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

Abstract

The invention relates to a low-orbit satellite short burst signal high-precision capturing method and device, equipment and a medium. The method comprises the following steps: sequentially carrying out digital down-conversion and L-time signal pseudo code rate down-sampling on a low earth orbit satellite short burst signal sequence sampled by an ADC (Analog to Digital Converter) to obtain a down-sampled signal sequence; performing pre-accumulation processing on the down-sampling signals of every adjacent L points in the down-sampling signal sequence, and performing coarse capture on the pre-accumulated signal sequence by adopting a PMF-FFT algorithm to obtain a coarse pseudo code phase and a coarse frequency offset value; and performing serial code phase search on the down-sampling 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 precision of the coarse frequency offset value according to the fine pseudo code phase and a frequency offset estimation algorithm based on a phase relation to obtain a fine frequency offset value. By adopting the method, the acquisition precision and speed of the short burst signal of the low-orbit satellite can be improved.

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: 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; 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; 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, optimizing to obtain a fine pseudo-code phase, and optimizing the estimation precision of the coarse frequency offset value based on the fine pseudo-code phase and a frequency offset estimation algorithm based on the phase relationship to obtain a fine frequency offset value.

[0007] In one of the embodiments, 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, comprising: receiving a pilot segment signal sequence of the ADC-sampled digital intermediate frequency signal, denoted as: ; 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; by the digital down-conversion processing, multiplying with a local carrier to strip the carrier to obtain a pilot segment zero intermediate frequency signal sequence, denoted as: ; inputting the signal sequence after the digital down-conversion into a decimation filter, performing anti-aliasing processing by a low-pass filter in the decimation filter, and then performing LThe 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.

[0008] In one embodiment, for each adjacent downsampled signal sequence L The downsampled signal at each point undergoes pre-accumulation processing, including: 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 .

[0009] 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: 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 In the case of code alignment, the signal passes through the first... p The output of each PMF is represented as: ; in, For Doppler frequency, The preset signal pseudocode rate, p For PMF index and , The initial phase of the carrier; 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: ; in, , ; The contribution of PMF to the normalized amplitude-frequency response is expressed as: ; The contribution of FFT to the normalized amplitude-frequency response is expressed as: ; In N Before FFT, the following window function is used for windowing: ; 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: ; Judge whether the peak value exceeds the set threshold value, if it exceeds, judge that the signal capture is successful, record the current pseudo code phase as the coarse pseudo code phase , and calculate the peak value corresponding to the Doppler frequency shift as the coarse frequency offset value , expressed as: ; Otherwise, the next group of short burst signal sequence is subjected to coarse capture.

[0010] In one of the embodiments, the desampling signal sequence is subjected to serial code phase search based on the coarse pseudo code phase and the coarse frequency offset value, and the fine pseudo code phase is optimized, including: Based on the coarse pseudo code phase and the coarse frequency offset value , the desampling signal sequence is subjected to code phase correction and frequency offset correction respectively, to obtain the corrected signal sequence , expressed as: ; Wherein, k is a sequence index and , the sampling rate ; The local pseudo code sequence L is generated at times the signal pseudo code rate, and is moved forward and backward respectively by L- 1 sampling point, a total of 2 L- 1 new local pseudo code sequences are obtained, expressed as: ; The 2 L -1 new local pseudo code sequences are respectively multiplied by Conjugate multiplication is performed to obtain a set of correlation values, the maximum value of the set of correlation values is obtained, and the code phase is updated to the code phase corresponding to the maximum value of the correlation values, to obtain a fine code phase .

