Earth-moon space-oriented high-dynamic weak DSSS signal capturing method
By introducing a symbol search matrix and linear operations into the KT-LVT method, the problems of energy cancellation and signal-to-noise ratio loss caused by data symbol jumps in the acquisition of high dynamic weak DSSS signals in the Earth-Moon space are solved, and efficient energy accumulation and acquisition under extremely low carrier-to-noise ratio conditions are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING INST OF TECH
- Filing Date
- 2026-01-28
- Publication Date
- 2026-05-01
AI Technical Summary
Existing KT-LVT methods cannot effectively achieve energy accumulation in the acquisition of highly dynamic and weak DSSS signals in the Earth-Moon space due to the cancellation of coherent accumulation energy caused by data symbol jumps. Furthermore, nonlinear square operations introduce signal-to-noise ratio loss under extremely low carrier-to-noise ratio conditions.
By using Doppler grouping center frequency demodulation to generate baseband Doppler demodulated signal, the received and local signals are constructed in segments. After performing fast correlation operation in the frequency domain, Keystone transform and symbol search matrix correction are performed. Doppler motion compensation and energy accumulation are performed in combination with Lv's transform. Linear operation is used to replace nonlinear square operation.
It achieves efficient coherent accumulation of signal energy in extremely low carrier-to-noise ratio and extremely high dynamic environment, improves acquisition sensitivity and reliability, avoids signal-to-noise ratio loss, and ensures effective energy focusing.
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Figure CN121966607A_ABST
Abstract
Description
A method for capturing high-dynamic weak DSSS signals in the Earth-Moon space Technical Field
[0001] This invention relates to the field of direct sequence spread spectrum technology, and in particular to a method for capturing high dynamic weak DSSS signals in the Earth-Moon space. Background Technology
[0002] Direct sequence spread spectrum technology is one of the key technologies for aerospace telemetry, tracking, and command (TT&C) communication. For lunar exploration missions, signal acquisition faces the dual challenges of extremely low carrier-to-noise ratio (due to ultra-long distances) and extremely high dynamics. Against this backdrop, improving processing gain through long-term coherent accumulation has become an inevitable choice for capturing weak signals. To cope with the changes in signal parameters caused by high dynamics, the existing technology based on the combination of Keystone Transform (KT) and Lv's Transform (LVT) shows good potential. It can effectively compensate for pseudocode phase shift and Doppler frequency shift under the second-order dynamic model. In the ideal scenario without data symbol transitions, it can achieve high signal-to-noise ratio gain and good energy focusing effect.
[0003] The KT-LVT method faces a key bottleneck in practical applications: it is highly sensitive to the transitions of modulated data symbols. In real telemetry and communication, data symbols are unknown to the receiver. During long-term accumulation, symbol transitions can cause signal components at different time points to be out of phase. Direct coherent accumulation will cause energy cancellation and spectral peak splitting, severely reducing acquisition performance. Existing technologies have used squaring operations to eliminate symbol bits, but this nonlinear operation introduces squared loss under extremely low carrier-to-noise ratio conditions, further weakening the already weak signal. This limits the effectiveness of the method in practical applications. The core issue is how to effectively overcome the negative impact of data symbol transitions on long-term coherent accumulation without introducing additional signal-to-noise ratio loss. Summary of the Invention
[0004] In view of the aforementioned existing problems, the present invention is proposed.
[0005] Therefore, this invention provides a high-dynamic weak DSSS signal acquisition method for the Earth-Moon space, which solves the technical problems of existing KT-LVT methods, such as the cancellation of coherent energy accumulation due to data symbol jumps, and the introduction of signal-to-noise ratio loss due to nonlinear square operations to resist jumps, thus making it impossible to achieve effective energy accumulation under extremely low carrier-to-noise ratio conditions.
[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for acquiring high-dynamic weak DSSS signals in the Earth-Moon space, comprising: demodulating the received complex baseband signal using the center frequency of the current Doppler group to generate a baseband Doppler demodulated signal; generating a local pseudo-code signal based on the initial value of the current time delay segment; segmenting the baseband Doppler demodulated signal and the local pseudo-code signal according to partial correlation time, and constructing a received signal dual block and a local signal dual block respectively; and performing a fast frequency domain correlation operation on the received signal dual block and the local signal dual block. The process involves obtaining partial correlation results; performing a Keystone transform on these partial correlation results to correct pseudocode phase shift, generating corrected partial correlation results, and establishing a symbol search matrix; using the symbol search patterns in the symbol search matrix to perform symbol correction on the corrected partial correlation results, resulting in symbol-corrected partial correlation results; performing an Lv's transform on the symbol-corrected partial correlation results to achieve Doppler shift compensation and energy accumulation, generating a detection quantity; and traversing all symbol search patterns and all delay units to perform a selection and threshold decision on the detection quantity, completing signal acquisition.
[0007] As a preferred embodiment of the high dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the following steps are included: demodulating the received complex baseband signal using the center frequency of the current Doppler group to generate a baseband Doppler demodulated signal, and generating a local pseudo-code signal based on the initial value of the current time delay segment: generating a complex exponential signal using the center frequency of the current Doppler group, multiplying the generated complex exponential signal with the received complex baseband signal; the result of the multiplication operation is defined as the baseband Doppler demodulated signal; and extracting corresponding code chips from the local pseudo-code sequence based on the initial value of the current time delay segment, with the extracted code chip sequence being used to generate the local pseudo-code signal.
