A GPS weak signal acquisition method and system based on inter-code difference and code parallelism

Abstract

The present invention belongs to the field of satellite navigation technology, and discloses a method and system for capturing weak GPS signals based on code difference and code parallelism, including a digital down-conversion module, a code merging module, a data storage module, a Doppler stripping module, a data folding module, a step-by-step matching coherent module, a code difference module, a Doppler compensation module, a step-by-step coherent module and a step-by-step incoherent module, a peak judgment module, a Doppler search completion judgment module, a Doppler control module, and a result output module. The high-orbit GPS signal capture method based on code difference and code parallelism of the present invention provides a fast and efficient capture algorithm for a navigation receiver; the use of the code difference algorithm avoids the influence of navigation data jumps on the coherent integration time, and improves the capture sensitivity of the GPS signal by increasing the coherent integration time. The present invention adopts step-by-step coherent and step-by-step incoherent algorithms to achieve rapid capture of signals of different strengths and shorten the first positioning time of the navigation receiver.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite navigation, and in particular relates to a method and system for capturing GPS weak signals using inter-code difference and code parallelism. Background Art

[0002] At present, with the development of satellite navigation systems, satellite navigation has gradually expanded from the initial military field to all aspects of the civilian field. Tunnels, forests, subways, and indoor places such as the interior of large buildings or underground garages have gradually become important places for the application of navigation technology. The rapid growth in demand for satellite navigation services has put increasing pressure on traditional ground measurement and control stations. If satellites or spacecraft have the ability to autonomously locate and determine their orbits, the cost of satellite measurement and control will be greatly reduced. People have begun to explore the design of high-orbit satellite navigation receivers to provide positioning and navigation services for satellites and spacecraft.

[0003] Traditional high-orbit GPS navigation receivers obtain the coherent integration value through the code parallel algorithm and then perform incoherent processing on the data, such as the algorithm mentioned in "Block Acquisition of Weak GPS Signals in a Software Receiver". This method is affected by navigation data jumps, the coherent duration is limited, and the multiple introduction of square noise leads to a decrease in capture sensitivity. Another example is the method shown in the patent "GPS capture circuit based on optimized parallel code phase search", which consumes a lot of resources and has low capture sensitivity. At the same time, traditional GPS navigation receivers use a fixed capture duration to capture signals in a high-orbit environment, which wastes a lot of capture time for strong signals in a high-orbit environment. The high-orbit GPS signal capture method based on inter-code difference and code parallelism can avoid the influence of navigation data jumps on the coherent integration duration and improve the capture sensitivity of the navigation receiver. At the same time, the algorithm incorporates step-by-step coherence and step-by-step incoherence algorithms to speed up the capture of signals and meet the requirements of fast capture and high-sensitivity capture of signals in a high-orbit environment.

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

[0005] (1) Traditional high-orbit GPS navigation receivers are affected by navigation data jumps through code parallel algorithms, the coherence time is limited, and the multiple introductions of square noise lead to a decrease in capture sensitivity.

[0006] (2) The GPS acquisition circuit method based on optimizing parallel code phase search consumes large resources and has low acquisition sensitivity.

[0007] (3) Traditional GPS navigation receivers use a fixed capture time to capture signals in a high-orbit environment, which wastes a lot of capture time for strong signals in a high-orbit environment. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method and system for capturing GPS weak signals based on inter-code difference and code parallelism, and in particular relates to a method, system, medium, device and terminal for capturing high-orbit GPS weak signals based on inter-code difference and code parallelism, aiming to solve the problem of high-orbit GPS navigation receivers capturing satellite signals with high sensitivity and quickly.

[0009] The present invention is implemented as follows: a GPS weak signal acquisition system with code difference and code parallelism, the GPS weak signal acquisition system with code difference and code parallelism comprises:

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

[0011] A code combining module is used to accumulate and combine zero intermediate frequency data according to the sampling rate to obtain half code data, and send the data to the data storage module for storage;

[0012] A data storage module is used to perform ping-pong storage of the obtained half-code data for 10 milliseconds, and the stored data is sent to the Doppler stripping module after being read out;

[0013] A Doppler stripping module is used to perform Doppler stripping on the stored data in units of 10 milliseconds, remove the Doppler frequency in the data, and send the data to a data folding module;

[0014] A data folding module is used to fold the 10 milliseconds of data after Doppler stripping into 1 millisecond data blocks one by one according to the corresponding code phase, and transmit the folded data blocks one by one to the step-by-step matching coherence module;