[0011] In one of the embodiments, the estimation accuracy of the coarse frequency offset value is optimized according to the fine code phase and the frequency offset estimation algorithm based on the phase relationship, to obtain a fine frequency offset value, including: The current code rate is calculated according to the ratio of the code Doppler and the carrier Doppler For: ; Wherein, is the carrier transmission frequency, is a preset signal code rate; The current code rate is multiplied by L to generate a local code sequence ; Based on the coarse frequency offset value and the fine code phase obtained by the serial code phase search , the desampling signal sequence is respectively subjected to frequency offset correction and code phase correction, to obtain a corrected signal sequence , which is expressed as: ; The signal is multiplied by to obtain a signal , which is expressed as: ; Wherein, is the signal amplitude, is the autocorrelation function of the code, is the phase deviation of the input signal and the local signal, is the residual frequency offset, is the initial phase deviation of the input signal and the local signal; at this time, the 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; In order to reduce the influence of signal noise and abnormal values, the residual frequency offset is segmented to obtain the signal , which is evenly divided into q segments according to its length, and q +1 sampling time points containing the starting sampling point are extracted, which is expressed as ; these time points are sequentially divided into groups, a total of q +1) / 2 groups, which is expressed as ; wherein, q is a positive odd number;​ The frequency offset value is calculated for each group of two time points respectively; wherein, for the first time point of each group , the phase of the signal at the time point is represented as: ; wherein, 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 the time point is represented as: ; Ignoring short-term changes, assuming the phase difference between the two time points and remains unchanged, a frequency offset value is calculated using the phase difference between the two time points, represented as: ; wherein, ; By calculating the frequency offset value for the two time points in all groups, a total of q +1) / 2 frequency offset values are obtained and the average value is calculated to obtain the residual frequency offset , represented as: ; wherein, is the th frequency offset value, is the frequency offset value sequence number; then the fine frequency offset value is the sum of the coarse frequency offset value and the residual frequency offset : .

[0012] In one embodiment, the above method further comprises: The parameters X and N set in the PMF-FFT algorithm satisfy the following constraints: .

[0013] A low-orbit satellite short-burst signal high-precision acquisition device, the device comprises: 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; 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. The fine-tuning module is used to perform serial code phase search on the downsampled signal sequence based on the coarse pseudo-code phase and coarse frequency offset, optimize to obtain the fine pseudo-code phase, and optimize the estimation accuracy of the coarse frequency offset based on the fine pseudo-code phase and the frequency offset estimation algorithm based on the phase relationship to obtain the fine frequency offset.

[0014] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program performing the following steps: Step 1: Perform digital down-conversion and sequential processing on the short burst signal sequence of low-orbit satellites sampled by the ADC. L The signal pseudocode rate is doubled and downsampled to obtain the downsampled signal sequence; Step 2, for each adjacent signal 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. Step 3: Perform serial code phase search on the downsampled signal sequence based on the coarse pseudocode phase and coarse frequency offset to optimize and obtain the fine pseudocode phase. Then, based on the fine pseudocode phase and the frequency offset estimation algorithm based on the phase relationship, optimize the estimation accuracy of the coarse frequency offset to obtain the fine frequency offset.

[0015] A computer-readable storage medium having a computer program stored thereon, the computer program performing the following steps when executed by a processor: Step 1: Perform digital down-conversion and sequential processing on the short burst signal sequence of low-orbit satellites sampled by the ADC. L The signal pseudocode rate is doubled and downsampled to obtain the downsampled signal sequence; Step 2, for each adjacent signal 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. Step 3: Perform serial code phase search on the downsampled signal sequence based on the coarse pseudocode phase and coarse frequency offset to optimize and obtain the fine pseudocode phase. Then, based on the fine pseudocode phase and the frequency offset estimation algorithm based on the phase relationship, optimize the estimation accuracy of the coarse frequency offset to obtain the fine frequency offset.

[0016] 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 multiple times in 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, and the frequency offset estimation accuracy is further optimized. 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

[0017] Figure 1 It is a flowchart of a low-orbit satellite short-burst signal high-precision acquisition method in an embodiment; Figure 2 It is a schematic diagram of a down-sampling filter in an embodiment; Figure 3 It is a flowchart of a windowed PMF-FFT algorithm in an embodiment; Figure 4 It is a schematic diagram of the internal structure of a computer device in an embodiment. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application clearer, further detailed description will be made to the present application 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 are not used to limit the present application.

[0019] 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: Step 1, preprocessing: 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.

[0020] Step 1.1, digital down-conversion: The pilot signal sequence of the ADC-sampled digital intermediate frequency signal is received, denoted as: ; Wherein, A is the signal amplitude, is the pseudo-code function, For digital intermediate frequency signals, For Doppler frequency, The sampling interval is... k For sequence index and , For code phase, The initial phase of the carrier. It is an imaginary number; Through digital down-conversion processing, Multiplying the signal by the local carrier and stripping the carrier yields the zero-IF signal sequence of the pilot band, expressed as: .

[0021] Step 1.2, L Downsampling of pseudocode rate: Generally, the sampling rate is still very high after digital downconversion, resulting in a large amount of data. To reduce the computational load and improve processing speed in subsequent signal processing, downsampling is required in the preprocessing stage, provided that no information loss is incurred.