[0008] As a preferred embodiment of the high-dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the method involves: segmenting the baseband Doppler demodulated signal and the local pseudocode signal according to partial correlation time, and constructing a received signal dual block and a local signal dual block respectively, including the following steps: setting the coherent accumulation time length and the partial correlation time length; dividing the baseband Doppler demodulated signal into continuous segments in time, with each segment's duration equal to the partial correlation time; dividing the local pseudocode signal into continuous segments in time, with each segment's duration equal to the partial correlation time; taking two adjacent segments from the continuous segments of the baseband Doppler demodulated signal and combining them into a received signal dual block with a length of 2L sampling points; and supplementing each segment of the local pseudocode signal with L zero values to construct a local signal dual block with a length of 2L sampling points.
[0009] As a preferred embodiment of the high dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the following steps are included: performing a fast frequency domain correlation operation on the received signal dual block and the local signal dual block to obtain a partial correlation result: performing a 2L-point fast Fourier transform on the received signal dual block to obtain a first frequency domain; performing a 2L-point fast Fourier transform on the local signal dual block to obtain a second frequency domain; multiplying the conjugates of the first frequency domain and the second frequency domain point by point; performing a 2L-point fast inverse Fourier transform on the multiplication result; and taking the first L points of the fast inverse Fourier transform result as the partial correlation result.
[0010] As a preferred embodiment of the high dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the method includes the following steps: performing Keystone transformation on the partial correlation results, correcting pseudocode phase shift, generating corrected partial correlation results, and establishing a symbol search matrix. This includes: performing Keystone transformation on the partial correlation results along column time, with the output of the Keystone transformation defined as the corrected partial correlation results; determining the dimension of the symbol search matrix based on the ratio of coherent accumulation time to data bit width, and generating the symbol search matrix.
[0011] As a preferred embodiment of the high-dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the following steps are included: using the symbol search pattern in the symbol search matrix to perform symbol correction on the corrected partial correlation results to obtain the symbol-corrected partial correlation results: dividing the matrix form of the corrected partial correlation results into N blocks according to the data symbol period; selecting a symbol search pattern from the symbol search matrix; constructing a diagonal correction matrix using the symbol search pattern; multiplying the diagonal correction matrix by the matrix; and defining the result of the matrix multiplication as the symbol-corrected partial correlation result.
[0012] As a preferred embodiment of the high-dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the method involves performing an Lv's transform on the symbol-corrected partial correlation results to achieve Doppler motion compensation and energy accumulation, thereby generating a detection quantity. This includes the following steps: selecting a column of data from the symbol-corrected partial correlation results, where the column corresponds to a fixed pseudocode delay; performing an Lv's transform on the selected column data along the column time, outputting an energy-focused peak on the two-dimensional Doppler-Doppler rate of change plane; and performing a modulo operation on the Lv's transformed result, with the result of the modulo operation defined as the detection quantity.
[0013] As a preferred embodiment of the high dynamic weak DSSS signal acquisition method for the Earth-Moon space described in this invention, the following steps are included: traversing all symbol search patterns and all delay units, selecting the maximum value and making a threshold decision on the detection quantity to complete signal acquisition: traversing all H symbol search patterns in the symbol search matrix, traversing all L delay units in the partially correlated results after symbol correction, recording the peak value of the detection quantity and the corresponding parameter estimate value generated in each traversal; selecting the maximum value among all recorded peak values of the detection quantity, comparing the selected maximum peak value of the detection quantity with a preset detection threshold, and determining that the signal acquisition is successful when the maximum peak value of the detection quantity exceeds the detection threshold.
[0014] In a second aspect, the present invention provides a computer device including a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program is executed by the processor, it implements any step of the high dynamic weak DSSS signal acquisition method for Earth-Moon space as described in the first aspect of the present invention.
[0015] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, it implements any step of the method for capturing highly dynamic weak DSSS signals in the Earth-Moon space as described in the first aspect of the present invention.
[0016] The beneficial effects of this invention are as follows: By introducing a symbol search matrix and performing symbol correction on some of the correlation results after Keystone transform correction, the estimation of unknown data symbols is transformed into a parallel search for a finite number of symbol jump modes. This replaces the traditional nonlinear square operation with linear operation, eliminating energy cancellation caused by symbol jumps while completely avoiding square loss under extremely low signal-to-noise ratios, thus laying a lossless foundation for energy accumulation. By performing Lv's transform on the symbol-corrected results, the second-order Doppler shift is further compensated, and the signal energy caused by frequency diffusion is refocused into a sharp peak on the two-dimensional plane. Through the progressive processing of code phase correction, symbol jump compensation, and frequency shift focusing, efficient coherent accumulation of signal energy is achieved under extremely low carrier-to-noise ratios and extremely high dynamic environments, improving acquisition sensitivity and reliability. Attached Figure Description
[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 is a flowchart showing the correspondence between data symbols and related peak columns.
