Software Receiver and Positioning Method for GNSS Carrier Phase Differential Positioning

Abstract

The present application provides a software receiver for GNSS carrier phase differential positioning, comprising: a signal receiving module, configured to receive satellite signals and generate digital signals after analog-to-digital conversion; a signal processing module, configured to perform acquisition, pre-bit synchronization before tracking, and tracking on the digital signals to obtain signal synchronization parameters and signal tracking results of the satellite signals, the signal synchronization parameters including carrier phase, pseudo-code phase, and Doppler frequency; an information processing module, configured to demodulate the message in the signal tracking results and extract the message time information; an observable extraction module, configured to calculate the original observables of the satellite signals according to the signal synchronization parameters and the message time information, and calculate the estimated observables corresponding to the local extraction time of the corresponding software receiver according to the original observables, the estimated observables including pseudo-range, Doppler frequency, and integrated Doppler; and a positioning and solution module, configured to perform carrier phase differential positioning and solution according to the pseudo-range, Doppler frequency, and integrated Doppler of the estimated observables.

Description

Technical Field

[0001] This specification generally relates to the technical field of navigation and positioning, and particularly relates to a software receiver for GNSS carrier phase differential positioning and a positioning method. Background Art

[0002] The Global Navigation Satellite System (GNSS) has been continuously developing, and six navigation systems have been formed, namely the Global Positioning System (GPS) of the United States, the Beidou Navigation System (BDS) of China, GLONASS of Russia, Galileo of Europe, the Quasi-Zenith Satellite System (QZSS) of Japan, and the Indian Regional Navigation Satellite System (IRNSS). Each satellite navigation system is still evolving, innovating on the original signal system, and releasing new navigation signal frequencies and formats; at the same time, the service fields of satellite navigation technologies are continuously expanding, and the demand for high-precision positioning is getting higher and higher, requiring GNSS receivers to have the ability of differential positioning or precise point positioning. These new requirements force GNSS receivers to upgrade algorithms to increase functions and improve performance. However, traditional hardware receivers are restricted by elements such as filtering bandwidth, sampling rate, and interruption mechanism, with strong design specificity and poor scalability, resulting in an uncertain development cycle and uncontrollable R & D costs.

[0003] A GNSS software receiver is a receiver based on the idea of software radio, which has more flexible development scalability and more efficient development iteration ability compared with traditional hardware receivers. A GNSS software receiver can implement all modules such as baseband signal processing, generation of raw observables, positioning solution, and differential positioning by software, developed using C / C++ language, and running on a computer (Personal Computer) platform, overcoming the problem of insufficient scalability of the hardware architecture of hardware receivers, and being able to effectively control the development cycle and cost.

[0004] A GNSS software receiver needs to use a GNSS antenna and a radio frequency front end to complete the transformation of radio frequency analog signals into digital intermediate frequency signals. After the signal transformation, a digital intermediate frequency data acquisition card is used to collect digital signals, and the collected data is stored in a hard disk, and then the software receiver completes baseband signal processing, generation of raw observables, positioning solution, etc.

[0005] Carrier phase differential positioning technology is a high-precision positioning technology, which is based on processing the carrier phase measurement values of two receivers. To distinguish between the two receivers, one receiver is called the reference station and the other is called the user receiver. Carrier phase differential positioning requires obtaining the observation information of the reference station, and eliminating the measurement errors in the observation values through the differential combination of the carrier phase measurement values of the user receiver and the reference station. There are three models for differential combination, namely single difference, double difference, and triple difference. The accuracy of carrier phase differential positioning is very high, and it can reach the centimeter level.

[0006] Currently, most technical solutions of software receivers only focus on the quality of pseudorange in the generation of original observations, and do not conduct in-depth research on the quality of carrier phase; some technical solutions have the ability to generate and differentiate carrier phases, but the number of available carrier phases is small, and the success rate of achieving centimeter-level positioning accuracy is low. Summary of the Invention

[0007] In order to solve the technical problems in the prior art, the present application provides a software receiver for GNSS carrier phase differential positioning, which has the ability of carrier phase differential positioning and can achieve centimeter-level positioning accuracy under static conditions.

[0008] An embodiment of the present application discloses a software receiver for GNSS carrier phase differential positioning, including:

[0009] A signal receiving module, configured to receive satellite signals and generate digital signals after digital-to-analog conversion;

[0010] A signal processing module, configured to capture, perform pre-bit synchronization before tracking, and track the digital signals to obtain the signal synchronization parameters and signal tracking results of the satellite signals, where the signal synchronization parameters include carrier phase, pseudo-code phase, and Doppler frequency;

[0011] An information processing module, configured to demodulate the message of the signal tracking result and extract the message time information;

[0012] An observation extraction module, configured to calculate the original observations of the satellite signals according to the signal synchronization parameters and the message time information, and calculate the estimated observations corresponding to the local extraction time of the software receiver through an interpolation algorithm according to the original observations of the satellite signals. The estimated observations include pseudorange, Doppler frequency, and integrated Doppler;

[0013] A positioning solution module, configured to perform carrier phase differential positioning solution according to the pseudorange, Doppler frequency, and integrated Doppler of the estimated observations.

[0014] In a preferred example, the software receiver is a multi-mode navigation software receiver, and the signal receiving module is used to receive multi-mode satellite signals and generate multiple digital signals after digital-to-analog conversion according to the satellite signal frequency.

