Low-orbit satellite short-burst signal high-precision capturing method, device, equipment and medium

Abstract

This application relates to a method, apparatus, device, and medium for high-precision acquisition of short burst signals from low-Earth orbit (LEO) satellites. The method includes: sequentially performing digital down-conversion and... L The signal pseudocode rate is doubled for downsampling to obtain a downsampled signal sequence; each adjacent... L The downsampled signal is pre-accumulated, and the PMF-FFT algorithm is used to coarsely acquire the pre-accumulated signal sequence, obtaining coarse pseudo-code phase and coarse frequency offset. Based on the coarse pseudo-code phase and coarse frequency offset, a serial code phase search is performed on the downsampled signal sequence to optimize and obtain a fine pseudo-code phase. Then, based on the fine pseudo-code phase and a frequency offset estimation algorithm based on phase relationships, the estimation accuracy of the coarse frequency offset is optimized to obtain a fine frequency offset. This method can improve the acquisition accuracy and speed of short burst signals from low-Earth orbit satellites.

Description

TECHNICAL FIELD

[0001] The application relates to the field of satellite communication and navigation, in particular to a low-orbit satellite short-burst signal high-precision acquisition method, device, equipment and medium. BACKGROUND

[0002] Low-orbit communication satellites have developed rapidly in recent years and have become an important part of global communication infrastructure, showing great potential in filling gaps in ground network coverage, emergency communication, satellite Internet of Things, navigation enhancement and other fields. Low-orbit satellites can be used for communication services and also for improving the performance of navigation services. The short-burst communication and navigation integrated signal has important application value because it carries communication data and navigation ranging information at the same time through the same frequency band.

[0003] For low-orbit satellite short-burst communication and navigation integrated signals, a high-precision acquisition method is a key technology. On the one hand, due to the high-speed motion of the satellite, the receiver will face a more significant Doppler frequency shift and Doppler frequency rate of change in the transmission process than the relative high-orbit satellite, and the Doppler frequency rate of change is as high as 1000Hz / s, which increases the difficulty of signal acquisition and reception. On the other hand, due to the short-time characteristics of the signal, the receiving process cannot use a closed-loop feedback method with a long convergence time and usually uses an open-loop estimation method, but the precision and complexity are a pair of contradictory. L The Doppler frequency shift of a frequency band stationary receiver can reach ±40KHz, and this high dynamic characteristic increases the difficulty of signal acquisition and reception. On the other hand, due to the short-time characteristics of the signal, the receiving process cannot use a closed-loop feedback method with a long convergence time and usually uses an open-loop estimation method, but the precision and complexity are a pair of contradictory. The synchronization accuracy of the Doppler frequency and the code phase will affect the signal demodulation and despreading, and then affect the frequency measurement and ranging accuracy refinement for navigation, and the signal needs to search and capture multiple visible stars at the same time for navigation, so the high algorithm complexity will increase the design difficulty and processing delay of the terminal, and thus a high-performance acquisition method needs to be designed and implemented for low-orbit satellite short-burst signals.

[0004] The acquisition of a low-orbit satellite short-burst signal is a two-dimensional search for code phase and frequency offset. To reduce the search complexity and cope with the large Doppler frequency offset and large signal-to-noise ratio variation in low-orbit satellite communication, the PMF-FFT (partial matching filter-fast Fourier transform) algorithm has become a mainstream acquisition scheme due to its parallel search capability. The core idea is to realize parallel search of code phase through PMF and realize parallel estimation of Doppler frequency offset through FFT for frequency domain analysis. However, since the frequency offset resolution of a single PMF-FFT is limited by the number of FFT points, it is difficult to meet the high-precision requirement. If the number of FFT points is directly increased to improve the resolution, the computational complexity will increase dramatically, that is, the traditional PMF-FFT algorithm has a contradiction between computational complexity and acquisition precision in a low-orbit high-dynamic environment. SUMMARY

[0005] Therefore, it is necessary to provide a low-orbit satellite short-burst signal high-precision acquisition method, device, equipment and medium to balance the relationship between the calculation complexity and the acquisition precision, improve the acquisition probability under the conditions of low signal-to-noise ratio and high dynamics, and obtain better acquisition precision.

[0006] A low-orbit satellite short-burst signal high-precision acquisition method, the method comprising:

[0007] Step 1, sequentially performing digital down-conversion and L times signal pseudo-code rate decimation on the low-orbit satellite short-burst signal sequence sampled by an ADC (analog-to-digital conversion sampling), to obtain a decimated signal sequence;

[0008] Step 2, performing pre-accumulation processing on the decimated signals of each adjacent L point in the decimated signal sequence, and performing coarse acquisition on the pre-accumulation signal sequence by using a PMF-FFT algorithm, to obtain a coarse pseudo-code phase and a coarse frequency offset value;

[0009] Step 3, performing serial code phase search on the decimated signal sequence based on the coarse pseudo-code phase and the coarse frequency offset value, to obtain an accurate pseudo-code phase, and performing optimization on the estimation accuracy of the coarse frequency offset value based on the accurate pseudo-code phase and a frequency offset estimation algorithm based on the phase relationship, to obtain an accurate frequency offset value.