[0019] Figure 2 is a block diagram of the algorithm structure.
[0020] Figure 3 is a schematic diagram of a method for capturing high-dynamic weak DSSS signals in the Earth-Moon space. Detailed Implementation
[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.
[0024] Example 1, referring to Figures 1-3, is the first embodiment of the present invention. This embodiment provides a method for capturing high dynamic weak DSSS signals in the Earth-Moon space, including the following steps: S1, demodulating the received complex baseband signal using the center frequency of the current Doppler group to generate a baseband Doppler demodulated signal, and generating a local pseudocode signal based on the initial value of the current time delay segment.
[0025] S1.1. Using the center frequency of the current Doppler group, generate a complex exponential signal, and multiply the generated complex exponential signal with the received complex baseband signal.
[0026] Furthermore, a complex exponential signal is generated based on the center frequency value fdp of the p-th Doppler group currently being searched. The specific form of this complex exponential signal is exp-j2πfdpti, where j represents the imaginary unit and ti represents the discrete sampling time. The generated complex exponential signal exp-j2πfdpti is then multiplied point by point with the received complex baseband signal Si. This multiplication operation is called frequency mixing or down-conversion in signal processing. Its purpose is to shift the spectrum of the received complex baseband signal Si by fdp units on the frequency axis.
[0027] The expression for the baseband Doppler demodulated signal is:
[0028] in, This is the baseband Doppler demodulated signal. For the received complex baseband signal, For discrete-time indexing, The imaginary unit, For the first The center frequency of each Doppler group S1.2 is the discrete sampling time; the result of the multiplication operation is defined as the baseband Doppler demodulated signal. According to the initial value of the current time delay segment, the corresponding chip is extracted from the local pseudo-code sequence, and the extracted chip sequence is used to generate the local pseudo-code signal.
[0029] Furthermore, the baseband Doppler demodulated signal is used as the signal to be processed. Based on the initial value of the q-th time delay segment currently being searched, a chip corresponding to the starting time is extracted from the complete local pseudocode sequence. The extracted chip sequence is directly defined as the local pseudocode signal. The expression of the local pseudocode signal is given by [expression]. The output signal is named the local pseudocode signal.
[0030] S2. The baseband Doppler demodulated signal and the local pseudocode signal are segmented according to partial correlation time, and the received signal dual block and the local signal dual block are constructed respectively.
[0031] S2.1 Set the coherent accumulation time length and the partial correlation time length to divide the baseband Doppler demodulated signal into continuous segments in time, with the duration of each segment equal to the partial correlation time.
[0032] Furthermore, the coherent accumulation time is set to be equal to N times the data bit width, and the partial correlation time is set to be equal to L times the sampling period. Then, the baseband Doppler demodulation signal is... The time axis is divided into M continuous signal segments with the partial correlation time length as the interval. Each signal segment contains L sampling points, thus completing the time segmentation of the baseband Doppler demodulated signal.
[0033] S2.2 Divide the local pseudocode signal into continuous segments in time, with the duration of each segment equal to the partial correlation time.
[0034] Furthermore, the local pseudo-code signal SLi is divided into M continuous signal segments on the time axis with the same partial correlation time length tL. Each signal segment also contains L sampling points, thus completing the time segmentation of the local pseudo-code signal.
[0035] S2.3 From the continuous segments of the baseband Doppler demodulated signal, take two adjacent segments and combine them into a double block of received signal with a length of 2L sampling points.
[0036] Furthermore, for the M-segment of the baseband Doppler demodulated signal, starting from the first and second segments, two adjacent segments are taken sequentially, and the 2L sampling points contained in these two segments are sequentially spliced together to form a new data block. This new data block is defined as the received signal dual block xml, where m represents the sequence number of the dual block and l represents the index of the sampling point within the block. Specifically, the received signal dual block is output.
[0037] S2.4. Add L zero values after each segment of the local pseudocode signal to construct a local signal dual block with a length of 2L sampling points.
[0038] Furthermore, for each segment of the local pseudocode signal SLi, after the L sampling points contained in each segment, an additional L sampling points with zero values are added, so that each segment of the local signal is constructed into a data block with a length of 2L sampling points. This new data block is defined as the local signal double block. The local signal double block is output, and the overall implementation prepares an input data block of appropriate format for subsequent frequency domain fast correlation operations.
[0039] S3. Perform fast frequency domain correlation on the two blocks of received signal and the two blocks of local signal to obtain partial correlation results.
[0040] S3.1 Perform a 2L-point Fast Fourier Transform on the two blocks of the received signal to obtain the first frequency domain, and perform a 2L-point Fast Fourier Transform on the two blocks of the local signal to obtain the second frequency domain.
[0041] Furthermore, a 2L-point Fast Fourier Transform (FFT) operation is performed on the two blocks of the received signal. The result of the FFT operation is defined as the first frequency domain, where k represents the frequency domain index, and its value ranges from 0 to 2L-1. At the same time, a 2L-point FFT operation is performed on the two blocks of the local signal. The result of the FFT operation is defined as the second frequency domain, thus completing the operation of converting the two blocks of the time-domain signal to the frequency domain.