[0015] The step-by-step matching coherence module is used to perform fast Fourier transform on the data blocks with different folding times, multiply them with the conjugate result of the fast Fourier transform of the local pseudo code, and then perform inverse fast Fourier transform on the complex multiplication result to obtain the coherence values ​​with different coherence time lengths, and then send the coherence values ​​to the inter-code difference module and the peak decision module at the same time;

[0016] The code difference module is used to differentiate the coherent data obtained by the step-by-step matching coherent modules. The difference method adopts the code difference method, which takes the conjugate of one coherent value in the adjacent code phase and multiplies it with the other one, and sends the difference result to the Doppler compensation module;

[0017] A Doppler compensation module is used to compensate for the code phase offset caused by the Doppler effect, so that the differential result code phases are aligned with each other, and then the data is transmitted to the step-by-step coherent module and the step-by-step incoherent module;

[0018] The step-by-step coherent module and the step-by-step incoherent module are used to perform step-by-step accumulation K times and take the modulus at the corresponding position of the result obtained by the Doppler compensation module to obtain coherent values ​​with different signal-to-noise ratios; the coherent accumulated value is taken modulo and then accumulated step-by-step L times to obtain coherent data with different capture time lengths, and the data is transmitted to the peak decision module;

[0019] The peak value judgment module is used to perform peak value detection on the results obtained by the step-by-step matching coherent module, the step-by-step coherent module and the step-by-step incoherent module to determine whether the peak-to-average ratio exceeds the capture threshold; if the peak value exceeds the threshold, it will enter the result output module; if it does not exceed the threshold, it will enter the Doppler search completion judgment module;

[0020] The Doppler search completion judgment module is used to judge whether the Doppler frequency search is completed when the current satellite is not captured. If the search is completed, it will enter the result output module; if the search is not completed, it will enter the Doppler control module;

[0021] The Doppler control module is used to control 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.

[0023] Furthermore, the step-by-step matching coherence module performs code-parallel coherence on data with different folding times and local pseudocodes to obtain code-parallel search results with different coherence durations, including:

[0024] The data selector is used to select the data source to be processed by FFT. When the capture starts, the data selector selects the data source as the local pseudo code. When the local pseudo code processing is completed, the data source is selected as the folded data, the data source of the FFT core is selected and switched, and the selected data is transmitted to the FFT unit.

[0025] An FFT unit is used to convert the data with different folding times and the local pseudo code into the frequency domain through Fourier transform, transmit the Fourier transform value of the local pseudo code to the storage unit, and transmit the data with different folding times to the complex multiplication unit after Fourier transform;

[0026] A storage unit, used to store the FFT conjugate value of the local pseudo code, and to send the data to the complex multiplication unit when in use;

[0027] A complex multiplication unit is used to conjugate the Fourier transform value of the data and the Fourier transform value of the local pseudo code and then multiply them, use frequency domain multiplication instead of time domain convolution, and transmit the complex multiplication result to the IFFT unit;

[0028] The IFFT unit is used to perform inverse Fourier transform on the complex multiplication result, convert the coherent result from the frequency domain to the time domain, transmit the data to the code division module, and transmit the data to the peak decision module after taking the modulus.

[0029] Another object of the present invention is to provide a method for capturing GPS weak signals using inter-code difference and code parallelism using the GPS weak signal capture system using inter-code difference and code parallelism, wherein the method for capturing GPS weak signals using inter-code difference and code parallelism comprises the following steps:

[0030] Step 1: Use a digital down-conversion module to mix the baseband data and the locally generated carrier signal to obtain zero intermediate frequency data, and then code-combine the zero intermediate frequency signal to obtain half-code data;

[0031] Step 2: Use the data storage module to perform ping-pong storage on the merged chip data; use the Doppler stripping module to mix the stored chip data with the locally generated Doppler frequency, remove the Doppler frequency in the data, and obtain zero Doppler data;

[0032] Step 3: The zero Doppler data is folded step by step through a data folding module to obtain a 1 millisecond data block; the 1 millisecond data block is coherently correlated with a local pseudo code to obtain coherent values ​​of different code phases;

[0033] Step 4, performing Doppler compensation on the coherent data after passing through the inter-code difference module, and obtaining coherent data of different time lengths after passing through the step-by-step coherent module and the step-by-step incoherent module;

[0034] Step 5: Determine 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.

