A Method and System for Weak BDS Signal Acquisition Based on Inter-Code Difference and Zero-Padded Blocks

Abstract

The present invention belongs to the technical field of Beidou satellite navigation, and discloses a Beidou weak signal acquisition method and system for inter-code difference and zero-padding blocks, including a digital down-conversion module, a code merging module, a data block splicing module, a Doppler stripping module, a local zero-padding module, a code parallel coherence module, an inter-code difference module, a Doppler compensation module, a step-by-step coherence module and a step-by-step non-coherence module, a peak decision module, a Doppler search completion judgment module, a Doppler regulation module and a result output module. The present invention adopts the inter-code difference algorithm to avoid the influence of the NH code jump in the D1 navigation data and the too fast rate of the D2 navigation message on the coherent integration duration, and improves the acquisition sensitivity of the Beidou signal by increasing the coherent integration duration; adopts the coherence of the zero-padding block and the data block to avoid the influence of the NH code jump and the navigation data jump on the coherent value, and obtains a complete 1-millisecond coherent value; adopts the step-by-step coherence and step-by-step non-coherence algorithms to achieve the compatible acquisition of strong and weak signals.

Description

Technical Field

[0001] The present invention belongs to the technical field of Beidou satellite navigation, and in particular relates to a method and system for capturing weak Beidou signals with inter-code difference and zero-padding blocks. Background Technique

[0002] At present, with the development of China's Beidou satellite navigation system, satellite navigation receivers are gradually applied to various fields. Navigation receivers are slowly developing from land, navigation, and aviation fields to the aerospace field. Installing a satellite navigation receiver on a satellite or spacecraft can improve its autonomy and greatly reduce the monitoring cost of ground control stations. Therefore, Beidou satellite navigation receivers applied to high-orbit environments have become the focus of research by researchers. At the same time, the development of Beidou navigation receivers suitable for high-orbit environments is conducive to the rapid development of China in the aerospace field in the future and further enhances China's advantages in the aerospace and deep space exploration fields.

[0003] Traditional high-sensitivity Beidou navigation receivers use delay difference and zero-padding blocks to avoid the influence of the NH code in the D1 navigation message on the coherent integration value. However, this method requires storing a large amount of data during the difference process, resulting in very high design costs and iteration costs. For example, in the improved difference algorithm proposed in Han Zhifeng's article "Beidou Weak Signal Capture Algorithm Based on Improved Zero Padding / Difference", this algorithm needs to store 20 milliseconds of coherent data during delay difference, and the capture sensitivity of this algorithm is relatively low. At the same time, due to the too fast rate of the Beidou D2 navigation message, the sign of the difference result of this algorithm for the D2 navigation message is still unknown, resulting in the inability to extend the coherent integration duration and the inability to capture weak D2 navigation message signals. Another example is the NH code half-bit search method mentioned in the patent "Method and Device for Capturing BDS Signals" to avoid the influence of the NH code on coherent data. It needs to traverse and search all NH code phases during implementation, resulting in a long capture time. At the same time, when performing half-bit search on the NH code, the coherent value will be suppressed to a certain extent, resulting in low capture sensitivity. Therefore, there is an urgent need to design a new high-orbit Beidou signal capture method and system.

[0004] Through the above analysis, the problems and defects existing in the prior art are as follows:

[0005] (1) The traditional high-sensitivity Beidou navigation receiver uses the method of delay difference and zero-padding blocks, which requires storing a large amount of data during the difference process, resulting in very high design costs and iteration costs.

[0006] (2) The existing improved difference algorithm needs to store 20 milliseconds of coherent data during delay difference, and the capture sensitivity of this algorithm is relatively low; and the sign of the difference result for the D2 navigation message is still unknown, resulting in the inability to extend the coherent integration duration and the inability to capture weak D2 navigation message signals.

[0007] (3) In the implementation process of the existing NH code semi-bit search method, it is necessary to traverse and search all the code phases of the NH code, resulting in a long acquisition time. At the same time, when performing semi-bit search on the NH code, the coherence value will be suppressed to a certain extent, resulting in low acquisition sensitivity. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a Beidou weak signal acquisition method and system based on inter-code difference and zero-padding block, and particularly relates to a high-orbit Beidou signal acquisition method, system, medium, device and terminal based on inter-code difference and zero-padding block, aiming to solve the problem of fast and high-sensitivity acquisition of D1 and D2 navigation messages with extremely few hardware resources in a high-orbit Beidou navigation receiver.