[0042] S3.2 Multiply the conjugates of the first and second frequency domains point by point, perform a 2L-point fast inverse Fourier transform on the multiplication result, and take the first L points of the fast inverse Fourier transform result as the partial correlation result.
[0043] Furthermore, a pointwise multiplication operation is performed on the complex conjugates of the first and second frequency domains. That is, the result of this pointwise multiplication operation is calculated for each frequency domain index, which is equal to the correlation product in the frequency domain. Then, a 2L-point fast inverse Fourier transform operation is performed on the frequency domain correlation product to transform the signal from the frequency domain back to the time domain. The fast inverse Fourier transform operation generates a time domain sequence of length 2L points. Finally, the first L points are extracted from this time domain sequence and defined as the partial correlation result.
[0044] The expression for frequency domain multiplication: ;in, The result is obtained after the two blocks of the received signal undergo a 2L-point Fast Fourier Transform. The result is obtained by performing a 2L-point Fast Fourier Transform on two local signal blocks. This is the complex conjugate of the result obtained after the two blocks of the local signal undergo a 2L-point Fast Fourier Transform. For frequency domain indexing.
[0045] S4. Perform Keystone transformation on the partial correlation results to correct the pseudocode phase shift, generate corrected partial correlation results, and establish a symbol search matrix.
[0046] S4.1. Perform Keystone transformation on the partial correlation results along column time. The output of the Keystone transformation is defined as the corrected partial correlation results.
[0047] Furthermore, the Keystone transform is applied to the partial correlation results along the column time. The Keystone transform is a scaling resampling operation for time-frequency data, designed to compensate for time delays or linear frequency drifts caused by linear distance changes or uniform motion. In this application, the Keystone transform is specifically used to correct the pseudo-code phase linear shift caused by the Doppler scaling factor. After the Keystone transform, a new two-dimensional data matrix is output. This new matrix is defined as the corrected partial correlation results. The Keystone transform eliminates the code phase shift, aligning the pseudo-code autocorrelation peaks in time.
[0048] S4.2 Determine the dimension of the symbol search matrix based on the ratio of coherent accumulation time to data bit width, and generate the symbol search matrix.
[0049] Furthermore, firstly, the ratio N of the coherent accumulation time to the data bit width is calculated. This ratio N represents the number of data symbols contained in the total coherent accumulation time. Then, the dimension of the symbol search matrix is determined based on the ratio N. The symbol search matrix B is constructed as an N-row H-column matrix, where H equals 2 to the power of N-1. This H represents the number of all possible data symbol transition modes. Each column bh of the symbol search matrix B is an N-dimensional column vector representing a specific symbol correction mode. Its elements consist of 0 or 1 and are used to indicate whether to perform an inversion operation on the corresponding data block.
[0050] S5. Use the symbolic search pattern in the symbolic search matrix to perform symbolic correction on the corrected partial correlation results to obtain the symbolically corrected partial correlation results.
[0051] S5.1 Divide the matrix form of the corrected partial correlation results into N blocks according to the data symbol period, and select a symbol search pattern from the symbol search matrix.
[0052] Furthermore, the matrix form of the corrected partial correlation junction is divided according to the data symbol period Tdata. The entire matrix RKT is divided into N consecutive data blocks. Each data block corresponds to the partial correlation result within a data symbol period. Then, a symbol search pattern bh is selected sequentially from the symbol search matrix. The symbol search pattern bh is an N-dimensional vector whose elements take values of 0 or 1 to guide subsequent symbol correction operations.
[0053] S5.2 Construct a diagonal correction matrix using the symbolic search pattern, multiply the diagonal correction matrix by the matrix, and define the result of the matrix multiplication as the symbolically corrected partial correlation result.
[0054] Furthermore, a diagonal correction matrix is constructed using a symbolic search pattern. This diagonal correction matrix is a block diagonal matrix, where each block on the diagonal is a submatrix. The dimension of the submatrix is determined by the size of each data block. Each submatrix is an identity matrix multiplied by a scalar coefficient, which is determined by the value at the corresponding position in the symbolic search pattern. Specifically, the calculation is 1 minus 2 multiplied by the value of the corresponding element in bh. This makes the coefficient of elements in bh with a value of 0 positive 1 and the coefficient of elements in bh with a value of 1 negative 1. Then, matrix multiplication is performed, multiplying the constructed diagonal correction matrix by the partitioned corrected partial correlation result matrix. The result of the matrix multiplication is defined as the symbolically corrected partial correlation result matrix.
[0055] The expression for the partially correlated result matrix after sign correction is as follows: ;in, This is the partial correlation result matrix after sign correction. This refers to matrix multiplication.
[0056] S6. Perform Lv's transform on the partially correlated results after sign correction to achieve Doppler motion compensation and energy accumulation, and generate detection quantity.
[0057] S6.1 Select a column of data from the partially correlated results after symbol correction. The column of data corresponds to a fixed pseudocode delay.
[0058] Furthermore, a column of data is selected from the partially correlated result matrix after symbol correction. This column of data corresponds to a fixed pseudocode delay. This means that the specific column with a fixed delay at all time points is extracted from the matrix. This column of data is a time series containing signal components that change over time under a fixed pseudocode delay.