[0035] Furthermore, the inter-code difference and code parallel GPS weak signal acquisition method also includes:

[0036] The data folding module folds the 10 milliseconds data after Doppler stripping into 1 milliseconds data blocks one by one according to the corresponding code phase, and transmits the folded data blocks one by one to the step-by-step matching coherence module;

[0037] The step-by-step matching coherence module performs fast Fourier transform on the data blocks with different folding times, and multiplies them with the conjugate result of the fast Fourier transform of the local pseudo code; the complex multiplication result is inversely transformed by fast Fourier transform to obtain the coherence values ​​with different coherence time lengths, and the coherence values ​​are simultaneously sent to the inter-code difference module and the peak decision module;

[0038] The code difference module differentiates the coherent data obtained by the step-by-step matching coherent modules. The difference method adopts the code difference method, which takes the conjugate of one coherent value in the adjacent code phase and multiplies it with the other one, and sends the difference result to the Doppler compensation module.

[0039] The Doppler compensation module compensates for the code phase offset caused by the Doppler effect, aligns the differential result code phases with each other, and transmits the data to the progressive coherent module and the progressive incoherent module.

[0040] Furthermore, the inter-code difference and code parallel GPS weak signal acquisition method also includes:

[0041] The step-by-step coherent module and the step-by-step incoherent module perform K-times step-by-step accumulation and modulus on the corresponding positions of the results obtained by the Doppler compensation module to obtain coherent values ​​with different signal-to-noise ratios; the coherent accumulated value is modulo-accumulated L times step-by-step to obtain coherent data with different capture durations, and the data is transmitted to the peak decision module;

[0042] The peak decision module performs peak detection on the results obtained by the step-by-step matching coherent module, step-by-step coherent module and step-by-step incoherent module to determine whether the peak-to-average ratio exceeds the capture threshold. If the peak exceeds the threshold, it will enter the result output module; if it does not exceed the threshold, it will enter the Doppler search completion judgment module;

[0043] The Doppler search completion judgment module determines whether the Doppler frequency search is completed if the current satellite is not captured. If the search is completed, it enters the result output module; if the search is not completed, it enters the Doppler control module, adjusts the current Doppler frequency to be searched and transmits it to the Doppler stripping module; the result output module transmits the captured Doppler information, satellite number and code phase to the tracking module.

[0044] Furthermore, the inter-code difference module differentiates the coherence results of the code parallel search, and the differential method adopts the inter-code difference method, and differentiates the adjacent code phase coherence values ​​among the coherence values ​​of 2048 code phases to obtain a differential result with 2047 symbols fixed, and differentiates the first code phase coherence value and the 2048th code phase coherence value to obtain the 2048th differential result.

[0045] Furthermore, the step-by-step coherent module and the step-by-step incoherent module successively coherently and successively incoherently perform post-coherent results of Doppler compensation; different coherence times are used to obtain coherence values ​​of different coherence durations; and coherence values ​​of different durations are used to capture signals of different intensities.

[0046] Another object of the present invention is to provide a computer device, the computer device comprising a memory and a processor, the memory storing a computer program, and when the computer program is executed by the processor, the processor performs the following steps:

[0047] The baseband data and the locally generated carrier signal are mixed by the digital down-conversion module to obtain zero intermediate frequency data; the zero intermediate frequency signal is code-merged to obtain half-code data; the merged chip data is ping-pong stored by the data storage module; the stored chip data and the locally generated Doppler frequency are mixed by the Doppler stripping module to remove the Doppler frequency in the data to obtain zero Doppler data;

[0048] The zero Doppler data is folded step by step through the data folding module to obtain a 1 millisecond data block; the 1 millisecond data block is coherently matched with the local pseudo code using the step-by-step matching coherence module to obtain coherent values ​​of different code phases; the coherent data passing through the inter-code difference module is Doppler compensated using the Doppler compensation module, and coherent data of different durations are obtained through the step-by-step coherence module and the step-by-step incoherence module;

[0049] The peak value is used to determine whether the satellite signal is captured. 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 is used to determine whether to continue the capture until the current satellite is captured or all Doppler frequencies are searched.

[0050] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the following steps:

[0051] The baseband data and the locally generated carrier signal are mixed by the digital down-conversion module to obtain zero intermediate frequency data; the zero intermediate frequency signal is code-merged to obtain half-code data; the merged chip data is ping-pong stored by the data storage module; the stored chip data and the locally generated Doppler frequency are mixed by the Doppler stripping module to remove the Doppler frequency in the data to obtain zero Doppler data;

[0052] The zero Doppler data is folded step by step through the data folding module to obtain a 1 millisecond data block; the 1 millisecond data block is coherently matched with the local pseudo code using the step-by-step matching coherence module to obtain coherent values ​​of different code phases; the coherent data passing through the inter-code difference module is Doppler compensated using the Doppler compensation module, and coherent data of different durations are obtained through the step-by-step coherence module and the step-by-step incoherence module;

[0053] The peak value is used to determine whether the satellite signal is captured. 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 is used to determine whether to continue the capture until the current satellite is captured or all Doppler frequencies are searched.