[0009] The present invention is implemented as follows. A Beidou weak signal acquisition system based on inter-code difference and zero-padding block, the Beidou weak signal acquisition system based on inter-code difference and zero-padding block includes:

[0010] A digital down-conversion module, which is used to perform digital down-conversion on the baseband data, remove the residual carrier in the data, obtain zero-intermediate-frequency data, and transmit the data to the code merging module;

[0011] A code merging module, which is used to accumulate and merge the zero-intermediate-frequency data, obtain half-code data and then transmit the data to the data block splicing module;

[0012] A data block splicing module, which is used to store and overlap-combine the chip data to form a 2-millisecond data block, and transmit the data block to the Doppler stripping module;

[0013] A Doppler stripping module, which is used to strip the Doppler frequency in the 2-millisecond data block to obtain zero-Doppler data, and then send the data to the code parallel coherence module for FFT processing;

[0014] A local zero-padding module, which is used to perform zero-padding on the local pseudo-code to obtain a zero-padding block with the same length as the 2-millisecond data block, and send the local zero-padding module to the FFT core for Fourier transform;

[0015] A code parallel coherence module, which is used to perform coherence on the 2-millisecond data block and the local zero-padding block by using FFT and IFFT to obtain coherence values of different code phases, and send the first 4096 coherence data to the inter-code difference module;

[0016] An inter-code difference module, which is used to perform difference on the coherence values of different code phases. The difference adopts the inter-code difference method to avoid the influence of NH code jumps in the D1 navigation message, the too fast rate of the D2 navigation message, and navigation data jumps on the acquisition sensitivity, and then send the difference data to the Doppler compensation module;

[0017] The Doppler compensation module is used to compensate for the code phase offset generated within the coherent duration due to the Doppler effect. The data after phase correction is sent to the successive coherence module and the successive incoherence module;

[0018] The successive coherence module and the successive incoherence module are used to perform N times of successive coherence on the result obtained by the Doppler compensation module to obtain coherence values with different signal-to-noise ratios; then, after taking the modulus of the coherent accumulation value, perform M times of successive incoherence, and send the results of different coherence times to the peak decision module;

[0019] The peak decision module is used to perform peak detection on the code phase coherence values of different coherence times, determine whether the satellite signal is captured, and select the next operation according to the decision result;

[0020] The Doppler search completion judgment module, when the peak decision module determines that the satellite signal is not successfully captured, determines whether the Doppler frequency search is completed; if the search is completed, the capture program ends; if the search is not completed, it enters the Doppler regulation module and performs the next round of capture until the Doppler search is completed or the current satellite signal is captured;

[0021] The Doppler regulation module is used to regulate the Doppler frequency to be searched currently and transmit it to the Doppler stripping module;

[0022] The result output module is used to transmit the captured Doppler information, satellite number, and code phase to the tracking module according to the processing results of the peak decision module and the Doppler search completion judgment module.

[0023] Furthermore, the code parallel coherence module is also used to perform frequency-domain complex multiplication on the local zero-padding block and the 2-millisecond data block to achieve code parallel coherence, including:

[0024] The local zero-padding block is used to pad zeros to the local pseudo-code to make its length consistent with the length of the 2-millisecond data block. At the beginning of the capture, the local zero-padding block is sent to the FFT unit;

[0025] The FFT unit is used to perform Fourier transform on the 2-millisecond zero-Doppler data and the local zero-padding block. After Fourier transform, the local zero-padding block takes the conjugate and is sent to the storage unit, and the 2-millisecond zero-Doppler data after Fourier transform is sent to the complex multiplication unit;

[0026] The storage unit is used to store the FFT conjugate value of the local zero-padding block for subsequent use in complex multiplication;

[0027] A complex multiplication unit is used to perform complex multiplication on the Fourier transform value of a 2 - millisecond data block and the conjugate of the Fourier transform of a locally zero - padded block, replacing time - domain convolution with frequency - domain multiplication. By using a zero - padded block coherent with the 2 - millisecond data block, the influence of NH code jumps and navigation data jumps on coherent integration is avoided, and a complete 1 - millisecond frequency - domain coherent value is obtained and sent to the IFFT unit.

[0028] An IFFT unit is used to perform an inverse Fourier transform on the complex multiplication result, converting the coherent result from the frequency domain to the time domain, and the converted time - domain coherent value is sent to the inter - symbol difference module.

[0029] Another object of the present invention is to provide a method for capturing weak Beidou signals using the inter - symbol difference and zero - padded block of the Beidou weak signal capture system using the inter - symbol difference and zero - padded block. The method for capturing weak Beidou signals using the inter - symbol difference and zero - padded block includes the following steps:

[0030] Step 1: Remove the residual carrier signal of the baseband data through a digital down - conversion module to obtain zero - intermediate - frequency data; use a code merging module to merge the zero - intermediate - frequency data into half - code data, and use a 2 - millisecond data splicing module to store and overlap the half - code data to form a 2 - millisecond data block.

[0031] Step 2: Use a Doppler stripping module to strip the Doppler frequency in the 2 - millisecond data block and send it to a code - parallel coherent module for sliding coherence with a locally zero - padded block to obtain coherent values at different code phases.

[0032] Step 3: Use the coherent values to avoid the influence of NH code jumps and navigation data jumps through inter - symbol difference processing, and obtain coherent data of different durations through a step - by - step coherent module and step - by - step non - coherence.

[0033] Step 4: Determine whether a satellite signal is captured through peak decision. If a satellite signal is captured, the captured information is transmitted to the tracking module and the capture program is terminated. If a satellite signal is not captured, it is determined by a Doppler search completion judgment module whether to continue the capture until the current satellite is captured or all Doppler frequencies are searched through.

