by those skilled in the art.

Assuming that the spreading ratio is 1022, the adopted spreading sequence is a local pseudo code, the adopted modulation mode is QPSK, the acquisition precision is 600Hz, the chip rate is 10.24MHz, and the Doppler frequency offset range is-200 kHz.

Let the down-converted received signal be expressed as:

y(t)＝Ad(t)c(t-τ)cos(ω ₀ +ω _d )t+n(t)

wherein A is the signal amplitude; d (t) is QPSK modulated data information; c (t- τ) is the local pseudo code; omega ₀ Is the carrier frequency; omega _d Is Doppler shift; n (t) is additive white gaussian noise.

And (3) performing double downsampling on the received signal to obtain y (n), and performing low-pass filtering on the y (n) to filter out high-frequency components and out-of-band noise.

As shown in fig. 2, which is a schematic diagram of a coarse capturing flow in a doppler capturing method according to an embodiment of the present invention, a received signal after the above processing is subjected to coarse capturing processing, and is first subjected to time-frequency two-dimensional full parallel search, that is, convolution of a local pseudo code in a time domain and received data is changed into multiplication in a frequency domain after FFT, so as to obtain a correlation value of the local pseudo code in the frequency domain and the received data, and then the correlation value in the time domain is obtained by inverse fourier transform of the correlation value in the frequency domain. The correlation formula is as follows:

/>

wherein y (m) is the m-th element in the sequence, c (m-N) is the local pseudo code, N bits are shifted right by taking the m-th element as a reference, N is the number of points of a time domain discrete signal, k is the number of a frequency domain signal, the value range of k is more than or equal to 0 and less than or equal to N1, e ^-2πjkn/N 、e ^-2πjkm/N And e ^2πjk(m-n)/N For a set of orthogonal bases in an N-dimensional complex space, z (N) is the local pseudo-code sum in the time domainThe convolution operation result of the target signal is that Z (k) is a correlation value in a frequency domain, Y (k) is a received signal in the frequency domain, and C (k) is a local pseudo code signal in the frequency domain.

And obtaining correlation values of the two sequences by utilizing the steps, carrying out peak-to-average ratio calculation on the obtained results after coherent accumulation, comparing the peak-to-average ratio with a threshold value, and judging whether signals are captured or not.

Specifically, the correlation values over a certain period of time are accumulated using differential coherent accumulation. The differential coherent accumulation is to multiply the conjugate of the current coherent accumulation result and the last coherent accumulation result, and the expression is as follows:

where V+ represents the forward accumulation of differential coherent demodulation correlation values, L represents the differential correlation value yk in each small segment represents the kth coherent accumulation result,

representing the conjugate of the k+1th coherent accumulation result.

When the data chain frame format contains the synchronous sequence, the general capturing algorithm can be adopted to successfully complete capturing, and when the synchronous sequence of all 0 or all 1 is not available, the maximum effect on capturing is that the correlation peak cannot be accumulated directly through coherent accumulation, so that capturing failure is caused. The positive correlation peak and the negative correlation peak are obtained by utilizing the positive accumulation, the negative accumulation and the correlation peak calculation formulas of the differential coherent demodulation correlation values respectively, the magnitudes of the positive correlation peak and the negative correlation peak are compared, the correlation peak is taken as the final correlation peak in the coarse capturing process, namely if the positive correlation peak in the K-th coherent accumulation result is larger, the synchronous head is judged to be 1, the negative correlation peak is larger, the synchronous head is judged to be-1, the synchronous head is compared with a judgment threshold (the coarse capturing judgment threshold is 20), if the correlation peak is larger than the threshold, the first capturing is successful, the second capturing is carried out, and if the deviation difference value of the chips captured in the two times is smaller than 2, the coarse capturing is successful; if the first acquisition fails, the acquisition is performed again.

The expression of the differential coherent demodulation negative coherent accumulation is:

the correlation peak calculation formula is:

CB＝max|V| ² /E(V)

wherein V_represents negative accumulation of differential coherent demodulation correlation values, y _k Representing the result of the kth coherent accumulation,

After the signal is captured by the coarse capturing module, a more accurate capturing can be performed on the signal, but the coarse capturing can possibly generate a capturing error condition, so that a fine capturing process can be increased to perform fine capturing.