[0054] Another object of the present invention is to provide an information data processing terminal, which is used to implement the inter-code difference and code parallel GPS weak signal acquisition system.

[0055] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0056] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, the technical solutions to be protected by the present invention and the results and data during the research and development process are closely combined to analyze in detail and deeply how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about after solving the problems. The specific description is as follows:

[0057] The step-by-step coherent module and the step-by-step incoherent module provided by the present invention successively coherently and successively incoherently perform post-coherence results of Doppler compensation, and coherence values ​​with different coherence durations can be obtained with different coherence times. The coherence values ​​with different durations can be used to capture signals of different intensities, and at the same time, the leakage of stronger signals can be prevented, thereby improving the capture probability of signals.

[0058] The present invention adopts the inter-code difference algorithm to avoid the influence of navigation data jump on the coherent integration time, and improves the capture sensitivity of GPS signals by increasing the coherent integration time. The present invention adopts the step-by-step coherent and step-by-step incoherent algorithms to achieve the rapid capture of signals of different strengths and shorten the first positioning time of the navigation receiver.

[0059] Second, considering 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 described in detail as follows:

[0060] The high-orbit GPS signal acquisition method based on inter-code difference and code parallelism provided by the present invention provides a fast and efficient acquisition algorithm for a navigation receiver.

[0061] Third, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0062] The technical solution of the present invention fills the technical gap in the industry at home and abroad: in order to avoid the influence of navigation data jumps on coherent integral symbols, traditional navigation receivers usually use incoherent accumulation to improve signal capture sensitivity, but incoherent accumulation will introduce square noise, inhibit the improvement of signal-to-noise ratio, and limit the capture sensitivity of navigation receivers. The present invention uses an inter-code difference algorithm to avoid the influence of navigation data jumps on coherent integral symbols, and improves the signal-to-noise ratio by continuing to coherently accumulate the differential results, thereby improving the capture sensitivity of GPS signals. At the same time, the present invention uses a step-by-step coherent and step-by-step incoherent method to capture signals of different intensities, which can greatly shorten the capture time and enable the receiver to quickly complete positioning and solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0064] Figure 1 It is a flow chart of a method for capturing weak GPS signals using code-to-code difference and code-to-code parallelism provided in an embodiment of the present invention;

[0065] Figure 2 It is a structural block diagram of a GPS weak signal acquisition system using inter-code difference and code parallelism provided by an embodiment of the present invention;

[0066] Figure 3 It is a block diagram of a step-by-step matching coherent structure provided by an embodiment of the present invention;

[0067] Figure 4 is a block diagram of an inter-code difference structure provided by an embodiment of the present invention;

[0068] Figure 5 This is a capture result diagram provided by an embodiment of the present invention when the signal strength is -149dBm;

[0069] Figure 6 This is a result diagram of different code phase coherence values ​​obtained by searching different Dopplers at a signal strength of -147 dBm provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0070] 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.

[0071] In view of the problems existing in the prior art, the present invention provides a method and system for capturing weak GPS signals using inter-code difference and code parallelism. The present invention is described in detail below in conjunction with the accompanying drawings.

[0072] 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.

[0073] like Figure 1 As shown, the GPS weak signal acquisition method using code difference and code parallelism provided in the embodiment of the present invention includes the following steps:

[0074] S101, using a digital down-conversion module to mix the baseband data and a locally generated carrier signal to obtain zero intermediate frequency data, and then code-combining the zero intermediate frequency signal to obtain half-code data;

[0075] S102, using a data storage module to perform ping-pong storage on the combined chip data; using a Doppler stripping module to mix the stored chip data with a locally generated Doppler frequency, remove the Doppler frequency in the data, and obtain zero Doppler data;

[0076] S103, the zero Doppler data is folded step by step through a data folding module to obtain a 1 millisecond data block; the 1 millisecond data block is coherently correlated with a local pseudo code to obtain coherent values ​​of different code phases;

[0077] S104, performing Doppler compensation on the coherent data passing through the inter-code difference module, and obtaining coherent data of different time lengths through the step-by-step coherent module and the step-by-step incoherent module;

[0078] S105, 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.