[0059] S6.2. Perform Lv's transformation on the column data of the selected symbol-corrected partial correlation results along the column time, and the output forms an energy-focused peak on the two-dimensional Doppler-Doppler rate of change plane.
[0060] Furthermore, the column data of the partially correlated results after sign correction are subjected to Lv's transform along the column time. Lv's transform is a parameter estimation algorithm for linear frequency modulated signals that can compensate for the linear change of frequency, i.e., Doppler walk. This transform maps a one-dimensional time series to a two-dimensional Doppler frequency and Doppler rate of change plane. When the parameters of the input signal match the transform, an energy-focused peak will be formed on the two-dimensional plane.
[0061] S6.3 Perform a modulo operation on the result after Lv's transformation. The result of the modulo operation is defined as the detection quantity.
[0062] Furthermore, a modulo operation is performed on the result of the Lv's transform. The modulo operation calculates the amplitude value of the complex number. This operation converts the complex value generated by the Lv's transform into a real value representing the signal energy intensity. The result of the modulo operation is defined as the detection quantity. The mathematical expression of the detection quantity describes its composition, which includes the amplitude factor, sign matching factor, pseudocode, the square of the autocorrelation function, two sinc function terms, and noise components. When the signal parameters are matched, the detection quantity will show a significant peak.
[0063] The expression for the detection quantity is: ;in, For detection volume, For amplitude factor, For sign matching factor, For the autocorrelation function of the pseudocode, For the Doppler frequency search variable, Search for variables for Doppler rate of change. This represents the noise component.
[0064] S7. Traverse all symbol search patterns and all delay units, select the maximum value and make a threshold decision on the detection quantity, and complete the signal acquisition.
[0065] S7.1. Traverse all H symbol search patterns in the symbol search matrix, traverse all L delay units in the partially correlated results after symbol correction, and record the peak value of the detection quantity and the corresponding parameter estimate value generated in each traversal.
[0066] Furthermore, the established symbol search matrix is traversed, and each symbol search pattern in the symbol search matrix is selected sequentially, where h varies from 0 to H-1, and H is the total number of columns in the symbol search matrix. For each selected symbol search pattern, all L delay units in the symbol-corrected partial correlation result matrix are traversed, and each delay unit is selected sequentially, where n varies from 0 to L-1. For each specific combination of symbol search pattern and delay unit, the operation is performed, namely, Lv's transformation, and the detection quantity is generated. The peak value of the detection quantity generated in each traversal and the corresponding parameter estimate value, including the time delay estimate, Doppler frequency estimate, and Doppler rate of change estimate, are recorded.
[0067] S7.2 Select the maximum value among all recorded detection peak values, compare the selected maximum detection peak value with the preset detection threshold, and determine that the signal acquisition is successful when the maximum detection peak value exceeds the detection threshold.
[0068] Furthermore, the system searches for the maximum value (global maximum) among all recorded detection peaks. This global maximum value is then compared with a preset detection threshold, which is a constant pre-set based on the false alarm probability requirement. If the global maximum value is greater than or equal to the preset detection threshold, the signal is considered successfully captured, and the parameter estimate corresponding to the global maximum value is output as the final capture result, including the time delay estimate, Doppler frequency estimate, and Doppler rate of change estimate. If the global maximum value is less than the preset detection threshold, the signal capture within the current search unit is considered to have failed, requiring adjustment of the Doppler group index or time delay segment index, and a new search process is initiated. Through the selection of the maximum value and threshold decision, the confirmation of signal capture and parameter output are finally completed.
[0069] This embodiment also provides a computer device applicable to the high dynamic weak DSSS signal acquisition method for the Earth-Moon space, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the high dynamic weak DSSS signal acquisition method for the Earth-Moon space as proposed in the above embodiment.
[0070] The computer device can be a terminal, comprising a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.
[0071] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the high-dynamic weak DSSS signal acquisition method for Earth-Moon space as proposed in the above embodiments. The storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.
[0072] In summary, this invention transforms the estimation of unknown data symbols into a parallel search for a finite number of symbol-jumping modes by introducing a symbol search matrix and correcting some correlation results after Keystone transform correction. This replaces traditional nonlinear square operations with linear operations, eliminating energy cancellation caused by symbol jumps while completely avoiding square loss under extremely low signal-to-noise ratios, thus laying a lossless foundation for energy accumulation. By performing an Lv's transform on the symbol-corrected results, second-order Doppler shift is further compensated, and the signal energy caused by frequency diffusion is refocused into a sharp peak in the two-dimensional plane. Through progressive processing of code phase correction, symbol jump compensation, and frequency shift focusing, efficient coherent accumulation of signal energy is achieved under extremely low carrier-to-noise ratios and extremely high dynamic environments, improving acquisition sensitivity and reliability.
[0073] Example 2, referring to Figures 1-3, is the second embodiment of the present invention. This embodiment provides a method for capturing high dynamic weak DSSS signals in the Earth-Moon space, including the following steps: In order to solve the problem that the energy of extremely low carrier-to-noise ratio and extremely dynamic DSSS signals is difficult to focus due to factors such as pseudo-code phase shift, data bit jump, and Doppler frequency shift in the Earth-Moon space telemetry and control communication scenario, a method for capturing high dynamic weak DSSS signals in the Earth-Moon space is proposed.
