A method and apparatus for implementing carrier tracking processing

Abstract

The application discloses a carrier tracking processing method and device, which comprises the following steps: when a frequency difference is obtained through frequency discrimination processing, a current frequency error is estimated according to previous motion state information of a receiver; and a carrier frequency is corrected and recovered once again according to the frequency difference obtained through frequency discrimination processing and the current frequency error estimated. The application improves the tracking performance of a navigation receiver, reduces the error rate of demodulation and decoding, and improves the positioning accuracy of the navigation receiver.

Description

TECHNICAL FIELD

[0001] The present application relates to, but is not limited to, navigation technology, and in particular to a method and apparatus for implementing carrier tracking processing. BACKGROUND

[0002] With the development of science and technology, the research on navigation and positioning technology of human beings has entered the satellite positioning era. In order to provide accurate position and speed information in a global and all-weather manner, the concept of Global Navigation Satellite System (GNSS) is proposed. Global satellite navigation system plays a very important role in many fields; including military, navigation, exploration, monitoring, measurement, communication timing, etc. With the development of civil technology in recent years, global satellite navigation system has gradually penetrated into daily life, from mobile phones, personal computers, cars, civil aircraft to missiles, warplanes, all of which cannot be separated from satellite navigation technology. Global Navigation Satellite System includes the Global Positioning System (GPS) of the United States, the Global Navigation Satellite System (GLONASS) of Russia, the Galileo system of Europe and the Compass Navigation System (BD) of China; among them, the GPS of the United States is the first global space satellite navigation system, which has a satellite constellation of 32 satellites and adopts Code Division Multiple Access (CDMA) satellite addressing method. The GLONASS system of Russia is similar in principle and function to the GPS system, and its satellite constellation is composed of 24 satellites and adopts Frequency Division Multiple Access (FDMA) satellite addressing method. Russia is carrying out GLONASS modernization work, which adopts CDMA method to realize compatibility with GPS and Galileo system. The Galileo system is a satellite navigation and positioning system being built by the European Union, which has a satellite constellation of 30 satellites and adopts code division multiple access method for satellite addressing. The Galileo system can complete multi-system compatibility with GPS and GLONASS and can provide more civil services. "Beidou 1" is the first generation of satellite navigation system independently developed by China, which is composed of 3 satellites and has no ranging and height measuring function. The "Beidou 2" being built is composed of 3 inclined synchronous orbit satellites, 27 medium orbit satellites and 5 geostationary orbit satellites, which can meet the condition of global coverage.

[0003] As a core component of the GPS satellite navigation and positioning system, the GPS receiver's primary function is to receive signals transmitted from satellites and extract navigation message information and pseudorange observations for positioning calculations. Therefore, high-performance baseband processing algorithms are required to capture and track the received GPS signals under different environments to obtain navigation messages and pseudorange observations. At the GPS satellite signal transmitter, the GPS carrier signal is modulated with a coarse acquisition code (C / A code) and a navigation message data code. Correspondingly, at the GPS receiver, in order to demodulate the navigation message data code from the received satellite signal, the receiver, during tracking operations, needs to thoroughly remove the carrier, including the Doppler shift, from the digital intermediate frequency signal through mixing, and also needs to thoroughly remove the C / A code from the signal through C / A code correlation operations. The receiver's tracking operation consists of a carrier tracking loop and a code tracking loop. The receiver continuously adjusts its locally replicated carrier through the carrier tracking loop to ensure that the replicated carrier frequency (or phase) is consistent with the carrier frequency (or phase) of the received intermediate frequency signal, ultimately achieving carrier stripping through down-conversion mixing. The receiver continuously adjusts its locally replicated C / A code through a code tracking loop to ensure that the phase of its replicated C / A code is consistent with the phase of the C / A code in the received intermediate frequency signal. Finally, C / A code stripping is achieved through code correlation operations. After tracking is achieved, the receiver can obtain fine Doppler frequency shift and C / A code phase values ​​for satellite positioning.