[0015] In a preferred example, the signal processing module further includes:

[0016] A capture module, used to capture the digital signal using a parallel code phase capture algorithm to obtain a rough estimate of the pseudo code phase and a rough estimate of the Doppler frequency;

[0017] A pre-tracking bit synchronization module, used for performing pre-tracking bit synchronization on the digital signal by using a frequency estimation algorithm combined with a maximum likelihood estimation algorithm to obtain a bit boundary of the digital signal;

[0018] The tracking module is used to generate a coherent integral according to the estimated value of the pseudo code phase and the rough estimated value of the Doppler frequency to obtain the signal synchronization parameter and the signal tracking result.

[0019] In a preferred example, the pre-tracking bit synchronization module is also used to determine whether the pre-tracking bit synchronization is successful. If successful, the tracking module performs coherent integration of one bit period to obtain the three-way correlation cumulative value of the leading path, the immediate path and the lagging path. If unsuccessful, the tracking module performs coherent integration of one pseudocode period to obtain the three-way correlation cumulative value of the leading path, the immediate path and the lagging path.

[0020] In a preferred example, the satellite signal includes the GPS L1 frequency and / or the Beidou B1I frequency, wherein when the pre-tracking bit synchronization is successful, the integration time used by the GPS L1 frequency and / or the Beidou B1I frequency is 20ms; when the pre-tracking bit synchronization is unsuccessful, the integration time used by the GPS L1 frequency and / or the Beidou B1I frequency is 1ms.

[0021] In a preferred example, when the bit synchronization before tracking is unsuccessful, the bit synchronization is completed according to the maximum likelihood estimation algorithm during the tracking process to obtain the bit boundary of the digital signal, and the coherent integration of one pseudo code period is changed to the coherent integration of one bit period.

[0022] In a preferred example, the observed quantity extraction module is further used for:

[0023] The starting time of each pseudo code cycle and the original observation amount corresponding to the starting time of each pseudo code cycle are calculated according to the signal synchronization parameter and the message time information, and the estimated observation amount corresponding to the local extraction time of the software receiver is calculated according to the interpolation algorithm, wherein the local extraction time is the selected estimated observation amount extraction generation time, wherein the interpolation algorithm includes:

[0024] Determine the start times of two pseudo-code periods according to the local extraction time, where the start times of the two pseudo-code periods are respectively the start times of the pseudo-code periods closest to and after the local extraction time; and

[0025] Interpolate the estimated observation corresponding to the local extraction time from the original observations corresponding to the start times of the two pseudo-code periods.

[0026] In a preferred example, the observation extraction module is further configured to:[[]]

[0027] Discriminate the quality of the original observations through a signal quality criterion, thereby discriminating the quality of the estimated observations, where the signal quality criterion is obtained through the phase error statistical value output by the phase discriminator, the signal energy parameter, and the carrier-to-noise ratio;

[0028] Wherein, the phase discriminator is the carrier phase discriminator in the tracking module, which is used to discriminate the phase difference between the input signal and the output signal of the tracking module, and the phase error statistical value is obtained through the expectation and maximum value of the absolute value of the phase difference output by the phase discriminator;

[0029] The signal energy parameter is obtained through the coherent integration output by the tracking module.

[0030] In a preferred example, frame the pseudorange, Doppler frequency, and integrated Doppler at the generation time of the estimated observation deduced according to the interpolation algorithm, and write them into the original observation file.

[0031] Another embodiment of the present application also discloses a positioning method for a software receiver based on GNSS carrier phase differential positioning, including:[[]]

[0032] Receive multi-mode satellite signals, input them in parallel according to the signal frequency points, and generate multiple digital signals after digital-to-analog conversion;

[0033] Capture, perform pre-bit synchronization before tracking, and track the multiple digital signals to obtain signal synchronization parameters, where the signal synchronization parameters include accurate estimated values of carrier phase, pseudo-code phase, and Doppler frequency;

[0034] Demodulate the message from the result of the tracking output and extract the time information and ephemeris parameters;

[0035] Calculate the pseudorange, Doppler frequency, and integrated Doppler corresponding to the selected local extraction time;

[0036] Perform RTK positioning calculation according to the transmission time, Doppler frequency, integrated Doppler of the satellite signal, and the differential information provided by the external reference station.

[0037] In a preferred example, the steps of capturing the multiplex digital signals, performing pre-bit synchronization and tracking, and obtaining signal synchronization parameters further include:

[0038] Capture the digital signals by using a parallel code phase capture algorithm to obtain a rough estimate of the pseudo-code phase and a rough estimate of the Doppler frequency;

[0039] Perform pre-bit synchronization on the digital signals by using a frequency estimation algorithm in combination with a maximum likelihood estimation algorithm to obtain the bit boundary of the digital signals;

[0040] Generate a coherent integration according to the estimated value of the pseudo-code phase and the rough estimate of the Doppler frequency to obtain the signal synchronization parameters and the signal tracking result.

[0041] In a preferred example, the method further includes: determining whether the pre-bit synchronization is successful. If successful, perform a coherent integration for one bit period to obtain the correlation accumulation values of the early path, the prompt path, and the late path. If not successful, perform a coherent integration for one pseudo-code period to obtain the correlation accumulation values of the early path, the prompt path, and the late path.

[0042] In a preferred example, when the pre-bit synchronization is not successful, complete the bit synchronization according to the maximum likelihood estimation algorithm during the tracking process to obtain the bit boundary of the digital signals, and change the coherent integration for one pseudo-code period to the coherent integration for one bit period.