As shown in a flow chart of fine acquisition in a doppler acquisition method provided in an embodiment of the present invention, the fine acquisition step is to demodulate an input signal according to a carrier doppler compensation amount acquired by a coarse acquisition module, translate the input signal in three ways, that is, delay three-bit translation with respect to a chip offset obtained by coarse acquisition, delay two-bit translation with respect to a chip offset obtained by coarse acquisition, delay one-bit translation with respect to a chip offset obtained by coarse acquisition, spread spectrum operation is performed on the processed three-way data and a local pseudo code respectively, and the local pseudo code at this time is a result obtained by performing kronecker product with a known local pseudo code after a synchronization head difference operation obtained by coarse acquisition judgment, and since the first bit of the synchronization head obtained by coarse acquisition judgment is uncertain when performing the difference operation, the first bit is 1 and the first bit is-1, respectively performing operation on the two kinds of synchronization heads, and performing spread spectrum processing on the two kinds of synchronization heads and the local pseudo code respectively to obtain the fine acquired local pseudo code; and then multiplying the processed three paths of input data with two fine acquisition local pseudo codes respectively, performing coherent accumulation, performing FFT on the six sequences, taking the square of a modulus, finding the maximum value, and comparing with a decision threshold (the fine acquisition decision threshold is 100) to finish the fine acquisition process.

Example III

Based on the same inventive concept, the embodiment of the present invention further provides a doppler capturing device, and because the principle of solving the problem by using the device and the apparatus is similar to that of the doppler capturing method provided by the present invention, the implementation of the device and the apparatus can refer to the implementation of the method, and the repetition is omitted.

As shown in fig. 4, a schematic diagram of a doppler capturing device according to an embodiment of the present invention includes:

a preprocessing module 21 for preprocessing the received signal to obtain an initial target signal;

the sampling module 22 is configured to sample the initial target signal to obtain a first target signal; when the first coarse capturing is successful, sampling the initial target signal to obtain a second target signal;

a coarse capturing module 23, configured to perform a first coarse capturing process for a first target signal and perform a second coarse capturing process for a second target signal; when the chip offset difference value is not smaller than a preset threshold value, re-performing the second coarse acquisition;

a first determining module 24, configured to determine a chip offset of the first coarse acquisition and a chip offset of the second coarse acquisition according to the final correlation peak in the first coarse acquisition and the final correlation peak in the second coarse acquisition, respectively; determining a chip offset difference value according to the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition;

A first determining module 25, configured to determine whether the chip offset difference is less than a preset threshold;

an ending module 26 is configured to end the second coarse acquisition when the chip offset difference is less than a preset threshold.

In one embodiment, the coarse capture module comprises:

In one embodiment, the apparatus further comprises:

In one embodiment, the preprocessing module includes:

In one embodiment, the coherent accumulation sub-module includes:

wherein,,

The conjugate of the k+1th coherent integration result is represented, L represents the number of coherent integration times, CB represents the correlation peak, y represents the differential coherent demodulation correlation value integration, and E (V) represents the expectation of the differential coherent demodulation correlation value integration.

For convenience of description, the above parts are described as being functionally divided into modules (or units) respectively. Of course, the functions of each module (or unit) may be implemented in the same piece or pieces of software or hardware when implementing the present invention.

Having described a Doppler acquisition method and apparatus according to an exemplary embodiment of the present invention, a computing apparatus according to another exemplary embodiment of the present invention is described next.

Those skilled in the art will appreciate that the various aspects of the invention may be implemented as a system, method, or program product. Accordingly, aspects of the invention may be embodied in the following forms, namely: an entirely hardware embodiment, an entirely software embodiment (including firmware, micro-code, etc.) or an embodiment combining hardware and software aspects may be referred to herein as a "circuit," module "or" system.

In some possible implementations, a computing device according to the invention may include at least one processor, and at least one memory. Wherein the memory stores program code that, when executed by the processor, causes the processor to perform the steps in a doppler acquisition method according to various exemplary embodiments of the invention described above in this specification. For example, the processor may perform step S11 shown in fig. 1, and perform preprocessing on the received signal to obtain an initial target signal; step S12, sampling the initial target signal to obtain a first target signal; step S13, performing first coarse acquisition on the first target signal; step S14, when the first coarse acquisition is determined to be successful, sampling an initial target signal to obtain a second target signal; step S15, performing a second coarse acquisition on a second target signal; step S16, when the second coarse capturing is determined to be successful, determining the chip offset of the first coarse capturing and the chip offset of the second coarse capturing according to the final correlation peak in the first coarse capturing and the final correlation peak in the second coarse capturing respectively; step S17, determining a chip offset difference value according to the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition; and S18, ending the second coarse acquisition if the chip offset difference value is smaller than a preset threshold value, and carrying out the second coarse acquisition again if the chip offset difference value is not smaller than the preset threshold value.