[0004] In related technologies, receiver tracking operations are basically based on phase-locked loops (PLLs), frequency-locked loops (FLLs), or a combination of both. Both PLLs and FLLs consist of a discriminator, a loop filter, and a digitally controlled oscillator (NCO). The discriminator in a PLL is a phase detector, while the discriminator in a FLL is a frequency detector. The discriminator identifies the frequency difference or phase difference between the local carrier frequency and the input signal frequency. The loop filter removes loop noise from the frequency or phase difference and feeds the filtering result back to the local carrier frequency in the next loop iteration as a correction. Figure 1 This is a structural block diagram of a navigation receiving device in related technologies, such as... Figure 1As shown, when the navigation receiver transitions from the acquisition phase to the tracking phase, the local code numerically controlled oscillator (CCO) reconstructs the local C / A code based on the phase of the acquired coarse C / A code. This local C / A code is then correlated with the intermediate frequency (IF) signal entering the tracking processing section via a correlator to remove the C / A code. The local carrier numerically controlled oscillator (CCO) reconstructs the local carrier based on the acquired coarse Doppler frequency. This local carrier is then mixed with the C / A code-removed IF signal via a mixer to eliminate the carrier Doppler frequency. The processing result is then integrated and accumulated by an integration and accumulation unit to improve the signal-to-noise ratio (SNR). The carrier-to-noise ratio (CNR) unit calculates the CNR based on the integrated and accumulated result. This integrated and accumulated result is also used for frequency discrimination by a frequency discriminator to obtain the frequency difference. The frequency discrimination result is then smoothed by a smoothing unit to eliminate sudden and large increases in frequency error, enabling the carrier tracking loop to track stably and avoiding loop oscillations caused by erroneous values ​​in the loop. After the smoothing process, the result is filtered by a loop filter to remove loop noise. The result of the loop noise removal process is then fed back to the carrier numerically controlled oscillator for correction and reproduction of the carrier frequency in the next iteration.

[0005] When the motion state of the navigation receiver suddenly changes, the smoothing process weakens the suddenly increased frequency error, making it difficult for the receiver to quickly synchronize with the actual motion state. For example, when a vehicle navigation system suddenly accelerates, the smoothing process weakens the suddenly increased frequency error. In addition, when the motion state changes significantly, the reduced frequency error due to the smoothing process lowers the tracking performance of the navigation receiver, leading to an increase in the error rate of subsequent demodulation and decoding, and deteriorating the accuracy of the positioning results. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] This invention provides a method and apparatus for implementing carrier tracking processing, which can improve the tracking performance of a navigation receiver, reduce the demodulation and decoding error rate, and improve the positioning accuracy of the navigation receiver.

[0008] This invention provides a method for implementing carrier tracking processing, comprising:

[0009] When obtaining the frequency difference through frequency discrimination processing, the current frequency error is estimated based on the receiver's previous motion state information;

[0010] Based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error, the carrier frequency is corrected and reproduced in the next iteration.

[0011] Optionally, the step of correcting and reproducing the carrier frequency in a subsequent iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error includes:

[0012] The absolute difference is obtained by subtracting the estimated current frequency error from the frequency difference obtained by frequency discrimination processing, and then taking the absolute value of the calculated difference.

[0013] When it is determined that the obtained absolute difference is greater than a preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the estimated current frequency error.

[0014] Optionally, when it is determined that the obtained absolute difference is less than the preset threshold value, the method further includes:

[0015] The carrier frequency is corrected and reproduced in the next iteration based on the frequency difference obtained from the frequency discrimination process.

[0016] Optionally, the step of estimating the current frequency error based on the receiver's previous motion state information includes:

[0017] When the frequency discrimination process obtains the frequency difference, the current frequency error is obtained based on the receiver's velocity, acceleration, and Doppler frequency prediction in the previous second.

[0018] On the other hand, embodiments of the present invention also provide an apparatus for implementing carrier tracking processing, comprising: a prediction unit and a processing unit; wherein,

[0019] The estimation unit is used to: when obtaining the frequency difference through frequency discrimination processing, estimate the current frequency error based on the receiver's previous motion state information;

[0020] The processing unit is used to: correct and reproduce the carrier frequency in the next iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error.

[0021] Optionally, the processing unit is specifically used for:

[0022] The absolute difference is obtained by subtracting the estimated current frequency error from the frequency difference obtained by frequency discrimination processing, and then taking the absolute value of the calculated difference.

[0023] When it is determined that the obtained absolute difference is greater than a preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the estimated current frequency error.

[0024] Optionally, the processing unit is further configured to:

[0025] When it is determined that the obtained absolute difference is less than the preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the frequency difference obtained by the frequency discrimination process.

[0026] Optionally, the estimation unit is specifically used for:

[0027] When the frequency discrimination process obtains the frequency difference, the current frequency error is obtained based on the receiver's velocity, acceleration, and Doppler frequency prediction in the previous second.