[0043] In a preferred example, the steps of calculating the pseudo-range, Doppler frequency, and integrated Doppler corresponding to the selected local extraction time further include:

[0044] Calculate the start time of each pseudo-code period and the original observation corresponding to the start time of each pseudo-code period according to the signal synchronization parameters and the message time information, and deduce the estimated observation corresponding to the local extraction time of the software receiver according to the interpolation algorithm. Wherein, the local extraction time is the generation time of the selected estimated observation, and the interpolation algorithm includes:

[0045] Determine two start times of pseudo-code periods according to the local extraction time, and the two start times of pseudo-code periods are respectively the start times of the pseudo-code periods closest to and after the local extraction time; and

[0046] Interpolate the estimated observation corresponding to the local extraction time according to the original observations corresponding to the two start times of the pseudo-code periods.

[0047] In a preferred example, the method further includes:

[0048] The quality of the original observation quantity is judged by a signal quality criterion, so as to judge the quality of the estimated observation quantity. The signal quality criterion is obtained from the phase error statistical value output by a phase discriminator, a signal energy parameter, and a carrier-to-noise ratio.

[0049] Among them, the phase discriminator is the carrier phase discriminator in the tracking module, which is used to discriminate the phase difference between the input signal and the output signal of the tracking module. The phase error statistical value is obtained from the expectation and maximum value of the absolute value of the phase difference output by the phase discriminator.

[0050] The signal energy parameter is obtained by coherent integration output by the tracking module.

[0051] Compared with the prior art, the present application has the following beneficial effects:

[0052] Compared with the current software receiver solution, the present invention supports the generation of carrier phases and differential positioning for the three systems of GPS, Beidou, and Galileo, and can be adapted to any two systems at the same time. The quantity and quality of the carrier phase observation quantities fully meet the requirements of all-weather precise differential positioning, and have the high-precision positioning ability of being accurate, stable, and independently controllable.

[0053] A large number of technical features are recorded in this specification, distributed in various technical solutions. If all possible combinations of technical features (i.e., technical solutions) of the present application are to be listed, the specification will be too long. To avoid this problem, each technical feature disclosed in the above-mentioned invention content of this specification, each technical feature disclosed in the following embodiments and examples, and each technical feature disclosed in the drawings can be freely combined with each other to form various new technical solutions (these technical solutions should all be regarded as having been recorded in this specification), unless the combination of such technical features is technically infeasible. For example, in one example, features A+B+C are disclosed, and in another example, features A+B+D+E are disclosed. Features C and D are equivalent technical means that play the same role, and only one of them can be used technically and it is impossible to use both at the same time. Feature E can be combined with feature C technically. Then, the solution of A+B+C+D should not be regarded as having been recorded because it is technically infeasible, and the solution of A+B+C+E should be regarded as having been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The non-limiting and non-exhaustive embodiments of the present application are described with reference to the following drawings, in which the same reference numerals refer to the same parts in each view unless otherwise specified.

[0055] Figure 1 It is a block diagram of a software receiver for GNSS carrier phase differential positioning according to the first embodiment of this specification.

[0056] Figure 2 is a block diagram of a signal processing module according to the first embodiment of this specification.

[0057] Figure 3 is a block diagram of a software receiver according to an embodiment of this specification.

[0058] Figure 4 is a flowchart of the specific steps for positioning calculation based on a software receiver according to an embodiment of this specification.

[0059] Figure 5 is a flowchart of bit synchronization before tracking satellite signals according to an embodiment of this specification.

[0060] Figure 6 is a flowchart of bit synchronization and tracking before tracking satellite signals according to an embodiment of this specification.

[0061] Figure 7 is a flowchart of generating raw observables according to an embodiment of this specification.

[0062] Figure 8 is a timing block diagram of generating raw observables according to an embodiment of this specification.

[0063] Figure 9 is a flowchart of a positioning method for a software receiver based on GNSS carrier phase differential positioning according to the second embodiment of this specification. Specific Embodiments

[0064] In the following description, many technical details are provided to help readers better understand this application. However, those of ordinary skill in the art can understand that the claimed technical solution of this application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0065] Some innovations in the embodiments of this application are as follows:

[0066] In view of the different processing mechanisms of software receivers and hardware receivers, corresponding carrier phase generation methods and calculation methods are designed to ensure the rationality of carrier phase generation. In the present invention, the baseband signal processing can be adapted to the GPS, Beidou, and Galileo systems, or any combination of any two of these systems. In baseband processing, the available number of satellites can be increased by using bit synchronization before tracking; in carrier phase generation, quality control measures can be added to improve the quality of carrier phase observations. Therefore, the technical solution of the present invention has the ability to stably, accurately, and reliably generate and differentiate carrier phases, and thus has centimeter-level positioning ability.

[0067] To make the objectives, technical solutions, and advantages of this application more clear, the following will further describe in detail the implementation manners of this application with reference to the accompanying drawings.

[0068] In the first implementation manner of this application, a software receiver for GNSS carrier phase differential positioning is disclosed. Figure 1 The block diagram of the software receiver 100 is shown, including: a signal receiving module 101, a signal processing module 102, an information processing module 103, an observable extraction module 104, and a positioning and solution module 105.

[0069] The signal receiving module 101 is used to receive satellite signals and generate digital signals after digital-to-analog conversion. In one embodiment, the software receiver 100 is a multi-mode navigation software receiver, and the signal receiving module 101 is used to receive multi-mode satellite signals and generate multiple digital signals after digital-to-analog conversion by frequency division according to the satellite signal frequency points. In one embodiment, the satellite signals include the GPS L1 frequency point and the Beidou B1I frequency point.

[0070] The signal processing module 102 is used to capture, perform pre-tracking bit synchronization, and track the digital signal to obtain the signal synchronization parameters and signal tracking results of the satellite signal. The signal synchronization parameters include carrier phase, pseudo-code phase, and Doppler frequency.