[0010] In one embodiment, sequentially performing digital down-conversion and L times signal pseudo-code rate decimation on the low-orbit satellite short-burst signal sequence sampled by an ADC, to obtain a decimated signal sequence, comprises:

[0011] Receiving a pilot segment signal sequence of the ADC-sampled digital intermediate frequency signal, denoted as:

[0012] ;

[0013] wherein, A is a signal amplitude, is a pseudo-code function, is a signal digital intermediate frequency, is a Doppler frequency, is a sampling interval, k is a sequence index and , is a code phase, is a carrier initial phase;

[0014] By the digital down-conversion processing, the is multiplied by a local carrier to strip the carrier, to obtain a pilot segment zero intermediate frequency signal sequence, denoted as:

[0015] ;

[0016] The digitally down-converted signal sequence is input to a downsampling filter. After anti-aliasing processing by a low-pass filter, it is then passed through a decimator. L The signal pseudocode rate downsampling is performed, and the resulting downsampled signal sequence is represented as follows: Sampling rate Sampling interval ;in, The preset signal pseudocode rate.

[0017] In one embodiment, for each adjacent downsampled signal sequence L The downsampled signal at each point undergoes pre-accumulation processing, including:

[0018] downsampled signal sequence Each adjacent L The downsampled signal at each point is pre-accumulated to obtain the pre-accumulated signal sequence, denoted as follows: ; sampling rate .

[0019] In one embodiment, the PMF-FFT algorithm is used to coarsely acquire the pre-accumulated signal sequence to obtain coarse pseudocode phase and coarse frequency offset, including:

[0020] The windowed PMF-FFT algorithm is used to first accumulate the signal sequence. and locally generated pseudocode sequences enter P Filter using PMFs, assuming the pseudocode sequence length is . M PMF length set to X The number of PMFs is P = M / X X In the case of code alignment, the signal passes through the first... p The output of each PMF is represented as:

[0021] ;

[0022] in, For Doppler frequency, The preset signal pseudocode rate, p For PMF index and , The initial phase of the carrier;

[0023] Perform PMF output N Point FFT, at this time the FFT output of the th n The normalized amplitude-frequency response of the point is:

[0024] ;

[0025] wherein, , ; is the contribution of PMF to the normalized amplitude-frequency response, denoted as:

[0026] ;

[0027] is the contribution of FFT to the normalized amplitude-frequency response, denoted as:

[0028] ;

[0029] Before the point FFT, the following window function is used for windowing: N

[0030] ;

[0031] wherein, is the window function, is a discrete integer variable, is a tuning coefficient;

[0032] The contribution of the windowed FFT to the normalized amplitude-frequency response is:

[0033] ;

[0034] The normalized amplitude-frequency response of the PMF-FFT algorithm after windowing is:

[0035] ;

[0036] It is determined whether the peak value of exceeds a set threshold value, if yes, it is determined that the signal acquisition is successful, the current pseudo-code phase is recorded as a coarse pseudo-code phase , and the peak value corresponding Doppler shift is calculated as a coarse frequency offset value , denoted as:

[0037] ;

[0038] Otherwise, the next group of short burst signal sequences are subjected to coarse acquisition.

[0039] In one embodiment, a serial code phase search is performed on the down-sampling signal sequence based on the coarse pseudo-code phase and the coarse frequency offset value, and an optimized fine pseudo-code phase is obtained, including:

[0040] Based on the coarse pseudo-code phase and the coarse frequency offset value , a serial code phase search is performed on the down-sampling signal sequence ​Code phase correction and frequency offset correction are performed separately to obtain the corrected signal sequence. , represented as:

[0041] ;

[0042] in, k For sequence index and Sampling rate ;

[0043] by L Double signal pseudocode rate to generate local pseudocode sequence and will Move forward and backward one by one. L- One sampling point yielded a total of 2 L- A new local pseudocode sequence is represented as:

[0044] ;

[0045] 2 L -1 new local pseudocode sequence respectively with Perform conjugate multiplication to obtain a set of correlation values. Obtain the maximum value of this set of correlation values ​​and update the code phase to the pseudo-code phase corresponding to the maximum correlation value, thus obtaining the refined pseudo-code phase. .

[0046] In one embodiment, the estimation accuracy of the coarse frequency offset is optimized based on the precise pseudocode phase and a frequency offset estimation algorithm based on phase relationships to obtain the precise frequency offset, including:

[0047] Calculate the current pseudocode rate based on the ratio between code Doppler and carrier Doppler. for:

[0048] ;

[0049] in, For carrier transmission frequency, The preset signal pseudocode rate;

[0050] use L Double the current pseudocode rate Generate local pseudocode sequences ;

[0051] Based on coarse frequency bias The precise pseudocode phase obtained by searching the serial code phase downsampled signal sequence Frequency offset correction and code phase correction are performed separately to obtain the corrected signal sequence. , represented as:

[0052] ;

[0053] will be multiplied by to get the signal , which can be expressed as:

[0054] ;

[0055] where, is the signal amplitude, is the autocorrelation function of the pseudo code, is the phase deviation between the input signal and the local signal, is the residual frequency offset, is the initial phase difference between the input signal and the local signal; at this time, the pseudo code is stripped from the input signal, is the continuous wave signal, and the residual frequency offset can be obtained by the phase change at two time points;