[0022] like Figure 2 As shown, the signal sequence after digital down-conversion is input into a downsampling filter. Considering that directly reducing the sampling rate often causes aliasing in the frequency domain, a low-pass filter is used in the downsampling filter for anti-aliasing processing, followed by a decimator. L Double signal pseudocode rate downsampling decimation, L The value can be set according to the hardware processing capabilities, for example... L= 2 or L= 4. The downsampled signal sequence obtained after extraction is represented as follows: Sampling rate Sampling interval ;in, This is the preset pseudocode rate of the signal. Specifically, downsampling filters such as CIC (cascaded integrator comb) filters, polyphase filters, and half-band filters can be used.

[0023] Step 2, Coarse Search Phase: For each adjacent signal 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.

[0024] Step 2.1, Pre-accumulation processing: To significantly reduce the computational load in the coarse search stage and improve the acquisition speed in this stage, the sampling rate of the pre-processed sampled signal can be further reduced to the pseudocode rate. Compared to direct intervals LCompared with decimation operation, the pre-accumulation processing can effectively utilize high sampling rate data and improve the signal-to-noise ratio of the decimated signal.

[0025] The pre-accumulation processing is performed on the decimated signal sequence of each adjacent L point in the decimated signal sequence to obtain a pre-accumulation processed signal sequence, denoted as . The sampling rate of the pre-accumulation processed signal sequence is , i.e. .

[0026] Step 2.2, PMF-FFT coarse acquisition: The PMF-FFT algorithm has the advantages of both the partial matched filter and the FFT algorithm, and can quickly capture the pseudo-code signal. However, in the face of high dynamic low signal-to-noise ratio scenarios, the algorithm will have a large gain attenuation and spectral leakage, resulting in performance degradation. Therefore, for the pre-accumulation processed signal sequence, a windowed PMF-FFT algorithm is used in combination with a subsequent fine adjustment stage frequency offset estimation method to select appropriate parameters for coarse acquisition, which can effectively improve the peak attenuation and spectral leakage.

[0027] The processing process of the windowed PMF-FFT algorithm is shown in Figure 3 , the pre-accumulation processed signal sequence and the locally generated pseudo-code sequence are input P into a PMF, the pseudo-code sequence length is set to M , the PMF length is set to X , and the PMF number is set to P = M / X ; in the case of code alignment, the output of the signal through the first p PMF is represented as: ; wherein p is the PMF index and , is generated by an NCO (numerical control oscillator) and a code generator.

[0028] The output of the PMF is subjected to N point FFT, and the normalized amplitude-frequency response of the first n point of the FFT output is: ; wherein , ; is the contribution of the PMF to the normalized amplitude-frequency response, and is represented as: ; The contribution of FFT to the normalized amplitude-frequency response is expressed as: ; 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: ; in, For window functions, For discrete integer variables, This is the tuning factor, which can be set to, for example, 1.71; 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: ; 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. , represented as: ; Otherwise, coarsely capture the next set of short burst signal sequences.

[0029] The coarse frequency offset estimation accuracy of the PMF-FFT algorithm in the coarse search phase is: ; The estimated frequency offset error range is ( Here, the signal pseudocode rate To determine the value, N and X In addition to considering the frequency offset search range, the value of needs to be set in conjunction with the relevant parameters of the frequency offset estimation method in the subsequent fine-tuning stage, which will be introduced below.

[0030] Step 3, Fine-tuning stage: Based on the coarse pseudo-code phase and coarse frequency offset, the serial code phase of the downsampled signal sequence is searched and optimized to obtain the fine pseudo-code phase. Then, based on the fine pseudo-code phase and the frequency offset estimation algorithm based on the phase relationship, the estimation accuracy of the coarse frequency offset is optimized to obtain the fine frequency offset.

[0031] Step 3.1, Serial Code Phase Search: In the coarse search stage, to improve the coarse acquisition efficiency of PMF-FFT, the downsampled signal sequence is... A pre-accumulation process is performed, which causes a certain code phase precision loss. In the fine adjustment stage, if the code phase precision is insufficient, the dynamic compensation of the Doppler shift will be inaccurate, so the application improves the code phase estimation precision through serial code phase search, including the following steps: First, based on the coarse pseudo code phase And the coarse frequency offset value The down-sampled signal sequence Respectively, the code phase correction and the frequency offset correction are performed to obtain the corrected signal sequence , which is expressed as: ; Wherein, k is the sequence index and , the sampling rate ; Then, the local pseudo code sequence L is generated at times the signal pseudo code rate, and is moved forward and backward by L -1 sampling points respectively, a total of 2 L -1 new local pseudo code sequences are obtained, which are expressed as: ; The 2 L -1 new local pseudo code sequences are respectively multiplied by , a group of correlation values are obtained, 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 value, to obtain the fine pseudo code phase .