[0034] Furthermore, the method for capturing weak Beidou signals using the inter - symbol difference and zero - padded block further includes:

[0035] Use a Doppler compensation module to compensate for the code - phase offset generated within the coherent duration due to the Doppler effect.

[0036] When the peak decision module determines that a satellite signal has not been successfully captured, it is determined whether the Doppler frequency search is completed. If the search is completed, the capture program will end. If the search is not completed, it will enter the Doppler regulation module for the next round of capture until the Doppler search is completed or the current satellite signal is captured.

[0037] Use the Doppler control module to control the Doppler frequency to be searched currently and transmit it to the Doppler stripping module; use the result output module to transmit the captured Doppler information, satellite number, and code phase to the tracking module according to the processing results of the peak decision module and the Doppler search completion judgment module.

[0038] Further, the data block splicing module stores the chip data and forms 2-millisecond data blocks. When storing the data, it takes 1-millisecond data as a unit, and combines two adjacent 1-millisecond data blocks to form a 2-millisecond data block; when forming 2-millisecond data, each intermediate 1-millisecond data block is used twice overlapped.

[0039] Further, the inter-code difference module performs inter-code difference on the first 4096 coherence values obtained by the code parallel coherence module. Since 8192 code phase coherence values are obtained after the zero-padding block is coherent with the 2-millisecond data, and the code phase only appears in the first 4096 positions during code parallel search, only the first 4096 coherence values are intercepted for difference during inter-code difference; the difference method uses the inter-code difference method to perform difference on the coherence values of adjacent code phases, obtaining 4095 difference results, and performing difference on the last code phase coherence value and the first code phase coherence value, a total of 4096 difference results are obtained.

[0040] Further, the successive coherence module and the successive non-coherence module perform successive coherence and successive non-coherence on the data obtained by the inter-code difference module, where the number of successive coherence times is N and the number of successive non-coherence times is M; through successive coherence and successive non-coherence, coherence values of different capture durations are obtained, and signals of different intensities are captured through peak decision.

[0041] Another object of the present invention is to provide a computer device, the computer device includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the following steps:

[0042] Remove the residual carrier signal of the baseband data through the digital down-conversion module to obtain zero-intermediate frequency data; use the code merging module to merge the zero-intermediate frequency data into half-code data, and use the 2-millisecond data splicing module to store and overlap the half-code data to form 2-millisecond data blocks; use the Doppler stripping module to strip the Doppler frequency in the 2-millisecond data block and send it to the code parallel coherence module for sliding coherence with the local zero-padding block to obtain coherence values of different code phases;

[0043] The influence of NH code jumps and navigation data jumps is avoided by performing inter-code differential processing on the coherence values, and coherence data of different durations are obtained through a step-by-step coherent module and a step-by-step incoherent module; it is determined whether a satellite signal is captured through peak decision. If a satellite signal is captured, the captured information is transmitted to the tracking module and the capture program is terminated. If a satellite signal is not captured, it is judged by the Doppler search completion judgment module whether to continue the capture until the current satellite is captured or all Doppler frequencies are searched through.

[0044] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which when executed by a processor causes the processor to perform the following steps:

[0045] The residual carrier signal of the baseband data is removed through a digital down-conversion module to obtain zero-intermediate-frequency data; the zero-intermediate-frequency data is merged into half-code data by a code merging module, and the half-code data is stored and overlapped by a 2-millisecond data splicing module to form a 2-millisecond data block; the Doppler frequency in the 2-millisecond data block is stripped by a Doppler stripping module and sent to a code parallel coherence module for sliding coherence with a local zero-padding block to obtain coherence values of different code phases;

[0046] The influence of NH code jumps and navigation data jumps is avoided by performing inter-code differential processing on the coherence values, and coherence data of different durations are obtained through a step-by-step coherent module and a step-by-step incoherent module; it is determined whether a satellite signal is captured through peak decision. If a satellite signal is captured, the captured information is transmitted to the tracking module and the capture program is terminated. If a satellite signal is not captured, it is judged by the Doppler search completion judgment module whether to continue the capture until the current satellite is captured or all Doppler frequencies are searched through.

[0047] Another object of the present invention is to provide an information data processing terminal for implementing the Beidou weak signal capture system of the inter-code difference and zero-padding block.

[0048] Combined with the above technical solutions and the solved technical problems, the advantages and positive effects of the technical solution to be protected by the present invention are analyzed from the following aspects:

[0049] First, aiming at the technical problems existing in the above-mentioned prior art and the difficulty of solving this problem, closely combining the technical solution to be protected by the present invention and the results and data in the R & D process, etc., analyze in detail and deeply how the technical solution of the present invention solves the technical problems and the creative technical effects brought after solving the problems. The specific description is as follows:

[0050] The high-orbit Beidou signal acquisition system based on inter-code difference and zero-padding block provided by the present invention removes the residual carrier signal of the baseband data through a digital down-conversion module to obtain zero-intermediate-frequency data; uses a code merging module to merge the zero-intermediate-frequency data into half-code data, and a 2-millisecond data splicing module stores and overlaps the half-code data to form a 2-millisecond data block; uses a Doppler stripping module to strip the Doppler frequency in the 2-millisecond data block and send it to a code parallel coherent module to perform sliding coherence with the local zero-padding block to obtain coherence values at different code phases; uses the coherence values to avoid the influence of NH code jumps and navigation data jumps through inter-code difference processing, and obtains coherent data of different durations through a step-by-step coherent module and a step-by-step incoherent module; finally, determines whether the satellite signal is captured through peak judgment. If the satellite signal is captured, the captured information is transmitted to the tracking module and the acquisition program is terminated. If the satellite signal is not captured, it is judged by the Doppler search completion judgment module whether to continue the acquisition until the current satellite is captured or all Doppler frequencies are searched through.

[0051] The present invention also has the following advantages:

[0052] (1) The present invention adopts the inter-code difference algorithm to avoid the influence of NH code jumps in D1 navigation data and the too fast rate of D2 navigation message on the coherent integration duration, and improves the acquisition sensitivity of Beidou signals by increasing the coherent integration duration.

[0053] (2) The present invention uses the zero-padding block to perform coherence with the data block, avoiding the influence of NH code jumps and navigation data jumps on the coherence value, and obtaining a complete 1-millisecond coherence value.

[0054] (3) The present invention adopts the step-by-step coherent and step-by-step incoherent algorithms to achieve the compatible acquisition of strong and weak signals.

[0055] (4) The present invention adopts the inter-code difference algorithm, avoiding the problem of storing a large amount of data in the traditional algorithm, and at the same time solving the problem that the traditional high-sensitivity receiver cannot improve the acquisition sensitivity of D2 navigation data.

[0056] Second, regarding the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are specifically described as follows:

[0057] The present invention proposes a high-orbit Beidou signal acquisition method based on inter-code difference and zero-padding block, providing an acquisition algorithm with low hardware resource consumption, fast acquisition speed, and high sensitivity for navigation receivers.

[0058] Third, as the creative auxiliary evidence of the present invention, it is also reflected in the following important aspects:

[0059] The technical solution of the present invention fills the technical gaps at home and abroad in the industry: The present invention adopts the inter-code differential algorithm. Through this algorithm, the influence of the NH code jump and the navigation data jump on the long-time coherent accumulation is avoided, so that the algorithm can increase the coherent integration time, improve the signal-to-noise ratio of the signal, and further improve the acquisition sensitivity of the Beidou satellite signal. At the same time, the inter-code differential algorithm does not require storing a large amount of data, saving a large amount of resources for the navigation receiver. In addition, the inter-code differential avoids the influence of the navigation data jump. For the D2 navigation message with too fast code rate, it can greatly extend the coherent integration time and improve the acquisition sensitivity. Fundamentally, the problem of insufficient acquisition sensitivity of the traditional navigation receiver for the D2 navigation message is solved, and at the same time, the high-sensitivity acquisition of the D1 navigation message is taken into account. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments of the present invention. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0061] Figure 1 It is a flowchart of the Beidou weak signal acquisition method with inter-code differential and zero-padding block provided by the embodiment of the present invention;

[0062] Figure 2 It is a block diagram of the system structure of the Beidou weak signal acquisition with inter-code differential and zero-padding block provided by the embodiment of the present invention;

[0063] Figure 3 It is a block diagram of the data block splicing structure provided by the embodiment of the present invention;

[0064] Figure 4 It is a block diagram of the inter-code differential structure provided by the embodiment of the present invention;

[0065] Figure 5 It is a capture result diagram of the Beidou-3 satellite under the condition of -145 dBm signal strength provided by the embodiment of the present invention;

[0066] Figure 6 It is a capture result diagram of the Beidou No. 24 satellite under the condition of -146 dBm signal strength provided by the embodiment of the present invention;

[0067] Figure 7 It is a code phase result diagram of the Beidou satellite capture under the condition of -143 dBm signal strength provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0068] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0069] In view of the problems existing in the prior art, the present invention provides a Beidou weak signal capture method and system with inter-code difference and zero-padding block. The present invention is described in detail below with reference to the accompanying drawings.

[0070] 1. Explanatory Examples In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an illustrative example that expands and describes the technical solution of the claims.

[0071] like Figure 1 As shown, the Beidou weak signal acquisition method of inter-code difference and zero padding block provided by the embodiment of the present invention includes the following steps:

[0072] S101, removing the residual carrier signal of the baseband data through the digital down-conversion module to obtain zero intermediate frequency data; using the code merging module to merge the zero intermediate frequency data into half code data, and using the 2 millisecond data splicing module to store and overlap the half code data to form a 2 millisecond data block;

[0073] S102, using the Doppler stripping module to strip the Doppler frequency in the 2 millisecond data block, and sending it to the code parallel coherence module and the local zero padding block for sliding coherence to obtain coherence values of different code phases;

[0074] S103, using the coherent value to perform inter-code differential processing to avoid the influence of NH code jump and navigation data jump, and obtaining coherent data of different time lengths through step-by-step coherent modules and step-by-step incoherent modules;

[0075] S104, judging whether the satellite signal is captured by the peak value, if the satellite signal is captured, the captured information is transmitted to the tracking module and the capture program is terminated. If the satellite signal is not captured, the Doppler search completion judgment module determines whether to continue the capture until the current satellite is captured or all Doppler frequencies are searched.