[0056] In order to reduce the influence of signal noise and outliers, the residual frequency offset is calculated by segmentation. The signal is divided into q segments according to its length, and q +1 sampling time points containing the starting sampling point are extracted, which are denoted as ; these time points are sequentially divided into groups, a total of q +1) / 2 groups, denoted as ; wherein, q is a positive odd number;

[0057] The frequency offset value is calculated for each group of two time points. For the first time point of each group, the phase of the signal at time is expressed as:

[0058] ;

[0059] where, represents the imaginary part of the signal, represents the real part of the signal; for the second time point of each group, the phase of the signal at time is expressed as:

[0060] ;

[0061] Ignoring short-term changes, assuming remains unchanged at and two time points, a frequency offset value is calculated using the phase difference at these two time points, denoted as:

[0062] ;

[0063] wherein, ;

[0064] By calculating the frequency offset value at two time points in all groups, a total of (N-1) / 2 frequency offset values are obtained and the average value is calculated to obtain the residual frequency offset q , which is expressed as:

[0065] ;

[0066] wherein, is the i-th frequency offset value, is the frequency offset value sequence number; The fine frequency offset value

[0067] is the sum of the coarse frequency offset value and the residual frequency offset

[0068] .

[0069] In one embodiment, the above method further comprises:

[0070] The parameters set in the PMF-FFT algorithm X and N satisfy the following constraints:

[0071] .

[0072] A low-orbit satellite short-burst signal high-precision acquisition device, the device comprising:

[0073] A preprocessing module for sequentially performing digital down-conversion and L times signal pseudo-code rate down-sampling on the ADC-sampled low-orbit satellite short-burst signal sequence to obtain a down-sampled signal sequence;

[0074] A coarse search module for performing pre-accumulation processing on the down-sampled signals of every adjacent L point in the down-sampled signal sequence, and performing coarse acquisition on the pre-accumulation signal sequence using a PMF-FFT algorithm to obtain a coarse pseudo-code phase and a coarse frequency offset value;

[0075] A fine adjustment module for performing serial code phase search on the down-sampled signal sequence based on the coarse pseudo-code phase and the coarse frequency offset value, optimizing to obtain a fine pseudo-code phase, and optimizing the estimation accuracy of the coarse frequency offset value according to the fine pseudo-code phase and a frequency offset estimation algorithm based on the phase relationship to obtain a fine frequency offset value.

[0076] ​​​A computer device comprises a memory and a processor, the memory stores a computer program, and the processor implements the following steps when executing the computer program:

[0077] Step 1, sequentially performing digital down conversion and L times signal code rate decimation on a low-orbit satellite short-burst signal sequence sampled by an ADC to obtain a decimated signal sequence;

[0078] Step 2, performing pre-accumulation processing on decimated signals of each adjacent L point in the decimated signal sequence, and performing coarse capture on the pre-accumulation signal sequence by using a PMF-FFT algorithm to obtain a coarse code phase and a coarse frequency offset value;

[0079] Step 3, performing serial code phase search on the decimated signal sequence based on the coarse code phase and the coarse frequency offset value, optimizing to obtain a fine code phase, and optimizing the estimation accuracy of the coarse frequency offset value according to the fine code phase and a frequency offset estimation algorithm based on a phase relationship to obtain a fine frequency offset value.

[0080] A computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the following steps:

[0081] Step 1, sequentially performing digital down conversion and L times signal code rate decimation on a low-orbit satellite short-burst signal sequence sampled by an ADC to obtain a decimated signal sequence;

[0082] Step 2, performing pre-accumulation processing on decimated signals of each adjacent L point in the decimated signal sequence, and performing coarse capture on the pre-accumulation signal sequence by using a PMF-FFT algorithm to obtain a coarse code phase and a coarse frequency offset value;

[0083] Step 3, performing serial code phase search on the decimated signal sequence based on the coarse code phase and the coarse frequency offset value, optimizing to obtain a fine code phase, and optimizing the estimation accuracy of the coarse frequency offset value according to the fine code phase and a frequency offset estimation algorithm based on a phase relationship to obtain a fine frequency offset value.

[0084] The low-orbit satellite short-burst signal high-precision acquisition method, device, equipment and medium described above, based on the two-step hierarchical strategy of "coarse search + fine adjustment", in the coarse search stage, the high sampling rate data can be effectively utilized through pre-accumulation processing, which not only improves the signal-to-noise ratio of the down-sampled signal, but also reduces the operation amount and calculation complexity of the PMF-FFT algorithm for coarse search; in the fine adjustment stage, the code phase accuracy loss caused by the pre-accumulation processing can be reduced through serial code phase search, the estimation accuracy of the code phase is improved, and through the frequency offset estimation algorithm based on the phase relationship, the pilot signal with the stripped code can be calculated according to the phase change in multiple segments to obtain the accurate residual frequency offset, and the residual frequency offset and the coarse frequency offset value are combined to obtain the fine frequency offset value, further optimizing the frequency offset estimation accuracy. The present application can improve the acquisition accuracy and speed of the low-orbit satellite short-burst signal under the conditions of low signal-to-noise ratio and high dynamics, and meet the high-precision requirements of demodulation, despreading and integrated signal navigation and ranging. BRIEF DESCRIPTION OF DRAWINGS

[0085] Figure 1 It is a flowchart of a low-orbit satellite short-burst signal high-precision acquisition method in an embodiment;

[0086] Figure 2 It is a schematic diagram of a down-sampling filter in an embodiment;

[0087] Figure 3 It is a flowchart of a windowed PMF-FFT algorithm in an embodiment;

[0088] Figure 4 It is a schematic diagram of the internal structure of a computer device in an embodiment. DETAILED DESCRIPTION

[0089] In order to make the purpose, technical scheme and advantages of the present application clearer, further detailed description of the present application will be made below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0090] In an embodiment, as shown in Figure 1 a low-orbit satellite short-burst signal high-precision acquisition method is provided, which includes the following steps:

[0091] Step 1, preprocessing: sequentially performing digital down-conversion and L times signal code rate down-sampling on the ADC-sampled low-orbit satellite short-burst signal sequence to obtain a down-sampled signal sequence.