[0079] like Figure 2As shown, the high-orbit GPS signal acquisition system based on code difference and code parallelism provided by the embodiment of the present invention includes a digital down-conversion module, a code merging module, a data storage module, a Doppler stripping module, a data folding module, a step-by-step matching coherent module, an inter-code difference module, a Doppler compensation module, a step-by-step coherent module and a step-by-step incoherent module, a peak judgment module, a Doppler search completion judgment module, a Doppler control module and a result output module. The digital down-conversion module mixes the baseband data with the locally generated carrier signal to achieve the stripping of the residual carrier signal to obtain zero intermediate frequency data. The code merging module merges the zero intermediate frequency signal into half-code data by accumulation. The data storage module stores the merged chip data. In order to prevent data interruption, two RAMs are used to perform ping-pong storage on the data, and each RAM can store 10 milliseconds of data. The Doppler stripping module mixes the stored chip data with the locally generated Doppler frequency to remove the Doppler frequency in the data to obtain zero Doppler data. The data folding module folds the 10 millisecond zero Doppler data step by step to obtain 1 millisecond data blocks, thereby reducing the amount of calculation and improving the signal-to-noise ratio. The step-by-step matching coherence module uses FFT and IFFT to obtain the step-by-step folded data blocks obtained by the data folding module and the local pseudo-random coherence to obtain coherent data of different coherent durations. The inter-code difference module differentiates the coherent data of different code phases to avoid the influence of navigation data jumps on the coherent data symbols. The Doppler compensation module performs Doppler compensation on the differential data and corrects the code phase of the differential data according to the Doppler frequency. The step-by-step coherence module and the step-by-step incoherence module successively coherent and incoherent the Doppler compensated data to obtain coherent data of different capture durations. The peak decision module makes decisions on the coherent data results of different durations, finds the best code phase and the best Doppler, and determines whether the satellite signal is captured by the threshold value. The Doppler search completion judgment module determines whether the Doppler search of the current satellite is completed when the current capture process fails to capture the satellite signal. If the Doppler frequency search is completed, the capture process ends. If the Doppler frequency search is not completed, the remaining Doppler frequencies of the current satellite continue to be searched. The Doppler control module generates a Doppler control word based on the Doppler range to be searched, and generates the corresponding Doppler frequency through the Doppler control word. The result output module transmits the Doppler frequency, code phase, maximum value of coherent data and mean value of coherent data obtained at the end of the capture to the tracking module.

[0080] The step-by-step matching coherence module provided by the embodiment of the present invention performs code parallel coherence on data with different folding times and local pseudocode to obtain code parallel search results with different coherence durations, and includes: a data selector, used to select a data source to be processed by FFT, when the capture just starts, the data selector selects the data source as the local pseudocode; when the local pseudocode is processed, the data source is selected as the folded data, and the data source of the FFT core is selected and switched to realize the sharing of the FFT core, save processor resources, and transmit the selected data to the FFT module; the FFT module is used to convert the data with different folding times and the local pseudocode into the frequency domain through Fourier transform, The Fourier transform value of the local pseudo code is transmitted to the storage module, and the data with different folding times is transmitted to the complex multiplication module after Fourier transform; the storage module is used to store the FFT conjugate value of the local pseudo code, and transmit the data to the complex multiplication module when in use; the complex multiplication module is used to conjugate the Fourier transform value of the data and the Fourier transform value of the local pseudo code and multiply them, that is, use frequency domain multiplication instead of time domain convolution, and transmit the complex multiplication result to the IFFT module; the IFFT module is used to perform inverse Fourier transform on the complex multiplication result, that is, convert the coherent result from the frequency domain to the time domain, on the one hand, transmit the data to the code division module, and on the other hand, take the modulus of the data and transmit it to the peak decision module.

[0081] like Figure 3 As shown, the present invention adopts a step-by-step matching coherent method, mainly using FFT and IFFT to match data with local pseudocodes to achieve code parallel search. When the capture starts, the local pseudocode is selected by the data selector for FFT operation, and the FFT value of the local pseudocode is conjugate for storage. The data source is selected by the data selector to achieve the purpose of sharing the FFT core and saving resources. Data with different folding times will be sent to the FFT core for processing in sequence. For example, when the 1st millisecond data is read out from the 10 millisecond data storage RAM, the data will be stored in the folding RAM and sent to the FFT core at the same time. When the data of the 2nd millisecond is read out and the data of the 1st millisecond is accumulated, it will also be sent to the folding RAM and FFT core. By analogy, the folding data with different folding times will be processed by FFT. At the same time, the module will multiply the FFT values ​​of the data with different folding times with the stored local pseudocode FFT conjugate value, and the frequency domain coherence value will be obtained at this time. It is only necessary to perform IFFT transformation on the data at this time to convert the coherence value to the time domain. This processing method will obtain coherent data of different durations while realizing code parallel search. In subsequent operations, by performing peak detection on coherent data of different durations, rapid capture of signals of different intensities can be achieved.