[0071] In one embodiment, referring to Figure 2 as shown, the signal processing module 102 further includes: a capture module 1021, a pre-tracking bit synchronization module 1022, and a tracking module 1023. The capture module 1021 is used, for example, to capture the digital signal by using a parallel code phase capture algorithm to obtain a rough estimate of the pseudo-code phase and a rough estimate of the Doppler frequency. The pre-tracking bit synchronization module 1022 is used to perform bit synchronization on the digital signal by using a frequency estimation algorithm combined with a maximum likelihood estimation algorithm to obtain the bit boundary of the digital signal. The tracking module 1023 is used to generate a coherent integration according to the estimated value of the pseudo-code phase and the rough estimate of the Doppler frequency to obtain the signal synchronization parameters and signal tracking results. The steps executed by the pre-tracking bit synchronization module are processed before the steps supported by the tracking module, which can be beneficial for obtaining the bit boundary, using long-time coherent integration, reducing noise, improving tracking sensitivity, and increasing the number of available satellites.

[0072] In one embodiment, as Figure 6As shown, the pre-tracking bit synchronization module 1022 is further configured to determine whether bit synchronization is successful before the tracking process. If successful, coherent integration for one bit period (e.g., 20 milliseconds) is performed to obtain the correlation accumulation values of the early path, the prompt path, and the late path. If not successful, coherent integration for one pseudo-code period (e.g., 1 millisecond) is performed to obtain the correlation accumulation values of the early path, the prompt path, and the late path. Specifically, in one embodiment, the satellite signal includes the GPS L1 frequency band and / or the Beidou B1I frequency band. When the pre-tracking bit synchronization is successful, the integration time for the GPS L1 frequency band and / or the Beidou B1I frequency band is 20 ms. When the pre-tracking bit synchronization is not successful, the integration time for the GPS L1 frequency band and / or the Beidou B1I frequency band is 1 ms. The three-way correlation accumulation value herein can also be replaced by a five-way correlation accumulation value, etc., and the present invention is not limited thereto.

[0073] Moreover, when the pre-tracking bit synchronization is not successful, bit synchronization needs to be completed according to the maximum likelihood estimation algorithm during the tracking process to obtain the bit boundary of the digital signal, and the coherent integration for one pseudo-code period is changed to the coherent integration for one bit period.

[0074] In one embodiment, the information processing module 103 is configured to demodulate the signal tracking result and extract the message time information.

[0075] The observable extraction module 104 calculates the original observables of the satellite signal according to the signal synchronization parameters and the message time information, and calculates the estimated observables corresponding to the local extraction time of the software receiver according to the original observables of the satellite signal. The estimated observables include pseudorange, Doppler frequency, and integrated Doppler. In one embodiment, the observable extraction module 104 is further configured to: calculate the original observables at the start time of each pseudo-code period according to the signal synchronization parameters and the message time information, and deduce the estimated observables corresponding to the local extraction time of the software receiver according to the linear interpolation algorithm, where the local extraction time is the generated time of the selected estimated observable. In one embodiment, the satellite transmission time, Doppler frequency, and integrated Doppler at the generated time of the estimated observable deduced according to the linear interpolation algorithm are framed and written into the original observable file.

[0076] In one embodiment, the positioning and solution module 105 is configured to perform carrier phase differential positioning and solution according to the pseudorange, Doppler frequency, and integrated Doppler of the estimated observables.

[0077] To better understand the technical solutions of this specification, a specific example is described below. The details listed in this example are mainly for easy understanding and do not limit the protection scope of this application.

[0078] I. Composition of Multimode GNSS Software Receiver

[0079] The multimode GNSS software receiver according to an embodiment of the present invention includes a GNSS multimode antenna, a radio frequency front end, and a general computer. The composition block diagram of the software receiver is shown in Figure 3 the figure. Among them, the antenna and the radio frequency front end are used to implement the functions of the signal receiving module, while the functions of the signal processing module, the information processing module, the observable extraction module, and the positioning and solution module can all be implemented on the general computer.

[0080] The GNSS multimode antenna has the ability to receive signals from navigation systems such as GPS, Beidou, and Galileo. The radio frequency front end adopts a configurable dual-channel digital intermediate frequency architecture and simultaneously receives two radio frequency signals, namely GPS L1 / Galileo E1 (1575.42 MHz) and Beidou B1I (1561.098 MHz). The general computer uses software programming to implement baseband processing and carrier phase differential positioning. The processing flow block diagram is shown in Figure 4 the figure. The baseband processing is divided into two parts: signal processing and information processing. Signal processing refers to the signal processing of the carrier and the pseudo-code to obtain signal synchronization parameters and signal tracking results, including: pseudo-code phase, carrier Doppler frequency, carrier phase, etc. Information processing refers to demodulating the navigation message from the correlation values of the signal tracking results. For example, time information and ephemeris parameters are extracted from the navigation message, and raw observables such as pseudo-range and integrated Doppler are extracted from the signal synchronization parameters. Carrier phase differential positioning can be completed through the raw observables provided by the baseband processing and the differential information provided by an external reference station.

[0081] II. Specific Steps of Signal Reception and Processing, Information Processing, Observable Extraction, and Positioning and Solution

[0082] 1. The GNSS multimode antenna receives GPS L1, BD B1I, and GAL E1 signals. The received satellite signals are output in two paths. After being amplified by an active low-noise amplifier, the signals are connected to two independent channels of the radio frequency front end.

[0083] 2. One of the two channels of the radio frequency front end supports the GPS L1 / GAL E1 frequency point, and the other supports the BD B1I frequency point. The radio frequency front end first completes the quadrature down-conversion of the analog radio frequency signal to generate two intermediate frequency analog signals, namely I and Q; then completes the analog-to-digital conversion and digital down-conversion to convert the I and Q intermediate frequency analog signals into I and Q intermediate frequency digital signals; finally, through the data acquisition card in the radio frequency front end, the converted intermediate frequency digital signals are stored in the hard disk in the form of data files.