[0092] Step 1.1, digital down-conversion:

[0093] The pilot signal sequence of the ADC-sampled digital intermediate frequency signal is received, denoted as:

[0094] ;

[0095] wherein, A is a signal amplitude, is a pseudo code function, is a signal digital intermediate frequency, is a Doppler frequency, is a sampling interval, k is a sequence index and , is a code phase, is a carrier initial phase, is an imaginary number;

[0096] Through a digital down-conversion process, the signal sequence is multiplied by a local carrier to strip the carrier and obtain a zero intermediate frequency signal sequence of the pilot segment, denoted as:

[0097] .

[0098] Step 1.2, L times signal pseudo code rate downsampling: After digital down-conversion, the sampling rate is still high, and the data volume is large. In order to reduce the operation amount of the subsequent signal processing process and improve the processing speed, the signal needs to be down-sampled and extracted in the pre-processing process on the premise of ensuring that no information loss is caused.

[0099] As shown in FIG. 2, the signal sequence after digital down-conversion is input into a downsampling filter. Directly reducing the sampling rate often causes aliasing of the signal in the frequency domain. Therefore, an anti-aliasing process is performed on the signal in the downsampling filter through a low-pass filter, and then the signal is extracted by an extractor at a rate of Figure 2 times signal pseudo code rate, L The value of N can be set according to the hardware processing capability, for example, N = 2 or N = 4. The down-sampled signal sequence obtained after extraction is denoted as Xdown(n), the sampling rate is fdown, and the sampling interval is Tdown. Wherein, fdown=1 / Tdown, and fdown=N*f0, wherein f0is a preset signal pseudo code rate. Specifically, a CIC (Cascaded Integrator Comb) filter, a polyphase filter, and a half-band filter, etc. can be used as the downsampling filter. L L= L=

[0100] Step 2, coarse search stage: the down-sampled signals of every adjacent L points in the down-sampled signal sequence are pre-accumulated, and the PMF-FFT algorithm is used to coarsely capture the pre-accumulated signal sequence to obtain a coarse pseudo code phase and a coarse frequency offset value.

[0101] ​​​​​​​​Step 2.1, pre-accumulation processing: in order to reduce the operation amount of the coarse search stage and improve the capture speed of the stage, the sampling rate of the pre-processed sampling signal can be further reduced to the code rate . Compared with the operation of directly decimating every interval L , the pre-accumulation processing can effectively utilize high sampling rate data and improve the signal-to-noise ratio of the down-sampled signal.

[0102] The pre-accumulation processing is performed on the down-sampled signals of each adjacent point in the down-sampled signal sequence L , to obtain a pre-accumulation processed signal sequence, denoted as . The sampling rate of the pre-accumulation processed signal sequence is the previous , that is .

[0103] Step 2.2, PMF-FFT coarse capture: the PMF-FFT algorithm has the advantages of both the partial matched filter and the FFT algorithm, and can quickly capture the code signal. However, in the case of high dynamic and low signal-to-noise ratio, the algorithm will have large gain attenuation and spectrum leakage, resulting in performance degradation. Therefore, for the pre-accumulation processed signal sequence, the application adopts a windowed PMF-FFT algorithm and cooperates with the subsequent fine adjustment stage to select appropriate parameters for coarse capture, which can effectively improve the peak attenuation and spectrum leakage.

[0104] The processing process of the windowed PMF-FFT algorithm is shown in Figure 3 . The pre-accumulation processed signal sequence and the locally generated code sequence are input P into a PMF. Assuming that the code sequence length is M , the PMF length is set to X , and the PMF number is P = M / X ; in the case of code alignment, the output of the signal through the first p PMF is represented as:

[0105] ;

[0106] wherein p is the PMF index and , is generated by an NCO (numerical control oscillator) and a code generator.

[0107] The output of the PMF is subjected to N point FFT, and at this time, the normalized amplitude-frequency response of the first n point of the FFT output is:

[0108] ;

[0109] in, , ; The contribution of PMF to the normalized amplitude-frequency response is expressed as:

[0110] ;

[0111] The contribution of FFT to the normalized amplitude-frequency response is expressed as:

[0112] ;

[0113] exist N Adding a window before pointwise FFT can improve peak attenuation and spectral leakage. The window function can be expressed in the following form:

[0114] ;

[0115] in, For window functions, For discrete integer variables, This is the tuning factor, which can be set to, for example, 1.71;

[0116] The contribution of the windowed FFT to the normalized amplitude-frequency response is:

[0117] ;

[0118] The normalized amplitude-frequency response of the windowed PMF-FFT algorithm is:

[0119] ;

[0120] judge If the peak value exceeds the set threshold, the signal is considered successfully acquired, and the current pseudo-code phase is recorded as the coarse pseudo-code phase. The Doppler frequency shift corresponding to the peak value is calculated as the coarse frequency offset. , is represented as:

[0121] ;

[0122] Otherwise, coarsely capture the next set of short burst signal sequences.