[0076] like Figure 2As shown in the figure, the high-orbit Beidou signal acquisition system based on inter-code difference and zero-padding block provided by the embodiment of the present invention includes a digital down-conversion module, a code merging module, a 2-millisecond data splicing module, a Doppler stripping module, a local zero-padding module, a code parallel coherence module, an inter-code difference module, a Doppler compensation module, a successive coherence module and a successive non-coherence module, a peak decision module, a Doppler search completion judgment module, a Doppler regulation module, and a result output module. The digital down-conversion module is used to perform digital down-conversion on the baseband data, remove the residual carrier in the data, and obtain zero-intermediate-frequency data. The code merging module merges the zero-intermediate-frequency signals into half-code data by means of accumulation, and the merged code rate is 4.096 MHz. The data block splicing module stores the chip data and combines it into data blocks. In this process, the RAM can store 3 milliseconds of data, and the RAM is divided into 3 1-millisecond data blocks. When 2 milliseconds of data is stored for the first time and the data is full, the data will be read and processed. In the subsequent storage process, the first two data blocks of the currently stored data block will be read and processed as a data block. In this way, the data can be overlapped and combined into data blocks, improving the utilization rate of the data and shortening the acquisition time. The Doppler stripping module mixes the 2-millisecond data block with the locally generated Doppler frequency to remove the Doppler frequency in the data and obtain zero-Doppler data. The local zero-padding module performs zero-padding on the local pseudo-code to obtain a zero-padding block of the same length as the 2-millisecond data block. When there is an NH code transition or a navigation data transition in the 2-millisecond data block, the zero-padding block and the 2-millisecond data are used for sliding coherence to still obtain a complete 1-millisecond coherence value, reducing the impact of NH code and navigation data transitions on the 1-millisecond coherence value. The code parallel coherence module performs code parallel coherence on the 2-millisecond data block and the local zero-padding block by using FFT and IFFT to obtain coherence values at different code phases. The inter-code difference module differentiates the first 4096 code-phase coherence values obtained by the code parallel coherence module. The differentiation adopts the form of adjacent data differentiation. This differentiation method can avoid the impact of NH code transitions or navigation data transitions on the long-time coherence integration. The Doppler compensation module performs Doppler compensation on the differentiated data and corrects the code phase. The successive coherence module and the successive non-coherence module perform successive coherence and non-coherence on the data after phase correction to obtain coherence data with different acquisition durations. The peak decision module compares the data results with different coherence durations and determines whether a satellite signal is acquired through a threshold. The Doppler search completion judgment module determines whether the Doppler search of the current satellite is completed when a satellite signal is not acquired. If the Doppler frequency search is completed, the acquisition process ends. If the Doppler frequency search is not completed, the remaining Doppler frequencies are continuously searched. The Doppler regulation module generates a Doppler control word according to the current Doppler range to be searched and generates a corresponding Doppler frequency through the Doppler control word.The result output module transmits information such as the Doppler frequency, code phase, maximum value of coherent data, and average value of coherent data obtained at the end of capture to the tracking module.

[0077] As Figure 3 shown, the present invention forms 2 ms data blocks in an overlapping allocation manner. This allocation method consumes less storage space during data storage, improves data utilization, and shortens the capture time. And when cohering 2 ms of data with the local zero-padding block, the influence of NH codes and navigation data can be avoided, and a complete 1 ms coherent integration value can be obtained.

[0078] Among them, the data block splicing module stores the chip data and forms 2 ms data blocks. It takes 1 ms of data as a unit during data storage and combines two adjacent 1 ms data blocks to form a 2 ms data block. When forming 2 ms of data, each 1 ms data block in the middle will be used overlapped twice, thereby improving data utilization and shortening the capture duration.

[0079] As Figure 4 shown, the present invention adopts the method of inter-code difference to perform difference on the coherent values of the first 4096 code phases, avoiding the influence of navigation data jumps and NH code jumps on long-term coherent accumulation. After inter-code difference, the coherent integration duration can be increased to improve the signal-to-noise ratio, thereby improving the capture sensitivity. At the same time, when only using the first 4096 coherent data to complete the search of all code phases, the calculation amount can be reduced.

[0080] Among them, the inter-code difference module performs inter-code difference on the first 4096 coherent values obtained by the code parallel coherent module. Since 8192 code phase coherent values will be obtained after cohering the zero-padding block with 2 ms of data, and the code phase only appears in the first 4096 positions during code parallel search, only the first 4096 coherent values are intercepted for difference during inter-code difference. The difference method adopts the inter-code difference method, that is, the coherent values of adjacent code phases are differenced. At this time, 4095 difference results will be obtained, and the coherent value of the last code phase is differenced from the coherent value of the first code phase, and a total of 4096 difference results are obtained. The inter-code difference results are not affected by NH code jumps and navigation data jumps. Therefore, during the capture process, the coherent integration time can be extended to achieve high-sensitivity capture of D1 and D2 navigation messages. At the same time, the inter-code difference algorithm does not require storing a large amount of data, saving a large amount of storage resources for the navigation receiver.