[0074] When considering first-order and second-order dynamics, the received complex baseband signal can be modeled as follows: (1) Among them, The modulation data symbol is unknown, and the data symbol width is... The data symbol rate is , It is a spread spectrum pseudocode, with a chip width of The code rate is The spreading code length is Spread code period , For discrete sampling time, The sampling period is , The initial phase of the carrier wave, The carrier Doppler frequency of the received signal, The Doppler variation rate of the carrier signal. Doppler scaling factor The Doppler rate of change scaling factor. For speed, For acceleration, For the signal carrier frequency, The noise is Gaussian white noise. Let the power spectral density of the Gaussian white noise be... The carrier-to-noise ratio in the above equation can be defined as follows: Normally, there is This results in different magnitudes of the effects of Doppler and Doppler rate of change on data symbols, pseudocodes, and carrier waves. Therefore, Equation (1) neglects the effects of Doppler and Doppler rate of change on data symbols and the effects of Doppler rate of change on spread spectrum pseudocodes when modeling.
[0075] Due to the extremely long communication distance in the Earth-Moon space scenario, the received signal amplitude is very weak, resulting in an extremely low carrier-to-noise ratio. Therefore, long-term accumulation is necessary to suppress noise during acquisition. The acquisition coherent accumulation time is taken as... ,in For positive integers, according to equation (1), the influence during the coherent accumulation time mainly includes: 1) Doppler scaling factor This will cause code phase shift, resulting in a one-dimensional shift in the peak envelope of the coherent accumulation result, leading to accumulation loss and code phase estimation error; 2) The coherent accumulation time includes Each data symbol, and data symbol jumps will cause spectral peak splitting, further affecting energy accumulation; 3) Large carrier Doppler variation rate This will cause Doppler shift during the coherent accumulation time, resulting in spectral expansion, reduced peak value, and impact on energy accumulation and Doppler frequency estimation.
[0076] The proposed method for acquiring high-dynamic weak DSSS signals in the Earth-Moon space requires processing the complex baseband signal received by equation (1). To achieve rapid acquisition and address key issues such as code phase shift, data bit transition, and Doppler frequency shift caused by long-term accumulation of extremely low carrier-to-noise ratio and extremely dynamic DSSS signals, the time delay estimate of the received signal is obtained. Doppler estimates And Doppler rate of change estimates To cover possible received signal delays and Doppler frequency ranges, the entire Doppler search range is typically divided into [number] segments during acquisition. The entire time delay search range is divided into groups. part.
[0077] With any number The first Doppler group and the first Taking time-delayed segmented acquisition as an example, the basic implementation process of a high-dynamic weak DSSS signal acquisition method for the Earth-Moon space is as follows: Step 1: Using the first time-delayed segmented acquisition method... The center frequency of each Doppler group Generates a complex exponential signal to receive a complex baseband signal. Doppler group demodulation is performed to generate a baseband Doppler demodulated signal. (2) Step 2: According to the first Initial values of each time delay segment , generate local signals (3) Step 3: Take the captured coherent accumulation time as From the zero-phase moment of the local signal Initially, the baseband Doppler demodulated signal within the coherent accumulation time was analyzed. Divide the signal into non-overlapping, equal-length segments in chronological order. The duration (or partial correlation time) of each segment is... The number of sampling points is The number of segments is The number of segments within the data bit width is Given a positive integer, then take any two adjacent segments and the total... Point data constructs a dual-block baseband Doppler demodulation signal (4) Among them, For double-block labeling, any number of blocks The length of each signal double block is One sampling point, The sampling point is labeled.
[0078] Step 4: Similarly, starting from the zero-phase moment of the local signal Initially, the local signal within the coherent accumulation time... Divide the signal into non-overlapping, equal-length segments in chronological order. The duration of each segment is... The number of sampling points is The number of segments is Number of segments within the data bit width Given a positive integer, then take any segment of the signal and construct a local signal double block by padding with zeros, i.e. (5) Among them, For double-block labeling, any number of blocks The length of each signal double block is One sampling point, The sampling point is labeled.
[0079] Step 5: Using a length of Pointed and Perform fast correlation operations in the frequency domain and generate the results cyclically. Group Point out relevant results, then take the top results of each group. Points are considered as partially relevant results, i.e. (6) (7) Among them, For amplitude factor, For the time period, These are labels for the number of partially related result groups. For the time of execution, The labels for each group of relevant results. For the fast inverse Fourier transform operator, for of Point FFT result, for The FFT results, To delay time difference, Doppler frequency difference. The above equation shows a partial correlation between the received pseudocode and the local pseudocode. Along the train time If movement occurs in a one-dimensional space, we must find a way to eliminate the impact of the movement on subsequent accumulation.
[0080] Step 6: Perform Keystone transformation on some of the correlation results to correct the column timing of the correlation results in the pseudocode. One-dimensional movement produces corrected partial correlation results, namely (8) of which (9) Among them, Keystone Transformation for Column Time The column time generated after the size transformation. For labeling.