[0123] The coarse frequency offset estimation accuracy of the PMF-FFT algorithm in the coarse search phase is:

[0124] ;

[0125] The estimated frequency offset error range is ( Here, the signal pseudocode rate To determine the value, N and X The value of the frequency offset search range needs to be considered in addition to the setting of the frequency offset estimation method related parameters in the subsequent fine adjustment stage, which will be introduced below.

[0126] Step 3, fine adjustment stage: based on the coarse pseudo code phase and coarse frequency offset value, the down-sampling signal sequence is searched for serial code phase, the fine pseudo code phase is optimized, and the estimation accuracy of the coarse frequency offset value is optimized according to the fine pseudo code phase and the frequency offset estimation algorithm based on the phase relationship, to obtain the fine frequency offset value.

[0127] Step 3.1, serial code phase search: in the coarse search stage, in order to improve the efficiency of PMF-FFT coarse capture, the down-sampling signal sequence is pre-accumulated, which will cause a certain loss of code phase accuracy. In the fine adjustment stage, if the code phase accuracy is insufficient, it will lead to inaccurate dynamic compensation of the Doppler shift, so the application improves the code phase estimation accuracy through serial code phase search, including the following steps:

[0128] First, based on the coarse pseudo code phase and the coarse frequency offset value , the down-sampling signal sequence is corrected for code phase and frequency offset respectively, to obtain the corrected signal sequence , which is expressed as:

[0129] ;

[0130] wherein, k is the sequence index and , the sampling rate ;

[0131] Then, generate a local pseudo code sequence L at times the signal pseudo code rate, and move forward and backward by L -1 sampling points respectively, to obtain a total of 2 L -1 new local pseudo code sequences, which are expressed as:

[0132] ;

[0133] Conjugate multiply the 2 L -1 new local pseudo code sequences with respectively to obtain a group of correlation values, obtain the maximum value of the group of correlation values, and update the code phase to the pseudo code phase corresponding to the maximum value of the correlation value, to obtain the fine pseudo code phase .

[0134] Step 3.2, phase relationship-based frequency offset estimation algorithm: Since the low-orbit satellite short-burst signal pilot signal time is short, assuming that the signal frequency offset is constant, the signal frequency offset can be calculated by the phase change at two times within a period. To reduce the influence of noise in the calculation process, the present application proposes to calculate the frequency offset according to the phase change in multiple segments after stripping the pilot signal of the pseudo code, and then take the average to obtain the accurate residual frequency offset, and combine the residual frequency offset with the coarse frequency offset value to obtain the fine frequency offset value. The specific process is as follows:

[0135] (1) Calculate the current pseudo code rate according to the ratio of code Doppler and carrier Doppler :

[0136] ;

[0137] Wherein, is the carrier transmission frequency.

[0138] (2) Use L times the current pseudo code rate to generate the local pseudo code sequence .

[0139] (3) Based on the coarse frequency offset value and the fine pseudo code phase obtained by serial code phase search , the down-sampled signal sequence is respectively corrected for frequency offset and code phase, to obtain the corrected signal sequence , expressed as:

[0140] .

[0141] (4) Multiply and to obtain the signal , which can be simplified as:

[0142] ;

[0143] Wherein, is the signal amplitude, is the autocorrelation function of the pseudo code, is the phase deviation of the input signal and the local signal, is the residual frequency offset, is the initial phase difference between the input signal and the local signal; at this time, the pseudo code is stripped from the input signal, is the continuous wave signal, and the residual frequency offset can be obtained by the phase change at two times.

[0144] (5) To reduce the influence of signal noise and outliers, the residual frequency offset is segmented to obtain the signal Divide it into equal parts according to its length q Segment, extract the portion containing the starting sampling point q +1 sampling time, represented as These moments are grouped into pairs in sequence, resulting in a total of ( ). q +1) / 2 groups, represented as ;in, q It is a positive odd number.

[0145] (6) Calculate the frequency offset for each of the two time points in each group; where, for the first time point of each group ,Signal exist The phase at time t is represented as:

[0146] ;

[0147] in, Indicates the imaginary part of the signal. Represents the real part of the signal; for the second time step of each group ,Signal exist The phase at time t is represented as:

[0148] ;

[0149] neglect Short-term changes, assuming exist and These two moments remain unchanged. Using the phase difference between these two moments, a frequency offset value is calculated, expressed as:

[0150] ;

[0151] in, ;

[0152] By calculating the frequency offset values ​​at two time points within all groups, a total of ( q +1) / 2 frequency offset values.

[0153] To ensure that the obtained frequency offset value is not blurred, the phase difference... Must be smaller than Otherwise, the phase difference will have integer ambiguity. This requires that the frequency offset estimation accuracy in the coarse search stage be within a certain range. For example... A value of 1ms means there is no ambiguity when the current residual frequency offset is less than 1kHz, which requires the residual frequency offset output in the coarse search phase to be less than 1kHz. Based on this requirement, the parameters set for the PMF-FFT algorithm in the coarse search phase are as follows: N and X The following constraints must be satisfied:

[0154] .