[0081] The present invention uses a code parallel coherent module to perform frequency domain complex multiplication on a locally zero-padded block and a 2-millisecond data block to achieve code parallel coherence. It includes: a locally zero-padded block, which makes the length of the local pseudo-code the same as that of the 2-millisecond data block by padding zeros. At the beginning of acquisition, the locally zero-padded block is sent to the FFT module; an FFT module, which is used to perform Fourier transform on the 2-millisecond zero-Doppler data and the locally zero-padded block. After the locally zero-padded block undergoes Fourier transform, it takes the conjugate and is sent to the storage module, and the 2-millisecond zero-Doppler data is sent to the complex multiplication module after Fourier transform; a storage module, which is used to store the FFT conjugate value of the local zero-padded block for subsequent use in complex multiplication; a complex multiplication module, which is used to perform complex multiplication on the Fourier transform value of the 2-millisecond data block and the Fourier transform conjugate value of the locally zero-padded block, replacing time domain convolution with frequency domain multiplication. Using the zero-padded block and the 2-millisecond data block for coherence can avoid the influence of NH code jumps and navigation data jumps on coherence integration, obtain a complete 1-millisecond frequency domain coherence value, and send the frequency domain coherence value to the IFFT module.

[0082] An IFFT module, which is used to perform inverse Fourier transform on the complex multiplication result, convert the coherence result from the frequency domain to the time domain, and send the converted time domain coherence value to the inter-symbol difference module.

[0083] The present invention uses a successive coherence module and a successive incoherence module to perform successive coherence and successive incoherence on the data obtained by the inter-symbol difference module, where the number of successive coherence times is N and the number of successive incoherence times is M. Through successive coherence and successive incoherence, coherence values with different acquisition durations can be obtained, and signals with different intensities can be captured through peak decision.

[0084] II. Application embodiments. In order to prove the creativity and technical value of the technical solution of the present invention, this part is an application embodiment of the technical solution of the claims on specific products or related technologies.

[0085] A satellite navigation receiver usually realizes the reception of satellite signals by using a field programmable gate array (FPGA) in combination with a DSP or an application specific integrated circuit (ASIC) in combination with a DSP. In the present invention, the satellite navigation receiver uses a field programmable gate array (FPGA) in combination with a DSP to realize the acquisition of satellite signals. Its specific implementation scheme is as follows:

[0086] The navigation receiver first receives the navigation signal transmitted by the satellite through the antenna, and then processes the signal through the radio frequency circuit for amplification, filtering, and down-conversion, so that the signal becomes an intermediate frequency signal. Subsequently, the intermediate frequency signal is converted into a digital signal through an analog-to-digital converter, and satellite information is obtained through baseband signal processing.

[0087] Satellite baseband signal processing mainly includes the acquisition, tracking, and settlement of satellite signals. This invention mainly focuses on the acquisition of satellite signals in baseband signal processing. First, when the programmable logic gate array on the intermediate frequency board receives the acquisition start signal from the DSP, it mixes the digital signal transmitted by the analog-to-digital converter with the local carrier to remove the intermediate frequency carrier in the signal and obtain a zero-intermediate frequency signal. Subsequently, the zero-intermediate frequency signal is subjected to chip merging to obtain half-code data with a code rate of 4.096 MHz, and the half-code data is stored. The storage module can store 3 milliseconds of data. During the data storage process, by controlling the data reading, the half-code data is read out in the form of 2-millisecond overlapping blocks. Then, the data block is mixed with the local Doppler frequency to remove the Doppler frequency in the data. Subsequently, the data block and the local zero-padding block are converted to the frequency domain for complex multiplication, and the complex multiplication data is converted to the time domain to obtain the code-parallel coherence value.

[0088] Since the D1 navigation message contains the NH code, and at the same time, due to the excessive rate of the D2 navigation message and the excessive navigation data jumps, the coherence value obtained at this time is only the coherence value of 1 millisecond of data. At this time, the coherence values of different code phases are processed through the inter-symbol difference algorithm to avoid the influence of NH code jumps and navigation data jumps. Subsequently, Doppler compensation is performed on it and coherent processing is carried out to improve the signal-to-noise ratio of the data. When the coherent duration reaches a certain time, non-coherent integration is performed on it to improve the acquisition sensitivity. At the same time, the peak decision module will make real-time judgments on the 1-millisecond coherence values of different code phases, the coherence values after inter-symbol difference, and the non-coherent accumulation values to determine whether a satellite signal has been acquired. When the acquisition is completed, the acquisition module will transmit information such as the currently acquired Doppler frequency and code phase to the tracking module. If the current satellite acquisition is completed, the DSP will control the acquisition module to search for the next satellite by changing the satellite number.