[0032] Step 3.2, frequency offset estimation algorithm based on phase relationship: due to the short time of the pilot signal of the low-orbit satellite short burst signal, it is assumed that the signal frequency offset is constant, and the phase change at two times in a period can be used to calculate the signal frequency offset. In order to reduce the influence of noise in the calculation process, the application proposes to calculate the frequency offset according to the phase change in multiple segments after stripping the pseudo code of the pilot signal, and then take the average value 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: (1) The current pseudo code rate is calculated according to the ratio of code Doppler and carrier Doppler: ; Wherein, is the carrier transmission frequency.

[0033] (2) The local pseudo code sequence L is generated at times the current pseudo code rate .

[0034] (3) Based on the coarse frequency offset value and the fine pseudo-code phase obtained by serial code phase search The down-sampling signal sequence is respectively subjected to frequency offset correction and code phase correction to obtain a corrected signal sequence , which is expressed as: .

[0035] (4) The product of and is obtained as a signal , which can be simplified as: ; 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 time points.

[0036] (5) In order to reduce the influence of signal noise and abnormal values, the residual frequency offset is obtained by segmentation. The signal is evenly divided into q segments according to its length, and q +1 sampling time points containing the starting sampling point are extracted, which is expressed as ; these time points are sequentially divided into groups, a total of q +1) / 2 groups, which is expressed as ; wherein, q is a positive odd number.

[0037] (6) The frequency offset value is calculated for each group of two time points; wherein, for the first time point of each group, the phase of the signal at the time point is expressed as: ; wherein, 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 the time point is expressed as: ; ignoring short-term changes, it is assumed In and The two moments remain unchanged, and a frequency offset value is calculated using the phase difference of the two moments, denoted as: ; Among them, ; By calculating the frequency offset value of all groups of two moments, a total of ( q +1) / 2 frequency offset values are obtained.

[0038] In order to ensure that the obtained frequency offset value is not ambiguous, the phase difference must be less than , otherwise the phase difference will have a whole cycle ambiguity. This requires the frequency offset estimated in the coarse search stage to be within a certain range. For example the value is 1ms, then there is no ambiguity when the current residual frequency offset is less than 1kHz, that is, the residual frequency offset output by the coarse search stage must be less than 1kHz. According to this requirement, the parameters N and X set by the PMF-FFT algorithm in the coarse search stage need to satisfy the following constraint relationship: .

[0039] (7) Calculate the average value of the calculated ( q +1) / 2 frequency offset values to obtain the residual frequency offset , denoted as: ; Among them, is the th frequency offset value, is the frequency offset value number; then the fine frequency offset value is the sum of the coarse frequency offset value and the residual frequency offset : .

[0040] Through the above acquisition scheme and the relevant model parameters set according to the system requirements, high-precision acquisition of low-orbit satellite short-burst signals can be completed, and the next step of demodulation and spread spectrum processing and integrated navigation signal ranging related processing can be carried out.

[0041] In summary, the low-orbit satellite short-burst signal high-precision acquisition method based on the two-step hierarchical strategy of "rough search + fine adjustment" provided in the application reduces the signal data amount by using pre-accumulation in the rough search stage to reduce the operation amount of the PMF-FFT algorithm, and reasonably constrains the related parameters of the PMF-FFT algorithm to make the frequency estimation meet certain accuracy requirements, laying a foundation for efficient and accurate frequency offset estimation. In the fine adjustment stage, the code phase and frequency offset are optimized respectively, and an improved frequency offset estimation method based on phase relationship is proposed for the frequency offset optimization process, which effectively improves the acquisition accuracy and speed of the low-orbit satellite short-burst signal, and makes the accuracy meet the needs of further processing of demodulation, despreading and integrated navigation signal ranging.