[0155] (7) For the calculated ( q The residual frequency offset is obtained by averaging the +1) / 2 frequency offset values. , is represented as:

[0156] ;

[0157] in, For the first Individual frequency offset value, This is the frequency offset value index;

[0158] Then the fine frequency deviation coarse frequency bias With residual frequency offset The sum of:

[0159] .

[0160] The above-mentioned acquisition scheme and the relevant model parameters set according to system requirements can be used to achieve high-precision acquisition of short burst signals from low-orbit satellites, and further processing such as demodulation, amplification, and communication-navigation fusion signal ranging can be carried out.

[0161] In summary, the high-precision acquisition method for short burst signals from low-Earth orbit satellites based on a two-step hierarchical strategy of "coarse search + fine adjustment" provided in this application reduces the signal data volume by pre-accumulation in the coarse search stage to decrease the computational load of the PMF-FFT algorithm, and reasonably constrains the relevant parameters of the PMF-FFT algorithm to ensure that the frequency estimation meets certain accuracy requirements, laying the foundation for efficient and accurate frequency offset estimation. In the fine adjustment stage, code phase and frequency offset are optimized separately, and an improved frequency offset estimation method based on phase relationship is proposed for the frequency offset optimization process. This effectively improves the acquisition accuracy and speed of short burst signals from low-Earth orbit satellites, making its accuracy meet the needs of further processing in navigation and ranging of demodulation, diffraction, and communication-navigation fusion signals.

[0162] In one embodiment, a high-precision acquisition device for short burst signals from low-Earth orbit satellites is provided, comprising:

[0163] The preprocessing module is used to sequentially perform digital down-conversion and... L The signal pseudocode rate is doubled and downsampled to obtain the downsampled signal sequence;

[0164] The coarse search module is used to search each adjacent element in the downsampled signal sequence. L The downsampled signal at the point is pre-accumulated, and the PMF-FFT algorithm is used to coarsely capture the pre-accumulated signal sequence to obtain the coarse pseudocode phase and coarse frequency offset.

[0165] a fine adjustment module, configured to perform a serial code phase search on the down-sampling signal sequence based on the coarse pseudo-code phase and the coarse frequency offset value, to obtain a fine pseudo-code phase, and to optimize the estimation accuracy of the coarse frequency offset value based on the fine pseudo-code phase and a frequency offset estimation algorithm based on phase relationship, to obtain a fine frequency offset value.

[0166] The specific limitations of the low-orbit satellite short-burst signal high-precision acquisition device can refer to the limitations of the low-orbit satellite short-burst signal high-precision acquisition method described above, and will not be repeated here. Each module in the low-orbit satellite short-burst signal high-precision acquisition device described above can be realized by software, hardware, and a combination thereof, in whole or in part. The above-mentioned modules can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the memory in the computer device in software form, so as to be called and executed by the processor to perform the operations corresponding to each of the above modules.

[0167] In one embodiment, a computer device is provided, which can be a terminal, and its internal structure diagram can be as shown in Figure 4 The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected through a system bus. The processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium to run. The network interface of the computer device is configured to communicate with external terminals through network connection. The computer program is executed by the processor to implement a low-orbit satellite short-burst signal high-precision acquisition method. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen. The input device of the computer device can be a touch layer overlaid on the display screen, or a key, trackball, or touchpad provided on the shell of the computer device, or an external keyboard, touchpad, or mouse, etc.

[0168] Those skilled in the art can understand that Figure 4 the structure shown in the above figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. A specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different component arrangement.

[0169] In one embodiment, a computer device is provided, which includes a memory and a processor. The memory stores a computer program. The processor implements the following steps when executing the computer program:

[0170] Step 1, sequentially performing digital down-conversion andL down-sampling the signal at the pseudo-code rate by 4, to obtain a down-sampled signal sequence;

[0171] Step 2, pre-accumulation processing is performed on the down-sampled signals of each adjacent L point in the down-sampled signal sequence, and PMF-FFT algorithm is used to perform coarse acquisition on the pre-accumulation processed signal sequence, to obtain coarse pseudo-code phase and coarse frequency offset value;

[0172] Step 3, serial code phase search is performed on the down-sampled signal sequence based on the coarse pseudo-code phase and coarse frequency offset value, to obtain optimized fine pseudo-code phase, and the estimation accuracy of the coarse frequency offset value is optimized according to the fine pseudo-code phase and phase relation based frequency offset estimation algorithm, to obtain fine frequency offset value.

[0173] In one embodiment, a computer readable storage medium is provided, which stores a computer program, and the computer program is executed by a processor to implement the following steps:

[0174] Step 1, digital down-conversion and L down-sampling the signal at the pseudo-code rate by 4, to obtain a down-sampled signal sequence;

[0175] Step 2, pre-accumulation processing is performed on the down-sampled signals of each adjacent L point in the down-sampled signal sequence, and PMF-FFT algorithm is used to perform coarse acquisition on the pre-accumulation processed signal sequence, to obtain coarse pseudo-code phase and coarse frequency offset value;

[0176] Step 3, serial code phase search is performed on the down-sampled signal sequence based on the coarse pseudo-code phase and coarse frequency offset value, to obtain optimized fine pseudo-code phase, and the estimation accuracy of the coarse frequency offset value is optimized according to the fine pseudo-code phase and phase relation based frequency offset estimation algorithm, to obtain fine frequency offset value.