[0089] It should be noted that the embodiments of the present invention can be implemented through hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated designed hardware. Those of ordinary skill in the art can understand that the above devices and methods can be implemented using computer-executable instructions and / or included in the processor control code. For example, such code is provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits of programmable hardware devices such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips and transistors, or field programmable gate arrays and programmable logic devices, can also be implemented by software executed by various types of processors, or can be implemented by a combination of the above hardware circuits and software, such as firmware.

[0090] III. Evidence of the effects related to the embodiments. During the research and development or use of the embodiments of the present invention, some positive effects have been achieved, and there are indeed great advantages compared with the prior art. The following content will be described in combination with the data, charts, etc. in the test process.

[0091] First, a satellite signal acquisition card is used to collect the Beidou signals emitted by a satellite simulator, and the collected data is simulated. The acquisition results of Beidou-3 satellites under the condition of an intensity of -145 dBm are as Figure 5 shown. At this time, the acquisition results of the acquisition algorithm for D2 navigation data under weak signals can be clearly distinguished.

[0092] Under the condition of an intensity of -146 dBm, the acquisition of Beidou-24 satellites is carried out, and the acquisition results are as Figure 6 shown. According to the simulation results, the present invention has a high acquisition sensitivity for weak signals of both Beidou D1 and D2 navigation messages, and solves the problem that the acquisition sensitivity of traditional navigation receivers for D2 navigation data is seriously insufficient.

[0093] Subsequently, a navigation receiver is used to perform real-time acquisition on the signals emitted by the satellite simulator, and the acquisition results are as Figure 7 shown. This figure shows the code phase results of Beidou satellite acquisition under the condition of a signal intensity of -143 dBm. It can be clearly seen from the figure that the accurate code phase coherence value is higher than other code phase coherence values.

[0094] The present invention has extremely low resource consumption compared with traditional navigation receivers, and at the same time has a high acquisition sensitivity for Beidou signals.

[0095] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A Beidou weak signal acquisition system with inter-code difference and zero-padding blocks, characterized in that The Beidou weak signal acquisition system of code - interval difference and zero - padding block includes: A digital down - conversion module, which is used to perform digital down - conversion on baseband data, remove the residual carrier in the data, obtain zero - intermediate - frequency data, and transmit the data to the code combination module; A code combination module, which is used to accumulate and combine the zero - intermediate - frequency data, obtain half - code data, and then transmit the data to the data block splicing module; A data block splicing module, which is used to store and overlap - combine the chip data to form a 2 - millisecond data block, and transmit the data block to the Doppler stripping module; A Doppler stripping module, which is used to strip the Doppler frequency in the 2 - millisecond data block to obtain zero - Doppler data, and then send the data to the code - parallel coherent module for FFT processing; A local zero - padding module, which is used to zero - pad the local pseudo - code to obtain a zero - padding block with the same length as the 2 - millisecond data block, and send the local zero - padding module to the FFT core for Fourier transform; A code - parallel coherent module, which is used to coherently process the 2 - millisecond data block and the local zero - padding block by using FFT and IFFT to obtain coherent values of different code phases, and send the first 4096 coherent data to the code - interval difference module; A code - interval difference module, which is used to perform difference on the coherent values of different code phases. The code - interval difference method is adopted to avoid the influence of the NH code jump in the D1 navigation message, the too - fast rate of the D2 navigation message, and the navigation data jump on the acquisition sensitivity. Then, the differential data is sent to the Doppler compensation module; A Doppler compensation module, which is used to compensate for the code - phase offset generated by the Doppler effect within the coherent duration. The data after phase correction is sent to the step - by - step coherent module and the step - by - step non - coherent module; The step - by - step coherent module and the step - by - step non - coherent module are used to perform N - times step - by - step coherence on the results obtained by the Doppler compensation module to obtain coherent values of different signal - to - noise ratios; then, after taking the modulus of the coherent accumulation value, perform M - times step - by - step non - coherence, and send the results of different coherence times to the peak decision module; A peak decision module, which is used to perform peak detection on the code - phase coherent values of different coherence times, judge whether the satellite signal is captured, and select the next operation according to the judgment result; A Doppler search completion judgment module. When the peak decision module determines that the satellite signal is not successfully captured, it judges whether the Doppler frequency search is completed; if the search is completed, the acquisition program ends; if the search is not completed, it enters the Doppler regulation module and performs the next round of acquisition until the Doppler search is completed or the current satellite signal is captured; A Doppler regulation module, which is used to regulate the Doppler frequency to be searched currently and transmit it to the Doppler stripping module; A result output module, which is used to transmit the acquired Doppler information, satellite number, and code phase to the tracking module according to the processing results of the peak decision module and the Doppler search completion judgment module.