[0084] 3. After the general computer reads the stored data file, it can pre-process the signal according to the data format of different intermediate frequency signals to generate a unified complex data format, with I and Q channels occupying 8 bits each. After signal pre-processing, capture, tracking, telegram demodulation, original observation quantity generation, and carrier phase differential positioning solution are completed in sequence.

[0085] a) Satellite capture

[0086] In one embodiment of the present invention, the software receiver adopts a parallel code phase acquisition algorithm, which uses the property that the time domain convolution of the signal is equivalent to the frequency domain multiplication, see formula (1), to quickly complete the search of the pseudo code phase dimension. The parallel code phase searches the phase dimension in one dimension at one time, but the search of the frequency dimension is still serial.

[0087] x(k)*code(k)=IFFT[FFT * {x(k)}·FFT{code(k)}} (1)

[0088] Where code(k) is the local pseudo code, x(k) is the digital intermediate frequency signal, and FFT represents Fourier transform.

[0089] b) Tracking the previous bit synchronization

[0090] like Figure 5 As shown in the figure, the purpose of completing bit synchronization before tracking is to improve the tracking sensitivity of the signal and increase the number of available satellites; at the same time, it can reduce loop noise and improve the tracking quality of the carrier phase. For different satellite navigation systems, the processing of bit synchronization before tracking is different. Thanks to the design of the signal system, the GAL E1 signal has been synchronized after successful capture, so there is generally no need to perform synchronization specifically, and this step can be skipped directly. After the coherent integration of one pseudo code time for GPS L1 and BD B1I is completed, DFT (Discrete Fourier Transformation) frequency rotation is used to combine maximum likelihood estimation to complete fine frequency deviation estimation and bit synchronization. After the bit synchronization is successful, the coherent integration time reaches one bit duration (GPS L1 20ms, BD B1I non-GEO 20ms, GEO 2ms), and the frequency deviation is precisely estimated through DFT frequency rotation, and a tracking loop with a bit duration is entered; after the bit synchronization timeout fails, a tracking loop with a pseudo code cycle duration is entered.

[0091] The flowchart of DFT frequency rotation joint maximum likelihood estimation is shown in Figure 5 As shown, the implementation steps are as follows:

[0092] I. The coherent integration of one pseudo-code period is completed using the DFT method to perform frequency translation, i.e., frequency conversion. The expression for multiplying the coherent integration with complex carriers of M different translation frequencies is as follows (2), and M paths of coherent accumulation values are obtained.

[0093]

[0094] In the formula The variance is consistent with N i and the signal-to-noise ratio of each path of the signal remains unchanged. m = 0 to M - 1

[0095] II. The output of each path of coherent accumulation value is divided into K groups, with 20 data in each group. The 20 data bits within the group represent 20 bit positions. Each data group is subjected to matched filtering, and the result of the output of the matched filter for each data group is expressed as formula (3):

[0096]

[0097] In the formula, h l is the matched filter coefficient. For GPS L1, it is all 1. For the BD B1I non-GEO signal, it is the NH sequence in B1IICD. k is the data group serial number, k = 0 to K - 1, δ = 0 to 19 represents the bit positions, and m is the frequency point serial number after frequency conversion.

[0098] III. For the results of the matched filtering of the K groups of data, the envelope accumulation expression according to the bit position correspondence is as (4):

[0099]

[0100] The value H δ，m after envelope accumulation is subjected to joint frequency and bit position search, and the frequency point and bit position corresponding to the maximum value are selected as the estimated values.

[0101] IV. For the verification of the estimated results, the result of the matched filtering of the frequency point and bit position corresponding to the maximum value should be equal to 20. If the verification is successful, the success flag and the estimated value are output. If the detection fails, the failure flag is output.

[0102] c) Tracking

[0103] The purpose of tracking is to obtain signal synchronization information such as the precise carrier phase and pseudo-code phase of the satellite signal. This software receiver uses a frequency-locked loop (FLL), a phase-locked loop (PLL), and a delay-locked loop (DLL) on the carrier to stably track the satellite signal. The software flow chart is shown in Figure 6, and the specific implementation steps are as follows:

[0104] First, after successful capture, the digital intermediate-frequency signal is multiplied by the local carrier containing the roughly estimated Doppler frequency, and then multiplied by the local code with the roughly estimated code phase. There is formula (5):

[0105]

[0106] In the formula, c[kT s +τ] is the local pseudo-code sequence, τ is the phase difference between the input pseudo-code and the local pseudo-code, is the Doppler frequency shift roughly estimated by the capture module.

[0107] Second, perform coherent integration on the digital intermediate-frequency signal after successful capture for a pseudo-code period time, and the integration time is T I . For GPS L1 and BD B1I, the integration time in this step is 1 ms; for GAL E1, the integration time is 4 ms. The integration output result is shown in formula (6)

[0108]

[0109] In the formula, M is the total number of sampling points within the integration time, is the complex Gaussian white noise sequence output by the correlator, and L is the correlator cumulative loss caused by the residual code phase and Doppler frequency offset. The expression is: Among them is the coherent integration loss caused by the Doppler frequency offset. R(τ) is the spreading code autocorrelation function. When the code phase difference is within one chip range, the correlation value is a linear function of the phase difference.