[0081] Step 6: Based on coherence accumulation time With data bit width ratio ,Establish Dimensional data symbol search matrix ,in for Dimension symbol search style, Includes A symbol search style is used to eliminate the impact of data symbol jumps on accumulation during the coherent accumulation time.
[0082] The mathematical principle of this step is as follows: According to equations (8) and (9), after the Keystone transformation, the pseudocode autocorrelation function With time Irrelevant. According to the properties of the pseudocode autocorrelation function, when... hour, This will retrieve the maximum value, and the maximum values will be in the same column. (10) The position of the autocorrelation peak The data symbol index corresponding to the column satisfies (11) It can be seen that the data symbols corresponding to the columns containing the relevant peak values are Only contains Each discrete value.
[0083] In this way, it can be done According to data symbols Divided into Block, i.e. (12) Among them, All 3D matrix This represents the number of partially related groups contained within a data bit width, as shown in Figure 1. The data symbols corresponding to the relevant peak columns are: , The data symbols corresponding to the relevant peak columns are: .
[0084] Because data symbols are unpredictable, although The relevant peak values are all located in the first place. While columns can be processed sequentially, the different data symbols they correspond to still lead to energy accumulation losses. Therefore, a feasible technical approach is to use the first block matrix... Data symbols of related peaks For reference, the style is applied by searching for design symbols. Each block will Data symbols of the relevant peak column Revised to be with Same sign. Therefore, the symbol search matrix can be defined in the following form: (13) Among them, for dimensional symbol search matrix, for Dimension symbol search style, , When generating the symbol search matrix, the subscripts are... Convert to the corresponding The search pattern uses binary numbers as the search term, with element 0 representing no operation and element 1 representing the sign of the data being inverted. Each sign search pattern... The first element is always 0, representing the first partitioned matrix. Data symbols Unchanged, using it as a reference. When At that time, the search symbol matrix is Dimension, in the following form: (14) Using symbol search patterns right Perform symbol search and correction, that is (15) Among them, It uses search styles Constructed 3D diagonal matrix The purpose of the operation is to In this case, a 0 element is mapped to a 1, indicating that the elements in the block remain unchanged; The 1 element is mapped to -1, which is used for inverting the sign of the data. The diagonal elements have only two values: ±1, and are in the following form: (16) When and The data symbols for the relevant peak columns are respectively and At that time, symbol search style Matching it, its mapping is The corrected data symbols are respectively and Compare the data symbols before and after the correction. and It can be seen that by using matching styles After correction, The data symbols have the same sign and are the same as Same. Thus, satisfied. The relevant peak column of the condition can be rewritten in the following form: (17) It can be seen that when matching symbol search patterns, data symbols and Irrelevant, the relevant peak column can achieve efficient energy accumulation, eliminating the impact of sign jumps on subsequent column processing; when the sign search pattern does not match, the data sign will follow... The occurrence of ±1 jumps severely affects column energy accumulation.
[0085] Step 7: Based on the established symbol search matrix , using the Symbol search style structure 3D diagonal matrix The sign correction is completed using the following formula: (18) Among them, dimension To utilize symbol search styles right The result of the correction, Correlation results of the two-dimensional part after Keystone transformation In matrix form.
[0086] Step 8: Remove The Column, along the column time LVT (Lv's Transform) and modulus operations are performed to further eliminate the effects of Doppler motion, achieving energy focusing after long-term accumulation, and generating the current column in two dimensions. The detection quantity of the plane, i.e. (19) Among them, For amplitude, This is the matching factor for the symbol search pattern; when the search pattern matches, Otherwise, losses will be incurred. and A constant scaling factor. The Doppler was determined One-dimensional sinc function main lobe width, Determines the rate of change of Doppler One-dimensional sinc function main lobe width, The scaling factor is the Keystone transform scaling factor in LVT. The larger the value, the better the Keystone performance, but the worse the Doppler rate of change estimation accuracy, so a compromise needs to be made.
[0087] Step 9: For two-dimensional Detection quantity of the plane Select the largest value, calculate and store the current peak value and the estimated value, that is... (20) Among them, the current Initial value, then Add (input / output) to the current position. The column index coordinates from step 8, and For the current two dimensions The coordinates of the plane peak. This is the initial value for the current code phase segment. This represents the center frequency of the current Doppler group.
[0088] Step 10: Repeat steps 8 to 9, first traversing... All List; then repeat steps 7 through 9 to iterate through all. Each symbol search pattern. Based on the above traversal logic, the final result is a search pattern that traverses all symbols. and The highest peak and estimated value from all columns are denoted as... (21) Step 11: For the set Peak within A second selection and threshold judgment are performed. If the result of the second selection exceeds the threshold, the capture is declared successful, and the peak value of the second selection result is recorded. Corresponding estimated value As part of the capture result output, The label corresponds to the peak value of the second-order selection result; otherwise, the control logic unit will adjust the center frequency of the Doppler group. Or initial value of time delay segment This continues until all Doppler groups and time delay segments have been traversed.