2. The BeiDou weak signal acquisition system with inter-symbol difference and zero-padding block as claimed in claim 1, wherein The code - parallel coherent module is also used to perform frequency - domain complex multiplication on the local zero - padding block and the 2 - millisecond data block to achieve code - parallel coherence, including: A local zero - padding block, which is used to zero - pad the local pseudo - code to make the length consistent with the 2 - millisecond data block length. At the beginning of the acquisition, the local zero - padding block is sent to the FFT unit; An FFT unit is used to perform Fourier transform on 2-millisecond zero-Doppler data and a locally zero-padded block. After the Fourier transform, the conjugate of the locally zero-padded block is taken and sent to a storage unit, and the 2-millisecond zero-Doppler data is sent to a complex multiplication unit after Fourier transform; A storage unit is used to store the FFT conjugate value of the locally zero-padded block for subsequent use in complex multiplication; A complex multiplication unit is used to perform complex multiplication on the Fourier transform value of the 2-millisecond data block and the Fourier transform conjugate value of the locally zero-padded block, replacing time-domain convolution with frequency-domain multiplication, and using the zero-padded block and the 2-millisecond data block for coherence to avoid the influence of NH code jumps and navigation data jumps on coherent integration, obtaining a complete 1-millisecond frequency-domain coherence value, and sending the frequency-domain coherence value to an IFFT unit; An IFFT unit is used to perform inverse Fourier transform on the complex multiplication result, converting the coherent result from the frequency domain to the time domain, and sending the converted time-domain coherence value to an inter-symbol difference module.

3. A method for capturing weak Beidou signals of the inter-code difference and zero-padding block in a Beidou weak signal capture system applying the inter-code difference and zero-padding block as described in any one of claims 1 to 2, characterized in that, The Beidou weak signal acquisition method using inter-symbol difference and zero-padded block includes the following steps: Step 1, removing the residual carrier signal of the baseband data through a digital down-conversion module to obtain zero-intermediate frequency data; using a code merging module to merge the zero-intermediate frequency data into half-code data, and using a 2-millisecond data splicing module to store and overlap the half-code data to form a 2-millisecond data block; Step 2, using a Doppler stripping module to strip the Doppler frequency in the 2-millisecond data block and sending it to a code parallel coherence module for sliding coherence with a locally zero-padded block to obtain coherence values at different code phases; Step 3, using the coherence values to perform inter-symbol difference processing to avoid the influence of NH code jumps and navigation data jumps, and obtaining coherent data of different durations through a progressive coherence module and progressive non-coherence; Step 4, determining whether a satellite signal is captured through peak decision. If a satellite signal is captured, the captured information is transmitted to a tracking module and the acquisition program is terminated. If a satellite signal is not captured, it is determined by a Doppler search completion judgment module whether to continue the acquisition until the current satellite is captured or all Doppler frequencies are searched through.

4. The BeiDou weak signal acquisition method of inter-code difference and zero-padding block according to claim 3, characterized in that, The Beidou weak signal acquisition method using inter-symbol difference and zero-padded block further includes: Using a Doppler compensation module to compensate for the code phase offset generated within the coherent duration due to the Doppler effect; When the peak decision module determines that the satellite signal is not successfully captured, it is judged whether the Doppler frequency search is completed. If the search is completed, the acquisition program will end. If the search is not completed, it will enter a Doppler regulation module for the next round of acquisition until the Doppler search is completed or the current satellite signal is captured; Using a Doppler regulation module to regulate the Doppler frequency to be searched currently and transmit it to a Doppler stripping module; using a result output module to transmit the acquired Doppler information, satellite number, and code phase to a tracking module according to the processing results of the peak decision module and the Doppler search completion judgment module.

5. The BeiDou weak signal acquisition method of inter-symbol difference and zero-padding block according to claim 3, characterized in that The data block splicing module stores the chip data and forms a 2-millisecond data block. When storing the data, it takes 1-millisecond data as a unit, and merges two adjacent 1-millisecond data blocks to form a 2-millisecond data block; when forming the 2-millisecond data, each intermediate 1-millisecond data block is used twice overlappingly.

6. The Beidou weak signal acquisition method of inter-code difference and zero-padding block according to claim 3, characterized in that The inter-code difference module performs inter-code difference on the first 4096 coherence values obtained by the code parallel coherence module. Since 8192 code phase coherence values are obtained after the zero-padding block is coherent with 2 ms of data, and the code phase only appears in the first 4096 positions during code parallel search, only the first 4096 coherence values are intercepted for inter-code difference during inter-code difference. The difference method uses the inter-code difference method to perform difference on the coherence values of adjacent code phases, obtaining 4095 difference results, and performing difference on the coherence value of the last code phase and the coherence value of the first code phase, resulting in a total of 4096 difference results.

7. The BeiDou weak signal acquisition method of inter-symbol difference and zero-padding block according to claim 3, characterized in that, The successive coherence module and the successive non-coherence module perform successive coherence and successive non-coherence on the data obtained by the inter-code difference module, where the number of successive coherence times is N and the number of successive non-coherence times is M. Through successive coherence and successive non-coherence, coherence values with different acquisition durations are obtained, and signals with different intensities are acquired through peak decision.

8. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of the Beidou weak signal acquisition method of inter-code difference and zero-padding block as described in any one of claims 3 to 7.

9. A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the processor executes the steps of the Beidou weak signal acquisition method of inter-code difference and zero-padding block as described in any one of claims 3 to 7.

Images