In some possible embodiments, aspects of a doppler acquisition method provided by the present invention may also be implemented in the form of a program product, which includes a program code for causing a computer device to perform the steps of a doppler acquisition method according to various exemplary embodiments of the present invention described above, when the program product is run on the computer device, for example, the computer device may perform step S11 shown in fig. 1, preprocessing a received signal to obtain an initial target signal; step S12, sampling the initial target signal to obtain a first target signal; step S13, performing first coarse acquisition on the first target signal; step S14, when the first coarse acquisition is determined to be successful, sampling an initial target signal to obtain a second target signal; step S15, performing a second coarse acquisition on a second target signal; step S16, when the second coarse capturing is determined to be successful, determining the chip offset of the first coarse capturing and the chip offset of the second coarse capturing according to the final correlation peak in the first coarse capturing and the final correlation peak in the second coarse capturing respectively; step S17, determining a chip offset difference value according to the chip offset of the first coarse acquisition and the chip offset of the second coarse acquisition; and S18, ending the second coarse acquisition if the chip offset difference value is smaller than a preset threshold value, and carrying out the second coarse acquisition again if the chip offset difference value is not smaller than the preset threshold value.

The program product may employ any combination of one or more readable media. The readable medium may be a readable signal medium or a readable storage medium. The readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or a combination of any of the foregoing. More specific examples (a non-exhaustive list) of the readable storage medium would include the following: an electrical connection having one or more wires, a portable disk, a hard disk, random Access Memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

The program product for doppler acquisition of embodiments of the present invention may employ a portable compact disc read only memory (CD-ROM) and include program code and may run on a computing device. However, the program product of the present invention is not limited thereto, and in this document, a readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

The readable signal medium may include a data signal propagated in baseband or as part of a carrier wave with readable program code embodied therein. Such a propagated data signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination of the foregoing. A readable signal medium may also be any readable medium that is not a readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

Program code for carrying out operations of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device, partly on a remote computing device, or entirely on the remote computing device or server. In the case of remote computing devices, the remote computing device may be connected to the user computing device through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computing device (e.g., connected via the Internet using an Internet service provider).

It should be noted that although several units or sub-units of the apparatus are mentioned in the above detailed description, such a division is merely exemplary and not mandatory. Indeed, the features and functions of two or more of the elements described above may be embodied in one element in accordance with embodiments of the present invention. Conversely, the features and functions of one unit described above may be further divided into a plurality of units to be embodied.

Furthermore, although the operations of the methods of the present invention are depicted in the drawings in a particular order, this is not required to either imply that the operations must be performed in that particular order or that all of the illustrated operations be performed to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step to perform, and/or one step decomposed into multiple steps to perform.

It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A method of doppler acquisition comprising:

Preprocessing the received signal to obtain an initial target signal;

sampling the initial target signal to obtain a first target signal;

performing first coarse acquisition on a first target signal;

performing a second coarse acquisition on a second target signal;

2. The method according to claim 1, characterized in that the coarse capturing is performed according to the following procedure:

if yes, determining that the coarse capturing is successful;

if not, determining that the coarse acquisition fails.

3. The method of claim 1, further comprising, after ending the second coarse capture:

performing Fast Fourier Transform (FFT) on each spread spectrum sequence;

taking the square of each sequence after FFT;

determining the maximum of the squares of all sequence modes;

judging whether the maximum value is larger than a judgment threshold;

if yes, the fine capture is successful;

if not, the fine capture fails.

4. The method according to claim 1, wherein the preprocessing of the received signal to obtain the initial target signal comprises:

Sampling the baseband signal to obtain a sampling signal;

5. The method of claim 4, wherein determining the correlation value between the initial spreading code and the shifted target signal in the time domain based on the initial spreading code and the shifted target signals of the plurality of segments of target signals, specifically comprises:

6. The method of claim 5 wherein the correlation value of the initial spreading code and the shifted target signal in the time domain is determined by the formula:

7. The method according to any one of claims 1-6, wherein differential coherent accumulation is performed on correlation values of an initial spreading code and a shifted target signal in a time domain to obtain a positive correlation peak and a negative correlation peak of the first target signal in each shifting mode, and the method specifically includes:

wherein,,

8. A doppler acquisition device comprising:

9. A computing device comprising at least one processor, and at least one memory, wherein the memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the method of any of claims 1-7.

10. A computer readable medium, characterized in that it stores a computer program executable by a terminal device, which program, when run on the terminal device, causes the terminal device to perform the steps of the method according to any of claims 1-7.