[0028] In another aspect, embodiments of the present invention also provide a computer storage medium storing computer-executable instructions for performing the above-described methods.

[0029] Furthermore, embodiments of the present invention also provide a terminal, comprising: a memory and a processor; wherein,

[0030] The processor is configured to execute program instructions in memory;

[0031] The program instructions are read by the processor and perform the following operations:

[0032] When obtaining the frequency difference through frequency discrimination processing, the current frequency error is estimated based on the receiver's previous motion state information;

[0033] Based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error, the carrier frequency is corrected and reproduced in the next iteration.

[0034] Compared with related technologies, the technical solution of this application includes: when obtaining the frequency difference through frequency discrimination processing, estimating the current frequency error based on the receiver's previous motion state information; and performing correction and reproduction of the carrier frequency in the subsequent iteration based on the frequency difference obtained through frequency discrimination processing and the estimated current frequency error. The embodiments of this invention improve the tracking performance of the navigation receiver, reduce the error rate of demodulation decoding, and improve the positioning accuracy of the navigation receiver.

[0035] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0036] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0037] Figure 1 This is a structural block diagram of a navigation receiving device in related technologies;

[0038] Figure 2 This is a flowchart illustrating the carrier tracking processing method according to an embodiment of the present invention;

[0039] Figure 3This is a structural block diagram of a device for implementing carrier tracking processing according to an embodiment of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0041] The steps illustrated in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases the steps shown or described may be performed in a different order than that presented here.

[0042] Figure 2 This is a flowchart illustrating the carrier tracking processing method according to an embodiment of the present invention, as shown below. Figure 2 As shown, it includes:

[0043] Step 201: When obtaining the frequency difference through frequency discrimination processing, the current frequency error is estimated based on the receiver's previous motion state information.

[0044] Optionally, in embodiments of the present invention, the estimation of the current frequency error based on the receiver's previous motion state information includes:

[0045] When the frequency discrimination process obtains the frequency difference, the current frequency error is obtained based on the receiver's velocity, acceleration, and Doppler frequency prediction in the previous second.

[0046] Step 202: Based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error, perform correction and reproduction of the carrier frequency in the next iteration.

[0047] Optionally, in embodiments of the present invention, the correction and reproduction of the carrier frequency in a subsequent iteration based on the frequency difference obtained through frequency discrimination processing and the estimated current frequency error includes:

[0048] The absolute difference is obtained by subtracting the estimated current frequency error from the frequency difference obtained by frequency discrimination processing, and then taking the absolute value of the calculated difference.

[0049] When it is determined that the obtained absolute difference is greater than a preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the estimated current frequency error.

[0050] Optionally, when it is determined that the obtained absolute difference is less than the preset threshold value, the method of this embodiment further includes:

[0051] The carrier frequency is corrected and reproduced in the next iteration based on the frequency difference obtained from the frequency discrimination process.

[0052] Compared with related technologies, the technical solution of this application includes: when obtaining the frequency difference through frequency discrimination processing, estimating the current frequency error based on the receiver's previous motion state information; and performing correction and reproduction of the carrier frequency in the subsequent iteration based on the frequency difference obtained through frequency discrimination processing and the estimated current frequency error. The embodiments of this invention improve the tracking performance of the navigation receiver, reduce the error rate of demodulation decoding, and improve the positioning accuracy of the navigation receiver.

[0053] Figure 3 This is a structural block diagram of a device for implementing carrier tracking processing according to an embodiment of the present invention, as shown below. Figure 3 As shown, it includes: a prediction unit and a processing unit; wherein,

[0054] The estimation unit is used to: when obtaining the frequency difference through frequency discrimination processing, estimate the current frequency error based on the receiver's previous motion state information;

[0055] Optionally, in this embodiment of the invention, the estimation unit is specifically used for:

[0056] When the frequency discrimination process obtains the frequency difference, the current frequency error is obtained based on the receiver's velocity, acceleration, and Doppler frequency prediction in the previous second.

[0057] The processing unit is used to: correct and reproduce the carrier frequency in the next iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error.

[0058] Optionally, in this embodiment of the invention, the processing unit is specifically used for:

[0059] The absolute difference is obtained by subtracting the estimated current frequency error from the frequency difference obtained by frequency discrimination processing, and then taking the absolute value of the calculated difference.