[0042] In one embodiment, a low-orbit satellite short-burst signal high-precision acquisition device is provided, comprising: a preprocessing module configured to sequentially perform digital down-conversion and L down-sampling of a code rate of a signal frequency on an ADC-sampled low-orbit satellite short-burst signal sequence to obtain a down-sampled signal sequence; a rough search module configured to perform pre-accumulation processing on the down-sampled signals of each adjacent L point in the down-sampled signal sequence, and perform rough acquisition on the pre-accumulated signal sequence by using a PMF-FFT algorithm to obtain a rough code phase and a rough frequency offset value; a fine adjustment module configured to perform serial code phase search on the down-sampled signal sequence based on the rough code phase and the rough frequency offset value, to obtain a fine code phase, and to optimize the estimation accuracy of the rough frequency offset value based on the fine code phase and a frequency offset estimation algorithm based on phase relationship, to obtain a fine frequency offset value.

[0043] The specific limitations of the low-orbit satellite short-burst signal high-precision acquisition device can be referred to the limitations of the low-orbit satellite short-burst signal high-precision acquisition method in the foregoing, which 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 combinations thereof, in whole or in part. The above 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 module.

[0044] In one embodiment, a computer device is provided, which can be a terminal, and its internal structure diagram can be as Figure 4As shown in the figure. The computer device includes a processor, a memory, a network interface, a display screen and an input device connected by a system bus. Among them, the processor of the computer device is used 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 used to communicate with the external terminal through the 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, and the input device of the computer device can be a touch layer overlaid on the display screen, or a key, trackball or touchpad arranged on the shell of the computer device, or an external keyboard, touchpad or mouse, etc.

[0045] Those skilled in the art can understand that, Figure 4 The structure shown in the 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. The 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.

[0046] In one embodiment, a computer device is provided, comprising a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the following steps: 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 the ADC to obtain a decimated signal sequence; 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; 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, 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 phase relationship to obtain a fine frequency offset value.

[0047] 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: 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 the ADC to obtain a decimated signal sequence; Step 2, pre-accumulation is performed on each adjacent L point in the down-sampling signal sequence, and PMF-FFT algorithm is used to perform coarse acquisition on the pre-accumulated signal sequence to obtain coarse pseudo-code phase and coarse frequency offset value; Step 3, serial code phase search is performed on the down-sampling signal sequence based on the coarse pseudo-code phase and coarse frequency offset value, and the fine pseudo-code phase is obtained by optimization, 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 phase relationship to obtain the fine frequency offset value.

[0048] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by a computer program instructing related hardware, and the computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments. Any reference to memory, storage, database or other medium used in the embodiments provided by 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).

[0049] Any combination of the technical features of the above embodiments can be made. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0050] 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 noted that for those of ordinary skill in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the 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. 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 octuple signal pseudo-code rate down-sampling, to obtain a down-sampled signal sequence, comprising: The pilot segment signal sequence of the digital intermediate frequency signal of the ADC sampling 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, k is the sequence index and , 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 , a sampling rate , and a 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 each adjacent L point of the down-sampled signal is pre-accumulated to obtain a pre-accumulated signal sequence, denoted as ; sampling rate .

4. The method of claim 3, wherein, The PMF-FFT algorithm is adopted to perform coarse acquisition 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 , ; PMF contribution to the normalized amplitude-frequency response, 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 capture is successful, recording the current pseudo code phase as the coarse pseudo code phase , and calculating the Doppler frequency shift corresponding to the peak value as the coarse frequency offset value , which is expressed as: ； Otherwise, performing coarse acquisition on the next group of short burst signal sequences.

5. The method of claim 4, wherein, Performing 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, 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 The local pseudo code sequence is generated at the double signal pseudo code rate And Move 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 5, wherein, 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, 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; Using L times the current pseudo code rate generating a local pseudo code sequence ; Based on a coarse frequency offset value and a fine pseudo code phase obtained from a serial code phase search on a down-sampled signal sequence respectively, to obtain a corrected signal sequence is represented as: ； 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, 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 calculated by segmentation, and the signal is divided into q segments averagely according to the length, and the time points containing the initial sampling point and q +1 sampling points are extracted and expressed as ; these time points are divided into q +1) / 2 groups in sequence two by two, and 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 is represented by the phase at the time instant ​ ； 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: ； 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: 。 7. The method of claim 6, wherein, The method further comprises: Parameters set in the PMF-FFT algorithm X and N satisfy the following constraints: 。 8. 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 the ADC-sampled low earth orbit satellite short-burst signal sequence, 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. 9.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-8 when the computer program is executed by the processor. The processor executes the computer program to implement the steps of the method in any one of claims 1 to 7.

10. 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 in any one of claims 1 to 7.

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