[0177] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when the computer program is executed, the processes of the above-mentioned embodiments of the methods can be included. Any reference to memory, storage, database or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0178] The technical features of the above embodiments can be combined in any way. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, but as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0179] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for high-precision acquisition of a short-burst signal of a low-orbit satellite, characterized in that, The method comprises: Step 1, sequentially performing digital down-conversion and L octuple signal pseudo-code rate down-sampling on the low-orbit satellite short-burst signal sequence sampled by the ADC to obtain a down-sampled signal sequence; Step 2, pre-accumulation is performed on every adjacent L point in the down-sampling signal sequence, and PMF-FFT algorithm is used to coarsely capture the pre-accumulated signal sequence to obtain coarse pseudo-code phase and coarse frequency offset value; Step 3, performing serial code phase search on the down-sampling signal sequence based on the coarse pseudo-code phase and coarse frequency offset value, optimizing to obtain a fine pseudo-code phase, and optimizing the estimation accuracy of the coarse frequency offset value according to the fine pseudo-code phase and the phase relation-based frequency offset estimation algorithm to obtain a fine frequency offset value; Wherein, the estimation accuracy of the coarse frequency offset value is optimized according to the fine pseudo-code phase and the phase relation-based frequency offset estimation algorithm to obtain a fine frequency offset value, comprising: According to the proportional relationship between code Doppler and carrier Doppler, the current code rate is calculated is: ； wherein, is a carrier transmission frequency, is a preset signal pseudo-code rate, is a coarse frequency offset value; Using L times the current pseudo code rate generating a local pseudo code sequence ; k for sequence index and ; Based on a coarse frequency offset value and serial code phase search to obtain a fine pseudo code phase to a down-sampled signal sequence respectively, to obtain a corrected signal sequence is expressed as: ; fs is the sampling rate; The signal is multiplied with the signal , which can be represented as: ； wherein, is the signal amplitude, is the autocorrelation function of the pseudo code, is the phase deviation of the input signal from the local signal, is the residual frequency deviation, is the initial phase deviation of the input signal from the local signal; at this time, the pseudo code is stripped from the input signal, is the continuous wave signal, and the residual frequency deviation can be obtained by the phase change at two time instants. To reduce the influence of signal noise and abnormal value, the residual frequency offset is segmented to calculate, and the signal is divided into q segments averagely according to the length, and the q +1 sampling time points containing the starting sampling point of the signal are extracted and expressed as ; these time points are divided into groups in order two by two, and there are q +1) / 2 groups in total, expressed as ; wherein q is a positive odd number; The frequency offset value is calculated for each group of two time instants, respectively; wherein for the first time instant of each group , the signal The phase at the time instant is represented as: ； wherein represents the signal imaginary part, represents the signal real part; for the second time instant of each set , the signal The phase at time instant is represented as: ； neglect short term variation, assuming in and The two moments remain unchanged, and the phase difference between the two moments is used to calculate a frequency offset value, denoted as: ； wherein ; By calculating the frequency offset values at two time instants in all groups, a total of (N / 2) frequency offset values are obtained and the average value is calculated to obtain the residual frequency offset q +1) / 2, which is expressed as: ​ ； wherein is the th frequency offset value, is the frequency offset value index; then the fine frequency offset value is the coarse frequency offset value and the residual frequency offset is the sum: 。 2.The method of claim 1, wherein, The low-orbit satellite short-burst signal sequence sampled by the ADC is sequentially subjected to digital down-conversion and L Pseudo-code rate decimation of the multiplied signal, to obtain a decimated signal sequence, comprising: The pilot segment signal sequence of the received ADC-sampled digital intermediate frequency signal is represented as: ； wherein, A is the signal amplitude, is the pseudo code function, is the signal digital intermediate frequency, is the Doppler frequency, is the sampling interval, is the code phase, is the carrier initial phase; By digital down-conversion processing, the The carrier is stripped by multiplying the local carrier, and a zero intermediate frequency signal sequence of the pilot section is obtained, denoted as: ； The digital down-converted signal sequence is input into a decimation filter, in which an anti-aliasing process is performed by a low-pass filter, and then a decimation is performed by a decimator L at a signal pseudo-code rate, and the decimated signal sequence obtained after the decimation is represented as , the sampling rate , and the sampling interval ; wherein, is a preset signal pseudo-code rate. 3.The method of claim 2, wherein, pre-accumulating the down-sampled signals of each adjacent L point in the down-sampled signal sequence, including: down-sampled signal sequence pre-accumulates the down-sampled signals between each adjacent L point, to obtain a pre-accumulated signal sequence, denoted as ; sampling rate .