[0110] Third, the signal enters the tracking loop stage. In an embodiment of the present invention, the phase-locked loop theory is used to complete the estimation of the code phase, carrier frequency, and carrier phase. In order to provide accurate carrier phase observables, an embodiment of the present invention uses the frequency-locked loop and phase-locked loop working schemes to complete signal tracking. The loop working scheme and steps are as follows:

[0111] I. After the intermediate-frequency digital signal is multiplied by the local carrier, it is then multiplied by the early (E), prompt (P), and late (L) three-way local pseudo-codes respectively; according to the synchronization check flag obtained in the third step, select the accumulation time, complete coherent accumulation, and obtain the E, P, and L three-way correlation values, the early, prompt, and late paths

[0112] II. Obtain the estimation of the three parameters of the output signal of the correlator through the FLL, PLL loops, and DLL loops. The estimation equations are as follows in formulas (7)-(9).

[0113]

[0114]

[0115]

[0116] Among them, Equation (10) and (11) represent the carrier loop, and Equation (12) represents the chip loop. These loops are negative feedback loops composed of a parameter residual discriminator, a filter, and a numerically controlled oscillator. The technical solution of the present invention adopts the classical theory for the FLL and PLL loop algorithms.

[0117] III. Obtain the corrected values of the carrier and frequency through the PLL and DLL loops, and then calculate the carrier phase and pseudorange phase at the starting position of the next coherent integration time data as shown in Equations (10)-(11):

[0118] θ carrier (n + 1) = θ carrier (n) + j·2π*f carrier (n + 1)·T coh (10)

[0119] τ code (n + 1) = τ code (n) + f code (n + 1)·T coh (11)

[0120] Among them, θ carrier (n) and τ code (n) represent the carrier phase and the pseudocode phase at the nth coherent integration period respectively, f carrier (n) is the carrier frequency corrected by the PLL loop, and f code is the pseudocode frequency corrected by the DLL loop. Repeat the operations in steps i-iii, and the parameter residuals in the PLL and DLL loops converge to achieve signal tracking.

[0121] c) Pseudorange and carrier phase extraction

[0122] In an embodiment of the present invention, the method for extracting the pseudorange and carrier phase of the software receiver is very different from that of the traditional receiver. In the traditional receiver, the observations of all channels are simultaneously latched under the trigger of the observation interruption to ensure the time consistency of the observations of each channel. In an embodiment of the software receiver of the present invention, the generation time of the pseudorange and carrier phase can be at any time, and the signal transmission time, Doppler frequency shift, and carrier phase of each satellite at this time are calculated; the software receiver uses the processing mechanism of data slices, and the observed value of the carrier phase can be recorded immediately after power-on to output an accurate carrier phase measurement value. The flowchart of the generation of the original observations is as Figure 7 shown, and the timing block diagram is as Figure 8 shown, and the implementation process is as follows:

[0123] First, obtain the transmission time of the start point of the received first-frame data. During frame synchronization operation, the TOW (seconds within a week) and the local recording time N where the TOW frame header is located can be obtained. tow The local recording time refers to the time of the software receiver. The local recording time may not be consistent with the time recorded on the satellite (including the telemetry sent by the satellite), and there is a fixed deviation. The transmission time, such as the transmission time of the start point of the first-frame data, the transmission time of the start point of the pseudo-code period data, etc., all refer to the time recorded on the satellite.

[0124] Second, obtain the transmission time of the start point of the nth pseudo-code period data, the integrated Doppler, and the local recording time corresponding to the transmission time of the start point of the pseudo-code period data. Calculate the transmission time of the start point of each pseudo-code period data, the integrated Doppler, and the local recording time corresponding to the transmission time of the start point of the pseudo-code period data from the start point of the first-frame data. That is, as shown in the following formulas (12)-(14). Through the satellite transmission time, the pseudo-range can be calculated, that is, as shown in the following formula (15).

[0125]

[0126]

[0127]

[0128]

[0129] Where is the satellite transmission time at the start moment of the nth pseudo-code period data, TOW is the seconds within a week of the first frame, T code is a pseudo-code period, Integrated Doppler, f d，n is the Doppler frequency shift given by the carrier loop at the current moment, is the local recording time corresponding to the start moment of the nth pseudo-code period data, τ code，n is the residual phase of the pseudo-code at the current moment, f code，n is the code frequency correction value given by the delay lock loop at the current moment, is the pseudo-range at the current moment, and c is the speed of light.

[0130] Third, select the local extraction time at the generation moment of the original observables (software receiver), that is, the generation and extraction time of the pseudo-range and the carrier phase.

[0131] Fourth, calculate the generation moment of the original observables For example, the original observations at the start of each pseudo code cycle are calculated based on the signal synchronization parameters and the message time information, and the estimated observations of the local extraction time of the corresponding software receiver are calculated based on the linear interpolation algorithm. First, calculate arrive The offset is calculated according to the first-order Taylor expansion (16). The transmission time, Doppler frequency shift, and integrated Doppler are as shown in equations (17)-(19), and then the time is generated by the original observation and satellite launch time Calculate the pseudorange into formula (20):

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] in, is the integral of the carrier phase,

[0138] Because there is a clear conversion relationship between pseudorange and the transmission time of satellite signals (such as formula 15), the concept of "pseudorange" in the application document includes "the transmission time of satellite signals".