[0060] When it is determined that the obtained absolute difference is greater than a preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the estimated current frequency error.

[0061] Optionally, the processing unit in this embodiment of the invention is further configured to:

[0062] When it is determined that the obtained absolute difference is less than the preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the frequency difference obtained by the frequency discrimination process.

[0063] This invention also provides a computer storage medium storing computer-executable instructions for executing the above-described method for implementing carrier tracking processing.

[0064] This invention also provides a terminal, comprising: a memory and a processor; wherein,

[0065] The processor is configured to execute program instructions in memory;

[0066] The program instructions are read by the processor and perform the following operations:

[0067] When obtaining the frequency difference through frequency discrimination processing, the current frequency error is estimated based on the receiver's previous motion state information;

[0068] Based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error, the carrier frequency is corrected and reproduced in the next iteration.

[0069] The following application examples clearly and in detail illustrate the methods of the embodiments of the present invention. These application examples are only used to describe the present invention and are not intended to limit the scope of protection of the present invention.

[0070] Application Examples

[0071] This application example assumes the intermediate frequency signal is S(t) = AC(t)D(t)cos(2πf). s t); where A is the intermediate frequency signal amplitude, C(t) is the signal C / A code, D(t) is the modulated navigation message, f s The frequency of the intermediate frequency signal received during the tracking operation of the navigation receiver;

[0072] After the acquisition module successfully acquires a visible satellite, it uses the captured coarse C / A code phase as the initial code phase of the local code NCO to generate the C / A code, and uses the captured coarse Doppler frequency as the initial frequency value of the local carrier NCO to generate the local carrier. The local carrier signal is usually processed by two mutually orthogonal signals, namely the in-phase (I) path and the quadrature (Q) path, and the intermediate frequency signal.

[0073] Assuming that correlation processing can completely strip away the C / A code, the correlation signal after correlation processing is r(t) = AD(t)cos(2πf) s t);

[0074] The local carrier signal is modeled as follows:

[0075] L I (t)=cos(2πf I t)

[0076] L Q (t)=sin(2πf I t);

[0077] Among them, f I To capture the approximate Doppler frequency;

[0078] The correlated signal after C / A code stripping is subjected to image suppression processing with the local carrier. The result is as follows:

[0079]

[0080]

[0081] The integration and accumulation process is equivalent to a low-pass filter, filtering out high-frequency signals. Therefore, the second harmonic signal in the above result is filtered out, and the result after integration and accumulation is:

[0082]

[0083]

[0084] The carrier-to-noise ratio is calculated based on the results of the above integration and accumulation. The calculation includes:

[0085] Calculate the sequence Z of the sum of squares of the integral results at each time step, i.e. i represents the current time;

[0086] The mean of the Z-sequence is The sum and variance are

[0087]

[0088]

[0089] The mean of the signal power, i.e.

[0090] Noise variance, i.e.

[0091] Carrier-to-noise ratio T is the integration time.

[0092] When the carrier-to-noise ratio (CNR) is lower than the preset CNR threshold, the signal in the tracking loop is considered lost, and the process returns to the acquisition operation for reacquisition. When the CNR is higher than the preset CNR threshold, the signal tracking is considered good. When the CNR is higher than the threshold, the frequency discriminator performs frequency discrimination processing.

[0093] Frequency discrimination is performed based on the result of the above integral accumulation. The frequency discrimination process includes the following calculations:

[0094]

[0095] in, T is the integration time, Δf = f I -f s This is the frequency difference between the received signal and the local signal.

[0096] This application example uses the Positioning, Velocity, and Timing (PVT) modules to estimate the current frequency error based on motion state information (including receiver speed, acceleration, and Doppler frequency at the previous moment). The estimated frequency error is then compared with the frequency discrimination difference obtained from the frequency discrimination process.

[0097] The absolute difference is obtained by subtracting the estimated current frequency error from the frequency difference obtained by frequency discrimination processing, and then taking the absolute value of the calculated difference.

[0098] When it is determined that the obtained absolute difference is greater than a preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the estimated current frequency error.

[0099] When it is determined that the obtained absolute difference is less than the preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the frequency difference obtained from the frequency discrimination process.