[0082] The step-by-step coherent module and the step-by-step incoherent module provided in the embodiments of the present invention perform successive coherence and successive incoherence on the post-coherence results of Doppler compensation. Different coherence times can obtain coherence values ​​with different coherence durations. The coherence values ​​with different durations can be used to capture signals of different intensities. At the same time, it can prevent the leakage of stronger signals and improve the signal capture probability.

[0083] like Figure 4 As shown in the figure, the inter-code difference method is adopted, which mainly utilizes the fixed characteristics of the GPS code structure to differentiate the coherence values ​​of different phases to avoid the influence of navigation data jump on the coherence value symbol. The differential method adopts the inter-code difference method, that is, the adjacent code phase coherence values ​​are differentiated in the coherence values ​​of N code phases to obtain the differential result with N-1 symbols fixed, and finally the first code phase coherence value and the Nth code phase coherence value are differentiated to obtain the Nth differential result. The result symbol obtained by the inter-code difference method is not affected by the navigation data jump, and the signal-to-noise ratio can be improved by re-coherence to achieve the improvement of capture sensitivity.

[0084] The code difference module avoids the influence of navigation data jump on the coherent value symbol by differentiating the coherent results of code parallel search. The difference method adopts the code difference method, that is, the adjacent code phase coherent values ​​are differentiated in the 2048 code phase coherent values ​​to obtain the differential result with 2047 fixed symbols, and finally the first code phase coherent value and the 2048th code phase coherent value are differentiated to obtain the 2048th differential result.

[0085] 2. Application Examples: In order to prove the creativity and technical value of the technical solution of the present invention, this section provides application examples of the technical solution of the claims on specific products or related technologies.

[0086] The present invention realizes the capture of GPS signals through a programmable logic gate array (FPGA) and a DSP. First, the navigation receiver amplifies the signal sent by the satellite simulator and transmits the amplified signal to the radio frequency processing board. The radio frequency processing board will perform secondary amplification, filtering, and down-conversion processing on the signal in turn. At the same time, the down-conversion module has an automatic gain control function to meet the navigation receiver's capture requirements for signals of different strengths. After the signal of the radio frequency processing board is output, the analog-to-digital conversion module will convert it to obtain a digital signal.

[0087] When the DSP triggers the capture start signal, the FPGA will process the data signal. First, the digital signal is mixed with the locally generated intermediate frequency signal to remove the residual intermediate frequency signal in the data. Then, it is accumulated to obtain half-code data with a code rate of 2.048MHz, and the half-code data is stored. The storage uses two RAMs with a depth of 20480 for ping-pong storage to ensure that the data is not interrupted during the capture process. When the data in a RAM is full, it is read, and the read data is multiplied with the local Doppler frequency to remove the Doppler frequency in the data. Then it is folded step by step and cohered with the local pseudo code. The coherence uses FFT and IFFT to realize code parallel coherence in the frequency domain. The data blocks with different folding times and the coherence values ​​of the local code can detect strong signals of different strengths. After obtaining the coherence, it is differentially performed between codes to avoid the influence of navigation data jumps on the coherence value symbols. At this time, the differential data is Doppler compensated and then coherently integrated step by step to improve the signal-to-noise ratio of the signal. At the same time, the real-time coherent integration data is judged to see whether the satellite signal is captured. When the step-by-step coherence reaches a certain number of times, a small amount of incoherence is performed to improve the sensitivity of GPS signal capture. When the capture time meets the set time, the final coherent data is peak detected and judged to achieve the judgment of weak signal capture. In this process, the judgment module first judges the coherence value of different code phases under a single Doppler frequency, and then obtains the accurate Doppler frequency and code phase by judging the maximum coherence value in different Dopplers. At the end of the capture, the obtained Doppler frequency, code phase, maximum and average coherence value will be transmitted to the tracking module. At the same time, the DSP completes the rapid capture of all satellites by changing the satellite number and transmitting it to the capture module.

[0088] It should be noted that the embodiments of the present invention can be implemented by 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 design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as 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. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0089] 3. Evidence of the effects of the embodiments. The embodiments of the present invention have achieved some positive effects during the development or use process, and indeed have great advantages over the prior art. The following content is described in conjunction with the data, charts, etc. of the test process.

[0090] To verify the feasibility of the present invention, the satellite signal is first collected by the acquisition card for simulation verification. When the signal strength is -149dBm, the capture result is as follows: Figure 5 shown.

[0091] Depend on Figure 5 It can be seen that at the extreme sensitivity of -149 dBm, the algorithm in the present invention can still accurately capture GPS satellite signals.

[0092] At the same time, in order to verify the reliability of the navigation receiver, the navigation receiver is connected to the satellite signal simulator to capture the satellite signal in real time and output the coherent values ​​of different code phases, such as Figure 6 shown.