[0139] Fifth, since the software receiver adopts a data slice processing mechanism, the time t0 here is the power-on time. Therefore, a quality control scheme can be added to ensure the quality of the output carrier phase observation values. The quality control scheme determines whether the carrier phase is available by judging the quality of signal tracking. The criteria for signal tracking quality consist of, for example, the loop state, the statistical values of the phase error output by the phase discriminator (expected value of the absolute value, maximum value), the signal energy parameter, and the carrier-to-noise ratio. The statistical values of the phase error are used to judge the overall trend of the tracking quality and whether the signal has entered a stable state; the signal energy parameter is used to judge the tracking quality at the current moment and whether there are drastic changes in the signal. After the criteria are passed, the carrier phase measurement value is set to valid. In one embodiment, the quality of the original observation is judged by the signal quality criteria, so as to judge the quality of the estimated original observation. The signal quality criteria are obtained from the statistical values of the phase error output by the phase discriminator, the signal energy parameter, and the carrier-to-noise ratio; wherein, the phase discriminator is the carrier phase discriminator in the tracking module, which is used to distinguish the phase difference between the input signal and the output signal of the tracking module. The statistical value of the phase error is obtained from the expected value and the maximum value of the absolute value of the phase difference output by the phase discriminator; the signal energy parameter is obtained by the coherent integration output by the tracking module.

[0140] Expected value of the absolute value of the phase error statistical value:

[0141]

[0142] Signal parameter:

[0143] Sixth, generation of the original observation and data packetization. Assemble the satellite number, satellite system, satellite launch time, carrier-to-noise ratio, Doppler frequency shift, integral Doppler integer weeks, fractional weeks, local sampling time, and cycle slip flag of the original observation and write them into the original observation file.

[0144] e) Carrier phase differential positioning solution

[0145] The carrier phase differential positioning solution mainly relies on the RTKLIB software. The specific implementation steps are as follows:

[0146] First, obtain the differential information of the reference station. The differential information includes the original observations of the reference station and the satellite ephemeris during the measurement time period;

[0147] Second, use the RTKLIB high-precision positioning software to process the local original observations and the differential information of the reference station to complete the carrier phase differential positioning.

[0148] The second embodiment of the present application also discloses a positioning method for a software receiver based on GNSS carrier phase differential positioning. Figure 9 The flowchart of the positioning method is shown, including:

[0149] Step 901: Receive multi-mode satellite signals, split and input them according to signal frequency points, and generate multiple digital signals after digital-to-analog conversion.

[0150] Step 902: Perform acquisition, pre-bit synchronization before tracking, tracking on the multiple digital signals, and obtain signal synchronization parameters, where the signal synchronization parameters include accurate estimated values of carrier phase, pseudo-code phase, and Doppler frequency.

[0151] Step 903: Demodulate the message of the tracking output result and extract time information and ephemeris parameters.

[0152] Step 904: Calculate the pseudo-range, Doppler frequency, and integrated Doppler corresponding to the selected locally extracted time.

[0153] Step 905: Perform RTK positioning calculation according to the transmission time, Doppler frequency, integrated Doppler of the satellite signal, and differential information provided by an external reference station.

[0154] The first implementation mode is the corresponding device implementation mode of this implementation mode. The technical details in the first implementation mode can be applied to this implementation mode, and the technical details in this implementation mode can also be applied to the first implementation mode.

[0155] It should be noted that in the application documents of this patent, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one" does not exclude the existence of another identical element in the process, method, article or device including the element. In the application documents of this patent, if it is mentioned that a certain action is performed according to a certain element, it means at least performing the action according to the element, including two cases: only performing the action according to the element, and performing the action according to the element and other elements. Expressions such as multiple, multiple times, and multiple types include 2, 2 times, 2 types, as well as more than 2, more than 2 times, and more than 2 types.

[0156] All documents mentioned in this specification are considered to be incorporated herein by reference in their entirety so that they can be used as a basis for modification if necessary. In addition, it should be understood that the above are only preferred embodiments of this specification and are not intended to limit the scope of protection of this specification. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this specification shall be included within the scope of protection of one or more embodiments of this specification.

[0157] In some cases, the acts or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired result. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A software receiver for GNSS carrier phase differential positioning, characterized in that, Comprising: A signal receiving module, configured to receive satellite signals and generate digital signals after digital-to-analog conversion; A signal processing module, configured to perform acquisition, pre-tracking bit synchronization, and tracking on the digital signals to obtain signal synchronization parameters and signal tracking results of the satellite signals, where the signal synchronization parameters include carrier phase, pseudo-code phase, and Doppler frequency; An information processing module, configured to demodulate the message in the signal tracking results and extract message time information; An observable extraction module, configured to calculate the start time of each pseudo-code period and the corresponding original observables at the start time of each pseudo-code period according to the signal synchronization parameters and the message time information, and deduce the estimated observables corresponding to the local extraction time of the software receiver according to the interpolation algorithm, where the local extraction time is the selected generation time of the estimated observables extraction, and the interpolation algorithm includes: determining two pseudo-code period start times according to the local extraction time, where the two pseudo-code period start times are respectively the pseudo-code period start times before and after closest to the local extraction time; and interpolating the estimated observables corresponding to the local extraction time according to the original observables corresponding to the two pseudo-code period start times, where the estimated observables include pseudo-range, Doppler frequency, and integrated Doppler; A positioning solution module, configured to perform carrier phase differential positioning solution according to the pseudo-range, Doppler frequency, and integrated Doppler of the estimated observables.

2. The software receiver according to claim 1, characterized in that, The software receiver is a multi-mode navigation software receiver, and the signal receiving module is configured to receive multi-mode satellite signals and generate multiple digital signals after digital-to-analog conversion by frequency division according to the satellite signal frequency points.

3. The software receiver according to claim 1, characterized in that, The signal processing module further includes: An acquisition module, configured to acquire the digital signals by using an acquisition algorithm with parallel code phase to obtain a rough estimated value of the pseudo-code phase and a rough estimated value of the Doppler frequency; A pre-tracking bit synchronization module, configured to perform pre-tracking bit synchronization on the digital signals by using a frequency estimation algorithm combined with a maximum likelihood estimation algorithm to obtain the bit boundary of the digital signals; A tracking module, configured to generate coherent integration according to the estimated value of the pseudo-code phase and the rough estimated value of the Doppler frequency to obtain the signal synchronization parameters and signal tracking results.