4. The method of claim 3, wherein, The PMF-FFT algorithm is used to perform coarse capture on the pre-accumulated signal sequence to obtain a coarse pseudo-code phase and a coarse frequency offset value, comprising: The windowed PMF-FFT algorithm is adopted, the pre-accumulated signal sequence and the locally generated pseudo code sequence are input into P PMFs, the length of the pseudo code sequence is set as M , the length of the PMF is set as X , and the number of the PMFs is set as P=M / X ; in the case of code alignment, the output of the signal after passing through the first p PMF is represented as: ； wherein, is a Doppler frequency, is a preset signal pseudo code rate, p is a PMF index and , is a carrier initial phase; The output of the PMF is N pointed FFT, the normalized amplitude frequency response of the FFT output at the n point is: ； wherein , ; the contribution of the PMF to the normalized amplitude-frequency response is denoted as: ； The contribution of the FFT to the normalized amplitude frequency response is denoted as: ； In N The following window function is used for windowing before the FFT: ； wherein is a window function, is a discrete integer variable, is a tuning coefficient; The contribution of the windowed FFT to the normalized amplitude-frequency response is: ； The normalized amplitude-frequency response of the windowed PMF-FFT algorithm is: ； determining whether the peak value exceeds a set threshold value, if yes, determining that the signal acquisition is successful, recording the current pseudo code phase as the coarse pseudo code phase , and calculating the Doppler shift corresponding to the peak value as the coarse frequency offset value , which is expressed as: ； Otherwise, the next group of short burst signal sequences is captured coarsely.

5. The method of claim 4, wherein, The serial code phase search is performed on the down-sampling signal sequence based on the coarse pseudo-code phase and coarse frequency offset value to optimize to obtain a fine pseudo-code phase, comprising: based on a coarse pseudo-code phase and a coarse frequency offset value to a down-sampled signal sequence code phase correction and frequency offset correction, respectively, to obtain a corrected signal sequence is represented as: ； wherein k is a sequence index and , sampling rate ; With L Generating local pseudo code sequence with double signal pseudo code rate And Moving forward and backward respectively by one sample point each L -1, a total of 2 L -1 new local pseudo code sequences, denoted as: ； The 2 L -1 new local pseudo code sequences are respectively multiplied by to obtain a group of correlation values, the maximum value of the group of correlation values is obtained, and the code phase is updated to the pseudo code phase corresponding to the maximum value of the correlation values to obtain the fine pseudo code phase . 6.The method of claim 1, wherein, The method further comprises: Parameters set in the PMF-FFT algorithm X and N satisfying the following constraints: 。 7. A low earth orbit satellite short burst signal high precision acquisition device, characterized in that, The device comprises: a pre-processing module, configured to sequentially perform digital down-conversion and L octuple signal pseudo-code rate decimation on a low earth orbit satellite short-burst signal sequence sampled by an ADC, to obtain a decimated signal sequence; a coarse searching module, configured to perform pre-accumulation processing on the down-sampling signals of each adjacent L point in the down-sampling signal sequence, and perform coarse acquisition on the pre-accumulated signal sequence by using a PMF-FFT algorithm to obtain a coarse pseudo-code phase and a coarse frequency offset value; The fine adjustment module is configured to perform serial code phase search on the down-sampling signal sequence based on the coarse pseudo-code phase and coarse frequency offset value to optimize to obtain a fine pseudo-code phase, and optimize the estimation accuracy of the coarse frequency offset value according to the fine pseudo-code phase and the phase relation-based frequency offset estimation algorithm to obtain a fine frequency offset value; Wherein, the estimation accuracy of the coarse frequency offset value is optimized according to the fine pseudo-code phase and the phase relation-based frequency offset estimation algorithm to obtain a fine frequency offset value, comprising: According to the proportional relationship between code Doppler and carrier Doppler, the current code rate is calculated is: ； wherein, is a carrier transmission frequency, is a preset signal pseudo code rate, is a coarse frequency offset value; Using L times the current pseudo code rate generating a local pseudo code sequence ; k for sequence index and ; Based on a coarse frequency offset value and serial code phase search to obtain a refined pseudo code phase to a down-sampled signal sequence respectively to obtain a corrected signal sequence is expressed as: ; fs is the sampling rate; The signal is obtained by multiplying with , which can be expressed as: ； wherein, is the signal amplitude, is the autocorrelation function of the pseudo code, is the phase deviation of the input signal from the local signal, is the residual frequency deviation, is the initial phase deviation of the input signal from the local signal; at this time, the pseudo code is stripped from the input signal, is the continuous wave signal, the residual frequency deviation can be obtained by the phase change at two time instants; To reduce signal noise and the impact of outliers, the residual frequency offset is segmented and calculated, and the signal is... Divide it into equal parts according to its length q Segment, extract the portion containing the starting sampling point q +1 sampling time, represented as These moments are grouped into pairs in sequence, resulting in a total of ( ). q +1) / 2 groups, represented as ;in, q It is a positive odd number; The frequency offset value is calculated for each group of two time instants, respectively; wherein for the first time instant of each group , the signal at the time instant is represented by the phase ； wherein, represents the signal imaginary part, represents the signal real part; for the second time instant of each set , the signal The phase at the time instant is represented as: ； neglect short term variation, assuming in and The two moments remain unchanged, and the phase difference between the two moments is used to calculate a frequency offset value, denoted as: ； wherein ; By calculating the frequency offset values at two time instants in all groups, a total of (N / 2) frequency offset values are obtained and the average value is calculated to obtain the residual frequency offset q +1) / 2, which is expressed as: ​ ； wherein is the th frequency offset value, is the frequency offset value index; then the fine frequency offset value is the coarse frequency offset value and the residual frequency offset is the sum: 。 8. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that, The processor executes the computer program to implement the steps of the method of any one of claims 1 to 6.

9. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method of any one of claims 1 to 6.

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