[0093] Figure 6 The figure shows different code phase coherence value results obtained by the navigation receiver searching for different Dopplers at a signal strength of -147dBm. It can be seen from the figure that the navigation receiver can still accurately capture satellite signals at this strength.

[0094] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A GPS weak signal acquisition system with code difference and code parallelism, characterized in that: The inter-code differential and code parallel GPS weak signal acquisition system comprises: The digital down-conversion module is used to perform digital down-conversion on the baseband data, remove the residual carrier in the data, obtain zero intermediate frequency data, and then transmit the data to the code combining module; A code combining module is used to accumulate and combine zero intermediate frequency data according to the sampling rate to obtain half code data, and send the data to the data storage module for storage; A data storage module is used to perform ping-pong storage of the obtained half-code data for 10 milliseconds, and the stored data is sent to the Doppler stripping module after being read out; A Doppler stripping module is used to perform Doppler stripping on the stored data in units of 10 milliseconds, remove the Doppler frequency in the data, and send the data to a data folding module; A data folding module is used to fold the 10 milliseconds of data after Doppler stripping into 1 millisecond data blocks one by one according to the corresponding code phase, and transmit the folded data blocks one by one to the step-by-step matching coherence module; The step-by-step matching coherence module is used to perform fast Fourier transform on the data blocks with different folding times, multiply them with the conjugate result of the fast Fourier transform of the local pseudo code, and then perform inverse fast Fourier transform on the complex multiplication result to obtain the coherence values ​​with different coherence time lengths, and then send the coherence values ​​to the inter-code difference module and the peak decision module at the same time; The code difference module is used to differentiate the coherent data obtained by the step-by-step matching coherent modules. The difference method adopts the code difference method, which takes the conjugate of one coherent value in the adjacent code phase and multiplies it with the other one, and sends the difference result to the Doppler compensation module; A Doppler compensation module is used to compensate for the code phase offset caused by the Doppler effect, so that the differential result code phases are aligned with each other, and then the data is transmitted to the step-by-step coherent module and the step-by-step incoherent module; The step-by-step coherent module and the step-by-step incoherent module are used to perform step-by-step accumulation K times and take the modulus at the corresponding position of the result obtained by the Doppler compensation module to obtain coherent values ​​with different signal-to-noise ratios; the coherent accumulated value is taken modulo and then accumulated step-by-step L times to obtain coherent data with different capture time lengths, and the data is transmitted to the peak decision module; The peak value judgment module is used to perform peak value detection on the results obtained by the step-by-step matching coherent module, the step-by-step coherent module and the step-by-step incoherent module to determine whether the peak-to-average ratio exceeds the capture threshold; if the peak value exceeds the threshold, it will enter the result output module; if it does not exceed the threshold, it will enter the Doppler search completion judgment module; The Doppler search completion judgment module is used to judge whether the Doppler frequency search is completed when the current satellite is not captured. If the search is completed, it will enter the result output module; if the search is not completed, it will enter the Doppler control module; The Doppler control module is used to control the Doppler frequency to be searched currently and transmit it to the Doppler stripping module; The result output module is used to transmit the captured Doppler information, satellite number and code phase to the tracking module.

2. The GPS weak signal acquisition system of inter-code difference and code parallelism as claimed in claim 1, characterized in that: The step-by-step matching coherence module performs code-parallel coherence on data with different folding times and local pseudocodes to obtain code-parallel search results with different coherence durations, including: The data selector is used to select the data source to be processed by FFT. When the capture starts, the data selector selects the data source as the local pseudo code. When the local pseudo code processing is completed, the data source is selected as the folded data, the data source of the FFT core is selected and switched, and the selected data is transmitted to the FFT unit. An FFT unit is used to convert the data with different folding times and the local pseudo code into the frequency domain through Fourier transform, transmit the Fourier transform value of the local pseudo code to the storage unit, and transmit the data with different folding times to the complex multiplication unit after Fourier transform; A storage unit, used to store the FFT conjugate value of the local pseudo code, and to send the data to the complex multiplication unit when in use; A complex multiplication unit is used to conjugate the Fourier transform value of the data and the Fourier transform value of the local pseudo code and then multiply them, use frequency domain multiplication instead of time domain convolution, and transmit the complex multiplication result to the IFFT unit; The IFFT unit is used to perform inverse Fourier transform on the complex multiplication result, convert the coherent result from the frequency domain to the time domain, transmit the data to the code division module, and transmit the data to the peak decision module after taking the modulus.