4. The software receiver according to claim 3, characterized in that, The pre-tracking bit synchronization module is further configured to determine whether the pre-tracking bit synchronization is successful. If successful, the tracking module performs coherent integration for one bit period to obtain the correlation accumulation values of the leading path, the in-phase path, and the trailing path. If not successful, the tracking module performs coherent integration for one pseudo-code period to obtain the correlation accumulation values of the leading path, the in-phase path, and the trailing path.

5. The software receiver according to claim 4, wherein, The satellite signals include GPS L1 frequency point and / or Beidou B1I frequency point. Wherein, when the pre-tracking bit synchronization is successful, the integration time used for the GPS L1 frequency point and / or Beidou B1I frequency point is 20 ms; when the pre-tracking bit synchronization is not successful, the integration time used for the GPS L1 frequency point and / or Beidou B1I frequency point is 1 ms.

6. The software receiver according to claim 4, characterized in that, When the bit synchronization before tracking is unsuccessful, the bit synchronization is completed according to the maximum likelihood estimation algorithm during the tracking process to obtain the bit boundary of the digital signal, and the coherent integration of one pseudo code period is changed to the coherent integration of one bit period.

7. The software receiver according to claim 3, characterized in that, The observation quantity extraction module is further used for: The quality of the original observation is judged by a signal quality criterion, thereby judging the quality of the estimated observation, wherein the signal quality criterion is obtained by a phase error statistic value, a signal energy parameter and a carrier-to-noise ratio output by a phase detector; Wherein, the phase detector is a carrier phase discriminator in the tracking module, which is used to identify the phase difference between the input signal and the output signal of the tracking module, and the phase error statistical value is obtained by the expectation and maximum value of the absolute value of the phase difference output by the phase detector; The signal energy parameter is obtained by coherent integration of the output of the tracking module.

8. The software receiver according to claim 1, wherein The pseudorange, Doppler frequency and integrated Doppler at the time of generating the estimated observation amount calculated according to the interpolation algorithm are framed and written into the original observation amount file.

9. A positioning method for a software receiver based on GNSS carrier phase differential positioning, characterized in that, include: Receive multi-mode satellite signals, input them in different channels according to the signal frequency, and generate multiple digital signals after digital-to-analog conversion; Capturing the multi-channel digital signals, tracking pre-bit synchronization, tracking and obtaining signal synchronization parameters, wherein the signal synchronization parameters include accurate estimation values ​​of carrier phase, pseudo code phase and Doppler frequency; Performing telegram demodulation on the tracking output result and extracting time information and ephemeris parameters; The starting time of each pseudocode cycle and the original observation amount corresponding to the starting time of each pseudocode cycle are calculated according to the signal synchronization parameter and the time information of the telegram, and the estimated observation amount corresponding to the local extraction time of the software receiver is deduced according to the interpolation algorithm, wherein the local extraction time is the selected estimated observation amount extraction generation time, wherein the interpolation algorithm includes: determining two pseudocode cycle starting times according to the local extraction time, and the two pseudocode cycle starting times are respectively the pseudocode cycle starting times before and after the local extraction time that are closest to the local extraction time; and interpolating the original observation amounts corresponding to the two pseudocode cycle starting times to obtain the estimated observation amount corresponding to the local extraction time, wherein the estimated observation amount includes pseudorange, Doppler frequency, and integrated Doppler; The RTK positioning solution is performed according to the transmission time, Doppler frequency, integrated Doppler of the satellite signal and the differential information provided by the external reference station.

10. The positioning method according to claim 9, characterized in that, The step of capturing the multi-channel digital signals, tracking the pre-bit synchronization, and tracking and obtaining the signal synchronization parameters further comprises: The digital signal is captured using a parallel code phase capture algorithm to obtain a rough estimate of a pseudo code phase and a rough estimate of a Doppler frequency; Using a frequency estimation algorithm combined with a maximum likelihood estimation algorithm to perform pre-tracking bit synchronization on the digital signal to obtain a bit boundary of the digital signal; A coherent integration is generated according to the estimated value of the pseudo code phase and the rough estimated value of the Doppler frequency to obtain the signal synchronization parameter and the signal tracking result.

11. The positioning method according to claim 9, wherein The method further includes: determining whether bit synchronization before tracking is successful. If it is successful, coherent integration for one bit period is performed to obtain the correlation accumulation values of the early path, the prompt path, and the late path. If it is not successful, coherent integration for one pseudo-code period is performed to obtain the correlation accumulation values of the early path, the prompt path, and the late path.

12. The positioning method according to claim 11, wherein When the bit synchronization before tracking is not successful, bit synchronization is completed according to the maximum likelihood estimation algorithm during the tracking process to obtain the bit boundary of the digital signal, and the coherent integration for one pseudo-code period is changed to the coherent integration for one bit period.

13. The positioning method according to claim 9, characterized in that, The method further includes: judging the quality of the original observation quantity through a signal quality criterion, thereby judging the quality of the estimated observation quantity, where the signal quality criterion is obtained through the phase error statistical value output by the phase discriminator, the signal energy parameter, and the carrier-to-noise ratio; wherein, the phase discriminator is the carrier phase discriminator in the tracking module, which is used to discriminate the phase difference between the input signal and the output signal of the tracking module, and the phase error statistical value is obtained through the expectation and the maximum value of the absolute value of the phase difference output by the phase discriminator; the signal energy parameter is obtained through the coherent integration output by the tracking module.

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