[0089] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A method for capturing high-dynamic weak DSSS signals in the Earth-Moon space region, characterized in that: This includes demodulating the received complex baseband signal using the center frequency of the current Doppler group to generate a baseband Doppler demodulated signal, and generating a local pseudocode signal based on the initial value of the current time delay segment. The baseband Doppler demodulated signal and the local pseudocode signal are segmented according to partial correlation time, and a received signal dual block and a local signal dual block are constructed respectively. A fast frequency domain correlation operation is performed on the received signal dual block and the local signal dual block to obtain partial correlation results. A Keystone transform is applied to the partial correlation results to correct pseudocode phase shift, generating corrected partial correlation results, and a symbol search matrix is established. The corrected partial correlation results are then symbol-corrected using the symbol search pattern in the symbol search matrix to obtain symbol-corrected partial correlation results. The Lv's transform is applied to the partially correlated results after symbol correction to achieve Doppler motion compensation and energy accumulation, generating a detection quantity; all symbol search patterns and all delay units are traversed, and the detection quantity is selected and thresholded to complete signal acquisition.
2. The method for acquiring high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 1, characterized in that: The received complex baseband signal is demodulated using the center frequency of the current Doppler group to generate a baseband Doppler demodulated signal, and a local pseudo-code signal is generated based on the initial value of the current time delay segment. The process includes the following steps: generating a complex exponential signal using the center frequency of the current Doppler group; multiplying the generated complex exponential signal with the received complex baseband signal; the result of the multiplication operation is defined as the baseband Doppler demodulated signal; and extracting corresponding code chips from the local pseudo-code sequence based on the initial value of the current time delay segment. The extracted code chip sequence is used to generate the local pseudo-code signal.
3. The method for capturing high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 2, characterized in that: The baseband Doppler demodulated signal and the local pseudocode signal are segmented according to partial correlation time, and a received signal dual block and a local signal dual block are constructed respectively. The steps include: setting the coherent accumulation time length and the partial correlation time length; dividing the baseband Doppler demodulated signal into continuous segments in time, with the duration of each segment equal to the partial correlation time; dividing the local pseudocode signal into continuous segments in time, with the duration of each segment equal to the partial correlation time; taking two adjacent segments from the continuous segments of the baseband Doppler demodulated signal and combining them into a received signal dual block with a length of 2L sampling points; supplementing each segment of the local pseudocode signal with L zero values to construct a local signal dual block with a length of 2L sampling points.
4. The method for capturing high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 3, characterized in that: The process of performing a frequency domain fast correlation operation on the received signal dual blocks and the local signal dual blocks to obtain a partial correlation result includes the following steps: performing a 2L-point fast Fourier transform on the received signal dual blocks to obtain a first frequency domain, performing a 2L-point fast Fourier transform on the local signal dual blocks to obtain a second frequency domain; multiplying the conjugates of the first and second frequency domains point by point, performing a 2L-point fast inverse Fourier transform on the multiplication result, and taking the first L points of the fast inverse Fourier transform result as the partial correlation result.
5. The method for capturing high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 4, characterized in that: The partial correlation results are subjected to Keystone transformation to correct pseudocode phase shift, generating corrected partial correlation results and establishing a symbol search matrix. The steps include: performing Keystone transformation on the partial correlation results along column time, with the output of the Keystone transformation defined as the corrected partial correlation results; determining the dimension of the symbol search matrix based on the ratio of coherent accumulation time to data bit width, and generating the symbol search matrix.
6. The method for capturing high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 5, characterized in that: The symbolic correction of the corrected partial correlation results is performed using the symbolic search pattern in the symbolic search matrix to obtain the symbolic correction of the partial correlation results. The steps include: dividing the matrix form of the corrected partial correlation results into N blocks according to the data symbol period; selecting a symbolic search pattern from the symbolic search matrix; constructing a diagonal correction matrix using the symbolic search pattern; multiplying the diagonal correction matrix with the matrix; and defining the result of the matrix multiplication as the symbolic correction of the partial correlation results.
7. The method for capturing high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 6, characterized in that: The Lv's transform is applied to the symbol-corrected partial correlation results to achieve Doppler motion compensation and energy accumulation, generating a detection quantity. This process includes the following steps: selecting a column of data from the symbol-corrected partial correlation results, where the column corresponds to a fixed pseudocode delay; performing an Lv's transform on the selected column data along the column time, outputting an energy-focused peak on the two-dimensional Doppler-Doppler rate of change plane; and performing a modulo operation on the Lv's transform result, with the result defined as the detection quantity.
8. The method for capturing high-dynamic weak DSSS signals in the Earth-Moon space as described in claim 6, characterized in that, The process of traversing all symbol search patterns and all delay units, selecting the maximum value and making a threshold decision on the detected quantity, and completing signal acquisition includes the following steps: traversing all H symbol search patterns in the symbol search matrix, traversing all L delay units in the partially correlated results after symbol correction, and recording the peak value of the detected quantity and the corresponding parameter estimate value generated in each traversal; selecting the maximum value among all recorded peak values of the detected quantity, comparing the selected maximum peak value of the detected quantity with a preset detection threshold, and determining that the signal acquisition is successful when the maximum peak value of the detected quantity exceeds the detection threshold.
9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the high dynamic weak DSSS signal acquisition method for Earth-Moon space as described in any one of claims 1 to 8.
10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the high dynamic weak DSSS signal acquisition method for Earth-Moon space as described in any one of claims 1 to 8.