3. A method for capturing GPS weak signals using inter-code difference and code parallelism using the GPS weak signal capture system using inter-code difference and code parallelism as claimed in any one of claims 1 to 2, characterized in that: The GPS weak signal acquisition method using inter-code difference and code parallelism comprises the following steps: Step 1: Use a digital down-conversion module to mix the baseband data and the locally generated carrier signal to obtain zero intermediate frequency data, and then code combine the zero intermediate frequency signal to obtain half-code data; Step 2: Use the data storage module to perform ping-pong storage on the merged chip data; use the Doppler stripping module to mix the stored chip data with the locally generated Doppler frequency, remove the Doppler frequency in the data, and obtain zero Doppler data; Step 3: The zero Doppler data is folded step by step through a data folding module to obtain a 1 millisecond data block; the 1 millisecond data block is coherently correlated with a local pseudo code to obtain coherent values ​​of different code phases; Step 4, performing Doppler compensation on the coherent data after passing through the inter-code difference module, and obtaining coherent data of different time lengths after passing through the step-by-step coherent module and the step-by-step incoherent module; Step 5: Determine 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.

4. The method for capturing weak GPS signals by code-to-code difference and code-to-code parallelism as claimed in claim 3, characterized in that: The GPS weak signal acquisition method using inter-code difference and code parallelism also includes: The data folding module folds the 10 milliseconds data after Doppler stripping into 1 milliseconds data blocks one by one according to the corresponding code phase, and transmits the folded data blocks one by one to the step-by-step matching coherence module; The step-by-step matching coherence module performs fast Fourier transform on the data blocks with different folding times, and multiplies them with the conjugate result of the fast Fourier transform of the local pseudo code; the complex multiplication result is inversely transformed by fast Fourier transform to obtain the coherence values ​​with different coherence time lengths, and the coherence values ​​are simultaneously sent to the inter-code difference module and the peak decision module; The code difference module differentiates the coherent data obtained by the step-by-step matching coherent modules. The difference method adopts the code difference method, which takes the conjugate of one coherent value in the adjacent code phase and multiplies it with the other one, and sends the difference result to the Doppler compensation module. The Doppler compensation module compensates for the code phase offset caused by the Doppler effect, aligns the differential result code phases with each other, and transmits the data to the progressive coherent module and the progressive incoherent module.

5. The method for capturing weak GPS signals by code-to-code difference and code-to-code parallelism as claimed in claim 3, characterized in that: The GPS weak signal acquisition method using inter-code difference and code parallelism also includes: The step-by-step coherent module and the step-by-step incoherent module perform K-times step-by-step accumulation and modulus on the corresponding positions of the results obtained by the Doppler compensation module to obtain coherent values ​​with different signal-to-noise ratios; the coherent accumulated value is modulo-accumulated L times step-by-step to obtain coherent data with different capture durations, and the data is transmitted to the peak decision module; The peak decision module performs peak detection on the results obtained by the step-by-step matching coherent module, step-by-step coherent module and step-by-step incoherent module to determine whether the peak-to-average ratio exceeds the capture threshold. If the peak exceeds the threshold, it will enter the result output module; if it does not exceed the threshold, it will enter the Doppler search completion judgment module; The Doppler search completion judgment module determines whether the Doppler frequency search is completed if the current satellite is not captured. If the search is completed, it enters the result output module; if the search is not completed, it enters the Doppler control module, adjusts the current Doppler frequency to be searched and transmits it to the Doppler stripping module; the result output module transmits the captured Doppler information, satellite number and code phase to the tracking module.

6. The GPS weak signal acquisition method using code difference and code parallelism as claimed in claim 3, characterized in that: The inter-code difference module differentiates the coherent results of the code parallel search, and the difference method adopts the inter-code difference method. The adjacent code phase coherent values ​​are differentiated among the coherent values ​​of the 2048 code phases to obtain a differential result with 2047 symbols fixed, and the first code phase coherent value and the 2048th code phase coherent value are differentiated to obtain the 2048th differential result.

7. The GPS weak signal acquisition method using code difference and code parallelism as claimed in claim 3, characterized in that: The step-by-step coherent module and the step-by-step incoherent module successively coherently and incoherently perform post-coherence results of Doppler compensation; different coherence times are used to obtain coherence values ​​of different coherence durations; and coherence values ​​of different durations are used to capture signals of different intensities.

8. A computer device, characterized in that: 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 executes the steps of the GPS weak signal acquisition method of inter-code difference and code parallelism as described in claim 3.

9. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of the GPS weak signal acquisition method using inter-code difference and code parallelism as claimed in claim 3.

10. An information data processing terminal, characterized in that: The information data processing terminal is used to implement the inter-code difference and code parallel GPS weak signal acquisition system as described in any one of claims 1 to 2.

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