[0100] When the absolute difference is greater than a preset threshold, this application example determines that the frequency difference obtained by the frequency discrimination process is an outlier (i.e., an abnormal value), and performs the correction and reproduction of the carrier frequency in the next iteration based on the estimated current frequency error; when the absolute difference is less than the preset threshold, the frequency difference obtained by the frequency discrimination process is determined to be a normal value, and performs the correction and reproduction of the carrier frequency in the next iteration based on the frequency difference obtained by the frequency discrimination process.

[0101] In this embodiment of the invention, the frequency difference is processed by a loop filter to remove loop noise. The frequency difference after noise removal is used as a correction factor and fed back to the initial frequency of the local carrier signal generated by the carrier NCO in the next loop iteration, i.e., f. I-next =f I -Δf.

[0102] Simulation results show that the receiver in this application example achieves stable signal tracking in high dynamic environments, ensuring tracking accuracy and improving tracking performance.

[0103] Those skilled in the art will understand that all or part of the steps in the above methods can be implemented by a program instructing related hardware (e.g., a processor), and the program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk. Optionally, all or part of the steps in the above embodiments can also be implemented using one or more integrated circuits. Accordingly, each module / unit in the above embodiments can be implemented in hardware, such as by an integrated circuit to implement its corresponding function, or it can be implemented in the form of a software functional module, such as by a processor executing a program / instruction stored in memory to implement its corresponding function. This invention is not limited to any particular combination of hardware and software.

[0104] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for implementing carrier tracking processing, characterized in that, include: When obtaining the frequency difference through frequency discrimination processing, the current frequency error is estimated based on the receiver's previous motion state information; Based on the frequency difference obtained from the frequency discrimination process and the current frequency error obtained from the prediction, the carrier frequency is corrected and reproduced in the next iteration. The step of correcting and reproducing the carrier frequency in the next iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error includes: The absolute difference is obtained by subtracting the estimated current frequency error from the frequency difference obtained by frequency discrimination processing, and then taking the absolute value of the calculated difference. When it is determined that the obtained absolute difference is greater than a preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the estimated current frequency error. When it is determined that the obtained absolute difference is less than the preset threshold, the carrier frequency is corrected and reproduced in the next iteration based on the frequency difference obtained by the frequency discrimination process.

2. The method according to claim 1, characterized in that, The process of estimating the current frequency error based on the receiver's previous motion state information includes: When the frequency discrimination process obtains the frequency difference, the current frequency error is obtained based on the receiver's velocity, acceleration, and Doppler frequency prediction in the previous second.

3. An apparatus for implementing carrier tracking processing, characterized in that, include: Prediction unit, processing unit; among which, The estimation unit is used to: when obtaining the frequency difference through frequency discrimination processing, estimate the current frequency error based on the receiver's previous motion state information; The processing unit is configured to: perform a correction and reproduction of the carrier frequency in a subsequent iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error, wherein the correction and reproduction of the carrier frequency in a subsequent iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error includes: subtracting the estimated current frequency error from the frequency difference obtained from the frequency discrimination process, taking the absolute value of the calculated difference to obtain an absolute difference; determining that the obtained absolute difference is greater than a preset threshold value, performing the correction and reproduction of the carrier frequency in a subsequent iteration based on the estimated current frequency error; determining that the obtained absolute difference is less than the preset threshold value, performing the correction and reproduction of the carrier frequency in a subsequent iteration based on the frequency difference obtained from the frequency discrimination process.

4. The apparatus according to claim 3, characterized in that, The estimation unit is specifically used for: When the frequency discrimination process obtains the frequency difference, the current frequency error is obtained based on the receiver's velocity, acceleration, and Doppler frequency prediction in the previous second.

5. A computer storage medium storing computer-executable instructions for performing the method of any one of claims 1 to 2.

6. A terminal for implementing carrier tracking processing, comprising: Memory and processor; among which, The processor is configured to execute program instructions in memory; The program instructions are read by the processor and executed as follows to implement carrier tracking processing: When obtaining the frequency difference through frequency discrimination processing, the current frequency error is estimated based on the receiver's previous motion state information; The carrier frequency is corrected and reproduced in a subsequent iteration based on the frequency difference obtained from the frequency discrimination process and the estimated current frequency error. This correction and reproduction includes: subtracting the estimated current frequency error from the frequency difference obtained from the frequency discrimination process; taking the absolute value of the calculated difference to obtain an absolute difference; determining that the obtained absolute difference is greater than a preset threshold value; and performing the carrier frequency correction and reproduction in a subsequent iteration based on the estimated current frequency error when the obtained absolute difference is less than the preset threshold value.

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